Kind Of Powders Research Articles

Effect of Limestone and Quartz Fillers in UHPC with Calcined Clay

Ultra-high-performance concrete (UHPC) is a material developed to maximize the engineering characteristics of hydraulic concrete, in terms of durability and mechanical properties, but the adoption of this technology in practice has not turned out as desired, mainly due to the high amounts of cement and silica fume required for its production, and for its consequences on both economic and ecological costs. As an option to improve the impact of UHPC, both on costs and on sustainability, this work evaluates four UHPC series with metakaolin additions of 5%, 10%, 15% and 20%, and the substitution of 37.5% of the Portland cement volume by limestone or quartz filler. The compressive strength, the bulk electrical resistivity and a set of tests for microstructural characterization (TGA, XRD and quantitative EDS) were utilized to better understand the role of calcite on the hydration and pozzolanic reactions in ternary Portland cement-metakaolin-limestone filler. Results indicate that the reaction of calcite is scarce and should be considered as a mere filler, as no increase in AFm phases were found. Nevertheless, the ternary mixture with 15% of metakaolin in addition to cement, and with 37.5% of the Portland cement volume substituted by limestone filler, was the one that presented the best performance in terms of compressive strength and bulk electrical resistivity. The results of the microstructural characterization indicate that the high kaolin content in the metakaolin originated the most significant hydration and pozzolanic reactions development between the ages of 7 and 28 days, as between 28 and 91 the reaction remained dormant. In general, the whole set of results included in this work indicate that limestone filler doesn't act as a better filler than other kind of powders when used in ternary Portland cement-metakaolin- filler systems.

Comparative study between natural and synthetic Hydroxyapatite: structural, morphological and bioactivity properties

In this work, a study of hydroxyapatite (HAp) powders obtained using both, porcine bones and chemical precursors was carried put. In the case of HAp obtained by means of porcine bones, physical processes as cooking, washing and milling were developed, for removing the organic material from the bones; after that, the powders were submitted to a thermal treatment at 800 °C, during 12 h. This procedure was carried out without adding chemical alkalines that are harmful for the environment and the human health. On the other hand, HAp powders were also synthetized using the chemical precipitation method widely reported, showing successful results. Moreover, both kind of powders were characterized using x ray diffraction, Fourier transformer infrared spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. Furthermore, the bioactivity of the materials was determined using the simulated biological fluid (SBF) method. Results showed that the natural HAp exhibited better crystallographic properties. Moreover, according to these results, HAp obtained from porcine bones contains traces of elements as Na and Mg that are favorable for the bioactivity, according to the materials behavior when they are immersed in SBF. Keywords: Hydroxyapatite, porcine bones, chemical precipitation, simulated biological fluid.

Free flowing and cohesive powders agitation in a cylindrical convective blender- kinetics experiments and Markov chain modelling

An original methodology for studying powder flow in a cylindrical convective blender has been developed. A free-flowing and a cohesive powder were studied, at a fixed stirring speed, in rolling regime. For both powders, three apparent flow mechanisms were evidenced: convection in the volume swept by the blades, diffusion/shearing between the agitated zone and the stagnant one, as well as in the stagnant zone itself, and avalanches at the powder bed surface between agitated and stagnant zones. After defining six zones in the blender, tracing experiments were carried out by placing appropriate tracers in different starting zones and sampling the whole bed at different stirring times, which lead to mixing kinetics of the powders into themselves. A Markov chains model of the blender allowed the quantification of the three mechanisms respective magnitude by fitting the experimental data. This simple model has a good agreement with the free-flowing powder data, but is not able to represent well the observations for the cohesive powder. Bed consolidation should probably be taken into account for this kind of powders and thus a linear Markov model is not sufficient.

Experiment and Research on the Mechanism of Foam Dedusting Agent

This paper explains how to solve the problem that the foam dedusting agent is not able to dedust efficiently according to its low foaming rate and poor wettability and finally obtains an optimal formula of foam dedusting agent. We first studied the mechanism of foam dedusting and learned that the process of foam-dedusting is comprised of interception, adhesion, wetting, and sedimentation. Then the optimal formula named Foam Dedusting Agent CNSD-1 were obtained, which is comprised of Sodium Dodecyl sulfate being foaming agent, Soluble starch being foam stabilizer, Dioctyl sodium sulfosuccinate being wetting agent, by an advanced ROSS-Miles experiment and contact angle measurement. The mass concentration of the three kind of powders respectively are 0.5%, 0.06% and 0.3%. Through the field application the conclusion can be draw that the total coal dust dedusting percentage of it is 96.35% and the respiratory coal dust dedusting percentage of it is 86.08%, the Effect is remarkable.

J0450102 SPS成形したAg/ダイヤモンド複合材料の熱物性に及ぼすダイヤモンドのバイモーダルな粒度分布の影響([JO45-01]知的材料・構造システム(1),機械材料・材料加工部門)

Diamond-particle-dispersed-silver (Ag) matrix composites were fabricated in solid-liquid co-existent state by Spark Plasma Sintering (SPS) process from the mixture of diamond powders, Ag powders and Si powders. As the diamond powders, two kind of powders, monomodal diamond powders of 310μm in diameter and a bimodal diamond powder mixture of 310μm and 34.8μm in diameter, were used. The microstructures and thermal conductivities of the composites fabricated were examined. These composites were all well consolidated by heating at a temperature range between 1113K and 1188K for 0.45ks during SPS process. No reaction at the interface between the diamond particle and the Ag matrix was observed by scanning electron microscopy for the composites fabricated under the sintering conditions employed in the present study. Although the relative packing density of the monomodal composite decreased from 97.4% to 93.4% with increasing the diamond volume fraction in a diamond volume fraction range between 50% and 60%, that of the bimodal composite was higher than 97% in a diamond volume fraction range up to 65%. The thermal conductivity of the bimodal composite was 576-723W/mK, which is higher than that of the monomodal composite in a diamond volume fraction range between 55% and 65%, and it is 678-723W/mK in a diamond volume fraction range between 55 and 65vol.%.

Development of characterisation methods on U(Mo) powders for material testing reactors (MTRs)

The necessity for Material Testing Reactors (MTRs) to use a low-enriched uranium (LEU) fuel has leaded to the development of a dense fissile material based on γ-U(Mo) alloys. The designed fuel is a composite material, made of dispersed γ-U(Mo) particles embedded in an Al based matrix. Depending on the nature of the particles obtained with various fabrication processes (centrifugal atomisation or mechanical grinding), noticeable differences about gas retention capabilities and behaviour under irradiation of the fuel are observed [1,2]. Up to now, no precise links between the microstructure of the fuel and its behaviour under irradiation have been established.Several methods of characterisation have then been developed, more particularly, to characterise various types of defects and the γ-U(Mo) phase stability, which are both supposed to influence the gas retention capacities of the fuel [1,2,3].Our method is based on a multi-scale approach, high temperature X-Ray diffraction experiments have first been carried out followed by observations using transmission electron microscopy (TEM). X-Ray diffraction has revealed being a pertinent tool in order to study the kinetic of decomposition of the γ-U(Mo) phase as a function of temperatures and times, for different kind of powders. TEM is also among one of these techniques and allows a microstructure characterisation at a grain size scale. It has required the development of an original protocol set up for producing thin sections from large particles introducing a minimum quantity of defects within the material.This protocol has provided first encouraging results with the observation of dislocations within different kind of U-(Mo) powder particles. Obtained results, in both cases, are also discussed together with the fabrication processes of the studied powders.

SPS 成形したAg/ ダイヤモンド複合材料の熱物性に及ぼすダイヤモンドのバイモーダルな粒度分布の影響

Diamond-particle-dispersed-silver (Ag) matrix composites were fabricated in solid-liquid co-existent state by Spark Plasma Sintering (SPS) process from the mixture of diamond powders, Ag powders and Si powders. As the diamond powders, two kind of powders, monomodal diamond powders of 310 µm in diameter and a bimodal diamond powder mixture of 310 µm and 34.8 µm in diameter, were used. The microstructures and thermal conductivities of the composites fabricated were examined. These composites were all well consolidated by heating at a temperature range between 1113 K and 1188 K for 0.45 ks during SPS process. No reaction at the interface between the diamond particle and the Ag matrix was observed by scanning electron microscopy for the composites fabricated under the sintering conditions employed in the present study. Although the relative packing density of the monomodal composite decreased from 97.4 % to 93.4 % with increasing diamond volume fraction between 50 % and 60 %, that of the bimodal composite was higher than 97 % in a diamond volume fraction range up to 65 %. The thermal conductivity of the bimodal composite was higher than that of the monomodal composite in a diamond volume fraction range between 55 % and 65 %. The coefficient of thermal expansion of the composites falls in the upper line of Kerner's model, indicating strong bonding between the diamond particle and the Al matrix in the composite.

J045053 SPS成形したAl/ダイヤモンド複合材料の熱伝導率に及ぼすダイヤモンドのバイモーダルな粒度分布の影響([J045-05]知的材料・構造システム(5))

Diamond-particle-dispersed-aluminum (Al) matrix composites were fabricated in solid-liquid co-existent state by Spark Plasma Sintering (SPS) process from the mixture of diamond powders, Al powders and Al-5mass%Si powders. As the diamond powders, two kind of powders, monomodal diamond powders of 310μm in diameter and a bimodal diamond powder mixture of 310μm and 34.8μm in diameter, were used. The microstructures and thermal conductivities of the composites fabricated were examined. These composites were all well consolidated by heating at a temperature range between 798K and 876K for 1.56ks during SPS process. No reaction at the interface between the diamond particle and the Al matrix was observed by scanning electron microscopy for the composites fabricated under the sintering conditions employed in the present study. Although the relative packing density of the monomodal composite decreased from 99.1% to 87.4% with increasing the diamond volume fraction in a diamond volume fraction range between 50% and 60%, that of the bimodal composite was higher than 99% in a diamond volume fraction range up to 65%. The thermal conductivity of the bimodal composite was 455-581W/mK, which is higher than that of the monomodal composite in a diamond volume fraction range higher than 60%, and it is 530-58 lW/mK in a diamond volume fraction range between 60 and 70vol.%. -

Structure and photoluminescence properties of nanocrystal Eu3+-doped gadolinium tungsten red emitting phosphors excited by blue light

A co-precipitation reaction was used to prepare nanocrystal Gd6WO12:Eu3+ and Gd2WO6:Eu3+ red emitting phosphor powders with different Eu3+ doping levels. It is found that under the same preparation conditions, different doping level leads to different crystal structures; Gd6WO12-like with a tetragonal lattice structure tends to be synthesized at low doping level (10–40mol%) yet Gd2WO6-like with a monoclinic lattice structure easily to grow at high doping level (60–80mol%). The strong red emission of 5D0→7F2 transitions at 620nm was observed for all powders under either near ultraviolet or blue light excited and the most intense emission was obtained at the concentration of 40mol%. This kind of powders might find their promising application to compensate the white LEDs for the lack of red light component and to improve rendering index.

Rate enhancement of hydrogen generation through the reaction of magnesium hydride with water by MgO addition and ball milling

The variations of the amount of hydrogen generated with the kind of powders and the condition of the magnesium and magnesium hydride powders were investigated. By the reaction of Al, TiH 2 and unmilled and milled Mg powders with water, the H 2 generation rates were very low and the quantities of H 2 generated were extremely small. The quantity of H 2 generated by the reaction of unmilled MgH 2 powder with water was greater than those generated by the reactions of Al, TiH 2, and unmilled and milled Mg powders with water. The MgH 2 powder milled for 2 h, with finer particles, generated much more H 2 by its reaction with water than unmilled MgH 2 powder. The MgH 2 + 5%MgO powder milled for 2 h generated much more H 2 by its reaction with water than the Al, TiH 2, unmilled Mg, milled Mg, unmilled MgH 2, and milled MgH 2 powders.

型形状と粉末種類が異なった放電焼結の熱解析

Distributions of the voltage and temperature were obtained during spark sintering, for punch-die-compact systems using compacts with two kinds of shapes, simple cylinder and two-step cylinder, and two kinds of powders, titanium as a conductor and alumina as an insulator. The voltage and temperature were calculated on the basis of Ohm's and Fourier's laws. The calculated voltage and temperature were in good agreement with those measured by a voltmeter and thermocouples, respectively. The calculated temperature distribution changed in the simple cylindrical compact system depending on the kind of powders, because of the difference in the amount of Joule's heat generation in the compacts due to the kind of powders. In contrast, for the two-step cylindrical titanium compact system, the temperature distribution was affected by the difference in the amount of the current density depending on the cross-sectional area.

Surface morphology and reactivity of microcrystalline MgO: Single and multiple acid–base pairs in low coordination revealed by FTIR spectroscopy of adsorbed CO, CD 3CN and D 2

The surface morphology of two types of high specific surface area MgO powders (an ex-hydroxide MgO and a smoke one, eroded by H 2O and CO 2 attack) was studied by high resolution transmission electron microscopy (HRTEM) and infrared spectroscopy of adsorbed probe molecules. HRTEM images show that significant morphological defects are present on the surface of MgO microcrystals in both cases. Insights at a molecular level provided by the IR spectra of adsorbed probe molecules (CO, CD 3CN, D 2) indicate that Mg 2+ ions on corners, edges and (1 0 0) faces are exposed in comparable amount on the surface of the microcrystals of both kind of powders. By contrast, relevant differences were found for multiple cationic sites and reactive Mg 2+O 2− pairs located in region with enhanced irregularity, constituted by steep successions of steps of one unit-cell dimension. This suggests that, besides the presence of different types of single morphological defects, the presence of ensembles of such sites must be taken into account when adsorption properties and surface reactivity of different type of microcrystalline MgO materials are compared.