DE1571601B1 - Refractory products containing magnesia - Google Patents

Description

The invention relates to a refractory mixture of non-acidic, refractory grains, which contain at least 10 percent by weight of very fine-grained magnesia, as a basic ingredient, and with a magnesium alfate-yielding material, which 0.5 to 5 l) / (, magnesium sulfate, based on is the weight of the finest grained magnesia.

The use of refractory products for lining furnaces, especially for lining metallurgical furnaces, which operate at high temperatures work runs into a problem. If the refractory products contain magnesia, z. B. in the form of perildas or burnt magnesite, and these are magnesia-containing refractory products before pressing, pouring, ramming or similar treatments mixed with water some of the magnesia is hydrated to give magnesium hydroxide. When heating these refractory bodies, e.g. B. during the period when the inner If the furnace lining is brought to working temperature, the magnesium hydroxide decomposes. Cause the decomposition of Mg (OH), and the subsequent evolution of water vapor a violent exploding of this magnesium hydroxide-containing body developing water vapor cause these magnesium hydroxide-containing bodies to explode violently.

Attempts have already been made to reduce the tendency of the magnesia-containing refractory bodies to become hydrated by adding small amounts of certain admixtures. For example, it is known (German Auslegeschrift 1066 472) to add MgSO to the base material magnesia. However, it has been found that the addition of magnesium sulfate alone does not lead to satisfactory results.

The invention is therefore based on the object of a refractory Specify mixture of the type described above, with which the hydration of the Magnesia is almost completely prevented.

The refractory mixture solves this task if it results in a boron oxide Material is added in such an amount that there is a weight ratio of MgSO,: B, 0, of less than 4: 1.

It is also known (German Auslegeschriften 1171323, 1 200 186 - or book by S ear 1 e, "Refractory Materials% 1950, p. 469, paragraph 2) to add boric acid to a refractory mixture with the basic component magnesium oxide, which as a result of decomposition, B, 0, yields. It has been found, however, that in a refractory mixture of the type described at the outset, the addition of boric acid in the conventional amounts is not sufficient to prevent the hydration of the magnesia, but that under certain conditions the hydration is even promoted. Only if the relative proportions between the magnesium sulfate and the boron oxide-producing material are within the limits of the invention can the mentioned hydration of the magnesia be essentially prevented.

The mixture of the invention is useful, for example, as a mortar, but it is particularly useful in refractory batches used in the manufacture of bricks or other shaped objects, or in the pressing, pouring and spraying of mixtures. Any desired compatible, granular, refractory material can be admixed with such offsets, especially non-acidic or basic materials such as periclase, dead-burned magnesite, chromite, spinels or suitable mixtures of such grains with one another. Preferably, an amount of 10 to 60 % magnesia is used based on the weight of the refractory mixture.

The finely divided magnesia should fall completely through a sieve, the mesh of which has a clear width of 0.50 mm, preferably less than 0.149 mm.

A material that is preferably used as a supplier of magnesium sulfate is hydrous magnesium sulfate M9S04'Hlol z. B. the mineral kleserite. Other materials that can be used are the Epsom salt, M .-. S04 - 7 H, 0 and sulfuric acid. Thus, if the dry material is mixed with water to a reaction between the magnesium sulfate and the finely divided magnesium oxide is to take place to give a kind of Sorel cement. The materials which produce magnesium sulphate include not only magnesium sulphate, but also those matehalls which produce magnesium sulphate as a result of a reaction with magnesium oxide. So you can z. B. Add sulfuric acid to the batch, the reaction between the sulfuric acid and the magnesium oxide MgO yielding magnesium sulfate, which in turn will react with further MgO in the batch to form a Sorel cement.

The boron-containing material that prevents hydration can be any product which, on firing, gives B, 0. One preferably the used material is boric acid. Other useful products are: borax, sodium borate, Pyroboric acid, pyroborates and similar products. The B, 0, resulting material is preferably at least slightly soluble in water.

The advantage of the mixtures according to the invention is demonstrated by the differential thermal analysis curves of the various mixtures listed in Table 1.

In a differential thermal analysis, the temperature difference between a sample to be examined and a non-reacting standard specimen, which is not subject to any thermal effect in the temperature range of the examination, is measured. The measurements on both specimens are carried out in an oven which is heated in such a way that the rate of temperature increase is constant. The results are plotted in such a way that the temperature difference in degrees Celsius is the ordinate, while the temperature in the center of the inert standard specimen is the abscissa. If temperature effects, either endothermic or exothermic, occur in the sample to be examined, the temperature of this sample will lag behind the temperature of the standard specimen or it will increase faster than this last temperature, and the temperature difference between the two specimens will be a value other than zero to have. In the case of magnesium hydroxide, which loses its water of hydration between 400 and 500 ° C , a specimen which contains significant amounts of this hydroxide will therefore result in a temperature shift and a subsequent gradient in the curve of the differential thermal analysis if it is in this Temperature range is heated because water is released according to the equation Mg (OH), - MgO + H, 0. In the case of a sample containing, for example, magnesium hydroxide, the size of this gradient or the peak point of the curve of the differential thermal analysis depends on the amount of magnesium hydroxide in the sample which is decomposed. In other words, a large temperature effect or a steep slope in the differential thermal analysis curve indicates a relatively large amount of hydrated magnesia in the sample, while a small slope or a small temperature effect indicates a small amount of magnesium hydroxide in the sample. Accordingly, in the case of samples containing magnesia which are subjected to conventional manufacturing and storage processes, the apex of the curve of the differential thermal analysis shows the relative extent of the hydration taking place.

The figure shows curves of the differential thermal analysis in the temperature range from 400 to 500 ° C for the various masses given in Table I. The letters on the curves correspond to the designations of the samples in Table I. The samples were in a hole of 0.63 cm in diameter and 0.96 cm deep in a nickel block and placed in the middle of a tubular furnace heated by electrical resistances. The standard inert copy AI, 0, was placed in a similar hole in the same block. Panel I. mgs04 # B, 0, mgso, / B203 Sample parts by weight parts by weight relationship A periclase without additives B periclase with 100 /, water C - 0.564 D 4.46 - - E 4.46 0.564 7.90 F 4.46 1.13 3.94 G 4.46 1.69 2.64 H 2.15 0.423 5.08 1 2.15 0.846 2.54 J 2.15 1.13 1.90 x 0.892 0.451 1.98 Y 0.892 - Curve A applies to a dry, completely unhydrated periclase grain which passes completely through a sieve with a mesh size of 0.149 mm and which contains approximately 98 % magnesium oxide, the remainder being impurities. As can be seen, there is no temperature effect in the temperature range of 400 to 500 ° C , indicating that there is no magnesium hydroxide in the sample. The masses B to J in table I were mixed with 10 % water, left to stand for a quarter of an hour at room temperature, dried at 110 ° C. and then subjected to a differential thermal analysis. Curve B applies to periclase without any addition other than water and shows a pronounced slope of the curve which indicates significant hydration of the material. Curve C shows the effect of adding 10/0 boric acid to this periclascome, the large decrease in the slope of the differential thermal analysis curve indicates a large decrease in hydration when boric acid is added. The mixture containing D periclase and 5 0/0 kieserite as binding agent, while the mixture E periclase, 5 0, 1 "/ boric acid / and kieserite. The curve E shows a very steep slope, indicating that the degree of hydration of the material is even greater than the hydration of the periclase grain without additives (curve B) or than the hydration of the periclase grain with kieserite alone (curve D). The remaining curves in the figure show the relative degrees of hydration for various amounts of boric acid and listed in Table 1 From these curves and from the results given in Table I it can be seen that the hydration of kieserite-containing periclase masses is only smaller than the hydration of periclase without additives or than the hydration of periclase with kieserite as the only addition if the weight ratio Von M9S04 to B, 0, is less than 4: 1, and that the least amount of hydration occurs when the ratio is no greater than about 2: 1 is.

As a practical application example of this invention, two mixtures were prepared with 100 parts by weight of a high-purity Periklaskornes which magnesium oxide 2 0 /, contained 98 0 /, and impurities, as well as with 1 weight part kieserite as a binding material. The entire amount of the periclase grain fell through a sieve with a mesh size of 4.76 mm and 25%, fell through a sieve with a mesh size of 0.149 mm. The first of these mixtures (X in Table I) was added 0.8 parts by weight of boric acid, while no boric acid was added to the second mixture (Y in Table 1). Both mixtures were water (based on the weight of the dry additives) mixed with 6 0 / and poured into a mold to form blocks of 30.50 cm side length. A thermocouple was embedded in the center of each block. After both blocks had hardened, they were exposed to a temperature increase of 100 ° C. per hour in an oven. The block with no boron additives burst when the embedded thermocouple read about 450'C, whereas the other block was heated to over 500'C without bursting.

From the foregoing it follows that it thanks to the invention Mixtures is possible to produce periclash-containing refractory masses, which magnesium sulfate as a binding material and which have a higher resistance to hydration in the Compared to the known mixtures.

In the description and in the claims, the percentages relate on the weight of the dry additives. The compositions of the mineral substances are reproduced in the usual way and expressed as simple oxides, z. B. Mg0, SiO2, even if the existing components of the mixture in composite In the form of, for example, magnesium silicate.

Claims (2)

Claims: 1. Magnesia-containing, refractory products made from non-acidic, refractory grains, which contain at least 10 percent by weight of finely-grained magnesia, as a basic component, and with a magnesium sulfate-yielding material, which is 0.5 to 5111, magnesium sulfate, based on the weight of the finest-grained magnesia, results, characterized in that a boron oxide-giving material is added to the mixture in such an amount that a weight ratio of M9S04: BIOS of less than 4: 1, preferably 2: 1, results. 2. The refractory mixture according to claim 1, characterized in that the refractory grains contain at least 10 "/, magnesia which fall through a sieve with a mesh size of 0.149 mm , and that the boron oxide resulting material has a weight ratio of M9S04 to B.0 , of approximately 2: 1. 3. The refractory mixture according to claim 1, characterized in that it consists of periclase grains, of which at least 100 /, fall through a sieve with a mesh size of 0.50 mm, and that they are between 0.5 and 5111, the weight of periclase falling through a sieve of 0.50 mm contains kieserite, as well as boric acid, the weight ratio of MgSO to B20 being less than 4: 1. 4. The refractory mixture according to spoke 3, characterized in that at least 100 /, the Perildaskörner through a sieve having a mesh width of 0.149 mm fall through the kieserite between 0.5 and 5 is 0 /, of mm through a sieve of 0.149 falling Periklasgewichtes of magnesium sulfate and the addition of boric acid ensures a weight ratio of M9S04 to B103 of approximately 2: 1. 5. A refractory mixture according to claims 1 to 4, characterized in that it mainly consists of 1 part by weight of kieserite, 0.8 parts by weight of boric acid and 100 parts by weight of periclase, of which 25 0 / fall through a sieve with a mesh size of 0.149 mm .