ICMCTF2016 Session TSP: Symposium TS Poster Session

Gas barrier properties of SiOC (-H) thin films prepared by plasma enhanced CVD (PECVD) at low pressure are suitable for applying to food or beverage packaging. These properties, however, deteriorate when synthesized under atmospheric pressure due to higher content of methyl groups. It is important to reduce methyl termination in order to densify SiOC (-H) thin films. Thus, we focused on the effects of pulse repetition frequency on the gas barrier properties and the structure of SiOC (-H) thin films.

Plasma Electrolytic Oxidation (PEO) encounters an increasing interest due to its potential capability to replace and surpass anodizing. If both processes may look similar, the mechanisms underlying both processes are significantly different. If anodizing is governed by redox reactions and Faraday’s law, PEO coating growth is mainly due to the presence of non-equilibrium micro-plasmas. Mechanisms of both plasma ignition and oxidation are not well understood yet.

For instance, it had been shown since the early development of PEO, that the use of AC current rather than DC anodic (when sample is anode), promotes denser and more homogeneous coatings. Despite the beneficial effect of the cathodic half-period in AC treatments, it had been long time assumed that cathodic discharge are not observable in PEO.

However, cathodic discharges have been observed recently and characterized by mean of optical emission spectroscopy. It has shown a composition and physical properties of the micro-discharges - electron density and temperature respectively in the range of 5.10¹⁵.cm^-3 and 0.7 eV - that are similar to anodic discharges and compatible with breakdown in liquids. However effect on the material is different since they remove locally the coating that has been formed during anodic half-period. It is then of high importance to be able to predict and avoid the formation of such discharges.

On the basis of the work of Lukes et al., we have shown that discharges can be prevented or promoted at a given polarization depending on the oxide surface charge that is. pH dependant. The isoelectric point (IEP), that represents the pH at which surface charge equals zero, is also to be considered. Indeed it appears that working at pH higher (resp. lower) than IEP promotes anodic (resp. cathodic) breakdown and prevents the cathodic (resp. anodic) one. Most of the publications on PEO of aluminium have been done with electrolyte pH far above the IEP of aluminium (9.1) which explains why cathodic discharges had not been observed until recently.

Due to various assets such as easiness of the set-up, atmospheric pressure treatment (in water), the unnecessary pretreatment (both chemical and mechanical) and a high growth rate (up to several µm.min^-1) Plasma Electrolytic Oxidation (PEO) is a promising process. However PEO does not allow growing a broad range of substrate/coating combinasion since the coating results from substrate oxidation (e.g. Al₂O₃ on Al, MgO on Mg …). On the other hand, magnetron sputtering allows depositing wide variety of materials on different substrates but is limited in the ultimate coating thickness.

The present communication deals with the PEO treatment of aluminum substrate previously coated with a zirconium layer deposited by magnetron sputtering.

In-situ optical emission spectroscopy of the PEO micro-discharges (MD) showed the simultaneous presence of a broad continuum and of discrete lines. The continuum is likely due to galvanoluminescence, while discrete emission line come from the MD plasma emission.

Though MDs release an important density of energy that provokes local thermal and mechanical stress on the sample surface, it is worth noting that the zirconium layer still adheres to the aluminum substrate and is subsequently oxidized. The Zr deposited layer was hence successfully oxidized into α- and β-ZrO₂ as confirmed by micro-Raman analyses of cross sections. The main part of the coating consists of a multilayer of α-β-α ZrO₂ and remaining zirconium. The presence of β-ZrO₂ is assumed to be due to the small grain size of the zirconium pre-coating. This suggests that this first step of oxidation occurs by a mechanism of diffusion or by electrochemical reactions assisted by plasma (galvanoluminescence).

However, spheres with a typical diameter equal to 250 µm can be observed on the sample surface. Those spheres are mainly composed of a α-ZrO₂ and Al₂O₃ bilayer without remaining Zr. Crater-like areas, typical from the arcs present in PEO process, appear exclusively on those spheres and are composed of a mix of Al₂O₃, α- and β-ZrO₂. In the latter case, β-ZrO₂ is assumed to be stabilized by the presence of high internal stress due to high heating/cooling rates inherent to plasma discharges.

Oxide growth mechanisms will be discussed on the basis of combined plasma and oxide layer characterizations. It will be shown that stabilization of β-ZrO₂ likely occurs because of high internal stress due to high heating/cooling rates inherent to plasma discharges.

alloy via radio frequency (RF) magnetron sputtering. The phase composition, microstructure, and surface

morphology of the HA coatings were investigated using X-ray diffraction and atomic force microscopy.

The polarization tests in a 3.5 wt.% NaCl solution were performed to examine the corrosion behaviour of

the HA-coated magnesium alloy. Two HA coating thicknesses of 700 nm and 1500 nm were studied. The

coatings homogeneously covered the entire surface of the substrates. In the case of a greater coating

thickness, larger crystallites were formed. The potentiodynamic polarization test demonstrated that a

1500-nm thick nanocrystalline HA coating significantly improved the corrosion resistance of the bare

AZ31 magnesium alloy. We thank Mr. M. Syrtanov for the help with the XRD measurements and T.M. Mukhametkaliyev for the help with the fabrication of the HA thin films. The authors acknowledge the support of the Russian Science Foundation (project number 14-13-00274).

An experimental investigation was carried out to assess the self-healing characteristics of aluminium hybrid composites reinforced primarily with mixed proportion of silica sand and bamboo leaf ash. Charpy impact test samples were machined from the aluminium hybrid composites and a ϕ 1mm pre-cracked hole was created 1mm away from the notch. Two different self-healing treatments were given to the test samples prepared from the composites. Firstly, a 3mm diameter hole was drilled along the sample and a low melting point alloy (60Sn-40Pb) which served as secondary reinforcing material was pierced into the hole and then heat treated at a temperature of 250 ͦC . The second treatment that was adopted involved subjecting the test samples to two-steps under-aged treatment. The process involved ageing at 160 ͦC for 15 minutes and quenched in water. Thereafter, the second ageing treatment was carried out at 50 ͦC for 24h. The samples were then subjected to impact testing. The results show that both self-healing treatments improved the energy absorbed during the tests when compared to the untreated samples. Although, the samples subjected to under-aged treatment had a slightly higher absorbed energy in comparison with the samples containing 60Sn-40Pb, the presence of silica sand and bamboo leaf ash did not have any influence on the absorbed energy. The highest healing efficiency obtained was 61%.

Magnetron Sputtering is a well-established industrial process that produces a broad spectrum of coatings for a wide range of applications (automotive, aerospace, energy, biomedical…). However the production is still much dependent on costly prototyping and trial and error. The results presented in this communication are part of the MOMS4HVM project (Modelling of Magnetron Sputtering for High Value Manufacturing)¹ and the focus is on the plasma and plasma-target interaction.

Magnetron discharges are non-uniform owing to the strong magnetic anisotropy and the partial consumption of the sputtering target; which can decrease the process efficiency. Modelling of target erosion and the discharge is therefore of interest. After an experimental benchmarking of the magnetic simulation of our magnetron it has been possible to link the erosion profile with the magnetic field strength (experiment & simulation). Results with target material of different sputtering yields will be presented (Al, Ti, and Cu)

Various models exists for plasma discharges and sheaths, with different modelling processes (Particle in Cell, Monte-Carlo…) but it is challenging to model magnetron sputtering discharges at reasonable computational cost. Moreover, although the physics of the sheath is relatively well established for conventional plasmas (Child-Langmuir) the presence of the external magnetic field makes both physics and subsequent modelling more complicated in magnetrons. Results obtained by wavelength filtered imaging of magnetron discharges and sheaths, allowing the mapping of the excitation of different elements from target (Al, Cu, Ti) and gas (Ar). Comparison of experimental results with simulation based on different physical assumptions provides insight into the various phenomena (e.g. Bohm diffusion) influencing the plasma/target interaction.

¹ This work is part of a programme sponsored by Innovate UK/EPSRC

This study is focussed on compositional analysis of aluminium-based PVD metallic thin films deposited by magnetron sputtering; compositional consistencies in the coatings were also studied. To affirm coatings reproducibility/repeatability, AlNiTiSiB(N) PVD metallic films were deposited (in an argon/nitrogen plasma) on two types of substrates materials (AISI 304 and silicon wafer) while varying nitrogen flow rates (from 0 to 20 sccm); duration of deposition was also varied (30 mins and 120 mins). Compositional analysis of these films was carried out by glow discharge optical emission spectroscopy (GDOES). The results hereby presented are: a detailed compositional analysis of the thin films deposited on AISI 304 for 120 mins; compositional comparisons amongst the coatings across different substrate materials, as well as over the different durations of deposition used. These results show excellent compositional consistency in the AlNiTiSiB(N) thin films across the substrate materials and deposition duration used.

The development of economical and energy-efficient processes to sustainable production of fuels and chemicals has been increasingly important because of declining of petroleum resources and political and environmental concerns about fossil fuels [1].

Biomasses, especially lignocellulosic biomass are abundant, renewable, and nonedible. Additionally it is the only sustainable source of organic carbon and the biofuels from biomass generate less greenhouse gas emissions than fossil fuels[1]. These characteristics has attracted scientific researchers around the world to develop technologies to convert it into fuels and chemicals without affecting food supplies [2].

Lignocellulosic is much more difficult to convert into ethanol than sugars, starches and oils. Lignocellulose is the fibrous material that forms the cell walls of the plants “architecture”, It consists of three major components: Cellulose, Hemicellulose and Lignin[3]. To obtain more sugar to convert in alcohol is necessary to extract the lignin. In this paper we studied the use of plasma discharge in liquid at atmospheric pressure to extract lignin from sugar cane biomass. The biomass was inserted in the reactor containing 400 mL of a solution of sodium hydroxide and sodium carbonate. The biomass was plasma treated for 2 hours then filtered and the resultant liquid was analyzed by spectrophotometry to calculate the lignin concentration extracted. This process extracted 58,3 % of lignin on the sugar cane bagasse. The biomass was analyzed by X-ray microtomography and Raman before and after plasma treatment.

Acknowledgments: This work was supported by CNPq, CAPES, and FAPESP

References:

[1] G.W. Huber, S. Iborra, A. Corma, Synthesis of Transportation Fuels from Biomass : Chemistry , Catalysts , and Engineering, 2 (2006) 4044–4098.

[2] Z. Li, Y. Ge, Extraction of Lignin from Sugar Cane Bagasse and its Modification into a High Performance Dispersant for Pesticide Formulations, 22 (2011) 1866–1871.

[3] R. Quintero-Ramirez, Hydrolysis of lignocellulosic biomass, Autonomous, Editora Edgard Blücher, 2008. doi:http://dx.doi.org/10.5151/BlucherOA-Sugarcane-SUGARCANEBIOETHANOL_60.