Silicon Carbide


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Silicon Carbide by Geordie Osler, CEO of Sublime Technologies

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Silicon Carbide

  1. 2. Discovery of Silicon Carbide <ul><li>In 1891 Edward G Acheson produced a small amount of Silicon Carbide </li></ul><ul><li>while conducting experiments with the aim of obtaining a hard material </li></ul><ul><li>from the reaction of clay and carbon. </li></ul><ul><li>He passed a strong electric current from a carbon electrode through a mixture </li></ul><ul><li>of clay and coke contained in an iron bowl, which served as the second electrode. </li></ul><ul><li>Acheson recognized the abrasive value of the crystals obtained, had them </li></ul><ul><li>analyzed, found the formula to be SiC, incorporated The Carborundum Company </li></ul><ul><li>in September 1891, and filed application for a patent on May 10, 1892. </li></ul>
  2. 3. SiC Production Process
  3. 5. SiC Furnace Recovery
  4. 6. Inside a SiC Furnace
  5. 7. SiC Properties <ul><li>high hardness </li></ul><ul><li>high thermal consistency </li></ul><ul><li>very good resistance at high temperatures </li></ul><ul><li>low thermal expansion </li></ul><ul><li>electrical conductivity </li></ul><ul><li>is a semiconductor </li></ul><ul><li>non linear electrical resistance </li></ul><ul><li>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. </li></ul>Crystal Structure of Silicon Carbide
  6. 8. SiC Versus FeSi for Metallurgical Applications <ul><li>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: </li></ul><ul><li>More graphite nuclei are formed </li></ul><ul><li>Lower impurity level </li></ul><ul><li>Reduced carbon injection time </li></ul><ul><li>SiC is a potent de-oxidiser </li></ul><ul><li>Reduced Cost </li></ul>Crystal Structure of Silicon Carbide
  7. 9. Benefits of increased formation of Graphite Nuclei <ul><li>Improved Machinability </li></ul><ul><li>Improved and uniform mechanical properties </li></ul><ul><li>Less returns/scrap </li></ul><ul><li>Why? </li></ul><ul><li>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 </li></ul><ul><li>Closely connected Si and C leads to local hypereutectic “super concentration” and maximum graphite formation </li></ul><ul><li>SiC contributes Silicon but also 50 atomic % carbon increasing graphite formation and its “protection” in the melt. </li></ul>
  8. 10. increased formation of Graphite Nuclei (Continued…) <ul><li>Dissolution of SiC is endothermic, slowing the diffusion rate which further stabilises the graphite </li></ul><ul><li>Metgrade SiC contains a small percent of SiO₂, melting at 1,700⁰C forming a protective skin on the SiC particle and further positively influencing formation and life of the graphite </li></ul><ul><li>By Contrast, Ferro Silicon… </li></ul><ul><li>Melts at 1,210⁰ exothermically </li></ul><ul><li>Contains no carbon which, in the case of graphite nucleation can only originate from the melt </li></ul>
  9. 11. <ul><li>Use of Silicon Carbide reduces the quantity of carbon containing sulphur to be introduced – Lower quantities of de-sulphurising agents (CaC₂) are required </li></ul><ul><li>Silicon Carbide is relatively low in aluminium (SiC - 0.3% vs FeSi - 2%) N, H and S </li></ul>Benefits of lower impurity levels
  10. 12. <ul><li>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: </li></ul><ul><li>SiC + FeO = Si + Fe + CO </li></ul><ul><li>Removing these elements to the slag and increasing the life of furnace linings </li></ul>Benefits of SiC as a de-oxidising agent
  11. 13. Cost Benefit Analysis SiC vs FeSi FeSi + C cost analysis           Assumptions   Required % Carbon 3.3% FeSi 75% Silicon Required Silicon 2.5%   25% Fe Steel 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  
  12. 14. Cost Benefit Analysis SiC vs FeSi SiC + 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 cost Steel 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
  13. 15. Presenter Geordie Osler CEO: Sublime Technologies   BSc (Eng) Mech (Hon) : UCT B.Comm : UNISA   Columbus Stainless Steel 1995 – 1997 Pyromet 1997- 2006 Sublime 2001 - present