Kyanite concentrate of the Karabash deposit: Phase transformations during heating

Abstract

Results are provided for a study of the phase transformation during heating of kyanite concentrates of the Karabash deposit, and the effect of temperature, soaking at the final temperature, and grain size on parameters of kyanite thermal decomposition. IR-spectra for kyanite concentrate of a different degree of transformation, and the microstrcuture of a partially decomposed kyanite grain are given. It is shown that thermal decomposition of kyanite proceeds in the range 1300 -1400°C, and linear expansion, temperature for the start and decomposition rate depend on kyanite grain size, and the relaxation of elastic stresses of the kyanite crystal lattice is mainly limited by the decomposition reaction factor.One of the most important trends in the world for developing production of aluminisilicate refractories is expansion of the output of high-alumina and a reduction in the production of chamotte that is due to the better stability of high-alumina refractories towards the action of elevated temperatures and corrosive agents. Production of high-alumina refractories is based on artificial starting materials (commercial aluminina, electrocorundum) and on natural raw material, i.e. rock laid down with minerals of a high Al 2 O 3 content. The reserves of these minerals in nature are significant, and this gives rise to their extensive use in the production of refractories in many countries. The main condition for use of natural raw material is its low cost compared with artificial materials that are normally produced by quite complex and very energy-consuming technology. If in a complicated economic situation a natural raw material appears to be cheaper, it provides the required Al 2 O 3 content in refractories, and the level of the concentration technology makes it possible to obtain quite pure material free from impurities, then use of this raw material is preferable. From a physicochemical point of view the advantage of high-alumina materials over artificial materials is the fact that the Al 2 O 3 content is more active in heat treatment since it enters into the structure of compounds (silicates, hydrates, etc.) preventing a change in the crystal lattice during heating.One of the forms of natural high-alumina raw material are minerals of the silliminite group (kyanite, andalusite, silliminite). Interest in them is also due to their facility to decompose thermally with expansion into mullite and silica glass. Currently the proportion of unmolded refractories in linings of heating units continues to increase, among which aluminisilicate refractories comprise a considerable part, and therefore the requirement for additions balancing shrinkage, and also high quality shrinkage-free fillers is also considerable.The reserves of kyanite minerals of Russia occupy one of the first positions in the world. Large northern (Kiev, Khizovaarsk) and also Eastern Siberia (Kyakhtinsk, Kitoisk, Chainytsk) deposits are well known but they are difficult to access. There are deposits of Kyanite in the Ural (Borisov, Karabash, Mikhailov, Mal...

The influence of feldspar rock additions on densification and mechanical properties of ceramic membrane using economic raw materials

“…In the case of porous ceramic membranes, the microstructures and the mechanical strength which depend on the behavior of the phases during sintering. Usually, ceramic membranes made from refractory clays are porous membranes based on the mixture of plastic clays (kaolin), fluxes (feldspar, talc, kyanite, etc) and non-plastic raw 8 . The chemical, physical and structural transformations of kaolinite have been extensively studied in the literature, releasing the heating effect on final properties and microstructural aspects [9][10][11][12][13][14][15][16] In a ceramic framework, feldspar is playing a flux role which can reduce the temperature of new phase and liquide phase formation, and to form viscous glassy phase that helps in vitrification and densification 17 .…”

Cold-setting refractory composites from cordierite and mullite–cordierite design with geopolymer paste as binder: Thermal behavior and phase evolution

“…Natural kyanite, Al 2 SiO 5 , (theoretical weight composition 63.1% Al 2 O 3 and 36.9% SiO 2 ) is a metastable nesosilicate, that on heating at 1100 C [16] breaks down into mullite (87.6%) and vitreous silica (12.4%) via the following reaction:…”

“…It was established that the conversion proceeds from the surface toward the depth of a grain, and is limited by the relaxation of elastic stresses of the kyanite crystal lattice. After kyanite decomposition, amorphous silica crystallizes into cristobalite at low temperature [16].…”

Effect of oxides RO, R 2O3, RO2 and impurity materials on decomposition during heating of kyanite in oxidizing and reducing atmospheres

“…The effect of temperature, time and kyanite grain size on its thermal decomposition parameters has been studied previously [1]. It has been established that conversion proceeds from the surface into the depth of a grain and is limited by relaxation of elastic stresses of the kyanite crystal lattice.…”

“…In an oxidizing atmosphere oxide Cr 2 O 3 leads to an increase by 20 -30°C in the temperature for the start and maximum rate of occurrence of kyanite concentrate decomposi- (1, 3 -5, 7, 9, 11 ) and reducing atmospheres (2, 6, 8, 10, 12 ) without impurities (1,2 ) and with 5% of impurities CaO (3 ), MgO (4 ), Fe 2 O 3 (5, 6 ), Cr 2 O 3 (7, 8 ), TiO 2 (9, 10 ), ZrO 2 (11, 12 ), fired at 1400°C with soaking for 4 h. tion reactions. According to x-ray phase analysis data (see Fig.…”