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[en] Highlights: • The alkaline cation nature and amount control the shrinkage values at room temperature. • Shaping of geopolymers in complex geometries is possible. • The chemical composition of geopolymer induces three behaviors after heating. • M/Al ratio (M = Na, K) controls fire resistance of geopolymers at high temperature. This paper presents results from experimental studies on the thermal resistance and dilatometry analysis of various geopolymer formulations, which were prepared by mixing alkaline solutions, metakaolin and reinforcements. Nine compositions were tested by dilatometric analysis and thermal resistance at high temperature (800 °C). Structural and microstructural analysis was conducted to verify the geopolymerization, and differential thermogravimetric analysis was performed to evaluate the nature of water, depending on the formulation. Some key parameters were identified as critical parameters that influenced the geopolymer properties, such as the nature (Na or K) and the molar concentration of the alkaline cation ([M] < 16 mol/L), the molar concentration of silicon ([Si] < 39 mol/L) and the alkaline metal to aluminum ratio (M/Al < 0.65). Finally, it was possible to arrange the various formulations in a ternary scheme as functions of the metal, aluminum and silicon concentrations. This scheme may represent a roadmap for controlling the thermal resistance of geopolymer materials.
[en] Water splitting by Sulfur iodine (54) cycle is one of the promising thermochemical processes for hydrogen production due to its high efficiency. The decomposition of H2SO4 to produce SO2 is the reaction with the highest energy demand in the S-I cycle and it shows a large kinetic barrier. Sulfuric acid being highly corrosive and its endothermic decomposition needs elevated temperatures (>850 °C). The total operating pressure in the whole process reach upto 6 MPa. Henceforth, before the scale-up of this process plant there is a need to explore various materials of construction under very harsh acidic environments and phase changing conditions. Corrosion studies on possible material (metals/ alloys/) of construction have been studied in detail and the most corrosion resistant materials were chosen to construct a pilot-scale sulfuric acid decomposition plant section and was fabricated, installed and commissioned at Indian Institute of Technology (IIT), Delhi. (author)
[en] A new method was developed to study and control solidification processes by means of differential dilatometry. A mathematical analysis of this method is made and first results are presented. A relation is established between the variations of the volume of the sample and that of the solid obtained. The gravimetric method used for volume measurement is also mathematically analyzed. These results are applied to two solidification experiments on InSb, in strongly perturbed and controlled cooling regimes. Precisions are given on the limits of this method, and further developments towards phase transformation studies and control are envisaged
[fr]La methode d'etude et de controle de la solidification par dilatometrie differentielle decrite precedemment fait ici l'objet d'une analyse mathematique et d'une exploitation preliminaire. Une relation entre les variations de volume de l'echantillon et le volume de solide forme est etablie. La methode gravimetrique utilisee pour la mesure du volume est egalement analysee mathematiquement. L'application de ces resultats a deux cas de solidification du compose InSb correspondant a des regimes de refroidissement controle et fortement perturbe a permis de preciser quelques limites de la methode et de concevoir un mode d'exploitation simplifie. Les possibilite offertes par ce nouveau procede pour l'etude et le controle de divers types de transformation de phase sont envisagees