Propylsulfonic acid-functionalized partially crystalline silicalite-1 materials: synthesis and characterization

Propylsulfonic acid-functionalized partially crystalline silicalite-1 materials were synthesized via one step co-condensation technique by varying the molar ratio of organosilane source, 3-mercaptopropyltrimethoxysilane (3MP) to tetraethylorthosilicate (TEOS) in the range of 0.05–0.30, and subsequent oxidation of thiol group to propylsulfonic acid using hydrogen peroxide (H₂O₂). These materials were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and nitrogen adsorption–desorption method. The structure of these materials was determined by Fourier transform infrared spectroscopy (FT-IR) and ²⁹Si and ¹³C solid state NMR. XRD results show that % crystallinity of the materials decreased with the increase in 3MP concentration in the synthesis mixture. Selected area electron diffraction (SAED) showed the presence of crystalline and amorphous phases in the samples. An amorphous phase was formed when 3MP concentration was 30 mol% of the total silica source. After elimination of the structure directing agent (SDA) by calcination at 420 °C, thermogravimetric analysis (TGA) shows that the structure was thermally stable up to 550 °C. Ammonia temperature-programmed desorption (NH₃-TPD) shows that the acid capacity of these materials was in the range of 1.19–1.83 mmol H⁺/g, which shows that these materials could be used as potential heterogeneous acid catalyst.     

Chinese yam polysaccharide enhances growth performance and cellular immune response in weanling rats

BACKGROUND: In order to develop a novel dietary additive for potential application in domestic animals and humans, a fraction of Chinese yam polysaccharide (CYP) was prepared and a study was conducted to determine the effects of dietary supplementation with CYP on the immune response and growth performance in weanling rats. RESULTS: Dietary supplementation with CYP increased the average daily feed intake and average daily gain but decreased the feed/gain ratio overall compared with the non‐supplemented group. CYP also significantly increased the serum contents of interleukin‐2 and tumour necrosis factor and the proliferation activity of peripheral lymphocytes but decreased the serum contents of low‐density lipoprotein, total cholesterol and triglyceride compared with the non‐supplemented group. CONCLUSION: The increase in cellular immunity in CYP‐supplemented weanling rats confers an important protective role in the non‐specific defence against infections. This herbal polysaccharide, as a natural green dietary additive for promoting the immune response and healthy growth, may offer an effective alternative to antibiotics for weanling animals. Copyright © 2009 Society of Chemical Industry     

Fabrication and characterization of reaction-bonded silicon carbide with poly(methyl methacrylate) as pore-forming agent

Reaction-bonded silicon carbide (RBSC) ceramics were prepared by liquid silicon infiltration at 1600 °C using a carbon biscuit. The green body was made by slip casting a stabilized carbon powder slurry, followed by pyrolysis in a vacuum furnace at 1000 °C for 2 h; the density of the biscuit (ρ_b) was controlled using poly(methyl methacrylate) (PMMA) powder as pore former in mass proportion from 30% to 50% in 5 percentage point intervals. The particle size of the PMMA had significant effects on the microstructure, distribution of residual silicon, and the mechanical properties of the ceramic. For 40 mass% PMMA with d₅₀=1.17 μm and d₅₀=0.51 μm, ρ_b was 0.81 and 0.82 g/mL, with corresponding biscuit porosities of 51% and 50%, which gave peak values of both RBSC ceramic density of 3.07 and 3.10 g/mL, and flexural strength of 741 and 794 MPa, respectively. XRD analysis showed that the main phase was β-SiC, with a small quantity of α-SiC. Using PMMA with d₅₀=0.51 μm, a small quantity of residual Si was well dispersed with grain size <1 μm. “Black core” residual carbon in the RBSC was successfully avoided when ρ_b≤0.82 g/mL (mass proportion PMMA≥35%). PMMA as pore former favored the elimination of the detrimental black core and the preparation of dense RBSC with good mechanical properties.     

Continuous authentication on relational streams

According to the database outsourcing model, a data owner delegates database functionality to a third-party service provider, which answers queries received from clients. Authenticated query processing enables the clients to verify the correctness of query results. Despite the abundance of methods for authenticated processing in conventional databases, there is limited work on outsourced data streams. Stream environments pose new challenges such as the need for fast structure updating, support for continuous query processing and authentication, and provision for temporal completeness. Specifically, in addition to the correctness of individual results, the client must be able to verify that there are no missing results in between data updates. This paper presents a comprehensive set of methods covering relational streams. We first describe REF, a technique that achieves correctness and temporal completeness but incurs false transmissions, i.e., the provider has to inform the clients whenever there is a data update, even if their results are not affected. Then, we propose CADS, which minimizes the processing and transmission overhead through an elaborate indexing scheme and a virtual caching mechanism. In addition, we present an analytical study to determine the optimal indexing granularity, and extend CADS for the case that the data distribution changes over time. Finally, we evaluate the effectiveness of our techniques through extensive experiments.     

等温热处理对U-2Nb合金力学性能的影响研究

采用光学显微镜、扫描电镜、拉伸、压缩实验等分析测试方法,系统地研究了U-2Nb合金450℃~635℃的等温相变过程及其对应的力学性能变化,对结构与性能的关联做了分析总结。结果表明U-2Nb合金在550℃-635℃的等温热处理过程中存在两类特征鲜明的显微组织样貌,影响它们力学性能的主要因素是针状组织或者胞状组织的片层间距,受温度与时间的共同影响。片层间距主要取决于其形成温度,温度越高,片层间距越大,强度随之降低,塑性随之提升,等温时间与片层间距呈正相关。这一温区内获得的最好综合性能为延伸率22%,断面收缩率27.4%,抗拉强度875Mpa,屈服强度410Mpa。在450℃~500℃进行淬火并回火的样品主要形貌特征为针状马氏体与回火形成的团状组织共存状态,影响其力学性能的主要因素可能是针状马氏体的织构与回火生成的颗粒状组织的分布与大小,其整体强度高,均在1000Mpa以上,塑性差,延伸率与断面收缩率均在5%以内。等温温度对其强度的影响相对塑性更大,延长等温时间对其塑性有微弱改善。     

高速电弧喷涂FeMnCrNi/Cr3C2涂层的工艺优化及磨损性能

采用高速电弧喷涂技术在Q235钢表面制备了FeMnCrNi/Cr₃C₂涂层。通过正交试验研究了喷涂电压、喷涂电流和喷涂距离对涂层形貌及性能的影响,获得了涂层制备的最佳工艺参数。利用扫描电镜、X射线衍射仪、能谱仪、显微硬度仪与激光共聚焦显微镜等研究了最佳工艺参数下制备的FeMnCrNi/Cr₃C₂涂层的形貌及性能。结果表明:影响涂层性能的主次因素顺序为:喷涂距离、喷涂电压、喷涂电流。最佳工艺参数为:喷涂电压31 V、喷涂电流240 A、喷涂距离200 mm。采用最佳工艺参数制备的涂层孔隙率为1.99%,显微硬度为719 HV0.1,是Q235钢的3.5倍,涂层的平均磨痕宽度、深度和截面积分别为281.95μm、4.42μm和564.81μm2,相比Q235钢分别减小了60%、72%和89%,具有更优的耐磨性;涂层的主要磨损形式为磨粒磨损。     

废石−风砂高浓度料浆管道输送数值模拟及管输阻力新模型

为研究废石?风砂高浓度充填料浆自流输送管道输送特性,将矿山实际充填管路进行还原,应用FLUENT软件进行输送模拟研究。结果表明:充填料浆在管道的管径方向有明显的速度梯度;随料浆流速的增大,料浆的输送沿程阻力损失基本呈线性增大;质量浓度对管输阻力的影响非常大,在充填料浆质量浓度相差2%左右时,管道单位长度的阻力损失会相差20%~30%。通过对不同骨料比的充填料浆进行数值模拟,可知废石风砂质量比为6:4的浆体稳定性和流动性相对较好,更有利于管道输送。建立了管输阻力新模型,并通过工业试验对模型进行检验,验证了新的管输阻力模型的可靠性,研究结果为该矿选取充填系统的运行参数提供了重要依据。     

Additive manufacturing and foundry innovation

Additive manufacturing is expected to transform and upgrade the traditional foundry industry to realize the integrated manufacturing and rapid and low-cost development of high-performance components with complex shapes. The additive manufacturing technology commonly applied in casting mold preparation (fusible molds, sand molds/cores and ceramic cores) mainly includes selective laser sintering (SLS) and binder injection three-dimensional printing (3DP). In this work, the research status of SLS/3DP-casting processes on material preparation, equipment development, process optimization, simulation and application cases in aerospace, automotive and other fields were elaborated. Finally, the developing trends of the additive manufacturing technology in the future of foundry field are introduced, including multi-material sand molds (metal core included), ceramic core-shell integration and die-casting dies with conformal cooling runners.     

铸轧区长度对Al-8Si合金铸轧板显微组织的影响

采用连续铸轧方法制备Al-8Si合金铸轧带坯,利用光学显微镜(OM)、扫描电镜(SEM)和能谱分析(EDS)等手段,研究不同铸轧区长度对铸轧板微观显微组织和中心层偏析的影响。研究表明,随着铸轧区长度的增加,偏析范围先增大、后减小。这是由于铸轧区长度的增加,导致铸轧区域冷却强度加大,较强的冷却速度加快了金属的凝固,从而减轻了中心偏析程度。Al-8Si合金同一铸轧区表层和中心部位共晶硅组织的形貌有较大区别,表层共晶硅呈网状分布,微观形貌大部分呈纤维状,小部分呈瓣片状,中心层共晶硅形貌为沿不同取向的集簇状,形成中间线偏析。这是由于:铸轧坯料在轧制时,上、下表层先与轧辊面接触,而中心层相较于上、下表层的冷却速度较慢,所以,最后凝固,使上、下表层相较于中心层晶粒更加细小。     

退火温度对21Cr-0.3Cu铁素体不锈钢组织性能的影响

通过光学显微镜、拉伸试验及背散射电子衍射,研究了退火温度对21Cr-0.3Cu超纯铁素体不锈钢显微组织、力学性能、成形性能和微观织构的影响。结果表明,试验钢经970 ℃退火时,晶粒细小且均匀,组织处于完全再结晶状态。退火温度低于970 ℃时,再结晶不完全;退火温度高于970 ℃时,再结晶晶粒异常长大,这两种情况均出现混晶组织。试验钢在970 ℃退火时,综合力学性能最佳,抗拉强度为473 MPa,屈服强度为315 MPa,伸长率35.7%。随退火温度的升高,试验钢的平均塑性应变比r_m值先增加后减少。当退火温度达到970 ℃时,r_m可以达到最大值1.82。γ纤维织构密度变化趋势与r_m值一致,退火温度为970 ℃时,γ纤维增强明显,此时其取向密度达到最大值f(g)=20.56,成形性能最佳。