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Burner Technology for Hydrogen Fuel
Published in Debi Prasad Mishra, Advances in Combustion Technology, 2023
Debi Prasad Mishra, Swarup Y. Jejurkar
Among the metal hydrides, compounds with elemental metals include magnesium hydride (MgH2) and aluminum hydride (AlH3). MgH2 requires high temperatures above 573 K for activation to overcome the thermodynamic and kinetic restrictions [4]. While storage could be as high as 7%, this is still a developing field. AlH3 bonds hydrogen rather weakly and could enable densities as high as 10% at 373 K. However, manufacture (also called regeneration) of AlH3 is very difficult [4]. Intermetallic hydrides and their processing are expensive [4]. Alanates are complex metal hydrides in which hydrogen is part of a complex (AlH4–) anion bonded with a cation (e.g. Na+). Due to the presence of light elements in alanates, gravimetric hydrogen capacities increase, although high temperatures are required for their activation [4].
Deep Reactive Ion Etching for Bulk Micromachining of Silicon Carbide
Published in Mohamed Gad-el-Hak, MEMS, 2005
Glenn M. Beheim, Laura J. Evans
Dry etching of SiC is usually performed using a primary source of fluorine radicals, with secondary gases added to control or enhance the process. Some primary gases that have been investigated include CF4, SF6, NF3, CHF3, and C2F6. Additives include O2, Ar, H2, and N2. The primary gases NF3 and SF6 exhibit the highest etch rates, as a result of their rapid dissociation in plasma. Although NF3 tends to etch SiC at a faster rate [Leerungnawarat, 2001], SF6 is more desirable for use as a feed gas because it is less expensive and safer. C2F6 has lower perfluorinated compound (PFC) emissions than both NF3 and SF6. Combinations of primary gases have also been investigated to enhance etch rates or reduce residues. The addition of oxygen to the plasma acts to enhance the generation of reactive fluorine atoms and to facilitate removal of carbon in the form of COx [Chabert, 2001]. Oxygen also helps to maintain a clean system by reducing sulfur-based deposition (from SF6) on the walls of the reactor [Chabert, 2001]. If too much oxygen is added, the primary gas becomes diluted, and the etch rate is lowered; also, the etch rate may be further reduced by the formation of SiOn on the surface [Khan, 2001]. Hydrogen additives are used as metal scavengers, e.g., forming volatile aluminum hydride compounds (AlHz) [Yih, 1997]. The addition of hydrogen also results in decreased etch rates (caused by gas-phase reactions with fluorine atoms), greater risk of contamination, and reduced aspect ratios (increased polymer formation can lead to outward sloping sidewalls that can limit trench depth). Physical sputtering of the substrate surface can be increased by adding nonreactive gases such as argon, helium, or nitrogen. The addition of such gases can reduce the formation of residues in the etched areas by sputtering away etch-resistant materials that would otherwise interfere with the etch process.
Amino acids: Building blocks for the synthesis of greener amphiphiles
Published in Journal of Dispersion Science and Technology, 2018
Nausheen Joondan, Sabina Jhaumeer Laulloo, Prakashanand Caumul
Amino acidbased surfactants containing chiral amino alcohols are important in asymmetric and pharmaceutical synthesis.[65] Amino alcohols are obtained by the reduction of amino acid esters with sodium or lithium aluminium hydride or sodium borohydride. Methylation of reduced amino acids using a mixture of formic acid/formaldehyde gave the N,N-dimethyl derivatives, which upon reaction with alkyl halides of varying chain lengths gave the optically active QUATS 55 and 56.[66,67] Reaction of N-dimethyl phenylalaninol with dodecanoyl chloride followed by methyl bromide in acetonitrile yielded the surfactant 57 (Figure 14) in which the hydrophobic tail was attached to the alcohol moiety via an ester linkage.[68]
Innovations in graphene-based nanomaterials in the preconcentration of pharmaceuticals waste
Published in Environmental Technology Reviews, 2018
Ayub Khan, Fazli Khuda, Ahmed Mourtada Elseman, Zaynab Aly, Mohamed M. Rashad, Xiangke Wang
Generally, the cost of SPE techniques used in the preconcentration of PhAs mainly associated with the preparation of GBNMs. Like for example, various reducing agents (hydrazine, lithium aluminium hydride, sodium borohydride etc) are used for the reduction of graphene oxide. However, they are associated with one or the other type of problem (see graphene-based nanomaterials section). We need such reducing agents which are not only cheap but also eco-friendly. We are working on one such project and achieved satisfactory results in the reduction of GO and synthesis of air-stable carbon-capped zero-valent iron oxide. We also suggest the orange juice as cheap reducing agent for GO reduction and zero-valent iron oxide synthesis. In addition, the persistent advancement of exceedingly proficient and particular extraction media is basic for meeting the vital technique identification limits instituted by regulatory agencies. The natural results of test planning must likewise keep on being considered. Various advances have been made toward the scaling down of extraction and purification system that empower the treatment of smaller sample and dissolvable volumes. These organizations incorporate microdevices, microextraction sorbents, and microextraction procedures that will probably keep on providing arrangements where conventional macroscale sample preparation is limited.
Characterisation of paraffin-based hybrid rocket fuels loaded with nano-additives
Published in Journal of Experimental Nanoscience, 2018
Md. Zishan Akhter, M. A. Hassan
A novel hybrid rocket fuel composition has been proposed which comprises of Paraffin wax and HTPB as base, blended with Lithium aluminium hydride (LiAlH4) and Magnesium hydride (MgH2) nanoparticles. A detailed investigation on rheological, thermal and ballistic characterisation of the paraffin-based hybrid rocket fuels had been carried out. It was observed that the Magnesium hydride doped hybrid fuels exhibit lower viscosity as compared to the Lithium aluminium hydride doped counterpart. It signifies comparatively greater entrainment-aided combustion phenomenon in the former case. LiAlH4 doped hybrid fuels exhibit solid-like behaviour in contrast to the MgH2 doped fuels. Thus, LiAlH4 doped fuels are predicted to be comparatively more stable in the solid phase than the MgH2 doped one. TGA/DTA data revealed that LiAlH4 doped fuel is thermally more stable and produces relatively greater residual-mass as compared to the MgH2 doped fuel. Static ballistic firing provided the regression behaviour of prepared fuels. It was obtained that regression rate is significantly enhanced by nanoparticle doping in comparison to the base fuel (PW-HTPB). This can be attributed to the dehydrogenation of metal hydrides and production of metal nanoparticles (Al; in case of LiAlH4) during combustion. Nascent hydrogen promotes pyrolysis of solid grain while metal nanoparticles undergo exothermic oxidation thereby enhancing heat transfer to the fuel surface. The enhancement in regression rate of all the prepared fuels was observed to be significantly higher (350%–475%) than the conventional HTPB hybrid fuel, as predicted in literature. A power law governing regression rate of the tested hybrid fuels was developed.