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Tribological properties of polymer materials are traditionally tested on small-scale test rigs because of cost-efficiency and flexibility. For highly loaded applications (e.g., sea lock doors, retaining walls, positioning systems) however, large-scale tests should be performed for estimating the frictional behaviour and wear lifetime of different engineering polymers more accurately under nearly working conditions. In present paper, two filled polymer grades covering a broad range of mechanical properties polyethylene terephtalate (PET)/teflon (PTFE) and ultra high molecular weight polyethylene (UHMWPE)/carbon are slid against high alloy steel, stainless steel and epoxy resin, in order to make a selection for its use as bearing material under dry and lubricated conditions. A general thermal model is evaluated for present test rig. The coefficients of friction on large-scale tests are lower than those obtained from small-scale testing. Polymer wear rates are calculated from weight loss and compared to dimensional measurements (thickness reduction) including elastic deformation, thermal expansion and creep. Microscopic observation of the worn surfaces shows different wear mechanisms of PET/PTFE after sliding against stainless steel, developing a transfer layer onto the polymer surface, and after sliding against high alloy steel, causing polymer transfer onto the steel surface. The better adherence of a polymer transfer film onto a steel counterface is explained by higher attractive forces resulting from its high surface energy, while there is little adherence on stainless steel counterfaces in accordance with its lower surface energy and lower friction. Wear of PET/PTFE after sliding against stainless steel is partly caused by the incorporation of steel particles. After sliding of UHMWPE/carbon, no wear debris was observed as its higher toughness allows for tearing of the surface without particle detachment. The high surface toughness and abscence of a transfer film results however in higher friction.

For economical, ecological and even technical reasons for some years there has been a tendency to introduce self-lubricating materials for bearing applications. In this way external lubricants such as oil or grease can be excluded, the design can be simplified and maintenance cost can be reduced. Among the self-lubricating materials the so-called engineering plastics have increasing importance. Unfortunately, data on their friction and wear characteristics are very disparate and often there is a lack of general understanding of the physical phenomena involved. In the present paper some basic types of engineering plastics (PA, oil-filled PA PTFE-filled PETP, POM-H) are experimentally investigated by means of small-scale reciprocating tribotesting. The tribological behaviour is explained in correlation with the chemical and mechanical properties of the materials. The basic failure processes are described for mild wear conditions as well as for overload conditions.

In literature, the stick–slip phenomenon is usually explained from an initial stick-phase. The stability conditions with respect to stick–slip (the occurrence or not) are also derived by checking the reoccurrence of a relative standstill (stick-phase) after the slip-phase that has been following an initial stick-phase. However, stick–slip can also arise from an initial situation of pure slip. In this paper, it is experimentally shown that friction induced tangential oscillations during stick–slip can merge into stick–slip during an impressed deceleration, if their amplitude is sufficiently large. Owing to the interaction between friction phenomena and the dynamic behaviour of the mechanical system of which the friction interface is a part, the (negative) friction force–relative speed gradient (d F /d v rel ), which gives rise to the tangential oscillations and has to be considered for the study of stick–slip, must be derived from changes of the relative speed with the same time-constant as the mechanical system. It is also experimentally shown that the risk of stick–slip during deceleration is enhanced by an increase of the time-length of deceleration and by an increase of the tangential stiffness of the mechanical system. The correlation of the experimental results with previous theoretical analysis is clarified. As a result, some widely accepted models for the friction as a function of the relative speed have to be put in question. It is also shown that the major problem in determining the gradient d F /d v rel is the inadequateness of the classical friction test rigs.

Wear processes in general are influenced by the surrounding atmosphere, humidity especially. For fretting wear several authors have examined the influence of humidity on the wear scar morphology, the wear volume and the composition of the wear debris. No agreement between the different results has been found, yet. In the present study, the influence of the humidity in the ambient air on the fretting process is examined. The friction, the wear volume and material transfer are measured for the fretting of a bearing steel ball against a flat steel specimen under gross-slip regime, in running-in as well as steady state conditions. The wear and material transfer are quantitatively measured with Thin Layer Activation method. It has been observed that high ambient humidity inhibits adhesion and accompanying material transfer. As a result, high humidity has a beneficial influence on fretting wear, in opposition to generally accepted hypothesis.

Fretting wear is the typical wear form caused by small, oscillatory, tangential movements between two normally loaded surfaces. In the present research a bearing ball is subjected to fretting against a flat surface in gross-slip conditions. Because of the small wear volumes it is very difficult to quantify fretting wear accurately. In the present research, fretting wear measurements on the fretting of a bearing ball against cold-drawn steel are carried out by various methods: thin layer activation (TLA), spherical cap modelling (SCM), normal displacement measurement (ND), three-dimensional surface topography (3DST) and scanning electron microscopy (SEM). It is concluded that TLA gives the most accurate measurements. SCM largely overestimates and 3DST underestimates the fretting wear. ND is mainly influenced by particle escape from the contact zone. It is shown that the fretting process consists of two stages. During a running-in stage of about 200 000 cycles the wear rate and the coefficient of friction are high. The wear particles remain trapped in the contact zone for about 8000 cycles. After 200 000 cycles a steady state stage of the fretting process starts, characterised by an increase of the wear scar area rather than the wear scar depth, an increase in the wear of the harder, spherical specimen and readhesion of the wear particles to the surface of the flat specimen.

Fretting wear occurs when normally loaded surfaces are subject to oscillatory relative tangential movements with small amplitude. As a result, the fretting wear volumes are much smaller than macroscopic wear volumes and by consequence are much more difficult to measure. Usually, qualitative or semi-quantitative but discontinuous techniques are used to measure fretting wear (SEM, scar size measurements, 3D topography). This means that the wear can be measured only at the end of the experiment and that many experiments are required in order to obtain a wear curve (wear as a function of number of cycles). In this work it will be shown that continuous measurement of the normal approach between the specimens can be used to obtain wear curves of both test specimens separately. Apart from measuring the normal approach during the test, correct measurement of the wear volumes of both specimens at the end of the experiment is needed. Thin layer activation (TLA) is used for this measurement. A suitable, geometrical wear model is used to obtain continuous wear curves based on the above data. This paper describes the geometrical wear model used and the procedure to convert normal approach measurements into wear volume curves. Some experimental data are used to illustrate the application of the wear model.

In this paper a new method is proposed for the calculation of the impedance of arbitrary electrodes containing noncylindrical pores and/or having place-dependent impedances. The method is based on splitting up the pore and the surrounding material into N discs. For the equivalent circuit of each disc a transmission line with constant impedances is adopted. By matrix calculations the impedance of the porous electrode can be obtained. A comparison is made between this, very general, matrix method and a recursion method developed by Keiser et al. for purely capacitive interface behaviour of pores in an electrode material with negligible impedance. It is shown that the matrix method requires much smaller N-values owing to the use of transmission lines for each disc. This makes it more appropriate to be used in curve fitting procedures. Moreover, it is shown that the typical behaviour of the pore impedance at low penetration depths is much better simulated with the matrix method. Furthermore, an attempt is made to provide more general knowledge about the impedance behaviour of noncylindrical pores as a function of the penetration depth of the a.c. signal. Finally, the theory is enlarged using constant phase elements instead of capacities to describe the behaviour of the electrode/electrolyte interfaces.

The method of one-dimensional modelling of the pore impedance is validated on pores drilled in AISI 316 stainless steel. Impedance measurements were carried out in 0.511 sulphuric acid solution. Experimentally, it is found that, for cylindrical pores with a radius/pore length-ratio smaller than 0.5, the one-dimensionality condition is satisfied. Furthermore, impedance measurements on noncylindrical, scaled-up pores provide evidence that a geometric constant Ag has to be introduced, as in Part I. In accordance with this theory it is found that for pores with narrowing cross section Ag is less than 1/3, while for pores with a broadening cross section Ag is greater than 1/3. Moreover, it is shown that the matrix method, presented in Part I, provides a way of calculating the impedance of a non-cylindrical pore by using a highly reduced number of discs, N, compared to the recursion method of Keiser et al. This is an advantage in fitting procedures.

For anodizing of aluminium in a sulphuric acid (15 mass%) solution at constant voltage, the current initially jumps to a high value and decreases rapidly to a low value in the first few seconds; thereafter the current rises to a constant level. The course of the current versus time is common for all applied voltages and temperatures. However, the higher the voltage and temperature are, the faster and higher the rise and constant level will be. The shape of this current-time curve is representative for the specific anodization layer. Exponential relations has been found for the different characteristic points (minimum, maximum and steady-state current and the corresponding times) of the current density-time curve versus voltage and temperature. Also for the thickness and the apparent specific mass of the oxide layer, exponential functions versus voltage and temperature were found. In this work it has been proved that a correlation exists between the measured steady-state current density, the thickness and the apparent specific mass of the layer. For the formed oxide layers the measured mean real specific mass value is the same as that one which has already been published.

The membrane aging phenomenon and its influences on the kinetics of cobalt(II) permeation by the liquid surfactant membranes (LSM) process has been studied. The experimental results showed that the emulsion formulated from the internal aqueous phase and the membrane (organic phase) of a certain age has far-reaching consequences on the kinetics of metal extraction and emulsion stability. The investigations have revealed that there exists an optimal age and composition of the membrane in which the highest extraction (synergism) and the lowest emulsion swelling are achieved. Analytical and instrumental examinations of the membrane phase during aging have shown various chemical and physical changes as a result of the surfactant decomposition, reaction products precipitation and self-association, and macroemulsion formation. ∗Present address: Christian Doppler Laboratorium, Institut fur Thermische Verfahrenstechnik und Umwelttechnik, Technische Universitat Graz, Inffeldgasse 25, A-8010 Graz, Austria.

In this second paper, wear experiments are performed on wires of different uncoated and coated materials. A theoretical model for the wear rate of uncoated wires is proposed, and it is investigated to what extent the method can be used for the testing of coatings ( e.g. galvanization layers) on a wire.

The pore-filling method is a known process for measuring the porosity of porous anodic oxide layers on aluminium. This method has been used to study the relationship between the anodizing conditions and the porosity of the porous anodic film. In a series of experiments, the influence of the anodization voltage and temperature on the porosity, of an anodization layer formed in 15 wt.% sulphuric acid was investigated. From these results a mathematical equation was deduced that gives the porosity as a function of the anodization voltage and temperature. In the second part of the study the height of the voltage jump, on which the thickness of the barrier layer at the start of the re-anodization process depends, was investigated as a function of the anodization voltage. A linear relationship was found between the voltage jump and the anodization voltage.

A study of metal extraction from a multi-component system was carried out by applying a liquid surfactant membrane (LSM) process. The system was an industrial effluent which contains a mixture of metallic species such as Na(I), Mn(II), Co(II), Ni(II), Fe(III) and Cr(III). Concurrently, an analogous research programme was conducted on model solutions reproducing nearly the same physical and chemical composition as the industrial feed. The main goal behind this endeavour was to elucidate the effect of impurities and other components co-existing alongside the metallic species in the industrial feed. Di-2-ethylhexyl phosphoric acid (D2EHPA) was used as a carrier with tri-n-butyl phosphate (TBP). The latter's influence on the kinetics of metal extraction occupied a major part of the investigations. It was found that an optimal composition of the extracting mixture exists (5.5 vol.% D2EHPA + 0.5 vol.% TBP) at which a maximum extraction efficiency can be achieved. It has also been revealed that, although the selectivity is relatively poor, it can be improved by varying the concentration of TBP in the membrane phase. The raffinate kinetic profiles of the simulated solutions have been shown to fit those of the industrial effluent adequately.

A study has been carried out to investigate the kinetics of surfactant decomposition during ageing of the membrane (organic phase) of the emulsion used in an liquid surfactant membrane (LSM) process for metals separation. At this stage of research, the process of Span 80 hydrolysis has been exclusively studied in the membrane phase, and thus, the effect of the carrier di-2-ethylhexyl phosphoric acid (D2EHPA) on the rate of hydrolysis. The effect of tri-n-butyl phosphate (TBP) and the membrane composition on the kinetics of Span 80 hydrolysis have been studied as well. It has been found that the bimolecular irreversible second-order kinetic model describes fairly well the experimental data. A numerical best-fit routine of a polynomial form has been exploited to modify the final model, which takes into account the TBP effect on the result rate of the proposed model.

A study on emulsion stability during metals extraction by liquid surfactant membranes (LSM) process has been conducted. The investigations were focused on the emulsion performance during metals permeation from simulated and industrial effluents. To examine the internal aqueous phase leakage which is a symptom of emulsion instability, the internal tracer technique has been applied. The effect of the membrane composition and particularly tri-n-butyl phosphate (TBP) on the stability has been investigated extensively. It has been revealed that, there exists an optimal range of TBP concentrations where a maximum metal extraction and minimum emulsion instability can be achieved. The internal phase leakage model proposed by Boyadzhiev and co-workers has been modified to meet the present system hydrodynamical conditions. The experimental data fit quite well the proposed model.

Recently, chlorinated high density hydrocarbons have been proposed as diluent or as additive to more common solvents for the liquid-liquid extraction of some base metals (1,2,3). In this communication the extraction curves of some transition metals from chloride solutions with a currently used anionexchanger (triisooctylamine) solved in perchloroethylene are presented. The results are compared with those obtained for more commonly used solvents in liquid-liquid extraction: SHELLSOL K (an aliphatic diluent) and SOLVESSO 150 (an aromatic diluent).

The physical and chemical properties of sorbitan monooleate have been described comprehensively. Emulsion stability is affected by the occurrence of various physical and chemical phenomenona, e.g. macroemulsion formation in the membrane phase and sorbitan monooleate hydrolysis. The hydrolysis products have been isolated and identified. The effect of ageing of the membrane phase containing diethylhexyl phosphoric acid (D2EHPA), Span 80 in Shellsol T has been investigated and the influence of tri-n-butyl phosphate on emulsion stability improvement has been highlighted

Dental amalgam waste contains metals such as mercury, silver and tin. Extraction of mercury by distillation was realized in a testing equipment filled with argon at ambient pressure. The influence of temperature and time on the recovery of mercury was investigated. The minimum temperature at which the distillation started was 360°C. For a fast and complete extraction a temperature of at least 500°C was needed.

Recently a graphical method for the determination of the charge transfer resistance, obtained from impedance measurements, was developed. The original method was limited to perfect, semicircular Nyquist plots. Extension to inclined or depressed semicircular arcs is made possible by a few simple mathematical and graphical manipulations.

The copper electrode reaction kinetics have been studied in acid CuSO, solutions. Dissolved oxygen was used to remove the reaction intermediate Cu+ from the electrode. This shifted the equilibrium potentials of the two partial reactions in an opposite direction allowing a somewhat unusual interpretation of impedance measurements. The charge transfer resistance of the Cu2+ → Cu+ reaction was always higher than that of the Cu+ → Cu reaction. In the neighbourhood of the open circuit potential an additional “surface step” in the latter reaction made it rate-controlling. The slow diffusion of cuprous ions was manifested in an inductive impedance component in this region.

Amalgam is universally the most used material for dental appliances. It is the result of mixing mercury with a silver-tin alloy. Dental amalgam contains about 50% mercury, 35% silver and 15% tin. Moreover it can contain smaller quantities of other substances such as copper and zinc. Once the mixture has been made, a part of it is used for the restoration. The rest should be considered as dental amalgam waste. Nevertheless these quantities of hardened or hardening amalgam still remain valuable because of their metal content. The recovery of these precious and semi-precious metals has been the aim of a number of investigations. For the recovery of dental amalgam, the extraction of mercury by distillation is the first step. In most of the cases the extraction of the other metals is realized by application of hydrometallurgical techniques [1]. A few years ago a process was developed in which the amalgam waste was transformed into mercury and a dental amalgam alloy, ready for use [2]. In our laboratory, experiments were carried out on the recovery of dental amalgam waste. Similarly to investigations performed in other scientific studies, the extrac

The a.c. impedance behaviour of porous aluminium oxide films has been investigated. According to the characteristics of the equivalent circuit, the capacitance corresponding to the porous film layer can be obtained for the frequency ω → ∞. As the capacitance is related to the thickness of the layer, it provides a method for the evaluation of the thickness of the porous aluminium oxide film. Measurements were performed in the range from 2 mHz to 100 kHz. Results showed that the capacitance measured does not correspond to that of the porous film. Since the capacitance attained at high frequencies is closely related to the anodization voltage, and since it is independent of the anodization time, it can be ascribed to the thin barrier layer.

The potential of a copper electrode elastically strained in an acid aerated CUSO 4 solution displays a very characteristic, reproducible and reversible transient change. The shape and magnitude of the transients are closely related to the kinetics of the different reaction steps, as shown by impedance measurements, taken under the same conditions. It is shown that the analysis of the response may produce information equivalent to the impedance spectra. Consequently, elastic stressing may be used as a diagnostic tool in the investigation of the reaction kinetics particularly when adsorption is involved.

The process in which aluminium covered with a porous layer is re-anodized to obtain a compact layer is known as the pore-filling method. The purpose of this work was to study the relationship between anodizing conditions and the structure of the porous anodic film on aluminium by application of the pore-filling method. In a first series of experiments the influence of the anodization voltage on the porosity was examined. It was found that the inverse of the porosity is a function of the square root of the anodization voltage. The second part of our investigations consisted in studying the dependence of the thickness of the barrier layer on the anodization voltage. At each stage of the anodization process this barrier layer thickness is a function of the anodization voltage. Moreover, there is some evidence of a variation in the thickness of the barrier layer during an anodization process performed at a constant voltage.

A dimensional change occurs during the setting of a dental amalgam. A measurement circuit, which makes it possible to register these changes, is introduced. To this purpose strain gages were used. The registration instrument is tested by comparing different dental amalgam products.

In recent years alloys with a high copper content were developed to improve the corrosion resistance of dental amalgam by elimination of the γ 2 (Sn-Hg) phase. The purpose of the present investigation was to compare the electrochemical behaviour of high copper amalgams obtained from single composition amalgam alloys (Indiloy; Shofu, Dental Corp., Menlo Park, USA) with those that used the additive mode of copper alloying (Dispersalloy; Johnson & Johnson, East Windsor, USA).

At high frequencies, electrochemical impedance behavior for corroding dental amalgams cannot be interpreted in terms of a simple Randles equivalent circuit. This may often be ascribed to the imperfect cell geometry resulting in a nonuniform current distribution. However, the insertion of a constant phase element (CPE) in the non-faradaic branch of the equivalent circuit offers a new scope for interpretation as the circuit provides an m-parameter corresponding to the degree of distortion. The decrease of m as a function of time was explained by a mathematical model reflecting an increasing number of pores. Moreover, that same model allows a better understanding of the passivating effect of NaHCO3 and of the differences between conventional and Cu-rich dental amalgams.