Preparation Of Ultrafine Powders Research Articles

Phytochemical properties and antioxidative activities of ginseng superfine powders prepared by wet grinding method with high-pressure homogenization

Ginseng is widely used in agricultural products, dietary health supplements, and pharmaceutical preparations, which has significant market potential. It is of great significance to develop a more efficient and environmentally friendly production process of ginseng powder. However, ginseng is difficult to be milled to an ideal state by dry grinding method because of its higher fiber content. In the meantime, ginseng has high viscosity when suspended in a liquid, which can pose challenges during wet grinding processes. In order to develop a production process for ginseng powder with excellent physicochemical properties, three kinds of powders were obtained by both dry grinding method (ball mill) and wet grinding method (colloid mill&high-pressure homogenizer) in this study. The powder properties, structural properties, saponin contents,and antioxidant activity of different ginseng powders were also investigated. The results showed that wet grinding technology using a high-pressure homogenization process could significantly improve the powder properties，including the particle size, specific surface area, span value, water holding capacity, and appearance. Moreover, both the saponin contents and the antioxidant activity of the powder had been significantly enhanced. The findings indicated that high-pressure homogenization process was a promising technique for producing plant powders rich in bioactive compounds, which could enhance their bioactivity. The method was argued to be a significant alternative technology for production of ginseng ultrafine powders. Furthermore, it offered theoretical and technical support for the application of the high-pressure homogenization process in the preparation of ultrafine powders with reduced particle sizes from high-fiber plants.

Preparation of ferric oxide powders by ultrasonic‐assisted impinging stream reaction

AbstractIn this paper, Fe3O4 powder was prepared by the chemical precipitation method using impinging stream technology. The influences of feed flow rate, L/D, reactant concentration, ratio of iron ion concentration, reaction temperature, and impact time on the size and distribution of particles were investigated by the orthogonal experiment method. The microstructure and morphology of Fe3O4 powders were characterized by scanning electron microscopy, X‐ray diffractometer, and granulometer. The results showed that when ratio of iron ion concentration c(Fe2+):c(Fe3+) = 0.75, reactant concentration c(Fe3+) = 0.4 mol · L−1, feed flow rate Q = 800 L · h−1, L/D = 3, reaction temperature T = 20°C, impact time t = 50 min, the prepared Fe3O4 had an average particle size of 1.815 μm and the most uniform distribution. The influence of ultrasonic enhancement on the mixing process and powder preparation in an impinging stream reactor was investigated. The size and distribution of the powders were significantly affected by ultrasonic enhancement. With the increase in ultrasonic power, the particle size of the powders decreased and the distribution became narrower. The particle size was reduced by 68.78%, and the particle distribution range was narrowed by 84.34% under ultrasound enhancement. This study promised the effective utilization of ultrasonic cavitation in the optimization of experimental equipment and the preparation of ultrafine powder, which provides a basis for process optimization of powder preparation.

Preparation of ultra-fine powders from polysaccharide-coated solid lipid nanoparticles and nanostructured lipid carriers by innovative nano spray drying technology

In this study, five polysaccharides were applied as natural polymeric coating materials to prepare solid lipid nanoparticles (SLN) and nanostructure lipid carriers (NLC), and then the obtained lipid colloidal particles were transformed to solid powders by the innovative nano spray drying technology. The feasibility and suitability of this new technology to generate ultra-fine lipid powder particles were evaluated and the formulation was optimized. The spray dried SLN powder exhibited the aggregated and irregular shape and dimension, but small, uniform, well-separated spherical powder particles of was obtained from NLC. The optimal formulation of NLC was prepared by a 20⿿30% oleic acid content with carrageenan or pectin as coating material. Therefore, nano spray drying technology has a potential application to produce uniform, spherical, and sub-microscale lipid powder particles when the formulation of lipid delivery system is appropriately designed.

Preparation of Ultra-Fine Powder Using Supercritical Fluids: A Review

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.

Study of Scale Effect on the Iron Oxide Reduction

According to the analysis of iron element purification in the current process of steel production and the study on reduction experiment of ultrafine iron ore powder, this study first summarizes and puts forward the scale effect on reduction of iron oxide. And on this basis, a new concept is proposed, named precise reduction, which includes the pre-processing—dissociation of iron oxide, preparation of ultrafine powder and the post processing—non-molten magnetic separation. Taking high phosphorus hematite, steelmaking slag and metallurgical dust as the study objects, and the better achievement shows that the low grade iron-bearing material, after precise reduction, can be transformed to the valuable resource without residue, and the process is environment friendly with low energy and material consumption, so that the zero discharge can be achieved. Not only does the steel plant be changed to be environment friendly, but also the resource is got.

Solid‐State Synthesis of Nanocrystalline BaTiO3: Reaction Kinetics and Powder Properties

The formation of BaTiO3 nanoparticles by a solid‐state reaction between nanocrystalline raw materials BaCO3 and TiO2 was studied as a function of temperature (400°–800°C), time (1–24 h), and titania particle size (15 and 30 nm). The reaction starts at 500°C and a high reaction rate is already observed at 600°C for the finest titania, with up to 90% conversion after 2 h. Two main reaction stages were observed at 600°–700°C. The first step is dominated by nucleation and growth of BaTiO3 at the TiO2–BaCO3 contact points and at the TiO2 surface. Surface diffusion of BaCO3 is, most likely, the prevailing mass transport mechanism responsible for the rapid formation of BaTiO3, even in the absence of a significant contribution from lattice diffusion. The second stage begins when the residual TiO2 cores are completely covered by the product phase. For longer times, the reaction can only proceed by the slower lattice diffusion, resulting in a strong decrease of the reaction rate. Single‐phase BaTiO3 nanopowders with a specific surface area of 12–15 m2/g, an average particle size of 70–85 nm, a relative density of 96.5%–98.3%, and a tetragonality of 1.005 were obtained by calcination at 700°–800°C. Critical parameters in the preparation of ultrafine powders by solid‐state reactions are the particle size of both raw materials, the absence of large hard agglomerates, and the homogeneity of the mixture. The use of fine raw materials and optimization of the reaction conditions make mechanical activation unnecessary.

New approach to the fabrication process of bulk high-Tcsuperconducting oxide materials with strong pinning of magneticflux

A new approach to the fabrication process of bulk HTSCmaterials is proposed, using the initial mixture of components (YBa2Cu3O7-x and non-superconducting inclusions) in the formof nanocrystalline powders. The preparation of ultra-fine powders is by meansof the pulse-plasma channel method, which allows metallic, oxide and alloymaterials etc (including HTSC) to be dispersed into spherical particles of20-200 nm size. Bulk specimens of YBa2Cu3O7-x(d~250 nm) + 2% ZrO2 (d~70 nm) were produced by pullingthe initial mixed powders through a gradient furnace. The results ofstructural, magnetic, and magneto-optical measurements are reported for thepowders and the bulk samples. The critical current density, jc, of the bulkcomposites range from 104 to 2×104 A cm-2 at 77 K inzero magnetic field. The magnetic measurements and magneto-opticalobservations reveal that jc is independent of direction in the compositeand corresponds to the transport current through the whole sample. The meandistance between pinning sites coincides with the mean grain size of YBa2Cu3O7-x, which confirms homogeneous distribution of theinclusion particles.

Preparation of ultrafine powders of Nb2O3 by hydrothermal H2O2 oxidation starting from metallic Nb

Abstract Ultrafine powders of Nb2O5 were prepared by hydrothermal H2O2 oxidation of metallic Nb, resulting in the formation of the high pressure pseudo-hexagonal phase. After annealing at 600 °C for 24 h, a transformation to the orthorhombic L-phase Nb2O5 occurred, which is also a high pressure phase.

A device for dispersing salt solutions during cryochemical preparation of ultrafine powders

A device for dispersing salt solutions during cryochemical preparation of ultrafine powders

Preparation of ultrafine powders by nanopowder process

Preparation of ultrafine powders by nanopowder process

粉体成形技術によるハイブリッド化

粉体成形技術によるハイブリッド化

Preparation of ultrafine powders of AlN and (AlN + Al) by nitrogen plasma-Al reaction

Ultrafine powders of AlN and (AlN+Al) with particle sizes of less than 0.5μm were produced by arc melting of Al in atmospheres of N2+Ar, N2+H2, N2+NH3 at 0.1MPa pressure. The size, surface area, chemical composition, and crystal structure of obtained powders were determined by electron microscope, BET method, chemical analysis and X-ray diffraction analysis respectively. The following results were obtained.(1) AlN ratio in (AlN+Al) powders obtained in (N2+Ar) atmospheres decreases from 0.3 to zero with decreasing nitrogen partial pressure.(2) AlN ratio in (AlN+Al) powders obtained in (N2+NH3) atmospheres increases from 0.3 to 0.95 with increasing NH3 partial pressure.(3) Projections were formed on molten Al surface by evolved nitrogen gas from the melt and by reaction between nitrogen and molten Al.The reaction between nitrogen plasma and molten Al plays an important role in the formation of ultrafine particles. The driving force for the formation of ultrafine particles can be explained as follows; In arc melting of Al in a nitrogen atmosphere, molten Al simultaneously contacts with two gas phases, one is atomic nitrogen in the arc gas phase and another is the molecular nitrogen in the non-arc gas phase. The extent of dissolution of atomic nitrogen in the molten Al is much larger than that of molecular one. Then, the dissolved nitrogen through the arc gives higher nitrogen content for the non-arc gas phase. That is, super-saturated nitrogen will evolve in non-arc gas phase carrying with Al vapor. A kind of enhanced evaporation of Al is induced. This Al vapor reacts with surrounding gas species near the arc such as N2, N, NH3, NH2, NH in high temperature ranges (above 1600K) to form AlN or (AlN+Al) vapor which condense to ultrafine particles.

Preparation of Ultrafine Powders of AlN and (AlN+Al) by Nitrogen Plasma-Al Reaction

Ultrafine powders of AlN and (AlN+Al) with particle sizes of less than 0.5μm were produced by arc melting of Al in atmospheres of N2+Ar, N2+H2, N2+NH3 at 0.1MPa pressure. The size, surface area, chemical composition, and crystal structure of obtained powders were determined by electron microscope, BET method, chemical analysis and X-ray diffraction analysis respectively. The following results were obtained.(1) AlN ratio in (AlN+Al) powders obtained in (N2+Ar) atmospheres decreases from 0.3 to zero with decreasing nitrogen partial pressure.(2) AlN ratio in (AlN+Al) powders obtained in (N2+NH3) atmospheres increases from 0.3 to 0.95 with increasing NH3 partial pressure.(3) Projections were formed on molten Al surface by evolved nitrogen gas from the melt and by reaction between nitrogen and molten Al.The reaction between nitrogen plasma and molten Al plays an important role in the formation of ultrafine particles. The driving force for the formation of ultrafine particles can be explained as follows; In arc melting of Al in a nitrogen atmosphere, molten Al simultaneously contacts with two gas phases, one is atomic nitrogen in the arc gas phase and another is the molecular nitrogen in the non-arc gas phase. The extent of dissolution of atomic nitrogen in the molten Al is much larger than that of molecular one. Then, the dissolved nitrogen through the arc gives higher nitrogen content for the non-arc gas phase. That is, super-saturated nitrogen will evolve in non-arc gas phase carrying with Al vapor. A kind of enhanced evaporation of Al is induced. This Al vapor reacts with surrounding gas species near the arc such as N2, N, NH3, NH2, NH in high temperature ranges (above 1600K) to form AlN or (AlN+Al) vapor which condense to ultrafine particles.

水熱反応法による超微粒子粉体の合成

水熱反応法による超微粒子粉体の合成

液相からの超微粒子粉体の製造

液相からの超微粒子粉体の製造