How to Produce High-Quality Black Silicon Carbide for Sandpaper and Emery Cloth
High-quality black silicon carbide (SiC) for sandpaper and emery cloth demands strict control over raw materials, production processes, and quality testing to ensure optimal hardness, particle distribution, and abrasive performance. Here's a production approach:
1. Choose good Raw Material
The core raw materials are high-purity silica (SiO₂, ≥98% purity, e.g., quartz sand) and high-carbon coke (fixed carbon ≥85%, low ash content ≤2%). Impurities like iron oxide (Fe₂O₃) or aluminum oxide (Al₂O₃) must be minimized, as they reduce SiC hardness and cause uneven abrasion. Raw materials are crushed to 1–3mm particles, then dried to ≤0.5% moisture content to prevent reaction instability during sintering.
2. High-Temperature Synthesis in Resistance Furnaces
The dried mixture (SiO₂:coke ratio ≈1:0.6 by weight) is loaded into graphite-lined resistance furnaces. The furnace is heated to 2200–2400°C under an inert atmosphere (to avoid oxidation) and held for 8–12 hours. At this temperature, the reaction SiO₂ + 3C → SiC + 2CO↑ occurs, forming blocky SiC. Precise temperature control is critical: temperatures below 2200°C leave unreacted raw materials, while over 2400°C causes SiC decomposition, both lowering quality.
3. Crushing, Grading, and Purification
After cooling, SiC blocks are crushed in stages (jaw crushers → cone crushers → impact mills) to avoid particle fragmentation. Air classification or wet screening then grades particles into standardized sizes (e.g., 400-mesh for fine sandpaper), ensuring uniform particle size distribution (PSD)-a key factor for consistent sanding. Magnetic separation removes iron impurities, and acid washing (with dilute hydrochloric acid) eliminates residual oxides, raising SiC purity to ≥98%.
4. Quality Testing and Post-Treatment
Final testing focuses on critical parameters:
Hardness: Measured via Vickers hardness test (target: ≥2800 HV) to ensure abrasive durability.
Particle Uniformity: PSD is verified using laser diffraction; more than 90% of particles must fall within the target mesh range.
Impurity Content: Fe₂O₃ ≤0.15% and F.C.≤0.15%.
Qualified SiC is coated with a coupling agent (e.g., silane) to enhance adhesion to sandpaper backings, completing production of high-performance black silicon carbide for abrasive applications.
