Advanced Materials Research Vols. 79-82

Abstract: In this paper, 2.5D SiO2f/SiO2 composites were fabricated via sol-gel process employing 2.5D braided silica fiber fabrics as reinforcements and high pure silicasol as slurry. The process parameters are optimized and the optimal parameters are as follows: the silicasol of 30.8 wt. % as slurry, microwave drying, and sintering at 900 °C. Utilizing the optimal process parameters, the density and the flexural strength of the composites can reach 1.65 g•cm-3 and 80.68 MPa respectively. Dielectric properties of the 2.5D SiO2f/SiO2 composites were also measured, and the real part of the permittivity is 3.40 at 5 GHz. The excellent mechanical and dielectric properties of the 2.5D SiO2f/SiO2 composites can well meet the requirements of radome materials.

Abstract: In recent years, the concrete material subject to chloride corrosion which impacts greatly on the durability of the building project in the marine or coastal environment has been reported repeatedly. With the problems becoming more and more serious, much attention has been paid on it gradually. To improve the durability of the concrete structure in the marine environment, the author tried to add the different content of steel fiber into the concrete and research the permeability of the concrete in the chloride environment. Four different volumes of steel fiber were selected to prepare the concrete. The dates of the proportion are as follows, 1)0.5%; 2)1%; 3)1.5%; 4)2%. Leave the steel fiber reinforced concrete and plain concrete to soak in the sodium chloride solution which mass percent is 3.5%. The soak time is 30, 60, 90,120, 180 days separately. Among this, the test items include the penetration depth of chloride, the chloride ion content and the splitting strength after soaking period. As a result of the test, it is demonstrated that chloride penetration-resistant of steel fiber reinforced concrete is better than plain concrete. The best performance is obtained when the content of steel fiber is 1.5%. The results will be very useful to the concrete professional dealing with chloride-ion penetration. In conclusion, it is convinced that the application of this result in marine engineering will bring well economic and social environmental benefits for the society.

Abstract: Low carbon steel was coated by hot-dipping into a molten Al-10%Si bath. The high-temperature oxidation was performed at 700oC for 1 h to 49 h in air, air +100% H2O, and air + 30% ethanol under atmospheric pressure. An elemental composition distribution, morphologies of the aluminide layer and the oxide scale were characterized by OM, XRD, and SEM/EDS. After hot-dipping treatment, the coating layers consisted of Al, Si, FeAl3, τ5-Fe2Al8Si, and Fe2Al5. The results of high temperature oxidation tests showed the oxidation rate were parabolic law in three different atmospheres. The polyhedral τ1-(Al,Si)5Fe3 formed at a short time oxidation completely transformed to FeAl2 and FeAl due to the composition gradient and the chemical diffusion. The effect of water vapor on the oxidation resistance of the Al-Si coating may be attributed to increase in Al and Fe ions transport, leading to loss of protective aluminide layer by formation of iron oxide nodules on the coating surface and at interface between aluminide layer and the steel substrate.

Abstract: To examine the role of nanoclays in the enhancement of interlaminar shear strength (ILSS) of glass fiber reinforced diallyl phthalate (GFR-DAP) composites, the GFR-DAP laminates were manufactured by hand lay-up techniques using two nanoclays, DK2 and MHAB-MMT, respectively. Χ-ray diffraction (XRD) were conducted to characterize the morphology of the dispersed clay particles in the DAP matrix. The mechanical performances were characterized by flexural strength and LISS measurements. XRD scans shows that the clays disperse uniformly in the DAP matrix and form an intercalated structure with a basal spacing of 3.86 nm and 3.98 nm for DK2 and MHAB-MMT, respectively. Short beam shear tests show that only 2.5 wt% clay loading in DAP matrix increased the ILSS of resulting GFR-DAP laminates by 7.64% and 14.80% for DK2 and MHAB-MMT, respectively, with respect to the neat DAP. The fractured surfaces of resulting laminates were observed by scanning electron microscope (SEM).

Abstract: Pavement straw composite fibers (PSCF), a new material, were independently invented and developed by blending agriculture waste straw and modified bentonite, as showed in this paper. The chemical corrosion properties of PSCF in different pH values were test in microscale, and digital imaging processing technology was adopted to analyzing quantitatively the physical and mechanical properties, including particle area, pores connectivity rate and compressive strength, before and after PSCF were corroded. Research results show that the particle area of acidified PSCF is smaller than that of alkalized PSCF, however, the fractal dimension of acidified PSCF is bigger than that of alkalized PSCF. The change of PSCF microstructure has significant effect on its macromechanics properties. The compressibility of acidified PSCF was obviously bigger than that of alkalized PSCF, so the strength of acidified PSCF decreased significantly with the acidifying time increasing. The main reason was gradually decreasing of the particle area, decreasing of the fractal dimension and the loose tendency of fibers particle distribution. The interaction between mineral composition of PSCF and hydrochemistry solution was the basic factors determining straw structural characteristics, and the physical and mechanical properties of PSCF were affected by its structural characteristics. The main process was that mineral compositions of PSCF were cemented by the corrosive action of hydrochemistry solution, or some compositions were dissolved and precipitated, the porosity and particle area of PSCF, the arrangement pattern of soil particles as well as other microstructures changed. And deformation properties of PSCF changed correspondingly with the change of PSCF structure shape. Moreover, the constitutive model of PSCF with effect of acid and alkali was presented according to test data of digital image. It provided reliable techniques to quantitatively evaluate the pavement performance of PSCF in micro and macro scales. Furthermore, the chemical corrosion theory was improved, and the reference for constitutive model research was provided.

Abstract: Vanadium oxide/carbon nanotubes (VOx/CNTs) composites were prepared by sol-gel hydrothermal synthesis. The composites were characterized in terms of surface morphology and structure using SEM, TEM, XRD, FT-IR, respectively. The electrochemical behaviors of the composites were investigated by means of galvanostatic charge-discharge cycling. The result shows that the vanadium oxides nanotubes and carbon nanotubes contacted each other and the composites have great cycleability as well as capacity characteristics which arrived at 303.5 mAh/g in the first discharge process and 200.4 mAh/g after 50th discharge cycles.

Abstract: Microstructure evolution and mechanical properties of 7A09 aluminum alloy ribbon prepared by rapid cooling solidification are studied. Single roller is applied to produce rapid solidification ribbon of 7A09 aluminum alloys. Microstructure characteristics and mechanical properties of the rapid solidified ribbon of 7A09 aluminum alloys are studied by means of X-ray diffraction (XRD), scan electron microscopy (SEM) and hardness measurement. The results show that the rotate speed of the roller is the key factor affecting the ability of the forming ribbon. At a roller rotate speed of 1500rpm, the ribbon with a good quality can be obtained. Microstructure features of the rapid solidification ribbon are refined with the increase of the cooling rate, all of the crystals translate into nanocrystalline. All the hardness of the rapid solidification ribbon of 7A09 aluminum alloys is higher than that of the original alloys and increases with the rotate speed of the rotor.

Abstract: Preparation of semi-solid microstructure with less liquid content of 7A09 aluminum alloy industrial extrusion billets is studied in this paper. In the treatment, melting-stirring and predeformation of the alloy billets are not required. The influences of different heating temperatures and insulation time on the microstructure evolution are studied and the obtained microstructure is observed and analyzed by optical microscopy. The results indicate that a fine microstructure can be obtained with the proposed process and the processing parameters can be controlled over a wide range. The liquid content can be controlled within a certain range.

Abstract: Inorganic antibacterial materials consist of the antibacterial ions, the additives and the carrier. In this study, we synthesized a new inorganic antibacterial material, of which Ag+ was selected to be the antibacterial ion, lanthanum nitrate served as the additives, and the white carbon black was chosen as the carrier, which was prepared by a sol-gel method. The as-synthesized antibacterial material was characterized by inductively coupled plasma, particle size measurement instrument, and enumeration tests. The result showed that this material has loose and dispersive structure, good thermal and light stability. The possible antibacterial mechanism was also proposed through all the experimental data in this study.

Abstract: The interface is the area where two type of materials are connected, the strength and property of interface are important for the application of the clad. In this paper, interfacial strength and fracture properties of stainless steel-aluminum clad are analyzed with the methods of interfacial shear test and four point bending test, and the interfacial crack and the interfacial fracture structure are analyzed with SEM. The results show that the bonding of stainless steel and aluminum is successfully realized by explosive welding, the interfacial shear strength reach 70.90MPa, and the interfacial energy release rate is 1.725 MPa•m, the thickness of transition layer is about 10μm at the interface, the interfacial fracture happen and extend in the transition layer along the interface and the interface fracture structure is inclined to brittle fracture.