Compressive silicon carbides

Armor. Silicon carbide is used as a candidate in composite armor protection systems. Its high hardness, compressive strength, and elastic modulus provide superior ballistic capability to defeat high velocity projectile threats. In addition, its low specific density makes it suitable for applications where weight requirements are critical (11). 

The values of the creep parameters (p, n and Q) identifying the superplastic behaviour of ceramic-related materials are not unique to such materials, nor to the same type of materials. As shown in the review papers, these parameters are very similar in tension as in compression in zirconia-based materials (probably the most widely studied ceramics in the widest experimental conditions), although that depends strongly on the purity of the ceramics 5,7 however, their behaviour seems to be very different in compression than in tension when an aid-sintering phase is necessary during the processing, as in silicon carbide and silicon nitride ceramics.8... 

According to the data in Table 25.5 and to Eq. (25.6) the compressive strength of filaments of refractory materials such as carbon and silicon carbide have compressive strengths about 10 times as large as those of organic fibres. This would seem to be a serious restriction to the use of organic polymers such as aramids in their application in composites. For most of the applications this restriction is of minor importance, however, since long before ac max is reached, instability in the construction will occur. The resistance of a column or a panel under pressure is proportional to the product of a load coefficient and a material efficiency criterion ... 

Results on other composite materials are similar to those obtained by Morrell and Ashbee.56 Creep asymmetry has been demonstrated for two grades of siliconized silicon carbide,35,60,61 SiC whisker-reinforced silicon nitride,53 HIPed silicon nitride,29 and vitreous-bonded aluminum oxide.29 Again, stresses required to achieve the same creep rate were at least a factor of two greater in compression than in tension. In two grades of siliconized silicon carbide,35,58-61 the stress exponent changed from 4 at creep rates below... 

Particulate microcomposite Silica, carbon black, calcium carbonate, glass bead, glass balloons, silicon carbide Mechanical mixing and casting, compression moulding, matched-die moulding... 

Some elements such as carbon and silicon m be considered as ceramics. Traditional ceramic raw materials include cl minerals such as kaolinite, whereas more recent materials include aluminium oxide, known as alumina and also include silicon carbide and tungsten carbide. Ceramic materials are brittle, hard, and strong in compression, weak in shearing and tension. They... 

Uniaxial and triaxial compression tests of silicon-carbide ceramics under quasistatic loading conditions were performed by Brannon et al. [33]. Their SiC-N specimens were prepared in the form of a right circular cylinder, as is indicated schematically in Fig. 1.43a next to the experimental set-up. 

Fig. 5.16 Stress-strain curves of silicon nitrides, where, A and B are mostly (a -sialon deformed in compression, and C and D are mostly j -sialon with 30 vol% silicon carbide deformed in tension. Note that A and B have much less strain hardening than C and D [3], With kind permission of John Wiley and Sons...

Table 13.1 compares the mechanical properties under compression of crosslinked vanadia (X-VO and crosslinked surfactant-templated silica (X-MP4-T045) with other strong materials. For application in armor, the figure of merit is the specific energy absorption, where both crosslinked vanadia and templated silica far surpass even silicon carbide ceramics. 

Jones SC, Robinson MC, Gupta YM (2003) Ordinary refractive index of sapphire in unitixial tension and compression along the c axis. J Appl Phys 93 1023-1031 Balzaretti NM, da Jornada JAH (1996) Pressure dependence of the refractive index of diamond, cubic silicon carbide and cubic boron nitride. Solid State Commun 99 943-948 Balzaretti NM, da Jornada JAH (1996) Pressure dependence of the refractive index and electronic polarizability of LiF, MgF2 and CaF2. J Phys Chem Solids 57 179-182... 

Ultimate Compressive Strength of Investment Cast Silicon Carbide SCS-Al... 

The high-density iimer pyrolytic carbon (IPyC) layer protects the kernel and buffer from chemical attack by chlorine compounds, which are generated as byproducts during deposition of the silicon carbide (SiC) layer. The IPyC layer also provides a surface for deposition of the SiC layer and delays transport of radionuclides to the SiC layer. The IPyC layer shrinks with the accumulation of fast neutron fluence, which helps to maintain the SiC layer in compression, provided the bond between the IPyC and SiC layers remains strong and continuous during irradiation. 

Less common situations to consider are when studies of surface contamination are required and when the surface cannot be separated and brought to the instrument. In the first example, a practical solution is to grind a small amount of alkali halide powder (KBr or KCl) at the point of the contamination. This will result in the transfer of some of the contaminant to the alkali halide, and this in turn may be examined either by the compressed pellet technique or by diffuse reflectance. A way to assist this surface extraction is to add a few drops of a solvent, such as methylene chloride, in the area of the contamination. In the second situation, sampling may be performed by gently abrading the surface with silicon carbide paper. This action will transfer a small amount of the surface to the abrasive paper, and this in turn may be examined with the aid of a diffuse reflectance accessory. 

One other technique, previously described, is the abrasion of the surface of the sample with a silicon carbide paper. The abraded material may be collected as a dust and analyzed as a compressed alkali halide pellet or by diffuse reflectance. Alternatively, the spectrum of the sample from the surface of the abrasive paper may be obtained with a diffuse reflectance accessory. 

A very tough 177-204 C versatile curing resin with a continuous service temperature range of -59 to 204 C, and short-term up to 232 C, and designed for RTM. Offers excellent compression properties after impact. Suitable for glass, carbon, aramid, silicon carbide and other fibre reinforcement. 

This plastic has high mechanical and physical strength properties including a high compression strength. PBI can bear loads for short periods at temperatures up to 650°C (1,200 F). When reinforced with silicon-carbide fibers, it can thwart an attack even from laser weapons. It has a low coefficient both of friction and of thermal expansion (0.000013 in./in./T). 

---