Silicon Carbide Manufacturing Guide

This guide explains how silicon carbide is manufactured using the Acheson process, from raw-material preparation and electric resistance furnace operation to lump crushing and product classification. It also shows how furnace temperature and position influence SiC purity, crystal structure, and the resulting silicon carbide grades.

Understanding these production stages helps buyers evaluate metallurgical-grade silicon carbide by chemistry, recovery, sizing, and consistency rather than by nominal SiC content alone.

FerrumX’s silicon carbide production

FerrumX uses dedicated power infrastructure to support the high and stable electrical load required for silicon carbide smelting.

Acheson Method

Silicon carbide was accidentally discovered by E.G. Acheson in 1891 while synthesizing synthetic diamond. As shown in the figure below, an electric current is passed through a carbon electrode surrounded by a mixture of SiO₂ and carbon powder. The heat generated by the current produces silicon carbide. This method is known as the Acheson process.

Reaction

The reaction is as follows: 96 g of raw materials are charged, producing 40 g of silicon carbide, while the remainder is released as gas (CO). Because carbon monoxide is toxic and combustible, furnace off-gas requires controlled collection and treatment in accordance with the applicable plant process and environmental requirements.

SiO₂(60g)+3C(36g)→SiC(40g)+2CO(56g)

When silicon carbide is produced using the Acheson process, the high temperatures around the electrode allow for high-quality (high-purity) silicon carbide. However, as the distance from the electrode increases, the temperature drops and the SiC yield decreases. Therefore, only the central portion is selected as the final product, while the lower-purity peripheral material (below 85%) is recovered and reused in the next furnace charge along with new raw materials.

Raw Materials

Silicon Source

SiO₂ is used as the silicon source, specifically quartz and silica sand. Silica sand has high purity (low impurities), especially low Al content. Green silicon carbide uses silica sand as raw material, and black silicon carbide uses quartz as raw material. However, for quality and productivity reasons, in recent years, the proportion of silica sand in black silicon carbide raw material has increased. As listed in the table, the SiO₂ purity of quartz and silica sand used is above 99%. This is due to our factories being located in regions with abundant raw materials.

Component	Silica Ore	Silica Sand
SiO₂	99.4	99.8
Al₂O₃	0.26	0.01
Fe₂O₃	0.16	0.01

Carbon Source

Generally, petroleum coke is used as the carbon source. FerrumX uses low-sulfur petroleum coke with low sulfur content.

SiO₂/C Ratio, Residual SiO₂, Residual C

According to the reaction formula, the ratio of carbon source to silicon source in raw material (called the carbon coefficient) is 0.6. If mixed according to this value, it should produce 100% SiC. In reality, due to various reasons, the reaction rate does not reach 100%. The product contains not only the desired silicon carbide but also unreacted C (F-C) and unreacted SiO₂ (F-SiO₂). To improve this, during raw material charging, observe the reaction tendency and slightly adjust the carbon coefficient. The production goal always targets SiC with low F-C and F-SiO₂ content.

Additionally, to reduce F-C and F-SiO₂ in the product, mix raw materials rich in F-C to produce large pieces, then use washing and burning methods to reduce residual carbon (F-C), resulting in SiC with low F-SiO₂ and low F-C.

Manufacturing of Silicon Carbide Lumps

The diagram shows the manufacturing process of silicon carbide Lumps(Acheson method).

At FerrumX, one manufacturing cycle takes 9 days. As shown, the transformer supplies two furnaces: one furnace is electrified while the other is in the removal and charging stage. The process follows a cycle of “charging → electrification → removal.”

Grade 1, 2, and 3 Recovered Raw Materials

There are several methods to classify silicon carbide by grade, such as >98%, >97%, >95%, >90%, >85%. At FerrumX, >98% is Grade 1, >88% is Grade 2, and >70% is Grade 3.

SILICON CARBIDE SMELTING PRODUCT INOICATORS

Grade	SIC(%)	F.C(%)	Fe2O3(%)	H2O(%)
Grade I	≥98.50	≤0.25	≤0.30	≤0.30
Grade II	≥88.50	≤2.80	≤3.00	≤0.50
Grade III	≥70.50	≤8.00	≤3.50	≤1.00

SILICON CARBIDE PROCESSING PROOUCTINOICATORS

Grade	SIC(%)	F.C(%)	Fe2O3(%)	H2O (%)
99#	≥99.00	≤0.10	≤0.10	≤0.10
98#	≥98.00	≤0.25	≤0.30	≤0.30
97#	≥97.00	≤0.30	≤0.40	≤0.30
95#	≥95.00	≤1.00	≤1.00	≤0.30
88#	≥88.50	≤2.80	≤3.00	≤0.50
70#	≥70.50	≤8.00	≤3.50	≤1.00

The table lists the chemical compositions of Grade I, II, and III. The diagram shows the positions of Grade I, II, and III in the Acheson furnace. The farther outward, the lower the temperature, and the lower the silicon carbide formation ratio.

The crystallized phases undergo the following changes: Grade I is mainly 6H (6-layer hexagonal structure), Grade II, and III is 15R (15-layer rhombohedral) and 4H (4-layer hexagonal), with an increase in peak quantity. The unreacted outer layer acts as an insulating layer.

Black Silicon Carbide and Green Silicon Carbide

Composition Characteristics

Silicon carbide is mainly divided into black silicon carbide and green silicon carbide. Pure silicon carbide is colorless and transparent. It becomes black or green due to solid solution of impurities such as Al and N. The more impurities, the darker the color. At FerrumX, both black and green silicon carbide are produced from quartz. For green silicon carbide, salt is added to remove Al.

Electricity Consumption

FerrumX electricity consumption is 6,000–10,000 kWh/t. Black silicon carbide consumes less electricity, while green silicon carbide consumes more. The difference exists because green silicon carbide has higher quality requirements. Grade 2 is not used as product, so the output per furnace is smaller, resulting in higher electricity consumption. Electricity is the main energy consumption in silicon carbide production. In regions with high electricity prices, products made from purchased electricity have been decreasing. FerrumX produces electricity at 0.03 USD/kWh, which is a strong advantage and a key reason we reduce costs.

Effect of Aluminum

The formation of the 4H phase depends on the aluminum content in silicon carbide crystals. Higher aluminum content increases 4H phase content; without aluminum, the 4H phase is not observed. Most aluminum comes from raw materials, especially the silicon source (quartz, etc.), and remains largely in the crystal. To increase silicon carbide purity, strong acid treatment is sometimes applied, but metals such as iron cannot be removed. Completely removing aluminum dissolved in crystals is very difficult.

Color and Impurities

The representative crystal phase of silicon carbide is 6H. Pure 6H silicon carbide is colorless and transparent. In the market, silicon carbide is sold in various colors, mostly black or green. Color is affected by impurities. Higher purity silicon carbide appears green, caused by impurity atoms such as nitrogen. The table below shows the relationship between trace elements in silicon carbide crystals and color.

Impurities	Al	Al(High)	N	N	N	N	N (Low)	N
Polytype	6H	6H	24R	6H	3C	27R	4H	8H
Color	Blue	Purple	Purple	Green	Yellow-green	Red	Light brown	Orange-yellow

F-Si in Products

A small amount of silicon is generated during reaction in the high-temperature part of the central electrode. As shown, Grade 1 near the furnace center has more silicon than Grade 2. When used as refractory material, the presence of silicon is sometimes undesirable.

Element	Content	Element	Content
SiC	98.19	Mg	0.001
Si (in SiC)	68.73	Ti	0.01
C (in SiC)	29.46	Fe₂O₃	0.19
Free Silicon	0.019	Al₂O₃	1.83
SiO₂	0.45	CaO	0.04
Free Carbon	0.40	MgO	0.002
Fe	0.13	TiO₂	0.017
Al	0.97	S	0.001
Ca	0.026	P	0.0019

Process Control and Energy Management

Furnace Temperature and Reaction Time Control

In the Acheson process, the furnace core typically operates at approximately 2,000–2,500 °C. Power input and reaction time are adjusted according to furnace design and the raw-material charge. Temperature distribution strongly influences SiC formation, purity, and crystal development.

Electricity Consumption Control

Electricity consumption varies with furnace design, feed composition, operating practice, and the target grade. Green silicon carbide generally requires tighter raw-material and process control than black silicon carbide, which can increase energy demand and reduce usable yield. Stable power supply and careful furnace control are therefore important production considerations.

Precise Impurity Control

Quality control focuses on aluminum, iron, sulfur, free silicon, free carbon, and residual silica because these constituents can affect crystal development and downstream performance. Acceptance limits should be matched to the intended metallurgical, refractory, or abrasive application.