DE102006003534A1 - Refining of optical glass with temperature-regulated electrodes - Google Patents

Abstract

In optical glass refining, molten glass is introduced to a chamber incorporating electrically heated coils with two or more electrodes in contact with the molten material. The chamber also incorporates one or more facing electrodes. One or more of the electrically heated electrodes is set at a voltage that minimizes the reaction between the electrode and substances present in the molten glass. An independent claim is included for an apparatus for the above process, employing alternating current at ca. 8 kHz and operating above 1700[deg]C.

Description

Summary

The The invention relates to a method and a device for corrosion protection of electrodes and to reduce gas bubbles in a melt. According to the invention this is by applying a direct current between at least two heating electrodes and at least one counter electrode in a glass melting or refining device reached.

description

The The invention relates to a method for influencing the temperature of a Melt in particular a method for refining and / or cleaning of melts according to the preamble of claim 1. The invention also relates a device for influencing the temperature and / or for refining and / or Purification of melts according to the preamble of claim 49 as well a product, in particular a glass product, which according to the inventive method and / or melted in the device according to the invention and / or refined and / or cleaned and / or manufactured.

in the first process step in the production of glasses the starting substance, the so-called glass batch, is melted down. The smelting takes place in tubs and is usually due the thermal load capacity of the wall material at melting temperatures up to 1650 ° C limited. After the mixture has become liquid with increasing temperature is, begins to use in the glass homogenization process, the means there is a thorough mixing of all starting substances.

After this the mixture has been heated to produce a glass melt, begins in a second process step the purification. This can be done in a so-called fining chamber. In the refining chamber the melt will improve homogeneity and remove bubbles thoroughly mixed and degassed. An essential goal in purification it is the gases physically and chemically bound in the melt release and remove.

The origin of the gases occurring in the melt is usually in the always contained in the molten glass of water at the usual glass melting temperatures is split into a more or less large percentage in hydrogen and oxygen. Since the noble metal used to coat parts of a glass melting apparatus is permeable to hydrogen, the migration of hydrogen at the phase interface between noble metal and glass melt leads to an accumulation of oxygen, which is taken up in the glass melt in the form of small bubbles, thereby increasing the quality of the produced Glass products can be significantly affected. Other gases that can be found in the glass are SO ₂ , CO ₂ and N ₂ , which have their origin in the raw materials and the surrounding atmosphere.

The for the Blistering necessary driving force is due to a temporary supersaturation the refining gas, the corresponding oxygen or gas partial pressure is at least 1 bar, depending on the type of melt and up to 5 bar.

Trigger this supersaturation is usually a temperature increase. The state of supersaturation then arises depending on the melt, refining agent, melting process, Shard share etc. from a respective characteristic minimum temperature, the so-called refining temperature, one.

From this there is a fundamental problem: above the refining temperature the melt is unstable against a spontaneous Neublasenbildung, So this competes with the reduction of the supersaturation against the actual intended bladder enlargement. The situation is aggravating therefore for melting, on the one hand are very oversaturated, and on the other hand only about have a low bubble load, as with pre-purified Melting is the case.

During refining, it is important that all bubbles to be cleared succeed in an irreversible ascent to the free enamel surface. On the one hand, the dwell time available for this purpose is limited by the specific throughput in the respective melting aggregate; on the other hand, the minimum necessary rise time follows from the viscosity of the glass and the radii of the smallest bubbles yet to be clarified. In the continuous production of glasses, however, this leads to a contradiction under economic boundary conditions, which can only be resolved if the blistering phase can be preceded by a chemical lautering step. The basic principle of this lautering step is simple: the starting bubbles increase in size by the inclusion of the homogeneously dissolved chewing gases in the glass. The transport of these gases takes place diffusively from the gas volume to the bubble edges. The necessary chemical driving force is based on the temporary supersaturation of the refining gas. The corresponding gas partial pressure is at least 1 bar, possibly even up to 5 bar. The trigger of this supersaturation is usually a temperature increase. In this case, it is important to follow the "Bladder Enlargement" refining step with an ascent zone that produces not only the inflated blisters but also the neoplasms filters out.

The Neolubes are formed in the region of moderate supersaturation, that is, at pressures below of 100 bar, and thus exclusively via the path of heterogeneous nucleation. As germs here are all walls and installations in the melting, transport and refining units conceivable. Particularly at risk however, are metal electrodes because of the forced mass transfer from outside at the interface Electrode / glass active by lautering reactions supports can be.

For the kinetics of bubble formation and bubble separation, the interfacial tensions at the 3-phase metal / glass / bubble interface are of crucial importance. On the one hand, this structure is highly glass- and electrode-specific; on the other hand, the chemical composition of the electrode surface can be controlled very strongly by redox processes. On the one hand, oxidation can lead to the formation or reinforcement of metal oxide layers. This leads to the formation of passivating MoO ₂ layers on the surface of a molybdenum electrode. On the other hand, a reduction can lead to the degradation of oxide films to alloying with glass components, such as the formation of MoSi ₂ layers on molybdenum electrodes.

Next the effect on blistering also has a major influence on the actual corrosion of the electrodes. The two fundamentally different Corrosion mechanisms are: anodic dissolution of the electrode over the Formation of ions or their cathodic destruction by transformation into their liquid Alloy phase. Analogous to the corrosion protection of iron alloys in aqueous Media is also for Electrodes the phenomenon the passivation known. Passivating the targeted installation of alloying constituents, such as silicon or zirconium in molybdenum, the cathodic passivation of molybdenum in (sulphate-refined) Lime-soda melting or the anodic passivation of molybdenum in lead glass melts.

Ultimately results in the local load on the electrode surface with anodic or cathodic currents as the sum of the externally applied direct currents (battery circuits) plus the rectification effects during the passage of the heating currents (AC polarization) plus the direct currents through internal balancing procedures between different names Parts of the electrodes (thermal batteries). The sum of the currents determined together with the electroless corrosion processes the polarization of the electrode and thus their electrochemical potential.

For precious metals, one also knows the special mechanism of AC sputtering. A current-assisted ionization of surface atoms is partially followed by the electroless reduction of the noble metal ions to noble metal clusters. The most important reaction partners in the glass are the reducing ions such as Sn ²⁺ , As ³⁺ or Sb ³⁺ . High temperatures promote this type of reaction because, on the one hand, the melt becomes less noble with increasing explanation and, on the other hand, the noble metal ions become increasingly noble. The reactions take place at the rate of the heating frequency and it is clear from experimental series that the lower the heating frequency and the higher the current densities, the more important the irreversible dissolution of noble metal particles becomes. If it comes to the formation of the finest precious metal particles, they can in turn serve as germs for new bubbles in the event of a supersaturation of the melt in the vicinity of the electrodes.

Precious metal walls, specially made of platinum-rhodium alloys, have in glass contact more special Bubble formation mechanisms that rely on the exchange of hydrogen between the platinum, in which it is atomically soluble, and the glass, in to which he is bound as water.

You catch namely the dissolved hydrogen in platinum on the back with oxygen to form water vapor, it produces a hydrogen flow in the Platinum, only from a decomposition of water at the interface between Nourished glass and melt can be. But this is the elementary step of oxygen formation on the platinum. Parallel to the decomposition of water one observes a shift of the electrochemical potential in anodic direction and as soon as at a partial pressure of oxygen of 1 bar a critical potential reached, hits the oxygen production into an oxygen bubble formation. The Water decomposition corresponds to an electroless anodic polarization the precious metal electrode.

Conversely, targeted injection of hydrogen through the platinum wall into the glass can provoke further bubble formation reactions. Depending on the flux densities primarily hydrogen or water bubbles which are converted in the mixing bubbles with substantial amounts of SO _2, CO ₂ and N ₂ form. The same type of mixed bubble can also be detected with cathodic polarization of the platinum / glass interface.

With the anodic and cathodic processes on the platinum surfaces, one can therefore in principle define a potential process window in which no blistering takes place. At temperatures between 1400 ° C and 1500 ° C, this is approximately between the oxygen partial pressure with 10 ^-3 bar as the lower limit for mixed bubble formation and 10 ^-1 bar as the upper limit for oxygen bubble formation.

Out the previous comments it can be seen that the Chemistry of the water dissolved in the glass size Has parallels to the refining chemistry. Water is at least in direct contact with precious metals, especially with platinum alloys, a polyvalent and redoxchemical active glass component. Hydrous glasses can therefore also without oxidic Refining agent additives redoxchemical be very active.

Corrosion processes and Blistering on the surfaces the electrodes are excluded by the temperature-controlled gas supersaturation additionally by the factors electrode material, Electrode composition, surface condition, temperature gradients, local current density and frequency of the heating current, local load with direct currents as well as possibilities for hydrogen flows in the Electrode affected. When glass play in addition to the basic composition of the content of water and refining agents and the redox state an essential role.

Highly viscous Glass melts, especially those of the type of alkali-free glasses, AF glasses require very high refining temperatures. One needs Temperatures above 1700 ° C and you want this by electrical Generate heating by means of electrodes, so prohibits the use of Pt or platinum-rhodium alloys, above 1800 ° C accounts also molybdenum and Tungsten. As an electrode material comes here in principle only Iridium, special alloys are currently not available.

Furthermore, current densities of well above 1 A / cm ^{2 force} the use of medium frequency generators with a frequency of at least 5 kHz.

For the material combination of alkali-free glass and an iridium electrode at temperatures above 1700 ° C and local current densities above 2 A / cm ² at 8 kHz Neublasenbildung observed. The bubble contents in the vicinity of the electrodes could not be clearly determined, the resulting product bubbles were of the mixed-bubble type, they had a rather narrow size distribution of around 500 μm. The analysis of the aggregate-specific bubble growth and bubble ascent processes supports the suggestion that a significant portion of the neoplasms must have a peel size below 200 pm. In addition to blistering, there was minimal corrosion to form the finest Ir particles.

One Starting point to the refining to improve the glass melt and the required refining time To reduce, lies in the use of the highest possible refining temperatures. By a temperature increase Among other things, the viscosity is the glass melt is lowered and the rate of ascent of increased in the melt bubbles.

One Another starting point is the use of so-called refining agents. The principle of this refining agent lies in the melt, in particular the molten glass, Add substances which are at high temperatures below Decompose gas release or oxygen release. The of the refining agents suddenly released gases "collect" in the melt located gases, thereby grow to larger bubbles, which faster to the surface the melt rise and thus are able to melt to leave.

The choice of the refining agent depends primarily on the temperature of the molten glass during the refining. While the refining agent arsenic pentoxide As ₂ O ₅ decomposes into arsenic As ₂ O ₃ and oxygen at temperatures above 1250 ° C, the high-temperature extinguishing agent SnO ₂ does not decompose at temperatures above 1500 ° C in ½ SnO and ½ O ₂ . However, the resulting oxides remain in the melt and can be detected in the final glass product. Arsenic present in the final glass product is particularly disadvantageous if ecologically harmless glasses are desired. A disadvantage of using refining agents such as As, Sb, Sn oxide is that they cause molybdenum and tungsten electrodes to self-passivate through the formation of thin metal oxide films. However, the resulting protective films are significantly weakened depending on the glass composition and above 1800 ° C molybdenum and tungsten are vulnerable exposed to corrosive attack by the dissolved oxygen in the glass.

It There is therefore a need for opportunities for purification at very high temperatures, ie at temperatures above 1650 ° C, for the purification perform more efficiently to be able to. Such a temperature increase is however after conventional Method only and in known devices with great disadvantages, especially through reinforced Corrosion of the metal parts of the devices connected.

The heating of the glass melt is done conventionally by oil or gas burners, which are located in the upper furnace. The heat is introduced here via the glass surface. As additional heating, in particular with low-absorbing glasses, additional electrical heating by means of electrodes takes place. For this purpose, the molten glass is conductively heated with alternating current, that is, it is heated directly. The electrodes are to this Purpose attached to the bottom or the side walls of the vessel and are in direct contact with the molten glass.

Molybdenum, platinum and platinum group metals are mainly used as the electrode material. In the conventional mode of operation or in known devices, however, these materials are also exposed to possible corrosion, especially by aggressive silicate melts. Molybdenum electrodes therefore have a strong tendency to oxidize. They must therefore be protected during the starting process by an inert gas atmosphere. Likewise, melters such as As ₂ O ₅ , molybdenum or even platinum electrodes can be involved in the melt. Compared to electrodes made of molybdenum, platinum electrodes are significantly more inert, but can be used for extended periods of time only up to temperatures of 1500 ° C. Due to the corrosion, the electrodes destroyed by corrosion are constantly replaced by the introduction of new electrodes in the melt. This means that an additional consumption of expensive electrode material, a high load on the electrode holder and a reduction in the availability of the device.

In the publication US 4246433 describes the use of cooled, in particular water-cooled, rod electrodes, which are introduced through the side walls into a melting vessel. By water cooling, the stability of the electrode against corrosion at higher temperatures is still guaranteed, so higher temperatures can be set in the melt, without having to accept a breaking or deformation of the electrodes. Therefore, the maximum achievable melting temperature is no longer limited by the application limit temperature of the electrode material by the cooling.

By the possibility, increased refining temperatures to be able to adjust or at the refrain particularly corrosive glasses results from a reinforced Attack on the wall and the electrodes of the aggregate an increased material input in the glass melt and thus also in the final glass product. Mostly Platinum used as wall or electrode material is on the one hand very expensive, on the other hand aggregates of platinum or Platinum alloys have the disadvantage that they due to the corrosivity and friction the glass melts small amounts of platinum or other alloying ingredients the wall and the electrodes in the melt. These are then both in ionic form and finely distributed in elemental Form in glass end product. This board entry on ionic or elemental metal in the molten glass may vary depending on the concentration and particle size in the final glass product to an undesirable Discoloration and to a reduced transmission of electromagnetic radiation to lead.

In the document DE 19939780 A1 describes the continuous refining of glasses in aggregates in which the melt is heated by direct coupling of high frequency energy. The aggregate used in this case consists of cooling circuits, which are almost "invisible" to the high frequency radiation used to heat the melt. On these cooled walls of the aggregate, the melt solidifies and forms a so-called skull layer between the molten glass and the wall material, which can renew itself again and again. Due to the skull layer on the mostly water-cooled metal pipes, the tightness of the aggregate is ensured, moreover, the attack of the molten glass is minimized to the vessel wall, which has a much lower material input into the molten glass result.

One advantage for the high frequency melting in such skull crucibles in that glass melts can be heated to temperatures above 1700 ° C, since the temperature resistance the aggregate wall due to the formed by the cooling skull layer is no longer a limiting factor. By directly coupling the High frequency in the glass melt can melt in the edge area of the smelting plant colder be as in the middle. Through the skull layer can also be high-melting and strongly corrosive glasses melt and purify.

Another advantage of high-frequency melting or melting at high temperatures lies in the availability of so-called high-temperature bleaching agents. This makes it possible to use environmentally harmful and toxic refining agents such as As ₂ O ₅ or Sb ₂ O ₅ , as described in the publication DE 19939771 is described to renounce and instead, for example, to use the less questionable SnO ₂ as refining agent.

However, the heating of the melt by means of high frequency has the disadvantage that the melting glasses, glass ceramics, ceramics or crystals must have a sufficiently high electrical conductivity at the melting temperature, so that the registered using the high frequency energy is greater than that on the skull walls dissipated amount of heat. The electrical conductivity of glass and glass ceramic melts is generally determined by the alkali content and, to a lesser extent, the alkaline earth content of these melts. Although the limit of required electrical conductivity also depends on a number of apparatus parameters, it has been found in practice that the electrical conductivity of the melt should be above 10 ^-1 Ω ^-1 cm ^-1 .

In practical experiments, however, it has been found that, in particular, the high-melting glasses, for which the high-frequency melting in the skull crucible would be particularly suitable due to the high temperatures, have too low an electrical conductivity, in particular below 10 ^-1 Ω ^-1 cm ^-1 . Thus, with the high frequency melting technique, a number of important technical glasses can not be processed.

To the glasses with low electrical conductivity and high temperature resistance belong next to glasses, which for Pharmaceutical packaging and high temperature resistant lamps are needed also glasses, such as display glasses, the be coated in the further processing. With display glasses are Alkaline contents in the glasses undesirable, because these metals can easily diffuse out of the glasses and so get into the functional layers of the display. These too glasses possess due to the low or nonexistent alkali content too little electrical conductivity to be good enough with the To couple high frequency.

In PCT / EP 03/13353 discloses a method and an apparatus for Heating of melts described. In this apparatus becomes a Glass melt heated by a current between at least two in turn cooled Electrodes flow, wherein the electrodes each replace a part of the wall of the melting vessel. The wall of the melting vessel is cooled in the device described at least in one area. adversely However, in the described device that is the electrodes below the upper edge of the skull crucible, thus must the energy for starting is led into deeper layers of the glass, which puts a heavy strain on the skull crucible, both thermally as well as high electrical voltages.

moreover especially when starting up the device problems caused by flashovers. The full Forming a Skullschicht is also not possible, since this is the coupling that of the as part of the vessel wall provided electrodes emitted electromagnetic energy would prevent in the melt.

In the published patent application DE 198 02 071 A1 describes a method for heating glass melting aggregates, wherein a direct current component is impressed on the alternating current serving to heat the melt in order to considerably reduce the corrosion of the electrode material used. In this case, an additional voltage drop is generated in one of the two partial currents of the alternating current in a heating circuit containing a transformer and at least two electrodes projecting into the molten glass. The application further describes a positive and a negative connected electron series, wherein on the negatively connected electrode row, especially the removal of the electrode material in the melt and on the positively connected electrode row, especially the formation of possibly liquid alloys is suppressed. The disadvantage, however, is that at the positively connected electrode row, a removal of the electrode material is not prevented in the melt.

Out US 4,624,002 It is known to reduce the problem of corrosion of electrodes, in particular of molybdenum electrodes by the method of low-frequency passivation. The heating current used is an alternating current with a low frequency of 50 or 60 Hz, which reduces the removal of molybdenum electrodes in glass melts. The heating current itself passivates the electrodes. The disadvantage is that it can come at the current densities used to a strong polarization of the electrodes, which can lead to bubble formation, whereby the boundary layer (protective layer) of the electrodes is damaged again.

Out DD 139 572 a method is known in which the heating the melt serving AC in the manner of a DC superimposed on a DC power source that will all be protected Electrodes have a negative electrical potential compared to the Refractory material or across from one or more auxiliary electrodes or against the refractory material accept. However, this process is limited to silicate melts, which contain no ions of heavy metals, their melting points are at or below the temperature of the melt. Furthermore is achieved with this method that contained in the melt Heavy metal ions are discharged at the electrodes and there a Form protective layer. This will cause the corrosion of the electrodes prevents the aggressive melt. The disadvantage here is that through the protective layer of heavy metal ions the surface and the surface properties the electrodes changed drastically become.

task

In front In this background, the present invention has the object underlying, a possibility for influencing the temperature of a melt, in particular for refining and Cleaning of melts, as well as a product, which according to the invention melted and / or purified and / or purified and / or manufactured available to put, while the above mentioned To avoid disadvantages as much as possible.

Especially should be a possibility to disposal be placed on the one hand, the electrodes of the device sufficient to protect against corrosion and to effectively minimize the fraction of gas bubbles in the melt.

The object comprises the aim of enabling the melt to be refined at temperatures higher than 1700 ° C. and at least to reduce the use of fining agents in the melt and, in particular, to minimize the amount of fining agents, in order to avoid toxic substances such as, for example, As ₂ O ₅ to be able to do without. Also, despite high temperature, the entry of ions from the melt contact surface of the wall and the electrode of the device should be minimized.

These Tasks become surprisingly simple Way solved by a method having the features of claim 1. Advantageous Further developments can be found in the respectively associated subclaims.

The The invention provides a method for influencing the temperature of a Melt in a space defining a space for receiving a melt, in particular in a melting and / or refining unit, available which for heating the melt at least by means of ohmic resistance heating at least two heating electrodes arranged in contact with the melt be provided, and at least one counter electrode, and at least one heating electrode opposite to the counter electrode a potential is set at which surface reactions of the heating electrode material with reactants from the melt be reduced.

By the arrangement of the at least two electrodes in the region of the melt is advantageously the electromagnetic energy for heating the Melt particularly easily coupled to the material to be melted. By providing the counter electrode and the application of a Potential between at least one heating electrode and the counter electrode the electrodes are sufficiently protected against corrosion. simultaneously Advantageously, the proportion of gas bubbles in the melt minimized by the blistering by the inventive method already at the heating electrodes is greatly reduced compared to the implementation without the application of the potential.

The The invention provides for the potential by applying a DC voltage between the at least one heating electrode and the counter electrode to create. The surface the heating electrodes shows in carrying out the method according to the invention, especially independent from the heating current load, a high gloss, lowest roughness and a high wettability with glass melt. Under heating current load done over it In addition, advantageously substantially no removal of particles of the electrode material in the melt, which is a long-term stabilization the heating electrodes result. Because of with the help of the invention realizable surface properties the heating electrode, which almost does not change during operation, is also achieved that cooled Melt easily dissolves from the heating electrodes and not, as previously common the heating electrodes "sticks".

The unchanged surface texture by the protection of the heating electrodes from corrosion thus advantageously causes a significant reduction of the bubble content in the region of the heating electrodes and in the melt. It turned out that near the electrodes occurred not clearly be determined bubbles and the bubbles were detectable type mixing bubbles with shares of O _2, SO _2, CO ₂ and N _2. These had a size with a diameter of about 500 microns. The occurrence of these bubbles can be explained by the high wettability of the iridium. The gas bubbles adhere to the metal, enlarge by diffusion and rise to the surface of the melt as soon as they have grown to a diameter in the range of about 200 microns to 1000 microns.

At unprotected Electrodes with oxidized surface let yourself do not observe this process. The glass / metal oxide interface is poorly wettable. Bubbles adhere to the surface of the electrode material not or only badly and can thus not by including small, in the melt Bubbles grow.

Furthermore leads the Protecting the electrodes from corrosion by applying a potential between at least one heating electrode and at least one counter electrode and the use of iridium as the electrode material is too substantial higher Service life of the heating electrodes due to a much lower Removal of the chemically unchanged Electrode material in the form of its oxide. In addition, it will be more advantageous Perform both the regeneration of minute hydrogen bubbles at the glass / metal interface Oxidation of iridium significantly reduced, as well as the formation of salable Bubbles with a diameter of 200 μm from single small, in the melt located bubbles, which have a diameter substantially of 50 μm up to 80 μm and are too small to leave the melt promoted. The removal of the electrode material leads to a significant increase in blister nuclei, thereby the heterogeneous nucleation in the melt is further enhanced.

By doing at least a portion of the melt is cooled, which for example in an edge region surrounding the melt treated by the process can be located, is advantageously the possibility created, where the melt with melt-carrying components come into contact can lower the temperature, so that the risk of corrosion and / or entry of components of such components in the melt can be reduced. In particular, in the cooled areas the melt a crust of solidified, the melt characteristic Material, a so-called Skullschicht be formed, which forming a vessel, in which the melt is treated. Then there is the melt Advantageously, in an environment of a material of its own, in which reduces the risk of contamination as much as possible is.

In The material to be melted and / or melted can at the method according to the invention, especially at elevated Temperature, different process steps run side by side. For one thing further smelting operations on the other hand, the refining of the melt can take place, besides gas bubbles also the product properties of the later glass negative influencing substances can be removed, that is, the melting and / or lautering can be superimposed on a cleaning step be.

The The invention further provides to carry out the method such that the melt in the arrangement defining a space for receiving a melt, in particular a vessel ready is placed, wherein the arrangement is cooled at least partially. The arrangement may, for example, by lines, in particular Pipes through which a coolant flows can, be formed. The term "arrangement" thus includes Any structure which at least temporarily absorb the melt can. These include especially vessels, such as For example, lautering units and / or melting tanks.

in the The following is used for the sake of simplicity, the term "vessel", which however, as stated above, is not to be understood that the arrangement is on one Structure out of context flat Limited components.

By arranging the electrodes in the region of the melt, in particular in the space of the vessel, increases Advantageously, the cooling surface of the side walls and thus the cooling effect. hereby be while the operation of the entire side walls with a Skullschicht covered, causing the vessel walls in front an attack of the melt, and the melt itself before material entry protected by the vessel wall.

In An advantageous development is provided that at least a side wall and / or at least a portion of a bottom plate the arrangement cooled such will that one Skullkruste formed on the vessel walls becomes. With the method according to the invention can therefore particularly high temperatures are realized in the melt, at the same time sufficiently low temperatures at the vessel walls can be ensured.

By The self-adjusting temperature profile also creates an advantageous Convection in the vessel, causing The introduced into the melt energy evenly in the melting or molten material is introduced. Thus, the Invention an energy-efficient effect on the temperature of a Melt.

advantageously, is according to the method of the invention the electromagnetic energy for heating the melt is particularly easy coupled to the material to be melted. This can be done in the melt particularly high temperatures can be realized. This is possible through the arrangement of the at least two electrodes in the space of the vessel, thereby Advantageously, the cooling surface of side walls and thus the cooling effect increased to the melt. This will be during operating the entire side walls with a crust of solidified, covered by its own material, whereby the vessel walls against attack of the melt, and the melt itself be protected against material entry from the side of the vessel wall. As a result, the entire side walls are solidified with a crust, covered by species-specific material.

The while In addition, the scull layer, which permanently renews the operation, also reduces An attack on the wall of the unit and reduces the material input in the glass melt and thus also in the final glass product. As wall material can because of the Skullschicht advantageously much cheaper Materials such as copper instead of the otherwise commonly used expensive platinum used.

As a result of the particularly high temperatures in the interior of the melt and the low temperatures in the region of the side walls, a flow profile is formed through the vessel, which advantageously allows a homogeneous distribution of the introduced energy in the melt. Because at the high temperatures which can be realized with the invention, and the optimal flow of the material to be melted by the device by means of the inventive method for refining and / or cleaning of melts, the removal of bubbles and / or other uner If desired substances are promoted, it is also possible to use significantly smaller amounts of refining agents.

According to one preferred development is between the at least one heating electrode and the counterelectrode a temporally constant potential applied to over the entire duration to maintain the same operating parameters and corrosion safely avoid the electrodes. Depending on the specific requirements or the extent of Corrosion, which is without use of the invention in the electrochemical cohere between electrode material and components of the molten glass would, exists within the scope of the invention, however, also the possibility between the at least one heating electrode and the counterelectrode are temporarily in time constant potential. That means over a period of time constantly creates a temporally constant potential in this period becomes.

One temporary Applying a temporally constant potential comes in particular then considered when a "memory effect" of the heating electrodes after the potential exists. Such a memory effect shows For example, in heating electrodes, which include iridium and cathodically polarized by after raising the potential between the heating electrodes and the counter electrode corrosion of the Heating electrodes, which would otherwise be observed without the potential, in particular over several Stays away for days.

The Method according to the invention can be done in particular be, by between the at least one heating electrode and the Counterelectrode a potential with an amount in the range of greater or equal to 50 mV to less than or equal to 500 mV, more preferably of 300 mV is applied.

Which Values are used exactly, depends on the respective Application. For alkali-free glass and heating electrodes with iridium as the melt contact material For example, a potential with an amount of 50 mV may be sufficient depending on current flow too even smaller, for example 20 mV can be. For alkaline Fiolax glass and Heating electrodes with iridium as a melt contact material can, for example a potential with an amount of 300 mV can be selected.

The Potential to be applied reflects the conditions at the interface between Iridium and glass with little iridium again. Iridium is mostly Made of an alloy that always has significant levels of impurities by base compounds such as some 100 ppm to 1000 ppm of molybdenum, Tungsten and zirconium, may have. These impurities are electrochemically effective and determine that in an alkaline-containing Fiolax melt-adjusting potential. For the properties of the interface between Iridium and glass, it is irrelevant whether the dissolution or suppression of a Iridium oxide film chemically by a caustic alkali or electrochemical by a sufficient negative potential is enforced. The creation of a potential prevents the formation of a layer of iridium oxide on the heating electrodes, which has the consequence that the electrodes also of strongly alkaline Melting will not be attacked.

In a preferred embodiment of the invention, a local direct current density of less than or equal to 100 μA / cm ² , preferably of smaller or equal to metallic components of the arrangement, in particular to the heating electrodes and / or the counter electrode and / or the side wall and / or the bottom plate equal to 50 uA / cm ² , adjusted and / or controlled and / or regulated, since it has been found that then blistering can be particularly reliably prevented.

For the inventive method can different materials depending on the requirements of the case be used as heating electrodes. For example, electrodes can are used, which in particular as a melt contact material Osmium, hafnium, molybdenum, Tungsten, platinum, iridium, platinum metals and / or which alloys of the aforementioned elements. As counter electrode can a Electrode can be used, which molybdenum, tungsten, platinum or alloys the aforementioned elements.

Around Metallic material to protect at locations vulnerable to corrosion sees the invention advantageously before, the counter electrode in an overflow and / or floor drain of the arrangement to order.

Around at the counter electrode forming bubbles or from the Counterelectrode ablated particles of the electrode material not in To enter the melt, the counter electrode can advantageously in a flow dead zone the arrangement can be arranged.

The invention offers various possibilities, depending on the electrochemical relationships between the materials of the melt and the heating electrodes and optionally further metallic components of the arrangement to apply differently directed potentials. For example, the counter electrode can be connected as an anode. The heating electrodes can be switched as cathodes. It is also within the scope of the invention to scarf the counter electrode as the cathode The heating electrodes can then be switched as anodes.

In an advantageous development of the method according to the invention, the melt is heated via the heating electrodes with alternating current, preferably with an alternating current frequency in a frequency range of greater than or equal to 1 kHz to less than or equal to 100 kHz, particularly preferably with an alternating current frequency of 10 kHz ± 3 kHz, in particular 8 kHz heated. By such a heating frequency, the blistering can be significantly reduced compared to lower heating frequencies, in particular, a reduction by a factor of at least 100, in particular of at least 500 can be achieved. This can be further supported by the fact that the heating electrodes are subjected to a current density of above 2 A / cm ² .

This can be further improved by cooling the electrodes. Advantageously, according to the invention, the electrodes can be regulated separately and / or controllably and / or adjustably cooled. Thus, an accurate Adjustment of for the respective electrode required cooling power to those in their Environment prevailing temperatures in a simple manner possible. Of Furthermore, at least one electrode holder can also be cooled. This carries advantageously for further protection of the electrodes.

According to the inventive method is it further provided that the bottom of the vessel at least cooled in one area becomes. This advantageously forms on the floor area a skull crust, which is the corrosion of the soil or prevents the entry of soil material in the material to be melted.

Becomes the soil only partially cooled, arise Areas with different electrical conductivity in the melt, which is a corresponding displacement of the electric field condition upwards from these floor areas. This is special energetically favorable when starting, because thereby the introduced electromagnetic energy in the upper Area of the vessel interior is coupled. If the smelting process begins there, the resulting sinks Melt down and through the onset of recirculation is the wished flow profile going through the vessel set. An arrangement of the electrodes near the surface of the The material to be melted supports these processes in this phase.

The cooling can according to the invention by Passing a cooling fluid, in particular air and / or water, by at least one electrode and / or at least one electrode holder and / or at least one Part of the vessel wall and / or the soil done in a particularly simple manner.

The Method can advantageously be used at particularly high average Temperatures of the melt are carried out. According to the invention Temperature of the melt in at least one area to at least 1700 ° C, preferably at least about 1800 ° C, more preferably at least about 2000 ° C heated. Because at the high temperatures, which with the invention can be realized and the associated optimal flow of the material to be melted through the device removing bubbles and / or other unwanted Promoted substances is, it is advantageously possible, significantly lower amounts of refining agents use.

To the Reducing the bubble concentration in the material to be melted are such high values for the Temperature advantageous because they except an increase in Transport speeds of the substances to be removed in the Melt cause a reduction in viscosity, which is the escape of the facilitates the removal of substances.

A Particularly suitable design of the airfoil in the vessel and a correspondingly efficient energy utilization can be achieved by that the temperature difference between the melt in a wheel area of the vessel and the melt in the central region of the vessel to more than about 150 K, preferably more than about 250 K is set.

Around the inventive method to integrate in a particularly simple manner in the implementation of conventional methods and these conventional ones This process can further develop the vessel in the top described inventive way operated as part of a continuously operated melting plant become. It can also advantageously the vessel be continuously fed and discharged to be melted Good. For example can the material to be melted advantageously from a melting tank fed to the vessel and essentially be discharged in molten form from the vessel. As a result, a direct coupling of the method according to the invention as a step in the treatment process of the material to be melted from the raw material to the end product possible.

By supplying and removing the material to be melted in or out of the vessel, a main flow direction of the melt is defined. The electromagnetic energy for heating the melt can be coupled in particularly efficiently if the heating current between the electrodes is substantially the same Chen along this main flow direction or perpendicular to it flows.

The heating current flows perpendicular to the main flow direction the melt, so a so-called cross-heating is performed, the melt flows defined into the vessel. The glass "falls" clean into the vessel.

Thereby the risk of overflow is lower across from a driving manner in which the heating flow along the main direction of flow the melt flows, So a so-called longitudinal heating carried out becomes. Depending on the requirements of the particular application can the transverse heating are preferably used, the longitudinal heating is, however, also usable in principle.

to Influencing the flow profile the melt through the vessel or for influencing the temperature profile in the melt offers the Invention advantageously further possibilities.

Especially can all electrodes are supplied with current of the same current intensity. It Further, at least one pair of electrodes may also be powered a strength which is dependent on the value of the current, with which acts on at least one other pair of electrodes is different. Furthermore, can interconnected the electrodes in an advantageous development are that crossing one another heating currents, in particular according to a Scott circuit, with a phase shift generated.

On Particularly simple way, the melt through a gutter with free surface introduced into the vessel and be removed from the vessel. An implementation of the procedure with as possible few intermediate steps to the lead the melt is advantageously possible because the melt by an inlet and outlet in the area of the molten bath surface Vessel closed and is discharged from the vessel. To the materials in particular in the area of the outlet of the vessel through to preserve the very high temperatures of the melt, is provided according to the invention, that the drainage area of the vessel at least partially cooled becomes.

A in terms of time and efficiency of energy use optimized implementation of the Method is further made possible by the residence time distribution and / or the mean residence time the melt in the vessel regulated and / or controlled and / or adjusted. Likewise, the flow profile and / or the average flow velocity the melt in the vessel regulated and / or controlled and / or adjusted. In particular, the volume can of the vessel so dimensioned be that the melt in the vessel has an average residence time from at least about 10 minutes to a period of about 2 Has hours. According to the invention is a Clue for a corresponding dimensioning of the vessel can be seen therein that the Vessel with one Volume is provided which is smaller by at least a factor of 10 is the volume of a melting tank upstream of the vessel.

Around advantageously to ensure that the existing or formed bubbles from the melt during the passage of the Vessel out the melt can escape provided that the height of Melt regulated in the outlet vessel and / or controlled and / or adjusted so that one on the ascent rate of the smallest bubbles at the existing middle one flow rate agreed height the melt which travels as the bubbles rise must become, can be realized. The lautering step the bladder enlargement is thus followed by a rise zone, not just the bloated bubbles, but also filters out the new bubbles by giving this opportunity ascend and leave the melt.

The Neublasenbildung takes place in the range of moderate supersaturation of the melt, that is when pressed below 100 bar, and thus exclusively by way of heterogeneous Nucleation. As germs come all the walls and installations of the aggregates into consideration. Particularly at risk Here are metal electrodes with electricity, since the forced from outside Mass transfer at the interface Electrode / melt by refining agent reactions still actively supported can be.

By The invention will use the electrodes as active elements within of the hot Area of the material to be melted used. The skull against it is isolated over Mass and electrodes. This will increase the risk of rollovers, in particular reduced when starting. The parameters of the ohmic resistance heating can therefore without danger for the materials used of vessel and electrodes are chosen such that also low-resistance glasses can be treated. Thus, it becomes possible also glasses and also to melt glass ceramics and ceramics or purify or to clean, which has a low electrical conductivity exhibit. For example, the invention can be used for purification of aluminosilicate glass, in particular display glass and lamp glass as well for the purification of Borosilicate glass, in particular for use in pharmaceutical packaging.

The inventive method can in preferably be carried out such that a melt having an electrical conductivity at the melting temperature in a range of greater than or equal to 10 ^-3 to less than or equal to 10 ² Ω ^-1 · cm ^-1 , preferably from greater than or equal to 10 ^-2 to less or equal to 10 ¹ Ω ^-1 · cm ^{-1 is} treated. With a conductivity in this preferred range, the coupling of the electromagnetic energy by means of the invention is particularly efficient.

The inventive method can be for different Melting be used. For example, a melt of a alkali-free glass used or a Fiolax melt used become.

By The movement of charged particles can, in addition to the known and in particular controllable with the aid of the method according to the invention Effects of cargo transports Interference currents occur. To interference reactions due to such potential interference currents, the invention offers the possibility to provide at least one grounding device for removing interference currents. Especially can the entire arrangement with at least one, preferably at least two earthing devices are provided to in the smelting unit an additional To provide ground loop in the manner of a voltage divider circuit, at which by adjusting the respective resistance to be overcome the lead away of interference in the respective areas of the arrangement can be designed.

Around by corrosion particularly vulnerable components such as components comprising platinum, in addition to protect, the invention provides, the arrangement with at least one auxiliary earthing device to provide. As an auxiliary grounding device can be a ground electrode be used, which in particular between the counter electrode and a metallic component of the device is switched. In question come in particular platinum components such as gutters or Stirrer.

The Auxiliary earthing device may advantageously be in an overflow and / or a floor drain of the arrangement are arranged. If the auxiliary earthing device is grounded directly, a noise current is low discharged at the components, in particular on components with platinum, over.

Around a grounding on reliable and easy to implement is provided within the scope of the invention, to provide a grounding device and / or an auxiliary grounding device, which is a series connection of a DC resistor and an alternating current resistance.

Around to be able to facilitate the start advantageously further is according to the method of the invention provided that a starting operation is performed, wherein in the At least a melting path with sufficient electrical conductivity between the electrodes for coupling the electromagnetic energy is provided in the melt. For this purpose, the electrodes and / or Parts of the wall during the starting process with a heating device are heated as far as that their temperature is above the dew point of the upper furnace atmosphere. An entry of substances from the upper furnace atmosphere into the melt can thus be largely avoided.

ever according to the melt to be processed and the used Electrode given electrochemical conditions may be within the scope of the invention the heating electrodes electrochemically passivated before starting and be transferred in particular to a glazed state. Likewise, the Electrodes passivated electrochemically before starting and be transferred in particular to a glazed state.

advantageously, can the methods of the invention be operated automatically. One way to do that is the regulation and / or control of the heating power of the electrodes Control and / or control and / or adjustment of the current, which flowing through the electrodes, he follows. Another possibility lies in the fact that the regulation and / or control of heating power the electrodes by regulation and / or control and / or adjustment the applied electrical power takes place. The choice between both ways can be made according to the properties of the melting material.

Especially with glasses takes the electrical conductivity with increasing temperature too. Will the introduced power be constant held, decreases with decreasing electrical resistance, so increasing Conductivity, the current consumption through the electrodes too. That's the danger damage to the Electrode material given. With a current control can therefore react quickly to self-building streamlines, which due to the danger of overheating in glasses, their conductivity from Current flow depends, extremely disadvantageous for the Product features are.

A further danger for the product properties lies in the possible entry of material the side walls and / or the bottom of the vessel in the Melt. This danger is especially at high temperatures, which enables the invention given.

In order to remove unwanted substances, in particular gas bubbles, from the melt, it is possible to add at least one high-temperature alkylating agent, for example tin dioxide. Thereby, the use of conventional refining agents such as As ₂ O ₅ can be reduced. These conventional refining agents are particularly disadvantageous with regard to ecological glasses, because their residues in the final product may have a toxic effect. It is thus an advantage of the invention to be able to achieve such high temperatures in an energy-efficient manner that high-temperature intermediates such as tin dioxide can be used, which can not fully develop their lautering effect at the usual lower temperatures.

The The above objects are further achieved by a device for Temperature influencing a melt, which at least one Space for receiving a melt defining arrangement, in particular a melting and / or refining unit, for receiving molten material, at least two heating electrodes for ohmic Resistance heating of a melt in the room to accommodate the Melt and at least one counter electrode, wherein the heating electrodes at least during of the operation protrude into the melt.

Around the risk of corrosion of the material of the vessel walls is to be countered provided that at least one wall of the device is coolable. The wall of the device can be used on the inside during operation of the Device include a Skullkruste to those described above Advantages with regard to the temperature distribution in the vessel, the corrosion protection the wall material and the almost completely inhibited entry to achieve wall material in the melt.

With the term "inside" is here to the Melt, so to the interior facing side of the wall meant.

The Electrodes can had different geometries and shapes. In particular, the Heating electrodes and / or the counter electrode plate and / or button and / or ball and / or rod and / or Rogowski and / or T and / or hammer and / or railings electrodes include.

shape and geometry of the electrode thereby affect the efficiency of the Energy input into the material to be melted. As a particularly advantageous when installing the electrodes, especially in the bottom of the vessel, have Stick electrodes proved, which as solid material and / or as Cap electrodes executed could be. Electrodes with a specifically enlarged surface, such as for example, as plate electrodes or in the form of a hammer the advantage of stressing the electrode surface due to excessive current densities to be able to reduce. This can further contribute to a corresponding design of the form, where sharp transitions like especially edges are avoided. Advantageously, have rounded outer boundaries the electrodes proved. By rounding the edges, the Values at current density peaks are lowered, which in particular achieved a reduction of bladder regeneration by a factor of 10 can be.

The Arrangement of the electrodes, in particular the distance of the center of the electrode from the next one adjacent wall, depending on the conductivity the melt selected become. The use of stick electrodes becomes a possibility created the side walls of the vessel completely in Skull, which increases the cooling surface of the side walls and thus also the cooling effect on the melt, which also supports the convection can.

By the distance to the particular cooled side walls of Electrodes can overflow between the electrode and the side wall are avoided. Another Advantage is that the entry point of the electrode into the vessel in one is relatively cold area and thus electrically isolated accordingly is. The inventive arrangement of Electrodes also has the advantage that no with the chilled ones Associated with crucible walls cooled Components protrude into the upper furnace room. Advantageously, it can thereby Corrosion of components by the existing in the upper furnace atmosphere Sulfur compounds are avoided.

critical for the possible use a material as an electrode in the device according to the invention it is that the material at the operating temperature of the device not react with the melt. According to the invention, the electrodes may be a melt contact material which metals such as osmium, hafnium, molybdenum, tungsten, Iridium, tantalum, platinum, platinum metals and / or their alloys includes. Iridium is of particular importance as the active electrode material to.

The term "active" element refers to the multiple function that the electrode exerts: In addition to the heating, the flow of the melt is also reached via the electrode, forming a kind of drive for the convection flow in the vessel Skull, which causes a downward flow of the melt in the vessel, a part of the so-called convection motor. also called thermal spring, around the electrode, an upward flow of the melt forms in the vessel. The electrode thus has, on the one hand, the function of heating and, on the other hand, that of a convection motor and is therefore referred to as an "active" element.

The inventive combination Made of skull crucible and electrode prevented by the advantageous Design of the airfoil the melt through the vessel the overflow of the Crucible. Through the use of iridium very high operating temperatures can be achieved up to 2000 ° C will be realized.

Next Electrodes, in particular metal electrodes, is made of solid material according to the invention, it is also possible to use electrodes to use which only a layer of a material in question exhibit. For this purpose, the electrode may have a core, preferably a ceramic core include. Advantageously, it is further provided that at least one electrode is provided with a layer which especially osmium, hafnium, molybdenum, tungsten, iridium, tantalum, Platinum, platinum metals and / or alloys thereof. Also coatings with any other suitable material according to the invention for use possible in the device.

Around on changed Requirements for the electrodes to be used and / or for damage to electrodes Being able to react flexibly in a simple manner is further according to the invention provided that at least one electrode replaceable on the device is appropriate.

Around reduce the temperature load on the electrodes and thus especially To be able to realize high melting temperatures, at least one electrode cooled be. For this purpose, an electrode can pass at least one channel of a fluid.

Of the Bottom of the vessel can for example, from a fusion cast refractory material such as Zirkonsilikat exhibit, resulting in the high operating temperatures still a much higher one Resistance as the melt ensures. By the arrangement of cooling pipes Across the electrodes, the floor can be protected from corrosion and uncontrolled Current flow protected become.

The Container of the device according to the invention can in a preferred embodiment a chilled one Ground as well as cooled side walls have, of which two opposing side walls the Form inlet and drain. The vessel can be designed as a skull crucible. The skull walls can do this be designed so that they are in the installed state below the melt surface around an angle to the outside are angled, creating a collar is formed. Especially easy to produce is such a collar when the angle for all Skullwände about 90 °. The side walls are then L-shaped angled.

Around the ohmic resistance heating in the device according to the invention to be able to realize it is provided that the device has a device for generating of alternating current, preferably with an alternating current frequency in a frequency range bigger or equal to 1 kHz to less than or equal to 100 kHz, more preferably with an AC frequency of 10 kHz ± 3 kHz, in particular 8 kHz includes.

In According to an advantageous development, the device comprises a device for generating direct current, preferably for applying a potential between the at least one heating electrode and the counter electrode with an amount ranging from greater than or equal to 100 mV less than or equal to 500 mV, preferably of 300 mV.

According to the invention comprises the device at least one inlet area and / or at least one Drain area and / or at least one overflow area. At least one Part of the overflow area and / or the drainage area can be used as a counter electrode for applying the Be designed DC voltage. Furthermore, the invention provides that the arrangement a flow dead zone in which the counter electrode is positioned. In a advantageous development is at least a part of the overflow area and / or the drainage area designed as a cooling section.

Around depending on the electrochemical conditions for the particular melt and the materials further used corrosion or Blistering intensified to be able to counteract can Heating electrodes and / or a counter electrode are used, which an original one State in which they, especially before starting the Device, are electrochemically passivated and in particular a glass coating include.

For deriving interference currents it is provided to provide the arrangement with at least one, in particular with at least two grounding devices. Furthermore, the arrangement may comprise at least one auxiliary earthing device. In a preferred embodiment of the invention, the auxiliary grounding device has a grounding electrode, which is connected in particular between the counterelectrode and a metallic component of the arrangement. The auxiliary grounding device can be arranged, for example, in an overflow and / or a bottom drain of the arrangement. advantage Properly, the auxiliary earthing device is grounded directly.

The Grounding device and / or the auxiliary earthing device can in Frame of the invention, in particular in the form of a series connection from a DC resistor and an AC resistor to be provided. The grounding device and / or the auxiliary grounding device can thereby an electrode comprising platinum and / or molybdenum and / or Tungsten has.

Materials, which come into contact with the material to be melted, according to the invention in such a way selected, that they chemically against the material to be melted and its melt are essentially resistant. This is true for electrodes and / or the walls the vessel alike too. As material for the vessel come therefore, for example, iridium, rhodium or molybdenum in question.

The inventive device has a vessel with a geometry that is as small as possible relationship between surface and volume allows about energy losses over the surface to be largely avoided. Such geometry may be in modifications of the main body of a cube In particular, the vessel can be a polygonal, in particular rectangular, in particular square or round, in particular oval, in particular circular Have floor plan.

The inventive device can be used in particular as part of a larger system. If a certain amount of melt is provided in such a plant, of which only one part is to be further processed in this way, that the advantages associated with the invention are realized can, the invention further provides that a current divider for Splitting a melt flow into at least two partial streams provided is, so that at least one device according to the invention in one of substreams can be arranged, and the other partial flow in a different way can be processed further. The device can as refining and / or Cleaning and / or melting module can be used, which is a following unit can be preceded, in particular a Homogenizing unit and / or a shaping unit.

As well can the device of the invention as a refining and / or cleaning and / or melt module and / or homogenization module used which are upstream of an overflow downdraw unit can. This will be possible that the present invention enables the production of a highly homogeneous melt, which in particular as a starting material for the production of for example display glass in an overflow downdrawing process.

The The invention may further be used as a refining and / or cleaning module are used, which in a melting tank, that is in a flowed through by melt Vessel, installed becomes. The melting tank can do this, for example, in one area to a refining and / or cleaning module to be formed.

This can be realized in particular by the bottom of the melting tank is built from a so-called wall. This wall can be for example chilled Have walls, which include molybdenum. In the inner region of the wall, the device of the invention to get integrated.

Especially the device may be connected to the walls in the region of its side walls, which form the wall.

Of the level the melting tank in the flow direction seen in front of or behind the wall can be significantly larger as the level in the Area of the refining and / or cleaning module. This can be achieved by that the module is "hooked" into the wall, so to speak, and the height from the bottom of the module up to to its upper limit is significantly less than the distance from the bottom of the melting tank to the upper boundary of the wall.

There in such an arrangement, the path which bubbles out of the melt for leaving the same in the refining and / or cleaning module to cover have, is small compared to the corresponding way in the Melting tank, is the lautering effect clearly improved. Contributes to this in particular the high temperature of the melt at, which with the Device according to the invention in refining and / or cleaning module can be achieved.

to solution The above-mentioned objects further provide the invention Product, in particular a glass product available, which according to the inventive method and / or in the device according to the invention melted and / or purified and / or cleaned and / or manufactured.

Such products can be characterized, for example, by the value of the ratio of the amount of Sn ⁴⁺ to the amount of Sn ²⁺ . At higher temperatures, the ratio is shifted towards Sn ²⁺ . Due to the high temperatures which can be realized by means of the invention, the value for the ratio of the amount is Sn ⁴⁺ to the amount of Sn ²⁺ shifted so that at least 4% to at least 40% more Sn ²⁺ are present in the mixture. In particular, the product has a content of tin of less than 0.4 wt .-%, preferably less than 0.2 wt .-% and particularly preferably less than 0.1 wt .-% to.

There the refining and / or cleaning action, in particular by the very high achievable Temperatures is greatly improved by the invention, it is possible, more cost-effective To use starting material, that is to say that of lower purity, because the required quality of the product due to the high refining and cleaning effect still ensured by the invention can be. For example, water, sulfur and halogens while of the refining or cleaning process removed from the melt.

Parameters that characterize inferior raw materials may be a particularly high water content, a particularly high sulfur content, a particularly high content of volatile components such as chloride. With regard to the iron content, it should be remembered that Fe contributes to the refining and the ratio of the amounts of Fe ³⁺ to Fe ²⁺ is shifted towards Fe ²⁺ .

The Product, in particular the glass product according to the invention can at least a glass and / or at least one glass ceramic and / or at least have a ceramic which has a low electrical conductivity Has. In particular, the product aluminosilicate glass, in particular Display glass or Include lamp glass. The product may in particular be borosilicate glass, especially in an application for pharmaceutical packaging.

The The invention further relates to aggressive glasses such as For example, zinc silicate or Lanthanbratgläser, which otherwise very difficult to melt. Lead silicate glasses can also be produced by means of the invention be handled.

in the With regard to the products which are melted by means of the invention and / or purified and / or purified and / or can be produced, There are special advantages in that they are particularly low in bubbles and / or particularly small bubbles.

By the use of iridium as electrode material respectively as counterelectrode material are minor residues iridium or Iridium ions detectable in the product. The product therefore has one Proportion of iridium from about 1 ppm to about 500 ppm, preferably about 1 ppm to about 100 ppm, more preferably from about 2 ppm to about 20 ppm.

Of the Percentage of bubbles and the iridium content of the glass represent this essential parameters of the glass, which melted according to the invention and / or purified and / or cleaned and / or manufactured.

By the total required only very small Use of refining agents are the residues of refining agents in the product, such as the Zinnoxydgehalt also very low. The product therefore has a content of less tin as 0.4% by weight, preferably less than 0.2% by weight, and especially preferably less than 0.1% by weight.

The Invention allows also the production of glasses with a lower content of nodes. Nodes are areas, off which substances such as sodium and / or boron evaporate and thus others Strength properties are brought about. By such Nodes are particularly problems with pipe drawing. The invention allows Therefore, the production of particular pipes but also other glasses, which essentially have no nodes.

The The invention will be described below with reference to the attached figures based on embodiments describe. The same components are in all figures with the same Reference number marked.

It demonstrate:

1 a schematic representation of various electrodes,

2 a schematic representation of the device according to the invention in cross section in a sectional plane perpendicular to the direction of flow of the melt through the vessel with Skullkruste,

3 a schematic representation of the device according to the invention in cross-section in a sectional plane perpendicular to the direction of flow of the melt through the vessel in the filled state,

4 a schematic representation of the device according to the invention in cross-section in a sectional plane parallel to the direction of flow of the melt through the vessel in operation with additional heating,

5 Detailed view of the convection roller in the flow during operation according to an arrangement as in 9 shown,

6 a schematic representation of the device according to the invention in cross section in a sectional plane parallel to the flow direction of the melt according to another embodiment with additional heating and the flow of the melt influencing internals,

7 a schematic representation of the device according to the invention in cross-section in a sectional plane perpendicular to the direction of flow of the melt through the vessel to illustrate the cooling of the vessel bottom,

8th schematic representations of the device according to the invention in supervision,

9 schematic representations of the device according to the invention in supervision,

10 schematic representations of the device according to the invention in supervision,

11 schematic representations of the device according to the invention with upstream pre-melting device in a perspective view.

12 schematic representations of the device according to the invention with upstream pre-melting device in a perspective view.

For the arrangement in the interior of the vessel according to the device according to the invention, inter alia rod railing, T or plate electrodes can be used. In 1 is an exemplary selection of such electrodes 4 shown. Stick electrodes can be a round ( 1A ) Section and also interconnected as railing electrodes ( 1C ) be used. Also plate electrodes ( 1B ) can be varied in their geometry as well as connected in series ( 1D ) be used. The connection of the individual electrodes together leads in a particularly advantageous manner to a much higher stability of the electrode arrangements. Also, the use of T-electrodes ( 1E ) can be beneficial.

If the device according to the invention is operated as a skull crucible as intended, a scull crust forms. An arrangement of the device with this scull crust 14 is in 2 shown. In the device 1 to influence the temperature of the melt forms in the interior of the vessel wall 10 a skull crust, namely a layer of solidified melt 14 because of the vessel wall 10 cooled so much that the melt from the inside of the vessel to the wall 10 stiffens. A cooling of the vessel wall can be done by passing coolant through the tubes of Skulltiegels. So does the device 1 corresponding nozzles for the coolant inlet 121 or the coolant outlet 122 on. As in 3 shown in operation of the device according to the invention 1 the melt 16 not with the vessel wall 10 the skull crucible in contact, because in between the solidified melt 14 is designed as Skullkruste.

Above the surface of the molten bath 18 is the upper furnace area 26 , To cool the melt 16 at the melt surface 18 To reduce or avoid, it may be useful to the device 1 to operate with an additional heating. According to the in 4 illustrated embodiment is an arrangement of gas burners 24 provided, for example, in a support frame 25 can be arranged so that by means of the gas burner 24 the upper furnace area 26 can be heated.

In 5 is in detail the then adjusting convection roller 28 shown. The melt passes over the inlet 20 into the vessel 2 one. Due to the cooling of the wall of the skull crucible 10 the melt solidifies in the form of the skull crust 14 , The incoming melt meets after passing through the inlet on a very cold area when it is the inlet 20 leaves, and rushes down into the interior of the vessel 2 down. Inside the vessel 2 the heating takes place by means of the ohmic resistance heating by the in 10 not shown electrodes. The melt 16 heats up and therefore rises in the vessel 2 up. Was the temperature distribution in the vessel 2 adjusted accordingly, the convection roller runs 28 stationary. Fluid elements heated to particularly high temperatures leave via the casserole 22 , which in relation to the inlet 20 is provided with a greater length to serve as a cooling section, the vessel 2 ,

6 shows another embodiment of the device 1 , which here with additional heating in the upper oven room 26 over gas burner 24 is operated in a carrying frame 25 are arranged, with the support frame 25 Also as a suspension for flow-influencing internals 30 serves, which are dipped from above into the melt. In addition, flow-influencing internals 30 also on the side walls 10 of the vessel 2 be provided. For adjusting the temperature distribution as well as the residence time distribution inside the vessel 2 By adjusting the flow profile, the flow influencing internals 30 inside the vessel 2 to be ordered. One possibility for such an arrangement is in 6 also shown.

To the ground 8th of the skull crucible to protect against high temperature loads and corrosion, this is in the device according to the invention 1 cooled. In 7 is in the simplified representation the device 1 the cooling of the vessel bottom by on the bottom plate 8th resting pipes 81 shown. The skull crust 14 Forms accordingly around the pipes 81 around or can grow into the interior of the vessel in such a way that the cooling tubes 81 on the bottom of the vessel from the skull crust 14 be enclosed.

A plan view of the vessel with arranged at different locations counter electrodes is in the 8th . 9 and 10 shown. 8th shows electrodes 4 , which are arranged in two rows next to each other. The rows are parallel to that of the inlet 20 through the vessel 2 the end 22 directed flow direction of the melt arranged. Inlet and outlet of the side walls 10 of the vessel 2 are designed so angled that the kinked part of the vessel 2 is directed away and so a collar 6 forms. Following the collar is the environment 7 the device in 8th for orientation. The counter electrode 5 is in 8th in the middle of the process 22 arranged. 9 shows an embodiment in which the counter electrode 5 at the inlet 20 of the vessel 2 is positioned. Another particular embodiment is in 10 shown. In this embodiment, the edge is between the vessel 2 and expiration 22 designed as a flat counter electrode.

11 shows a schematic representations of the device according to the invention with an upstream device in a perspective view. This figure shows three ways of positioning the counter electrode 5 in a vessel 2 upstream device. In this case, the counterelectrode can in a first embodiment as a rod electrode into the interior of the device 21 protrude or according to a second embodiment, a boundary surface of this. Also, the inlet through which the melt is supplied, as a counter electrode 5 be designed.

In 12 is a schematic representations of the device according to the invention with an upstream device shown in a perspective view. In the illustrated embodiment, the counter electrode is 5 in the exit section 23 a vessel 2 with electrodes 4 , For example, a refining unit positioned. In 12 it can be seen which flow path the gas bubbles after leaving the vessel 2 is available for ascent to the surface of the melt. Also, the height of the melt in the downstream of the vessel and thus the flow rate of the melt can be regulated and / or controlled and / or adjusted so as to achieve a quantitative as possible rise of the bubbles.

Because with the device according to the invention with the arrangement of heating electrodes inside a skull crucible especially high temperatures of the melt can be realized, the invention allows the melting and / or refining and / or cleaning even difficult to handle glasses such as of the display glass AF37. About that addition, have the use of auxiliary electrodes and the application a direct current between the counter electrodes and the heating electrodes essential increased Service life of the electrodes and lower bubble inclusions Episode. For treating the glass AF37, the device may in particular be such operated, that the mean residence time at least 10 min is. This results in corresponding ratios of the values for the volume of the vessel and the throughput. Decisive here, in particular, are the glasartabhänige viscosity and the volume expansion coefficient.

It It will be apparent to those skilled in the art that the invention is not limited to the above described embodiments limited is, but rather in more diverse Way can be varied. In particular, the characteristics of each embodiments also be combined with each other.

1

contraption for influencing the temperature of a melt

2

vessel

4

electrode

44

electrode holder

5

counter electrode

6

collar of the vessel

7

Surroundings of the vessel

8th

ground of the vessel

81

Cooling the vessel bottom

9

power supply for electrodes

10

wall of the vessel

12

Tube of the skull crucible

121

Coolant inlet

122

Coolant flow

123

insulation the skull segments

14

froze melt

16

melt

18

melting bath

20

Intake

21

premelter

22

procedure

23

final leg

24

gas burner

25

carrying frame for heating devices

26

Upper furnace area

28

convection

30

flow conditioning fixtures

32

starting electrodes

34

power supply for starting electrodes

36

melting

Claims (70)

A method for influencing the temperature of a melt in an arrangement defining a space for receiving a melt, in particular in a melting and / or refining unit, wherein at least two heating electrodes are arranged in contact with the melt for heating the melt at least by ohmic resistance heating, characterized in that at least one counter electrode is provided, and at least one heating electrode opposite to the counter electrode is set to a potential at which surface reactions of the heating electrode material with reactants from the melt are reduced. Method according to claim 1, characterized in that that at least a part of the melt is cooled. Method according to one of the preceding claims, characterized characterized in that Melting in the one room defining the inclusion of the melt Arrangement, in particular a vessel is provided, wherein the arrangement is cooled at least partially. Method according to one of the preceding claims, characterized characterized in that at least one Side wall and / or at least a portion of a bottom plate of Arrangement cooled in such a way will that one Skullkruste formed on the vessel walls becomes. Method according to one of the preceding claims, characterized characterized in that the potential by applying a DC voltage between the at least one heating electrode and the counter electrode is produced. Method according to one of the preceding claims, characterized characterized in that between the at least one heating electrode and the counter electrode is applied a temporally constant potential Method according to one of the preceding claims, characterized characterized in that between the at least one heating electrode and the counter electrode temporarily a temporally constant potential is applied. Method according to one of the preceding claims, characterized characterized in that between the at least one heating electrode and the counter electrode has a potential in the range of bigger or equal to 100 mV to less than or equal to 500 mV, more preferably of 300 mV is applied. Method according to one of the preceding claims, characterized in that on metallic components of the arrangement, in particular on the heating electrodes and / or the counter electrode and / or the side wall and / or the bottom plate, a local direct current density of less than or equal to 100 μA / cm ² , preferably of less than or equal to 50 μA / cm ² , adjusted and / or controlled and / or regulated Method according to one of the preceding claims, characterized in that electrodes are used as heating electrodes, which osmium, hafnium, molybdenum, Tungsten, platinum, iridium, platinum metals and / or which alloys of the aforementioned elements. Method according to one of the preceding claims, characterized in that it uses an electrode as the counterelectrode which is made of molybdenum, Tungsten, platinum, or alloys of the aforementioned elements. Method according to one of the preceding claims, characterized characterized in that Counter electrode in an overflow and / or floor drain of the arrangement is arranged. Method according to one of the preceding claims, characterized characterized in that Counterelectrode in a flow dead zone the arrangement is arranged. Method according to one of the preceding claims, characterized characterized in that Counter electrode is connected as an anode. Method according to one of the preceding claims, characterized characterized in that Heating electrodes are connected as cathodes. Method according to one of the preceding claims, characterized characterized in that Counter electrode is switched as a cathode. Method according to one of the preceding claims, characterized characterized in that Heating electrodes are connected as anodes. Method according to one of the preceding claims, characterized in that the melt flows through the heating electrodes with alternating current before zugt with an alternating current frequency in a frequency range of greater than or equal to 1 kHz to less than or equal to 100 kHz, particularly preferably with an AC frequency of 10 kHz ± 3 kHz, in particular 8 kHz is heated. Method according to one of the preceding claims, characterized in that the heating electrodes are subjected to a current density of above 2 A / cm ² . Method according to one of the preceding claims, characterized characterized in that all Heating electrodes are supplied with current of the same current. Method according to one of the preceding claims, characterized characterized in that at least one A pair of heating electrodes is supplied with current of a strength which different from the value of the current, which is acted upon by at least one further pair of heating electrodes is different. Method according to one of the preceding claims, characterized characterized in that Heating electrodes each separately controllable and / or controllable and / or adjustable cooled become. Method according to one of the preceding claims, characterized characterized in that Heating current between the heating electrodes substantially along the Main flow direction the melt or perpendicular to it flows. Method according to one of the preceding claims, characterized characterized in that Heating electrodes are connected in such a way that cross-heating currents, in particular according to a Scott circuit, with a phase shift. Method according to one of the preceding claims, characterized characterized in that Control and / or control of the heating power of the heating electrodes by regulation and / or control and / or adjustment of the current he follows. Method according to one of the preceding claims, characterized characterized in that Control and / or control of the heating power of the heating electrodes by regulation and / or control and / or adjustment of the power he follows. Method according to one of the preceding claims, characterized characterized in that Heating electrodes electrochemically passivated before starting and thereby be transferred in particular in a glazed state. Method according to one of the preceding claims, characterized characterized in that Electrodes passivated electrochemically before starting and be transferred in particular to a glazed state. Method according to one of the preceding claims, characterized characterized in that Arrangement as part of a continuously operated melting plant is operated. Method according to one of the preceding claims, characterized characterized in that the melt through a gutter, in particular a gutter with a free surface in the Arrangement introduced and / or by a groove, in particular a groove with a free surface, removed from the arrangement becomes. Method according to one of the preceding claims, characterized characterized in that the melt through an inlet and outlet in the area of the molten bath surface. and is discharged. Method according to one of the preceding claims, characterized in that the residence time distribution and / or the mean Residence time of the melt in the vessel regulated and / or controlled and / or adjusted. Method according to one of the preceding claims, characterized characterized in that the flow profile and / or the average flow velocity the melt in the vessel regulated and / or controlled and / or adjusted. Method according to one of the preceding claims, characterized characterized in that Height of the melt regulated in the drain vessel and / or controlled and / or adjusted. Method according to one of the preceding claims, characterized characterized in that Melt in at least one area within the space of the arrangement to a temperature of at least 1700 ° C, preferably of at least To 1800 ° C, more preferably set and / or controlled by at least 2000 ° C. and / or regulated. Method according to one of the preceding claims, characterized characterized in that Temperature difference between the melt in the edge region of the vessel and the melt in the central region of the vessel to more than about 150 K, preferably more than about 250 K is set. Method according to one of the preceding claims, characterized in that at least one Hochtemperaturläutermittel added to the melt is set. Method according to one of the preceding claims, characterized characterized in that it is operated automatically. Method according to one of the preceding claims, characterized in that a melt having an electrical conductivity at the melting temperature in a range of greater than or equal to 10 ^-3 to less than or equal to 10 ² Ω ^-1 · cm ^-1 , preferably greater than or equal to 10 ^-2 to less than or equal to 10 ¹ Ω ^-1 · cm ^{-1 is} treated. Method according to one of the preceding claims, characterized characterized in that a melt of an alkali-free glass used becomes. Method according to one of the preceding claims, characterized characterized in that a Fiolax melt is used. Method according to one of the preceding claims, characterized characterized in that at least one grounding device for discharging Interference currents provided becomes. Method according to one of the preceding claims, characterized characterized in that the arrangement with at least one, preferably at least two earthing devices is provided. Method according to one of the preceding claims, characterized in that the arrangement is provided with at least one auxiliary earthing device becomes. Method according to one of the preceding claims, characterized in that the auxiliary grounding device is a grounding electrode is used, which in particular between the counter electrode and a metallic component of the device is switched. Method according to one of the preceding claims, characterized characterized in that the auxiliary earthing device in an overflow and / or a floor drain of the arrangement is arranged. Method according to one of the preceding claims, characterized in that the auxiliary earthing device is grounded directly becomes. Method according to one of the preceding claims, characterized in that a grounding device and / or an auxiliary grounding device which is a series connection of a DC resistor and an AC resistor. Device for influencing the temperature of a melt full: one at least one space for receiving a melt defining arrangement, in particular a melting and / or refining unit, for receiving molten material, at least two heating electrodes for ohmic Resistance heating of the melt in the room and at least one Counter electrode, wherein the heating electrodes at least during the Project into the melt. Apparatus according to claim 49, which comprises at least one coolable Wall includes. Device according to one of claims 49 to 50, characterized that the Wall on its inside during operation of the device a skull crust includes. Device according to one of Claims 49 to 51, characterized that the Heating electrodes and / or the counterelectrode plate and / or button and / or ball and / or rod and / or Rogowski and / or T and / or Railing electrodes include. Device according to one of Claims 49 to 52, characterized that the Electrodes have a melt contact material, which at least a metal, in particular osmium, hafnium, molybdenum, tungsten, iridium, tantalum, Platinum, platinum metals and / or their alloys. Device according to one of claims 49 to 53, characterized that the Device, a device for generating alternating current, preferably with an AC frequency in a frequency range greater than or equal to equal to 1 kHz to less than or equal to 100 kHz, more preferably with an AC frequency of 10 kHz ± 3 kHz, in particular 8 kHz includes. Device according to one of Claims 49 to 54, characterized that the Device, a device for generating direct current, preferably for applying a potential between the at least one heating electrode and the counter electrode with an amount in the range of greater than or equal to 100 mV to less than or equal to 500 mV, preferably of 300 mV. Device according to one of claims 49 to 55, characterized that the Device at least one inlet area and / or at least one Drain area and / or at least one overflow area includes. Device according to one of claims 49 to 56, characterized in that at least one part of the overflow area and / or the discharge area is designed as a counter electrode for applying the DC voltage. Device according to one of claims 49 to 57, characterized that the Arrangement a flow dead zone in which the counter electrode is positioned. Device according to one of claims 49 to 58, characterized that at least a part of the overflow area and / or the drainage area is designed as a cooling section. Device according to one of Claims 49 to 59, characterized that the Heating electrodes and / or the counter electrode to an original state in which they, in particular before starting the device, electrochemically passivated and in particular include a glass coating. Device according to one of claims 49 to 60, characterized that the Arrangement at least one, in particular at least two grounding devices having. Device according to one of Claims 49 to 61, characterized that the Arrangement comprises at least one auxiliary earthing device. Device according to one of Claims 49 to 62, characterized that the Auxiliary grounding means comprises a ground electrode, which in particular between the counter electrode and a metallic component of the device is switched. Device according to one of claims 49 to 63, characterized that the Auxiliary earthing device in an overflow and / or a floor drain the arrangement is arranged. Device according to one of claims 49 to 64, characterized that the Auxiliary earthing device is grounded directly. Device according to one of claims 49 to 65, characterized that the Grounding device and / or the auxiliary grounding device provided is a series connection of a DC resistor and a AC resistance includes. Device according to one of claims 49 to 66, characterized that the Grounding device and / or the auxiliary grounding device an electrode comprising platinum and / or molybdenum and / or tungsten. Product, in particular glass product, which according to the method according to claim 1 to 48 and / or in and / or with the device according to claim 49 to 67 melted and / or purified and / or purified and / or homogenized and / or produced. Product according to claim 68, characterized that this Product has a content of tin of less than 0.4 wt .-%, preferably of less than 0.2% by weight, and more preferably less than 0.1 wt .-%. Product according to claim 68, characterized that this Product has a proportion of iridium of from about 1 ppm to about 500 ppm, preferably from about 1 ppm to about 100 ppm, more preferably from about 2 ppm to about 20 ppm.