Papers by Keyword: Ultra-Fine Particles

Abstract: Ultrafine drug powders have higher bioavaibability than the larger signed particles. Ultrafine powders of clarithromycin were produced by anti-solvent recrystallization with the acetone - water solvent systems. The effects of volume ratio of clarithromycin acetone solution to anti-solvent, stirring speed, precipitation temperature and precipitation time on the preparation process were investigated. The results show that ultrafine powders can be yielded and well-controlled under the following optimal conditions: the volume ratio of clarithromycin acetone solution to anti-solvent 1:10, stirring speed 900 r/min, precipitation temperature 20°C, and precipitation time 10 min. The ultrafine powders with the rod-shape and the mean diameter of 1.8μm with the narrow distribution were successfully obtained. The yield of drug powders is more than 83%. The powders were analyzed with FT-IR and metalloscope. The purity of drug powders is more than 98%, according with Chinese Pharmacopoeia. The operation of the experiment was very simple, and the powders were separated easily.

Abstract: The sedimentation in the field of gravity provides a practicable and scientific principle for solid-liquid separation of ultra-fine particles. According to the fractal theory, a model of ultra-fine particles for gravity sedimentation was developed, considering the aggregation effects and particles interference, and the aggregation promoting coefficient was put forward. The fractal structure and FSD of aggregates were also analyzed. Furthermore, the comparison between theoretical and experimental values of ultra-fine particles sedimentation showed that the two results were more consistent with each other for the suspension concentration ranging from 1 wt% to 5 wt%.

Abstract: The size of ultrafine particles ranges between 1~1000nm, including metal, non-metallic, organic, inorganic and biological powder materials. Because of its inherent surface effect, small size effect and quantum effect, it has special optical properties, thermal properties, magnetic properties and mechanical properties which had been widely used in various industrial fields. Supercritical fluid technology has been used to obtain ultra-fine powder of several kind of materials. This work is focused on the systematic production of ultra-fine powder using RESS and SAS process. A systematic summary is made and different measures adopted according to the related circumstances are presented. We also summarize the effect of the process parameters of RESS and SAS process. The ongoing and more extensive research on mechanism and control measures of size, morphology and size distribution of particle should provide a better understanding of particle formation mechanism and achieve the goal of integrated use of different measures to control particle preparation process in the near future.

Abstract: This study aims to investigate the effects of hybrid micro/nano powders in a micro metal injection molding (μ-MIM) process. A novel type of mixing-injection molding machine was used to produce tiny specimens (<1mm in size) with high trial efficiency using a small amount of feedstock (<0.05cm3 in volume). Small dumbbell specimens were produced using various feedstocks prepared by changing binder content and fraction of nano-scale Cu powder (130nm in particle size). The effects of adding the fraction of nano-scale Cu powder on the melt viscosity of the feedstock, microstructure, density and tensile strength of sintered parts were discussed.

Abstract: Fine powder of CaZrO3 (CZ) was synthesized by using ultra-fine and highly dispersed CaCO3 as a precursor. The results showed that the calcination temperature could be reduced to inhibit grain growth of CZ. Mean grain size of the CZ fine powder was 80 nm. Moreover, the CZ powder was used to synthesize a solid solution of (Ba,Ca)(Zr,Ti)O3 (BCZT) to examine the effect of the powder’s grain size on the reactivity of BT and CZ. It was found that the fine CZ powder enhanced the BT and CZ reaction.

Abstract: The authors have observed directly and simultaneously the laser-induced plasma and keyhole behavior by high speed frame/streak camera using a special optical systems during the pulsed YAG laser welding of Al-Mg alloys in air and argon atmospheres. The dynamic behavior of Al-Mg alloys plasma was very unstable and this instability fluctuation period was about 440µs. After laser termination, abrupt collapse of keyhole within 600µs was observed and it was related to the formation of porosity. The authors also performed the spectroscopic analysis of laser-induced plasma, and clarified the structure and composition of evaporated particles during pulsed laser welding of Al-Mg alloys. In the air environment, the intensities of molecular spectrum of AlO and MgO were different each other depending on the power density of laser beam. Under the low power density irradiation condition, the MgO band spectrum was predominant in intensity, while the AlO spectrum became much stronger in higher power density. The same result was revealed in analyzing the composition of evaporated particles. These results were attributed to evaporation phenomena of metals with different boiling points and latent heats of vaporization.