Micromechanical properties of BN and B–C–N coatings obtained by r.f. plasma-assisted CVD

We have obtained highly transparent and hard BN films in a capacitively coupled r.f. plasma-assisted CVD reactor from three different gas mixtures: B₂H₆–H₂–NH₃, B₂H₆–N₂ and B₂H₆–N₂–Ar. It was found that the films were smooth, dense, and had a textured hexagonal structure with the basal planes perpendicular to the film surface. The microhardness, friction coefficient and adhesion of these coatings were measured by nanoindentation and microscratching. BC_xN_y films were also prepared in the same plasma-assisted CVD reactor from B₂H₆–N₂–CH₄ gas mixtures. The carbon content in the films was varied by using different CH₄ flow rates. These films had a less ordered structure. The mechanical properties of these films had been compared to those of hexagonal BN films. Microhardness measurements showed that there is a correlation between film composition and hardness of the BCN films.     

Consolidation of nanoscale iron powders

The consolidation behavior of two types of nanoscale iron powders-vacuum condensed (nanograins in nanoparticles) and ball-milled (nanograins in microparticles), was studied. The consolidation of two microscale powders, atomized and ground, was also characterized for comparison. Consolidation techniques investigated were cold closed die-compaction, cold isostatic pressing (CIPing), and after CIPing, sintering or hot isostatic pressing (HIPing). The mechanical properties, density, and microstructure of the resulting compacts were found to depend on the original powder type and its consolidation history. Significant differences were found between the microscale and nanoscale powders. An additional reason, besides the dissimilarity in grain size, for the differences observed relates to the fact that the nanograin powders contained significant amounts of oxygen, which ultimately resulted in a distinctly two-phase bulk microstructure. The vacuum condensed powder achieved satisfactory green strength on CIPing, and high hardness (440 Hv) on low temperature sintering. While unnecessary for complete consolidation, HIPing at 500 °C was found to be beneficial and compacts of this powder thus treated were found to have a hardness of 520 Hv and high compressive yield strength (1800 MPa). For ball-milled powders, HIPing was found to be essential for achieving effective consolidation: ball-milled material, which remained friable after CIPing and sintering at 580 °C, achieved exceptionally high hardness (820 Hv) when HIPed at 580 °C and 175 MPa. The ductility was greatly improved when HIPed at temperatures between 700 °C and 850 °C, while preserving its relatively high strength. The behavior of these nanoscale powders can be understood by invoking the usual densification, particle bonding, and grain growth mechanisms. Optimization of these processes may result in unique mechanical properties of ball milled powders.     

Macroscopic synthesis of onion-like graphitic particles

In this paper, we present a method for macroscopic synthesis of onion-like graphitic particles, which may be used to study physical properties. This method is based on annealing carbon nanotubes under high pressure. By transmission electron microscopy (TEM), the microstructure of carbon nanotubes is found to transform into quasi-spherical graphitic structures when the sample has been treated at 770 °C and 950 °C under 5.5 GPa. The high pressure assumes an important role in this transformation.     

促进学习投入的信息技术教学策略

在信息时代,教育质量的评价方式逐渐偏向于学习过程,而其中最重要的一个评价方式就是学习投入.因此,研究中学生在信息技术课堂的学习投入对提高课程教学质量、培养学生的信息技术素养具有重要意义.本文分析了中学生在信息技术课堂的学习投入现状,并提出针对性的策略,以帮助学生提高学习投入.     

In-situ synthesis of novel plate-like Co(OH)2 co-catalyst decorated TiO2 nanosheets with efficient photocatalytic H2 evolution activity

Efficient separation of photo-generated electrons and holes is a crucial aspect for photocatalytic hydrogen evolution. Herein, novel plate-like Co(OH)₂ decorated TiO₂ nanosheets for photocatalytic water splitting were synthesized by a facile in-situ synthetic method. The results of X-ray diffractometry (XRD), transmission electron microscope (TEM), UV–Vis diffusion reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS) indicate the successfully incorporation of Co(OH)₂ co-catalysts onto the surface of TiO₂ nanosheet photocatalysts. Further photocatalytic hydrogen evolution experiments illustrate that all Co(OH)₂ decorated TiO₂ samples show higher rate of hydrogen production performance than pure TiO₂ sample and the composite sample with Co(OH)₂ loading amount of 0.5mol% presents the highest photocatalytic hydrogen production activity of 746.93 μmol g^?1·h^?1. It is indicated that plate-like Co(OH)₂ particle act as an electron collector, which leads to photo-generated electrons transfer from TiO₂ to Co(OH)₂, and therefore enhance the photocatalytic activity. Based on above results, a possible mechanism is proposed and further verified by surface photovoltage spectra (SPV).     

The morphological evolution of the Bi2Mo3O12(010) surface in air–H2O atmospheres

Atomic force microscopy (AFM) has been used to examine the morphological evolution of the Bi₂Mo₃O₁₂(010) surface at 400–600 °C in dry air and air–2.3% H₂O. The (010) cleavage surface is characterized by atomically flat terraces separated by straight steps that are integer multiples of b/2 (5.75 Å) in height. During treatments at or above 500 °C, the surface is etched due to the volatilization of Mo. In dry air, etching affects both steps and flat terraces and results in step recession, the development of half-unit-cell (b/2) step loops (pits and islands), and the accumulation of Bi-rich surface deposits. In air–2.3% H₂O, steps are etched with preference to terraces, and this leads to step recession as well as the formation of Bi-rich deposits. Mo volatilization proceeds at an enhanced rate in air–2.3% H₂O and culminates in the nucleation and growth of Bi₂MoO₆ and Bi₂Mo₂O₉ precipitates at 500 and 600 °C, respectively.     

Investigation of the effect of surface modifications on the mechanical properties of basalt fibre reinforced polymer composites

Unsaturated polyester-based polymer composites were developed by reinforcing basalt fabric into an unsaturated polyester matrix using the hand layup technique at room temperature. This study describes basalt fibre reinforced unsaturated polyester composites both with and without acid and alkali treatments of the fabrics. The objective of this investigation was to study the effect of surface modifications (NaOH & H₂SO₄) on mechanical properties, including tensile, shear and impact strengths. Variations in mechanical properties such as the tensile strength, the inter-laminar shear strength and the impact strength of various specimens were calculated using a computer-assisted universal testing machine and an Izod Impact testing machine. Scanning Electron Microscope (SEM) observations of the fracture surface of the composites showed surface modifications to the fibre and improved fibre–matrix adhesion. The result of the investigation shows that the mechanical properties of basalt fibre reinforced composites are superior to glass fibre reinforced composites. This work confirms the applicability of basalt fibre as a reinforcing agent in polymer composites.     

Synthesis and characterization of three-dimensional ordered mesoporous-macroporous bioactive glass

Three-dimensional ordered mesoporous-macroporous bioactive glass (MMBG) was synthesized by a combination of surfactant and polystyrene bead templates, the sol-gel method, and the evaporation-induced self-assembly process. The incorporation of regular spherical macropores only slightly perturbed the mesoporous network. The bioactivity of the MMBG was assessed by its immersion in simulated body fluid for different lengths of time and the subsequent determination of hydroxycarbonate apatite formation. The synthesized MMBG displayed good in vitro bioactivity and may have potential applications in bone tissue engineering.     

Corrosion inhibition by the trace amount of sulphide ion in CO2-saturated brine solutions

By accurately controlling the concentration of sulphide ion in CO₂-saturated solutions, it was demonstrated that the corrosion behaviour of mild steel was sensitive to the trace amount of sulphide ion additions. An obvious inhibition effect on cathodic reactions was observed at an extremely low level of sulphide ion, while a detrimental effect on corrosion was gradually emerged as its dosage increased higher than 0.5?mg?L^?1. These positive and negative synergy effects would be strengthened after immersing for longer time. The sensitivity of CO₂ corrosion to sulphide ion was attributed to the modification of surface properties by the presence of iron sulphides.