In recent years, heteroepitaxial monocrystalline diamond has been grown by bias voltage technique and its size has been increased to over inch level. Since the application of bias can act as a means to significantly promote nuclear capability of diamound, therefore, the bias voltage technology may be used to prepare oriented diamond films, nano diamond films and ultra-nano diamond films etc. In this paper, the mechanism related with the action of bias technology, the forms and devices of bias technology, as well as the mechanism of surface reaction model, thermal peak model and sublayer injection model are reviewed. The commonly used bias techniques include DC bias, DC pulse bias, pulse overlap bias and bipolar pulse bias. The effect of bias voltage on the microstructure and properties of diamond films are also introduced, and the effect of applied bias voltage on the orientation growth, secondary nucleation rate, amorphous carbon-graphite-diamond phase transition, growth rate and bonding force of diamond films are described in detail. Biasing can change the energy of bombarded particles and the concentration of specific groups, affect the transformation of diamond phase and grain orientation and size, and then affect the optical, mechanical, thermal and electrical properties of diamond films. Some shortcomings in the present research work are also discussed, such as the mechanism related with the action of bias is still not clear, the change of electron concentration and the effect of hydrogen etching are still not clearly explained. Finally, the future research and application directions of bias voltage technology for diamond preparation are also prospected.
The thermal deformation behavior of TA5 Ti-alloy was investigated via Gleeble-3800 thermal simulation machine in temperature range of 850~1050℃ by strain rate within 0.001~10 s-1, while the maximum deformation of 60%; A strain compensation constitutive model in consideration of the relevant physical parameters was established, and the processing diagram was obtained according to the DMM model. The results show that: TA5 Ti-alloy is a kind of material with positive strain rate sensitivity and negative deformation temperature dependence; By taking physical parameters into account, the established strain compensation constitutive model has high prediction accuracy with a correlation coefficient R of 0.99, while the average relative error AARE is 8.95%. It was found that the main deformation mechanism in the instability zone (850~990℃, 0.05~10 s-1) was local flow, which accords well with the analysis result of processing diagram coupled with observation of the microstructure; The deformation mechanisms in the stable region (870~990℃, 0.005~0.05 s-1) are mainly dynamic recovery and dynamic recrystallization. It follows that the optimal processing parameters for thermal deformation of TA5 Ti-alloy are 870-990℃ and 0.005~0.05 s-1.
Microwaves assisted selective etching technique was used to prepare few-layered Ti3C2 with atomic layer spacing of 1.28 nm. The mass specific capacitance is 377.64 F/g, which is 154.27% higher than that of multilayer Ti3C2. The kinetic analysis of two kinds of Ti3C2 electrochemical storage processes shows that the charge storage of few-layered Ti3C2 is mainly contributed by surface capacitance, which is 76.28%.
The scratch characteristics in micron scale on 16 kinds of materials (2 kinds of glasses, 2 kinds of polymers, 4 kinds of ceramics, 4 kinds of metals and 4 kinds of metallic glasses) were assessed by means of Rockwell C diamond indentation with progressive load. The results show that these materials all have the maximum scratch retention rate (the ratio of residual indentation depth to indentation depth) related to elastic recovery, which can be used as the transition point of the apparent friction coefficient curve. The apparent friction coefficient of scratches is composed of adhesive friction coefficient and furrow friction coefficient. The three-dimensional mechanical contact model can be used to accurately characterize the friction coefficient except for metallic glass. The initial friction coefficient of the material is related to the Poisson's ratio. Polymeric materials (PC and PMMA) have special double scratch grooves due to stacking and sinking effects. The ratio of the hardness of scratched materials to the indentation hardness for 16 kinds of materials is 0.33~2.5, and there is a linear relationship between the scratch hardness and the volume modulus. The linear elastic fracture mechanics (LEFM) model and microscopic energy size effect (MESEL) model were used to calculate the fracture toughness of the material. The results show that: LEFM model, Akono's MESEL model and Hubler's MESEL model can accurately characterize the fracture toughness of materials with low fracture toughness (glasses, ceramics and polymers), while the deviation of calculation results for metal materials with high fracture toughness is large. Liu's MESEL model can be used to characterize the fracture toughness of materials with large fracture toughness (metallic materials and some metallic glasses). The fracture toughness of the material has a piecewise linear correlation with Poisson's ratio.
The photocatalytic degradation of tetracycline by Si-doped Li2SnO3 was investigated. The results show that, through iso-electron Si doping the optical absorption band gap of Li2SnO3 may be reduced, while its optical absorption coefficient is increased, in consequence, the photocatalytic degradation efficiency of the Si-doped Li2SnO3 fortetracycline is enhanced. The isoelectronicaly Si-doped Li2SnO3 is a pure and irregular mass solid, and its lattice parameters tend to decrease with the increase of Si doping amount. The photocatalytic performance of the Si-doped Li2SnO3 was significantly improved by Si doping. Under UV irradiation for 25 min, the photocatalytic degradation efficiency of tetracycline by the Si 10%-doped Li2SnO3 is 75.8%, which is about twice as that by the simple Li2SnO3. The photocatalytic degradation behavior of Si-doped Li2SnO3 conforms to the pseudo-first-order kinetic model, and the fitting rate constant is 0.02464 min-1. The Si-O bond formed on the top of the valence band of Si-doped Li2SnO3 reduces the optical absorption band gap and enhances its optical absorption capacity. The photocatalytic degradation mechanism of Si-doped Li2SnO3 is cave-dominated.
The effect of Y addition on the microstructure and mechanical properties of Mg-14Al-5Si alloy was investigated by means of scanning electron microscope (SEM), energy dispersive spectrometer (EDS), optical microscope (OM) and X-ray diffractometer (XRD), as well as Bloch hardness tester and electronic universal testing machine. The results show that the addition of 0.5%, 0.8%, 1.0% and 1.5% (mass fraction) Y can induce obvious changes of phases in the Mg-14Al-5Si alloy, namely, the silicide phase Mg2Si changes from coarse dendrite to polygon and round shape, and the eutectic phase β-Mg17Al12 changes from coarse continuous grid to fine grid and islets like. The alloying effect for the Y addition amount of 1.0% is the best i.e., the average size of Mg2Si reduced from 42.21 μm to 8.15 μm, the mechanical properties of the alloy also reach the best with hardness of 135HB, tensile strength of 147 MPa, yield strength of 76 MPa and elongation of 5.04% respectively. White block Mg-Si-Y compound is found in the alloy with Y1.5%. The element Y can promote the nucleation of Mg2Si and inhibit the anisotropic growth of Mg2Si. At the same time, Y segregates in the front of the growth of β-Mg17Al12 phase, forming a supercooled structure and inhibiting its growth.
A novel magnetic amino acid functionalized aluminum alginate gel polymer Gly/Al/SA@Fe3O4 was prepared via droplet polymerization technique with sodium alginate (SA) as raw material, which was crosslinked with Al(Ⅲ) ions, while glycine (Gly) and Fe3O4 were simultaneously added. The prepared Gly/Al/SA@Fe3O4 was characterized by means of scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), Fourier infrared spectroscopy (FT-IR), X-ray diffractometer (XRD) and vibrating sample magnetometer (VSM). Its absorption performance for azo dyes was also investigated. The results show that Gly/Al/SA@Fe3O4 is a kind of three-dimensional network-like polymer particles with a fancy fold structure on the surface, and its magnetic response ability is good. Gly/Al/SA@Fe3O4 shows strong adsorption performance with high adsorption rate for Direct Black 19(DB 19) and Direct Brown 2(DB 2) dyes in water. The dynamic equilibrium adsorption capacities reached 2500 mg/L and 3126 mg/L, respectively for the above two dyes in 15min and 60 min. The adsorption process can be described by a quasi-second-order rate equation, and the isothermal adsorption data conform to Langmuir model. The interaction between the adsorbents and dye molecules was synergistic through electrostatic adsorption, hydrogen bonding, ligand exchange and chemisorption. Gly/Al/SA@Fe3O4 particles are green and environment-friendly, and have strong water purification ability for wastewater containing high concentration azo dye, therefore, it can be used for rapid solid-liquid separation with magnetic field.
The microstructure, texture and properties of samples intercepted at different deposition heights and directions of the Ti6Al4V alloy fabricated by selective laser melting were investigated by metallographic analysis, XRD and tensile test. The results show that the vertical section parallel to the building direction presents microstructure of columnar-like prior-β grains filled with acicular martensite, while the cross section perpendicular to the building direction presents a block-like microstructure. The texture for the later cross section is stronger than that for the former one. The size of the columnar prior-β grains influences the mechanical properties along the building direction of the Ti6Al4V alloy fabricated by selective laser melting. The tensile strength and yield strength decrease first and then increase with the increase of deposition height, while the elongation variation has an opposite trend. The strength and plasticity of samples perpendicular to the building direction is higher than those parallel to the building direction due to the formed defects related with the weaker-texture and poor-fusion.
