The novel epoxidized soybean oil-modified-phenolic resin/clay nanocomposites(ESO-M-PR/CN) was prepared. The coupling agent-benzyldimethylphenylammonium chloride [C6H5CH2N+(CH3)2C6H5Cl−, B2MP] was adopted to modify the interface between the organic and inorganic phases. The effect of the nanocomposite structure on its physical and chemical properties was discussed. During the synthesizing process of ESO-M-PR/CN, the phenol hydroxyl was etherified by ESO or ESO epoxy resin prepolymer to provide long ESO epoxy segments. Long ESO epoxy resin chain segments enhanced the crosslink density of ESO-MPR/CN. The thermal and mechanical properties exhibit a significant improvement. The temperature at which a weight loss of 5% occurs increases from 287.1 °C to 402.3 °C. The flexural strength increases by 25%, while the flexural modulus increases by 39%. Moreover, the properties of resin were enhanced by the effect of the inorganic nanoparticles, while the size of the nanomontmorillonites in the phenolic resin was characterized with a scanning electron microscope. The particle size of inorganic montmorillonites in the modified system is less than 100 nm.
The surface organic modification of Fe3O4 nanoparticles with silane coupling reagent KH570 was studied. The modified and unmodified nanoparticles were characterized by FT-IR, XPS and TEM. The spectra of FT-IR and XPS revealed that KH570 was coated onto the surface of Fe3O4 nanoparticles to get Fe-OSi bond and an organic coating layer also was formed. Fe3O4 nanoparticles were spheres partly with mean size of 18.8 nm studied by TEM, which was consistent with the result 17.9 nm calculated by Scherrer’s equation. KH570 was adsorbed on surface and formed chemistry bond to be steric hindrance repulsion which prevented nanoparticles from reuniting. Then glycol-based Fe3O4 magnetic liquids dispersed stably was gained.
Under certain conditions of proper temperature and pH value, sodium silicate was hydrolyzed in liquid ammonia chloride, and spherical microfine SiO2 powder in micrometer-size was prepared. In this experiment, the relationship between needed time and proper pH value, temperature, density of the solution, and its current capacity were found. The optimum conditions are pH 8.5, 70 °C, and the concentration of sodium silicate is 0.6 mol/L for the density of the solution. The structure of spherical microfine silicon was charactetized by SEM and XRD.
CeO2-TiO2 films and CeO2-TiO2/SnO2:Sb (6 mol%) double films were deposited on glass substrates by radio-frequency magnetron sputtering (R.F. Sputtering), using SnO2:Sb(6 mol%) target, and CeO2-TiO2 targets with different molar ratio of CeO2 to TiO2 (CeO2:TiO2=0:1.0; 0.1:0.9; 0.2:0.8; 0.3:0.7; 0.4:0.6; 0.5:0.5; 0.6:0.4; 0.7:0.3; 0.8:0.2; 0.9:0.1; 1.0:0). The films are characterized by UV-visible transmission and infrared reflection spectra, scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The obtained results show that the amorphous phases composed of CeO2-TiO2 play an important role in absorbing UV, there are Ce3+, Ce4+ and Ti4+ on the surface of the films; the glass substrates coated with CeO2-TiO2 (Ce/Ti=0.5:0.5; 0.6:0.4)/SnO2:Sb(6 mol%) double films show high absorbing UV(>99), high visible light transmission (75%) and good infrared reflection (>70%). The sheet resistance of the films is 30–50 Ω/∟. The glass substrates coated with the double functional films can be used as window glass of buildings, automobile and so on.
Nanocrystalline Gd1.77Yb0.2Er0.03O3 samples were prepared by combustion and precipitation methods. Structures and upconversion luminescence properties of samples were studied. The results of XRD show that all samples are cubic structure, the average crystallite size could be calculated as 23 nm and 39 nm, respectively. The lattice constants were obtained. The FT-IR spectra were measured to investigate the vibrational feature of the samples. Upconversion luminescence spectra of samples under 980 nm laser excitation were investigated. The strong red emission of samples were observed, and attributed to 4F9/2→4I15/2 transitions of Er3+ ions, the emission intensity for sample synthesized by precipitation method is stronger compared to that of combustion method. The possible upconversion luminescence mechanisms in nanocrystalline Gd1.77Yb0.2Er0.03O3 were discussed.
Leucite particles were synthesized from feldspar mixed with 0% to 52% potassium nitrate fi red from 800 °C to 1 200 °C by solid state method. The X-ray Diffraction (XRD) patterns show that in the temperature range from 800 °C to 1 200 °C, the leucite can be removed as the single crystalline phase. Kalsilite may be crystallized with leucite at 800 °C, but can be eliminated after prolonged heating. The scanning electron Microscopy (SEM) images clearly display the that crystals of micrometer scale leucite, and the leucite crystals distribute evenly in the matrix. The Thermal expansion coeffi cient (TEC) of the samples fabricated is as high as 20.52sx10−6 °C−1 measured from 20 °C to 500 °C. The mechanism of transformation from feldspar to leucite was proposed.
The solid solution characteristics of Pb(B1/3Nb2/3)O3-based (B=Zn2+, Mg2+, Ni2+) composite ceramics prepared by two-phase mixed-sintering method were developed based on dielectric measurements. Results show that there are double dielectric peaks for PZN-based composite ceramic, implying two phases coexist. However single dielectric peak was presented in PMN-and PNN-based composite ceramics, respectively. It is indicated that obvious solid solution reaction exists during the sintering process of these two systems. The effects of B-site ion difference on the solid solution characteristics were discussed by crystal chemistry. SEM was employed to investigated the microstructures of composite ceramics. The influences of solid solution reaction on grain growth were discussed.
The morphology, mechanical properties of unsaturated polyester(UP) resin modified with TDI were studied via dynamic FT-IR spectra, SEM, DMA and mechanical property testing. Results show that companying with the cured cross-linking reaction of UP resin, TDI can firstly react with UP and produce polyurethane(PU), and then UP and PU form the cross-linking nets together. The impact fracture section morphology of modified UP resin manifested the typical sea-islands structure. Testing of mechanical properties showes that for introducing of PU, the TDI has an obvious effect on the toughness and strength of UP resin. When the ratio of TDI/UP (w/w) was 7.5%, the modified UP resin exhibited the best mechanical properties with flexural strength of 125 MPa, impact strength of 18 kJ·m−2 and tensile strength of 72 MPa.
A comparative study for two different series, La0.67Ca0.33Mn1−xCr xO3 and La0.67+xCa0.33−xMn1−xCr xO3, is performed with χ changing from 0.04 to 0.08 through measurements of zero-field resistivity (π), magnetoresistance (MR) and ac susceptibility (χ) as functions of temperature (T). For the second group, a single insulator-metal transition was characterized by the resistivity maximum appears in π vs. T curve. For the first group, besides the resistivity peak appearing at higher temperatures, the sample shows evidence for the existence of another peak appearing at lower temperatures. Compared to the first group, the second group shows a significant enhancement in MR effect, while the measurement of χ-T dependence does not display obvious differences for the two series. Different behaviors observed in the two series are discussed by considering possible exchange interaction between Mn3+ ion and Cr3+ ion.
A novel lanthanum and sulfur co-doped TiO2 photocatalyst was synthesized by precipitation-dipping method, and characterized by X-ray diffraction(XRD), transmission electron microscopy(TEM) and UV-Vis diffuse reflectance spectroscopy. Compared with the S-doped TiO2, La-doped TiO2 and the standard Degussa P25 photocatalysts, the lanthanum and sulfur co-doped TiO2 photocatalyst (the molar percentage of La is 3.0%) calcined at 450 °C for 2 h showed the strongest absorption for visible light and highest activities for degradation of reactive blue 19 dye in aqueous solution under visible light(λ>400 nm) irradiation. It was also discovered that the co-doping of lanthanum and sulfur hindered the aggregation and growth of TiO2 particles, and the doping of lanthanum reduced slightly the phase transition temperature of TiO2 from anatase to rutile.
Ordered Ni70Fe30 nanowire array was fabricated in a porous alumina template by alternating current electrodeposition. The structural and magnetic properties of the as-obtained nanowire array were investigated by SEM, TEM, XRD, EDS and VSM. The results indicate that the as-obtained Ni70Fe30 nanowires exhibit a diameter of about 69.9 nm and aspect ratio of more than 60. Meanwhile, a preferred orientation [110] of bcc lattice was observed. The as-obtained nanowire array has an obvious magnetic anisotropy, of which the easy direction is perpendicular to the surface of the array. Moreover, after annealed, the Ni70Fe30 nanowire array exhibits an enhanced magnetic anisotropy.
Nanoparticles of hydroxyapatite(HAP), strontium half substituted hydroxyapatite (SrCaHAP) and strontium totally substituted hydroxyapatite (SrHAP) were prepared by sol-gel-supercritical fluid drying (SCFD) method. The nanoparticles were characterized by element content analysis, FT-IR, XRD and TEM, and the effects of strontium substitution on crystal structure, crystallinity, particle shape and antibacterial properties of the nanoparticles on Escherichia coli, Staphylococcus aureus, Lactobacillus were researched. Results show that strontium can half and totally substitute for calcium and enter the structure of apatite according to the initial atomic ratios of Sr/[Sr+Ca] as 0.5, 1. The substitution decreases the IR wavenumbers of SrCaHAP and SrHAP, and changes the morphology of the nanoparticles from short rod shaped HAP to needle shaped SrCaHAP, and back to short rod shaped SrHAP. The crystallinity of HAP is higher than that of SrCaHAP, but is lower than that of SrHAP. Moreover, the antibacterial property of SrCaHAP and SrHAP are improved after the calcium is half and totally substituted by strontium.
Fe3O4 magnetic nanoparticles were prepared by co-precipitation of Fe2+ and Fe3+ in an ammonia solution, and its size was about 36 nm measured by an atomic force microscope. Fe3O4 magnetic nanoparticles were modified by L-dopa or dopamine using sonication method. The analysis of FTIR clearly indicated the formation of Fe-O-C bond. Direct immobilization of trypsin (EC: 3.4.21.4) on Fe3O4 magnetic nanoparticles with L-dopa and dopamine spacer was investigated using glutaraldehyde as a coupling agent. No significant changes in the size and magnetic property of the three kinds of magnetic nanoparticles linked with or without trypsin were observed. The existence of the spacer molecule on magnetic nanoparticles could greatly improve the activity and the storage stability of bound trypsin through increasing the flexibility of enzyme and changing the microenvironment on nanoparticles surface compared to the naked magnetic nanoparticles.
A novel heat substrate technique, high frequency inductive heat deposition (IHD), was introduced to coat porous carbon materials, C/C and carbon felt to improve their bioactivity. The morphologies, composition and microstructure of the resulting coatings were examined by scanning electron microscopy (SEM), energy dispersive spectra (EDS), X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR). The results show that, the calcium phosphate consisted of non-stoichiometric, CO3-containing and plate-like octacalcium phosphate (Ca 8−xH2(PO4)6, OCP) could uniformly cover the entire porous surfaces of carbon materials. Good adhesion of the coating to carbon material substrates was observed.
The structural change in phase transition of hybrid (Cl2H25NH3)2MnCl4 was investigated. The temperature and the structures of the phase transition is investigated by thermal gravimetry (TG) and differential scanning calorimetry (DSC), infrared spectrum (IR) and X-ray diffraction (XRD). The results suggest that the phase transition is reversible and the structural change arises from the conformation change of the organic chain. The interlayer distance increases when the hybrid transforms from low temperature phase to high temperature phase. This is explained by the diffusion of gauche-bond along the organic chains and they move away from each other when the phase transition occurs. Combining the experimental data with theoretical calculation, we propose that organic chain of the hybrid in high temperature phase is the conformation of gauche-bond alternating with trans bond (noted as GTG′TGTG′TGTG′T).
A novel UV-curable prepolymer polypropyleneglycol diglycidyl ether diacrylate (PPGGEA) was synthesized by utilizing polypropyleneglycol diglycidyl ether (PPGGE) and acrylic acid (AA) as starting materials, N, N-dimethylbenzylamine as catalyst and p-hydroxyanisole as inhibitor. The optimum synthetic conditions were in the following: the concentration of N, N-dimethylbenzylamine was 0.80 wt% of reactants, the concentration of p-hydroxyanisole was 0.3 wt% of reactants, the reaction temperature was 90–110 °C, and the molar ratio of PPGGE to AA was 1:2.2. Meanwhile, 1-hydroxycyclohexyl phenyl ketone of a UV-cured initiator was added to the synthesized PPGGEA to prepare a kind of UV-cured coating. The mechanical properties of the UV-cured films were determined, giving 29.99 MPa of tensile strength, 834.27 MPa of the Young’s modulus and 5.66% of elongation at tear.
The structure and electrical properties of (Na0.5Bi0.5)0.94Ba0.06TiO3 ceramic doped with 0.5 wt% of MnO were investigated in comparison with those of (Na0.5Bi0.5)0.94Ba0.06TiO3 ceramic. It was ascertained that the MnO addition did not cause remarkable change in crystal structure and microstructure. The MnO addition mainly displayed a hard effect on the electrical properties, an increase of coercive field (E c) and mechanical quality factor (Q m) together with a decrease of dielectric constant (ɛ r) and piezoelectric constant (d 33). An enhancement of electromechanical coupling factor (k p) with the MnO addition was obtained too. An essential relation between the piezoelectric properties and ferroelectric nature of the ceramics was detected. It was found that the piezoelectric properties of the ceramics highly depended on the corporative contribution of remanent polarization (P r) and coercive field.
Alkali induced morphology and property improvements of TiO2 by hydrothermal reaction were investigated. The products were characterized by SEM, TEM, XRD, TG, EDX, FT-IR and DRS. The results indicate that, with the phase transformation from anatase to rutile, the morphologies changed from high aggregated particles to nanofibers with the diameter of about 100 nm and the length up to several tens of micrometers, meanwhile the process is controllable by manipulating the nature of the alkali, alkalinity and hydrothermal temperature. DRS analysis shows the property improvement of the nanofibers in the UV-Vis light absorption compared with the raw materials, implying the products have potential application in photocatalysis.
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 °C, with NaOH of 0.15 mol/L, in contrast to 200 °C 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 Néel temperature, Curie temperature and decomposition temperature of the synthesized BiFeO3 powders were detected to be 301 °C, 828 °C and 964 °C, respectively. The hydrothermal reactions mechanism to fabricate BiFeO3 powders were discussed based on the in-situ transformation process.
The chiral materials were prepared by using the carbon fiber helices as chiral inclusions, and the composite of Fe3O4 and polyaniline as matrix. The electromagnetic properties, including the rotation angles, the axial ratios and the complex chirality parameters, were measured by using a circular waveguide method in the 8.5–11.0 GHz frequency range. The dependence of these electromagnetic properties on the frequency and the concentration of the Fe3O4 in the composite matrix were analyzed. The results show that an appropriate concentration of Fe3O4 in the matrix is useful in improving the electromagnetic properties of the chiral material.
Nano/micro replication, a technique widely applied in the microelectronics field, was introduced to prepare the hydrophobic bionics microstructure on material surface. Poly(vinyl alcohol) (PVA) and polystyrene (PS) moulds of the mastoid microstructure on lotus leaf surface were prepared respectively by the nano/micro replication technology. And poly(dimethylsiloxane) (PDMS) replicas with the mastoid-like microstructure were prepared from these two kinds of polymer moulds. Scanning electronic microscope (SEM) was employed to investigate the morphology and microstructures on moulds and replicas. Both the static and dynamic contact angles between water droplet and PDMS replicas’ surface were also measured. As a result, similar microstructure can be observed clearly on the surface of PDMS replicas and the static contact angle on PDMS replicas was enhanced dramatically by the existence of these microstructures.
Calcium sulphoaluminate was prepared with chemical reagents in this paper. The formation mechanism of calcium sulphoaluminate and effect of CuO on the formation mechanism of calcium sulphoaluminate were investigated by the chemical analysis, X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The results show that there are three ways in the formation of calcium sulphoaluminate. CuO can promote the decomposition of calcium carbonate and decrease the formation temperature of calcium sulphoaluminate
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. When the burning temperature is below 1 000 °C, the addition of CuO can promote the formation of calcium sulphoaluminate, while CuO can not favor the formation of calcium sulphoaluminate above 1 000 °C.The bonding status and chemical environment of SiO4 and AlO4 tetrahedras of three types of geopolymeric products were systematically investigated by infrared spectroscopy. The relationship between amorphous geopolymeric products and zeolite crystals with the same overall chemical compositions was also discussed. The infrared evidence shows that SiO4 tetrahedra is partially bonded by AlO4 during the hydration process of geopolymeric cement. The two types of tetrahedras jointly construct the three dimensional framework structures of the geopolymeric products. The mutual transformation between geopolymeric products and corresponding zeolite crystals will take place once the reaction condition is suitable, which reveals that the nature of geopolymeric products are probably the amorphous equivalent of the corresponding zeolite crystals.
Microwave boriding layer microstructure of carbon steels and its diffusion mechanics were studied. The results show that the existence of microwave field in the boriding can’t change the growth mechanics of boriding layer. Compared with conventional boriding, if the treatment temperature and time remain constantly, the descend rate of the boriding layer thickness with the increase of carbon content of steel is smaller. The diffusion activation energy of T8 steel is 2.6×105 J/mol between the temperature of 750 °C and 900 °C in microwave field, which is in the same order of conventional boriding.
A theoretical model based on BCT lattice structure was developed. Resultant force in the BCT lattice structure was deduced, following the interaction force of two kinds of magnetic particles. According to empirical FroHlich-Kennelly law, the relationship between the magnetic induction and the magnetic field was discussed, and a predictive formula of shear stresses of the BCT lattice structure model was established for the case of small shear deformation. Compared with the experimental data for different particle volume fractions, the theoretical results of the shear stress indicate the effects of the saturation magnetization and the external magnetic field on the shear stress.
Microspheres of conducting polymers poly N-methylaniline (PNMA) were successfully synthesized through oxidation of N-methylaniline without any template. The average diameter of the microspheres with a smooth surface was about 0.40 μm when 0.2 M N-methylaniline was oxidized with 0.2 M ammonium persulfate in 0.2 M of HClO4 solution. The size of microspheres can be controlled by changing reaction time and temperature. The acid concentration was critical for the formation of microspheres with smooth surfaces. The excellent antibacterial performance of PNMA in novolac epoxy coating to sulfate reducing bacteria was demonstrated. Moreover, in API media, PNMA inhibited growth of SRB and then reduced the corrosion rate of carbon steel remarkably.
Chitosan and β-cyclodextrin were used to prepare microspheres with theophylline for pulmonary delivery by spray drying method. The characteristics, mucociliotoxicity, permeation rate and drug release were studied. The drug entrapments of microspheres I, II and III were from 35.70% to 21.09% and 13.33%, while yields and encapsulation efficiencies were higher than 45% and about 90% respectively. The microspheres possessed low tap densities (0.34–0.48 g/cm3), appropriate diameters (3.35–3.94 μm) and theoretical aerodynamics diameters (2.20–3.04 μm). SEM images showed the microspheres were spherical with smooth or wrinkled surface surfaces. FT-IR demonstrated theophylline had formed hydrogen bonds with chitosan and β-cyclodextrin. The microspheres could effectively reduce the ciliotoxicity and easy to penetrate the memberine. The in vitro release of the microspheres was related to the ratio of drug/polymer and microspheres II had a prolong release, providing the release of 72.00% in 12 h. The results suggestes that chitosan/β-cyclodextrin microspheres II are a promising carrier as sustained release for pulmonary delivery.
Tin was found in the bottom of float borosilicate glasses. To simulate the enriched amounts of SnO found on the surface of the float borosilicate glasses, a series of glasses were produced in which the stannous concentration was varied from 0.1 wt% to 9.0 wt%, while the relative concentration of other components were held constant. Infrared spectra were obtained to probe the effect of increased amounts of SnO on the structure of the glass samples. The results show that SnO plays the role of an intermediate in glasses studied. When FO/SnO>1.0, SnO takes the role of network-former. And when FO/SnO<1.0, SnO can give the free oxygen as network-modifier. Besides, SnO has intensive effect on thermal performance of borosilicate glasses.
The dynamic recrystallization (DRX) behavior of Nb-Ti microalloyed steels was investigated by isothermal single compression tests in the temperature range of 900–1 150 °C at constant strain rates of 0.1–5 s−1. DRX was retarded effectively at low temperature due to the onset of dynamic precipitation of Nb and Ti carbonitrides, resulting in higher values of the peak strain. An expression was developed for the activation energy of deformation as a function of the contents of Nb and Ti in solution as well as other alloying elements. A new value of corrective factor was determined and applied to quantify the retardation produced by increase in the amount of Nb and Ti dissolved at the reheating temperature. The ratio of critical strain to peak strain decreases with increasing equivalent Nb content. In addition, the effects of Ti content and deformation conditions on DRX kinetics and steady state grain size were determined. Finally, the kinetics of dynamic precipitation was determined and effect of dynamic precipitation on the onset of DRX was clarified based on the comparison between precipitate pinning force and recrystallization driving force.
The alumina ceramics with the homogeneous microstructure and the higher density were fabricated via the modified-starch consolidation process by 1.0 wt% of a modified starch as a consolidator/binder. The swelling behavior of the modified oxidized tapioca starch was analyzed by optical microscope, and two other corn starches (common corn starch and high amylose corn starch) were also analyzed for comparison. The modified starch used as a binder for the consolidation swelled at about 55 °, began to gelatinize at 65 ° and then was completely gelatinized at 75 °. But the corn starches could not be completely gelatinized even at 80 ° for 1 h. The high-strength green bodies (10.6 MPa) with the complex shapes were produced. The green bodies were sintered without any binder burnout procedure at 1 700 ° and a relative density of 95.3% was obtained for the sintered bodies, which is similar to that of the sintered sample formed by conventional slip casting. In addition, the effect of temperature on the apparent viscosity of the starch/alumina slurry in the process was investigated, and the corresponding mechanism for the starch consolidation was discussed.
The technology and microstructure of glass-ceramics and ceramic composite materials were studied. A suitable ceramic body was chosen on the basis of the sintering temperature of CaO-Al2O3-SiO2 system glass-ceramics. According to the expansion coefficient of the ceramic body, that of CaO-Al2O3-SiO2 system glass-ceramics was adjusted. β-wollastonite was found present as the major crystalline phase in glassceramic. The CaO-Al2O3-SiO2 system glass-ceramic layer and ceramic body could be sintered together by adjusting the sintering period. The compositions of glass-ceramic layer and ceramic body diffuse mutually at 1 100 °C, resulting in an interface between them. To achieve good sintered properties of glass-ceramics and the chosen ceramic body, at least a four-hour sintering time is used.
The delamination of kaolinite was performed via the combination of intercalation and sonication. The morphology including shape, size, and crystal structure before and after the treatment were investigated by using XRD, SEM, TEM and SED (selective electron diffraction). The results not only show that the particle size is significantly reduced after short time sonication treatment, such as BET area up to 52.29 m2/g after only 1 h sonication treatment, but also indicate that the treated particles keep good crystal structure. A new aluminum silicate nanoclub-like crystal formed after sonication treatment.
Single fiber pull-out testing was conducted to study the origin of the functional responses to loading of carbon fiber reinforced cement-based composites. The variation of electrical resistance with the bonding force on the fiber-matrix interface was measured. Single fiber electromechanical testing was also conducted by measuring the electrical resistance under static tension. Comparison of the results shows that the resistance increasing during single fiber pull-out is mainly due to the changes at the interface. The conduction mechanism of the composite can be explained by the tunneling model. The interfacial stress causes the deformation of interfacial structure and the interfacial debonding, which have influences on the tunneling effect and result in the change of resistance.
The properties of the passivation film formed on 316L stainless steel were studied by Electrochemical Impedance Spectroscopy (EIS), Mott-Schottky and Voltammetry measurements in high-temperature acetic acid. The results show that the passivation film formed on 316L stainless steel is stable in 60% acetic acid solution from 25 °C to 85 °C. As temperature increased, the polarization resistance decreased but the interface capacitance increased. There was hardly any relation between temperature and the intrinsic property semiconductor. The passivation film represents the p-semiconductor property in the potential interval of −0.5–0.1 V; represents the n-semiconductor property in the potential interval of 0.1–0.9 V; and represents the p-semiconductor property in the potential interval of 0.9–1.1 V. The voltammetry measurements show that the structure of the passivation film is stable when the temperature is lower than 55 °C and that its stability decreased when this temperature is exceeded.
By ring test and bend test, the improvement of waste tire rubber particles on the crackresistance and flexural behaviors of cement-based materials were investigated. Test results show that the cracking time of the ring specimens can be retarded by the incorporation of rubber particles in the cement paste and mortar. The improvement in the crack-resistance depended on the rubber fraction. When the rubber fraction was 20% in volume, the cracking time was retarded about 15 h for the paste and 24 d for the mortar respectively. Flexural properties were evaluated based on the bend test results for both mortar and concrete containing different amount of rubber particles. Test results show that rubberized mortar and concrete specimens exhibit ductile failure and significant deformation before fracture. The ultimate deformations of both mortar and concrete specimen increase more than 2–4 times than control specimens.
The effect of freezing and thawing cycles on mechanical properties of concrete (compressive, splitting tensile strength) was experimentally investigated. According to the pullout test data of three kinds of deformed steel bars, the bond stress-slip curves after freezing and thawing were obtained. The empirical equations of peak bond strength were proposed that the damage accounted for effects of freezing and thawing cycle. Meanwhile, the mechanism of bond deterioration between steel bars and concrete after freezing and thawing cycles was discussed. All these conclusions will be useful to the durability design and reliability calculation of RC structures in cold region.
The high water-cement ratio concrete specimens under biaxial compression that completed in a triaxial testing machine were experimentally studied. Strength and deformations of plain concrete specimens in two loading direction under biaxial compression with stress ratio of α=0, 0.25, 0.5, 0.75, 1.0 were obtained after 0, 25, 50 cycles of freeze-thaw. Influences of freeze-thaw cycles and stress ratio on the peak stress and deformation of this point were analyzed according to the experimental results. Based on the test data, the failure criterion expressed in terms of principal stress after different cycles of freeze-thaw, and the failure criterion with consideration of the influence of freeze-thaw cycle and stress ratio were proposed respectively.