Stanisława Jonas

A new non-silicate refractory of low thermal expansion

Abstract Preliminary experiments were conducted aimed at developing refractory ceramics of low thermal expansion based on calcium dialuminate CaAl 4 O 7 . This compound was synthesized by a specific cycle of calcination, regrinding and firing (finally at 1450°C), the emerging phases having been identified by X-ray diffraction. The obtained product was combined in various proportions with the highly refractory calcium zirconate CaZrO 3 ; also,CaAl 4 O 7 specimens were impregnated with SiC using the chemical vapour deposition (CVD) technique. Thermal expansion up to 900°C and porosity data were established for a number of compositions. The obtained microstructures were shown as scanning electron microscope pictures. From among the potential applications, the continuous casting of steel is indicated, the composites containing CaZrO 3 and vapour deposited SiC being regarded as promising materials for submerged nozzles.

Stability of a-C:N:H Layers Deposited by RF Plasma Enhanced CVD

A series of amorphous hydrogenated carbon layers doped with nitrogen (a-C:N:H) was deposited on Si (001). The synthesis was performed from gaseous N2/CH4 mixture using PE CVD (RF CVD technique; 13,56 MHz). An influence of the processing conditions on layer-growth rate was analysed. Thickness of the layers deposited during 1 hour at various temperatures, pressures and RF powers were taken as a basis. It has been proved that the substrate temperature is a key parameter for the layer formation. Temperature rise results in the deposition rate decrease. This unfavourable effect may be reduced by application of increased gas pressure and/or higher plasma RF generator power. At optimal conditions (46 oC; 0,8 Tr; 60 W) the deposition rate reaches up to 600 nm/hour. FT-IR spectra of the layers were measured within 1250 - 4000 cm-1 and discussed with regard to the atomic structure. The intensities of the characteristic absorption bands were compared. The results show that the layers have various N/C ratios according to the applied processing conditions.

Influence of SiC infiltration on some properties of porous carbon materials

The work concerns the investigation of the microstructure changes of carbon industrial materials of various porosity after the pulse chemical vapour infiltration (PCVI). The authors have focused their study on the initial steps of infiltration method up to 100 pulses. The experimental data indicate the complex nature of infiltration process due to complex geometry of pores in these materials, non-stability of matrix, influence of thermal stresses. At the initial steps of infiltration process, apparent improvement of oxidation resistance can be observed.

Surfaces Modification of Al-Cu Alloys by Plasma-Assisted CVD

Aluminum-copper alloys (Al-Cu) are nowadays widely used in various applications, mainly in automotive and aviation industry, because of their unique properties such as high strength, low density and good corrosion resistance. However, usages of aluminum alloys are partially limited due to their reduced hardness, wear resistance and poor tribological parameters. Desired useful parameters can be improved by application of PA CVD technology. This work presents the results concerning determination and analysis of the structure and the selected properties of the modified surfaces of Al-Cu alloys (2xxx series) that were prepared using plasma assisted MW CVD (Micro-Wave Chemical Vapour Deposition) method. To ensure effectiveness of the substrate modification process, the covered surface was subjected to pre-treatment with argon plasma and/or nitriding process. In conclusion, the research has confirmed that the wear resistance of the Al-Cu alloy can be successfully modified by application of MW CVD technique. The obtained results can serve as a basis in the design of the technology of a-Si:C:N:H layers for diverse applications.

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 the Ti6Al4V Alloy with Silicon Carbonitride Layer Deposited by PACVD Method

Abstract Four different layers of various silicon, carbon and nitrogen contents on the Ti6Al4V alloy and (001)Si wafers have been deposited by means of Plasma Assisted Chemical Vapor Deposition (PACVD) method. The layers were obtained from reactive gas mixture containing SiH4, CH4, NH3 and Ar. After deposition the structure and chemical composition of modified surfaces have been analyzed with use of SEM/EDS technique. Based on these results and thermodynamic calculations, the diffusion coefficients, D, for nitrogen and carbon in alloy were discussed. Scratch test shown that silicon carbonitride layers have good adhesion to metal surface. In order to determine atomic structure of obtained layers, FTIR spectra for layer-(001)Si and layer-Ti6Al4V were registered.

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.

Surface Modification of Polyetheretherketone by Helium/nitrogen and Nitrous Oxide Plasma Enhanced Chemical Vapour Deposition

Abstract The surface of the polyetheretherketone (PEEK) samples was modified by the plasma enhanced chemical vapor deposition (PECVD) in the mixture of He and N2 as well as in the N2O atmosphere. Morphological characterization of the PEEK as well as its surface roughness, chemical structure, and surface free energy were investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and sessile drop technique, respectively. The highest increase in the polar component of the total surface energy was observed for PEEK modified by He+N2 plasma, which correlated with significant increase in the concentration of oxygen and nitrogen-containing chemical functionalities as revealed by XPS. For PEEK submitted to N2O plasma treatment significant changes in surface topography and increase in roughness were observed, but changes in surface chemistry and surface free energy were mild.

Polymer-Surface Modification with a-C:N:H Layers Plasma Chemically Deposited in RF CVD and MW CVD Systems

The paper demonstrates that polymer surface may be modified by means of carbon nitride layers (a C:N:H) formed by Plasma Enhanced Chemical Vapor Deposition method. The layers were deposited from CH4/N2/Ar plasma generated by radio-frequency waves (13.56 MHz) and microwaves (2.45 GHz). A series of experiments enabled determination of technological parameters appropriate to deposit well-adhering and high quality layers on PC, Plexi and PET surfaces. The obtained layers were subjected to structural and chemical composition studies employing energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT IR) techniques. It was established that roughness parameters of the samples with layers were visibly lower than the parameters characterizing the surfaces after pre-treating with Ar plasma and remained on the same level or were slightly lower than those for raw polymer surfaces.

Model Studies of Microstructure Changes in Sintering of Ceramics

In this article an experiment is described which is included into a course in materials science and allows for better understanding of a nature of sintering. It is a fusion of a computer simulation and a physical experiment – both performed in model systems. Part I of the experiment concerns microstructure of powders. Packing density and coordination numbers of the grains in the sintered powder are analysed with application of computer simulation. In part II of the exercise, the kinetics of the sintering of glass grains is measured via microstructure-evolution observations. The results may be used to discuss the mass transport mechanism.