Gradient Changing Morphology Research of Cross-linked Polyethylene Thick Insulation of 110 kV Power Cable

The thick insulation layer of 110 kV XLPE power cables will result in the gradient changing morphology with the radius due to crosslinking process and cooling of the XLPE insulation. In this paper, the morphology of cross-linked polyethylene （XLPE） insulation of 110 kV cable and the uniforming effect of the heating process on it are researched by the differential scanning calorimetry （DSC） and X-ray diffraction （WAXD）. The middle layer morphology structures of insulation produced by normal technology are of better uniform, while the crystallinity of the inner and outer layer of the insulation is lower than that of the middle one. The melting enthalpy AHm of materials displays the difference of the crystal morphologies sensitively. The difference of crystallizing morphology in different layers of the high-voltage power cable insulation can be improved by heating process. But the uniforming of morphology of the insulation by heating process requires sufficient ttanperature and time. The effect of the on-line stress-relaxation equipment used widely by cable works now should be doubted. The test results of WAXD reveal that thermal stress changes the interplanar distances in the crystal region. So the radical stress in the insulation is tensile mainly.     

Morphologic characteristics and growth interface stability of nano-micron FeS2 whiskers

Micromorphology is further studied on the basis of our previous researches concerned with the nano-micron FeS2 whisker. There are obvious differences in the intensive degree, diameter and micro- morphology among the FeS2 whiskers growing in different stages. From the early to late stage, the intensive degree increases, the diameter decreases, and the surface micro-morphology changes following the regularity： protrusive nodulation → coarse → smooth → flat. According to the theory of crystal growth, the geological setting and processes of whisker formation, we discuss the stability and evolution of crystal growth interface of FeS2 whisker occurring in Gengzhuang gold deposit （Shanxi Province, China）. The results suggest that the negative temperature gradient and the supercooling appear in the early stage of the whisker growth, whereas the positive temperature gradient of reposeful state appears in the late stage. In the whisker growth stage, the component concentration changes through the three stages： severely nonhomogeneous in the early stage, relatively homogeneous in the middle stage, more homogeneous in the late stage. The general changing process of the interfacial state is from unstable to stable. Micromorphology of FeS2 whisker in Gengzhuang is the result of synergism of temperature, component concentration and stability of crystal interface phase in hydrothermal system. The micromorphology not only reflects the physical and chemical characteristics of the hydrothermal system during the whisker growth, but also indicates the stability characteristics of the interface phase and records the changing process of the whisker growth.     

Crystallogeny fundamentals of the cholesterol gallstone

The nucleation mechanism and crystal growth process of the cholesterol gallstone are studied and a systematic theory expounded by crystallogeny is proposed. Normal feed and stone-forming feed were used to raise guinea pigs in the control and stone-causing groups respectively. The state and transformation of liquid crystal vesicles, the appearance of crystal nuclei, and the formation of microcrystal grains were observed under a polarizing microscope during the experimental period. It was found that the liquid crystal vesicles in the bile of the control group were small, scattered, and always existed as single forms, and no shaped gallstone crystals were formed. While in the stone-causing group, liquid crystal vesicles grew to larger ones, and then aggregated to form large liquid crystal cells. Solid crystal growth along the edge of these liquid crystal cells formed microcrystal grains. These demonstrated that bile liquid crystal vesicles form the basic nuclei of cholesterol gallstone. Heterogeneous nucleation is the common process in the formation of crystal nuclei and crystal growth.     

Crystallogeny fundamentals of the cholesterol gallstone

The nucleation mechanism and crystal growth process of the cholesterol gallstone are studied and a systematic theory expounded by crystallogeny is proposed. Normal feed and stone-forming feed were used to raise guinea pigs in the control and stone-causing groups respectively. The state and transformation of liquid crystal vesicles, the appearance of crystal nuclei, and the formation of microcrystal grains were observed under a polarizing microscope during the experimental period. It was found that the liquid crystal vesicles in the bile of the control group were small, scattered, and always existed as single forms, and no shaped gallstone crystals were formed. While in the stone-causing group, liquid crystal vesicles grew to larger ones, and then aggregated to form large liquid crystal cells. Solid crystal growth along the edge of these liquid crystal cells formed microcrystal grains. These demonstrated that bile liquid crystal vesicles form the basic nuclei of cholesterol gallstone. Heterogeneous nucleation is the common process in the formation of crystal nuclei and crystal growth.     

3D TEM study on hollow α-Fe_2O_3 nanostructures and nanorings

Controlled synthesis of hollow structures with non-spherical holes is significant in fabricating nanomaterials with well-defined geometries and specific catalytic and electrochemical properties. Here we report the synthesis of uniform hexagonal bipyramid hematite(α-Fe_2O_3) nanoparticles with hollow and faceted interior via directional etching process in solution. The delicate hollow structures were investigated by electron tomography and growth mechanism was revealed unambiguously. The three-dimensional visualization demonstrates the outside surfaces of hematite particles are enclosed by six {104} and twelve {113} planes, due to the stabilizing effect of the F-anions on the exposed surfaces. The concurrent etching process is a reverse process of crystal growth and leads to the dissolution occurring at the edges and tips of the hexagonal bipyramid particles, resulting in the perforated crystals with exposed {102} internal facets or overetched nanorings with hexagonal cross-sections.This nanoscale growth and etching process still strictly follows the bulk crystal growth mechanism, thus shedding light on the synthesis of other nanoparticle with controlled morphologies and porous structures.     

Effect of reactor pressure on the growth rate and structural properties of GaN films

The effect of reactor pressure on the growth rate, surface morphology and crystalline quality of GaN films grown on sapphire by metalorganic chemical vapor deposition is studied. The results show that as the reactor pressure increases from 2500 to 20000 Pa, the GaN surface becomes rough and the growth rate of GaN films decreases. The rough surface morphology is associated with the initial high temperature GaN islands, which are large with low density due to low adatom surface diffusion under high reactor pressure. These islands prolong the occurrence of 2D growth mode and decrease the growth rate of GaN film. Meanwhile, the large GaN islands with low density lead to the reduction of threading dislocation density during subsequent island growth and coalescence, and consequently decrease the full width at half maximum of X-ray rocking curve of the GaN film.     

Effects of Ti additive on HPHT diamond synthesis in Fe-Ni-C system

Diamond crystals with low nitrogen concentration were synthesized from the Fe-Ni-C system with Ti additive at high pressure and high temperature （HPHT） in a china-type cubic high pressure apparatus （CHPA）. The synthesis pressure range was 4.8-5.2 GPa, and the temperature range was 1420-1600 K. The lowest synthesis pressure for diamond fell first and then rose with the increase of Ti additive. The color, shape, surface morphology and nitrogen impurity concentration of the synthesized diamond crystals were characterized using optical microscopy （OM）, scanning electron microscopy （SEM） and micro Fourier transform infrared （FTIR） spectrometry. The results show that the Ti additive has significant effects on color, growth rate, crystal shape, surface morphology and nitrogen impurity con- centration of the synthesized diamond crystals. The color of diamond crystals synthesized without Ti additive is yellow, while that with Ti additive becomes light and nearly colorless. The growth rate without Ti additive is higher than that with Ti additive. The crystal shapes of as-grown diamond crystals vary with the increase of Ti additive. The {111} crystal faces become dominant and some {311} crystal faces appear with the increase of Ti additive. The concentration of nitrogen impurity in diamond crystals without Ti additive is higher than that with Ti additive.     

A comparison study on the melt crystallization kinetics of long chain branched and linear isotactic polypropylenes

The isothermal and non-isothermal crystallization kinetics of LCBPP and linear-iPP was investigated by optical microscopy and differential scanning calorimetry （DSC）. The optical microscopy results in the isothermal crystallization process show that the crystals of LCBPP grow slower than the crystals of the linear-iPP. This originates from the low chain mobility, or in other words, the lower chain diffusion rate of LCBPP due to the existence of long side chains. The DSC results in the isothermal crystallization process show that the LCBPP exhibits, however, a higher overall crystallization rate with respect to the linear-iPP. This is related to the higher nucleation ability of LCBPP since the isothermal crystallization process of both LCBPP and linear-iPP are nucleation-dominated. Avrami analysis indicates that the nucleation nature and crystal growth manner of LCBPP and linear-iPP are about the same. The analyses of the non-isothermal crystallization processes indicate an increment in crystallization rate with increasing cooling rate. But at any cooling rate, the linear-iPP crystallizes more quickly than the LCBPP. This implies that the non-isothermal crystallization processes of LCBPP and linear-iPP are diffusion-dominated, in which the lower chain diffusion rate of LCBPP results in the slower crystallization of it.     

Spheroidization of molybdenum powder by radio frequency thermal plasma

To control the morphology and particle size of dense spherical molybdenum powder prepared by radio frequency (RF) plasma from irregular molybdenum powder as a precursor, plasma process parameters were optimized in this paper. The effects of the carrier gas flow rate and molybdenum powder feeding rate on the shape and size of the final products were studied. The molybdenum powder morphology was examined using high-resolution scanning electron microscopy. The powder phases were analyzed by X-ray diffraction. The tap density and apparent density of the molybdenum powder were investigated using a Hall flow meter and a Scott volumeter. The optimal process parameters for the spherical molybdenum powder preparation are 50 g/min powder feeding rate and 0.6 m3/h carrier gas rate. In addition, pure spherical molybdenum powder can be obtained from irregular powder, and the tap density is enhanced after plasma processing. The average size is reduced from 72 to 62 μm, and the tap density is increased from 2.7 to 6.2 g/cm3. Therefore, RF plasma is a promising method for the preparation of high-density and high-purity spherical powders.     

Relationship between Microcellular Foaming Injection Molding Process Parameters and Cell Size

In order to study the relationship between the main process parameters and the cell size, the mathematical model of cell growth of microcellular foaming injection process is built. Then numeric simulation is employed as experimental method, and the Taguchi method is used to analyze significance of effect of process parameters on the cell size. At last the process parameters are focused on melt temperature, injection time, mold temperature and pretidied volume. The significance order from big to small of the effect of each process parameters on cell size is melt temperature, pre-filled volume, injection time, and mold temperature. On the basis of above research, the effect of each process parameter on cell size is further researched. Appropriate reduction of the melt temperature and increase of the pre-filled volume can optimize the cell size effectively, while the effects of injection time and mold temperature on cell size are less significant.     

Preliminary study of non-isothermal phase change phenomena in vertical Bridgman crystal growth

Axisymmetric dual reciprocity boundary element method (DRBEM) with augmented items is extended to simulate the heat and mass transfer problems in the vertical Bridgman method (VBM) crystal growth of HgCdTe and CdZnTe. Axial solute concentration redistribution of three regions numerically reap-pears, and the influence of the pulling rate of the ampoule on it is further studied. Secondly, one di-mensional transient phase change phenomena is studied, and non-isothermal phase change phe-nomena is obtained from the initial transient region through the steady growth region to the final tran-sient region. Thirdly, the two-dimensional axisymmetric phase change interface position, interfacial shape and the temperature field of the melt and the crystal are numerically captured under the condi-tion to arrive at the steady state with zero pulling rate of the ampoule. Finally, the study of transient axisymmetric non-isothermal phase change phenomena is stressed and the results are compared with those in isothermal phase change. The influence of the pulling rate on non-isothermal phase change phenomena is revealed.     

Photocatalytic property of TiO2 sensitized by different crystal phase CdS

TiO2 samples sensitized by different crystal phase CdS(CT) are synthesized by hydrothermal process at different reaction temperature. The samples are characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM), and UV-Vis diffuse reflectance(UV-Vis). The XRD result reveals that the crystal phase of CdS is transformed from cubic phase to hexagonal phase with the increase of hydrothermal reaction temperature(120-160 ℃). The absorption edge of CT is extended from 498 nm to 546 nm. The photocatalytic degradation of rhodamin B(RhB) in aqueous solution is used to evaluate the photocatalytic activity of CT. With the increase of the preparation temperature, the photocatalytic activity of CT becomes stronger. The degradation rate of RhB by CdS/TiO2 at 160 ℃(CT-160 ℃)reaches 78%.     

Effects of gravity on the electrodeposition and characterization of nickel foils

The effects of gravity on nickel electrodeposition, the morphology and mechanical properties of deposits were studied in a super gravity field. Predictions in a microgravity field were also presented based on the obtained experimental tendency. Linear sweep voltammetry reveals that the nickel electrodeposition process is enhanced by increasing the gravity coefficient (G). The limiting current density changes from 10.2 to 293.0 mA·cm-2 with the increase of the G value from 10-4 to 354. The morphology of deposits was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The images show that the morphology deposited in the super gravity field has finer grain sizes and denser and smoother surfaces. The roughness reduces from 48.3 to 4.9 nm with the increase of the G value from 10-4 to 354. Meanwhile, mechanical tests indicate that the mechanical properties of nickel foils are greatly improved due to introducing a super gravity field during electrodeposition.     

Synthesis and formation mechanism of micro/nano flower-like MgCO3·5H2O

Micro/nano magnesium carbonate pentahydrate（MgCO3 ·5H2 O） with flower-like morphology was synthesized using magnesite as a substrate and potassium dihydrogen phosphate as an additive. The synthesized samples were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry and differential scanning calorimetry. The influence of pyrolysis time on crystal morphology was explored. The formation mechanism was investigated on the basis of the characterized results and the crystal structure of MgCO3 ·5H2 O. The results showed that the flower-like MgCO3 ·5H2 O was 1.5-3.0 μm in length and 100-500 nm in diameter and was successfully obtained with a pyrolysis time of 30 min. The formation mechanism of flower-like MgCO3 ·5H2 O is suggested to be the selective adsorption of potassium dihydrogen phosphate on the surface. The process of flower-like crystal growth is as follows： amorphous nanoparticles formation, acicular and rod monocrystal formation, flower-like monocrystal formation, and flower-like polymers（MgCO3 ·5H2 O） crystallization. In the MgCO3 ·5H2 O crystal, the magnesium ion presents two different octahedral coordinations corresponding to2 26 Mg（H O）＋and2 2 2 4 23 [Mg（H O）（CO） ]--, and the chemical formula of the crystal is2 2 6 2 4 23 Mg（H O） Mg（H O）（CO）2.     

Effects of cooling rate and Al on MnS formation in medium-carbon non-quenched and tempered steels

The effect of Al on the morphology of MnS in medium-carbon non-quenched and tempered steel was investigated at three different cooling rates of 0.24, 0.43, and 200℃·s-1. The formation mechanisms of three types of MnS were elucidated based on phase diagram information combined with crystal growth models. The morphology of MnS is governed by the precipitation mode and the growth conditions. A monotectic reaction and subsequent fast solidification lead to globular Type I MnS. Type II MnS inclusions with different morphological characteristics form as a result of a eutectic reaction followed by the growth in the Fe matrix. Type III MnS presents a divorced eutectic morphology. At the cooling rate of 0.24℃·s-1, the precipitation of dispersed Type III MnS is significantly enhanced by the addition of 0.044wt% acid-soluble Al (Al_s), while Type II MnS clusters prefer to form in steels with either 0.034wt% or 0.052wt% Al_s. At the relatively higher cooling rates of 200℃·s-1 and 0.43℃·s-1, the formation of Type I and Type II MnS inclusions is promoted, and the influence of Al is negligible. The results of this work are expected to be employed in practice to improve the mechanical properties of non-quenched and tempered steels.     

Electroplating of Ni/Co–pumice multilayer nanocomposite coatings: Effect of current density on crystal texture transformations and corrosion behavior

The present paper aims to investigate the influence of the current density in the electroplating process on the microstructure, crystal texture transformations, and corrosion behavior of Ni/Co-pumice multilayer nanocomposite coatings. The Ni/Co-pumice composite coatings were prepared by deposition of Ni, followed by the simultaneous deposition of pumice nanoparticles (NPs) in a Co matrix via an electroplating process at various current densities. Afterward, the morphology, size, topography, and crystal texture of the obtained samples were investigated. Furthermore, electrochemical methods were used to investigate the corrosion behavior of the produced coatings in a solution of 3.5wt% NaCl. The results indicated that increasing the plating current density changed the mechanism of coating growth from the cell state to the column state, increased the coating thickness, roughness, and texture coefficient (TC) of the Co (203) plane, and reduced the amount of pumice NPs incorporated into the Ni/Co-pumice composite. The electrochemical results also indicated that increasing the current density enhanced the corrosion resistance of the Ni/Co-pumice composite.     

Simulation of sub-micron particle formation and growth during combustion processes

Sub-micron particle formation and growth during combustion processes is very complex because of its strong uncertainty and randomness. A model to simulate the sub-micron particle formation and growth during the combustion process is developed based on the gas kinetic theory and is expressed by the vapor concentration changes and particle loading changes, which reflects effect characteristics of different mechanism (nucleation, condensation and coagulation) in particle formation processes. The developed characteristic time is used to token the three mechanisms. It is thought that environmental temperature and pressure, vapor temperature and critical pressure are important factors influencing the sub-micron particle formation and growth. The sub-micron particle formation processes under different conditions are studied and the effect characteristics of these mechanisms are analyzed, which show that the nucleation, condensation,and coagulation occur simultaneously during the sub-micron particle formation and growth process. Nucleation contributes to the sub-micron particle formation, while condensation and coagulation is helpful to the growth of the particle size.     

Corrosion behavior and characteristics of the product film of API X100 steel in acidic simulated soil solution

The short-term corrosion behavior of API X100 steel in an acidic simulated soil was investigated by electrochemical measurements and soaking experiments, followed by corrosion morphology observations and X-ray photoelectron spectroscopy analyses. The results show that X100 steel exhibits an obvious pitting susceptibility in an acidic soil environment. Pits nucleate after approximately 10 h of immersion. Along with the nucleation and growth of the pits, the charge-transfer resistance and open-circuit potential first increase sharply, then decrease slowly, and eventually reach a steady state. The maxima of the charge-transfer resistance and open-circuit potential are attained at approximately 10 h. The evolution of the electrochemical process is confirmed by the analysis of the product film. The product film exhibits a porous and loose structure and could not protect the substrate well. The product film is primarily composed of ferrous carbonate and ferrous hydroxide (Fe(OH)₂). The concentration of Fe(OH)₂ in the product film increases from the inside to the outside layer.     

Synchrotron X-ray diffraction techniques for in situ measurement of hydride formation under several gigapascals of hydrogen pressure

The high-pressure technique is a fundamental tool for realizing novel phase transitions, chemical reactions, and other exotic phenomena. Hydrogenation is one example of a high-pressure reaction; at high pressures of several gigapascals, hydrogen becomes chemically active and reacts with metals and alloys to form hydrides. This paper covers a high-pressure study of the hydrogenation process and the synthesis of hydrides using a cubic-type multi-anvil apparatus. The experimental details of a hydrogenation cell assembly, high-temperature and highpressure generation, and an in situ observation technique are presented. These experiments are conducted with the aid of in situ synchrotron radiation X-ray diffraction measurements operated in an energy-dispersive mode in the conventional manner for time-resolved measurements and a newly developed angle-dispersive mode for observation of the crystal growth process during formation of metal hydrides. Two successful cases of high-pressure hydrogenation are presented： aluminum hydride, Al H3, and an aluminum-based alloy hydride, Al2 Cu Hx, which are potential candidates for hydrogen storage materials.