Sabeur Msolli

A nanocrystalline structured NiO/MnO2@nitrogen-doped graphene oxide hybrid nanocomposite for high performance supercapacitors

Nitrogen doped graphene oxide (NGO) has been widely used to investigate active electrode materials for high-performance supercapacitors. NGO has attracted wide attention due to the efficient method of doping with GO, which can increase the electron mobility, leading to desirable electrochemical properties. Therefore, in the present study we focus on the ternary hybrid composite of NiO/MnO2@nitrogen-doped graphene oxide, which was synthesized via a hydrothermal process. The synthesized hybrid nanocomposite was characterized using Raman spectra, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), and field-emission transmission electron microscopy (FE-TEM). The structural and morphological studies of the hybrid nanocomposite shows its nanocrystalline behaviour. The nanocrystalline hybrid composite exhibited a high specific capacitance of 1490 F g−1 at a current density of 0.5 A g−1, energy density of 477 W h kg−1, and power density of 1844 W kg−1, together with good rate capability and cyclic stability. The results show a good specific capacitance retention of ∼98% after 2000 continuous charge–discharge cycles; this indicates that the hybrid nanocomposite can be a promising electroactive material for supercapacitors. The improved performance of the NiO@MnO2/NGO electrode structure means that it offers an effective way to fabricate high performance supercapacitors.

Experimental characterization of the mechanical behavior of two solder alloys for high temperature power electronics applications

An experimental investigation of two potential candidate materials for the diamond die attachment is presented in this framework. These efforts are motivated by the need of developing a power electronic packaging for the diamond chip. The performance of the designed packaging relies particularly on the specific choice of the solder alloys for the die/substrate junction. To implement a high temperature junction, AuGe and AlSi eutectic alloys were chosen as die attachment and characterized experimentally. The choice of the AlSi alloy is motivated by its high melting temperature Tm (577°C), its practical elaboration process and the restrictions of hazardous substances (RoHS) inter alia. The AuGe eutectic solder alloy has a melting temperature (356°C) and it is investigated here for comparison purposes with AlSi. The paper presents experimental results such as SEM observations of failure facies which are obtained from mechanical shear as well as cyclic nano-indentation results for the mechanical hardening/softening evaluation under cyclic loading paths.

Synthesis of a Co3O4@gold/MWCNT/polypyrrole hybrid composite for DMMP detection in chemical sensors

Chemical sensors based on a nanocrystalline Co3O4/gold@MWCNT/polypyrrole decorated hybrid composite were fabricated, and their sensitivity properties to stimulant dimethylmethylphosphonate (DMMP) were characterized. The hybrid composite was decorated by a hydrothermal process in the presence of cobalt/gold precursors, and the characteristics were determined by Raman, XRD, XPS, SEM-EDX, and FE-TEM analysis. The cyclability and linearity of the detection response for chemical sensors in the presence of DMMP vapor were determined by using a crystal microbalance. The hybrid composite material should possess excellent selectivity, stability, and reasonable sensitivity in the presence of N2 gas at room temperature for DMMP detection. The response of the composite showed retainability when exposed to the DMMP component, due to the high resistance response, fast response time, rapid recovery, and good reproducibility.

Effects of the Unified Viscoplastic Formulation and Temperature Terms on the Thermomechanical Behavior of Soldering Materials

Solder materials are critical packaging compounds and due to usually weakest melting temperature among packaging constitutive materials, thus, they are frequently subjected to a multitude of physical phenomena: creep, fatigue and combined hardening effects. The complexity and interaction of such factors must be considered in suitable way in the mechanical behavior modeling using the appropriate material behavior laws. The choice of the mechanical model depends on several factors such as the complexity of constitutive equations to be integrated, the availability and suitability of implementation in the FE codes, the number of parameters to be identified, the capability of the model to represent the most common physical features of the material… Following these observations and in order to deal with these critical remarks, comparisons between the most common unified viscoplastic models should be done in the local and finite element levels for the decision upon the most efficient model. That is the aim of this paper with application to a tin based solder token as the test material.

Rod-Like Structure of Cotton Cellulose/Polyvinyl Alcohol/Tellurium Dioxide (TeO2) Hybrid Nanocomposite and Antimicrobial Properties

ABSTRACT We report on the in situ synthesis through sol-gel processing of a tellurium dioxide (TeO2)–cellulose–polyvinyl alcohol (PVA) hybrid composite. The cellulose–PVA hybrid composite was synthesized through chemical graft in the presence of aqueous sodium hydroxide. Field emission scanning electron microscopy, SEM-EDX, high-resolution transition microscopy (FE-TEM) revealed that polycrystalline nanorods were uniformly distributed with sizes of 20 nm in the cotton cellulose–PVA–TeO2 hybrid nanocomposite. The average size of TeO2 crystallite was calculated to be 0.292 nm, as shown in the FE-TEM, SAED, and X-ray diffraction analysis. Furthermore, the hybrid nanocomposites were studied for their antimicrobial activity against Bacillus cereus and Escherichia coli strains, which was inhibited at a size of 10–12 mm after 24 h of incubation. GRAPHICAL ABSTRACT

Experimental and Mechanical Characterizations of a Lead Free Solder Alloy for Electronic Devices

Electronic power modules devices are paramount components in the aeronautical, automotive and military applications. The solder layers are the most critical parts of the module and are usually subjected in their whole life to complex loading conditions. To improve the design task, realistic thermoelastoviscoplastic and lifetime prediction models which can describe efficiently the deformation-damage of the electrical device must be chosen carefully. Some of the most common behavior models are based on the separation between creep and plasticity deformations such as power law, Garofalo, Darveaux… So, to take into account the creep-plasticity interaction, the thermal cycling as well as the hardening-softening effects, unified viscoplastic models are increasingly being used to describe more efficiently the physical state of the material. We propose in this framework a survey of some unified viscoplastic models used in the electronic applications for the viscoplastic modeling of the solder as well as creep-fatigue life prediction rules. The models are used for the characterization of a SnAgCu solder and are briefly compared within tensile, creep data and stabilized responses.

Efficiency and robustness of some behavior laws in the description of viscoplastic deformation and degradation of solder materials

Solder materials are critical packaging compounds and due to usually weakest melting temperature among packaging constitutive materials, thus, they are frequently subjected to a multitude of physical phenomena: creep, fatigue and combined hardening effects. The complexity and interaction of such factors must be considered in suitable way in the mechanical behaviour modelling using the appropriate material behaviour laws. The choice of the mechanical model depends on several factors such as the complexity of constitutive equations to be integrated, the availability and suitability of implementation in the FE codes, the number of parameters to be identified, the capability of the model to represent the most common physical features of the material... Following these observations and in order to deal with this critical remarks, comparisons between the most common unified viscoplastic models should be done in the local and finite element levels for the decision upon the most efficient model. That is the aim of this paper with application to a tin based solder token as the test material.