V. A. Perepelitsyn

Production and properties of magnesia concretes with sodium phosphate bond

ConclusionsThe processes of the forming of magnesian concrete with a sodium phosphate bond consist mainly of the formation of new chemical compounds and their high-temperature conversion to liquid phase. It was established that bryanite Na2CaMg(PO4)2 is one of the new compounds.The concrete with the best properties is one with a bond of sodium hexametaphosphate (NaPO3)6 and this is the type, therefore, which should be subjected to industrial trials.

Reaction between phosphate bonds and magnesium oxide

ConclusionsDuring the reaction of phosphate bonds with magnesium oxide, magnesium phosphates are formed confering hardness on the magnesia concretes.In the specimens based on aluminophosphate bond the magnesia reacts with monosubstituted aluminum phosphate, and under these conditions di- and trisubstituted magnesium phosphates and aluminum orthophosphate are formed, which in turn react with magnesia at temperatures above 1000°C, with the formation of magnesium orthophosphate and magnesia-alumina spinel. Spinel develops at 600°C in the specimens based on chrome-phosphate bond.The phosphate bonds in contrast to orthophosphoric acid reduce the quantity of magnesia-phosphate glass in the specimens by a factor of 1.5–3.The aluminophosphate bond to a greater degree contributes to recrystallization of the periclase compared with H3PO4, magnesium- and chromium-phosphate bonds.

Effect of graphite on the properties of periclase-carbon products

ConclusionsWe recommend utilization of (15±2)% graphite kish (a waste product of metallurgical industry) as a polyphase material containing carbon and an antioxidant for producing periclase-carbon refractories.The presence of graphite kish facilitates low-temperature densification of the structure of the products.In the specimens containing graphite kish, a positive effect is obtained due to three factors, viz., the presence of an antioxidant in their composition, intensified evolution of a dense structure of the products during the process of heat treatment, and decreased degree of decarbonization.Wide application of the graphite kish-containing periclase-carbon refractories in the linings of steelmaking furnaces makes it possible to improve their service life and to solve an important problem of National Economy, namely, to develop waste-free technological routes in certain ferrous industries.

Periclase-carbon articles made from production waste obtained from electrotechnical periclase

ConclusionsWaste from the production of electrotechnical periclase consists of high-quality material with a concentration of 98% magnesia, heat processed at different temperatures with Δmcalc of note more than 0.3%. In order to organize the complete waste-free production of electrotechnical periclase its waste should be used for making periclase-carbon concrete articles using the technology developed by the East Institute of Refractorires. Experimental periclase-carbon articles prepared at the Experimental factory of the Institute were tested in the lining of a 100-ton electric steel-melting furnace at OKhMK; they showed the same resistance as fired PKhS articles.

Periclase-carbon parts with a graphite kish (periclase-carbon refractories for steel melting production)

ConclusionsA method has been developed for production of periclase-carbon parts from periclase-lime patching powders with the addition of graphite kish. The periclase-carbon parts made using parallel mixing of the components possess higher properties.In the Tar-Bonded Dolomite Shop of Chelyabinsk Metallurgical Combine 116 tons of periclase-carbon parts were produced. In the lining of a 130-ton converter they showed a life 25–30% longer than the life of tar-bonded dolomite parts.

Vapor-phase recrystallization (redeposition) processes in periclase-carbon products

ConclusionsWe studied the mechanism of vapor-phase recrystallization of periclase and forsterite in the periclase-carbon products during rapid heating in air up to 1710–1720°. The formation of secondary crystals of periclase and forsterite occurs from the gaseous phase simultaneously with their crystallization in the form of filamentary and dendritic crystals in the developed cavity and with recrystallization of isometric periclase.

Properties and behavior of periclase-carbon systems during the firing-process under oxidizing conditions

ConclusionsIt is not advisable to introduce more than 20% graphite into the composition of the periclase-carbon refractories because, in this case, the strength of the products decreases significantly and their porosity increases.The temperature corresponding to the beginning of carbon depletion (burn off) does not depend on its content in the body and amounts to 550–560°C.Caustic periclase introduced for achieving additional low-temperature densification of the strucutre with reduced degree of carbon depletion did not give the expected effect: the temperature at which carbon depletion begins does not depend on its content in the body.When fired under oxidizing conditions, a reducing atmosphere is created within the periclase-carbon products which actively reacts with periclase; at and above 1650°C, one observes reduction of MgO up to Mg vapor with its subsequent oxidation and redeposition in the form of a dense layer of secondary MgO; a relict polygonized grain structure of MgO forms in the products and is accompanied by the development of a layered texture exhibiting cyclic recurrence.

Physicochemical wear processes in periclase concrete articles used to line buckets

ConclusionsPericlase-chromite grade PKhBK-851 concrete articles in a standard form are suitable for the linings of high-temperature buckets.Articles do not cleave in use. At low service temperatures (1600°C) the articles are encrusted with slag and at high temperatures (2200°C) they dissolve in the slags.The wear mechanism on the concrete articles during service is as follows: The articles become saturated, predominantly with calcium and iron oxides, and have a sharply expressed boundary between the slag and working zones. In this case the formation of a dense working zone occurs and at low service temperatures this is overgrown mainly with dicalcium silicate and at high temperatures it dissolved in the slag forming calcium chromoaluminoferrite.The reason for the improved resistance of the concrete articles is the formation of the dense working zone with a high concentration of periclase.

Interaction between zinc sinters and refractory items

ConclusionsThe interaction between zinc sinters and refractory products has been studied. The greatest resistance to the action of the zinc-sinter melt is found in the articles made from grade PShSP and MChVP products. In this case the structure and porosity of the products are found to have a significant effect on their wear resistance.The wear on chrome-magnesite and periclase-spinel products currently used to line Weltz furnaces is caused by the penetration of the refractory by iron oxides and SiO2 forming olivine of a complex composition, pyroxene, glass, ferrites, and aluminates and silicates of zinc. In the periclase-spinel products, these processes occur to a lesser extent than in the chrome-magnesite ones.On the basis of the results from these studies it is recommended that the MChVP and PSpSP products be used in the linings of Weltz furnaces; the use of ChM and PSpSO products is not recommended.

The wear of magnesia refractories in electric furnaces for melting cast iron

ConclusionsThe wear of magnesia refractories, i. e., magnesite, perictase — spinel, and magnesite — chromite bricks and magnesite — phosphate mortar, in the walls of electric furnaces for melting cast iron is the result of the solution predominantly of the periclase crystals and to a lesser extent of the spinel in the lowbasicity ferrosilicate slag melt. Brick of the PShS type proved to be the most durable refractory. The use of high-alumina brick in the roof of the furnaces accelerates the wear of the magnesia bricks in the walls.To increase the durability of the lining of these furnaces trials should be carried out with an all-basic wall lining constructed of high-density PShSP-type brick on MF-1-type magnesite — phosphate mortar and a roof lining constructed of MKhS brick and the same mortar.