The formation of a given phosphate depends not only on the composition of the melt but also on the rate of cooling. The further cooling of the remanent melt depleted of high-melting oxides results in the formation of more mixed orthophosphates; when cooled rapidly (quenched) a melt containing an adequate proportion of SiO 2 is converted to the glass phase. In long-term firing (over 20 h) at 1600~ or higher the sodium ions are volatilized out of the melt. The complete vaporization of the sodium and the crystallization of the liquid phase are followed by the formation of mixed calcium and magnesium orthophosphates, e.g., Ca3Mg3(PO4) 4. A further increase in the firing temperature and time results in the gradual volatilization of the P205 from the phosphate bond until the latter is completely decomposed. LITERATURECITED

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The service life of refractories in a blast-furnace stack is 3.5-4 years, whereas in the hearth and hearth bottom it is from 10 to 12 years [1]. This means that an increase in the period between stack repairs is an urgent problem which requires a tLmely solution.The durability of the stack lining depends on the composition of the primary slags, the amount of alkalies and zincite in the blast-furnace charge, the composition of the gaseous medium, the abrasive wear by the charge, the thermal stresses, and the conditions under which the furnace is operated, its design, and other factors [2].The specific influence exerted by each of these factors on the durability of the lining differs from one factory to another. This complicates the creation of a universal refractory with all the necessary properties and makes it difficult to establish the most important characteristics governing the stability of artifacts during service. For this reason, there is no agreement concerning the selection of refractories for blastfurnace stacks; however, laboratory and factory investigations have shown that compact kaolin refractories with an A1203 content of 42-45% are promising materials for the lining of the cooled part of the stack.Compact kaolin artifacts with a porosity of less than 12% are being manufactured at the Zaporozhe Refractory Works and the Chasov Yar Refractory Artifact Works, and chamotte artifacts with a porosity of

The most important task facing the refractories industry is to save energy, material, and labor resources.Its solution to a large extent depends on the creation and introduction of effective resistant refractories and their rational use in service.In the blast furnace the resistance of refractories in the various sections varies widely.For example, in the bottom and the hearth the life is mainly 15-18 years, while in the shaft, bosh, and shoulders it varies from 2 to 12 years.Analysis of the service of refractories shows that their life in these parts depends on the design of the structure, its cooling, the quality of the refractories, the operating schedule, the running of the furnace, and other factors.At the present time the commonest refractories are those made from pure kaolinitic clays with weight proportions of AI20a of 41-42% and with a porosity of 8-12%.Apparently, dense chamotte refractories, up to the end of the current century, will prevail over the others. However, in economically developed countries, in parallel with improvements in dense chamotte articles, intensive research is going on into the development of new types of refractories.In the shaft, bottom, and shoulders of blast furnaces the bricks are subjected to the action of alkalis and slags, thermal stresses, abrasion from the batch, and other factors. Since chamotte refractories do not possess sufficient resistance in these conditions, in the shaft, in addition to dense chamotte (41-44%* AI20~) refractories, a start has been made with the use of other types: electrofused corundum and mullite, graphite and semigraphite, silicon--carbide-graphite, and also self-bonded silicon carbide and nitride-bonded silicon carbide or oxynitride bonded forms [1][2][3][4].Recently authors [5] have recommended the use of corundum-chromite and spinel refractories.All these researches have so far failed to produce a single answer to the question about the use of the optimum refractories.Studies were therefore carried out into the resistance of sintered and fused mullite, corundum, silicon carbide with oxynitride and nitride bonds, to the action of destructive factors.It is shown that the highest resistance is possessed by refractories based on self-bonded silicon carbide and oxynitride-bonded SiC. On the basis of laboratory studies, refractories containing 23.4% C, 66.7% Si and 7.7% N are recommended for use in the shoulders of blast furnaces [I, 2]. The increased thermal conductivity [1 = 10.3 W/m'~ provides an inertness to these refractories, in blast-furnace cooling conditions, to the destructive factors at the lower reaction temperatures of I150~ and with a structure thickness of 530 mm.The SiC refractories Annasikon 93 from the Annawerk (FRG) firm have been tested in the lower part of the shafts of five blast furnaces, and showed a slight wear compared with chamotte bricks [3].In the lower part of the shaft of a blast furnace that has a diameter of 9 m, the wear of silicon-carbide refractories bonded with oxynitride is half that of phosphate-impregnated f...