The influence of sintering temperature on the properties of compacted bovine hydroxyapatite

On the sintering characteristic of hydroxyapatite (HA), the resulting microstructure and properties are influenced not only by the characteristic and impurities of materials but also are found to be dependent on the thermal history during the fabrication process. This research is concerned with the effect of sintering temperature on the relative density, hardness, and phase purity after sintering process. Bovine HA (BHA) powder obtained from heated local cortical bovine bone at 900 °C for 2 h was uniaxially pressed at 156 MPa into green bodies using a 20 mm cylindrical dies. The compacted green body was pressurelessly sintered in air atmosphere at temperatures ranging from 1000 to 1400 °C, at a furnace ramp rate of 5 °C/min and dwell time of 2 h. The BHA starting powder was characterized using XRD and FTIR. SEM was also used for observing the microstructures of the starting material. The sintered BHA specimens were analyzed using Archimedes method for measuring density; XRD for phase stability; and Vickers method for hardness measurement. The analysis results show that the starting BHA powder and the sintered BHA specimens contain HA. The intensity of the three main peaks of HA decreases with increasing sintering temperature which may be due to decomposition of HA at high temperature. The density and hardness of BHA increases with increasing sintering temperature based on the results obtained.     

Characterization and optical properties of m-Li2ZrO3 prepared by optimized solid-state reaction

m-Li₂ZrO₃ powders were successfully prepared by solid-state reaction method using Li₂CO₃ and ZrO₂ as raw materials. The synthesis was optimized by varying the ball-milling time (0–96 h); Li₂CO₃ excess (0 or 5 wt%), reaction temperature (700, 800, 900 or 1000 °C), and reaction time (3, 6, 9 or 12 h). The structural, morphological and optical properties of m-Li₂ZrO₃ powders were examined by X-Ray Diffraction, Thermogravimetric and Differential-Thermal analysis, Scanning Electron Microscopy, High-Resolution Transmission Electron Microscopy, Laser Diffraction, Dynamic Light Scattering and UV–Vis Diffuse Reflectance Spectroscopy. The results show that precursors suitable for the synthesis of fine powders require ball-milling times longer than or equal to 6 h. Highly crystalline m-Li₂ZrO₃ was synthesized under two distinctive calcination conditions as follows: 900 °C/6h without Li₂CO₃ excess or 1000 °C/12 h using 5 wt% of Li₂CO₃ excess. Particle size of as-synthesized powders was found to be in the range from 200 nm to 1 µm. m-Li₂ZrO₃ was found to be a wide band gap material with apparent optical band gap of 5.5 eV (direct) and 5.1 eV (indirect), which can be used in UV-C applications.     

Synthesis of titanium carbide and TiC–SiO2 nanocomposite powder using rutile and Si by mechanically activated sintering

High-energy ball milling was applied with subsequent heat treatment for synthesizing nanoparticles of TiC powders by the carbothermic and carbosilisisothermic reduction of titanium oxide (rutile type). The milling procedure involved milling of TiO₂/C and TiO₂/Si/C powders at room temperature in an argon atmosphere. The progress of the mechanically induced solid state reaction was monitored using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that TiC nanoparticles were duly synthesized in the TiO₂/C system at 1700 °C in 60-h milled samples. In the non-milled samples, although heated at the same temperature, only a minor amount of a lower degree of titanium oxide (Ti₃O₅) was observed to form. Further, in other non-milled samples, but with Si initially present, despite heating to 1550 °C no TiC phase was detected. However, using Si as a reducing agent accompanied by graphite, after 60 h ball milling, only Si remained as a distinguishable crystalline phase. Further, heat treatment of activated powders by forming the interphase compounds (such as Ti₃Si₅ and Ti₅Si₃) remarkably decreased the synthesis temperature to 900 °C for the 60 h milled samples.     

Magnetic and microwave-absorbing properties of SrAl<Subscript>4</Subscript>Fe<Subscript>8</Subscript>O<Subscript>19</Subscript> powders synthesized by coprecipitation and citric- combustion methods

Al-substituted M-type hexaferrite is a highly anisotropic ferromagnetic material. In the present study, the coprecipitation and the citric-combustion methods of synthesis for SrAl₄Fe₈O₁₉ powders were explored and their microstructure, magnetic properties, and microwave absorptivity examined. X-ray diffraction (XRD), scanning electron microscopy (SEM), a vibrating sample magnetometer, and a vector network analyser were used to characterize the powders. The XRD analyses indicated that the pure SrAl₄Fe₈O₁₉ powder was synthesized at 900°C and 1000°C for 3 h by coprecipitation, but only at 1000°C for the citric-combustion processes. The SEM analysis revealed that the coprecipitation process yielded a powder with a smaller particle size, near single-domain structure, uniform grain morphology, and smaller shape anisotropy than the citric-combustion process. The synthesis technique also significantly affected the magnetic properties and microwave-absorptivity. Conversely, calcining temperature and calcining time had less of an effect. The grain size was found to be a key factor affecting the property of the powder. The powders synthesized by coprecipitation method at calcining temperature of 900°C exhibited the largest magnetization, largest coercivity, and best microwave absorptivity.     

A study on the synthesis of nanostructured WC–10 wt% Co particles from WO<Subscript>3</Subscript>, Co<Subscript>3</Subscript>O<Subscript>4</Subscript>, and graphite

The formation of the nanostructured WC–10 wt% Co powder from WO₃, Co₃O₄, and graphite is studied. The effects of the processing parameters of high-energy ball milling, reduction in H₂ atmosphere, and carburization in Ar/CO atmosphere are investigated. The crystallite size of the as-synthesized WC is 30–40 and 40–50 nm for 900 and 1000 °C carburized powders, respectively. The powder is agglomerated with the size of the primary particles ranging from 50 to 700 nm. High-energy ball milling of WO₃–Co₃O₄–C powder mixtures leads to finer particle and crystallite sizes with larger surface area. Such milled powders can be reduced to nanostructured W at 570 °C and carburized to form WC at temperatures as low as 900 °C. Crystal growth has taken place during carburization, particularly at 1000 °C, which results in the formation of truncated triangular prisms and nanoplates of WC at 1000 °C.     

A comparative study of ZnNb2O6 nanoceramics synthesized by high energy ball milling and subsequent conventional and microwave annealing

Ball-milling and subsequent conventional and microwave assisted heating processes have been applied to synthesize ZnNb₂O₆ nanoceramic. X-ray diffraction, simultaneous thermal analysis, scanning electron microscope (SEM), transmission electron microscope (TEM) and BET techniques were utilized to characterize the as-milled and annealed samples. Characterization of synthesized powders revealed that in spite of the very short heating time in the microwave process without soaking time, the powder heated at 550 °C had all physical properties similar to powders synthesized in conventional heating at the 650 °C temperature with a heating rate of 10 °C/min and a soaking time of 1 h. In addition, SEM, TEM and BET observations of synthesized powders showed that the particle size of powders lies in the nano meter range.     

Processing and electrochemical characterization of Ni2Si intermetallic compound produced by vacuum sintering

In this study, a powder metallurgy approach for fabrication of Ni₂Si intermetallic compound was utilized. In this regard, mechanically activated Ni-33 at.% Si powders were used as feedstock. The powders were investigated by differential scanning calorimetry to study phase transformations that occurred during heating in the calorimeter. It was shown that the milled powders reacted after heating up to 850 °C. In order to fabricate bulk Ni-33 at.% Si, the as-milled powders were cold-pressed and subsequently sintered at 900 °C for 1 h in a vacuum furnace. X-ray diffraction results indicated that the phase composition of sintered materials consisted of only δ-Ni₂Si intermetallic. Consolidated samples exhibit 12% porosity and microhardness up to 773 HV_0.05. Further investigations showed the corrosion rate of sintered compound is higher than that of Ni–Si alloys reported in the literature. Here, anodic dissolution near the surface pores seems to be corrosion mechanism which resulted in increase in surface porosity up to 27% after corrosion.     

Reduction of vacuum sublimation by ion beam treatment for e-beam deposited SiC films

We report on the low temperature (≤1000 °C) vacuum sublimation behavior of e-beam evaporative deposited SiC film and a method to reduce the vacuum sublimation by an ion beam process. The density of SiC film deposited by e-beam evaporation method was ∼60% of the density of bulk source material. In this sample, we found that sublimation became appreciable above ∼750 °C under 1.5 × 10⁻⁵ torr pressure and the sublimation rate increased with increasing temperature, reaching ∼70 nm/h at 950 °C when the coated sample was heated for 5 h. When the film was irradiated with 70 keV N⁺ ions prior to heating, the sublimation rate decreased down to ∼23 nm/h at a fluence of 1 × 10¹⁷ ions/cm². However, further increase in fluence beyond this value or extended heating period did not change (decrease or increase) the sublimation rate any more.     

Preparation and characterization of hydroxyapatite synthesized from oyster shell powders

The ready availability and the low cost of oyster shells, which is composed predominantly of calcium carbonate with rare impurities, along with natural wastes are attractive features for converting the biological material into hydroxyapatite (HA) powders for biomedical applications. The HA powder was synthesized using oyster shell powders and dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) through ball milling and subsequently heat treatment. The HA was initiated through sintering the 1-h milled sample at 1000 °C for 1 h, while pure HA phase is formed after sintering the 10-h milled sample. The as-prepared samples, obtained after 5 or 10 h of milling and then heat-treating at 1000 °C for 1 h, contain the phase of β-tricalcium phosphate (β-TCP). Moreover, the result of FTIR analysis showed that the as-prepared HA sample is A- and B-type carbonate-containing calcium phosphates. The as-synthesize HA powder containing trace elements Mg and Sr exhibited good crystallinity (96.3%) and high phase-purity.     

Enhanced performance of high temperature aluminate cementitious materials incorporated with Cu powders for thermal energy storage

Cementitious materials have been extensively developed in thermal energy storage system of solar thermal power. This paper deals with the volume heat capacity, thermal conductivity, thermal expansion coefficient, and compressive strength of aluminate cementitious thermal energy storage materials with the addition of metal Cu powders. The specimens were subjected to heat-treatment at 105, 350, and 900 °C, respectively. In the heating process, Cu powders gradually oxidized to Cu₂O and CuO, providing a so-called mass compensation mechanism for the composite paste. Meanwhile, it indicates that volume heat capacity and thermal conductivity both increase with increasing Cu powders content and decrease with the rising temperature. The optimum thermal properties were obtained at 15 wt% Cu powders loading. In addition, Calorimetric Test, XRD, TG–DSC, and MIP are performed for characterizing the hydration rates, the phases, the mass/heat evolution, and the pore distribution, respectively.     

Sintering behaviour of monodispersed ZnS powders

The sintering behaviour of monodispersed ZnS powders having particle size of 0.1–0.9 μm, which were prepared from aqueous zinc nitrate solution by a homogeneous precipitation method using thioacetamide, was studied. Dry-pressed pellets of ZnS powders were fired at 900–1250 °C for 2 h in a nitrogen atmosphere. Monodispersed ZnS powders showed high sinterability in comparison with agglomerated or aggregated ZnS powders. The sinterability increased with decrease in particle size, and ZnS powders with particle size of 0.1 μm were densified to above 98% theoretical density by conventional sintering at 1000 °C for 2 h. Ultrafine monodispersed, spherical particles gave a uniform and fine-grained microstructure. This revised version was published online in November 2006 with corrections to the Cover Date.     

The effect of yttrium oxide in hydroxyapatite/aluminum oxide hybrid biocomposite materials: Phase,mechanical and morphological evaluation

This study presents the fabrication and characterization of composite materials of hydroxyapatite and aluminum oxide. Hydroxyapatite powder was obtained from bovine bones via conventional calcination routine. Although hydroxyapatite shows great biocompatibility with the human body, its applications are limited to non‐load bearing areas. For this purpose, fine powders of hydroxyapatite/alumina were admixed with 1 and 5 wt.% yittria. Powder‐compacts were sintered by two‐step sintering route by increasing temperature to 1550 °C for 2 h and then sintering at 1450 °C for 4 h. The effect of increasing yittria content on sintering behavior and mechanical properties was investigated in biocomposite hybrid materials.     

Effect of environment atmosphere on thermal shock resistance of the ZrB2–SiC–graphite composite

The thermal shock resistance of the ZrB₂–SiC–graphite composite was evaluated by measuring the retention of the flexural strength after the electrical resistance heating to the temperature ranging from 1000 °C up to 2500 °C. The experiment was operated in two different environment atmospheres (pure oxygen and low oxygen partial pressure which mixed O₂ and Ar with 1:9) at total pressure 2000 Pa. The residual strength for the specimen decreased gradually as the temperature increased up to 2200 °C, and it was slightly higher when heated in low oxygen partial pressure environment than in pure oxygen. In contrast to the specimen heated in low oxygen partial pressure environment, the residual strength for the specimen in pure oxygen increased steeply as the temperature increased from 1600 °C up to 1800 °C. The analysis of the SEM observations combined with EDS confirmed that the surface oxidation played a positive role in the thermal shock resistance of the ZrB₂–SiC–graphite composite with different environment atmospheres. The results here pointed out a potential method for charactering the effect of environment atmosphere on thermal shock resistance of the ZrB₂–SiC–graphite composite.     

Combustion characteristics of the heat pellet prepared from the Fe powders obtained by spray pyrolysis

Fe powders for thermal batteries were prepared by reduction of iron oxide powders obtained by spray pyrolysis. The iron oxide powders prepared by spray pyrolysis had fine size, spherical shape and high surface area. The morphologies of the Fe powders were affected by the preparation temperatures of the iron oxide powders. The Fe powders obtained from the iron oxide powders prepared by spray pyrolysis at 900 and 1000 °C had slightly aggregated structure of the primary powders with several microns sizes. The powders had pure Fe phases at reducing temperatures between 600 and 800 °C. The heat pellets with diameter of 18.2 mm were prepared using Fe powders and potassium perchlorate (KClO₄). The porosity of the prepared heat pellet was about 40%. The break strength of the heat pellet was 0.9 kgf. The ignition sensitivity of the heat pellet was 4 W. The maximum burn rate of the heat pellet obtained from the Fe powders were 8.6 cm s^?1.     

Nanohydroxyapatite prepared from non-toxic organic Ca2+ compounds by precipitation in aqueous solution

Nanocrystalline hydroxyapatites were prepared by the precipitation method using a water soluble Ca²⁺ organic compounds and (NH₄)₂HPO₄. The fine nanohydroxyapatites had spherical, needle-like or mixed morphology and specific areas around 150 m²/g. The nanocrystalline powders differed by thermal stability and they were transformed to bi- or three-phasic systems with hydroxyapatite, βTCP and αTCP phases after annealing at 1000 °C.     

Thermal history induced variable relaxor behavior in the high TC ternary ferroelectric 0.6Bi(Mg1/2Ti1/2)O3–0.05Bi(Zn1/2Ti1/2)O3–0.35PbTiO3

Studies carried out on a perovskite-structured rhombohedral 0.6Bi(Mg_1/2Ti_1/2)O₃–0.05Bi(Zn_1/2Ti_1/2)O₃–0.35PbTiO₃ (xBZT–yBMT–zPT) ceramic quenched from temperatures below 1000 °C show that the dielectric properties are dramatically altered by the thermal history. Samples quenched from temperatures 650 °C–900 °C show classical ferroelectric switching behavior that is not observed on either side of this temperature range. The quenched states lose their switchable ferroelectric properties when heated to temperatures as low as 400 °C. The results demonstrate for the first time that the dielectric and electromechanical response, as observed at room temperature, can be varied between normal to relaxor behavior by changing thermal quenching conditions.     

Synthesis and properties of LaNi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3−δ</Subscript> as cathode materials in SOFC

The synthesis of LaNi_{1− x} Fe _x O_3−δ (LNF) perovskites with x = 0.0–1.0, for use as cathode materials for an IT-SOFC, was investigated using four combustion methods, Water Citrate (WC), Modified Water Citrate (MWC), Nitric Citrate (NC), and Modified Nitric Citrate (MNC). The structures and homogeneities of the synthesized powders were examined using an XRD, and the particle sizes were examined using an SEM and a particle size analyzer. All four combustion methods gave the single phase perovskites with the same structure. The main difference was shown in a particle size that the smallest to the largest sizes were obtained from MNC, MWC, NC, and WC, respectively. In this LNF series, as x is 0–0.5, the crystal structure is cubic and rhombohedral at the calcination temperature of 700 and 900 °C, respectively. Further investigation indicated that the cubic structure changed to rhombohedral structure at 900 °C, and was stable up to 1200 °C. As x is 0.6–1.0, the crystal structure is in orthorhombic phase when calcined between 700 and 1000 °C. This orthorhombic phase decomposed above 1100 °C. From the XRD and SEM–EDX results, LaNi_0.6Fe_0.4O_3−δ (LNF64) has a good chemical compatibility with 8YSZ from room temperature up to 900 °C. In addition, its thermal expansion coefficient is 13.2 × 10⁻⁶ K⁻¹ close to that of 8 mol% Y₂O₃ (8YSZ). Therefore, LNF64 also has a good physical compatibility with 8YSZ.     

Synthesis of nanocrystalline carbonated hydroxyapatite powder via nonalkoxide sol–gel method

Nanocrystalline hydroxyapatite powder was synthesized via nonalkoxide sol–gel method. Ca(NO₃)₂·4H₂O and P₂O₅ were mixed in ethanol, which led to a stable sol. STA, XRD and FTIR were used to characterize the calcined powders. The degrees of crystallinity and crystallite sizes were thereafter calculated from XRD patterns. The microscopic observations of the powder were performed using SEM and TEM. Results showed that a nanocrystalline hydroxyapatite powder was obtained after being heated at 450 °C for 6 h. Furthermore, increasing the calcining temperature caused both the formation of carbonate bonds and the increase in the crystallite sizes, and the degree of crystallinity.     

Structural and chemical changes of thermally treated bone apatite

The thermal behaviour of the animal by-product meat and bone meal (MBM) has been investigated in order to assess how it is affected structurally and chemically by incineration. Initially composed of intergrown collagen and hydroxyapatite (HAP), combustion of the organic component is complete by 650 °C, with most mass loss (50–55%) occurring by 500 °C. No original proteins were detected in samples heated at 400 °C or above. Combustion of collagen is accompanied by an increase in HAP mean crystallite size at temperatures greater than 400 °C, from 10 nm to a constant value of 120 nm at 800 °C or more. Newly formed crystalline phases appear beyond 400 °C, and include β-tricalcium phosphate, NaCaPO₄, halite (NaCl) and sylvite (KCl). Crystallite thickness as judged by small angle X-ray scattering (SAXS) increases from 2 nm (25–400 °C) to 8–9 nm very rapidly at 550 °C, and then gradually increases to approximately 10 nm. The original texture of HAP within a collagen matrix is progressively lost, producing a porous HAP dominated solid at 700 °C, and a very low porosity sintered HAP product at 900 °C.     

Microwave hybrid synthesis of silicon carbide nanopowders

Nanosized silicon carbide powders were synthesised from a mixture of silica gel and carbon through both the conventional and microwave heating methods. Reaction kinetics of SiC formation were found to exhibit notable differences for the samples heated in microwave field and furnace. In the conventional method SiC nanopowders can be synthesised after 105 min heating at 1500 °C in a coke-bed using an electrical tube furnace. Electron microscopy studies of these powders showed the existence of equiaxed SiC nanopowders with an average particle size of 8.2 nm. In the microwave heating process, SiC powders formed after 60 min; the powder consisted of a mixture of SiC nanopowders (with two average particle sizes of 13.6 and 58.2 nm) and particles in the shape of long strands (with an average diameter of 330 nm).