Boron aluminum oxide

The principal reinforcements for metal matrices include continuous fibers of carbon, boron, aluminum oxide, silica, aluminosilicate compositions and... 

Boron oxide (s. a. Boron aluminum oxide) 13,131 suppl. 26... 

Glass fiber. From the melt of naturally occurring silicon, boron, aluminum oxides, etc., textile glass... 

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. 

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). 

The third control is by use of a fixed burnable poison. This consists of rods containing a mixture of aluminum oxide and boron carbide, included in the initial fuel loading using the vacant spaces in some of the fuel assembhes that do not have control clusters. The burnable poison is consumed during operation, causing a reactivity increase that helps counteract the drop owing to fuel consumption. It also reduces the need for excessive initial soluble boron. Other reactors use gadolinium as burnable poison, sometimes mixed with the fuel. 

These are made of boron carbide ia a matrix of aluminum oxide clad with Zircaloy. As the uranium is depleted, ie, burned up, the boron is also burned up to maintain the chain reaction. This is another intrinsic control feature. The chemical shim and burnable poison controls reduce the number of control rods needed and provide more uniform power distributions. 

Unlike boron, aluminum, gallium, and indium, thallium exists in both stable univalent (thaHous) and trivalent (thaUic) forms. There are numerous thaHous compounds, which are usually more stable than the corresponding thaUic compounds. The thaUium(I) ion resembles the alkaU metal ions and the silver ion in properties. In this respect, it forms a soluble, strongly basic hydroxide and a soluble carbonate, oxide, and cyanide like the alkaU metal ions. However, like the silver ion, it forms a very soluble fluoride, but the other haUdes are insoluble. Thallium (ITT) ion resembles aluminum, gallium, and indium ions in properties. 

Chrornium—cobalt—alurninum oxide [68187-11-1]—Cl Pigment Blue 36, Cl No. 77343. A blue—green pigment obtained by calcining a mixture of chromium oxide, cobalt carbonate, and aluminum oxide. It may contain small amounts (<1% each) of oxides of barium, boron, siUcon, and nickel. 

Metallic elements with low ionization energies commonly form basic ionic oxides. Elements with intermediate ionization energies, such as beryllium, boron, aluminum, and the metalloids, form amphoteric oxides. These oxides do not react with or dissolve in water, but they do dissolve in both acidic and basic solutions. 

For example, the reaction of nitronates (123) with a zinc copper pair in ethanol followed by treatment of the intermediate with aqueous ammonium chloride a to give an equilibrium mixture of ketoximes (124) and their cyclic esters 125. Heating of this mixture b affords pyocoles (126). Successive treatment of nitronates (123) with boron trifluoride etherate and water c affords 1,4-diketones (127). Catalytic hydrogenation of acyl nitronates (123) over platinum dioxide d or 5% rhodium on aluminum oxide e gives a-hydroxypyrrolidines (128) or pyrrolidines 129, respectively. Finally, smooth dehydration of a-hydroxypyrrolidines (128) into pyrrolines (130f) can be performed. 

Many barium aluminosilicate-based compositions will eventually react with the chromium oxide or aluminum oxide scales on the metal interconnect or metal edge rails to form barium chromate or a celsian phase at the interface [6], This can cause a mechanical weakness that is easily delaminated. Also, compositions that contain boron can react over time with water (steam) to produce B2(OH)2 or B(OH)3 gas. This can decompose the glass and greatly limit the lifetime of the seal. Thus many of the new investigations have emphasized low or no boron glass compositions. 

The organic deposition sources are made of a variety of materials including ceramics (e.g., boron nitride, aluminum oxide, and quartz) or metallic boats (e.g., tantalum or molybdenum). Deposition is carried out in high vacuum at a base pressure of around 10-7 torr. The vacuum conditions under which OLEDs are fabricated are extremely important [41] and evaporation rates, monitored using quartz oscillators, are typically in the range 0.01 0.5 nm/s in research and development tools. In manufacturing, higher rates or multiple sources may be used to reduce tact times. 

However, unlike gas-phase reactions, the boron particles are oxidized at their surfaces, so that some unreacted boron remains after combustion. A significant difference between B and A1 is that the amount of oxygen gas (O2) needed to produce boron oxide is 2.22 kg [02]/kg [B] whereas the amount required to produce aluminum oxide is just 0.89 kg [02]/kg [Al]. Since the amount of oxygen needed to burn boron particles is approximately 2.5 times larger than that needed to burn alum-... 

The rate of silicate sol and gel formation is pH and water-alcohol-sensitive as is the solubility of the amorphous silica that is formed. Silica networks are based on (Si04) " tetrahedra modified by (O3 Si-O, M+) units and often addition of boron oxide, aluminum oxide, titanium IV oxide, or zirconium IV oxide. 

Manufactured abrasives include silicon carbide, fused aluminum oxide, sintered aluminum oxide, sol-gel sintered aluminum oxide, fused zirco-nia-alumina, synthetic diamond, cubic boron nitride, boron carbide, slags, steel shot, and grit. 

Metallic elements with low ionization energies commonly form ionic oxides. As remarked in Section 10.1, the oxide ion is a strong base, so the oxides of most of these metals form basic solutions in water. Magnesium is an exception because its oxide, MgO, is insoluble in water. However, even this oxide reacts with acids, so it is regarded as basic. Elements with intermediate ionization energies, such as beryllium, boron, aluminum, and the metalloids, form amphoteric oxides. These oxides do not react with water, but they do dissolve in both acidic and basic solutions. 

Metals and ceramics (claylike materials) are also used as matrices in advanced composites. In most cases, metal matrix composites consist of aluminum, magnesium, copper, or titanium alloys of these metals or intermetallic compounds, such as TiAl and NiAl. The reinforcement is usually a ceramic material such as boron carbide (B4C), silicon carbide (SiC), aluminum oxide (A1203), aluminum nitride (AlN), or boron nitride (BN). Metals have also been used as reinforcements in metal matrices. For example, the physical characteristics of some types of steel have been improved by the addition of aluminum fibers. The reinforcement is usually added in the form of particles, whiskers, plates, or fibers. 

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