Alteration of diaspore by thermal treatment

Abstract

Diaspore (α-AlOOH) was heated at various temperatures from 300 to 1 000 °C for 2 h. The alteration of diaspore by thermal treatment was investigated by differential thermal analysis, thermogravimetric analysis and X-ray diffraction. The mechanism of thermal decomposition of diaspore was discussed according to the Coats-Redfern equation. It is found that after thermal treatment at 500 °C, diaspore is transformed entirely to corundum (α-Al₂O₃). Combined with the mass loss ratio obtained from the thermogravimetric analysis data, the activation energies for the thermal treatment of diaspore are calculated as E_a=10.4 kJ/mol below 400 °C and E_b=47.5 kJ/mol above 400 °C, respectively, which is directly related to the structural alteration of diaspore during the thermal treatment. The results indicate that the thermal decomposition of diaspore is conducted primarily by means of an interfacial reaction.

Keywords

diaspore / thermal treatment / X-ray diffraction / thermal analysis / activation energy

References

[1] SarikayaY, OnalM, BaranB. The effect of thermal treatment on some of the physicochemical properties of bentonite [J]. Clays and Clay Minerals, 2000, 48(5): 557-562

[2] BalekV, SubrtJ, RouquerolJ, et al.. Emanation thermal analysis study of synthetic gibbsite [J]. Journal of Thermal Analysis and Calorimetry, 2003, 71(3): 773-782

[3] KakaliG, PerrakiT, TsivilisS, et al.. Thermal treatment of kaolin: the effect of mineralogy on the pozzolanic activity [J]. Applied Clay Science, 2001, 20(1–2): 73-80

[4] LiaoL, SennaM. Thermal behavior of mechanically amorphized talc [J]. Thermochimica Acta, 1992, 197: 295-306

[5] PigaL. Thermogravimetry of a kaolinite-alunite ore [J]. Thermochimica Acta, 1995, 265: 177-187

[6] ShovalS, GaftM, PanczerG. Luminescence of Cr³⁺ in natural and calcined diaspore [J]. Journal of Thermal Analysis and Calorimetry, 2003, 71(3): 699-706

[7] Garcia-GuineaJ, RubioJ, CorrecherV. Luminescence of α-Al₂O₃ and α-AlOOH natural mixtures [J]. Radiation Measurements, 2001, 33(5): 653-658

[8] AgliettiE F, Porto-LopezJ M. Physicochemical and thermal properties of mechanochemically activated talc [J]. Materials Research Bulletin, 1992, 27(10): 1 205-1 216

[9] PerrottaA J. Nanosized corundum synthesis [J]. Materials Research Innovation, 1998, 2(1): 33-38

[10] ChandrasekhrS, PramadaP N. Thermal studies of low silica zeolites and their magnesium exchanged forms [J]. Ceramics International, 2002, 28(2): 177-186

[11] RuanH D, FrostR L, KloproggeJ T. Far-infrared spectroscopy of alumina phases [J]. Spectrochimica Acta A, 2002, 58(2): 265-272

[12] MacKenzieK J D, TemuujinJ, OkadaK. Thermal decomposition of mechanically activated gibbsite [J]. Thermochimica Acta, 1999, 327(1–2): 103-105

[13] MacKenzieK J D, TemuujinJ, SmithM E, et al.. Effect of mechanochemical activation on the thermal reactions of boehmite [J]. Thermochimica Acta, 2000, 359(1): 87-94

[14] KloproggeJ T, RuanH D, FrostR L. Thermal decomposition of bauxite minerals: infrared emission spectroscopy of gibbsite, boehmite and diaspore [J]. Journal of Materials Science, 2002, 37(6): 1 121-1 129

[15] TsuchidaT, HorigomeK. The effect of grinding on the thermal decomposition of alumina monohydrate [J]. Thermochimica Acta, 1995, 254: 359-370

[16] CoatsA W, RedfernJ P. Kinetic parameters from thermogravimetric data [J]. Nature, 1964, 201: 68-70