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951.
Systematical investigations of zero-field resistivity, magnetoresistance and magnetization were performed for a typical manganese compound La2/3Ca1/3MnO3. It is argued that the common origin for insulator-metal and paramagenetic ferromagnetic-transitions as well as colossal magnetoresistance is due to the formation of ferromagnetic clusters in the paramagnetic background. The transition to metallic state is resulted from percolation of ferromagnetic metallic clusters, while the colossal magnetoresistance is due to the application of magnetic field, which accelerates the growth of ferromagnetic metallic clusters and causes the shift of the onset temperature for the metallic percolation to higher temperature. Based on the random resistor network model, the zero-field resistivity versus temperature dependence is simulated by using experimental parameters, and experimental data well agree with those in whole temperature range, giving a strong support to our approach. 相似文献
952.
贺海燕 《武汉理工大学学报(材料科学英文版)》2009,24(3):359-362
Fatigue-free Bi3.2La0.8Ti3O12 ferroelectric thin films were successfully prepared on p-Si (100) substrates using metalorganic solution deposition process. The orientation and formation of 5-layers thin films
were studied under different processing conditions using XRD. Experimental results indicate that increase in annealing time
at 700 °C after preannealing for 10 min at 400 °C can remarkably increase (200)-orientation of the films derived from the
precursor solutions with two contents of citric acid. Meanwhile, high content of citric acid increases the film thickness
and is conducive to the a-orientation of the films with the preannealing, and low concentration of the solution is conducive to the c-orientation of
the films without the preannealing. 相似文献
953.
A series of dimer acid-based polyamides were synthesized by melt-polycondensation of dimer acid and various aromatic diamines,
and were characterized by Fourier transform infrared spectrum (FT-IR) and nuclear magnetic resonance (1H NMR). The physical properties of the polyamides, such as glass transition temperature, melting temperature, decomposition
temperature and mechanical properties were also investigated. The polyamides’ intrinsic viscosity ranges from 1.8 dL·g−1 to 2.2 dL·g−1, and the melting temperature ranges from 140 °C to 181 °C. The glass transition temperatures, observed from dynamic mechanical
analysis, fall in the range of 34.8–48.2 °C. The physical and mechanical properties of the resultant polyamides are similar
to those of the PA1212. The heat resistance and mechanical properties of poly (4, 4′-diphenylsulfone dimeramide) (PSD) and
poly(4, 4′-diphenyl dimeramide) (PPDI) are comparable to those of PA1212. 相似文献
954.
艾桃桃 《武汉理工大学学报(材料科学英文版)》2009,24(5):732-735
Al2O3/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al TiO2 and Nb2O5, and the microstructure and mechanical properties were investigated. The results indicate the fine Al2O3 particles tend to disperse on the grain boundaries. The grain size of TiAl matrix decreases and the hardness increases with increasing Nb2O5 content. The bending strength and fracture toughness reach to a maximum when Nb2O5 content is 6 wt%, under 642 MPa and 6.69 MPa·m1/2, respectively. Based on the fractography and the observation of crack propagation path, it is concluded that the strengthening and toughening of such composites at room temperature can be attributed to the refinement of the TiAl matrix, the deflection behavior in the crack propagation and the dispersion of Al2O3 particles. 相似文献
955.
Fe-Ni-Al mixtures as hot-pressing sintering additive to Titanium diboride (TiB2) were studied. It is found that liquid alloy formed under high temperature hardly has effects on the densification behaviors
of TiB2-independent. Fe-Ni-Al additive just works as filler between TiB2 particles and does not change the TiB2-independent sintering behaviors. Pressing mode has a great effect on the liquid flowing between TiB2 particles. Multiple-steps pressing mode will give more time and space for the liquid flowing and improve the relative density
of TiB2-Fe-Ni-Al cermet. 相似文献
956.
洪雷 《武汉理工大学学报(材料科学英文版)》2010,25(4):609-612
The conductivity property of graphite slurry infiltrated steel fiber concrete (GSIFCON) was investigated by the four-probe
method. The experimental results show that the electrical resistivity of GSIFCON decreases significantly at a specific concentration
of graphite, i e, the percolation concentration. A model was accordingly developed to explain its conductive mechanism, where graphite particles
could be served as bridge for conductive network between unconnected fiber chains. For an application, snow melting test of
GSIFCON was carried out and a simple heating power analysis was performed. The results reveal that the thermal energy produced
by GSIFCON makes snow melting effectively and the electrothermal efficiency can reach approximately 20%. 相似文献
957.
W-25Cu alloys were microwave sintered in a 2.45 GHz multimode applicator. The densification, microstructure and their dependence
on sintering mode and Fe addition were investigated in detail. Owing to the volumetric heating intrinsic in microwave processing,
a microstructure with larger W grain size in center regions was observed as against larger grain size in edge regions for
conventional sintering. Microwave sintering demonstrates its intrinsic advantages such as rapid heating rate, densification
enhancement and microstructural homogeneity; but it undesirably promotes W grain growth. Under microwave sintering, the role
of Fe addition on compact consolidation is not so substantial as under conventional sintering. Moreover Fe degrades the microstructural
quality, generating worse uniformity and coarser W grains. 相似文献
958.
Calcined kaolin/TiO2 composite particle material (CK/TCPM) was prepared with TiO2 coating on the surfaces of calcined kaolin particles by the mechano-chemical method. X-ray diffraction (XRD) and scanning
electron microscope (SEM) were used to investigate the microstructures and morphologies, respectively. The mechanism of the
mechano-chemical reaction between calcined kaolin and TiO2 was studied by infrared spectra (IR). The results show that TiO2 coats evenly on the surfaces of calcined kaolin particles by Si-O-Ti and Al-O-Ti bonds on their interfaces. The hiding power
and whiteness of CK/TCPM are 17.12 g/m2 and 95.7%, respectively, presenting its similarity to TiO2 in pigment properties. 相似文献
959.
靳鸿 《武汉理工大学学报(材料科学英文版)》2010,25(4):588-591
The behavior of resistance high-g impact of EMC (epoxy molding compound) with two package models, small outline package (POS)
and Globtop, was evaluated by experimental method used Hopkinson bar. At 120,000 g (generated in the Hopkinson bar with widths
about 70 μ s) no damage in either the POS devices or the Globtop devices was observed. In order to enhance the EMC’s ability
of resistance high-g impact, buffering effect of epoxy resin was also studied. The experimental results above all show that
EMC has a better performance of impact resistance at about 120,000 g, and epoxy resin can absorb the stress wave to have the
protected ability. The study of this paper could serve as a basis for selection packaging materials and enhance its reliability
in high-g impact environment. 相似文献
960.
刘娟红 《武汉理工大学学报(材料科学英文版)》2010,25(4):619-623
The effects of different curing systems on the properties of high volume fine mineral powder RPC (reactive powder concrete)
and the appearances of hydrates were studied. The experimental results show that dry-heating curing promotes the development
of pozzolanic reactivity of fine mineral powder; due to low cement content, 0.20 water-bind ratio and high reactive fine mineral
powder content, the strength of RPC increases by around 200% after steam curing and subsequent dry-heating curing. Scanning
electron microscopy and energy spectrum diagram showed that: after the high volume fine mineral powder RPC with 0.16 water-bind
ratio underwent steam curing and dry-heating curing, there was no significant change in the appearance of hydrates; after
the RPC with 0.20 water-bind ratio, the cement content of 150 kg/m3 and more steel slag powder underwent dry-heating curing, there was a certain change in the appearance of C-S-H, the structure
of gel was more compact and was uniformly distributed, and the Ca/Si of C-S-H gel decreased from 1.41 to around 1.20. 相似文献