Consolidation of cements and geopolymers can be explained by the formation of alkali
silicate or alumino-silicate gels formed in situ during materials setting. To control such a system, a
study concerning the use of sodium silicate gel as binder was initiated to manufacture consolidated
materials with different size distribution of silica. The gels used as precursor of binder were
synthesised by acidifying with hydrochloric acid, a concentrated sodium silicate. Consolidated
materials were obtained by mixing the previous solution before gelation with granular materials
(fine silica powder and sands).
The existence domain of consolidated materials depends on the size distribution of sand.
Consolidation of material is strong when the amount of silica is high. This result suggests a
dissolution / precipitation reaction between gel and silica. Therefore, consolidation could be
explained by the dissolution of small particles of silica and their precipitation into the grain
boundary of sand. Mechanical properties are closed to those of cement materials.
Abstract:In this work, effect of vanadium doping of CaCu 3 Ti 4 O 12 (CCTO) on microstructure and complex dielectric constant over wide frequency (100 Hz-1 MHz) and temperature (0°C -160°C) ranges has been studied. The vanadium doping of CCTO system results in an increase of grain size, the grains being surrounded by melted-like grain boundaries. Real parts of dielectric constant of all samples are similar at low frequency (<1 kHz). In doped samples, above 1 kHz, a relaxation appears which is evidenced by a drop of real part of permittivity and a peak of its imaginary part. This relaxation phenomenon is very significant at relatively low doping rates and then decreases again as vanadium content increases. AC conductivity behavior of vanadium-doped CCTO can be divided in three regions depending on conduction processes. The calculated activation energies were close to 0.46 eV.
Abstract:The role perovskite-type CaCu 3 Ti 4 O 12 (CCTO) dope by molybdenum (Mo) on the microstructure, dielectric properties and the temperature dependence of Electron Spin Resonance (ESR) has been investigated in this work. The solid state reaction has been used to synthesize CCTO ceramic samples. Substitution on Ti-site by Mo helps to increase the grain size of samples and therefore increase the dielectric constant according to the IBLC theory. There is no great difference between the ESR spectra of pure CCTO and CCTO doped by Molybdenum as a function of temperature. For a given temperature, ESR signal spectrum intensity increases as the Mo content increases. The magnetic susceptibility varies according to the composition only when the temperature is higher than 70K. The antiferromagnetic character of the CCTO decreases when the Mo content increases.
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