No description available.

No description available.

Vapor-liquid equilibria (VLE) in alkanes and alcohols was measured and a contribution Patel-Teja (GPT) equation proposed in this work. systems of nmodified Group of state was Isothermal vapor-liquid equilibria at temperatures between 298.7K and 333. 7K have been measured for the binary systems n-pentane + n-hexane. n-pentane + noctane. n-pentane + n-decane. and n-pentane + l-propanol. The data were found to be consistent according to a point-to-point consistency test and were correlated using the Wilson. NRTL. and UNIQUAC activity coefficient models. The parameters of the models were estimated using the maximum likelihood principle. A new version of the Group contribution Patel-Teja equation of state was proposed in which a new temperature dependent group interaction expression was introduced. Group interaction parameters for four constituent groups of the alcohols and n-alkanes (viz. CH 2• CH 3 • CH and OH) were determined. These parameters were then used for the prediction of VLE in mixtures of n-alkane + n-alkane. n-alkane + n-alcohol. and n-alcohol + n-alcohol. VLE predictions with the new GPT equation of state were found to be superior to predictions with the original group contributions with molecular equations. The modified equation can be used in systems of nalkanes and alcohols where data for molecular parameters are lacking. The proposed temperature dependence of the group interaction parameters improved predictions over a wide range of temperature and pressure.

Thesis (Ph. D.)--Landbouwhogeschool te Wageningen, 1981. / Summary in Dutch. Includes bibliographical references (p. 170-176).

.. Detailed experimental and thermodynamic studies of. the isothermal phase equilibria for the / Thesis (Ph.D.)-University of Natal, 1990.

No description available.

No description available.

The thesis examines ion-assisted physical-vapour deposition (PVD) of thin coatings on non-flat three-dimensional samples, concentrating on the case of free-standing edges and comers. Changes in the electric field in the vicinity of sharp edges lead to local changes in the ion bombardment (ion flux and angle of incidence) which can significantly affect the ion-surface interaction and thus the properties and the performance of the coatings growing in the edge region. This work presents a detailed electron microscopy study of the edge-related changes in the coating properties and develops a physical model to explain and quantify the effects. The problem is studied on a system typical for industrial coating of cutting tools used in dry high speed cutting: TiAlN-type coatings (TiAlN/VN and TiAlCrYN) deposited on wedge-shaped samples by closed-field unbalanced magnetron sputtering (UBM), using high-flux, low-energy Ar+ ion irradiation (J[i]/J[me]~4, E[i] = 75-150 eV). The morphology and composition of the coatings in the edge region, as a function of the edge geometry (angle and radius of curvature) and the deposition conditions (substrate bias), is studied using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM+EDX). The internal structure of the coatings growing on sharp edges is examined by transmission electron microscopy (TEM). A detailed theoretical analysis of the effects, based on the simulations of the plasma sheath around the samples and the resulting ion bombardment distribution, is presented. A direct relationship between the experimentally observed magnitude and spatial extent of the changes in the edge region and the simulated characteristics of the plasma sheath around the edges is shown.

A critical stage of the combined steered arc and unbalanced magnetron process is the metal ion pre-treatment which improves the adhesion of the TiN coating. In this study, Conversion Electron Mossbauer Spectroscopy (CEMS) has been used to investigate surface interactions in a commercial Arc Bond Sputtering (ABS) coating system. A novel application of the Liljequist theory of CEMS has been used to determine ion etch rates for deposited natural iron on stainless steel substrates, for various Ti ion pre¬treatment processes. The approach has estimated an etch rate of 60 nm min.'1 for samples positioned without substrate rotation at a cathode-sample distance of 250 mm. This has been calculated to correspond to a bias current density of 6.68 Amps m-2. Similar experiments involving modes of rotation yield an average etch rate of approximately 40 nm min.-1 To detect small quantities of iron containing phases formed during a pre-treatment process it has been necessary to enrich substrates with the Mossbauer isotope, 57Fe to achieve greater surface sensitivity. The enrichment used the technique of the deposition of an estimated 25 nm of 57Fe on polished mild steel substrates followed by annealing to generate an 57Fe diffusion profile into the near surface region. A diffusion model has been used to predict the 57Fe depth profile due to the adopted annealing process parameters. Verification of the estimated thickness of the deposited 57Fe overlayer and the diffusion profile has been provided by SIMS and SNMS. Using the 57Fe enriched mild steel samples, CEMS has investigated the formation of iron- titanium phases after a typical industrial ten minute pre-treatment process using substrate rotation, at a substrate bias voltage of -1200 V. Significant phase formation of both crystalline Fe[x]Ti[1-x] and amorphous Fe[x]Ti[1-x] have been identified. The formation of the crystalline phase has been confirmed by XRD. Using a model of the 57Fe isomer shift dependence of x, in amorphous alloys yielded x=0.31 +/-0.08 for Fe[x]Ti[1-x] Further experiments using an estimated 25 nm of 57Fe deposited on mild steel without annealing, showed the presence of magnetite and a small quantity of crystalline FeTi for a 25 s pre¬treatment process. After a 300 s pre-treatment time the oxide layer is removed and significant quantities of both crystalline and amorphous FeTi are formed. CEMS has also showed increased 57Fe removal at a 6 x 10-5 mbar Ar operating pressure within the coating chamber compared with a pre-treatment performed at a higher Ar pressure of 3 x 10-3 mbar, showing the greater effect of the Ti ion etching under these conditions. During the experiments performed at different Ar pressures, CEMS also identified iron carbonitride phases. Similar phases have also been identified in the early growth stages of a compound layer in a process performed using a modified Balzers coating system. CEMS has proved to be a powerful technique, enabling the investigation of surface interaction phenomena occurring in the near surface region of 57Fe enriched substrates treated by Physical Vapour Deposition (PVD) processes. The information provided by the technique makes it strategically important in the future research of interface regions generated by PVD processes.

No description available.