Berlinite, amorphization

It can be seen from Fig. 12.20 that berlinite amorphizes at a pressure of 33 GPa and amorphous aluminium phosphate recrystallizes at a pressure of 27 GPa. The observed phase transitions are in accord with the experimental results (Kruger and Jeanloz, 1990), but the transition pressures are different from experiment (15 + 3 GPa and 5 GPa, respectively, with a hysteresis of about 13-15 GPa). In this study the hysteresis is about 6 GPa. This discrepancy could be attributed to several factors. First, the fact that a perfect crystal is... 

Deep and geothermal wells are inherently hot and are well served by aluminum phosphate formulations (see Chapter 11). The dynamic temperature in these wells is 250 °F (121°C) or higher, and the static temperature is >350 °F (235°C). For these wells, berlinite-based CBPC works well with its maximum solubility at 244 °F (118°C) of alumina and phosphoric acid solution. As we have seen in Chapter 11, this reaction takes place at 302 °F (150°C) that is in the range of the temperatures of deep and geothermal wells [7]. Even at these temperatures, the solubility of aluminum oxide is too low, but addition of a small amount of microcrystalhne or amorphous aluminum hydroxide aids in increasing the soluble ions in the solution. With its large surface area, alumina provides the necessary solubility at the given downhole temperamre. 

Bordes N, Ewing RC (1995) Ion-beam and electron beam induced amorphization of berlinite (AIPO4). Mater Res Soc Symp Proc 373 395-400... 

Vessal (1991) has studied the simulation of amorphization of crystalline A1P04 berlinite using the constant pressure MD method. When the system is depressurized gradually, amorphous A1P04 is observed to recrystallize back to the crystalline phase. These observations are in agreement with recent experiments (Kruger and Jeanloz, 1990). The simulation was undertaken with a pressure interval of 1 GPa between two consecutive cycles. During pressurization, the behaviour of the system was studied to detect a phase transition. After amorphization, the amorphous material was pressurized further to see if there... 

The four main peaks in the Al-Al RDF are located at 4.52, 5.07, 5.56, and 5.39 A at zero pressure (see Fig. 12.23). As the pressure on the system is increased these peaks shift to shorter distances. The peak at 5.56 A will disappear completely at a pressure of 24 GPa. At a pressure of 33 GPa the shape of the RDF changes drastically, which indicates the amorphization of berlinite, where three broad peaks at 3.36, 4.65, and 5.63 A are observed in the Al-Al RDF at 33 GPa. During the decompression process the reverse trend is observed. At 28 GPa there is clearly a phase transition and the system becomes more ordered. The four Al-Al peaks that are observed for the recrystallized material are at exactly the same positions as the peaks for the starting crystalline material. 

Vocadlo L, Wall A, Parker SC, Price GD (1995) Absolute ionic-diffusion in MgO - computer calculations via lattice-dynamics. Phys Earth Planet Int 88 193-210 Watson GW, Parker SC (1995) Dynamical instabilities in a-Quartz and a-Berlinite A mechanism for amorphization. Phys Rev B-Cond Mat 52 13306-13309 Watson GW, Parker SC (1995) P-Quartz amorphization - a dynamical instabihty. Phil Mag Let 71 59-64. Watson GW, Parker SC, Wall A (1992) Molecular-dynamics simulation of fluoride-peiovskites. J Phys-Cond Mat 4 2097-2108... 

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