Metal oxide particles

Only about 10 elements, ie, Cr, Ni, Zn, Sn, In, Ag, Cd, Au, Pb, and Rh, are commercially deposited from aqueous solutions, though alloy deposition such as Cu—Zn (brass), Cu—Sn (bronze), Pb—Sn (solder), Au—Co, Sn—Ni, and Ni—Fe (permalloy) raise this number somewhat. In addition, 10—15 other elements are electrodeposited ia small-scale specialty appHcations. Typically, electrodeposited materials are crystalline, but amorphous metal alloys may also be deposited. One such amorphous alloy is Ni—Cr—P. In some cases, chemical compounds can be electrodeposited at the cathode. For example, black chrome and black molybdenum electrodeposits, both metal oxide particles ia a metallic matrix, are used for decorative purposes and as selective solar thermal absorbers (19). 

Raman spectroscopy has provided information on catalytically active transition metal oxide species (e. g. V, Nb, Cr, Mo, W, and Re) present on the surface of different oxide supports (e.g. alumina, titania, zirconia, niobia, and silica). The structures of the surface metal oxide species were reflected in the terminal M=0 and bridging M-O-M vibrations. The location of the surface metal oxide species on the oxide supports was determined by monitoring the specific surface hydroxyls of the support that were being titrated. The surface coverage of the metal oxide species on the oxide supports could be quantitatively obtained, because at monolayer coverage all the reactive surface hydroxyls were titrated and additional metal oxide resulted in the formation of crystalline metal oxide particles. The nature of surface Lewis and Bronsted acid sites in supported metal oxide catalysts has been determined by adsorbing probe mole-... 

Velazquez-Vargas, L.G. et al., Hydrogen Production from Coal derived Syn Gas Using Novel Metal Oxide Particles, Proceedings of the 23th Annual International Pittsburgh Coal Conference, Pittsburgh, PA, September 2006. 

Jiang, Y. Decker, S. Mohs, C. Klabunde, K.J. Catalytic solid state reactions on the surface of nanoscale metal oxide particles. J. Catal. 1998,180,24-35. 

The -potential of the metal-oxide particles was measured by means of the micro-electrophoresis method (11). 

In the specific case of biomass gasification, several alkaline salts and heavy metals and metal oxides particles may act as additional poisons by enhancing the sintering of the Ni crystallites or by being adsorbed on the Ni sites [44]. While acid supports such as alumina react with alkali to form crystalline phases, basic supports (like MgO) do not react directly with them however, alkali causes coverage of the surface and plugging of the pores. 

Making uniform nano-sized metal oxide particles is also of interest. Such particles could have a higher specific surface area and a higher density of surface defects than those made by conventional preparation methods. This could be beneficial to their catalytic properties. If the oxide particle is multi-component, then such nano-sized particles, each containing the various components would provide more intimate contact or... 

As noted before, many conventional methods rely on hydrolysis/precipi-tation chemistry to deposit Pt and other metals onto carbon, followed by chemical or gas-phase reduction. One common method is the use of metal sulfito chemistry. This method involves the preparation of metal sulfito complexes (e.g., Na3[Pt(S03)2(0H)2]) in water, the addition of carbon, and precipitation of metal by oxidation to deposit metal oxide particles. The route has advantages in that alkali metals and halides are excluded from the preparation. The method has been extended to bimetallics such as PtRu. 

Since pyrolants are mixtures of various chemicals, such as crystalline particles, metal particles, metal oxide particles, and/or polymeric materials, the physico-... 

The chosen combinations of these chemicals and metals depend on the requirements of the specific application. Gasless combustion prevents pressure increase in a closed combustion chamber. Some combinations of metal particles and metal oxide particles or of metal particles and crystalline oxidizers are chosen as chemical ingredients of gasless pyrolants. On the other hand, hydrocarbon polymers are used to obtain combustion products of low molecular mass, such as H2O, CO, CO2, and H2. High pressure is thus obtained by the combustion of hydrocarbon polymers. Table 10.6 shows the chemical ingredients used to formulate various types of pyrolants. 

KGIO4, NH4GIO4, KGIO3, KNO3, NaN03, NH4NO3, HNF Metal particles + metal oxide particles... 

When metal oxide particles are used as oxidizers, metal particles are used as fuel components. Since the melting point and gasification temperatures of metal oxide particles are very high, the oxidation reaction only occurs when the metal particles... 

Al and Mg particles are favored metals in the formulation of pyrolants because of their high potential for ignitability and combustion. However, the combustion products of Al and Mg particles tend to agglomerate to form relatively large metal oxide particles. Since the densities and heats of combustion of Ti and Zr are higher than those of Al and Mg, Ti and Zr are more favorable for use as fuel metals in ducted rockets. 

Metal particles incorporated into a gas-generating pyrolant act as flame holders to keep the flame in the ramburner. Fach metal particle flows with the combustible gas and becomes a hot metal or metal oxide particle. Since the flow velocity of such a hot particle is lower than that of the combustible gas, the flow velocity of the combustible gas just downstream of the hot particle is decreased due to the aerody-... 

Although it is known that the colour of black body radiation is only dependent upon temperature, sparks have colours that are also dependent upon the type of emitting material. However, the form of the radiance curves does not relate exactly with known molecular energy transitions. This suggests that the mechanism of emission in excess of black body radiation is not yet fully established. It is possible that some emission bands only become active when the metal oxide particle is molten, or that the energy is dissipated simply via collisions with other molecules rather than the emission of photons. 

---