Single w/o microemulsion templating of CdS nanoparticles

We report the synthesis of monodispersed CdS nanoparticle with tunable size by controlling the reaction aging time in a single water in oil (w/o) microemulsion system. The w/o microemulsion system consists of nonionic surfactant poly (oxyethylene)₅ nonyl phenol ether (NP5), poly (oxyethylene)₁₀ nonyl phenol ether (NP10), cyclohexane and aqueous solution (cadmium salt and thioacetamide). Thioacetamide (TAA) has been utilized as a source for slow release of sulfur ions in the in situ synthesis of CdS. UV-Visible spectra shows obvious blue shift for the CdS nanoparticles as compared to the bulk material due to quantum size effect. CdS nanoparticle size depends on the reaction aging time where longer reaction aging time yields bigger particles. CdS nanoparticles growth behaviour as a function of reaction aging time in the microemulsion system was characterized by UV-Visible spectroscopy. The particle growth follows a power law with an exponential in the order of 0.17. Energy Filter Transmissions Electron Microscopy (EFTEM) reveals monodispersed CdS nanoparticles with standard deviation, less than 8%.     

Effect of grain size on mechanical,surface and biological properties of microwave sintered hydroxyapatite

Hydroxyapatite (HA) compacts having average grain sizes of 168 ± 0.086 nm, 1.48 ± 0.627 μm and 5.01 ± 1.02 μm are processed from synthesized HA powder by microwave sintering at varying sintering temperature for different times. Superior mechanical and biological properties are shown by nano-grain HA compacts as compared to their micron grained counterparts. Compressive strength, indentation hardness, and indentation fracture toughness are increased with the decrease in HA grain size. The highest surface energy and maximum wettability are exhibited by nano-grain HA. HA compacts are assessed for cell–material interaction by SEM, MTT and immunochemistry assays using human osteoblast cell line for 1, 5 and 11 days. MTT assays showed higher number of living cells and faster proliferation on nano-grain HA surface. Osteoblast cells on nano-grain HA surface expressed significantly higher amount of vinculin and alkaline phosphatase (ALP) protein markers for cell adhesion and differentiation respectively. This study shows the effect of grain size on physical, mechanical and in vitro biological properties of microwave sintered HA compacts.     

Hydroxyapatite nanopowders: Synthesis,densification and cell–materials interaction

Hydroxyapatite (HA) nanopowders with different aspect ratios were synthesized using reverse micelle template system. Nanopowders were characterized using X-ray diffraction (XRD), BET specific average surface area analysis and transmission electron microscopy (TEM). It was observed that increase in aqueous to organic ratio (A/O) and pH decreased the aspect ratio of the nanopowders. HA nanopowders with the highest aspect ratio (rod-shaped) of 7.2 ± 3.2 and the lowest aspect ratio (spherical) of 1.3 ± 0.3 were synthesized for processing dense compacts. Effect of powder morphology on densification at 1250 °C was studied with different amount of rod-shaped and spherical nanopowders. It was observed that an increase in high aspect ratio powder content in the compacts decreased sintered density under pressureless sintering condition. Also, due to excessive grain growth, no nanoscale morphology could be retained in the sintered microstructure. Mineralization study in simulated body fluid (SBF) showed formation of apatite layer on the entire surface of both compacts made with spherical and rod-shaped particles. Cytotoxicity result with OPC1 human osteoblast cells showed excellent cell attachment and cell spreading on samples after 5 days in culture.     

Sintering of hydroxylapatite-zirconia composite materials

Sintering of hydroxylapatite-zirconia (doped with 3 mol% Y₂O₃) composite powder compacts was studied. Hydroxylapatite powder was prepared from Ca(OH)₂ and H₃PO₄, and zirconia powder was prepared from ZrOCl₂ · 8H₂O and YCl₃. The sinterability of hydroxylapatite-zirconia composite powder compacts depends strongly on differential shrinkage between the powder components of the composite. Smaller differential shrinkage results in better sinterability. By increasing the calcination temperature of zirconia powder and/or decreasing that of hydroxylapatite powder improves the sinterability of the composite powder compacts. The phase distribution and total amounts of crystal phases depend on the sintered density of compacts. Hydroxylapatite and cubic zirconia are the major phases of compacts with high sintered densities, whereas - and -tricalcium phosphate and CaZrO₃ are the major phases of compacts with low sintered densities.     

Effect of powder characteristics on the sinterability of hydroxyapatite powders

The effect of different sintering conditions on the sintered density and microstructure of two different hydroxyapatite (HA) powders was examined. The powder characteristics of a laboratory synthesized HA powder (Lab HA) were low crystallinity, a bimodal particle size distribution, a median particle size of 22 m and a high specific surface area (SSA) of 63 m²/g. By contrast, a commercial calcined HA (commercial HA) was crystalline and had a median particle size of 5 m and a low SSA of 16 m²/g. The different powder characteristics affected the compactability and the sinterability of the two HA powders. Lab HA did not compact as efficiently as commercial HA, resulting in a lower green density, but the onset of sintering of powder compacts of the former was approximately 150 °C lower than the later. The effect of compaction pressure, sintering temperature, time and heating rate on the sintered densities of the two materials was studied. Varying all these sintering conditions significantly affected the sintered density of commercial HA, whereas the sintered density of Lab HA was only affected significantly by increasing the sintering temperature. The Vickers hardness, H_v, of Lab HA was greater than commercial HA for low sintering temperatures, below 1200 °C, whereas for higher sintering temperatures the commercial HA produced ceramics with greater values of hardness. These trends can be related to the sinterability of the two materials.     

Pressureless sintering of dense hydroxyapatite–zirconia composites

Hydroxyapatite (HA)–TZP (2.5 mol% Y₂O₃) containing 2, 5, 7.5 and 10 wt% TZP were prepared using calcium nitrate, diammonium hydrogen orthophosphate, zirconium oxychloride and yttrium nitrate. The composite powder was prepared by a reverse strike precipitation method at a pH of 10.5. The precipitates after aging and washing were calcined at 850°C to yield fine crystallites of HA and TZP. TEM study of the calcined powder revealed that while HA particles had both spherical and cuboidal morphology (∼50–100 nm) the TZP particles were only of spherical nature (∼50 nm). X-ray analysis showed that the calcined powder of all the four composition had only HA and t-ZrO₂. Uniaxially compacted samples were sintered in air in the temperature range 1,150–1,250°C. High sintered density (>95% of theoretical) was obtained for composites containing 2 and 5 wt% TZP, while it was 92% for 7.5 wt% and 90% for 10 wt% TZP compositions. X-ray analysis of sintered samples shows that with 2 wt% TZP, the retained phases were only HA and t-ZrO₂. However, for 5, 7.5 and 10 wt% TZP addition both TCP and CaZrO₃ were also observed along with HA and t-ZrO₂. Bending strength was measured by three point bending as well by diametral compression test. While in three point bending, the highest strength was 72 MPa, it was 35.5 MPa for diametral compression. The strength shows a decreasing trend at higher ZrO₂ content. SEM pictures show near uniform distribution of ZrO₂ in HA matrix. The reduction in sintered density at higher ZrO₂ content could be related to difference in the sintering behaviour of HA and ZrO₂.     

The effect of osteopenia on the osteointegration of different biomaterials: histomorphometric study in rats

The osteointegration of Hydroxyapatite (HA), Titanium (Ti-6Al-4V: Ti), Zirconia (ZrO₂), Alumina (Al₂O₃) and 2 biological glasses (AP40 and RKKP) was comparatively investigated in normal and osteopenic rats by means of histomorphometry. Thirty-six Sprague Dawley female rats were left intact (Group C) while 36 were ovariectomized (Group OVX). Group C and OVX were further divided into 6 subgroups. After 16 weeks all animals were submitted to the femoral implant of nails made of the above-mentioned materials. Eight weeks after implantation the animals were euthanized, the femurs were harvested for histomorphometric analysis. The data showed that: (1) all the tested materials were biocompatible in vitro; (2) no significant differences existed in Affinity Index (AI) of Group C; and (3) results from paired comparison applied to the AI showed significant differences among the Groups C and OVX. The AI did not significantly change among intact groups, while it significantly decreased when some materials were implanted in OVX subgroups (AP40, ZrO₂ and Ti-6Al-4V: , and ). It is confirmed that bone mineral density is a strong predictor of the osteointegration of an orthopedic implant and that the use of pathological animal models is necessary to completely characterize biomaterials.     

Effect of high pressure and torsional strain on the structure,microstresses, 55Mn NMR,and magnetoresistance of La0.6Sr0.3Mn1.1O3 ± δ nanopowders

The effects of high pressure (3 GPa) and torsional strain on the structure and properties of compacts prepared from nonstoichometric lanthanum-strontium manganite La_0.6Sr_0.2Mn_1.2O_{3 ± δ} (LSMO) nanopowder with a perovskite structure have been studied for the first time using X-ray diffraction, low-temperature Ar adsorption, electron microscopy, and magnetic (χ_ac, ⁵⁵Mn NMR, and magnetoresistance) measurements. The laws governing the influence of this treatment on the structure, local valence and magnetic states of manganese ions and their inhomogeneous environment (involving other ions and defects), and on the resistivity, microstresses, coercivity, Curie temperature, and magnetoresistance of LSMO nanopowder compacts have been determined. A positive effect of several cycles of torsion under pressure on the magnetoresistance of this material has been observed for the first time.     

Production of Si55 Al20 Fe10 Ni5 Cr5 Zr5 bulk amorphous alloy by hot pressing

Abstract

The temperature dependence of the relative density was examined for a Si₅₅ Al₂₀ Fe₁₀ Ni₅ Cr₅ Zr₅ alloy which was produced by hot pressing of the amorphous powder during heating up to various temperatures under a critical pressure of 1·5 GPa through a heating/pressing cycle. The density of the compacts increased with increasing temperature and reached a maximum near the crystallisation temperature of 698 K. The relative density of the compacts reached 98·3% at the critical condition of 1·5 GPa and 687 K. The hardness value of the bulk specimen was 940 HV(10 gf, 0·098 N), corresponding to that of the amorphous ribbon. Exposure to higher temperatures resulted in the precipitation of the crystalline phase. The present results indicate that Si based alloys can be produced in a compact form with a low fraction of voids by hot pressing the amorphous powder.     

Rapid recovery of dilute copper from a simulated Cu-SDS solution with low-cost steel wool cathode reactor

Copper-surfactant wastewaters are often encountered in electroplating, printed circuit boards manufacturing, and metal finishing industries, as well as in retentates from micellar-enhanced ultrafiltration process. A low-cost three-dimensional steel wool cathode reactor was evaluated for electrolytic recovery of Cu ion from dilute copper solution (0.2mM) in the presence of sodium dodecyl sulfate (SDS), octylphenol poly (ethyleneglycol) 9.5 ether (TX), nonylphenol poly (oxyethylene) 9 ether (NP9) and polyoxyethylene (20) sorbitan monooleate (TW) and also mixed surfactants (anionic/nonionic). The reactor showed excellent copper recovery ability in comparison to a parallel-plate reactor. The reactor rapidly recovered copper with a reasonable current efficiency. 93% of copper was recovered at current density of 1 A m(-2) and pH 4 in the presence of 8.5mM SDS. Initial solution pH, cathodic current density, solution mixing condition, SDS concentration, and initial copper concentrations significantly influenced copper recovery. The copper recovery rate increased with an increase in aqueous SDS concentrations between 5 and 8.5mM. The influences of nonionic surfactants on Cu recovery from SDS-Cu solution depended not only on the type of surfactants used, but also on applied concentrations. From the copper recovery perspective, TX at 0.1mM or NP should be selected rather than TW, because they did not inhibit copper recovery from SDS-Cu solution.     

Dispersion and rheology of nickel nanoparticle inks

Nickel nanoparticles were dispersed in α-terpineol solvents, and their rheological behaviour and suspension structure were examined using various organic surfactants, surfactant concentrations (0–10 wt.% of the powder) and solids loadings (φ=0.01–0.28 in volumetric ratios) over a shear-rate range 10⁰–10³ s⁻¹. A surfactant of oligomer polyester was found effective in the nanoparticle dispersion. An optimal surfactant concentration ca. 2–4 wt.% of the solids was found; beyond which, the apparent viscosity increased adversely. The oligomer-polyester molecules appeared to adsorb preferentially on the nanoparticle surface, forming a steric layer which facilitates the ink flow for the improved dispersion. A pseudoplastic flow behaviour was found as shear rate increased, and a maximum solids concentration (φ_m) was estimated as φ_m=0.32. The interparticle potential was dominated by van der Waals attraction in the terpineol liquid, and a reaction-limited cluster aggregation (RLCA) featuring with a fractal dimension (D _f) of 2.0 was calculated. This finding together with the reduced φ_m reveals that the nanoparticle inks were flocculated in character even with the presence of polyester surfactant. Additionally, a porous (electrically conductive) particulate network was expected to form if the inks were printed on a non-conductive substrate followed then by drying and sintering in practice.     

Aerosol route synthesis of Ni-CeO2-Al2O3 hybrid nanoparticle cluster for catalysis of reductive amination of polypropylene glycol

We demonstrated an aerosol-based approach to synthesize Ni-CeO₂-Al₂O₃ hybrid nanostructure as a potent nanopowder catalyst for the production of polyetheramine via reductive amination of polypropylene glycol. The method combines a gas-phase evaporation-induced self-assembly with two-stage thermal treatments of the aerosol particles. The hybrid Ni-CeO₂ nanoparticles (NPs) composed of ultrafine, homogeneously-distributed nanocrystallites of metallic Ni and ceria were shown to uniformly decorate on the surface of Al₂O₃ nanoparticle cluster (NPC). The composition, physical size and surface state of the hybrid nanostructure were tunable by design. It was found that hybridization with Al₂O₃ or CeO₂ enhanced catalytic activity of the Ni catalyst. A high yield of ≈77% of the desired PEA and a high selectivity to primary amine (≈100%) achieved simultaneously. The surface nitridation of Ni catalyst was effectively suppressed via the incorporation with CeO₂ NPs. An enhanced operation stability was observed by using the Ni-CeO₂-Al₂O₃ hybrid nanostructure as catalyst in comparison to the Ni-only NP. The work demonstrated a facile route for controlled gas-phase synthesis of hybrid nanopowder catalysts using Al₂O₃ NPC as the support matrix and CeO₂ NP as the promoter to further enhance the performance of Ni catalyst toward reductive amination.     

Characterisation and mechanical testing of hydrothermally treated HA/ZrO2 composites

Hydrothermal treatment is traditionally employed to improve the sinterability of powder compacts by reducing porosity and increasing apparent density. The effect of hydrothermal treatment on green powder compacts has been assessed in order to better understand how treatment may affect the sinterability of the bodies. Laboratory synthesised nano sized hydroxyapatite (HA) and a commercial zirconia (ZrO₂) powder have been ball milled together to create composite mixtures containing 0–5 wt% ZrO₂ loadings. Disc shaped bodies have been formed using uniaxial and subsequent isostatic pressure. The resultant coherent samples were subjected to hydrothermal treatment at either 120 or 250°C for 10 h in order to assess the effect of this processing technique on the physical, mechanical and microstructural properties of the green composites. ZrO₂ loadings up to 3 wt% increased apparent density from 90 to 92%, whereas increased loading to 5 wt% increased flexural strength, from 6 to 9 MPa. Increasing the hydrothermal treatment temperature increased open porosity, from ~44 to ~48% and reduced biaxial flexural strengths of the treated bodies compared to those of their room temperature isostatically pressed counterparts (~10 to ~6 MPa).     

Mechanical properties of hydroxyapatite–zirconia compacts sintered by two different sintering methods

Microwave sintering is traditionally employed to reduce the sintering temperature required to densify powder compacts. The effect of microwave heating on hydroxyapatite (HA)–zirconia (ZrO₂) green bodies has been investigated in order to understand how microwave energy may affect the physical and mechanical properties of the resultant densified composites. Laboratory synthesised nano-sized HA and a commercial nano-sized ZrO₂ powder have been ball milled to create mixtures containing 0–5 wt% ZrO₂ loadings. Compacts were microwave sintered at either 700, 1000 or 1200°C with a 1 h hold time. Comparative firings were also performed in a resistive element furnace using the same heating profile in order to assess the differences between conventional and microwave heating on the physical, mechanical and microstructural properties of the composites. Samples sintered at 700°C show little sign of densification with open porosities of approximately 50%. Composites conventionally sintered at 1000°C were between 65 and 75% dense, whereas the samples microwave sintered at this temperature were between 55 and 65% dense. Samples sintered at 1200°C showed the greatest degree of densification (>80%) with a corresponding reduction in open porosities. TCP generation occurred as a consequence of sintering at 1200°C, even with 0 wt% ZrO₂, and increased degradation of the HA phase to form significant amounts of TCP occurred with increasing additions of ZrO₂, along with increasing open porosity. Nanosized ZrO₂ prevents the densification of the HA matrix by effectively pinning grain boundaries and this effect is more pronounced in the MS materials. Similar strengths are achieved between the microwave and conventionally sintered samples. Greater amount of open porosity and pore interconnectivity are seen in the MS samples, which are considered to be useful for biomedical applications as they can promote osteo-integration.     

Synthesis of Ti2SnC from Ti/Sn/TiC powder mixtures by pressureless sintering technique

Ti/Sn/TiC powder mixtures were first employed to synthesize Ti₂SnC powder by pressureless sintering in the temperature range of 950–1250 °C at vacuum atmosphere. Ti₂SnC began to form at 950 °C, its content increased with increasing temperature. High purity of Ti₂SnC was obtained by sintering the mixtures with deficient Sn and TiC at 1200 °C for 15 min. A reaction mechanism was proposed to explain the formation of Ti₂SnC. The Ti₂SnC powder was characterized by scan electron microscopy (SEM) and X-ray diffraction (XRD). Using the above mixtures and process, the Ti₂SnC ceramic powder can be obtained on a larger scale.     

Growth of optically active multilayer metal oxide films on a plastic substrate

An optically active ITO/Au/ITO multilayer coating (where ITO stands for an indium tin oxide with the composition 90% In₂O₃ + 10% SnO₂ and Au is nanoparticulate gold on a thin-film poly(ethylene terephthalate) substrate) has been prepared by a solution-phase process using an ITO nanopowder dispersion in isopropanol and a solution of chloroauric acid, which was converted to colloidal gold by photolysis. A sol–gel process has been proposed for the synthesis of tin-doped indium oxide nanopowder. The properties and composition of the powder were assessed by IR spectroscopy, thermal analysis, electron microscopy, and X-ray diffraction. The phase composition of the ITO nanopowder and the optical properties of the films grown using the nanopowder have been shown to depend on the thermal annealing conditions during synthesis. Layer-by-layer growth of metal oxide films in ITO/Au/ITO coatings influences the absorption in the composite in the IR spectral region.     

Titanium—hydroxyapatite porous structures for endosseous applications

Materials for uncemented endosseous implants have to assure an as short as possible osseointegration time. Thus, a material with both surface bioactivity and a porous outer structure can become a preferred choice for this type of applications. This paper presents a class of titanium-base PM composites, reinforced with particulate hydroxyapatite. Raw materials were titanium powder, obtained through hydriding—milling—dehydriding, with the grain size of 63–100 μm, and sol-gel hydroxyapatite (HA) powder, produced by the reaction between Ca(NO₃)₂⋅4H₂O and (NH₄)₂HPO₄. Blends with 5 to 50% HA were prepared and pressed in a rigid die, producing single composition or gradual composition samples. The applied pressure was of 400, 500 or 600 MPa. Sintering was performed in vacuum, at 1160 ^∘C. All samples, although well sintered, displayed swelling during sintering, due to diffusion into the matrix. The increase in volume is more severe for higher amounts of HA in the green compacts and for higher applied compaction pressure. Compacts with a gradual increase of the HA content are recommended from the functional and mechanical point of view, but the increase should be slow, not to produce interlayer cracks. The outer surface shows interconnected pores, suitable for the ingrowth of vital new bone.     

Preparation of high surface area LaTiO2N photocatalyst

Nanocrystalline LaTiO₂N with a surface area of 27.5 m²/g was synthesized by nitridation of amorphous La₂O₃/TiO₂ composite powder at 900 °C for 8 h using NH₃ as the reactant gas. X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the as-prepared LaTiO₂N nanocrystals had a mean diameter of about 30 nm. It was found that the absorption edge of the oxynitride is significantly red-shifted compared with that of La₂Ti₂O₇ as increasing the nitridation temperature. The UV–vis absorption spectra indicated that the synthesized oxynitrides displayed good light absorption properties not only in the ultraviolet light but also in the visible-light region.     

Oxide nanoparticle arrays for sensors of CO and NO2 gases

Metal oxide sensors with active films from Fe₂O₃ and CoFe₂O₄ hexagonally assembled nanoparticle (NP) arrays were studied. NPs were synthesized by high-temperature solution phase reaction. Sensing NP layers were deposited by Langmuir-Blodgett (LB) technique. LB layers were characterized by XRD, SEM and magnetic measurements. NPs are monodomain and superparamagnetic at RT. Sensor active films are formed from 1 or 7 LB monolayers deposited on the alumina substrates equipped with heating meander and interdigitated contacts. LB layers were heat-treated or UV irradiated to remove the insulating surfactant. Sensing properties were studied in a test chamber containing reducing (CO) or oxidizing (NO₂) gas in concentrations between 5 and 100 ppm in the mixture with dry air. Response current signal (I_gas/I_air) vs. temperature and response vs. gas concentration calibration curves were measured. Best response values were obtained with CoFe₂O₄ devices between 300 and 400 °C, being 3 and 10 for 100 ppm of CO and 5 ppm of NO₂, respectively. The response and recovery times of sensors are between 3 and 30 min. The Fe₂O₃ and CoFe₂O₄ sensors with response of 8 or 10 to 5 ppm of NO₂ might be of practical applications in the detection of explosives.     

Low-temperature fabrication of 0.65 PMN–0.35 PT by a mixed oxide method

Single-phase perovskite 0.65 PMN–0.35 PT was achieved at low temperature by a conventional mixed oxide method. It was prepared by ball-milling a mixture of PbO(orthorhombic), TiO₂, Nb₂O₅ and (MgCO₃)₄Mg(OH)₂·5H₂O instead of MgO and heat treatment at 800 °C for 2 h. The formation was studied by means of DSC, FT-IR, Coupled TG-Mass, XRD, and SEM. It proceeded via formation of PbO(tetragonal) and Pb₂Nb₂O₇(P₂N) intermediates to form perovskite phase. The pure perovskite PMN-PT powder was obtained in particle size of 0.5–0.8 μm, agglomerate-free, and pseudo-cube. The powder calcined at 600 °C was sintered to 97% T.D. at 900–1000 °C for 2 h and showed room temperature dielectric constant of 3200, loss of 1–2%, and specific resistance of 5 × 10¹¹ Ω cm.