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21.
The conductive composites were prepared using two different types of conductive black (Conductex and Printex XE2) filled in
matrices like EVA and NBR and their different blends. The electromagnetic interference shielding effectiveness (EMI SE) of
all composites was measured in the X band frequency range 8–12 GHz. Both conductivity and EMI SE increase with filler loading.
However, Printex black shows higher conductivity and better EMI SE at the same loading compared to Conductex black, and this
can be used as a material having high EMI shielding effectiveness value. The conductivity of different blends with same filler
loading generally found to increase slightly with the increase in NBR concentration. However, EMI SE has some dependency on
blend composition. EMI SE increases linearly with thickness of the sample. EMI SE versus conductivity yields two master curves
for two different fillers. EMI SE depends on formation of closed packed conductive network in insulating matrix, and Printex
black is better than Conductex black in this respect. Some of the composites show appreciably high EMI SE (>45 dB). 相似文献
22.
Yifei Gu Wei Xiao Linnan Lu Wenhai Huang Mohamed N. Rahaman Deping Wang 《Journal of Materials Science》2011,46(1):47-54
Borate bioactive glasses are receiving increasing attention as scaffold materials for bone repair and regeneration. In this
study, the kinetics and mechanisms of converting three groups of sodium–calcium–borate glasses with varying CaO:B2O3 ratio to hydroxyapatite (HA) in 0.25 M K2HPO4 solution were investigated at 10–70 °C. Glass disks with the composition 2Na2O·(2 − x)CaO·(6 + x)B2O3 (x = 0, 0.5, and 1.0) were immersed for up to 8 days in the potassium phosphate solution. The conversion kinetics to HA were
monitored by measuring the weight loss of the glass, while X-ray diffraction, scanning electron microscopy, and Fourier transform
infrared spectroscopy were used to study structural and compositional changes. All three groups of glasses formed HA on their
surfaces, showing that the glasses were bioactive. At 10–37 °C, the conversion kinetics was well fitted by the contracting
sphere model. Also, the contracting sphere model has a good fit for the early stage of conversion at 70 °C, whereas a three-dimensional
(3D) diffusion model provided a good fit to the data of the later stage. The results of this study provide kinetic and structural
data for the design of borate bioactive glasses for potential applications in bone tissue engineering. 相似文献
23.
Atiar Rahaman Molla Anal Tarafder Basudeb Karmakar 《Journal of Materials Science》2011,46(9):2967-2976
Glasses were prepared by the melt-quench technique in the K2O–SiO2–Bi2O3–TiO2 (KSBT) system and crystallized bismuth titanate, BiT (Bi4Ti3O12) phase in it by controlled heat-treatment at various temperature and duration. Different physical, thermal, optical, and
third-order susceptibility (χ3) of the glasses were evaluated and correlated with their composition. Systematic increase in refractive index (n) and χ3 with increase in BiT content is attributed to the combined effects of high polarization and ionic refraction of bismuth and
titanium ions. Microstructural evaluation by FESEM shows the formation of polycrystalline spherical particles of 70–90 nm
along with nano-rods of average diameter of 85–90 nm after prolonged heat treatment. A minor increase in dielectric constants
(εr) has been observed with increase in polarizable components of BiT in the glasses, whereas a sharp increase in εr in glass–ceramics is found to be caused by the formation of non-centrosymmetric and ferroelectric BiT nanocrystals in the
glass matrix. 相似文献
24.
The effect of crystalline particulate inclusions of mullite or zirconia on the sintering and crystallization of a mullite powder matrix was investigated as a function of the inclusion volume fraction and size. The mullite powder was synthesized by sol-gel processing and, within the limits of X-ray diffraction, was amorphous. Composites containing up to 22.5 vol % zirconia reached almost full density after sintering at 1500 °C for 1 h. Under identical conditions, the sintered density of the composites containing crystalline mullite inclusions was considerably lower. The zirconia inclusions were inert but the mullite inclusions enhanced the independent nucleation and growth rate of the mullite crystals in the matrix. The lower sintering rate of the matrix reinforced with crystalline mullite is attributed to the enhanced matrix crystallization. 相似文献
25.
In 51 actively purging cholera patients the efficacy of doxycycline, a long-acting tetracycline, was compared with a placebo and tetracycline hydrochloride. Seventeen patients who were given doxycycline at the recommended dose of 2 mg/kg at the beginning of the study, at 12 h, and at the repeated dose once daily purged a mean volume of 5.1 liters of stool and received an average of 5.7 liters of intravenous fluid. Nineteen patients receiving the placebo purged 10.1 liters of stool and received 9.7 liters of fluid. Fifteen patients given tetracycline hydrochloride at 6-h intervals passed 4.8 liters of stool and received 5.5 liters of fluid. The durations of diarrhea calculated in 8-h periods were 3.5, 8.0, and 4.1 h in the respective groups receiving doxycycline, placebo, and tetracycline. The differences between the doxycycline and placebo treatments and the tetracycline and placebo treatments were statistically significant. Those receiving doxycycline became vibrio-free in about 3 days as compared with 2 days for those receiving tetracycline; the group given the placebo were vibrio positive for the duration of their hospitalization. The results show that in the treatment of cholera the administration of doxycycline once daily has effects equal to those when tetracycline is administered at 6-h intervals. This is a distinct advantage because it decreases the demand on nursing personnel in epidemics. Also, doxycycline may be safely administered in cases of suspected renal failure from prolonged shock in cholera. 相似文献
26.
Mohamed N. Rahaman Lutgard C. De Jonghe May-Ying Chu 《Journal of the American Ceramic Society》1988,71(5):237-C
A thin cylindrical powder compact (3-mm diameter by 20-mm) with a nominal composition of YBa2 Cu3 Ox was sintered in a static temperature gradient of 25°C/mm in air for 12 h. The temperature at the hot end of the sample was maintained at 940°±5°C. Considerable mass transport and chemical demixing occurred along the length of the sample. The results are consistent with the formation of a liquid phase at the hot end of the sample, transport of the liquid down the temperature gradient, and the formation of different eutectic compositions along the length of the sample. The implications for processing high-Tc superconductors in the system Y-Ba-Cu-O are discussed. 相似文献
27.
Yanchun ZHOUM.N.Rahaman 《材料科学技术学报》1995,11(6):429-434
Nanocrystalline CeO2 powders (particle size ≈10-15 nm), doped with up to 20 at.-% of Mg,Ca or Y were prepared by chemical precipitation under hydrothermal conditions. The particle size and shape of the powders change slightly with the dopant concentrations. The the of the dopants on the sintering of the compacted powders was investigated during heating at a constant rate of 10℃/min. The elemental composition and the concentration of the dopant has significant efFect on the densification and grain growth. Compared to undoped CeO2, the dopants produce a shift in the densification curve to higher temperatures. For the same dopant concentration and under identical sintering conditions, the Ca doped samples reach nearly full density with the smallest grain size (≈50 nm), however, the Mg doped sample has the lowest density (≈95% of the theoretical) with the largest grain size (≈1 μm) 相似文献
28.
The oxidation behaviour of attrition-milled Al88Si12/Al2O3 powder mixtures was investigated for the formation of mullite/Al2O3 composites by the reaction bonded alumina (RBAO) process. Cylindrical powder compacts were heated at 5°C min–1 to temperatures between 450 and 1400°C. Oxidation occurred rapidly between ca. 400 and 750°C. Dense, outer reaction layers which formed at the lower temperatures inhibited complete oxidation and led to fracture of the body during continued heating to higher temperatures (above ca. 850°C) While the incorporation of ZrO2 improved the oxidation of the samples, X-ray analysis indicated that the Si in the alloy reacted with the ZrO2 to form phases which prevented the formation of mullite at the temperatures used in the experiments. 相似文献
29.
Ashutosh Kumar Singh Asish Bera Hafizur Rahaman Jimson Mathew Dhiraj K.Pradhan 《中国电子科技》2009,7(4):336-342
An error tolerant hardware efficient verylarge scale integration (VLSI) architecture for bitparallel systolic multiplication over dual base, which canbe pipelined, is presented. Since this architecture has thefeatures of regularity, modularity and unidirectionaldata flow, this structure is well suited to VLSIimplementations. The length of the largest delay pathand area of this architecture are less compared to the bitparallel systolic multiplication architectures reportedearlier. The architecture is implemented using Austria Micro System's 0.35 μm CMOS (complementary metaloxide semiconductor) technology. This architecture canalso operate over both the dual-base and polynomialbase. 相似文献
30.
A polymer nanocomposite was produced by acrylonitrile‐butadiene‐styrene (ABS) and α‐alumina was prepared through sol‐gel process using aluminum nitrate and citric acid. The particle size was analyzed by X‐ray diffraction and scanning electron microscopy (SEM) studies. The nanocomposites were characterized through tensile strength, Young's modulus, strain% at break, flexural strength, flexural modulus, and impact strength. The ABS/Al2O3 nanocomposites are found to have slightly higher Young's modulus, but lower tensile strength, strain% at break, flexural and impact strength than the virgin ABS. But its flexural modulus increases with increasing Al2O3 content in ABS matrix. The d‐spacing was calculated in nanocomposites to evaluate the interaction between Al2O3 and ABS. The particle distributions in nanocomposites were studied by SEM. The fractured surfaces of tensile test samples were also examined through SEM and show that the ductile fracture of ABS is converted to brittle fracture with addition of Al2O3. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers 相似文献