Effect of Powder Particle Size on the Properties and Microstructure of Ti(C,N)-Based Cermet

The influence of raw powder particle size on the properties and microstructures of Ti (C, N)-based cermets has been studied. The conclusions are as follows: The microstructures of cermets were composed of two kinds of grains, the one with black cores surrounded by obvious rim structures, and the other whose cores were white with unconspicuous rim structures and adhesive phase. In the cermet made from fine powders, the amount of grains with white cores was much more than that in cermet made from coarse powders. In addition, their properties were also much better.

PREPARATION OF TEM THIN FOIL CONTAINING POWDER PARTICLE BY ELECTRODEPOSITION METHOD

A practical technique to prepare transmission electron microscopy （TEM） thin foil containing powder particle was described and the data for the codeposition of two type particles with copper in the electroplating were presented. By depositing the particles which were distributed in CuSO4 electrolyte on cathode together with Cu^2＋ in electrodeposition bath, composite coating with suitable thickness could be formed. The thin coating was separated from the substrate and cut into a disc with diameter of 3mm for electropolishing. When the Cu matrix was thinned during electropolishing, the particles contained in the coating plate were also thinned to meet the suitable thickness for TEM observation. Various experimental results revealed that during electrodepositing the current density, pH-value of electrolyte and stirring mode all have significant effects on the distribution of particles in composite coating and the surface quality of the composite coating. The proper parameters used during electrodepositing to prepare TEM thin foil containing powder particle were discussed.

Particle Size Distribution,Powder Agglomerates and Their Effects on Sinterability of Ultrafine Alumina Powders

An intensive study of the particle size distribution of four commercial ultrafine alumina powders to obtain information about the powder agglomeration and relate them to the compactibility and the sinterability has been made.

Effects of Particle Size and Content of Silicon Powder on Strength and Microstructure of Coked Al_2O_3-ZrO_2-C Refractories

Effects of particle size （A：d50 = 336. 9 μm, B：d50 =123.5μm, C： d50=19.5 μm, D： dso=2.21μm） and content （1 wt% , 3 wt% , 5 wt% , 7 wt% ） of silicon powder on cold crushing strength （CCS） , pore size distribution and microstructure of Al2O3 - ZrO2 - C refractories coked at high temperature had been investigated by means of mercury porosimeter, SEM, EDS, tic. The results indicated that particle size and content of silicon powder affected the cold crushing strength of coked specimens. It increased with the addition of silicon powder and its finer particle size. However, it decreased greatly when using too fine silicon powder. The particle size and content of silicon powder also impacted the phase evolution and microstructure of coked specimens, much more β-SiC whiskers constituted network structure and well distributed in specimens with reduction of their slenderness ratios when finer silicon powder was added, corresponding to that, the specimens＇ pore size distribution range became narrower with smaller pore diameter, but β-SiC whiskers were distributed sparsely and the specific pore volume of small pores increased when much finer powder was added. It was worthly mentioned that some nitride could form in specimens with addition of appropriate particle size and content of silicon powder.

Numerical simulation of powder effect on solidification in directed energy deposition additive manufacturing

An integrated simulation of powder effects on particle temperature and microstructural evolution in laser directed energy deposition additive manufacturing process was carried out.The spatial distribution of the flying powder particles was simulated by the discrete element method to calculate the energy for the flying powder particles under the laser−particle interaction with electromagnetic wave analysis.Combined with the phase field method,the influence of particle size on the microstructural evolution was studied.The microstructural evolution is validated through comparison with experimental observation.Results indicate that the narrow particle size distribution is beneficial to obtaining a more uniform temperature distribution on the deposited layers and forming smaller equiaxed grains near the side surfaces of the sample.Appropriate powder particle size is beneficial to the conversion of the electromagnetic energy into heat.Particles with small size are recommended to form equiaxed grains and to improve product quality.Appropriate powder flow rate improves the laser energy efficiency,and higher powder flow rate leads to more uniform equiaxed grains on both sides of the cross-section.

Dynamic simulation and experimental study of the effect of one-dimensional vibration on the packing of wood powder particles

In the industry of production of high-density fiberboards without adhesive,applying vibration to the particle packing system before pressing and molding is an effective way to improve the uniformity of particle packing and reduce porosity.In this work,physical experiments combined with numerical simulations are used to systematically investigate the packing structure behavior of wood powder particles under different vibration conditions.Macroscopic and microscopic properties such as porosity,coordination number,radial distribution function,and contacts are characterized and analyzed.The results indicate that when the vibration frequency is 72 Hz and the vibration amplitude is 1 mm,the porosity of wood powder particles closely packed is minimized.The results of the Discrete Element Method show that the distribution of the coordination number is approximately normal.As the vibration conditions change,the packing structure becomes tighter,but the main peak of the radial distribution function becomes blurred or even disappears.Vibration does not significantly change the type of contact in the packing structure.The conclusions can provide more comprehensive vibration conditions and microscopic theories for the uniform spreading of wood powder particles before pressing,ensuring that the finished panels have excellent mechanical and physical properties.

Particle Size Effects on Antioxydant and Hepatoprotective Potential of Essential Oil from Eucalyptus camaldulensis Leaves against Carbon Tetrachloride-Induced Hepatotoxicity in Rats

Particle size fractionation by sieving is used to optimize antioxydant potential of natural substances. The aim of the present study was to evaluate particle size effects on antioxidant and hepatoprotective potential of Eucalyptus camaldulensis essential oils (EO) on CCl4-induced hepatic damage in Wistar rats. Animals were daily orally treated with the EOs extracted by hydrodistillation from powder sieved at four particle sizes (≥355, 200 - 355, 100 - 200, ≤100 μm) and those of the unsieved powder at dose of 50 mg/Kg for 7 days. Compounds that are evaluated for these activities are hydrocarbons and oxygenated terpenes that were identified and quantified by GC/MS. Activities of enzymes markers of hepatocellular damage in serum and antioxidant enzymes in the liver homogenates were measured. In this research, EOs significantly prevented the increase in serum ALT and AST (p < 0.05), total cholesterol, triglyceride and LDL-cholesterol level in acute liver damage induced by CCl4 and significant increase level of plasma HDL-cholesterol. Also, significantly (p < 0.05) decreased the extent of malondialdehyde (MDA) formation and elevated the activities of superoxide dismutase (SOD) and catalase (CAT) liver in comparison to negative control group. The best antioxidant and hepatoprotective activities were those of EOs from two fine powder fractions (≤100 μm and 100 - 200 μm) was correlated to their high concentration in oxygenated terpenes (70.9% and 46.4%, respectively), when compared to the large particles (200 - 355 μm and ≥355 μm, with 33.3% and 41.8%, respectively) and unsieved powder (37.4%).

Influence of Rare Earth on Carbide in Weld Metal

The physical characteristics of Ni based superalloy powder with different particle sizes produced by plasma rotation electrode process (PREP) and the microstructure and mechanical properties of P/M superalloy products were investigated. The experimental results show that the optimum powder particle sizes should be in the range of 50-100 μm or 50-150 μm, which can reduce production cost, simplify process and guarantee P/M product quality.

DEM analysis of the effect of electrostatic interaction on particle mixing for carrier-based dry powder inhaler formulations

Particle interactions play a significant role in controlling the performance of dry powder inhalers （DPIs）, which mainly arise through van der Waals potentials, electrostatic interactions, and capillary forces. Our aim is to investigate the influence of electrostatic charge on the performance of DPIs as a basis for improv- ing the formulation of the particle ingredients. The mixing process of carrier and active pharmaceutical ingredient （API） particles in a vibrating container is investigated using a discrete element method （DEM）. The number of APl particles attaching to the carrier particle （i.e., contact number） increases with increas- ing charge and decreases with increasing container size. The contact number decreases with increasing vibrational velocity amplitude and frequency. Moreover, a mechanism governed by the electrostatic force is proposed for the mixing process. This mechanism is different from that previously proposed for the mixing process governed by van der Waals forces, indicating that long-range and short-range adhesive forces can result in different mixing behaviours.

An investigation into flow mode transition and pressure fluctuations for fluidized dense-phase pneumatic conveying of fine powders

This paper presents the results of an ongoing investigation into the fluctuations of pressure signals due to solids-gas flows for dense-phase pneumatic conveying of fine powders. Pressure signals were obtained from pressure transducers installed along different locations of a pipeline for the fluidized dense-phase pneumatic conveying of fly ash （median particle diameter 30μm; particle density 2300 kg/m^3; loose- poured bulk density 700 kg/m^3） and white powder （median particle diameter 55 p.m; particle density 1600 kg/m^3 ; loose-poured bulk density 620 kg/m^3） from dilute to fluidized dense-phase. Standard deviation and Shannon entropy were employed to investigate the pressure signal fluctuations. It was found that there is an increase in the values of Shannon entropy and standard deviation for both of the prod- ucts along the flow direction through the straight pipe sections. However, both the Shannon entropy and standard deviation values tend to decrease after the flow through bend（s）, This result could be attributed to the deceleration of particles while flowing through the bends, resulting in dampened particle fluctua- tion and turbulence. Lower values of Shannon entropy in the early parts of the pipeline could be due to the non-suspension nature of flow （dense-phase）, i.e., there is a higher probability that the particles are concentrated toward the bottom of pipe, compared with dilute-phase or suspension flow （high velocity）, where the particles could be expected to be distributed homogenously throughout the pipe bore （as the flow is in suspension）. Changes in straight-pipe pneumatic conveying characteristics along the flow direction also indicate a change in the flow regime along the flow.

Flow behavior and deposition study of pollen-shape carrier particles in an idealized inhalation path model

Pollen-shape （spiked sphere） hydroxyapatite （HA） particles for drug carrier application are studied. The particle shape and size effect on flow characteristics and deposition are assessed. The pollen-shape HA particles are synthesized to have comparable size as typical carrier particles with mean diameter of 30-50 μm and effective density less than 0.3 g/cm^3. The flow behaviors of HA and commonly used lactose （LA） carrier particles are characterized by the Carr＇s compressibility index （CI）. The HA particles have lower CI than the LA particles for the same size range. The flow fields of HA and LA carrier particles are measured in an idealized inhalation path model using particle image velocimetry （PLY） technique. The particle streamlines indicate that a large portion of particles may deposit at the bending section due to inertial impaction and gravitational deposition. The flow field result shows that HA particles give smaller separation regions than the LA particles for the same size range. The pollen-shape HA particles are found to be able to follow the gas flow in the model and minimize undesired deposition. Deposition result confirms the bending section to have the most deposition. Deposition is found to be a function of particle properties. An empirical correlation is derived for the deposition efficiency of the pollen-shape particles as a function of particles Stokes number.

Relationship between single and bulk mechanical properties for zeolite ZSM5 spray-dried particles

In this work typical mechanical properties for a catalyst support material, ZSM5 （a spray-dried granular zeolite）, have been measured in order to relate the bulk behaviour of the powder material to the single particle mechanical properties. Particle shape and size distribution of the powders, determined by laser diffraction and scanning electron microscopy （SEM）, confirmed the spherical shape of the spray-dried particles. The excellent flowability of the material was assessed by typical methods such as the Hausner ratio and the Cart index, This was confirmed by bulk measurements of the particle-particle internal friction parameter and flow function using a Schulze shear cell, which also illustrated the low compressibility of the material. Single particle compression was used to characterize single particle mechanical properties such as reduced elastic modulus and strength from Hertz contact mechanics theory. Comparison with surface properties obtained from nanoindentation suggests heterogeneity, the surface being harder than the core. In order to evaluate the relationship between single particle mechanical properties and bulk compression behaviour, uniaxial confined compression was carried out. It was determined that the Adams model was suitable for describing the bulk compression and furthermore that the Adams model parameter, apparent strength of single particles, was in good agreement with the single particle strength determined from single particle compression test.

Mechanical Properties and Fracture Behavior of Mg-Al/AlN Composites with Different Particle Contents

In this study, magnesium matrix composites reinforced with different loading of AlN particles were fabricated by the powder metallurgy technique. The microstructure, bending strength and fracture behavior of the resulting Mg-Al/Al N composites were investigated. It showed that the 5 wt% AlN reinforcements led to the highest densification and bending strength. The total strengthening effect of AlN particles was predicted by considering the contributions of CTE mismatch between the matrix and the particles,load bearing and Hall-Petch mechanism. The results revealed that the increase of dislocation density,the change of Mg17Al12 phase morphology, and the effective load transfer were the major strengthening contributors to the composites. The fracture of the composites altered from plastic to brittle mode with increasing reinforcement content. The regions of clustered particles in the composites were easy to be damaged under external load, and the fracture occurred mainly along grain boundaries.

Measuring powder flowability with a modified Warren Spring cohesion tester

The measurement of powder flowability is a major concern for most industrial processes that deal with the handling of bulk solids as raw materials, intermediates, or products. The development of devices that measure the flowability of non-aerated powders has not progressed as rapidly as might have been hoped since most research activities have been based on various types of shear testers intended to aid the design of hoppers. A new flowability indicator named as weighted cohesion （WS） is established using newly improved version of direct cohesion texture. A cornerstone of the proposed technique is that the procedure is automated, using a digital Warren Spring tester called Warren Spring-University of Malaya cohesion tester （WSUMCT）, thus making results operator-insensitive. Besides being a practical tool to diagnose the cohesion of experimental powders, the ratio between measured cohesion （using WSUMCT） and aerated density （using Hosokawa PT-S） provides us with a powerful technique to research fundamental particle internal cohesion forces directly and use these data to indicate the flowability. In this work, a series of fine （9.4μm） and coarse （60 μm） porous silica gel particle mixtures, and mixtures of fine （28μm） and coarse （72 μm） glass ballotini as well, were used as test powders. The results from these tests agree well with relative flowability determined on our newly driven indicator using WSUMCT. The validation of aerated weighted cohesion （WSA） as a flowability indicator was authenticated by comparing the conducted parameter with established measured Hausner ratio （HR） and angle of repose （AoR）.