Advanced Materials Research Vols. 152-153

Abstract: With the increasing demand for high strength concrete, more attention has been paid to the problem of high viscosity mixture in high strength concrete technology by academic and engineering circles. This project studied the effects of ultra-fine limestone powder on the workability and viscosity of fresh concrete using the ultra-fine limestone powder (LP) obtained by ultra-fine grinding of limestone powder, building sandstone processing waste, as fine mineral admixture of high strength concrete. The experimental results show that the viscosity of fresh high strength concrete with ultra-fine limestone powder decreases significantly. At the same time, the influence of ultra-fine limestone powder on the strength of the concrete at different ages is very little.

Abstract: Copper nitride thin films were prepared by reactive radio frequency magnetron sputtering at various substrate temperatures. The surface morphology and crystal structure of the thin films were characterized by atomic force microscope (AFM) and X-ray diffraction (XRD), respectively. The AFM images demonstrate that the films have a compact structure. The XRD test indicates that growth orientation of the thin films prefers the (111) or (100) at different substrate temperature. The optical transmission properties of the thin films were obtained by an ultraviolet visible spectrometer. The optical band gap of the thin films decreases with increasing substrate temperature.

Abstract: This study investigates the thermal degradation of poly(L-lactic acid) (PLLA) oligomers into L-lactide（LA）by modification of the oligomer terminal groups. Pure PLLA oligomer (OLLA) was synthesized by condensation polymerization of L-lactic acid. Poly-hydroxyl-terminated OLLA (OLLAPOH) and two-carboxylic acid-terminated OLLA (OLLACOOH) were prepared by adding a small amount of polyfunctional substance, such as 1,4-butanediol, pentaerythritol, or adipic acid, to L-lactic acid. The thermal degradation behaviors of these oligomers were compared at 210-220 °C under 0.3-0.5 kPa. The results show that OLLAPOH has a 10-20% higher yield than OLLA and OLLACOOH. The order of decreasing yield is as follows: OLLAPOH>OLLA >OLLACOOH. The hydroxyl ends of the chains induce the reaction. OLLAPOH simultaneously starts depolymerization from each hydroxyl end to speed up the reaction, to shorten the time the substance remains at high temperature, and to reduce the byproducts. This results in an increased L-lactide yield. A practical approach for L-lactide production by thermal degradation of OLLAPOH is adopted by using a degradation mechanism, which is an unzipping reaction beginning from the hydroxyl ends of the chains.

Abstract: Various structure scales at the surface of SS400 hot rolled strip were fabricated by heat treatment processes involving different temperatures. A simulation about the effect of various temperatures on the oxide scale structure during the coiling process was carried out. The structure and corrosion behavior of different oxide scales formed at the surface of hot rolled strip were investigated in sodium bisulfite (NaHSO3) solution by scanning electron microscope (SEM), X-ray diffraction (XRD), polarization curves and electrochemical impedance spectroscopy (EIS). The scale prepared at 550 °C is mainly composed of one layer of Fe3O4 phase. The scales prepared at 600 °C and 700 °C consist of the outer thin Fe2O3 layer and the inner (Fe3O4+Fe particles) layer. The scale prepared at 650 °C is mainly composed of Fe3O4 phase as well as a spot of Fe2O3 phase. The thickness of scale prepared at 650°C is observed to be more homogeneous than that of other scales and the bonding between the scale and substrate is found to be very strong. The experimental results clearly reveal that the hot rolled strip with scale prepared at 650 °C exhibits the most excellent corrosion resisting property in 0.01 mol/L NaHSO3 solution.

Abstract: An experimental study of bipolar pulse electroforming nickel is presented in this paper. Based on the principles of electric double layer and double diffusing layer, the advantages of pulse electroforming over direct current electroforming, bipolar pulse electroforming over single pulse and pulse-reverse current were explained in the view of microcosmic. The influence of major technological parameters on the process of electroforming was investigated. The experimental results indicate that the the quality and precision of the electroformed coating, as well as the mechanical properties of electroformed parts, can be improved, with the bipolar pulse power.

Abstract: The electrical resistivity of liquid PbSnBi alloy has been precisely measured by the Direct Current (DC) four-probe technique in our experiment. It was found that the electrical resistivity-temperature (ρ-T) curves changed discontinuously at several-hundred degrees above liquidus. However, the ρ-T curves was linear before this turning point with increasing temperature. Moreover, the ρ-T curve of the different composition alloys showed different turning points. The anomalous behavior of electrical resitivity indicates the alteration of the electron transport properties and the mean free path LZ of conduction electrons, since resistivity as one of the physical properties sensitive to the structure and this discontinuous alteration induced by temperature suggests the liquid-liquid structural transition taking place in PbSnBi melts. This present Letter makes a beneficial attempt at studying electrical resistivity to investigate liquid-liquid structural transition.

Abstract: A drilling and compression method was designed to produce samples with artifical inner crack. According to the morphology, two types of crack were defined. After heating and holding at different temperatures, the crack healing results were observed under SEM. The starting temperature of crack healing is between 900°C and 950°C. Pseudo-equilibrium phase diagram of 12%Cr was calculated by the Thermo-Calc software to investigate the influence of transformation on the crack healing. It is found that the diffusive transformation has a positive influence on the crack healing behavior. Through experimental results and analysis, we conclude that crack healing is a physical process in association with diffusion, nucleation and grain growth. Any factor which can accelerate diffusion, nucleation and grain growth rate is favorable for the crack healing.

Abstract: Six different kinds of fabrics were weaved using the 2.5D woven fabrics with warp-stuffer, The three point beam test method was employed to test bending behavior. The effect of yarn count, yarn fineness, fabric layers on the bending behavior of fabrics was analyzed. The results showed that warp and weft load, flexural stress, flexural strain and flexural modulus were increased as the yarn counts increasing; Warp and weft load, flexural stress and flexural strain increases as the fabric layers increased, flexural modulus decreased as the fabric layers increasing; load, flexural stress, flexural strain and flexural modulus increased as the yarn linear density increasing.

Abstract: The mixed structures of bainite matrix, austenite and nodular graphite were obtained in nodular cast iron treated by controlled cooling and austempering in electric oven instead of nitrate salt bath. The relations between bainitic morphology and mechanical properties were investigated. Experimental results show that, the nodular cast iron treated by controlled cooling in water bath and austempering has microstructures of upper bainite and austenite, the mechanical properties fluctuate greatly due to its relatively narrow temperature region in processing. The consistency of mechanical properties of lower bainite nodular cast iron is superior to upper bainite nodular cast iron. The comprehensive mechanical properties of lower bainite nodular cast iron are improved by tempering. However, the brittleness increases greatly when martensite appears in mixed structures, while good mechanical properties can still be obtained by tempering at elevated temperatures.

Abstract: By using homogenous coordinate transformation principle and Denavit-Hartenberg analysis method, a measurement kinematics model and a error model to arbitrary point of automobile panels in normal mechanical parameter measurement instrument, which the movement of the probe center is relative to machine reference frame is construct. On the basis of using wielding matrix function total differential method, building up the error delivery relation of parameter error of measuring motion model transform to the probe center, and having verified what be built the error model correctness by simulation. The error is enlarge mainly in the process of delivery from angle error, while length error are very minor in error effects. This research can establish a base for studying the measuring-error of portable type measures instrument and it's measuring accuracy.