纳米级ZSM-12分子筛的合成及表征

采用双季铵盐模板剂溴代1,4-二氮甲基哌啶基-丁烷,通过动态水热晶化法成功制备了纳米级ZSM-12分子筛。采用X射线衍射、扫描电镜、透射电镜、红外光谱分析及N2吸附-脱附技术等测试方法对所得颗粒进行了研究。所合成的颗粒呈长条形状,长约150 nm,宽约30 nm。所得的ZSM-12沸石结晶体结构完整,无明显骨架缺陷,富含微孔和介孔孔隙。介孔孔隙来源于ZSM-12纳米晶粒之间的堆积孔隙。在酸分布上,所得的HZSM-12分子筛的中强酸及B酸比例较多,使得该沸石在催化反应中具备优良的反应活性。     

纳米氧化锌高效催化左旋丙交酯制备及工艺研究

以纳米氧化锌为催化剂,通过两步制备法:乳酸(LA)低聚物制备和低聚物裂解环化,制备左旋丙交酯(L-LA).进一步采用红外光谱、核磁共振、差式扫描量热法对所制备L-LA样品进行深入表征.研究旨在优化丙交酯的制备工艺条件以提高产品收率,因而详细探究了催化剂含量、脱结合水反应温度、反应时间、馏出温度等参数对L-LA收率的影响...     

Direct ink writing additive manufacturing of porous alumina-based ceramic cores modified with nanosized MgO

Alumina-based ceramic cores, widely applied to cast alloy, have been restricted by the increased complexity of castings, the resultant complex equipment and cost. In this research, to address the aforesaid disadvantages, direct ink writing, a green additive manufacturing method, is utilized to directly fabricate a new kind of nanosized MgO strengthened alumina-based ceramic cores. Slurries with various compositions exhibits ideal shear-thinning behaviors, owing to the hydrogen bond formed between polyvinylpyrrolidone and kaolin molecules. We notice that introducing nanosized MgO reduces drying shrinkage of green specimens and greatly promotes liquid-phase sintering, leading to rather more densified samples. Overall, it is anticipated that the current approach is effective in rapidly manufacturing alumina-based ceramics and some other ceramics with high strength, low shrinkage and high quality.     

High strength silica-based ceramics material for investment casting applications: Effects of adding nanosized alumina coatings

A nanosized alumina coating was synthesized on the surface of fused silica particles by electrostatic attraction. The effects of the coated fused silica particles on the cristobalite crystallization behavior, microstructure evolution, and flexural strength of silica-based ceramic cores were investigated. X-ray diffraction (XRD) was used to characterize phase transformations in the specimens, and the results indicated that the formed nanosized alumina coatings could retard cristobalite formation by inducing compressive stress on the fused silica particle surface. A mullite phase was also found due to the reaction of the nanosized alumina coating and the surface of the fused silica when the sintering temperature was increased to 1300 °C. Analysis using scanning electron microscopy equipped with energy dispersive spectrometry (SEM/EDS) suggested that alumina nanoparticles in the coated layer dispersed into a liquid phase and formed a barrier layer to impede the movement of the liquid phase, preventing the pore-filling process and increasing the open porosity of the ceramic specimens. Flexural strengths at room temperature were tested, indicating that increases in the sintering temperature of the specimens without coated fused silica powders had little effect on flexural strength. However, the flexural strength of the specimens with coated fused silica powders increased with increases in sintering temperature. The improvement in flexural strength was related to the reinforcement by sintering necks between particles and the improvement in the strength of the coated fused silica powder.     

Recent progress of nanotechnology in enhancing hydrogen storage performance of magnesium-based materials: A review

Hydrogen has attracted wide attention in the field of new energy, triggering a comprehensive study of hydrogen production, storage and application. This paper mainly studies the hydrogen storage capacity of magnesium-based materials with nanostructure. The reversible hydrogen capacity of Mg-based hydrogen storage materials can reach 7.6 wt%, but due to its poor kinetic and thermodynamic properties, its hydrogen storage performance is not as good as other hydrogen storage materials. In order to reduce the desorption temperature of materials, many studies have been carried out. Alloying, nanostructure and adding catalyst are feasible methods to improve the properties of Mg-based hydrogen storage alloys. By adding catalyst and alloy with other transition elements, the dehydrogenation temperature of magnesium-based materials has been reduced to less than 200 °C. The hydrogen storage of magnesium-based alloys has been practically applied.     

Nanosized Composite Pt‐Ru Catalysts for Production of Modern Modified Fuels

A Pt‐Ru/2 % Ce/(θ+α)‐Al₂O₃ nanosized catalyst was developed for selective catalytic oxidation of CH₄ to synthesis gas. The process was carried out entirely with the formation of synthesis gas at high selectivity by H₂ and CO with H₂:CO = 2.0 ratio only at Pt:Ru = 2:1 or 1:1 atomic ratio and short contact time on Pt‐, Ru‐, and Pt‐Ru low‐percentage catalysts. Samples, which were reduced by H₂ at high temperature, presented a mixture of Pt‐, Ru‐, and Pt‐Ru nanosized particles, its alloy in the mixed catalysts. The correlation between experimental results and data of physicochemical research was established. The activity together with physicochemical properties and quantum chemical calculations for the developed low‐percentage Pt‐Ru catalysts was investigated.     

On the shell theory on the nanoscale with surface stresses

Below we discuss the derivation of the governing nonlinear shell equations taking into account the surface stresses. The surface effects are significant for the modeling of some structures as nanofilms, nanoporous materials and other nano-size structures. In particular, the surface stresses are responsible for the size effect, i.e. dependence of the material properties on the specimen size. The theory of elasticity with surface stresses is applied to the modeling of shells with nano-scaled thickness. It will be shown that the resultant stress and couple stress tensors can be represented as a sum of two terms. The first term in the sum depends on the stress distribution in the bulk material while the second one relates to the surface stresses. Hence, the resultant stress and couple stress tensors are linear functions with respect to the surface stresses. As an example the effective stiffness properties of a linear elastic Cosserat shells taking into account the surface stresses are presented.     

纳米二氧化钛掺杂改性后的光催化性能的评价

考察了掺杂改性后纳米TiO2的光催化性能,在产品光催化活性的测定中,选择甲基橙作为降解的模型化合物,提高了光催化降解效率,降解和脱色效果都比较好。     

Injection moulding of 316L stainless steels reinforced with nanosize alumina particles

Abstract

This study aims to compare the effect of Al₂O₃ nanoparticle additions on the densification and mechanical properties of the injection moulded 316L stainless steels. The 316L stainless steel and Al₂O₃ nanoparticles were dry mixed and moulded using a wax based binder. The critical powder loading for injection moulding were 60 vol.-% for all samples. Debinding process was performed in solvent using thermal method. After the debinding process, the samples were sintered at 1405°C for 60 and 120 min under vacuum. Metallographic examination was conducted to determine the extend of densification and the corresponding microstructural changes. The sintered samples were characterised by measuring tensile strength, hardness and wear behaviour. Wear loss was determined for all the samples after wear testing. All the powders, fracture surfaces of moulded and sintered samples were examined using scanning electron microscope. The sintered density of straight as well as Al₂O₃ nanoparticles reinforced injection moulded 316L stainless steels increases with the increase in sintering time. The additions of Al₂O₃ nanoparticles improve the hardness and wear resistance with the increase of sintering time.     

Influence of CsCl addition on the nanostructured voids and optical properties of 80GeS2-20Ga2S3 glasses

The influence of CsCl content on the void evolution in (80GeS₂-20Ga₂S₃)_100-x(CsCl)_x, x = 0; 5; 10; 15, chalcogenide glasses and changes of the optical response of these glasses due to CsCl addition are investigated. It is shown that structural agglomeration of voids occurs at addition and increasing of CsCl amount in base glasses. Supersaturation of GeS₂-Ga₂S₃-CsCl glasses by CsCl results in the contraction of void volumes in (80GeS₂-20Ga₂S₃)₈₅(CsCl)₁₅. By applying positron-positronium decomposition algorithm it was established that CsCl not only transforms voids in glass, but also forms new positron-trapping sites in Ge-Ga-S glassy matrix. Therefore, CsCl addition results in the shift of fundamental transmission edge in the visible region. It is shown that doping by larger concentrations of CsCl may lead to “supersaturation” of base glasses and that adding 10 mol% of CsCl is apparently an optimal doping level in view of further modification of glasses with rare-earth ions.