Mg-H system

Table 2.1 shows the crystal structure data of the phases existing in the Mg-H system. Pnre Mg has a hexagonal crystal structure and its hydride has a tetragonal lattice nnit cell (rutile type). The low-pressure MgH is commonly designated as P-MgH in order to differentiate it from its high-pressure polymorph, which will be discussed later. Figure 2.2 shows the crystal structure of p-MgH where the positions of Mg and H atoms are clearly discerned. Precise measurements of the lattice parameters of p-MgH by synchrotron X-ray diffraction yielded a = 0.45180(6) mn and c = 0.30211(4) nm [2]. The powder diffraction file JCPDS 12-0697 lists a = 0.4517 nm and c = 0.30205 nm. The density of MgH is 1.45 g/cm [3]. 

Under increasing hydrogen pressure, substantial changes occnr in the Mg-H system. Bastide et al. [5] investigated the behavior of MgH phase nnder high pressures up to 80 kbar and found that at ambient temperature (20°C) and 80 kbar of... 

Table 2.17 Selected results of XRD analysis and DSC analysis of the reactively milled powders in the Mg-H system [63]... 

The Minitran system, by 3M Health Care, is a monolithic transdermal system that deUvers nitroglycerin at a continuous rate of 0.03 mg/(cm h) (81). The dmg flux through the skin is higher than the previous two systems thus the Minitran system is a smaller size for equivalent dosing. For example, the 0.1 mg/h dose is achieved with a 3.3 cm system rather than the 5 cm systems of Transderm-Nitro or Nitro-dur. Because the skin is rate-controlling in a monolithic system and the Minitran flux is higher than the similar monolithic Nitro-dur system flux, it appears that 3M Health Care has included an additive to increase the skin flux to 0.03 mg/(cm h). Whereas this information is not apparent in Reference 81, patent information supports the hypothesis (96). 

Although some applications for preparative-scale separations have already been reported [132] and the first commercial systems are being developed [137, 138], examples in the field of the resolution of enantiomers are still rare. The first preparative chiral separation published was performed with a CSP derived from (S -N-(3,5-dinitrobenzoyl)tyrosine covalently bonded to y-mercaptopropyl silica gel [21]. A productivity of 510 mg/h with an enantiomeric excess higher than 95% was achieved for 6 (Fig. 1-3). 

Mihaly et al. [128] identified the carboxylic acid derivative of primaquine as a major plasma metabolite. After oral administration of 45 mg of primaquine to healthy volunteers, absorption of the drug was rapid, with peak primaquine levels of 153.3 ng/mL at 3 h, followed by an elimination half-life of 7.1 h, systemic clearance of 21.1 L/h, volume of distribution of 205 L and cumulative urinary excretion of 1.3% of the dose. Primaquine was converted rapidly to the carboxylic acid metabolic, which achieved peak levels of 1427 ng/mL at 7 h. 

In spite of the above mentioned Co(EII) compounds, kinetically labile metal complexes may provide fast product/substrate exchange and some of these systems show real catalytic activity. In native dinuclear phosphatases Mg(II), Mn(II), Fe(II/III), or Zn(II) ions are present in the active centers. Although the aqua complexes of the weakest Lewis acids, Mg(H) and Mn(II), show measurable acceleration of e.g. the transesterification of 2-hydroxypropyl p-nitrophenyl phosphate HPNP, [Mn(II)] = 0.004 M, kobs/ uncat = 73 at pH 7 and 310 K, [38] or the hydrolysis of S -uridyluridine (UpU) [39], only a few structural [40] but no functional phosphatase-mimicking dinuclear complexes have been reported with these metal ions. 

A mechano-chemical synthesis in the Mg-Fe-H system was examined as well [2], Two types of hydrides have been observed, non-crystalline (possibly amorphous) and crystalline. By the addition of a catalytic metaF the enthalpy of desorption improves as shown in Figure 8. 

Figure 8. PCT curves for composite Mg/MWNT-H system at different temperatures HYDROGEN CONTAINER MATERIALS...

S. Orimo, H. Fujii, Hydriding properties of the Mg Ni-H system synthesized by reactive mechanical grinding, /. Alloys Compd. 232 (1996) L16-L19. 

The complex hydride Mg CoH is very similar to Mg FeH. In the binary system of Mg-Co there is no solubility of Co in either solid or liquid Mg and no inter-metallic compound, Mg Co, exists in equilibrium with other phases. However, in contrast to the Mg-Fe system, the intermetallic compound MgCo exists in equili-brium in the Mg-Co binary system (e.g., [14, p. 251]). The theoretical hydrogen capacity of Mg CoH is only 4.5 wt% which is obviously lower than that of Mg FeHg due to the presence of the heavier Co element and one less H atom in the hydride formula. 

B. Bogdanovi, A. Reiser, K. ScWichte, B. Sphethoff, B. Tesche, Thermodynamics and dynamics of the Mg-Fe-H system and its potential for thermochemical thermal energy storage , J. Alloys Compd. 345 (2002) 77-89. 

H. Shao, H. Xu, Y. Wang, X. Li, Synthesis and hydrogen storage behavior of Mg-Co-H system at nanometer scale , J. Solid State Chem. 177 (2004) 3626-3632. 

Y. Nakamori, G. Kitahara, K. Miwa, N. Ohba, T. Noritake, S. Towata, S. Orimo, Hydrogen storage properties of Li-Mg-N-H systems , J. Alloys Compd. 404-406 (2005) 396-398. 

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