We report the effects of MgSiO3 addition on the crystal growth and characteristics of type-Ib diamonds synthesized in Fe–Ni–C system. The experiments were carried out with pressure at 5.5 GPa, temperature at 1385℃...We report the effects of MgSiO3 addition on the crystal growth and characteristics of type-Ib diamonds synthesized in Fe–Ni–C system. The experiments were carried out with pressure at 5.5 GPa, temperature at 1385℃–1405℃, and duration of 23.1 h. As MgSiO3 increases from 0.0 wt% to 3.0 wt%, the diamond growth temperature increases from1385℃ to 1405℃, the addition of MgSiO3 and the movement of P–T diagram toward the higher temperature direction result in a series of effects to the Fe–Ni–C system and crystal growth. Firstly, it increases the content of metastable recrystallized graphite and accelerates the competition with the carbon source needed for diamond growth, thus causing the decreased crystal growth rate. Diamond crystals exhibit the combination form of {111}, {100}, {113}, and {110}sectors, the decreased {100} and {113} sectors, dominated {111} sector are all attributed to the higher growth rate in [100]direction caused by the synergy of MgSiO3 and the movement of P–T diagram. The higher growth rate in [100] direction also increases the metal catalyst and graphite inclusions and leads to the increase of residual tensile stress on the crystal surface. Accompanying with the high growth rate, a higher dissolution rate along [100] and [113] directions than [111]direction occurs at the microstructure and forms the significantly developed(111) stepped growth layer. In addition to the movement of P–T diagram, the addition of MgSiO3 poisons the catalyst and increases the nitrogen content of diamond from 120 ppm to 227 ppm.展开更多
根据硅镁型红土镍矿中镁硅酸盐存在形式,采用化学沉淀法合成Mg Si O3,通过正交实验考察反应温度、反应时间、液固比和Na OH浓度对Mg Si O3在Na OH亚熔盐体系中的浸出过程的影响,得出优化实验条件为:反应温度为210℃,反应时间为180min,...根据硅镁型红土镍矿中镁硅酸盐存在形式,采用化学沉淀法合成Mg Si O3,通过正交实验考察反应温度、反应时间、液固比和Na OH浓度对Mg Si O3在Na OH亚熔盐体系中的浸出过程的影响,得出优化实验条件为:反应温度为210℃,反应时间为180min,液固比为6:1,Na OH浓度为80%。在优化实验的基础上,采用Raman光谱对反应过程进行在线检测,利用XRD和IR光谱分析反应后的水浸渣结构变化,解析Mg Si O3在Na OH亚熔盐体系中的反应机理。结果表明:在反应过程中,Si O4中的Si—O被破坏,Na OH介入硅酸盐晶格中,其中间产物为Mg2Si O4和Na2Mg Si O4,Mg2+经过碱浸过程可以脱离Si O4阵列,以Mg(OH)2形式从其硅酸盐中得以释放。展开更多
The intense blue emitting phosphors Sr2MgSiO5∶Ce 3+ were synthesized by high temperature solid state reaction method,and their luminescence properties were studied.The intense blue-emission band present a peak fixed ...The intense blue emitting phosphors Sr2MgSiO5∶Ce 3+ were synthesized by high temperature solid state reaction method,and their luminescence properties were studied.The intense blue-emission band present a peak fixed at 420 nm,which consists of two peaks located at 408 and 445 nm,respectively.The two peaks are originated from the transition 5d→ 2F 5/2（4f）and 5d→ 2F 7/2（4f）of Ce 3+ ions.The energy level difference value of the two emission bands is 2 038 cm-1,which is consistent with the theoretic value（2 000 cm-1）between the ground state:2F 5/2 and 2F 7/2 of Ce 3+ ions.The excitation spectra extend from 250 to 400 nm and the peak positions around 365 nm.In addition,the effect of the concentration of Ce 3+ ions and the role of charge compensation of different ions to the emission intense were investigated,the experiment results suggest that when the proportion of Ce 3+ ions to Sr2MgSiO5 were 0.03（molar ratio）,the strongest emission was obtained.Li+,Na+,K+ and Cl-ions can all enhance the intensity of the emissions;especially Cl-ions gave the best improvement.展开更多
A Mg-6Zn-3Gd(mass fraction,%) alloy,noted as ZG63,was coated by different micro-arc oxidation(MAO) processes,and the coating structure and corrosion resistance of the alloy were studied using scanning electron microsc...A Mg-6Zn-3Gd(mass fraction,%) alloy,noted as ZG63,was coated by different micro-arc oxidation(MAO) processes,and the coating structure and corrosion resistance of the alloy were studied using scanning electron microscopy(SEM),glancing angle X-ray diffractometry(GAXRD) and various electrochemical methods.The micro-arc oxidation process consists of three stages and corresponds with different coating structures.In the initial stage,the coating thickness is linearly increased and is controlled by electrochemical polarization.In the second stage,the coating grows mainly inward and accords with parabolic regularity.In the third stage,the loose coating forms and is controlled by local arc light.The looser coating is mainly composed of MgSiO3 and the compact coating is mainly composed of MgO.From micro-arc oxidation stage to local arc light stage,the corrosion resistance of the coated alloy firstly increases and then decreases.The satisfied corrosion resistance corresponds to the coating time ranging from 6 to10 min.展开更多
Isotope fractionation during the evaporation of silicate melt and condensation of vapor has been widely used to explain various isotope signals observed in lunar soils, cosmic spherules, calcium-aluminum-rich inclusio...Isotope fractionation during the evaporation of silicate melt and condensation of vapor has been widely used to explain various isotope signals observed in lunar soils, cosmic spherules, calcium-aluminum-rich inclusions, and bulk compositions of planetary materials. During evaporation and condensation, the equilibrium isotope fractionation factor(α) between high-temperature silicate melt and vapor is a fundamental parameter that can constrain the melt's isotopic compositions. However, equilibrium α is difficult to calibrate experimentally. Here we used Mg as an example and calculated equilibrium Mg isotope fractionation in MgSiO_3 and Mg_2SiO_4 melt-vapor systems based on first-principles molecular dynamics and the hightemperature approximation of the B igeleisen-May er equation. We found that, at 2500 K, δ25 Mg values in the MgSiO_3 and Mg_2SiO_4 melts were 0.141 ± 0.004 and 0.143 ± 0.003‰ more positive than in their respective vapors. The corresponding δ26 Mg values were0.270 ± 0.008 and 0.274 ± 0.006‰ more positive than in vapors, respectively. The general α-T equations describing the equilibrium Mg α in MgSiO_3 and Mg_2SiO_4 melt-vapor systems were: α Mg(1)-Mg(g) = 1+(5.264×10~5)/T^2(1/m-1/m') and α Mg(1)-Mg(g)=1+(5.340×10~5)/T2(1/m-1/m'),respectively, where m is the mass of light isotope 24 Mg and m' is the mass of the heavier isotope, 25 Mg or 26 Mg. These results offer a necessary parameter for mechanistic understanding of Mg isotope fractionation during evaporation and condensation that commonly occurs during the early stages of planetary formation and evolution.展开更多
基金This work was supported by the National Natural Sci- ence Foundation of China, （NSFC No. 10274055）, the Natural Science Foundation of Gansu Province of China （No. 3ZS051-A25-027） and the Natural Science Foundation of Education Department of Gansu Province of China （No. 0410-01）.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51772120,51872112,and 11804305)the China Postdoctoral Science Foundation(Grant No.2017M622360)the Project of Jilin Science and Technology Development Plan(Grant No.20180201079GX).
文摘We report the effects of MgSiO3 addition on the crystal growth and characteristics of type-Ib diamonds synthesized in Fe–Ni–C system. The experiments were carried out with pressure at 5.5 GPa, temperature at 1385℃–1405℃, and duration of 23.1 h. As MgSiO3 increases from 0.0 wt% to 3.0 wt%, the diamond growth temperature increases from1385℃ to 1405℃, the addition of MgSiO3 and the movement of P–T diagram toward the higher temperature direction result in a series of effects to the Fe–Ni–C system and crystal growth. Firstly, it increases the content of metastable recrystallized graphite and accelerates the competition with the carbon source needed for diamond growth, thus causing the decreased crystal growth rate. Diamond crystals exhibit the combination form of {111}, {100}, {113}, and {110}sectors, the decreased {100} and {113} sectors, dominated {111} sector are all attributed to the higher growth rate in [100]direction caused by the synergy of MgSiO3 and the movement of P–T diagram. The higher growth rate in [100] direction also increases the metal catalyst and graphite inclusions and leads to the increase of residual tensile stress on the crystal surface. Accompanying with the high growth rate, a higher dissolution rate along [100] and [113] directions than [111]direction occurs at the microstructure and forms the significantly developed(111) stepped growth layer. In addition to the movement of P–T diagram, the addition of MgSiO3 poisons the catalyst and increases the nitrogen content of diamond from 120 ppm to 227 ppm.
文摘根据硅镁型红土镍矿中镁硅酸盐存在形式,采用化学沉淀法合成Mg Si O3,通过正交实验考察反应温度、反应时间、液固比和Na OH浓度对Mg Si O3在Na OH亚熔盐体系中的浸出过程的影响,得出优化实验条件为:反应温度为210℃,反应时间为180min,液固比为6:1,Na OH浓度为80%。在优化实验的基础上,采用Raman光谱对反应过程进行在线检测,利用XRD和IR光谱分析反应后的水浸渣结构变化,解析Mg Si O3在Na OH亚熔盐体系中的反应机理。结果表明:在反应过程中,Si O4中的Si—O被破坏,Na OH介入硅酸盐晶格中,其中间产物为Mg2Si O4和Na2Mg Si O4,Mg2+经过碱浸过程可以脱离Si O4阵列,以Mg(OH)2形式从其硅酸盐中得以释放。
文摘The intense blue emitting phosphors Sr2MgSiO5∶Ce 3+ were synthesized by high temperature solid state reaction method,and their luminescence properties were studied.The intense blue-emission band present a peak fixed at 420 nm,which consists of two peaks located at 408 and 445 nm,respectively.The two peaks are originated from the transition 5d→ 2F 5/2（4f）and 5d→ 2F 7/2（4f）of Ce 3+ ions.The energy level difference value of the two emission bands is 2 038 cm-1,which is consistent with the theoretic value（2 000 cm-1）between the ground state:2F 5/2 and 2F 7/2 of Ce 3+ ions.The excitation spectra extend from 250 to 400 nm and the peak positions around 365 nm.In addition,the effect of the concentration of Ce 3+ ions and the role of charge compensation of different ions to the emission intense were investigated,the experiment results suggest that when the proportion of Ce 3+ ions to Sr2MgSiO5 were 0.03（molar ratio）,the strongest emission was obtained.Li+,Na+,K+ and Cl-ions can all enhance the intensity of the emissions;especially Cl-ions gave the best improvement.
文摘A Mg-6Zn-3Gd(mass fraction,%) alloy,noted as ZG63,was coated by different micro-arc oxidation(MAO) processes,and the coating structure and corrosion resistance of the alloy were studied using scanning electron microscopy(SEM),glancing angle X-ray diffractometry(GAXRD) and various electrochemical methods.The micro-arc oxidation process consists of three stages and corresponds with different coating structures.In the initial stage,the coating thickness is linearly increased and is controlled by electrochemical polarization.In the second stage,the coating grows mainly inward and accords with parabolic regularity.In the third stage,the loose coating forms and is controlled by local arc light.The looser coating is mainly composed of MgSiO3 and the compact coating is mainly composed of MgO.From micro-arc oxidation stage to local arc light stage,the corrosion resistance of the coated alloy firstly increases and then decreases.The satisfied corrosion resistance corresponds to the coating time ranging from 6 to10 min.
基金V. ACKN0WLEDGEMENTS This work was supported by the National Natural Science Foundation of China （No.10574096）, the Natural Science Foundation of Gansu Province of China （No.3ZS051-A25-027） and the Scientific Research Foundation of Education Bureau of Gansu Province of China （No.0410-01）.
基金provided by the strategic priority research program(B)of CAS(XDB18010104)China NSFC Grant No.41490635 to Professor Huiming Bao
文摘Isotope fractionation during the evaporation of silicate melt and condensation of vapor has been widely used to explain various isotope signals observed in lunar soils, cosmic spherules, calcium-aluminum-rich inclusions, and bulk compositions of planetary materials. During evaporation and condensation, the equilibrium isotope fractionation factor(α) between high-temperature silicate melt and vapor is a fundamental parameter that can constrain the melt's isotopic compositions. However, equilibrium α is difficult to calibrate experimentally. Here we used Mg as an example and calculated equilibrium Mg isotope fractionation in MgSiO_3 and Mg_2SiO_4 melt-vapor systems based on first-principles molecular dynamics and the hightemperature approximation of the B igeleisen-May er equation. We found that, at 2500 K, δ25 Mg values in the MgSiO_3 and Mg_2SiO_4 melts were 0.141 ± 0.004 and 0.143 ± 0.003‰ more positive than in their respective vapors. The corresponding δ26 Mg values were0.270 ± 0.008 and 0.274 ± 0.006‰ more positive than in vapors, respectively. The general α-T equations describing the equilibrium Mg α in MgSiO_3 and Mg_2SiO_4 melt-vapor systems were: α Mg(1)-Mg(g) = 1+(5.264×10~5)/T^2(1/m-1/m') and α Mg(1)-Mg(g)=1+(5.340×10~5)/T2(1/m-1/m'),respectively, where m is the mass of light isotope 24 Mg and m' is the mass of the heavier isotope, 25 Mg or 26 Mg. These results offer a necessary parameter for mechanistic understanding of Mg isotope fractionation during evaporation and condensation that commonly occurs during the early stages of planetary formation and evolution.
基金This work was supported by the National Natural Science Foundation of China （No.11064007 and No.11164013）, the Natural Science Foundation of Gansu Province of China （No.1014RJZA046）, the Program for New Century Excellent Talents in University, and the Key Project of Chinese Ministry of Education （No.209127）.
