Materials Science Forum Vols. 514-516

Abstract: Nanocrystalline indium tin oxide (ITO) thin films were deposited on Si/SiO2 substrates by laser ablation from a ceramic target with a composition of 0.9 In2O3 . 0.1 SnO2. Samples were prepared in the pressure range from 10-1 to 5mbar, either in-situ at 500°C or at room temperature and heat-treated in air at 500°C. X-ray diffraction results show that the films are not oriented, except the ones made at high temperature which exhibit strong (400) orientation. AFM pictures show that the grains are round shaped and the sizes are in the range between 50 and 200nm, except for films made in-situ at 10-1mbar which are elongated and faceted. For higher pressures the grains tend to be small and to form agglomerates. The porosity of the films increases with the deposition pressure and the thicknesses reach a maximum of 2.8µm at 1mbar for the films made at room temperature and of 1.2µm at 2mbar for the ones made in-situ; for higher pressures the growth rate drop drastically, as revealed from SEM observations of cross-sections. The electrical resistance increases with the deposition pressure due to the increase in porosity, changing from 3.3k to 38.9M for films deposited at room temperature and from 20 to 265k for the ones made in-situ.

Abstract: AgxNi1-x (x=0.0-1.0) films were grown on Cu substrates by electrodeposition method. The films were found to be a nanocrystalline mixture of pure silver and nickel. The grain sizes were determined by X-ray diffraction and electron microscopy techniques. The minimal value was 3.3 m for the alloy with 70 wt% concentration of Ni. The stability of the grown films upon heating in ir and in vacuum was examined. An increase in the grain size was found to begin at 150°C.

Abstract: In cutting applications hard thin films of coated tools are expected to be wear and oxidation resistants, and with strong adhesion to the substrate. Due to the high loads involved in the contacts, the main efforts must be supported by the substrate and it is supposed that the coatings follow their elasto-plastic deformation, with a subsequent delay of the crack propagation. The commercial thin films used for these applications are generally monolithic and homogeneous or heterogenous(chemical compositional gradient up-down). Even the nanostructured coatings will perform under these loads as monolithic coatings, and the crack generation and propagation will be ruled by the same mechanisms as in the monolithic coatings. Hence, the hard coatings for cutting tools must be able to deflect surface cracks and exhibit the highest adhesion to the substrate. In order to achieve these characterisitics, the common Ti-Al-N was selected as hard coating, and thin ductile metal interlayers (few tenths of nanometres) were introduced inside Ti-Al-N thin film as long period multilayer coatings – nanolaminate coatings. The presence of interlayers revealed efficiency in dissipation of the energy generated during the application, decreasing the propagation cracks across the coating and ensuring the best adhesion. The mechanical behavior observed is homotethic of macrolaminate composite bulk materials. The failure of the coating is layer-by-layer, always exposing the ductile layer, which function is also to be a fuse that protect the remaining coating. The material of the interlayer and the period (interlayer/coating) selected resulted from the balance between the maximum performance of coating to avoid service failure and the minimum decrease of relevant mechanical properties of the monolitic hard coating as hardness.

Abstract: Electrolytic coatings Ni-Mo with PPy were obtained by electrodeposition and electropolymerization from a galvanic bath containing Ni2+, MoO4 2–, ClO4 – ions and pyrrole (Py). The cyclic chronovoltamperommetric curve was used to determine the potential and current density of electrodeposition process. As the electropolymerization is anodic process while the electrodeposition is cathodic one, the electrode was working alternately as anode and cathode. The process was conducted under alternating potentiostatic or galvanostatic conditions. Comparative tests were carried out for Ni-Mo alloy. The results of structural investigation of the obtained coatings by the X-ray diffraction method show, the Ni-Mo layers are nanocrystalline solid solution of molybdenum in nickel (α phase), whereas the Ni-Mo+PPy coatings are characterized by decreased peaks coming from Ni-Mo base. Surface morphology of obtained Ni-Mo+PPy and Ni-Mo coatings was investigated by scanning microscope. It was stated, that the coatings obtained by alternating potentiostatic method exhibit multilayer character, whereas the coatings obtained under alternating galvanostatic conditions are characterized by the presence of Ni-Mo nanoagglomerates plated on polymer surface.

Abstract: Ni+Mo+Si coatings were obtained by electrolytic codeposition of crystalline nickel with molybdenum and silicon powders from an electrolyte containing suspension of these powders. These coatings were obtained in galvanostatic conditions, at the current density of -0.100 A cm-2. Thermal treatment of these coatings in argon atmosphere was done at temperature of 1100oC for 1 hour. A scanning electron microscope was used for surface morphology characterization of the coatings. Chemical composition of obtained coatings was determined by Xray fluorescence spectroscopy method and phase composition investigations were conducted by Xray diffraction method. It was found that introduction of molybdenum and silicon into nickel matrix, causes of obtained coatings about very rough surface. Thermal treatment of these coatings influenced their surface. The surface after thermal treatment is more compact and less rough than the as-deposited one.

Abstract: The mechanical behaviour of semicrystalline polymers is dependent upon the property of both the amorphous and crystalline phases and their eventual interactions. In this context, heat shrinkable films have been evidenced as an interesting material model to investigate the influence of the amorphous phase on the mechanical behaviour of semicrystalline polymers, as upon heating these materials only show changes on the extensibility of the amorphous phase (macromolecular conformational state). The effect of the amorphous phase on the mechanical behaviour can therefore be studied independently. In this work are investigated the mechanical properties of a heat shrinkable polyethylene films as processed and after annealing at 60 °C (for 15 min). The morphology of the film before and after the annealing treatment was characterised by 2D-SAXS patterns. The tensile tests were performed at 50 mm/min and room temperature (23 °C) in different directions respectively to the longitudinal film direction, LD (0, 30, 45, 60 and 90º). The results show that the conformational state of the amorphous phase affects the tensile modulus and the deformation capabilities of the films, namely in the transverse machine direction. No influence on the sustained stress level was observed. Furthermore, the essential work of fracture is determined at large extent by the conformational state of the amorphous phase. This study suggests the high importance of the amorphous network on the initial strain levels and on deformation capabilities of the lamellar structure loaded transversely to the crystalline phase orientation.

Abstract: Fractal and aggregate structures of porous materials were studied by a variety of the structure characterization techniques (TEM, small angle X-ray scattering, nitrogen sorption). Scattering data (SAXS, USAXS) for porous materials measured with laboratory equipment and synchrotron technique were interpreted in terms of Guinier, Emmerling, Freltoft, modified Freltoft theories, and simple power law expressions. The evaluation of scattering measurements resulted in fractal dimensions, sizes of the elementary units, the fractal domains or the aggregates. TEM images confirmed the sizes of the elementary building units, while the pore size distributions could be obtained by nitrogen adsorption. The specific surface area was calculated with respect to the possibility of multilayer formation during nitrogen absorption.

Abstract: A hydride tungsten complex, [WH2(η2-OOCCH3)(Ph2PCH2CH2PPh2)2][BPh4], was entrapped in the interlayer of a pillared layered clay (PILC) and in NaY zeolite. The adsorption of the complex in the liquid phase was the immobilization process used. The free complex and the new materials were characterized by several techniques: structural analysis by DRX, nitrogen adsorption isotherms and spectroscopic methods (ICP-AES, FTIR and UV/Vis). Analysis of the data indicates that the tungsten(IV) complex is immobilized in the host microporous structures, and exhibit structural properties that are different from those of the free complex. These differences could arise either from distortions caused by steric effects imposed by the structures or from interactions with the host matrix.

Abstract: SiO2/polystyrene nanocomposite particles were synthesized via miniemulsion polymerization using sodium dodecyl sulfate (SDS) as surfactant and hexadecane as hydrophobe in the presence of silica particles coated with methacryloxy(propyl)trimethoxysilane (MPS) surface coupling agent. The silica particles were individually coated with polymer yielding a very homogenous nanocomposite latex which was very stable in a wide range of ionic strengths. Monomer conversion was reasonably high and fast.

Abstract: New lanthanotungstocobaltates with the Keggin structure and general formula KxHy[Ln(CoW11O39)(H2O)3]⋅nH2O or KxHyLn[Ln(CoW11O39)(H2O)3]⋅nH2O, LnIII = Ce, La, Eu, Sm, Tb, were prepared and characterized for the first time. Hybrid silica materials, with the polyoxoanions anchored to spherical silica particles, were also prepared and characterised. Their study by IR spectroscopy and EDS suggested that the structure of the Keggin-type polyanions is maintained when they are immobilized in the silica material.