Several mature technical routes have been established for the preparation of calcium sulfate whiskers. The mainstream processes and their characteristics are as follows:
Mainstream Industrial Preparation Processes
Hydrothermal Method (High-Pressure Hydrothermal Method)
Core Process:Selected gypsum raw materials are placed in a sealed pressure vessel. Under saturated steam pressure at temperatures exceeding 100°C, a dissolution-recrystallization process converts gypsum dihydrate into fibrous calcium sulfate hemihydrate whiskers. The product is then stabilized, dehydrated, and dried.
Process Characteristics: The product features high purity, uniform morphology, and good dispersibility; however, the process requires high-temperature and high-pressure conditions, entailing significant equipment investment.
Atmospheric Acidification Method
Core Process: A high-concentration raw gypsum suspension is directly converted into needle-like or fibrous calcium sulfate whiskers within an acidic solution at atmospheric pressure and a specific temperature. The product is subsequently obtained through solid-liquid separation and drying.
Process Characteristics: This method eliminates the need for high-temperature and high-pressure conditions, resulting in lower production costs and facilitating large-scale industrial production; however, the acidic environment imposes strict requirements for equipment corrosion resistance.
Other Auxiliary Preparation Processes
Ion Exchange Method: Calcium ions from an ion-exchange resin react with a sulfate-containing solution to controllably produce fibrous calcium sulfate whiskers; while the product purity is high, the yield is relatively low.
Microemulsion Method:This method utilizes the confinement effect of microemulsion micro-reactors to precisely control whisker nucleation and growth, enabling the production of nanoscale calcium sulfate whiskers with extremely fine diameters.
Mineral Conversion Method: A derivative of the hydrothermal method, this process uses various minerals or industrial by-product gypsums-such as natural gypsum, phosphogypsum, and desulfurization gypsum-as raw materials. It is a simple, clean process that generates no secondary pollution.
