[en] Highlights: • ZrC-rich surface layer with a thickness of 100 μm was obtained in C/C composites. • ZrC-rich surface layer improves the ablation resistance of the C/C composites. • ZrC-rich layer seal the surface defects to restrain the ablation of defects area. • Strengthened ZrC-rich surface layer reduces the mechanical denudation. - Abstract: Zirconium carbide (ZrC) rich surface layer with a thickness of 80–100 μm was prepared on carbon/carbon (C/C) composites. The ZrC-rich layer consisted of submicron ZrC particles, homogeneously dispersed in the carbon matrix. The mass ablation rate of the composite with the ZrC-rich layer was 69% lower than that of the bare C/C composites. The ZrC-rich layer could seal the surface pores and cracks to restrain the preferential ablation in the defect area and form a continuously melting ZrO₂ layer to prevent the carbon from oxidizing during ablation. The strengthened ZrC-rich layer could reduce the mechanical denudation of the composites

[en] Bamboo slices have been pyrolyzed by heat treatment in an inert atmosphere at 1000 deg. C. The reaction of gaseous SiO and pyrolyzed bamboo slices at 1300 deg. C resulted in the formation of SiC nanowires. Microstructure characterization of the SiC nanowires was carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). XRD analysis showed that the reaction product is crystalline β-SiC. The diameter and the length of the SiC nanowires is ranging from 20∼70nm to 10∼20μm. Most of the SiC nanowires possess straight and smooth morphology. SiC nanowires have a preferential growth axis parallel to the [111] direction.

[en] Highlights: • The C/C-Zr-Si-O with a density of 1.71g/cm³ was obtained by 8 cycles of hydrothermal co-deposition/carbothermal reduction. • The mass ablation rate of the composites was as low as 0.112 mg/cm²·s owing to the fine grain and homogeneous Zr and Si. • The formation of ablation bubbles is significant to achieve the attractive ablation resistance of the composites. C/C-Zr-Si-O composites were prepared by carbothermal reduction of hydrothermal co-deposited ZrO₂, SiO₂, and C. The bulk density of composites reached 1.71 g/cm³ with 8 cycles of co-deposition. The matrix of the composites includes ZrC, SiC, ZrO₂, and SiO₂ with fine grain size (300–500 nm) and homogeneous distribution. The mass and linear ablation rate of C/C-Zr-Si-O composites were 0.112 mg/cm²·s and 0.46 μm/s, respectively, under a plasma flame for 120 s. The attractive ablation resistance of the composites resulted from its unique structure, which tends to form a continuous ZrO₂-SiO₂ glass layer in the ablation center, a layer of SiO₂-ZrO₂ bubbles in the transition region, and fluffy SiO₂ nanowires layer in the heat-affected region. These ablation layers were barriers to restrain the diffusion of oxidative gas and heat. The C/C-Zr-Si-O composites provide an alternative ceramics system with attractive ablation resistance, while carbothermal reduction of hydrothermal co-deposited oxides is a feasible method for the structural design of carbon fiber reinforced ultra-high temperature ceramic.

[en] Highlights: • C/C-ZrC composites were prepared by hydrothermal deposition of ZrO₂ and carbon. • Sub-micrometer ZrC particles were uniformly dispersed in the matrix. • The composites presented a typical pseudo-plastic fracture behavior. • Formation of ZrO₂ glass and ZrO₂ skeleton layer reduce the ablation of composites. Carbon fiber reinforced carbon matrix containing ZrC (C/C–ZrC) composites were prepared by hydrothermal deposition combined with carbothermal reduction. The submicron ZrC particles (100–300 nm) were dispersed in the matrix. The stress-strain curves of the composites presented a typical pseudo-plastic fracture behavior. The mass and linear ablation rates of the composites were 3.7 × 10⁻³ g/s and 4.2 × 10⁻³ mm/s, respectively. The formation of ZrO₂ glass layer reduced erosion of the composites in the ablation center. The continuous C–ZrC–ZrO₂ skeleton layer generated from the oxidation of ZrC can protect the composites from erosion at the ablation brim region. The obtained C/C–ZrC composites present a promising potential as ablation resistance materials.

[en] As an alternative to TiO₂ photocatalysts, ZnO exhibits a large potential for photocatalytic (PC) applications in environmental treatments, such as degradation of wastewater, sterilization of drinking water, and air cleaning. However, the efficiency achieved with ZnO to date is far from that expected for commercialization, due to rapid charge recombination, photo-corrosion as well as poor utilization of solar energy. Fortunately, in recent years, a great number of breakthroughs have been achieved in PC performance (including activity and stability) of micro-/nano- structured ZnO by forming heterojunctions (HJs) with metal nanoparticles (NPs), carbon nanostructures and other semiconductors. In most cases, the improvement of PC performance was ascribed to the better charge separation at the interfaces between ZnO and the other components. Sometimes, the formation of hybrids is also in favor of visible light harvesting. This review summarizes recent advances in the fields of environmental photocatalysis by ZnO based HJs, and especially emphasizes their abilities in degradation of organic pollutants or harmful substances in water. We aim to reveal the mechanism underlying the enhanced PC performance by constructing HJs, and extend the potential of ZnO HJ photocatalysts for future trends, and practical, large-scale applications in environment-related fields. (topical review)

[en] The incorporation of inorganic nanoparticles into polymers is a hot research spot, since it endows the nanocomposites with new or improved properties by exploiting synergistic effects. Here we report a facile one-pot synthesis of polyacrylamide (PAM)–metal (M = Au, Ag, or Pd) nanocomposites in ethylene glycol (EG). The simultaneous polymerization of the acylamide (AM) monomer and formation of metal nanoparticles lead to a homogeneous distribution of metal nanoparticles in the PAM matrix. The sizes of Au, Ag, and Pd nanoparticles are 55.50 ± 10.6, 14.15 ± 2.57, and 7.74 ± 1.82 nm, respectively. The reaction system only includes EG, AM monomer, and corresponding metal salt. EG acts as both the solvent and the reducing reagent. Also, no initiator for AM polymerization and no surfactant for stabilization of metal nanoparticles are used. Furthermore, this simple synthetic route does not rely on any special or expensive equipment, thus can be exploited to the synthesis of similar polymer–inorganic nanocomposites. Compared to PAM, the PAM–metal nanocomposites showed enhanced thermal stability and antibacterial properties