Development and tribological characterisation of nanostructured Zn-Ni and Zn-Co coatings: a comparative study

International audienceZn-Ni and Zn-Co alloy coatings were electrodeposited on mild steel from sulphate-based baths. The morphology, microstructure, microhardness and tribological behaviours of the coatings have been studied and discussed. While the Zn-5wt-% Co layers presented a nanocrystalline simple nodular structure (45 ± 5 nm), the Zn-14wt-% Ni showed a particular structure called cauliflower morphology (30 ± 7 nm). The X-ray diffraction analysis showed that each of the electrodeposits was formed from zinc solid solution with a uniform zinc-cobalt intermetallic phase γ 2 (CoZn 13) for Zn-5wt-% Co alloy. However, a single γ-phase (intermetallic compound Ni 5 Zn 21) was presented for the Zn-14wt-% Ni alloys. The Zn-14wt-% Ni films were found to be harder and rougher than the Zn-5wt-% Co layers. Plastic deformation and oxide layers production were the main wear mechanisms for the investigated coatings. The Zn-14wt-% Ni coatings were found to have the best wear resistance due to their microhardness and particular structure. ARTICLE HISTOR

Autochthonous fungal strains with high ligninolytic activities from Tunisian biotopes

6 p.-2 tab.-3 fig.This work represents the first report on the ability of autochthonous fungi of Tunisia to produce ligninolytic enzymes. Three hundred fifteen fungal strains were isolated from different Tunisian biotopes. These fungal strains were first screened for lignin-modifying enzymes on solid media containing Poly R-478 or ABTS. Of the 315 tested strains, 49 exhibited significant ABTS-oxidation activity, expressed within the first week of incubation and only 18 strains decolourised the Poly R-478. These positive strains were further screened in liquid culture and laccase, and lignin and Mn2+-oxidizing peroxidases activities were assayed. Of the 67 strains grown on liquid medium, 28 produced at least one of these 3 enzymes. The 8 highest producers of ligninolytic activities were identified by molecular techniques and 3 among them produced Lac, MnP and LiP simultaneously. New isolates reported in this work as fungi with significant ligninolytic activities includes Oxyporus, Stereum and Trichoderma. The isolated Trametes trogii CTM 10156 was the best Lac producer. Culture conditions and medium composition were optimised for this strain and resulted in high Lac production of 110 U ml-1 within 15 days of incubation (367 times higher than control medium).This research was supported by EU contract N° ICA3-CT-1999-00010 and “Contrats Programmes SERST, Tunisia.Peer reviewe

Autochthonous fungal strains with high ligninolytic activities from Tunisian biotopes

This work represents the first report on the ability of autochthonous fungi of Tunisia to produce ligninolytic enzymes. Three hundred fifteen fungal strains were isolated from different Tunisian biotopes. These fungal strains were first screened for lignin-modifying enzymes on solid media containing Poly R-478 or ABTS. Of the 315 tested strains, 49 exhibited significant ABTS-oxidation activity, expressed within the first week of incubation and only 18 strains decolourised the Poly R-478. These positive strains were further screened in liquid culture and laccase, and lignin and Mn2+-oxidizing peroxidases activities were assayed. Of the 67 strains grown on liquid medium, 28 produced at least one of these 3 enzymes. The 8 highest producers of ligninolytic activities were identified by molecular techniques and 3 among them produced Lac, MnP and LiP simultaneously. New isolates reported in this work as fungi with significant ligninolytic activities includes Oxyporus, Stereum and Trichoderma. The isolated Trametes trogii CTM 10156 was the best Lac producer. Culture conditions and medium composition were optimised for this strain and resulted in high Lac production of 110 U ml-1 within 15 days of incubation (367 times higher than control medium).African Journal of Biotechnology Vol. 4 (5), pp. 431-436, 200

Health-related Quality of Life Assessment on 100 Tunisian Patients with Ankylosing Spondylitis using the SF-36 Survey

Objectives: The main objective of the study was to examine the self reported health status in patients with ankylosing spondylitis (AS) compared with the general population and the secondary objective (in the AS group) was to study the association between health status, demographic parameters, and specific disease instruments in AS.Methods: A cross sectional study of 100 AS patients recruited between 2006 and 2009 at the Department of Rheumatology. Health status was assessed by using the SF-36 health questionnaire in patients with AS. Demographic characteristics and disease specific instruments were also examined by the questionnaire. A sample of 112 healthy individuals was also surveyed using the SF-36 health questionnaire.Results: This study showed a great impairment in the quality of life of patients with AS involving all scales. All male patients with AS reported significantly impaired health-related quality of life on all items of the SF-36 compared with the general population whereas female patients reported poorer health on three items only, namely physical functioning, general health and bodily pain. Mental health was mostly affected than physical role. The physical role was significantly higher in patients with high education level than in patients with low education level (p=0.01). Physical functioning was better in employed patients. All scales of SF-36 were correlated with BASFI, BASDAI and BAS-G. Only physical functioning and general health were correlated with BASMI.Conclusion: Impairment in the quality of life can be significantwhen suffering from AS, affecting mental health more than physicalhealth. Among disease parameters, functional impairment,disease activity, mobility limitation, and spinal pain were the most associated factors resulting to the deterioration of quality of life

Type and concentration effects of particulate solid lubricants on the microstructure, friction, and wear of electrodeposited Ni composite coatings

International audienceNickel-MoS 2 composite coatings were obtained by electrodeposition from a nickel electrolyte containing suspended MoS 2 particles. The coating composition, morphology, crystalline structure, microhardness, and frictional behavior were studied as a function of MoS 2 concentration. The results obtained in this study revealed that the codeposited lubricant particles strongly influenced the composite nickel coating properties. It was found that increasing codeposited MoS 2 decreases the average grain size of nickel crystallites and leads to the formation of clusters which, in turn, lead to rough coatings with a high and variable thickness. The results of tribological response indicated that the reduction of friction coefficient and the improvement of wear resistance were performed until an optimal value of MoS 2 concentration, which provided the best condition that promoted the tribo-layer stability and maintained the matrix integrity. A comparison of tribological and micromechanical properties between the coating containing the optimal fraction of MoS 2 particles and the coating containing nearly the same fraction of graphite particles has been undertaken. Unlike the case of the addition of graphite particles, the microhardness of composite coating has been enhanced with the incorporation of MoS 2 particles. However, the incorporation of graphite particles in the coating induced more effective lubrication and wear resistance

Structural, Micromechanical and Tribological Characterization of Zn-Ni Coatings: Effect of Sulfate Bath Composition

International audienceZn and Zn-Ni alloy coatings were electrode-posited on mild steel from sulfate-based bath containing Sn as additive. The effect of Ni content on the microstructure, morphology, micro hardness and the tribological behavior of these coatings were studied and discussed. Adding Sn in the sulfate bath had a significant effect on the surface morphology, particularly on the Zn-8 wt% Ni coatings. By increasing the Ni concentration from 8 to 14 wt%, the X-ray patterns showed that the phase structure of Zn-Ni alloy coatings was changed from g-phase Ni 3 Zn 22 to c-phase Ni 5 Zn 21. The plastic deformation and delamination were found to be wear mechanisms for the investigated coatings. While the Zn-14 wt% Ni alloys had the best wear resistance, Zn films had the most severe wear volume loss and the highest friction coefficient

Structural, Micromechanical and Tribological Analyses of Electrodeposited Nickel-Graphite Coatings with Different Fractions of Graphite Microparticles

International audienceNickel-graphite composite coatings were electrodeposited on a steel substrate from typical watts bath and with specific operating conditions for different weight fractions of graphite microparticles. The weight percentage of particles in coatings and the microstructure were studied, respectively, by atomic absorption, scanning electron microscope and X-ray diffraction. The influence of graphite fraction on roughness and microhardness were also investigated. It was found that roughness increases with the increase of particle content while microhardness decreases. The tribological response was examined against high chromium steel ball using linear reciprocating tribometer. The results indicated that the friction coefficient decreases when graphite content increases. This was ascribed to the development of tribo-layer on the wear track and transfer film on the counterface. However, it was found that the improvement of wear resistance was obtained until an optimal value of graphite concentration, which provided the best condition that promoted the tribo-layer stability and maintained the matrix integrity

Structural, Micromechanical and Tribological Characterization of Zn-Ni Coatings: Effect of Sulfate Bath Composition

International audienceZn and Zn-Ni alloy coatings were electrode-posited on mild steel from sulfate-based bath containing Sn as additive. The effect of Ni content on the microstructure, morphology, micro hardness and the tribological behavior of these coatings were studied and discussed. Adding Sn in the sulfate bath had a significant effect on the surface morphology, particularly on the Zn-8 wt% Ni coatings. By increasing the Ni concentration from 8 to 14 wt%, the X-ray patterns showed that the phase structure of Zn-Ni alloy coatings was changed from g-phase Ni 3 Zn 22 to c-phase Ni 5 Zn 21. The plastic deformation and delamination were found to be wear mechanisms for the investigated coatings. While the Zn-14 wt% Ni alloys had the best wear resistance, Zn films had the most severe wear volume loss and the highest friction coefficient