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.