Improved continuous precipitation kinetics and tensile properties of extruded AZ80 alloy through {10-12} twin formation

This study investigates the effect of{10-12}deformation twins on the continuous precipitation behavior of an extruded Mg-8.0Al-0.5Zn-0.2Mn(AZ80)alloy during aging.The extruded AZ80 alloy is compressed along the transverse direction to introduce{10-12}twins,followed by an aging treatment at 300℃.The extruded material exhibits a twin-free microstructure with low internal strain energy,whereas the pre-twinned material possesses abundant{10-12}twins and has high internal strain energy.The aging results reveal that the peak-aging time of the pre-twinned material(1 h)is one-eighth of that of the extruded material(8 h).Although Mg_(17)Al_(12)continuous precipitates(CPs)are observed in both the peak-aged materials,these CPs are much smaller and more densely distributed in the pre-twinned material despite the significantly shorter aging time.The CPs size in the peak-aged materials increases in the following order:twinned region in the pre-twinned material(0.47μm)<residual matrix region in the pre-twinned material(1.71μm)<matrix region in the extruded material(2.55μm).Moreover,the CPs number density in the twinned region of the pre-twinned material is approximately 11 times higher than that in the matrix region of the extruded material.The peak-aged pre-twinned material exhibits significantly higher tensile strength and ductility than the peak-aged extruded material.These results demonstrate that the formation of{10-12}twins in the extruded AZ80 alloy substantially accelerates the static precipitation of CPs during aging at 300℃and improves the tensile properties of the peak-aged material.

Preparation of Yb:YAG Transparent Laser Ceramics with Urea Co-Precipitation Method

YAG phosphor doped with Yb (3+) for transparent ceramics was prepared by the co-precipitation method with urea used as precipitant. DTA-TG,XRD,SEM and IR spectrum analyzers were used to investigate the structure and morphology of the precursor and the sintered poly-crystal. The results indicates that the weight loss is about 40% as the powder calcined at 1200 ℃,and well-crystallized YAG powder is obtained with particle size in the range of 100～150 nm. The SEM analysis of the fracture surface of the sintered body shows that the grain size is about 1～2 μm and the pore volume is very low. The ceramics body with favorite optical properties is obtained by sintering at 1700 ℃.

Improvement of 6–15 Day Precipitation Forecasts Using a Time-Lagged Ensemble Method

A time-lagged ensemble method is used to improve 6-15 day precipitation forecasts from the Beijing Climate Center Atmospheric General Circulation Model,version 2.0.1.The approach averages the deterministic predictions of precipitation from the most recent model run and from earlier runs,all at the same forecast valid time.This lagged average forecast （LAF） method assigns equal weight to each ensemble member and produces a forecast by taking the ensemble mean.Our analyses of the Equitable Threat Score,the Hanssen and Kuipers Score,and the frequency bias indicate that the LAF using five members at time-lagged intervals of 6 h improves 6-15 day forecasts of precipitation frequency above 1 mm d-1 and 5 mm d-1 in many regions of China,and is more effective than the LAF method with selection of the time-lagged interval of 12 or 24 h between ensemble members.In particular,significant improvements are seen over regions where the frequencies of rainfall days are higher than about 40％-50％ in the summer season; these regions include northeastern and central to southern China,and the southeastem Tibetan Plateau.

Efficient stabilization of dredged sludge with high water content using an improved bio-carbonation of reactive magnesia cement method

This study proposed an improved bio-carbonation of reactive magnesia cement(RMC)method for dredged sludge stabilization using the urea pre-hydrolysis strategy.Based on unconfined compression strength(UCS),pickling-drainage,and scanning electron microscopy(SEM)tests,the effects of prehydrolysis duration(T),urease activity(UA)and curing age(CA)on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed.The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80%high water content.A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing,which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples.Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield,but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates(HMCs),which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples.The optimum formula was determined to be the case of T?24 h and UA?10 U/mL for dredged sludge stabilization.A 7-day CA was enough for bio-carbonized samples to obtain stable strength,albeit slightly affected by UA.The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization.This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil,such as dredged sludge.

Controlled Synthesis of Dental Enamel-like Hydroxyapatite Whiskers via Hydrothermal Homogeneous Precipitation

Dental enamel-like hydroxyapatite whiskers with high crystallinity and homogeneous morphology were synthesized by a hydrothermal homogeneous precipitation method.The composition,crystallinity and morphology of prepared hydroxyapatite whiskers were characterized by Ⅹ-ray diffraction and scanning electron microscopy.The effects of urea and sorbitol on their morphology and composition were investigated.Homogeneous and well crystallized enamel-like hydroxyapatite whiskers with 1.17±0.08 μm in length and 84± 14 nm in width were obtained at 0.80 mol · L-1 urea and 0.26 mol · L-1 sorbitol.These hydroxyapatite whiskers may be close to nature hydroxyapatite dental enamel in terms of the morphology and composition,suggesting that they could have potential application as dental restorative materials in the field of stomatology.

COMPARISON STUDY ON THE INTRASEASONAL VARIATIONS IN CIRCULATIONS AND PRECIPITATION MODULATED BY THE TROPICAL CYCLOGENESIS OVER SOUTH CHINA SEA-WESTERN PACIFIC DURING GUANGDONG FLOODING PERIOD

Based on tropical cyclone datasets from Shanghai Typhoon Institute of China Meteorological Administration,the National Centers for Environmental Prediction (NCEP,USA) reanalysis data and the rainfall records from 743 stations in China,the impacts of cyclogenesis number over the South China Sea and the western Pacific are studied on the 30-60-day oscillations in the precipitation of Guangdong during the flooding period.The year with more-than-normal (less-than-normal) tropical cyclogenesis is defined as a 'high year' ('low year').In light of the irregular periodic oscillations,the method used to construct the composite life cycle is based on nine consecutive phases in each of the cycles.Phases 1,3,5,and 7 correspond to,respectively,the time when precipitation anomalies reach theminimum,a positive transition (negative-turning-to-positive) phase,the maximum,and a negative transition phase.The results showed that the precipitation of the 30-60-day oscillations is associated with the interaction between a well-organized eastward propagation system from the Arabian Sea/Bay of Bengal and a westward-propagating system (with cyclonic and anticyclonic anomalies in the northwest-southeast direction) from the South China Sea to western Pacific during the high years,whereas the precipitation is affected during a low year by the circulation over the South China Sea and western Pacific (with cyclonic and anticyclonic anomalies in the northeast-southwest direction).During the high year,the warm and wet air mass from the ocean to the west and south are transported to Guangdong by westerly anomalies and an enclosed latitudinal cell,which ascends in the Northern Hemisphere low latitudes and descends in the Southern Hemisphere low latitudes.During the low year,the warm and wet air mass from the ocean to the south is transported to Guangdong by southwesterly wind anomalies and local ascending movements.Because the kinetic energy,westerly,easterly shift,vertical velocity and vapor transportation averaged over (109-119° E,10-20° N) is stronger in high years than those in low years,the precipitation of the 30-60-day oscillations in Guangdong is higher in high years than that in low years.

Multi-time Scale Analysis of the Precipitation Series in Chengde City in Recent 58 Years

[ Objective] The research aimed to analyze variation rule of the precipitation series in Chengde City in recent 58 years. [Method] Mexi- can hat wavelet was used to analyze multi-scale characteristics of the monthly precipitation data in Chengde from 1951 to 2008. We revealed multi- time-scale complex structure of the precipitation change in Chengde, analyzed change cycles and mutation points of the precipitation series under different time scales, and identified primary period in each series. [ Result]There were high/low value centers of the precipitation under interdec- adal scale （more than 10 years）. Under interannual scale （below 10 years）, oscillation was complex and variable, but 4-year scale had obvious high-frequency oscillation. Wavelet variance analysis verified existence of the 4-year precipitation cycle, and M - K test also confirmed conclusions of the wavelet analysis. [ Conclusion] We could judge from alternating wet and dry conditions that the wet year decreased significantly, and the cur- rent Drecioitation was still less than normal.

Synthesis and luminescence properties of nanocrystalline Gd_3Ga_5O_(12):Eu^(3+) by a homogeneous precipitation method

Nanocrystalline Gd3Ga5O12:Eu3+ with cubic phase was prepared by a urea homogeneous precipitation method. X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric and differential thermal analysis (TG-DTA) and photoluminescence spectra were used to characterize the samples. The effects of the initial solution pH value and urea content on the structure of the sample were studied. The XRD results show that pure phase Gd3Ga5O12 can be obtained at pH =6 and pH =8 of the initial solution. The average crystallite size can be calculated as in the range of 24~33 nm. The average crystallite size decreases with increasing molar ratio of urea to metal ion. The results of excitation spectra and emission spectra show that the emission peaks are ascribed to 5D0→7FJ transitions of Eu3+, and the magnetic dipole transition originated from 5D0 →7F1 of Eu3+ is the strongest; the broad excitation bands belong to change transfer band of Eu?O and the host absorption of Gd3Ga5O12. An efficient energy transfer occurs from Gd3+ to Eu3+.

A STUDY ON RESPONSE OF PRECIPITATION IN CHINA TO MONSOON INTRASEASONAL OSCILLATION

Temporal and spatial evolution characteristics of the 30-60 day oscillation (intraseasonal oscillation, ISO) of summer rainfall in China and the effects of East Asian monsoon on the rainfall ISO are analyzed in this paper. Results show that the annual and decadal variations of the oscillation exist between 1960 and 2008, and the intensity is weakest in the late 1970s and early 1980s. In the typical strong years of the rainfall ISO obtained from empirical orthogonal functions (EOF mode 1), an anticyclone is in northwestern Pacific and a cyclone is in the east of China. In the typical weak years, the wind ISO is much weaker. The low-frequency zonal wind and water vapor transport from the low latitudes to mid-latitudes in the typical strong years, and the oscillation strength of diabatic heating is much stronger than that in the weak years of the rainfall ISO. The anomaly characteristics of the rainfall ISO show anti-phases between the Yangtze River basin and south of China. As for the typical strong years of the rainfall ISO in the Yangtze River basin (EOF mode 2), the main oscillation center of water vapor is in the east of China (20-30°N, 110-130°E). In the peak (break) phase of the rainfall oscillation, a low-frequency cyclone (anticyclone) is in the Yangtze River basin and an anticyclone (cyclone) is near Taiwan Island. In addition, the peak rainfall corresponds to the heat source in the Yangtze River basin and the heat sink in the Qinghai-Tibet Plateau. As for the typical strong years of the rainfall ISO in the south of China, the main oscillation center of water vapor is south of 20°N. In the peak (break) phase of the rainfall ISO, a low-frequency cyclone (anticyclone) is in the south of China and an anticyclone (cyclone) is in the Philippines. The peak rainfall corresponds to the heat source in the south of China and the South China Sea, and the heat sink in the west of Indochina.

Laboratory investigation of a new scale inhibitor for preventing calcium carbonate precipitation in oil reservoirs and production equipment

The formation of mineral scale is a complex problem during the oilfield operations. Scale inhibitors are widely used to prevent salt precipitation within reservoirs, in downhole equipment, and in production facilities. The scale inhibitors not only must have high effectiveness to prevent scale formation, but also have good adsorption- desorption characteristics, which determine the operation duration of the scale inhibitors. This work is focused on the development of a new scale inhibitor for preventing cal- cium carbonate formation in three different synthetic for- mation waters. Scale inhibition efficiency, optical density of the solution, induction time of calcium carbonate for- mation, corrosion activity, and adsorption-desorption ability were investigated for the developed scale inhibitor. The optimum concentration of hydrochloric acid in the inhibitor was determined by surface tension measurement on the boundary layer between oil and the aqueous scale inhibitor solution. The results show that the optimum mass percentage of 5 % hydrochloric acid solution in the inhi- bitor was in the range of 8 % to 10 %. The new scale inhibitor had high efficiency at a concentration of 30 mg/L. The results indicate that the induction period for calcium carbonate nucleation in the presence of the new inhibitor was about 3.5 times longer than the value in the absence of the inhibitors. During the desorption process at reservoir conditions, the number of pore volumes injected into the carbonate core for the developed inhibitor was significantly greater than the volume of a tested industrial inhibitor, showing better adsorption/desorption capacity.

Synthesis and Biological Activities of 2,4-Dichlorophenoxyacetyl(thio)urea and S-(+)-3-Methyl-2-(4-chlorophenyl)butyramide Derivatives

2,4-Dichlorophenoxyacetyl（thio）urea and S-（＋）-3-methyl-2-（4-chlorophenyl）butyramides were synthesized via acylation,aminolysis,esterification and addition reactions,and the partial new compounds have desirable bioactive activity.

Synthesis of 1-aryl-3-(3,4-dihydro-2H-chromen-5-yl) ureas as TNF-αinhibitors

A new series of compounds, 1-aryl-3-（3,4-dihydro-2H-chromen-5-yl） ureas, have been synthesized and their structures were confirmed by FAB-MS and IH NMR. The preliminary pharmacological screening showed that these compounds inhibited TNF-α production in lipopolysaccharide （LPS）-stimulated THP-1 cells.

Synthesis and Bioactivity of 1-((2-Carbamoylguanidino) (furan-2-ylmethyl)urea

1-((2-Carbamoylguanidino)(furan-2-ylmethyl)urea was synthesised by coupling purified furfural with urea. The compound was characterized by GC-MS, FTIR, and 1H-NMR. The pathogens, Escherichia coli, Salmonella typhi, Staphylococcus aureus and Bacillus subtilis were isolated and screened with different concentrations of 1-((2-carbamoylguanidino)(furan-2-ylmethyl)urea. All the pathogens were susceptible to the synthesized compound except Bacillus subtilis. Due to this broad spectrum of activity, 1-((2-Carbamoylguanidino)(furan-2-ylmethyl))urea) can be use for various medicinal purposes and is therefore encouraged for the development of a novel drug in future.

均匀沉淀法制备Al_(2)O_(3)负载的铜基催化剂及其催化合成吗啉的研究

以尿素为沉淀剂,通过均匀沉淀法制备了Al_(2)O_(3)负载的铜基催化剂。利用XRD、SEM和H_(2)-TPR等手段对催化剂进行表征,并考察活性组分铜镍摩尔比、载体质量分数和尿素摩尔分数对其催化合成吗啉的影响。结果表明,铜镍摩尔比为3∶1、载体质量占催化剂质量的40%、尿素物质的量占金属硝酸盐物质的量的5.25倍时,所制备催化剂具有最高的催化性能。相比于商品催化剂,均匀沉淀法制备的催化剂具有更低的还原温度、更小的平均粒径、疏松的表面结构和优良的稳定性。

尿酶对共沉淀法制备球形α-氧化铝的影响

本文以硫酸铝铵(AA)和尿素为原料,酶催化沉淀合成球形氧化铝前驱体,在1220℃高温焙烧,得到粒度均一,安息角为51.8°的α相球形氧化铝。在脲酶作用下,加快尿素的水解速度,沉淀反应从8 h缩短到2.5 h。并用XRD,SEM,激光粒度仪对前驱体及焙烧产物进行了表征。研究发现,颗粒的粒度分布可以由反应物的配比来控制,随着硫酸铝铵的量0.8 mol/L变为1.1 mol/L,氧化铝的中位径从5.6μm变为4.6μm。与碳酸铝铵法制备的球形氧化铝相比较,本工艺制备的球形氧化铝能直接干压成型,线收缩率为10.8%,密度为3.8 g/mL,满足精细陶瓷的要求。

尿素水解法制备(1-x)SnO_2·xSb_2O_3导电颜料的研究

以尿素为沉淀剂 ,利用均匀沉淀法制备 (1-x)SnO2 ·xSb2 O3 导电颜料 (以下简称ATO) ;探讨了导电机理 ,对不同制备方法进行了对比 ;

亚微米球形Y_(2)O_(3)粉体及其透明陶瓷的制备

Y_(2)O_(3)以其优良的物理化学性质和在280 nm~8μm宽频段内的高透明性,而广泛应用于激光介质或光学窗口等领域。制备高透明的Y_(2)O_(3)陶瓷是目前的研究热点和难点,而高质量的粉体是制备高透明Y_(2)O_(3)陶瓷的关键,尿素均相沉淀法以其爆发成核和均匀可控的阴离子释放机制成为制备单分散颗粒的主要方法。本工作以硝酸钇和尿素为原料,采用尿素均相沉淀法制备了单分散、亚微米级的球形Y_(2)O_(3)粉体。采用不同方法研究了Y_(2)O_(3)前驱体和煅烧后粉体的结构、物相演变和形貌。前驱体的颗粒尺寸约为330 nm,800℃煅烧2 h得到的Y_(2)O_(3)粉体尺寸约为260 nm。在800℃煅烧后即可得到纯相的Y_(2)O_(3)粉体,粉体呈球形,分散性好,且粒径均匀。以该Y_(2)O_(3)粉体为原料,添加原子分数0.3%的Nb_(2)O_(5)为烧结助剂,在1780℃通过真空无压烧结成功制备了透明Y_(2)O_(3)陶瓷。材料的光学性质优良,即样品(厚度1 mm)的直线透过率在1100 nm处达到76.9%,在400 nm处达到65.6%。本工作为制备性能优良的Y_(2)O_(3)透明陶瓷提供了一种新的方法。

以尿素为沉淀剂制备超细α-Al_2O_3粉体

以硫酸铝为原料,尿素为沉淀剂,采用均匀沉淀法制备了α-A12O3超细粉体。系统考察了反应温度、Al2SO·418H2O初始浓度以及沉淀剂用量对产率的影响。通过DTA-TG,XRD与SEM分析,研究了前躯体胶体的脱水过程及粉体的结构与形貌。结果表明,当前躯体在1200℃下煅烧时可得到结晶完善,纯度高,粒径均匀的球形超细α-A12O3粉体。

均匀沉淀(尿素水解)法合成CO_3^(2-)型MgAl-LDH

采用均匀沉淀法(尿素水解法)合成了高结晶度的CO32-型MgAl-LDH,探索了温度和时间对产物的影响.研究发现,n(Mg)/n(Al)进料比为2时,较低反应温度(如100℃)下很难得到n(Mg)/n(Al)=2的LDH.这可能与Mg(OH)2溶解度较高,Mg2+难以与Al3+一同沉淀有关.为提高产物n(Mg)/n(Al),我们采用提高n(Mg)/n(Al)投料比(如3∶1,4∶1,5∶1)的方法.研究发现,反应时间较短时,可得较纯的LDH相,但产物的n(Mg)/n(Al)远低于进料比;若反应时间延长,会出现水菱镁矿(hydromagnesite)和菱镁矿(magnesite,MgCO3)的杂相.由此推断,为得到高n(Mg)/n(Al)的LDH,不能单纯增加n(Mg)/n(Al)进料比,其他条件如尿素浓度,尤其是反应温度等也需改变.

超声波-微波辅助尿素基沉淀法制备超分散TiO_2颗粒

以Span80为表面活性剂,尿素为沉淀剂,采用化学沉淀法制备超分散TiO_2粉体颗粒,重点研究反应体系经常规加热、微波和超声波微波系统3种不同形式的能量场预处理后对所制备超分散TiO_2粉体形貌、粒径大小及分散性能的影响。通过FT-IR、XRD、Zeta粒度分析仪、SEM和TEM等手段加以表征。结果表明:Span80添加量为3%,尿素用量为理论量3倍时,Span80自身与所得产物无桥联作用引发的团聚,结合尿素缓慢分解,释放NH_3,解离产生-OH,所得产物TiO_2为锐钛矿型结构,且随着尿素含量的增加其粒径有所增大;以超声波微波系统为能量输入形式,且超声波占空比为0.4时,可有效控制TiO_2粉体颗粒的团聚性能、粉体形貌及粒径大小,在有机介质中的分散性最佳。