scholarly journals Visualizing the three-step freezing process and three-phase reaction not predicted by the (NH4) 2SO4/H2O phase diagram

2021 ◽  
Author(s):  
Anatoli Bogdan
Keyword(s):  
Phase Diagram ◽  
Differential Scanning Calorimetry ◽  
Freezing Process ◽  
Phase Reaction ◽  
Effective Strategy ◽  
Scanning Calorimetry ◽  
Lamellar Eutectic ◽  
Three Phase ◽  
Concentrated Solution ◽  
Fast Freezing

According to the conventional phase diagrams, aqueous solutions freeze at the liquidus and are frozen/solid below the eutectic solidus. Herein, using differential scanning calorimetry (DSC) and optical cryo-microscopy (OC-M), we demonstrate that hy-poeutectic, eutectic 40 wt% (NH4)2SO4 and hypereutectic (NH4)2SO4/H2O remain liquid well below the eutectic solidus before freezing in three steps: fast-slow-fast. The first fast freezing produces a ramified ice microstructure (IM) and freeze-concentrated solution (FCS) containing up to ~70 wt% (NH4)2SO4. As temperature decreases further, the slow freezing of FCS precedes its fast freezing, which produces a striped IM and (NH4)2SO4 microcrystals. Videos recorded upon warming of frozen (NH4)2SO4/H2O reveal a new three-phase reaction, which is the recrystallization of ice and (NH4)2SO4 microcrystals into the lamellar eutectic ice-(NH4)2SO4 superlattice. This work demonstrates limitations of the (NH4)2SO4/H2O phase diagram and pro-poses an effective strategy for studying other deeply supercooled solutions whose behavior is not predicted by the phase dia-gram.

scholarly journals Measuring Enthalpies of Formation Using Thick Multilayer Foils and Differential Scanning Calorimetry

1995 ◽  
Vol 382 ◽  
Author(s):  
T.P. Weihs ◽  
T.W. Barbee ◽  
M.A. Wall
Keyword(s):  
Differential Scanning Calorimetry ◽  
Diffusion Constant ◽  
Enthalpies Of Formation ◽  
Nominal Composition ◽  
Phase Reaction ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Two Phases ◽  
Sputter Deposited ◽  
Multi Phase

ABSTRACTThe exothermic, solid state reaction of Al and Zr has been studied in thick AL/Zr multilayers using Differential Scanning Calorimetry and X-ray diffraction. The multilayersamples were magnetron sputter deposited into highly textured alternate layers of Al and Zr with nominal composition A13Zr. The samples used in this study were 47μm thick with a 427Å period. When samples were isochronally scanned from 25º to 725ºC, a large exotherm at ˜350ºC was followed by one or two smaller exotherms at ˜650ºC. The first exotherm is dominated by a diffusionbased reaction of Al and Zr that produces two phases in isochronal scans: amorphous AI-Zrand cubic A13Zr, and two additional phases in isothermal anneals: A12Zr and tetragonal AI3Zr. The exothermic heat from this multi-phase reaction is measured using isochronal scans and isothermal anneals, and the heat flow is analyzed using a l-D diffusion based model. An average activation energy and a diffusion constant are determined. In the isothermal scans, the total exothermic heat increases linearly with √ime, and layer thicknesses vary linearly with heat.

Mixtures of d- and l-carvone: I. Differential scanning calorimetry and solid-liquid phase diagram

1996 ◽  
Vol 274 ◽  
pp. 231-242 ◽  
Author(s):  
H.E. Gallis ◽  
F. Bougrioua ◽  
H.A.J. Oonk ◽  
P.J. van Ekeren ◽  
J.C. van Miltenburg
Keyword(s):  
Phase Diagram ◽  
Differential Scanning Calorimetry ◽  
Liquid Phase ◽  
Scanning Calorimetry ◽  
Solid Liquid

Incidence of the melting-degradation process of vitamin C on the determination of the phase diagram with acetaminophen enhanced by high performance liquid chromatography tools

2015 ◽  
Vol 39 (3) ◽  
pp. 1938-1942 ◽  
Author(s):  
Yohann Corvis ◽  
Marie-Claude Menet ◽  
Philippe Espeau
Keyword(s):  
Phase Diagram ◽  
Differential Scanning Calorimetry ◽  
High Performance Liquid Chromatography ◽  
Liquid Chromatography ◽  
High Performance ◽  
Degradation Process ◽  
Liquid Equilibrium ◽  
Scanning Calorimetry ◽  
Solid Liquid

The exact solid–liquid equilibrium between ascorbic acid and acetaminophen was established combining high performance liquid chromatography and differential scanning calorimetry.

scholarly journals Thermodynamic study of binary mixture of citric acid and tartaric acid

2012 ◽  
Vol 10 (5) ◽  
pp. 1584-1589 ◽  
Author(s):  
Viorica Meltzer ◽  
Elena Pincu
Keyword(s):  
Phase Diagram ◽  
Differential Scanning Calorimetry ◽  
Citric Acid ◽  
Binary Mixture ◽  
Tartaric Acid ◽  
Heat Of Mixing ◽  
Scanning Calorimetry ◽  
Entropy Of Fusion ◽  
Excess Thermodynamic Functions ◽  
Solid Liquid

AbstractThe solid — liquid phase equilibria for binary mixture of citric acid with tartaric acid were measured using differential scanning calorimetry. The phase diagram showed the existence a simple eutectic behavior. The thermal properties of this system as heat of mixing, entropy of fusion and excess thermodynamic functions were computed using enthalpy of fusion values. The composition of eutectic was determined using a Tammann diagram.

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