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71.
Fluoride in teas of different types and forms and the exposure of humans to fluoride with tea and diet 总被引：1，自引：0，他引：1
Human exposure to the fluoride (F) from commercial teas was assessed. The efficacy of the F leaching was determined from the total F (Ft) contents in the teas (53–435 mg/kg) and the F concentrations in tea infusions (0.31–3.55 mg/l of free F available to human organism). Both were determined with a fluoride ion selective electrode. The efficacies of F leaching from the green, oolong and black teas were 55–90% with continuous, and 74–100% by repeated infusions, and were not affected by the type or the manufactured form. Lower efficacies were observed from Pu’erh teas, 21–38% with continuous, and 37–59% by repeated infusions. The daily intake of F with daily consumption of five cups of tea can represent 9–101% of the adequate intake (AI) for an adult person with 70 kg, and with tea and diet 25–173% of the AI in non-fluoridated and 35–210% of AI in fluoridated areas. The upper limits of these intakes can be already associated with a risk of developing F-related adverse effects. 相似文献
72.
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74.
75.
SKF炉精炼钢中Als含量对夹杂总量的影响 总被引：3，自引：0，他引：3
对ＳＫＦ精炼炉中Ａｌｓ的含量与夹杂一的关系进行了研究,研究了当Ａｌｓ在０．０１５％￣０．０３０％的范围时,可以有效地控制夹杂总量,提高钢的纯净度。 相似文献
76.
77.
《Materials and Manufacturing Processes》2012,27(3):309-314
ABSTRACT In the present paper the influence of solution temperature 450–550°C on microstructure and mechanical properties of cast Al-12%-0.3% Mg and Al-16%-0.3% Mg alloys has been reported. It was observed that an increase in solution temperature increased the tensile strength of all alloys under investigation. Ductility was adversely affected. Higher solution temperature produced better refinement and distribution of eutectic silicon crystals than a low temperature. Heat treatment of all alloys showed spheroidization of eutectic silicon crystals. Scanning electron microscopy (SEM) of tensile-fractured surfaces was carried out to investigate the influence of solution temperature on the mode of fracture. 相似文献
78.
《Materials and Manufacturing Processes》2012,27(7-8):793-797
The creep properties of as-cast Ti-48Al-2Cr (at%) alloy which had been strengthen with addition of 2 at% Cr were investigated. Tensile creep experiments were performed in air at temperatures from 600–800°C and initial stresses ranging from 150 to 180 MPa. Stress exponent and activation energy were both measured. Data indicates that the alloy exhibits steady state creep behavior and the steady state creep rate is found to depend on the applied load and temperature. The measured power law stress exponent for steady state creep rate is found to be close to 3 and the apparent activation energy for creep is calculated to be 15.7 kJ/mol. The creep resistance of the present alloy was also compared with binary Ti-48Al (at%) to evaluate the effect of Cr addition on creep resistance of TiAl. It is concluded that addition of 2 at% of Cr does not have significant effect on the creep resistance of TiAl. 相似文献
79.
《Materials and Manufacturing Processes》2012,27(6):637-643
The current work presents a detailed study on the high temperature processing of solution treated Al–Mg–Si alloy in the temperature range of 623 K to 773 K and at different strain rates in the range of 5 × 10−5 to 6 × 10−2 s−1. A constitutive relation that can be used in modeling the forming process of this alloy under similar hot working conditions is established. Also, the prevailing deformation mechanism was investigated through relations of the steady state stress dependence on strain rate which revealed a stress exponent of 8.5 (strain rate sensitivity; m ∼ 0.12). This stress exponent is higher than what is usually observed in Al and Al–Mg alloys under similar experimental conditions. This high stress exponent may arise from the presence of threshold stress that results from dislocation interaction with second phase particles (Mg2Si), precipitating during the deformation at high temperatures. The values of threshold stress showed an exponential increase with decreasing temperature and a dependence with an energy term Qo = 38 kJmol−1. The apparent activation energy for solution treated condition was calculated to be about 320 kJmol−1, which is higher than the activation energy for self-diffusion in Al (Qd = 143 kJmol−1) and for the diffusion of Mg in Al (115–130 kJmol−1). By incorporating the threshold stress in the analysis, the true activation energy was calculated to have a value of 111 kJmol−1, and the normalized strain rates can be represented by a power function of the effective stress with stress exponent of ∼3. Ductility was documented to reveal the best working condition for this alloy in solution treated condition. The ductility exhibited a maximum value of about 120% at 773 K at a strain rate of 0.064 s−1. The results of the current work is, also, compared to the results of another heat treatment condition (T4-naturally aged) to reveal which ever condition holds better hot forming characteristics. 相似文献
80.
《Advanced Composite Materials》2012,21(4):227-237
SiCP/Al–Fe–V–Si (Al–Fe–V–Si reinforced with SiC particles) composite prepared by spray deposition was densified by hot pressing and then rolled into sheets. Microstructure of the composite was observed, and fracture properties and fractographies of the composite at different tensile temperatures were investigated. The results show that uniform distribution of SiC particles and strong bonding between the particles and the matrix are obtained by rolling after hot pressing. It is found that fracture properties and fractographies of the composite are affected by the distribution and orientation of SiC particles. The composite is characterized by the fractographies of the composite varying with the elevation of temperature. Cracking of SiC particles is the dominant rupture mode because of the strong interface bonding with the tensile temperature below 300 °C. Debonding at SiC/Al matrix interfaces becomes the dominant rupture mode with tensile temperature above 300 °C, particles breakage reduces sharply as the tensile temperature is elevated, while tensile strength and elongation of the composite decreases rapidly as the tensile temperature increases. 相似文献