233 research outputs found
X-Ray synchronotron study of phase transforms in illite clays to extract information on sigillata manufacturing processes.
The technique of sigillata really began in central Italy during the first century B. C. with the
development of red vitrified slips obtained through vitrification of a clay preparation. These
ceramics, usually decorated with raised motifs and standardised shapes, quickly took over as
semi luxury crockery. Given this success, this technique quickly extended to the entire Italian
peninsula and then to the Mediterranean coast. From the very start of our era, great centres of
production were set up in the south of Gaul.
The aspect of sigillata comes from the nature and the texture of its slip. Studies have shown that
sigillata slips of quality were obtained from a non calcareous clay while the local calcareous clay
was used for the bodies. During firing the slips are vitrified and get a specific microstructure
containing hematite and nanometric corundum crystals [1]. An investigation of the clays
surrounding La Graufesenque site started and it seems that only the Trias levels are chemically
compatible with the composition of antique slips. Apart from the in depth study of the
mineralogical nature of these clays realized at a geological Laboratory, we have studied the
structural transformations as a function of temperature of two of these clays, chosen for the
quality of vitrification in the firing temperature range of sigillata [1030-1080°C]. The main
difference between the chemical composition of these two clays is the amount of Mg (2.4 % and
4.5 % in oxide weight).
Time-resolved measurements were made at
Daresbury (station 2.3) up to 1100oC in
oxidizing conditions. An abrupt increase of the
hematite cell was observed around 850°C.
Above 1000°C, the hematite peaks get sharper
which indicate an increase of coherence length
(Fig. 1). A spinel phase with cell parameter
close to MgAl2O3 was detected from this
temperature. As for the hematite, its coherence
length increases with the temperature but also
during the beginning of the cooling. For the
clay sample with the smaller amount of Mg, a
corundum phase with very small coherence
length was detected above 1000°C. Slips were
prepared from the last clay by modern potters and firing at 1050°C in oxidizing atmosphere. A
mineral quantitative analysis performed using the Rietveld method revealed that the amount of
spinel phase is very high while the corundum contributes to a small part of crystal phases. It is
the inverse in the antique slip where the amount of Mg in oxide weight is around 1%. It is clear
that the amount of Mg plays a key role in the corundum/spinel competition and that the present
slips contain too much Mg. Two questions arise: (i) As the Trias levels are quite heterogeneous
is it possible to find clay with less Mg? and (ii) Did the gallo-roman potters eliminated a great part
of Mg during the slip preparation process? We discuss the merits of these two alternative
hypotheses
Corrosion behaviour of single layered ZrNxOy thin films in artificial sweat solutions
Applications of coloured thin films can be found on the production of high-quality
consumer products, such as eyeglass frames, wristwatch casings and wristbands. These components should possess scratch and corrosion resistant surfaces through the desired lifetime. Recently, metal oxynitrides, MeNxOy (Me = early transition metal) were proposed for decorative applications. In these materials, variations on the amount of oxygen allow the film properties to be tailored, originating a wide range of colours. Additionally, these materials should also fulfil the wear and corrosion requirements above referred.
In the present work the corrosion behaviour of single layered zirconium oxynitride, ZrNxOy
films, immersed in artificial sweat solutions, is described. Films were produced by rf reactive magnetron sputtering at a constant substrate temperature of 300 ºC, from a pure Zr target. The main processing variable was the flow rate of reactive. The corrosion resistance was evaluated by potentiodynamic polarisation tests and Electrochemical Impedance Spectroscopy (EIS) at different immersion times, at room temperature.
The corrosion resistance of the films is strongly affected by the O/N ratio. A slight
tendency to improving the corrosion resistance of the films was found with the increasing in the atomic fraction of oxygen. Nevertheless, pitting was found in all samples. However, the amount of pits seems to be strongly dependent not only on the composition of the film, but also on the processing-induced defects distribution.European Union, FCT- Portugal and European community (FEDER)
Tribocorrosion behaviour of zrNxOy thin films for decorative applications
The main aim of this work is the investigation of the tribocorrosion behaviour of single layered zirconium oxynitride, ZrNxOy, thin films in alternative linear regime of sliding and immersed in an artificial sweat solution at room temperature. The films were produced by rf reactive magnetron sputtering, using a pure Zr target at a constant temperature of 300º C. Two different sets of samples were produced. In the first set of films the substrate bias voltage was the main variable, whereas in the second set, the flow rate of reactive gases (oxygen/nitrogen ratio) was varied. The control of the amount of oxygen allowed the film properties to be tailored from those of covalent zirconium nitride to those of the correspondent ionic oxide. During the wear test both the open circuit potential and the corrosion current were monitored. Also, Electrochemical Impedance Spectroscopy (EIS) tests were performed before and after sliding in order to evaluate, in detail, the modification of the protective character of the coating introduced by the joint action of wear and corrosion. The modifications of the coating microstructure and/or chemical composition induced by the variation of the deposition parameters was also evaluated and correlated with the corrosion mechanisms occurring in each system
Corrosion resistance of ZrNxOy thin films obtained by rf reactive magnetron sputtering
The main aim of this work is the investigation of the corrosion resistance of single layered zirconium oxynitride, ZrNxOy, thin films in
artificial sweat solution at ambient emperature. The films were produced by rf reactive magnetron sputtering, using a pure Zr target at a constant temperature of 300 8C. Two different sets of samples were produced. In the first set of films, the substrate bias voltage was the main
variable, whereas in the second set, the flow rate of reactive gases (oxygen/nitrogen ratio) was varied. The control of the amount of oxygen allowed the film properties to be tailored from those of covalent zirconium nitride to those of the correspondent ionic oxide. The corrosion behaviour was evaluated by potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) tests. The analysis of EIS data provided detailed information of the corrosion processes occurring at the surface of the system throughout the immersion time. The modifications of the coating microstructure and/or chemical composition induced by the variation of the deposition parameters were also evaluated and correlated with the corrosion mechanisms occurring in each system
Elastic-strain distribution in metallic film-polymer substrate composites
Synchrotron x-ray radiation was used for in situ strain measurements during uniaxial tests on polymer substrates coated by a metallic gold film 400 nm thick deposited without interlayer or surface treatment. X-ray diffraction allowed capturing both components elastic strains and determining how these were partitioned between the metallic film and the polymeric substrate. For strains below 0.8%, deformation is continuous through the metal-polymer interface while above, the onset of plasticity in the metallic film induces a shift between film and substrate elastic strains
Synchrotron X-ray diffraction experiments with a prototype hybrid pixel detector
International audienceA prototype X-ray pixel area detector (XPAD3.1) has been used for X-ray diffraction experiments with synchrotron radiation. The characteristics of this detector are very attractive in terms of fast readout time, high dynamic range and high signal-to-noise ratio. The prototype XPAD3.1 enabled various diffraction experiments to be performed at different energies, sample-to-detector distances and detector angles with respect to the direct beam, yet it was necessary to perform corrections on the diffraction images according to the type of experiment. This paper is focused on calibration and correction procedures to obtain high-quality scientific results specifically developed in the context of three different experiments, namely mechanical characterization of nanostructured multilayers, elastic-plastic deformation of duplex steel and growth of carbon nanotubes
Effect of thermal treatments on the structure of MoNxOy thin films
Article in PressMoNxOy films were deposited on steel substrates by dc reactive magnetron sputtering. The depositions were carried out from a pure molybdenum target, varying the flow rate of reactive gases. X-ray diffraction
(XRD) results revealed the occurrence of cubic MoNx and hexagonal (d-MoN) phases for the films with high nitrogen flow rates. The increase of oxygen content induces the decrease of the grain size of the molybdenum nitride crystallites. The thermal stability of a set of samples was studied in vacuum, for
an annealing time of 1 h, for temperatures ranging from 500 to 800 C in 100 C steps. The results showed that pure molybdenum nitride films changed their structure from a meta-stable cubic MoN to hexagonal d-MoN and cubic g-Mo2N-type structures with increasing annealing temperatures. The samples with molybdenum nitride films evidenced a good thermal stability, but those with molybdenum
oxynitride coatings showed a tendency to detach with the increase of the annealing temperature.Fundação para a Ciência e a Tecnologia (FCT)
- POCTI/CTM/38086/200
Physical and morphological characterization of reactively magnetron sputtered TiN films
The present paper reports the influence of growth conditions on the properties of TiN thin films deposited by rf reactive magnetron sputtering in the low-pressure range. The effects of rf power at the Ti target and the negative bias voltage at the substrate in the morphology, structure, electrical resistivity and colour of the samples were studied in detail. X-Ray diffraction results showed that the delta-TiN phase (a(0) similar to 0.430 nm) is detected in all the samples. The sample prepared with grounded substrate revealed a lattice parameter close to the bulk value (0.424 nm), which is a consequence of a low stress state, due to the absence of ion bombardment. The sample deposited at 1000 W has a lattice parameter of 0.426 nm, close to that of the stress-free material (a(0) =0.424 nm), probably due to some stress relief. All films have a columnar-type structure, lying in the T and I zone of the Thornton Model. The resistivity of the TiN films is almost constant and close to 60 muOmega cm independently of the preparation conditions, except for the films deposited at 1000 W, p similar to 215 muOmega cm, and for the grounded sample, p similar to 153 muOmega cm. These values are probably due to cracks associated with stress relieves, in the first case, and the lack of ion bombardment that leads to films with lower density and higher number of defects in the second. No significant variations in colour were observed
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