How to choose the refractory SiC ceramics & kiln furniture

There're many refractory ceramic materials and each one has its own advantages & function. LENGSTech mainly focus on SiC based ceramics which include RSiC-recrystallized silicon carbide, NSiC-advanced nitride bonded silicon carbide, SiSiC/RBSiC-reaction bonded silicon carbide,SSiC-pressureless sintered silicon carbide, OSiC-oxide bonded silicon carbide. Also, we can provide related materials such as Si3N4-silicon nitride, Cordierite Mullite, Alumina etc.

Now, we're here to introduce these materials and aims to help our customer to identify & select the right one for their working conditions.

1, Recrystallized Silicon Carbide (RSiC or Re-SiC)

    RSiC is made by human hands with slip-casting technology. The working temperature is 1650-1700℃, bulk density 2.72g/cm³, porosity 16-17%, thermal conductivity 23w/mk and SiC content above 99%. RSiC has the advantages of high strength, no deformation, thin, light weight, less engery consumption, space saving, long working life etc.

    RSiC is mainly applied in technical ceramic factories such as alumina, zirconia, ceramic foam/filter/honey comb/fiber, cordierite, mullite, ITO, magnetic etc and also aerospace, metallurgy, chemicals, pharmacy industries & equipments manufacturing. It has very wide applications as customer may consider to use this material at basically temperatures more than 1400℃.

   However, it has dis-advantages too, for example, thermal shock is critical to RSiC as you have to keep dry enough before use it & packed into kiln. And control temperature rising & dropping slowly, naturally. Open the kiln very slowly a little bit and waiting temperature drop to 200-300℃ then open the gate. It's fragile and need to be handled very carefully. It has porosity and cannot be used for chemicals sealing & isolation. RSiC is not precision ceramic and not be able to make into very much accurate parts and tolerances are not that much low. 

2, Nitride Bonded Silicon Carbide (NSiC)

    NSiC can be slip-casted fine type and machine pressed large grains type. LENGSTech is able to provide both of them. Here, we introduce the advanced type made by slip casting technology. The working temperature is below 1450℃, bulk density 2.8g/cm³, porosity below 1% after 2nd time firing and it's 2 times fired, thermal conductivity 17w/mk, SiC content 70-80%, Si3N4 contect 20-30%. NSiC also has the advantages of RSiC. It also has unique advantages like it can contact directly with metal fluids and not adding any Fe.

    NSiC is mainly applied in daily used ceramic factories such as dinnerware, stone ware, sanitary ware, hand-made pottery & porcelain, art ceramics and also electric ceramics as kiln furniture. On the other hand, NSiC is widely applied in metallurgy & chemicals industries because of its unique advantages & low porosity. The anti-thermal shock is better than RSiC, but customers still need to notice the similar dis-advantages.

    The shaped products include plates, setters, beams as kiln furniture and riser tubes, thermocouple protection tubes, radiant tubes, furnace tubes, saggers & crucibles etc.

3, Reaction Bonded Silicon Carbide (SiSiC/RBSiC)

    SiSiC is mainly machine pressed these years as slip-casting is too low production efficiency. SiSiC is very common applied material below working temperature 1380℃ or 1350℃. The bulk density is 3.02g/cm³, porosity below 1%, thermal conductivity 45w/mk, SiC contect 85%. SiSiC has the similar advantages too, but the working temperature has to below 1380℃ or the material will getting soften and bended.

    SiSiC is mainly applied in daily used ceramic factories same like NSiC. But there're much differences as NSiC is mostly made into plates and setters however, SiSiC is mostly made into beams as kiln furniture system. Plates & setters are very rare to be made because this material is not ideal for making into plates. And SiSiC is also used in metallurgy & chemicals industries, but it cannot contact directly with metal fluids which is the main difference with NSiC. And NSiC is better in thermal shock than SiSiC, but SiSiC is much higher in thermal conductivity. Most important, NSiC is much higher in cost than SiSiC. 

    Now, you see the difference between NSiC & SiSiC. So, the perfect combination is NSiC shelves with SiSiC beams. And for metallurgy industry, it's better to know if you need to contact material with metal.

4, Oxide Bonded Silicon Carbide (OSiC)

    OSiC is machine pressed type with expansion gaps on the plates. The max working temperature is below 1400℃ as the technology and materials have increased these years and the max temperature can reach upto 1450℃. And the thickness becomes thinner than before, can do around 10-12mm. The bulk density is 2.8g/cm³. Porosity below 15% and thermal conductivity 14w/mk, SiC contect 85%.

    OSiC is mainly applied in daily used ceramic factories same like NSiC. And it mainly made into plates and supports etc. The difference is OSiC is much lower cost and mostly commonly used than NSiC. The surface is not as perfect like as NSiC, but the function is same and economic.

5, Cordierite Mullite

   This material is the cheapest as kiln furniture compared to NSiC, SiSiC, OSiC. It's thick & heavy and working temperature better below 1200℃, or it will get melted and deformed. The thermal conductivity is very much low, about 1w/mk. So it is mostly applied in big daily used ceramic factories and sanitary ware factories with very bulk wares loading. 

    So, now we see NSiC, OSiC & Cordierite Mullite all can be made into plates, and all of them work with SiSiC beams as combination. The costs from high to low is NSiC>SiSiC>OSiC>Cordierite Mullite. You may choose one of them for your working conditions.

6, Silicon Nitride (Si3N4)

    Si3N4 is mainly applied in metallurgy industry, shaped products are mainly tubes like thermocouple protection tubes, riser/stalk tubes, heating protective tubes and some abrasive parts and customized shapes. The working temperature is below 1000℃, bulk density 3.2 g/cm³, porosity below 1%. It has same function with NSiC, but with very much higher cost and much longer working life.

7, Alumina

    We mainly provide Alumina Rollers, Tubes and Alumina Balls. Can also provide RSiC rollers and SiSiC rollers. 

None of the above materials are precision ceramics, so the complicated designs and very tight tolerances are not suitable to us. I mean the ceramic parts above can be machining, CNC, grinding or making holes etc. But, they're still basically refractory function. Making a qute will take a lot of time and energy, and a lot of people will get involved, we hope you respect their time and not just comparing pricing level or doing a pricing survey in the market.

And we don't provide free samples and don't save instock products because each customer has its own designs. There're nomal procedures to make the ceramic parts, which will need basic production time, so plz kindly make plans in advance. Thank you so much for your kind understanding and cooperation. 

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