Advanced Materials Research Vols. 418-420

Abstract: The dehydration kinetics of phase change material KAl(SO₄)₂•12H₂O was studied under non-isothermal conditions and the Kissinger’s method was applied to analyze the TG and DSC data in order to calculation of activation energies and pre-exponential factors for different heating rates. It was concluded that dehydration of KAl(SO₄)₂•12H₂O occurred in three steps. The activation energies and pre-exponential factors were calculated as 95.9 kJ/mol and 1.95×1010min-1 for step I, 128.8kJ/mol and 3.67×1012 min-1 for step II, 159.6kJ/mol and1.92×1013min-1 for step III, respectively. In addition, various materials have been tested to prevent the KAl(SO₄)₂•12H₂O supercooling.

Abstract: This paper utilized a novel oxidative co-precipitation method to synthesis hexagonal Fe₃O₄ nanometer particles, which assisted by a weakly magnetic field. The crystallinity, morphology, particle size distribution, compositions and magnetic properties of the as-prepared particles were investigated using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), ultrasonic particle sizer (UPS), X-ray photoelectron spectra (XPS) and vibrating sample magnetometer (VSM). The formation mechanism of the hexagonal Fe₃O₄ nanometer particles, which assisted by a weakly magnetic field was also discussed. The results shown that the as-prepared hexagonal particles were purity magnetite (Fe₃O₄), and the weakly magnetic field could accelerate the phase transformation from goethite (α-FeOOH) to magnetite (Fe₃O₄), increase the particle size and uniform the morphology. The values of saturation magnetization (Ms) and coercivity (H) of the hexagonal magnetic particles are 71.05 emu•g^-1 and 474.3 Oe, respectively, which contributed to the morphology anisotropy of the particles.

Abstract: Abstract. In this article, nano-ZnO films were deposited on SiO2/Si (100) substrates by RF (radio frequency) magnetron sputtering using high purity (99.99%) ZnO target. The effects of deposition time and annealing temperature have been investigated. XRD (X-ray diffraction) and FSEM (Field Emission Scanning Electron Microscopy) were employed to characterize the quality of the films. The results show that the ZnO film with thickness of 600nm annealed at 900°C has higher quality of both C-axis orientation and crystallization. And for the Zone film with thickness of 300nm annealed at 850°C, the quality of both C-axis orientation and crystallization is higher than that annealed at 900°C and 950°C.

Abstract: Zeolite A was successfully synthesized via convenient hydrothermal process using potassium-extracted residue of potassium feldspar as a combined source for silica and alumina. Optimization studies on the molar ratios of Na2O/SiO2 and H2O/SiO2, and aging time have been conducted. The results were that pure zeolite A with high crystallinity could be synthesized when the reaction mixture with molar ratios of Na2O/SiO2 and H2O/SiO2 of 2.0 and of 85, respectively, were crystallized at 100°C for 3h. Aging was found to be not prerequisite for the formation of zeolite A in the system. The product was characterized by XRD, FTIR, SEM and calcium exchange capacity. Finally, a comparative study of the zeolite A formation from the potassium-extracted residue and other industrial waste or natural silicate minerals was also carried out.

Abstract: In this study, a nano-fibrous PLLA scaffold with hierarchical pore was sucessfully fabricated using combined TIPS and particle leaching method.The scaffold had a nano-fibrous PLLA matrix (fiber size 100-800 nm), an interconnective hierarchical pores (1.0- 425 μm), high porosity (>96%). The compressive modulus of scaffold with different pore size was between 0.16 MPa to 0.2 Mpa and it decreased with the increased salt size embedded in. The new nano composite scaffold is potentially a very promising scaffold for tissue engineering.

Abstract: The replacement of steel stirrups with FRP stirrups in concrete structures can significantly improve the durability under severe environmental conditions, increase the service life of the structure. In some cases where the application of traditional concrete structures is restricted, such as structures that require the environment without magnetic and electric interferences, the best way is to use nonmetallic materials. Considering the unique properties compared with traditional reinforcements, FRP reinforcements is very suitable in such cases. This paper discussed the behavior of FRP stirrups used as shear reinforcement for concrete structures, continuous FRP rectangular spirals, a type of FRP stirrups, was used in the experimental investigation. Inspired by the test method suggested by ACI Committee 440, L shape specimen and U shape specimen are designed to test the tensile strength of continuous FRP rectangular spirals. Through the analysis of test results, it is indicated that the strength of the bent portion of FRP spirals is significantly lower than that of the straight portion, and the strength of FRP spirals would increase as the concrete strength or the embedment length of the bent portion increased. The loading mechanism of continuous FRP rectangular spirals embedded in concrete beams can be better represented by U shape specimen compared with L shape specimens, it is suggested by the author that the U shape specimen can be use when the dimension of FRP stirrups or spirals does not meet the requirements of ACI Committee 440 test method.

Abstract: Metal atoms confined in finite cylindrical nanopores exhibit helical morphologies because of the high rotational symmetry of confined surfaces and energy minimum of (111) facets. Herein, we present adirect nanoconfinement induced helical symmetry breaking phenomenon resulting from asymmetric atomic arrangements around the surfaces of nanoconfinements. In cylindrical nanopores, the critical value transforming from helical nanowires to crystalline ones is larger than corresponding free-standing nanowires, indicating nanopores with high rotational symmetry are propitious to form (111)facets wrapped outside of nanowires

Abstract: Polystyrene spheres were prepared by soap free emulsion polymerization method. The effects of styrene concentration, polymerization time and self-assemble methods on the diameter of the polystyrene spheres were investigated. Different size of polystyrene microspheres could be obtained by changing styrene concentration and polymerization time. Polystyrene templates with good uniform and highly ordered can be assembled by means of vertical deposition method. Based on this template, three-dimensional ordered macroporous (3DOM) perovskite-type oxides LaFeO₃ were successfully prepared which were confirmed by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was also found that 1mol/L metal precursor solution which used ethanol solution of metal nitrates with citric acid addition gave the best 3DOM perovskite-type LaFeO₃ oxides. The pores are uniform, flexible and arranged in a highly ordered form.

Abstract: Dy-B-Si-O glass-doped Ba_0.6Sr_0.4TiO₃ (BST) ceramics based on sol-gel-derived powders were prepared. Effects of B₂O₃-SiO₂ in Dy-B-Si-O glass on phase structure, microstructures and dielectric properties of the BST ceramics were investigated. The results showed that the main crystal phase of BST ceramics with appropriate B₂O₃-SiO₂ in Dy-B-Si-O glass had a perovskite type structure. Grain size decreased and density increased compared with pure BST ceramics. However, the secondary phase Ba₂TiSi₂O₈ was detected when the percentage of B₂O₃-SiO₂ in Dy-B-Si-O glass additive was over 7 mol%, and increased with the increasing of B₂O₃-SiO₂. With the increasing of B₂O₃-SiO₂, the dielectric constant increased firstly and then decreased, the dielectric loss decreased firstly and then increased, the Curie temperature moved to lower temperature firstly and then to higher temperature.

Abstract: This study utilizes tungsten oxide as the research subject and investigates changes between different argon/oxygen gas flow ratio and deposits on ITO substrates through RF reactively sputtering. Propylene carbonate (PC) is further mixed with LiClO₄ for the preparation of electrolyte. After packaged into components, electric voltage is applied to the films to generate reduction or oxidization, which can obtain different colored/bleached states. Lastly, Raman spectroscopy analysis is performed to get a greater understanding of electrochromic mechanisms. The results of the experiment discovered that as-deposited tungsten oxide thin film shows the formation of W⁺⁶ states, and the application of driving voltage causes the formation of W+5 states. At the same time, the thin film coloring effect appears. Increases in driving voltage cause the gradual conversion of W^{+ 6} states into W⁺⁵ states, which further leads to a more significant coloring effect. On the other hand, W-O-W deformed crystal lattice structures are also produced, which also affects the incidence of electrochromic property.