Length change – adsorption relations for the water – porous glass system to −40 °C

1970 ◽  
Vol 48 (2) ◽  
pp. 287-297 ◽  
Author(s):  
R. F. Feldman
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Low Temperature ◽  
Saturated Vapor Pressure ◽  
Capillary Condensation ◽  
Saturated Vapor ◽  
Length Change ◽  
Adsorptive Capacity ◽  
Volumetric Expansion ◽  
Adsorption Of Water

Adsorption of water has been studied extensively above 0 °C, but the problem of the phase transition of adsorbates in porous materials is presented at temperatures below 0 °C. Experiments that show how phase transitions modify length change – adsorption relationships are described.Adsorption – length change measurements from −40 to −0.5 and isotherms at −20 and −0.5 °C were obtained. In another group of experiments different forms of isosteres were also obtained; the principle that water should be allowed to enter the sample at the low temperature was usually followed.Isotherms and length change – adsorption characteristics below 0 °C are qualitatively similar to those above 0 °C, but a decrease in adsorptive capacity and length change was observed. These results and those obtained from the isosteres lead to the conclusion that capillary condensation and menisci theories are operative and that a solid meniscus exists. It follows therefore that the saturated vapor pressure of frozen adsorbate is greater than that of bulk ice and that its volumetric expansion on freezing is similar to the bulk phase transition. It is shown how these phenomena can predict migration of water and generation of pressure within the porous body when it is subjected to cooling and warming cycles.

Mössbauer Studies of Fe2+ in Iron Langbeinites and other Crystals with Langbeinite Structure

1998 ◽  
Vol 53 (1-2) ◽  
pp. 27-37 ◽  
Author(s):  
M. Windhaus ◽  
B. D. Mosel ◽  
W. Müller-Warmuth
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Low Temperature ◽  
High Spin State ◽  
Cubic Phases ◽  
Debye Temperatures ◽  
Phase Transition Temperatures ◽  
Abrupt Changes ◽  
Temperature Dependences

Abstract 57 Fe Mössbauer spectra have been measured at various temperatures between 4.2 K and 300 K for iron langbeinites A 2 Fe 2^04)3 with A = K, NH 4 , Rb, T1 and magnesium, manganese and cadmium lang-beinites doped with Fe" + . The spectra revealed several contributions whose isomer shifts and quadru-pole splittings have been obtained by fitting program routines. For the high-temperature cubic phases two crystallographically non-equivalent iron sites have been identified, characteristic of Fe2+ in the high-spin state. Abrupt changes of the quadrupole couplings indicated phase transitions; in some cases, the spectra have also revealed several sites for Fe2+ in low temperature phases. From the temperature dependences, phase transition temperatures, crystal field splittings and Debye temperatures have been derived.

PHASE TRANSITIONS OF WATER AND XENON ADSORBED IN POROUS VYCOR GLASS

1963 ◽  
Vol 41 (12) ◽  
pp. 3095-3107 ◽  
Author(s):  
G. Litvan ◽  
R. McIntosh
Keyword(s):  
Phase Transition ◽  
Capillary Condensation ◽  
Adsorbed Water ◽  
Surface Concentration ◽  
Adsorptive Capacity ◽  
Temperature Cycle ◽  
Length Variation ◽  
Vycor Glass ◽  
Porous Vycor Glass ◽  
Lower Temperature

Measurements of the expansion of porous Vycor glass containing fixed quantities of adsorbed water indicate that in every instance a phase transition starts below −50 °C, with the main change occurring below −160 °C. Two other anomalies of the length variation were observed near −22 °C and −7 °C when the amount of adsorbed water exceeded the value equivalent to two monolayers. The length of the adsorbent after completion of a temperature cycle was different from the initial length. This is thought to be due to damage suffered by the glass and to the fact that the length of the adsorbent is different for adsorption and desorption although the quantity adsorbed may be the same.The phase transition of adsorbed xenon takes place below the normal triple point and is a function of surface concentration as shown by length variations and equilibrium pressures for fixed quantities adsorbed. All transitions are gradual and hysteresis is exhibited by the isosteres. The adsorption isotherms for xenon – Vycor glass show a decreasing adsorptive capacity and a contraction of the hysteresis loop with lower temperature. The inadequacy of the capillary condensation theory of adsorption in relation to these results is discussed.

Surface Tension and Bubbles

2011 ◽  
Vol 354-355 ◽  
pp. 37-40
Author(s):  
Cai Xia Xu ◽  
Hai Rong Tang
Keyword(s):  
Phase Transition ◽  
Surface Tension ◽  
Liquid Phase ◽  
Vapor Pressure ◽  
Saturated Vapor Pressure ◽  
Saturated Vapor ◽  
Surfactant Solution ◽  
Liquid Phase Transition ◽  
Almost All

From a molecular perspective, we described the origin of surface tension. Surface tension is exceptionally good at rounding things out, such as bubbles can produce in surfactant solution , also in liquid or vapor-liquid phase transition. Through the experiment of determination of saturated vapor pressure of pure liquids, maybe we can conclude that almost all the bubbles were generated as result of the breakup of the gas-liquid interface.

scholarly journals Overview of Low-Temperature Heat Capacity Data for Zn2(C8H4O4)2.C6H12N2 and the Salam Hypothesis

Symmetry ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 657
Author(s):  
Svetlana Kozlova ◽  
Maxim Ryzhikov ◽  
Denis Pishchur ◽  
Irina Mirzaeva
Keyword(s):  
Phase Transition ◽  
Heat Capacity ◽  
Phase Transitions ◽  
Low Temperature ◽  
Metal Organic Framework ◽  
Model System ◽  
Temperature Heat ◽  
Metal Organic ◽  
Low Temperature Heat Capacity ◽  
Capacity Data

The review presents the progress in the analysis of low-temperature heat capacity of the metal-organic framework Zn2(C8H4O4)2.C6H12N2 (Zn-DMOF). In Zn-DMOF, left-twisted D3(S) and right-twisted D3(R) DABCO molecules (C6H12N2) can transform into each other by tunneling to form a racemate. Termination of tunneling leads to a phase transition in the subsystem of twisted molecules. It is suggested that Zn-DMOF may be considered a model system to study the mechanisms of phase transitions belonging to the same type as hypothetical Salam phase transitions.

Low-Temperature Specific Heat of LiquidHe3near the Saturated Vapor Pressure and at Higher Pressures

1959 ◽  
Vol 115 (4) ◽  
pp. 836-842 ◽  
Author(s):  
D. F. Brewer ◽  
J. G. Daunt ◽  
A. K. Sreedhar
Keyword(s):  
Low Temperature ◽  
Vapor Pressure ◽  
Specific Heat ◽  
Saturated Vapor Pressure ◽  
Saturated Vapor ◽  
Low Temperature Specific Heat

scholarly journals Selected solid-state behaviour of three di-tert-butyl-substituted N-salicylideneaniline derivatives: temperature-induced phase transitions and chromic behaviour

2021 ◽  
Vol 77 (10) ◽  
pp. 659-667
Author(s):  
Helen E. Mason ◽  
Judith A. K. Howard ◽  
Hazel A. Sparkes
Keyword(s):  
Phase Transition ◽  
Hydrogen Bond ◽  
Phase Transitions ◽  
Solid State ◽  
Low Temperature ◽  
Schiff Bases ◽  
Photochromic Properties ◽  
Keto Form ◽  
Single Crystal Structures ◽  
State Behaviour

The synthesis, single-crystal structures and chromic behaviour of three related Schiff bases, namely, (E)-2,4-di-tert-butyl-6-{[(4-fluorophenyl)imino]methyl}phenol, C21H26FNO, 1, (E)-2,4-di-tert-butyl-6-{[(4-chlorophenyl)imino]methyl}phenol, C21H26ClNO, 2, and (E)-6-{[(4-bromophenyl)imino]methyl}-2,4-di-tert-butylphenol, C21H26BrNO, 3, are reported. Two polymorphs of 1 were obtained, which were found to have different photochromic properties. Schiff bases 2 and 3 were found to be isostructural and underwent a phase transition upon cooling which was attributed to the dynamic disorder in one of the tert-butyl groups resolving at low temperature. All of the structures were found to exist in the enol rather than the keto form based on the C—O(H) and imine C=N bond lengths, and contained an intramolecular O—H...N hydrogen bond alongside weaker intermolecular C—H...O contacts.

scholarly journals The phase transitions of 4-aminopyridine-based indolocarbazoles: twinning, local- and pseudo-symmetry

2019 ◽  
Vol 75 (1) ◽  
pp. 97-106 ◽  
Author(s):  
Thomas Kader ◽  
Berthold Stöger ◽  
Johannes Fröhlich ◽  
Paul Kautny
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Low Temperature ◽  
Group Symmetry ◽  
Temperature Phase ◽  
Space Group ◽  
Local Symmetries ◽  
Group Symmetries ◽  
Low Temperature Phase

The phase transitions and polymorphism of three 4-aminopyridine-based indolocarbazole analogues are analyzed with respect to symmetry relationships and twinning. Seven polymorphs were structurally characterized using single-crystal diffraction. 5NICz (the indolo[3,2,1-jk]carbazole derivative with the C atom in the 5-position replaced by N) crystallizes as a P21/a high-temperature (270 K) polymorph and as a Pca21 low-temperature (150 K) polymorph. Even though their space-group symmetry is not related by a group–subgroup relationship, the local symmetries of both belong to the same order–disorder (OD) groupoid family. Both are polytypes of a maximum degree of order and are twinned by point operations of the other polytype. 2NICz (C atom in the 2-position replaced by N) likewise crystallizes in a high-temperature (Pcca, 280 K) polymorph and a low-temperature (P21/c, 150 K) polymorph. Here, the space-group symmetries are related by a group–subgroup relationship. The low-temperature phase is twinned by the point operations lost on cooling. The crystal structure of bulk 2,5NICz (N-substitution at the 2- and 5-positions) was unrelated to 2NICz and 5NICz and no phase transition was observed. Isolated single crystals of a different polymorph of 2,5NICz, isotypic with 2NICz, were isolated. However, the analogous phase transition in this case takes place at distinctly higher temperatures (> 300 K).

Electron microscopy of the commensurate-incommensurate phase transition with the discommensuration network in 1T-TaS2

1990 ◽  
Vol 48 (4) ◽  
pp. 168-169
Author(s):  
Takashi Ishiguro ◽  
Hiroshi Sato
Keyword(s):  
Electron Microscopy ◽  
Phase Transition ◽  
Transmission Electron Microscopy ◽  
Phase Transitions ◽  
High Resolution ◽  
Low Temperature ◽  
Transmission Electron ◽  
Continuous Rotation ◽  
T Phase ◽  
New Phase

Phase transitions of lT-TaS2 both on cooling from the incommensurate (IC) phase and on heating from the commensurate (C) phase are investigated by high resolution (HR) transmission electron microscopy because phase transitions are strongly hysteretic. The phases which had been identified were Normal(T>543K,no modurated wave, the Cdl2 type of structure, ao=0.336nm co=0.590nm), IC(354K< T< 543K), NC(non-commensurate or nearly commensurate, 185K<T<353K) and C(T<K). On heating from the C phase, the new phase called the T phase (nearly commensurate triclinic ) appears between 200K and 280K, and that has the discommensuration (DC) network. The HR observations at low temperature reveal both the three dimentional structure of the C phase and the DC network structure of the T phase.On cooling from the IC phase, the structure of the NC phase is essentially incommensurate in the basal plane and a continuous rotation of the moduration direction towards the C phase occurs.

Phase transitions of modulated Co-åkermanite, Ca2CoSi2O7

1997 ◽  
Vol 212 (7) ◽  
Author(s):  
M. Riester ◽  
H. Böhm
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Low Temperature ◽  
Primary Objective ◽  
Temperature Phase ◽  
Temperature Step ◽  
X Ray ◽  
Lock In ◽  
Low Temperature Phase ◽  
Modulation Wavelength

AbstractThis paper deals with X-ray single crystal experiments of modulated cobalt åkermanite at temperatures between 30 K and 600 K. The primary objective of these investigations was to study the predicted lock-in phase transition into a commensurate low temperature phase. Upon cooling the phase transition occurs at 160 K, provided that the time for thermodynamic equilibration at each temperature step is guaranteed. The low temperature phase turns out to be incommensurate with a modulation wavelength of 3.086(6) ·

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