Reduction temperature

Metal teUurides for semiconductors are made by direct melting, melting with excess teUurium and volatilizing the excess under reduced pressure, passing teUurium vapor in an inert gas carrier over a heated metal, and high temperature reduction of oxy compounds with hydrogen or ammonia. 

Both processes also use up-graded ilmenite (slags). About 30% of the world s titanium feedstocks are suppHed by titanium slag producers in Canada, South Africa, and Norway. Slags are formed by the high temperature reduction of ilmenites in electric furnaces. Much of the iron oxide content is reduced to metallic iron and separated as a saleable by-product. Magnesium and other impurities may also be incorporated in the following equations. 

FIG. 29-43 Firing temperature reduction needed to offset IN 718 corrosion by sodium and vanadium. 

If /] is higher than /q, it will be positive and will suggest a temperature rise. If /, is lower than / then it will be negative and will suggest a temperature reduction. 

Although condensation can be accomplished either by reducing the temperature or by increasing the pressure, in practice it is usually done by temperature reduction only. 

Temperature reduction potential using passive cooling by natural nighttime ventilation... 

Metallic Sr and Ba are best prepared by high-temperature reduction of their oxides with Al in an evacuated retort or by small-scale electrolysis of fused chloride baths. They have limited use as getters, and a Ni-Ba alloy is used for sparkplug wire because of its high emissivity. Annual production of Ba metal is about 20-30 tonnes worldwide and the 1991 price about 80-140/kg depending on quality. 

Arsine, AsHs, is formed when many As-containing compounds are reduced with nascent hydrogen and its decomposition on a heated glass surface to form a metallic mirror formed the basis of Marsh s test for the element. The low-temperature reduction of AsCls with LiAlH4 in diethyl ether solution gives good yields of the gas as does the dilute acid hydrolysis of many arsenides of electropositive elements (Na, Mg, Zn, etc.). Similar reactions yield stibine, e.g. ... 

High-temperature reduction of Na2Ti03 with hydrogen produces nonstoichiometric materials, Na jTi02 (jr = 0.20-0.25), called titanium bronzes by analogy with the better-known tungsten bronzes (p. 1016). They have a blue-black, metallic appearance with high electrical conductivity and are chemically inert (even hydrofluoric acid does not attack them). 

By contrast, ZrCl and ZrBr, also prepared by the high temperature reduction of ZrX4 with the metal, appear to be genuine binaiy halides. They are comprised of hep double layers of metal atoms surrounded by layers of halide ions, leading to metallic conduction in the plane of the layers, and they are thermally more stable than the less reduced phases. Zrl has not been obtained, possibly because of the large size of the iodide ion, and, less surprisingly, attempts to prepare reduced fluorides have been unsuccessful. 

The movement of air by fan, conveying outside air into the room or expelling air or both. Filtration, heating and control of the distribution pattern may be included. It is not cooling in the sense of temperature reduction but can be used to limit temperature rise when the outside air is below that of the space being treated. 

Cool inlet air is desirable. For every 5°F of ambient air temperature reduction, the volume of compressed air generated increases by 1 per cent with the same power consumption. This increase in performance is due to the greater density of the intake air. 

Many of the warmer climates have a dry atmosphere (see Figure 23.8). In such areas, considerable dry bulb temperature reduction can be gained by the adiabatic saturation cycle (Section 24.4). The apparatus draws air over a wetted pad and discharges it into the conditioned space. It is termed an evaporative or desert cooler (Figure 25.3). 

The free ligands were obtained by visible photolysis in acetonitrile and were characterized by elemental analyses and H- and 13C-NMR spectroscopies. Low-temperature reduction in ESR tubes also provided the green Fe1 19e complexes which gave the characteristic 3g values typical of the rhombic distortion of Fe1 [77],... 

A more general route to 4-acetoxy-l,3-dioxanes utilizes the reductive acylation of l,3-dioxane-4-ones [46] (Scheme 21). l,3-Dioxane-4-ones 126 are prepared from the corresponding -hydroxy carboxylic acids. Low temperature reduction with DIBALH generates a diisobutylaluminum hemiacetal (127) which undergoes acylation in situ with AC2O in the presence of pyridine and DMAP. This method allows for the preparation of a wide range of 4-acetoxy-l,3-dioxanes, without the problem of a-epimerization. This method also represents a general approach to acylic a-acetoxy ethers, which are themselves useful synthetic intermediates [47,48]. 

Absorption of heat (auto-refrigeration) and consequent temperature reduction on flashing may have a serious effect on associated heat transfer media, upon the strength of materials of construction, and result in frosting at the point of leakage. Exposure of personnel carries a risk of frostbite. 

The introduction of a Pt function influences weakly the behavior of the two high-temperature reduction peaks, but markedly decreases the temperature of the minor low-temperature reduction step from 700 K to 350 K (Figure 5b). These data suggest that some reduction of WOx-Zr02 species can occur during n-alkane isomerization reactions (440-500 K). These reducible W species may act as redox sites required for the conversion of H-atoms to H species on WOx-based solid acids. 

Another particularly reactive form of titanium is generated by including 0.25 equivalent of I2. This reagent permits low-temperature reductive deoxygenation to alkenes.241... 

We have been recently studying new pathways leading to polysilanes with low polydispersity and controlled structures. Our research is focused on three areas. The first one is low temperature reductive coupling in the presence of ultrasound. This leads to monomodal polymers with molecular weights in the range from Mn=50,000 to Mn=300,000 and polydispersities as low as Mw/Mn=1.20 (in addition to usually formed cyclic oligomers). 

The addition of substantial amounts (up to 32%) of aluminium powder to conventional explosives enhances the energy release by up to 100% [1], involving high temperature reduction of liberated carbon dioxide and water by the metal [2]. 

A calorimetric study of reaction with sodium or potassium hydroxides in ethanol or 2-propanol is given. At starting temperatures below 70°C the product is the appropriate nitrophenyl ether above that temperature, reduction of the nitro groups may come into play, to give much more energy and a variety of other products. This reaction is inhibited by oxygen. There is potential for runaway if such reactions are operated industrially with poor temperature control. The editor suspects that the stimulus for this study was an accident which sprayed the German environment with 2-nitroanisole. 

The highly reactive cadmium can be prepared by two different methods. One approach is a room temperature reduction of CdC with lithium naphthalide in THF or DME. The second approach allows the preparation of the reactive metal in a hydrocarbon solvent. First, lithium naphthalide is prepared in benzene addition of this solution to CdC produces a highly reactive cadmium powder. 

The highly oxophilic nature of the cobalt powder was readily demonstrated by its reaction with nitrobenzene at room temperature. Reductive coupling was quickly effected by 2 to give azo- and azoxy derivatives. Nitrobenzene reacted with 2 to give azobenzene in yields up to 37%. In some cases small amounts of azoxybenzene were also formed. With 1,4-diiodonitrobenzene, 2 reacted to give low yields of 4,4-diiodoazoxy-benzene and 4,4-diiodoazobenzene. 

---