Sintering and recrystallization of chromium oxide

Abstract

Investigations of the sintering of chromium oxide have shown that the most effective sintering additive is titanium dioxide, and the crucial factor in obtaining dense specimens is a reduction on the partial pressure of the oxygen P02 in the firing atmosphere [12,[1][2][3][4]. However, the linking of both conditions has been studied only at one temperature --in [1-4] for a single composition , and in [3] in a limited range of TiO= concentrations. In actual conditions the sintering of Cr203 occurs in a wide temperature range and POd range, created either in furnaces with a controlled atmosphere, or in the presence of carbon-containing agents. Therefore, to clarify the mechanism of chromium-oxide sintering and the differentiation of the properties of refractories, we need to obtain data on the combined influence of P02 and sintering additive in a rather wide temperature range. This paper gives the results of a study of the sintering of Cr20s without additives and with an addition of from 0.5 to 20% * Ti02 at 1200-1600~ in the range P02 = 2"104-10-6 Pa and recrystallization of the chromium oxide with an addition of 1% TiO= and MgO at 1450-1760~ in air, and in an atmosphere with a reduced oxygen concentration. The subject of the investigation consisted of powdered Cr=03 grade OKhM-I and Ti02 of chemical purity grade, the properties of which were given in [5]. The variable partial pressure of oxygen in the furnace and its measurement were provided with apparatus described previously [12]. The crystal size were determined by the section method, and the ceramic and strength factors of the specimens were measured with the standard methods. *Here and subsequently, molar proportions are used. so~~oo~c L. 1~oo'c , t 15oo~ ! 16oo~ ,o --~ 2.107 2or 1 s ]1o-' .3"!o ~ ,~-'~=----" 16~ I 3./0" I 9 lO-J I I 0 " ~ iO'~ I0 "s 0 4 8 f2 16 20 ~ 8 12 I6 20 # 8 f2 16 204 8 12 f6 20 4 8 12 1620Content of riOz, %

Influence of oxide additives and firing atmosphere on the recrystallization of chromium oxide

“…The accelerating action of titania on recrystallization is probably connected with its influence on the sintering and is ensured by the formation of a defective solid solution of Ti02 in Cr20s [i0,Ii].…”