Halide gaseous

The heats of formation of the gaseous atoms, 4, are not very different clearly, it is the change in the bond dissociation energy of HX, which falls steadily from HF to HI, which is mainly res ponsible for the changes in the heats of formation. 6. We shall see later that it is the very high H—F bond energy and thus the less easy dissoeiation of H—F into ions in water which makes HF in water a weak aeid in comparison to other hydrogen halides. 

Bond energies of gaseous polyvalent metal halides... 

Molten halides are liquid electrolytes in many instances, and their decomposition may be canned out in principle to produce the metal and halogen, usually in the gaseous state. The theoretical decomposition voltage, E°, is calculated from the Gibbs energy of formation tlrrough the equation... 

Fluorinated sulflnates are prepared from sodium dithionite and liquid per-fluoroalkyl halides [74] (equation 67). For the transformation of the gaseous and poorly reactive trifluoromethyl bromide, it is necessary to use moderate pressure [75] (equation 68) These reactions are interpreted by a SET between the intermediate sulfur dioxide radical anion and the halide The sodium trifluorometh-anesulfinate thus obtained is an intermediate for a chemical synthesis of triflic acid. 

Recently, the parent A -halomethylpyridinium halides 7a, 7b, and 7f-7i (X-CH2-Py X , X = Cl, Br) have been synthesized with yields up to 90% by treating a mixture of an equimolar amount of SOX2 (X = Cl, Br) and the corresponding pyridine with gaseous formaldehyde in CH2CI2 or MeCN at 0°C. Tire formaldehyde was generated externally from paraformaldehyde in a special apparatus (99JOC3113). 

The outstanding characteristics of the noble metals are their exceptional resistance to corrosive attack by a wide range of liquid and gaseous substances, and their stability at high temperatures under conditions where base metals would be rapidly oxidised. This resistance to chemical and oxidative attack arises principally from the Inherently high thermodynamic stability of the noble metals, but in aqueous media under oxidising or anodic conditions a very thin film of adsorbed oxygen or oxide may be formed which can contribute to their corrosion resistance. An exception to this rule, however, is the passivation of silver and silver alloys in hydrochloric or hydrobromic acids by the formation of relatively thick halide films. 

Purely gaseous method Articles are suitably jigged inside a retort chamber and vapours of chromium halide, usually diluted with a reducing gas, are circulated. The temperature is maintained within the range 950-1 200°C for chromising of iron and ferrous alloys (recent Russian work on... 

Semi-gaseous method The articles, surrounded by a solid compound containing chromium metal, are packed in a retort chamber, and vapours of chromium halide or halogen compound are circulated in the chamber, which is maintained at 950-1 200 C. 

Iron Low-carbon steels Low-carbon alloy steels Decarburised malleable Chromium 980-1 050 (Halide) 1. Gaseous 2. Semi- gaseous 3. Pack 25-75 urn Solid-solution (ferritic) 20-25% Cr Ductile (200-300 HV) Weldable Heat treatment acceptable ... 

Hydrofluoride synthesis is based on the simultaneous fluorination by ammonium hydrofluoride of niobium or tantalum oxides with other metals compounds (oxides, halides, carbonates etc.) [105]. Table 13 presents some properties of ammonium hydrofluoride, NH4HF2 [51, 71]. Ammonium hydrofluoride is similar to anhydrous HF in its reactivity, but possesses some indisputable advantages. The cost of ammonium hydrofluoride is relatively low, it can be dried and handled easily, recycled from gaseous components, and its processing requires no special equipment. 

All the hydrogen halides are gaseous at room temperature but hydrogen fluoride liquefies at 19.9°C and 1 atmosphere pressure. The most important chemistry of the hydrogen halides relates to their aqueous solutions. All of the hydrogen halides dissolve in water to give solutions that conduct electric current, suggesting that ions are present. The reactions may be written ... 

Different results can be found in the solid state and solution gaseous HX (X= halide) adds cis to solid IrCl(CO)(PPh3)2 and in benzene solution, but in polar solvents like methanol a mixture of cis- and trans-products is found. 

The available experimental data, because of their paucity and their inaccuracy, do not permit the extensive testing of these figures. The directly determined susceptibilities for helium, neon, and argon are in gratifying agreement with the theoretical ones (Table YI). From the mole refraction results we may expect ions in solution to have values of % near those for gaseous ions. KoenigsbergerJ has made determinations of % for seven alkali halides in aqueous solution, in... 

The gaseous reagents were distilled and collected inside the enclosure. The 10 vol.% alkylaluminum and 1 vol.% f-butyl halide solutions were freshly prepared. The reaction mixtures were stored manually or by a vortex stirrer. Since PIB tended to precipitate out of solution in highly swollen form, relative rates could thus be established by visual observation. 

Properties of some halides useful in CVD are listed in Table 3.3. As can be seen, some of these halides are gaseous or liquid at room temperature and, as such, are easily transported in the reaction chamber. The solid halides, however, must be heated to produce sufficient vapor. This sometimes presents a problem which can be bypassed by generating the halide in situ (see Ch. 5). Most halides are available commercially. 

Boron trifluoride, sulphur and disulphur dichlorides, phosphorus trichloride in the liquid state cause potassium to combust. The same is true for phosphorus pentachloride in the solid state. In the latter case the same accident happened with gaseous halide. The same is also true for the bromide analogues of these compounds. 

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