Two reactive organic modifiers were firstly synthesized by reaction of triglycidyl p-aminophenol (TGPAP) with bromo-n-butane (BB) and 2-bromoethanol (BE) respectively. By using the two modifiers, two different types of organic clays (B-Clay and E-Clay) with the same reactive functional groups but different in compatibility with epoxy were prepared. Epoxy/clay nanocomposites were then synthesized with the above two organoclay via "clay-slurry compounding method''. The effect of two reactive organic modifiers on the structure and thermal/mechanical properties of the nanocomposites was studied. It is shown that E-Clay gave a highly exfoliated structure in epoxy matrix because of its better compatible with epoxy pre-polymer, while B-Clay presented an exfoliated/intercalated mixed structure. Remarkable improvement in tensile strength and modulus were obtained for the nanocomposites due to the formation of strong interfacial bonding between epoxy matrix and clay layers, which derived from reactions of organic modifiers on the organoclay with curing agent during curing. For the nano-composite with incorporation of 3.0% clay, the tensile strength and modulus enhanced by 76.47% and 258% for E-Clay respectively, while that with B-Clay were 52.51% and 236.92%. Besides, the glass transition temperature (Tg) of the two type of nanocomposites was marginally improved relative to neat epoxy resin.
TiO2/PAA composite fiber membranes were prepared by high-voltage electrospinning, and then were thermally imidized to obtain TiO2/PI composite fiber membranes. The physical properties, mechanical properties and electrochemical properties of TiO2/PI composite fiber separators were assessed by means of scanning electron microscope, Fourier infrared spectrometer, thermogravimetric analyzer and electrochemical workstation. The results show that the membrane have clear three-dimensional network structure, and the tensile strength, the porosity and the liquid absorption rate of the modified TiO2/PI composite membrane increase to 16.74 MPa, 77.5% and 550%, respectively comparing with the plain PI membrane; the membrane have good thermal shrinkage performance; excellent overall electrochemical performance; the prepared Li-battery of LiFePO4 (lithium iron phosphate positive electrode)/TiO2/PI/C (graphite negative electrode) presents excellent cycle stability and high discharge capacity, after 100 cycles at 1 C、at 25°C and 120°C, the cell coulombic efficiency is as high as 96.7% and 90.7%, respectively.
Films of Ti-Co alloy were firstly prepared on ITO glass by magnetron sputtering and then were anodized in electrolyte of ethylene glycol + DI water + NH4F to produce films of the Co-doped TiO2 nanotube arrays. The effect of Co doping on the morphology, microstructure, optical and photocatalytic reduction performance under visible light was assessed for the acquired films. The results show that the films of Co-doped TiO2 nanotube arrays are composed of anatase, the same as the plain TiO2, while the preferred orientation changed to (001) from (101) of the plain TiO2. The incorporation of Co improved the absorption of visible light and promoted the separation of photo-generated electro-hole pairs simultaneously. Compared to the film of plain TiO2, the ones of Co-doped TiO2 nanotube arrays exhibit better photocatalytic reduction performance. The film with 0.19%Co (atomic fraction) shows the best photocatalytic reduction efficiency, it is 98.4% after visible light irradiation for 150 min.
The micro-arc oxidization (MAO) ceramic layer on AZ31 Mg-alloy was post-treated by hydrothermal treatment at 125℃ for 18 h with two solutions of different compositions. The effect of hydrothermal solutions on the microstructure and corrosion resistance of MAO ceramic layer was studied, and the relevant formation- and corrosion-mechanism of the film generated via hydrothermal treatment were discussed. The results show that MgO on the MAO ceramic layer was partially dissolved during hydrothermal treatment, and the released Mg2+ was combined with OH- in alkaline hydrothermal solution to form Mg(OH)2 nanosheets, which deposited on the surface of ceramic layer and pores; whereas Al3+ and Co2+ in the other solution might replace some Mg2+ in Mg(OH)2 to form layered double hydroxides (LDH) nanoplates, which could seal the micro-poles and cracks on the MAO ceramic layer. Wettability and electrochemical test results show that the sealing effect of hydrophilic Mg(OH)2 coating on MAO ceramic layer can improve the corrosion resistance of MAO ceramic layer to some extent. However, hydrophobic LDH coating can significantly improve the corrosion resistance of MAO ceramic coating due to the sealing effect and the ion exchange ability of LDH.
Carbon-constraint NiS2 nanomaterials (NiS2@C) with core-shell structure were successfully synthesized by a combination method of arc evaporation and solid-state vulcanization. Characterization results of X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy show that there existed rich defects in the carbon shell. The thickness of the carbon shell was 4 nm, and the diameter of the NiS2 core was 28 nm. The electrochemical performance of NiS2@C electrode was measured as the cathode materials for Na-S batteries. The Coulombic efficiency of NiS2@C electrode remained above 90% after four cycles at a current density of 100 mA·g-1, and the reversible specific capacity of 106.8 mAh·g-1 remained after 500 cycles, which showed high cyclic stability. The electrochemical impedance analysis reveals that the electrode reactions were accelerated and the dynamic equilibrium of ion migration at the interface was maintained due to its good electronic conductivity and excellent structural stability by the constraint of the external carbon layer.
The powder metallurgy (P/M) Ti-22Al-25Nb (atomic fraction, %) alloy sintered by spark plasma sintering (SPS) at 950℃/80 MPa/10 min was used as the initial material and the alloy experienced the solution treatment at the temperature range of 940~1100℃ for 10~120 min and subsequently aged at 800℃/8 h. The effect of solution- and aging-treatment on the microstructure and microhardness of P/M Ti-22Al-25Nb alloy was investigated, while the model of microhardness evolution was proposed. The results show that the grain size and uniformity of B2 phase increase with the increase of solution temperature and holding time. The growth rate of B2 phase grain is the lowest in the temperature range of 940~1010℃, and the grain size uniformity reaches the maximum 0.84 at 1100℃. The size and number of secondary lath O-phase have a significant effect on the properties of the alloy. After aging in the (B2+O) two-phase region, with the increase in the volume fraction of the secondary lath O-phase and the decrease in the size of the laths, especially the increase in the number of intersecting and entangled O/O phases, the microhardness of the alloy was enhanced. The microhardness of the alloy reached the maximum value 434.92 HV after solution and aging treatment at 1060℃/60 min/water cooling (WC)+800℃/8 h/furnace cooling (FC).
Diopside tailings-based glass-ceramics were prepared via melting method plus one-step crystallization heat treatment with Shandong gold tailings and Guyang iron tailings as the main raw material. Then the influence of heat treatment soaking time on the crystal growth and properties of the prepared glass-ceramics was investigated by DSC, XRD, Raman spectroscopy, SEM, and universal mechanical properties tester. The results show that diopside crystals can grow through nucleation and whereafter growth when heat treated at 720℃ for 30 min. With the increase of heat treatment time, the size of diopside crystals gradually increased and the morphology of the crystals evolved from spherical to dendritic. When the heat treatment temperature was 820℃, the morphology and structure of the diopside crystals did not change with the increase of soaking time. Thus, heat treatment at 820℃ for 2 h can be considered to be the optimal. The prepared glass ceramics exhibit an excellent comprehensive performance with density of 2.97 g/cm3, bending strength of 211.0 MPa, hardness of 789.0 MPa, acid resistance of 99.4% and alkali resistance of 99.3 % respectively.
The combined deformation processing technology of equal channel angular pressing (ECAP) and rotary swaging at indoor temperatures was applied to industrial pure titanium. Then the deformation behavior of the acquired ultrafine grained pure titanium by applied strain rates of 0.01, 0.1 and 1 s-1 at 200, 300, 350, 400 and 450°C was investigated via thermal compression test with the Gleeble 3800 thermal simulator. The results show that the dynamic recrystallization characteristics of the experimental true stress-strain curve are significant, and the apparent single peak stress appears. According to the Arrhenius constitutive equation based on the peak stress value of the acquired ultrafine grained pure titanium, the peak stress can effectively be predicted with an average relative error of only 4.44%. Since the large plastic deformed sample was subjected to pre-heat insulation treatment before thermal compression, the critical strain for dynamic recrystallization was increased, of which the material constant is 0.8329. The dynamic recrystallization behavior during deformation mainly occurs in the stage where the strain is greater than 0.1 and less than 0.4. Whereas the strain is greater than 0.4, the material undergoes secondary hardening.
A ternary alloy with composition of Mg-13Gd-1Zn (%, mass fraction) was prepared by conventional smelting and casting technique. The microstructure and mechanical properties of the as-cast, as-annealed, as-extruded and as-aged (T5) alloy were investigated. The results show that the microstructure of the as-cast alloy consists of α-Mg matrix, (Mg, Zn)3Gd eutectic and a 14H long period staking ordered (14H-LPSO) phase. The significant increase of 14H-LPSO phase after annealing and ageing (T5) treatment in the alloy microstructure indicates that the precipitation of the 14H-LPSO phase occurs in a wide temperature range (200~510oC). The β' and β1 precipitates have also been observed in the alloy after ageing (T5) treatment. Under the combined action of precipitation strengthening and LPSO strengthening, the tensile strength, yield strength and elongation of the alloy are 397 MPa, 197 MPa and 2.56%, respectively. The creep properties of the Mg-13Gd-1Zn alloy are higher than those of the WE54 alloy in the two experimental conditions of 200oC/80 MPa and 200oC/120 MPa.
304 austenitic stainless steel was pre-heated in the conditions of different temperatures and time to produce samples with close texture but different grain size. Then the effect of the subsequent compression and heat treatment on the microstructure evolution and properties of the obtained samples was investigated. Results show that the initial grain size played an important role in the final texture of the sample after deformation and heating. The texture in the initial sample with coarse grains changed much more than that in the sample with finer grains. For the samples with close textures, grain size has greater effect on their tensile strength; For samples with different texture, the texture has greater effect on mechanical properties rather than the grain size and micro stain. During the deformation and subsequent heating, the increase of macro strain within the grains and high angle boundaries with high energies lowered the corrosion resistance of 304 steel. However, after deformation, the preferred orientation texture with four planes of close-packed lattice emerged on the samples, thereby, the corrosion resistance of the steel could be increased to some extent.