Effect of Dust Grains on the Electrical Properties of Torch Discharge

Measurements of capacitance and active resistance of the high frequency torch discharge burning in the air while it had been polluted by the dust of dielectric and conducting materials were made. Increasing of active resistance of the torch discharge while it had been polluted by the dust of nickel was determined. The coefficient of conversion of electromagnetic energy into thermal energy was calculated. It has been shown that the maximum coefficient of conversion of the electromagnetic energy into thermal energy can be observed when the degree of dust pollution is 6·10{−6}

Solid-state nuclear magnetic resonance spectroscopy of cements

Cement is the ubiquitous material upon which modern civilisation is built, providing long-term strength, impermeability and durability for housing and infrastructure. The fundamental chemical interactions which control the structure and performance of cements have been the subject of intense research for decades, but the complex, crystallographically disordered nature of the key phases which form in hardened cements has raised difficulty in obtaining detailed information about local structure, reaction mechanisms and kinetics. Solid-state nuclear magnetic resonance (SS NMR)spectroscopy can resolve key atomic structural details within these materials and has emerged as a crucial tool in characterising cement structure and properties. This review provides a comprehensive overview of the application of multinuclear SS NMR spectroscopy to understand composition–structure–property relationships in cements. This includes anhydrous and hydrated phases in Portland cement, calcium aluminate cements, calcium sulfoaluminate cements, magnesia-based cements, alkali-activated and geopolymer cements and synthetic model systems. Advanced and multidimensional experiments probe 1 H, 13 C, 17 O, 19 F, 23 Na, 25 Mg, 27 Al, 29 Si, 31 P, 33 S, 35 Cl, 39 K and 43 Ca nuclei, to study atomic structure, phase evolution, nanostructural development, reaction mechanisms and kinetics. Thus, the mechanisms controlling the physical properties of cements can now be resolved and understood at an unprecedented and essential level of detail

Interplay between silicate and hydroxide ions during geopolymerization

International audienceTwo sets of activating solutions with increasing sodium hydroxide contents were prepared either with or without silicates. Their buffer capacities, i.e. their ability to resist changes in pH, were determined and compared using the Hammett acidity function, a measure of acidity appropriate for concentrated solutions. This is the first time the Hammett acidity function of sodium silicate solutions has been measured. The effects of the buffer capacity and of the initial Hammett acidity function on the reactivity of metakaolin-based pastes were assessed using isothermal conduction micro-calorimetry. The reactivity of metakaolin in sodium hydroxide solutions is shown to be directly related to the initial Hammett acidity function, whereas for sodium silicate mixtures, the buffer capacity is a more pertinent parameter. The mechanism deduced for the role of hydroxide ions during geopolymerization also highlights the role of silicate species as a hydroxide reservoir that nurtures the dissolution process

Molecular understanding of tricalcium silicate hydration in absence and in presence of aluminate ions

Resumen del trabajo presentado 2nd Workshop Calcium-Silicate Hydrates Containing Aluminium (C-A-S-H II), celebrado en Empa, Dübendorf (Switzerland) del 23 al 24 de abril de 2018

Starch Reinforcement of Raw Earth Constructions

International audienceThe restoration, the protection, or the creation of earthen buildings require improving the mechanical strength of the material. The first way to do that is to use inorganic additives, but these additives change the structural properties of earth and have a high carbon footprint. In contrast, the other way to consolidate is the use of organic additives such as vegetal derivatives that rearrange the minerals in the earth, with the lowest carbon footprint as they are from waste management. After preliminary tests with ten different organic additives from traditional recipes, we found that wheat starch improves the earth strength up to 50 %. In this study, we related the mechanical strengthening to the physicochemical interactions between clays and starch. We focus on three clays that represent the three main groups of clays: kaolinite, illite and montmorillonite. For this study, we mainly focused on compressive test and rheological tests. We showed that the improvement of the mechanical strength with starch is depending on clay nature and their chemistry. Then, we can recommend formulations based on the earth nature for new sustainable buildings. Furthermore, we can understand why it was an interesting way to use starch as a strengthening agent in traditional recipes and how it could be used to repair and protect buildings made of earthen material

Hydrophobization of Silica Nanoparticles in Water: Nanostructure and Response to Drying Stress

International audienceWe report on the impact of surface hydrophobization on the structure of aqueous silica dispersions and how this structure resists drying stress. Hydrophilic silica particles were hydrophobized directly in water using a range of organosilane precursors, with a precise control of the grafting density. The resulting nanostructure was precisely analyzed by a combination of small-angle X-ray scattering (SAXS) and cryo-microscopy (cryo-TEM). Then, the dispersion was progressively concentrated by drying, and the evolution of the nanostructures as a function of the grafting density was followed by SAXS. At the fundamental level, because the hydrophobic character of the silica surfaces could be varied continuously through a precise control of the grafting density, we were able to observe how the hydrophobic interactions change particles interactions and aggregates structures. Practically, this opened a new route to tailor the final structure, the residual porosity, and the damp-proof properties of the fully dried silica. For example, regardless of the nature of the hydrophobic precursor, a grafting density of 1 grafter per nm2 optimized the interparticle interactions in solution in view to maximize the residual porosity in the dried material (0.9 cm3/g) and reduced the water uptake to less than 4% in weight compared to the typical value of 13% for hydrophilic particles (at T = 25 °C and relative humidity = 80%)

Interplay between silicate and hydroxide ions during geopolymerization

International audienceKeywords: Silicate Hydroxide Hammet Alkali Metakaolin Dissolution Condensation A B S T R A C T Two sets of activating solutions with increasing sodium hydroxide contents were prepared either with or without silicates. Their buffer capacities, i.e. their ability to resist changes in pH, were determined and compared using the Hammett acidity function, a measure of acidity appropriate for concentrated solutions. This is the first time the Hammett acidity function of sodium silicate solutions has been measured. The effects of the buffer capacity and of the initial Hammett acidity function on the reactivity of metakaolin-based pastes were assessed using isothermal conduction micro-calorimetry. The reactivity of metakaolin in sodium hydroxide solutions is shown to be directly related to the initial Hammett acidity function, whereas for sodium silicate mixtures, the buffer capacity is a more pertinent parameter. The mechanism deduced for the role of hydroxide ions during geopo-lymerization also highlights the role of silicate species as a hydroxide reservoir that nurtures the dissolution process

Strengthening mechanisms of clay building materials by starch

International audienceEarth has a renewed interest in eco-friendly building materials. Starch is a promising additive, but its strengthening origin needs understanding to promote better solutions according to soil variability. This multiscale study examined natural clays and starches interactions. Clays and starches were evaluated based on mechanical and rheological properties. Kaolinite was found to be better reinforced by starches. At microscopic scale, starches modified the arrangement of grains and clays, but the role of botanical origin is unclear. At molecular scale, the ratio between amylose and amylopectin led the interactions with kaolinite. These results help to understand how bio-additives affect earth-based building materials