Fast in-situ X-ray scattering reveals stress sensitivity of gypsum dehydration kinetics

The dehydration of gypsum to hemihydrate has been studied for decades because it is an important model reaction for understanding fluid-triggered earthquakes, and due to the global use of plaster of Paris in the construction industry. The dehydration kinetics of gypsum strongly depend on temperature and water vapour pressure. Here, we perform fast, time-resolved synchrotron X-ray scattering on natural alabaster samples, finding that a small elastic load accelerates the dehydration reaction significantly. The mechanical acceleration of the reaction consumes about 10,000 times less energy than that due to heating. We propose that this thermodynamically surprising finding is caused by geometry-energy interactions in the microstructure, which facilitate nucleation and growth of the new crystalline phase. Our results open research avenues on the fundamental thermo-mechanics of crystal hydrates and the interaction of stress and chemical reactions in crystalline solids with a wide range of implications, from understanding dehydration-triggered earthquakes to the energy-efficient design of calcination processes.

On the stress sensitivity of the dehydration kinetics of gypsum: insights from fast in-situ synchrotron X-ray scattering

<p>The potential role of differential stress for mineral stability and the kinetics of mineral replacement reactions remains a matter of hot debate. We present a series of unique in-situ laboratory experiments on the dehydration of polycrystalline natural gypsum to hemihydrate, which were designed to test if the application of small differential stresses affects the mineral transformation rate. The dehydration experiments were conducted in a purpose-built loading cell suitable for in-situ monitoring with synchrotron transmission small- and wide-angle X-ray scattering (SAXS/WAXS). The time-resolved SAXS/WAXS data provide measurements of the transformation kinetics and the evolution of nano-pores of the dehydrating samples.</p><p>In our experiments, the kinetic effects of two principal variables were examined: dehydration temperature and axial confinement of the sample discs. In contrast to most previous dehydration experiments conducted in triaxial deformation apparatus, we applied different axial pre-stresses to the radially unconfined sample discs, which were well below the uniaxial compressive strength of the test material. This loading condition corresponds to constant-displacement rather than constant-stress boundary conditions. We find that in natural gypsum alabaster with randomly oriented grains an increase in axial pre-stress leads to a significant acceleration of the dehydration rate. Simple estimates of the energy budget suggest that the acceleration of the dehydration rate due to elastic straining is significantly cheaper energetically than due to heating. We hypothesise that the observed strong effect of differential stress on dehydration kinetics can be explained by geometry-energy interactions in the granular sample microstructure.</p>

Development of powder based ginger drink: analysis of dehydration kinetics and moisture sorption isotherm

The perishable herb ginger (Zingiber officinale) possesses natural aroma and different biologically active components which are beneficial for our health. This can be dried for preservation in pick season for shelf-life increment. This study studied the analysis of the chemical composition, moisture sorption isotherm, dehydration kinetics of ginger for preservation. Air drying was carried out using a cabinet dryer at different temperatures and thickness. According to the sorption isotherm study, monolayer moisture content (MMC) is higher as per Guggenheim-Anderson-DeBoer (GAB) equation compared to the Brunauer-Emmett-Teller (BET) equation. Drying rate increased with the increase in temperature at constant thickness while the adverse result was found with the increase in thickness at a constant temperature. Then, powder-based drinks were prepared by using five different percentages of ginger. The preferences of consumers were measured by statistical analysis of the scores obtained from the response of organoleptic taste panel. The sample containing 1.84% ginger powder was considered the best in overall acceptability