Cavern formation in pulp suspensions using side-entering axial-flow impellers

Pulp fibre suspensions display non-Newtonian rheology, including a yield stress. In mixing operations, this creates regions of active motion around the impellers with the cavern size affecting the quality of mixing attained. Due to the opacity of the suspensions, two non-invasive techniques were evaluated for determining cavern dimensions: electrical resistance tomography (ERT) and ultrasonic Doppler velocimetry (UDV), with ERT chosen for most tests due to the speed of data acquisition. Cavern volume as a function of impeller speed is reported for a range of mixing conditions (hardwood and softwood pulp, suspension mass concentrations from one to five percent, two impeller offsets from the wall, and three suspension height-to-chest diameter ratios). A scaled version of a commercial axial flow impeller was used in a standard side-entering configuration. Measured cavern diameters were compared against model predictions available in the literature. The discrepancy between experimental data and model predictions were significant and were attributed to interaction between the developing cavern and the vessel walls. An alternative model was developed for predicting cavern volume taking this interaction into account.     

Adiabatic versus non-adiabatic approach to the inner sphere vibrational effects on electrochemical reduction rates

This work is a theoretical comparative study on the adiabatic and non-adiabatic mechanisms of electrochemical reductions. In our previous paper [A. Ignaczak, W. Schmickler, Electrochim. Acta 52 (2007) 5621] several aspects of the reaction kinetics were discussed for the adiabatic electron transfer from the electrode to the reactant, taking aquocomplexes as a testing case. In the present work the same reactions are studied in the non-adiabatic approach. First order perturbation theory is applied to analyze the rate dependence on quantum effects associated with inner sphere nuclear vibrations using the same model Hamiltonian. It describes independently the solvent reorganization and the intramolecular modification of the reactant. In case of complexes the ligand shell in the oxidized and reduced states is characterized by two different frequencies, ω₁ and ω₂, respectively, so the ratio θ = ω₂/ω₁ describes asymmetry of the potential energy surface. An influence of different θ values combined with high and low ligand frequencies on the rate enhancement due to the nuclear tunnelling is tested.The quantum correction, calculated as k_q/k_s (k_q, the non-adiabatic rate; k_s, the adiabatic rate), is found to depend strongly on θ and ω₁ parameters as well as on the overpotential applied. The rate enhancement is especially sensitive to the initial state frequency ω₁ for systems characterized by larger θ values. For overpotential η = 0 V, when ω₁ = 250 cm⁻¹ the ratio k_q/k_s is equal to 1.35 (θ = 2/3), 0.65 (θ = 1) and 0.38 (θ = 3/2), while for ω₁ = 1000 cm⁻¹ the corresponding values are 4.05, 3.94 and 4.77. These values increase significantly when the overpotential is applied, up to 14 for the largest values of ω₁ and θ. The transfer coefficient is also presented for the two reaction mechanisms as a function of all parameters tested. An effect of the reactant-electrode interaction and the friction parameter on the rate constants is also analyzed for all cases.     

Tailoring the Texture and Mechanical Anisotropy of Multi-cross Rolled Mg-Zn-Gd Alloy by Annealing

The unidirectional rolled Mg-Zn-Gd sheet usually exhibited non-basal texture with two peaks whose tilting angle were about 42° from normal direction to transverse direction (TD), which would cause the mechanical anisotropy. In this study, multi-cross rolling followed by annealing was used to tailor the texture and mechanical anisotropy for Mg-Zn-Gd alloy. With increasing annealing temperature, the rolled basal texture with two peaks gradually transformed into the circle texture with multi-peaks. In order to figure out different texture components evolution during annealing, the basal texture, R-texture and T-texture component were defined and studied. The results showed that the change of R-texture and T-texture component was asynchronous with increasing annealing temperature from 250 to 400 °C. The tilting angle of R-texture component increased slightly, while the tilting angle of T-texture component increased obviously, and this phenomenon was attributed to the preferential nucleation at grain nucleation stage rather than preferential grain growth. The yield strength along TD was more sensitive to annealing temperature compared with that along rolling direction (RD), resulting in different descending slopes and yield strength anisotropy with increasing annealing temperature. Annealing at 300 °C was the best annealing temperature due to low yield strength anisotropy, moderate strength and good elongation among these annealing temperatures. The Schmid factor for basal slip indicated that the activity of basal slip along RD increased slightly, while that along TD increased obviously with increasing annealing temperature from 250 to 400 °C, which should be caused by the asynchronous change of R-texture component and T-texture component, consequently resulting in the transformation from isotropic yield strength to anisotropic yield strength.     

材料力学性能与液压胀接性能的关系

应用弹塑性力学的基本原理分析了材料的力学性能与液压胀接性能的关系,根据应力-应变曲线分析了胀接原理,给出了可实现胀接的必要条件,为选择合理的管子和管板材料提供理论依据。     

Failure of Zr61Ti2Cu25Al12 bulk metallic glass under torsional loading

The torsional properties of the Zr₆₁Ti₂Cu₂₅Al₁₂ BMG have been tested using cylinder samples, including the shear yield strength, shear elastic strain limit and shear modulus. Under torsional loading, the BMG fails via a major shear band, without obvious macroscopic plasticity on the specimen surface. The shear band maintained stable propagation by a distance of ∼300 μm (∼20% of cylinder radius) before final catastrophic failure, owing to the constraint of stress gradient along the radial direction. The combined tensile, compressive and torsional properties of the Zr₆₁Ti₂Cu₂₅Al₁₂ BMG suggest that recent ellipse criterion and eccentric ellipse criterion are more appropriate than other well-known ones in describing the yield behavior of this BMG. The cooperative shear model underestimates the shear elastic strain limit, because of its default assumption that the yielding behavior follows the Tresca yield criterion.     

试制X80输油气管线钢的包申格效应研究

研究某厂试生产的X80输油气管线钢的显微组织结构和常规力学性能。该钢板以针状铁素体组织为主 ,晶粒 12级。采用四点弯曲方法 ,模拟制管工艺进行钢板的包申格效应研究。在屈服变形阶段 ,随预变形量的增加 ,由包申格效应导致的屈服强度损失单调的增加 ,此现象与屈服过程中 ,钉扎位错的脱钉 ,形成大量有方向性的可动位错有关。按API标准 ,从试制的 610mm× 7.9mm螺旋钢管取样进行测试 ,结果发现钢管由包申格效应导致的屈服强度损失 ,除卷板头部和尾部略高外 ,沿板长平均在 5 5MPa至 75MPa之间。包申格效应的影响不可忽视     

非对称式行星齿轮分动器

阐述传统分动器的不足之处,以奔驰车为例,详细介绍带有差速功能的非对称式行星齿轮分动器的特点、工作原理、扭矩分配特性、差速特性及在特殊行驶条件下的使用。     

低碳马氏体不锈钢0Cr13Ni4Mo磨削表层屈服强度的研究

借助X射线应力分析技术测量了屈服强度在马氏体不锈钢0Cr13Ni4Mo磨削影响层上的分布,同时测量或计算了残余应力、X射线衍射线半高宽、显微硬度、嵌镶块尺寸、微观应变和位错密度等参量的沿层深分布。结果表明,该影响层的屈服强度大幅度提高了,与用半高宽和显微硬度比较起来,用屈服强度作指标能够更好地反映磨削影响层的强化。磨削表面的条件屈服强度提高了约50%,嵌镶块尺寸从约64nm减小到约28nm,微观应变从约7×10-4增高至约14×10-4。磨削影响层的条件屈服强度σ0.2与位错密度的平方根之间存在线性关系。这些结果说明,磨削表面发生了严重的塑性形变。冷作塑性形变强化是磨削影响层的屈服强度得以提高的根本原因。     

MONTE CARLO SIMULATION OF SPIN-POLARIZED SECONDARY ELECTRONS FROM IRON

A Monte Carlo model considering the electron spin direction and spin asymmetry has been developed. The energy distribution of the secondary electron polarization and the primary energy dependence of the polarization from Fe are studied. The simulation results show that: (1) the intensity of the spin-up secondary electrons is larger thanvthat of thevspin-down secondary electrons, suggesting the secondary electrons are spin polarized; (2) the spin polarization of secondary electrons with nearly zero kinetic energy is higher than the average valance spin polarization, Pb=27% for Fe. With increasing kinetic energy, the spin polarization of the secondary electrons decreases to the value of Pu remaining constant at higher kinetic energies; (3) the spin polarization increases with an increase in the primary energy and reaches a saturation value at higher primary energy in both the Monte Carlo simulation and experimental results.     

Si3N4-SiC真空氮化炉三相负载不对称时的功率分析

本文对氮化硅结合碳化硅(Si3N4-SiC)制品烧制生产过程中,真空氮化炉三相负载由于支路断路造成三相负载不对称时的相电压和功率进行了分析和计算。对常见的故障,提出了继续升温完成氮化烧成,产品出炉后再更换元件的经济有效的应对措施。为Si3N4-SiC制品绿色生产提供了理论依据。