Catalytic properties of ion-exchanged carnegieite powders. Isomerization of n-butenes

The mist decomposition method was applied to the solgel type synthesis. Resulting carnegieite and its ionexchanged derivatives were tested by means of butene isomerization. Carnegieite showed weak but stable activity originating from its base sites. The results of the reaction suggested the development of more active sites by the magnesium ion exchange and new acid sites by the ammonium ion exchange. These are examined by acid-base measurements.

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Ageing of wet-synthesized oxide powders

Wet chemical synthesis of precursor oxide ceramics is a method to obtain small particulate powders. Such powders are far more prone to ageing in air than more traditional precursors. Thermogravimetric analysis is used to highlight the species responsible for the ageing of ceramic precursors. Indeed water and carbon dioxide are observed to evolve from aged powders. Ceramics obtained from aged precursors can reach a very low final density with respect to the theoretical value. A large degree of the original sintering properties can be recovered after washing the aged powders with ethanol in a basic medium.     

Ammonolysis of magnesiothermic tantalum powders

Tantalum nitrides are synthesized by ammonolysis of a mesoporous magnesiothermic tantalum powders. The effect of specific surface area of the powders and synthesis temperature on product composition is shown. Nitrogen content in the ammonolysis product of tantalum powder with a specific surface area of 56 m² g^–1 corresponds to oxynitride TaON exposed to 600°C for 1 h. The specific surface area of the oxynitride is 35 m² g^–1.     

Synthesis of yttrium orthoborate powders

Yttrium orthoborate YBO₃ is synthesized by calcining precursors precipitated with aqueous ammonium hydroxide from yttrium nitrate or yttrium chloride solutions (with concentrations ranging from 4.8 × 10^?3 to 0.0165 mol/L) and with a more than tenfold excess of boric acid. Single-phase YBO₃ is obtained at pH 5–6. Higher pHs result in the formation of mixtures of yttrium orthoborate and yttrium hydroxide phases. Dehydration occurs up to 288°C as shown by differential thermal analysis. Further heating induces crystallization. Addition of surfactants (polyvinylpyrrolidone (PVP) or ammonium polyacrylate (APA)) to the starting solution in an amount of 1 wt % of the yttrium salt affects the sizes and shapes of the precipitated particles. YBO₃ platelets with nanometer thicknesses are obtained. The temperature of the low-temperature ? high-temperature vaterite phase transition in YBO₃ is 977°C upon heating and 640°C upon cooling.     

Diffuse reflectance spectroscopy of powders

Diffuse reflectance (DRIFT) spectra in the mid-IR region, especially of inorganic powders, often reveal inverted or derivative-like structures (“reststrahlen” bands) which make their straightforward interpretation in terms of the Kubelka-Munk theory difficult. A simulation technique based on a combination of single scattering (Mie theory) and radiative transfer (with Kubelka-Munk as a special case) is reported that allows measured DRIFT spectra to be described without use of any free “fit” parameters. The results for silica glass microspheres and silicon carbide powder show that not specular reflectance but prominent structures in the single particle scattering cross-section are responsible for the reststrahlen features which cannot be suppressed even by diluting the powder in an excess of KBr. The efficiency of a “blocker” device in DRIFTS is also discussed.     

Sintering of hydroxyapatite lath-like powders

Hydroxyapatite powders, which consisted of lath-like single-crystalline particles, were calcined at two different temperatures. Green and calcined powders were used for sintering HAp ceramic samples under uniaxial pressing. Powders and sintered samples were studied using various analytical techniques in order to determine how calcination affects the particle properties and the sintering behavior of HAp powders. It was found that calcination decreases the particles length and changes the particles morphology from lath-like to spherical shape. The relative density increases with increasing calcination temperature and aging time. It was found that long aging time favor the formation of thermally stable HAp particles, whereas a shorter one results in the formation of β-calcium phosphate during thermal treatment. Sintering of compacted powders begins at temperatures greater than 900°C, with a trend to increase the onset temperature as the calcination temperature is increased.     

p-Type zinc oxide powders

Zinc oxide powders prepared by decomposition of zinc peroxide and zinc nitrate show evidence of acceptor states from iodometric titrations. Chemical analysis also shows the presence of nitrogen in the samples prepared by nitrate decomposition. The evidence for acceptor states disappears on heating samples, eliminating the possibility of transport measurements on sintered samples. Complex impedance spectra suggest room temperature conductivities as high as 5 × 10⁻⁴ and 2 × 10⁻³ S/cm for these peroxide and nitrate derived zinc oxide powders, respectively. As zinc oxide particles become small there is an increase in unit cell dimensions and a red shift of the absorption edge. An even stronger red shift is observed in the case of N doping.     

Plasma synthesized nano-aluminum powders

The plasma electro-condensation process was used to synthesize nano-sized aluminum powders. Adding different chemicals modified the physical and chemical properties of these powders. To characterize the nano-sized powders, X-ray diffraction, TEM, BET analyses, and simultaneous TG/DSC analyses were performed. TG/DSC analyses revealed a dramatic degradation of the aluminum oxide layer after storage of the aluminum powder in air for a period of several months. The burning rate of the model solid propellant with nano-sized aluminum was experimentally examined. The combustion behavior of nano-sized aluminum will be presented and will be compared with the combustion behavior of the micron-sized powders.     

DNA typing of fingerprints using capillary electrophoresis: effect of dactyloscopic powders.

DNA typing is a useful tool in crime solving, not only for blood samples, sperm, or saliva but also for traces of DNA left on tools or pieces of clothing used in burglaries or thefts. On these kinds of samples, the sources of DNA are extremely small amounts of skin debris left after gripping tools. When a sensitive technique such as polymerase chain reaction (PCR) coupled with capillary electrophoresis is used, it is possible to get a profile from these low amounts of DNA. The classic technique in such cases, used in forensic sciences, is to reveal fingerprints by different dactyloscopic powders. Therefore, DNA profiling was performed on physical fingerprints left on glass and wooden plates, in order to establish eventual problems or interferences involved by using both techniques simultaneously. Eleven dactyloscopic powders were investigated on their influence on DNA typing. The results show that some can be used together with DNA profiling but that serious precautions have to be taken to avoid contamination.     

Heating of powders in an r.f. inductively coupled plasma under dense loading conditions

A study was carried out of the heating of powders in an r.f. inductively coupled plasma under dense loading conditions. The results obtained using a mathematical model taking into account plasma-particle interaction effects reveal an important cooling of the plasma caused by the presence of the particles. This, in turn, gave rise to a corresponding drop of the efficiency of the melting of the particles in the plasma. The effect is shown to depend strongly on the thermodynamic properties of the material of the powder.     

Magnetic properties of nanosized hexaferrite powders

Hexagonal ultradispersed ferrites were obtained in a high energy planetary mill by mechanochemical treatment. Their structural characteristics — average size and internal stress — were studied. Fundamental magnetic characteristics — saturation magnetization and effective fields of crystal anisotropy — were examined in pulse magnetic fields with the law of approach to saturation, as well as by ferromagnetic resonance technique in the 26–53 GHz frequency range. It was demonstrated that size reduction of powders to a few tens of nanometers influenced significantly the effective anisotropy field. A model accounting for anisotropy contribution from the disturbed subsurface layer and magnetoelastic interactions was suggested. Mechanical activation was shown to be an alternative to chemical substitution for magnetic anisotropy control.     

Micro-homogeneity studies of boron carbide powders

We have studied the micro-homogeneity of boron carbide powders by inductively coupled plasma optical emission spectrometry (ICP-OES) and total reflection X-ray fluorescence spectrometry (TXRF) using slurry sampling. To get information on the particle size distributions of the powders, the stabilized slurries of boron carbide powders were nebulized, the aerosols were transported into a Batelle impactor and the droplets were collected on the impactor stages bearing TXRF sample holders. In a first series of measurements, parameters of the impaction like the duration of the impaction and the use of glutinous substance on the sample holders were optimized. The different mass size fractions for industrial boron carbide powders were determined by weight measurements of the fractions collected on the different stages. The established particle size distributions were in the range of 0.5 to >16 μm and found similar to those determined by laser diffraction reported elsewhere. Analyses of the mass fractions by slurry sampling TXRF showed that Ca, Ti, Cr, Mn, Fe, Ni and Cu within the measurements errors were homogeneously distributed over the mass fractions between 0.5 and 4 μm and that their concentrations agreed with the bulk composition, as determined with ICP-OES subsequent to digestion. However, light underestimates were found at the 5 (Mn) up to 150 μg g^?1 (Fe) level. Finally, boron carbide powders were washed out with nitric acid with different concentrations and leaching solutions and the residues were analyzed by ICP-OES and TXRF respectively. It is shown that up to 60% of the residual trace impurities in the powder studied can be removed by leaching with 34% (v/v) of nitric acid.

球形纳米氧化锌的合成

本文报道了一种使用流变相法制备球形纳米氧化锌的方法.首先将氧化锌和尿素按摩尔比1:4混合均匀,加适量水调制成流变态,在300℃反应生成胶状物;然后将胶状物在高速搅拌下水解,将水解产物在120℃下分解;最后研究了热分解产物的表面形貌与粒度分布.实验结果表明在120℃左右生成白色球形纳米ZnO粉体,粒度分布在30-80nm...