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Milti-principal cation oxide ceramics with excellent mechanical properties for potential applications in coating materials. A Multi-principal cation mullite (MPCM) ceramic is synthesized with MgO, TiO 2 , Cr 2 O 3 , ZrCl 2 O·8H 2 O and Al 2 O 3 , SiO 2 via solid state reaction at 1600 °C. It is determined that 96.9 % of the sample composition is mullite. MPCM ceramic exhibits higher compressive strength (981 ± 19 MPa) and fracture toughness (3.37 ± 0.05 MPa∙m1/2), the compressive strength has raised by 453 MPa, and the added value of solution strengthening (452 MPa) is gained by using solid-solution strengthening theory. The improvement of compressive strength is mainly due to the solution strengthening effect of the four oxides(Mg, Ti, Zr, Cr), and the improvement of fracture toughness is caused by the grain hindrance during crack propagation. Moreover, its application at the high-temperature resistant coating is verified through experimentation. The interfacial binding force, as an important mechanical property index for ceramics, is researched. In this study, pure mullite powder and MPCM powder are coated onto the refractory TaWNbV alloy matrix by slurry coating method, and the interfacial toughness of the two coatings mingled with the matrix is calculated to be 72.9 and 62.6 J·m−2, respectively. The "shrinking cylinder" model is introduced to interpret the oxidative weight gain mechanism of the two coatings. [ABSTRACT FROM AUTHOR]

In this paper, high thermal conductivity PcBN composites with Al–Si as binder and diamond as additive were prepared by high temperature and high pressure (HTHP) sintering at 5 GPa and 1500 °C. The effects of diamond content on the phase composition, microstructure, density, thermal conductivity, and volume resistivity of PcBN composites were characterized and studied. With the increase of diamond content, the thermal conductivity of PcBN samples increases first and then decreases. When the diamond content is 4 wt%, the thermal conductivity of PcBN composites is the highest, reaching 146.3 W m−1K−1, which is 20.2% higher than the thermal conductivity without diamond. At the same time, the reduction of the residual silicon liquid phase in the sintered body also increases the volume resistivity of the composites. With the increase of diamond content, the volume resistivity of PcBN composites also increases. The volume resistivity of PcBN composite with diamond content of 16 wt% reaches 1.25 * 1010 Ω·cm. [ABSTRACT FROM AUTHOR]

In this study, W-MeC-Si/PCD (Me = Ti, Zr, Hf, V, Nb and Ta) composite materials were prepared via high pressure and high temperature (HPHT, 5.5 GPa and 1600 °C) sintering, the effect of the addition of transition metal carbides on the micromorphology, phase composition and mechanical properties of PCD has been systematically studied, and various mechanical data of W-TaC-Si/PCD have been provided. The results show that the addition of MeC is conducive to the improvement of the mechanical properties of PCD. The sample with TaC has the best mechanical properties, and its flexural strength, relative density, hardness and fracture toughness reached 743.5 MPa, 99.75%, 63.4 GPa and 8.1 MPa m1/2, respectively. Finally, the toughening mechanism of W-MeC-Si/PCD is also discussed. The improvement of fracture toughness can be attributed to the change of fracture mode and the pinning effect of MeC dispersion in the binder. [ABSTRACT FROM AUTHOR]

At present, the ultra-fine particulate matter (UPM) with diameter less than 1 μm cannot be filtered efficiently and precisely by the current filtration materials, which leads to the UPM being the main source of air pollution. Here, we prepared Kaolin/silica/mullite fiber multilayer membranes (KSFMs) by a simple vacuum filtration. The UPM filtration efficiency has been significantly improved by the nanoporous kaolin layer coated on the support body constructed by Si-sol bonded mullite fiber. By controlling the size and amount of kaolin particles in the mixed suspension, the structure and filtration efficiency and filtration resistance of the multilayer membranes are optimized. The multilayer membranes exhibit high UPM filtration efficiency with 99% for 0.3 μm and low filtration resistance (lower than 70 Pa at 0.3 m/s). [ABSTRACT FROM AUTHOR]

Abstract Here, we developed silica/mullite fiber composite membranes with double-layer structure by a simple vacuum procedure for the removal of sub-micrometer dust. The support with three-dimensional skeleton structure exhibited high porosity (higher than 90%), low density (lower than 0.25 g/cm3) and high compressive strength (higher than 0.55 MPa) at 1000 °C. By controlling the mass ratio of silica sol to mullite fiber, we can obtain uniform and complete filtering layers with different thicknesses. The composite membranes exhibited high PM filtration efficiency with 99% for 1–10 µm, 97% for 0.5 µm and 90% for 0.3 µm. These samples had high air flow with very low pressure drop (lower than 600 Pa when airflow velocity reached 1 m/s). These results indicated that the silica/mullite fiber composite membranes were very promising for PM pollution control in the field of hot gas filtration. [ABSTRACT FROM AUTHOR]

This study presents a novel approach to control the crystalline phase and surface morphology of substable ε-Ga 2 O 3 thin films by regulating the hydrogen flow rate during chemical vapor deposition (CVD). The objective is to achieve high-quality and cost-effective heteroepitaxial pure-phase single-crystalline ε-Ga 2 O 3 thin films on sapphire substrates. The crystalline phases and crystalline qualities of the thin films were determined by X-ray diffraction (XRD) and Raman spectroscopy. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results show that the surface of the ε-Ga 2 O 3 films prepared by this method is flat and the minimum value of the surface roughness (RMS) is 4.130 nm. We explain the reason for the differences in the surface morphology of the films from the point of view of hydrogen passivation. Measurements by UV–Visible spectrophotometer, the UV cut-off edge is located at 250 nm and the optical band gap is about 4.9 eV. The experimental results show that with the increase of hydrogen flow rate, the content of β-Ga 2 O 3 in the films and the surface roughness and maximum height of the contour (RZ) decreases, until a smooth surface of the pure-phase ε-Ga 2 O 3 film is produced. The success of the chemical vapor deposition method for heterogeneous epitaxy of high-quality ε-Ga 2 O 3 films on sapphire substrates greatly reduces the production cost and expensive investment in production equipment, which makes its application in high electron mobility transistors, piezoelectric resonators, and sun-blind detectors have great potential, and at the same time, this method provides ideas for the preparation of other metastable materials. [ABSTRACT FROM AUTHOR]

ZTM ceramics were successfully derived from coal gangue. The effect of zirconium source (ZrO 2 and ZrOCl 2 ∙8H 2 O) and content on properties of the ZTM ceramics has been studied. The phase composition, density, and microscopic morphology were characterized with X-ray diffraction (XRD), Archimedes method and scanning electron microscopy (SEM). The influence of zirconium source, sintering temperature, zirconia content on flexural properties and fracture toughness was studied. The sample, with ZrOCl 2 ∙8H 2 O added 12% zirconia (Z2TM12) sintered at 1475 °C for 3 h has the highest density of 2.83 g/cm3. Partially stable t -ZrO 2 was present in samples with zirconium oxychloride (ZrOCl 2 ∙8H 2 O) as the zirconium source, due to the constraints of mullite crystals. Therefore, Z2TM12 had both microcrack toughening and stress phase transformation toughening mechanisms. The flexural strength was increased from 162.40 MPa to 285.04 MPa, while the fracture toughness was improved to 3.55 MPa m1/2 from 2.38 MPa m1/2. Our achievement can be used as a reference to fabricate ZTM ceramics from coal gangue with high-value additions. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA) is a well-known material for biomedical applications and its performance depends greatly on its morphological features. Therefore, preparation of mesoporous HA with high surface area and adsorption capacity is highly deserved. In this research, a hydrothermal approach to synthesize mesoporous HA without post-processing calcination step is presented. The possibility using different polyphenols to generate mesoporous HA as well as using different phosphate sources to tailor the morphological features of HA is investigated. The as-prepared mesoporous HA particles are characterized by XRD, FTIR, SEM, TEM, BET, and zeta potential. Besides, the impacts of HA morphological features on model drug Dox are also studied. It is expected the strong interaction between –OH of polyphenols and Ca 2+ makes polyphenols molecules occupy the inner sites of growing HA particles. After the removal of polyphenols by hydrothermal treatment and ethanol extraction, the occupied sites are transformed into mesopores. The typical mesoporous HA generated in present work has a rod-like morphology with BET specific surface area of 106.6 m 2 /g and an average pore size of 14.4 nm. [ABSTRACT FROM AUTHOR]