Recently,the preparation of ultra-high temperature HfC ceramic coating has gained significant attention,particularly through the application of the HfCl_(4)-CH_(4)-H_(2)-Ar system via Chemical Vapor Deposition(CVD),wh...Recently,the preparation of ultra-high temperature HfC ceramic coating has gained significant attention,particularly through the application of the HfCl_(4)-CH_(4)-H_(2)-Ar system via Chemical Vapor Deposition(CVD),which has been found widely applied to C/C composites.Herein,an analysis of the reactions that occur in the initial stage of the CVD-HfC coating process is presented using Density Functional Theory(DFT)and Transition State Theory(TST)at the B3LYP/Lanl2DZ level.The results reveal that HfCl4 can only cleave to produce hypochlorite,which will further react with methyl to synthesize intermediates to form HfC.According to the analysis of the energy barrier and reaction constant,HfCl preferentially reacts with methyl groups to form complex adsorptive intermediates at 1573 K.With a C—Hf bond production energy of 212.8 kcal/mol(1 kcal=4.18 kJ),the reaction rate constant of HfCl+CH is calculated to be 2.15×10^(-18) cm^(3)/s at 1573 K.Additionally,both the simulation and experimental results exhibit that the upward trend of reaction rate constants with temperature is also consistent with the deposition rate,indicating that the growth curve of the reaction rate constants tends to flatten out.The proposed reaction model of the precursor’s decomposition and reconstruction during deposition process has significant implication for the process guidance.展开更多
Precursors were prepared by solid state chemical reaction between LaCl_3 and C_2H_2O_4·2H_2O or NH_4HCO_3 at ambient temperature. Differential temperature analysis (DTA) and thermogravimetric analysis (TGA) were ...Precursors were prepared by solid state chemical reaction between LaCl_3 and C_2H_2O_4·2H_2O or NH_4HCO_3 at ambient temperature. Differential temperature analysis (DTA) and thermogravimetric analysis (TGA) were used to determine the decomposing temperature. Oxide (La_2O_3) was obtained by decomposing the precursor for about 2.5 h. X-ray diffraction (XRD), scanning electronic microscope (SEM) and ZETA potentiometer were respectively used to analyze the composition, morphology and size distribution of the products. The results show that La_2O_3 prepared by LaCl_3 and C_2H_2O_4·2H_2O is of ball-like shape and the diameter of particles (95%) is below 50 nm, while La_2O_3 prepared by LaCl_3 and NH_4HCO_3 is net-like.展开更多
The aging process of pure copper precursors and copper-zinc binary precursorswere studied by XRD, TG-DTG and TPR techniques. The catalytic activity and stability of CuO/ZnOwere tested using fixed-bed flow reactor, and...The aging process of pure copper precursors and copper-zinc binary precursorswere studied by XRD, TG-DTG and TPR techniques. The catalytic activity and stability of CuO/ZnOwere tested using fixed-bed flow reactor, and the physical properties of the catalysts and Cuspecies were characterized with N_2 adsorption and N_2O passivation method, respectively. For theCu-Zn binary system prepared at the precipitating condition of pH=8.0 and temperature=80℃, theinitial phase was a mixture of copper nitrate hydroxide Cu_2(NO_3)(OH)_3, georgeite and hydrozinciteZn_5(CO_3)_2(OH)_6. By increasing the duration of its aging time, the phase of Cu_2(NO_3)(OH)_2first transited to georgeite, and then interdiffused into Zn_5(CO_3)_2(OH)_6 and resulted in two newphases: rosasite (Cu,Zn)_2CO_3(OH)_2 and au-richalcite (Zn,Cu)_5(CO_3)_2(OH)_6. The former phasewas much easier to be formed than the latter one, while the latter phase was more responsible forthe activity of methanol synthesis than the former one. It is found that the composition andstructure of the precursors altered obviously after the colour transition point. The experimentalresults showed that methanol synthesis is a structure-sensitive catalytic reaction.展开更多
The first necessary condition for the onset of an earthquake is the penetration of explosive gas into an explosive zone as a result of physical or chemical reaction. The second necessary condition is to ensure the sub...The first necessary condition for the onset of an earthquake is the penetration of explosive gas into an explosive zone as a result of physical or chemical reaction. The second necessary condition is to ensure the subsequent propagation of the flame after ignition. The latter condition has made it possible to explain the impact of a cyclone on the emergence of 42 strongest earthquakes in the 21st century. If violation of this condition can be achieved with the help of vibrators or explosions, this will result in a decrease in the magnitude of an earthquake or even a complete prevention of earthquakes. Thus, the second condition is essentially a “pressure lock” that opens (with a decrease in the pressure caused by a cyclone), which leads to an earthquake or closes (with an increase in the pressure caused by an anticyclone or human interference using vibrators or explosions), which leads to earthquake prevention. Kinetic equations of the 2nd type were used to describe chemical reactions and obtain formulas for the precursor time, which made it possible to describe earthquakes of the chemical channel. The set of experimental time values of the earthquake precursor described by the physical model includes about 20% of all earthquakes;80% of earthquakes can be attributed to the chemical channel for earthquakes that occurred in Dushanbe in 1983. All earthquakes in Tiberias in June 2018 passed through the chemical channel, which can be concluded from the small magnitude of these earthquakes. Several proposals have been made, including: 1) creating a new sensor for the geochemical method, which allows determining the epicenter of a future earthquake;2) creating a network of stations with a new sensor for determining the epicenter and an atmospheric pressure meter installed at each station (this will determine if the “pressure lock” is closed by an anticyclone, which can lead to a decrease in the magnitude of an earthquake or even prevent an earthquake);3) installing vibrators in epicenters (or making daily explosions with explosives delivered by trucks, drones, airplanes or helicopters, which should lower the magnitudes of future dangerous earthquakes);4) alerting the public to the expected future earthquake;5) developing specialized vibrators for reducing the magnitude of an impending catastrophic earthquake. Thus, this article is a breakthrough, describing a new mechanism in earthquakes for understanding and theory of earthquakes, which are used for the vast majority of earthquakes, including for program to reduce the magnitude of dangerous earthquakes.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 52293373 and 52130205)the National Key Research and Development Program of China (No. 2021YFA0715803)ND Basic Research Funds of Northwestern Polytechnical University, China (No. G2022WD)
文摘Recently,the preparation of ultra-high temperature HfC ceramic coating has gained significant attention,particularly through the application of the HfCl_(4)-CH_(4)-H_(2)-Ar system via Chemical Vapor Deposition(CVD),which has been found widely applied to C/C composites.Herein,an analysis of the reactions that occur in the initial stage of the CVD-HfC coating process is presented using Density Functional Theory(DFT)and Transition State Theory(TST)at the B3LYP/Lanl2DZ level.The results reveal that HfCl4 can only cleave to produce hypochlorite,which will further react with methyl to synthesize intermediates to form HfC.According to the analysis of the energy barrier and reaction constant,HfCl preferentially reacts with methyl groups to form complex adsorptive intermediates at 1573 K.With a C—Hf bond production energy of 212.8 kcal/mol(1 kcal=4.18 kJ),the reaction rate constant of HfCl+CH is calculated to be 2.15×10^(-18) cm^(3)/s at 1573 K.Additionally,both the simulation and experimental results exhibit that the upward trend of reaction rate constants with temperature is also consistent with the deposition rate,indicating that the growth curve of the reaction rate constants tends to flatten out.The proposed reaction model of the precursor’s decomposition and reconstruction during deposition process has significant implication for the process guidance.
文摘Precursors were prepared by solid state chemical reaction between LaCl_3 and C_2H_2O_4·2H_2O or NH_4HCO_3 at ambient temperature. Differential temperature analysis (DTA) and thermogravimetric analysis (TGA) were used to determine the decomposing temperature. Oxide (La_2O_3) was obtained by decomposing the precursor for about 2.5 h. X-ray diffraction (XRD), scanning electronic microscope (SEM) and ZETA potentiometer were respectively used to analyze the composition, morphology and size distribution of the products. The results show that La_2O_3 prepared by LaCl_3 and C_2H_2O_4·2H_2O is of ball-like shape and the diameter of particles (95%) is below 50 nm, while La_2O_3 prepared by LaCl_3 and NH_4HCO_3 is net-like.
文摘The aging process of pure copper precursors and copper-zinc binary precursorswere studied by XRD, TG-DTG and TPR techniques. The catalytic activity and stability of CuO/ZnOwere tested using fixed-bed flow reactor, and the physical properties of the catalysts and Cuspecies were characterized with N_2 adsorption and N_2O passivation method, respectively. For theCu-Zn binary system prepared at the precipitating condition of pH=8.0 and temperature=80℃, theinitial phase was a mixture of copper nitrate hydroxide Cu_2(NO_3)(OH)_3, georgeite and hydrozinciteZn_5(CO_3)_2(OH)_6. By increasing the duration of its aging time, the phase of Cu_2(NO_3)(OH)_2first transited to georgeite, and then interdiffused into Zn_5(CO_3)_2(OH)_6 and resulted in two newphases: rosasite (Cu,Zn)_2CO_3(OH)_2 and au-richalcite (Zn,Cu)_5(CO_3)_2(OH)_6. The former phasewas much easier to be formed than the latter one, while the latter phase was more responsible forthe activity of methanol synthesis than the former one. It is found that the composition andstructure of the precursors altered obviously after the colour transition point. The experimentalresults showed that methanol synthesis is a structure-sensitive catalytic reaction.
文摘The first necessary condition for the onset of an earthquake is the penetration of explosive gas into an explosive zone as a result of physical or chemical reaction. The second necessary condition is to ensure the subsequent propagation of the flame after ignition. The latter condition has made it possible to explain the impact of a cyclone on the emergence of 42 strongest earthquakes in the 21st century. If violation of this condition can be achieved with the help of vibrators or explosions, this will result in a decrease in the magnitude of an earthquake or even a complete prevention of earthquakes. Thus, the second condition is essentially a “pressure lock” that opens (with a decrease in the pressure caused by a cyclone), which leads to an earthquake or closes (with an increase in the pressure caused by an anticyclone or human interference using vibrators or explosions), which leads to earthquake prevention. Kinetic equations of the 2nd type were used to describe chemical reactions and obtain formulas for the precursor time, which made it possible to describe earthquakes of the chemical channel. The set of experimental time values of the earthquake precursor described by the physical model includes about 20% of all earthquakes;80% of earthquakes can be attributed to the chemical channel for earthquakes that occurred in Dushanbe in 1983. All earthquakes in Tiberias in June 2018 passed through the chemical channel, which can be concluded from the small magnitude of these earthquakes. Several proposals have been made, including: 1) creating a new sensor for the geochemical method, which allows determining the epicenter of a future earthquake;2) creating a network of stations with a new sensor for determining the epicenter and an atmospheric pressure meter installed at each station (this will determine if the “pressure lock” is closed by an anticyclone, which can lead to a decrease in the magnitude of an earthquake or even prevent an earthquake);3) installing vibrators in epicenters (or making daily explosions with explosives delivered by trucks, drones, airplanes or helicopters, which should lower the magnitudes of future dangerous earthquakes);4) alerting the public to the expected future earthquake;5) developing specialized vibrators for reducing the magnitude of an impending catastrophic earthquake. Thus, this article is a breakthrough, describing a new mechanism in earthquakes for understanding and theory of earthquakes, which are used for the vast majority of earthquakes, including for program to reduce the magnitude of dangerous earthquakes.
