The oxidation behaviour of molten ZK60 and ME20 magnesium alloys in 1% 1,1,1,2-tetrafluoroethane/air atmospheres at 720 °C was compared with that of molten magnesium. The oxidation kinetics of these three melts w...The oxidation behaviour of molten ZK60 and ME20 magnesium alloys in 1% 1,1,1,2-tetrafluoroethane/air atmospheres at 720 °C was compared with that of molten magnesium. The oxidation kinetics of these three melts was determined by thermograyimetric measuring instrument, and the surface films of the oxidized samples were examined by scanning electron microscope (SEM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the oxidation rate of molten ZK60 or ME20 alloys is much lower than that of molten magnesium in 1% 1,1,1,2-tetrafluoroethane/air atmospheres. The surface film formed on the molten magnesium is composed of MgF2, MgO and C, while the film formed on ZK60 melt mainly consists of MgF2, MgO, C and some ZrF4, and the film on ME20 mainly consists of MgF2, MgO, C and a small amount of CeF4. The good oxidation resistances of ZK60 and ME20 alloy melts may be caused by their major alloying elements Zr and Ce, respectively.展开更多
A new crossover equation of state in the dimensionless Helmholtz free energy for the thermodynamic properties of 1, 1,1 ) 2-tetrafluoroethane (R 134a ) has been developed that incorporates singular thermodynamic behav...A new crossover equation of state in the dimensionless Helmholtz free energy for the thermodynamic properties of 1, 1,1 ) 2-tetrafluoroethane (R 134a ) has been developed that incorporates singular thermodynamic behavior near the critical point with regular thermodynamic behavior far from the critical point. The equation of state is capable of representing all the thermodynamic properties of R134a including press ure-density-temperature properties, the isochoric and isobaric heat capacities, and the sound velocity in the entire region,at temperatures from the triple point to 453K, pressures up to 70MPa and densities from zero to three times and a half the critical density. The results have been compared with experimental thermodynamic-property data in the entire region and with other equations of state near the critical point.展开更多
以取自鱿鱼卵的富含多不饱和脂肪酸的磷脂酰胆碱为底物,在亚临界1,1,1,2-四氟乙烷(R134a)中通过磷脂酶 D 催化酰基转换反应制备了富含多不饱和脂肪酸的磷脂酰丝氨酸,并利用响应面法对影响磷脂酰丝氨酸合成的工艺条件进行了优化。结果表...以取自鱿鱼卵的富含多不饱和脂肪酸的磷脂酰胆碱为底物,在亚临界1,1,1,2-四氟乙烷(R134a)中通过磷脂酶 D 催化酰基转换反应制备了富含多不饱和脂肪酸的磷脂酰丝氨酸,并利用响应面法对影响磷脂酰丝氨酸合成的工艺条件进行了优化。结果表明,磷脂酶 D 在亚临界 R134a 中显示出高活性,可以高效地催化酰基转换反应制备富含多不饱和脂肪酸的磷脂酰丝氨酸,反应时间短,转化率高;反应时间、底物摩尔比、初始水分是影响转化率的显著因素。通过对转化率的拟合模型响应面分析,得到了优化工艺条件:在亚临界 R134a 体系中,体系压力6MPa,温度40℃,反应时间5.60h,酶量9.6U,鱿鱼卵磷脂75mg,L-丝氨酸1.02g,溶于2.30mL pH5.5磷酸盐缓冲液。在此优化工艺条件下,转化率的预测值为92.21%,实验值为89.06%,响应面模型的有效性得到了验证。展开更多
基金Project (SJ08-ZT05) supported by the Natural Science Basic Research Plan in Shaanxi Province of ChinaProject (ZK1050) supported by the Key Scientific Research Plan of Baoji University of Arts and Science, China
文摘The oxidation behaviour of molten ZK60 and ME20 magnesium alloys in 1% 1,1,1,2-tetrafluoroethane/air atmospheres at 720 °C was compared with that of molten magnesium. The oxidation kinetics of these three melts was determined by thermograyimetric measuring instrument, and the surface films of the oxidized samples were examined by scanning electron microscope (SEM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the oxidation rate of molten ZK60 or ME20 alloys is much lower than that of molten magnesium in 1% 1,1,1,2-tetrafluoroethane/air atmospheres. The surface film formed on the molten magnesium is composed of MgF2, MgO and C, while the film formed on ZK60 melt mainly consists of MgF2, MgO, C and some ZrF4, and the film on ME20 mainly consists of MgF2, MgO, C and a small amount of CeF4. The good oxidation resistances of ZK60 and ME20 alloy melts may be caused by their major alloying elements Zr and Ce, respectively.
文摘A new crossover equation of state in the dimensionless Helmholtz free energy for the thermodynamic properties of 1, 1,1 ) 2-tetrafluoroethane (R 134a ) has been developed that incorporates singular thermodynamic behavior near the critical point with regular thermodynamic behavior far from the critical point. The equation of state is capable of representing all the thermodynamic properties of R134a including press ure-density-temperature properties, the isochoric and isobaric heat capacities, and the sound velocity in the entire region,at temperatures from the triple point to 453K, pressures up to 70MPa and densities from zero to three times and a half the critical density. The results have been compared with experimental thermodynamic-property data in the entire region and with other equations of state near the critical point.
文摘以取自鱿鱼卵的富含多不饱和脂肪酸的磷脂酰胆碱为底物,在亚临界1,1,1,2-四氟乙烷(R134a)中通过磷脂酶 D 催化酰基转换反应制备了富含多不饱和脂肪酸的磷脂酰丝氨酸,并利用响应面法对影响磷脂酰丝氨酸合成的工艺条件进行了优化。结果表明,磷脂酶 D 在亚临界 R134a 中显示出高活性,可以高效地催化酰基转换反应制备富含多不饱和脂肪酸的磷脂酰丝氨酸,反应时间短,转化率高;反应时间、底物摩尔比、初始水分是影响转化率的显著因素。通过对转化率的拟合模型响应面分析,得到了优化工艺条件:在亚临界 R134a 体系中,体系压力6MPa,温度40℃,反应时间5.60h,酶量9.6U,鱿鱼卵磷脂75mg,L-丝氨酸1.02g,溶于2.30mL pH5.5磷酸盐缓冲液。在此优化工艺条件下,转化率的预测值为92.21%,实验值为89.06%,响应面模型的有效性得到了验证。
