Kinetics and optimization of temperature and time regimes for sintering naturally pure Russian dolomites

Abstract

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...

Solid state sintering of lime in presence of La2O3 and CeO2

“…The higher hydration resistance (lesser wt gain) of sintered lime by La 2 O 3 addition is due to the development of large grain size. The rate and degree of hydration of sintered CaO depends on the rate of chemisorption of water on the grain boundary surface (Gropyanov and Novikov 1923). The more the grain size the lesser will be the grain boundary surface area, hence the diffusion of water will be minimized.…”