Crystalline oxidizer particles

Real ignition processes are rather complicated and heterogeneous because igniters contain various types of metal particles and crystalline oxidizer particles. The metal particles are oxidized by the gaseous oxidizer fragments and produce high-... 

Various types of polymers are used to formulate propellants and explosives. The nature of polymers is identified by their chemical bond structure. Two types of copolymers are used to formulate modern propellants and explosives (1) polyurethane copolymer and (2) polybutadiene copolymer. The chemical bond structures of polyether and polyester are used for polyurethane copolymers. Since the molecular concentration of oxygen is relatively high for polyurethane binder, this class of binder is used to achieve high combustion efficiency with low oxidizer concentration of crystalline materials. On the other hand, the heat of formation of polybutadiene copolymer is high and the molecular concentration of oxygen is low when compared with polyurethane copolymer. This class of binder is used to achieve a high combustion temperature when mixed with crystalline oxidizer particles. 

Precipitation from solution under hydrothermal conditions has been known for decades as a method for synthesizing fine, crystalline oxide particles (68). Interest in the method has increased in recent years because of the need for fine, pure powders in the production of ceramics for electronic applications. The process involves heating reactants, often metal salts, oxide, hydroxide, or metal powder. 

Another important class of titanates that can be produced by hydrothermal synthesis processes are those in the lead zirconate—lead titanate (PZT) family. These piezoelectric materials are widely used in manufacture of ultrasonic transducers, sensors, and minia ture actuators. The electrical properties of these materials are derived from the formation of a homogeneous soHd solution of the oxide end members. The process consists of preparing a coprecipitated titanium—zirconium hydroxide gel. The gel reacts with lead oxide in water to form crystalline PZT particles having an average size of about 1 ]lni (Eig. 3b). A process has been developed at BatteUe (Columbus, Ohio) to the pilot-scale level (5-kg/h). 

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-... 

Practical Aspects There are a number of process-specific concerns that are accounted for in good design. In regenerate systems, sorbents age, losing capacity because of fouling by heavy contaminants, loss of surface area or crystallinity, oxidation, and the like. Mass-transfer resistances may increase over time. Because of particle shape, size distribution, or column packing method,... 

Available textbooks and reviews provide a detailed introduction to MB spectroscopy (e.g., Hawthorne 1988 Burns 1993). MB spectra provide quantitative information about the distribution of Fe among its oxidation and coordination states (e.g., octahedrally coordinated Fe3+), identification of Fe-bearing phases, relative distribution of Fe among those phases, and can help to constrain crystallinity and particle size. 

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. 

The polymeric hydrocarbon also acts as a binder of the particles, holding them together so as to formulate a propellant grain. Ammonium perchlorate (AP) is a typical crystalline oxidizer and hydroxy-terminated polybutadiene (HTPB) is a typical polymeric fuel. When AP and HTPB are decomposed thermally on the propellant surface, oxidizer and fuel gases are produced, which diffuse into each other and react to produce high-temperature combustion gases. 

The ballistic properties of ADN, HNF, and HNIW as monopropellants and as oxidizers in composite propellants have been extensively studied.P2-351 Since ADN, HNF, and HNIW particles produce excess oxygen among their combustion products, these particles are used as oxidizer crystals in composite propellants. The pressure exponents of crystalline ADN and HNIW particles are both approximately about the same value as those for HMX and RDX when they are burned as pressed pellets. However, the pressure exponent of HNF is 0.85-0.95,135] higher than those of the other energetic crystalline oxidizers. 

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. 

Vinylidene fluoride hexafluoropropene polymer (Vt) Metal particles + crystalline oxidizers... 

In general, pyrolants composed of a polymeric material and AN particles are smokeless in character, their burning rates are very low, and their pressure exponents of burning rate are high. However, black smoke is formed as i decreased and carbonaceous layers are formed on the burning surface. These carbonaceous layers are formed from the undecomposed polymeric materials used as the matrix of the pyrolant. When crystalline AN particles are mixed with GAP, GAP-AN pyrolants are formed. Since GAP burns by itself, the GAP used as a matrix for AN particles decomposes completely and bums with the oxidizer gases generated by the AN particles. 

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