Nitrides bonding

Sihcon carbide is comparatively stable. The only violent reaction occurs when SiC is heated with a mixture of potassium dichromate and lead chromate. Chemical reactions do, however, take place between sihcon carbide and a variety of compounds at relatively high temperatures. Sodium sihcate attacks SiC above 1300°C, and SiC reacts with calcium and magnesium oxides above 1000°C and with copper oxide at 800°C to form the metal sihcide. Sihcon carbide decomposes in fused alkahes such as potassium chromate or sodium chromate and in fused borax or cryohte, and reacts with carbon dioxide, hydrogen, ak, and steam. Sihcon carbide, resistant to chlorine below 700°C, reacts to form carbon and sihcon tetrachloride at high temperature. SiC dissociates in molten kon and the sihcon reacts with oxides present in the melt, a reaction of use in the metallurgy of kon and steel (qv). The dense, self-bonded type of SiC has good resistance to aluminum up to about 800°C, to bismuth and zinc at 600°C, and to tin up to 400°C a new sihcon nitride-bonded type exhibits improved resistance to cryohte. 

Compounds with nitrogen-metal (nitride) bonds... 

Why do carbides and nitrides exhibit the properties that make them so useful in industrial applications It is well accepted that these properties are related to the strength of interatomic bonding.2 In transition metal carbides and nitrides, bonding is believed to have both covalent and ionic contributions.3 The carbon or nitrogen atoms occupy interstitial sites in the metal lattice and are believed to promote strong metal-to-nonmetal and metal-to-metal bonds.1 More detailed bonding explanations require... 

The largest quantity of Si3N4 by weight is applied in nitride bonded silicon carbide refractories which are produced in amounts of 20,000 t/year [14]. 

Fig. 4.14 Cavity formation in silicon nitride, (a) Lenticular cavities form at grain boundaries for grades of silicon nitride bonded by highly refractory glasses, (b) Crack-like cavities form at boundaries for grades of silicon nitride that are less refractory, (c) In addition to these interfacial cavities, more irregular, /urn-size cavities are also observed at multigrain junctions in silicon nitride. From Hockey and Wiederhom,94 Luecke et a/.101 and Wiederhom et al.100...

Cast Refrax Silicon Nitride Bonded Silicon Carbide, Form A-2379, Niagara Falls,... 

The most widely manufactured carbide is SiC which has been in use for a long time as an abrasive because of its extreme hardness, either in powdered form or in that of tools bound by inorganic or organic binders. Electrical heating elements are made of SiC with a small excess of silicon which facilitates sintering and reacts with the tar binder producing secondary SiC. Materials bound with oxide or nitride bonds (see below) are used as refractory structural materials in the construction of furnaces... 

Refrax [Carborundum.]. TM for silicon nitride-bonded silicon carbide refractories. Available in brick and precision-formed shapes and parts. 

This product group is based on oxide- or nitride-bonded SiC grains and exhibits an apparent porosity of up to 20% by volume. A fracture surface of a silicon nitride bonded SiC is shown in Fig. 12a. 

Figure 12. Microstructure of various SiC ceramics (a) KSiC, nitride bonded SiC (AnnaSicon 25) (b) RSiC, recrystallized SiC (AnnaNox CK) (c) SiSiC silicon infiltrated SiC (AnnaNox CD), (d) SSiC, B/C doped (Ekasic F), (e) LPSSiC, equiaxed SiC grains (Ekasic T), (f) LPSSiC, platelet SiC grains (ESK), (g) HPSiC,Al-doped (ESK), (h) HIPSiC, undoped (ESK).

Ciftlik AT, Gijs MAM. Parylene to silicon nitride bonding for post-integration of high pressure microfluidics to CMOS devices. Lab Chip2011 12(2) 396. 

Chiao M, Lin L (2006) Device-level hermetic packaging of microiesonators by RTF aluminum-to-nitride bonding. J Microelectromech Syst 15(3) 515-522... 

Ch. 9), to form the saltlike nitrides. Bonding with the transition metals occurs mostly by the sharing of electrons (covalent bonds) and by metallic bonding. Bonding with boron, aluminum, and silicon is essentially covalent (see Ch. 12). 

Mechanical properties Symbol Units Silicon carbide, sintered Silicon carbide, silicon- infiltrated Silicon carbide, recrystallized Silicon carbide, nitride-bonded Boron carbide... 

Density is 1.9 to 2.3 kg/1 and flexural strength 30 to 90 mPa. Silicon oxynitride is used as a lining for cells for the electrolysis of AICI3 to A1 and ZnCl2 to Zn, and as crucibles and tubes for molten salts. It occurs as a constituent of nitride bonds (see silicon nitride, SILICON carbide) and has been used to strengthen silica optical fibres by surface coating. 

These reaction should be followed by the condensation reaction between =Si-NH2 s to form nitride bonds. The incorporation of nitrogens into the glass network by replacing oxygens in the resultant glass fibers was confirmed from the chemical shift of SiK X-ray fluorescence line toward crystalline Si20N2 and Si3N4. It was also shown... 

Fig. 1.1 The records of (a) open porosity of nitride-bonded silicon carbide side lining refractories (in the customer s specification, the open porosity should be below 18 %) (b) the cold crushing strength of nitride-bonded silicon carbide side lining refractories (in the customer s specification, the cold crushing strength should be above 150 Mpa)...

Hardness testing of the refractories is not an everyday procedure, yet it is very useful to remember that the hardness of self-bonded silicon carbide ceramics is in the range of 20-25 GPa, the hardness of nitride-bonded silicon carbide refractories is 16-20 GPa, and the hardness of alumina ceramics is 12-16 GPa, which is three to four times higher than with dense alumina silica dense refractories. 

---