共查询到20条相似文献,搜索用时 46 毫秒
1.
纳米钛酸钡陶瓷的特殊烧结方法和新颖特性的研究进展 总被引:1,自引:0,他引:1
对近年来有关纳米钛酸钡陶瓷最新的烧结方法、新颖性质进行了综合评述和讨论。当晶粒尺寸减小到纳米尺度时,钛酸钡陶瓷的晶体结构在不同的温度下出现了不同的多相共存。这可以用纳米钛酸钡陶瓷相变产生的应力来解释。纳米钛酸钡陶瓷的铁电性能表现出新颖的特性。它的介电常数先随晶粒尺寸的减小而降低,但当晶粒尺寸降低到小于50nm甚至小于10m时,介电常数表现出反常的增加,同时铁电向顺电的转变峰变为一个很宽的峰,表现出弥散相变的特征。 相似文献
2.
3.
掺镍对钛酸钡陶瓷结构及介电性能的影响 总被引:1,自引:0,他引:1
采用溶胶-凝胶(Sol-gel)法制备均匀掺镍钛酸钡纳米晶粉体及其陶瓷.通过XRD和SEM对掺镍钛酸钡粉体及陶瓷进行表征,并测定陶瓷的介电性能,主要研究掺镍量对钛酸钡陶瓷的相组成、显微组织和介电性能的影响.结果表明:采用Sol-gel法制得掺镍钛酸钡基纳米晶立方相粉体(25nm),经烧结后可得到四方相钛酸钡.氧化镍在钛酸钡陶瓷中的溶解限约为0.9 at.%(约为固相掺杂时的2倍);掺镍量低于此溶解限时,随着掺镍量的增大,陶瓷晶粒的长大趋势受到抑制,陶瓷的居里温度降低;当掺镍量高于此溶解限时,陶瓷晶粒长大,陶瓷的居里温度保持在85℃;随掺镍量的增加,陶瓷最大介电常数εm呈先增大后减小的趋势. 相似文献
4.
5.
纳米BaTiO3及其陶瓷材料的特殊物性的研究 总被引:1,自引:0,他引:1
报导了硬脂酸凝胶法制备的BaTiO3纳米晶及烧制的陶瓷材料的特殊物性,用X射线衍射、高分辨透射电镜、X荧光光谱、表面光电子能谱、介电谱、热释电谱研究了纳一粉及陶瓷材料的晶体结构,晶粒尺寸体相和表面相组份及铁电性能。结果表明,所有样品在室温下均为立方结构,没有铁电性,陶瓷样品在低温下具有铁电性。并发现纳米晶BaTiO3及陶瓷具有湿敏特性。 相似文献
6.
7.
8.
PLT10纳米晶材料结构和性能的研究 总被引:2,自引:0,他引:2
本文用硬脂酸凝胶法合成了PLT10纳米晶,研究了粒径对微观结构和介电性能的影响。结果表明,随着粒径的减少,PLT10在室温下由四方相转变为立方相,晶胞参数发生明显变化。铁电-顺电相变温度随粒径的减少而增加;当粒子尺寸小于20nm时,相变消失。室温介电常数也随粒径呈规律性变化。 相似文献
9.
采用快速退火工艺在Pt/Ti/SiO2/p-Si衬底上制备了Bi4Ti3O12铁电薄膜.研究了退火温度对薄膜微观结构、铁电特性及介电性能的影响.研究表明:退火温度对Si基Bi4Ti3O12铁电薄膜晶相结构的影响显著,对晶粒尺寸和表面形貌的影响较小,但退火温度超过800℃后会出现焦绿石等杂相;低于750℃时,薄膜的剩余极化随退火温度升高而增大,高于750℃时却有所减小,但矫顽电场随退火温度升高而逐渐降低;退火温度对薄膜的漏电流密度有一定的影响,薄膜的漏电流密度在200kV/cm极化电场作用下低于3×10-9A/cm2,750℃时的剩余极化和矫顽电场分别为11μC/cm2和77kV/cm,具有较好的铁电和介电性能. 相似文献
10.
采用溶胶-凝胶结合二次煅烧的方法制备了高介电常数BaTiO3陶瓷,通过X射线衍射分析得到所制备的体系为四方相和立方相共存结构,从扫描电镜的图像中能观察其晶粒尺寸为1μm。通过TF2000铁电分析仪得到其介电常数在煅烧温度为1310℃,保温时间为4h,室温、测试频率为100Hz、测试电压为100V的条件下最大值为38306。研究了BaTiO3铁电陶瓷的反转电流随温度、频率和电压的影响规律,研究发现随着温度的升高反转电流缓慢降低,而随着电场和频率的增加反转电流迅速升高。从能量的观点也能进一步分析温度和电场对于反转电流的影响。 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.
Steffen Müller-Probandt 《材料科学与工程:中英文B版...》2018,(4):161-177
We associate a variety of innovations with the term "Industry 4.0". The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di... 相似文献
13.
A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils. 相似文献
14.
15.
Janet Lang 《Materials and Manufacturing Processes》2017,32(7-8):857-866
ABSTRACTThe production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them. 相似文献
16.
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
17.
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
18.
S. K. Malhotra Paramanand Singh A. Thirunavukkarasu 《Materials and Manufacturing Processes》2006,21(7):652-657
Al2O3-ZrO2 nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness. 相似文献
19.
The end of over unit products of more than Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits beer wine yellow wine fruit syrup wine others cover over % of the national top-branded liquor products.…… 《中国标准化(英文版)》2008,25(1):30
The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.…… 相似文献
20.
Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster. 相似文献