Papers by Keyword: Lamellar

Abstract: Mg_xMn_1-xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.5, 0.6 0.8 and 1.0) spinel ferrite system was synthesized by the chemical co-precipitation route. Subsequent characterization of synthesized Mg-Mn ferrites was carried out by X-ray powder diffraction and transmission electron microscopy to study the structural and textural properties of photocatalysts. Porosity, surface area and equivalent surface free energy of different Mg-Mn ferrite photocatalysts were calculated. The photocatalytic activity of synthesized photocatalysts was evaluated by degradation of nitrobenzene in aqueous medium under ultraviolet light irradiation. The results demonstrated that the percentage degradation of nitrobenzene was decreased with increase in Mg concentration (x) from x = 0.0 0.5 and further increase in concentration from x = 0.6 1.0 results increase in percentage degradation of NB. This dissimilarity in the percentage degradation of NB may be due to the change in grain morphology, optical energy band gap, role played by d-electrons and porosity as a function of Mg-substitution for Mn²⁺ in the system. The percentage degradation was further confirmed by chemical oxygen demand (COD) analysis.

Abstract: Lamellas important for micropores were well formed during extrusion and annealing process in melt-spinning and stretching method. This unusual crystalline structure and its changing during annealing and stretching process were well studied in term of lamellar size, lamellar crystallite orientation, degree of lamellar and observation of morphology. Lamellar and microfibril model was accepted as mechanism of making micropore for this process. Gas permeability and porosity testing experimental were used to characterize membrane properties.

Abstract: The lamellar nanostructured yttrium films on α-Al₂O₃ substrates were successfully synthesized by electroless deposition using the lyotropic liquid crystalline templating strategy. The reaction of hydrazine hydrate and Y³⁺ dissolved within the aqueous domains of the lyotropic liquid crystalline phase produced the nanostructured yttrium films. The low-angle X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscope (SEM) indicated that the as-resulted films possessed lamellar regular array of nanochannels with periodicity of 6 nm. With well-defined nanochannels and higher surface areas, the nanostructured films may find applications in the field of electronic materials.

Abstract: This paper is focused on the preparation and characterization of different lamellar silica prepared by liquid crystal templating and silanisation. The initial template can be removed and replaced in the interlamellar spaces by different types of silane, being covalently grafted to the solid by reaction with the surface silanols. The lamellar stacking periodicity remains after this modification. The surfactant extraction can lead in significant grafting of isopropanol if the solid is simply refluxed in isopropanol, which have the effect of preserving the periodicity of the lamellar stacking. The surfactant extraction in an Soxhlet equipment avoid this reaction, with the effect of platelets organization collapsing. The lamellar silica studied exhibit great specific surface and combination of meso and microporosity, making them interesting materials for nanocomposite or catalysis applications.

Abstract: The coherent fine-lamellae consisting of the 2H-Mg and the 14H-type long period stacking ordered (LPSO) structure within α'-Mg matrix have been observed in an as-cast Mg–Gd–Zn–Zr alloy. During subsequent solid solution heat treatment at 773 K, in addition to the lamellae within matrix, a novel lamellar X phase [Mg–(8.37±1.0)Zn–(11.32±1.0)Gd] with the 14H-type LPSO structure was transformed from the dendritical β phase. The 14H-type LPSO structure existing in Mg–Gd–Zn–Zr alloys derives from two variant ways: formation of the 14H-type LPSO structure comes from two variant means: i.e., the formation within matrix and the phase transformation from the β phase to the X phase in grain boundaries.

Abstract: In laboratory, there polymorphs’ nano-calcium carbonates were synthesized through adding on different crystal controlling agents by the bath-type carburizing reagent in the given conditions. When selecting addition J as the crystal controlling agent, lamellar nano-calcium carbonate products with average size about 150×110×15 nm were synthesized. When selecting annexing agent I as the crystal controlling agent, rod nano-calcium carbonates were synthesized, which average grain diameter was 90 nm, average length was 944 nm, and aspect ratio was 10.5. When selecting annexing agent G as the crystal controlling agent, chain nano-calcium carbonate with average grain size 20~30nm, aspect ratio 10~15nm were synthesized.

Abstract: A Landau-de Gennes type model for the direct isotropic/smectic A phase transition is used to study surface-enhanced smectic ordering in the stable smectic temperature regime. A unified surface-free energy functional is proposed which can be utilized for homeotropic and planar surface anchoring. The time-dependent complex Landau-Ginzburg evolution equations and boundary conditions are derived for thin-film geometry. Simulation results are presented for the two types of anchoring and compared to observations from experiments and previous simulations. Simple visualization software for smectic layering was developed and is also presented that is compatible with discretized numerical solutions of the model.

Abstract: Ti-45.5Al-2Cr-4Nb-0.4B alloy was cast by vacuum arc melting at high purity Ar atmosphere using high purity sponge Ti, granular Al (99.99%), flake Nb (99.9%), lump Cr (99.9%) and TiB2 (99.5%) and subsequently heat-treated to obtain a couple of microstructures, i.e. lamellar and near γ. The heat treatment consisted of annealing at a high temperature (1200 ~ 1330oC) of different phase fields for 24 hrs and stabilizing at 900oC for 4 hrs followed by air cooling. Fracture toughness was measured on the specimens with different microstructures at room temperature. The value of KQ of specimen with fully lamella structure was obtained as 18.68 MPa √m, much higher than that of specimen with near γ structure (11.84 MPa √m). It was also revealed that the KQ value was decreased as the annealing temperature decreased.

Abstract: Nanoindentation tests on a folded chain crystal of polyethylene are implemented with the molecular dynamics simulation. The orthorhombic crystal is made of the planar zig-zag chains and has the thickness of about 10nm. The ideal Berkovich indenter is plunged into upper surface of the crystal down to 2nm with the constant loading rate of 200m/s or 2000m/s. After the holding time of 1000fs at the maximum depth, the indenter is then pulled up with the same speed. The results are summarized as follows; a) The indentation of 2000m/s remains the residual depression while that of 200m/s recovers the hollow, b) No elastic component is found in the deformation under the both rate of 200m/s and 2000m/s, c) The crystal deforms statically under the indentation of 200m/s while that of 2000m/s shows delayed response.

Abstract: The porous Ti-45at.%Al-1.6at.%Mn intermetallic alloys were fabricated by reactive sintering process using warm extruded mixtures consisting of elemental titanium and aluminum alloy powders and subsequent heat treatment. At the extrusion stage, three different extrusion ratios were tried in order to provide the various types of porous structure in the microstructure. It was clearly found that the shape of pore and porosity are largely dependent on extrusion ratio. With increasing extrusion ratio the porosity decreased, on the other hand, aspect ratio of porous structure increased. The porosity measured was in the range from 35% to 45%. The maximum porosity of 45% can be obtained when the specimen was reactively sintered with the extrusion ratio of 1. A directionality of pores oriented parallel to the extrusion direction was found when the extrusion ratio of powder mixtures is 6 and above.