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Sonochemically-generated Ti−Al−B reactive mixed-metal nanopowders were tested by seeding them into a premixed, fuel-lean (Φ = 0.63), methane/air flame to investigate their combustion characteristics. Tests were conducted on powders with and without cryogenic milling. The attenuation of a diode laser beam was measured to calculate the time-resolved concentration of the powder in the flame. Radiant heat flux was measured with three gauges at different heights (1 cm, 6 cm, and 12 cm) along the axis of the flame. Flame spectra were collected to monitor chemiluminescence of intermediate species, and a multi-wavelength pyrometry method was applied to the spectra to calculate the temperature of the hot particulates in the flame. Commercially available metal powders were tested as a benchmark. These included micron-scale aluminum, nano-scale aluminum, micron-scale boron, and inert nano-scale alumina powders. The spectra from flames seeded with the sonochemically-generated Ti−Al−B powder show strong chemiluminescence from the BO 2 , an indicator of boron oxidation. Peak temperatures measured with flame pyrometry were approximately 2100 K, which is below the vaporization point of B 2 O 3 . The radiant heat flux from the seeded flame increased with concentration faster for the Ti−Al−B material than for any of the commercial powders, suggesting a greater gravimetric power density. Based on these results, the Ti−Al−B powders show promising combustion and heat-release characteristics, and therefore warrant further examination as a high-performance solid fuel. [ABSTRACT FROM AUTHOR]

TiB 2 -TiC-WB composite ceramic powders have been prepared by fast combustion synthesis from Ti, W and B 4 C, by coupling the weak exothermic reaction of W + B = WB with strong ones of Ti + 2B = TiB 2 and Ti + C = TiC. With increasing W/(Ti + W) ratio, the reaction temperature and heating rate decrease while the content of WB increases, and unreacted W appears for W/(Ti + W) = 0.24. The addition of excessive B 4 C leads to lower reaction temperature, smaller grain size, and formation of WB 2 . The products show a homogeneous microstructure without element segregation on the scale of agglomerates, and in most products the average grain size is smaller than 1 µm. [ABSTRACT FROM AUTHOR]

A common method for measuring the reactivity of rapidly deflagrating materials has been to loosely pack a desired mixture into an approx. 10 cm long×3 mm diameter acrylic tube, ignite the material on one end, and report the observed self-propagating flame velocity through the material. While this method can yield qualitative information, linking this to quantitative intrinsic properties, such as particle burn time, has remained challenging. In this work, we significantly redesign the traditional burn tube experiment. Between 25 and 250 mg of nanocomposite aluminum/copper oxide (Al/CuO) thermite is loosely packed into the capped end of a 1.8 m long tube, and the remainder of the tube is left unfilled. The material is ignited using a hot wire, resulting in a steadily-propagating luminous front, which extends part, or all, of the way down the length of the tube. We suggest the behavior is a result of 'reactive entrainment', which occurs when the reaction time scale becomes longer than the characteristic momentum relaxation time scale. When this criterion is met, and when there are significant pressure gradients present or produced during the reaction, material will be entrained by the gases before and/or during the reaction; a behavior very different from conventional thermites, which use larger particle sizes. The effect of sample mass and tube diameter on propagation velocity is investigated, and we find a linear scaling with mass and a power law scaling with tube radius ( r−1.3) between 1.56 and 4.76 mm radii. For several conditions, we observe the reaction complete; defined by the distance where the propagation velocity decreases to a fixed fraction of its steady value. The ratio of quench distance to propagation velocity was found to approach a constant value of 3.29±0.70 ms, which we suggest is the burn time of the Material. For the range of masses studied in this work, the burn time was found to be independent of mass, implying that it is an intrinsic particle burn time. We expect other quantitative information can be deduced from this experiment, so long as the chosen sample mass and tube dimensions allow one to observe the full extent of reaction. [ABSTRACT FROM AUTHOR]

This paper is aimed at characterizing combustion dynamics of fine magnesium powders. Two spherical, micron-sized Mg powders with different particle size distributions were introduced into an air–acetylene flame. Particles were observed to burn in laminar flames as well as in flames with turbulence induced by an auxiliary swirling air flow. Particle emission was detected above the flame emission background and emission pulses for individual particles were recorded using an array of three filtered photomultiplier tubes. Particle size distributions were correlated with their emission times, interpreted as burn times, for different turbulence levels. Ratios of the recorded filtered emission signals were used to obtain temperatures of the burning particles. Partially burned particles were collected and examined. Particle burn times were approximately proportional to d 0.8 , where d is the particle diameter. The particle spherical shapes were not preserved. For the coarser powder, halos of condensed ultrafine MgO crystals were observed around quenched particles. Presence of slightly greater amounts of MgO on the surface of as received particles of the finer powder resulted in their longer burn times and elevated temperatures. These observations are interpreted assuming that the initial small MgO particles adhered to the metal surface result in the formation of solid MgO islands and inclusions on surface of the burning Mg droplets. Such islands block evaporation of magnesium and thus reduce the burn rates. In addition, they serve as condensation centers for the combustion products and grow rapidly during combustion. As a result, a relatively small number of the initial fine MgO particles can cause substantial disruption in the burning particle shape, surface morphology, and burn rate. Larger MgO inclusions can be heated above the Mg boiling point resulting in an increased measured temperature. [ABSTRACT FROM AUTHOR]

Nd x Bi 1− x Fe 0.95 Co 0.05 O 3 ( x =0, 0.05, 0.10, 0.15) nanopowders were prepared by a combustion-derived method. The Rietvelt fitting of the X-Ray diffraction data from the Nd x Bi 1− x Fe 0.95 Co 0.05 O 3 (NBFCO) powders showed nanopowders with rhombohedral BiFeO 3 crystalline structure (R3c) for x ≤10 and a partial structural transition to orthorhombic phase (Pnma) for x =0.15. The differential thermal analysis and thermogravimetric analysis (DTA/TGA) showed a crystallization temperature of 180 °C. Transmission electronmicroscopy (TEM) images revealed that the NBFCO nanopowders were composed of fine particles under 60 nm. From Raman spectroscopy, a band of disordered anion lattice was observed at 653 cm −1 . In spite of the antiferromagnetic nature of bulk BiFeO 3 , the NBFCO nanopowders obtained displayed a ferromagnetic hysteresis loop, with coercivity about 0.1 T and remanent magnetization of 1.02–4.33 A m 2 /kg were obtained at room temperature. This ferromagnetic behavior is due to increasing and uncompensated spins at the surface and the canted internal spin by the tilt of FeO 6 octahedral units. We have developed a novel synthetic route for the preparation of ferromagnetic BFO-derived nanopowder materials by a surfactant-assisted combustion-derived method. [ABSTRACT FROM AUTHOR]

Abstract: The combustion process in air for aluminum nanopowders (nAl), micron-sized powders of aluminum (μAl), titanium (μTi) and zirconium (μZr) was accompanied by the predominant reaction of the metals with N2 and the subsequent stabilization of the nitride phases (from 38wt.% of ZrN for μZr combustion to 72wt.% of AlN for nAl combustion) in the condensed combustion products (CCP). The combustion process, composition and structure of CCP of nAl, μAl, μTi, and μZr were studied. Scanning electronic microscopy (SEM), X-ray diffraction (XRD), energy dispersive (X-ray) spectroscopy (EDX), and chemical analysis were performed on both initial powders and CCP. The combustion mechanism for the studied metal powders was experimentally proved. The formation of a large amount of non-equilibrium products (AlN, ZrN, TiN) instead of oxides in air is the special feature of the above mentioned experimental conditions. Nitride formation in air was defined by high temperatures and high burning rates during combustion of powdery Al, Ti and Zr. [Copyright &y& Elsevier]

Powders of titanium alloy (Ti-6Al-4V) and bioactive glass (45S5) were deposited by flame spraying to fabricate composite porous coatings for potential use in bone fixation implants. Bioactive glass and titanium alloy powder were blended and deposited in various weight fractions under two sets of spray conditions, which produced different levels of porosity. Coatings were characterized with cross-sectional optical microscopy, x-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Immersion testing in simulated body fluid (SBF) was conducted for 0, 1, 7, and 14 days. Hydroxyapatite (HA) was found on the bioactive glass-alloy composite coatings after 7 days of immersion; no HA was observed after 14 days on the pure titanium alloy control coating. The HA formation on the alloy-bioactive glass composite coating suggests that the addition of bioactive glass to the blend may greatly increase the bioactivity of the coating through enhanced surface mineralization. [ABSTRACT FROM AUTHOR]

method for measuring the acoustic admittance of the burning surface of solid propellants using a two-dimensional combustion chamber (T-burner) is considered. The paper presents the results of an experimental study of the effect of the pressure and frequency of acoustic oscillations in the combustion chamber and the effects of the composition, mass content, and aluminum powder particle size on the acoustic admittance of the burning surface of composite solid propellants. [ABSTRACT FROM AUTHOR]

The article presents information on the study conducted to determine the combustion mode of compacted metal powder samples. The combustion mode was determined from the front shape during combustion by using thermocouple measurements. The experiment determined the surface and the layer combustion mode of the porous niobium powder samples in a gaseous nitrogen atmosphere.

Abstract: Ultrafine Y2.9Tb0.1Al5−x Ga x O12 phosphor powders with different Ga concentration were prepared by a nitrate–citrate sol–gel combustion process. Mono-phase cubic phosphors were obtained at 900°C by directly crystallizing from amorphous materials determined by X-ray diffraction (XRD) technique and no intermediate phase was observed. The resultant phosphor powders heat-treated at 1000°C are uniform with good dispersity and the particle size is about 80nm. The photoluminescence (PL) spectra of Tb3+ substituted for Y3+ in Yttrium aluminum garnet (Y3Al5O12, YAG) with different Ga concentrations were measured on samples calcined at 1000°C. The luminescence intensity was effectively improved because of the replacement of Al with Ga in YAG. [Copyright &y& Elsevier]

Abstract: Y2O3:Eu3+ powders were prepared by combustion method with and without gel process. The crystal structures and morphologies of the powders were studied by XRD, SEM and HRTEM. The combustion-derived powders were sintered into ceramics in vacuum and then in N2 atmosphere without any additives. SEM images indicate that the ceramics derived from different powders have different microstructures. Excitation and emission spectra were recorded for both powders and ceramics. Pronounced changes in excitation spectra of them were observed. [Copyright &y& Elsevier]

The combustion characteristics of a MoO3+SiO2+Mg system diluted with sodium chloride have been studied in order to synthesize molybdenum disilicide (MoSi2) fine powders. The effect of processing variables, including the sodium chloride content and the reactants proportion on the phase composition and microstructure of the final products, was obtained. Both the combustion temperature and the wave velocity decreased with an increase in the amount of sodium chloride. With the appropriate processing parameters, the reacted product consisted of solid crystalline MoSi2, and an MgO phase was prepared in the molten sodium halide matrix at 1100°–1350°C. The final product purification resulted in MoSi2 powder with a particle size of 100–500 nm. The mechanism of the MoSi2 formation in the sodium chloride matrix is discussed by analyzing the phase evaluation in the extinguished combustion wave. [ABSTRACT FROM AUTHOR]

Porous Ti with controlled pore structure was fabricated by thermal decomposition and sintering process using TiH2 powders and Polymethylmethacrylates (PMMA) beads as pore forming agent. The beads sizes of 8 and 50 μm were used as a template for fabricating the porous Ti. The TiH2 powder compacts with 20 and 70 vol% PMMA were prepared by uniaxial pressing and sintered for 2 h at 1100°C. TGA analysis revealed that the PMMA and TiH2 were thermally decomposed at about 400°C forming pores and at about 600°C into metallic Ti phase. The porosity increased with increase in the amount of PMMA addition. Also, the microstructure observation showed that the pore size and shape were strongly dependent on the PMMA shapes. [ABSTRACT FROM AUTHOR]

This article presents technical abstracts and notes about police science. "Expert Witness," by W. V. Evans, published ion the August 1954 issue of "Industrial and Engineering Chemistry"; "Spontaneous Combustion of Metal Powders," by B. Kopelman and V. B. Compton, published in the February 1953 issue of "Metal Progress"; "Superimposition," by C. E. Engel, published in the 1954 issue of "Medical Radiography and Photography."