Boron/aluminum materials

Historically, polymer-matrix composite materials such as boron-epoxy and graphite-epoxy first found favor in applications, followed by metal-matrix materials such as boron-aluminum. Ceramic-matrix and carbon-matrix materials are still under development at this writing, but carbon-matrix materials have been applied in the relatively limited areas of reentry vehicle nosetips, rocket nozzles, and the Space Shuttle since the early 1970s. 

Let s address the issue of nonlinear material behavior, i.e., nonlinear stress-strain behavior. Where does this nonlinear material behavior come from Generally, any of the matrix-dominated properties will exhibit some degree of material nonlinearity because a matrix material is generally a plastic material, such as a resin or even a metal in a metal-matrix composite. For example, in a boron-aluminum composite material, recognize that the aluminum matrix is a metal with an inherently nonlinear stress-strain curve. Thus, the matrix-dominated properties, 3 and Gj2i generally have some level of nonlinear stress-strain curve. 

Triflates of boron, aluminum, and gallium were found to be efficient catalysts in Friedel-Crafts acylations.46 However, these are water-sensitive materials and were required to be used in equimolar quantities to be effective. More recently various water-tolerant and recyclable triflate salts, which were also tested in alkylation, were found to exhibit similar good characteristics in Friedel-Crafts acylations. Although benzene cannot be acylated, Sc triflate,47 48 lanthanum triflates,48-51 and Hf triflate52 usually give high yields of aryl ketones in acylation with acid anhydrides. In many cases, Li perchlorate was found to accelerate the reactions.48 52... 

Zinc borate in PC/ABS and polyamide—when zinc borate is used in conjunction with bisphenol-A-bis-diphenyl phosphate in PC/ABS, it was reported that borophosphate and zinc phosphate were generated during polymer combustion.111 The formation of these materials could be beneficial for passing the more stringent Are tests, such as UL-95 5 V. When Firebrake 500 is used in conjunction with aluminum diethylphosphinate and melamine polyphosphate in polyamide, Schartel et al. reported the formation of boron aluminum phosphate in the condensed phase.112... 

In another paper [ the results of specific heat measurements on 10 metallic alloy samples were considered. This paper discusses specific heat measurements on four composite (i.e., fiber-reinforced) materials, one of which (boron/aluminum) is essentially metallic, and the other three are resin-based. The resin-based composites are more difficult to measure than metallic samples, and in analyzing the resulting data, the assembling of an appropriate fitting function is more complicated. As with the Fe-Ni base alloys [ ], specific heats were measured in the low-temperature range (3 to 20 K) and at the intermediate temperatures 80 K and 300 K. Because of difficulties associated with long thermal-relaxation times at these temperatures, considerable experimental scatter is associated with the results for the resin-based specimens. 

Although absent in the fitting functions for metallic alloys [ ] and metallic composites such as boron/aluminum, the presence of a quadratic term in T is essential for a proper description of the specific heat-temperature dependences of the resin-based materials in the temperature range above 6 K. Below that temperature, good fits are obtained with what are essentially cubic functions. 

The three covalent nitrides are low-density materials with melting points which are higher than those of their parent elements boron, aluminum, and silicon. Of the three, boron nitride has the highest melting point... 

Once boron-containing SSZ-24 is obtained, it can be easily converted to a form having tetrahedrally coordinated framework aluminum species by first calcining the boron-containing material to remove boron from the lattice and then incorporating A1 into the created defect sites by refluxing the material in an aluminum nitrate solution [ 101 ]. True aluminum incorporation into the framework was proven by Al MAS NMR spectroscopy and catalytic activity in Br0n-sted-acid catalyzed reactions [101]. 

The unbonded spot between a silicon atom and a boron atom is a hole that a free electron can occupy. Because this hole attracts an electron, it is viewed as if it were positively charged. Semiconductors that are doped with boron, aluminum, or gallium are p-type semiconductors, the p standing for positive. P-type semiconductors conduct electricity better than pure silicon because they provide spaces that moving electrons can occupy as they flow through the material. 

Materials that are classified as fibers are either polycrystalline or amorphous and have small diameters fibrous materials are generally either polymers or ceramics (e.g., the polymer aramids, glass, carbon, boron, aluminum oxide, and silicon carbide). Table 16.4 also presents some data on a few materials that are used in fiber form. 

The superalloys, as well as alloys of aluminum, magnesium, titanium, and copper, are used as matrix materials. The reinforcement may be in the form of particulates, both continuous and discontinuous fibers, and whiskers concentrations normally range between 10 and 60 vol%. Continuous-fiber materials include carbon, silicon carbide, boron, aluminum oxide, and the refractory metals. However, discontinuous reinforcements consist primarily of silicon carbide whiskers, chopped fibers of aluminum oxide and carbon, or particulates of silicon carbide and aluminum oxide. In a sense, the cermets (Section 16.2) fall within this MMC scheme. Table 16.9 presents the properties of several common metal-matrix, continuous and aligned fiber-reinforced composites. 

Thus, a silicon material having a room-temperature p-type electrical conductivity of 50 (D m) must contain 1.60 X 10 at% boron, aluminum, gaUimn, or indium. 

Except for siUca and natural abrasives containing free siUca, the abrasive materials used today are classified by NIOSH as nuisance dust materials and have relatively high permissable dust levels (55). The OSHA TWA allowable total dust level for aluminum oxide, siUcon carbide, boron carbide, ceria, and other nuisance dusts is 10 mg/m. SiUca, in contrast, is quite toxic as a respkable dust for cristobaUte [14464-46-1] and tridymite [15468-32-3] the allowable TWA level drops to 0.05 mg/m and the TWA for quartz [14808-60-7] is set at 0.1 mg/m. Any abrasive that contains free siUca in excess of 1% should be treated as a potential health hazard if it is in the form of respkable dust. Dust masks are requked for those exposed to such materials (see Industrial hygene). 

Soft magnetic materials are characterized by high permeabiUty and low coercivity. There are sis principal groups of commercially important soft magnetic materials iron and low carbon steels, iron—siUcon alloys, iron—aluminum and iron—aluminum—silicon alloys, nickel—iron alloys, iron-cobalt alloys, and ferrites. In addition, iron-boron-based amorphous soft magnetic alloys are commercially available. Some have properties similar to the best grades of the permalloys whereas others exhibit core losses substantially below those of the oriented siUcon steels. Table 1 summarizes the properties of some of these materials. 

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