Materials Science Forum Vols. 561-565

Abstract: The catalytic combustion technique was used to synthesize carbon nanotubes and carbon nanofibers. In this paper, we report that carbon nanofibers were synthesized by ethanol catalytic combustion technique. The as-grown products were characterized by means of scanning electron microscopy, transmission electron microscopy, Raman spectroscopy. The results showed that the products have a mass of carbon nanofibers. However, morphology and microstructure of carbon nanofibers are affected by synthesis conditions, such as stability of flames and sampling time, sampling temperature etc. Different Influence factors were depicted in detail. Ethanol catalytic combustion technique offer a simple method to synthesize carbon nanotubes and carbon nanofibers, it also has some advantages, such as flexible synthesis conditions, simple setup, and environment-friendly.

Abstract: Martensitic transformation temperatures were measured and transformation strains were evaluated in a promising high temperature shape memory alloy TiAu with a compositional range from 46 to 53mol%Au. It was found by differential scanning calorimetry that martensitic transformation start temperature (Ms) is kept almost constant value of 880K in the Au-rich side of the stoichiometric composition. On the other hand, Ms decreases monotonically with decreasing Au content in the Au-poor side. X-ray diffraction analysis revealed that apparent phase of all the alloys at room temperature is B19 martensite phase. Under an assumption that the atomic volume is constant during martensitic transformation, the lattice parameters of B2 parent phase and maximum transformation strain were calculated. It was found that the maximum transformation strain depends on chemical composition and that it reaches 10.75% for Ti-53mol%Au alloy. The value is comparable to that of Ti-Ni.

Abstract: While magnesium cast components have found their application in the transportation industries the interest is now spreading to wrought alloys due to the possibility to get even more homogeneous and better properties compared to cast parts. Therefore alloy and process development especially for extrusion is a main concern to enhance the application of Magnesium wrought alloys. This paper gives an overview on the actual status of the process and alloy development of extruded Magnesium wrought alloys.

Abstract: Silk fibroin (SF), isolated from silkworm (Bombyx mori) cocoons, is a natural biodegradable polymer. Over the past decade, there was some interest in using SF as a biomedical material. As part of a project to develop tissue-engineered constructs for the surgical restoration of the ocular surface (cornea, conjunctiva), we have investigated the capacity of SF to function as a substratum for the attachment and growth of corneal stem/progenitor cells harvested from the corneoscleral limbus of donor human corneal tissue. SF membranes were produced from cocoons following a protocol involving successive dissolution steps, filtration, dialysis, evaporation, and methanol treatment. Human limbal epithelial cells were harvested from donor tissue and seeded onto SF membranes. After 5 days, the culture was fixed and stained with specific agents to visualize the cells. The study indicated profuse cellular attachment and growth. SF membranes appear to be suitable as a substratum for the repair of damaged ocular surface.

Abstract: A layer of bioceramic HA was coated on laser gas nitrided and grit-blasted pure Ti substrates using plasma-spraying technique, respectively. X-ray diffraction analysis showed that the microstructures of the coating were mainly composed of HA, amorphous calcium phosphate and some minute phases of tricalcium phosphate, tetracalcium phosphate and calcium oxide. The experimental results showed that the 3-D TiN dendritic scaffold structure produced on the surface of pure Ti using laser gas nitriding technique in advance could anchor the HA coating and improved the interfacial adherence significantly as compared with those on the grit blasted surfaces.

Abstract: In this paper we propose several new mathematical models for estimating effective diffusivities of a drug released from a cylinder device to an external finite volume. These models can handle problems with ‘initial burst’ and boundary layers. Analytical solutions to the models are derived. To determine the unknown effective diffusivity, time of a initial burst and width of the effective boundary layer, a least-squares method can be used for a given experimental data set. The models were tested using experimental data and the numerical results show the usefulness and accuracy of these models.

Abstract: The effect of small amount of cation dopant on phase stability of zirconia bioceramics is evaluated by ageing in hot water. The phase transformation progresses with time in all specimens. However, the tetragonal to monoclinic transformation behavior is much different depending on the dopant. In case that the small amount of tetravalent soluble element is added, the transformation is promoted if the ionic radius of the element is larger than that of zirconium, and the transformation is suppressed if the element with smaller ionic radius than zirconium ion is added, which is explained from the change in the axial ratio, c/a. However, the change in phase stability of 7.7mol%TiO2-doped TZP cannot be simply explained from the change in the axial ratio, c/a. XRD analysis reveals that the distance between nearest neighbor anion and cation site significantly decreases only in 7.7mol%TiO2-doped TZP. This result indicates that the binding energy between dopant and oxygen vacancy affects the phase stability as well as the change in the axial ratio, c/a.

Abstract: A high magnetic field is a useful tool to control the crystal alignment of ceramic materials. In this study, a horizontal 10T static magnetic field was imposed on slurry containing hydroxyapatite (HAp) crystals under the horizontal mold rotation during slip casting process so as to introduce uni-axial alignment for some amount of crystals in the sample, and then it was sintered in atmosphere without the magnetic field. From X-ray diffraction, it has been found that the HAp crystals in the sample treated with the mold rotation under the magnetic field were aligned its c-axis to a particular direction.

Abstract: As the extension of mineral processing, recycling metals from wastes is very important for a sustainable society. We have been working on mechanochemistry and its engineering applications. One of the applications is to recover and separate useful components from different kinds of wastes emitted in our society. When a waste sample is subjected to grinding in air so called mechanical treatment, it changes its structure to disordered system, resulting in chemical reactions with other substances when it takes over the certain level of energy. Depending on the existing states of target elements in the wastes, mechanical activation and mechanochemical (MC) reaction can be applied for the recycling of useful compositions and a process based on MC treatment has been developed. We will report several examples from our research experiences at the conference. The first example is to recover rare earths from fluorescent powders in waste lamps. The waste is firstly subjected to dry grinding to cause amorphization of their structures. This amorphization makes it possible to dissolve the rare earths from the waste at high yield by leaching with mild acid solution at room temperature. Similar phenomenon can be seen in the case of ITO (indium tin oxide) scrap when it is ground, followed by leaching with acid solution. In this case, dry grinding the scrap induces disordering the In2O3 in the scrap, leading to high dissolution of In2O3 by leaching with weak acid solution at room temperature. The presence of alumina (α-Al2O3) in the scrap plays a significant role to the amorphization. Another advanced waste processing is to recover molybdenum (Mo), vanadium (V) and nickel (Ni) sulphide in catalysts in oil refineries. The processing is based on MC reactions between the sulphides and additives. That is, the sulphides are subjected to dry grinding with additives such as CaO, MnO2 and Na2CO3 to transform them into molybdate and vanadate. Subsequent water leaching allows us to recover Mo and V from the ground product. Other successful example is dry grinding metals or their oxides with polyvinyl chloride (PVC) to transform into chlorides, which dissolve easily in water at ambient condition. The waste processing described above is now in the investigation on industrial applications, and this is a great expectation in the field of industries which emit such waste materials.

Abstract: Hydrogenation / dehydrogenation properties of a series of ternary face centered cubic (FCC) hydrides “Mg7MHx” (M = Sc, Ti, V, Zr, Nb, Hf and Ta), which were prepared by a high-pressure technique, were investigated. Differential scanning calorimeter (DSC) measurements under hydrogen atmosphere revealed that these hydrides exhibited reversible hydrogen releasing and re-storing properties at around 600 and 560 K, respectively. These releasing temperatures are lower by 100 ~ 120 K than that of MgH2. Furthermore, pressure-composition isotherm at 523 K shows that these FCC hydrides release 3.8 - 5 wt. % hydrogens.