Aluminum boride

Aluminium, n. aluminum, aluminium, -blech, n. sheet aluminum, -bor, n. aluminum boride, -draht, m. aluminum wire, -eisen, n. ferro-aluminum. -erz, n. aluminum ore. -feilspane, m.pl. aluminum filings, -fluorwasserstoff-saure, /. fluoaluminic acid, -folie, /. aluminum foil, -formiat, n. aluminum formate, -giesserei, /. aluminum foundry or founding. -griess, m. (coarse) aluminum powder aluminum shot. guss, m. aluminum cast-ing(s), cast aluminum. 

Aluminum Block Expansion Test is similar to the Lead Block Expansion Test,but superior to it when testing brisant expls, especially those contg Al. A brief description of this test is given under Trauzl Tests Aluminum Boride. See under Borides... 

The process of forming boron-boron bonds is carried on further in aluminum boride, AIB, which has a very simple hexagonal structure, consisting of hexagonal layers of boron a,toms, like the layers of carbon atoms in graphite, with aluminum atoms in the spaces between the layers (Pig. 11-15). The B—B bond length is 1.73 A, corresponding to n = 0.66 that is, two valence electrons per boron atom are used in the B—B bonds, which are two-thirds bonds. 

There are several aluminum boride phases known. One of the more common, AIB12, is employed in the manufacture of lightweight armor, as a catalyst for organic reactions, and as a economical replacement for diamond abrasive. It has a complex stmcture composed of B12 icosahedra, B19 units (twinned icosahedra), and single boron atoms in a 2 1 1 ratio. The aluminum atoms are distributed statistically over all the boron sites. AIB12 is synthesized by direct combination of the elements at 1100 °C or by reaction of aluminum with Na4B40y at 1100 °C. 

An aluminum boride that is intermediate between the two extremes above, AIB4, has a stmcture consisting of Be octahedra that are hnked by By units forming tunnellike cavities in which the aluminum atoms lie (see Boron Inorganic Chemistry). 

Eq. (11) is not written as a simple exchange reaction, but rather includes the stable titanium aluminide and aluminum boride phases expected to be in equilibrium with molten Al. Consideration of the formation of inter-metallics must not be overlooked during analysis of reinforcement stability because these, not the free element, are the most likely phases to form (presuming, of course, they exist at the growth temperature). 

Many phases, known for system Al-B-N-O , except aluminum borides, are present in the CCP. All boron is probably burned in the gas phase for mixture... 

Boron filaments (BFs) consist of polyciystalline boron with a core of tungsten and tungsten borides, which form during processing [/4]. B/Al MMCs are usually fabricated by diffusion bonding BFs between aluminum foils [/5]. Aluminum borides (i.e., AIB12 and AIB2) have been found at BF-matrix interfaces [/6],... 

Finally, three elements of the periodic system occupy an intermediate position with regard to the ability to form refractory metal-like and non-metallic compounds. These elements, beryllium, magnesium, and aluminum, are capable of forming fairly refractory semiconductor compounds with nonmetals (beryllium, magnesium, aluminum borides, aluminum nitride, magnesium silicides), and they may also enter into the composition of intermetallic compounds of the beryllide, aluminide, etc., type. 

Boron/aluminum MMCs experience severe corrosion in chloride environments and are significantly less corrosion resistant than unreinforced aluminum alloys. The concentration of corrosion in these composites has been found at fiber/matrix interfaces and at the bonds between foils (Ref 4, 5). The accelerated corrosion at these sites has been attributed to imperfect bonding and fissures in the composite and emphasizes the need for eliminating fabrication flaws to reduce corrosion of boron/aluminum MMCs in chloride environments (Ref 4). Corrosion at the fiber/matiix interfaces has also been attributed to the presence of aluminum boride formed during hibticalion (Ref 5). 

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