共查询到20条相似文献,搜索用时 62 毫秒
1.
以无水乙醇为溶剂、氨水为催化剂,利用正硅酸乙酯水解所得的SiO2微球为内核,以硝酸亚铈为铈源、六亚甲基四胺为沉淀剂,采用化学沉淀法制备了具有草莓状包覆结构的CeO2@SiO2复合颗粒.利用X射线衍射仪、透射电子显微镜、场发射扫描电镜、能谱仪、X射线光电子能谱仪、纳米激光粒度分布仪等对所制备样品的结构进行了表征.将所制备的包覆结构CeO2@SiO2复合磨料用于光学石英玻璃的化学机械抛光,采用原子力显微镜观察了抛光表面的微观形貌,并测量了表面粗糙度.结果表明,所制备的CeO2@SiO2复合颗粒呈规则球形,粒度分布均匀,粒径为150~200nm,且具有明显的草莓状包覆结构,大量纳米CeO2颗粒紧密包覆在SiO2表面.AFM测量结果表明,抛光后玻璃表面划痕得到明显改善,在10μm×10μm范围内表面粗糙度RMS值由1.65nm降至0.484nm. 相似文献
2.
铁系元素掺杂的Pt基疏水催化剂的制备及活性研究 总被引:2,自引:0,他引:2
以炭黑为载体、乙二醇为溶剂, 利用高压微波加热法分别制备了铁系元素(即Fe、Co、Ni三种元素)掺杂的Pt基二元催化剂. 采用TEM、XRD、EDX、XPS等手段分析了催化剂的微观结构. 活性金属粒子在炭黑载体表面分布均匀; Fe、Co、Ni掺杂后, 催化剂中活性金属粒子的粒径分布变窄, 平均粒径明显减小(由4.57nm分别降低至2.17、2.41、2.55nm); 催化剂中Pt存在Pt(0)、Pt(II)、Pt(IV)三种价态. 将催化剂分散于聚四氟乙烯乳液中, 采用自然浸渍法负载于泡沫镍, 制得Pt基疏水催化剂, 考查了其对氢-水液相交换反应的催化活性. 与单一Pt基疏水催化剂相比, 过渡金属掺杂后的二元疏水催化剂对氢-水液相交换反应的催化活性明显提高. 其催化活性由高到低依次为: PtFe/C/FN>PtCo/C/FN>PtNi/C/FN>Pt/C/FN. 催化活性的提高可能主要来源于催化剂活性金属粒径的减小. 此外, H2O分子在Fe系元素表面的解离行为也有一定的贡献. 相似文献
3.
4.
5.
6.
7.
8.
采用溶胶-凝胶法制备掺杂金属改性的TiO2光催化剂,并研究其光催化还原CO2制甲酸甲酯的反应效果。以钛酸丁酯为主要原料,制备纳米TiO2。通过改变金属掺杂量、焙烧温度、前躯体pH等,确定出适宜的催化剂制备条件。结合SEM、XRD、UV-vis等对催化剂进行了形貌、结构和吸光行为的表征。进而考察了其光催化还原CO2的活性。结果表明:溶胶-凝胶法制备掺杂金属的TiO2,可使金属均匀地分布于TiO2表面,经催化活性评价,获得适宜的掺杂元素和掺杂量,优选的制备条件为溶胶pH=2.5~3、凝胶焙烧温度500℃,在催化剂用量1mg/mL,光照强度2880μw/cm2的反应条件下,可有效地促进TiO2光催化还原CO2制甲酸甲酯。 相似文献
9.
负载型超小尺寸金属纳米颗粒在多相催化过程中表现出优异的催化性能.虽然已经发展了一些合成方法,但仍缺少便捷地合成超小尺寸催化剂的方法.通常情况下,加氢金属催化剂往往需要经过高温还原过程.但过量的还原剂,如H2,会导致金属纳米颗粒的聚集.本研究利用含有有机配体的钯前驱体合成了金属氧化物负载的超小尺寸钯催化剂.在惰性气氛下,通过简单的煅烧即可得到尺寸均一、超小的Pd纳米颗粒(~1 nm).有机配体中的-CHx基团与氧化物载体的表面氧物种反应促进了Pd物种的还原.同时,反应过程中原位产生的CO和氧空位稳定了超小尺寸纳米颗粒.该方法所制备得到的催化剂具有较高的抗烧结能力、优异和稳定的催化加氢反应性能. 相似文献
10.
通过采用不同金属催化剂进行乙烯催化裂解制备了具有不同微观结构的纳米炭纤维。利用纳米二氧化硅负载的铁、镍以及铁镍合金催化剂在适当的反应条件下分别制备了管状、实心鱼骨状以及空心鱼骨状的纳米炭纤维。由于金属催化剂与纳米二氧化硅间的强相互作用导致在低反应温度下也能达到高的反应活性,所以能够合成出高收率、小直径而且分布均匀的纳米炭纤维。不同结构的纳米炭纤维归因于金属催化剂的不同分散性以及不同的生长机理。通常利用铁催化剂进行乙烯裂解制备纳米炭纤维需要高于650℃,但是在我们的实验中发现500℃低温下利用纳米二氧化硅负载的铁催化剂进行乙烯裂解就能够合成出管状纳米炭纤维。 相似文献
11.
《International journal for numerical methods in engineering》2018,113(9):1488-1506
In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method. 相似文献
12.
Standards are the basis for production enterprises to organize production ex-factory inspection trade 《中国标准化(英文版)》2008,25(1):24-25
Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.…… 相似文献
13.
14.
A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa. 相似文献
15.
On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.…… 相似文献
16.
Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß. 相似文献
17.
C. Qihong W. Zhan‐Wen J. Yi J. Yehua L. Fei F. Hanguang 《Materialwissenschaft und Werkstofftechnik》2014,45(7):582-590
In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M2(B,C), (W,Mo)2(B,C), M3(B,C), M23(B,C)6 type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm2. The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K1 mill housing of bar mill. 相似文献
18.
Dimiter Hadjistamov 《材料科学与工程:中英文B版...》2019,(2):56-65
The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ... 相似文献
19.
《中国标准化(英文版)》2014,(4)
正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from 相似文献
20.
《中国标准化(英文版)》2014,(5)
正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively. 相似文献