Doping dependent metal to insulator transition in the(Bi,Pb)-2212 system:The evolution of structural and electronic properties with europium substitution

The present work investigates the effect of europium substitution on the （Bi, Pb）-2212 system in the concentration range 0.5 ≤ x ≤1.0. Phase analysis and lattice parameter calculations on the powder diffraction data and the elemental analysis of EDX show that the Eu atoms are successfully substituted into the （Bi, Pb）-2212 system. Resistivity measurements （64-300 K） reveal that the system exhibits superconductivity at x ≤ 0.5 and semiconductivity at x 〉 0.5. With the complete suppression of superconductivity which is known to be a quasi-two dimensional phenomenon in these materials, a metal to insulator transition takes place at x = 0.6 and the predominant conduction mechanism is found to be variable range hopping between localized states, resulting in macroscopic semiconducting behaviour. The results of electrical and structural properties of the doped （Bi, Pb）-2212 compounds suggest that the decrease of charge carrier concentration and the induced structural disorder are the more effective and dominant mechanisms in the origin of the metal to insulator transition and suppression of superconductivity due to Eu substitution at its Sr site.

Silicon Nitride Bonded Silicon Carbide Bricks YB/T 4035-2007

1 Scope This standard specifies the definition, classifica- tion, technical requirements, test methods, quality appraisal procedures, packing, marking, transportation, storage, and quality certificate of silicon nitride bonded silicon carbide bricks.

Effect of Silicon Content on Wear Resistance of Al-Si Alloys

The sliding wear behavior of hypoeutectic, eutectic and hypereutectic Al - Si alloys under lubricating condition was investigated. The wear mechanism of three kinds of alloys was discussed and an effective way to improve the wear reslstance of Al - Si alloys was put forward, that is increasing the silicon content.

Symplectic analysis for elastic wave propagation in two-dimensional cellular structures

On the basis of the finite element analysis, the elastic wave propagation in cellular structures is investigated using the symplectic algorithm. The variation principle is first applied to obtain the dual variables and the wave propagation problem is then transformed into two-dimensional （2D） symplectic eigenvalue problems, where the extended Wittrick-Williams algorithm is used to ensure that no phase propagation eigenvalues are missed during computation. Three typical cellular structures, square, triangle and hexagon, are introduced to illustrate the unique feature of the symplectic algorithm in higher-frequency calculation, which is due to the conserved properties of the structure-preserving symplectic algorithm. On the basis of the dispersion relations and phase constant surface analysis, the band structure is shown to be insensitive to the material type at lower frequencies, however, much more related at higher frequencies. This paper also demonstrates how the boundary conditions adopted in the finite element modeling process and the structures＇ configurations affect the band structures. The hexagonal cells are demonstrated to be more efficient for sound insulation at higher frequencies, while the triangular cells are preferred at lower frequencies. No complete band gaps are observed for the square cells with fixed-end boundary conditions. The analysis of phase constant surfaces guides the design of 2D cellular structures where waves at certain frequencies do not propagate in specified directions. The findings from the present study will provide invaluable guidelines for the future application of cellular structures in sound insulation.

Properties and Microstructure Evolution of Al_2O_3-Si Material Fired in Different Atmospheres

A1203-Si composite specimens were prepared using fused corundum, ultra-fine α-A1203 and Si powder as starting materials and resin as binder. Effects of sintering atmospheres on properties, phase composition and microstructure of specimens after firing at 1 500 ℃ were investigated. The results show that： （ 1 ） after .firing in oxidizing or weak oxidizing atmosphere, there is some Si in the specimens and some glass phases containing mullite form on specimen surface, the density and strength at room temperature are relatively high, but hot modulus of rupture and thermal shock resistance are relatively poor; （2） after firing in, weak reducing or reducing atmosphere, Si reacts completely with CO or N2forming whisk-phere, Si reacts completely with CO or N2forming whisk-er-like SiC, granular Si2N20 or 0＇-SiAION, and the er-like SiC, granular Si2N20 or O＇-SiMON, and the thermo-mechanical properties of specimens are enhanced;（3） after firing in nitrogen atmosphere, Si reacts completely with N2, CO or G forming wbisker-like SiC and columnar β-SiA10N crystals, the hot modulus of rupture and thermal shock resistance of specimens are enhanced noticeably.

Effect of Pyrophyllite Particle Size on Properties of AI_2O_3-SiC-C Bricks for Iron Ladles

The Al2O3 -SiC-C bricks for iron ladles were pre-pared asing bauxite, fused corundum,pyrophyllite, SiC powder and flake graphite as main starting materials, and phenolic resin as binder. The effect of pyroph,yllite particle size on permanent change in dimensions, cold crushing strength, oxidation resistance, and corrosion resistance of Al2O3 - SiC - C bricks was investigated. The results show that with the decrease of the pyrophyllite particle size, the permanent change in dimensions of Al2O3 - SiC - C bricks decreases, cold crushing strength increases, the oxidation resistance at 1400 ℃ increases, and the corrosion resistance at 1500℃ decreases.

Thermo-mechanical Properties of In-situ Formed Al_2O_3-SiC-SiAION Composites

Al2 O3 - SiC - SiAION composite specimens have been prepared using fused alumina, ultra fine α-Al2O3, Si and Al powders as starting materials and liquid phenol formaldehyde resin as binder and firing at 1 500 ℃ for 3 h in carbon embedded condition. Thermo-mechanical properties of Al2 O3 - SiC - SiAlON composites have been studied. The results show ： （ 1 ） Al2 O3 - SiC - SiAION composites can be prepared and sintered at 1 500 ℃ under carbon embedded condition. When Si/Al ratio is 8/0 and 7/1, the prepared composite is Al2O3 - SiC - O＇ -SiAlON; when Si/Al ratio is 5/3 and 3/5, the pre- pared composite is Al2 O3 - SiC - β-SiAION. （ 2 ） The composites possess high temperature strength properties. Hot modulus of rupture at 1 400 ℃ is 10 - 30 MPa. They are in elastic range up to 1 000 ℃, after which plastic deformation is observed; even at 1 400 ℃, amount of deformation is relatively low. （3） The com- posites possess good thermal shock resistance, their resid- ual strength ratio （AT = 1 100 ℃ ） is 65% - 80%. （4） The marked improvement in thermo-mechanical properties of Al2O3 - SiC - SiAlON composites may be at- tributed to the in-situ formation of SiC, SiAlON and AIN, the fibrous SiC, columnar SiAlON and tabular-like AlN fill in the corundum skeleton structure creating strengthening and toughening effects.

Flexibility of Burned Al_2O_3-C Due to Bending Tests at Room Temperature

Simple three-point bending test at ambient tempera- ture characterized the mechanical behavior of burned Al2O3 -C refractories before and after thermal shock in association with the processing parameters （graphite content and coking temperature, etc. ）. The results showed that non-linear plastic-elastic behavior under load lower than cold modulus of rupture （CMOR） was registered in all specimens and real linear elastic behavior could be identified after the first load, The total deformation could be divided into two parts, plastic and elastic areas. The graphite content and joint bonding system of carbon and ceramic phases were responsible for mechanical behavior of Al2O3 - C refractories.

Effect of Treated Graphite on Properties of Al_2O_3-SiC-C Castables

Al2O3 - SiC - C castables with 2% pitch or 2%, 4% and 6% treated graphite, respectively, were prepared based on the basic formulation of traditional Al2O3 - SiC - C castables. The flowability of castables, and bulk density, volume stability, strength, oxidation resistance and slag resistance of specimens fired at 110 ℃, 1 100 ℃, and 1 500 9Z respectively were comparatively studied. The results showed that： （1） With carbon source changing from pitch to treated graphite and the increase of treated graphite addition, water addition of castables increased, bulk density of specimens fired at different temperatures increased firstly and then decreased, strength after drying decreased obviously, strength after firing and oxidation resistance changed slightly, hot modulus of rupture increased obviously; （2） Slag resistance of specimen with treated graphite was worse than that of specimen with the same amount of pitch, but the former was obviously improved with the increase of treated graphite addition.

Impact of Bauxite on Performance and Structure of SiC-mullite Brick

SiC- mullite brick is widely used in the upper and lower transitional zones of cement rotary kilns, due to excellent thermal shock resistance, and abrasion resist- ance. The investigation of different bauxites was made on the performance and micro-structure of SiC - mullite brick, especially thermal shock resistance. In two batches of bricks （ G1 and G2 ） , and two grades of bauxites （ L1 and I_2 ）, samples＇ physical and chemical properties were tested, and microstructure and phase composition were studied by SEM and XRD. The results show that raw material I2, containing large numbers of micro- pores smaller than 4 μm, has well developed mullite phase. While using L2 as aggregates and flues, SiC- mullite brick G2 has excellent thermal shock resistance. Therefore, for manufacture of SiC - mullite brick, not only chemical composition, bulk density and open porosi- ty of bauxite are important, but also its microstructure has to be considered, such as phase composition, crystal size and pore size distribution.

Development and Application of Al_2O_3-Si_3N_4 Refractories Used in Blast Furnace

Newly developed Al2O3-Si3N4 composite refractories used for blast furnace is introduced in this work. Al2O3-Si3N4 composite refractories attacked by alkali vapor and blast furnace slag was investigated. High performance Al2O3-Si3N4 composite refractories was produced and used at both 2560m^3 blast furnaces of Tan-gsteel and No. 5 blast furnace of Shaosteel.

Influences of Al and Si Powders on Microstructure and Hot Mechanical Properties of Al_2O_3-C Slide Plates

The basic formulation of Al2O3- C slide plates was65%（ in mass,the same hereinafter） white fused corundum particles,25% white fused corundum fines,6% active α-Al2O3 micropowder,4% carbon black and flake graphite, and additional 4% phenolic resin.Based on this formulation,3% Al powder,3% Si powder,and 3% Al ＋ 3% Si powder were used to substitute equivalent white corundum fines to improve the hot mechanical properties of Al2O3- C slide plates. The specimens with dimensions of 140 mm × 25 mm × 25 mm were pressed at 150 MPa,dried at 200 ℃ for 24 h,and hot treated at 1 400 ℃ for 3 h in carbon embedded condition. Then hot modulus of rupture and thermal shock resistance of the specimens were tested and the phase compositions and microstructure were analyzed. The results show that specimen with 3% Al powder has the higher hot modulus of rupture but lower residual modulus of rupture after thermal shock than the specimen with3% Si powder; the specimen with 3% Al ＋ 3% Si powders exhibits the highest hot modulus of rupture and the best thermal shock resistance; the change of mechanical property is closely related with the in-situ formed nonoxides： AlN in the form of bars is formed in specimens with Al powder; fibrous SiC whiskers are formed in specimens with Si powder; in the specimens with both Al and Sipowders,besides AlN and SiC whiskers,hexagonal tabular SiAlON is in-situ synthesized,which interlocks with each other.

Effect of Pelletized Graphite Addition on Properties of Al_2O_3-SiC-C Castables

Al2O3 - SiC - C castables with pelletized graphite addition of 0. 2%, 4% or 6% （by mass, the same hereinafter ） were prepared using brown fused corundum （8 - 5, 5 - 3 and 3 - 1 mm ） , dense fused corundum （ ≤1 and 0. 045 mm） and SiC （ ≤1 and ≤0. 064 mm） its main starting materials with mass ratio of aggregate： matrix = 71： 29, 2% silicon powder and 0. 4% B4C as antioxidants, and pelletized graphite as carbon source, Effect of pelletized graphite addition on physical properties, oxidation resistance, slag resistance arid thermal shock resistance of Al2O3 -SiC- C eastables was researched. The results show that： with the in.crease of pelletized graphite addition, the required water amount of castables increases, the bulk density and strength reduce; with 4% pelletized graphite, the eastable performs the best oxidation resistance; the increase of graphite is beneficial to the improvement of slag penetration resistance and corrosion resistance; with 6% pelletized graphite, the thermal shock resistance is the best.

THEORETICAL STUDIES OF THE NATURE OF THE 2210 cm^(-1) IR ABSORPTION PEAK IN SILICON CRYSTAL CONTAINING HYDROGEN (Ⅲ)——TEMPERATURE EFFECTS OF THE PEAK SHAPEAND THE SYMMETRIC BREAKING OF DEFECT COMPLEX

It is verified that the phonon scattering process and the residual linewidthare the dominant factors of the linewidth of 2210 cm^(-1) IR absorption peak except the anomalous linewidth at 200 K. By investigating the anomalities of the peak shape and thelinewidth of the peak at 200 K, we put forward a mechanism that the T_d symmetry of defect-complex corresponding to the 2210 cm^(-1) peak can he transferred into the D_(2d) symmetry as temperature rises to above 200 K. The quantitative analysis shows that the V+4H-model is indeed of two states: The T_d configuration is stable at temperature lower than 200 K, while the D_(2d) one is stable at temperature higher than 200 K. We can draw the conclusion that the V +4H-model corresponds to the 2210 cm^(-1) IR absorption peak from the symmetric breaking mechanism, which can quantitatively fit the experimental results.

户外绝缘子积污特性的试验与仿真(英文)

Flashover on polluted insulators is the most common accident occuring in power system.A great amount of work has been done to study the flashover characteristics on various kinds of insulators with several theoretical models proposed.In these models,the amount and the distribution of the pollution on the insulator is critical to the flashover performance.However,very few simulation works has been carried out to study the pollution accumulation characteristics on the insulators.In this paper,both experimental and numerical efforts were given to study the pollution accumulation characteristics in order to evaluate the flashover probability.Experiments were performed first to have a bird view on the overall pollution distributions considering several crucial influential factors such as the wind speed and wind direction.AC porcelain insulators(XWP_2-160 type) were selected as the experimental samples and the equivalent salt deposit density(ESDD) was measured after the total predetermined amount of pollution was reached.Then, aerodynamic simulation was carried out to study the airflow and velocity distributions on each part of the insulator in clean air with regard to different wind speed and direction.It was found that the amount of the pollution on each section of the insulator has clear connections to the wind speed or air pressure distribution on the insulator surface.These distributions coincide to the pollution distribution obtained from experiments.Besides,the wind speed and air pressure distribution along the insulator chain was also studied.This work has shown that the numerical simulation may predict the pollution distribution on the insulators with practical accuracy.It is also possible to design new insulator shapes to reduce the pollution accumulation on critical areas according to the analysis in this work.

Refractories for RH Degassers and Ways of Improving Their Lining Life

This paper attempts to clarify the systematic works of the refractories for the RH degassers and the ways of improving their lining life. It includes ： （ 1 ） types of RH degassers ; （2） the operating conditions of refining and the severely damaged areas in RH degassers ; （3） the reasons why side wall and bottom of lower vessel, throat and snorkels become the severe wear areas are analyzed, such as erosion and abrasion caused by the high circula- tion rate of treated molten steel, thermal and structural spalling by the violent temperature change, high corrosion by the Fe-oxides containing siliceous slag and CaF：riched desulfurization powders attack, degradation of texture by the vaporization of refractory components in vacuum and in oxygen blowing; besides the above men- tioned factors, what other reasons to make the snorkels become the most quick wear elements are also explained; （4） the studies of resistance to refining slags attack and slag penetration and its prevention ; the evaluation of va- rious refractory materials to withstand the attack of slags is based on the experimental results of rotating cylinder method, rotary drum test and induction furnace test, and the phase diagrams analyses; the measures to reduce the slag penetration are discussed, for example the deep of slag penetration can be decreased by reducing the size of brick pores ; （5） suitable refractory materials selection and recent developments for the different severe wear areas in RH, and lining maintenance; （6） refractories for RH to refine silicon steel; （7） the ways of improving RH lining life.

Application Research of Dense Sintered Alumina in Iron Runner Castables

Three different kinds of corundum aggregates-tabular sintered alumina, dense sintered alumina, and fused dense corundum-were introduced into the silica fume .free or silica fume containing Al2O3 -SiC - C iron runner castables to investigate their influences on the flow ability, linear change on heating, bulk density, apparent porosity, cold strength, hot modulus of rupture, therm, al shock resistance, slag resistance, oxidation resistance as well as wear resistance of Al2O3 - SiC - C iron runner castables. The results show that （ 1 ） compared with the specimens with fused dense corundum, the specimens with dense sintered alumina have equivalent installation property, slag resistance and oxidation resistance, equivalent or even higher cold modulus of rupture, cold crushing strength and hot modulus of rupture, exhibiting better thermal shock resistance and cold wear resistance ; （2） adopting bimodal alumina micropowder LISAL22RABL as well as water reducers ZX2 and ZD2 can well reduce the water requirement of silica fume free castables, solving the problem of deteriorated flow ability resulted from the lack of silica fume; since the lack of silica fume avoids the formation of low melting point liquid, the hot modulus of rupture and the thermal shock resistance of the silica fume free castables are both better than those of the silica fume containing castables ; （3） the density of the castable specimens with dense sintered alumina is 4% -6% lower than that of the castable specimens with Jhsed dense corundum so the refractories consumption of one iron runner reduces by 5% by using the tastable with dense sintered alumina, which obviously reduces the cost of refractories.

Protection strategy for improved catalytic stability of silicon photoanodes for water oxidation

Silicon-based electrodes have attracted great attention in the artificial photosynthetic systems that mimic natural photosynthesis and directly convert the solar energy into chemical energy. Despite significant efforts to date,catalytic stability of the silicon photoelectrodes is limited by their poor electrochemical stability. The formation of passivation or protective layers provides a feasible strategy to improve the photocatalytic stability of silicon photoelectrodes. Many candidates including metals, metal oxides, metal silicides and polymers have been explored as the protection layers for silicon photoelectrodes. The present review gives a concise overview of the protected silicon photoanodes for water oxidation with a focus on the relationship between the structural architecture of silicon photoanodes and their photocatalytic activity and stability.

Relationship between the parent charge transfer gap and maximum transition temperature in cuprates

One of the biggest puzzles concerning the cup- rate high temperature superconductors is what determines the maximum transition temperature （Tc,max）, which varies from less than 30 to above 130 K in different compounds. Despite this dramatic variation, a robust trend is that within each family, the double-layer compound always has higher Tc,max than the single-layer counterpart. Here we use scanning tunneling microscopy to investigate the electronic structure of four cuprate parent compounds belonging to two different families. We find that within each family, the double layer compound has a much smaller charge transfer gap size （ACT）, indicating a clear anticorrelation between AcT and Tc,max. These results suggest that the charge transfer gap plays a key role in the superconducting physics of cuprates, which shed important new light on the high To mechanism from doped Mott insulator perspective.

Epitaxy of GaAs thin film with low defect density and smooth surface on Si substrate

Device-quality GaAs thin films have been grown on miscut Ge-on-Si substrates by metal-organic chemical vapor deposition. A method of two-step epitaxy of GaAs is performed to achieve a high-quality top-layer. The initial thin buffer layer at 360 ℃ is critical for the suppression of anti-phase boundaries and threading dislocations. The etch pit density ofGaAs epilayers by KOH etching could reach 2.25 × 10^5 cm^-2 and high-quality GaAs top epilayers are observed by transmission electron microscopy. The band-to-band photoluminescence property of GaAs epilayers on different substrates is also investigated and negative band shifts of several to tens of meVs are found because of tensile strains in the GaAs epilayers. To achieve a smooth surface, a polishing process is performed, followed by a second epitaxy of GaAs. The root-mean-square roughness of the GaAs surface could be less than 1 nm, which is comparable with that of homo-epitaxial GaAs. These low-defect and smooth GaAs epilayers on Si are desirable for GaAs-based devices on silicon substrates.