The paper presents the change in grain-size composition of lignite under cyclic freezing-thawing (FTC) and wetting-drying (WDC). The article shows that in the spring and autumn periods the lignites can be subjected to...The paper presents the change in grain-size composition of lignite under cyclic freezing-thawing (FTC) and wetting-drying (WDC). The article shows that in the spring and autumn periods the lignites can be subjected to repeated freezing-thawing and wetting-drying, which determines the possibility of changing their grain-size composition and structure. Experimental studies in laboratory conditions on the influence of cyclic freezing-thawing (FTC) and wetting-drying (WDC) on the quality indicators of lignites have been carried out, their granulometric (fractional) composition has been studied. Freezing-thawing cycle conditions are as follows (FTC): minimum exposure temperature: -20°C;maximum: +5°C;relative humidity: 30%;number of processing cycles: 3. Wetting-drying cycles are as follows (WDC): drying temperatures are +20, +40, +60, +80°C, drying time 90 minutes, the coals are further subjected to rain (soaking) for a period of water saturation to humidity of 30% - 40% and dry again. The number of wetting-drying cycles is 3 times. The tests have revealed the destructive effects of FTC and WDC on the samples of lower metamorphic grade coal, and the cycles of wet-dry lead to the much higher yield of fine sizes (-6+0;-13+0 mm) than the cycles of freeze-thaw. Furthermore, it is found that the increase in the yield of fines depends on the heating temperature: coal disintegration proceeds more intensively at a higher temperature of drying.展开更多
Surface sediments from the Changjiang River （Yangtze River） Estuary, Hangzhou Bay, and their adjacent waters were analyzed for their grain size distribution, organic carbon （OC） concentration, and stable carbon is...Surface sediments from the Changjiang River （Yangtze River） Estuary, Hangzhou Bay, and their adjacent waters were analyzed for their grain size distribution, organic carbon （OC） concentration, and stable carbon isotope composition （δ13C）. Based on this analysis, about 36 surface sediment samples were selected from various environments and separated into sand （〉0.250 ram, 0.125-0.250 ram, 0.063-0.125 mm） and silt （0.025-0.063 mm） fractions by wet-sieving fractionation methods, and further into silt- （0.004-0.025 mm） and clay-sized （〈0.004 mm） fractions by centrifugal fractionation. Sediments of six grain size categories were analyzed for their OC and 613C contents to explore the grain size composition and transport paths of sedimentary OC in the study area. From fine to coarse fractions, the OC content was 1.18%, 0.51%, 0.46%, 0.42%, 0.99%, and 0.48%, respectively, while the δ13C was -21.64‰, -22.03‰, -22.52‰, -22.46‰, -22.36‰, and -22.28%0, respectively. In each size category, the OC contribution was 42.96%, 26.06%, 9.82%, 5.75%, 7.09%, and 8.33%, respectively. The OC content in clay and fine silt fractions （〈0.025 ram） was about 69.02%. High OC concentrations were mainly found in offshore modern sediments in the northeast of the Changjiang River Estuary, in modern sediments in the lower estuary of the Changjiang River and Hangzhou Bay, and in Cyclonic Eddy modern sediments to the southwest of the Cheju Island. Integrating the distribution of terrestrial OC content of each grain size category with the δ13C of the bulk sediment indicated that the terrestrial organic material in the Changjiang River Estuary was transported seaward and dispersed to the Cyclonic Eddy modern sediments to the southwest of the Cheju Island via two pathways： one was a result of the Changjiang River Diluted Water （CDW） northeastward extending branch driven by the North Jiangsu Coastal Current and the Yellow Sea Coastal Current, while the other one was the result of the CDW southward extending branch driven by the Taiwan Warm Current.展开更多
The uniform transparent TiO2/SiO2 photocatalytic composite thin films are prepared by sol-gel method on the soda lime glass substrates, and characterized by UV-visible spectroscopy, X-ray diffraction (XRD), transmissi...The uniform transparent TiO2/SiO2 photocatalytic composite thin films are prepared by sol-gel method on the soda lime glass substrates, and characterized by UV-visible spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), BET surface area, FTIR spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that the addition of SiO2 to TiO2 thin films can suppress the grain growth of TiO2 crystal, increase the hydroxyl content on the surface of TiO2 films, lower the contact angle for water on TiO, films and enhance the hydrophilic property of TiO2 films. The super-hydrophilic TiO2/SiO2 photocatalytic composite thin films with the contact angle of 0((o) under bar) are obtained by the addition of 10%-20% SiO2 in mole fraction.展开更多
The high performance magnesium alloy was investigated by adding B2O3 in magnesium and magnesium alloys. Experiments include adding B2O3 in Mg, Mg-Al and Mg-RE alloys, respectively, studying the effects of B2O3 on the ...The high performance magnesium alloy was investigated by adding B2O3 in magnesium and magnesium alloys. Experiments include adding B2O3 in Mg, Mg-Al and Mg-RE alloys, respectively, studying the effects of B2O3 on the microstructure, were studied measuring the change of grain size and microhardness of the materials, discussing the change of grain size, morphology and distribution. The results show that adding 3% or 6%(mass fraction) B2O3 in Mg can bring twinning in Mg, adding B2O3 in Mg-Al alloys and Mg-RE alloys can refine the alloy grain size. Adding 3%B2O3 in Mg-6Al alloys can refine the average grain size by about 5μm, with the average hardness increased by 13.3% (53.3-60.4 HV0.03); adding 6%B2O3 in Mg-6Al alloys can refine the average grain size by about 13μm, with the average hardness increased by 15.8% (53.3-61.73 HV0.03); adding 3% and 6%B2O3 into Mg-6RE alloys can refine the grain size by about 5 and 9μm, respectively, with the average hardness decreased to HV0.03 64.66 and HV0.03 57.86, respectively from HV0.03 88.57. In the Mg-6Al alloy the content of aluminum is increased, while in the Mg-6RE alloy the content of oxygen is decreased. It can be concluded that it is beneficial to develop Mg-Al-B-O particle reinforce composite alloys, and it is feasible to develop nanometer crystallization of block material by Mg-B-O-RE.展开更多
There is fine and uniform clay with aluminous and ferrous cementation in the red clay found in Guigang, Guangxi. It has the characteristics of shrinkage outwardly, rigid upper but soft lower and well grown fissure. I...There is fine and uniform clay with aluminous and ferrous cementation in the red clay found in Guigang, Guangxi. It has the characteristics of shrinkage outwardly, rigid upper but soft lower and well grown fissure. In addition there are engineering characteristics such as high water content, low compactness and low compressibility, high strength and high contractility but slight expansibility. This paper discusses the red clay's engineering characteristics and its change regulation with depth by analyzing changes in the red clay's grain size composition, mineralogical constitution, and chemical composition.展开更多
The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si com...The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg_2Si particles(from 28 to 12 μm), the spacing of eutectic Mg_2Si(from 3 to 0.5 μm), and the grains of AA6061 alloy(from 102 to 22 μm). The morphology of the eutectic Mg_2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg_2Si phase and the grains in the Al–Mg_2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al–Mg_2Si composites and AA6061 alloy billets.展开更多
Alumina-Zirconia (Al2O3-ZrO2) composites especially Zirconia Toughened Alumina (ZTA) shows better mechanical properties over alumina. Al2O3-ZrO2 composites were prepared by powder compaction method varying 3 mol% yttr...Alumina-Zirconia (Al2O3-ZrO2) composites especially Zirconia Toughened Alumina (ZTA) shows better mechanical properties over alumina. Al2O3-ZrO2 composites were prepared by powder compaction method varying 3 mol% yttria stabilized zirconia (3Y-ZrO2) content from 0 to 20 vol% using small amount of MgO as sintering aid. The composites were sintered for two hours in air at 1580°C. At this temperature maximum density was achieved 99.31% of theoretical density for composite containing 20 vol% 3Y-ZrO2. Density measurement of sintered composites was carried out using Archimedes’s method. Hardness and fracture toughness measurement was carried out using Vickers indentation. Phase content and t-ZrO2 retention were detected by means of X-ray diffraction (XRD). Microstructure of the composites and grain size of alumina and zirconia was determined by Scanning Electron Microscopic (SEM) analysis. Maximum microhardness (17.46 GPa) was achieved for composite containing 5 vol% ZrO2 and maximum flexural strength (684.32 MPa) and fracture toughness (10.33 MPam0.5) was achieved for composite containing 20 vol% of 3Y-ZrO2. The aim of the present work is to investigate the optimum 3Y-ZrO2 content for obtaining maximum density, microhardness, flexural strength and fracture toughness of Al2O3-ZrO2 composites.展开更多
For developing high performance magnesium alloys, a new method in combination of B2O3 addition and melt stirring was applied. When 0, 3%, 6% and 12%( mass fraction) B2O3 was added into pure Mg, many twins were produce...For developing high performance magnesium alloys, a new method in combination of B2O3 addition and melt stirring was applied. When 0, 3%, 6% and 12%( mass fraction) B2O3 was added into pure Mg, many twins were produced in each alloy. The average grain size of Mg was about 200μm. In Mg-6Al alloy, the grain size is decreased from 50 to 35μm by B2O3 addition. In Mg-6RE (rare earth) alloys, the grain size is decreased from 35 to 15μm. The grain size of Mg-9Al- 6Ti-3B2O3 alloy is about 5μm. The hardness of pure Mg does not change by B2O3 addition. In Mg-6Al alloy, the hardness is increased by addition of 3% B2O3, however, the hardness of Mg-6RE alloy is decreased by B2O3 addition. Addition of B2O3 into Mg-Al, Mg-RE and Mg-Al-Ti alloys makes the fine grain structures, the hardness of Mg-RE alloy is decreased. This strange behavior may be interpreted with existence of many fine pores in the alloy. The mechanical properties of composite Mg-9Al-6Ti with 3%B2O3 are higher than those of AZ91C. The present results demonstrate the potential of this new method for developing high performance magnesium alloys.展开更多
文摘The paper presents the change in grain-size composition of lignite under cyclic freezing-thawing (FTC) and wetting-drying (WDC). The article shows that in the spring and autumn periods the lignites can be subjected to repeated freezing-thawing and wetting-drying, which determines the possibility of changing their grain-size composition and structure. Experimental studies in laboratory conditions on the influence of cyclic freezing-thawing (FTC) and wetting-drying (WDC) on the quality indicators of lignites have been carried out, their granulometric (fractional) composition has been studied. Freezing-thawing cycle conditions are as follows (FTC): minimum exposure temperature: -20°C;maximum: +5°C;relative humidity: 30%;number of processing cycles: 3. Wetting-drying cycles are as follows (WDC): drying temperatures are +20, +40, +60, +80°C, drying time 90 minutes, the coals are further subjected to rain (soaking) for a period of water saturation to humidity of 30% - 40% and dry again. The number of wetting-drying cycles is 3 times. The tests have revealed the destructive effects of FTC and WDC on the samples of lower metamorphic grade coal, and the cycles of wet-dry lead to the much higher yield of fine sizes (-6+0;-13+0 mm) than the cycles of freeze-thaw. Furthermore, it is found that the increase in the yield of fines depends on the heating temperature: coal disintegration proceeds more intensively at a higher temperature of drying.
基金The National Basic Research Program(973 Program)of China under contract No.2010CB428903the National Natural Science Foundation of China under contract Nos 41106050,41203085 and 41076036+1 种基金the Public Welfare Industry Research Specific Funding of China under contract Nos 201105014,201105012 and 201205008the Basic Scientific Research Fund of the Second Institute of Oceanography of State Oceanic Administration of China under contract Nos JG1108 and JG1219
文摘Surface sediments from the Changjiang River （Yangtze River） Estuary, Hangzhou Bay, and their adjacent waters were analyzed for their grain size distribution, organic carbon （OC） concentration, and stable carbon isotope composition （δ13C）. Based on this analysis, about 36 surface sediment samples were selected from various environments and separated into sand （〉0.250 ram, 0.125-0.250 ram, 0.063-0.125 mm） and silt （0.025-0.063 mm） fractions by wet-sieving fractionation methods, and further into silt- （0.004-0.025 mm） and clay-sized （〈0.004 mm） fractions by centrifugal fractionation. Sediments of six grain size categories were analyzed for their OC and 613C contents to explore the grain size composition and transport paths of sedimentary OC in the study area. From fine to coarse fractions, the OC content was 1.18%, 0.51%, 0.46%, 0.42%, 0.99%, and 0.48%, respectively, while the δ13C was -21.64‰, -22.03‰, -22.52‰, -22.46‰, -22.36‰, and -22.28%0, respectively. In each size category, the OC contribution was 42.96%, 26.06%, 9.82%, 5.75%, 7.09%, and 8.33%, respectively. The OC content in clay and fine silt fractions （〈0.025 ram） was about 69.02%. High OC concentrations were mainly found in offshore modern sediments in the northeast of the Changjiang River Estuary, in modern sediments in the lower estuary of the Changjiang River and Hangzhou Bay, and in Cyclonic Eddy modern sediments to the southwest of the Cheju Island. Integrating the distribution of terrestrial OC content of each grain size category with the δ13C of the bulk sediment indicated that the terrestrial organic material in the Changjiang River Estuary was transported seaward and dispersed to the Cyclonic Eddy modern sediments to the southwest of the Cheju Island via two pathways： one was a result of the Changjiang River Diluted Water （CDW） northeastward extending branch driven by the North Jiangsu Coastal Current and the Yellow Sea Coastal Current, while the other one was the result of the CDW southward extending branch driven by the Taiwan Warm Current.
基金This work was financially supported by the Foundation for University Key Teachers by the Ministry of Education, theKey Resear
文摘The uniform transparent TiO2/SiO2 photocatalytic composite thin films are prepared by sol-gel method on the soda lime glass substrates, and characterized by UV-visible spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), BET surface area, FTIR spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that the addition of SiO2 to TiO2 thin films can suppress the grain growth of TiO2 crystal, increase the hydroxyl content on the surface of TiO2 films, lower the contact angle for water on TiO, films and enhance the hydrophilic property of TiO2 films. The super-hydrophilic TiO2/SiO2 photocatalytic composite thin films with the contact angle of 0((o) under bar) are obtained by the addition of 10%-20% SiO2 in mole fraction.
文摘The high performance magnesium alloy was investigated by adding B2O3 in magnesium and magnesium alloys. Experiments include adding B2O3 in Mg, Mg-Al and Mg-RE alloys, respectively, studying the effects of B2O3 on the microstructure, were studied measuring the change of grain size and microhardness of the materials, discussing the change of grain size, morphology and distribution. The results show that adding 3% or 6%(mass fraction) B2O3 in Mg can bring twinning in Mg, adding B2O3 in Mg-Al alloys and Mg-RE alloys can refine the alloy grain size. Adding 3%B2O3 in Mg-6Al alloys can refine the average grain size by about 5μm, with the average hardness increased by 13.3% (53.3-60.4 HV0.03); adding 6%B2O3 in Mg-6Al alloys can refine the average grain size by about 13μm, with the average hardness increased by 15.8% (53.3-61.73 HV0.03); adding 3% and 6%B2O3 into Mg-6RE alloys can refine the grain size by about 5 and 9μm, respectively, with the average hardness decreased to HV0.03 64.66 and HV0.03 57.86, respectively from HV0.03 88.57. In the Mg-6Al alloy the content of aluminum is increased, while in the Mg-6RE alloy the content of oxygen is decreased. It can be concluded that it is beneficial to develop Mg-Al-B-O particle reinforce composite alloys, and it is feasible to develop nanometer crystallization of block material by Mg-B-O-RE.
文摘There is fine and uniform clay with aluminous and ferrous cementation in the red clay found in Guigang, Guangxi. It has the characteristics of shrinkage outwardly, rigid upper but soft lower and well grown fissure. In addition there are engineering characteristics such as high water content, low compactness and low compressibility, high strength and high contractility but slight expansibility. This paper discusses the red clay's engineering characteristics and its change regulation with depth by analyzing changes in the red clay's grain size composition, mineralogical constitution, and chemical composition.
基金financially supported by the Science and Technology Program of Guangzhou,China(No.2015B090926013)Postdoctoral Science Foundation of China(No.2015M581348)+1 种基金Postdoctoral Science Foundation of Northeastern University(No.20150302)the Doctoral Foundation of Chinese Ministry of Education(No.20130042130001)
文摘The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg_2Si particles(from 28 to 12 μm), the spacing of eutectic Mg_2Si(from 3 to 0.5 μm), and the grains of AA6061 alloy(from 102 to 22 μm). The morphology of the eutectic Mg_2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg_2Si phase and the grains in the Al–Mg_2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al–Mg_2Si composites and AA6061 alloy billets.
文摘Alumina-Zirconia (Al2O3-ZrO2) composites especially Zirconia Toughened Alumina (ZTA) shows better mechanical properties over alumina. Al2O3-ZrO2 composites were prepared by powder compaction method varying 3 mol% yttria stabilized zirconia (3Y-ZrO2) content from 0 to 20 vol% using small amount of MgO as sintering aid. The composites were sintered for two hours in air at 1580°C. At this temperature maximum density was achieved 99.31% of theoretical density for composite containing 20 vol% 3Y-ZrO2. Density measurement of sintered composites was carried out using Archimedes’s method. Hardness and fracture toughness measurement was carried out using Vickers indentation. Phase content and t-ZrO2 retention were detected by means of X-ray diffraction (XRD). Microstructure of the composites and grain size of alumina and zirconia was determined by Scanning Electron Microscopic (SEM) analysis. Maximum microhardness (17.46 GPa) was achieved for composite containing 5 vol% ZrO2 and maximum flexural strength (684.32 MPa) and fracture toughness (10.33 MPam0.5) was achieved for composite containing 20 vol% of 3Y-ZrO2. The aim of the present work is to investigate the optimum 3Y-ZrO2 content for obtaining maximum density, microhardness, flexural strength and fracture toughness of Al2O3-ZrO2 composites.
文摘For developing high performance magnesium alloys, a new method in combination of B2O3 addition and melt stirring was applied. When 0, 3%, 6% and 12%( mass fraction) B2O3 was added into pure Mg, many twins were produced in each alloy. The average grain size of Mg was about 200μm. In Mg-6Al alloy, the grain size is decreased from 50 to 35μm by B2O3 addition. In Mg-6RE (rare earth) alloys, the grain size is decreased from 35 to 15μm. The grain size of Mg-9Al- 6Ti-3B2O3 alloy is about 5μm. The hardness of pure Mg does not change by B2O3 addition. In Mg-6Al alloy, the hardness is increased by addition of 3% B2O3, however, the hardness of Mg-6RE alloy is decreased by B2O3 addition. Addition of B2O3 into Mg-Al, Mg-RE and Mg-Al-Ti alloys makes the fine grain structures, the hardness of Mg-RE alloy is decreased. This strange behavior may be interpreted with existence of many fine pores in the alloy. The mechanical properties of composite Mg-9Al-6Ti with 3%B2O3 are higher than those of AZ91C. The present results demonstrate the potential of this new method for developing high performance magnesium alloys.
基金the National Key Research and Development Program of China(No.2019YFB2006500)the High-tech Industry Technology Innovation Leading Plan of Hunan Province,China(No.2020GK2032)+1 种基金the Innovation Driven Program of Central South University,China(No.2019CX006)the Research Fund of the Key Laboratory of High Performance Complex Manufacturing at Central South University,China,for financial support。
