SE414632B - VIEW TO REDUCE OR PREVENT CHROMOXIDE-INDUCED OXIDATIVE DEFINITION OF COMPONENTS MANUFACTURED BY ELFAST METAL IN AN ELECTRIC OVEN WHILE AN OXIDE MIXTURE CONTAINING 0.5-10% WEIGHT OF CHROMOXIDE MELTED - Google Patents

Description

-7713168-9 are three or more electrodes arranged around the mouth. The eld- the solid oxides to be melted are charged, usually in the form of powders or granules, in the bowl-shaped oven so that they cover the mouth and the electrodes. After commissioning with use of a high temperature flame to form a first molten accumulation of oxides continues electric current through the electrodes and they melt the oxides to resist heat the oxides and thus to continued melting of the oxide materials. While the oxides melt they descend through the mouth into a fiber-shaped arrangement below. apparatus. Meanwhile, raw material is continuously fed into the mold of oxide powder in the furnace and melted for fiber formation, lunda continuously forms an oxide melt and then fibers. See- once a melting and fiber forming operation is well started it often runs continuously for several days, weeks or months.

This means that the electrodes must function satisfactorily during these time periods, as nothing often occurs occasion, once the smelting operation has started, to replace the repair the electrodes without stopping the oven operation. With ovens at which electrodes can be replaced while the oven is still on in operation, such an exchange is both difficult and costly.

Likewise, the mouth must essentially retain its shape or its dimensions throughout the operation, because the flow of molten oxide into the fiber forming unit is regulated by this mouth. The mouth is designed with a specific and accurately calculated diameter, so shaped so that a carefully regulated given amount of molten oxide flows down in the fiber forming unit under the oven. Quantity of fibers obtained and especially quality is directly dependent on the speed with which the oxide melt flows from the furnace through the orifice to the fiber the forming unit. The flow rate is regulated by means of a needle-like flow control device which in cooperation with the mouth regulates it amount of oxide flowing through the mouth. If the estuary deteriorates becomes substantially larger and can no longer, in conjunction with the the til "control device regulates the flow of oxide melt through the orifice.

The fiber forming unit is thus substantially "soaked" with excess shot oxide melt and can no longer achieve satisfactory fibers; This deterioration of the estuary is more critical for the operation É than the deterioration of the electrodes, since in some cases the electrodes, can be removed and / or the electric current can be set Å so that the deterioration of the electrodes is to some extent counteracted. However the fixed mouth can no longer be set to counteract 7713498-9 the removal of the refractory orifice metal and the associated of the mouth diameter.

As previously pointed out, electric furnaces have previously once used to produce "glass" melts consisting mainly of matter of mixtures of silica and soda ash, and refractory "melts consisting mainly of mixtures of silica and aluminum oxide. Often, small amounts of other oxides, such as titanium oxide, zirconium oxide, nium oxide, iron oxides and the like be present, in particular with The "glass fibers". It has not previously been observed that any of the said material has had any unnecessary detrimental effect on the operation of the electric furnaces.

In recent years, however, fibers of refractory oxide containing silica and alumina and up to about 10% chromium oxide widespread use. Such fibers have been found to be abundant effective as thermal insulation at temperatures up to approx 148 ° C. Typical examples of fibers containing chromium oxide are those sold under the name CERACHROME by Johns-Manville Corporation and as described in U.S. Pat. No. 3,449,137.

First, the chromium oxide-containing oxide melts were prepared in arc furnaces for fiber forming. Success with electric ovens with electric belief in refractory metal with other oxide melts led to attempts to produce chromium oxide-containing melts in such furnaces. However, it was covered that, when melts containing about 0.5-10% or more chromium oxide, by weight, was used in electric furnaces, the refractories the electrodes and orifices rapidly deteriorated and were worn away.

In some cases, electrodes and orifices deteriorated, some of which were used months with other types of oxide melts, in the presence of chromium oxide so quickly that the ovens have to be turned off for a few hours or days. All such previous attempts to melt chromium oxide-containing oxides in electrical -ka furnaces with electrodes and orifices of refractory metal have led to rapid deterioration of the electrodes and orifices and has treated as completely unsuccessful.

An object of the present invention is therefore to provide a way of melting chromium oxide-containing oxide mixtures in electrical furnaces in the presence of refractory metal electrodes and orifices ( such as molybdenum) while achieving a satisfactory operating life length of the orifice and electrode components.

According to the invention, a method of reducing is thus provided or prevent chromium oxide-doped oxidative deterioration of the component made of refractory metal, selected from molybdenum, vol- 7713498-9 'f front, rhenium, tantalum, osmium and iridium and their alloys, in an electric furnace in which a chromium oxide-containing oxide mixture which is characterized in that the furnace, in addition to oxidizing the mixture is fed with an additive material, which is present in a state of choice lower than the maximum of the additive material valence state and which can be oxidized by chromium dioxide or chromium trioxide to an oxide with a lower free formation energy per mole of oxygen than the oxides of the refractory metal and the chromium oxide (Cr2O3), so that during operation, the additive material is oxidized in front of the refractory metal ° len, reduces the higher chromium oxides to chromium oxide (Cr2O3) and forms an oxide inert to the refractory metal, wherein it the present reactive amount of additive material is 25-50%, calculated on the amount of Cr 2 O 3 in the mixture.

The present invention is based on the surprising the cover that, unlike others in refractory oxide melts malt oxides, chromium oxide (Cr2O3, medenicromene valence of 3) oxidizes in the presence of air, somrunmaltär5-contact with Oxidsmältäns surface, to form chromium dioxide (CrO2, with a chromium valence of 4) and chromium trioxide (CrO3, with a chromium valence of 6). Chromium dioxide and chromium the trioxide compounds then come into contact with the electrodes and the mouths of refractory metal, where those of the refractory metal reduced again to chromium oxide (Cr 2 O 3), leaving the refractory metal oxidized. The refractory metal oxides are then introduced into the oxide melt. with consequent deterioration and wear of the refractory furnaces the metal components.g This discovery of the oxidation-reduction mechanism of chromium oxides and concomitant oxidation of the orifice and electrodes of refractory metal in the presence of the chromium oxide-containing melts thus leads directly to the method of the present invention to prevent such deterioration, which means that in addition to oxide mixing feed the oven with an additive material, which is present in a state of choice lower than the maximum of the additive material valence state or oxidation state, and which reacts with the higher chromium oxides to form one or more oxides which has lower free energy of formation per mcl of oxygen Un the oxides of the the solid metal, so that the compounds formed are not reduced by electrodes or orifices of refractory metal (eg molybdenum). The so formed the oxides of the additive material must also have a lower free formation energy than the higher chromium oxides, so that the additive the material also reduces any chromium dioxide or chromium trioxide 7713498-9 ” before it can attack the molybdenum components. Additives the alet may be in elemental form or may be an oxide, there the oxygen element in the oxide is present in a valence state which is lower than its maximum valence state. In a specific embodiment embodiment of the invention, the additive material is carbonaceous and can present in the form of powdered carbon. The reactive amount of the batch material, which is determined with regard to the efficiency of the furnace degree, is 25-50%, based on the weight of Cr 2 O 3 present.

Figs. 1 and 2 are graphs showing the relationship between temperature. and various oxides of chromium, molybdenum, tungsten, silicon, aluminum and carbon free formation energy per mole of oxygen. Fig. 1 shows the typical the operating temperature range for refractory fiber furnaces and Fig. 2 shows the typical operating temperature range for fiberglass furnaces.

The present invention is based on the discovery of the mechanical nism with which electrodes and orifice of refractory metal (e.g. molybdenum) deteriorates in an electric furnace in which chromium oxide-containing oxides were melted, i.e. the discovery that chromium oxide initiates a series of unexpected oxidation-reduction reactions that ultimately lead to the formation of refractory metal oxides flowing into the melt. Up- the blanket led to the method of the present invention, which way eliminates or substantially reduces the tendency for this reaction series to occur. The method according to the invention is understood therefore best by first considering the series of oxidation-reduction reactions that have been shown to occur. To illustrate this reaction, series will hereinafter be referred to as U.S. Pat U.S. Pat. No. 3,449,137 and to an electric furnace with molybdenum components.

A typical such melt of refractory fibers is composed of 40-60% by weight of silica, 35-55% by weight of alumina and 1-8% by weight chromium oxide, which is the sesquioxide or "chromium oxide", Cr2O3. As shown in of U.S. Pat. No. 3,449,137 was used thereupon known technology aluminosilicate fibers consisting of roughly equal mixtures of alumina and silica. These are used still to a large extent and easily melted in electrical without significant problems in terms of degradation of molybdenum or molybdenum estuaries. It is only when chromium oxide is added set as a component as the difficulties arise. You have now discovery, as part of the discovery of the mechanism of action of the chromium oxide * induced the deterioration, that the alumina and silica are substantially inert to the molybdenum metal because the silicon and aluminum 7713498-9 the potassium in these respective oxides is present in their highest valence state and thus cannot be oxidized to a higher state.

However, the chromium oxide represents a critically different situation. tion.

The problem of chromium oxide is best understood with reference to Fig. 1 and 2. These figures show the relationship between temperature and free formation. energy per mole of oxygen in several of the oxides of interest see here. (The oxide curves are identical in the two figures that differ apart only in terms of operating temperature ranges). If at a given temperature the free formation energy of an oxide of a metal M is smaller (ie more negative or lower on the figure curve than of the oxide of a metal X, contact between the metal M and X the metal oxide to cause oxidation of the metal M and reduction of the X metal oxide. Thus, in Figs. 1 and 2, the free formation gin of either of the molybdenum oxides smaller (or lower) than it free formation energy of chromium trioxide. Consequently, contact leads between metallic molybdenum and chromium trioxide until the molar and the chromium trioxide is reduced to chromium oxide.

If, on the other hand, the free formation energy of the oxide of metal M is larger (ie less negative or higher on the chart) than it the free formation energy of an oxide of metal X, is the X metal oxide inert to the metal H and does not oxidize the latter. In Figs. 1 and 2 thus, the free formation energies of the molybdenum oxides are greater (or higher) than the free formation energy of chromium oxide. Chromium oxide in contact with the molybdenum metal therefore does not oxidize the latter. The curves in Figs. 1 and 2 strongly emphasize the nature of said covered. It is known from such published curves that aluminum oxide and silica have curves below the molybdenum oxide curve vorna, which thus shows their inertness towards metallic molybdenum. As can be seen from the above, these oxides of the hazard unit has been found to be inert to the molybdenum electrons of furnaces. and molybdenum estuaries. Likewise, the same published curves show that chromium oxide is also below the molybdenum oxide curves, which lunda clearly shows that chromium oxide should also be inert to molybdenum. However, the addition of chromium oxide to a melt was shown to lead to rapid degradation of the molybdenum components. It was the over- surprising discovery according to the invention that the chromium oxide is oxidized by contact with air to a higher valence form, such as chromium trioxide, whose curve is above the curves of the molybdenum oxides, which led to the method according to the invention. 7713498-9 The method of the present invention therefore comprises that incorporate a component in a chromium oxide-containing refractory oxide melt (or "additive") that minimizes the risk of chromium oxide oxidizing to chromium dioxide or chromium trioxy and which reduces each such higher chromium oxides which are reconstituted into chromium oxide before the higher ones the oxides may come into contact with the furnace electrodes and / or the furnace the mouth of refractory metal.

For the sake of simplicity, the invention has been mainly discussed here with reference to molybdenum metal components. The invention is however, not limited to furnaces using molybdenum components. Other materials, including tungsten and tantalum metals and tungsten and molybdenum alloys, were used or have been proposed for use in electric furnaces and are thus "refractory metal "in the sense referred to here because they are all sensitive to chromium oxide-induced oxidative deterioration. Other similar materials, including rhenium, osmium and iridium as well as lodges of these and the above elements (including alloys with small amounts) of other elements) the person skilled in the art is close at hand and thus within the scope of the invention. (Other metals sometimes classified as "refractory", such as platinum and rhodium, are not included in nition of "refractory metals" in the sense referred to here, since their melting points are lower than the melting points of the oxides melted in the oven).

A variety of materials can be used as the additive component. These can be easily determined by means of published tables or curves similar to Figures 1 and 2. A typical set of such tables and curves are found in Elliott et al, Thermochemistry For Steel making, vol l (1960), especially pages 214-215. By means of this data it can be easily determined that such materials as calcium, aluminum, titanium, zirconium, magnesium, cerium, vanadium, silicon and even chrome metal as such can be used. Other materials, such as manganese, Iron, niobium and sodium can also be used with oxide melts of lower temperature. The additive material may also be an oxide in which no the oxygen element is in an oxidation state of below maximum oxidation state. Different mixtures and / or medicinal rings of these materials are also suitable.

According to the invention, however, it is preferred to use carbon or a carbonaceous material as said additive. One reason for this is that the above-mentioned metallic elements form oxides which themselves become incorporated into the oxide melt and thus into the fibers produced therefrom. '7713k98-9 rerna. These oxides can serve as fluxes and can also be have a negative effect on the temperature limits of the fibers when they are used as thermal insulation. In many cases, especially with the "glass fibers", such additives are not critical, and the effects on the boundaries mean nothing because the fiber insulations are used at relatively low temperatures. For the refractory fibers of higher temperature, such as those described in U.S. Pat 3,449,137, however, the maximum operating temperature of the insulating fibers is rations very significant, and the negative effects of l significant amounts of other metal oxides in the fiber composition can often not tolerated. Unlike metals, however, they form carbon gaseous oxides which do not incorporate to any significant extent vase in the oxide melt flowing to the fiber forming unit. Follow- in fact, the melt is not contaminated or diluted for fiber formation of oxides other than those intended to be incorporated.

Another reason to use carbon or carbonaceous materials -is economics. Namely, such materials are cheaper and more easily available than many of the above metals.

Your third reason is shown in Fig. 1 een 2. * rlll difference from the metal oxides whose free formation energies increase with increasing temperature temperature, the free formation energy of carbon monoxide decreases rapidly with increasing temperature. The higher the temperature, the greater the tendency consequently, the carbon has to oxidize in front of the chromium oxide.

The stoichiometric amount (or "reactive amount") of additive required to substantially eliminate the oxidative erosion the refractory metal electrodes and orifices in the electric furnaces depend on the amount of chromium oxide present in the oxide melt. tan. Normal amounts are 25-50, preferably 30-40% by weight of additives. based on the weight of chromium oxide present in the oxide mixture.

Since electric furnaces do not work with full theoretical reaction efficiency, it is necessary to add a certain amount of shot of additive to safely cancel the deterioration of refractory metal. However, the excess additive amount depends on the excess additive the effect of the material on other oxides in the oxide melt and the stretch in which the excess remains in the melt. As dis- above, in some cases large amounts of additive material can be in the final fibers, while not in other cases.

The person skilled in the art can easily determine the optimal amount of additives, to be used in any given set of furnace operation tingelser., 7713498-9 When said additive is powdered or granular, such as is usually the case, it is preferably relatively finely divided rarer than coarse particles. The exact dimensions of "fine" in comparison movement with "coarse" particles varies with the different types of additive, but can be easily determined by those skilled in the art. For it preferred carbonaceous additives, powdered carbon, are the typical ones the dimensions for "fine carbon" l4% of over 30 mesh (Tyler Seive Series) and 86% of under 30 mesh, and for "coarse coal" 63% of over 30 mesh and 37% of under 30 mesh.

The additive component can be added to the oxide melt in the same way. as the oxide raw materials are added to the furnace. In a commonly used method, the oxides are granulated into fine powders, mixed and sprayed. was continuously in powdered form over the surface of the melt. Additive the material, such as a carbonaceous material, can likewise be granulated and mixed with the oxide powders before spreading over the surface of the melt.

Fresh additive material must be constantly added to the oxide melt together with fresh oxide raw materials because the additive material naturally depleted by its oxidation.

The method of the present invention was tested in an electrical refractory fiber furnace with three molybdenum electrodes and one molybdenum electrode mouth. The oxide melt used contained about 55% by weight of silica. 40% by weight of alumina and 4% by weight of chromium oxide, with less than about 0.5% by weight of other oxides. This material was melted at 198000. At earlier try using the same type of oven and essentially the same composition, electrode and orifice deterioration has been so rapid that satisfactory fiber forming operations lasted for at most approximately 40 h. Because a small amount of fiber could be produced during this short time period and because the entire electrode and orifice system thereafter required complete remodeling, such operations were considered economical and completely unsatisfactory.

Then, to test the method of the invention, was added carbon in the form of powdered bituminous carbon in an amount of 36%, calculated by weight of chromium oxide, as part of the oxide mixture continuously during the entire operating period. (An excess of carbon was used in an amount calculated on the yield 36% as the amount that actually reacted, based on the efficiency of the particular oven). This operating period lasted for 21 days and ended only when the desired amount fibers had been produced. Subsequently, the electrodes and mouthpieces were examined. and was found to have been significantly degraded by the chromium oxide to a greater extent than the electrodes in the control operation described above.

Claims (6)

The invention has been described with reference to deterioration of electrodes and / or orifices of refractory metal in electric furnaces, but can of course be applied to any refractory metal furnace component which may come into contact with the chromium oxide-containing oxide melt and which is sensitive to chromium oxide-induced oxidative deterioration PATENT Claim 1, Means of reducing or preventing chromium oxide-induced oxidative deterioration of components made of refractory metal selected from molybdenum, tungsten, rhenium, tantalum, osmium and iridium and alloys thereof, in an electric furnace, in which an oxide mixture Containing 0.5 to 10% by weight of chromium oxide is melted, characterized in that the furnace, in addition to the oxide mixture, is provided with an additive material which is present in a valence state below its maximum valence state and which can be oxidized by chromium dioxide or chromium trioxide to an oxide having a lower free formation energy per mole of oxygen than the oxides of the refractory metal and chromium oxy it, so that in operation the additive material is oxidized in front of the refractory metal, acts to reduce the higher chromium oxides to chromium oxide, Cr 2 O the weight of chromium oxide in the mixture. 2. A method according to claim 1, characterized in that the reactive amount of the additive material is 30-40%, calculated on the chromium oxide weight in the mixture. 3. A method according to claim 1, characterized in that the additive material is in the elemental state or is an oxide in which the non-oxygen element is present in a valentine state of below its maximum valence state. 4. A method according to claim 3, characterized in that the additive material is carbon in the form of carbonaceous material which contains carbon in the elemental state. 5. A method according to claim 4, characterized in that the carbonaceous material is carbon. 6. A method according to claim 3, characterized in that the additive material is elemental calcium, aluminum, titanium, zirconium, magnesium, cerium, silicon, vanadium, chromium, manganese, iron, niobium or sodium or combinations thereof; PROMISED PUBLICATIONS: France 2 osz 459 (coac 1/10) Great Britain 12 673/1900 Germany 1 158 672 (cosc 1/10), 1 421 910 (coac 1/10), 1 421 911 (coac 1/10) 1 _ 1 in ”