Silicon Carbide – Varieties And Uses
SiC-B
Black Silicon Carbide grains for bonded applications. Used in the manufacture of grinding wheels, polishing blocks, rubbing bricks, honing sticks, foundry fluxes, rice and dal-mill, shellers, for abrasive blasting, lapping, cutting and polishing of gems and granite, antiskid surfacing and other general purpose applications.
SiC-C
Black Silicon Carbide grains specially shaped and sized for coated applications. Used in the manufacture of coated abrasives on paper or cloth backing for wood, chipboard, floor sanding, stainless steel, non-ferrous metals, automative wet sanding and glass.
SiC-G
Green Silicon Carbide grains for bonded applications. Used in the manufacture of grinding wheels for cemented carbides and glass.
SiC-R
Black Silicon Carbide grains for refractory applications. Used in the manufacture of high-temperature refractories, Kiln furniture, bricks, platesetters and other special refractory shapes and crucibles.
SiC-M
Black Silicon Carbide in powder form for metallurgical applications. Used as a de oxidiser in steel mills and foundries with arc/induction furnaces. Also increases silicon and carbon contents in metal, imparts better machinability through reduced chill and increases fluidity of the slag.
SiC-MET
Black Silicon Carbide briquettes for metallurgical applications. Used in foundries as a de -oxidizer and to improve metal cleanliness to achieve desired graphite flake distribution, as silicon and / or carbon raiser, to impart better machinability, to reduce chill and to improve the fludity of the slag.
SiC-Mg
Black and Green Silicon Carbide of micro grit sizes. Used for manufacture of grinding wheels, super finishing stones and polishing of granite, marble, lenses and other general purpose applications.
Silicon Carbide – Specifications
Typical Chemical Analysis
| Variety / Composition | SiC B |
SiC C |
SiC G |
SiC R |
SiC M |
SiC MET |
SiC MG |
|---|---|---|---|---|---|---|---|
| SiC % | 98.0 | 98.0 | 98.0 | 98.0 | 85 | 74 | 97.5 |
| SiO2 | 0.75 | 0.75 | 0.40 | 0.75 | 5 | 8 | 1.00 |
| Free C | 0.40 | 0.40 | 0.40 | 0.40 | 3 | 3 | 0.40 |
| AI2O3 | 0.20 | 0.20 | 0.05 | 0.20 | – | – | 0.20 |
| Free Si | 0.06 | 0.06 | 0.30 | 0.60 | 1 | 1 | 1.00 |
| Surface Fe2O3 | 0.05 | 0.05 | 0.05 | 0.05 | 3 | 3 | 0.15 |
| Others | – | – | – | – | 3 | 11 | – |
| Green Count | 15 max | – | 80 min | – | – | – | – |
Product Range
| Variety | SiC-B & Grit Size | SiC-C & Grit Size | SiC-G & Grit Size | SiC-R & Group Size | SiC-M | SiC-MET | SiC-MG |
|---|---|---|---|---|---|---|---|
| Grit/Group Size | 8-220 | FEPA 12-220 | FEPA 16-220 | 14/24, 30/60, 30/90, 60/90 70 F & 100 F | 150 Microns & Finer | 100 x 100 x 100mm Bricks | 240-1200 in Black, Green & Coated Sizes 1F, 2F & 3F |
Physical Characteristics
| Crystal Form | Hexagonal |
|---|---|
| True Specific Gravity | 3.20 |
| Hardness | Knoop 2500; Moh 9.0-9.5 |
| Bulk Density Range | 1.45-1.75 gms/cc-depending upon grain size. |
| Reaction with Acids | Inert. Very slight reaction with boiling hydrofluoric acid – nitric acid. |
| Reaction with Alkalies | Inert. Slight reaction with hot strong alkalies |
| Melting Point | Dissociates at approximately 2300° C |
Silicon Carbide for Metallurgical Usage
Metallurgical grade Silicon Carbide is a high purity, effective additive in the production of Cast iron and steel having a typical analysis of:
- SIC : 88 %
- FreeC : 1.0 °A)
- Si : 1.0 /0-
- SiO2 : 1.5%
- AI2O3 : 0.2%
- S : <0.005%
Low levels of Aluminium, Sulphur and tramp elements in Silicon Carbide makes it an excellent alternative for 70% Ferro Silicon in the melt furnace.
Silicon Carbide is supplied in sizes of 0 to 12 mm or as briquettes of 100x100x100 mm. size. Each briqutte weights about 1.5 to 1.75 Kgs. the SiC content in the briquettes is about 85% min and Si content is 50% min.
The most predominant metallurgical usage of Silicon Carbde is as a Si and C source in the production of Foundry irons. In all irons, grey, ductile or malleable, Silicon Carbide is used to reduce FeO and MnO in the slag by the reaction:
SiC+FeO = Si+Fe+CO
Iron oxide is the most corrosive constituent of the slag in any refractory system, forming the lowest melting point two phase compounds. In silica linings FeO forms fayalite that melts at 1175°C. This is typically seen as a thin black film on the walls of the induction furnace walls. The stirring action of the induction furnace takes this fluid slag and “homogenizes” it like cream in milk. leaving thousands of very small particles of slag throughout the bath .This FeOSi02 or MnO-Si02 gets carried all theway from the furnace to the mold cavity and forms slag inclusions in the casting surfaces. Silicon Carbide removes the FeO and MnO to eliminate these extremely fluid slags.
Benefits of use of Metallurgical Silicon Carbide includes longer furnace lining life, reduced slag defects, lower shrink and chill tendancy and longer fade time. In ductile iron there is often little or no room for the silicon, 34 Kgs/Mt of SiC is added to the base iron. The same benefits can also be found in grey and malleable irons but there the additions levels are in the range of 10-15Kgsfi1 IT and 5- 10Kgs/MT.
In the cupola melter, SiC briquettes offer excellent Silicon recovery , improved manganese and iron recovery, reduced coke consumption and/or higher spout carbons with cleaner iron that is less prone to shrink and chill.
Silicon yield is in the 85-95% range in the cupola or electric furnace. Since it is the carbon in the SiC that does most of the deoxidising at iron temperatures carbon recoveries will vary with the amount ot oxygen /oxides available, but will generally be in the 80-90% range. SiC does not melt but dissociates exothermcally in to Silicon and Carbon. The silicon and carbon are nascent and highly reactive.
