Effect of sintering temperature on the morphology,crystallinity and mechanical properties of carbonated hydroxyapatite (CHA)

Effect of sintering temperature on the physical and mechanical properties of synthesized B-type carbonated hydroxyapatite (CHA) over a range of temperature in CO₂ atmosphere has been investigated. The B-type CHA in nano size was synthesized at room temperature by using a direct pouring wet chemical precipitation method. The synthesized CHA powders were subsequently consolidated by sintering treatment from 800 to 1100 °C. The sintered CHA samples were evaluated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, X-ray fluorescence (XRF), carbon-hydrogen-nitrogen-sulfur-oxygen (CHNS/O) elemental analyzer, Field emission scanning electron microscopy (FESEM), and Vicker's indentation technique. The results obtained from XRD and FESEM indicated that the synthesized B-type CHA powders were nanometer in size. The crystallinity and crystallite size of the sintered CHA samples were increased due to increasing sintering temperature. The heat treatment between 800 °C and 1000 °C has resulted in coarsening and increased hardness of the sintered CHA samples. However, these properties began to deteriorate when sintering beyond 1100 °C due the formation of calcium oxide.     

One-step synthesis of high purity ZnO micro/nanostructures from pure Zn and pre-alloyed brass powders by vapor phase transport

In this research, vapor phase transport (VPT) was introduced as a facile, inexpensive method to produce ZnO micro/nanostructures from various Zn sources such as pure Zn and alpha brass pre-alloyed powders (Cu–20Zn and Cu–28Zn) at different processing temperatures of 930 °C–1050 °C. Simultaneous thermal analysis (STA) was carried out to investigate Zn evaporation and ZnO micro/nanostructure formation. STA results showed an exothermic peck at 711 °C and 728 °C for Cu–20Zn and Cu–28Zn, respectively, due to oxidation of the evaporated Zn element and formation of ZnO micro/nanostructures. X-ray diffraction results showed that high purity ZnO micro/nanostructures were successfully synthesized via VPT process and the crystallite size was increased from ~60 nm to ~100 nm with increasing processing temperature. Field emission scanning electron microscopy observations showed morphology (e.g. rods, column, tetrapods, and combs) and size of the synthesized micro/nanostructures were dependent on the Zn sources and processing temperature, in which average diameter of the synthesized ZnO structures was increased with increasing the processing temperature. The smallest (98 nm) and largest (603 nm) average diameters of synthesized ZnO micro/nanostructures were attained from the pure Zn and Cu–28Zn brass powders at 930 °C and 1050 °C, respectively.     

Comparative analysis and antibacterial properties of thermally sintered apatites with varied processing conditions

Hydroxyapatite (HA) and biphasic hydroxyapatite/beta-tricalcium phosphate (biphasic HA/β-TCP) were synthesized using thermal sintering. The parameters- sintering temperature (600°C, 900°C, and 1200°C), biological source used (fish bone, egg shells, and fish scales), and soaking time (2, 6, and 10 hours) were permuted to study their effects on the properties of the resultant apatite. Morphological study revealed that the smallest (60 nm) spherical particle and the largest (470 nm) irregular shaped particle were obtained from the fish bone sample sintered at 600°C and at 1200°C respectively. FTIR and XRD results showed that as the sintering temperature is increased, the phase transformation from HA to β-TCP takes place. Only the final products from fishbone sample at 600°C are pure carbonated HA. The crystallinity of synthesized particles ranged from 79% to 98%. Soaking time has no effect on phase composition of the apatite but has significant effect on crystallite size; increase in soaking time increases crystallite size and particle shape becomes more spherical. Interestingly, the fish bone sample sintered at 900°C has higher crystallinity and crystallite size compared to the fish scale sample sintered at the same temperature. EDX confirmed that non-stoichiometric apatite with Ca/P ratio ranging from 1.47 to 1.91 can be obtained by varying the sintering conditions. The antibacterial test revealed that both calcium apatite obtained from fish bones and fish scales have inhibited bacterial growth; apatite from fish bone works faster than fish scales. The in vitro cytotoxicity test ensured that all the calcium apatite except for eggshell are non-cytotoxic. Thus, apatite with excellent microbial activity can be obtained by using fish wastes, and by tuning the sintering parameters, the apatite with desired types and properties can be synthesized for different biomedical applications.     

Investigation of photocatalytic and luminescence properties of Na0.5Ce0.5WO4 self-assembled photocatalysts under solar light irradiation: Morphological,temperature and pH role

Tungstate-based scheelite structures have attracted much attention for the photocatalytic, adsorption and luminescence. To improve their performance, several ways have been considered, such as morphology control, thermal treatment and nanostructuring materials. In this work, three uniform and homogeneous morphologies, such as spindles, spheres and flowers, of self-assembled three-dimensional Na_0.5Ce_0.5WO₄ were used as photocatalysts for methylene blue dye photodegradation under solar irradiation. Depending on morphology, they required different temperatures to reach crystallization. Thermal treatments at 500 °C and 800 °C resulted in changes in crystallite size, porosity, surface state, but also in bandgap and emission properties. Thus, the crystallite sizes are about 50 nm for samples (spindles and flowers) treated at 500°Cand 87–167 nm for those treated at 800 °C. Their respective bandgap values measured by diffuse reflectance were 2.85 eV beyond 3.15 eV. The samples treated at 500 °C showed a lower emission and a longer charge carrier lifetime. A strong trend to adsorption was revealed, especially at low pH value and for the samples treated at 500 °C, reaching 100% at a pH value of 2.5. With decreasing pH, the photocatalysis activity increases (up to 50%), being also more efficient with catalysts treated at low temperature. It follows that the degradation efficiency of spindles treated at 500 °C is clearly higher compared to other morphologies treated at different temperature, and suitable for solar photocatalysis.     

Preparation and characterization of nanocrystalline and mesoporous strontium titanate thin films at room temperature

The low temperature perovskite-type strontium titanate (SrTiO₃) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol–gel route. The prepared sol had a narrow particle size distribution with hydrodynamic diameter of about 17 nm. X-ray diffraction (XRD) revealed that the synthesized powders had a perovskite-SrTiO₃ structure with preferable orientation growth along the (1 0 0) direction. TEM images showed that the average crystallite size of the powders annealed in the range 300–800°C was around 8 nm. FE-SEM analysis and AFM images revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 25 nm at 600°C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure with BET surface area in the range 92–75 m²/g at 400–600°C. One of the smallest crystallite sizes and one of the highest surface areas reported in the literature were obtained, which can be used in many applications, such as photocatalysts.     

Effect of heat treatment on the synthesis of hydroxyapatite from Indian clam seashell by hydrothermal method

Hydroxyapatite (HA) powder has been successfully synthesized from low-cost Indian clam seashells by using hydrothermal method. The mixture of tri-calcium phosphate [Ca₃(PO₄)₂], heat-treated ball-milled clam seashell, and demineralized water are heat-treated at several temperatures (700 °C, 800 °C, 900 °C, 1000 °C, and 1100 °C) for various time periods (1 h, 2 h, and 3 h) to perform the hydrothermal reactions. The phases and microstructure of the solid-state reaction products are analyzed through X-ray diffraction (XRD) method and field emission scanning electron microscopy (FESEM) respectively. The crystallite size of all the synthesized powders is calculated by using Scherrer's model. Mainly HA phase is obtained in all the different reaction products. However, these HAs are found to be non-stoichiometric in nature. As per the literature, non-stoichiometric HA is a more biologically active material compared to the stoichiometric one. Almost pure HA is formed with any selected reaction temperature applied for 2 h time duration. The crystallinity and Ca/P ratio of the synthesized pure HA are estimated by using standard model and energy-dispersive X-ray spectroscopy (EDS) analysis, respectively. The highest amount of near stoichiometric crystalline HA has been obtained at 900 °C of reaction temperature applied for 2 h time duration. With raising reaction temperature, the grain size of pure HA is found to be increased. Needle/rod shaped nano grains are noticed to form at lower reaction temperature whereas; beyond 1000 ^oC of temperature globular/spherical shaped grains are also observed to form. At 3 h reaction time agglomeration of grains is found to occur in all the synthesized powders.     

Structural,thermal and thermoluminescence response of transition and alkaline earth metals activated on aluminium borate [Al2(B4O7)3:Mn,Mg]

Aluminium borate doped with manganese (Mn) and magnesium (Mg) at different concentrations are studied. The samples were synthesized by solid state sintering. The structure, morphology and crystallite size of the aluminium borate are affected by the dopants used. The crystallite size values calculated for different concentrations of manganese and magnesium used in doping of aluminium borate are within a range of 32.5–35.1 nm and 21.3–28.7 nm respectively. The particle size obtained using a scanning electron spectroscopy for Mn and Mg-doped aluminium borate are in the range of 30–40 nm and 20–30 nm respectively. A loss in weight from the thermal analysis performed for Mn and Mg-doped aluminium borate are observed to be 10.43% and 20.06%. The thermoluminescence glow peaks from all the samples measured at 1 °C.s^?1 following irradiation to 50 Gy showed a prominent glow peak at 96 °C with minor peak observed at higher temperature (178 °C) region of the glow curve. The activation energy for Mn and Mg-doped aluminium borate were determined to be approximately 0.78 ± 0.30 eV and 0.76 ± 0.25 eV by using the initial rise, glow curve deconvolution and variable heating rate method. The dose responses were considered from 1 to 300 Gy for Mn (0.4%) and Mg (0.3%) doped aluminium borate and were further studied by using the g(D) and f(D) functions.     

Synthesis of hexagonal boron nitride fibers within two hour annealing at 500 °C and two hour growth duration at 1000 °C

Several advantageous features like low density, large surface area, high porosity and tight pore size make the nanofiber suitable for a wide range of applications from medical to consumer products and industrial to high-tech applications. Present study concerns the synthesis of hexagonal boron nitride fibers (Ø=70–350 nm) from a mixture of Boron, Magnesium oxide and Iron oxide powders via a simple CVD technique. A relatively long annealing and growth duration of two hours at 500 °C and 1000 °C, respectively were utilized in this synthesis. The synthesized samples seem to have the BNFs of irregular curved human hair-like morphologies in lower resolution and solid cylinder-like structures in high resolution transmission electron microscopy. The presence of Boron and Nitrogen in the synthesized BNF's sample were confirmed via the B 1s peak at 190.7 eV and N 1s peak at 398.3 eV in the XPS survey whereas a major peak at 1370 (cm⁻¹) in the Raman spectrum corresponds to the vibration of E_2g mode in h-BN. The sharp peaks in the XRD pattern verify the h-BN phase and highly crystalline nature of the synthesized BNFs.     

A simple,low cost,and template-free method for synthesis of boron nitride using different precursors

In this research, hexagonal boron nitride (h-BN) was synthesized using a simple, low cost, and template-free method with urea-boric acid (UB), melamine-boric acid (MB), and melamine-urea and boric acid (MUB) precursors, followed by the pyrolysis and heat treatment in a nitrogen atmosphere at 1050 °C. Samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Raman Spectroscopy, Fourier transform IR (FT-IR), and Brunauer–Emmett–Teller (BET) techniques. The specific surface areas obtained for h-BN synthesized by UB, MB, and MUB precursors were 87.43, 573.07, and 1005.7 m²/g, respectively. The average diameters of the pores using the Barrett, Joyner, and Halenda (BJH) model were 37.78, 3.68, and 2.13 nm, respectively. A thermogravimetric analysis showed a wider range of decomposition temperatures after using three precursors for synthesizing h-BN. Crumpled, whisker, and flower-like morphologies for UB, MB, and MUB precursors were respectively found using FESEM investigations. The formation of h-BN within the MUB sample was confirmed using the XPS analysis with measured peaks of 398.5 and 190.6 eV belonging to N 1s and B 1s, respectively. Raman spectroscopy revealed a high-intensity peak in 1366 cm^?1 related to the E_2g mode for h-BN synthesized with MUB. Therefore, the results demonstrate that the employed method can increase the potential of using the h-BN porous powder with a high specific surface area as a lubricant, thermal insulation filler, anti-corrosion filler in paint coatings, adsorption of various gas and hydrocarbon molecules as well as its application in drug-delivery nanocarriers.     

The effect of reaction temperature on the structural and magnetic properties of nano CoFe2O4

Nano cobalt ferrites (CoFe₂O₄) were co-precipitated at various reaction temperatures (60, 70 and 80 °C) for 1 h. The reaction temperature greatly influenced the crystallite size and the magnetic behaviours of the nano CoFe₂O₄. The mean crystallite size ranged from 9 to 15 nm with the increase in the reaction temperature and the intensity of metal oxide vibrations at 568–550 cm⁻¹ were also inclined. The synthesized samples were in the stoichiometric ratio of 1:2 (Co:Fe) with roughly spherical morphology. The synthesized cobalt nanoferrites exhibited ferromagnetism at room temperature and 5 K, and the saturation magnetization increased from 6.4 to 20 emu/g with the crystallite size.     

A novel Route to Synthesize <Emphasis Type="Italic">p</Emphasis>-Terphenyl from Benzene by the Catalysis of h-BN Nanoparticles

We have investigated the catalytic effect of boron nitride (h-BN) nanoparticles. The experiments prove that p-terphenyl can be synthesized from benzene at 400 °C in the presence of h-BN nanoparticles, thereby implying that the observed catalytic property of the h-BN nanoparticles may expand the application field of inorganic nanocrystals. The paper also discusses the mechanism of the structural rearrangement and oligomerization from benzene to p-terphenyl.     

Low-temperature synthesis of tantalum carbide by facile one-pot reaction

Tantalum carbide (TaC) was synthesized by polycondensation and carbothermal reduction reactions from an inorganic hybrid. Tantalum pentachloride (TaCl₅) and phenolic resin were used as the sources of tantalum and carbon, respectively. FTIR of as-synthesized dried complexes revealed formation of Ta-O. Pyrolysis of the complexes at 800 °C/1 h under argon resulted in tantalum oxide which after heat treatment at 1000–1200 °C transformed to tantalum carbide. The mean crystallite size of the precursor-derived TaC ceramics was less than 40 nm and Ta and C elements were homogeneously distributed in the ceramic samples. Mechanism for formation of TaC ceramic was analyzed.     

Porous zirconium titanate ceramics synthesized by sol–gel process

Zirconium titanate, ZrTiO₄, was synthesized by sol–gel method from zirconium butoxide and titanium isopropoxide. Amorphous ZrTiO₄ powder was ground, calcined at 500 °C, and milled to homogenize size distribution of the powder. Milled powder was pressed into tablets and sintered at 900–1400 °C for 8 h. Differential scanning calorimetry and dilatometric studies indicated crystallization of ZrTiO₄ at 600–700 °C. Raman spectroscopy and X-ray diffraction analysis confirmed presence of crystallized ZrTiO₄ already at 900 °C, and crystallite size was determined by Scherrer equation. Scanning electron microscopy showed that ZrTiO₄ grains begin to sinter at higher temperatures, starting from 1200 °C, while preserving high porosity up to 1300 °C as confirmed by dilatometry and mercury intrusion porosimetry.     

Effect of synthesis parameters on the size of cobalt ferrite crystallite

Nanoparticles of cobalt ferrite (CoFe₂O₄) were synthesized by the EDTA/Citrate complexing method and hydrothermal method without addition of surfactant. The influence of the pH of the reaction medium (8, 9 or 10), the temperature of the thermal treatment (600 °C, 800 °C or 1000 °C for the EDTA/Citrate method, and 120 °C, 140 °C or 160 °C for the hydrothermal method), and the duration of the thermal treatment (2, 4 or 6 h for the EDTA/Citrate complexing method, and 6, 15 or 24 h for the hydrothermal method) on the average crystallite size was studied by means of an experimental design based on the results obtained by XRD. Statistical analysis led to quantification of the influence of the synthesis parameters on the crystallite size of the powders. Results showed that the pH of the reaction medium is the parameter that shows the greatest influence on the growth of the crystallites of the powders obtained by the hydrothermal method, while calcination temperature is the most significant one for the powders produced by the EDTA/Citrate complexing method.     

Nanostructured cerium oxide: preparation and properties of weakly-agglomerated powders

Nanocrystalline powders of cerium oxide were prepared from cerium(III) nitrate solution by a two-stage precipitation process which yielded weakly-agglomerated powders with a crystallite size smaller than 5 nm. Hydrogen peroxide was added to cerium nitrate at 5°C to slowly oxidise Ce³⁺ to Ce⁴⁺ and thereby initiate homogeneous precipitation with the formation of dense spherical agglomerates. The precipitation process was completed by the addition of ammonium hydroxide which disrupted the spherical agglomerates leaving a weakly-agglomerated power of hydrated ceria. The process was completed by hydrothermal treatment at 180°C without increase in crystallite size. The powders were characterised by X-ray diffraction, transmission electron microscopy and thermogravimetric analysis. The weakly-agglomerated state of the powder and the uniform crystallite size of under 5 nm are favourable characteristics for many applications.     

Thermally Induced Nano-Structural and Optical Changes of nc-Si:H Deposited by Hot-Wire CVD

We report on the thermally induced changes of the nano-structural and optical properties of hydrogenated nanocrystalline silicon in the temperature range 200–700 °C. The as-deposited sample has a high crystalline volume fraction of 53% with an average crystallite size of ~3.9 nm, where 66% of the total hydrogen is bonded as ≡Si–H monohydrides on the nano-crystallite surface. A growth in the native crystallite size and crystalline volume fraction occurs at annealing temperatures ≥400 °C, where hydrogen is initially removed from the crystallite grain boundaries followed by its removal from the amorphous network. The nucleation of smaller nano-crystallites at higher temperatures accounts for the enhanced porous structure and the increase in the optical band gap and average gap.     

Characterization and X-ray peak broadening analysis in PZT nanoparticles prepared by modified sol–gel method

Lead zirconate titanate nanoparticles (PZT-NPs) were synthesized by a modified sol–gel method and were calcinated at temperatures of 600, 650 and 700 °C. Fourier transform infrared (FTIR), powder X-ray diffraction (XRD) and thermal analysis (TGA/DTA), indicate that single-phase perovskite PZT-NPs are obtained after heat treatment at a temperature of 650 °C. The TEM results obtained from the PZT-NPs confirm that the morphology of the PZT nanoparticles is spherical, with an average diameter size of 17 nm. We also investigated the crystallite development in the nanostructured PZT by X-ray peak broadening analysis. The individual contribution of many small crystallite sizes and lattice strains to the peak broadening in the PZT nanoparticles prepared at different temperatures were studied using Williamson–Hall (W–H) analysis in the range of 2θ = 15–80°.     

Correlation of structure and dielectric response in Ce-doped double perovskite cobaltite

Double perovskite Bi₂Ca_2-xCe_xCoO₆; x = 0.00, 0.05, 0.10 and 0.15 (BCCCO) is synthesized by co-precipitation route. X-ray diffraction (XRD) confirms the monoclinic single-phase crystal structure with negligible variation in unit cell parameters, indicating that the Cerium (Ce) has been successfully incorporated. With Ce doping, the average crystallite size of Bi₂Ca₂CoO₆ (BCCO) nanoparticles decreases. Scherrer's formula was used to determine the crystallite sizes (33–37 nm) of BCCO nanoparticles. Jonscher's power law is used to investigate the conduction mechanism of all the prepared specimens. The power-law specifies the correlated barrier hopping for BCCCO x = 0.00 and 0.05, short polaron tunneling for x = 0.10, while BCCCO x = 0.15 follows overlapping large polaron tunneling. The dielectric permittivity has been calculated with a frequency range of 20 Hz - 3 MHz, and the Ce doped samples show a high value of dielectric permittivity ε_r = 1.79 × 10⁵ at 500 °C. The influence of crystallite size on the dielectric permittivity of BCCCO was examined in this work. The relaxation time and spreading factor of all samples are investigated using Non-linear Debye's function. All these features are studied as a function of frequency at temperatures ranging from 100 to 500 °C. Here, the DC electrical conductivity of BCCCO is investigated by the four-probe method at 50–400 °C. In Ce-doped specimen the lowest value of thermal conductivity (k = 0.797 W/m-K at 120 °C) has been observed.     

Densification behavior and microstructure development in TiB2 ceramics doped with h-BN

This paper aims to study the impacts of h-BN additive on the microstructural features and sintering behavior of TiB₂. For this objective, two different samples of monolithic TiB₂ and TiB₂-5 wt% h-BN were fabricated using spark plasma sintering (SPS) technique at 1900 °C. An external pressure of 40 MPa was exerted to the specimens during the sintering, and they were maintained at the maximum sintering temperature for 7 min. The characterization of as-fabricated ceramics was carried out using thermodynamical investigations, field emission SEM, and X-ray diffractometer. The thermodynamical and XRD studies revealed that the sintering process was non-reactive for both samples. However, introducing h-BN noticeably promoted the sinterability of TiB₂ through activating the liquid phase sintering mechanism, and a near-fully dense composite was attained. The fractographical assessment manifested that the intergranular fracture was the dominant type in both monolithic and h-BN doped specimens. Finally, the quantitative image analysis indicated the role of h-BN in refining the microstructure of the doped TiB₂ ceramic.     

Effects of doping content and crystallite size on luminescence properties of Eu3+ doped fluorapatites obtained from natural waste

In this study, Eu³⁺ doped natural fluorapatites [Ca₁₀(PO₄)₆F₂:xEu³⁺ (x = 0.1, 0.3 and 0.5)] were produced from a natural waste by solid-state powder synthesis, conventional sintering, and spark plasma sintering techniques. The effects of doping content and crystallite size on luminescence properties of fluorapatite were investigated by XRD, SEM, and PL analysis. The obtained results showed that luminescence emission's intensity significantly increased with doping content, but no effect was observed on the density and crystallite size. For the samples produced with different methods, emission intensity was the lowest for sintered samples by SPS (1150 °C, 10 min, 50 MPa) with the smallest crystalline size. In contrast, emission intensity was found much higher for synthesized powders with the largest crystallite size. Furthermore, upon excitation under UV radiation, the Eu doped fluorapatites demonstrated the characteristic ⁵D₀–⁷F₂ and ⁵D₀–⁷F₄ emission lines of Eu³⁺ at 618 nm and 704 nm (red region) with an ultrahigh intensity that has been firstly observed in the literature. Therefore, Eu doped fluorapatites, quickly produced from a natural waste in an eco-friendly and cost-effective way, carry a potential to be used in biological applications and lightning applications.