Expansion joints silicone sealants used in high speed railway construction suffer from ultraviolet radiation (UV), high temperature combined with the alkaline environment. To evaluate the durability and analyse the ageing mechanism, six one-component silicone sealants from different companies were selected and subjected to accelerated ageing tests including UV, thermal and alkali ageing treatments. The ageing effects on the performance of the sealants were evaluated via the appearance and the mechanical property changes. The changes in molecular structure were studied by means of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetry (TG). This study revealed that different materials displayed different sensibilities to the ageing methods, in which 15 % – 20 % decreases of mechanical properties could be observed under UV radiation test, owning the most significant effects. Structure analysis showed that the physical changes of aggregative states were the principal factors to the performance, along with the chemical slight changes. The glossiness dropped significantly in ageing test, which could be used as one of the effective evaluation parameters for ageing conditions in the field.

Sapphire, belonging to hexagonal crystal system, is typically anisotropic which makes it direction-sensitive. To research the effects of growth directions on properties of sapphire, c-[0001] seed (c-sapphire) and a-[11-20] seed (a-sapphire) were used to prepare sapphire by edge-defined film-fed growth (EFG) method. The samples were analyzed through lattice integrity, dislocation and corrosion performance by double-crystal XRD, OM, AFM, SEM and EDX. It was shown that the lattice integrities of two growth-direction crystals were both well due to the small FWHM values. While the average densities of dislocation in c-sapphire and a-sapphire were 9.2×10³ and 3.9×10³ cm^-2 respectively, the energy of dislocation in c-sapphire was lower than that in a-sapphire. During Strong Phosphoric Acid (SPA) etching, the surface of c-sapphire basically kept smooth but in a-sapphire there were many point-like corrosion pits where aluminum and oxygen atoms lost by 2:1. Our work means that it will be promising for growing c-[0001] seed sapphire by EFG if aided by parameter optimization.

α-Al₂O₃ powders with different morphologies, namely fibrous, sheet-like, and spherical, were prepared by the hydrothermal-thermolysis method. Subsequently, polycrystalline, transparent cerium doped lutetium aluminum garnet (Lu₃Al₅O₁₂:Ce³⁺) green phosphors were synthesized by high temperature solid-state method using commercial lutetium(III) oxide, cerium(III) oxide, and as-prepared Al₂O₃ powders with different morphologies. The phases, morphologies, and photoluminescent properties of the prepared phosphors were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM), and photoluminescence spectroscopy(PL). Moreover, the influences of the morphologies of α-Al₂O₃ on the types of crystal structure, morphologies, and photoluminescent properties of LuAG:Ce³⁺ green phosphors were investigated. The results indicated that the morphologies and particle sizes of the α-Al2O3 powders could be controlled by the additives and parameters. Notably, the spherical α-Al₂O₃ powders with good dispersibility were found to be the excellent base materials of LuAG:Ce³⁺ green phosphors for white light emitting diodes.

Borosilicate glasses, with xB₂O₃-(60-x)SiO₂-8ZrO₂-8Ta₂O₅-24Na₂O (7≤x≤59 mol%) composition, were fabricated by melt-quenching technique. NMR, UV-Vis, Raman and IR spectroscopic studies were utilized to investigate the structure of fabricated glasses. The NMR spectrum was deconvoluted into five Gaussian bands, assigned to ⁴B(0B,4Si), ⁴B(1B,3Si), ⁴B(2B,2Si), ³B(rings) and ³B(loose), to get their quantitative information. The relative dispersion deviation ΔP _g,F was attributed to the relative quantity of ³B (rings) but not all ³B groups, and B₂O₃ existed mainly as [BO₃] in rings firstly, and then as [BO₃] in loose condition. The UV-Vis spectra revealed that the quantity of non-bridging oxygen increased firstly and then decreased with increasing concentration of B₂O₃. Acting as complementary techniques, Raman and IR measurements revealed that four-coordinated boron and silica mainly existed as ⁴B-O-B, and Si-O-Si in Q², respectively, as chain structure but not framework structure, and [BØ₄] units prefered connections with borate rather than with silicate entities of the glass network in these studied glasses. In addition, the conclusion also certified that ³B in “loose” condition located in lower wavenumbers between 1 200^-1 600 cm-1 in Raman spectra.

Manganese-doped Ba_0.925Ca_0.075TiO₃ lead-free piezoelectric ceramics (abbreviated as BCT) with high mechanical quality factor were synthesized by conventional solid-state reaction method. The effects of excess Ba on the crystal structure, microstructure, and electrical properties of the ceramics were systematically investigated. X-ray diffraction and Raman spectra revealed that Ca²⁺ ions were pushed from Ba sites to Ti sites of BCT when 1.5 mol% extra Ba²⁺ ions were added after sintering. The grain size of the ceramics was decreased by adding extra Ba²⁺ ions. The mechanical quality factor and resistivity of the ceramics decreased dramatically when the excess Ba was more than 1.5 mol%. High piezoelectric coefficients ( d ₃₃ = 150–190 pC/N ) and high mechanical quality factors ( Q _m = 1 000–1 200 ) were obtained in the ceramics when the excess of Ba was between 0.5 mol% and 1 mol%. These results indicated that the properties of BCT ceramics could be tailored by adjusting the content of Ba.

Photocatalytic reduction of CO₂ was carried out on villiform spherical catalysts of Pd-TiO₂ in isopropanol solution. The catalysts were synthesized by hydrothermal method, their structures, morphologies and optical absorption properties were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and UV-vis absorption spectroscopy (UV-vis). The photocatalytic activities with different loading amounts and morphologies were evaluated for determining the dominant effect and optimizing the catalyst preparation. Based on a villiform spherical TiO₂ with the largest specific surface area in our experiments, we prepared a set of catalysts with various loading amounts of palladium and tested them by bubbling CO₂ through the slurry of catalyst and isopropanol. The highest formation rate of isopropyl formate was 276.6 μmol/g·cat/h. Eventually we proposed the reaction mechanism.

The effect of strains on the thermal conductivity of Si/Ge superlattices was investigated by nonequilibrium molecular dynamics (NEMD) simulation. The thermal conductivities experienced a near linear drop with increasing tensile and compressive strains. It was explained by the fact that the decrease of the phonons velocities and a mass of structural defects generated under strains. Meanwhile, a theoretical calculation based on Modified-Callaway model was performed and it was found that the theoretical results were in good agreement with the molecular dynamics results.

Ce-doped Bi₂O₃ nanopowders were prepared by reverse titration chemical coprecipitation from Bi³⁺ and Ce⁴⁺ containing aqueous solution. Techniques of X-ray diffraction (XRD), transmission electron microscopic (TEM) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize the as-synthesized materials. The XRD patterns indicated that the peaks can be easily indexed to β-Bi₂O₃ and no diffraction peaks of Ce or other impurity phases were detected in the prepared samples. The calculated average crystalline size decreased from 31.72 to 11.96 nm when the Ce content increased from 1 wt% to 10 wt%. The morphology changed from flake-like into the spherical-like with increase in Ce content. The electric conductivity of Ce-doped Bi₂O₃ electrolyte was also investigated by two probe DC method. Conductivity analysis exhibited that the rate of conductivity increased with increasing Ce²⁺ ratio, when the Ce concentration was up to 5 wt%, the as-synthesized Ce-doped Bi₂O₃ electrolyte showed the maximum value of conductivity(0.295 S·cm^–1).

Phase pure ZrB₂-SiC composite powders were prepared after 1 450 °C/3 h via carbothermal reduction route, by using ZrSiO₄, B₂O₃ and carbon as the raw materials. The influences of firing temperature as well as the type and amount of additive on the phase composition of final products were detailedly investigated. The results indicated that the onset formation temperature of ZrB₂-SiC was reduced to 1 400 °C by the present conditions, and oxide additive (including CoSO₄·7H₂O, Y₂O₃ and TiO₂) was effective in enhancing the decomposition of raw ZrSiO₄, therefore accelerating the synthesis of ZrB₂-SiC. Moreover, microstructural observation showed that the as-prepared ZrB₂ and SiC respectively had well-defined hexagonal columnar and fibrous morphology. Furthermore, the methodology of back-propagation artificial neural networks (BP-ANNs) was adopted to establish a model for predicting the reaction extent (e g, the content of ZrB₂-SiC in final product) in terms of various processing conditions. The results predicted by the as-established BP-ANNs model matched well with that of testing experiment (with a mean square error in 10^-3 degree), verifying good effectiveness of the proposed strategy.

The rare earth doped TiO₂ was prepared and characterized with Nd, Ho and Y as the doping agents, which have obvious absorption in visible light area. The particle size of the glomeration was about 200–400 nm. TiO₂ sensor performed a significant change in resistance when exposed to methanol vapor. By comparison, the Nd, Ho and Yb doped TiO₂ sensors exhibited a response of 2.22, 4.05 and 3.78, and lowered response and recovery times of 91, 56 and 67 s, respectively. The Ho doped TiO₂ showed the best methanol-sensing properties, which exhibited high selectivity and response to methanol compared with the other tested vapors. In concentration of 0–10 ppm, the sensor exhibited excellent stability for detecting methanol at various concentrations.

The electronic structure, cohesive energy and interfacial energy of ferrite (100)/NbC (100) and TiC (100)/NbC (100) interfaces have been investigated by the first-principles calculation. Moreover, the heterogeneous nuclei mechanism of NbC particle was also analyzed. The results showed that the stacking sequences have a great influence on the cohesive energy and equilibrium interfacial separation of the above-mentioned interfaces. Compared with C-terminated interfaces, the cohesive energy of Nb-terminated ones is lower while the equilibrium interface distance is larger. Among the two C-terminated interface structures, the interfacial energy between the NbC and ferrite is 4.54 J/m², which is larger than that of NbC/TiC interface (1.80 J/m²). Therefore, NbC particles prefer heterogeneous nucleation on TiC particles surface rather than the ferrite matrix, which agrees well with the experimental result.

A series of FePd based alloy films were deposited on glass substrates by DC magnetron sputtering. The Ag toplayer effect was studied using FePd(67.5 nm)/Ag(3.875, 7.75, 15.50, 31 and 38.75 nm) films annealed at 600 °C for different time in order to find the role of the Ag toplayer in disorder-order of FePd film. The results show that the Ag toplayer can accelerate the phase transition from FCC to FCT in films. The magnetic easy axis of the crystallites in this film is in-plane of substrate. The Ag toplayer can greatly enhance the coercive of FePd films. When the thickness of Ag is equal to 31 nm, the film has a very large in-plane coercivity of 2.8 kOe and a very low out-of-plane coercivity of 1.04 kOe.

To study the extraction difficulty of lithium ions from various crystal planes of Li₂TiO₃, according to the first principle, four representative crystal surfaces of Li₂TiO₃ (precursor), (-133), (-206), (002) and (-131), were selected to establish a model and to calculate the surface energy, bond length and population using Materials Studio 5.5 (MS 5.5). The results demonstrate that there is no direct relationship between the surface energy and the order of disappearance of the four diffraction peaks when lithium titanate is treated with hydrochloric acid, instead, the difficulty of Li⁺ extraction from various crystal faces corresponds to the Li-O bond strength. Lithium ion is easy to remove from (-133) and (-206) due to the relatively weak Li-O bond strength. In contrast, Li⁺ extraction requires a longer time for (002) and (-131).

The pastes containing different dosages of fly ash were taken into ultraviolet radiation and low temperature freeze condition simultaneously(URL) for 30 days and only ultraviolet radiation condition(UR) for 30 days after standard curing, so as to investigate the influences of the conditions on the deterioration characteristics of the pastes. Microscopic test methods, such as XRD, TG-DTA and SEM, were used to study the UR effect on the deterioration process of hardened paste. The results show that the deterioration tests, such as URL and UR, inhibit the common development of paste strength, especially after the standard curing age of 360 days. With the increase of fly ash dosage, from 0 to 50%, the reference value decreases, especially at early age. While at the later age, i e, 180 and 360 days, the paste strength cured for 30 days under URL and UR conditions all increase to different extent and the strength is slightly affected very low, especially for the paste containing 25% fly ash. From XRD results, URL and UR dispositions do not influence the hydration product kinds but the amount, especially Ca(OH)₂ and CaCO₃. Deterioration experiments can decrease the diffraction peak of Ca(OH)₂ sharply, and increase that of CaCO₃ rapidly, especially under only ultraviolet radiation. From TG-DTA and SEM results, with the increase of curing age, the content of Ca(OH)₂ decreases and that of CaCO₃ increases. The Ca(OH)₂ content of paste under continuous UR curing for 30 days is less than that under URL curing for 30 days, which indicates that UR has more negative effects on the pastes than URL.

To investigate the influence of preparation process on the properties of synthesized C₄AF, the powder was prepared via the self-propagating combustion reaction (SPCR) method using urea as fuel and metal nitrates as cation precursors. Synthesis mechanism of the SPCR method, calculation and adjusting principles of urea dosage were detailedly introduced. Material characterization of synthesized C₄AF was performed with the aid of X-ray diffractometry, Fourier transform infrared spectrometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, ²⁷Al nuclear magnetic resonance and isothermal microcalorimetric technique. Remaining content of transition phase of calcium carbonate in synthesized C₄AF was determined by quantitative analysis of X-ray diffractometry. It was found that there was no difference in the hydration behavior of C₄AF synthesized by the SPCR method and the traditional solid-state reaction (SSR) method. C3AH6 and amorphous iron (III) hydroxide (Fe(OH)₃) would be formed during the hydration of C4AF while CH not. Crystallite size of synthesized C₄AF was 16.1 Å and the apparent activation energy was 36.2 kJ/mol. Coordinated condition of Al in C₄AF can be detected by ²⁷Al NMR technique, but the peaks were broadened and the intensities were relatively low, supporting the use of ²⁷Al NMR for the quantitative analysis of C₃A in Portland cements.

Urea formaldehyde/epoxy resin microcapsules were prepared by an in situ polymerization method and the effect of emulsifier on the syntheses process of the microcapsules was discussed. The surface morphology of the microcapsules was observed by optical microscopy and scanning electron microscopy (SEM). Chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR). Thermal stability was obtained using simultaneous thermal analysis (STA). The microcapsules were composed of urea-formaldehyde resin shell and epoxy resin core. Emulsifier played an important role in the polymerization process when the core material was packed by pre-polymer, so the effects of different emulsifiers (OP-10, SDS and SDBS) were discussed respectively. Results showed that the particle size of the microcapsules was uniform when SDBS as an emulsifier. Microcapsules showed good thermal stability below 240 °C and the initial decomposition temperature of the microcapsules was 265 °C. The core materials released after microcapsules rupturing, which could be proven by the images of SEM. When implanted in cementitious composites, complete shape of microcapsules and good interface between microcapsules and cement specimen substrate could also be observed.

The feasibility of using different generations of recycled fine aggregate (RFA) in structural concrete in a chloride environment was evaluated by studying the performance of the RFA and the corresponding concrete. The different generations of RFA were recycled by following the cycle of ‘concrete - waste concrete - fine aggregate - concrete’. The properties of three generations of repeatedly recycled fine aggregate (RRFA) were systematically investigated, and we focused on the compressive strength and splitting tensile strength and chloride ion permeability of the related structural concretes with 25%, 75%, and 100% replacement of natural fine aggregates with RFA. The results indicated that the quality of RRFA presents a trend of slow deterioration, but the overall performance of all RRFA still fulfils the quality requirements of recycled fine aggregate for structural concrete. All RRFA concretes achieved the target compressive strength of 40 MPa after 28 days except for the second generation of the recycled aggregate concrete and the third generation of the recycled aggregate concrete with 100% replacement, and all the concrete mixes achieved the target compressive strength after 90 days. The insights obtained in this study demonstrate the feasibility of using at least three generations of RRFA for the production of normal structural concrete with a design service life of 100 years in a chloride environment.

The coupling mechanism of saturated concrete subjected to simultaneous 4-point fatigue loading and freeze-thaw cycles was, for the first time, experimentally studied by strain technology. The coupling strain, temperature strain and fatigue strain of concrete specimens were measured at the same time from one sample with stain analysis method and the relationship among these three kinds of strains was studied by fitting data to present coupling mechanism at macro level. The results showed that there was no interaction between fatigue strain and temperature strain and the coupling strain could be written by linear superposition of temperature strain and fatigue strain.

The fiber reinforced concrete has good dynamic mechanical properties. But corresponding research lacks the dynamic damage characteristics of the polypropylene fiber (fiber of low elastic modulus) and steel fiber (fiber of high elastic modulus) reinforced concrete under medium strain rate (10^-6 s^-1-10^-4 s^-1). In order to study the effect of strain rate on the damage characteristics of fiber reinforced concrete during the full curve damage process, the real time dynamic acoustic emission (AE) technique was applied to monitor the damage process of fiber reinforced concrete at three strain rates. The AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency at three strain rates were analyzed. With the accumulation of damage, the AE wavelet energy spectrum in ca8 frequency band increased first and then decreased, and the average AE peak frequency increased gradually. With the increase of strain rate, the AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency decreased gradually. The polypropylene fiber content has more obvious effect on the Dynamic increase factor (DIF) of the peak stress than the steel fiber content. The theoretical basis was provided for the monitoring of dynamic damage of fiber reinforced concrete based on the AE technique.

The influence of polyepoxysuccinic acid(PESA) on the solid phase products in hydrated Portland cement pastes was investigated by isothermal calorimetry, X-ray diffraction(XRD), ²⁹Si and ²⁷Al nuclear magnetic resonance(NMR). The results indicated that PESA bonds Ca²⁺ ions in pore solution to prevent portlandite formation, and also combines with Ca²⁺ ions on the surface of silicate minerals to prolong the control time of phase boundary reaction process, leading to the retardation of silicate mineral hydration. Meanwhile, the interlayer Ca²⁺ ions in Jennite-like structure bridging PESA and C-S-H gels prevent silicate tetrahedron and aluminum tetrahedron from occupying the sites of bridging silicate tetrahedron, which causes the main existence of dimer in C-S-H structure, deceases the degree of Al³⁺ substituting for Si⁴⁺ and promotes the transformation from 4-coordination aluminum to 6-coordination aluminum. Furthermore, the -Ca⁺ chelating group from reacting PESA with Ca²⁺ ions combines easily with SO₄ ^2- ions, resulting in transformation from ettringite, AFm to TAH(Third aluminum hydrate). However, with the higher addition of PESA, it will bridge the excess PESA by Ca²⁺ ions to form a new chelate with ladder-shaped double chains structure, which not only reduces the amount of PESA bonding Ca²⁺ ions, but also decreases its solidifying capability for SO₄ ^2- ions, leading to the transformation from TAH to AFm or ettringite. Meanwhile, at later hydration, the inhibition effect of PESA on cement hydration is weakened, and the transformation degree from TAH to AFm is higher than that to AFt with the addition of PESA.

Hydrothermal treatment has been widely applied in the synthesis of well crystalline calcium silicate hydrate (CSH), such as tobermorite and xonotlite. However, both morphology and crystallinity of CSH are greatly affected by the conditions of hydrothermal treatment including siliceous materials, temperature increase rate and isothermal periods. In this study, the influence of hydrothermal conditions on the growth of nano-crystalline CSH was investigated based on XRD analysis. Results showed that siliceous materials with amorphous nature (i e, nano silica powder) are beneficial to synthesize pure amorphous CSH, while the use of more crystallized siliceous materials (i e, diatomite and quartz powder) leads to producing crystalline CSH. Results also indicate that the formation of tobermorite and xonotlite is greatly affected by the temperature rise rate during hydrothermal treatment.

The effect of the borax content and magnesia to phosphate ratio (M/P) on the hydration properties of the magnesium potassium phosphate cement (MKPC) with large volume of fly ash was investigated, and a five-hydration-stage for MKPCs was proposed. The results show that MKPC sets rapidly with less than 8% of borax, which is unfavorable to the application of MKPC on construction. Adding more than 8% (including 8%) of borax results in a secondary hydration peak for MKPC, in which the process of hydration can be divided into five stages, namely, pre-induction period, induction period, acceleration period, deceleration period and stable period. M/P ratios could not change the multi-step reactive stages but higher M/P ratios could accelerate the hydration. Borax tends to impact the formation of Mg-containing hydrated products.

The self-propagating combustion reaction (SPCR) method was employed to synthesize C₄AF using metal nitrates as cation precursors and urea as fuel. Thermal decomposition behavior of dried gels, phase identification and crystallinity of synthesized C₄AF, and impact of urea to metal nitrates (UR/MN) molar ratio on synthesis effect were investigated with the aid of differential thermogravimetric analysis, X-ray diffraction and Fourier transform inferred spectrometry. It is found that pure C₄AF can be prepared by the SPCR method in 2 h at 500 °C. The UR/MN molar ratio plays a significant role in the thermal decomposition behavior of dried gel, purity, crystallinity and crystallite size of synthesized C₄AF. Ignition temperature should be not lower than 500 °C but higher temperatures were unnecessary. No trace of free lime in synthesized C₄AF is detected and calcium carbonate is the transition phase. Further calcining the synthesized C₄AF at high temperatures is beneficial for increasing crystallinity, purity and crystallite size. Reaction activation energy of the further calcination process is 119.6 kJ/mol. It is more efficient to improve the synthesis effect by increasing UR/MN molar ratio than further calcination at high temperatures.

C3S pastes containing 0%, 5%, 10%, and 15% nano-SiO2 mixed with de-ionized water and alkali solutions were prepared. When C3S was completely hydrated, the pastes were ground into powders with a particle size less than 80 μm. Adsorption and desorption characteristics of alkali ions adsorbed by C₃S-nano SiO₂ pastes mixed with de-ionized water immersed in alkali solutions and those in C₃S-nano SiO₂ pastes mixed with alkali solutions, were investigated. Meawhile, the adsorption mechanisms of alkali ions were discussed. Results showed that the contents of alkali ions adsorbed by C₃S-nano SiO₂ pastes mixed with de-ionized water increased with increasing substitution levels of nano-SiO₂ and/or the initial alkali concentrations. In C₃S-nano SiO₂ pastes mixed with de-ionized water, each paste was characterized by having a fixed alkali-adsorption capacity that was essentially independent of alkali concentration. No obvious difference between the adsorption capacity of a given paste for K⁺ and Na⁺ was observed. Adsorption of alkali ions in the pastes is considered to be caused by surface force which is related to the BET specific surface area of the paste, and charge compensation of C-S-H gel, mainly by electrostatic interactions. In C₃S-nano SiO₂ pastes mixed with alkali solutions, alkali ions may enter the structure of C-S-H gel to replace a part of Ca²⁺ in the interlayer. This assumption is supported by the structural characterization of C-S-H gel using ²⁹Si MAS NMR.

Reuse of solid industrial wastes is an effective approach to develop low-carbon construction materials. This paper examines how two materials, steel slag (ST) and granulated blast-furnace slag (SL) impact the mechanical performance and pore structure of cement-based systems. Analysis was done on the variations of the porosity, pore size, and pore volume distribution with the curing age and replacement content, and the fractal dimensions of pore surfaces. The results suggested that systems with both supplementary materials had lower early strengths than pure cement, but could generally surpass pure cement paste after 90 d; higher SL content was particularly helpful for boosting the late strengths. The addition of ST increased the porosities and mean pore sizes at each age, and both increased with ST content; SL was helpful for decreasing the system’s late porosity (especially harmless pores below 20 nm); The lowest porosity and mean pore size were obtained with 20% SL. Both systems had notably fractal characteristics on pore surfaces, with ST systems showing the highest dimensions at 10% ST, and SL systems at 20% SL. Compressive strength displayed a significant linear increase with fractal dimension.

Four Nb-Ti microalloyed steels were refined and rolled to study the composition optimization of Nb-Ti microalloyed steels. The effects of Nb and Ti on the microstructures, precipitates and properties of Nb-Ti microalloyed steel were investigated. The results showed that an increase in Ti content resulted in the appearance of many fine precipitates leading to a strong precipitation strengthening effect. Hence, the yield strength increased. Besides, the increased strength by the combined increase of Nb and Ti was similar to that observed for the increase in Ti content alone. This increase in strength was attributed widely to the increase in the Ti content alone rather than Nb. Moreover, the increase in Nb content beyond 0.036 wt% exerted no significant effect on the strength of Ti-Nb microalloyed steels, in which more Ti could be added to further improve the strength of steels.

In order to study the effects of aging treatment on the intergranular corrosion (IGC) and stress corrosion cracking (SCC) of 7003 aluminum alloy (AA7003), the intergranular corrosion test, electrochemical test and slow strain rate test (SSRT), combined with optical microscopy (OM) and scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM) observations have been carried out. The IGC and electrochemical test results showed that the IGC resistance of AA7003 for peak aged (PA) temper is the lowest, with double peak aged (DPA) the moderate, and retrogression and re-aging (RRA) the highest among three tempers, which is attributed to the continuous feature of precipitation on grain boundary of PA temper and the interrupted feature of precipitation on grain boundary of DPA and RRA tempers, as well as the wide precipitation free zones (PFZ) of RRA temper. In addition, the SSRT results indicated that all three tempers AA7003 are susceptible to SCC in IGC solution, and the change tendency of SCC susceptibility (I _SCC) of AA7003 for three tempers follows the order: I _SCC(RRA)<I _SCC(DPA)<I _SCC(PA).

The corrosion behavior of 16Mn steel was studied in saturated H₂S or H₂S/CO₂ solutions containing different Cl⁻ concentrations at 80 °C. The microstructure and chemical composition of the corrosion products were investigated through scanning electron microscopy, energy-dispersive X-ray spectroscopy, EPMA, and X-ray diffraction. Results showed that the corrosion rate decreased with increasing Cl₋ concentration in saturated H₂S or H₂S/CO₂ solution at pH 4. Conversely, the corrosion rate increased with increasing Cl⁻ concentration in saturated H₂S solution at pH 6. The relative H⁺ concentration decreased because of the increase of Cl₋ concentration at pH 4, and Cl⁻ acted as a catalyst in the corrosive medium at pH 6 because the net H⁺ concentration decreased obviously compared with the condition at pH4. Cl⁻ promoted the formation of Fe-deficient iron sulfide at pH 4, and the opposite effect was observed in the nearly neutral solution. The corrosion rate increased firstly with increasing Cl₋ concentration and then decreased in the saturated H₂S/CO₂ solution at pH 6. The corrosion products were mainly composed of two kinds of iron sulfide. Sulfide FeS_1−x was a kind of tetragonal crystal, whereas the other was the hexagonal/monoclinic iron sulfide Fe_1−xS. The corrosion film that was mainly composed of FeS_1−x did not confer a protective effect on the base metal. The atomic ratio of Fe/S was more than 1 for FeS_1−x. The appearance of sulfide FeS_1−x resembled a square block or small, needle-like, flocculent particles. The atomic ratio of Fe/S was less than 1 for Fe_1−xS, and the corrosion film mainly composed of Fe_1−xS conferred some protective property on the base metal. The sulfide FeS_1−x exhibited a long claviform morphology with a hexagonal or quadrilateral cross-sectional shape.

A CrZr-alloyed layer was prepared through a pre-zirconizing and subsequent chromizing treatment on a Ti6Al4V substrate. After the removal of the top Cr deposit and Ti₄Cr layers, a (Cr,Zr)-Ti solid-solution layer was obtained. The microstructure, composition, microhardness and toughness of the (Cr,Zr)-Ti solid-solution layer were evaluated. The results showed that the pre-addition of Zr played an important role in inhibiting the precipitation of the soft Ti4Cr phase, which in turn allowed us to obtain a material characterized by a remarkable hardness. Wear and fatigue tests showed that the (Cr,Zr)-Ti solid-solution layer could coordinately improve the properties of the Ti6Al4V alloy. This was mainly due to the good match of hardness and toughness of the (Cr,Zr)-Ti solid-solution layer. In addition, the gradual change in composition and mechanical properties was conducive to the coordinated deformation between the (Cr,Zr)-Ti solid-solution layer and the Ti6Al4V substrate during fatigue tests. This reduced the stress concentration in correspondence of the interface between the two materials.

The morphology, nanomechanical properties and interfacial regions of natural rubber (NR) and FeCo nanoparticles composite were determined by AFM nanomechanical mapping. The results showed that the size of FeCo particles was mostly from 40 to 100 nm and the FeCo nanoparticles were homogeneously dispersed in the NR bulk. The strength of NR composite increased with the FeCo nanoparticles loading. Young’s modulus of NR region, FeCo region and interfacial region was measured by AFM nanomechanical tapping as 1.6 ± 0.6, 16.7 ±4.2 and 5.8 ± 1.5 MPa, respectively. The width of the interface for NR5, NR10 and NR15 was determined to be 15±8.1, 26±14.3 and 32±16.4 nm, respectively.

The porphyrin derivatives, 5,10,15,20-tetra(4-(N-pentane-carboxamide) phenyl) porphyrin (4NC5-TPP), 5,10,15,20-tetra(4-(N-dodecane-carboxamide) phenyl) porphyrin (4NC12-TPP) and their zinc-complexes (4NC5-TPPZn and 4NC12-TPPZn), have been synthesized. Their thermal properties and morphologies were investigated via thermal gravity analysis (TGA), differential scanning calorimetry (DSC) and polarized optical microscopy (POM). It was found that the 4NC5-TPP was amorphous and the 4NC5-TPPZn was crystalline at room temperature, while the 4NC12-TPP formed the columnar liquid crystal and the 4NC12-TPPZn showed the spherulite texture. The electron state density distributions and the optimum configuration of the porphyrin derivatives were calculated by chemical simulation. The electrochemical oxidation and reduction abilities of the porphyrin derivatives were studied by cyclic voltammetry (CV). It was indicated that the porphyrin derivatives had the potential to develop organic photovoltaic (OPV) devices. Using the porphyrin derivatives as donor materials and the 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) as the acceptor material, the OPV devices were fabricated. The device structure is ITO/porphyrin derivatives:PTCDA/Al. The relationship between the morphology and performance of OPV was studied. It was found that the crystalline morphology of the film was beneficial to improve the efficiency of the devices.

Acrylate-terminated poly(lactic acid) (DPLA) was synthesized by polycondensation, using lactic acid, polyalcohol and acrylic acid as the raw materials. The prepolymer products in each process were characterized by FT-IR, ¹H-NMR, GPC and DSC. DPLAs were then formulated with reactive diluent and diphenyl ketone as photoinitiator and photopolymerized into film(FPLA). Thermal stability and degradation properties of the UV curing PLA film were studied. The results showed that the structures of prepolymer and the performances of the film could be adjusted by changing the types and content of the branching agent polyalcohol. After crosslinking modification, the degradation rate of FPLA was reduced and FPLA had better thermal stability than the pure PLA.

Nylon 10T and nylon 10T/1010 samples were synthesized by direct melt polymerization. The isothermal crystallization kinetics of nylon 10T and nylon 10T/1010 was investigated by means of differential scanning calorimetry (DSC). The crystallization kinetics under isothermal condition has been analyzed by the Avrami equation. It was found that the Avrami equation was well-suited to describe the isothermal crystallization kinetics, combined with the results of the Turnbull-Fisher equation. The values of T _m ⁰ and K _g were obtained by Hoffman-Weeks and Lauritzen-Hoffman equations, respectively. The activation energies for isothermal crystallization of nylon 10T and nylon 10T/1010 were determined using the Arrhenius equation and found to be -123.24 and -81.86 kJ·mol^-1, respectively, which reveals that the crystallization ability of nylon 10T/1010 was lower than that of nylon 10T during the isothermal crystallization process. The crystal morphology was observed by means of polarized optical microscopy (POM) and X-ray diffraction (XRD). It was found that the addition of sebacic acid comonomer did not change the crystal form of nylon 10T, but significantly increased the number and decreased the size of spherulites.

A multifunctional amine, 1,4-bis(2,4-diaminophenoxy)benzene (14BDAPOB), was prepared and used as a novel hardener for novolac epoxy resin (ER). The structure of 14BDAPOB was characterized with Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). The curing kinetics of the novolac epoxy resin/1,4-bis(2,4-diaminophenoxy)benzene (ER/14BDAPOB) system was studied by means of non-isothermal DSC experiments at five heating rates and determined by the Kissinger, Ozawa and Crane methods. The results showed that the activation energy E _a of the ER/14BDAPOB (74.56 kJ/mol) system was higher than that of the epoxy resin/LCA-30 (ER/LCA-30, 68.85 kJ/mol), where LCA-30 is a commercial modified diamine. The reaction order, frequency factor and the reaction rate constant at peak temperature of the two systems were calculated. The initial decomposition temperatures (T _onset) were 398.8 °C (ER/14BDAPOB) and 334.3 °C(ER/LCA-30). The tensile shear strengths were 21.63 MPa (ER/14BDAPOB) and 21.28 MPa (ER/LCA-30). The results showed that the two cured systems exhibited good thermal and mechanical properties.

Graded porous scaffold can be applied to study the interactions between cells and scaffold with different pore sizes. Polydimethylsiloxane (PDMS) scaffold with an axial pore size grade was successfully manufactured via vacuum-assisted resin transfer moulding (VARTM) and particle leaching technologies. The properties of graded PDMS scaffolds, including porosity, water absorption, interconnectivity, compression modulus, as well as compression strength were investigated. The results showed that the smaller the size of the NaCl particles is, the higher the porosity and water absorption of graded PDMS scaffolds would be. The graded PDMS scaffold fabricated had a compressive modulus and a compressive strength of 19.69±1.42 kPa and 4.76±0.22 kPa, respectively. Moreover, the graded chitosan (CS)-coated PDMS scaffolds were prepared by using dip-coating technique under low vacuum and their hydrophilicity was examined. It is found that the water contact angle (WCA) will decrease with an increase in the CS solution concentration and the coating time, which indicates that CS-coated PDMS scaffolds exhibit noticeable hydrophilicity compared with graded PDMS scaffold.

Two kinds of metal-PTFE multilayer composites, which were composed of a steel backing, a middle layer of sintered porous bronze and a surface layer of polytetrafluoroethylene (PTFE) filled by carbon nanotubes (CNTs) or not, were prepared. The wear properties of metal-PTFE multilayer composites oscillating against 45 carbon steel under dry condition were evaluated on an oscillating wear tester, and the effect of CNTs on wear behaviour of metal-PTFE multilayer composites was studied. The results showed that the worn surface of metal-PTFE multilayer composites was characterized by adhesive wear, abrasive wear and fatigue wear. The CNTs greatly increased the adhesion strength of PTFE in the metal-PTFE composites and thereby greatly reduced puck, ploughing, and fatigue failure of PTFE during wearing. The PTFE filled with CNTs prevented direct contact between the mating surfaces and served as fine self-lubricating film, in which the oscillating wear mechanism of the composites was changed to a slightly adhesive wear. Therefore, the CNTs significantly decreased the weight loss and obviously increased the wear resistance of metal-PTFE multilayer composites.

A simple non-isocyanate route synthesizing thermoplastic polyurethanes (TPUs) with good thermal and mechanical properties is described. Melt transurethane polycondensation of dimethyl 1,6-hexamethylene dicarbamate with 1,4-butanediol and 1,6-hexanediol was conducted at different molar ratios under the catalysis of tetrabutyl titanate. A series of crystallizable non-isocyanate TPUs with high molecular weight were prepared. The TPUs were characterized by gel permeation chromatography, FT-IR, ¹H-NMR, differential scanning calorimetry, thermogravimetric analysis, wide angle X-ray diffraction, AFM, and tensile tests. The TPUs exhibited M _n ranging from 12 500 to 26 400 g/mol, M _w from 16 700 to 56 400 g/mol, T _m up to 151.4 °C, and initial decomposition temperature over 241.8 °C. Their tensile strength reached 42.99 MPa with a strain at break of 30.00%. TPUs constructed simply with butylene, hexylene, and urethane linkages were successfully synthesized through a non-isocyanate route.

Ag-Pt bimetallic nanoparticles decorated on MWCNTs/PANI nanocomposites have been synthesized by in-situ chemical oxidative polymerization and chemical co-reduction method. The Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), ultraviolet-visible (UV-vis) absorption spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology and structure of the nanocomposites. It can be observed that the PANI was uniformly grown along the MWCNTs to form MWCNsT/PANI fiber-like nanocomposites with diameter about 60 nm, and the Ag-Pt binary nanoparticles were decorated onto MWCNTs/PANI with particle sizes around 6.8 nm. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the electrochemical performance of the prepared electrode. The results demonstrated that the obtained MWCNTs/PANI/Ag-Pt electrode displayed a good electrochemical activity and fast electron transport, which has potential applications in biosensors and supercapacitors.

Bacillus subtilis was selected as the suitable microorganism, which could produce alkaline phosphatase and constantly hydrolyzed phosphate monoester in the mixture solution of bacteria with substrate, and then the PO₄ ^3- was obtained. Bio-phosphate cement was prepared by alkaline earth element (Ba) ions reacting with PO₄ ^3- in the mixture solution. Structure, size and thermal properties of the bio-phosphate cement were characterized by energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and particle size analysis. The average crystallite sizes of chem-BaHPO₄ and bio-BaHPO₄ corresponded to 11.99 and 24.13 μm, respectively. Chem-BaHPO₄ and bio-BaHPO₄ were then adopted to bind loose sand particles. The results indicated that loose sand particles can be well cemented by the bio-BaHPO₄ powder into a bio-sandstone with a certain mechanical properties, and the average compressive strength of the bio-sandstones can be up to 0.83 MPa when the curing time was 14 d. Along with the method in future studies, there will be multiple new opportunities for engineering applications, for instance, the treatment of sandy soil foundation, remediation of heavy metals in contaminated soil, and so on.