Silicon carbide heating elements

Microwave technology has also been used for the Dimroth rearrangement of the aminothiazine 964 to the pyrimid-inethione 965. The optimized conditions involved heating a solution of the thiaztne 964 in toluene together with a silicon carbide heating element at 220°C for 30min to provide a 68% product yield after recrystallization <2006JOC4651>. 

Globar [Carborundum], TM for silicon carbide heating elements and resistors and accessories. 

Fig. 5 a) Silicon carbide heat element for hucto system devices b) Alumina hollow fiber for micro systan devices... 

The main disadvantage of silicon carbide heating elements is that they are extremely brittle and must be handled carefully, especially when being installed and wired. 

Crusilite. A silicon carbide heating element. (Trade-name Morganite Electroheat Ltd, London.). 

Silicon Carbide Heating Elements make use of SiC s semiconducting properties. They are made by proprietary methods, either from pressed or tamped a-SiC fired at 2200°C, or from P-SiC at a lower temperature. The objective is to form a central zone of high electrical resistance in a rod or tube, e.g. by using capillary suction to infiltrate the tube ends with molten silicon metal. The result is a coarse crystal structure cross-section... 

The furnace is heated with silicon carbide resistant elements to 1600 °C. The samples were impacted in the furnace by a pendulum hammer having a 23.65 in. arm length and a 0.411 lbs wedge-shaped, sintered alumina head, as shown in Fig. 2.2. 

Two common sources of infra-red radiation are the Nernst filament, an element of rare earth oxides, mainly zirconium oxide, fused together in a rod between 1 mm and 2 mm diameter, and the Globar, a larger diameter rod of silicon-carbide. Both elements are heated electrically, and at temperatures between 1,200° and 2,000° emit radiation with a maximum between 1 5// and 2 5// rather like a black body radiator. 

From 760 to 960°C, circulating fans, normally without baffles, are used to improve temperature uniformity and overall heat transfer by adding some convection heat transfer. They create a directional movement of the air or atmosphere but not the positive flow past the heating elements to the work as in a convection furnace. Heating elements ate commonly chrome—nickel alloys in the forms described previously. Sheathed elements are limited to the very low end of the temperature range, whereas at the upper end silicon carbide resistors may be used. In this temperature range the selection of heating element materials, based on the combination of temperature and atmosphere, becomes critical (1). 

Chrome—nickel alloy heating elements that commonly ate used in low temperature furnaces are not suitable above the very low end of the range. Elements commonly used as resistors are either silicon carbide, carbon, or high temperature metals, eg, molybdenum and tungsten. The latter impose stringent limitations on the atmosphere that must be maintained around the heating elements to prevent rapid element failure (3), or the furnace should be designed to allow easy, periodic replacement. 

Silicon carbide has very high thermal conductivity and can withstand thermal shock cycling without damage. It also is an electrical conductor and is used for electrical heating elements. Other carbides have relatively poor oxidation resistance. Under neutral or reducing conditions, several carbides have potential usehilness as technical ceramics in aerospace appHcation, eg, the carbides (qv) of B, Nb, Hf, Ta, Zr, Ti, V, Mo, and Cr. Ba, Be, Ca, and Sr carbides are hydrolyzed by water vapor. 

Globars" (silicon carbide rods) are the next most frequently used furnace heating elements. They will operate continuously at 1450 °C. and intermittently at 1500 C. A newer t3q>e of element. Mo wire coated with silicide, i.e.- MoSi2(to protect the Mo wire against oxidation), heis become... 

The dihydropyrimidinethione 30 has been obtained by microwave-induced rearrangement of a dihydrothiazine, using silicon carbide as a passive heating element <06JOC4651>. 

Heating elements -rhenium and rhenium alloys as [RHENIUM AND RHENIUM COMPOUNDS] (Vol 21) -silicon carbide in [CARBIDES - SILICON CARBIDE] (Vol 4) -use of silicon carbide [CARBIDES - SILICON CARBIDE] (Vol 4)... 

Method 2 produces what is usually referred to as self-bonded SiC by a process essentially the same as that developed for nuclear applications [2] and known as Refel silicon carbide. Refel silicon carbide contains a finely dispersed residual silicon phase accounting for between 5 and 10% of the total volume, the precise amount depending upon the porosity of the original preform. In the case of self-bonded silicon carbide elements the residual silicon is volatilized away by a final heat-treatment at over 2500 °C when recrystallization occurs resulting in grain growth and further bonding between primary and secondary carbide phases. 

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