CA6942 Calcium Sulphate Dihydrate Powder

Calcium Sulfate Dihydrate Powder Description

Calcium Sulfate Dihydrate (CaSO₄·2H₂O), commonly known as gypsum, is a naturally occurring inorganic compound with the chemical formula CaSO₄·2H₂O. It appears as a white crystalline powder or colourless monoclinic crystals, characterised by a glassy lustre and odourless nature. This compound exhibits a density of 2.32 g/cm³ and undergoes dehydration at elevated temperatures: it loses 1.5 water molecules at 128°C and fully dehydrates to anhydrous calcium sulfate above 163°C.

Its solubility is moderate in cold water (0.21 g/100 mL at 20°C) but remains insoluble in ethanol and most organic solvents. Calcium sulfate dihydrate demonstrates hygroscopic behaviour by absorbing moisture from the air, and it reacts with acids to release sulphur dioxide gas. The crystal structure comprises calcium ions (Ca²⁺), sulfate groups (SO₄²⁻) and two water molecules arranged in a layered lattice. These structural details contribute to its stability under standard conditions.

Thermally, it transitions to calcium sulfate hemihydrate (CaSO₄·0.5H₂O) between 107°C and 170°C and converts to anhydrous calcium sulfate (CaSO₄) above 200°C. These properties allow its application in several sectors, including construction (gypsum plaster, plasterboard), agriculture (soil conditioning), food (calcium fortification, coagulant), pharmaceuticals (dental materials) and various industrial processes (paint fillers, wastewater treatment).

Calcium Sulfate Dihydrate Powder Applications

Calcium Sulfate Dihydrate Powder is used in both industrial and biomedical contexts. Its hydration behaviour and neutral chemical properties make it suitable for defined applications. In construction, the dihydrate is calcined at 150–180°C to produce hemihydrate (CaSO₄·0.5H₂O), which is the primary constituent of plaster of Paris. This material is used in gypsum wallboards, moulds and fire-resistant coatings, relying on its rehydration-driven expansion and rapid setting. Uncalcined dihydrate is applied as a soil conditioner to improve sodic soil structure via calcium–sodium ion exchange. Medically, a high-purity form is employed as an osteoconductive bone void filler in orthopaedics and dentistry, utilising gradual resorption and calcium release without inducing inflammatory responses. In the food and pharmaceutical sectors, it is used as a GRAS-certified calcium fortifier (for example, in tofu and cereals) and as a tablet diluent, owing to its neutral taste and low reactivity. In industrial contexts, the powder is used to regulate cement setting kinetics, serve as a desiccant in packaging and act as a coagulant in tofu production. It is also employed in art conservation for fresco restoration and as an oxidiser in white fireworks, utilising its defined solubility, non-toxicity and reversible dehydration behaviour.

Calcium Sulfate Dihydrate Powder Packaging

Products are packed in customised cartons of various sizes determined by material dimensions. Smaller items are placed in PP boxes, while larger products are loaded into custom wooden crates. Packaging specifications are followed rigorously, and appropriate cushioning materials are used thereby ensuring protection during transportation.

Packaging: Carton, Wooden Box, or Customised.

Please refer to the packaging details provided for further information.

Manufacturing Process

1.       Testing Method

(1)    Chemical Composition Analysis – We verify the chemical composition using techniques such as GDMS or XRF to ensure compliance with established purity requirements.

(2)    Mechanical Properties Testing – We perform tensile strength, yield strength and elongation tests to evaluate material performance.

(3)    Dimensional Inspection – We measure thickness, width and length to confirm adherence to specified tolerances.

(4)    Surface Quality Inspection – We check for defects such as scratches, cracks or inclusions by means of visual and ultrasonic examinations.

(5)    Hardness Testing – We determine the hardness to confirm uniformity and mechanical reliability.

Please refer to the testing procedures provided by Stanford Advanced Materials (SAM) for detailed information.

Calcium Sulfate Dihydrate Powder FAQs

Q1. How does the dihydrate phase differ from hemihydrate or anhydrite in applications with strict performance criteria?

The dihydrate phase remains stable under ambient conditions with minimal deliquescence. Hemihydrate samples, which rehydrate rapidly, do not maintain constant crystalline integrity. In contrast, anhydrite forms require an activation step for reactivity. The retrograde solubility of the dihydrate phase results in controlled dissolution kinetics in aqueous systems.

Q2. Is the retrograde solubility behaviour practically relevant in formulation design?

Yes, solubility decreases with increasing temperature (0.255 g/100 mL at 0°C versus 0.205 g/100 mL at 100°C). Temperature-controlled processing is required for suspension or saturation preparations. This property restricts uncontrolled precipitation during thermal cycles and complicates hot-process sterilisation of medical composites.

Q3. What purity thresholds are mandatory for pharmaceutical versus construction-grade material?

For pharmaceutical grade material, the limits are ≤0.001% heavy metals (as Pb), ≤0.1% alkalies and microbiological controls (TAMC ≤1 000 CFU/g). In comparison, construction grade tolerates up to ≤0.3% carbonate impurities and a crystalline silica content not exceeding ≤1.5%. Verification of dihydrate crystallinity is conducted using XRD, notably recognising a characteristic d-spacing of 7.63 Å.

Related Information

1.       Common Preparation Methods

Calcium Sulfate Dihydrate Powder is produced industrially via two primary routes: natural gypsum processing and synthetic precipitation. In natural processing, mined gypsum ore (typically 70–95% CaSO₄·2H₂O) is crushed, ground and dry-screened to obtain a particle size of 80–150 μm, followed by calcination-controlled dehydration at 120–160°C to yield hemihydrate. This intermediate product is then rehydrated under controlled conditions (water/solid ratio 0.6–0.8, 40–60°C) with controlled agitation for 45–90 minutes to precipitate phase-pure dihydrate crystals. The resultant slurry is filtered, washed with deionised water to remove chloride/sodium impurities (<500 ppm) and dried in a fluid-bed dryer below 65°C to preserve the stoichiometry.

Synthetic production entails reacting calcium chloride waste streams (for example, from soda ash manufacturing) with sulphuric acid (93–98% concentration) at 70–80°C. A stoichiometric excess of 2–3% calcium ions is maintained to ensure complete sulphate precipitation. The resulting slurry is aged at a pH of 5.5–6.5 for crystal maturation, producing acicular or prismatic crystal morphologies depending on the use of additives (such as succinic acid for needle inhibition). Purification is carried out using froth flotation to remove silica/alumina contaminants, followed by three washing cycles. It is essential that temperatures do not exceed 65°C during the final drying step, thereby preventing irreversible formation of hemihydrate. Crystallographic integrity is confirmed using X-ray diffraction (with characteristic d-spacings of 7.63 Å and 4.28 Å) and thermogravimetric analysis (a theoretical mass loss of 20.93% at 100–160°C, which verifies dihydrate stoichiometry). Pharmaceutical grades undergo additional micronisation to achieve D90 < 20 μm and are sterilised via gamma irradiation.