Papers by Keyword: Property Analysis

Abstract: Poly (lactic acid) (PLA) has many potential uses, for example as packaging, textiles, biomedical fields, including suture, bone fixation material, drug delivery microsphere, and tissue engineering. However, PLA shows the poor toughness, slow degradation rate and relatively hydrophobic. The aim of this study was to investigate the ability of N-methyl-2-pyrrolidone (NMP) to improve the characteristics of PLA film. PLA films were prepared using a solvent casting method and their various properties were investigated. From tensile strength (TS), elongation at break (E) and young’s modulus (ε) determinations, the incorporated PLA films exhibited the softer behavior than plain PLA film. On the other hand, from the contact angle and surface free energy values, the PLA films incorporated with NMP could improve the wettability of solvents and also increased % water sorption (WS) and % weight loss (WL) than PLA films with NMP dose dependent. However SEM photographs revealed the more rather rough and cracked surface as the higher amount of NMP was incorporated in PLA film.

Abstract: The microstructure and properties of grade 700MPa steel with large heat input welding and its heat affected zone (HAZ) were investigated by use of the metallography, scanning electron microscopy, mechanical testing and welding thermal simulation. The results showed that the mechanical properties of the steel meet the technical requirements, namely the yield strength R_eL≥570 MPa, the tensile strength 685MPa≤R_m≤830MPa, the elongation A≥17%, the -20°C impact energy KV₂≥54J and the -20°C impact energy of HAZ≥47J. The steel also had good match between strength, toughness and anti-high heat input welding, the microstructure was tempered sorbite with small dispersed composite inclusions, which promoted the formation of acicular ferrite and were beneficial to the improvement of HAZ toughness.

Abstract: In this study, the Kevlar fabric composites were prepared by shear thickening compound to get the high impact resistance. The characterizations of the produced polyborondimethylsioxane (PBDMS) have been obtained by Differential Scanning Caborimetry(DSC), Thermal Gravimetric Analysis(TGA), etc. The controlled stress rheometer was used to characterize the rheological property. Meanwhile the ballistic and stab tests of this Kevlar composite were investigated and found to exhibit significant improvement. The mechanism of energy absorbing was tentatively discussed. It showed that these novel energy absorbing materials could be potentially used to fabricate flexible body armors and high-grade sports accessories with good perspective.

Abstract: In this paper, a new type of Ti₃SiC₂/Cu composites with the volume fractions of 30% Ti₃SiC₂ particle was prepared by hot pressing and vacuum sintering respectively. The effects of sintering temperature and holding time on the density, resistance and Vickers hardness of Cu-30vol%Ti₃SiC₂ composite were investigated. The results show that the mechanical properties of the composites prepared by hot pressing are better than that prepared by vacuum sintering. The relative densities of Cu-30vol% Ti₃SiC₂ composites are rather high in suitable sintering conditions. It achieved 100% for the composites prepared by hot pressing at 930°C for 2h, and 98.4% for the composites prepared by vacuum sintering at 1250°C for 1h. At the same time, the maximum Vickers hardness reached 1735MPa at 900°C by hot pressing. The resistance and Vickers hardness of the composites decreased with an increase in sintering temperature, whereas the density increased. Scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS) were used to observe the microstructure of the composites. The relationship between microstructure and mechanical properties was discussed.

Abstract: Electrical discharge machining can be used easily for the materials which has good conductivity. In order to improve conductivity of Si3N4 based ceramics, TiN/Si3N4 composite was sintered by adding TiN into Si3N4 powder. In the present research, influence of sintering temperature (1535-1925°C, 8 temperatures) on properties and microstructure of the TiN/Si3N4 composite were investigated with La2O3, AlN as sintering additives, liquid phase pressure less sintering used. Densities of the sintered sample were measured. Bending strength, hardness, fracture toughness and electrical resistively of the sample were tested. Phase composition and microstructure of the samples were analyzed by XRD, SEM and EDX. The results showed that the density and fracture toughness of the sintered bodies reached maximum at temperature of 1760°C (relative density of 97.9%; fracture toughness of 8.5 MPa•m1/2) in the sintering temperature range of 1535~1925°C. With increasing of temperature, the bending strength and hardness of the samples kept raising, reached maximum at temperature of 1925°C (bending strength of 634MPa and Vickers hardness of 1869). But the weight lost at the highest temperature was the severe. Microstructure and EDX showed that crystals of the Si3N4 transferred into complete β phase from α + β both phases. The grain of Si3N4 grew up into long columnar from equiaxial fine particles. The fine grain of TiN grew up also. The comprehensive performances of the samples are better at sintering temperature of 1760°C. The long columnar β-Si3N4 grains interweaved with conductive TiN particles, formed conductive nets through sintering. At this sintering temperature, the bending strength of TiN/Si3N4 sintered body was 560MPa，Vickers hardness 1708MPa. The conductivity of the sintered bodies was irregular with the difference of temperature. The minimum of the conductivity is 20Ω.

Abstract: Cu-TiB2 composite coatings were in-situ synthesized on the copper substrate by using a Nd: YAG laser. The microstructure of the coating and the bonding interface between the laser cladding layer and the substrate were studied by X-ray and SEM. The microhardness and the wear resisting property were tested. The results show that the TiB2 particles were well-proportioned and spherical existing in the coating layer, the bonding interface between the layer and substrate was metallurgical bonding. The microhardness reaches HV450 and the wear resistance is about 10 times as much as that of Cu substate.

Abstract: In this paper, ZnO nanopowders and dye sensitized solar cells were prepared by sol-gel and screen printing method, respectively. First, ZnO nanopowders were synthesized by using zinc acetate, ethanol and diethanolamined as raw materials. The effects of Zn2+ molar concentration on the microstructure and photocatalytic efficiency of ZnO nanopowders were investigated. When Zn2+molar concentration were 0.4M, 0.6M, 0.8M and 1.2M, ZnO nanoparticles with diameter of about 80~100nm were obtained. When Zn2+ molar concentration reached 2.4M, ZnO nanobowls consisted of nanoparticles with diameter about 80~100nm were synthesized. When Zn2+molar concentration reached 3.6M, ZnO nanoparticles were obtained, and particle size distribution of obtained ZnO nanoparticles became broader. Methyl orange degradation rate of ZnO nanopowders prepared with 0.4M, after treated by ultraviolet radiation for 8 hours, were up to 88.5%. ZnO nanopowders prepared with 1.2M and 3.6M were assembled into solar cells. The properties of the solar cell prepared with 1.2M were optimal. The short-circuit photocurrent, open-circuit photovoltage, fill factor and efficiency were 14.72 mA/cm2, 0.649V, 0.332 and 0.914%, respectively.

Abstract: Preparation, properties of autoclaved bricks from waste foundry sand and their strength formation mechanism were investigated in this article. Autoclaved bricks were prepared using waste foundry sand, crashed stone, fly ash, activators such as slaked lime, and special composite as starting materials, accompanying preparation process of wheel-rolling blending, molding with high pressure, and autoclaved curing process. Prepared autoclaved bricks have been authoritatively tested. The results show that strength reaches the standard of 15C, radium activity concentrations are lower than the limit in main building materials, coefficient of carbonization and data of drying shrinkage can be in consistent with Chinese fly ash brick standard. Leaching toxicity is lower than the standard. The strength formation mechanism was investigated by XRD and SEM techniques. The results show that under the conditions of high-temperature, high-pressure steam a mesh structure will be generated and assembly connected, thus forming the strength of autoclaved bricks.

Abstract: The biodegradable composite films were prepared from corn stalk microcrystalline cellulose as filler and chitosan as polymeric matrix. The crystallinity, the tensile properties and the thermal properties of the composites were tested. The results show that the tensile properties and thermal properties were improved with the addition of corn stalk microcrystalline cellulose. When corn stalk microcrystalline cellulose account for 10% of the chitosan quality, the initial decomposition and maximum weight loss rate temperature was raised by 13.19°C and 38.84°C, tensile strength increased by 83.55% and elongation at break increased by 77.38% compared to those of pure chitosan

Abstract: The mechanical properties and toughening mechanism of basalt fiber reinforced concrete (BFRC) with different fibers proportion ranging from 0 to 2.5 kg/m3 were tested in the experiment. The results show that the basalt fiber has little effect on the compressive strength of BFRC, but it can improve the impact toughness of BFRC significantly. Taking impact toughness as criterion, BFRC with 0.36% basalt fiber would be the best choice. The energy absorption characteristic of BFRC with different fibers dosages increases by 1.4~3.1 times than that of plain concrete when it is ultimately destroyed. Basalt fiber provides a secondary micro-reinforced system to BFRC when added into cement matrix. BFRC specimens show multi-cracking characteristics in the failure process, and the vice crack near the main crack is clearly observed while the final destruction.