is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. The aim of the study is to apply a plasma nitriding process to the 90CrMoV8 steel commonly employed in wood machining, and to determine its efficiency to improve both mechanical and electrochemical properties of the surface. Treatments were performed at a constant N 2 :H 2 gas mixture and by varying the temperature and process duration. The structural and morphological properties of nitrided layers were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with EDS microanalyses. Surface hardening and hardness profiles were evaluated by micro hardness measurements. To simulate the wood machining conditions, electrochemical tests were carried out with an oak wood electrolyte with the purpose of understanding the effects of the nitriding treatment on the corrosion resistance of the tool in operation. X-ray diffraction analyses revealed the presence of both γ′ (Fe 4 N) and ε (Fe 2-3 N) nitrides with a predominance of the ε phase. Moreover, α-Fe (110), γ′ and ε diffraction peaks were shifted to lower angles suggesting the development of compressive stresses in the post nitrided steel. As a result, it was shown that nitriding allowed a significant hardening of steel with hardness values higher than 1200 HV. The diffusion layers were always composed of an outer compound layer and a hardened bulk layer which thickness was half of the total diffusion layer one. No white layer was observed. Similarly, no traces of chromium nitrides were detected. The temperature seemed to be a parameter more influent than the process duration on the morphological properties of the nitrided layer, while it had no real influence on their crystallinity. Finally, the optimal nitriding conditions to obtain a thick and hard diffusion layer are 500°C for 10 h. On the other hand, to verify the effect of these parameters on the corrosion resistance, potentiodynamic polarization tests were carried out in an original "wood juice" electrolyte. After corrosion, surface was then observed at the SEM scale. Electrochemical study indicated that the untreated steel behaved as a passive material. Although the very noble character of steel was somewhat mitigated and the corrosion propensity increased for nitrided steels, the passive-like nature of the modified surface was preserved. For the same optimized parameters as those deduced from the mechanical characterization (500°C, 10 h), surface presented, in addition to a huge surface hardening, a high corrosion resistance.

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Carbon-carbon composites are a new class of engineering materials that are ceramic in nature but exhibit brittle to pseudoplastic behaviotir. Carbon-carbon is a unique all-carbon composite with carbon fibre embeded in carbon matrix and is known as an inverse composite. Due to their excellent thermo-structural properties, carbon-carbon composites are used in specialised application like re-entry nose-tips, leading edges, rocket nozzles, and aircraft brake discs apart from.several industrial and-biomedical applications. The multidirectional carbon-carbon product technology is versatile and offers design flexibility. This paper describes the multidirectional preform and carbon-carbon process technology and research and development activities within the country .Carbon-carbon product experience at DRDL has also been discussed. Development of carbon-carbon brake discs process technology using the liquid impregnation process is described-Further the test results on material characterisation, thermal, mechanical and tribological properties are presented.

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Group-theoretical methods have been accepted as exact and reliable tools in studying the physical properties of crystals and quasicrystalline materials. By group representation theory, the maximum number of non-vanishing and independent secondorder piezoelectric coefficients required by the seven pentagonal and two icosahedral point groups -that describe the quasicrystal symmetry groups in two and three dimensionsis determined. The schemes of non-vanishing and independent second-order piezoelectric tensor components needed by the nine point groups with five-fold rotations are identified and tabulated employing a compact notation. The results of this group-theoretical study are briefly discussed.

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Three simple and sensitive methods for the assay of Nifurtimox (NIF) which is an active antitrypanocide were developed. These methods are based on the formation of coloured species by treating either its reduction product with 3-methyl-2-benzothiazolinone hydrazone (MBTH) in the presence of ferric chloride (method A) or its hydrolysis product with 2-thiobarbituric acid (TBA) (method B) or by oxidizing it with excess N-bromosuccinamide (NBS) and determining the consumed NBS using p-N-methylaminophenol sulphate (metol)-isonicotinic acid hydrazide (INH) (method C). All variables have been optimized and the reaction mechanisms presented. Regression analysis of Beer's plot showed good correlation in the concentration range of 2.5-10, 2.5-30 and 1.25-7.5 microg/ml for methods A, B and C, respectively. No interference was observed from the additives and the validity of the methods was tested by analysing the tablets. Recoveries were 99.2-100.9%.