Phase composition of sintered lime refractories with TiO2 additions

Abstract

Incorporating TiO 2 additives markedly improves the sintering of CaO-based refractories [ 1, 2]. It reduces the rate of atmospheric hydrolysis of the sintered material, not only because of the improvement in its porosity, but also because of the formation of nonhydrolyzable compounds in the system CaO-TiO 2. Thus, TiO~_ as a sintering agent for CaO is suitably distinguished from other additives such as A1203, B203, SiO 2, etc. which are recommended in the literature [i].To improve the process for making lime refractories it is important to stress the firing cycle, since various calcium titanates are formed during firing, whose region of formation has not been precisely established.Investigations of the binary system CaO-TiO 2 suggest the existence of three double compounds: Ca2Ti207, Ca4Ti3Olo, and CaTiO 3. The authors of [3] detected only two compounds in this system -CaTiO 3 and Ca3TiaO 7. By studying the kinetics of their development, they showed that the rate of formation in the solid phase of perovskite CaTiO 3 may be 1.5-2 times greater than the rate of formation of Ca3Ti207. According to [4] the compounds Ca3TiO 7 and Ca4Ti30 94 melt incongruently at 1740 and 1755~ respectively, with the formation of CaTiO 3 and liquid. In [5] the authors established the presence of solid solutions between Ca3Ti207 and Ca4Ti3OlO.From the crystallochemical viewpoint the structure of perovskite CaTiQ is most conveniently considered to be a volume-centered cubic lattice, deformed along the axes [100] and [001], with the densest packing formed by atoms of calcium and oxygen [6], in which the titanium atoms occupy the octahedral spaces formed by the oxygen atoms. According to Goldschmidt, the formation of perovskite type structures ABO 3 requires a certain relationship to hold between the polarized radii A and B (r A and rg) and the radius of the oxygen ro:where t is a numerical multiplier, assuming values from 0.8 to 1.0.Compounds of the ABO 3 type with the perovskite structure can be divided into two main groups. The first covers those with a cubic structure, ideal or slightly deformed, and this deformation consists in a change in one or several lattice parameters, which leads to the formation of a tetragonal, rhombic, or rhombohedral structure (BaTiO3). The second group contains compounds in which the deformation causes an increase in the elementary cell (CaTiO3). Deformation of the cubic lattice CaTiO 3 leads to a reduction in the symmetry of this compound to the rhombic form.In the structure of Ca3Ti207 the double layers of perovskite are separated by CaO layers. The ratio of the axes c/a in Ca3Ti207 is 5:1 [6]. The authors of [7] confirmed the possibility of the existence of such compounds with ternary and quaternary layers ofperovskite, separated by CaO layers. In particular, the compound Ca4Ti3Olo has the ratio c:a = 7:1. The main parameters of the crystalline structure of calcium titanate are shown in Table 1.In order to study the solid phase sintering processes in the CaO-TiO 2 system we prepared mixtures of CO and T...

Behavior of TiO2 nanoparticles during incineration of solid paint waste: A lab-scale test

“…The calcium titanate was detected by XRPD in A1 ash, but the quantity of this species is unknown. Calcium titanate was produced in other studies by mechanochemical synthesis from a mixture of CaO and TiO 2 in anatase or rutile form (Mi et al, 1998), or by sinterization of CaO-based refractories with the addition of TiO 2 under a heat treatment at temperatures near 1500°C (Vezikova and Gropyanov, 1993). …”

Highly efficient use of limestone in steel smelting

“…It is recommended that a stabilizing additive amounting to 5 -6% be used [6]. It is also necessary to determine whether the slag of titanium production may be used as the stabilizing additive, or pigment titanium dioxide is needed.…”