Colloidal dispersion of nano-scale ZnO powders using amphibious and anionic polyelectrolytes

This article describes the dispersion of aqueous suspensions containing nano-scale ZnO powder by utilizing a hybrid of chemical dispersant and mechanical mixing/grinding process. The chemical dispersants included anionic or amphibious polyelectrolytes, i.e., sodium salt of polymethylacrylic acid (PMAA-Na) or polyacrylamide/(α-N, N-dimethyl-N-acryloyloxyethyl) ammonium ethanate (PDAAE). The optimum critical concentrations for each dispersants to achieve the lowest viscosity, smallest final sediment volume and particle size (d₅₀) for the nano-ZnO suspensions, 3 wt.% for PMAA-Na and 5 wt.% for PDAAE, were identified. The finely dispersed nano-ZnO powders were transferred to prepare sputtering target. The root-mean-square roughness (R_RMS) of thin films deposited by utilizing such a target was found to be 2.05 nm, which was lower than the R_RMS of the film (≈27.57 nm) deposited by using a commercial ZnO target comprised of micro-scale granules.     

Effect of Heat Source Sliding Contact on the CoPtCr-based Magnetic Recording Disk

Effect of heat source sliding contact on the CoPtCr-based magnetic recording disk was investigated.A tribo-test of the disk with low load heat source and the scan of disk with magnetic head were sequentially carried out.Then disk samples in the contact area were observed by atomic force microscopy(AFM)and magnetic force microscopy(MFM).A finite element model using thermomechanical coupling was developed to calculate the mechanical and thermal response of the disk under heat source sliding contact based on the experimental results.It was found that data loss load under sliding contact with a heat source was far less than that without a heat source,and mechanical scratches and demagnetization did not occur in the data loss area under the experimental conditions.The finite element analysis(FEA)results indicate that the thin surface DLC coating has more significant effect on the mechanical response than the thermal response of the magnetic layer.     

Nano-scale machining of polycrystalline coppers - effects of grain size and machining parameters

In this study, a comprehensive investigation on nano-scale machining of polycrystalline copper structures is carried out by molecular dynamics (MD) simulation. Simulation cases are constructed to study the impacts of grain size, as well as various machining parameters. Six polycrystalline copper structures are produced, which have the corresponding equivalent grain sizes of 5.32, 6.70, 8.44, 13.40, 14.75, and 16.88 nm, respectively. Three levels of depth of cut, machining speed, and tool rake angle are also considered. The results show that greater cutting forces are required in nano-scale polycrystalline machining with the increase of depth of cut, machining speed, and the use of the negative tool rake angles. The distributions of equivalent stress are consistent with the cutting force trends. Moreover, it is discovered that in the grain size range of 5.32 to 14.75 nm, the cutting forces and equivalent stress increase with the increase of grain size for the nano-structured copper, while the trends reserve after the grain size becomes even higher. This discovery confirms the existence of both the regular Hall–Petch relation and the inverse Hall–Petch relation in polycrystalline machining, and the existence of a threshold grain size allows one of the two relations to become dominant. The dislocation-grain boundary interaction shows that the resistance of the grain boundary to dislocation movement is the fundamental mechanism of the Hall–Petch relation, while grain boundary diffusion and movement is the reason of the inverse Hall–Petch relation.     

Ethanol-induced formation of precursor for 8 mol% Yttria-stabilized zirconia: Towards the production of well-dispersed,easily sintering,and high-conductivity nano-powders

This study aims to prepare novel precursor powders for 8 mol% yttria-stabilized zirconia nano-powders. Precursor powders were extracted from the ethanol-water solution, which utilizes the changing solvation energy for different ions impacted by ethanol. An aqueous solution containing zirconium sulfate tetrahydrate and yttrium sulfate octahydrate was mixed with different volumes of ethanol to prepare precursor powders, then calcinating to obtain 8 mol% yttria-stabilized zirconia nano-powders. The scanning electron microscope and particle size measurements for precursor powders suggested that the ideal volume ratio between ethanol and the aqueous solution was 2.5, corresponding to the complete precipitation and well-dispersion. The X-ray diffraction measurements, crystallization kinetics calculations, and scanning electron microscope after calcinating precursor powders indicated the successful formation of 8 mol% yttria-stabilized zirconia powders and the particle growth through a one-dimensional growth mechanism in the 60–120 nm size range. The densification experiments and electrochemical performance measurements after sintering 8YSZ nano-powders showed high density and high ionic conductivity compared with commercial powders. An efficient process, successfully designed to achieve the commercial requirement, was used to prepare 8YSZ nano-powders.     

On the influence of single grit micro-geometry on grinding behavior of ductile and brittle materials

Recently it has been proven that highly engineered grinding/polishing tools can be manufactured with controlled shapes and distributions of abrasives. This research is directed to understand the influence of the shapes of the micro-cutting edges (i.e. circular/square/triangular base frustums generated by laser ablation), emulating grits of these engineered abrasive tools, on the material removal mechanism for workpiece materials of different mechanical properties (ductile – copper, brittle – sapphire). 2D/3D micro-profilometry, scanning electron microscopy supported by sensory signals (e.g. cutting forces) enabled to understand the relationship between the ploughing/shearing of ductile and brittle behaviour materials upon the number and orientation of the cutting edges that emulate the tested single grit shapes. It was found that for copper the increase in number of cutting edges (NoCE) of the grits results in more localised material pile-up and the reduction of plastic deformations with inherent decrease of specific cutting force; nevertheless, it became apparent that to diminish specific cutting forces, both NoCE and effective contact area between the grit and workpiece material need to be considered. For sapphire, shearing/fracturing phenomena were preponderant in the material removal mechanism when using square/triangular shaped grits while major plastic deformations were found for circular base frustum; significant reduction of specific cutting forces were noted with the increase of NoCE. This preliminary work enables the understanding on the implications of using particular grit shapes when utilising the novel edge-controlled grinding/polishing tools for machining ductile/brittle workpiece materials.     

Development of fatigue cracks from mechanically machined scratches on 2024‐T351 aluminium alloy—Part II: finite element analysis and prediction method

A prediction method to evaluate the effect of scratch geometry on fatigue life of aluminium structures containing scribe marks was developed on the basis of the experimental results described in Part I of this paper. Finite element calculations were performed on scribed samples to investigate the local stress around scribes. Elastic and elastic‐plastic stress and strain distributions at the scribe root were computed under monotonic and cyclic tensile and bending loads evaluating the driving force behind initiation and propagation from scribes. Scribe shape, size and cladding regulated stress and strain distributions in the neighbourhood of scribe roots. Fatigue life of tested scribed samples was divided into initiation life, defined as the cycles spent to develop a 50 µm deep crack at scribe roots, and the remaining propagation life up to failure. Striation counting measurements were used to calculate propagation lives by integrating linear elastic da/dN versus ΔK curves. Only up to a maximum of 38% of total fatigue life was spent to propagate an initial 50 µm deep crack from scribe roots. The theory of critical distances was successfully applied to predict initiation lives of scribed samples from elastic stress distributions. A plastic correction was also suggested, in the frame of the theory of critical distances, to correlate initiation lives of clad and unclad specimens.     

New approach to local anodic oxidation of semiconductor heterostructures

We have experimentally explored a new approach to local anodic oxidation (LAO) of a semiconductor heterostructures by means of atomic force microscopy (AFM). We have applied LAO to an InGaP/AlGaAs/GaAs heterostructure. Although LAO is usually applied to oxidize GaAs/AlGaAs/GaAs-based heterostructures, the use of the InGaP/AlGaAs/GaAs system is more advantageous. The difference lies in the use of different cap layer materials: Unlike GaAs, InGaP acts like a barrier material with respect to the underlying AlGaAs layer and has almost one order of magnitude lower density of surface states than GaAs. Consequently, the InGaP/AlGaAs/GaAs heterostructure had the remote Si-delta doping layer only 6.5nm beneath the surface and the two-dimensional electron gas (2DEG) was confined only 23.5nm beneath the surface. Moreover, InGaP unaffected by LAO is a very durable material in various etchants and allows us to repeatedly remove thin portions of the underlying AlGaAs layer via wet etching. This approach influences LAO technology fundamentally: LAO was used only to oxidize InGaP cap layer to define very narrow ( approximately 50nm) patterns. Subsequent wet etching was used to form very narrow and high-energy barriers in the 2DEG patterns. This new approach is promising for the development of future nano-devices operated both at low and high temperatures.     

基于多方向Gabor滤波的导光板轻微线刮伤检测方法研究

导光板在加工、运输等生产过程,不可避免地会出 现各种缺陷,特别是轻微线刮伤,利用现有算法 无法准确提取缺陷区域。本文在分析导光板轻微线刮伤产生原因、成像特征的基础上,提出 了一种基于多 方向Gabor滤波和亚像素分析的导光板轻微线刮伤检测方法。首先,为了突出缺陷区域,设 计了一个多方 向的Gabor滤波器;进而,利用亚像素图像分析方法,准确将疑似缺陷区域从背景图中分割 出来;最后, 分析区域形状特征,准确提取轻微线刮伤缺陷。实验结果表明,该算法的运行效率和准确率 高,稳定性、鲁棒性强,能够有效检测轻微线刮伤。     

单晶硅表面机械划痕和氧化层在湿法刻蚀中的掩膜行为对比研究

摩擦诱导选择性刻蚀具有加工成本低、流程简单、低加工损伤等优势,是实现单晶硅表面微纳米结构构筑的重要途径.为探究摩擦诱导机械划痕在单晶硅表面微纳加工中的掩膜行为,实验研究了选择性刻蚀中机械划痕掩膜下的线/面结构形貌与高度特征,并将其与氧化层掩膜进行对比.实验发现机械划痕掩膜性能与氧化层无明显差异,并讨论了两种不同掩膜下选择性刻蚀中纳米结构的形貌演变机理.最后,实现了采用不同掩膜的复合纳米图案加工.研究结果可为基于摩擦诱导选择性刻蚀的单晶硅表面高质量可控加工提供依据.     

纳米复合含氟聚合物的制备及其涂层性能研究

以γ-甲基丙烯酰氧基丙基三甲氧基硅烷(MPTMS)、N-甲基全氟辛基磺酰基胺基丙烯酸乙醇(MPSAEA)、甲基丙烯酸甲酯(MMA)共聚，利用原位复合技术引入纳米SiO2微粒，制备了均匀透明的SiO2纳米复合含氟聚合物材料。用红外光谱(FT-IR)表征了复合材料的结构。将聚合物用做涂层材料，用扫描电镜(SEM)、原子力显徽镜(AFM)、接触角测定仪和紫外可见吸收光谱仪表征和测定了涂层的形貌、涂层与水的接触角和涂层的透光率。结果表明：纳米复合聚合物可在玻片表面形成均匀光滑的涂层，其厚度约1μm，纳米SiO2的引入显著提高了涂层的疏水性，且纳米复合聚合物涂层具有优良的透光率。