盐溶液种类和浓度对α-半水脱硫石膏合成的影响

为了解决脱硫石膏的大量堆存对环境造成的潜在危害,同时提高脱硫石膏的附加值,采用常压盐溶液水热法以电厂脱硫石膏为原料探究α-半水石膏的最佳合成工艺,重点研究了盐溶液种类及浓度对α-半水石膏的合成过程、合成产物组成及结构的影响。结果表明：在氯化钙、氯化镁盐溶液中,由于同离子效应和硫酸镁离子对的形成,导致半水石膏的形成过程受阻。较高浓度氯化钾和氯化钠盐溶液可使二水石膏发生转晶,其中氯化钾会致使半水石膏过度脱水生成无水钾石膏,氯化钠盐溶液可以使二水石膏转变为半水石膏并维持较长时间,通过比较得出最佳合成工艺为氯化钠溶液质量分数为15%、体系反应温度为95 ℃、固液质量比为1∶4、搅拌速率为150 r/min、合成时间为3 h,可以制得长径比约为5∶1的六方短柱状α-半水石膏。     

Effects of Ti,Y, and Hf additions on the thermal properties of ZrB2

Reactive hot pressing was utilized to synthesize and densify four ZrB₂ ceramics with impurity contents low enough to avoid obscuring the effects of dopants on thermal properties. Nominally pure ZrB₂ had a thermal conductivity of 141 ± 3 W/m K at 25 °C. Additions of 3 at% of Ti, Y, or Hf decreased the thermal conductivity by 20 %, 30 %, and 40 %, respectively. The thermal conductivity of (Zr,Hf)B₂ was similar to ZrB₂ synthesized from commercial powders containing the natural abundance of Hf as an impurity. This is the first study to demonstrate that Ti and Y additions decrease the thermal conductivity of ZrB₂ ceramics and report intrinsic values for thermal conductivity and electrical resistivity of ZrB₂ containing transition metal additions. Previous studies were unable to detect these effects because the natural abundance of Hf present masked the effects of these additions.     

Removal of zirconium from spent fuel solution by alginate gel polymer

The uptake behaviour of zirconium (Zr) in alginate gel polymer and removal of Zr from spent fuel solution have been studied by the batch and column methods. As a first step, alginate gel polymer was synthesized and conditioned. The uptakes of Zr were examined in several concentrations of HNO₃ solution (from 0.01 M to 9 M HNO₃) by a batch method. Stronger affinity of Zr was shown than strontium (Sr), cobalt (Co), uranium (U) and iron (Fe) in 1 M HNO₃. It has been reported that cation binding was stronger with ions of higher charge in the alginate gel polymer. In contrast, the free aqueous ion, Zr⁴⁺, is the dominant form of the Zr species in very acidic solution. Therefore, the strong affinity of Zr is explained. The uptake rate of Zr was also evaluated in 2.6 M HNO₃ solution, which was close to the HNO₃ concentration in actual HLLW from fuel reprocessing. The uptake of Zr reached equilibrium within 2 h. For the column experiment, fission products (FPs) solution containing rare earth elements (REEs), platinum group metals, alkaline metals, alkaline earth metals and the other elements was prepared from actual spent fuel and the concentration of HNO₃ was adjusted to 2.6 M. In the column experiment, the alginate gel polymer was packed into a column, and then a chromatographic experiment was performed using the FPs solution prepared from actual spent fuel. As a result, over 95% of the Zr was removed from the FPs solution. Molybdenum (Mo), technetium (Tc), yttrium (Y), palladium (Pd), tellurium (Te), cesium (Cs) and REEs were eluted by the successive use of H₂O, and 1 M and 3 M HNO₃.     

Exact and Approximate Solutions of Thermoelastic Stresses in Functionally Graded Cylinders

Thermoelasticity behavior of functionally graded thick hollow cylinders with power law and exponentially variations of material properties versus radius is studied analytically. Temperature, displacement and thermomechanical stress distributions are obtained and discussed. Approximate homogeneous multilayer semi-analytical method is used successfully with adequate accuracy and finite layers. Different combinations of ceramics and metals are checked out for thermoelastic stresses due to high temperature and internal pressure. We conclude that the approximate method is simple and has appropriate results. The effects of high temperature on the stresses are more important than the high internal pressure.     

曝氧量对污水聚合物黏度影响的室内实验研究

随着我国东部老油田含水率逐年自然上升,产出污水既造成了环境破坏,又导致资源的浪费,因此,使用采出污水配制聚合物溶液进行回注的技术被各大油田广泛使用。而如今普遍使用的污水曝氧技术,虽然能够减小甚至消除污水中厌氧细菌对聚合物分解所造成的溶液黏度降低,但是过度的曝氧也会引起聚合物分子链发生断裂,从而减低溶液的黏度。采用室内实验,采用曝氧污水及厌氧污水配制聚合物溶液的方法,研究氧分子对于聚合物溶液黏度以及稳定性的影响。实验结果发现,使用曝氧污水所配制聚合物溶液的黏度要高于使用厌氧污水所配制聚合物溶液的黏度,在此基础上确定污水最佳曝氧浓度约为5 mg/L。     

Origin of stress overshoot in amorphous solids

Based on the shear-transformation-zone (STZ) theory, we propose a constitutive model for describing homogeneous elastoplastic deformation of amorphous solids where the interaction of shear transformations and free volume dynamics is incorporated. This theoretical model can reproduce the stress overshoot behavior that shows the dependence of strain rate, temperature, STZ population and dilatancy of systems. It reveals that the stress overshoots its steady state value due to the delayed activation of shear transformations that results from the insufficient free volume in the system. However, the subsequent strain softening (stress drop) is attributed to the shear-induced dilatation that is a result of the positive interplay between shear transformations and free volume creation, the latter playing the dominant role. Our analysis also demonstrates that the STZs, as basic carriers of amorphous plasticity, govern the yielding of the system, whereas the free volume dynamics significantly affects the post-yielding behaviors.     

Closed form solution for predicting the horizontal capacity of masonry portal frames through limit analysis and comparison with experimental test results

The paper deals with the problem of evaluating the in-plane seismic capacity of unreinforced masonry portal frame, which can be considered the basic structural element in historical buildings. In particular, the Limit Analysis approach is used to provide simplified “closed form” expressions of the horizontal collapse multiplier, also taking into account the eventual contribution of steel tie rods. Both sliding shear and shear diagonal cracking are also considered in order to take into account the shear failure modes of the pier walls.The proposed formulations have been used for performing an extensive parametric analysis, with the aim of studying the effect of both geometry and vertical/horizontal loading distributions on the portal horizontal strength. Furthermore, the influence of the steel tie-rods has been addressed in order to understand their effectiveness on the portal seismic capacity.A comparison with the results of experimental tests on full-scale portal frames is also provided in terms of in-plane collapse multiplier and failure mechanism aimed to validate the proposed “closed form” expressions.Major outcome of this study is a simple rule of thumb, which can be used for the straightforward assessment of the horizontal strength of simple masonry structures, and for verifying the results of more complex structural analyses such as the nonlinear static analysis.