Decomposition processes of the quenched Zn-Al alloys were studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the stabilities o...Decomposition processes of the quenched Zn-Al alloys were studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the stabilities of supersaturated solid solution (SSS) of Zn-Al alloy and α' phase formed by quenching would reduce with the increase of Zn content and the precipitation of η-Zn phases even when aging at ambient temperature, so that the exothermic precipitation peak in DSC curve would disappear. The activation energy of the η-Zn precipitation and the reaction enthalpy were calculated and measured. The kinetics of α' decomposition or η-Zn formation was determined by XRD. The microstructure change during aging was observed by TEM.展开更多
X-ray powder diffraction data and crystal structure of NiSbY compound were studied by X-ray powderdiffraction. The compound belongs to the space group F43 m with MgAgAs structure type, and the parameters Z=4, a=0.6307...X-ray powder diffraction data and crystal structure of NiSbY compound were studied by X-ray powderdiffraction. The compound belongs to the space group F43 m with MgAgAs structure type, and the parameters Z=4, a=0.63075(2) nm.展开更多
The compound PrNiSn was studied by X ray powder diffraction technique. The crystal structure and the X ray diffraction data for this compound at room temperature were reported. The compound PrNiSn is orthorhombic wi...The compound PrNiSn was studied by X ray powder diffraction technique. The crystal structure and the X ray diffraction data for this compound at room temperature were reported. The compound PrNiSn is orthorhombic with lattice parameters a =0.74569(3) nm, b =0.76851(5) nm, c =0.45676(8) nm, V =0.26176 nm 3, Z =4 and D x=8.076 g·cm -3 , space group Pna2 1(33). The figure of merit F N for the compound is F 30 =54 (0.0093, 60).展开更多
The research on the application of X-ray diffraction in the quantitative analysis of Chinese medicines is rare. The main reason is that the technical problems related to the internal standard and the selection of quan...The research on the application of X-ray diffraction in the quantitative analysis of Chinese medicines is rare. The main reason is that the technical problems related to the internal standard and the selection of quantitative peaks are not well solved, and the accuracy and precision of the results are not satisfactory. This study employed the concept of mass absorption coefficient based on the internal standard method, and the full spectrum fitting and quantitative methods were used to solve the above technical problems. The sample was blended. the internal standard substance of zinc oxide was fully ground, and tablets were prepared by positive pressure method. Under certain instrumental conditions, the PXRD pattern was obtained by scanning. The percentage of gypsum fibrosum in Xiaokening tablet was obtained by quantitative analysis of full spectrum fitting internal standard by TOPAS software. The method was investigated by methodology. At the same time, the method was compared by ion chromatography, and SPSS software was used to make a significant t test on the results of the two methods. After the investigation, the average standard recovery rate of CaSO4-2H2O was 99.06%(RSD = 3.02%);and the recovery rate for simulated samples was 96.7%. The method had good specificity. After statistical analysis, there was no significant difference between the new PXRD method and the traditional method of ion chromatography.展开更多
X-ray free-electron lasers(XFELs)can generate bright X-ray pulses with short durations and narrow bandwidths,leading to extensive applica-tions in many disciplines such as biology,materials science,and ultrafast scien...X-ray free-electron lasers(XFELs)can generate bright X-ray pulses with short durations and narrow bandwidths,leading to extensive applica-tions in many disciplines such as biology,materials science,and ultrafast science.Recently,there has been a growing demand for X-ray pulses with high photon energy,especially from developments in“diffraction-before-destruction”applications and in dynamic mesoscale materials science.Here,we propose utilizing the electron beams at XFELs to drive a meter-scale two-bunch plasma wakefield accelerator and double the energy of the accelerated beam in a compact and inexpensive way.Particle-in-cell simulations are performed to study the beam quality degradation under different beam loading scenarios and nonideal issues,and the results show that more than half of the accelerated beam can meet the requirements of XFELs.After its transport to the undulator,the accelerated beam can improve the photon energy to 22 keV by a factor of around four while maintaining the peak power,thus offering a promising pathway toward high-photon-energy XFELs.展开更多
The compound CeNi 5Sn was studied by means of X ray powder diffraction technique and refined by Rietveld method. It has a hexagonal structure with space group P 6 3/ mmc (No.194), Z =4, the lattice constant...The compound CeNi 5Sn was studied by means of X ray powder diffraction technique and refined by Rietveld method. It has a hexagonal structure with space group P 6 3/ mmc (No.194), Z =4, the lattice constants a =0 48912(3) nm, c =1 973(2) nm and D x=8 974 g·cm -3 . The Rietveld structural refinement was performed, leading to R p=0 138 and R wp =0 185. The figure of merit F N for the XRD data is F 30 =82 1(0 0068, 54). The X ray powder diffraction data are presented.展开更多
There are two kinds of China- made X- ray thickness gaugemeters i.e. dual beam- dual detector system and single beam- single detector system- SM series, the latter is used dominantly in Chinese steel industries. The p...There are two kinds of China- made X- ray thickness gaugemeters i.e. dual beam- dual detector system and single beam- single detector system- SM series, the latter is used dominantly in Chinese steel industries. The performance comparison between domestic and foreign instruments as well as its developments and applications is presented in this paper.展开更多
To evaluate the residual stress in TiAl based alloys by X ray diffraction, X ray elastic constants (REC) of a γ TiAl alloy were determined. From these results, the stress state of a given phase in a duplex TiAl based...To evaluate the residual stress in TiAl based alloys by X ray diffraction, X ray elastic constants (REC) of a γ TiAl alloy were determined. From these results, the stress state of a given phase in a duplex TiAl based alloy under a uniaxial tensile loading has been characterized by X ray diffraction. The results show that the X ray elastic constants and the microscopic stresses of the given phase are different from the apparent elastic constants and the macroscopic stresses of the alloy. The reason of the different distribution of the alloy was also discussed. [展开更多
A series of GaAs/InAs/GaAs samples were studied by double crystal X ray diffraction and the X ray dynamic theory was used to analyze the X ray diffraction results. As the thickness of InAs layer exceeds 1.7 monolayer,...A series of GaAs/InAs/GaAs samples were studied by double crystal X ray diffraction and the X ray dynamic theory was used to analyze the X ray diffraction results. As the thickness of InAs layer exceeds 1.7 monolayer, 3 dimensional InAs islands appear. Pendellosung fringes shifted. A multilayer structure model is proposed to describe the strain status in the InAs islands of the sample and a good agreement is obtained between the experimental and theoretical curves.展开更多
The crystal structure of new compound Ba 3BPO 7 has been solved by X ray powder diffraction technique. As a new structure type, the positions of barium, boron and phosphate atoms have been determined by single crystal...The crystal structure of new compound Ba 3BPO 7 has been solved by X ray powder diffraction technique. As a new structure type, the positions of barium, boron and phosphate atoms have been determined by single crystal direct method after profile decomposition from Ba 3BPO 7 X ray powder diffraction patterns. The positions of oxygen atoms have been determined by the interpretation of their vibration spectra which indicate that in this crystal the boron and phosphorus atoms form BO 3 and PO 4 polyhedra. The structure has been refined by Rietveld technique based on the above model.展开更多
Structural determination plays a pivotal role in chemical research by providing detailed insights into molecular architecture and functionality.Single-crystal X-ray diffraction(SCXRD)is widely regarded as the premier ...Structural determination plays a pivotal role in chemical research by providing detailed insights into molecular architecture and functionality.Single-crystal X-ray diffraction(SCXRD)is widely regarded as the premier technique for achieving precise three-dimensional structural elucidation[1].The persistent challenge of determining atomic-level structures for non-crystalline or conformationally flexible molecules has driven transformative innovations in crystallographic methodologies[2-5].展开更多
High-pressure research has emerged as a pivotal approach for advancing our understanding and development of optoelectronic materials,which are vital for a wide range of applications,including photovoltaics,light-emitt...High-pressure research has emerged as a pivotal approach for advancing our understanding and development of optoelectronic materials,which are vital for a wide range of applications,including photovoltaics,light-emitting devices,and photodetectors.This review highlights various in situ characterization methods employed in high-pressure research to investigate the optical,electronic,and structural properties of optoelectronic materials.We explore the advances that have been made in techniques such as X-ray diffraction,absorption spectroscopy,nonlinear optics,photoluminescence spectroscopy,Raman spectroscopy,and photoresponse measurement,emphasizing how these methods have enhanced the elucidation of structural transitions,bandgap modulation,performance optimization,and carrier dynamics engineering.These insights underscore the pivotal role of high-pressure techniques in optimizing and tailoring optoelectronic materials for future applications.展开更多
Grating optics lie in the heart of X-ray spectroscopy instruments.The low efficiency and angular dispersion of conventional single-layer-coated gratings significantly limit the transmission and energy resolution of mo...Grating optics lie in the heart of X-ray spectroscopy instruments.The low efficiency and angular dispersion of conventional single-layer-coated gratings significantly limit the transmission and energy resolution of monochromators and spectrometers,particularly in the tender X-ray region(E=1-5 keV).Multilayer-coated blazed gratings(MLBGs)operating at high diffraction orders offer the advantage of achieving both high efficiency and high dispersion simultaneously.Tender X-ray monochromators and spectrometers using different high-order MLBGs have been designed,all demonstrating one to two orders of magnitude higher transmission compared to conventional systems.By employing a 2400 l/mm MLBG at the-4th or-8th diffraction order,the theoretical energy resolution of the instrument is improved by two to three times at 2.5 keV.Two MLBGs operating at the-2nd and-4th orders have been fabricated,showcasing remarkable efficiencies of 34%-12%at 2.5 keV,surpassing that of single-layer-coated gratings by an order of magnitude.Further optimization of manufacturing accuracy can yield even higher efficiencies.The measured angular dispersion agrees well with theoretical predictions,supporting the potential for high resolution.High-order MLBG optics pave the way for a new generation of tender X-ray monochromators/spectrometers that offer both high transmission and high resolution.展开更多
In this paper, we report the use of blowing nitrogen gas for the successful fabrication of a composite layer composed of Ti/TiN on a substrate of commercially pure titanium （cp-2） using the friction stir processing ...In this paper, we report the use of blowing nitrogen gas for the successful fabrication of a composite layer composed of Ti/TiN on a substrate of commercially pure titanium （cp-2） using the friction stir processing technique. The prepared composite layer was characterized by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectrometry. The maximum microhardness of the Ti/TiN composite reached 1024 HV, which is 6.4 times higher than that of the titanium substrate. The results of wear test indicated that the Ti/TiN composite layer possesses excellent abrasive and adhesive wear resistance because of the formation of the TiN and its high hardness.展开更多
Aim To prepare and characterize solid dispersions of silymarin with the intention of improving their dissolution properties. Methods The solid dispersions were prepared by the fusion method with polyethylene glycol ...Aim To prepare and characterize solid dispersions of silymarin with the intention of improving their dissolution properties. Methods The solid dispersions were prepared by the fusion method with polyethylene glycol 6000(PEG 6000) as the carrier. Evaluation of the properties of the dispersions was performed using dissolution studies, X ray powder diffraction and Fourier transform infrared (FT IR) spectroscopy. Results The rate of dissolution of silymarin was considerably improved as compared with pure silymarin when formulated in solid dispersions with PEG 6000. The data of the X ray diffraction showed some changes in the parameters of lattice spacing [ d ], peak position and relative intensities. FT IR together with those from X ray diffraction showed the absence of well defined drug polymer interactions. Conclusion The dissolution improvement of poorly soluble silymarin could be illuminated by the changes of the lattice parameters of PEG 6000 and the drug.展开更多
In order to investigate the effects of two mineral admixtures （i. e., fly ash and ground slag）on initial defects existing in concrete microstructures, a high-resolution X-ray micro-CT（ micro-focus computer tomogra...In order to investigate the effects of two mineral admixtures （i. e., fly ash and ground slag）on initial defects existing in concrete microstructures, a high-resolution X-ray micro-CT（ micro-focus computer tomography）is employed to quantitatively analyze the initial defects in four series of highperformance concrete （HPC）specimens with additions of different mineral admixtures. The nigh-resolution 3D images of microstructures and filtered defects are reconstructed by micro- CT software. The size distribution and volume fractions of initial defects are analyzed based on 3D and 2D micro-CT images. The analysis results are verified by experimental results of watersuction tests. The results show that the additions of mineral admixtures in concrete as cementitious materials greatly change the geometrical properties of the microstructures and the spatial features of defects by physical-chemistry actions of these mineral admixtures. This is the major cause of the differences between the mechanical behaviors of HPC with and without mineral admixtures when the water-to-binder ratio and the size distribution of aggregates are constant.展开更多
The silicon-containing poly (amic acid)s were synthesized from bis (3, 4-dicarboxyphenyl) dimethylsilane dianhydride (SIDA), pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (4,4'-ODA) in N, N-dimethylacetam...The silicon-containing poly (amic acid)s were synthesized from bis (3, 4-dicarboxyphenyl) dimethylsilane dianhydride (SIDA), pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (4,4'-ODA) in N, N-dimethylacetamide (DMAc). The poly (amic acid) films were obtained by solution-cast method from DMAc solutions and thermally converted into transparent, flexible and tough polyimide films. The wide-angle X-ray diffraction diagrams revealed that all the polyimides possessed amorphous character, and the regulation of those polyimides were decreased with the increase of the molar ratio of SIDA to PMDA. Differential scanning calorimeter measurements showed that the introduction of SIDA to polyimide backbone would make glass transition temperature shift to lower temperature. Thermogravimetric analyses indicated that the silicon-containing polyimides lowered decomposition temperature as compared with PMDA/4, 4′-ODA polyimides. However, UV-visible transmission and reflection spectra showed that the optical transparency of silicon-containing polyimide thin films was superior to that of PMDA/4, 4'-ODA polyimide thin films.展开更多
文摘Decomposition processes of the quenched Zn-Al alloys were studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the stabilities of supersaturated solid solution (SSS) of Zn-Al alloy and α' phase formed by quenching would reduce with the increase of Zn content and the precipitation of η-Zn phases even when aging at ambient temperature, so that the exothermic precipitation peak in DSC curve would disappear. The activation energy of the η-Zn precipitation and the reaction enthalpy were calculated and measured. The kinetics of α' decomposition or η-Zn formation was determined by XRD. The microstructure change during aging was observed by TEM.
文摘X-ray powder diffraction data and crystal structure of NiSbY compound were studied by X-ray powderdiffraction. The compound belongs to the space group F43 m with MgAgAs structure type, and the parameters Z=4, a=0.63075(2) nm.
文摘The compound PrNiSn was studied by X ray powder diffraction technique. The crystal structure and the X ray diffraction data for this compound at room temperature were reported. The compound PrNiSn is orthorhombic with lattice parameters a =0.74569(3) nm, b =0.76851(5) nm, c =0.45676(8) nm, V =0.26176 nm 3, Z =4 and D x=8.076 g·cm -3 , space group Pna2 1(33). The figure of merit F N for the compound is F 30 =54 (0.0093, 60).
文摘The research on the application of X-ray diffraction in the quantitative analysis of Chinese medicines is rare. The main reason is that the technical problems related to the internal standard and the selection of quantitative peaks are not well solved, and the accuracy and precision of the results are not satisfactory. This study employed the concept of mass absorption coefficient based on the internal standard method, and the full spectrum fitting and quantitative methods were used to solve the above technical problems. The sample was blended. the internal standard substance of zinc oxide was fully ground, and tablets were prepared by positive pressure method. Under certain instrumental conditions, the PXRD pattern was obtained by scanning. The percentage of gypsum fibrosum in Xiaokening tablet was obtained by quantitative analysis of full spectrum fitting internal standard by TOPAS software. The method was investigated by methodology. At the same time, the method was compared by ion chromatography, and SPSS software was used to make a significant t test on the results of the two methods. After the investigation, the average standard recovery rate of CaSO4-2H2O was 99.06%(RSD = 3.02%);and the recovery rate for simulated samples was 96.7%. The method had good specificity. After statistical analysis, there was no significant difference between the new PXRD method and the traditional method of ion chromatography.
基金supported by the National Grand Instrument Project No. SQ2019YFF01014400the Natural Science Foundation of China (Grant Nos. 12375147, 12435011, 12075030)+2 种基金the Beijing Outstanding Young Scientist Project, Project for Young Scientists in Basic Research of Chinese Academy of Sciences (YSBR-115)the Beijing Normal University Scientific Research Initiation Fund for Introducing Talents No. 310432104the Fundamental Research Funds for the Central Universities, Peking University
文摘X-ray free-electron lasers(XFELs)can generate bright X-ray pulses with short durations and narrow bandwidths,leading to extensive applica-tions in many disciplines such as biology,materials science,and ultrafast science.Recently,there has been a growing demand for X-ray pulses with high photon energy,especially from developments in“diffraction-before-destruction”applications and in dynamic mesoscale materials science.Here,we propose utilizing the electron beams at XFELs to drive a meter-scale two-bunch plasma wakefield accelerator and double the energy of the accelerated beam in a compact and inexpensive way.Particle-in-cell simulations are performed to study the beam quality degradation under different beam loading scenarios and nonideal issues,and the results show that more than half of the accelerated beam can meet the requirements of XFELs.After its transport to the undulator,the accelerated beam can improve the photon energy to 22 keV by a factor of around four while maintaining the peak power,thus offering a promising pathway toward high-photon-energy XFELs.
文摘The compound CeNi 5Sn was studied by means of X ray powder diffraction technique and refined by Rietveld method. It has a hexagonal structure with space group P 6 3/ mmc (No.194), Z =4, the lattice constants a =0 48912(3) nm, c =1 973(2) nm and D x=8 974 g·cm -3 . The Rietveld structural refinement was performed, leading to R p=0 138 and R wp =0 185. The figure of merit F N for the XRD data is F 30 =82 1(0 0068, 54). The X ray powder diffraction data are presented.
文摘There are two kinds of China- made X- ray thickness gaugemeters i.e. dual beam- dual detector system and single beam- single detector system- SM series, the latter is used dominantly in Chinese steel industries. The performance comparison between domestic and foreign instruments as well as its developments and applications is presented in this paper.
文摘To evaluate the residual stress in TiAl based alloys by X ray diffraction, X ray elastic constants (REC) of a γ TiAl alloy were determined. From these results, the stress state of a given phase in a duplex TiAl based alloy under a uniaxial tensile loading has been characterized by X ray diffraction. The results show that the X ray elastic constants and the microscopic stresses of the given phase are different from the apparent elastic constants and the macroscopic stresses of the alloy. The reason of the different distribution of the alloy was also discussed. [
文摘A series of GaAs/InAs/GaAs samples were studied by double crystal X ray diffraction and the X ray dynamic theory was used to analyze the X ray diffraction results. As the thickness of InAs layer exceeds 1.7 monolayer, 3 dimensional InAs islands appear. Pendellosung fringes shifted. A multilayer structure model is proposed to describe the strain status in the InAs islands of the sample and a good agreement is obtained between the experimental and theoretical curves.
文摘The crystal structure of new compound Ba 3BPO 7 has been solved by X ray powder diffraction technique. As a new structure type, the positions of barium, boron and phosphate atoms have been determined by single crystal direct method after profile decomposition from Ba 3BPO 7 X ray powder diffraction patterns. The positions of oxygen atoms have been determined by the interpretation of their vibration spectra which indicate that in this crystal the boron and phosphorus atoms form BO 3 and PO 4 polyhedra. The structure has been refined by Rietveld technique based on the above model.
文摘Structural determination plays a pivotal role in chemical research by providing detailed insights into molecular architecture and functionality.Single-crystal X-ray diffraction(SCXRD)is widely regarded as the premier technique for achieving precise three-dimensional structural elucidation[1].The persistent challenge of determining atomic-level structures for non-crystalline or conformationally flexible molecules has driven transformative innovations in crystallographic methodologies[2-5].
基金supported by the National Nature Science Foundation of China(NSFC)(Grant Nos.22275004,62274040,and 62304046)the Shanghai Science and Technology Committee(Grant No.22JC1410300)+2 种基金the Shanghai Key Laboratory of Novel Extreme Condition Materials(Grant No.22dz2260800)the National Key Research and Development Program of China(Grant No.2022YFE0137400)the Shanghai Science and Technology Innovationaction Plan(Grant No.24DZ3001200).
文摘High-pressure research has emerged as a pivotal approach for advancing our understanding and development of optoelectronic materials,which are vital for a wide range of applications,including photovoltaics,light-emitting devices,and photodetectors.This review highlights various in situ characterization methods employed in high-pressure research to investigate the optical,electronic,and structural properties of optoelectronic materials.We explore the advances that have been made in techniques such as X-ray diffraction,absorption spectroscopy,nonlinear optics,photoluminescence spectroscopy,Raman spectroscopy,and photoresponse measurement,emphasizing how these methods have enhanced the elucidation of structural transitions,bandgap modulation,performance optimization,and carrier dynamics engineering.These insights underscore the pivotal role of high-pressure techniques in optimizing and tailoring optoelectronic materials for future applications.
基金National Key Research and Development Program of China(2022YFA1603503)National Natural Science Foundation of China(12075170)。
文摘Grating optics lie in the heart of X-ray spectroscopy instruments.The low efficiency and angular dispersion of conventional single-layer-coated gratings significantly limit the transmission and energy resolution of monochromators and spectrometers,particularly in the tender X-ray region(E=1-5 keV).Multilayer-coated blazed gratings(MLBGs)operating at high diffraction orders offer the advantage of achieving both high efficiency and high dispersion simultaneously.Tender X-ray monochromators and spectrometers using different high-order MLBGs have been designed,all demonstrating one to two orders of magnitude higher transmission compared to conventional systems.By employing a 2400 l/mm MLBG at the-4th or-8th diffraction order,the theoretical energy resolution of the instrument is improved by two to three times at 2.5 keV.Two MLBGs operating at the-2nd and-4th orders have been fabricated,showcasing remarkable efficiencies of 34%-12%at 2.5 keV,surpassing that of single-layer-coated gratings by an order of magnitude.Further optimization of manufacturing accuracy can yield even higher efficiencies.The measured angular dispersion agrees well with theoretical predictions,supporting the potential for high resolution.High-order MLBG optics pave the way for a new generation of tender X-ray monochromators/spectrometers that offer both high transmission and high resolution.
文摘In this paper, we report the use of blowing nitrogen gas for the successful fabrication of a composite layer composed of Ti/TiN on a substrate of commercially pure titanium （cp-2） using the friction stir processing technique. The prepared composite layer was characterized by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectrometry. The maximum microhardness of the Ti/TiN composite reached 1024 HV, which is 6.4 times higher than that of the titanium substrate. The results of wear test indicated that the Ti/TiN composite layer possesses excellent abrasive and adhesive wear resistance because of the formation of the TiN and its high hardness.
文摘Aim To prepare and characterize solid dispersions of silymarin with the intention of improving their dissolution properties. Methods The solid dispersions were prepared by the fusion method with polyethylene glycol 6000(PEG 6000) as the carrier. Evaluation of the properties of the dispersions was performed using dissolution studies, X ray powder diffraction and Fourier transform infrared (FT IR) spectroscopy. Results The rate of dissolution of silymarin was considerably improved as compared with pure silymarin when formulated in solid dispersions with PEG 6000. The data of the X ray diffraction showed some changes in the parameters of lattice spacing [ d ], peak position and relative intensities. FT IR together with those from X ray diffraction showed the absence of well defined drug polymer interactions. Conclusion The dissolution improvement of poorly soluble silymarin could be illuminated by the changes of the lattice parameters of PEG 6000 and the drug.
基金The Scholarship Supported by Ministry of Education of China for Research Abroad(No.3037[2006])the Excellent Doctoral Dissertation Foundation of Southeast University (No.YBTJ-0512)the National Basic Research Program of China(973Program)(No.2009CB623203)
文摘In order to investigate the effects of two mineral admixtures （i. e., fly ash and ground slag）on initial defects existing in concrete microstructures, a high-resolution X-ray micro-CT（ micro-focus computer tomography）is employed to quantitatively analyze the initial defects in four series of highperformance concrete （HPC）specimens with additions of different mineral admixtures. The nigh-resolution 3D images of microstructures and filtered defects are reconstructed by micro- CT software. The size distribution and volume fractions of initial defects are analyzed based on 3D and 2D micro-CT images. The analysis results are verified by experimental results of watersuction tests. The results show that the additions of mineral admixtures in concrete as cementitious materials greatly change the geometrical properties of the microstructures and the spatial features of defects by physical-chemistry actions of these mineral admixtures. This is the major cause of the differences between the mechanical behaviors of HPC with and without mineral admixtures when the water-to-binder ratio and the size distribution of aggregates are constant.
文摘The silicon-containing poly (amic acid)s were synthesized from bis (3, 4-dicarboxyphenyl) dimethylsilane dianhydride (SIDA), pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (4,4'-ODA) in N, N-dimethylacetamide (DMAc). The poly (amic acid) films were obtained by solution-cast method from DMAc solutions and thermally converted into transparent, flexible and tough polyimide films. The wide-angle X-ray diffraction diagrams revealed that all the polyimides possessed amorphous character, and the regulation of those polyimides were decreased with the increase of the molar ratio of SIDA to PMDA. Differential scanning calorimeter measurements showed that the introduction of SIDA to polyimide backbone would make glass transition temperature shift to lower temperature. Thermogravimetric analyses indicated that the silicon-containing polyimides lowered decomposition temperature as compared with PMDA/4, 4′-ODA polyimides. However, UV-visible transmission and reflection spectra showed that the optical transparency of silicon-containing polyimide thin films was superior to that of PMDA/4, 4'-ODA polyimide thin films.
