Overview
Model plaster is a specialized form of calcium sulfate hemihydrate (CaSO₄·0.5H₂O) produced by calcining gypsum at controlled temperatures. Unlike construction-grade plasters, it features ultra-fine particles (typically <100 microns) for smooth surface reproduction. The material has been used since ancient Egypt for art and construction, with modern industrial production standardizing its properties for precision applications. In B2B contexts, model plaster is classified by setting expansion (<0.3%), compressive strength (20-40 MPa), and working time (5-15 minutes). Dental and art industries often require Type III or IV plasters per ISO 6873 standards, which undergo additional purification to minimize impurities affecting cast detail.
Physical and Chemical Properties
When mixed with water (typically 40-60 ml per 100g powder), model plaster undergoes rehydration to form gypsum dihydrate (CaSO₄·2H₂O), creating an interlocking crystal matrix. This exothermic reaction peaks at 50-60°C, with final hardness achieved within 1-2 hours. The material's low thermal conductivity makes it ideal for metal casting molds. Key quality indicators include water demand (ratio affecting porosity), wet-to-dry shrinkage (<0.1%), and surface hardness (often measured via Brinell scale). High-purity variants contain <0.5% insoluble residue and maintain consistent pH (6.5-7.5) to prevent mold degradation.
Main Applications
In dentistry, model plaster creates accurate study models and working dies for prosthodontics, requiring minimal expansion (0.08-0.2%) to ensure crown/denture fit. Art studios use it for life casts and sculpture prototypes, where its slight hygroscopicity aids clay separation. Industrial applications include aerospace investment casting cores and ceramic shell mold backups. Some architectural firms employ colored plasters for presentation models. Emerging uses include 3D-printed gypsum composites, where modified plasters serve as binder jetting materials with 85-100 μm layer resolution.
Safety and Storage
Though non-combustible, plaster dust poses inhalation risks (TLV 10 mg/m³ for particulates). Facilities should use local exhaust ventilation during mixing and store bags away from humidity to prevent premature setting. Spills require dry cleanup to avoid slurry formation. Reclaimed plaster should never exceed 10% of fresh material due to altered crystallization kinetics. Containers must bear GHS07 hazard symbols for eye irritation (H319). Shelf life is typically 12 months in original packaging, extended with desiccants in humid climates.
B2B Procurement Guide
Industrial buyers should specify: 1. Particle size distribution (D50 value for detail reproduction) 2. Batch consistency certificates (color, setting time variance <±1 min) 3. Packaging options (moisture-proof bags vs bulk silos) Bulk purchases (5+ tons) often qualify for 15-20% discounts, while dental-grade plasters command 30-50% premiums over basic formulations. Consider regional distributors for just-in-time delivery to minimize warehouse moisture exposure. Sample testing should evaluate slurry flowability and post-curing surface defects.
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