黄土地基中工程桩摩阻力发挥值的变化特性

基于试桩及工程桩的实测结果 ,分析了黄土地基中试桩的摩阻力发挥特性及实际工程桩的摩阻力发挥值随时间 (随施工进行 )的变化特性 ,分析表明 ,实际工程桩的摩阻力发挥值分布与试验桩的分布不同 ,工程桩中的桩土摩阻力发挥值具有鲜明的时间效应 ,受桩、土及基础的共同工作影响较大。     

耐温耐盐增稠型表面活性剂体系的应用

在表面活性剂S10中添加了改性超细二氧化硅(CXS)作为增稠剂,得到了增稠型表面活性剂体系S10/CXS。研究了CXS添加量对体系黏度、油水界面张力的影响,评价了S10/CXS体系的耐温耐盐性能、封堵性能和提高采收率能力。实验结果表明,CXS可以提高表面活性剂溶液的黏度,增稠作用明显;0.5%S10/2.3%CXS体系的油水界面张力可达到超低(10~(-3) mN/m)级别;该体系耐温耐盐性能好;在非均质并联填砂模型驱替实验中,S10/CXS体系较S10表活剂驱可提高采收率15.9百分点。CXS的聚并封堵作用可提高波及体积,S10可降低油水界面张力从而提高洗油效率,在两者的协同作用下,S10/CXS体系具有较好的驱油效果。     

重熔对NiCrBSi涂层组织及高温耐磨性能的影响

目的改善Ni Cr BSi涂层的组织及高温耐磨性能。方法采用等离子喷涂在45号钢基体上制备Ni Cr BSi涂层,并用氩弧对其进行重熔处理。利用扫描电子显微镜、能谱仪和X射线衍射仪对喷涂层与重熔层的形貌、微观组织、成分与物相进行分析。采用显微硬度仪与纳米压痕仪测试涂层的硬度、弹性模量,并计算出涂层的断裂韧性。通过室温、300℃、500℃的摩擦磨损试验评价和比较喷涂层与重熔层的耐磨性能。结果重熔层各元素分布较均匀,主要由γ-(Fe,Ni)、Cr2B、Mn5Si2和α-Fe等物相组成。重熔层由喷涂层的层状结构转变为致密的铸态组织,孔隙率由7.2%降低至0.4%,重熔层与基体之间形成了冶金结合。涂层重熔后硬度由724HV降低至608HV,但是弹性模量与断裂韧性分别由161.15 GPa和0.63 MPa·m~(1/2)提高至195.92 GPa和7.18 MPa·m~(1/2)。结论重熔处理改善了涂层的组织,使得重熔层在室温、300℃、500℃的耐磨性能均优于喷涂层。随着温度的升高,喷涂层氧化脱落越来越严重,而重熔层无明显氧化脱落。     

Temperature coefficients of grain boundary resistance variations in a ZnO/p-Si heterojunction

使用磁控反应溅射技术在Si(100)衬底上异质外延未掺杂的ZnO薄膜。制备得到的一些样品分别在氮气800°(S1)和氧气800°(S2)的条件下退火1个小时。对所有的样品进行了深能级瞬态谱(DLTS)和电流-电压(I-V)的测量。我们发现S1的晶界电阻具有正温度系数(PTC),而S2的晶界电阻具有负温度系数(NTC)。同时,S2的电流特性类似于普通的p-n结,而S1和未退火样品的电流特性呈现出双肖特基势垒的行为,这与理想的pn异质结模型的电流特性是矛盾的。结合DLTS的结果,揭示了在不同气氛下退火,导致了ZnO晶粒中的本征缺陷浓度和ZnO/p-Si异质结中的界面态密度的不同变化,影响了ZnO/p-Si异质结中的晶界势垒,产生了可调的电学特性,这个特性也许适合不同的应用。     

1500 ℃工业条件合成β-Sialon的研究

研究了在1500℃的流动氮气中用工业纯铝粉、硅粉和氧化铝粉制备不同Z值β-Sialon相材料的氮化烧结技术.氮化后最终产物为β-Sialon,其实际Z值接近配方Z值.高Z值试样残余少量Al2O3并伴生少量15R相.β-Sialon的显微形貌特征随Z值变化明显,从低Z值的纤维状向板带状或长剑状过渡,直到高Z值的棱柱状.β-Sialon的抗碱侵蚀能力在配方Z值为1.5～2.5时最佳,抗高炉渣侵蚀能力随Z值的降低而增强.     

碱性锌锰电池恒阻恒流放电中的若干关系

LR6型碱性锌锰电池在恒阻恒流连续放电时 ,在一定的电流范围内 ,恒流放电电流或恒阻放电时的平均电流与有效放电时间的关系符合In·t=k方程。恒阻连续放电时 ,在一定的放电电阻范围内 ,放电电阻与有效放电时间的关系为t=x·R -A ,据此二者关系可预测电池的连续放电容量与有效放电时间。     

Heat transfer modelling of dropwise condensation behaviour of magnesium vapours in the electrothermal production of magnesium

ABSTRACT

During the extraction of magnesium by the electrothermal process, the condensation of magnesium vapours in the condenser is critical to achieve operational efficiency. In the present work, a mathematical heat transfer model has been developed to predict the growth rate of a single liquid metal drop during dropwise condensation (DWC) of magnesium vapours in the electrothermal process. Homogeneous DWC model has been developed considering negligible thermal resistance at the liquid–vapour interface for a single cycle of liquid magnesium layer formed at vapour–liquid interface. The heterogeneous DWC has been modelled taking into account all possible thermal resistances. The role of constriction resistance on transient droplet growth behaviour has been studied and the parametric sensitivity analysis has been conducted. Parameters i.e. degree of undercooling (ΔT), contact angle (θ), thickness of condenser wall (δ )and constriction effect cause (β) has been studied for droplet growth behaviour. Heat transfer and specially the constriction resistance was found to be quite significant for heterogeneous DWC of magnesium metal vapours. Alongwith other parameters, the thermally inactive region (β) on the condenser surface inversely affects the growth. The model-based predicted Mg droplet growth profiles during condensation have been validated with published data on similar DWC studies.     

A compare of electrical characteristics in Al/p-Si (MS) and Al/C20H12/p-Si (MPS) type diodes using current–voltage (I–V) and capacitance–voltage (C–V) measurements

In this study, both the metal-semiconductor (MS) and metal-polymer-semiconductor (MPS), (Al/C₂₀H₁₂/p-Si), type Schottky barrier diodes (SBDs) were fabricated using spin coating method and they were called as D₁ and D₂ diodes, respectively. Their electrical characterization have been investigated and compared using the forward and reverse bias I–V and C–V measurements at room temperature. The main electrical parameters such as ideality factor (n), reverse saturation current (I_o), zero-bias barrier height (Φ_Bo), series (R_s) and shunt (R_sh) resistances, energy dependent profile of interface states (N_ss), the doping concentration of acceptor atoms (N_A) and depletion layer width (W_D) were determined and compared each other and literature. The rectifying ratio (RR) and leakage current (I_R) at ±3 V were found as 2.06×10³, 1.61×10⁻⁶ A and 15.7×10³, 2.75×10⁻⁷ A for D₁ and D₂, respectively. Similarly, the R_s and R_sh values of these diodes were found as 544 Ω, 10.7 MΩ and 716 Ω and 1.83 MΩ using Ohm’s Law, respectively. In addition, energy and voltage dependent profiles of N_ss were obtained using the forward bias I–V data by taking into account voltage dependent effective barrier height (Φ_e) and n and low-high frequency capacitance (C_LF–C_HF) methods, respectively. The obtained value of N_ss for D₂ (MPS) diode at about the mid-gap of Si is about two times lower than D₁ (MS) type diode. Experimental results confirmed that the performance in MPS type SBD is considerably high according to MS diode in the respect of lower values of N_ss, R_s and I_o and higher values of RR and R_sh.     

On the quantification of the controlling regimes in automotive catalytic converters

The conversion of pollutants in automotive catalytic converters is influenced by a number of physical and chemical processes that take place in the gaseous and solid phases as the exhaust gases flow through the converter. A detailed understanding of the complex processes involving flow dynamics, heat and mass transport and heterogeneous surface reactions is of crucial importance to improve the converter design. The main objective of the present study is to quantify the magnitudes of the external and internal mass transfer as well as chemical reaction limiting processes as a function of the converter operating temperature. To this end, experimental data, obtained for a three way catalyst (TWC) under real world operating conditions, are analyzed and compared against analytical expressions that allow for the quantification of the different limiting processes involved. The results demonstrate that (i) the external mass transfer resistance overlaps the reaction resistance only at moderate operating temperatures and not immediately above the ignition temperature as generally considered in the literature, (ii) the transport phenomena (external and internal mass transfer) represents 90% of the total resistance for temperatures higher than 792 K, (iii) the internal mass transfer in the porous washcoat presents a larger resistance than the external mass transfer from the bulk fluid to the washcoat wall even at high operating temperatures, and (iv) based on the quantification of the individual resistances as a function of the TWC operating temperature, it was demonstrated both the influence of the substrate cell density and of the effective diffusivity on the TWC conversions. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Primary and secondary distributions after a small-amplitude potential step at disk electrode coated with conducting film

The set of equations and boundary conditions for the “primary potential/current distribution” after a small-amplitude potential step has been analyzed for a film-coated disk electrode in contact with an electrolyte. The solution of these equations provides the overall short-time resistance of this system, R_tot, which is determined by the short-time resistance of the electrolyte solution in contact with the bare disk electrode, R_s, and the short-time film resistance to the current passage in the normal direction, (r_o, disk radius; L_f, film thickness; κ_f, its specific conductivity). The deviation of R_tot from the sum of these resistances, R_s + R_f, originates from a three-dimensional potential/current distribution in solution. Procedures to calculate the film resistance and its specific conductivity on the basis of the measured values of R_tot and R_s have been proposed. Similar analysis has also been carried out for the “secondary potential/current distribution” in the same system. The overall resistance for this regime is related to the short-time solution resistance, R_s, and to the total resistance of the electrode, equal to the sum of the resistance, R_f, and two interfacial resistances, R_m/f and R_f/s. A method to determine the bulk-film parameters, R_f and κ_f, from data for the secondary distribution is discussed. Advantages and restrictions of the proposed route to transport parameters of a film at the electrode surface are analyzed, in comparison with existing methods of their determination.