Formation of high-density scintillation ceramic from LuAG:Ce + Lu2O3 powders obtained by co-precipitation method

The results of formation of the high density effective scintillation ceramics consisting of two compounds of the cubic symmetry, LuAG:Ce and Lu₂O₃ (LuAG:Ce + Lu₂O₃), are described. Powders of a novel material LuAG:Ce + Lu₂O₃ were synthesized by co-precipitation method. The introduction of Lu₂O₃ into LuAG:Ce was shown to increase the density of the ceramics obtained and modify its scintillation properties.     

The optimum conditions for solid-state-prepared (Y3−xCex)Al5O12 phosphor using the Taguchi method

Using the Taguchi method, the authors analyzed the optimum conditions for (Y_3?xCe_x)Al₅O₁₂ (YAG:Ce) phosphor, which is prepared using the solid-state reaction method. The controllable factors used in this study consisted of the following: (1) the duration of milling, (2) the quantity of substitution, (3) the duration of sintering, and (4) the temperature of sintering. Under optimum conditions, a confirmation experiment was carried out, and the average photoluminescence (PL) intensity of YAG:Ce phosphor was found to be up to 270.84 (a.u.). The percentage contribution of each controllable factor was also determined. Most interestingly, the temperature of sintering is the most influential factor within current investigation range to the solid-state-prepared YAG:Ce phosphor, and its value of percentage contribution is up to 70.90%. Aside from this, through the optimum conditions, the average PL intensity of YAG:Ce phosphor can be substantially promoted from 193.88 (a.u.), the average PL intensity of YAG:Ce phosphor sintered at 1500 °C for 6 h that was usually used to sinter YAG:Ce phosphor.     

Coating and spark plasma sintering of nano-sized TiN on Y-α-sialon

TiN coating on Y-α-sialon was accomplished by depositing TiO₂ on their particle surfaces through controlled hydrolysis of TiCl₄ and Ti(O-i-C₃H₇)₄ and subsequent nitridation with NH₃ gas at 1000 °C. TiN particles covering Y-α-sialon were about 20 nm in size. Spark plasma sintering (SPS) of TiN/Y-α-sialon particles produced composite ceramics with continuous TiN networks at 1400 °C, but with TiN grains isolated in elongated β-sialon grains at 1600 °C. The relative density and Vickers hardness of TiN/sialon ceramics SPSed at 1400–1600 °C containing 25 vol.% TiN were measured. The electrical resistivity was in a wide range of 10⁻⁴ to 10⁰ Ω cm for the ceramics sintered at 1400 °C, but lowered to the order of magnitude of 10⁻¹ and 10⁵ Ω cm at higher temperatures ≥1500 °C. It was found that the complete transition to β-sialon increased the resistivity to 10³ to 10⁵ Ω cm, due to breaking up continuous TiN layers by elongated β-sialon grains.     

Synthesis and phases evolution of Si–C–Ti from polycarbosilane (PCS) and metal Ti

Si–C–Ti ceramics were synthesized by reactive pyrolysis of polycarbosilane (PCS) precursor filled with metal Ti powder. Pyrolysis of mixture with atomic ratio of Ti:Si through 3:1–3:2 was carried out in argon atmosphere at given temperature up to 1500 °C. The metal–precursor reactions, and phase evolution were studied using X-ray diffraction and scanning electron microscopy with EDX. The Ti₃SiC₂ phase was obtained firstly from reaction of PCS and Ti. Ti₃SiC₂ formation starts at 1300 °C and its amount increases significantly in a narrow temperature range between 1400 °C and 1500 °C. In addition, addition of CaF₂ can promote the formation of Ti₃SiC₂ phase.     

A study on the phase transformation of the nanosized hydroxyapatite synthesized by hydrolysis using in situ high temperature X-ray diffraction

The biodegradable hydroxyapatite (HA) was synthesized by hydrolysis and characterized using high temperature X-ray diffraction (HT-XRD), differential thermal analysis and thermogravimetry (DTA/TG), and scanning electron microscopy (SEM). The in situ phase transformation of the HA synthesized from CaHPO₄·2H₂O (DCPD) and CaCO₃ with a Ca / P = 1.5 in 2.5 M NaOH_(aq) at 75 °C for 1 h was investigated by HT-XRD between 25 and 1500 °C. The HA was crystallized at 600 °C and maintained as the major phase until 1400 °C. The HA steadily transformed to the α-tricalcium phosphate (α-TCP) which became the major phosphate phase at 1500 °C. At 700 °C, the minor CaO phase appeared and vanished at 1300 °C. The Na⁺ impurity from the hydrolysis process was responsible for the formation of the NaCaPO₄ phase, which appeared above 800 °C and disappeared at 1200 °C.     

Effects of Zr/Ce molar ratio and water content on thermal stability and structure of ZrO2–CeO2 mixed oxides prepared via sol–gel process

ZrO₂–CeO₂ mixed oxides were synthesized via sol–gel process. Thermal stability, structure and morphology of samples were investigated by powder X-ray diffraction, FT-Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. In this approach, the solvent composition and Zr/Ce molar ratio have great influences on the structure and morphology of final products. With decreasing water content in the mixed solvent, specific surface area of powders increased and the single tetragonal phase was obtained. Only when the volume ratio of water and ethanol and the Zr/Ce molar ratio were 1:1, tetragonal t″-Zr_0.5Ce_0.5O₂ could be stabilized in powders at temperature as high as 1000 °C. Meanwhile, tetragonal (t′) and (t″) phases coexisted in Zr_0.5Ce_0.5O₂ solid solution without peak splitting after calcination at 1100 °C, further transforming into cubic and tetragonal (t′) phases at 1200 °C. The effective activation energy for Zr_0.5Ce_0.5O₂ nanocrystallite growth during annealing is about 5.24 ± 0.15 kJ/mol.     

Influence of yttrium dopant on the synthesis of ultrafine AlN powders by CRN route from a sol–gel low temperature combustion precursor

Y-doped ultrafine AlN powders were synthesized by a carbothermal reduction nitridation (CRN) route from precursors of Al₂O₃, C and Y₂O₃ prepared by a sol–gel low temperature combustion technology. The Y dopant reacted with alumina and thus forming yttrium aluminate of AlYO₃, Al₃Y₅O₁₂ and Al₂Y₄O₉, which formed a liquid at about 1400 °C and promoted the transformation of Al₂O₃ to AlN and the growth of AlN particles. Compared with the conventional solid CRN process, Y dopant reduced the synthesis temperature by 150 °C, and Al₂O₃ transformed to AlN completely at 1450 °C. The content of Y dopant had little effect on the synthesis temperature of AlN whereas it influenced the phase of Y compounds in the products. As the Y/Al molar ratio was in the range of 0.007648–0.022944, the particle sizes of Y-doped AlN powders synthesized at 1450 °C were 150–300 nm.     

Electrochemical properties of 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2 composite cathode powders prepared by large-scale spray pyrolysis

0.3Li₂MnO₃·0.7LiNi_0.5Mn_0.5O₂ composite cathode powders with a mixed-layer crystal structure comprising Li₂MnO₃ and LiNi_0.5Mn_0.5O₂ phases are prepared by spray pyrolysis. The composition of the cathode powders is found to be Li_1.19Ni_0.39Mn_0.61O₂ by ICP analysis. At a constant current density of 30 mA g^?1, the initial discharge capacities of the composite cathode powders post-treated at 700, 750, 800, and 850 °C are 177, 202, 215, and 212 mAh g^?1, respectively. The discharge capacity of the composite cathode powders post-treated at 800 °C decreases from 215 mAh g^?1 to 205 mAh g^?1 by the 40th cycle, in which the capacity retention is 95%. The first cycle has a low Coulombic efficiency of 75%. However, in the subsequent cycles, the Coulombic efficiency is retained at nearly 100%. The dQ/dV curves show that Mn exists as Mn⁴⁺ in the sample. The Mn⁴⁺ ions in the cathode powders become increasingly active as the cycle number increases and participate in the electrochemical reaction.     

Al2TiO5–Al2O3–TiO2 nanocomposite: Structure,mechanical property and bioactivity studies

Novel biomaterials are of prime importance in tissue engineering. Here, we developed novel nanostructured Al₂TiO₅–Al₂O₃–TiO₂ composite as a biomaterial for bone repair. Initially, nanocrystalline Al₂O₃–TiO₂ composite powder was synthesized by a sol–gel process. The powder was cold compacted and sintered at 1300–1500 °C to develop nanostructured Al₂TiO₅–Al₂O₃–TiO₂ composite. Nano features were retained in the sintered structures while the grains showed irregular morphology. The grain-growth and microcracking were prominent at higher sintering temperatures. X-ray diffraction peak intensity of β-Al₂TiO₅ increased with increasing temperature. β-Al₂TiO₅ content increased from 91.67% at 1300 °C to 98.83% at 1500 °C, according to Rietveld refinement. The density of β-Al₂TiO₅ sintered at 1300 °C, 1400 °C and 1500 °C were computed to be 3.668 g cm^?3, 3.685 g cm^?3 and 3.664 g cm^?3, respectively.Nanocrystalline grains enhanced the flexural strength. The highest flexural strength of 43.2 MPa was achieved. Bioactivity and biomechanical properties were assessed in simulated body fluid. Electron microscopy confirmed the formation of apatite crystals on the surface of the nanocomposite. Spectroscopic analysis established the presence of Ca and P ions in the crystals. Results throw light on biocompatibility and bioactivity of β-Al₂TiO₅ phase, which has not been reported previously.     

Effect of aluminum source on the synthesis of AlN powders from combustion synthesis precursors

In the present work, the carbothermal reduction method was employed to fabricate the AlN powders by utilizing the combustion synthesized precursor derived from the mixed solution comprised of an aluminum source (Al(NO₃)₃ or Al₂(SO₄)₃ or AlCl₃), glucose, nitric acid, and urea. Effects of aluminum source on the particle size and morphology of precursors as well as synthesized AlN powders were studied in detail. The size and morphology of precursors, derived from various aluminum sources, had exhibited significant differences. The precursor from Al(NO₃)₃ source had completed the nitridation reaction at 1500 °C in 2 h. However, the nitridation reactions of the precursors from Al₂(SO₄)₃ or AlCl₃ source furnished at increased temperature of 1550 °C in 2 h. Moreover, the AlN powders from various aluminum sources have been synthesized directly from γ-Al₂O₃ without γ-Al₂O₃ to α-Al₂O₃ phase transition. The AlN powders from Al(NO₃)₃, calcined at 1550 °C for 2 h, were comprised of well-distributed spherical particles with an average size of 80 nm. While the AlN powders from AlCl₃ or Al₂(SO₄)₃ consisted of heterogeneously distributed spherical particles ranging from 100 to 200 nm or from 80 to 150 nm, respectively.     

Y2O3–Nd2O3 double stabilized ZrO2–TiCN nanocomposites

Yttria-neodymia double stabilized ZrO₂-based nanocomposites with 40 vol% electrical conductive TiCN were fully densified by means of pulsed electric current sintering (PECS) in the 1400–1500 °C range. The Y₂O₃ stabilizer content was fixed at 1 mol% whereas the Nd₂O₃ co-stabilizer content was varied between 0.75 and 2 mol% in order to optimise the mechanical properties. The mechanical (Vickers hardness, fracture toughness and bending strength), electrical (electrical resistivity) and microstructural properties were investigated and the hydrothermal stability in steam at 200 °C was assessed.The nanocomposites with 1–1.75 mol% Nd₂O₃, PECS at 1400 or 1450 °C, have an excellent fracture toughness of 8 MPa m^1/2, although the grain size of both ZrO₂ and TiCN phases after densification is in the 100 ± 30 nm range. Moreover, the composites combine a hardness of about 13 GPa, a bending strength of 1.1–1.3 GPa with a low electrical resistivity (1.6–2.2 × 10^?5 Ω m) allowing electrical discharge machining. The hydrothermal stability of the double stabilizer nanocomposites was higher than for yttria-stabilized ZrO₂-based composites with the same overall stabilizer content.     

Scintillation properties of Pr3+-doped lutetium and yttrium aluminum garnets: Comparison with Ce3+-doped ones

Scintillation properties of Pr³⁺-doped LuAG and YAG crystals were investigated and compared with those of Ce³⁺-doped ones. The highest L.Y.’s were observed with the longest shaping time 10 μs. They can reach up to ～16,000 ph/MeV or ～23,500 ph/MeV for LuAG:Pr and LuAG:Ce, respectively. Energy resolutions (FWHM) are a bit better with LuAG:Pr than those of LuAG:Ce, e.g. at 662 keV FWHM are around 6% and between 8–12%, respectively. There were observed no large changes in proportionality of Pr³⁺- or Ce³⁺-doped LuAG or YAG crystals but the best proportionality has YAP:Ce crystal. Pr³⁺- or Ce³⁺-doped LuAG crystals exhibit slow decay components in the time range 1.5–3.5 μs while those of YAG ones have shorter decay components between 0.3–1.7 μs.     

Preparation,structure and optical properties of Pr:Gd2O3 phosphor

Pr³⁺-doped Gd₂O₃ phosphor powders were prepared by co-precipitation method. Their structures during heat-treatments were studied by XRD and IR methods. The pH was optimized to be 8 in the co-precipitation process and the hydroxide precursors were transformed into pure phase cubic Gd₂O₃ at 500 °C for 1 h. Optical properties of Pr:Gd₂O₃ phosphor powders were reported. The main emission bands are assigned to ¹D₂ → ³H₄, ³P₀ → ³H₆, ³P₀ → ³F₂ transition of Pr³⁺ under excitation at 255 and 488 nm. The emission intensities increase with increasing sintering temperature. Concentration quenching appears as the Pr³⁺ doping-concentration up to 1 at.%.     

Fabrication of transparent Lu3NbO7 by spark plasma sintering

We demonstrated the first successful fabrication of a transparent Lu₃NbO₇ body by spark plasma sintering (SPS). First, Lu₃NbO₇ powder was synthesized by a solid-state reaction of Lu₂O₃ and Nb₂O₅ powders at 1473 K for 7.2 ks and was sintered by SPS at 1723 K for 2.7 ks. The transparent Lu₃NbO₇ body had a cubic defect-fluorite structure and uniform microstructure with an average grain size of 0.77 μm. The transmittance at 550 nm reached 68%.     

Rapid carbothermal synthesis of nanostructured silicon carbide particles and whiskers from rice husk by microwave heating method

This paper reported a simple and rapid route to large-scale synthesis of nanostructured SiC powders using rice husk as the precursor. Rapid carbothermal reduction reactions were achieved in a 2.45 GHz microwave field in an argon atmosphere. The XRD patterns revealed that complete carbothermal reduction of silica was achieved at 1300 °C for 60 min or at 1500 °C for only 15 min by microwave heating, resulting in β-SiC formation. The FE-SEM images showed that the β-SiC powders were mixtures of particles and whiskers. The β-SiC particles had diameters of 60–130 nm and the β-SiC whiskers, which were several to tens of micrometers in length, had diameters of 110–170 nm. The β-SiC powder synthesized at 1500 °C for 15 min showed the highest BET surface area of 12.2 m²/g. Compared to the conventional heating method, the microwave heating method proved to be an efficient approach for synthesis of SiC in terms of energy and time saving, as well as for fabrication of nanostructured SiC.     

The synthesis and photoluminescence of nanocrystalline Zr0.80Zn0.20O1.80+δ powders via glycine nitrate process

Nanocrystalline Zr_1−xZn_xO_2−x+δ (x = 0, 0.20, 1.00) powders were synthesized by glycine nitrate process route and the Zr_0.80Zn_0.20O_1.80+δ powders were calcined in the temperature range between 500 and 800 °C. An intense UV emission band centered at 382 nm with excitation at 292 nm has been observed in Zr_0.80Zn_0.20O_1.80+δ powders calcined at 600 °C, and X-ray diffraction analysis indicates that the powders exhibit a single phase with cubic ZrO₂ structure with the average grain size is about 7 nm. According to the results of photoluminescence and annealing experiments in different atmospheres, it can be proposed that the intense UV emission band is related to the defect states involving oxygen vacancies. Compared with pure ZrO₂, the incorporation of Zn²⁺ ions enhances UV emission intensity. Our experimental results also show that photoluminescence intensity depends on the concentration of defects and the peak position is related to the crystal phase structure. The novel strong UV emission properties of this material may be very interesting for further application.     

Magnetic and catalytic properties of cubic copper ferrite nanopowders synthesized from secondary resources

Cubic copper ferrite CuFe₂O₄ nanopowders have been synthesized via a hydrothermal route using industrial wastes. The synthesis conditions were systematically studied using statistical design (Box–Behnken Program) and the optimum conditions were determined. The results revealed that single phase of cubic copper ferrite powders can be obtained at different temperatures from 100 to 200 °C for times from 12 to 36 h with pH values 8–12. The crystallite size of the produced powders was in the range between 24.6 and 51.5 nm. The produced copper ferrite powders were appeared as a homogeneous pseudo-cubic-like structure. A high saturation magnetization (M_s 83.7 emu/g) was achieved at hydrothermal temperature 200 °C for 24 h and pH 8. Photocatalytic degradation of the methylene blue dye using copper ferrite powders produced at different conditions was investigated. A good catalytic efficiency was 95.9% at hydrothermal temperature 200 °C for hydrothermal time 24 h at pH 12 due to high surface area (118.4 m²/g).     

Mechanically induced self-propagating reaction and consequent consolidation for the production of fully dense nanocrystalline Ti55C45 bulk material

We employed a high-energy ball mill for the synthesis of nanograined Ti₅₅C₄₅ powders starting from elemental Ti and C powders. The mechanically induced self-propagating reaction that occurred between the reactant materials was monitored via a gas atmosphere gas-temperature-monitoring system. A single phase of NaCl-type TiC was obtained after 5 h of ball milling. To decrease the powder and grain sizes, the material was subjected to further ball milling time. The powders obtained after 200 h of milling possessed spherical-like morphology with average particle and grain sizes of 45 μm and 4.2 nm, respectively. The end-products obtained after 200 h of ball milling time, were then consolidated into full dense compacts, using hot pressing and spark plasma sintering at 1500 and 34.5 MPa, with heating rates of 20 °C/min and 500 °C/min, respectively. Whereas hot pressing of the powders led to severe grain growth (~ 436 nm in diameter), the as-spark plasma sintered powders maintained their nanograined characteristics (~ 28 nm in diameter). The as-synthesized and as-consolidated powders were characterized, using X-ray diffraction, high-resolution electron microscopy, and scanning electron microscopy. The mechanical properties of the consolidated samples obtained via the hot pressing and spark plasma sintering techniques were characterized, using Vickers microhardness and non-destructive testing techniques. The Vickers hardness, Young's modulus, shear modulus and fracture toughness of as-spark plasma sintered samples were 32 GPa, 358 GPa, 151 GPa and 6.4 MPa·m^1/2, respectively. The effects of the consolidation approach on the grain size and mechanical properties were investigated and are discussed.     

Temperature-dependence of Raman spectroscopy on the phase transition in LuBO3

Temperature-dependence of Raman spectroscopy on LuBO₃ structure was performed in order to obtain information on structural changes induced by temperature evolution. The stability of the calcite phase and low-temperature vaterite phase of LuBO₃ were both evaluated. For the sample with low-temperature vaterite phase, a strong first-order phase transition occurred during 1000–1200 °C, as indicated by the behavior of the Raman modes: the Raman bands split and new bands appear. The transition was associated with the B–O bond being broken in the cyclic B₃O₉ groups at high temperature, forming an open B₃O₉ group consisting of BO₄ and BO₃. Moreover, the influence of In³⁺ content on the structural characteristics of LuBO₃ was investigated. It was found that the calcite phase of LuBO₃ can be stabilized up to 1550 °C at least when the n(In)/n(Lu + In) ratio was more than 20 at%. The crystal growth and characterizations of Lu_1?xIn_xBO₃:Ce materials deserve further investigation.     

Thermoluminescent properties of Mn-doped YAP synthesized by the solution combustion method

The work describes results of Mn-doped YAlO₃ (YAP) nanocrystalline materials synthesized by the solution combustion method using urea as a fuel. The materials were characterized by X-ray powder diffraction, scanning electron microscopy and luminescence techniques. The combustion synthesis method with codoping with Hf⁴⁺ ions allows to obtain highly efficient YAP:Mn²⁺ phosphor with negligible emission from Mn⁴⁺ ions that can be applicable for thermoluminescent dosimetry of ionizing radiation. Namely, the phosphor has a single dominating thermal glow peak at about 200 °C with the green emission near 530 nm related to Mn²⁺(Y) ions.