Local order in aqueous solutions of rare gases and the role of the solute concentration: a computer simulation study with a polarizable potential

Aqueous solutions of rare gases are studied by computer simulation employing a polarizable potential for both water and solutes. The use of a polarizable potential allows to study the systems from ambient to supercritical conditions for water. In particular the effects of increasing the concentration and the size of the apolar solutes are considered in an extended range of temperatures. By comparing the results at increasing temperature it appears clearly the change of behaviour from the tendency to demix at ambient conditions to a regime of complete solubility in the supercritical region. In this respect the role of the hydrogen bond network of water is evidenced.Comment: Accepted for publication in Molecular Physics 2004. 19 pages, 10 figure

Widom line and dynamical crossovers as routes to understand supercritical water

Supercritical water is fundamental in many fields of applications and a precise characterization of the supercritical state is of uttermost importance for this liquid. In a fluid, when moving from the critical point into the single-phase region, the thermodynamic response functions show maxima reminiscent of the critical divergence. Here we study the thermodynamic properties of water in the supercritical region by analysing both available experimental data and our computer simulation results. We find that the lines connecting the maxima of the response functions converge on approaching the critical point in a single line, the Widom line. We further show that the Widom line coincides with a crossover from a liquid-like to a gas-like behaviour clearly visible in the transport properties. These thermodynamic and dynamic features show that the supercritical state in water is far more complex than what was so far believed, indicating a new perspective in the characterization of the thermodynamics of this state

Towards Traditional Carbon Fillers: Biochar-Based Reinforced Plastic

The global market of carbon-reinforced plastic represents one of the largest economic platforms. This sector is dominated by carbon black (CB) produced from traditional oil industry. Recently, high technological fillers such as carbon fibres or nanostructured carbon (i.e. carbon nanotubes, graphene, graphene oxide) fillers have tried to exploit their potential but without economic success. So, in this chapter we are going to analyse the use of an unconventional carbon filler called biochar. Biochar is the solid residue of pyrolysis and can be a solid and sustainable replacement for traditional and expensive fillers. In this chapter, we will provide overview of the last advancement in the use of biochar as filler for the production of reinforced plastics

Introducing the Novel Mixed Gaussian-Lorentzian Lineshape in the Analysis of the Raman Signal of Biochar

In this research, an innovative procedure is proposed to elaborate Raman spectra obtained from nanostructured and disordered solids. As a challenging case study, biochar, a bio-derived carbon based material, was selected. The complex structure of biochar (i.e., channeled surface, inorganic content) represents a serious challenge for Raman characterization. As widely reported, the Raman spectra are closely linked to thermal treatments of carbon material. The individual contributions to the Raman spectra are difficult to identify due to the numerous peaks that contribute to the spectra. To tackle this problem, we propose a brand new approach based on the introduction, on sound theoretical grounds, of a mixed Gaussian-–Lorentzian lineshape. As per the experimental part, biochar samples were carbonized in an inert atmosphere at various temperatures and their respective spectra were successfully decomposed using the new lineshape. The evolution of the structure with carbonization temperature was investigated by Raman and XRD analysis. The results of the two techniques fairly well agree. Compared to other approaches commonly reported in the literature this method (i) gives a sounder basis to the lineshape used in disordered materials, and (ii) appears to reduce the number of components, leading to an easier understanding of their origin

A Review on the Use of Biochar Derived Carbon Quantum Dots Production for Sensing Applications

Since their discovery, carbon dots have attracted a great deal of interest for their perspective biological applications. Nevertheless, the quenching of carbon dots photoluminescence represents an interesting feature for quantitative analysis in very low concentration of many species. A particular approach for the production of carbon dots is the use of biochar, a carbonized biomass, as a precursor. In this work, we overview the main achievements accomplished by using biochar-derived carbon dots for detecting and quantifying inorganic and organic species. We also provide background knowledge of the main properties, production and purification routes of carbon dots

High-Temperature Annealed Biochar as a Conductive Filler for the Production of Piezoresistive Materials for Energy Conversion Application

In this research work, we develop a prototype that is able to convert mechanical strain into an electrical signal. To reach this scope, we evaluated the electrical properties of a thermally anneale..

Influence of Commercial Biochar Fillers on Brittleness/Ductility of Epoxy Resin Composites

Production of versatile composites is a very attractive field. Carbon containing epoxy resins are one of the most relevant reinforced plastics used for a wide number of applications. In this research, we studied the influence of five different commercial biochar samples for the selective enhancement of brittleness and ductility of an epoxy based composite. We proved the relationship between biochar morphology and composites mechanical properties with the aid of FT-IR and FE-SEM analysis. We were able to improve the neat resin mechanical properties by doubling its Young’s modulus and ultimate tensile strength using a wheat straw derived material, and to increase its elongation by 40%, we used a Miscanthus derived biochar

Evaluation of the environmental benefits of biochar addition into concrete-based composites

Biochar is a carbon by-product obtained from a termochemical conversion of biomass. Currently, biochar is generally treated in biomass landfill, representing an economic and environmental cost. Recent works focus their attention to the use of biochar as an alternative filler to produce more economic and environmental friendly composites. Some studies proved that the introduction of biochar as carbon filler can also increase mechanical [1] or electrical [2] properties. As a consequence, large scale production of composites containing biochar could have important effects both on the economic and environmental point of view. Please click on the file below for full content of the abstract

High Frequency Electromagnetic Shielding by Biochar-Based Composites

We report on the microwave shielding efficiency of non-structural composites, where inclusions of biochar—a cost effective and eco-friendly material—are dispersed in matrices of interest for building construction. We directly measured the complex permittivity of raw materials and composites, in the frequency range 100 MHz–8 GHz. A proper permittivity mixing formula allows obtaining other combinations, to enlarge the case studies. From complex permittivity, finally, we calculated the shielding efficiency, showing that tailoring the content of biochar allows obtaining a desired value of electromagnetic shielding, potentially useful for different applications. This approach represents a quick preliminary evaluation tool to design composites with desired shielding properties starting from physical parameters

Tuning the microwave electromagnetic properties of biochar-based composites by annealing

Abstract We report on the effects of thermal treatment of biochar embedded in epoxy-based composites on their microwave electrical properties, linking such properties to the material structure investigated by Raman, X-ray photoelectron spectroscopy, and X-ray diffraction. Annealing temperatures in the range 900–1500 °C and biochar concentrations in the epoxy matrix in the range from 5 to 25 wt.% were investigated. The microwave analysis, in the range from 250 MHz to 6 GHz, allowed us to determine the complex permittivity of composites and, through a proper deconvolution technique, to determine the contribution of biochar inclusions alone. High values of real permittivity (up to 220) and conductivity (up to 17 S/m) were evaluated for the biochar particles at 5 GHz, after the 1500 °C thermal treatment. A clear correlation between electrical properties and the biochar microstructure emerged from the dataset, with real permittivity and conductivity increasing as carbon inclusions transform from amorphous to nanocrystalline graphite. Conversely, the percentage of aromatic carbon has a weaker influence on the microwave properties. This study opens to the possibility of tailoring the high-frequency properties of biochar and biochar composites through proper thermal treatments