Search

In the present study, Mg-Al layered double hydroxide (Mg-Al/LDH) was synthesized on the surface of AZ31 Mg alloy substrate via in-situ hydrothermal treatment. Synthesis parameters were changed to determine their effect on the lateral size of LDH. For this purpose, etching in nitric acid and anodizing in sodium hydroxide solution were performed as surface pretreatments. Moreover, the influence of LDH solution pH (10 and 11) on the lateral size of LDH coating was investigated. Morphology, chemical composition, and crystalline structure were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD). The corrosion resistance of the coatings was investigated by H2 measurements, salt spray, and electrochemical impedance spectroscopy (EIS). Moreover, the epoxy coating was applied on the best anti-corrosive LDH sample for assessing the compatibility and effectiveness of LDH on the corrosion properties of the substrate with the epoxy layer. At pH = 11, the lateral size of LDH was smaller than samples at pH = 10. In addition, small-sized LDH, as well as LDH/epoxy coating, revealed enhanced corrosion protection.

Glass-ceramics containing pyroelectric Sr2TiSi2O8 (STS) crystals are produced from parent glasses of compositions STS + 0.8 SiO2 + (0.2 − x) Na2O + x CaO, with x = 0; 0.05; 0.10; and 0.15. The aim of this work is to investigate the effect of the additions to the stoichiometric STS composition on the crystallization mechanisms and on the piezoelectric properties of the glass-ceramic. The DSC analyses evidence that the glass transition temperatures Tg, the onset temperature of the crystallization peak To and the temperature Tc of the maximum of this peak increase with the CaO/Na2O ratio. On the basis of the DSC data, the crystallization of the parent glass samples was operated by thermal treatment. The observation of the cross-sections of the heat-treated samples highlights that the competition between the surface and volume crystallization mechanisms is influenced by the CaO/Na2O ratio and the temperature. For all the samples, the XRD analyses performed on the surfaces as obtained after the crystallization treatment evidenced a preferential orientation of the STS crystals with the plans (00l) parallel to the surface. The XRD analyses performed after grinding the surface show that only the surface crystallized layers are preferentially oriented. Moreover, changes in preferential orientation to plans (202) or (201) are observed over the depth, depending on the composition and the temperature of the thermal treatment. These changes influence the polarization of the surface crystallized layer and, consequently, its piezoelectric charge coefficient d33. The highest values of d33 were measured on the glass-ceramic samples exhibiting mainly a (202) preferential orientation over their thickness.

In recent years, numerous studies focused on the development of sustainable cement-based binders through the use of supplementary cementitious materials such slag, fly ash, metakaolin, silica fume, pozzolan, etc. The use of wood biomass for power generation is increasingly common which lead to an important amount of waste produced in the combustion process such as fly ash, which must be transported to landfills for deposition, or used as sludge in farming. Depending on their chemical and physical characteristics, wood biomass fly ashes could be reuse in blended cements as supplementary cementitious material. Different sources of biomass fly ashes have been selected to evaluate their potential for use as a cement replacement. Their chemical and mineralogical compositions, as well as their morphology were first evaluated via X-ray and laser diffraction (XRD), inductively coupled plasma (ICP) and scanning electron microscopy (SEM coupled with energy-dispersive X-ray spectroscopy (EDX). Fly ashes showed variable physicochemical characteristics but some present interesting compositions for the intended use. One fly ash present a high content of CaO and minors of SiO2 and Al2O3. The chemical composition does not allow to categorize this fly ash as a pozzolan material but it may have a latent hydraulic behaviour, which could be interesting as cement substitution. This fly ash has been incorporated into a cement paste by progressive replacement of Portland cement (from 0 to 70%). It has been observed that biomass fly ash has a higher water demand compared to Portland cement. This additional water demand was evaluated by the Vicat consistency test and by an evaporometry method. The setting time and kinetic hydration of the biomass fly ash pastes were also assessed with the standardized Vicat test and by isothermal calorimetry.