Advancer® Shelves for Gas Reduction & Soda Kilns
Gas-Fired Kilns
ADVANCER® Kiln Shelves are most widely used in gas fired oxidation and reduction kilns.
Soda Firing
ADVANCER® Kiln Shelves are a smart choice for soda firing where soda is introduced indirectly (not by direct spraying onto shelves). The extremely low porosity of the shelves allows for soda drips to be easily removed by scraping without the time consuming grinding typically associated with conventional cordierite or silicon carbide shelves.
Advancer® (NSiC) vs. Crystolon® Conventional (SiC) Shelves in
All silicon carbide oxidizes and subsequently forms glass on its surface. The actual process is oxidation of the silicon carbide grain. Advancer® is twice fired including in an oxidizing atmosphere to intentionally form a glass layer. The resulting glass surface is actually a protective layer that prohibits further oxidation of the Advancer® SiC matrix beneath. Advancer forms more of a glass layer than Conventional, ram pressed SiC because it has a higher surface area due to its fine grain sizing and virtually zero porosity.
The combustion material (wood) in the atmosphere of these kilns is a likely source of alkalis (e.g., potassium). These alkalis are likely fluxing the glass layer and dropping its viscosity so that it drips more readily. When the glass viscosity drops, two things occur that compound the problem:
1. Oxygen can penetrate the glass layer faster by diffusion thereby increasing the oxidation rate.
2. Oxidation off gases produce bubbles in the glass which is the "frothing" or "foaming" observed. The bubbling is more pronounced in humid environments because a surface reaction with water can give off extra CO gas. The wood is also a likely source of water that can make a bad situation worse.
Once again, the main difference between the oxidation rate of Advancer® and conventional SiC is surface area. Conventional SiC will likely exhibit an increased oxidation rate when the surface oxide (glass layer) is infected by alkalis. However, the oxidation rate will be significantly slower than that of Advancer® given the low surface area. Bubbling or "frothing" would also be less pronounced with Conventional SiC given its low surface area.
Generally speaking Advancer has much better oxidation resistance (i.e. a protective bond) than Conventional SiC, but the ultimate life of Advancer in this environment will have to come from experience. The exact properties of the altered glass layer are difficult to predict, are variable and are greatly influenced by temperature and the type of alkalis that are created as a by-product of the combustion of wood.
If you require any further technical information please get in touch.