Discovery of Silicon CarbideIn 1891 Edward G Acheson produced a small amount of Silicon Carbidewhile conducting experiments with the aim of obtaining a hard material from the reaction of clay and carbon.

He passed a strong electric current from a carbon electrode through a mixtureof clay and coke contained in an iron bowl, which served as the second electrode.

Acheson recognized the abrasive value of the crystals obtained, had themanalyzed, found the formula to be SiC, incorporated The Carborundum Companyin September 1891, and filed application for a patent on May 10, 1892.

SiC Production ProcessSiO₂ + 3C = SiC +2CO

(28 + 2 X 16) + (3 X 12) = 96 (28 + 12) + (2 X (12 + 16)) = 96

8,000 KWH/MT

Approx 6,000MT

Silica Coke/Coal

Sorting Crushing Screening

80% Metallurgical

Grade SiC

20% Crystalline Grade SiC

SiC Furnace Recovery

Inside a SiC Furnace

30-40% SiC

85% SiC

97%+ SiC

SiC Properties high hardness high thermal consistency very good resistance at high temperatures low thermal expansion electrical conductivity is a semiconductor non linear electrical resistance Si and C as an alloying additive - Silicon Carbide

dissociates in molten iron and the silicon reacts with the metal oxides in the melt. This reaction is of use in the metallurgy of iron and steel.

Crystal Structure of Silicon Carbide

SiC Versus FeSi for Metallurgical Applications

The trend to use Silicon Carbide to replace Ferro Silicon in the production of pig iron and gray iron castings is supported by the following reported benefits:

More graphite nuclei are formed Lower impurity level Reduced carbon injection time SiC is a potent de-oxidiser Reduced Cost

Crystal Structure of Silicon Carbide

Benefits of increased formation of Graphite Nuclei

•Improved Machinability•Improved and uniform mechanical properties•Less returns/scrapWhy?The faster the rate of dissolution of silicon carriers, the lower the nucleation effect – SiC does not melt (no liquid phase) and gradually dissolves over an extended period – graphite is “protected” by SiC enriched areas

Closely connected Si and C leads to local hypereutectic “super concentration” and maximum graphite formation

SiC contributes Silicon but also 50 atomic % carbon increasing graphite formation and its “protection” in the melt.

increased formation of Graphite Nuclei (Continued…)

Dissolution of SiC is endothermic, slowing the diffusion rate which further stabilises the graphite

Metgrade SiC contains a small percent of SiO₂, melting at 1,700 C forming a protective skin on the SiC particle and ⁰further positively influencing formation and life of the graphite

By Contrast, Ferro Silicon… Melts at 1,210 exothermically⁰ Contains no carbon which, in the case of graphite

nucleation can only originate from the melt

Use of Silicon Carbide reduces the quantity of carbon containing sulphur to be introduced – Lower quantities of de-sulphurising agents (CaC₂) are required

Silicon Carbide is relatively low in aluminium (SiC - 0.3% vs FeSi - 2%) N, H and S

Benefits of lower impurity levels

Silicon and Carbon are released from SiC as charged atoms. Carbon works as a de-oxidiser removing free oxygen and reducing unstable oxides (e.g. FeO and MnO), typically:

SiC + FeO = Si + Fe + CO

Removing these elements to the slag and increasing the life of furnace linings

Benefits of SiC as a de-oxidising agent

Cost Benefit Analysis SiC vs FeSiFeSi + C cost analysis

Assumptions

Required % Carbon 3.3% FeSi 75% SiliconRequired Silicon 2.5% 25% FeSteel Scrap cost/kg R 3.50

Ferro silicon cost/kg R 13.50

Carbon cost/kg R 4.50

Steel scrap Silicon 0.3%

Steel scrap Carbon 0.4%

Based on melt of kg 1 000

Component Yield kg cost/kg Total cost

Steel scrap 95% 1 053 R 3.50 R 3 684

Ferro Silicon 90% 33 R 13.50 R 440

Carbon 100% 29 R 4.50 R 131

Add (FeSi) Fe benefit 100% 8 R 3.50 R -29

R 4 226

Cost Benefit Analysis SiC vs FeSiSiC + C cost analysis SiC = (70% Si, 30% C)Assumptions SiC 85%Required % Carbon 3.3% Silicon 60%Required Silicon 2.5% Carbon 26%

Steel Scrap cost/kg R 3.50 Free C 5%SiC cost/kg R 10.00

Carbon cost/kg R 4.50 Steel scrap Silicon 0.3% Steel scrap Carbon 0.4% Based on melt of kg 1 000

Component Yield kg cost/kg Total costSteel scrap 95% 1 053 R 3.50 R 3 684 Silicon Carbide 90% 41 R 10.00 R 411 Carbon 100% 29 R 4.50 R 131 Add Free C benefit 100% 13 R 4.50 R -56 R 4 169

PresenterGeordie Osler CEO: Sublime Technologies

  BSc (Eng) Mech (Hon) : UCTB.Comm : UNISA Columbus Stainless Steel 1995 – 1997Pyromet 1997- 2006 Sublime 2001 - present