Papers by Keyword: Powder Characteristics

Abstract: Powder characteristics and granule morphology of steel slag cooled by water-quenching and air splashing were observed with SEM and their rest angle, compressed density and mechanical characteristics were measured. The result shows that particle sphericity of air splashing steel slag is lower than that of water-quenching steel slag. A compressive stress has a more effective on the deaggregation of water-quenching steel slag powder. Both of the two steel slag powders are typical Coulomb powder. Compared with the water-quenching steel slag powder, air splashing steel slag powder has a higher internal friction angle and cohesiveness. The cementitious activity of BOFS Powder can only meets the standard of the second grade powder according to the Chinese National Standards.

Abstract: A novel process was developed to make micro-fine spherical high Nb containing TiAl alloyed powders in quantity. Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y(at%) ingot prepared by vacuum induction melting was heat-treated for homogenization, and then machined with a crusher. The chippings were refined by fluidized bed jet milling, and subsequently spheroidized with radio frequency (RF) argon plasma. The effects of processing parameters on powder characteristics were studied. By fluidized bed jet milling, the particle size and distribution uniformity both decline with the rise of classifier frequency. Above 5800rpm, the number-average diameter is lower than 20μm with a bimodal particle size distribution. The powders consist of coarse plate-shaped particles and some finer flaky debris, and with the further rise of the frequency, the amount of debris gradually increases. The plasma-spheroidized powders are found to possess good sphericity and composition homogeneity with phase dominated by supersaturated α2-Ti3Al. The granulometric characteristics of the spherical powders strongly depend on those of the feed powders. For the jet milled powders below 5800rpm, due to the relatively lower size distribution uniformity, the fine particle fraction reduces after spheroidization, which causes an obvious improvement of distribution uniformity and the corresponding increase of number-average diameter

Abstract: Spherical molybdenum powders were synthesized by (RF) plasma with irregular molybdenum powders. The powder characteristics and spheroidization efficiency of the feeding rate for obtain the spherical molybdenum powders were studied. The phase composition and morphological properties of the powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). As a result, the fine spherical powders composed of pure molybdenum with favorable dispersity and its surface became smooth. The spheroidization efficiency of synthesized powders was almost 100 % at feeding rate of 5g/min. LMS analysis indicated that the as-prepared powder had narrow particle size distribution and the spheroidization efficiency of the sample decreases gradually as increasing of the feeding rate. The RF plasma spheroidization of molybdenum powder is an ideal route synthesis of well- spherical molybdenum powders used as near net-shape technology and powder metallurgy.

Abstract: The setting reaction of magnesium phosphate cements starts with water addition to a mixture of ammonium phosphate and magnesium oxide, is very fast and takes place at room temperature (cold setting). Literature shows that controversy is still going on about the reaction mechanism, hence, about the effect on the setting time of factors such as the water/cement ratio or the magnesia specific surface area. This work is focused on the magnesia powder characteristics, which were varied by calcining MgO at temperatures ranging from 900 to 1050°C, for periods of 30 to 60 min. Cement pastes were obtained by mixing MgO and diammonium phosphate with water and setting aids. The pastes were left to set in air and were characterized in terms of mineralogical composition (XRD) and microstructure (SEM). The results obtained show how the combined effect of the magnesia characteristics can be used to control the workability and adjust the setting time.

Abstract: A feedstock of Ti(Al,O)-Al2O3 composite powders was produced by high energy milling of a mixture of Al and TiO2 powders followed by a thermal reaction process. The feedstock was then thermally sprayed using a high velocity oxygen-fuel (HVOF) technique on H13 steel substrates to produce Ti(Al,O)-Al2O3 composite coatings. The performance of the coatings was assessed in terms of thermal fatigue behaviour and reaction with molten aluminium (soldering). The composite powders and coatings were characterised using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). This paper reports the experimental observations and discusses characteristics and potential applications of the composite coatings.

Abstract: In this study, the effect of SiC powder characteristic on the rheological properties of the feedstock was investigated. It was found that the viscosity of the feedstock decreased with the increase of the particle size. For the binary powder mixtures, the viscosity of the feedstock decreased with the increase of the particle size ratio of the larger particle to finer particle, which is attributed to the increase of the tap density of the powder.