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 15 毫秒
1.
储召华  郝桂霞 《化工时刊》2009,23(12):47-48
利用水溶液降温法生长了掺杂稀土离子Nd^3+、L-赖氨酸和硫脲的TGS晶体。测试了掺杂TGS晶体的晶胞参数和热释电性能。实验表明,三掺杂的TGS晶体的热释电系数、热释电优值比和内偏压场大于纯TGS。  相似文献   

2.
《Ceramics International》2022,48(15):21451-21458
During the deposition of a-C:H film, defects (pinholes or discontinuities) caused by excessive stress will inevitably appear, which will reduce the corrosion resistance of the a-C:H film. In this study, top a-C:H:Si:O layers (thickness of approximately 0.3 μm) on the surface of a-C:H films were deposited on a large scale by PACVD technology using acetylene (C2H2) and/or hexamethyldisiloxane (HMDSO) as reactants, to improve the corrosion resistance of a-C:H films while ensuring the appropriate overall hardness of the films. The corrosion behaviors of the films were studied by electrochemical impedance spectroscopy (EIS) and Tafel polarization. We found that the a-C:H/a-C:H:Si:O films possess a lower electrolyte penetration rate due to their stronger capacitance characteristics. In addition, the corrosion current density of the a-C:H/a-C:H:Si:O films (10?10 A cm?2) were reduced by 2 orders of magnitude compared to the a-C:H film (10?8 A cm?2), and by 3 orders of magnitude compared to 316 stainless steel (10?7 A cm?2). The impedance results obtained by EIS were simulated using appropriate equivalent circuits, and the corresponding electrical parameters were used to further verify the electrochemical protection behavior of the top a-C:H:Si:O layer.  相似文献   

3.
4.
5.
在LiNbO3中掺进CeO2 ,MnCO3生长Ce∶LiNbO3和Ce∶Mn∶LiNbO3晶体 ,晶体被极化和还原处理。X射线衍射仪测试晶体的晶格常数 ,采用UV -Spectrophotometer测试晶体的吸收光谱。讨论了掺杂离子对晶格常数的影响、掺杂离子在晶体中的占位及使LiNbO3晶体吸收边发生红移的机理。利用二波耦合实验测试了晶体的指数增益系数、衍射效率和响应时间 ,结果表明 :Ce∶Mn∶LiNbO3晶体的最大指数增益系数达到 2 2cm- 1 ,Ce∶LiNbO3晶体的最大指数增益系数为 17cm- 1 ;Ce∶Mn∶LiNbO3和Ce∶LiNbO3晶体的有效载流子浓度分别为 0 .4× 10 1 5cm- 3和 0 .2× 10 1 5cm- 3;最大衍射效率分别为 85 %和 72 % ;Ce∶LiNbO3和Ce∶Mn∶LiNbO3晶体的二波耦合响应时间分别为 3min和 3.5min。与Ce∶LiNbO3晶体相比 ,Ce∶Mn∶LiNbO3是性能更为优良的光折变晶体  相似文献   

6.
7.
The Zeta-potential of different types of cement and fly ashes has been measured under various conditions of pH and ionic strength. The results obtained are in full agreement with the modified Stern-Grahame-model of the reactive double layer of cement. The data further indicate that Na+ and K+ are potential determining ions for cement in an aqueous medium.  相似文献   

8.
在NaYF4基质中掺杂Y3 和Er3 ,合成了上转换材料NaYF4:Yb:Er,并对所得到的产物进行了表征.探讨了在合成NaYF4:Yb:Er过程中,Yb和Er的掺杂浓度、溶液的酸度、活化的温度等因素对形成六方相NaYF4:Yb:Er的影响.  相似文献   

9.
The general framework of the Chemical Engineering studies in Spain includes the Bachelor's Degree (4 years), Master's Degree (the most common duration is 1.5 years) and Doctorate (3-4 years). In 2008, the Conference of Directors and Deans of Chemical Engineering (CODDIQ) was constituted with the main objective of promoting and improving the quality of Chemical Engineering studies in Spain. Currently, Faculties and Schools of 29 Spanish universities are members of CODDIQ. An analysis of the most characteristic indicators provides a representative radiography of the Chemical Engineering Studies in Spain, whose most outstanding data are: (i) 7,396 undergraduate students, 1,014 Master students and 556 PhD students, (ii) according to the gender profile of undergraduates and graduates, the percentage of women is similar to that of men, while for faculty staff, the percentage of women is 43% and 46% for Associate and Assistant Professor (respectively) and 23% for the category of Full Professor category; (iii) after completing the Bachelor studies, most of them continue their training in the MSc in Chemical Engineering, (iv) the employability after obtaining the Master's degree is very high (>75%), which in the case of PhDs is close to 100%. The studies of Chemical Engineering in Spain have a very direct relationship with society, especially in the chemical, environmental, biotechnological and energy fields. The companies that collaborate in the training of future professionals are distributed throughout the national territory, which allows a strong connection with the socioeconomic environment.  相似文献   

10.
Sinanodonta woodiana (Lea, 1834) is a large Unionid species with a real invasion success. It colonized Europe, Central America, the Indonesian Islands and recently North America. The species life cycle involves a larval parasitic stage on freshwater fish species which contributes to the spread of the mussel. In this paper we describe, for the first time, eight polymorphic microsatellite loci for the species Sinanodonta woodiana. The genetic screening of individuals confirmed that all loci were highly polymorphic. The number of alleles per locus ranged from 7 to 14 and the observed heterozygosity ranged from 0.650 to 0.950. These loci should prove useful to study the species population genetics which could help to infer important aspects of the invasion process.  相似文献   

11.
The surface activity of spent sulphite liquor (SSL) and the separation of surface active components by foam fractionation were studied. The maximum activity (lowest surface tension) of SSL was observed at a high pH. The surface tension was found to be 42 mN/m and 38 mN/m at acidic and basic pH values, respectively, and also a maximum foaminess (Σ) of 7 min was observed at pH 10. Foam fractionation reduced the surfactant concentration by 90% at an optimum pH of 10. The surfactants were concentrated in the collapsed foam as shown by the fact that the critical micelle concentrations of the unfractionated SSL and foam were 70% (v/v) and 10% (v/v), respectively. The removed surfactants were concentrated in 20% of the original liquid volume.  相似文献   

12.
The local order around Nd3+ ions in Nd:MgO:LiNbO3 and Nd:ZnO:LiNbO3 codoped samples has been investigated by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Independently from the codoping atom, the main position of the Nd ions has been determined to be near the Li lattice site.  相似文献   

13.
The paper focuses on operation of simple refrigeration cycles and considers the selection of controlled variables for two different cycles. One is a conventional sub-critical ammonia refrigeration cycle and the other is a trans-critical CO2 refrigeration cycle. There is no fundamental difference between the two cycles in terms of degrees of freedom and operation. However, in practical operation there are differences. For the ammonia cycle, there are several simple control structures that give self-optimizing control, that is, which achieve in practice close-to-optimal operation with a constant setpoint policy. For the CO2 cycle on the other hand, a combination of measurements is necessary to achieve self-optimizing control.  相似文献   

14.
The thermal conductivity of traditional ceramic materials is known to be a function of their porosity or bulk density. However, the scatter in the thermal conductivity–bulk density data in certain studies, particularly when data from industrially processed brick are involved, suggests that thermal conductivity depends, apart from porosity, on other characteristics such as mineralogical composition, microstructure, humidity, and the presence of soluble salts.A standard red-firing clay used in brick manufacture has been used in this study with a view to systematising the impact of the different variables that could influence thermal conductivity and mechanical strength. Part I of the study presented the results obtained when the dry bulk density of the pieces and their firing temperature were modified.Part II examines the influence of the mineralogical composition of the starting raw materials mixture on the thermal conductivity and mechanical strength of clay brick products. The findings suggest that to manufacture traditional ceramics with high thermal insulation and appropriate mechanical properties, it is advisable to use illitic-kaolinitic clays. Large-sized potassium feldspar and quartz particles adversely affect fired mechanical strength. In addition, quartz has high thermal conductivity. The addition of carbonates or the use of calcareous clays has a positive effect on mechanical strength, because carbonate acts as a pore-forming agent and generates crystalline phases during firing that enhance mechanical strength.  相似文献   

15.
Active carbons with a burn-off of 52% have been prepared from four coals of different rank and origin after preoxidation to different degrees at 543 and 473 K, and further carbonization at 1123 K. The activation has been carried out with CO2 at 1123 K at two flow rates viz. 7 cm3 min−1 and 500 cm3 min−1. Active carbons have also been prepared from a preoxidized coal by activation to different degrees of burn-off between 10 and 80%. The effect of the degree of oxidation, the flow rate of the activating gas and the extent of burn-off on the porous structure development of active carbons has been examined. The active carbons prepared from unoxidized coal have poor textural characteristics (porosity, N2 and CO2 surface area). Nevertheless, the textural characteristics are enhanced as the degree of preoxidation of the coal is increased. The low flow rate of CO2 (activating gas) produces active carbons with a better microporous character. The degree of activation (the extent of burn-off) of the carbon determines the porous structure of the active carbon. At low degrees of burn-off (less than 50%) the product is largely microporous. At higher degrees of burn-off between 35–65% the product has a mixed porous structure and contains all types of pores. Active carbons with a given textural character can be obtained by controlling the degree of oxidation of coal and the degree of activation of the carbonized material.  相似文献   

16.
The matrix/reinforcement interphase in aramid fiber/epoxy and carbon fiber/epoxy composites were modeled by coating an internal reflection spectroscopy (IRS) element with a thin layer of an aramid or of carbonized poly(acrylonitrile) (PAN). The coated element was then used as a substrate on which the curing of an epoxy resin took place. Infrared (IR) spectroscopy was used to demonstrate that the simulated reinforcement surfaces modified the crosslinking chemistry in the first 200–400 nm of epoxy matrix adjacent to the surfaces, producing an interphase of matrix material with properties different from those of the bulk of the epoxy matrix. This hypothesis was confirmed by the fabrication and testing of a series of unidirectional aramid fiber/epoxy and carbon fiber/epoxy composites.  相似文献   

17.
18.
This paper aims to be a quick reference guide to start-up decentralized membrane bioreactors (MBRs). The first part of this study focuses on the impact of different operational parameters on the start-up of decentralized MBRs, which can be easily reproduced in the field. Whereas wastewater is not an option to start-up decentralized MBRs, domestic activated sludge has shown to handle the input of wastewater in a better way than the municipal one. Starting-up at low mixed liquor suspended solids (MLSS) concentration is feasible, and a possible optimum concentration (~ 1 g L? 1) has been suggested. In turn, particle size distribution has shown how determined conditions release fine particles in the sub-micron range (0.1–1 μm), impacting negatively the filterability of the initial inoculum and thus the operation. However, in the case of the air scouring rate, even releasing sub-micron particles to the media, high rates demonstrated to extend the operation. Regarding ambient conditions, low temperatures and associated deflocculation processes should be avoided. Chemical oxygen demand and NH4+–N removal efficiencies showed values over 87% and 75% respectively whereas suspended solids and removal of pathogens maintained low values (50 mg L? 1 and absence respectively) in the permeate, allowing the reuse of regenerated water since the first day of operation under the different conditions imposed. None of the analyzed parameters (i.e., MLSS, sludge volumetric index and dissolved organic carbon), influenced significantly the filterability of the initial inoculum. Contrarily, the input of wastewater has demonstrated to be the most important factor governing the fouling process of the membrane rather than the changes in the microbiology. As a final consideration, an efficient pretreatment and both low hydraulic retention time and fluxes can help to extend the operation and reach an easy transition between the start-up and the steady-state.  相似文献   

19.
The reaction between methane and cerium oxide to produce syngas has been studied at 700°C in a pulse apparatus. The cerium oxide was supported on γ-Al2O3 and promoted by re-impregnation with Pt or Rh. The promoters drastically enhanced the conversion of methane. TPR with hydrogen shows that Pt and Rh also lowered the temperature necessary to reduce the cerium oxide. Studies of the reaction between methane and promoted cerium oxide showed that the selectivity to syngas depends on the degree of reduction of the cerium oxide. The promoters also led to some carbon formation. Regeneration of the reduced oxide was studied both with oxygen and carbon dioxide.  相似文献   

20.
Small particles and droplets encounter normal shocks in a variety of applications. The particle-shock interaction subjects the particles to large unsteady drag forces behind the shock front. In the present paper, an analysis has been made of the relative importance of the Basset history integral in the equation of motion for particle displacement and velocity behind a normal shock wave. The effect of the Basset integral has been related to gas stagnation conditions upstream of the shock and the local gas Mach number. In the present theoretical study it has been demonstrated that particle velocity and displacement relative to the gas behind the shock is unaffected by the inclusion of the Basset term until the latter stages of particle relaxation. The effect of the Basset history integral, that results from diffusion of vorticity from the decelerating particle, has been shown to decrease the particle drag or increase the displacement of the particle behind the shock. The effect is magnified with increasing stagnation pressures and particle diameters but with decreasing gas stagnation temperatures.  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