Technical Details

This new alpha hemihydrate plaster (dubbed Hi-PSI-G) exhibits some of the aspects of beta plasters, but with the water demand of a true alpha hemihydrate. Under suitable conditions, it is possible to form a finely divided gypsum into briquettes, calcine these briquettes under steam pressure, then grind and dry to produce a consistent quality alpha hemihydrate with a water demand of between 35 and 50 ml/100g. As described in the U.S. Pat. Appl. No. 10/800,780, during calcination the hemihydrate crystals are constrained when recrystallizing as hemihydrate thereby forming low aspect ratio crystals that result in a low water demand plaster . A schematic outlining this patented process is shown in Figure 7.

A key to the technology is the ability to reduce calcination times down to as little as 30 minutes. As well, this unique process surpasses conventional thinking in that briquettes can be formed at pressures that exceed 14 MPa. In fact, pressures on the order of 200 MPa have been used to produce high-quality briquettes. Briquetting at these pressures were not considered feasible prior to the GBT process. Despite the departure from this conventional thinking, GBT has demonstrated that its unique process is one of the fundamental bases for Hi-PSI-G’s low water demand.

Other parameters which impact the material properties of Hi-PSI-G include the addition of certain additives, process speed and hemihydrate conversion rates, and subsequent grinding methods of the resulting briquette.

Figure 7. Schematic of the Patented Calcination Process