三维光学扫描技术在3D打印中的应用

采用先进的三维光学扫描技术,借助计算机软件对SLS打印的缸盖上水夹层砂芯进行三维数字化全尺寸扫描,检测分析了SLS打印砂芯尺寸精度及尺寸变化规律。检测结果显示:上水夹层砂芯不满足打印设备精度要求,需要改进打印工艺。根据三维光学扫描检测分析结果明确了3D打印工艺调整方向,改进了工艺打印的缸盖上水夹层砂芯,经过三维光学扫描检测,砂芯尺寸精度得到了有效地提高。通过对三维光学扫描技术在3D打印中的应用研究,对SLS打印砂芯精度检测提供了一种更为准确直观的测量方法,三维光学扫描检测结果作为SLS打印工艺参数调整依据,为SLS打印出合格的砂芯奠定基础。     

Preparation and properties of chitosan/acidified attapulgite composite proton exchange membranes for fuel cell applications

A composite proton exchange membrane chitosan (CS)/attapulgite (ATP) was prepared with the organic–inorganic compounding of ATP and CS. The composite membranes were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). The mechanical properties, thermal stability, water uptake, and proton conductivity of the composite membranes were fully investigated. The composite membranes exhibited an enhanced mechanical property, dimensional and thermal stability compared to CS membrane, owing to the interface interaction between ATP and CS. The maximum tensile strength of 53.1 MPa and decomposition temperature of 223.4°C was obtained, respectively. More importantly, the proton conductivity of the composite membrane is also enhanced, the composite membrane with 4 wt% ATP content (CS/ATP-4) exhibited the highest proton conductivity of 26.2 mS cm⁻¹ at 80°C with 100% relative humidity, which is 25.1% higher than pure CS membrane. These results may explore a simple and green strategy to prepare CS-based PEMs, which have a great potential in the application of proton exchange membrane fuel cells.     

Bond strength and adaptation of pulp capping materials to dentin

This study evaluated the shear bond strength (SBS) and internal marginal adaptation of pulp‐capping materials to dentin. Flat occlusal deep dentin surfaces were produced and randomly assigned to two groups (sound or artificial caries‐affected dentin). The specimens in each group were assigned to one of seven subgroups according to the materials used: Biodentine, Theracal LC, Ultra‐Blend plus, Calcimol LC, ApaCal ART, EQUIA Forte, and Ionoseal. Buildups (3‐mm inner diameter and 2‐mm deep) were made over the dentin surfaces. The bonded specimens were tested under shear forces at a crosshead speed of 0.8 mm/min and fracture modes were determined using a stereomicroscope at 25× magnification. The materials were applied to the pulp floor of prepared Class I cavities and then the cavities were restored with composite resin. Restored molar teeth were subjected to 5,000 thermocycles and sectioned in a bucco–lingual direction. Resin replicas were made to determine the adaptation at the pulp floor with scanning electron microscopy. Significant differences were determined among both bond strengths and gap formations of the materials. EQUIA Forte applied to both dentin substrates had a significantly higher SBS than the other materials. The bond strength of each material was not influenced by the dentin condition. Biodentine (3.03%), EQUIA Forte (7.83%), and Theracal LC (13.37%) had lower gap formations compared to other materials but were not significantly different from each other.     

Effect of fatigue loading-confining stress unloading rate on marble mechanical behaviors: An insight into fracture evolution analyses

Rocks in underground works usually experience rather complex stress disturbance. For this, their fracture mechanism is significantly different from rocks subjected to conventional triaxial compression conditions. The effects of stress disturbances on rock geomechanical behaviors under fatigue loading conditions and triaxial unloading conditions have been reported in previous studies. However, little is known about the dependence of the unloading rate on fatigue loading and confining stress unloading (FL-CSU) conditions that influence rock failure. In this paper, we aimed at investigating the fracture behaviors of marble under FL-CSU conditions using the post-test X-ray computed tomography (CT) scanning technique and the GCTS RTR 2000 rock mechanics system. Results show that damage accumulation at the fatigue stage can influence the final fracture behaviors of marble. The stored elastic energy for rock samples under FL-CSU tests is relatively larger compared to those under conventional triaxial tests, and the dissipated energy used to drive damage evolution and crack propagation is larger for FL-CSU tests. In FL-CSU tests, as the unloading rate increases, the dissipated energy grows and elastic energy reduces. CT scanning after the test reveals the impacts of the unloading rate on the crack pattern and a fracture degree index is therein defined in this context to represent the crack dimension. It shows that the crack pattern after FL-CSU tests depends on the unloading rate, and the fracture degree is in agreement with the analysis of both the energy dissipation and the amount of energy released. The effect of unloading rate on fracture evolution characteristics of marble is revealed by a series of FL-CSU tests.     

自动矿物学：Ⅰ. 技术进展与应用

近年来，“自动矿物学”（或“定量矿物学”）的概念和相关技术得到了显著的发展和广泛的应用，使矿物学研究，尤其是工艺矿物学研究从人工测试走向自动化测试、从定性研究走向定量研究。本文评述了自动矿物学的技术进展与应用，主要包括：①矿物分析技术发展阶段；②自动矿物学技术国际研究进展与国内研究现状；③自动矿物学的应用领域及发展趋势。在此基础上，总结了基于扫描电镜的自动矿物学技术的基本原理以及选矿产品环氧树脂抛光片制备过程中需要注意的一些问题。以期为固体地球科学研究和矿产资源开发利用过程中遇到的一些瓶颈问题提供新的研究途径和新的思路。     

Quantitative estimation of crystallization kinetics in GeGaS and Au-doped GeGaS glass-ceramics

Ge_26.7Ga₈S_65.3 (GGS) and 0.1% Au-doped Ge_26.7Ga₈S_65.3 (GGS-Au) glasses were prepared and annealed at a temperature that is 20 K higher than their respective glass transition temperature in order to create chalcogenide glass-ceramics. X-ray diffraction results showed that, thermal annealing can induce large amount of the crystal growth in the pure glass but this can be significantly suppressed by Au doping in the glass, which is in agreement with the previous results. We further employed various calorimetric methods, together with Mauro-Yue-Ellison-Gupta-Allan viscosity model, to investigate their crystallization kinetics. The crystal growth rate at annealing temperature of 723 K was quantitatively deduced to be 2.5 × 10⁻⁸ μm/s in Au-doped GGS, which is about 20 times slower than that in the pure GGS with a growth rate of 4.7 × 10⁻⁷ μm/s.     

Hydrostatic pressure influence on electric relaxation response of bismuth manganite ceramics

Electrical impedance of bismuth manganite ceramics was studied under ambient and high hydrostatic pressure. Local disorder of crystal lattice was confirmed using XRD and DSC. Two relaxation processes were discerned. One was attributed to small polarons, which showed a changeover from variable range hopping features related to Fermi glass and structural disorder to the nearest neighbor hopping behavior in higher temperature range related to uniform distribution of energy levels. Hydrostatic pressure shortened relaxation times that would be interesting for applications. The second process, which was assigned to the nearest neighbor hopping of polarons, also exhibited a changeover to glassy features in a high-temperature range.     

The dual capacity of the NiSn alloy/MWCNT nanocomposite for sodium and hydrogen ions storage using porous Cu foam as a current collector

A nanostructured NiSn alloy/multi-walled carbon nanotube (MWCNT) composite was successfully synthesized for highly reversible sodium and hydrogen ions storage by using an electrochemical deposition process on porous Cu foam. The surface morphology of the resulting NiSn alloy/MWCNT nanocomposite was characterized using a field-emission scanning electron microscope, indicating the formation of sphere-like NiSn alloy nanoparticles with an average size of 190 nm. On the other hand, X-ray diffraction analysis, energy dispersive and Fourier transform infrared spectroscopies were employed to determine the crystalline structure, elemental surface and chemical composition of the nanocomposite electrode. The initial sodium discharge capacity of the electrode was maximized at ∼550 mAh g⁻¹ under the current density of 1000 mA g⁻¹, and a high hydrogen discharge capacity of 5200 mAh g⁻¹ was obtained at 1100 mA g⁻¹ after 20 cycles. A comprehensive comparison between the sodium and hydrogen ions capacities in this study and those of the literature for different materials and structures was also performed. Accordingly, the resulting nanocomposite electrode with dual capacity may offer promising applications in both sodium-ion battery and hydrogen storage.     

Comprehensive branching analysis of polyethylene by combined fractionation and thermal analysis

Linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) differ significantly in their branching types and branching distributions. For a comprehensive analysis, preparative temperature rising elution fractionation and/or preparative molar mass fractionation are used to fractionate typical LLDPE and LDPE bulk resins into narrowly distributed fractions. The chain structures of the bulk resins and their fractions are further analysed using SEC, crystallization analysis fractionation, DSC and high‐temperature HPLC to provide detailed information on short chain branching in LLDPE and long chain branching in LDPE. For LDPE it is shown that the multiple fractionation approach is a powerful source of sample libraries that may have similar molar masses and different branching structures or alternatively similar branching but different molar masses. The analysis of these library samples by thermal analysis provides a much deeper insight into the molecular heterogeneity of the samples compared to bulk sample analysis. © 2018 Society of Chemical Industry     

Mechanical properties,corrosion resistance,and rubber pad forming of cold differential speed-rolled pure titanium for bipolar plates of proton-exchange membrane fuel cells

Due to problems such as pores on surface-treated coatings, the corrosion resistance of pure titanium bipolar plates for proton-exchange membrane fuel cells can be further improved by increasing the corrosion resistance of pure titanium by using differential speed-rolling (DSR); however, these materials have not yet reached the standard requirements of bipolar plates (corrosion current density i_corr＜10³ nA·cm^?2). In this work, the corrosion resistance of pure titanium was improved by optimizing the DSR process while the strength was maintained. The best corrosion resistance of the DSR pure titanium was achieved when the roller speed ratio was 2, while i_corr was 429 nA·cm^?2 in a solution of 0.5 M H₂SO₄ and 2 mg/L HF at room temperature. The formability of the DSR pure titanium for bipolar plates was verified. The optimal holding pressure range was 6.8–7.0 kN.