Orthorhombic alloys

Fig. 15. Oxidation kinetics for Ti-22 Al-23Nb orthorhombic alloys in air at temperatures in the range 500-900 °C (left) and the effect of Nb content on the parabolic rate constant for Ti-25 at% Al alloys at 800°C (right).

Fig. 24. Schematic diagram of the scale and interstitial affected zone (IAZ) which forms on orthorhombic alloys in the temperature range 500-800 °C (left) and the time dependence of the IAZ thickness (right).

The orthorhombic alloys have been reported to be less susceptible to environmental embrittlement than the ot2 alloys [92], however, more recent work [59,93] has indicated that this is not generally the case. The microstructure of the alloy is substantially modified by the oxidation process, as indicated schematically in Figure 24. An interstitial affected zone (IAZ) in which the volume fraction of a2 is increased, forms in the alloy below the scale. A very small angular phase also develops in this... 

Fig. 25. Room temperature ductility (measured in 3-point bending) of orthorhombic alloys after 100 hours exposure in air at various temperatures.

Cockeram and Rapp have evaluated the kinetics of silicide coatings on Ti [103] and have used a halide-activated pack-cementation method to form boron- and germanium-doped silicide coatings on orthorhombic alloy substrates [104]. The coatings greatly decreased the cyclic oxidation kinetics and microhardness measurements did not indicate diffusion of oxygen into the substrate. 

Fig. 31. Schematic diagram of the oxidation morphology and cracking observed in orthorhombic alloy/SiC composites (left) and the oxidation rates of the composites over the temperature range 500-900 °C (right).

In the region 25.5- 33.34mol % Sb2Se3 rhombohedral and orthorhombic alloys coexist. 

The iron-carbon solid alloy which results from the solidification of non blastfurnace metal is saturated with carbon at the metal-slag temperature of about 2000 K, which is subsequendy refined by the oxidation of carbon to produce steel containing less than 1 wt% carbon, die level depending on the application. The first solid phases to separate from liquid steel at the eutectic temperature, 1408 K, are the (f.c.c) y-phase Austenite together with cementite, Fe3C, which has an orthorhombic sttiicture, and not die dieniiodynamically stable carbon phase which is to be expected from die equilibrium diagram. Cementite is thermodynamically unstable with respect to decomposition to h on and carbon from room temperature up to 1130 K... 

The stable form of arsenic is the gray or metallic form, although other forms are known. Cooling the vapor rapidly produces yellow arsenic, and an orthorhombic form is obtained if the vapor is condensed in the presence of mercury. Arsenic compounds are used in insecticides, herbicides, medicines, and pigments, and arsenic is used in alloys with copper and lead. A small amount of arsenic increases the surface tension of lead, which allows droplets of molten lead to assume a spherical shape, and this fact is utilized in the production of lead shot. 

Alloys Fe-C alloys face-centred cubic to body-centred tetragonal structure change (fee —>bet) Cu-Sn alloys bcc fcc Au-Cd alloy (48% Cd) bcc — orthorhombic. 

Because of the inherently non-equilibrium nature of the production route, the first question which needed to be answered was whether the phases present in the alloy were in fact stable, so that equilibrium calculations could actually be used to design these alloys. To this end CALPHAD calculations were combined with a detailed experimental characterisation of a Fe7oCrigMo2B o alloy (Kim et al. 1990, Pan 1992). The TEM and XRD results confirmed earlier work (Xu et al. 1985) which stated that an orthorhombic boride M2B was present and its composition was Cr-rich. However, they also showed that a proportion of the borides ( 10%) were Mo-rich and that the Fe-based matrix was martensitic. The latter result was particularly surprising because of the high level (20at%) of a-ferrite stabilisers Cr and Mo. Furthermore, initial analysis of difiiaction patterns from the TEM work indicated that the shuctuie of the Mo-rich boride was a tetragonal type whose structure had not been reported in previous literature (Kim and Cantor 1988). 

Bromo-pentammino-rhodium Bromide, [Rh(NH3)5Br]Br2, is prepared in a similar manner to the cliloro-salt by heating rhodium-zinc alloy with a mixture of bromine and hydrobromic acid, or by warming aquo-pentammino-rhodium bromide with excess of hydrobromic acid to 100° C.1 2 It separates in small orthorhombic yellow crystals which are almost insoluble in cold water and insoluble in alcohol and hydrobromic acid. It has the same constitution as the ehloro-compound. Treated with nitric acid, hydrochloric acid, or silver carbonate, it yields the corresponding salts respectively, and with moist silver oxide yields an unstable hydroxide, [Rh(NIT3)5Br](OH)2. The methods from the preparation of the bromo-salts are like those for the ehloro-salts. 

Nd-Pd-Sb. Marazza et al. (1980) established the Caln2 type structure with a = 0.4580, c = 0.7716 for NdPdSb compound by using X-ray powder diffraction and metal-lographic analyses. For the sample preparation and the purity of starting components, see Y-Pd-Sb system. The crystallographic characteristics were confirmed from powder diffraction of arc melted and annealed at 1073 K alloys with a = 0.4577, c = 0.7676 (Zygmunt and Szytula, 1995). Mehta et al. (1995) reported an orthorhombic structure for NdPdSb at room temperature SG Pmma, a = 0.45833, b = 0.77189, c = 0.7937. 

The transformations above room temperature (monoclinic-orthorhombic, orthorhombic-tetragonal I) are more easily understood. One notes the expected decrease in transition temperature with increasing sodium content, as is found in many alloy phase diagrams. Attempts to observe transitions to a cubic phase at higher temperatures failed, owing to sublimation of samples of very low sodium content (x < 0.02) or decomposition at higher sodium concentrations. 

RDX forms orthorhombic crystals with a melting point of 206 Celsius. 1 Gram dissolves in 25 milliliters of acetone, but its solubility in alcohol, ether, ethyl acetate, and glacial acetic acid is even less. It is insoluble in water, carbon tetrachloride, and carbon disulfide. RDX is one of the most important military explosives known to man. It is highly versatile, being resistant to heat, shock and percussion, and is capable of being alloyed with many different secondary explosives. RDX is very well known in several of the most important explosives compositions. These compositions include semtex, C4, and composition B, all of which are widely used in military operations. RDX is by far one of the most important explosives in occurrence, and it is manufactured on an industrial scale. 

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