To evaluate the property of the organic coatings in oil and gas plants, the aging process was studied in high temperature and high CO2 partial pressure environment. Correlations were developed between the macroscopic properties and microstructure of the organic coatings. The surface appearance, mechanical properties, and permeability of the organic coatings were measured. Furthermore, the crystal structure of the organic coatings was investigated through synchrotron radiation grazing incidence X-ray diffraction (GIXRD) on the BL14B1 beam line in Shanghai Synchrotron Radiation Facility. Combined with the Fourier transform infrared spectroscopy, the molecular structure of the organic coatings was investigated. The experimental results indicate that the thickness variation and weight loss of the organic coatings increase with the immersion time, and the penetration resistance of the coating obviously decreases as the temperature rises. Moreover, the degradation of the organic coatings with immersion time in high temperature and high CO2 partial pressure environment is caused by the amorphization of the organic coatings as the groups and bonds of the organic coatings were not damaged.
Mineral carbonation using waste cement is a promising method to solve the problems caused by CO2 emission and waste cement. Compaction pressure is an important parameter for mineral carbonation of calcium hydroxide, one of the most dominant composite of waste cement that can be carbonated. The carbonation degree, morphology of products and compressive strength of carbonated compacts are influenced by compaction pressure significantly. Results show that the carbonation degree of calcium hydroxide increases at first (0-8 MPa) and then decreases in the higher compaction pressure range (10-14 MPa). At the meantime, results also indicate that lower compaction pressure accelerates the early carbonation but hinder carbonation in the later stages. For the morphologies of carbonation products, calcium carbonate tends to form typical crystal morphology of calcite (rhombohedral) under lower compaction pressure, while it will become ellipsoid-like when compaction pressure reaches 8 MPa. TGA and water content results show that there is an optimal water content for the carbonation. In addition, lower water content is adverse to the carbonation at later stage and the CO2 is difficult to penetrate into the inside of compacts when water content is high, which will hinder the carbonation. XRD and TGA results show that the carbonation products are calcite and small amount of amorphous calcium carbonate.
PMMA/reactive nanoclay nanocomposites were prepared by emulsion polymerization using two different reactive nanoclays. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) results confirmed that the reactive nanoclays, kaolinite and montmorillonite, were obtained by the silylation reaction and the double bonds were grafted onto the edges and surfaces of the nanoclays. The presence of reactive nanoclays could increase the average molecular weights, the glass transition temperatures (T g) and improve the thermal properties of nanocomposite. The tensile properties, Young’s modulus, and the aging properties of the nanocomposite films were also enhanced while the light transmittance decreased. Furthermore, the nanocomposites with the reactive kaolinite presented better performances than that with the reactive montmorillonite. Finally, the action mechanism of the reactive nanoclays to the performances of PMMA/reactive nanoclay nanocomposites was proposed.
Single-phase insulating 12CaO∙7Al2O3 (C12A7) powder was synthesized using an optimized hydrothermal method. Pure phase of C12A7 was got at a comparatively lower temperature (c.a. 300 °C) than that has been previously reported. The crystallite size of the synthesized C12A7 powder was 7±2 nm. The surface area values calculated for all the samples at a synthesis temperature range of 250-800 °C for 5 h were in the range of about 19-24 m2/g, with pore sizes of 12-20 nm. This low-temperature-based synthetic strategy along with nano porous structures and a high surface area value can facilitate catalyst application.
Zn0.8Cd0.2O thin films prepared using the spin-coating method were investigated. X-ray diffraction, scanning electron microscopy, and UV-Vis spectrophotometry were employed to illustrate the effects of the pre-heating temperature on the crystalline structure, surface morphology and transmission spectra of Zn0.8Cd0.2O thin films. When the thin films were pre-heated at 150 °C, polycrystalline ZnO thin films were obtained. When the thin films were pre-heated at temperatures of 200 °C or higher, preferential growth of ZnO nanocrystals along the c-axis was observed. Transmission spectra showed that thin films with high transmission in the visible light range were prepared and effective bandgap energies of these thin films decreased from 3.19 eV to 3.08 eV when the pre-heating temperature increased from 150 °C to 300 °C.
Adsorption of 2, 4, 6-trichlorophenol (TCP) onto the calcined Mg/Al-CO3 layered double hydroxide (CLDH) was investigated. The prepared Mg/Al-CO3 layered double hydroxide (LDH) and CLDH were characterized by powder X-ray diffraction (XRD) and thermo gravimetric analyzer-differential scanning calorimeters (TG-DSC). Moreover, 2,4,6-trichlorophenol (TCP) was removed effectively (94.7% of removal percentage in 9 h) under the optimized experimental conditions. The adsorption kinetics data fitted the pseudo-second-order model well. The Freundlich, Langmuir, and Tempkin adsorption models were applied to the experimental equilibrium adsorption data at different temperatures of solution. The adsorption data fitted the Freundlieh adsorption isotherm with good values of the correlation coefficient. A mechanism of the adsorption process is proposed according to the intraparticle diffusion model, which indicates that the overall rate of adsorption can be described as three steps.
Surface functionalization of carbon nanofibers (CNFs) was carried out, i e, CNFs were firstly oxidized and then the surface was silanized by 3-Aminopropyltriethoxysilane (APTES) via an assembly method. A new kind of high wear resistance s-CNFs/epoxy composite was fabricated by in-situ reaction. FTIR spectroscopy was used to detect the changes of the functional groups produced by silane on the surface of CNFs. The tribological properties and microstructures of modified and unmodified CNFs/epoxy composites were studied, respectively. The expremental results indicate that APTES is covalently linked to the surface of CNFs successfully and improves the dispersion of CNF in epoxy matrix. The friction coefficients and the wear rates of s-CNFs/epoxy composites are evidently lower than those of u-CNFs/epoxy composites under the same loads. Investigations also indicate that abrasive wear is the main wear mechanism for u-CNFs/epoxy composite, with slight adhesive wear for s-CNFs/epoxy composite under the same sliding wear condition.
A novel fluorescent probe for H2PO4 - was designed and fabricated based on the carbon dots/Fe3+ composite. The carbon dots were synthesized by an established one-pot hydrothermal method and characterized by transmission electron microscope, X-ray diffractometer, UV-Vis absorption spectrometer and fluorescence spectrophotometer. The carbon dots/Fe3+ composite was obtained by aqueous mixing of carbon dots and FeCl3, and its fluorescence property was characterized by fluorescence spectrophotometer. The fluorescence of carbon dots was quenched by aqueous Fe3+ cations, resulting in the low fluorescence intensity of the carbon dots/Fe3+ composite. On the other hand, H2PO4 - reduced the concentration of Fe3+ by chemical reaction and enhanced the fluorescence of the carbon dots/Fe3+ composite. The Stern-Volmer equation was introduced to describe the relation between the relative fluorescence intensity of the carbon dots/Fe3+ composite and the concentration of H2PO4 -, and a fine linearity (R 2=0.997) was found in the range of H2PO4 - concentration of 0.4-12 mM.
ZnMn2O4 films for resistance random access memory (RRAM) were fabricated with different device structures by magnetron sputtering. The effects of electrode on I-V characteristics, resistance switching behavior, endurance and retention characteristics of ZnMn2O4 films were investigated. The ZnMn2O4 films, using p-Si and Pt as bottom electrode, exhibit bipolar resistive switching (BRS) behavior dominated by the space-charge-limited conduction (SCLC) mechanism in the high resistance state (HRS) and the filament conduction mechanism in the low resistance state (LRS), but the ZnMn2O4 films using n-Si as bottom electrodes exhibit both bipolar and unipolar resistive switching behaviors controlled by the Poole-Frenkel (P-F) conduction mechanism in both HRS and LRS. Ag/ZnMn2O4/p-Si device possesses the best endurance and retention characteristics, in which the number of stable repetition switching cycle is over 1000 and the retention time is longer than 106 seconds. However, the highest R HRS/R LRS ratio of 104 and the lowest V ON and V OFF of 3.0 V have been observed in Ag/ZnMn2O4/Pt device. Though the Ag/ZnMn2O4/n-Si device also possesses the highest R HRS/R LRS ratio of 104, but the highest values of V ON,V OFF, R HRS and R LRS, as well as the poor endurance and retention characteristics.
Transparent conductive aluminum doped zinc oxide (ZnO:Al, AZO) films were prepared on glass substrates by rf (radio frequency) magnetron sputtering from ZnO: 3wt% Al2O3 ceramic target. The effect of argon gas pressure (P Ar) was investigated with small variations to understand the influence on the electrical, optical and structural properties of the films. Structural examinations using X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that the ZnO:Al thin films were (002) oriented. The resistivity values were measured by four-point probe with the lowest resistivity of 5.76×10-4 Ω·cm (sheet resistance=9.6 Ω/sq. for a thickness=600 nm) obtained at the P Ar of 0.3 Pa. The transmittance was achieved from ultraviolet-visible (UV-VIS) spectrophotometer, 84% higher than that in the visible region for all AZO thin films. The properties of deposited thin films showed a significant dependence on the P Ar.
Ultra-high molecular weight polyethylene (UHMWPE) fiber/epoxy composites were fabricated by a vacuum assisted resin infused (VARI) processing technology. The curing condition of composites was at a cure temperature of 80 °C for 3h in a drying oven. The characteristics of 2.5D (shallow bend-joint and deep straight-joint) structure and 3D orthogonal structure were compared. The failure behavior, flexural strength, and microstructures of both composites were investigated. It was found that the flexural property was closely related to undulation angle θ. The flexural strength of 3D orthogonal structure composite was superior to the other two structures composites with the same weave parameters and resin.
CeO2 stabilized ZrO2 ultra fine nanoparticles were successfully synthesized via a simple and effective sol-gel synthetic approach by using zirconylchloride octahydrate, cerium nitrate hexahydrate, and citric acid as starting materials. A series of techniques, including X-ray diffraction (XRD), thermogravimetry (TG), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and N2-sorption analysis, were used to characterize the structure and morphology of the as-prepared samples. XRD studies indicate that the as-synthesized sample is of well crystallized tetragonal phase of CeO2 stabilized ZrO2 with high purity. TEM images show that the as-synthesized sample is composed of a large number of fine dispersive nanoparticles with an average size about 10 nm. The as-synthesized tetragonal CeO2 stabilized ZrO2 sample was heated at different temperatures in order to evaluate its thermal stability. The exprimental results reveal that the as-synthesized tetragonal CeO2 stabilized ZrO2 sample exhibits excellent stability without the occurrence of phase transformation.
The microstructure and the electrical, thermal, friction, and mechanical properties of Cu/Ti2AlC fabricated by hot-pressing at 900 °C for 1 h were investigated in the present work. Microstructural observations have shown that the plate-like Ti2AlC grains distribute irregularly in the network of Cu grains, and well-structured, crack-free bonds between the layers. With the increase in the content of Ti2AlC from layer A to layer D, the electrical resistivity increases from 1.381×10-7 Ω·m to 1.918 ×10-7 Ω·m, the hardness increases from about 980.27 MPa to about 2196.01 MPa, and the friction coefficient from above 0.20 reduces to about 0.15. Oxidation rate increases with the increases of temperature. Exfoliation was obviously observed on the surface of oxidation layer A. The surface of layer D was still intact and the spalling and other defects were not found. The mass decreases in the acid solution, and increases in the alkaline solution. The largest corrosion rate is found in 6.5% HNO3 or 4% NaOH solution.
Potassium and phosphate were extracted at low temperature by acid hydrolysis process to decompose a new type of associated phosphorus and potassium ore. The main factors affecting the dissolution rate were investigated, such as grinding fineness, the amount of sulfuric acid and fluoride salt, reaction time and temperature, etc. Meanwhile, the effects of various factors on the formation of soluble potassium and phosphate were also discussed. The reaction products and residues were determined by X-ray diffraction (XRD), scanning electron microscopic (SEM) analysis and other means. The results showed that the dissolution rates of potassium and phosphorus were 70wt% and 93.7wt%, respectively, under the conditions of a grain size of 95.64wt% lessthan 0.074 mm, 9.78 g•g-1 sulfuric acid, 0.5 g•g-1 ammonium fluoride, 160 °C and a reaction time of 2 h. The thermodynamic and chemical reaction mechanism was revealed that the primary reaction could be completed spontaneously in a temperature range of 298-433 K. The increase of reaction temperature had an important influence on ion exchange reaction, which was more conducive to the spontaneous process. The research will open up a new way for efficient use of potassium ore resources.
We investigated microstructure morphologies of three asphalts (SK, Karamay, and Esso) used in China using atomic force microscopy (AFM). The topography and phase contrast images were obtained. Topographic profile and three dimensional images were described. Roughnesses of microstructure were calculated. And the chemical compositions of asphalt were tested to explain the microstructural mechanism of the asphalt. The results show that the topography and phase image in atomic force microscopy are appropriate to evaluate the microstructure of the asphalt binder. There are significant differences in microstructural morphologies including bee-like structure, topographic profile, 3D image, and roughness for three asphalts in this study. There are three different phases in microstructure of asphalt binder. The oil source and chemical composition of asphalt, especially asphaltenes content have a great influence on the microstructure.
Influence of aluminum addition on the structures and properties of SiO2-B2O3-Al2O3-CaO vitrified bond at low sintering temperature and high strength was discussed. FTIR and XRD analyses were used to characterize the structures of the basic vitrified bond with different contents of aluminum. The bending strength and the thermal expansion coefficients were also tested. Meanwhile, the microstructures of composite specimens at sintering temperature of 660 °C were observed by scanning electron microscope (SEM). The experimental results showed that the properties of vitrified bond with 1wt% aluminum were improved significantly, where the bending strength, Rockwell hardness, and thermal expansion coefficient of the vitrified bond reached 132 MPa, 63 HRB, and 6.73×10-6 °C-1, respectively.
Structural, anisotropic, and thermodynamic properties of Imm2-BCN were studied based on density function theory with the ultrasoft psedopotential scheme in the frame of the generalized gradient approximation (GGA). The elastic constants were confirmed that the predicted Imm2-BCN is mechanically stable. The anisotropy of elastic properties were also studied systematically. The anisotropy studies of Young’s modulus, shear modulus, linear compressibility, and Poisson’s ratio show that the Imm2-BCN exhibits a large anisotropy. Through the quasi-harmonic Debye model, the relations between the equilibrium volume V, thermal expansion α, the heat capacity C V and C P, the Grüneisen parameter γ, and the Debye temperature Θ D with pressure P and temperature T were also studied systematically.
The aim of this work was to investigate the effects of low-resistivity interlayer on the physical properties of periodic Ba0.9Sr0.1Ti0.99Mn0.01O3 (BSTM) multilayers prepared by a chemical solution deposition method. A LaNiO3 (LNO) layer was inserted into the periodic BSTM multilayer artificially to form a sandwiched configuration of BSTM/LNO/BSTM. The capacitances at low frequencies (<100 kHz) of the sandwiched multilayer are significantly enhanced compared to that of the pure BSTM multilayer. The space charge accumulated at the LNO layer was proposed to explain the enhancement based on Maxwell-Wagner (M-W) model. However, LNO interlayer leads to an increase in the leakage current. A non-Ohmic conduction region is observed for BSTM/LNO/BSTM multilayer when the electric field exceeds 100 kV/cm. The results offer a new approach to achieve dielectric films with high dielectric constant.
In order to enhance the oxidation resistance of C/SiC composites, mullite/yttrium silicate coatings were fabricated on C/SiC composites through dip-coating route. Al2O3-SiO2 sol with high solid content was selected as the raw material for mullite and “silicone resin + Y2O3 powder” slurry was used to synthesize yttrium silicate. The microstructure and phase composition of coatings were characterized, and the investigation on oxidation resistance and anti-oxidation mechanism was emphasized. The as-fabricated coatings consisting of SiO2-rich mullite phase and Y2Si2O7 phase show high density and favorable bonding to C/SiC composites. After oxidized at 1 400 °C and 1 500 °C for 30min in static air, the coating-containing C/SiC composites possess 91.9% and 102.4% of the original flexural strength, respectively. The desirable thermal stability of coatings and the further densification of coatings due to viscous flow of rich SiO2 and Y-Si-Al-O glass are responsible for the excellent oxidation resistance. In addition, the coating-containing composites retain 99.0% of the original flexural strength and the coatings exhibit no cracking and desquamation after 12 times of thermal shock from 1 400 °C to room temperature, which are ascribed to the combination of anti-oxidation mechanism and preferable physical and chemical compatibility among C/SiC composites, mullite and Y2Si2O7. The carbothermal reaction at 1 600 °C between free carbon in C/SiC substrate and rich SiO2 in mullite results in severe frothing and desquamation of coatings and obvious degradation in oxidation resistance.
We investigated the aging effect on the chemical structure of silicone rubber composite materials under outdoor environment. The variations of low molecular weight siloxanes in silicone rubber were probed by gas chromatography-mass spectrometry during the degradation process. The experimental results indicate that a series of cyclic siloxanes exist in both the virgin and aged silicone rubber samples, while the additional low molecular weight siloxanes (hexamethyl cyclotrisiloxane) only appear in the aged samples. Meanwhile, the total amounts of low molecular weight siloxanes in the aged samples are much less than those in the virgin ones. The loss of low molecular weight siloxanes is induced by the chain scission and depolymerization.
We demonstrated a facile method to prepare photoluminescent graphene quantum dots using commercial polyacrylonitrile (PAN) based carbon fibers (CFs) as the raw material by facile chemical oxidation and exfoliation method. The as-prepared GQDs with uniform size exhibit an excitation-independent photoluminescence behavior, which is similar to other semiconductor quantum dots. Moreover, when acting as catalyst the uniform GQDs have better activity for electrochemical oxidation of dopamine (DA) than graphene oxides (GOs). The square wave voltammogram (SWV) peak values of GQDs are in good correspondence with DA concentrations and can act as a sensor of DA.
Adsorption of poly(L-lysine) on surface-attached poly(methacrylic acid) monolayers formed through in situ free radical polymerization was investigated. A strong “template effect” was observed for the adsorption of poly(L-lysine) on poly(methacrylic acid) layers, which were perpendicularly grown from the surface of substrates. The adsorbed amount of poly(amino acid) increases linearly with the increase in initial layer thickness of poly(methacrylic acid) monolayers. In addition, the adsorbed poly(amino acid) is relatively stable in medium concentration of salt solution but can be completely released from the brush in high salt concentration.
The compressive strength of mortar containing glass powder (GP) and/or glass aggregate (GA) was tested, and its microstructure was also studied by thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), energy dispersive spectroscopic analysis (EDX), and X-ray diffraction (XRD) techniques. The incorporation of GA would decrease the compressive strength of the mortar in the absence of GP. Incorporating both GA and GP could change the hydration environment, promote pozzolanic reaction of GP and improve the compressive strength. GP does not lead to but can effectively control ASR (Alkali Silica Reaction). GP and GA do not transform the type of hydrates, but have a great influence on the amounts of hydration products, and generate more calcium silicate hydrate (C-S-H gel) with lower Ca/Si ratio. GP and GA with good gradation will make the microstructure denser.
The high-temperature creep behavior of asphalt mixture was investigated based on micromechanical modeling and virtual test by using three-dimensional discrete element method (DEM). A user-defined micromechanical model of asphalt mixture was established after analyzing the irregular shape and gradation of coarse aggregates, the viscoelastic property of asphalt mastic, and the random distribution of air voids within the asphalt mixture. Virtual uniaxial static creep test at 60 °C was conducted by using Particle Flow Code in three dimensions (PFC3D) and was validated by laboratory test. Based on virtual creep test, the micromechanical characteristics between aggregates, within asphalt mastic, and between aggregate and asphalt mastic were analyzed for the asphalt mixture. It is proved that the virtual test based on the micromechanical model can efficiently predict the creep deformation of asphalt mixture. And the high-temperature behavior of asphalt mixture was characterized from micromechanical perspective.
The influence of polycarboxylic-type admixture on the strength of autoclaved aerated concrete (AAC) was investigated. The flexural strength and compressive strength of AAC with polycarboxylic admixture (PA) were tested. The microstructure of AAC reinforced by PA was analyzed using scanning electron microscopic (SEM) methods. The crystal structure analysis of AAC with PA was also carried out using X-ray diffraction (XRD). The results showed that the compressive strength and flexural strength of AAC were increased by 43.9% and 42.8%, respectively, when 1.5wt% of PA was mixed. In addition, the dosage of admixture influenced the reinforcing effect. Admixture affected pore structure and surface characteristic of the products in autoclaved curing process and improved the formation of high crystallite tobermorite which led to the enhancement of the compressive and flexural strength of AAC.
B2O3-SiO2-ZnO-BaO-Al2O3 glass with different Al2O3 contents (1mol%, 3mol%, 5mol%, and 7mol%) was prepared, and it was intended to be used as lead-free and low-melting glass sealants for solid oxide fuel cells. The effects of Al2O3 content on the structures, thermal properties, and sintering behaviors of the B2O3-SiO2-ZnO-BaO-Al2O3 glass were investigated in detail. The Al2O3 content largely influenced the structures and thermal properties of the glass. When the Al2O3 content 5mol%, the transition temperature of the glass decreased with the Al2O3 content, while the crystallization temperature increased with the Al2O3 content. However, higher Al2O3 content degraded the stability of the glass. The B2O3-SiO2-ZnO-BaO-Al2O3 glass with 5 mol% Al2O3 content exhibits the optimal sintering densification characteristics and can be used as glass sealants for solid oxide fuel cells.
In order to research the sulfate attack resistance of shotcrete, the sulfate attack of shotcrete in the presence and absence of steel fiber was experimentally studied by using dry-wet cycle method. Meanwhile, compared with ordinary concrete by the same mixture, the difference of sulfate attack resistance of shotcrete was studied. The experimental results showed that, with dry-wet cycles increasing, the changes of loss rate of relative dynamic elastic modulus and mass loss rate of specimens included three stages: initial descent stage, stable stage, and rapid descent stage, respectively. However, the changes of mechanical properties first increased and then decreased. Furthermore, the corrosion products of shotcrete after sulfate attack were observed by using the method of XRD, thermal analysis, and SEM, respectively, and the failure mode of shotcrete turned from ettringite destruction to ettringite-gypsum comprehensive failure. Meanwhile, the contents of ettringite and gypsum increased with increasing dry-wet cycle. Simultaneously, the stratified powders drilled from shotcrete under 150’s dry-wet cycle were analyzed for the mineral phase composition and thermal analysis. With the dry-wet cycle increasing, the content of ettringite first increased and then decreased and tended to stable. However, the determination of gypsum decreased gradually and even to 0 when the depth was more than 12 mm.
Diffusion has been systematically described as the main mechanism of chloride transport in reinforced concrete (RC) structure, especially when the concrete is in a saturated state. However, the single mechanism of diffusion is not able to describe the actual chloride ingress in the nonsaturated concrete. Instead, it is dominated by the interaction of diffusion and convection. With the synergetic effects of various factors taken into account, this study aimed to modify and develop an analytical convection- diffusion coupling model for chloride transport in nonsaturated concrete. The model was verified by simulation of laboratory tests and field measurement. The results of comparison study demonstrate that the analytical model developed in this study is efficient and accurate in predicting the chloride profiles in the nonsaturated concrete.
The effect of post weld heat treatment on the microstructure and fracture toughness of friction welded joints of Ti-6.5Al-1Mo-1V-2Zr alloy was studied. The experimental results show that equiaxial grains were formed at the center of the weld metal while highly deformed grains were observed in the thermomechanically affected zone. The fracture toughness of the weld metal was lower than that of the thermomechanically affected zone under as-weld and post weld heat treatment conditions. With increasing temperature of post weld heat treatment, the fracture toughness of weld center and thermomechanically affected zone increased. The fractographic observation revealed that the friction welded joints fractured in a ductile mode.
The residual stress distribution was studied by an analytical model, due to shot peening on the welding carbon steel surface layer. The initial welding residual stresses before shot peening were taken into consideration in this analytical model. The Hertzian elastic contact theory was used to get the elastic compression stress state after impact on the surface layer. The initial welding stress field and the shot peening stress field would superpose and the welding surface layer would yield based on the elastic-plastic evaluation, then the residual stress after shot peening can be achieved. The influence of initial welding residual stress on the stress distribution after shot peening was analyzed and discussed. A series of experiments were carried out and the residual stress on the welding surface was determined by X-ray diffractometer before and after shot peening. The calculation results of the analytical model are consistent with the experimental results. The critical shot velocities when welding surface layer yielded and reverse yielded were calculated. While the welded joint surface material reversely yielded, the maximum compressive residual stress would not obviously increase with the increase of shot velocity, the thickness of the compressive stress layer would be increased. Welding residual tensile stress can enlarge the thickness of the compressive stress layer at the same shot velocity when reverse yield appeared.
Thermal cycling tests of repeated melting/freezing processes were performed to check the thermal stability of Mg-25Al-15Zn-14Cu alloy as phase change thermal storage material(PCM). Latent heat storage capacity and phase transition temperature of the PCMs were determined by differential scanning calorimetry (DSC) technique as a function of repeated thermal cycles such as 0, 100, 200, and 1000. The present work also comprised the investigation of the density and microstructure of Mg-25Al-15Zn-14Cu alloy before and after thermal cycles by using the hydrostatic method and optical microscopy (OM), X-ray diffraction (XRD), and electron probe microanalysis (EPMA), respectively. The results show that the melting temperature of alloy after 1000 thermal cycles is 415.1 °C and the latent heat value is 190.4 J/g. Compared with the original alloy, the phase transition temperature will increase by 1.87% and the value of phase change latent heat will decrease by 7.35%, which are in a suitable range. Therefore, Mg-25Al-15Zn-14Cu alloy has a good thermal reliability in terms of the change in its thermal properties with respect to thermal cycling for 1000, and can be used for a middle-temperature thermal storage utility.
The effects of the heating process and hot extrusion on the microstructure and properties of inconel 625 alloy were studied. The experimental results showed that the properties of Inconel 625 alloy could be improved through the heating process and hot extrusion concomitant with a reduced corrosion rate. The M23C6 carbide, generated in the heating process, was retained and distributed at the grain boundary during the process of hot extrusion, which had an important influence on both elongation and corrosion resistance. The improvement of the comprehensive properties of the material, as measured by a tensile test at room temperature, was correlated with the dissolution of segregation Nb. A typical ductile fracture changed to a cleavage fracture where secondary cracks could be clearly seen. With the increase of the extrusion ratio, the real extrusion temperature was higher, which led to more dissolution of the M23C6 carbide, decreased the number of secondary cracks, enhanced the effect of solid solution strengthening, and reduced the intergranular corrosion rate. Under the condition of a high extrusion ratio and a high extrusion speed, the less extrusion time made it possible to obtain organization with a smaller average grain size. Moreover, in this case, the M23C6 carbide and segregated Nb did not have enough time to diffuse. Thus all samples exhibited medium strengths and corrosion rates after extrusion.
The selection of milling tools for SiC14Cu4Mg0.5Si based on Aluminium matrix 2A14 was analyzed, and the factors that affect the efficiency of the milling were discussed. The SiC14Cu4Mg0.5Si was designed for use on the moon landing vehicle or missile wings, but the hardness of aluminium-silicon carbide composite material was very high, much higher than the general hardness of cemented carbide, which will bring many difficulties in the aluminium-silicon carbide composite material processing. The chemical compositions of SiC14Cu4Mg0.5Si were analyzed. A new selected indexable cutter was designed to mill SiC14Cu4Mg0.5Si. The structure design of milling cutter was different from the conventional milling cutter, breaking the previous limitations to a certain extent, pioneering the idea. The tool material wear was detected by experiments. The mechanical and physical properties of SiC14Cu4Mg0.5Si were also tested. SiC14Cu4Mg0.5Si exhibited different surface quality characteristics under different milling tools.
The stress corrosion of S355 steel in 3.5% NaCl solution under the different strain rates was analyzed with the slow strain rate test (SSRT), the stress corrosion cracking (SCC) behaviors of S355 steel under the different strain rates in the solution were investigated, and the fracture morphologies and compositions of corrosion products under the different strain rates were analyzed with scanning electron microscopy (SEM) and energy dispersive spectrometerry (EDS), respectively. The experimental results show that the SCC sensitivity index is the highest when the strain rate is 2×10-6, and the medium corrosion is the main reason resulting in the highest SCC sensitivity index. The SCC sensitivity index is the least when the strain rate is 5×10-6, and the stress is the main reason resulting in the stress corrosion. The SCC sensitivity index is the middle when the strain rate is 9×10-6, the interaction of stress and medium is the stress corrosion fracture mechanism.
We assessed the in vitro cytotoxicity of Mg-6Zn alloy and analyzed the cell apoptosis rate and the expression of caspase-3 to evaluate the effects of Mg-6Zn alloy extracts on apoptosis of intestinal epithelial cells (IEC)-6. IEC-6 cells were cultured in different concentrations of Mg-6Zn alloy extracts (40%, 20%) and in the control group. The indirect effects of Mg-6Zn alloy on IEC-6 cells were studied by calculating the cell relative growth rate (RGR), measuring the apoptosis of IEC-6 cells through flow cytometry, and investigating the expression of caspase-3 using real-time polymerase chain reaction. The experimental results show that the cytotoxicity of these extracts is Grade 0-1. The level of apoptosis in IEC-6 cells cultured in 40% Mg-6Zn alloy extracts is significantly higher than that in cells treated with 20% extract and the control group. The expression of caspase-3 is found to be up-regulated in the 40% extract as compared to 20% extract and the control group. Taken together, the data show that the Mg-6Zn alloy in 40% and 20% concentration extracts proves noncytotoxicity. But the 40% con-centration of Mg-6Zn alloy extract can induce the apoptosis and the related caspase-3 expression in vitro.
Novel insulin-loaded nanoparticles based on hydroxypropyl-β-cyclodextrin modified carboxymethyl chitosan (CMC-HP-β-CD) were prepared to improve the oral bioavailability of insulin. The CMC-HP-β-CD was characterized by FT-IR spectroscopy and 1H-NMR spectra. The insulin-loaded nanoparticles were prepared through crosslinking with calcium ions, and the morphology and size of the prepared nanoparticles were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Cumulative release in vitro study was performed respectively in simulated gastric medium fluid (SGF, pH=1.2), simulated intestinal fluid (SIF, pH=6.8) and simulated colonic fluid (SCF, pH=7.4). The encapsulation efficiency of insulin was up to 87.14 ± 4.32% through high-performance liquid chromatography (HPLC). Statistics indicated that only 15% of the encapsulated insulin was released from the CMC-HP-β-CD nanoparticles in 36 h in SGF, and about 50% of the insulin could be released from the nanoparticles in SIF, whereas more than 80% was released in SCF. In addition, the solution containing insulin nanoparticles could effectively reduce the blood glucose level of diabetic mice. The cytotoxicity test showed that the samples had no cytotoxicity. CMC-HP-β-CD nanoparticles are promising candidates as potential carriers in oral insulin delivery systems.
The aim of this study was to obtain the fillers in the lumen of hollow nerve conduits (NCs) to improve the microenvironment of nerve regeneration. A pH-induced injectable chitosan (CS)-hyaluronic acid (HA) hydrogel for nerve growth factor (NGF) sustained release was developed. Its properties were characterized by gelation time, FT-IR, SEM, in vitro swelling and degradation. Furthermore, the in vitro NGF release profiles and cell biocompatibility were also investigated. The experimental results show that the CS-HA aqueous solution can undergo a rapid gelation 3 minutes after its environmental pH is changed to 7.4. The CS-HA hydrogel has interconnected channels with a controllable pore diameter and with a porosity of about 80%. It has a favorable swelling behavior and can be degraded by about 70% within 8 weeks in vitro and is suitable for NGF release. The CS-HA/NGF hydrogel exhibits a lower cytotoxicity and is in favor of the adhesion and proliferation of the BMMSCs cells. It is indicated that the CS-HA/NGF will be a promising candidate for neural tissue engineering.
The thioglycollic acid (TGA) as a capping agent, CdTe/TGA quantum dots (QDs) with excellent properties were synthesized under microwave irradiation. The TGA/Cd/Te molar ratios, reaction time, temperature and pH are the crucial factors for properties of QDs. The QDs were characterized by UV-vis absorption and fluorescence spectra, transmission electron microscopy and Fourier transform infrared spectroscopy. The experimental results show that when the pH value is 11.5 and molar ratio of TGA:Cd:Te is 1.2:1:0.4 at 100 °C heating for 15 min, the resulted QDs exhibit a high fluorescence quantum yield of 78%. The fluorescence full width at half maximum (FHMW) of QDs is around 23 nm. The products are spherical with average size of 3-5 nm. There is a strong coordination effect between TGA and Cd2+. Moreover, the results of interaction between as-made QDs and bovine serum albumin (BSA) suggest that the QDs-BSA binding reaction is a static quenching. The negative values of free energy (△G<0) suggest that the binding process is spontaneous, △H<0 and △S<0 show that hydrogen bonds and van der Waals interactions play a major role in the binding reaction between QDs and BSA.