Boron oxide layer

Thus, the oxidation kinetics due to the boron oxide vaporization at temperatures above 1200 C result in weight loss of specimens (Fig. 13), which becomes linear in time after the first 30 min of oxidation. On oxidation at temperatures below llOO C a liquid boron oxide layer T of amorphous B2O3 is 450°C [110]) uniformly covers the specimen surface. 

Adding carbon or carbon-containing compounds such as aluminum carbide, SiC or related compounds to remove any boron oxide layers from the boron carbide particle surface. This in turn will increase the surface energy and inhibit exaggerated grain growth due to evaporation-condensation [382]. 

The oxidation of carbon fibers can be inhibited to some extent by the use of dopants such as boron. Three mechanisms could be involved in the inhibition process active site blockage resulting from the formation of a boron oxide layer, chemical inhibition by electron transfer, and development of fiber structure/microtexture which is catalyzed by boron. For example, at 700°C, the oxidation rate of the T300 fiber decreases 30 fold when 2000 ppm B are added and the P55 fibers having 5% B never reach 25% burn-off [67]. 

Strong oxidising acids, for example hot concentrated sulphuric acid and nitric acid, attack finely divided boron to give boric acid H3CO3. The metallic elements behave much as expected, the metal being oxidised whilst the acid is reduced. Bulk aluminium, however, is rendered passive by both dilute and concentrated nitric acid and no action occurs the passivity is due to the formation of an impervious oxide layer. Finely divided aluminium does dissolve slowly when heated in concentrated nitric acid. 

Fig. 9. Fabrication sequence for an oxide-isolated -weU CMOS process, where is boron and X is arsenic. See text, (a) Formation of blanket pod oxide and Si N layer resist patterning (mask 1) ion implantation of channel stoppers (chanstop) (steps 1—3). (b) Growth of isolation field oxide removal of resist, Si N, and pod oxide growth of thin (<200 nm) Si02 gate oxide layer (steps 4—6). (c) Deposition and patterning of polysihcon gate formation of -source and drain (steps 7,8). (d) Deposition of thick Si02 blanket layer etch to form contact windows down to source, drain, and gate (step 9). (e) Metallisation of contact windows with W blanket deposition of Al patterning of metal (steps 10,11). The deposition of intermetal dielectric or final...

As a second example, results from a TOP ERDA measurement for a multi-element sample are shown in Fig. 3.65 [3.171]. The sample consists of different metal-metal oxide layers on a boron silicate glass. The projectiles are 120-MeV Kr ions. It can be seen that many different recoil ions can be separated from the most intense line, produced by the scattered projectiles. Figure 3.66 shows the energy spectra for O and Al recoils calculated from the measured TOF spectra, together with simulated spectra using the SIMNRA code. The concentration and thickness of the O and Al layers are obtained from the simulations. 

In thick samples, a boron oxide/boron carbide crust has been detected on the surface of the polymer. This inorganic surface layer has a shielding effect on the inner polymer layers, further enhancing the thermal stability of the material. Poly(m-carborane-siloxane)s have therefore been considered as surface coatings for organic materials, providing protection from erosion effects. 

Fig. 8. Effect of an oxide film on the subsurface hydrogen concentration produced by a given exposure to plasma gases. The two curves refer to deuteration for 1 hr at 150°C of samples with a boron concentration of 1017 cm-3, one with and one without an oxide layer. 

Boron oxide can easily be deposited from BCl3/02 gas mixtures. It is normally incorporated in the first buffer layer because it decreases the softening point of silica and therefore replaces the fire-polishing step often applied to guarantee a starting tube with smooth surfaces. 

Most borides are chemically inert in bulk form, which has led to industrial applications as engineering materials, principally at high temperature. The transition metal borides display a considerable resistance to oxidation in air. A few examples of applications are given here. Titanium and zirconium diborides, alone or in admixture with chromium diboride, can endure temperatures of 1500 to 1700 K without extensive attack. In this case, a surface layer of the parent oxides is formed at a relatively low temperature, which prevents further oxidation up to temperatures where the volatility of boron oxide becomes appreciable. In other cases the oxidation is retarded by the formation of some other type of protective layer, for instance, a chromium borate. This behavior is favorable and in contrast to that of the refractory carbides and nitrides, which form gaseous products (carbon oxides and nitrogen) in air at high temperatures. Boron carbide is less resistant to oxidation than the metallic borides. 

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