Composite material and method of producing

A process for making a composite material, comprising:

• mixing ground gypsum and a plurality of host particles together with water to form a slurry, said host particles being generally insoluble in said water but having voids on their surfaces and/or within their bodies penetrable by the slurry menstruum containing suspended and/or solubilized gypsum and said slurry being sufficiently dilute to wet out said host particles with slurry menstruum and to foster the growth of acicular calcium sulfate alpha hemihydrate crystals when heated under pressure;
• heating the slurry under pressure to a temperature sufficient to calcine the gypsum to calcium sulfate hemihydrate;
• maintaining the slurry heated and under pressure while allowing the calcium sulfate molecules to nucleate and form crystals in-situ in and about the voids in the host particles;
• relieving the pressure and dewatering the slurry;
• and
• drying the dewatered solids to remove substantially all the remaining free water and stabilize the calcium sulfate while still physically interlocked with the host particles.

A process for making a board of composite material, comprising:

• mixing ground gypsum and host particles together with sufficient water to form a slurry, said host particles each having voids on its surface and/or within its body penetrable by the slurry menstruum containing suspended and/or dissolved gypsum and said slurry being sufficiently dilute to substantially wet out the penetrable voids in the host particles and to foster the formation of acicular calcium sulfate alpha hemihydrate crystals when heated under pressure;
• heating the slurry in a pressure vessel, with continuous agitation, to a temperature sufficient to calcine the gypsum to calcium sulfate alpha-hemihydrate, and maintaining the slurry at such temperature until at least some calcium sulfate hemihydrate has substantially crystallized in and about the voids in the host particles;
• discharging the heated slurry onto a flat porous forming surface and removing a substantial portion of the water from it to form a filter cake;
• pressing the filter cake to form a board and to remove additional water therefrom before the temperature of the board falls below the temperature at which the calcium sulfate hemihydrate will rehydrate to gypsum;
• cooling the board to below the rehydration temperature and allowing the calcium sulfate hemihydrate to rehydrate to gypsum;
• and
• drying the board to remove the remaining free water.

A method of making a composite gypsum and wood fiber material which includes the steps of

• a) suspending a mixture of ground gypsum and wood fibers having hollows, fissures, pores, pits and/or other irregular surfaces over a portion of their body in a continously agitated aqueous medium;
• b) adding an amount of soluble gypsum in excess of that required to saturate the aqueous medium, wherein a portion of the gypsum is solubilized and a portion is suspended in the continuously agitated medium;
• c) heating the aqueous medium under pressure to precipitate the solubilized gypsum from solution as calcium sulfate alpha hemihydrate;
• and
• d) maintaining the reaction condition of step (c) for a sufficient period of time such that the growth of acicular calcium sulfate alpha hemihydrate crystals in, on and about the hollows, fissures, pores, pits and/or other irregular surfaces of the wood fibers is fostered.