Effects of the Hf content on the microstructure and magnetic properties of Co-Hf-Ta thin films

Effects of the Hf content in Co-Hf-Ta thin films on the microstructure and magnetic properties were investigated in this study. It was found that appropriate Hf addition can effectively refine the Co grain size. Co grain sizes sharply decreased from 50 nm down to 2.3 nm with increasing the Hf content from 1.02 at.% to 2.81 at.%, leading to the reduced magneto-crystalline anisotropy. The Co-Hf-Ta thin films with small Co grains reveal low anisotropy field, low coercivity, and high resistivity. By optimizing the Hf content, the film with Hf concentration of 2.81 at.% exhibits excellent soft magnetic properties: high saturation magnetization (4πM_S ∼ 13.6 kG), and low coercivity (H_C ∼ 0.6 Oe). The effective permeability of the film reaches 800 and remains constant up to 1 GHz.     

Mass transfer characteristics for VOC permeation through flat sheet porous and composite membranes: The impact of the different membrane layers on the overall membrane resistance

In this paper, the mass transfer coefficients for trichloroethylene (TCE), toluene (TOL) and dimethyl sulfide (DMS) are experimentally determined for different porous and composite membranes. For polypropylene/polyvinylidenedifluoride porous layer/thin film polydimethylsiloxane dense layer composite membranes, membrane mass transfer coefficients are 2.55E−03, 2.82E−03 and 2.90E−03 m/s for TCE, TOL and DMS in N₂ at 30.0 ± 0.1 °C, respectively. For polyester/polyacrylonitrile porous layer/thin film polydimethylsiloxane dense layer composite membranes, they are higher, namely 4.28E−03, 4.55E−03 and 4.81E−03 m/s for TCE, TOL and DMS in N₂ at 30.0 ± 0.1 °C, respectively. Analysis of the contribution of the dense layer of both composite membranes to the total membrane resistance for mass transfer, showed that this contribution was small for both composite membranes. The higher mass transfer coefficients of the thin film polydimethylsiloxane composite membranes from this study in comparison to others from the literature are primarily due to improvement of the mass transfer characteristics of the porous layer. Analysis of the mass transfer characteristics of the different porous layers of which the total porous layer is composed, showed that the contribution of the porous “backing” layer for mechanical support can be substantial in comparison to the porous layer in contact with the dense layer.     

Non-supercritically dried silica–silica composite aerogel and its possible application for confining simulated nuclear wastes

The simpler non-supercritical drying approach has been used for the first time for the preparation of silica–silica composite aerogels (CA) and the efficiency of the process being demonstrated by testing the use of the aerogels for simulated high level nuclear waste confinement. Compositions of 5, 10, 20, 30, 40 and 50 wt% of silica (aerosil® 380) in silica–aerogel were prepared by introducing pyrogenic silica in to silica sol derived by hydrolysis of Tetraethoxy silane (TEOS). The silica–silica composite aerogels (CA) possessed very high surface area and low bulk densities. The effectiveness of the prepared composite aerogels as precursor for high level nuclear waste immobilized glass is also presented. Neodymium nitrate dissolved in isopropanol is used to simulate +3 valent actinides. The stability of neodymium in the glass matrix has been found to be extremely high. Transmission electron microscopy (TEM) has been used to characterise the aerogels as well as neodymium incorporated sintered gels. X-ray diffraction (XRD) studies of the sintered samples reveal the formation of neodymium silicates.     

Effects of polymer concentration and coagulation temperature on the properties of regenerated cellulose films prepared from LiOH/urea solution

Aqueous 5 wt% LiOH/12 wt% urea solution pre-cooled to −12 °C has a more powerful ability to dissolve cellulose compared to that of NaOH/urea and NaOH/thiourea solution system. The influences of the cellulose concentration and coagulation temperature on the structure, pore size and mechanical properties of the cellulose films prepared from LiOH/urea system were investigated. The cellulose films exhibited good mechanical properties either at wet or dry state and their pore size and water permeability at wet state can be controlled by changing the cellulose concentration or coagulation temperature. With a decrease of the coagulation temperature, the mechanical properties and optical transmittance of the cellulose films enhanced, as a result of the formation of relative smaller pore size and denser structures. This work provided a promising way to prepare cellulose films with different pore sizes at wet state and good physical properties at dry state.     

A mixing rule for predicting frequency dependence of material parameters in magnetic composites

A number of mixing rules are proposed in the literature to predict the dependence of effective material parameters (permittivity and permeability) of composites on frequency and concentration. However, the existing mixing rules for frequency dependence of permeability in magnetic composites typically do not provide satisfactory agreement with measured data. Herein, a simple mixing rule is proposed. Its derivation is based on the Bergman-Milton spectral theory. Both the Bruggeman effective medium theory and the Maxwell Garnett approximation are included as particular cases of the proposed mixing rule. The derived mixing rule is shown to predict accurately the frequency dependence of permeability in magnetic composites, which contain nearly spherical inclusions.     

Effect of In ions doping on the structural and magnetic properties of Mg0.2Mn0.5Ni0.3InxFe2−xO4 spinel ferrites

Effect of substitution of diamagnetic trivalent indium ions on the composition Mg_0.2Mn_0.5Ni_0.3In_xFe_2−xO₄ with x varying from 0.1 to 0.3 in steps of 0.1 using citrate precursor techniques has been investigated. Single-phase cubic spinel structure of these samples has been confirmed from X-ray diffraction analyses. Micro structural features were examined by TEM images. Lattice constant ‘a’ initially increases up to x = 0.1 and thereafter it decreases with further increase in x. This indicates that variation of ‘a’ with x do not obey Vegard's law. Nonlinear behavior of ‘a’ with x may be due to substitutional effect of larger In³⁺ ions (0.91Å) with smaller Fe³⁺ ions (0.67Å) in Mg-Mn-Ni ferrite. Ferrites have been investigated for their structural and magnetic properties such as variations in lattice constant, saturation magnetization, coercivity, retentivity, initial permeability, magnetic loss and relative loss factor (RLF). Fairly constant value of initial permeability over a wide frequency range (0.075–10 MHz) and low values of relative loss factor of order of 10⁻⁶–10⁻⁵ in same frequency range are main achievement of present investigations. RLF has been reduced by three orders of magnitude as compared to those samples prepared by conventional method. Low values of relative loss factor even at a high frequency indicate that prepared materials may have great potential for use in microwave devices. Possible mechanisms contributing to these properties have been discussed in this paper.     

Effects of V2O5 addition on NiZn ferrite synthesized using two-step sintering process

The combined influence of a two-step sintering (TSS) process and addition of V₂O₅ on the microstructure and magnetic properties of NiZn ferrite was investigated. As comparison, samples prepared by the conventional single-step sintering (SSS) procedure were also studied. It was found that with 0.3 wt% V₂O₅ additive, the sample sintered by the two-step sintering process at a high temperature of 1250 °C for 30 min and a lower temperature of 1180 °C for 3 h exhibited more homogeneous microstructure and higher permeability with a high Q-factor. The results showed that the TSS method with suitable additive brought positive improvement of the microstructure and magnetic properties of NiZn ferrite.     

Effects of solvent in the casting of poly(1-trimethylsilyl-1-propyne) membranes

Poly(1-trimethylsilyl-1-propyne) (PTMSP) membranes were fabricated by solvent casting from solutions of toluene, cyclohexane and tetrahydrofuran. The effects of the casting solvent on the physical structure of PTMSP were investigated using wide angle X-ray diffraction and positron annihilation lifetime spectroscopy. The permeability of oxygen, nitrogen and carbon dioxide through the cast membranes was also measured. It was found that the nature of the casting solvent markedly influenced the conformation and the free volume of PTMSP, which in turn affected the gas permeability of the cast membranes.     

聚丙烯酰胺/柠檬酸铝胶态分散凝胶性质的研究

用低浓度不同分子量的部分水解聚丙烯酰胺（ Ｈ Ｐ Ａ Ｍ） 和柠檬酸铝制备了胶态分散凝胶（ Ｃ Ｄ Ｇ） ,并用奥氏粘度计、超细粒度分析仪、岩芯流动实验对 Ｃ Ｄ Ｇ 的性质进行了研究．结果表明, Ｃ Ｄ Ｇ 的粘度比 Ｈ Ｐ Ａ Ｍ 粘度低,粒径在４５０ ～５２０ｎ ｍ 之间．岩芯流动实验结果表明, Ｃ Ｄ Ｇ 能够使岩芯的流动阻力大幅度增加,且在岩芯中达到同样的流动阻力所需通过 Ｃ Ｄ Ｇ 的体积与形成 Ｃ Ｄ Ｇ 的 Ｈ Ｐ Ａ Ｍ 的分子量、浓度及岩芯渗透率有关．     

碳氢烧蚀层的厚度对聚乙烯醇薄膜阻气性能的影响

 以ICF实验塑料靶丸保气的需求为背景,研究了水蒸气在低压等离子体聚合碳氢（CH）膜、聚乙烯醇（PVA）膜、聚苯乙烯（PS）膜中的扩散渗透行为。根据实验数据,算出在40℃ 90%相对湿度下,水蒸气在三种样品膜中的渗透系数分别为1.906×10^-13,5.950×10^-15,.432×10 ^-14mol·m/(m²·s·Pa),并借助多层复合膜模型的近似算法,算出在40 ℃ 90%相对湿度的外界环境下,类似多层塑料微球结构的三层复合膜中,PVA阻气层所处环境的相对湿度为53.06%,推导出PVA所处环境的相对湿度与外层CH层厚度的关系式。研究表明：CH烧蚀层越厚,PVA所处环境的相对湿度越小,保气性能越好。