Hydrides pressure

Hydrogen homogeneity was controlled by metallographic examination. Metallography of hydride structure on radial-axial and radial-transverse sections shows a uniform hydride distribution with hydrides elongated in the longitudinal direction (Fig. 1). From the hydrided pressure tube material curved compact toughness (CTT) specimens were machined. Except for the thickness and the curvature of the tube, the in-plane dimensions of specimens were in proportion described for compact specimen in ASTM standard test method (E-399). 

Trimethylene dibromide (Section 111,35) is easily prepared from commercial trimethj lene glycol, whilst hexamethylene dibromide (1 O dibromohexane) is obtained by the red P - Br reaction upon the glycol 1 6-hexanediol is prepared by the reduction of diethyl adipate (sodium and alcohol lithium aluminium hydride or copper-chromium oxide and hydrogen under pressure). Penta-methylene dibromide (1 5-dibromopentane) is readily produced by the red P-Brj method from the commercially available 1 5 pentanediol or tetra-hydropyran (Section 111,37). Pentamethylene dibromide is also formed by the action of phosphorus pentabromide upon benzoyl piperidine (I) (from benzoyl chloride and piperidine) ... 

Uthium Mydride. Lithium hydride [7580-67-8] is very stable thermally and melts without decomposition. In the temperature range 600—800°C, the dissociation pressure for hydrogen, Pp, in units of kPa is expressed by... 

Sodium Hydride. Sodium hydride [7646-69-7] decomposes to its elements without melting, starting at ca 300°C. Decomposition is rapid at 420°C. The dissociation pressure in kPa between 100 and 600°C for the decomposition range 15—90% NaH can be found from... 

Magnesium titanium alloys form the hydrides Mg2TiHg [74811-18-0] and MgTi2H [58244-88-5] (17). Traces of a third metal are often added to adjust dissociation pressures and/or temperatures to convenient ranges. 

Storage as Hydrides. The discovery of metal compounds that reversibly absorb hydrogen is relatively recent. In the 1970s, the AB and AB family of alloys, which reversibly absorb hydrogen at room temperature and low pressure, were identified (205). Both A and B are metals. As of this writing many such compounds are known LaNi and TiFe are examples. 

Fig. 7. Pressure—composition relationships for the FeTi—H system at 40°C during formation of the hydride (o) and release of hydrogen ( ).

Fig. 2. Iron—titanium hydride vessel (508 kg hydride, 6.4 kg hydrogen) performance of the Provo-Orem (Utah) bus at 3.4 MPa (493 psi) charge pressure, having 22 cylinders, each with a 75 mm dia and 1750 mm length, where (-) indicates tank pressure. To convert MPa to psi, multiply by 145. See text.

Finally, selective hydrogenation of the olefinic bond in mesityl oxide is conducted over a fixed-bed catalyst in either the Hquid or vapor phase. In the hquid phase the reaction takes place at 150°C and 0.69 MPa, in the vapor phase the reaction can be conducted at atmospheric pressure and temperatures of 150—170°C. The reaction is highly exothermic and yields 8.37 kJ/mol (65). To prevent temperature mnaways and obtain high selectivity, the conversion per pass is limited in the Hquid phase, and in the vapor phase inert gases often are used to dilute the reactants. The catalysts employed in both vapor- and Hquid-phase processes include nickel (66—76), palladium (77—79), copper (80,81), and rhodium hydride complexes (82). Complete conversion of mesityl oxide can be obtained at selectivities of 95—98%. 

Lithium Iodide. Lithium iodide [10377-51 -2/, Lil, is the most difficult lithium halide to prepare and has few appHcations. Aqueous solutions of the salt can be prepared by carehil neutralization of hydroiodic acid with lithium carbonate or lithium hydroxide. Concentration of the aqueous solution leads successively to the trihydrate [7790-22-9] dihydrate [17023-25-5] and monohydrate [17023-24 ] which melt congmendy at 75, 79, and 130°C, respectively. The anhydrous salt can be obtained by carehil removal of water under vacuum, but because of the strong tendency to oxidize and eliminate iodine which occurs on heating the salt ia air, it is often prepared from reactions of lithium metal or lithium hydride with iodine ia organic solvents. The salt is extremely soluble ia water (62.6 wt % at 25°C) (59) and the solutions have extremely low vapor pressures (60). Lithium iodide is used as an electrolyte ia selected lithium battery appHcations, where it is formed in situ from reaction of lithium metal with iodine. It can also be a component of low melting molten salts and as a catalyst ia aldol condensations. 

Both zirconium hydride and zirconium metal powders compact to fairly high densities at conventional pressures. During sintering the zirconium hydride decomposes and at the temperature of decomposition, zirconium particles start to bond. Sintered zirconium is ductile and can be worked without difficulty. Pure zirconium is seldom used in reactor engineering, but the powder is used in conjunction with uranium powder to form uranium—zirconium aUoys by soHd-state diffusion. These aUoys are important in reactor design because they change less under irradiation and are more resistant to corrosion. 

The chain-growth catalyst is prepared by dissolving two moles of nickel chloride per mole of bidentate ligand (BDL) (diphenylphosphinobenzoic acid in 1,4-butanediol). The mixture is pressurized with ethylene to 8.8 MPa (87 atm) at 40°C. Boron hydride, probably in the form of sodium borohydride, is added at a molar ratio of two borohydrides per one atom of nickel. The nickel concentration is 0.001—0.005%. The 1,4-butanediol is used to solvent-extract the nickel catalyst after the reaction. 

Potassium Hydride. Potassium hydride [7693-26-7] KH, made from reaction of molten potassium metal with hydrogen at ca 200°C, is suppHed in an oil dispersion. Pressure Chemical Company (U.S.) is a principal suppHer. KH is much more effective than NaH or LiH for enolization reactions (63,64). Use of KH as a base and nucleophile has been reviewed (65). 

Hydrolysis of primary amides cataly2ed by acids or bases is very slow. Even more difficult is the hydrolysis of substituted amides. The dehydration of amides which produces nitriles is of great commercial value (8). Amides can also be reduced to primary and secondary amines using copper chromite catalyst (9) or metallic hydrides (10). The generally unreactive nature of amides makes them attractive for many appHcations where harsh conditions exist, such as high temperature, pressure, and physical shear. 

Oxidation. AH inorganic siUcon hydrides are readily oxidized. Silane and disilane are pyrophoric in air and form siUcon dioxide and water as combustion products thus, the soot from these materials is white. The activation energies of the reaction of silane with molecular and atomic oxygen have been reported (20,21). The oxidation reaction of dichlorosilane under low pressure has been used for the vapor deposition of siUcon dioxide (22). 

Zirconium is a highly active metal which, like aluminum, seems quite passive because of its stable, cohesive, protective oxide film which is always present in air or water. Massive zirconium does not bum in air, but oxidizes rapidly above 600°C in air. Clean zirconium plate ignites spontaneously in oxygen of ca 2 MPa (300 psi) the autoignition pressure drops as the metal thickness decreases. Zirconium powder ignites quite easily. Powder (<44 fim or—325 mesh) prepared in an inert atmosphere by the hydride—dehydride process ignites spontaneously upon contact with air unless its surface has been conditioned, ie, preoxidized by slow addition of air to the inert atmosphere. Heated zirconium is readily oxidized by carbon dioxide, sulfur dioxide, or water vapor. 

Other Arsenic Hydrides. Diarsine [15942-63-9] AS2H4, occurs as a by-product in the preparation of arsine by treatment of a magnesium aluminum arsenide alloy with dilute sulfuric acid and also may be prepared by passing arsine at low pressure through an ozonizer-type discharge tube (19). Diarsine is fairly stable as a gas but quite unstable (above — 100°C) in condensed phases. The for diarsine is +117 4 kJ/mol (28 1 kcal/mol) and... 

Fig. 20. Pressure concentration curves of MmNi (—) and LaNi (— ) at 45°C where open circles denote absorption and closed circles desorption of hydrogen. H/M represents the ratio in the hydride of the mole fraction of hydrogen to the mole fraction of the metal.

---