Hydration of Cement in the Presence of Biocidal Modifiers Based on Metal Hydrosilicates

This article presents the results of a study of the characteristics of hydration and properties of a composite biocidal cement binder containing hydrosilicates of barium, copper or zinc. It was found that copper hydrosilicates block hydration processes, and when zinc hydrosilicates are used, the rate of hydration is determined by the content of silicic acid. The limiting concentrations of biocidal modifiers have been established: zinc hydrosilicates—no more than 4% and copper hydrosilicates—no more than 0.5%, which are advisable to use for the manufacture of a biocidal composite binder. It is shown that modifying additives slow down the setting time, the amount of tricalcium silicate in cement stones increases, and their strength for some compositions decreases. Active binding of portlandite with the formation of calcium hydrosilicates occurs when the content of zinc hydrosilicates is 2%, which leads to an increase in the strength of the materials.

Fifty years of Rietveld refinement: Methodology and guidelines in superconductors and functional magnetic nanoadsorbents

The Rietveld refinement method has taken high relevance since its creation. Nowadays, it is an useful tool in many fields of industry, materials science, and technology. For these reasons, it becomes a need for scientists and engineers whom pretend to use it for proper analysis of their materials. However, the initiation in the method can be slow, taking into account the accelerated rhythm of the research and economic demands. Thus, this work is an intend to fulfill this hole, providing the basic foundations and methodology of the Rietveld refinement in a brief way, this along with the results of its application in superconducting samples of Yttrium Barium Copper Oxide and magnesium diboride, and functional magnetic nanoadsorbents of maghemite and a multiphasic composite (iron oxide, hydroxyapatite and secondary phases). In the process, an in-detail protocol was designed and provided. It was concluded that the samples were successfully refined and that this work represents a fast introduction to the Rietveld method for which beginners can obtain good results while making correct interpretations ofthe whole refinement process.

Geochemical modeling of the leaching behavior of municipal solid waste bottom ash.

Mineral trace elements (MTE) constitute an environmental restriction on the recycling of municipal solid waste incineration-bottom ash (MSWI-BA). The study of the speciation of MTE and the factors that control their release allows to predict their behavior under different environmental conditions and, consequently, suggest different actions to expand the management of MSWI-BA.A geochemical modeling led to a better understanding of the speciation of MTE. In this study, target elements were barium, copper, lead, nickel and zinc and the factors that control their release were identified.The results show that the leaching of metals as a function of pH mainly depends on the mineralogical phases. On the other hand, the organic matter has an influence in the leaching of MTE (for Ni, Cu and Pb notably); organic matter presents adsorbent or complexation properties. Les éléments traces métalliques (ETM) constituent une restriction environnementale pour le recyclage des mâchefers d'incinération des déchets non dangereux (MIDND). L'étude de la spéciation des ETM et des facteurs qui contrôlent leur mobilité permet de prédire le comportement des MIDND dans différentes conditions environnementales et de suggérer ensuite des actions pour élargir leur gestion. Une modélisation géochimique des MIDND a permis de mieux comprendre la spéciation des ETM. Dans cette étude, les éléments ciblés étaient le baryum, le cuivre, le plomb, le nickel et le zinc et les facteurs qui régissent leur mobilité ont été définis. Les résultats montrent que la lixiviation des métaux en fonction du pH dépend principalement des phases minéralogiques ; la matière organique joue également un rôle en tant qu'adsorbant ou complexant dans la lixiviation de certains éléments (Ni, Cu et Pb, notamment). Mots-clés Mâchefers d'incinération des déchets non dangereux (MIDND), éléments traces métalliques, capacité de neutralisation acide, modélisation géochimique, PhreeqCI.

Bio-dielectric based on superconductors yttrium calcium barium copper oxide (YCaBa2Cu3O7−x ) from eggshell as calcium oxide source via sol-gel process

Eggshell is a rich source of calcium that is a dielectric material used for doping in a superconductor. Yttrium calcium barium copper oxide (Y x Ca1−x Ba2Cu3O7) was prepared using the sol-gel process and fired at 900 °C or 1,000 °C. The stoichiometric ratio of the raw materials Y2O3:BaCl2:CuO:CaO was 1:2:3:1 based on the molar mass. The obtained YCaBCO had an orthorhombic crystal structure composed of distorted oxygen-deficient perovskite. The orthorhombic structure was unsymmetrical, providing a substantial increase in the physical electromagnetic properties of the superconductor. The YBCO-900-reference analyzed using an impedance analyzer in the range from 500 Hz to (1 × 106) Hz and at room temperature (27 °C) had the following values for capacitance, electrical conductivity, and dielectric constant ± standard error: 8,286.70 ± 28.49 pF, (3.60 ± 0.01) × 107 S/m, and 1,874.794 ± 6.446, respectively. The YCaBCO-900-eggshell (Y x Ca1−x Ba2Cu3O7) analyzed at 500 Hz at room temperature (27 °C) had high values for capacitance, electrical conductivity, and dielectric constant, namely, 8,540.10 ± 2.00 pF, (1.32 ± 0.00) × 108 S/m, and 1,988.540 ± 0.500, respectively. Furthermore, the YCaBCO-900-eggshell had electrical properties (capacitance, conductivity, and dielectric constant values) higher than those of YCaBCO-900-commercial grade measured under the same conditions. The YCaBCO-900-com grade had capacitance of 8,225.75 ± 0.73 pF, electrical conductivity of (1.40 ± 0.01) × 108 S/m, and dielectric constant of 1,874.59 ± 0.17, respectively. Therefore, eggshell is an alternative dielectric material useful for doping in yttrium barium copper oxide (YBCO) to form YCaBCO, thus causing an increase in its electrical properties. The obtained superconductor is a candidate that could be applied in many industries.

Synthesis and Effect of Al2O3 Added in Yttrium Barium Copper Oxide YBa2Cu3O? by Solid State Reaction Method

The aim of this research was synthesize YBa2Cu3O? (YBCO) and to study the effect of Al2O3 additions at x= 0.00, 0.10, 0.20, 0.50, 1.50 and 3.50 wt.%. The samples were investigated through Thermogravimetric Analyzer (TGA) and X-Ray Diffraction (XRD). All samples prepared by solid state reaction method with calcination process at 900°C and sintering process at 950°C. The TGA analysis indicated weight loss was complete at 910°C. XRD patterns showed the orthorhombic structure with lattice parameters a=3.821 Å, b= 3.880 Å and c= 11.663 Å, respectively. The Al2O3 added samples did not show any new peak however the sharpness and broadening peaks was changed. The crystallite sizes of the samples were calculated from the width of the selected peak and half maximum. The size is slowly increased by increasing the Al2O3 addition. These result indicated that addition does not affect on the structure but the crystallite sizes increase affect the morphology images

Optimized Omnidirectional High-Reflectance Using Octonacci Photonic Crystal for Thermographic Sensing Applications

The transmittance of waves through one-dimensional periodic and Octonacci photonic structures was studied using the theoretical transfer matrix method for both wave-polarization-modes. The first structures were made up of the SiO2 and TiO2 materials. The objective here was to obtain a broad omnidirectional high reflector covering the infrared spectrum of a thermographic camera [1–14µm] and, especially, to prevent the transmission of emitted human body peak radiation λmax = 9.341 µm. By comparing the periodic and Octonacci structures, we found that the last structure presented a main and wide photonic band gap near this human radiation. For that, we kept only the Octonacci structure for the rest of the study. The first structure did not give the aspired objective; thus, we replaced the TiO2 layers with yttrium barium copper oxide material, and a significant enhancement of the omnidirectional photonic band gap was found for both TE and TM polarization modes. It was shown that the width of this band was sensitive to the Octonacci iteration number and the optical thickness (by changing the reference wavelength), but it was not affected by the ambient temperature. The number of layers and the thickness of the structure was optimized while improving the omnidirectional high reflector properties.