Advanced Materials Research Vol. 530

Abstract: Tin nanoparticles were synthesized through compulsive reduction using a Tin(II) 2-ethylhexanoate precursor, and the effect of reductant (sodium borohydride) amount on the size distribution of the particles was surveyed. Issues caused by the absence of a capping agent (polyvinyl pyrrolidone) were similarly examined. An excessive amount of dissolved sodium borohydride caused variations in the tin nanoparticle sizes, from a few nanometers to several tens of nanometers. The formation of abnormally large particles was attributed to the vigorous coagulation among smaller tin particles. In the tin nanoparticles synthesized without polyvinyl pyrrolidone, an exceptionally wide size distribution was observed owing to irregularly coagulated and aggregated large particles.

Abstract: Native cellulose nanofibers with high strength ratio may create an alternative as the blade material for wind power field. In this work, cellulose nanofibers (CN) with high L/D ratio was fabricated by combined biological treatment and mechanical disintegration processes. Then, we created a high-performance cellulose layered nanocomposites via layer by layer (LBL) assembling strategy. Transmission electron microscopy (TEM) observations show that common paper pulp exhibits a nearly spherical or amorphous structure, while as-made cellulose nanofibers displays a high aspect ratio, with a length of ca. 10~100 μm and a diameter of ca. 30~100 nm. However, some relative big fibres bundles are still observed. Mechanical measurements demonstrate that the tensile strength, Young’s modulus and elongation at break of layered CN nanocomposites (CNLC) reach 114MPa. 7.0GPa and 68 %,respectively, while only 63MPa, 3.3 GPa and 27 % for layered common paper pulp composites (PFLC). Flexural tests results show that CNLC gives a flexural strength and modulus of 263 MPa and 19 GPa, while only 114 MPa and 11 GPa for PFLC. Fracture surface observations indicate that though layered structure can be observed for both PFLC and CNLC, much thinner layer and long fibrous structure only exist in CNLC, which results in high mechanical performance.

Abstract: We have fabricated several superconducting MgB₂ thin films on stainless steel substrates by using hybrid physical-chemical vapor deposition (HPCVD) in pure argon atmosphere. These films were observed by scanning electron microscopes (SEM) and used the energy dispersive X-ray spectroscopy (EDX) to make elements analyses. The film thickness is about 800~1000 nm. There were some cracks on the film surface when the film is bent by different angle. The number of cracks and their width increased with the increasing bending angle. Nevertheless, the films were attached to the substrates firmly. It concludes that the superconducting MgB₂ thin films have great ductility and adhesion to the stainless steel substrates. We found in these films many granules about tens of nanometers in size. These nano-granules can balance both the inner structure and the surface activity of the MgB₂ crystal. This might be an important reason for the ductility observed with the superconducting thin films. The exact explanation depends on further research.

Abstract: The effects of Chitosan/Nano-TiO₂ composite coating in extending postharvest life of stauntonvine and maintaining their qualities were investigated. Stauntonvine were treated by chitosan/nano-TiO₂ composite coating and chitosan coating respectively. Changes in respiration rate, ascorbic acid content, titrable acidity, soluble total sugar were measured and compared. Compared with chitosan coating, the application of Chitosan/Nano-TiO₂ composite coating could reduce the respiration rate and the loss of ascorbic acid, and also could increase the titrable acidity, soluble total sugar, and partially inhibited decay of fruit during storage.

Abstract: The performance of dissimilar activated tungsten inert gas (A-TIG) welding on the welds morphology, angular distortion, and mechanical properties in dissimilar metal plates were investigated. Autogenous TIG welding process was applied to the JIS G3131 mild steel and type 316L stainless steel through a thin layer of activating flux to produce a butt-joint weld. CaO, SiO₂, Fe₂O₃, and Cr₂O₃ fluxes were used as the activating fluxes. The experimental results indicated that the SiO₂, Fe₂O₃, and Cr₂O₃ fluxes can increase joint penetration in both of the 316L stainless steel and the JIS G3131 mild steel. The CaO flux only can increase the joint penetration of the mild steel. The reversed Marangoni convection are considered to the main factors for increasing penetration of A-TIG on dissimilar welds in this study. Furthermore, TIG welding with SiO₂ powder can significantly reduce the angular distortion and increase the tensile strength of the dissimilar weldment.

Abstract: High performance lightweight aggregate concrete is a kind of lightweight environment-protected building material with high strength, good workability, volume stability and durability, which is widely used in large scale engineering and some important engineering. In this paper water-binder ratio, fly ash content, pre-wetting time, sand ratio were tested to explore the comprehensive strength of lightweight aggregate concrete(LWAC). SEM was used to observe the microstructure characteristics of the specimens. The results showed that LWAC produced in the experiment present good performance, whose apparent density was 1760 Kg/m3～1930Kg/m3, 28d compressive strength was 55MPa～60MPa. Reasonable amounts of sand ratio(38%) and mineral admixtures(10%) were exited and the self-strength of lightweight aggregate played an important role in the preparation of LWAC. In the meanwhile, lightweight aggregates which were pre-wetted effectively increased the later strength.

Abstract: In this paper the reason of chromium coating seepage on piston rods is analyzed. The results show that the chromium coating seepage is mainly caused by the net structure of micro-cracks produced in electroplating process. According to this special structure of chromium coating, experiments are made to study the feasibility that the chromium coating is burnished by using the ultrasonic elliptical vibration burnishing (UEVB) process to prevent seepage. The results of study demonstrate that the UEVB process make the micro-cracks on the surface of chromium coating closed or eliminated because the UEVB process could make the chromium coating plastic-forming. Thereby airtightness of piston rods is increased and seepage is prevented approximately. Compressive stress within the material of chromium coating will produce so that the micro-cracks propagation would be restrained and the life of parts is extended.

Abstract: Water lubricated rubber bearing is one of the most appropriate bearings widely used in submerged pump for drainage. The water lubricated rubber bearings sometimes worked in absent-water conditions especially at the machine start or brake. The friction and wear characteristics of the water lubricated rubber/Nickel coating pair were tested under dry, wet and water lubrication conditions respectively on the high-speed ring-block friction and wear testing machine. The effect of load and speed on the friction coefficient was examined in the experiment. The friction and wear mechanism of the rubber/Nickel coating pair under different conditions was analyzed with the help of SEM in the paper. The results show that the adhesive wear mainly occurs under dry condition, the grain abrasion occurs under wet condition and boundary lubrication occurs under water lubrication.

Abstract: Nanocrystalline diamond composite films were fabricated on the WC-Co substrates using a bias-enhanced hot filament CVD system. Methanol solution pretreatment method for removing the Co in surface of WC-Co substrates was put forward. The composite structure was achieved by regulating the concentration of Ar in a mixture of acetone and a hydrogen gases in different stages. The surface morphologies, nucleation density, diamond films and composition of the nanocrystalline diamond composite films were observed with different techniques. The results showed that the introduction of Ar increased the second nucleation of diamond grains which made the diamond grains finer. Nanocrystallie diamond film can be successfully grown on the microcrystalline diamond films. The two-layer structure has the advantages of good adhesive strength and low surface roughness. Because of nano effects, the hardness of composite films decreases. This is prone to be polished and reduces the work load significantly. It is of great importance for the wide application of diamond films in the precision machining fields.

Abstract: The identification of physical parameters for manipulators is critical to the control precision of robots. Almost all the existing theories and methods are indirect solutions based on iteration techniques. Most of these algorithms are difficultly adopted in real engineering due to un-reachable or low precision measurement in Cartesian coordinate space of robots. An identification approach of physical parameters for nR serial robots is presented with its detailed process. The approach decreases the accumulated errors owing to the separately measure of each axis. At same time, the values of joint variables are accurately captured while physical parameters are gotten, and these values are significant to increase the precision of HOME position of robots. In addition, not only this approach can be used in D-H model but also it can be applied to modified D-H model without any changes of other steps of the process except the changes of Eq.1 to 7. Tested cased have identification performance of the proposed method satisfies engineering requirements of robot control.