Procedia Materials Science最新文献

Ni₂MnGa alloys are obtained by suction casting in water chilled cylindrical copper moulds 50 mm long and 1-4 mm in diameter; the microstructure and the magnetic properties are then investigated as functions of the cylinder diameter. The solidification substructures are characterized by scanning electron microscopy and confocal microscopy. The martensitic transformation temperatures, determined by magnetization vs. temperature measurements, are lower than those measured in bulk Ni₂MnGa single crystals (202 K). The demagnetization curves measured from saturation in the martensitic state show two steps: the first is at about+130 mT and the larger second one at relatively large inverse fields (about -300 mT), except in cylinders 4 mm in diameter, where these steps overlap at low inverse fields. These steps are likely to arise from a demagnetization mechanism involving field induced twin boundary motion in a few martensite variants,indicating a ferromagnetic shape memory effect in the cylinders.

The skill of ancient artisans manufacturing artistic or everyday artworks surprises the modern material scientists. We show, through the study of archaeological pieces, how laboratory research instruments use enlightens the fabrication processes of unique items at antic periods. The specificity of surface science research favouring non-invasive means for investigations on museum objects is emphasised. The examples concern:

- Nanostructured layers on ceramic surface to obtain the so-called lustre effect, invented by ancient Islam potters;

- Intentional coloration of metallic objects by chemical patination, attested in Egypt on 2nd millenary BC and still applied by Japanese artisans;

- The history of gilding objects: leaf gilding, mercury gilding, and other processes;

- The Fresco technique, a perennial wall painting, known by ancient Roman and propagated through centuries.

The examples open new fields belonging to the modern materials science, to understand the mechanism involved in processes with the constraint that one does not know all the fabrication steps.

In this paper, eddy current, induced voltage, solid loss and magnetic torque in circular thin conductors were systematically investigated using finite element method. Two-dimensional models were constructed using ANSYS MAXWELL to simulate the magnetic field and current in a transient environment. A rectangular permanent magnet made of alnico5 was used as the rotational magnet. Simulations were carried out for four highly pure conductor metals, silver, bronze, tungsten and graphite. The electrical resistance of the specimens was calculated. The results of the simulations for these specimens show that there is a strong correlation between bulk conductivity of the specimens and eddy current induced in the thin conductor metals. The model presented in this paper can be used in measuring the electrical resistivity of the samples and non-destructive test studies of thin conductor thin films.

In the past few years, application of electrospun nanofiber has gained intensive attention for membrane distillation (MD) that exhibit promising results. In this study the effects of three salt additives including calcium carbonate (CaCO₃), lithium chloride (LiCl) and calcium chloride (CaCl2) on the morphology, hydrophobicity, porosity and permeation performance of poly (vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP) nanofiber membranes were investigated. Scanning electron microscopy (SEM), geniometer, gravimetric method and air gap MD (AGMD) setup were used to characterize the resultant PVDF-HFP membranes. It was observed that addition of LiCl and CaCl₂ improved the electrospinability of polymer dope solution and changes the morphology of fibers from beaded fiber to a uniform fiber structure. Also the membrane made from the dope with LiCl as the additive salt possessed the highest porosity of % 89. The membrane hydrophobicity was affected less by CaCO₃ as compared with LiCl and CaCl₂. The synthesized membrane was applied in desalination via air gap membrane distillation, in which a water permeation flux of 13.6, 12.2 and 9.8 Lh^-1m^-2 were obtained when LiCl, CaCl₂ and CaCO₃ was used as the additive, respectively.

Films made from starches are colorless, tasteless, non-toxic, biodegradable, and economical, besides having a low permeability to oxygen. Moreover, the cross-linking modification (phosphatation) could improve its physicochemical properties by reinforcing the hydrogen links inside the granules. The goals of this study were to elaborate and characterize starch corn films 80:20 “waxy”:regular, from native and modified (cross-linked), to define their potential application. Results showed, that films with modified starch had highest hydrophilic properties which increased its thickness, permeability and solubility, and with mayor stability in acidic and alkaline medium. Finally, physicochemical properties and water vapor barrier data of the films denote the strong interaction phosphated starch-plasticizer.

Ferrous and non-ferrous alloys can be processed by PM. Complex shapes and good surface finishes can be achieved, leading to promising applications, if mechanical properties are demonstrated to be high enough. At the same time, both bainitic and carbide free bainitic microstructures have proved to be excellent candidates for wear applications. Therefore, the aims of this project were steered towards analysing wear behaviour of PM compacts, in relation to their bainitic microstructures.

Three materials were employed and two conditions were taken into account: materials before and after austempering. A reference material was considered, corresponding to Distaloy DC with Mo and Ni. Microstructure was analysed in all the cases by means of optical and scanning electron microscope and it was related to the behaviour observed. Pin on plate reciprocating sliding test without lubricant was utilised in order to measure friction coefficient and specific wear rate in the pins. Effects of alloying elements were also examined.

It was found that austempering decreased impact resistance, but enhanced hardness in Distaloy DC. In contrast, the other two materials presented the opposite behaviour. However, the presence of additional alloying elements in the initial composition fulfilled to increase wear resistance, compared to the reference material. A possible interaction between pores and oxides that may influence wear behaviour was observed. Si allowed carbide free bainitic microstructure to form but heterogeneity could not be prevented. Therefore, the advantage of this microstructure could not be fully used. Results obtained in the present work can lead to new wear applications for PM products, containing bainitic microstructures.

This research intends to analyse the potential use of CoAl₂O₄ as an opaque pigment for solar collector selective paints. The opacity of the pigment occurs when the average crystallite size is micrometric. The CoAl₂O₄ samples were synthesized through combustion methods using aspartic acid (Asp) or lysine (Lys) as fuels. The powders obtained were calcined at temperatures between 600 °C and 1100 °C. Afterwards, the product was characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). It was observed a CoAl₂O₄ phase in all the samples. The lowest average crystallite size was ≈24 nm corresponding to the sample obtained with Asp and calcined at 600 °C, while both powders calcined at 1100 °C showed sizes higher than 200 nm. In the light of these results it is suggested the use of even higher calcination temperatures so as to obtain opaque pigments for solar collectors selective paints.

Biocomposite materials based on natural fibres are of great interest, often due to their low cost origin. Natural fibre reinforced biocomposites are emerging as a possible substitute to glass fibre reinforced composites. Owing to the advantage of low cost, low density, reduced energy consumption, natural fibres offer an opportunity to developing countries to use their own natural resources for producing composite materials. Although glass and other synthetic fibre-reinforced plastics possess high specific strength, their fields of application are very limited because of the inherent higher cost of production. In the present work experiments have been conducted to study the influence of nano clay in polyester resin based composites reinforced with coir fibres. Themechanical properties of the composite are evaluated. The addition of nano clay to the coirfibre reinforced composites exhibited considerable enhancement in the mechanical propertiesat lower cost and therefore can be used as a substitute to glass fibres.