DE898575C - Cast refractory product based on alkaline earth chromite - Google Patents

Description

Cast refractory product based on alkaline earth chromite The invention relates to the production of cast bodies, the main component of which is a chromite Alkaline earth is.

Such cast bodies have proven to be very refractory or resistant against heat as well as chemical attack by flux, for example glass, proven.

Process and technique by which such castings are made are known per se.

Natural magnesium chromite is found together as the main component with iron chromite in chrome ores. These ores also contain clay and silica and as components of fired refractory products are very resistant Known against both acidic and basic fluxes. When trying chrome ore compositions by melting and casting to reduce their porosity and improve the To make the use of binders with flux properties superfluous, so shows that in order to achieve the highest level of resistance to chemical corrosion to achieve, the content of magnesia must be kept low. It did, however found that this unfavorable effect is obviously connected with the simultaneous one Presence of A1203 and silica, which cause the formation of the less resistant A1203 Mg 0 and apparently does not have a low resistance des Mg 0 'Cr203. It was even found to be offsets Chromium oxide and up to 21% magnesia are more resistant than a cast Chrome ore with low magnesia content. When an excess of magnesia used in excess of the amount required for the formation of the chromite is formed from the excess periclase, which is not very resistant to it Glass is. Chromium oxide, however, is very resistant in the crystalline phase, and an excess of this does not reduce the resistance. However, chromium oxide is even because of its high melting point and because of its easy reducibility very difficult to cast due to the furnace electrodes. Both for this reason and also because of the possible savings it is advantageous to use the full share of 210 /, Exploiting magnesia.

The subject of the invention is accordingly a cast from the melt flow Refractory product which, according to the analysis, consists essentially of chromium oxide and consists of at least one alkaline earth oxide, preferably the content of alkaline earth oxide or oxides is not significantly larger than the stoichiometric composition of the mono-alkaline earth chromate of the formula X 0 Cr, 03 corresponds.

Green chromium oxide, which is commercially available as a dye, and high-quality burnt or raw magnesite or purer types of magnesia can be used as raw materials for the production of such products. The usual lime contamination does not interfere in this case, but it is necessary to keep the silica or A1203 content low. Suitable offsets are, for example, the following Although such offsets are obviously more expensive than chrome ore offsets, their use is justified in cases in which high corrosion resistance is required in view of the coloring effect of dissolved Cr 2 O 3 on glass. The coloring effect is so strong that from this point of view it alone makes the use of such a poorly refractory body completely impossible and not only less desirable.

The other alkaline earths also form crystalline ones from melts Chromite, and it has been found that this too is very resistant to it chemical attack and are superior to magnesium chromite in some respects. Obviously, at the high temperatures used, MgO becomes partially gaseous Metal reduced, which under certain conditions in the solidifying refractory Body forms pores. Even if these pores are not connected to each other and therefore not as disadvantageous as the pores in fired refractories, yet they increase, if to a lesser extent, the surface open to attack is exposed for example by a glass melt. This disadvantage is avoided and at the same time the cost of the offset is reduced if this lime or contains limestone. Apart from the lower cost of the lime, the offset also cheaper because, because of the higher molecular weight, 27% of it for the formation of the chromite are required. Mixtures of chromites are also available resistant, which also enables the use of dolomite.

Examples of suitable offsets are given below: I. Composition of the casting Offset body according to the analysis Ca o I Cr. 03 73 parts of chromium oxide. . - 73 27 parts quicklime 27 - 27 73 II Composition of the casting Offset body according to the analysis Cr203 I Ca0 73 parts of chromium oxide. . 73 - 54 parts of limestone .... - 27 73 27 III Composition of the casting Offset body according to the analysis Cr203 Ca0 I Mg0 76 parts of chromium oxide. . 76 - - 46 parts of raw dolomite - 15 9 76 15) 9 The use of lime makes the offset cheaper and results in non-porous cast bodies, but these still have a deficiency in that they can easily contain a small proportion of calcium carbide. When such bodies are used, the reducible material contained in the glass, for example, can oxidize this carbide and generate gases which, through their stirring action, accelerate the detachment of saturated, protective intermediate layers and thereby increase corrosion. The importance of this in individual cases naturally depends on how the body is used.

From this point of view, the use of strontium oxide or barium oxide is advantageous, since these prove to be less reactive towards the electrode material at the temperatures necessary for melting. In the case of strontium oxide, a proportionate amount of 40% is necessary to form the chromite. While the man-made carbonate is more expensive than green chromium oxide, the natural sulfate, the cölestin, is cheaper and can be used. In the case of barium oxide, 50 % is necessary for the formation of the chromite, and in the case of this offset the smallest proportionate amount of the expensive chromium oxide is required. Ba0 appears to have the greatest flux action on chromium oxide, making such castings the easiest to manufacture. They are nonetheless refractory and just as resistant as the other chromites at all temperatures that are used in conventional glass melting. As with all alkaline earth chromites, an excess of Cr203 does not interfere, but it makes the offset more expensive. On the other hand, an excess of alkaline earth metal over the amount required for the formation of the chromite reduces the resistance very quickly. With the exception of the use of mixtures which occur in natural raw materials, such as in dolomite, there is little point in using mixtures if it is not desired to increase the flux effect. Suitable offsets for the production of strontium and barium chromites are the following: I. Composition of the casting Offset body according to the analysis Cr203 I Sr0 I B & 0 I Si02 60 parts of chromium oxide. . 60 - 72 parts of Cölestin ..... - 36.6I o.8 2.4 6o 36.6 o.8 (2.4 II Composition of the casting Offset body according to the analysis Cr205 I Ba0 I Si02 50 parts of chromium dioxide. . 50 - - 64 parts Witherit ..... - 49 1 0.7 50 49 0.7 III Composition of the casting Offset body according to the analysis Cr203 I Ba0 8o parts of chromium oxide. . 8o - 26 parts barium carbonate .......... - 20 80 20 In general, the oxides, carbonates, sulfates or other salts can be used in the batch, since the gases which are split off go away at the melting temperature. From the viewpoint of cost, it is advantageous to use natural raw materials such as magnesite, limestone, burnt limestone, raw or burnt dolomite, gypsum, strontianite, celestine, witherite and barite when the use allows it, but the silica content must be so low should be kept as possible, since silica and the other constituents form a glass phase that is not very resistant. However, usually the small amount that is found as an impurity in good grades of the named raw materials can be allowed.

Generally speaking, all alkaline earth chromites are very resistant to corrosion, and tests show only minor differences between one and the other. at Such castings react to very high temperatures when they are above the glass surface used, obviously with the condensed alkali vapors and oxygen and with these result in the low-melting alkali or alkaline earth chromate. In In any case, rapid erosion can be observed above the melt level. This does not take place, even at temperatures of 160 ° C, in the area of the mirror the melt and below it, so that the use of the cast body according to of the invention is to be limited to these areas or to such purposes in which non-oxidizing atmospheres are present.

In the claims the term "poured from the melt flow" is used used to mark a refractory product which solidifies through solidification is formed by molten material, as opposed to by the wet route products cast in a slip.

Claims (7)

PATENT CLAIMS: i. Refractory product poured from the melt flow, characterized in that, according to the analysis, it consists essentially of chromium oxide and consists of at least one alkaline earth oxide, preferably the content of alkaline earth oxide or oxides is not significantly larger than the stoichiometric composition of the mono-alkaline earth chromate corresponds to the formula X 0 Cr2 03, in which X is either Mg, Ca, Sr, Ba or mixtures of these elements. 2. What is poured from the melt flow Refractory product according to claim i, characterized in that it is essentially is free of clay. 3. Refractory product cast from the melt flow after Claim i, characterized in that it is essentially free of silica is. 4. Refractory product cast from the melt flow according to claim i, characterized characterized in that it contains only negligible amounts of clay or silica. 5. Refractory product cast from the melt flow according to one of the claims i to 4, characterized in that it consists essentially of at least one crystalline Alkaline earth chromite. 6. Refractory product poured from the melt flow according to one of claims i to 4, characterized in that it is essentially of at least one crystalline mono-alkaline earth chromite and crystalline chromium oxide consists. 7. Refractory product poured from the melt flow according to one of claims x to 4, characterized in that it is analyzed according to contains a considerable, but not exceeding 25%, content of magnesium oxide and the remainder consists essentially exclusively of chromium oxide. B. From the melt flow Cast refractory product according to one of Claims z to 4, characterized in that that, according to the analysis, it was a considerable, but not exceeding 30% of calcium oxide and the remainder essentially exclusively of chromium oxide consists. G. Refractory product cast from the melt flow according to one of the Claims x to 4, characterized in that the analysis after a considerable, but does not contain a content of strontium oxide exceeding 45% and the remainder im essentially consists exclusively of chromium oxide. so. Cast from the melt flow Refractory product according to one of Claims x to 4, characterized in that that, according to the analysis, it was a considerable, but not exceeding 55% of barium oxide and the remainder essentially exclusively of chromium oxide consists.