Grain Size Of Powder Research Articles

Preparation and excellent mechanical properties of nanocrystalline GW103K Mg alloy by HDDR technology

Grain size of GW103K Mg alloy powder were markedly refined to about 45 nm from 20 μm by an optimized hydrogenation-disproportionation-desorption-recombination (HDDR) process. By changing temperature, hydrogen pressure and time, the optimum hydrogenation conditions are explored by orthogonal design. Then the complete dehydrogenation process was determined by using single factor control variables. Furtherly, the HDDRed powder was spark plasma sintering (SPS) sintered and hot extruded to prepare GW103K alloy bulk. XRD, OM, scanning electron microscopy (SEM), and transmission electron microscope (TEM) were used to analyze the phase transformation and microstructure evolution, based on which the grain refining mechanism during the HDDR were discussed. The optimum HDDR parameters for preparing nanocrystalline Mg alloy powders are hydriding at 550 °C under 5 MPa hydrogen pressure for 24 h and dehydriding at 550 °C for 8 h in vacuum. The nanocrystalline GW103 alloy presents a notable dimensional stability and the grain size of the alloy bulk is 43 nm after SPS and hot extrusion. As a result, the nanocrystalline GW103K specimens exhibit excellent mechanical properties compared to the coarse-grained counterparts. Especially, the nanocrystalline GW103K alloy has a tensile elongation of 21.1% which is much more than those of the as-cast and as-extrusion alloys.

The influence of ball milling conditions on the powder characteristics and sintering densification of Mo[sbnd]Cu alloy

Mechanical alloying was utilized to produce Mo-30Cu(wt%) composite powder. The effects of milling conditions on the powder characteristics and sintering densification were investigated. The morphological evolution during the mechanical alloying process can be categorized into four stages: 1-individual Mo and Cu particles, 2-coexistence of Mo particles and blocky MoCu composite particles, 3-coarse irregular composite particles, and 4-refined near-spherical composite particles or lamellar MoCu composite particles, depending on whether process control agent (PCA) is added. The mechanical alloying degree of the MoCu composite powder was deepened gradually from stage 1 to 4, which is influenced by the ball milling parameters. As the milling speed and milling time increase, the lattice strain and the alloying degree of the MoCu composite powders increase while the grain size of molybdenum particles decreases, which is conducive to accelerating the sintering density. Among these ball milling parameters, an elevated milling speed notably accelerates the mechanical alloying process and the sintering density. Under the milling speed of 600 r/min, ball to powder ratio (BPR) of 10:1, and milling time of 4 h, the grain size, lattice strain, and average particle diameter of the composite powder were measured to be 48.4 nm, 0.247 %, and 21.04 μm, respectively, with the particle morphology being nearly spherical. The sintered density of the MoCu composite reached 98.1 %, larger than the other composites.

Unification of particle size analysis results, part 1 − comparison of particle size distribution functions obtained by various measurement methods

This article concerns comparing the grain size distribution functions of mineral powder samples and analyzes errors obtained by various measurement methods. The research used three standard and currently most frequently used methods: sieve analysis, laser diffraction analysis and vision analysis. The most important research, from the point of view of unification of results, consisted in performing precise analyses of the grain size of mineral powders (fly ash, gneiss, quartz sand and Cu ore) in various grain classes. The measurement techniques used in the research and issues related to measurement analytics were characterized. The distribution functions of the grain size distributions of the tested material samples were obtained by different measurement methods and the measurement errors were compared. Using the coefficient of variation CV calculated for characteristic particle diameters, the accuracy of measurements made using various methods was analyzed. It has been shown that different particle size measurement techniques give significantly different particle size distributions for the same material, with the grain size distribution of the measured samples having a greater impact on the results than the material itself. The lowest values of the coefficients of variation were obtained for wet sieve analysis and the highest for laser diffraction. Reliable data informing about grain size distributions were generated for further model calculations necessary to standardize the results between measurement methods.

Preparation of potato granules powder by low temperature ultrafine grinding and its effect on the texture of bread

AbstractIn this article, low temperature ultrafine grinding and other three kind of crushing methods were used to prepare potato granules powder. And the swelling power and solubility, water‐holding capacity, gelatinization characteristics, particle size, and chromaticity of different particle size levels of potato granules powder were determined. The experimental results showed that the potato granules powder prepared by low temperature ultrafine grinding had the highest solubility and swelling power, and the highest degree of pre‐gelatinization; With the increase in the addition of potato powder, the water absorption of the dough increased, and been more rheological. The volume of bread gradually decreases and the firmness increases. With the decrease of potato granules powder size, the water absorption of dough decreases and the bread hardness increases. In this experiment, when the grain size of potato powder was 200 mesh and the addition amount was 2%, the sensory score was the highest and the taste was the best. The result provides theoretical and practical basis for the production of potato bread and the comprehensive utilization of potato resources.Practical applicationsThe present study demonstrates the effective preparation of potato whole powder particles through low temperature ultrafine grinding. Comparative analysis with shear grinding, ball grinding, and room temperature grinding reveals that low temperature ultrafine grinding yields superior solubility, swelling, and gelatinization characteristics. Furthermore, incorporating 200 mesh fine potato powder in bread formulation significantly enhances dough rheological properties and water absorption while improving bread hardness and flavor. The findings offer a solid theoretical and practical foundation for the production of potato bread and the comprehensive utilization of potato resources.

Preparation of CrB2 mixtures and formation of briquettes for drill bit composites

The research described in the article concerns advanced methods of creating composite materials for drill bits used in extreme conditions of deep wells. The main attention is paid to development of multicomponent mixtures that ensure uniform distribution of powders of tungsten carbide, cobalt, chromium diboride and diamond. This is achieved through careful selection of particle size and proportions, which is critically important to ensure high strength and wear resistance of final materials. The Spark Plasma Sintering (SPS) method was chosen for the production of samples of carbide matrices and composite diamond-containing materials because of its ability to provide high density and uniformity of the material. SPS allows temperature and pressure control during sintering process, which contributes to the formation of materials with optimal physical properties. The article also discusses in detail design parameters of the diamond bit, including the choice of grain size of diamond powder and other components. These meters have been optimized to max-imize drilling efficiency and extend tool life. The diamond powders used in study were obtained from De Beers, South Africa and are characterized by high quality and uniformity. The results presented in the article can have a significant impact on future production of drilling tools, offering new approaches to choice of materials and methods of their processing, which ultimately can lead lower drilling costs and increased process safety. These innovations can also contribute to more efficient development of new fields, which is of great importance for the energy industry and the mining industry.

“Hexacelsian slurry development for 2D woven alumina fiber impregnation in CMC fabrication”

The rheological properties of BAS (BaAl2Si2O8) slurries are investigated in order to optimize the impregnation of an alumina preform to manufacture oxide/oxide composite materials. The fiber preform morphology has been deeply investigated, especially the fiber to fiber gap within tows and compared to the grain size of the matrix powder. The slurry viscosity is measured as a function of powder and organic additives concentration to find the best combination. The optimal combination is evaluated by different measurements including: zeta potential, sedimentation and wettability to verify the slurry behavior for the fibers infiltration. An aqueous slurry containing 20–25 vol% of BAS with 1 wt% of dispersing agent (Darvan 821-A™) improved the rheological properties for fibers infiltration. Finally, characterizations of the composite show a good infiltration in the fiber tows spaces and indicate a mean porosity of 37 vol%, including 9 vol% of macroporosity.

The Preparation of an Ultrafine Copper Powder by the Hydrogen Reduction of an Ultrafine Copper Oxide Powder and Reduction Kinetics.

Ultrafine copper powders were prepared by the air-jet milling of copper oxide (CuO) powders and a subsequent hydrogen (H2) reduction. After milling, the particle size and grain size of CuO powders decreased, while the specific surface area and structural microstrain increased, thereby improving the reaction activity. In a pure H2 atmosphere, the process of CuO reduction was conducted in one step, and followed a pseudo-first-order kinetics model. The smaller CuO powders after milling exhibited higher reduction rates and lower activation energies compared with those without milling. Based on the unreacted shrinking core model, the reduction of CuO powders via H2 was controlled by the interface reaction at the early stage, whereas the latter was limited by the diffusion of H2 through the solid product layer. Additionally, the scanning electron microscopy (SEM) indicated that copper powders after H2 reduction presented a spherical-like shape, and the sintering and agglomeration between particles occurred after 300 °C, which led to a moderate increase in particle size. The preparing parameters (at 400 °C for 180 min) were preferred to obtain ultrafine copper powders with an average particle size in the range of 5.43-6.72 μm and an oxygen content of less than 0.2 wt.%.

Synthesis of nanocrystalline W[sbnd]Cu powders via freeze-drying and hydrogen reduction

The preparation of nanocrystalline WCu powders plays a significant role in the production of high-performance WCu composites. The chemical reduction method is a promising approach for industrial nano-powder synthesis. However, the influence of various reduction parameters on the morphology and grain size of the reduced powders, as well as their underlying mechanisms, have remained unclear. In this study, we investigated the effects of reduction steps, temperature, duration, hydrogen inflow rate, and copper content on the grain size of the composite powders and disclosed the related mechanisms. Through optimization of reaction parameters, WCu powders with grain sizes below 50 nm were obtained. Moreover, the utilization of the synthesized nanocrystalline WCu powders as raw materials yielded a bulk W20Cu composite with an ultrahigh hardness of 600 HV30.

BN6BT ceramics via cold‐sintering with annealing: Effects of grain size of precursor powders and annealing temperature

AbstractIn this work, (Bi0.5Na0.5)0.94Ba0.06TiO3 (BN6BT) lead‐free ceramics were prepared via cold‐sintering followed by annealing, and effects of grain size of precursor powders and annealing temperature on microstructure, dielectric, and ferroelectric properties of the ceramics were studied. The precursor powders for cold sintering were obtained by mixing the powders with sub‐micrometer (average grain size, AGS = 0.26 μm) and nanometer (AGS = 73 nm) grains in various mass ratios (1:0, 1:1, 1:2, and 1:4). The precursor powders were mixed with deionized water and cold sintered at 180°C for 1 h under 500 MPa. The cold‐sintered samples were then annealed at temperatures between 800 and 1000°C for 2 h. For the ratios of 1:2 and 1:4, the corresponding ceramics annealed at 950°C exhibit dielectric and ferroelectric properties similar to those of the BN6BT ceramics sintered at 1170°C via the solid‐state sintering method. The present BN6BT ceramics exhibit dense microstructure with finer grains with AGS = 280 nm, higher breakdown strength (BDS = 160 kV· cm−1) compared to the solid‐state sintered BN6BT ceramics with AGS = 1.6 μm and BDS = 75 kV· cm−1. The results demonstrate that the cold‐sintering followed by annealing is effective in preparing BN6BT ceramics with fine grains and excellent dielectric and ferroelectric properties at relatively low temperatures.

Effects of carbon addition on the microstructure and mechanical property of in-situ reinforced TiAl matrix composite powders produced by plasma rotating electrode process

To investigate effects of carbon addition on microstructural characteristics of rapidly solidified TiAl alloys, Ti–43Al–6Nb-xC (x = 0,0.5,1.0 at.%) powders are produced by plasma rotating electrode process (PREP). Due to the greater viscosity of composite melts with carbides than those without carbides, the average sizes of carbon containing TiAl powders are much larger than theoretical average diameters. In addition, phase compositions of carbon-free TiAl powders usually consist of α phase and β phase, while α phase is predominant in carbon containing TiAl powders due to α-phase stabilizer. β→α phase transformation during the rapid solidification and Burgers relationships {110}β||(0001)α and <111>β||(11–20)α are illustrated in TiAl powders. Three types of microscopic structures are unfolded in TiAl composite powders: smooth structures, dendrite structures and equiaxed structures, which stem from various cooling rates. With carbon contents rising to 1.0 at.%, the average grain size in TiAl powders with the particle size range of 100∼150 μm is refined from 24.31 ± 0.38 μm to 11.32 ± 0.36 μm, moreover, the distribution ranges of particle sizes vary dramatically. Additionally, the micro-hardness of TiAl powders gradually upgrades as carbon contents ascend. The maximum micro-hardness of TiAl composite powders with 1.0 at.% carbon addition touches at 758.7 ± 15.4HV. Solid solution strengthening, refinement strengthening and second-phase strengthening are main sources for the ascent of micro-hardness.

Analysis on carbonization evolution behavior of tungsten carbide powders and its application in cutting tools

In this article, the microstructural evolution of tungsten carbide (WC) powder with coarse particle size was studied. The WC powders were prepared by directly carbonizing tungsten powders of 8.5 μm in Fisher sub-sieve size (FSSS) under various conditions. The sequence of chemical reactions was analyzed by calculating the Gibbs free energies, and the phase transition mechanisms of tungsten particles was studied by using characterization techniques including SEM and XRD. The experimental results showed that the phase transition process is dominated by carbon diffusion reaction, and the diffusion rate was studied by analyzing carbonized tungsten particles prepared at specific temperatures. The grain growth process and mechanism were also studied by analyzing the morphology and grain size of WC powders prepared at 1800 °C in different carbonization times, and the results are consistent with the recrystallization grain growth theory. Finally, technique of Electron Backscattered Diffraction (EBSD) was utilized to identify and measure the grain size of WC powders prepared from tungsten powder of 0.6 μm in FSSS. The cemented tungsten carbide substrate prepared from WC powder with higher average grain size exhibited higher performances in metal cutting application of turning and drilling.

Preparation and ionic conductivity of Ag8GeS6-based ceramic materials

Herein we present the results of the study of ceramic materials made on the basis of Ag8GeS6 powders with different dispersion. The average grain size of microcrystalline powders is 10…20 µm, and that of nanocrystalline powders is ~140 and ~180 nm, respectively. The powdered materials were investigated using the XRD and SEM methods. The Ag8GeS6-based ceramic samples were obtained by annealing (1073 K) of pressed (400 MPa) discs. Investigations of the ceramics surface by using the SEM and EDS methods indicate the homogeneity of the chemical composition of the obtained ceramics. The electrical conductivity of the obtained ceramics was studied using impedance spectroscopy in a wide frequency (1·101…3·105 Hz) and temperature (293…383 K) ranges. For all these ceramics, an increase in electrical conductivity with increasing frequency is observed. Based on the obtained results, the values of ionic conductivity and activation energy of the corresponding Ag8GeS6 ceramic samples were determined.

Synthesizing of SnS2 photocatalyst from SnO2 powders by thermal sulfurization with varying temperature (400 °C and 500 °C) and time

SnS2 from SnO2 powders was successfully produced by the thermal sulfurization method to obtain pure SnS2 powders by varying the sulfurization temperature and time. XRD analysis confirmed pure hexagonal SnS2 powders at 400 and 500 °C after 24 h of sulfurization. Grain size analysis in SEM indicated that the average grain size of powders synthesized at 400 °C and 500 °C were 1 and 11 μm, respectively. The band gap values of the obtained powders at 400 and 500 °C was determined by UV–vis spectroscopy as 2.26 eV and 2.24 eV, respectively. The photoelectrochemical analysis of the SnS2 photoelectrode produced at 500 °C revealed a flat band potential of −0.50 V, a charge carrier density of 1.49 × 1020 cm −3 and photocurrent density of 2.5 μA/cm2 at 0 V vs SCE. These results indicated that SnS2 synthesized for the first time by the thermal sulfurization technique from SnO2, which was a simple and cheap technique, was a promising candidate to be used as a photocatalysts.

Improved ultraviolet -visible optically transmittance and luminescent properties in Yb, Lu: Sr5(PO4)3F transparent ceramics via Lu3+ co-doping

The asymmetric hexagonal Sr5(PO4)3F (S-FAP) crystal material is considered to be the most suitable solid state laser gain medium for small laser diode pumping in the future due to its large absorption, emission interface, and long fluorescence lifetime. However, the mediocre optical transmittance of S-FAP transparent ceramics and the degradation of luminescence properties due to the doping of Yb activated ions seriously hinder its application prospects. In view of this, a series of 0.02Yb, xLu: S-FAP (x = 0–0.02) transparent ceramics with excellent optical properties were synthesized by hot pressing sintering. The powder SEM results show that Lu doping has no obvious effect on the morphology, grain size, and dispersion of powder. The linear transmissivity curves show that the ultraviolet (200 nm) and visible (500 nm) transmissivity increase by 54 % and 17 %, respectively, with Lu doping compared with the undoped ceramic samples. The surface SEM of ceramics revealed that Lu3+ promoted the increase of ceramic grain size significantly. The emission spectrum and fluorescence decay curves at room temperature also show that the emission intensity and fluorescence lifetime of ceramic samples increase significantly with Lu co-doping.

Grain size and coercivity tuning in Nd2Fe14B-based magnets prepared by high pressure hydrogen milling

Nd2Fe14B-based permanent magnets play important role in the emerging green energy technologies due to their superb energy product (BH)max. High coercivity at elevated operating temperatures is crucial for device performance and as an extrinsic property it is largely determined by the microstructure of the magnet. In this work, we use high pressure hydrogen milling to reduce the average grain size in Nd2Fe14B powders towards the critical single domain regime to study the influence on the resultant coercivity. In addition, Nd content has been varied in a broad range to investigate how it affects the coercivity. Milling in 100 bar hydrogen enables complete decomposition of the Nd2Fe14B phase into α-Fe, NdH2 and Fe2B at nominally room temperature. A subsequent hydrogen desorption heat treatment leads to the recombination to the parent phase, now with nearly two orders of magnitude reduction in the grain size. The results show that indeed Hc peaks around the critical single domain grain size of ≈200 nm of Nd2Fe14B. Higher contents of Nd-rich grain boundary phase lead to a continuous increase in coercivity up to μ0Hc = 1.5 T, likely due to the suppression of long-range magnetostatic interactions between the nanocrystalline Nd2Fe14B grains.

Aerosol deposition of alumina films on microstructured silicon substrates

Aerosol deposition (AD) is a room-temperature ceramic coating method, which has been used for many applications. Various substrates, such as metals and ceramics, have been used depending on the application, but it is not clear how the substrate microstructure affects the deposition processes and film quality. In this study, AD alumina films deposited on silicon substrates with microstructures consisting of line and space patterns were systematically investigated. The films were formed along the microstructure on the substrate when the linewidth was much larger than the grain size of the raw powder. Conversely, on narrow-linewidth substrates, the films were supported by the lines and the spaces were sealed. The effect of the substrate microstructure was analyzed in terms of the residual stress of the films.

Preparation of AlON Powder by Carbothermal Reduction and Nitridation with Assisting by Silane Coupling Agent

In the preparation processes of aluminum oxynitride (AlON) powders by carbothermal reduction and nitridation, the homogeneity of mixed raw powders between Al2O3 and C is a critical factor by which the final composition and related properties of AlON transparent ceramic will be decided. In this paper, a silane coupling agent was used as a dispersant to optimize the distribution uniformity of raw material of Al2O3 and C, and the preparation of AlON powder with controllable composition and its distribution is investigated. The results show that the silane dispersant could effectively improve the distribution uniformity of raw material. The silane coupling agent contains functional groups of -SiH3 and -CnH2n+1O. XPS showed that the silane could react with C and Al2O3 to form the Si-C bond and C-Al2O3 bond, respectively. The silane coupling agent provides a connected bridge for raw material powders. When the amount of the silane was 5 wt%, the mixed powder had a great distribution uniformity. The addition of silane coupling agent improved the reactivity of raw materials and decreased the synthesis temperature of AlON. The single-phase AlON powder was obtained after the Al2O3/C mixed powder was kept at 1670 °C for 30 min. Furthermore, the grain size of AlON powder was 100-200 nm with an AlN content of 27.5 mol%. With the increase of holding time to 4 h, the grain size increased to 15 μm, indicating that sintering between particles occurred, which may reduce the sintering activity of the powder.

New Gd3+ and Mn2+-Co-Doped Scheelite-Type Ceramics-Their Structural, Optical and Magnetic Properties.

New Gd3+- and Mn2+-co-doped calcium molybdato-tungstates with the chemical formula of Ca1−3x−yMny▯xGd2x(MoO4)1−3x(WO4)3x (labeled later as CaMnGdMoWO), where ▯ denotes vacant sites in the crystal lattice, 0 < x ≤ 0.2500 and y = 0.0200 as well as 0 < y ≤ 0.0667 and x = 0.1667 were successfully synthesized by high-temperature solid-state reaction method and combustion route. Obtained ceramic materials crystallize in scheelite-type structure with space group I41/a. Morphological features and grain sizes of powders under study were investigated by SEM technique. Spectroscopic studies within the UV-vis spectral range were carried out to estimate the direct band gap (Eg) and Urbach energy (EU) of obtained powders. EPR studies confirmed the existence of two types of magnetic objects, i.e., Mn2+ and Gd3+ ions, and significant antiferromagnetic (AFM) interactions among them.

Synthesis of n-type SnSe polycrystals with high and isotropic thermoelectric performance

p-type SnSe has the ultrahigh thermoelectric ZT over 2 at 773 K, as single crystal with a significantly anisotropic structure or polycrystals. In this study, a facile route of synthesizing n-type polycrystalline SnSe, which has high and isotropic thermoelectric performance, is proposed using simple ball milling, pre-annealing and spark plasma sintering processes, in sequence. The pre-annealing process effectively changes the major carrier from hole to electron and increases the crystallinity and grain size of the SnSe powder. The addition of SnCl2 as a dopant enables the electron concentration to be controlled in the range of 1.3 × 1016 cm−3 to 1.7 × 1018 cm−3 at 300 K. As a result, a remarkable ZT of 0.84–0.86 at 773 K was achieved for n-type polycrystalline SnSe0.92 with 4 wt% SnCl2, regardless of the sintering direction.

Effect of grain size of graphite powder in carbon paper on the performance of proton exchange membrane fuel cell

This work focuses on the effect of graphite powder grain size on the properties of carbon paper and proton exchange membrane fuel cell. In this paper, graphite powders of different grain sizes (0.5–30 μm) are added to carbon paper for proton exchange membrane fuel cell. Furthermore, the carbon paper is subjected to hydrophobic treatment at polytetrafluoroethylene (PTFE). The research results show that with the increase in graphite grain size, the cell performance increases at dry condition, the carbon paper containing 10 wt% PTFE and graphite powder grain size of 30 μm has the best performance, which power density of 892 mW cm−2 and limit current density of 2.40 A cm−2. With the increase in graphite grain size, the cell performance decrease at wet condition, the carbon paper containg 20 wt% PTFE and graphite powder grain size of 0.5 μm has the best performance, which power density of 524 mW cm−2 and limit current density of 1.84 A cm−2. The paper illustrates that reducing the grain size of graphite powder is beneficial to enhancing the water management ability of gas diffuse layer and reduces the performance loss at wet condition, while, increasing the gas transmission resistance and the performance loss at dry condition.