A visco-plastic rate-dependent homogenization theory for particle-reinforced composites was derived and the equivalent elastic constants and the equivalent visco-plastic parameters of these composites were obtained. A...A visco-plastic rate-dependent homogenization theory for particle-reinforced composites was derived and the equivalent elastic constants and the equivalent visco-plastic parameters of these composites were obtained. A framework of homogenization the- ory for particle-reinforced W-Ni-Fe composites, a kind of tungsten alloy, was established. Based on the homogenization theory and a fixed-point iteration method, a unit cell model with typical microstructnres of the composite was established by using dynamic analysis program. The effects of tungsten content, tungsten particle shape and particle size and interface strength on the mechanical properties and the crack propagation of the W-Ni-Fe composite are analyzed under quasi-static and dynamic loadings. The stress-strain curves of the composite are given and the relation between the macro-mechanical characteristics and the microstructure parameters is explored, which provides an important theoretical basis for the optimization of the W-Ni-Fe composites.展开更多
Micronized coal reburning (MCR) can not only reduce carbon in fly ash but also reduce NOx emissions as compared to the conventional coal reburning. However, it has two major kinetic barriers in minimizing NOx emissi...Micronized coal reburning (MCR) can not only reduce carbon in fly ash but also reduce NOx emissions as compared to the conventional coal reburning. However, it has two major kinetic barriers in minimizing NOx emission. The first is the conversion of NO into hydrogen cyanide (HCN) by conjunction with various hydrocarbon fragments. The second is the oxidation of HCN by association with oxygen-containing groups. To elucidate the advantages of MCR, a combination of Diffuse Reflection Fourier Transform Infrared (FTIR) experimental studies with Density Functional Theory (DFT) theoretical calculations is conducted in terms of the second kinetic barrier. FTIR studies based on Chinese Tiefa coal show that there are five hydroxide groups such as OH-n, OH-N, OH- OR2, self-associated OH and free OH. The hydroxide groups increase as the mean particle size decreases expect for free OH. DFT calculations at the B3LYP/6-31 G(d) level indicate that HCN can be oxidized by hydroxide groups in three paths, HCN + OH → HOCN + H (path 1), HCN + OH → HNCO + H (path 2), and HCN + OH -. CN + H20 (path 3). The rate limiting steps for path 1, path 2 and path 3 are IM2 → P1 + H (170.66 kJ/mol activated energy), IM1→IM3 (231.04 kJ/mol activated energy), and R1 + OH→ P3 + H2O (97.14 kJ/mol activated energy), respectively. The present study of MCR will provide insight into its lower NOx emission and guidance for further studies.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 11032002 and 91016013)the program for New Century Excellent Talents in University+1 种基金National Basic Research Program of China (Grant No. 2010CB832706)the project of State Key Laboratory of Explosion Science and Technology (Beijing Institute of Technology)(Grant No. ZDKT10-03a)
文摘A visco-plastic rate-dependent homogenization theory for particle-reinforced composites was derived and the equivalent elastic constants and the equivalent visco-plastic parameters of these composites were obtained. A framework of homogenization the- ory for particle-reinforced W-Ni-Fe composites, a kind of tungsten alloy, was established. Based on the homogenization theory and a fixed-point iteration method, a unit cell model with typical microstructnres of the composite was established by using dynamic analysis program. The effects of tungsten content, tungsten particle shape and particle size and interface strength on the mechanical properties and the crack propagation of the W-Ni-Fe composite are analyzed under quasi-static and dynamic loadings. The stress-strain curves of the composite are given and the relation between the macro-mechanical characteristics and the microstructure parameters is explored, which provides an important theoretical basis for the optimization of the W-Ni-Fe composites.
基金This work was supported by Doctoral Fund of Ministry of Education of China (2010), the National Natural Science Foundation of China (Grant No. 50876060) and China Postdoctoral Science Foundation funded project (2012M511091).
文摘Micronized coal reburning (MCR) can not only reduce carbon in fly ash but also reduce NOx emissions as compared to the conventional coal reburning. However, it has two major kinetic barriers in minimizing NOx emission. The first is the conversion of NO into hydrogen cyanide (HCN) by conjunction with various hydrocarbon fragments. The second is the oxidation of HCN by association with oxygen-containing groups. To elucidate the advantages of MCR, a combination of Diffuse Reflection Fourier Transform Infrared (FTIR) experimental studies with Density Functional Theory (DFT) theoretical calculations is conducted in terms of the second kinetic barrier. FTIR studies based on Chinese Tiefa coal show that there are five hydroxide groups such as OH-n, OH-N, OH- OR2, self-associated OH and free OH. The hydroxide groups increase as the mean particle size decreases expect for free OH. DFT calculations at the B3LYP/6-31 G(d) level indicate that HCN can be oxidized by hydroxide groups in three paths, HCN + OH → HOCN + H (path 1), HCN + OH → HNCO + H (path 2), and HCN + OH -. CN + H20 (path 3). The rate limiting steps for path 1, path 2 and path 3 are IM2 → P1 + H (170.66 kJ/mol activated energy), IM1→IM3 (231.04 kJ/mol activated energy), and R1 + OH→ P3 + H2O (97.14 kJ/mol activated energy), respectively. The present study of MCR will provide insight into its lower NOx emission and guidance for further studies.