Heat capacity and thermophysical properties of n-heptanoic cid from 5 to 350K

1991 ◽  
Vol 69 (11) ◽  
pp. 1796-1803 ◽  
Author(s):  
Abdul Karimeh Labban ◽  
Edgar Francis Westrum, Jr.
Keyword(s):  
Heat Capacity ◽  
Melting Point ◽  
Triple Point ◽  
Measurement Range ◽  
Drop Calorimetry ◽  
Heptanoic Acid ◽  
First Order ◽  
First Order Transition ◽  
Entropy Of Transition ◽  
Acid Melts

The sub-ambient heat capacity of heptanoic acid is characterized by a first order transition at 219.99 K which shows a Cp,m maximum greater than 400R and ΔtrsSm0 of 1.132R. The acid melts at the triple point 265.98 K and shows a Cp,m maximum greater than 8200R and ΔfusSm0 of 6.891R. At 298.15 K the values of ΔT0KK Sm0, ΔT0 KK Hm0, and Φm(T,0) are 38.89R, 6737R K, and 16.29R. Prior measurements by Adriaanse et al. (1964) with a micro calorimeter between 173 and the melting point did not reveal the transition, nor did the method-of-mixtures ("drop") calorimetry of Garner et al. (1924) between 213 K and the melting point although they claim to have confirmed the presence of both distinct crystalline phases. The somewhat greater measurement range of Schaake et al. (1982) — from 104 to 304 K — by adiabatic calorimetry on a characterized sample did reveal the transition albeit at a temperature 4.8 K higher and with 4% less entropy of transition (double the combined estimated standard deviation).Key words: n-heptanoic acid, heat capacity, transitions, triple point.

Glass-Formers and Viscous Liquid Slowdown since David Turnbull: Enduring Puzzles and New Twists

MRS Bulletin ◽  
2008 ◽  
Vol 33 (5) ◽  
pp. 544-555 ◽  
Author(s):  
C.A. Angell
Keyword(s):  
Heat Capacity ◽  
Glass Transition ◽  
Free Volume ◽  
Homogeneous Nucleation ◽  
Liquid Metals ◽  
Order Transition ◽  
Heat Capacity Change ◽  
Pure Liquid ◽  
First Order ◽  
First Order Transition

AbstractTo Turnbull's study of the kinetic problem of nucleation and growth of crystals, we add the further enquiry into what lies behind the slow nucleation kinetics of glass-formers. Our answer to this question leads to the proposal of conditions in which a pure liquid metal, monatomic and elemental, can be vitrified. Using the case of high-pressure liquid germanium, we give electron microscope evidence for the validity of our thinking.On the question of how liquids behave when crystals do not form, Turnbull pioneered the study of glass transitions in metallic alloys, measuring the heat capacity change at the glass transition Tg for the first time, and developing with Cohen the free volume model for the temperature dependence of liquid transport properties approaching Tg. We extend the phenomenological picture to include networks where free volume does not play a role and reveal a pattern of behavior that provides for a classification of glass-formers (from “strong” to “fragile”). Where Turnbull studied supercooled liquid metals and P4 to the homogeneous nucleation limit using small droplets, we studied supercooled water in capillaries and emulsions to the homogeneous nucleation limit near −40°C. We discuss the puzzling divergences observed that are now seen as part of a cooperative transition that leads to very untypical glass-transition behavior at lower temperatures (when crystallization is bypassed by hyperquenching). Finally, we show how our interpretation of water behavior can be seen as a bridge between the behavior of the “strong” (network) liquids of classical glass science (e.g., SiO2) and the “fragile” behavior of typical molecular glass-formers. The link is made using a “Gaussian excitations” model by Matyushov and the author in which the spike in heat capacity for water is pushed by cooperativity (disorder stabilization of excitations) into a first-order transition to the ground state, at a temperature typically below Tg. In exceptional cases like triphenyl phosphite, this liquid-to-glass first-order transition lies above Tg and can be studied in detail.

A Calorimetric Study of Ammonium, Rubidium, and Potassium Hexafluophosphate

1963 ◽  
Vol 18 (2) ◽  
pp. 148-154 ◽  
Author(s):  
L. A. K. Staveley ◽  
N. R. Grey ◽  
M. J. Layzell
Keyword(s):  
Heat Capacity ◽  
Low Temperatures ◽  
Potassium Salt ◽  
Room Temperature ◽  
Entropy Change ◽  
Ammonium Ion ◽  
Calorimetric Study ◽  
First Order ◽  
Rubidium Salt ◽  
First Order Transition

Measurements have been made of the heat capacities of ammonium, rubidium, and potassium hexafluophosphate from ∼ 20°K to ∼ 300°K. The heat capacity curve of the ammonium salt shows two anomalous regions, and an order-disorder change also occurs in the rubidium salt. The potassium salt, however, undergoes a first-order transition with a large entropy change. The heat capacity of the ammonium and rubidium salts in the neighbourhood of room temperature (but not that of the potassium salt) is altered by cooling to low temperatures. In certain ranges of temperature it was unusually difficult with the rubidium salt to obtain reproducible heat capacity values. The results show that the rotation of the ammonium ion is not completely free, but they are consistent with almost free rotation in one degree of freedom and partially restricted rotation in the other two. The possible significance of the entropy changes of the various transitions is briefly discussed.

scholarly journals First-order antiferromagnetic transitions of SrMn2P2 and CaMn2P2 single crystals containing corrugated-honeycomb Mn sublattices

2021 ◽  
Vol 118 (44) ◽  
pp. e2108724118
Author(s):  
N. S. Sangeetha ◽  
Santanu Pakhira ◽  
Qing-Ping Ding ◽  
Lennard Krause ◽  
Hyung-Cheol Lee ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Magnetic Susceptibility ◽  
Single Crystals ◽  
Nearest Neighbor ◽  
Second Order ◽  
Magnetic Structures ◽  
First Order ◽  
Slowing Down ◽  
First Order Transition ◽  
Antiferromagnetic Transitions

SrMn2P2 and CaMn2P2 are insulators that adopt the trigonal CaAl2Si2-type structure containing corrugated Mn honeycomb layers. Magnetic susceptibility χ and heat capacity versus temperature T data reveal a weak first-order antiferromagnetic (AFM) transition at the Néel temperature TN=53(1) K for SrMn2P2 and a strong first-order AFM transition at TN=69.8(3) K for CaMn2P2. Both compounds exhibit isotropic and nearly T-independent χ(T≤TN), suggesting magnetic structures in which nearest-neighbor moments are aligned at ≈120° to each other. The 31P NMR measurements confirm the strong first-order transition in CaMn2P2 but show critical slowing down above TN for SrMn2P2, thus also evidencing second-order character. The 31P NMR measurements indicate that the AFM structure of CaMn2P2 is commensurate with the lattice whereas that of SrMn2P2 is incommensurate. These first-order AFM transitions are unique among the class of (Ca, Sr, Ba)Mn2 (P, As, Sb, Bi)2 compounds that otherwise exhibit second-order AFM transitions. This result challenges our understanding of the circumstances under which first-order AFM transitions occur.

Electrical properties of MEM(TCNQ)2

1980 ◽  
Vol 58 (3) ◽  
pp. 334-342 ◽  
Author(s):  
M. Morrow ◽  
W. N. Hardy ◽  
J. F. Carolan ◽  
A. J. Berlinsky ◽  
Larry Weiler ◽  
...  
Keyword(s):  
Activation Energy ◽  
Heat Capacity ◽  
Dielectric Constant ◽  
Coulomb Interactions ◽  
One Dimensional ◽  
First Order ◽  
Nmr Data ◽  
First Order Transition ◽  
Electrical Data

Detailed studies of the dc and microwave conductivity and dielectric constant of the quasi-one-dimensional conductor, MEM(TCNQ)2 for 4.2 K < T < 360 K are presented. Particular attention is paid to the strong first-order transition at 335 K where the conductivity jumps by about three orders of magnitude on heating and the activation energy for the conductivity disappears. These electrical data are compared to previously published magnetic susceptibility measurements and to recent structural, heat capacity, and nmr data. The role of Coulomb interactions, in determining the temperature dependence of the conductivity, the susceptibility, and the structure, is emphasized.

scholarly journals Influence of the Porosity of Polymer Foams on the Performances of Capacitive Flexible Pressure Sensors

Sensors ◽  
2019 ◽  
Vol 19 (9) ◽  
pp. 1968 ◽  
Author(s):  
Sylvie Bilent ◽  
Thi Hong Nhung Dinh ◽  
Emile Martincic ◽  
Pierre-Yves Joubert
Keyword(s):  
Experimental Data ◽  
Linear Model ◽  
Dielectric Material ◽  
Pressure Sensors ◽  
Volume Ratio ◽  
Measurement Range ◽  
Polymer Foams ◽  
First Order ◽  
Non Linear ◽  
Flexible Pressure Sensors

This paper reports on the study of microporous polydimethylsiloxane (PDMS) foams as a highly deformable dielectric material used in the composition of flexible capacitive pressure sensors dedicated to wearable use. A fabrication process allowing the porosity of the foams to be adjusted was proposed and the fabricated foams were characterized. Then, elementary capacitive pressure sensors (15 × 15 mm2 square shaped electrodes) were elaborated with fabricated foams (5 mm or 10 mm thick) and were electromechanically characterized. Since the sensor responses under load are strongly non-linear, a behavioral non-linear model (first order exponential) was proposed, adjusted to the experimental data, and used to objectively estimate the sensor performances in terms of sensitivity and measurement range. The main conclusions of this study are that the porosity of the PDMS foams can be adjusted through the sugar:PDMS volume ratio and the size of sugar crystals used to fabricate the foams. Additionally, the porosity of the foams significantly modified the sensor performances. Indeed, compared to bulk PDMS sensors of the same size, the sensitivity of porous PDMS sensors could be multiplied by a factor up to 100 (the sensitivity is 0.14 %.kPa−1 for a bulk PDMS sensor and up to 13.7 %.kPa−1 for a porous PDMS sensor of the same dimensions), while the measurement range was reduced from a factor of 2 to 3 (from 594 kPa for a bulk PDMS sensor down to between 255 and 177 kPa for a PDMS foam sensor of the same dimensions, according to the porosity). This study opens the way to the design and fabrication of wearable flexible pressure sensors with adjustable performances through the control of the porosity of the fabricated PDMS foams.

scholarly journals The Effect of Topology on Phase Behavior under Confinement

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1220
Author(s):  
Arnout M. P. Boelens ◽  
Hamdi A. Tchelepi
Keyword(s):  
Phase Behavior ◽  
Density Functional ◽  
Capillary Condensation ◽  
Good Description ◽  
Functional Theory ◽  
Minkowski Functionals ◽  
First Order ◽  
Lennard Jones ◽  
And Topology ◽  
First Order Transition

This work studies how morphology (i.e., the shape of a structure) and topology (i.e., how different structures are connected) influence wall adsorption and capillary condensation under tight confinement. Numerical simulations based on classical density functional theory (cDFT) are run for a wide variety of geometries using both hard-sphere and Lennard-Jones fluids. These cDFT computations are compared to results obtained using the Minkowski functionals. It is found that the Minkowski functionals can provide a good description of the behavior of Lennard-Jones fluids down to small system sizes. In addition, through decomposition of the free energy, the Minkowski functionals provide a good framework to better understand what are the dominant contributions to the phase behavior of a system. Lastly, while studying the phase envelope shift as a function of the Minkowski functionals it is found that topology has a different effect depending on whether the phase transition under consideration is a continuous or a discrete (first-order) transition.

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