Carbides thermal stability

These solvents are characterized by a high affinity for aromatics, good thermal stability, and rapid phase separation. The Tetra extraction process by Union Carbide (Figure 2-2) uses tetraethylene glycol as a solvent. The feed (reformate), which contains a mixture of aromatics, paraffins. 

In thick samples, a boron oxide/boron carbide crust has been detected on the surface of the polymer. This inorganic surface layer has a shielding effect on the inner polymer layers, further enhancing the thermal stability of the material. Poly(m-carborane-siloxane)s have therefore been considered as surface coatings for organic materials, providing protection from erosion effects. 

The Van Arkel process can also be used to prepare actinide metals if the starting compound reacts easily with the transporting agent (I2). The thorium and protactinium carbides react with I2 to give volatile iodides above 350°C these are unstable above 1200°C and decompose into the actinide metals and iodine. Attempts to prepare other actinides, such as U and Pu, through the process were not successful, because from Th to Pu along the actinide series, the vapour pressure of the iodide decreases and the thermal stability increases. 

Any one of several commercially available PVC paste resins may be used. [Exon 654 (Firestone) and QYNV (Union Carbide) are used in the formulations given in Table I Geon 121 (Goodrich) has also been used (17, 19).] The various resins may not yield identical values for some of the propellant properties such as fluidity of uncured propellant, and the physical properties and thermal stability of the cured propellant,... 

Semiconducting Properties. Silicon carbide is a semiconductor it has a conductivity between that of metals and insulators or dielectrics (4,13,46,47). Because of the thermal stability of its electronic structure, silicon carbide has been studied for uses at high (>500° C) temperature. The Hall mobility in silicon carbide is a function of polytype (48,49), temperature (41,42,45—50), impurity, and concentration (49). In n-type crystals, activation energy for ionization of nitrogen impurity varies with polytype (50,51). 

Ucon HTF-500. Union Carbide Corp. manufactures Ucon HTF-500, a polyalkylene glycol suitable for liquid-phase heat transfer. The fluid exhibits good thermal stability in the recommended temperature range and is inhibited against oxidation. The products of decomposition are soluble and viscosity increases as decomposition proceeds. The vapor pressure of the fluid is negligible and it is not feasible to recover the used fluid by distillation. Also, because the degradation products are soluble in the fluid, it is not possible to remove them by filtration any spent fluid usually must be burned as fuel or discarded. The fluid is soluble in water. 

Meial Mairix Composites. Silicon carbide particles are contributing to easy-to-cast metal-matrix composites (MMCs). When compared with their non-reinforced counterparts, the SiCp/Al components are more wear resistant, stiffer, and stronger, accompanied by improved thermal stability. Additional advantages include lower density and lower cost. Nearly all prior aluminum MMCs required labor-intensive methods, such as powder metallurgy, diffusion bonding, squeeze casting, or thermal spraying. 

The V(110) surface was cleaned by repeated cycles of Ne+ sputtering at 600 K (1.0 kV 3 pA) followed by annealing to 1200-1400 K, as described in detail elsewhere.10 The impurity levels of residual C and S were less than 2% and 1% of a monolayer (ML), respectively, based on the AES measurements. The residual O impurity on the surface was estimated to be less than 6% of a ML from the HREELS measurements.10 Thin vanadium carbide films were produced by exposing the clean V(110) surface to ethylene or 1,3-butadiene at 600 K. Details concerning the formation and thermal stability of the thin carbide films on V(110) can be found elsewhere.4,11... 

Shimoo, T., Takeuti, H., Okamura, K., (2001), Thermal stability of polycarbosilane-derived silicon carbide fibers under reduced pressures , J. Am. Ceram. Soc., 84, 566-570. 

Most of these are gases or volatile liquids, some with little thermal stability, (CH4, CS2, CCI4) but the carbides of silicon and boron are thermally... 

Boron carbide (B4C) is one of the hardest known materials with excellent properties of low density, very high chemical and thermal stability, and high neutron absorption cross-section. Bulk B4C is conventionally synthesized by high temperature (up to 2400 °C) reactions, such as the carbothermal reduction of boric acid or boron oxide. Nanocrystalline B4C was solvothermally synthesized in CCI4 at 600 °C (Reaction (32)). 

Nonoxide ceramics, such as silicon carbides, silicon nitrides, and boron nitrides, have unique mechanical and functional characteristics. Silicon carbides with high thermal conductivity, high thermal stability, excellent mechanical strength, and chemical inertness are especially considered as effective catalyst supports. 

Zhao[266] demonstrated the successful synthesis of highly ordered mesoporous silicon carbides with unusually high surface areas (430-720 m2/g), uniform pore sizes (<3.5 nm), and extremely high thermal stabilities (up to 1400 °C) replicated by mesoporous silica hard templates via a one-step nanocasting process. Highly ordered 2-D hexagonal (p6m) and bicontinuous cubic (Ia3d) SiC nanowire arrays have been cast from the hard templates, mesoporous silica SBA-15 and KIT-6, respectively. 

Briefly, three points of porous SiC-based catalytic support properties can be emphasized (i) SiC shows very good mechanical properties which gives resistance to erosion and attrition, in addition to a high thermal stability (ii) SiC has a higher thermal conductivity compared with the more conventional supports which could prevent the metal sintering (iii) SiC is particularly inactive with respect to chemical reagents such as acids or bases. Therefore, the active phase can be easily reprocessed after simple acidic or basic treatments. Among refractory materials, the thermal conductivity of silicon carbide, SiC (500 W m-1K-1 for crystalline state, at room temperature) is close to that of metals such as Ag or Cu (400-500 Wm K-1). 

Polycarbosilanes can exhibit thermal stabilities greater than the analogous polysiloxane , contrary to their relative bond energies (Si—C, 78 kcalmol Si—O, 106 kcal mol" ). Thus polydimethylsilane is polymerized by heating the hexamer to 300-500°C, forming a product with thermal stability greater than 500°C and that can be spun into fiber, which in turn can be thermally oxidized, forming j5-silicon carbide, SifCHj) -,. 

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