Thermal behaviour of co-precipitated magnesium-aluminium hydroxides gel

Central Glass and Ceramic Research Institute, Kolkata-700 032, India Ceramic Engineering Division, Department of Chemical Technology, University of Calcutta, 92, Acharya Prafulla Chandra Road, Kolkata-700 009, India E-mail : tapanparya@yahoo.co.in Fax : 91-33-23519755 Manuscript received 5 May 2005, revised 14 August 2009. accepted 18 August 2009 Thermal behaviour or co-precipitated Mg-AI hydroxides gel towards the formation of composite powders or periclase and MgAI2O4 spinel at low temperature was investigated. The co-precipitated Mg-AI hydroxy compounds were synthesized at two different temperatures and at pH ranges in between 8.56 and 9.20 from chloride salts or respective ions with molar ratio for MgO : Al2O3 as 2 : 1 using various combinations or ammonium hydroxides, triethanol amine (TEA) and ammonium carbonate mixture as basic media for co-precipitation. The co-precipitated hydroxide gel dried at 110 ºC and heated at different temperatures up to 1000 ºC were characterised by DTA, TGA and XRD studies. In all cases the co-precipitated Mg-AI hydroxy phases collapsed at 400 ºC with the conversion to transient amorphous phases. Further heat treatment at higher temperatures led to the formation or MgAl2O4 spinel and minor periclase phases at temperature as low as 600 ºC. The co-precipitated Mg-AI hydroxides 1el derived from TEA-NH4OH basic media exhibited promising results so far as transformation to composite powders or MgAl2O4 spinel and periclase at relatively low temperature Is concerned