Synthesis of plate-like single-crystal hydroxyapatite rods with c-axis orientation by biotemplate small intestinal submucosa

Since hydroxyapatite crystals are characteristically c-axis orientation on the surface of vertebrate long bone, c-axis orientation HAP biomimetic synthesized will find extensive applications in long bone growth, remodeling and fracture healing. In this paper, plate-like single-crystal HAP rods with c-axis orientation was successfully synthesized at bone mineralization conditions in vivo, with small intestinal submucosa membrane as biomineralization template. The samples were characterized by XRD, FIIR, SEM, TEM and EDS to unveil the phase structure, composition, morphology, and a plausible growth mechanism was proposed. The results showed that morphology of samples changed from flower-like to plate-like with extension reaction time from 1 day to 10 days. The plate-like HAp rods were single-crystal with c-axis orientation. A unit of plate-like HAP rods is about 70 µm and the width is 4 µm. Phase composition transformed from octocalcium phosphate and HAp biphase to HAp phase with very little octocalcium phosphate phase. Finally, biocompatibility of the samples was evaluated by CCK8. The samples without significant cytotoxicity conformed to the need for substitute materials of bone regeneration.     

Spark plasma sintering of transparent Y2O3 ceramic using hydrothermal synthesized nanopowders

Y₂O₃ nanopowders were synthesized by the hydrothermal treatment of Y(NO₃)₃·6H₂O and citric acid (CA) as Y⁺³ and the capping agent, respectively. The effect of different CA:Y⁺³ mol ratios, heat treatment time, and calcination temperature was investigated in order to determine their influence on the morphology, particle size and phase of Y₂O₃ nanopowders. The narrow size distribution of particles was obtained with CA:Y⁺³ mol ratio=1.6, heat treatment time of 6 h, and a calcination temperature at 900 °C for 90 min. Then, the synthesized Y₂O₃ nanopowder was consolidated by the spark plasma sintering technique at 1500 °C with a heating rate of 100 °C/min and held for 8 min before turning off the power. As a result, the ceramic prepared with 3 mm thickness got the highest transmission of 80% at 2.5–6 µm wavelength. The highest density and the grain size of yttria ceramic were 99.58% and 1–1.2 µm at 1500 °C, respectively.     

Fabrication of micro-scale textured grooves on green ZrO2 ceramics by pulsed laser ablation

The green ZrO₂ ceramics were fabricated by cold isostatic pressing. Pulsed laser ablation with a wavelength of 1064 nm was performed to fabricate micro-scale textured grooves on the surface of green ZrO₂ ceramics. The influence of laser parameters on surface quality was studied. The heat-affected zone around the machined grooves and micromorphology of laser-irradiated surface were investigated. Results showed that micro-scale textured grooves with a width of 30–50 µm and a depth of 15–50 µm on the green ZrO₂ ceramic surfaces were successfully fabricated by pulsed laser ablation. The laser parameters had a profound influence on the surface quality of micro-scale textured grooves. Better surface quality could be obtained with frequency below 40 Hz, power below 6 W, and scanning velocity above 200 mm/s. A sintering layer was found on the laser-irradiated surfaces when frequency was above 60 Hz, power was above 10 W, and scanning velocity was below 150 mm/s. Analysis of this sintering layer revealed clear melting and resolidification of ZrO₂ particles.     

Low-temperature densification of Mg-doped hydroxyapatite fine powders under hydrothermal hot processing conditions

Densification of calcium hydroxyapatite fine powders doped with different concentrations of Mg (2, 4 and 6 mol% Mg, MgHA) was successfully achieved for the first time in a nearly fully dense state using the hydrothermal hot pressing (HHP) technique at low temperatures. Consolidation of MgHA powders was studied under different temperatures (150–240 °C), reaction times (1–6 h), and powder particle size (20 nm–1.5 µm). X-Ray diffraction analyses indicated that the particle densification under HHP conditions proceeded without any variation in the crystalline structure and regardless of the Mg content. The results from this work showed that an increase in temperature accelerates the reaction between MgHA particles and water (solvent) mixed during the hydrothermal treatment. Particle packing associated with bulk densification was achieved through a massive dissolution-recrystallisation mechanism, which induced the formation of small particles that rapidly crystallised on the surface of the partially dissolved original MgHA particles. The optimum conditions to obtain pellets with a high apparent density of 3.0758 ± 0.001 g/cm³ and tensile strength value of 12.6 ± 0.6 MPa were 10 wt% of water at a temperature of 240 °C with a 6 h reaction time and 6 mol% of Mg (MgHA3). The use of the HHP technique coupled with the fine particle size and reactivity of the MgHA precursor powders with water allowed us to produce disks that were compacted to a nearly full dense state with a low content of open porosity of 2.0%.     

Hydrothermal synthesis and formation mechanism of tetragonal barium titanate in a highly concentrated alkaline solution

Tetragonal cube-shaped barium titanate (BaTiO₃) was produced by the hydrothermal treatment of a peroxo-hydroxide precursor, a single-source amorphous barium titanate precursor, in a highly concentrated sodium hydroxide solution. Phase pure barium titanate with cube-shaped morphology and particle-sizes in the 0.2–0.5 µm range were formed at temperatures above 80 °C. Also, the cube-shaped morphology of the BaTiO₃ product was preceded by spherical- and plate-like morphologies with, respectively, a Ti-excess and Ba-excess. Coinciding with these morphological observations, changes in the reaction product were also observed. The formation of crystalline BaTiO₃ proceeded alongside secondary BaTi₂O₅ and Ba₂TiO₄ phases. These secondary phases disappeared as the reaction time was increased leaving only BaTiO₃ as the sole reaction product. Kinetic analysis of the formation of hydrothermal BaTiO₃ crystallization by the Johnson-Mehl-Avrami method showed that BaTiO₃ crystallization is a homogeneous dissolution-precipitation reaction. The mechanism is governed by nucleation and growth in the beginning of the reaction and dissolution-precipitation dominating throughout the hydrothermal reaction process.     

Microstructure and oxidation behavior of Si–MoSi2 functionally graded coating on Mo substrate

The Si–MoSi₂ functionally graded coating on Mo substrate consisting of a Si–MoSi₂ layer (2.5 µm), a MoSi₂ layer (18 µm) and a Mo–Mo₅Si₃–Mo₃Si layer (2–4 µm) was prepared by a liquid phase siliconizing method. The siliconized coating has a dense layered structure and no micro-cracks and holes. The Si element mainly enriches on the surface with the highest content of about 50 wt%, and inhibits the formation of Mo₅Si₃ and volatile MoO₃ and improves the high-temperature oxidation resistance of the coating. The mass gain of Si-MoSi₂ coating is only 0.17 wt% after oxidized at 1600 ℃ for 70 h. The Si–MoSi₂ functionally graded coating exhibits better high temperature oxidation resistance than pure MoSi₂ coating.     

Hydrothermal synthesis of dumbbell-shaped ZnO microstructures

Dumbbell-shaped ZnO microstructures have been successfully synthesized by a facile hydrothermal method using only Zn(NO₃)₂·6H₂O and NH₃·H₂O as raw materials at 150 °C for 10 h. The results from X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) show that the prepared ZnO samples exhibit dumbbell-shaped morphology and hexagonal wurtzite structure. The length of ZnO dumbbells is about 5–20 μm, the diameters of the two ends and the middle part are about 1–5 μm and 0.5–3 μm, respectively. The dumbbell-shaped ZnO microstructures may be formed by self-assembly of ZnO nanorods with 1–5 μm in length and 100–200 nm in diameter. The photoluminescence (PL) spectrum of dumbbell-shaped ZnO microstructures at room temperature shows three emission peaks at about 362, 384 and 485 nm.     

Hydrothermal synthesis of single-crystal α-tristrontium phosphate particles

Anisotropic ceramic bodies can be fabricated by a reactive template grain growth method; however, template particles with suitable powder properties are required to create the ceramics with well controlled anisotropy. Therefore, we synthesized well-isolated α-tristrontium phosphate (α-TSP) particles with a hexagonal plate-like shape as template particles for anisotropic strontium apatite ceramics using α-strontium hydrogen phosphate (α-SrHPO₄) precursor particles. Three synthetic parameters were varied: (i) precursor particle size, (ii) stirring rate, and (iii) hydrothermal temperature. Well-isolated hexagonal plate-like α-TSP single-crystal particles were successfully synthesized by hydrothermal treatment at 150 °C for 3 h at a stirring rate of 150 rpm using fine α-SrHPO₄ precursor particles. The developed plane of the hexagonal plate-like α-TSP particles was determined to be the {00l} plane, and the side planes were revealed to be not {h00} planes, but inclined {h0l} planes. The resulting α-TSP particles may provide a promising template for the development of anisotropic apatite-based ceramics.     

Synthesis and characterization of red pigment YAl1−yCryO3 prepared by the low temperature combustion method

In the present study, a red-shade pigment, based on the system YAl_1?yCr_yO₃ (y = 0–0.05), was synthesized for the first time using the low temperature combustion method. The single-phase synthesis of YAl_1?yCr_yO₃ was achieved at a temperature of 1000 °C. The resulting calcined powders were micron-sized particles (0.5–3 μm) with a well-developed cubic perovskite structure. The study specifically investigated the chemical composition, calcination temperature, Cr³⁺ content, and the effect of the mineralizer in order to elucidate the optimal conditions for pigment synthesis. Further, the color properties exhibited by the YAl_1?yCr_yO₃ pigment when it was added into basic glazes have also been obtained. In addition, the products were characterized by DTA, XRD, FESEM, EDX, and color spectrometry.     

Hydrothermal processing and in situ surface modification of metal oxide nanomaterials

In situ surface modification of TiO₂ and ZnO metal oxide particles has been carried out under hydrothermal conditions within a wide range of temperature and pressure (T = 150–400 °C; P = up to 20 MPa). The influence of the surfactant and selective doping with active metal ions on the crystal size, morphology, and photocatalytic activity of TiO₂ and ZnO particles has been carried out. A systematic characterization of the product has been carried out using powder XRD, FTIR, TGA, SEM/TEM, and UV–vis spectroscopy. Similarly the photocatalytic activity in these metal oxides varies with the size, shape and dopant metals.     

Preparation and characterization of LnMgAl11O19 (Ln=La,Nd, Gd) ceramic powders

Lanthanide hexaaluminate powders of LaMgAl₁₁O₁₉ (LMA), NdMgAl₁₁O₁₉ (NMA) and GdMgAl₁₁O₁₉ (GMA) were synthesized via the solid state reaction or sol–gel and calcination method. The LMA and NMA powders synthesized by the sol–gel and calcination method at 1600 °C for 8 h exhibit a single hexaaluminate phase with magnetoplumbite structure; however, the GMA powder synthesized by the sol–gel and calcination method at 1600 °C for 8 h contains both a hexaaluminate phase and a small amount of second phase GdAlO₃ with a perovskite structure. The powders synthesized by the solid state reaction method at 1500 °C for 4 h have a small particle size of 1–3 μm, and a large specific surface area and a good uniformity. The powders synthesized by the sol–gel and calcination method at 1600 °C for 8 h have a particle size of 5–20 μm, and exhibit to a certain extent agglomeration.     

Fabrication and characterization of anorthite–mullite–corundum porous ceramics from construction waste

In this work, anorthite–mullite–corundum porous ceramics were prepared from construction waste and Al₂O₃ powders by adding AlF₃ and MoO₃ as mineralizer and crystallization catalyst, respectively. The effects of the sintering temperature and time on open porosity, mechanical properties, pore size distribution, microstructure, and phase composition were characterized in detail. The results showed that the formation of the mullite whiskers and the properties of the anorthite–mullite–corundum porous ceramics depended more on the sintering temperature than the holding time. By co-adding 12 wt% AlF₃ and 4 wt% MoO₃, mullite whiskers were successfully obtained at sintering temperatures upon 1350 °C for 1 h. Furthermore, the resultant specimens exhibited excellent properties, including open porosity of 66.1±0.7%, biaxial flexural strength of 23.8±0.9 MPa, and average pore size of 1.32 µm (the corresponding cumulative volume percent was 37.29%).     

Formation of porous SiC ceramics via recrystallization

In this study, porous SiC ceramics with interconnected huge plate-like grains were fabricated from oxidized β-SiC powder with 1 wt% B₄C. When the β–α SiC phase transformation occurred at 2100 °C, rapid grain growth of α-SiC consumed the unstable β-SiC matrix resulting in an interconnected network structure with huge plate-like grains. The oxidation of β-SiC powder and the addition of B₄C are necessary conditions for rapid grain growth. The observed results are discussed based on thermodynamic considerations. The measured porosity of the specimens sintered at 2100 °C for 30 min was 47% and the mean pore size was 6–7 μm. The strength of the sintered specimen was 45 ± 5 MPa.     

Ethanol sensing properties of tungsten oxide nanorods prepared by microwave hydrothermal method

Tungsten oxide nanorods have been prepared by a simple microwave hydrothermal (MH) method via Na₂SO₄ as structure-directing agent at 180 °C for 20 min. The structure and morphology of the products are characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The obtained nanorods are about 20–50 nm in diameter and several micrometers in length. The ethanol sensing property of as-prepared tungsten oxide nanorods is studied at ethanol concentration of 10–1000 ppm and working temperature of 370–500 °C. It was found that the sensitivity depended on the working temperatures and also ethanol concentration. The results show that the tungsten oxide nanorods can be used to fabricate high performance ethanol sensors.     

Effects of AlF3 and MoO3 on properties of Mullite whisker reinforced porous ceramics fabricated from construction waste

Mullite-whisker-reinforced anorthite-mullite-corundum porous ceramics were prepared from construction waste and Al₂O₃ powder by adding AlF₃ and MoO₃ as the additive and crystallization catalyst, respectively. The effects of AlF₃ and MoO₃ content on the properties of mullite whiskers, such as open porosity, mechanical properties, pore size distribution, microstructure and phase structure, were investigated in detail. The results showed that the morphology of the mullite whiskers and properties of the porous ceramics were greatly influenced by the AlF₃ and MoO₃ content. The specimen obtained by co-adding 12 wt% AlF₃ and 3 wt% MoO₃, and sintering at 1350 °C for 1 h, exhibited excellent properties, including an open porosity of 67.4±0.5% and biaxial flexural strength of 24.0±0.8 MPa. The mullite whiskers were uniformly distributed; the whiskers had a diameter of 0.05–0.5 µm, length of 8–10 µm, and aspect ratios (length to diameter ratio) of 20–30 on average.     

Ultra-fine polishing of glass-ceramics by disaggregated and fractionated detonation nanodiamond

Ultra-fine polishing of glass-ceramics is extraordinarily difficult because of structure inconsistency, chemical inhomogeneity and high rigidity. Detonation nanodiamond particles(NDs) were disaggregated and fractionated by serial centrifuge separation to obtain four stable suspension with average sizes of 54.9 nm,103.8 nm,145.6 nm and 245.4 nm respectively. Those suspensions were then employed to polish glass-ceramics. The evolution of NDs has been carefully characterized by FTIR, Raman and XRD analysis and the finish surfaces of glass-ceramics were investigated with AFM. Results showed that disaggregation treatment modified only nanodiamond surface other than its structure. The amount of nitro-groups on NDs surface increased and the absolute value of ξ-potential was enhanced by least 6 times at the pH 4–5, which was propitious to disperse NDs in mild acidic solution and polish glass-ceramics. Coarse particles performed both higher removal rate and average roughness (Sa) than the finer one. By using the suspension with average size of 54.9 nm, a super smooth surface with Sa 0.208 nm (5 µm×5 µm) was achieved.     

Preparation of calcium doped LaCrO3 fine powders by hydrothermal method and its sintering

The synthesis of fine powders of LaCrO₃ and its solid solutions doped with calcium under hydrothermal conditions and the sintering of these powders were investigated. Precursor alkaline coprecipitated lanthanum chromite gels with three different compositions: LaCrO₃, La_0.9Ca_0.1CrO₃ and La_0.8Ca_0.2CrO₃, were processed under hydrothermal conditions at low temperatures (350–425 °C), for a reaction time between 30 and 120 min. Powders of a single phase with orthorhombic structure of LaCrO₃, La_0.9Ca_0.1CrO₃ and La_0.8Ca_0.2CrO₃ were obtained at a temperature as low as 350, 400 and 425 °C, respectively, for a short reaction interval of 1 h. SEM and TEM micrographs showed that particles with an irregular morphology and an average particle size of 300 nm, were mainly obtained under hydrothermal conditions. The powders were pressed by cold isostatic pressing at 200 MPa, and then sintered in air at a temperature range of 1200–1500 °C for various intervals (1 to 5 h). A maximum apparent density of 97.7% was achieved on specimens with high calcium content, La_0.8Ca_0.2CrO₃, at 1400 °C for 5 h. The average grain size measured on the sintered specimens was 6 μm.     

Microstructural evolution during the infiltration of boron carbide with molten silicon

The previously reported model that accounts for the formation of the core-rim structure in reaction-bonded boron carbide composites (RBBC) is expanded and validated by additional experimental observations and by a thermodynamic analysis of the ternary B–C–Si system. The microstructure of the RBBC composites consists of boron carbide particles with a core-rim structure, β-SiC and some residual silicon. The SiC carbide particles have a polygonal shape in composites fabricated in the presence of free carbon, in contrast to the plate-like morphology when the initial boron carbide is the sole source of carbon. In the course of the infiltration process, the original B₄C particles dissolve partly or fully in molten silicon, and a local equilibrium is established between boron carbide, molten silicon and SiC. Overall equilibrium in the system is achieved as a result of the precipitation of the ternary boron carbide phase B₁₂(B,C,Si)₃ at the surface of the original boron carbide particles and leads to the formation of the rim regions. This feature is well accounted for by the “stoichiometric saturation” approach, which takes into account the congruent dissolution of B₄C particles. The SiC phase, which precipitates form the silicon melt adopts the β-allotropic structure and grows preferably as single plate-like particles with an {1 1 1}_β habit plane. The morphology of the SiC particles is determined by the amount of carbon available for their formation.     

Effect of PyC interphase thickness on mechanical and ablation properties of 3D Cf/ZrC–SiC composite

Three-dimensional (3D) C_f/ZrC–SiC composites were successfully prepared by the polymer infiltration and pyrolysis (PIP) process using polycarbosilane (PCS) and a novel ZrC precursor. The effects of PyC interphase of different thicknesses on the mechanical and ablation properties were evaluated. The results indicate that the C_f/ZrC–SiC composites without and with a thin PyC interlayer of 0.15 µm possess much poor flexural strength and fracture toughness. The flexural strength grows with the increase of PyC layer thickness from 0.3 to 1.2 µm. However, the strength starts to decrease with the further increase of the PyC coating thickness to 2.2 µm. The highest flexural strength of 272.3±29.0 MPa and fracture toughness of 10.4±0.7 MPa m^1/2 were achieved for the composites with a 1.2 µm thick PyC coating. Moreover, the use of thicker PyC layer deteriorates the ablation properties of the C_f/ZrC–SiC composites slightly and the ZrO₂ scale acts as an anti-ablation component during the testing.     

Study on surface quality,precision and mechanical properties of 3D printed ZrO2 ceramic components by laser scanning stereolithography

Zirconia (ZrO₂) ceramic bars with three different printing sizes were fabricated by a stereolithographic (SLA) 3D-printing process and subsequent sintering. An anisotropic character of the ceramics surface quality was observed. The surface roughness of the horizontal surface was below 0.41 µm, whereas it reached 1.07 µm along the fabrication direction on the vertical surface. The warpage and flatness were utilized to measure the dimensional accuracy of the 3D printed ZrO₂. Furthermore, it was evaluated that the warpage and flatness were below 40 µm and 27 µm, respectively, even if the printed size of ceramic bar reached 3 mm × 4 mm × 80 mm. In addition, the flexural strength, the fracture toughness, the hardness and the density of ZrO₂ ceramics can reach to 1154 ± 182 MPa, 6.37 ± 0.25 MPa m^1/2, 13.90 ± 0.62 GPa and up to 99.3%, respectively. Moreover, the effects of scanning paths and printing size on properties of the sintered ZrO₂ samples were analyzed. The anisotropic character of surface quality was related to the various scanning paths. The warpage and flatness of 3D printed ZrO₂ bars were apparently affected by the various printed sizes. Also, the effects of special microstructure on the mechanical properties of sintered ZrO₂ samples were investigated.