Crystallographic Inversions of the Aluminum Orthophosphate Polymorphs and Their Relation to Those of Silica*

Abstract

The temperature-stability relationships of the AlPO, polyrnorphs have been studied by X ray, thermal analysis, and thermal expansion. The system parallels that of silica very closely. Following is a diagrammatic representation of the findings for AlPO,: 1 0 2 2 -500 Berlinite (sl'* *+; Tridymite form + + Cristobalite form +>16000> Fused AIPOI 586' +2O 93' +3' 130°(?) 2100 =t50 ff-6 t , BI t , 81a+-+-@ Conversions from one form to another are shown to be much more rapid than for Furthermore, the temperatures, with the exception of the corresponding silica cases. berlinite inversion. are all lower than for corresponding silica temperatures.

Water resistance and thermal behavior of metakaolin-phosphate-based geopolymer cements

“…This is in agreement with the results of X-ray patterns (Figure 1) and the IR spectra of the heated specimens ( Figure 5) which show the peaks of these crystalline phases. A weak endothermic peak which appears at around 590°C on the DSC curve of GPP1 corresponds to the polymorphic transformation of α-berlinite to β-berlinite [31,32]. The mass loss beyond 300°C observed on the TG curves of all geopolymer cements could be assigned to the further condensation of P-OH groups observed in the structure of metakaolin-phosphate-based geopolymer cements.…”

The Molecular Environment of Phosphorus in Sewage Sludge Ash: Implications for Bioavailability

“…Any residual AlPO 4 was converted from the tridymite type to the low quartz type. This phase transition between polymorphs occurs frequently and is reversible between 500 and 1000°C (Beck, 1949). …”

Coal fly ash utilization: Low temperature sintering of wall tiles

“…Due to increasing fuel costs, it is imperative to develop alternate binders/sintering compositions that sinter at lower temperatures and require minimum grinding energies (Amritphale and Chandra, 1995). Similar to the silica system, AlPO 4 is also reported to exist in berlinite structured (B-AlPO 4 ), tridymite structured (T-AlPO 4 ), and cristoballite structured (C-AlPO 4 ) polymorphs, but the respective transformation temperatures are lower than those in silica for corresponding phases (Beck, 1949). The work carried out in our laboratory has shown that alkaline phosphatic binders are useful in sintering the aluminosilicate-based materials in the temperature range of 950-1000°C (Chandra et al, 2005;Amritphale andChandra, 1995,1997;Amritphale et al, 2004Amritphale et al, ,2006Bhasin et al, 2003).…”