Μm Average Size Research Articles

Effect of grafting on microstructure, composition and surface and transport properties of ceramic membranes for osmotic evaporation

The effect of grafting with fluoroalkylsilanes on microstructure, composition and surface and transport properties of alumina membranes having different pore sizes (0.2, 0.5 and 0.8 μm) was studied. Surface and transport properties were evaluated in terms of contact angle, adhesion work and hydrodynamic membrane pore response. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS) were employed to evidence the induced microstructure and composition changes after grafting. Contact angle higher than 90°, in addition to low work adhesion and surface tension values confirmed the hydrophobic character of all three membranes after chemical treatment. SEM analysis showed facetted alumina grains in unmodified membranes while grains with rounded edges appeared after grafting. This effect induced compaction on internal and intermediate layers mainly on the 0.2 μm membrane. The insertion of hydrophobic chains on the outer surface and the porous structure of membranes after grafting, were evidenced by detection of fluor in the active and internal structure of treated membranes as well as by increments on the Si/Al ratios followed by EDXS. In addition, water permeability drastically decreased and intrusion pressure rose, mainly on the membrane of lower pore size tested. Hydrodynamic membrane response indicated pore size reductions of 53%, 65% and up to 82% in 0.2, 0.5 and 0.8 μm grafted membranes, respectively. However, silane chains inserted inside of 0.5 and 0.8 μm membrane pores were apparently more susceptible to flow induced deformation, limiting the potential application of these membranes on the osmotic evaporation process. Results from grafted 0.2 μm alumina membrane during OE of clarified cane juice and model sucrose solution indicate that feed and brine layer resistances contribute in less than 10% while membrane resistance contribution to the total process resistance was around 90%. Results from this work indicate that applicability of grafted alumina membranes in the OE process might further improve by using 0.2 μm < d P < 0.5 μm average pore size membranes and/or by decreasing membrane thickness.

Studies on Hydrochlorination of Silicon in a Fixed Bed Reactor

The work presented here pertains to the study of hydrochlorination of silicon in a fixed bed reactor to produce primarily trichlorosilane. Most of the data on this reaction system is patented. Reaction takes place between hydrogen chloride gas and dry silicon powder in a fixed bed condition. The optimum temperature for this reaction was determined by changing the reaction temperature and collecting the condensed product of this reaction, i.e. trichlorosilane, and was found to be 321°C at atmospheric pressure. Using the reaction kinetics theory, fixed bed reaction rate constants were determined for 124, 141, 160, 208 and 438 µm average silicon particle sizes at 321°C and atmospheric pressure. It was observed that the fixed bed reaction rate constant values were of the same order and around 0.7 s−1. The conversion of HCl increases with a decrease in particle size of silicon and lowering of the superficial velocity of HCl gas.

Fabrication of excellent mechanical properties AZ31 magnesium alloy sheets by conventional rolling and subsequent annealing

AZ31 magnesium alloy sheets were produced by conventional rolling at a temperature range of 433–523 K and subsequent annealing. The process could be optimized to produce sheets with grains as fine as 2.8 μm in average size. Obvious dynamic recrystallization was found to occur during rolling at temperature above 473 K. For the sheets rolled at temperature below 473 K, a subsequent annealing was needed to obtain a fine fully recrystallized microstructure, which gives rise to a significant increase in ductility as compared with the as-rolled state. The sheets produced by the processing route in the present study exhibit excellent mechanical properties, with the yield strength and tensile elongation achieving as high as 350 MPa and 35%, respectively. Their mechanical properties and the Hall–Petch relationship were compared with those magnesium alloys processed by other deformation methods. The results show that the present process offers a cost-effective way to produce high-performance Mg alloy thin sheets.

Effect of microstructural feature on the tensile properties and vibration fracture resistance of friction stirred 5083 Alloy

In this study, 5083 Al–Mg plates were friction stirred at optimal rotation speeds to investigate the tensile properties and vibration fracture resistance. As a result, grain refinement could be observed at the stir zone with 7 μm average grain size and fine particles could be observed as well. The tensile strain–elongation curves reveal that the tensile strength and elongation tended to increase as the microstructure was refined in the friction stirred sample. The D–N curves of the specimens recorded under an identical initial deflection show that there was a slight difference between the parent metal and the friction stirred sample. A refined grain size is partially responsible for an improvement in vibration fracture resistance; however there is another factor which plays a role too. It should be noted that the deterioration of vibration fracture resistance is a consequence of fine particles stirred into a softened matrix. From the crack propagation results, an intergranular crack propagation feature can be recognized in the friction stirred specimen, and it is reasonable to suggest that the fine particles played an important role in the deterioration of the vibration fracture resistance.

The production of a carbon-coated alumina foam

A method for producing ultra light carbon-coated alumina foam with a density of 0.04 g cm −3 and 99% porosity has been developed. It was synthesised from an aqueous aluminum nitrate–sucrose solution. The resin formed by heating this solution underwent foaming and set into solid green foam, which was sintered in the temperature range 1073–1873 K. The thermogram obtained by heating the green foam in argon showed 62 wt% mass loss occurring in three stages. The sintered foam constituted 81 wt% of γ-alumina in three-dimensional network and 19 wt% of carbon present as coating over the alumina framework. Phase analysis by X-ray diffraction revealed that carbon is in outer phase and γ-alumina is in the inner phase. Surface morphology of this foam, examined by scanning electron microscope showed open, fully interconnected and near spherical pores held together by hexagonal edges with a 300 μm average pore size. Energy dispersive X-ray spectroscopy revealed peaks corresponding to carbon, oxygen and aluminum indicating that the foam is free from nitrogen impurity. The surface concentration of carbon is nearly 85 wt% while it coating thickness is about 10 μm.

Hydrothermal synthesis of cubic boron nitride microcrystals

In this paper, combining the hydrothermal method and halide species-inducing effect, we reported cubic-phase BN microcrystals synthesized in hydrothermal condition with N(CH3)3 as nitrogen source. These polyhedral microcrystals presented nearly regular octahedral shapes of 0.5–1.5 μm in average size.

Fabrication and Characterization of SiC Preforms for Metal Matrix Composites

Abstract In this study, the effect of the PVA amount on the SiC preform properties was investigated. SiC particulates that have 60 μm average grain size were used as preform constituent. In order to produce SiC preforms, slurries that contains SiC, PVA, and colloidal silica were prepared with different amount of PVA and were dried at room temperature for 24 hours. Dried specimens were sintered at 1000°C for 3 hours. Also, specimens were characterized by Archimedes' tests for porosity. Mechanical and microstructural tests were carried out by bending and SEM analysis, respec- tively.

Suppression of Abnormal Grain Growth in WC-Co via Two-Step Liquid Phase Sintering

Microstructure refinement via two-step sintering and its mechanism have been investigated in 92WC–8Co (wt%) alloys. Samples were prepared using conventional and two-step sintering techniques. For conventional sintering, the powder compacts were sintered at 1400°C for various times. For two-step sintering, the powder compacts were heated up to 1500°C, immediately cooled down to 1400°C, and held for various times at 1400°C. In the conventional sintering, >99% relative density (RD) was obtained after 2 h; however, abnormal grain growth (AGG) occurred. In the two-step sintering, >99% RD was obtained without AGG for up to 2 h sintering times at 1400°C, showing a uniform microstructure with fine grains of ∼0.6 μm in average size. Computer calculation suggested a reduction of the maximum driving force for grain growth right after the first-step sintering at 1500°C. Retardation of AGG in two-step sintering is thus attributed to the change in average grain size and size distribution after the first step of sintering.

Basic drug analysis by strong cation‐exchange liquid chromatography–tandem mass spectrometry: simultaneous analysis of amisulpride, and of metamfetamine and amfetamine in serum/plasma

In the HPLC of basic drugs and metabolites, good efficiency and peak shape can often be attained using strong cation-exchange packings with isocratic 100% methanol eluents containing an ionic modifier at an appropriate pH* and ionic strength. Solvent extracts can be analysed directly, and use of ammonium acetate as modifier facilitates the use of atmospheric pressure chemical ionization (APCI)-tandem mass spectrometry, selected reaction monitoring mode. For the analysis of amisulpride and of metamfetamine/amfetamine in plasma (200 µL) after single oral doses in man, a column packed with Waters Spherisorb S5SCX (5 µm average particle size, 100 × 2.1 mm i.d.) was used with methanolic ammonium acetate (40 mmol/L, pH* 6.0, flow rate 0.5 mL/min) as eluent (35°C). Deuterated internal standards were used for each analyte. Detection was by positive-mode APCI. Responses for all analytes were linear over the calibration ranges. Intra-assay precision (RSD) was 2-18%, and inter-assay precision was 2-12%. The limit of detection was 0.5 µg/L for all analytes. No significant matrix effects or isobaric interferences were noted. The total analysis time was 7 min. Similar methodology can be applied to a wide range of basic analytes using MS/MS detection.

Influence of boric acid additive size on green lubricant performance

As the industrial community moves towards green manufacturing processes, there is an increased demand for multi-functional, environmentally friendly lubricants with enhanced tribological performance. In the present investigation, green (environmentally benign) lubricant combinations were prepared by homogeneously mixing nano- (20 nm), sub-micrometre- (600 nm average size) and micrometre-scale (4 μm average size) boric acid powder additives with canola oil in a vortex generator. As a basis for comparison, lubricants of base canola oil and canola oil mixed with MoS(2) powder (ranging from 0.5 to 10 μm) were also prepared. Friction and wear experiments were carried out on the prepared lubricants using a pin-on-disc apparatus under ambient conditions. Based on the experiments, the nanoscale (20 nm) particle boric acid additive lubricants significantly outperformed all of the other lubricants with respect to frictional and wear performance. In fact, the nanoscale boric acid powder-based lubricants exhibited a wear rate more than an order of magnitude lower than the MoS(2) and larger sized boric acid additive-based lubricants. It was also discovered that the oil mixed with a combination of sub-micrometre- and micrometre-scale boric acid powder additives exhibited better friction and wear performance than the canola oil mixed with sub-micrometre- or micrometre-scale boric acid additives alone.

Sintering Behavior and Dielectric Properties of Yttria/Silica-Coated BaTiO3 Material with Mn-Si-O Glass

Sintering behavior and dielectric performance of yttria/silica-coated BaTiO3 powders (YSBT) with the addition of Mn–Si–O glass (0–0.5 wt%) were investigated. The sample made with YSBT powder of 0.35 μm average particle size was fully sintered at 1300°C in 1 h, and further lowered to 1200°C with 0.2 wt% glass addition. The average grain size and secondary phases of sintered BaTiO3 were characterized with XRD and TEM analyses. The resulted dielectric properties, dielectric constant, dielectric loss, and temperature-capacitance characteristic, have been examined in air or reduced atmosphere, and discussed corresponding to microstructural features.

Application of electrophoretic deposition for inner surface coating of porous ceramic tubes

The direct coating of a nano-porous alumina layer on the inner surface of micro-porous alumina tubes was performed by electrophoretic deposition (EPD). A thin layer of polypyrrole (Ppy) was synthesized on the inside wall of the porous tubes by the chemical polymerization of pyrrole (Py) to give the wall electric conduction for the EPD electrode. The bimodal suspension of alumina powders with 0.6μm and 30nm average particle sizes was selected to control the nano-porous structure. The thickness of the coating layer was controlled by altering the applied voltage and deposition time. The interfacial connection of the coated layer and the substrate was observed by SEM before and after sintering. The pore size of the coated layer was characterized by its pore size distribution.

The Intrinsic Kinetics and Heats of Reactions for Cellulose Pyrolysis and Char Formation

The Intrinsic Kinetics and Heats of Reactions for Cellulose Pyrolysis and Char Formation

Microstructure and mechanical properties of Mg–Al–Mn–Ca alloy sheet produced by twin roll casting and sequential warm rolling

Microstructural evolution and mechanical properties of twin roll cast (TRC) Mg–3.3 wt.%Al–0.8 wt.%Mn–0.2 wt.%Ca (AM31 + 0.2Ca) alloy strip during warm rolling and subsequent annealing were investigated in this paper. The as-TRC alloy strip shows columnar dendrites in surface and equiaxed dendrites in center regions, as well as finely dispersed primary Al 8Mn 5 particles on interdendritic boundaries which result in the beneficial effect on microstructural refinement of strip casting. The warm rolled sheets show intensively deformed band or shear band structures, as well as finely and homogeneously dispersed Al–Mn particles. No evident dynamic recrystallization (DRX) takes place during warm rolling process, which is more likely attributed to the finely dispersed particle and high solid solution of Al and Mn atoms in α-Mg matrix. After annealing at 350 °C for 1 h, the warm rolled TRC sheets show fine equiaxed grains around 7.8 μm in average size. It has been shown that the present TRC alloy sheet has superior tensile strength and comparative elongation compared to commercial ingot cast (IC) one, suggesting the possibility of the development of wrought magnesium alloy sheets by twin roll strip casting processing. The microstructural evolution during warm rolling and subsequent annealing as well as the resulting tensile properties were analyzed and discussed.

Micrometer size grains of hot isostatically pressed alumina and its characterization

Alumina samples were prepared from two different particle size powders. Finer particle compacts when heated along with coarser particle compacts at same processing temperatures produce bigger grain microstructures due to higher grain growth. An unconventional method of etching by molten V2O5 was adopted to look at the microstructure for accuracy in reported data. On an average starting with finer particles give microstructure with a grain size of 5.5 μm and starting with coarser particles, give microstructure with 2.2 μm average grain size. The flexural strength is around 400 MPa for alumina samples prepared from finer powder in comparison with about 550 MPa for alumina samples prepared from coarser powder. The Vickers hardness in 5.5 μm grain microstructure is around 20 GPa in comparison to about 18 GPa in microstructure with smaller grains of 2.2 μm size.

Characterization of centrifugal cast functionally graded aluminum-silicon carbide metal matrix composites

The present investigation is on characterization of functionally graded composites based on 356 cast and 2124 wrought aluminum alloys reinforced with SiC particles of 23 μm average particle size processed by liquid metal stir casting followed by horizontal centrifugal casting. A maximum of 45 and 40% SiC particles are obtained at the outer periphery of the Al(356)-SiC and Al(2124)-SiC FGMMC casting respectively. The maximum hardness obtained at the outer periphery after heat treatment for Al(356)-SiC and Al(2124)-SiC FGMMC are 155 BHN and 145 BHN respectively. The freezing range of the matrix alloy has been found to dictate the nature of transition from particle enriched to depleted zone. These composites are suitable for making engineering components, which require very high surface hardness and wear resistances with high specific strength.

Poster Session I, July 14th 2010 — Abstracts Processing of the metallic foam coverings for the tennis table rackets

The ITTF’s mentions, in June 2007, on the VOC-free glue using rules, have been refined, in 1 Jan. 2009, up to higher standards due to the human health protection. Because of these reasons, the latest research focuses the processing of the table tennis rackets by materials and technologies that reduce or totally eliminate the using of glues.The processing of a sandwich composite plate based on Al alloy foam and rubber coating processed by injection moulding on the metallic foam provide the possibility to attach it to the wooden support of the tennis table racket by a mechanical route through the dovetail system. Thus, glues using is eliminated.The powder metallurgy (PM) technology has been used in order to process Al-based foams from Al alloys powder particles and NaCl granules. Powder particles of aluminum alloy of 200 μm average size, at 40% (wt.) content, are homogenized with NaCl granules for 3 mm and 4 mm, at 60% (wt.) content, followed by cold compaction at 500 MPa, sintering in argon atmosphere and ultrasonic washing. Thus, metallic foams are processed, having different properties depending on the NaCl granules sizes. For 3 mm NaCl granules, the metallic foams have the following characteristics: density (0.2…0.35) g/cm3, porosity (60…70) %, average diameter of the pores 2.15 mm. For 4 mm NaCl granules, the metallic foams have the following characteristics: density (0.15…0.25) g/cm3, porosity (65…75) %, average diameter of the pores 2.65 mm.The mixture of rubber and carbon black is deposited on the metallic foam surface by injection moulding process, developed at the injection pressure of 50 bar, temperature of (130…150)∘C. The injected rubber coating has the density of (0.9–1.4) g/cm3, the Shore hardness of (40…80) and (1 …4) mm thickness.The results of this research provide the following advantages: elimination of the glues as well as of the multiple gluing of the same rubber coating because of the injection moulding technique of the rubber on the foam; conservation of the tennis table racket weight because the metallic foam has a low density (0.15…0.35 g/cm3) and consequently a low mass (20…50 g) for a plate of 15 mm diameter and 1 mm thickness, including the dovetail system that allows the quick replacement of the covering.

Fabrication and characterization of porous silver powder prepared by spray drying and calcining technology

High porosity porous silver powder with about 100 µm average size and 5 µm pore size was fabricated by spray drying and calcining technology. Effects of calcining temperature and process of spray-dried powder on the phases, grain size, particle morphology and pore microstructure of silver powder were investigated. The results showed that porous silver with approximately spherical shape and via hole structure was obtained using 0.25 mol Ag 2CO 3 solution of ammonia water, which was spray-dried at 200 °C and calcined at 400 °C for 30 min with heat treatment technology curve of gradient temperature in air. And there were not Ag 2CO 3, Ag 2O and AgO phases existing in the porous silver. However, using 0.25 mol Ag 2CO 3 solution of ammonia water, the porous silver powder could not be fabricated by spray pyrolysis technology with a solution feed rate of 300 mL/h, flux of carrier gas of 0.30 MPa, and 640 °C furnace set temperature.

Particle size effect of starting SiC on processing, microstructures and mechanical properties of liquid phase-sintered SiC

Dense SiC (97.3–99.2% relative density) of 1.1–3.5 μm average grain size was prepared by the combination of colloidal processing of bimodal SiC particles with sintering additives (Al 2O 3 plus Y 2O 3, 2–4 vol%) and subsequent hot-pressing at 1900–1950 °C. The fracture toughness of SiC was sensitive to the grain boundary thickness which was controlled by grain size and amount of oxide additives. A maximum fracture toughness (6.2 MPa m 1/2) was measured at 20 nm of grain boundary thickness. The mixing of 30 nm SiC (25 vol%) with 800 nm SiC (75 vol%) was effective to reduce the flaw size of fracture origin, in addition to a high fracture toughness, leading to the increase of flexural strength. However, the processing of a mixture of 30 nm SiC (25 vol%)–330 nm SiC (75 vol%) provided too small grains (1.1 μm average grain size), resultant thin grain boundaries (12 nm), decreased fracture toughness, and relatively large defect of fracture origin, resulting in the decreased strength.

Computational modeling of flow-induced shear stresses within 3D salt-leached porous scaffolds imaged via micro-CT

Flow-induced shear stresses have been found to be a stimulatory factor in pre-osteoblastic cells seeded in 3D porous scaffolds and cultured under continuous flow perfusion. However, due to the complex internal structure of porous scaffolds, analytical estimation of the local shear forces is impractical. The primary goal of this work is to investigate the shear stress distributions within Poly( l-lactic acid) scaffolds via computation. Scaffolds used in this study are prepared via salt leeching with various geometric characteristics (80–95% porosity and 215–402.5 μm average pore size). High resolution micro-computed tomography is used to obtain their 3D structure. Flow of osteogenic media through the scaffolds is modeled via lattice Boltzmann method. It is found that the surface stress distributions within the scaffolds are characterized by long tails to the right (a positive skewness). Their shape is not strongly dependent on the scaffold manufacturing parameters, but the magnitudes of the stresses are. Correlations are prepared for the estimation of the average surface shear stress experienced by the cells within the scaffolds and of the probability density function of the surface stresses. Though the manufacturing technique does not appear to affect the shape of the shear stress distributions, presence of manufacturing defects is found to be significant: defects create areas of high flow and high stress along their periphery. The results of this study are applicable to other polymer systems provided that they are manufactured by a similar salt leeching technique, while the imaging/modeling approach is applicable to all scaffolds relevant to tissue engineering.