Superplastic behavior of reciprocating extruded Mg-6Zn-1Y-0.6Ce-0.6Zr from rapidly solidified ribbons

RRE-Mg66 alloy with a composition of Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6Zr was prepared by combinatorial processes of rapid solidification, reciprocating extrusion and extrusion. Microstructure was evaluated on SEM and TEM. The average grain size of the alloy is 0.7 ??m, the size of the second phase at grain boundary is 0.15 ??m, and the size of the intragranular precipitates in round shape is less than 20 nm. Superplastic behavior of the material was investigated in a temperature range of 150 to 250 °C and initial strain rate range of 3.3×10^?4 to 3.3×10^?2 s^?1 in air. The highest elongation of 270% was obtained at 250 °C and 3.3× 10^?3 s^?1. High-strain-rate superplasticity and low-temperature superplasticity were achieved. The superplasticity results from intragranular sliding (IGS) at temperatures from 170 to < 200 °C and grain boundaries sliding (GBS) at 250 °C. At 200 °C a combination of IGS and GBS contributes to the superplastic flow.     

Study on Graphene Oxide Modified Inorganic Phase Change Materials and Their Packaging Behavior

We prepared the nano-inorganic phase-change "alloy" materials through the modification of Na_2SO_4·10H_2O using Na_2HPO_4·12H_2O and GO nano-nucleating agent, and further investigated their thermophysical properties such as melting/solidification temperatures and enthalpies via differential scanning calorimetry. When the weight ratio of Na_2SO_4·10H_2O and Na_2HPO_4·12H_2O was 8:2 and the weight ratio of graphene oxide was 0.5% of phase change material, the phase change "alloy" material showed excellent performances, specifically, the melting temperature and latent heat were found to be 22 ℃ and 190 J/g with a degree of subcooling decreased from 8.6℃ to 2.1℃. In order to extend the application of the phase change "alloy" material to building energy saving field, it was adsorbed on expanded glass beads under vacuum and further covered with diatomite. When the adsorption rate of EGB(volume) and PCAM(weight) was 2.5:1, the particle size of diatomaceous earth was found to be 3.6μm, while the best packaging result was obtained with the melting temperature and latent heat being 21℃ and 135 J/g, and no leakage was observed.     

Microstructure and flow stress of Mg-12Gd-3Y-0.5Zr magnesium alloy

The microstructure and flow stress of the Mg-12Gd-3Y-0.5Zr magnesium alloy was investigated by compression test at temperatures ranging from 350 to 500 ℃ and the strain rates ranging from 0.01 to 20 s-1. The flow stress of the magnesium alloy increased with strain rate and decreased with deformation temperature. Flow stress can be expressed in terms of the Zener-Hollomon parameter Z, which describes the combined influence of the strain rate and temperature using an Arrhenius function.The values of the deformation activation energy were estimated to be 245.9 and 171.5 kJ/mol at deformation temperatures below 400 ℃ and above 400 ℃, respectively. Two constitutive equations were developed to quantify the effect of the deformation conditions on the flow stress of the magnesium alloy. The effects of deformation temperature and strain rate on the microstructure of the magnesium alloy were also examined and quantified by measuring the volume fraction of dynamically recrystallized grain Xd. Xd increased with increasing of deformation temperature. When the deformation temperature was below 475 ℃, Xd decreased with strain rate until it reached 0.15 s-1, then it increased again. When the deformation temperature was above 475 ℃, Xd increased with strain rate.     

Effect of ECAP on the microstructure and mechanical properties of a high-Mg<Subscript>2</Subscript>Si content Al-Mg-Si alloy

A high-Mg₂Si content Al alloy was extruded by equal channel angular pressing (ECAP) for 8 passes at 250 °C and an ultrafine-grained structure with an average grain size of about 1.5 μm was achieved. The coarse skeleton-shaped Mg₂Si phase presenting in the as-cast alloy are significantly fragmented into fine rod-shaped as well as equiaxed particles mostly less than about 230 nm and become relatively dispersed. The tensile strength 192.8 MPa and the elongation up to 31.3% at ambient temperature are attained in the 8-pass ECAPed alloy versus 163.3 MPa and 9.1% in the as-cast alloy. High-temperature creep test at 250 °C reveals that the ECAPed sample exhibits a high elongation close to 100% at a relatively high creep rate 7.64×10⁻⁵ s⁻¹, compared to the elongation 56% at a low strain rate 1.74×10⁻⁷ s⁻¹ in the as-cast alloy.     

Synthesis of C3S by sol-gel technique and its features

Sol-gel method is a technique to synthesize inorganic materials based on wet-chemical reaction theory. The results have shown that reactants tetraethyl orthosilicate (TEOS) and Ca(NO₃)₂·4H₂O can form sol and gel in solution at 50–60 °C, and the cosolvents are propyl alcohol (NPA) and H₂O, the catalyst is HNO₃. This sol-gel is burned for 12 h at 1 350–1 450 °C so that the organic matter, free water (moisture) in sol-gel system are removed and a solid reaction has taken place to form the resulting product. The product has been confirmed to be C₃S by XRD, SEM and ²⁹Si MAS NMR, as well as free lime content of the product which is less than 0.2% was determined by propanetriol-ethanol-method. The analysis determined by EDXA has indicated that the n(Ca)/n(Si) ratio in corresponding to micro-region is close to theoretical value of 3:1. This resulting product is C₃S with Si sites of Q⁰ polymerization, and has higher purity and hydraulic activities at earlier age of hydration.     

Effect of matrix composition on physical properties of Al<Subscript>3</Subscript>CON in-situ reaction reinforced corundum composite

60% white corundum used for aggregate, 5% aluminium powder for fixed additions and 35% various additives for matrix were prepared for specimens 1#,2#,3#. They were mixed uniformly with the suitable resin as a binder and pressed under pressure of 315 ton forging press, then dried at 200℃ for 24 h. Effects of various additives on 1500 ℃×2 h creep properties of Al3CON reinforced corundum composite were researched. The experimenal results show that creep coefficients of specimens 1#,2#,3# at 1500 ℃×2 h are 1.4×10^- 4, -9.4×10^-4, -22.6×10^-4, respectively. Crushing strength of the slide plate added with suitable additive A after fired at 1500 ℃ ×3 h reaches to 225 MPa, the creep rate is positive all the time from 0% to 0.014% at 1500 ℃ for 2 h. The microstructure result analysis shows that reinforced phases of Al3CON fiber composite have been formed after fired with Al powder in coke at high temperatures for specimen 1#, and the strength of the composite is increased. The hot modulus of rupture is up to 59 MPa at 1400 ℃ and the RUL is obviously higher than that at 1700 ℃. Its service life is two times as that of Al2O3-C slide plate when used in the process of pouring steel. The mechanism of creep rate resistance of the composites can be discovered by means of SEM and EDAX analysis. It is concluded that the active Al3CON and Al2O3 multiphases that were formed by N2 in gas, C, Al and Al2O3 inside the matrix of the composites during in-situ reaction,which gives the composites outstanding creep rate resistance for the dense zone resuiting from Al3CON oxidation that inhibits contraction at the high temperature. Besides, the matrix will turn into the multiphase with high refractoriness, N content and its Al3CON reinforced fiber will further increase accordingly. In addition, Al3CON formed by Al2O3 and C, Al in the matrix with N2 in gas will inhibit the creep rate and also greatly improve the creep rate resistance of the composites.     

Evolution and characterization of damage of concrete under freeze-thaw cycles

To study the internal damage of concrete under freeze-thaw cycles, concrete strains were measured using embedded strain gauges. Residual strain and coefficients of freezing expansion (CFE) derived from strain-temperature curves were used to quantify the damage degree. The experimental results show that irreversible residual strain increases with the number of freeze-thaw cycles. After 50 cycles, residual strains of C20 and C35 concretes are 320με and 100με in water, and 120 με and 60 με in saline solution, respectively. In lower temperature range (-10 ℃ to -25 ℃) CFE of C20 and C35 concretes decrease by 9.82×10-6/K and 8.44×10-6/K in water, and 9.38×10-6/K and 5.47×10-6/K in saline solution, respectively. Both residual strains and CFEs indicate that during the first 50 freeze-thaw cycles, the internal damage of concrete in saline solution is less than that of concrete in water. Thus residual strain and CFE can be used to measure the frost damage of concrete.     

Synthesis and tribological behaviors of Ti3SiC2 material prepared by vacuum sintering technique

The bulk Ti₃SiC₂ specimens with less than 1 wt% TiC impurity were prepared by vacuum sintering technique, and the average grain size was about 5–6 μm in the elongated direction. When the sintering temperature, soaking time and heating rate were 1 400 °C, 1 h and 10 °C·min^?1, respectively, the highest relative density of Ti₃SiC₂ specimens could reach 97.8%. Meanwhile, the lowest coefficient of friction (COF) and wear rate (WR) of the Ti₃SiC₂ samples were 0.55 and 1.37×10^?3 mm³(Nm)^?1 at a sliding speed of 0.35 m/s, load pressure of 10 N and ambient condition, respectively. The COF of the Ti₃SiC₂ sample reduced with the increasing of the load pressure, while the WRs fluctuated little. The WR increased with the increasing of the sliding speed, and weakly influenced the COF. These changing behaviors could be attributed to the presence and coverage of the amorphous mixture oxide film of Ti, Si, Al, and Fe on the Ti₃SiC₂ friction surface. The self-antifriction mechanism led to reducing of the COF. The increasing of the WR was attributed to the wearing consumption.     

Synthesis of refractory cordierite from calcined bauxite, talcum and quartz

A cordierite was synthesized from calcined bauxite, talcum, and quartz. The properties and microstructure of the cordierite sintered samples were characterized by Archimedes’ method, thermal dilatometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), and so on. The experimental results showed that calcined bauxite could broaden the range of synthesizing temperature from 1300 °C to 1420 °C and get pure cordierite. The bulk density and linear thermal expansion coeffi cient of the sample synthesized at 1420 °C for 2 h were 1.97 g·cm^?3 and 2.1×10^?6 °C^?1, respectively. The XRD analysis showed that the major crystalline phase was α-cordierite with almost no glassy matters, the SEM images illustrated a small vent hole and the size were 5–100 μm, the well-grown hexagonal and granular cordierite grains had the sizes distributed among 0.1–8 μm, and providing high mechanical strength and lower linear thermal expansion coeffi cient.     

Reaction products of MgO and microsilica cementitious materials at different temperatures

The paste was prepared by mixing MgO, microsilica and H2O in the presence of water reducer at different reaction ratios and temperatures, and characterized by XRD, DTA, TGA, IR, and solid-state 29Si NMR. The experimental results showed that, besides Mg(OH)2, magnesium silicate hydrate (M-S-H) was formed at a low temperature such as 25 and 50 ℃. At a high temperature of 100 ℃, Mg(OH)2 can be further transformed into M-S-H completely, for instance, within ca. 1 month in an excess of microsilica. The average composition and structure of M-S-H was mainly related to the reaction mixture and curing temperature and was discussed in detail.     

Thermodynamics and kinetics of calcium sulphoaluminate

The formation process of calcium suphoaluminate(C4A3S) was investigated by the X-ray diffraction technique and then the thermodynamics was analyzed, finally the kinetics of which was studied by SC-132. XRD results show that the formation of C4A3S is accomplished in three different kinds of ways: one is by solid reaction of Ca (OH)2/ CaO, Al2O3 and CaSO4, other two ways are through such interstitial products as CaO·Al2O3 and CaO·2Al2O3. The formation thermodynamics shows that C4A3S begins to form at 900 ℃-1 000 ℃ and increases as temperature rising; the quantity of reaches the highest at 1 300 ℃-1 350 ℃ and then falls at >1350℃. Kinetics study shows that the formation rate of C4A3S can be described as first-order kinetics at high temperature, and it belongs to the random nucleation growth mechanism. The apparent activation energy is 456.37 kJ·mol-1 and pre-exponential factor is 1.545×1012.     

Co-precipitation/hydrothermal synthesis of BiFeO<Subscript>3</Subscript> powder

A coprecipitation/hydrothermal route was utilized to fabricate pure phase BiFeO3 powders using FeCl3·6H2O and Bi（NO3）3·5H2O as starting materials, ammonia as precipitant and NaOH as mineralizer. The synthesized powders were characterized by XRD, SEM and DSC-TG analysis. In the process, single-phase BiFeO3 powders could be obtained at a hydrothermal reaction temperature of 180 ℃, with NaOH of 0.15 mol/L, in contrast to 200 ℃ and 4 mol/L for conventional hydrothermal route. Meanwhile, the micro-morphology of synthesized BiFeO3 powders changed with different reaction temperatures and concentrations of NaOH. The N6el temperature, Curie temperature and decomposition temperature of the synthesized BiFeO3 powders were detected to be 301 ℃, 828 ℃ and 964 ℃, respectively. The hydrothermal reactions mechanism to fabricate BiFeO3 powders were discussed based on the in-situ transformation process.     

In-Situ Preparation and thermal shock resistance of mullite-cordierite heat tube material for solar thermal power

In order to improve the thermal shock resistance of solar thermal heat transfer tube material, the mullite-cordierite composite ceramic as solar thermal heat transfer tube material were fabricated by pressureless sintering using α-Al2O3 , Suzhou kaolin, talc, and feldspar as starting materials. The important parameter for solar thermal transfer tube such as water absorption (Wa ), bulk density (Db ), and the mechanical properties were investigated. The phase composition and microstructure of the composite ceramics were analyzed by XRD and SEM. The experimental results show that the B3 sintered at 1 300 ℃ and holding for 3 h has an optimum thermal shock resistance. The bending strength loss rate of B3 is only 2% at 1 100℃ by air quenching-strength test and the sample can endure 30 times thermal shock cycling, and the water absorption, the bulk density and the bending strength are 0.32%, 2.58 g·cm-3 , and 125.59 MPa respectively. The XRD analysis indicated that the phase compositions of the sample were mullite, cordierite, corundum, and spinel. The SEM images illustrate that the cordierite is prismatic grain and the mullite is nano rod, showing a good thermal shock resistance for composite ceramics as potential solar thermal power material.     

Effect of the sputtering parameters on the structure and properties of Cu<Subscript>3</Subscript>N thin film materials

Copper nitride (Cu₃N) thin films were successfully deposited on glass substrates by reactive radio frequency magnetron sputtering. The effects of sputtering parameters on the structure and properties of the films were studied. The experimental results show that with increasing of RF power and nitrogen partial pressure, the preferential crystalline orientation of Cu₃N film is changed from (111) to (100). With increasing of substrate temperature from 70 °C to 200 °C, the film phase is changed from Cu₃N phase to Cu. With increasing sputtering power from 80 W to 120 W, the optical energy decreases from 1.85 eV to 1.41 eV while the electrical resistivity increases from 1.45 ×10² Ω · cm to 2.99 × 10³ Ω · cm, respectively.     

Effect of catalyst on structure of （PEO）8LiClO4-SiO2 composite polymer electrolyte films

（PEO）8LiClO4-SiO2 composite polymer electrolytes（CPEs） were prepared by in-situ reaction, in which ethyl-orthosilicate （TEOS） was catalyzed by HCl and NH3·H2O, respectively. The ionic conductivity, the contact angle and the morphology of inorganic particles in the CPEs were investigated by AC impedance spectra, contact angle method and TEM. The conductivities of acid-catalyzed CPE and alkali-catalyzed CPE are 2.2×10^-5 and 1.1×10^-5 S/cm respectively at 30 ℃. The results imply that the catalyst plays an important role in the structure of in-situ preparation of SiO2, and influences the surface energy and conductivity of CPE films directly. Meanwhile, the ionic conductivity is related to the surface energy.     

Chemical vapor deposition of SiC at different molar ratios of hydrogen to methyltrichlorosilane

Chemical vapor deposition (CVD) of SiC from methyltrichlorosilane (MTS) was studied at two different molar ratios of H₂ to MTS (n(H₂)/n(MTS)). The total pressure was kept as 100 kPa and the temperature was varied from 850 to 1 100 °C at a total residence time of 1 s. Steady-state deposition rates as functions of reactor length and of temperature, investigated at different n(H₂)/n(MTS) values, show that hydrogen exhibits strongly influences on the deposition rate. Especially, the deposition of Si co-deposit can be obtained in broader substrate length and at higher temperatures with increasing hydrogen partial pressure. Influence of hydrogen on the deposition process was also studied using gas phase composition and deposit composition analysis at various n(H₂)/n(MTS). SEM micrographs directly show the variation of surface morphologies at various n(H₂)/n(MTS). It can be found that the crystal grain of the deposit at 1 100 °C is better developed and the crystallization is also improved with increasing n(H₂)/n(MTS).     

Sulfonic acid modified hollow silica spheres and its application in proton exchange membranes

In order to improve the proton conductivity of hollow silica spheres (HSS)/perfluorosulfonic acid ion-exchange (PFSA) composite membranes as proton exchange membrane, sulfonic acid groups were grafted onto the surfaces of HSS via post grafting methods. TEM images and FT-IR spectra of the obtained sulfonic acid groups modified hollow silica spheres (SAMHSS) illustrated that the sulfonic acid groups were successfully grafted onto the surfaces of HSS. Water uptake and swelling degree of SAMHSS/PFSA composite membranes were found much higher than those of HSS/PFSA membranes due to the introduction of hydrophilic sulfonic acid groups. In a range from 50 °C to 130 °C, the highest conductivity of composite membranes was obtained when 5 wt% SAMHSS was loaded. The maximum conductivity reached 7.5×10⁻² S·cm⁻¹ at 100 °C and 100% relative humidity, even the temperature increased to 130 °C, the conductivity of composite membranes with 5 wt% SAMHSS could reach 3.7×10⁻² S·cm⁻¹ at 100 % relative humidity, while the conductivity of the recast PFSA was only 2.2×10⁻³ S·cm⁻¹.     

Ethylene Polymerization by a Novel Dinuclear Heter-oligated Titanium Complex with the Ligand of （Salicylaldiminato） （β-enaminoketonato）

The condensation of acetylacetone （CH3COCH2COCH3） with benzdine （H2N-C6H4-C6H4-NH2） yielded diimine ligand 1 [HOC（Me）C（H）（Me）C=N（p-C6H4）（C6H4-p）N= C（Me）C（H）C（Me）OH）], which was converted into sodium salts. And then the sodium salts reacted with monosalicylaldiminato titanium complex 2{[3,5-di-But′2-（O）C6H2CHN（PH）]TiCl3（THF）} in dried dichloromethane to give a new benzdine-bridged binuclear complex 3{[3,5-di-Bu′-2-（O）C6H2CHN（PH）]2 [OC（Me）C（H）（Me）C=N（p-C6H4）-（C6H4-p）N=C（Me）C（H） C（Me）]Ti2Cl4}. The complex 3 was characterized by ^1HNMR and elemental analysis. In the presence of MAO（methylaluminoxane）, the complex 3 in toluene was effective to catalyze polymerization, affording moderately high catalytic activity 1.93 × 10^5 g PE/（mol.Ti.h）]and high molecular weight polyethylene [5.63× 10^5 g/moll. The high temperature gel permeation chromatography （GPC） curve of polyethylene obtained revealed a single peak, but the molecular weight distribution （MWD = 3.21） is obviously broader than that of the similar mononuclear titanium complex. The melting points of the obtained polyethylene reaches 138 ℃, indicating that the polyethylene is of high crystallinity.     

Preparation, characterization and dielectric properties of Sr5RTi3Ta7O30 (R=Pr and Eu) ferroelectric ceramics

Polycrystalline samples of Sr₅PrTi₃Ta₇O₃₀ (SPTT) and Sr₅EuTi₃Ta₇O₃₀ (SETT) compounds were prepared by high-temperature solid-state reaction method and their formation, structure and dielectric properties were studied. They are found to be ferroelectric phase of filled tetragonal tungsten bronze (TB) structure at room temperature and undergoes diffuse type of ferroelectric-paraelectric phase transition around 34 °C and 31 °C, respectively. At 1 MHz SPTT exhibits high dielectric constants of 177 and low dielectric losses of 3.5×10⁻⁴ and SETT has high dielectric constants of 125 and low dielectric losses of 2.4×10⁻³.     

Study on the isothermal oxidation behavior in air of Ti3AlC2 sintered by hot pressing

The isothermal oxidation behavior at 900–1300°C for 20 h in air of bulk Ti₃AlC₂ with 2.8 wt% TiC sintered by means of hot pressing was investigated in the work. The isothermal oxidation behavior generally followed a parabolic rate law. The parabolic rate constants increased from 1.39×10⁻¹⁰ kg²·m⁻⁴·s⁻¹ at 900°C to 5.56×10⁻⁹ kg²·m⁻⁴·s⁻¹ at 1300°C. The calculated activation energy was 136.45 kJ/mol. It was demonstrated that Ti₃AlC₂ had excellent oxidation resistance due to the continuous, dense and adhesive protect scales consisted of a mass of α-Al₂O₃ and a little of TiO₂ and/or Al₂TiO₅. In principle, the oxide scale was grown by the inward diffusion of O²⁻ and the outward diffusion of Ti⁴⁺ and Al³⁺. The rapid outward diffusion of cations usually resulted in the formation of cracks, gaps, and holes.