Microwave boriding layer microstructure of carbon steels and its diffusion mechanics were studied. The results show that the existence of microwave field in the boriding can＇t change the growth mechanics of boriding ...
详细信息
Microwave boriding layer microstructure of carbon steels and its diffusion mechanics were studied. The results show that the existence of microwave field in the boriding can＇t change the growth mechanics of boriding layer. Compared with conventional boriding, if the treatment temperature and time remain constantly, the descend rate of the boriding layer thickness with the increase of carbon content of steel is smaller. The diffusion activation energy ofT8 steel is 2.6× 10^5 J/mol between the temperature of 750 ℃ and 900 ℃ in microwave field, which is in the same order of conventional boriding.
The morphology, mechanical properties of unsaturated polyester（UP） resin modified with TDI were studied via dynamic FT-1R spectra, SEM, DMA and mechanical property testing. Results show that companying with the cure...
详细信息
The morphology, mechanical properties of unsaturated polyester（UP） resin modified with TDI were studied via dynamic FT-1R spectra, SEM, DMA and mechanical property testing. Results show that companying with the cured cross-linking reaction of UP resin, TDI can firstly react with UP and produce polyurethane（PU）, and then UP and PU form the cross-linking nets together. The impact fracture section morphology of modified UP resin manifested the typical sea- islands structure. Testing of mechanical properties showes that for introducing of PU, the TDI has an obvious effect on the toughness and strength of UP resin. When the ratio of TDI/UP （w/w） was 7.5%, the modified UP resin exhibited the best mechanical properties with flexural strength of 125 MPa, impact strength of 18 kJ·m^-2 and tensile strength of 72 MPa.
W-15Cu composite powders prepared by mechanical alloying （MA） of raw powders were consolidated by spark plasma sintering （SPS） process at temperature ranged 1 230-1 300 ℃ for 10 min and under a pressure of 30 MPa...
详细信息
W-15Cu composite powders prepared by mechanical alloying （MA） of raw powders were consolidated by spark plasma sintering （SPS） process at temperature ranged 1 230-1 300 ℃ for 10 min and under a pressure of 30 MPa. By using high energy milling, particles containing very fine tungsten grains embedded in copper, called composite particles, could be produced. The W grains were homogeneously dispersed in copper phase, which was very important to obtain W-Cu alloy with high mechanical properties, fine and homogeneous microstructure. The microstructure and properties of W-15Cu alloys prepared by SPS processes at different temperature were researched. The results show that W-15Cu alloys consolidated by SPS can reach 99.6 % relative density, and transverse rupture strength （TRS） is 1 400.9 MPa, Rockwell C hardness （HRC） is 45.2, the thermal conductivity is 196 W/m-K at room temperature, the average grain size is less than 2 μm, and W-15Cu alloy with excellent properties, homogeneous and fine microstructure is obtained.
The influences of mass concentration of nickel chloride hexahydrate, sodium borohydride, ethylenediamine, pH value, bath temperature on deposition rate were studied with orthogonal experiments by a series of pre-treat...
详细信息
The influences of mass concentration of nickel chloride hexahydrate, sodium borohydride, ethylenediamine, pH value, bath temperature on deposition rate were studied with orthogonal experiments by a series of pre-treatments on micro-diamond particle, and the optimized parameters were obtained. Both the morphology and the composition of original diamond and the diamond with Ni-B coating were analyzed by SEM and XRD respectively. The SEM image shows that the spherical Ni-B particle is coated upon diamond. XRD pattern shows that the coating compositions are Ni and Ni2B.
Magnetization measurements on a single crystal of the high-Tc cuprate HgBa2CuO4 (Hg-1201) are performed for the two field orientations B||c and B||(a,b). Besides zero-field-cooling (zfc) – field-cooling (fc) and magn...
Magnetization measurements on a single crystal of the high-Tc cuprate HgBa2CuO4 (Hg-1201) are performed for the two field orientations B||c and B||(a,b). Besides zero-field-cooling (zfc) – field-cooling (fc) and magnetization studies, the flux creep relaxation is determined. The zfc curves exhibit pronounced step-like anomalies in the mixed state above the lower critical field Bc1. They are interpreted as those points in the phase diagram where the penetrating flux fronts meet at the center of the sample. In order to obtain more information about the flux pinning mechanism flux creep relaxation experiments are performed at different temperatures in magnetic fields of 0.15 and 2 T. The resulting supercurrent dependence on the mean activation energy is analysed according to the collective pinning theory which predicts U ∝ ((j/jc)−μ −1). The μ-values for B||c are 0.5 at higher temperatures and 2 at 5 K, and they vary between 1.1 and 1.5 for B||(a,b). The observed behaviour is quite different from that found for powder samples.
Mg2Si is a kind of narrow-band-gap n-type semiconductor, which is a promising environmental friendly thermoelectric material for its high electrical conductivity, low thermal conductivity, as well as non-toxicity and ...
详细信息
ISBN:
(纸本)9788880800842
Mg2Si is a kind of narrow-band-gap n-type semiconductor, which is a promising environmental friendly thermoelectric material for its high electrical conductivity, low thermal conductivity, as well as non-toxicity and non-pollution. In the present study, the fabrication process of Mg2Si thermoelectric material is systematically explored by spark plasma sintering technique (SPS) from Mg and Si raw powders. The density, phase and microstructure of the specimen are analyzed by XRD and FE-SEM. The results suggest that the complete reaction temperature for Mg and Si is 550°C, and the excessive content of Mg is helpful for obtaining the high purity Mg2Si. The relative density can reach 97% when the sample is prepared under the condition of 550°C-250MPa-10min, but crack is observed on the sample surface. Therefore, Mg and Si powder firstly react at 550°C-20MPa-30min, followed by sintering at 750°C-20MPa-5min. The sintered sample contains only Mg2Si phase with a high relative density near 100% and Mg2Si grains are fine and homogeneous.
The dynamic compressive behavior of Al2O3 (10% vol.) / TiB2 ceramic composite had been tested by using a split Hopkinson pressure bar in this paper. The results show that the main failure modes of the ceramic composit...
详细信息
The dynamic compressive behavior of Al2O3 (10% vol.) / TiB2 ceramic composite had been tested by using a split Hopkinson pressure bar in this paper. The results show that the main failure modes of the ceramic composite include crushed failure and split fracture along the loading direction. The former is the typical compressive failure of brittle materials. The later is tensile failure along the flaws produced during the composite manufacturing. The numerical simulation was also used to study the effect of the diameter/length ratio of the samples on the experimental results. The effect of the deformation in the bars' ends, which contacted with the samples, was also studied in the numerical models.
A series of B-C ceramics was simultaneously synthesized and densified from boron and carbon elements by using a Spark Plasma Sintering (SPS) method. A high relative density (>95%) was successfully obtained at 1900 ...
详细信息
ISBN:
(纸本)9788880800842
A series of B-C ceramics was simultaneously synthesized and densified from boron and carbon elements by using a Spark Plasma Sintering (SPS) method. A high relative density (>95%) was successfully obtained at 1900 °C. The main phases of the B-C ceramics were proved to be B4C and B13C2 with a small amount of unreacted free-C, and the grain size was ~500 nm. B/C ratios in the ceramics were measured by chemical analysis and the B/C ratio could be well controlled.
The electrostatic self-assembly of polymer on proton exchange membrane was studied by calorimetric tech-nique. The titration of poly diallyldimethylammonium chloride (PDDA) into Nation membrane was designed and perfor...
详细信息
The electrostatic self-assembly of polymer on proton exchange membrane was studied by calorimetric tech-nique. The titration of poly diallyldimethylammonium chloride (PDDA) into Nation membrane was designed and performed to determine the thermodynamic parameters. The enthalpy change △rH(○)m and binding constant K in the process of self-assembly were obtained from data analysis with the help of Origin. According to the calculated thermodynamic parameters, the electrostatic self-assembly of PDDA on the proton exchange membrane is an 'en-thalpy-driven' reaction. The released heat indicates decrease of energy, which is helpful for the occurrence of the self-assembly process, and the degree of disorder is reduced, which went against the adsorption process. As to everyion bond, the value of △rH(○)m of DDA is beyond PDDA because a small molecule can bind itself to the membranewithout steric hindrance.
暂无评论