Nanometer α-Al2O3 powders were synthesized by the method of low-temperature combustion synthesis （LCS） with aluminum nitrate nonahydrate and urea as raw materials. The prepared powders were studied by XRD, TG-DTA, ...Nanometer α-Al2O3 powders were synthesized by the method of low-temperature combustion synthesis （LCS） with aluminum nitrate nonahydrate and urea as raw materials. The prepared powders were studied by XRD, TG-DTA, FT-IR and TEM. It is found that the average size of particles is 6080nm. The optimal synthetic conditions are obtained, i.e., the suitable fuel is urea; the molar ratio of oxidizer to fuel is 1∶2 and the igniting temperature is 700℃. The results show that the size of particles is governed by synthesizing temperature, the fuel and the molar ratio of oxidizer to fuel. TEM image of the particles collected shows that the crystal habits of particles have a spheric structure and particles are polycrystal.展开更多
The synthesis of smectite clays is discussed. From literature studies the optimal ratios of precursor materials are suggested for the preparation of the four different basic forms of smectite clays. Conditions for the...The synthesis of smectite clays is discussed. From literature studies the optimal ratios of precursor materials are suggested for the preparation of the four different basic forms of smectite clays. Conditions for the preparation of clays with intermediate compositions are also suggested.展开更多
Let X<sub>1</sub>, X<sub>2</sub>, …, X<sub>n</sub> be i.i.d, with common two-parameter Weibull distribution; that is,W（x）=1-exp（-λx<sup>β</sup>）, where λ】0 is s...Let X<sub>1</sub>, X<sub>2</sub>, …, X<sub>n</sub> be i.i.d, with common two-parameter Weibull distribution; that is,W（x）=1-exp（-λx<sup>β</sup>）, where λ】0 is scale parameter, and β】0 is sharp parameter. Weibull distribution is very important in reliability theory. How to estimate sharp parameter is the key problem in Weibull data analysis. There are many methods to estimate it, such as maximum likelihood estimation. Fang stated a method to estimate it by using properties of moments.In this note we will propose a new method by using the relation between exponential distribution moments.展开更多
文摘Nanometer α-Al2O3 powders were synthesized by the method of low-temperature combustion synthesis （LCS） with aluminum nitrate nonahydrate and urea as raw materials. The prepared powders were studied by XRD, TG-DTA, FT-IR and TEM. It is found that the average size of particles is 6080nm. The optimal synthetic conditions are obtained, i.e., the suitable fuel is urea; the molar ratio of oxidizer to fuel is 1∶2 and the igniting temperature is 700℃. The results show that the size of particles is governed by synthesizing temperature, the fuel and the molar ratio of oxidizer to fuel. TEM image of the particles collected shows that the crystal habits of particles have a spheric structure and particles are polycrystal.
文摘The synthesis of smectite clays is discussed. From literature studies the optimal ratios of precursor materials are suggested for the preparation of the four different basic forms of smectite clays. Conditions for the preparation of clays with intermediate compositions are also suggested.
基金Project supported by the National Natural Science Foundation of ChinaNational Science Foundation of Beijng.
文摘Let X<sub>1</sub>, X<sub>2</sub>, …, X<sub>n</sub> be i.i.d, with common two-parameter Weibull distribution; that is,W（x）=1-exp（-λx<sup>β</sup>）, where λ】0 is scale parameter, and β】0 is sharp parameter. Weibull distribution is very important in reliability theory. How to estimate sharp parameter is the key problem in Weibull data analysis. There are many methods to estimate it, such as maximum likelihood estimation. Fang stated a method to estimate it by using properties of moments.In this note we will propose a new method by using the relation between exponential distribution moments.
