Materials Science Forum Vols. 730-732

Abstract: Beryllium and carbon are foreseen as materials for plasma facing components of future fusion devices. Erosion, re-deposition and thermal annealing events arising from heat-loads during reactor operation will produce mixed material layers and compounds on the plasma facing surfaces, leading to changes in the material properties. In order to mimic the erosion/deposition and compound formation processes, carbon layers have been evaporated onto beryllium plates and annealed in the 373 to 1073 K range for 90 min. Ion beam measurements revealed a smooth beryllium and carbon interdiffusion at the samples interface up to 773 K. A carbide formation reaction front became apparent for higher temperatures in scanning electron microscopy observations, with the volume fraction of Be₂C crystals resulting also evident in X-ray diffraction patterns. The annealing route induced delamination of large surface areas of the samples through telephone cords blistering, attributed to strain energy release. At 973 and 1073 K, cracking occurred preferentially along the blisters boundaries and evolved in time, leading to their final removal. This fracture behaviour seems caused by the different thermal expansion coefficients of the phases. The superficial films remain unchanged at lower temperatures. The results prove that the compound formation promotes by itself the occurrence of dust emission events in tokamaks.

Abstract: The aim of this work was production of tetraethoxysilane (TEOS) plasma polymerized thin films and optimization of their physical-chemical characteristic for sensor development. The films were analyzed using several techniques. It was possible to produce composites (graphite clusters imbibed by silicon oxide film) made from only one reactant (TEOS). Deposition rate can vary significantly, reaching a maximum of 30 nm/min; cluster formation and their size widely depending on deposition parameters. The film surface was hydrophobic but can be wetted by organic compounds, probably due to carbon radicals. These films are good candidates for sensor development.

Abstract: Tricone drill bits with hard ceramic inserts are often used in oil well drilling operations. However, the cutting action and breakdown of the rock formation produces failures on the tricone bits, which mainly are related to wear, partial or total rupture of the drill bit body or ceramic inserts, thermal shock, and corrosion. Brazing is a well established technique to joint metal-metal, ceramic-ceramic and ceramic-metal materials. Wetting phenomena plays an essential role in the production of metal/ceramic interfaces if a liquid phase is present. Stabilized zirconia with yttria and magnesia can be an interesting material for hard ceramic inserts application on drill bits when oil well or the drilling fluid has acid characteristics. In this work, silver based brazing alloys were melted onto zirconia substrates under high vacuum. The effect of oxide stabilizers and the metallized surface on the wetting behaviour were studied. Better results were found for the yttria stabilized zirconia system using AgCu with 3% Ti as filler alloy.

Abstract: Chemocapacitors are polymer coated Interdigital electrodes (IDE) where the transducer mechanism relies on the permittivity changes and swelling of the coating polymer (sensitive layer), usually in a form of a thin film, when exposed to an volatile organic compound (VOC). Despite several synthetic and natural polymers have already been produced by electrospinning, there have been fewer studies on rubbery polymers with low glass transition temperature (e.g. Poly(dimethyl siloxane) – PDMS). In this work we produce PDMS:PMMA 3:1 nanofiber (NF) layers by electrospinnig to be used as chemical sensitive layers on IDE chemocapacitors. The results show an enhanced response from the sensors with NFs with respect with sensors prepared with the same sensitive layers in the form of a homogeneous film.

Abstract: Surface treatment processes are usually applied to improve surface characteristics and resistance. Particularly duplex processes like nitriding combined with nanostructured based coatings are considered as the most advanced ones, with a large application potential in automotive industry. An example is an application in gear wheels, where fatigue loading in gear teeth roots exists besides contact fatigue on teeth sides. Contact fatigue, has to be therefore well balanced with pure fatigue resistance. Some surface treatments leading to excellent contact properties, wear resistance and extremely low friction coefficient may reduce resistance to pure fatigue crack initiation and subsequent growth to premature failure. In the paper, results of an experimental programme aimed at evaluation of fatigue resistance at repeated loading of nitrided steel after application of two types of coating, (i) nanostructured C-layer deposited by a modified cathodic arc technique according to Microcoat patent and (ii) Cr-WC:H-DLC layer produced according to Hauzer patent [1], are presented and discussed. Fatigue tests were carried out using small samples with 2.1 mm diameter, with nitrided layer of 0.35 mm thickness. Tests were completed with fractographical analyses of initiation areas. Results and analyses showed that coating effects depended on the specific technology and parameters. The Cr-WC:H-DLC layer affected fatigue limit favourably unlike the Microcoat C-layer, which resulted in reduction of fatigue strength. A detailed analysis of recorded data during static tensile tests indicated an occurrence of significant surface and subsurface residual stresses with a strong possible effect on fatigue crack initiation mechanisms. A significant, unfavourable effect of inclusions in the subsurface layer was demonstrated.

Abstract: The main goal of this research is to apply AFM to the analysis of coated paper topography in order to find out relationships between sheet gloss and some parameters obtained from AFM, such as roughness and fractal dimension (D). Flooding technique was also developed using appropriated software. Number of hills/flooding volume for 25%, 50% and 75% flooded volume was applied in this research. Ground calcium carbonate and precipitated calcium carbonate were applied in coating colour formulations, alone and blended in three formulations, 75:25, 50:50 and 25:75. The results obtained showed high correlations between sheet gloss with fractal dimension (D) parameter. Finally, flooding technique showed to be very interesting, all of them gave useful information in interpreting the influence of topography on sheet gloss.

Abstract: In this work, it is reported the characterization of the microstructure and electric properties of ZnO:Al thin films produced by magnetron sputtering. An AZOY sputtering target (98 wt% ZnO + 2 wt% Al₂O₃) was used as source material. The microstructure, optical and electrical properties of ZnO:Al thin films were investigated and correlated with substrate deposition temperature and post-annealing temperature. It is demonstrated that the microstructural, electrical and optical properties of the as-deposited thin films are dependent on the substrate temperature. The crystalline texture of ZnO:Al was improved with temperature deposition as shown in the EBSD analysis and X-ray diffraction. ZnO:Al thin film deposited at 250 °C exhibited very good electrical conductivity, as high as 200 S^.cm^-1 with an activation energy of 5.4 meV. As substrate temperature or heat treatment temperature is increased there is an apparent blue-shift on the absorption edge of the transmittance spectra, which can be explained by the Burnstein-Moss effect.

Abstract: Electronic, biology and chemical biology have pushed the scientists to develop new techniques to graft locally organic molecules on surfaces. The objective of the work was to develop a cheap and lithography-free technique by combining Scanning Electrochemical Microscopy (SECM) and electrografting processes in view of tuning locally chemical and physical surface properties on initially homogeneous substrates. The electrografting process was carried out with diazonium salts Plots, lines or more complex 2D-patterns have been “imprinted” on conducting substrates.

Abstract: This work deals with an experimental investigation of the microstructure/morphology of spin-casted composite thin films of poly(3-hexylthiophene) (P3HT) and silicon nanocrystals (Si-NCs), in the weight proportion 1:1, which develop under different deposition conditions. The experimental parameters considered were the following: i) solvent quality; ii) spinning rate; iii) spinning time and iv) solution concentration. The developed morphologies were characterized by means of optical microscopy and X-ray diffraction (XRD) measurements. The present work aims at a) establishing the relationship between processing conditions and resultant morphology and b) defining the most relevant processing parameters that govern and are of significance for the induced morphology.

Abstract: This work describes the production and characterization of a selective membrane useful for electronic devices. The membrane was a composite made by a thin film of plasma-polymerized HFE (methyl nonafluoro(iso)butyl ether) immersed in plasma-polymerized HMDS (hexamethyldisilazane) film, a third phase being 5 µm starch particles included in this matrix. The film was deposited on silicon substrates and its physical, chemical and adsorption characteristics were determined. Infrared and x-ray photoelectron spectroscopy analyses showed fluorine and carboxyl groups on the bulk and the surface, respectively. SEM results indicate the film is conformal even if starch is present. Optical microscopy analysis showed good resistance toward acid and base solutions. Quartz crystal microbalance indicated adsorption of polar organic compounds on ppm range. This thin film is environment-friendly and can be used as a protective layer or in electronic devices due to adsorption of volatile organic compounds.