首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Nanometer-sized SnO2 particles were prepared by a sol-gel method using inorganic salt as a precursor material. Its crystallization was investigated by means of TG-DTA, IR absorption spectra, X-ray diffractometry and TEM as well as its resistivity change and the gas sensitivity varied with temperature were measured in various reducing gas. The results indicate that well-crystallized nano-sized SnO2 with size around 15nm can be obtained at annealing temperature 600°C. The activation energy for the growth of nano-SnO2 was calculated to be 26. 55kJ. mol−1 when the annealing temperature was higher than 500°C. The measurements also show that there is a peculiar resistance change varied with temperature for nano-SnO2. It has relevance to the increase in surface adsorbed oxygen. The selective detectivities to C4H10 and petrol can be increased when ruthenium ion was doped in nano-SnO2 as a catalyst and so do the gas sensitivity to CO, CH4, H2 etc. when rhodium ion was doped in. The detection to the several reducing gas can be realized when the temperature ranged from 260°C to 400°C.  相似文献   

2.
Using SnxTi1-xO2 as carriers, CuO/Sn0.9Ti0.1O2 and CuO/Sn0.7Ti0.3O2 catalysts with different loading amounts of copper oxide (CuO) were prepared by an impregnation method. The catalytic properties of CuO/Sn0.9Ti0.1O2 and CuO/Sn0.7Ti0.3O2 were examined using a microreactor-gas chromatography (GC) NO CO reaction system and the methods of BET (Brun- auer-Emmett-Teller), TG-DTA (themogravimetric and differential thermal analysis), X-ray diffraction (XRD) and H2-temperature programmed reduction (TPR). The results showed that NO conversions of Sn0.9Ti0.1O2 and Sn0.7Ti0.3O2 were 47.2% and 43.6% respectively, which increased to 95.3% and 90.9% at 6 wt% CuO loading. However, further increase in CuO loading caused a decrease in the catalytic activity. The nitrogen adsorption-desorption isotherm and pore-size distribution curve of Sn0.9Ti0.1O2 and Sn0.7Ti0.3O2 represented type IV of the BDDT (Brunauer, Deming, Deming and Teller) system and a typical mesoporous sample. There were two CuO diffraction peaks (2θ 35.5° and 38.7°), and the diffraction peak areas increased with increasing CuO loading. TPR analysis also detected three peaks (α, β and γ) from the CuO-loaded catalysts, suggesting that the α peak was the reduction of the highly dispersed copper oxide, the β peak was the reduction of the isolated copper oxide, and the γ peak was the reduction of crystal phase copper oxide. In addition, a fourth peak (δ) of the catalysts meant that the SnxTi1-xO2 mixed oxides could be reductive.  相似文献   

3.
INTRODUCTION As one of the main forming materials for warm- forging accurate forming technology, 20CrMnTi cemented alloy steel is usually employed in the fab-rication of wearable parts subjected to medium dy-namic load, such as change gear, gear shaft, cross pin end, hub splines, etc., which are extensively adopted in the automobile industry. The application of warm forging technology (Hirschvogel and Dommelen, 1992; Sheljaskov, 1994; Shivpuri et al., 1994; Siegert et al., 1997; Lange…  相似文献   

4.
苄醇催化脱水制取苄醚的研究   总被引：2，自引：0，他引：2  
以单质碘为催化剂直接由苄醇催化脱水生产苄醚．考察了影响收率的因素．其最佳条件为：苄醇：催化剂：带水剂=2mol：1．2g：40ml。反应在回流温度下进行(158～160℃)。反应时间4h。产率91．2％．  相似文献   

5.
Nanocrystalline Fe25Ni75 powders were prepared by the mechanical alloying process. They were investigated by X-ray diffraction and magnetic measurements. The ball milling time dependence of grain size, internal strain and magnetic properties has been discussed. The results show that the formation of Fe25Ni75 alloy phase is almost completed after milling for 30 hours. The reduction of grain size accompanied by the growth of internal strain was observed after extended milling. An average grain size about 10–20 nm of alloyed powders has been determined by Sherrer formula estimation. The saturation magnetisation Ms has a slight increase when the average grain size continues to decrease by intensive milling. This fine size of mechanically alloyed powders (10–20 nm) results in a single domain magnetic structure and the formation of superparamagnetic phase.  相似文献   

6.
Bread wheat varieties as influenced by different nitrogen levels   总被引：4，自引：2，他引：2  
INTRODUCTION Dera Ismail Khan lies in Pakistan’s arid zone (71.07° longitude, 31.57° latitude and 500 m above sea level). This zone is in the extreme south of (NWFP) Pakistan at the bank of the River Indus. Dera Ismail Khan is bounded by Sulaiman Range to the West, the Indus River on the East, Marwat and Bhit- tani Ranges on the North and Vehowa Nala (Punjab) on the South. Besides certain local variability the area is comprised of four basic divisions viz mountains, a series …  相似文献   

7.
SO4^2- / TiO2-La2O3, a novel solid superacid, was prepared and its catalytic activities at different synthetic conditions are discussed with esterification of n-butanoic acid and n-butyl alcohol as probing reaction. The optimum conditions have also been found, mole ratio of n（La^3＋）：n（Ti^4＋） is 1：34, the soaked consistency of H2SO4 is 0.8 tool/L, the soaked time of HESO4 is 24 h, the calcining temperature is 480 ℃, the calcining time is 3 h. Then it was applied in the catalytic synthesis often important ketals and acetals as catalyst and revealed high catalytic activity. Under these conditions on which the molar ratio of aldehyde/ketone to glycol is l： 1.5, the mass ratio of the catalyst used in the reactants is 0.5%, and the reaction time is 1.0 h, the yields of ketals and acetals can reach 41.4%-95.8%.  相似文献   

8.
The effects of salinity(50 mmol/L NaCl) and Cd(1 μmol/L CdCl2) as sole and combined on growth and photosyn-thetic parameters were studied using two soybean genotypes,Huachun 18 and NGB.The concentrations of Cd2 ,Zn2 ,Ca2 ,Mg2 ,K and Na were also determined in seeds and pods.Huachun 18 suffered a more serious decrease than NGB in net photosynthetic rate(Pn) in the treatments of salinity stress alone and combined stress(NaCl Cd),showing that it is relatively sensitive to salinity.The decrease in Pn caused by salt stress in Huachun 18 was mainly due to the reduced total chlorophyll content and photosynthetic efficiency(the ratio of variable fluorescence to maximal fluorescence,Fv/Fm),whereas the decease in NGB was mainly related to reduced stomatal conductance(Gs).The combined stress of both Na and Cd did not induce further decrease in photosynthesis and fluorescence in the two genotypes relative to salt or Cd stress alone.Greater change in the pod concentrations of Zn2 ,Ca2 ,Mg2 ,K and Na was detected under salt stress for Huachun 18 than for NGB.The results suggested that the interactive effect of NaCl-Cd on growth and nutrient uptake differs between the two soybean genotypes.  相似文献   

9.
In order to locate a reasonable heating system, the austenite grain growth behavior of Nb microalloyed medium carbon steel has been experimentally studied at various austenitizing temperatures and for different holding times. It is indicated that austenite grain growth increases with increasing austenitizing temperatures and holding times. Particularly when the austenitizing temperature was above 1100 °C, austenite grains grew rapidly, and an abnormal austenite grain growth was observed. When the austenitizing temperature was lower than 1100 °C, austenite grain size and growth rate were small. The activation energy of grain growth in the tested steel is 397 679.5 J/mol. To ensure an absence of coarse grains in microstructures, the heating technology of the tested steel should be controlled for 1 h at 1100 °C. The relationships of austenite average grain size with soaking temperature and time of tested steel were obtained by mathematical calculation, and austenite average grain size was found to be in agreement with the measured size for different holding times.  相似文献   

10.
Based on the laboratory experiments with the saltwater and freshwater replacing each other in the level sand column, taking the kaolin, illite, smectite, bivalent hydrargyrum ion (Hg2+) and phenol (C6H5OH) as examples, this paper studies the applications of water sensitivity in situ remediation in saltwater-freshwater transition zone. In the water sensitivity process, the release and migration of clay minerals can make the hydraulic conductivity (HC) decrease and pollutants remove. A new type of low penetrable or impenetrable purdah can be built by adding clay minerals into the sand media to replace the underground concrete impenetrable wall to prevent seawater intrusion, and a number of the heavy metals and organic pollutants in the sand media can be removed by in situ remediation. The results show that the content of kaolin and illite influences the water sensitivity process slightly, and HC of the sand columns descends from 0.011 cm/s to 0.001 4 cm/s and 0.001 2 cm/s respectively even if the content reaches 12% (weight ratio, sic passim). However, for smectite, HC descends sharply to about 1×10−8 cm/s when its content reaches 4%, and no water can flow through the sand columns beyond 5%. The particle release and migration processes can remove the Hg2+ and C6H5OH out of the sand columns efficiently, the removing rate of Hg2+ is 31.68% when the freshwater and saltwater are filtered through the sand columns polluted by Hg2+, while it is 67.55% when the water sensitivity occurs. With the same method, the removing rates of C6H5OH under the fluid flow and water sensitivity are 55.71% and 43.43% respectively. Supported by National Natural Science Foundation of China (No. 40572142). HAN Zhiyong, born in 1976, male, Dr, associate Prof.  相似文献   

11.
In this study, liquid-phase aerobic oxidation of toluene catalyzed by Mn–Mo oxide was conducted in a 1.0 L batch reactor. The macroscopic kinetics of toluene consumption and benzaldehyde generation at 413–443 K were obtained from a combination of experimental observation and hypothetical models. The results clearly showed that both the oxidation rate of toluene and generation rate of the aromatic product were proportional to the concentration of the substrate, the partial pressure of oxygen and the surface area of the catalyst. The energy barrier of toluene oxidation to benzyl alcohol was the highest(≈ 81 kJ mol~(-1)), while that of benzyl alcohol oxidation to benzaldehyde was the lowest(≈ 57 kJ mol~(-1)). Moreover, the activation energy of further oxidation of benzaldehyde in an acetic acid solvent was only slightly lower(≈ 1.9 kJ mol~(-1)) than that of toluene oxidation. Significantly, the transformation of benzyl alcohol indeed contributed to the generation of benzaldehyde and this step conformed to a first-order parallel-consecutive model. Increased reaction temperature and residence time favored the transformation of benzyl alcohol to benzaldehyde. In addition, doping with molybdenum at Mn/Mo = 3/1 enhanced the catalytic performance of the heterogeneous catalyst and was attributed to the presence of a synergetic effect between different metal cations. Regarding the microscopic kinetics, the LH-OS-ND mechanism(Langmuir–Hinshelwood adsorption of reagents on the same type of active sites and non-dissociative adsorption of oxygen) was verified as responsible for the heterogeneous oxidation of toluene. Oxygen and benzaldehyde were weakly adsorbed(Δ H_(ads,Oxy) ≈~(-1)5 kJ mol~(-1), Δ H _(ads)0,Bald) ≈-30 kJ mol~(-1)), but showed strong mobility(Δ S_(ads,Oxy) ≈-22 J mol~(-1) K~(-1)), Δ S_(ads,Bald) ≈-39 J mol~(-1) K~(-1)). The fundamental intrinsic rates were deduced based on the LH-OS-ND mechanism and showed great consistency with the macroscopic results.  相似文献   

12.
The copolymerization of CO and styrene catalyzed by Pd/C toward the formation of polyketones(PK)was studied in the N-valeronitrile-N'-methylimidazolium hexafluorophosphate([C4CNmim]+PF-6) medium. The synthesized PK was characterized by Fourier transform infrared(FTIR), elemental analysis, 13C-nuclear magnetic resonance(13C-NMR), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA) and gel permeation chromatography(GPC). The supported ionic liquid film on the surface of Pd/C catalyst can prevent the products from covering the hole of active carbon due to its chemical stability and weak coordination ability with metal ions, and thus efficiently improve the catalytic activity. The effects of different amounts of ionic liquid on the catalytic activity and reusability of the catalyst and the molecular weight of PK were discussed. When the usage of ionic liquid is 10wt%(0.1 g ionic liquid / 1 g active carbon carrier) and the theoretical content of Pd2+ is 5wt%(0.05 g Pd2+/ 1 g active carbon carrier), the highest catalytic activity 2 963.64 gSTCO/(gPd·h) is achieved with the molecular weight and polydispersity index of PK as Mn=9 684, Mw=13 452 and Mw /Mn=1.389.  相似文献   

13.
研究目的：研究高产黑曲霉突变菌株以玉米粉为原料的生物反应器扩大发酵,以期获得适合于工业化生产柠檬酸的发酵工艺。 创新要点：以玉米粉为原料,系统地研究了筛选得到的高产菌株在50L生物反应器中不同糖浓度发酵生产柠檬酸的特性,最终优化出适合于工业化生产柠檬酸的发酵工艺。 研究方法：（1）利用淀粉酶对粉碎后的玉米进行液化,然后过滤,最终得上清液;（2）以50L生物反应器作为发酵设备,对筛选得到的高产柠檬酸菌株进行扩大培养;（3）通过测定不同培养时期中积累的柠檬酸含量和剩余的残总糖,最终优化出高效率生产柠檬酸的发酵工艺。 重要结论：以不同糖浓度的液化玉米粉上清液作为碳源,突变菌株H4002能积累177．7--196．0g,L的柠檬酸,效率能达到2．96～3．27g/（L·h）,尤其当糖浓度为210g／L,H4002菌株表现出最佳的柠檬酸生产水平,如柠檬酸积累187．5g/L,生产效率达3．13g／（L·h）。上述结果说明了突变菌株H4002拥有快速生产柠檬酸的能力。  相似文献   

14.
This article reports first-principles band structure calculations forRMn6Sn6 (R=Tb, Dy). The calculation uses the linear muffin-tin orbitals (LMTO) method in the atomic-sphere-approximation (ASA), and yields results showing that both TbMn6Sn6 and DyMn6Sn6 are ferrimagnetic compounds with antiparallel aligned moments ofR and Mn atoms. In this research the 4f states ofR atoms are treated as localized states, i.e., the hybridization of 4f states with other valence electrons is neglected. The moments of Mn in both compounds were determined to be 2.43 μB and 2.38 μB, respectively. The considerably small additional moments for Mn from the spin-orbit coupling indicates that the spin-orbital coupling is not dominated for Mn atoms. The total moments of Tb and Dy atoms are 10.28 μB and 11.20 μB. All the calculation findings accorded well with experimental results. Project supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry of China.  相似文献   

15.
Astaxanthin (AST), a carotenoid molecule extensively found in marine organisms and increasingly used as a dietary supplement, has been reported to have beneficial effects against oxidative stress. In the current paper, the effects of AST on viability of prostate cells were investigated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay; cell apoptosis and intracellular reactive oxygen species (ROS) levels were determined by flow cytometry; the mitochondrial membrane potential (MMP) was measured by fluorospectrophotometer; and activities of malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) were evaluated by a detection kit. The results show that copper ion (Cu2+) induced apoptosis, along with the accumulation of intracellular ROS and MDA, in both prostate cell lines (RWPE-1 and PC-3). AST treatments could decrease the MDA levels, increase MMP, and keep ROS stable in RWPE-1 cell line. An addition of AST decreased the SOD, GSH-Px, and CAT activities in PC-3 cell line treated with Cu2+, but had a contrary reaction in RWPE-1 cell lines. In conclusion, AST could contribute to protecting RWPE-1 cells against Cu2+-induced injuries but could cause damage to the antioxidant enzyme system in PC-3 cells.  相似文献   

16.
To investigate the effect of doxorubicin(DOX) on gene expression of the myocardial sarcoplasmic reticulum (SR) Ca2+ transport proteins and the mechanism of taurine(Tau) protecting cardiac muscle cells, 9 rabbits were injected with DOX, 8 rabbits with DOX and Tau, and 9 rabbits with normal saline. Cardiac function, concentration of calcium in cardiomycocytes (Myo [Ca2+] i ), activity of SR Ca2+-ATPase (SERCA2a), level of SERCA2a mRNA and Ca2+ released channels (RYR2) mRNA were detected. The left ventricle tissues were observed by electron microscopy. The results showed that cardiac index, left ventricular systolic pressure, activity of SR Ca2+-ATPase and level of SERCA2a mRNA decreased, while Myo[Ca2+] i increased in DOX-treated rabbits. DOX could not affect the level of RYR2 mRNA. Tau intervention could alleviate the increase of left ventricular diastolic pressure, Myo[Ca2+] i and the decrease of SERCA2a mRNA induced by doxorubicin. The results suggested that downregulation of SERCA2a gene expression was an important mechanism of DOX-induced cardiomyopathy and that Tau could partially improve the heart function by reducing calcium overload and alleviating downregulation of SERCA2a mRNA.  相似文献   

17.
In this work we study the behaviour of the dielectric constant of BaTiO3 single crystals doped with Cu and Fe for different ion percentages, particularly, the influence of these hetemvalent substitutions on the ferroelectric-paraelectric phase transition whose temperature is found at Tc=120℃ for pure samples. The dielectric constant e in terms of temperature shows that the Curie temperature decreases when the quantity of impurities increases and presents a broadening and flattering of the maximum oft（T） within higher values, with the transition becoming more and more diffuse. It is interesting to have a material with very high permittivity （high-k） because of its capacity to store an important quantity of electric charges. The t anisotropy and the Curie-Weiss law are also verified with a good ratio between the slopes ofε^-l（T） from both sides of the transition, leading to a Curie constant： C= 13 × 10^4 K for BaTiO3：1.6%Fe in the polar phase. BaTiO3 is a displacive ferroelectric going through a first-order phase transition. The substitutions have an effect on the dynamics of the perovskite lattice. They induce charges transfer to Ti and a diminution of elastic forces in BaTiO3. Then we discuss the transition but on the nature of the material. fact that the maximum of permittivity does not depend on the phase  相似文献   

18.
Up-conversion processes for the blue, green and red emissions were found two-photon phenomenon, known as the cooperative phenomenon. This phenomenon was assisted by Nd3+ → Yb3+ → Ho3+ energy transfer. The strong green emission due to the Ho3+ : (5F4, 5S2)→ 5I8 transitions was observed in Nd3+-Ho3+ co-doped ZrF4-based fluoride glasses under 800 nm excitation. As an attempt to enhance Ho3+ up-conversion luminescences in the Nd3+ – Ho3+ co-doped ZrF4-based glasses, Yb3+ ions were added to the glasses. As a result it was found that, in 800 nm excitation of 60 ZrF4. 30BaF2. (8-x)LaF3. lNdF3. xYbF3. 1HoF3 glasses (x=0 to 7), sensitized up-conversion luminescences are observed at around 490 nm (blue), 545 nm (green), and 650 nm (red), which correspond to the Ho3+ : 5F3 → 5I8, ( 5F4, 5S2)→5I8 and 5F5→ 5I8 transitions respectively. The intensities of the green and red emissions in a 3 mol % YbF3-containing glass were about 50 times stronger than those glasses without YbF3. This is based on sensitization due to Yb3+ ions. In particular, the green emission was extremely strong and the Nd3+-Yb3+-Ho3+ co-doped ZrF4-based glasses have a high possibility of realizing a green up-conversion laser glass. In this paper the up-conversion mechanism in the glasses is discussed in detail.  相似文献   

19.
With InCl3·4H2O being used as raw materials, the precursor of nano-sized In2O3 powder was prepared by hydrolysis, peptization and gelation of InCl3·4H2O. After calcination, nano-sized In2O3 powder was obtained. The powder was characterized by thermo-gravimetric and differential thermal analysis (TG-DTA), X-ray diffractometry (XRD) and transmission electron microscopy (TEM), respectively. Calculation revealed that the mean crystalline size increased with increasing the calcination temperature, but crystal lattice distortion rate decreased with the increasing in the average crystalline size. This indicated that the smaller the particle size, the bigger the crystal lattice distortion, the worse the crystal growing. The activation energies for growth of nano-sized In2O3 were calculated to be 4.75 kJ·mol−1 at the calcination temperature up to 500°C; and 66.40 kJ·mol−1 at the calcination temperature over 600°C. TEM photos revealed that the addition of the chemical additive (OP-10) greatly influenced the morphology and size of In2O3 particles.  相似文献   

20.
题目：改良型多介质土壤渗滤系统对甲鱼养殖废水的净化效果研究
　　目的：通过向多介质土壤渗滤系统（MSL）的土壤层添加污泥,研究改进后的系统对工厂化甲鱼养殖废水的处理效果,分析系统内微生物群落的变化,以期部分揭示其可能的作用机理。
　　创新点：工厂化甲鱼养殖废水排放量日益增大,且水体氨氮含量较高。目前市场上缺乏针对甲鱼养殖废水的处理技术,MSL系统对该废水的处理也未有报道。本文在 MSL 系统的基础上进行改良,并将其应用于甲鱼养殖废水处理上,提出一套有效的甲鱼养殖废水处理技术,并对 MSL 系统内微生物群落结构进行了分析。
　　方法：向4套MSL小试装置中分别添加0%、5%、10%和20%污泥,研究其对工厂化甲鱼养殖废水的净化效果。试验中水质指标测定均按国家标准方法进行,系统内微生物群落结构采用聚合酶链反应-变性梯度凝胶电泳（PCR-DGGE）法测定。
　　结论：MSL系统可有效地处理工厂化甲鱼养殖废水,向系统中添加20%污泥后处理效果更佳。添加20%污泥的系统内具有较高的硝化类细菌多样性和都较多的生物量。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号