Impedance Characteristics of MgO-ZrO2 Ceramics Doped with CeO2

The ultrafine CexMg0.06Zr1-xO1.94 （ x = 0 16% ） powders were synthesized by a chemical co-precipitated method. The pressed compacts were sintered in air at 1300, 1400, 1500, 1600℃ for 3 h, respectively. The phase of the ceramics was characterized by the X-ray diffraction （XRD） method. The conductivity of the ceramics was measured by the AC complex impedance technique at 700- 1200 ℃. The ratio of the cubic phase in the ceramics improves with increasing CeO2 content, leading to a enlargement of the oxygen ionic migration channel. The contact resistance between conductive phase particles decreases with increasing CeO2 content, leading to a lower migration hindrance of the oxygen ionic. Consequently, the ionic conductivity of the ceramics improves with increas- ing CeO2 content. Additionally, an analysis for this phenomenon was also presented.     

Modified-EISA synthesis of mesoporous high surface area CeO_2 and catalytic property for CO oxidation

Mesoporous CeO2 particles with high surface area were synthesized using a modified evaporation-induced self assembly(EISA) method which combined citric acid as complexing agent.As-prepared powder and further thermal treatment samples were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),selected area electron diffraction(SAED),Fourier transform infrared spectrometer(FTIR),thermogravimetry and differential thermal analysis(TG-DTA),Brunauer-Emmett-Teller(BET) and Barrett-Joyner-Ha...     

离子型稀土矿浸出过程微细颗粒迁移规律及调控

离子型稀土矿在浸出过程中浸出剂与矿石表面水合机制较为复杂,颗粒间的桥式胶结因离子吸附交换过程中存在多种作用力与分散作用而容易发生断裂,从而使微细颗粒发生迁移和重新排列,并在孔喉处沉淀,产生堵塞现象,影响离子型稀土的浸出效率。为揭示离子型稀土矿在原地浸出过程中微细颗粒的迁移规律,并找到适宜的调控方法,以龙南足洞离子型稀土矿为研究对象,采用实验室柱式溶浸法,考察了浸出剂质量浓度、黏度、流速、水力梯度、矿体高度及矿体含水率对微细颗粒迁移的影响。结果表明,离子型稀土矿浸出过程微细颗粒的迁移是影响浸出效率的重要因素之一。在外力的作用下,微细颗粒在浸出过程中易随浸出剂发生迁移运动。当调控浸出剂质量浓度低于4%,浸出剂黏度不超过1.5 mPa?s,水力梯度小于0.75,浸出剂流速低于3 mL/min,原矿含水量大于11%时,矿体中微细颗粒迁移率较低,矿体渗透性保持良好,有利于浸出液的渗流和稀土离子的浸取。     

化学淋洗法对铀污染土壤的修复效果研究

采用振荡淋洗方法对三种粒径(+2mm、-2mm+0.15mm、-0.15mm)某尾矿库周边铀污染土壤进行去污试验,选用盐酸、硝酸、柠檬酸、草酸为淋洗剂,通过控制淋洗浓度、液固比、时间、温度、混合淋洗等因素来确定较优的淋洗条件。结果表明:各淋洗剂对铀污染土壤的去污效果为草酸盐酸硝酸柠檬酸;当淋洗浓度大于0.5mol/L、淋洗时间大于8h或液固比大于10∶1时,其淋洗效果都逐渐趋于稳定;提高淋洗温度可显著提升淋洗效果;选用草酸+盐酸和草酸+硝酸两组较优混合淋洗组合对全粒径土壤进行淋洗时,土壤中铀去除率均达50%以上,总含铀量分别降至27.15、24.32mg/kg,均达到土壤修复目标(40mg/kg)。     

微波热解法制备氧化铈过程的可视化研究

针对传统液相法制备氧化铈纳米颗粒存在工艺流程复杂、高污水排放等问题,提出了一种高效绿色的实验方案,以七水合氯化铈为原料,采用微波射流热解技术制备出了高纯度氧化铈纳米颗粒.通过X射线衍射仪(XRD)、扫描电镜(SEM)和能谱仪(EDS)分析手段对产物进行了表征,借助数值模拟手段可视化分析了各物理场、各组分分布.考察了不同工艺条件(热解温度、气相速度、和添加柠檬酸)对实验产物中残余氯根含量和产物微观形貌的影响.结果表明,热解温度达到500℃时便可获得单相氧化铈,温度越高氧化铈纯度越高,颗粒形貌越规则.增大气相入口速度导致产物残余氯根增多,但有利于改善颗粒团聚.添加柠檬后氧化铈从球状颗粒逐渐破碎为伴有少量多孔结构的不规则形状颗粒,颗粒比表面积增大.柠檬酸浓度大于0.1 mol?L^-1后利于减少氯根含量.     

上海苏州河底泥重金属淋洗效果的研究

采用批提取实验n）atchexperiment）,利用柠檬酸溶液、酒石酸溶液、聚天冬氨酸溶液及EDTA溶液依次淋洗受重金属污染的苏州河底泥。分析不同溶液在不同浓度下其淋洗液中的重金属含量及其浸提率,优化重金属淋洗试剂及其相应的浓度。结果表明,柠檬酸溶液、酒石酸溶液和EDTA溶液对底泥重金属均有显著的淋滤效果．其中．柠檬酸溶液的淋洗效果最好,其浓度为0．75mol／L时,对不同重金属的浸提率均在90％以上。聚天冬氨酸溶液对重金属的浸提能力相对较差,对底泥中的Cu淋洗能力较强,但浸提率亦不足60％。聚天冬氨酸对碳酸盐态重金属有较好的淋洗效果．酒石酸淋洗可去除交换态、碳酸盐结合态和氧化物结合态的重金属。     

镧-钼复合氧化物超细微粒催化剂的合成及表征

以柠檬酸为络合剂,采用溶胶-凝胶法合成了镧-钼复合氧化物超细微粒催化剂,使用DTA-TG、IR、XRD以及BET比表面测试等表征手段,考察了制备条件与热处理条件对复合氧化物超细微粒形成、结构和表面积的影响.结果表明本方法制备的La2(MoO4)3复合氧化物的比表面积远远大于共沉淀法制得的类似样品的比表面积,在氮气气氛中分解镧-钼凝胶中的柠檬酸,可有效地避免柠檬酸分解发生氧化燃烧而引起微粒烧结.     

Citric Acid Enhanced Remediation of Soils Contaminated with Uranium by Soil Flushing and Soil Washing

Laboratory bench-scale soil washing (batch) and flushing (column flow) experiments were conducted to determine the efficiency of citric acid as an agent to extract uranium from a synthetically contaminated sandy soil. The results of soil washing and flushing experiments indicate that citric acid is highly effective in removing uranium, and that the extraction efficiency increases with increasing citric acid concentration, especially under slightly acidic to alkaline conditions in systems containing sand coated with secondary minerals (e.g., Fe). The enhanced U(VI) desorption in the presence of citrate may be explained through several processes, including the complexation of U(VI) with citrate and extraction of secondary coatings (e.g., Fe), which results in the liberation of Fe-citrate complexes into solution. In batch washing systems, the presence of 10?3?M citric acid enhances the extraction of uranium 2.8 times greater than water alone for the conditions of the experiment. A comparison of soil washing and flushing shows that the extraction efficiency is higher in bench-scale washing experiments. A removal efficiency of up to 98% was achieved with 10 mL of 10?3?M citric acid in batch systems, whereas it required 4 pore volumes (150 mL) of 0.1 M citric acid to accomplish similar extraction efficiencies in column soil flushing systems.     

吸光比浊法测定硝酸钴溶液中硫酸根

研究了用吸光比浊法检测硫酸根的最佳实验条件并建立了硝酸钴溶液中硫酸根的测定方法。在稀盐酸介质中,当温度为50℃时,SO₄^2-与Ba²⁺反应生成BaSO₄的细微颗粒,有保护剂(OP乳化剂-乙醇溶液)存在时,这种细微颗粒能均匀悬浮在溶液中,并且在390nm波长处硫酸根浓度与吸光度成良好的线性关系。实验表明,稳定剂的最佳加入量为5mL,温度在50～60℃时溶液浊度值在40min之内保持稳定,硫酸根的测定范围为1～8μg/mL,样品的加标回收率在95%～105%之间。方法应用于硝酸钴溶液的分析,SO₄^2-的测定值与离子色谱法的测定值相符。     

膨润土去除铅的研究

赤峰高纯膨润土,蒙脱石的含量较高,是一种具有的药用价值的钙基膨润土,但其铅量高达49.6 ppm,超过国家和出口标准。因此,如何降低该膨润土的含铅量至关重要。以柠檬酸为络合剂,对钙基膨润土中的铅进行去除。考察了络合剂种类、络合剂用量、反应温度、反应时间和料浆浓度等因素对膨润土除铅效果的影响。结果表明:最佳柠檬酸用量为50g/L,反应温度150℃,反应时间300 min,料浆浓度6%,得到的膨润土中固体铅含量9.15ppm,达到了((10 ppm)的国家标准,可作为药用膨润土的原料。因此,研究除去该钙基膨润土中的铅,使其达到药用膨润土的要求,对充分利用和开发该膨润土具有重要意义。     

Effect of various demineralizing agents on mineral contents of cementum surfaces (an electron probe analysis)

The purpose of this investigation was to determine the surface morphology and mineral content of periodontally diseased cementum surfaces following root planing and conditioning with either citric acid, tetracycline HCL and minocycline HCL. Mineral contents of cementum surfaces were determined with an electron probe. All 3 demineralizing agents caused the exposure of the collagen matrix on the root surface but citric acid was the more effective. Calcium (Ca) and phosphorus (P) showed higher values in citric acid and minocycline HCL treated cementum surfaces compared to nondiseased cementum surfaces. The Ca and P were found to be in similar proportions in the tetracycline HCL treated group and nondiseased cementum surfaces. Although citric acid is a strong demineralizing agent, our specimens' cementum surfaces to which citric acid was treated showed high Ca and P content. In our opinion this difference about the effects of demineralizing agents on the surface morphology and surface element content was found to be related to the facts that whether the total amount of hypermineralized cementum as removed or not with root planing and the lacking criteria to detects the amount of this removal. Our findings suggest that these demineralizing agents can demineralize cementum surface after root planing but can not remove all of the hypermineralized diseased cementum. For this reason, it may be stated that it is more important to remove the pathologically altered cementum than applying various chemical agents.     

Activity improvement of Pt/C catalysts by adding CeO2 nanoparticles

Carbon-supported platinum catalysts were prepared by NaBH4 reduction of metal precursors and the CeO2 nanoparticles were pre-pared by citric acid sol-gel method.The structure and morphology of two kinds of nanoparticles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM),respectively.The Pt particles were uniformly dispersed on the carbon surface and showed the rod-like morphology.The CeO2 was spherical in shape.The appropriate amount of CeO2 nanoparticles was added into Pt/C sys-tems to improve activity of the catalysts.Several electrochemical techniques such as cyclic voltammogram (CV),chronoamperometry (I-t) and electrochemical impedance spectroscopy (EIS) were used to investigate the properties of CeO2-Pt/C catalysts for methanol electrooxidation in 1 mol/L CH3OH+0.5H2SO4 aqueous solutions.The results revealed that compared with Pt/C catalysts CeO2-Pt/C exhibited a higher activity and stability for methanol electro-oxidation.Moreover,the effect of CeO2 content on the activity of Pt/C catalysts was discussed in detail.     

Sensitivity of the cough reflex in awake guinea pigs, rats and rabbits

BACKGROUND AND AIM: Medical literature provides heterogeneous author's opinions concerning the application of various laboratory animals to cough research. Therefore the cough response to chemical stimuli was compared in awake guinea-pigs, rats and rabbits. METHODS: 15 adult guinea-pigs (TRIK strain) of mean body weight 435 +/- 35 g, 28 adult rats (WISTAR strain) of mean body weight 400 +/- 30 g, and 18 rabbits of mean body weight 3.2 +/- 0.3 kg were used. Awake animals were inhaling the aerosols of both citric acid and capsaicin. Animals were placed in a bodyplethysmographic box and two procedures of chemical stimulation were used: 3-5 minutes lasting inhalation of overthreshold concentration of tussive agents, and the second procedure resided in an exposure to a dose-response study with doubled concentrations of citric acid. The cough was analysed on the basis of air-flow changes measured by pneumotachograph. The effect of mechanical stimulation of airway musosa was studied in 13 rats anaesthetised by urethane (1 g/kg b.w., i.p.). The cough was then analysed on the basis of changes in pleural pressure measured by electromanometer using pleural cannula. RESULTS: All awake guinea-pigs were coughing during the exposure to both citric acid and capsaicin, too. Citric acid was potent to elicit cough in 42.9% of awake rats and capsaicin only in 28.6% of them. 61.1% of rabbits expossed to citric acid were coughing. Capsaicin was ineffective to produce cough in rabbits. The highest intensity of cough was in guinea-pigs. Guinea-pigs were the species reacting most intensively to citric acid dose-response exposure. The intensity of cough was not correlated with the concentration of citric acid in awake rats and rabbits. Mechanically induced cough was present in 53.8% of exposed rats under light urethane anaesthesia. CONCLUSIONS: 1. Guinea-pigs are the most useful laboratory animal for experimental studies of chemically induced cough. 2. The sensitivity of cough reflex in awake guinea-pigs could be characterised by the relationship between the intensity of cough and the concentration of the tussive agent. 3. The mechanically induced cough could be elicited in half of the rats under light urethane anaesthesia. (Fig. 4, Tab. 1, Ref. 21.)     

低温燃烧法制备Ce_(0.8)Sm_(0.2)O_(1.9)电解质固溶体及其烧结性能的研究

采用柠檬酸–硝酸盐低温燃烧合成法,以Ce(NO_3)_3·6H_2O为氧化剂,柠檬酸为还原剂,制备Sm_2O_3掺杂的Ce_(0.8)Sm_(0.2)O_(1.9)(SDC)超细粉体,利用XRD、TG-DSC、FT-IR、SEM及FESEM等手段对制备样品的晶相结构、热分解过程、微观形貌以及团聚情况进行研究.结果表明:柠檬酸与硝酸盐组成的干凝胶自蔓延燃烧点火温度为270.0℃;粉体经600℃焙烧2 h后,形成了单一立方萤石型结构的固溶体,平均晶粒度为18.80 nm.粉体的结晶性能完善,分散性能良好,粒子间仅有微弱的软团聚.将素坯在1 250℃烧结2 h,即可得到相对密度为95.5%的陶瓷烧结体.     

Chemical Vapor Synthesis of Titanium Aluminides by Reaction of Aluminum Subchloride and Titanium Tetrachloride

A new process for developing titanium aluminides (TiAls) using chemical vapor synthesis was investigated in a laboratory experiment. Aluminum subchloride (AlCl) was used as the reducing agent in the reaction with TiCl₄ and the source of aluminum for Ti-Al alloy. Two types of products, with large crystals and fine particles, were fabricated. The large crystals were determined to be TiAl, with small amounts of Ti and Ti₃Al phases. The composition of fine particles, on the other hand, varied in wide range.     

酸沉淀法制备超微细球形钨粉

以钨酸铵为原料,在超声和机械搅拌下与强酸发生反应得到钨酸沉淀,再经干燥、研磨、过筛后在常规氢气炉中进行还原得到钨粉。研究了酸的种类及用量和分散剂对钨粉粒度、颗粒形貌及分散程度的影响。结果表明,强酸种类及用量都对钨粉形貌产生影响,当硫酸与钨酸铵的体积比为17∶100时所得钨粉粒度均匀且近乎球形。此外,采用硫酸为沉淀剂的反应体系中(H2SO4∶(NH4)2WO4=17∶100),分散剂十二烷基硫酸钠的加入可使钨粉粒度更均匀,颗粒更分散,形状为球形,平均粒径1.5μm左右。     

Effects of hyperbaric oxygen therapy on perfusion parameters and transcutaneous oxygen measurements in patients with intramedullary nailed tibial shaft fractures

Midazolam is a benzodiazepine with short elimination half-life, used as induction or continuous agent for general anesthesia. At present, only injectable solution is available from French hospital pharmacies. The aim of the study is the development of 5 mg midazolam sublingual tablets to realize a short general anesthesia without intravenous or intramuscular injection. Incorporation of citric acid in the tablet formulation leads to an increase of dissolution rates of active drug, but a decrease of diffusion through lipid membranes is observed with 10 mg of citric acid when using the Dibbern's Resomat three phases apparatus. One explanation of this result is that midazolam (pKa = 6.1) in presence of 10 mg of citric acid is ionised. The ionised form, more hydrophilic, cannot cross the artificial lipid membrane and therefore the diffusion decreases. On the other hand, the decrease of diffusion's rate, when pH increases, is explained by the precipitation of midazolam at pH higher than 6. A compromise between dissolution and diffusion results leads us to choose the sublingual formulation containing 5 mg of citric acid per tablet.     

非对称Fe_3Al金属间化合物粉末滤芯研究

采用湿法喷涂与真空高温烧结工艺,制备非对称Fe_3Al金属间化合物粉末滤芯。利用扫描电子显微镜、能谱仪及X射线衍射仪等设备,观察与分析了滤芯的微观形貌、成分及物相。研究了不同表面膜层厚度滤芯样品的孔隙特性,分析了黏结剂与固化剂对滤芯力学性能的影响,测试了实验样品表面膜层与基体的结合强度。结果表明:经真空高温烧结之后,滤芯表面膜层颗粒仍为球状形貌,颗粒之间形成了相互连接的烧结颈;粗大的滤芯基体颗粒与细小的膜层颗粒之间也形成了烧结颈,两者发生了冶金结合;表面膜层厚度在200μm时,孔径与渗透性具有较好的匹配关系;黏结剂与固化剂对滤芯力学性能没有明显影响;滤芯表面膜层与基体的结合强度高于25 MPa。     

Citrate sol-gel combustion preparation and photoluminescence properties of YAG:Ce phosphors

Yellow-emitting YAG:Ce3+ nanocrystalline phosphors were prepared by citrate sol-gel combustion method using citric acid as the fuel and chelating agent. The influence of mole ratio of citric acid to metallic ions (MRCM), pH value of the solution, calcination temperature and Ce-doped concentration on the structures and properties of as-prepared powders were investigated in detail. Higher crystallinity and better luminescence performance powders were obtained at MRCM=2, pH=3 and the calcination temperature of 1200 °C. The phosphors exhibited the characteristic broadband visible luminescence of YAG:Ce. The optimum concentration of Ce3+ was 1.0 mol.%, and the concentration quenching was derived from the reciprocity between electric dipole and electric quadrupole (d-q). Especially, the pH value of the solution was a key factor to obtain a stable sol-gel system and then obtain pure and homogeneous rare earth ions doped YAG phosphors at a lower tem-perature. The Y3Al5O12:Ce0.03 phosphor with optimized synthesis-condition and composition had a similar luminescence intensity with the commercial phosphor YAG:Ce.     

Citric Gel Synthesis and Luminescent Properties of Ce^3＋-Activated SrGa2O4 Phosphor

Ce^3＋-activated SrGa2O4 phosphor was synthesized by a method of citric gel,wherein citric acid served as a chelate agent,and the as-synthesized powder was calcined in a slightly reduced ambient.The crystallization characteristics of the sample varied with the calcining temperature.Compared with the phosphor prepared by the solid-state reaction,the phosphor synthesized by citric gel was calcined at a relatively lower temperature.Consequently,the volatilization of Ga2O3 during high-temperature calcining process was avoided.The typical double-peak emission of Ce^3＋ originated from 2D（5d）→4F5/2（4f）,and 2D（5d）→4F7/2（4f）was observed,and the intrinsic emission of SrGa2O4 host was much restricted.The emission intensity varied with the calcining temperature because the different crystallinity and the optimal concentration of Ce-dopant was determined at 3%.