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The kinetics of sintering at 2300-2400K naturally pure dolomites of the Melekhovo-Fedot'evo and Lis'egorsk Deposits is investigated experimentally at different heating rates. Kinetic parameters of the processes of densification and grain growth in sintering calculated from experimental data have made it possible to use the kinetic equation as a mathematical model for optimizing the temperature and time regimes of sintering in order to attain maximum densification rates and uniformity of the sintering process in the entire temperature and time range of fkring. Preliminary fine milling of the dolomite substantially intensifies sintering, which gives a high-density clinker after firing at temperatures of at most 2100 -2200K.A key problem in the technology of lime-periclase refractories from naturally pure Russian dolomites is the preparation of high-density ultra-disperse clinker. Since lumps of such dolomite are sintered only at temperatures exceeding 2400 -2500 K, there are at least two technologies for preparing sintered lime-periclase clinker.The first technology is known as a two-stage one. The initial lump dolomite is subjected to preliminary calcining at 1370 -1400K, for example, in rotary kilns, and then to milling or hydration, briquetting, and sintering at 2000 -2100 K [1 -3]. The second technology has one stage, in which the initial dolomite is sintered directly in lumps with slntering additions, for example, Fe203, or after fine miring and. briquetting at 2000-2300K [1,4]. In our opinion the second method should be preferred from ecological and economic considerations.However, the introduction of sintering additions in the form of scale substantially worsens the chemical composition and refractory properties of the naturally pure material, and therefore the use of preliminary fine milling of the initial dolomites, taking into account their high comminutability [5], can be justified. The main problem is that the naturally pure dolomites in Russia are poorly slntering materials and require special scientifically substantiated sinterlng regimes in order to attain high-density and ultradeuse states.The most reliable basis for the development of rational firing regimes is knowledge of the kinetic regularities of the processes of deusification and collective recrystallization of St. Petersburg Institute of Refra~ories, St. Petersburg, Russia. 280the material in the course of sintering. The aim of the present work is to determine the form and parameters of the kinetic equation with an estimate of their reliability and to develop methods of using the kinetic equation as a mathematical model for optimizing the temperature and time regimes of firing with the help of the theoretical apparatus of nonisotherreal kinetics. The kinetic equation obtained in [6] was based on a rheological sintering model and allowed for the decrease in the mobility of the structural components of crystalline bodies in collective crystallization (grain growth) accompanied by densification:p 1-P 0 where z= 1 -P Po istherelativereduction of...

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It is established that in order to increase the atmospheric resistance of compacts from lime and lime-periclase clinkers the temporary binder should contain high-molecular-weight resin and fatty acids, which form water-insoluble salts on the CaO surface, and surface-active substances in addition to a hydrophobic plasticizer. The reqifisite amounts of the acid-containing componcnt and the binder itself are calculated.The problem of temporary binding agents for the formation and preservation of lime and lime-periclase refractories has been discussed in the literature 2 more than once [1 -4]. Its complexity consists in that the binders should not only ensure a satisfactory formation process, but also protect the powders, the forming mixtures, and pressed and fared articles from atmospheric hydration. The mechanism of hydration, or, more exactly, hydroxylation, of lime consists in that at fwst a layer of physically adsorbed moisture forms very rapidly on the surface of CaO. The moisture transforms gradually into chemically bound water and forms portlandite Ca(OH)2 with CaO. The specific volume of portlandite is 1.5 times greater than that of CaO. The crystallization pressure of portlandite causes cracking and fracture of articles in storage or in the course of firing at 900 -1000 K. Consequently, the use of high-strength binders such as the basic processing binder for refractories (BPBR) [3,5,6] does not guarantee that the articles will be intact after molding and firing, because the physically bound water remains in the article and binder components containing [OH-] groups react with CaO and form portlandite [4,7].These facts imply that the development of temporary binders for refractories containing CaO should be based on the following considerations:-the temporary binder should contain a hydrophobic plasticizing component, which should protect CaO from contact with atmospheric moisture, have sufficient strength and plasticity, and be ecologically safe; on the one hand be insoluble in water and on the other hand suit the plasticizer; -at a minimum content of the temporary binder it should mix well with CaO particles and wet them properly without foaming, i.e., it should contain a surface active substance in an amount of 0.1 -1.0%; -the temperature of the beginning of intense decomposition or evaporation of the binder should be at least 700 K, when the equilibrium CaO + H20 ~:~ Ca(OH)2 is already strongly shifted to the left; -the processes of removal of physically bound water and the water formed in the interaction of CaO and Ca(OH)2 with the binder components should be completely finished during the preparation, mixing, and soaking; this determines the duration of mixing or soaking at a temperature of at least 380 -400 K. The upper temperature is limited by the beginning of intense evaporation and decomposition of the binder constituents.Even impure higher alkanes (from ceresin to petrolatum) can be a suitable least toxic and most available hydrophobic plasticizer having sufficient strength and thermal stability. ...