Melting Point of cis-1,4-Polybutadiene

1965 ◽  
Vol 38 (4) ◽  
pp. 921-923 ◽  
Author(s):  
J. C. Mitchell
Keyword(s):  
Melting Point ◽  
Thermodynamic Data ◽  
Experimental Techniques ◽  
Melting Point Depression ◽  
Melting Points ◽  
Heating Rates ◽  
Orientation Effects ◽  
Flory’S Theory

Abstract Melting point values for cis-1, 4-polybutadiene thus far reported in the literature have not exceeded +1° C. Varying values have been reported, both because of sample variations (differing amounts and distributions of chain imperfections) and because of variations in experimental techniques used to measure the melting point (in particular, varying heating rates). Some workers have extrapolated their data to predict that the melting point of a perfectly regular (100 per cent cis) cis-1, 4- polybutadiene (Tm°) would be close to +1° C. These extrapolations have been used to arrive at heats of fusion for the polymer from Flory's theory for melting point depression due to copolymeric impurities. One such value has been used in another investigation to estimate extents of crystallization from thermodynamic data. We wish to report observation of melting points several degrees higher than the assumed Tm° value of +1° C. Our experiments show that these higher values are not due to orientation effects.

Predictions of Current Attachment at Thermionic Cathode for TIG Arcs

2008 ◽  
Vol 580-582 ◽  
pp. 319-322 ◽  
Author(s):  
Manabu Tanaka ◽  
Kentaro Yamamoto ◽  
Tashiro Shinichi ◽  
John J. Lowke
Keyword(s):  
Melting Point ◽  
Work Function ◽  
Atmospheric Pressure ◽  
The Other ◽  
Numerical Calculations ◽  
Maximum Temperature ◽  
Arc Plasma ◽  
Melting Points ◽  
Thermionic Cathode ◽  
Uniform Current

Study of current attachment at thermionic cathode for TIG arc at atmospheric pressure is attempted from numerical calculations of arc-electrodes unified model. The calculations show that the maximum temperature of arc plasma close to the cathode tip for W-2% ThO2 reaches 19,000 K and it is the highest value in comparison with the other temperatures for W-2% La2O3 and W-2% CeO2, because the current attachment at the cathode tip is constricted by a centralized limitation of liquid area of ThO2 due to its higher melting point. The calculations also show that, in cases of W- 2% La2O3 and W-2% CeO2, the liquid areas of La2O3 and Ce2O3 are widely expanded at the cathode tip due to their lower melting points and then produce uniform current attachments at the cathode. It is concluded that the current attachment at thermionic cathode is strongly dependent on work function, melting point and Richardson constant of emitter materials.

Melting point depression study of polyacrylonitrile

1960 ◽  
Vol 43 (142) ◽  
pp. 467-488 ◽  
Author(s):  
W. R. Krigbaum ◽  
Noboru Tokita
Keyword(s):  
Melting Point ◽  
Melting Point Depression

Standard enthalpy of fusion of N,N′-ethylenebis (2,4-pentanedion-iminoato)nickel(II) complex by DTA-based melting point depression studies

2005 ◽  
Vol 59 (11) ◽  
pp. 1334-1337 ◽  
Author(s):  
S. Arockiasamy ◽  
P. Antony Premkumar ◽  
O.M. Sreedharan ◽  
C. Mallika ◽  
V.S. Raghunathan ◽  
...  
Keyword(s):  
Melting Point ◽  
Standard Enthalpy ◽  
Enthalpy Of Fusion ◽  
Melting Point Depression

Enthalpien von Kupfer- und Silberchalkogeniden / Enthalpies of Copper and Silver Chalcogenides

1978 ◽  
Vol 33 (2) ◽  
pp. 190-196 ◽  
Author(s):  
Roger Blachnik ◽  
Paul-G. Gunia
Keyword(s):  
Thermodynamic Data ◽  
Transition Temperatures ◽  
Melting Points ◽  
Drop Calorimeter ◽  
Silver Chalcogenides ◽  
Increasing Temperature ◽  
High Degree ◽  
Degree Of Order ◽  
Bond Character

The enthalpy contents of Cu2Se, Cu2Te, Ag2Se and Ag2Te at temperatures between 350 K to 50 K above the melting points were measured in an isoperibolic drop-calorimeter. Thermodynamic data of the compounds were derived from these measurements. An analysis of the data leads to the conclusion that a high degree of order is retained in the melts of these compounds, and that the bond character of these melts is partially ionic. An unusual decrease of Cp with increasing temperature immidiately after the transition temperatures could be confirmed.

scholarly journals Predicting Melting Points of Biofriendly Choline-Based Ionic Liquids with Molecular Dynamics

2019 ◽  
Vol 9 (24) ◽  
pp. 5367 ◽  
Author(s):  
Karl Karu ◽  
Fred Elhi ◽  
Kaija Põhako-Esko ◽  
Vladislav Ivaništšev
Keyword(s):  
Crystal Structure ◽  
Molecular Dynamics ◽  
Ionic Liquids ◽  
Melting Point ◽  
Chemical Space ◽  
Mean Square ◽  
Melting Points ◽  
Simulation Based ◽  
Predicted Values ◽  
Dynamics Simulations

In this work, we introduce a simulation-based method for predicting the melting point of ionic liquids without prior knowledge of their crystal structure. We run molecular dynamics simulations of biofriendly, choline cation-based ionic liquids and apply the method to predict their melting point. The root-mean-square error of the predicted values is below 24 K. We advocate that such precision is sufficient for designing ionic liquids with relatively low melting points. The workflow for simulations is available for everyone and can be adopted for any species from the wide chemical space of ionic liquids.

scholarly journals Effects of Local Heating and Premelting in the Terminal Part of the e+ Track

2012 ◽  
Vol 733 ◽  
pp. 15-18 ◽  
Author(s):  
Dmitry Zvezhinskiy ◽  
Sergey V. Stepanov ◽  
Vsevolod Byakov ◽  
Bożena Zgardzińska
Keyword(s):  
Melting Point ◽  
Temperature Dependence ◽  
Local Heating ◽  
Bulk Temperature ◽  
Melting Points ◽  
Terminal Part ◽  
Slowing Down ◽  
Positronium Lifetime ◽  
Molten Region

The terminal part of the e+ track (the positron blob) is formed during ionization slowing down and subsequent ion-electron recombinations produced by a positron. It releases up to 1 keV of energy, which is converted into heat within few picoseconds. If a bulk temperature of a medium is below, but close enough to its melting point, some region of a substance may melt, yielding a peculiar temperature dependence of the lifetime (LT) spectra. We have estimated properties of the molten region with a help of macroscopic heat con- duction equation and suggested a model describing temperature dependence of the ortho- positronium lifetime in frozen methanol, ethanol, butanol and water close to their melting points.

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