DE2916407A1 - Probe for determn. of active oxygen in molten metals - using solid electrolyte contg. alumina, minerals, flux, and silica forming vitreous phase - Google Patents

Abstract

The amt. of O2 is measured via the electromotive force of a cell which uses a carrier (1) functioning as a reference electrode and also a conductor. Carrier (1) is coated with a layer (2) which includes gamma-Al2O3; and only after immersion in the molten metal is the gamma-Al2O3 converted into beta-Al2O3 which conducts oxygen ions so layer (2) forms the solid electrolyte. Layer (2) pref. also contains Na2O, FeO, and/or K2O; plus a flux, esp. an alkali(ne earth) fluoride, e.g. CaF2, NaF, and/or clay or felspar; and also SiO2. Carrier (1) is pref. a metal bar; and plasma flame spraying is pref. used to apply layer (2) to bar (1), followed by using compressed air at min. 5 atmos. to compact layer (2) on bar (1). Reliable determn. of active O2 even below 0.001% at temps. above 1250 degrees C, e.g. in molten cast iron.

Description

Probe for determining the active oxygen

content in molten metal and process for the production thereof the The invention relates to a probe for determining the active oxygen content in molten metal by measuring the electromotive force of a cell, with a Solid electrolyte layer, which is arranged on a Dräger, which acts as a discharge and reference electrode, whereby the electrolyte layer contains aluminum oxide (Al2O3) and their oxygen ion conductivity changes when immersed in the molten metal.

Probes for determining the active oxygen content of molten metal are known. Such a probe usually consists of a tube made of quartz or something else refractory material, one end of which is sealed with the solid electrolyte and inside of which there is a mixture of chromium oxide powder in which a drant made of high-melting metal, especially Mol bdän, protrudes from it. The electromotive After dipping the Rönrchens into the molten metal between @ @ ser and @em metal wire measured and depends on the degree and direction of the Oxygen ion migration between the aera @ melt and the mixture of chromium and chromium oxide powders.

Probes have already been proposed in which the electrolyte on a carrier that serves both as a current conductor as well as a reference electrode, In particular, a metal rod is applied, in particular sprayed on. Such Probes can be used more universally, but have the disadvantage that the electrolyte both in the molten metal to be examined and with the one above it Comes into contact with air. At higher temperatures, especially temperatures above 1250 ° C and with a low oxygen content of the metal melt to be examined, in particular Oxygen activities in the melt below 0.001, namely according to the corresponding Warming up the probe of the electrolyte in the boundary layer between melt and air guiding what the ad im Falsified the sense of excessive acidic activity. This part shows the advantages (including a simpler construction) of this type of probe construction so much contrary to the conventional probes mentioned at the beginning that often the use of the described probe type must be dispensed with.

A probe has also been proposed (DE-OS 1 932 979), in which a sintered mixture of Mclybdän and finds use with an oxide. The arrangement can either be made in such a way that that the metal-ceramic body is provided with a surface layer that the Immersion in the melt as an electrolyte material that is permeable to oxygen ions is, act @ or so that when the metal-ceramic body is immersed in the melt on its surface a layer of an electrolyte material permeable to oxygen ions forms. As an electrolyte material permeable to oxygen ions, i.a.

Alumina suggested. This known probe apparently shows upon immersion, both ionic and electronic conductivity, with the Ion conductivity is compensated by the electron conductivity, so that cannot develop any electromotive force. Only by removing the nolybdenum powder then only the ion-conducting part of the surface layer of the probe should be Surface layers remain. But there is a melting out of the molybdenum, that has a melting point of about 26200C, not possible through technical melting molybdenum can only be dissolved out by penetrating steel, but who in turn is a first-class leader. It is therefore also bi such a probe to incorrect measurements, which is apparently the reason that too this probe has not found its way into practice.

The object of the invention is to provide a probe the To improve the type described above so that the known probes mentioned avoid your own disadvantages. and a reliable measurement even at higher levels Temperatures and low oxygen content of the metal melt is possible. The invention solves this problem in that the electrolyte layer located on the metallic support # Al2O3, which is only converted into ß-Al2O3 Is oxygen ion conductive, and contains at least one ineralizer material.

The invention is based on the knowledge that the electrolyte is to be trained in such a way that its full ionic conductivity is only achieved through contact the melt develops with the electrolyte surface. So it will only be that part the probe has good oxygen ion conductivity for the between molten metal and the conductive one Carrier taking place ion current, which was in intimate contact with the melt. With Probes of this type can now also contain extremely low levels of oxygen, including those below 0.001, for example in cast iron melts, at temperatures above 125,000 can be measured reproducibly when the probe is immersed in the melt the mineralizers germs, so that when exposed to high temperatures the The molten metal to be measured from the # - Al2O3 is particularly suitable for ion conduction Ä-Al203 phase can form. Sodium oxide is suitable as a mineralizer material (Na20), ferric oxide (FeO) or potassium oxide (K2O) Since the process of formation of the for ion conduction particularly suitable / -Al 2O3 phase, especially when not very high melt temperatures, is relatively slow, the probe would have to relative @@ @ge remain in the melt to form the 4-Al203 phase mentioned above to secure. To shorten this time, it is expedient within the scope of the invention if the electrolyte layer also a flux, in particular at least one alkali and / or Alkaline earth fluoride, e.g. calcium fluoride, sodium fluoride and / or clay or feldspar, contains. The addition of this flux accelerates the formation of the β-phase considerably and reduces the temperature necessary for the formation of this phase. In this way it is easily possible to achieve the desired conversion of the Al2O3 electrolyte into the ß-phase to be obtained even during a relatively short-term measurement.

For molten metals to be measured that have temperatures above 16000C, e.g. in the case of steel melts, this flux addition can be dispensed with, whereas this is not useful for probes for the measurement of lower melting metals is. This has been shown in experiments with flux-free probes in a cast iron melt to immerse (temperature about 13500C), that a correct measured value is only after ceases to be immersed several times.

Berner has found that it is within the scope of the invention It is beneficial if the electrolyte also contains silicon dioxide (SiO2). This addition promotes the formation of a glass phase, which promotes the tightness of the electrolyte is. On the ready-injected probe lies the £ 102 in X-ray amorphous form before.

The inventive method for producing the inventive The main feature of the probe is that the electrolyte substance, the aluminum oxide (Al203), the at least one mineralizer material and possibly a bleaching agent, in particular alkali and / or alkaline earth fluorides, and / or oxides Clay or feldspar or lithium bicarbonate (Li2C03) and / or silicon dioxide added are, contains, is applied in the flame spraying process or plasma spraying process. When the electrolyte is sprayed on, the metal rod surface is slightly oxidized, see above that the metal-metal oxide mixture necessary for the measurement is formed with the metal of the rod will be produced.

In order to avoid the addition of other metals and metal oxides disturb, unkilled, unleveled steel should be used as the support rod will. When the electrolyte is flame sprayed, an iron oxide mixed phase is formed here made of magnetite and wüstite. Tests have also been carried out with nickel. Included In addition to the economic disadvantage of the high price of nickel, it also became apparent there is a much more sluggish adjustment of the measured value after spraying on the probe mainly @ -Al2O3 and # -Al2O3. When immersed in the melt the t-Al203 content decreases and the ion-conductive one is formed ß-Al2O3 and a glass phase if there is an SiO2 additive. Since only that part of the sprayed-on electrolyte layer is implemented, which is in connection with the metal bath stood, the remaining part of the electrolyte layer remains ion-conductive to a limited extent. the The mentioned glass phase, which goes back to the addition of SiO2, is the tightness of the electrolyte conducive. The addition of SiO2 also improves the sprayability of the material. In the ready-injected probe, there is also a relatively large amount of additives no more quartz line on quartz. Obviously the one that got on the probe is lying Part of SiO2 before X-ray amorphous.

By achieving homogeneous properties of the applied electrolyte layer It is advantageous in the context of the invention to mix a mixture of Oxyclpulver in the flame Apply plasma spray process. In this case it is advisable to carry out a redensification of the applied coating by a compressed air jet, in particular with an operating pressure of at least 5 atmospheres.

In the context of the invention, the proportion of fluoride fluxes is expediently 0.3-10% by weight, when using clay or feldspar up to 40% by weight, the Proportion of mineralizers 0.5-10% by weight and the proportion of silicon dioxide O - 30% by weight, not counting the proportion introduced via the flux.

Example 1: It is an intimate mixture of powders of the following composition Uses: 70% Al2O3 (calcined clay, grain size 0.025 to 0.100 mm), 25 ß SiO2 (mostly i-quartz, grain size 0.01 to 0.1 mm), 2.3; Be203, 0.60% Na2co3, 2.1 % caF2. The sand contains a little feldspar and the clay about half a percent Sodium oxide. The mixture was sprayed with a powder flame spray gun with an oxygen-acetylene flame on a rod made of unkilled unalloyed steel 8 mm in diameter in a Layer thickness of 0.5 mm sprayed on as an electrolyte. Following the spraying the sprayed-on electrolyte layer was subsequently compressed by compressed air, with the compressed air pressure was 5 atm.

Example 2: A batch was used to produce another probe made from the following powders: 23 ß SiO2, 70% Al203, 7% clay. Otherwise was Proceed as in example 1.

These probes also proved to be functional.

Apparently the sodium oxide present in the clay formed the here Mineralizer and the clay the flux.

In the drawing is an embodiment of an inventive Probe shown schematically. The drawing shows a vertical section through the Probe.

A steel rod 1 with a diameter of 8 mm serves as a carrier for an electrolyte layer 2 made of a best body electrolyte with a thickness of 0.5 mm. The steel bar 1 consists of unalloyed, unquenched steel and serves as a derivation and at the same time Reference electrode. The electrolyte 2 consists of # -Al2O3, possibly also 203 and env contains at least one mineralizer material, in particular sodium oxide, iron oxide or potassium oxide.

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Claims (7)

P a t e n t a n s p r @ c h e 9 Probe for determining the active Oxygen content in metal melts by measuring the electromotive force a cell, with a solid body 'ectrolyte layer, which is arranged on a carrier which serves as a conductor and reference electrode, the electrolyte layer being aluminum oxide (Al2O3) and its oxygen ion conductivity when immersed in the molten metal changes, characterized in that the located on the metallic carrier Electrolyte layer # -Al2O3, which only occurs through conversion when it comes into contact with the metal melt in ß-Al2O3 becomes oxygen ion conductive, and at least one mineralizer material contains. 2. Probe according to claim 1, characterized in that the mineralizer material Contains Na2O, FeO or K2O. 3. Probe according to claim 1 or 2, characterized gekennzeicnnet that the Electrolyte layer also a γ Rmittel, in particular at least one alkali and / or Brdalkali fluoride, e.g. calcium fluoride, sodium fluoride, and / or clay or feldspar, contains. 4. Probe according to claim 1, 2 or 3, characterized in that the The electrolyte layer also contains silicon dioxide. 5. A method for producing a probe according to one of the claims 1 to 4, characterized in that the electrolyte substance, the aluminum oxide (Al2O3), the at least one mineralizer material and optionally a flux, in particular Alkali and / or alkaline earth fluorides and / or oxides and / or clay or feldspar and / or Silicon dioxide are added, contains, on a metal rod, in the flame spray process or plasma spraying @ drive is applied. 6. The method according to claim 5, characterized in that the proportion 0.3 to 10% by weight of fluoride fluxing agents when using clay and / or feldspar up to 40% by weight, the proportion of mineralizers 0.5 to 10% by weight and the proportion of silicon dioxide not introduced via the flux is from 0 to 30% by weight. 7. Verfahrea nac4 claim 5 or 6, characterized in that @ chnet a mixture of the components is applied in a flame or plasma spray process, wherein, preferably, a post-compression of the applied coating by a Preßluf @ jet, in particular with an operating pressure of at least 5 atmospheres.