As-received Powder Research Articles

Electrochemical Deposition of Vancomycin/Chitosan Composite on Ti Alloy

In order to reduce or prevent the probability of osteomyelitis, a novel method of vancomycin/chitosan composite coating on the Ti alloy implant has been carried out in the vancomycin/chitosan mixed aqueous solution by the electrochemical deposition. Though the deposition of vancomycin could not be carried out independently, it has been codeposited with chitosan by the hydrogen bonds between them. The coatings resulting from the deprotonation of chitosan by electrochemical reactions, were characterized by x-ray diffraction (XRD) for crystal phase, transmission electron microscopy (TEM) for microstructure, field emission scanning electron microscopy (FESEM) for the morphological observation, Fourier transform infrared (FTIR) spectroscopy for the specified chemical bonds, and ultraviolet/visible (UV/Vis) spectroscopy for the loading and releasing of vancomycin. It was found that the as-received chitosan powder was form II, the as-deposited film was the mixture of form I and form II, and form I became the major after immersed phosphate buffer solution (PBS). The chitosan film was composed of 2.0 nm diameter fibers which aligned in the direction of fiber axis, and further reduced to 1.6 nm by adding vancomycin due to the lowered pH. The vancomycin loading in the composite coating could be tuned from 150 to 550 μg/cm2 by the deposition time and potential. From antibacterial assay, no bacteria colonies were found in tubes containing the vancomycin/chitosan composite coating. In other words, the vancomycin was not denaturalized during the electrochemical deposition.

Microstructural Characterization of Nanosized Ceria Powders by X-Ray Diffraction Analysis

Spherically shaped nanocrystalline ceria powders were prepared by high energy ball milling (HEBM) of plate-shaped as-received ceria powders. Rietveld analysis was used to determine the surface weighted average crystallite size, lattice parameter, and lattice strain. The classical Williamson–Hall as well as modified Williamson–Hall method was used to determine the volume weighted average crystallite size. A comparison of the crystallite size obtained by the classical as well as modified Williamson–Hall method shows that the strain anisotropy consideration in the modified Williamson–Hall method yields a lower value of the crystallite size, and this difference becomes more pronounced with the increase in milling time. The modified Williamson–Hall method indicates that the dislocations present in the ceria powders are edge in character. The ceria powders also were characterized by field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) techniques.

Mechanochemical Synthesis and Characteristics of Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>

This paper presents a novel mechanochemical synthesis technique for making nano-structured Pb(Mg1/3Nb2/3)O3 (PMN) ferroelectric material without annealing treatment in a much shorter time and at much lower temperature than those reported in the literature, by using the starting precursors MgO, PbO, and Nb2O5. Specimens of various milling time (3-6h) are characterized from XRD patterns to track and analyze the synthesizing procedure of this mechanochemical processing route. The time used to make the desired PMN powders varies with different milling power. When the constituent oxides were mechanically activated at 1.8KW milling power for 6h, the perovskite phase PMN powder was obtained; while it was formed when milling at 3KW for only 3h. Typical SEM images of the as-received PMN powders show that the powders are aggregated of nano-particles of about 100nm in size.

Phase, thermal and impedance studies of nanosize [formula omitted] via mechanical milling and sintering

Nanosize Li 2WO 4 is successfully synthesized using a mechanical milling method. The mean particle size of milled Li 2WO 4 is 37 nm and 31 nm as measured by Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) analysis, respectively. The calculated lattice parameter of as-received and milled powder are 0.8326 and 0.8321 nm, respectively. Both powders have been hydrated at room temperature and are highly crystalline with the presence of different types of phases at varying sintering temperatures. There is no Li 2W 2O 7 (JCPDS 28-0598) phase present in the milled powder during the whole sintering process. Meanwhile, the thermogravimetric analysis (TGA) of both powders is in accordance with their phase changes as presented in the XRD spectra. The impedance measurements show that the milled powder has a lower conductivity than that of the as-received powder in overall. The conductivity of the as-received powder increases with sintering temperature but this phenomenon is vice versa for the milled powder. All these trends can be correlated with the Field Emission Scanning Electron Microscopy (FE-SEM) micrographs on both powders.

Effect of Cr<sub>3</sub>C<sub>2</sub>-NiCr Powder Characteristics on Structure and Properties of Thermal Sprayed Nanostructured Coatings

In most engineering fields there is increasing demand for materials with enhanced physical properties. Components of complex systems exposed to severe environments often require coatings for adequate thermal insulation and to prevent wear, erosion and/or oxidation. Coatings prepared with nanostructured material have, in general, exhibited higher hardness and strength compared to conventional coatings. This paper presents the microstructure, mechanical properties, thermal stability and erosion-oxidation resistance of HVOF (High Velocity Oxygen Fuel) sprayed coatings of Cr3C2-X(Ni20Cr) prepared using nanocrystalline and as-received (AR) powder as feedstock. Details about nanocrystalline powder synthesis and characterization are also presented.

The effect of multi-step milling and annealing treatments on microstructure and magnetic properties of nanostructured Fe–Si powders

Nanostructured Fe1−xSix (x=0.05, 0.1, 0.15 and 0.2) powders are prepared by different multi-step milling and annealing treatments. The microstructure and magnetic properties are investigated for all alloys. The minimum crystallite size of as-annealed powders (∼40nm) is found to be larger than in as-milled ones (∼15nm). It is found that microstrains of 2- and 4-step processes are close to those of the as-received powders. The lattice parameter decreased ∼0.5% and 0.9% for the powders that experienced milling and annealing at the last step, respectively. The Fe80Si20 powders prepared by 1- and 4-step treatments show the maximum (40–125Oe) and minimum (20–26Oe) coercivity, respectively. With increase in milling time, mass magnetization increased for all processes. This can be ascribed to diminution in magneto-crystalline anisotropy due to grain refinement. The maximum mass magnetization (160–199Am2/kg) is achieved for the 4-step process.

Effect of YSZ electrolyte surface modification on the performance of LSM/YSZ composite cathode

In order to understand the effect of YSZ electrolyte surface morphology on the performance of LSM/YSZ composite cathode, the YSZ electrolyte surface is structured with an interlayer of YSZ by screen printing. Three different YSZ powders are used for screen printing: the as-received original powder, the high-energy milled fine powder, and the pre-sintered coarse powder. The morphologies of different YSZ powders, the microstructures of the modified YSZ interlayers, and half cells with LSM/YSZ composite cathode are studied with scanning electron microscope. The performance of the LSM/YSZ cathodes is characterized with ac electrochemical impedance spectroscopy by using symmetric cells at 700–800 °C and OCV in air. The results indicate that the polarization resistance is decreased when pre-sintered coarse YSZ powder is screen printed onto the YSZ electrolyte surface. This is attributed to the increase of the effective surface area of the YSZ electrolyte.

Consolidation of ultrafine-grained Cu powder and nanostructured Cu–(2.5–10) vol%Al2O3 composite powders by powder compact forging

An as-received ultrafine-grained Cu powder and four nanostructured Cu–(2.5–10) vol%Al2O3 composite powders produced by high-energy mechanical milling of mixtures of the Cu powder and an Al2O3 nanopowder were consolidated using warm powder compaction followed by open die powder compact forging. The circular discs produced in the experiments achieved full densification. Tensile testing of the specimens cut from the forged discs showed that the Cu-forged disc had a fairly high yield strength of 330 MPa, UTS of 340 MPa and a plastic strain to fracture of 15%, but the Cu–Al2O3 composite-forged discs did not show any macroscopic plastic yielding. The fracture strength of the composite-forged discs decreased almost linearly with the increase of the volume fraction of Al2O3 nanoparticles. This study shows that a high level of consolidation of the ultrafine-grained Cu powder and the nanostructured Cu–2.5 vol%Al2O3 composite powder has been achieved by warm powder compacting at 350 °C and powder compact forging at 500 and 700 °C. However, this is not true for the nanostructured Cu–(5, 7.5 and 10) vol%Al2O3 composite powders, possibly due to their higher powder particle hardness at elevated temperatures in the range of 350–800 °C.

Spray drying of TiO 2 nanoparticles into redispersible granules

We have demonstrated how titania nanoparticles can be spray-dried to produce redispersible granules. The evaluation of different dispersants using rheology, particle size and electrokinetic measurements showed that an anionic carboxylated polyelectrolyte, Dispex N40, was able to stabilize the primary aggregates of the titania nanoparticles with a size of about 180 nm at an addition of 2.4% dry-weight basis over a relatively large pH-range. Transmission electron microscopy showed that the commercial P-25 titania nanopowder could not be deagglomerated down to the individual crystallite size of 15–40 nm. Spherical granules with a size between 20 and 50 μm and a minimum amount of dusty fines could be produced by spray drying the aqueous titania dispersions in a configuration with internal bag filters. The granules could be completely disintegrated and redispersed in water by ultrasonication into a stable suspension with a size distribution that is identical to the as-received powder. The possibility to prepare redispersible nanoparticle granules by spray drying is a route to minimize the risk of airborne exposure and facilitate the handling of nanopowders.

REACTIVE HOT PRESSING AND OXIDATION BEHAVIOR OF Hf-BASED ULTRA-HIGH- TEMPERATURE CERAMICS

A HfB2-SiC ceramics were fabricated via a reactive hot pressing using Hf , B4C , and Si as precursors. The reaction temperature for the reactive hot pressing between 1800 and 1900°C was determined by reaction of the precursor at different temperatures from 900 to 1800°C. The effective size reduction of precursors was investigated by vibration milling, which exhibited a critical role to achieve high densification and uniform microstructure. Also, it has affected the oxidation behavior of HfB2–SiC in air. Vibration milled sample showed uniform surface of SiO2 layer, but sample which was fabricated by as-received powder exhibited non-uniform oxidation behavior. Examination of the mechanical properties showed that particle size reduction via vibration also led to improved flexural strength, hardness and fracture toughness.

Synthesis and characterization of LaPO 4 powder heat treated at various temperatures

Lanthanum phosphate (LaPO 4) powder has been synthesized by direct liquid–liquid reaction of La(NO 3) 3·6H 2O and H 3PO 4. The as-received powder has been heat treated at various temperatures (100, 600, 800, 1000, or 1200 °C). The phase composition and microstructure of the powder have been characterized by XRD, SEM, HRTEM, and FFT. The anisotropic growth mechanism, phase transition from hexagonal to monoclinic structure, and shape evolution details of LaPO 4 nanoparticles are discussed. The results show that the phase composition and microstructure of the powder depend on the heat treatment temperature. The hexagonal phase converts to a monoclinic structure around 600 °C. Another consequence of the heat treatment is a change in the shape of the LaPO 4 as nanorods are converted into nanograins with increasing heat treatment temperature. Particularly, at 1000 °C, the nanorods begin a gradual transition to nanograins. When the temperature is increased to 1200 °C, all the LaPO 4 nanorods have transformed into spherical LaPO 4 nanoparticles with a diameter in the range of 300–500 nm.

The initial stage of liquid phase sintering for an Al–14Si–2.5Cu–0.5Mg (wt%) P/M alloy

The present paper focuses on the initial stage of the liquid phase sintering (LPS) of a commercially available P/M Al–Si alloy, with nominal composition Al–14Si–2.5Cu–0.5Mg (in wt%). The microstructural examination of the as-received powder showed that it is constituted by pure Al particles and master alloy particles with composition Al–28Si–5Cu–1Mg (in wt%). Its compressibility is lower than for the conventional elemental P/M aluminium premixes, but it is still better than for prealloyed Al powders and other P/M powders. Thermogravimetry experiments showed that the elimination of the organic lubricant takes place between 275 and 490 °C during heating to the sintering temperature. The phase transformations leading to the formation of the liquid phase were studied by differential scanning calorimetry (DSC). The dimensional changes associated with the generation of the liquid were measured by dilatometry. Samples quenched into water from different temperatures (between 450 and 575 °C) and times (between 0 and 30 min) were studied to reveal the microstructural evolution of the alloy. The first liquid is formed inside the master alloy particles at around 505 °C. This liquid spreads across the compact, enhancing the chemical homogenization of the material. The alloying elements diffuse from the liquid inside the originally pure Al particles, reducing their melting temperature. This alloying process is almost concluded at around 535 °C. When the temperature is increased the liquid starts to be formed also in the originally pure Al particles. The melting of the FCC Al-rich phase finishes around 575–590 °C. The full melting of the alloy occurs at about 635–645 °C. After analyzing the different possible causes, it is concluded that the main swelling mechanism is the volume change associated with the melting of a fraction of the material when the temperature is increased. The phases detected by X-ray diffraction (XRD) in the as-received powder and in the sintered compact are FCC Al-rich solid solution, Si, θ-phase (CuAl 2), and Q-phase (Cu 2Mg 8Si 6Al 5).

Strong Hierarchically Porous Monoliths by Pulsed Current Processing of Zeolite Powder Assemblies

Binderless hierarchically porous monoliths have been produced from silicalite-1 and ZSM-5 zeolite powders by a rapid and facile powder processing method where the zeolite powders are assembled in a graphite die and subjected simultaneously to a compressive pressure and a pulsed current. Pulsed current processing (PCP) or, as it is commonly called, spark plasma sintering, enables rapid thermal processing of zeolite powder assemblies with heating and cooling rates at 100 degrees C/minute or more, which results in the formation of strong powder bodies without any addition of secondary binders. Nitrogen adsorption measurements show that it is possible to form strong zeolite monoliths by PCP that maintain between 85 and 95% of the surface area of the as-received silicalite-1 and ZSM-5 powders. Line-broadening analysis of X-ray powder diffraction data by the Rietveld method and high-resolution electron microscopy showed that the formation of strong interparticle bonds is associated with a local amorphization reaction at the interfacial contact points between the zeolite particles. The PCP-treated binderless ZSM-5 monoliths display a high selectivity in xylene isomer separation.

Fe K-Edge XAFS Study of Slate Powders Heat Treated up to 1000°C

The use of ultra-bright, highly directional, high and variable energy associated to synchrotron radiation beams at SPring-8 when compared with conventional X-Ray diffraction analysis applied to slate powders heat treated at temperatures in the range of 600°C up to 1000°C is reported. Fe K-edge XAFS measurements of the products formed upon heating slate showed that in the temperature range 600-800°C, conversion of FeO present in the as-received slate powder into a mixed -Fe2O3/-Fe2O3 has occurred providing useful information on the short-range order atomic structure of the slate. Above 800°C, mainly -Fe2O3 was identified to be present in the slate. The change of the Fe valences within the slate network is most likely responsible for the detected colour change with the increasing temperature.

Swelling of Copper Powders during Sintering of Heat Pipes in Hydrogen-Containing Atmospheres

Swelling of copper powders often occurs during sintering of heat pipes and causes problems in removing core rods from the fixture. To address this problem, this study examines the effects of sintering atmospheres (H2, N2-10%H2, N2, and vacuum) and oxygen content in copper powders on the density and dimensional changes of loose-powder-sintered copper compacts. The results show that serious powder cracking occurs when high oxygen content is present in the as-received powder and when the sintering atmosphere contains hydrogen due to the hydrogen-oxygen reaction forming water vapors. The dilatometer curve indicates that such reaction starts between 673 and 723 K. Comparison of the pycnometer density and Archimedes’ density of sintered compacts suggests that the swelling is mainly caused by cracking of the powder, and that the plastic deformation caused by the expansion of trapped gas in isolated pores plays a minor role. To prevent such cracking and swelling, copper powders with low oxygen content should be used, and the sintering should be carried out in an atmosphere with low hydrogen content or under vacuum or inert gas atmosphere.

Synthesis of Stainless Steel/CNTs Nanocomposite Powders

Stainless steel/carbon nanotubes (CNTs) nanocomposite powders were synthesized by chemical vapor deposition (CVD) method with ethanol as a carbon source. The effects of synthesis temperature and time on microstructure and chemical composition of the powders were investigated. The as-received stainless steel powders were synthesized at temperature in between 550-800°C for 30-180 min at a pressure of 10 Torr. The optimum synthesis condition was found to be 800°C for 120 min. Average diameter of CNTs grown on stainless steel particles slightly increased with increasing growth temperature. The synthesis time, however, was found to have no effect on the size of CNTs.

In-situ formation of novel geopolymer-zeolite hybrid bulk materials from coal fly ash powder

Geopolymer–zeolite hybrid bulk materials were formed in-situ from as-received coal fly ash powder by a simple two-step treatment: (1) immersing the coal fly ash powder packed within a cylindrical acrylic pipe into a 3.5 mol/l Na(OH) solution at 80°C and (2) subsequent curing in a temperature–humidity-controlled chamber at a fixed condition: 50°C and 50% relative humidity. The content of the formed Na-X type (conversion ratio from the starting coal fly ash) in the sample was optimized to be approximately 10% when the duration of the immersion in Na(OH) solution reached 72 hours. The compressive strength at room temperature of the in-situ formed bulk samples exhibited a clear tendency to increase with both alkali immersion time and curing time, which could be due to the increase of the amount of the in-situ formed geopolymer. As a result, after the 96-hour-alkaline immersion followed by the 21 days curing, the average compressive strength at room temperature achieved 5.4 MPa. This value was found to be more than four times higher than that of the samples without curing treatment (1.3 MPa).

Texture and structural refinement using neutron diffraction data from molybdite (MoO3) and calcite (CaCO3) powders and a Ni-rich Ni50.7Ti49.30alloy

Preferred orientation or texture is a common feature of experimental powder patterns. The mathematics of two commonly used models for preferred orientation—the March-Dollase and the generalized spherical-harmonic models—is reviewed. Both models were applied individually to neutron powder data from uniaxially pressed molybdite (MoO3) and calcite (CaCO3) powders in Rietveld analyses, as well as the as-received powders. The structural refinement results are compared to single-crystal structures. The results indicate that reasonable refinement of crystal structures can be obtained using either the March model or generalized spherical-harmonic description. However, the generalized spherical-harmonic description provided better Rietveld fits than the March model for the molybdite and calcite. Therefore, the generalized spherical-harmonic description is recommended for correction of preferred orientation in neutron diffraction analysis for both crystal structure refinement and phase composition analysis. Subsequently, the generalized spherical-harmonic description is extended to crystal structure refinement of annealed and the aged polycrystalline Ni-rich Ni50.7Ti49.30shape memory alloys.

Influence of green state processes on the sintering behaviour and the subsequent optical properties of spark plasma sintered alumina

The present investigation gives a quantitative correlation between different green microstructures, and their sintering behaviour during spark plasma sintering. The green microstructures were elaborated via various green shaping processes such as direct casting and direct coagulation casting compared to uniaxial compaction of the as-received sub-micron grained corundum powder. Narrowing pore size distribution and reducing pore size (≈40 nm) in the green compact could favour cold densification during initial uniaxial pressing by grain sliding and rearrangement. This is attributed to the soft homogeneous touching network in direct-cast green samples. Consequently, grain growth was impeded and the onset of shrinkage was delayed. Moreover, the small pores and the narrow pore size distribution in the homogeneous green bodies led to higher final densities, with better optical properties compared to the less homogeneous green samples.

Glass-coated individual dispersed MWNTs in Alumina & its high temperature stability

An ultrasonication assisted sol-gel processing route for MWNTs/Alumina was proposed. Using aluminum ethoxide as an alumina precursor and ethanol/water as a solvent, the duration of the transformation from sol to gel under ultrasonication can be controlled by adjusting the water content. Purified MWNTs added under ultrasonication should be functionalized by alcohol at first and a well dispersion in alumina sol could be attained under the help of ultrasonic. With the evaporation of ethanol, sol transfers to gel and MWNTS dispersion can be kept in gel. Gel and calcine-powder show that individual MWNTs are enwrapped by amorphous alumina. As-received powders after a following heating-treatment under vacuum shows a good high stability for a glass coat formed on MWNTs. Raman results show the processing route has no obvious effect on the structure of MWNTs, even a high temperature (1273K) treatment is done under vacuum.