Witold Jastrzębski

Phase Transitions in BaTiO3 from IR Autocorrelation Spectrum

Temperature dependence of infrared spectrum from BaTiO 3 micro-crystals has been analysed. The measurements have been made within temperature range from 140 to 330 K in the IR region between 380 and 4000 cm−1 . The low temperature spectrum shows two clear bands at about 498 and 550 cm−1 that are in agreement with expectations for trigonal symmetry. The spectra at higher temperatures have the profiles that are difficult to be interpreted using a conventional peak fitting procedure. To explain the obtained results an autocorrelation method has been used for the frequency region between 480 and 700 cm−1 (where IR active vibrations occur). A special attention has been paid to the effects following the phase transitions. It has been possible to formulate some additional arguments concerning a complex character of the phase transitions in barium titanate with indication of an increasing role of order-disorder mechanism.

Silicon carbonitride layers deposited on titanium and polyurethane by PACVD method

This work reports the results concerning formation and tribological properties of SiCxNy(H) layers deposited on Ti Grade 2 and polyurethane foil. Depending on the substrate, two variants of PACVD were used. The SiCxNy(H) layers on titanium were deposited with application of MWCVD (2.45 GHz, 2 kW). The layers on polyurethane were deposited using RFCVD (13.56 MHz, 400 W). Good adhesion between the SiCxNy(H) layers and polymeric foil was achieved by formation of a transitional C:N:H layer and incorporating Si gradient into the structure of the SiCxNy(H) layer. The chemical composition of the layers was tailored by precise control of the gaseous precursors ratios: [SiH4]/[NH3], [SIH4]/[NH3]/[CH4], [SiH4]/[CH4] or [SiH4]/[N2]/[CH4]. The structure and chemical composition of the obtained layers were subjected to further studies (FTIR, SEM/EDS). The roughness, friction coefficient and wear resistance were also measured. The results show that SiCxNy(H) layers offer attractive tribological properties which make them good candidates for various applications, including biomedical devices.

Surface Modification of Titanium by Plasma Assisted Chemical Vapor Deposition (PACVD) Methods

One way of obtaining new materials with different properties is to modify existing ones to improve their insufficient properties. Due to the fact that many of the useful properties of materials, including wear and corrosion resistance, friction coefficient and biocompatibility, depend on the state of the surface, modern surface engineering methods are especially helpful. They involve the deposition of the layers with tailored chemical composition and structure. In terms of medical applications, amorphous or nanocrystalline layers containing carbon, nitrogen, silicon and hydrogen appear to be the most suitable. They combine the beneficial properties of silicon carbide SiC and silicon nitride Si3N4, and thus exhibit a strong resistance to oxidation at high temperatures, high modulus of elasticity, low friction coefficient and wear resistance. However, silicon carbonitride compound is not stable thermodynamically in normal conditions and therefore it must be obtained by non-conventional synthesis. One of such method is Plasma Assisted Chemical Vapour Deposition (PACVD). The authors of this paper anticipate that the modification of titanium surface by SiCxNy(H) layers make them proper for use as materials for long-term contact with human body. It contains results of research on titanium Ti Grade 2 surface modification by deposition amorphous carbon layers doped with nitrogen (a-C:N:H) and silicon carbonitride layers SiCxNy(H). What is more, for IR analysis, in the same plasmochemical methods process obtain layers on monocrystaline silicon (001)Si. The layers were synthesis by PACVD with plasma generated by radio waves (RFCVD, 400 W, 13.56 MHz) for a-C:N:H layers and microwaves (MWCVD, 2 kW, 2.45 GHz) for layers containing silicon, carbon, nitrogen and hydrogen. During deposition process metallic surface were ion-etching by argon plasma. The layers were obtained from reactive gas mixture containing CH4, N2 or NH3 for a-C:N:H layers and CH4, SiH4, N2 or NH3 for silicon carbonitride compound. In this process argon was used as an inert gaseous. Process conditions allowing obtaining good adhesive layer to the metallic substrate were specified. Obtained systems were subject for further research. Chemical composition of the materials were studied by SEM / EDS techniques with application ETD and BSED detectors. Compared images registered for titanium before surface modification and surfaces covered by a-C:N:H or SiCxNy(H) layers. More information about layers structure provided FTIR spectroscopy. Spectra FTIR was register transmition for (001)Si-layer and reflective for titanium-layer systems. Assessed the impact of different kind of substrate on the layers deposited structure. Operational properties of synergic layer-titanium systems were evaluated in the measurements of tribological parameters. This tests shown that silicon carbonitride layers have the lowest friction coefficient and the highest resistance to wear. Furthermore, it was possible, on the basis of the obtained result, to indicate directions the surface modifications ensuring optimization on their usable properties as medicine and another industries. In previous authors paper the layers were investigated in the aspect of possible application in medicine.