Black Silicon Carbide (C / CP / Refractory)

Overview

Black silicon carbide (black SiC, C-grade, carborundum) is the workhorse industrial SiC abrasive — synthesised by Acheson carbothermal reduction of quartz sand and petroleum coke at >1800°C, then crushed, acid-leached, dried, sieved, and classified into FEPA / ISO / GB / FEPA-P particle-size standards. SiC content ≥98.5%, with slightly higher Fe₂O₃ and free-C tail than the green grade — the difference that puts black SiC at a 15–25% per-kg discount and makes it the dominant choice for coated abrasives, foundry blast media, ceramic-bonded grinding wheels on general steels, refractory aggregate for high-temperature furnace linings, and steelmaking deoxidiser briquettes.

Three product forms cover the demand: F14–F220 particle-size sand for grinding wheels and shot-blast, P12–P2500 P-grit for coated abrasives (sand belts, sandpaper, sand cloth, polishing pads), and 0–1 mm / 1–3 mm / 200F / 325F refractory aggregates at graded SiC purity from 80% to 98% for kiln-furniture batters, steel-furnace linings, glass tank crowns, and ceramic kiln furniture.

The compound is a black to dark-grey crystalline solid, α-SiC (hexagonal) crystal system, Mohs hardness 9.2, density 3.21 g/cm³ (theoretical), bulk density 1.30–1.64 g/cm³ depending on grit. Service temperature 1450°C in oxidising atmospheres and 1600°C in inert or reducing atmospheres. Non-toxic, non-hazardous, RoHS / REACH / SVHC clean.

Technical Specifications

Applications

Coated Abrasives

Sand belts, sandpaper, sand cloth, polishing pads for woodworking (P40–P320 typical), metal finishing (P80–P600), automotive body refinishing (P800–P2000), and decorative-substrate sanding. The P-grit cut is narrower than F-grit cut — coated-abrasive manufacturers specify P-grit to keep belt scratch-pattern uniform.

Vitrified-Bonded Grinding Wheels

General-purpose grinding wheels for cast iron, low-carbon steel, brass, aluminium, and non-ferrous metals. F46–F120 are most common. The vitrified ceramic bond is fired at 1100–1250°C; SiC's thermal expansion matches the bond well, giving high wheel durability. Use green SiC instead when grinding hardened tool steel or carbide tools.

Foundry Blast Media

Sand-blast for surface preparation before painting, plating, or thermal-spray coating. F30–F100 typical. SiC has 30–40% longer service life than corundum at equal blast intensity; recyclable 8–12 times before fragmenting below recoverable size.

Refractory Aggregate

Steel furnace linings (BOF, EAF, AOD), tundish nozzles, ladle linings — black SiC refractory at SiC ≥95% is fired into Si₃N₄- or SiC-bonded shapes that resist steel-slag attack. Glass tank crowns use SiC ≥95% refractory because molten glass corrodes alumina-silicate refractories rapidly above 1500°C. Ceramic kiln furniture (saggers, posts, plates) for fine-ceramic firing uses lower SiC content (80–90%) refractory because the service temperature is lower.

Steel Deoxidiser

SiC briquettes (60–70% SiC) are charged into steel ladles to deoxidise and recarburise; SiC reacts with FeO in the slag to release Si and C into the melt, displacing more expensive ferrosilicon and graphite electrodes.

Wire-Saw Slurry

Black SiC F600–F1200 in glycol carrier for cutting silicon wafers for photovoltaic ingots — lower cost than diamond wire-saw at equivalent throughput. (Note: semiconductor-grade wafer cutting uses green SiC for lower Fe contamination.)

Functional Filler

Carbon-bonded SiC refractory bricks (slide-gate plates, runners, blast-furnace troughs) — black SiC fills the major refractory body, carbon binder protects against thermal-shock spalling.

Selection Guide vs Green Silicon Carbide

Choose black SiC for: cost-sensitive bulk abrasives (sand-belt, sandpaper, sand-cloth manufacture); general-purpose vitrified-bonded grinding wheels (cast iron, low-carbon steel, brass); foundry shot-blast and surface preparation; refractory aggregate for steel furnace, glass tank, ceramic kiln; steelmaking deoxidiser; PV silicon-ingot wire-sawing.

Choose green SiC instead for: precision grinding wheels for tool steel and carbide tools; semiconductor-grade silicon wafer cutting; optical glass and sapphire polishing; stainless steel or titanium polishing where Fe contamination would disqualify black SiC.

The two are interchangeable in grit-standard specification (same F / P / refractory size codes), so process design can specify "black or green SiC F100" with downstream selection on cost. The price differential is typically 15–25% per kg in favour of black.

Equivalent Grades

• Washington Mills Carbolon — North American premium black SiC abrasive
• Saint-Gobain Sika ABR — European black SiC abrasive and refractory grades
• Grindwell Norton (India) — Indian premium supplier
• Elektrokarbon (Slovakia) — EU regional supplier
• Generic Chinese black SiC — commodity grade ≥98.5%, Shandong / Ningxia / Qinghai origin