scholarly journals Systematically improved melting point prediction: a detailed physical simulation model is required

2019 ◽  
Vol 55 (80) ◽  
pp. 12044-12047 ◽  
Author(s):  
Marie-Madeleine Walz ◽  
David van der Spoel
Keyword(s):  
Melting Point ◽  
Simulation Model ◽  
Physical Simulation ◽  
Alkali Halides ◽  
Melting Points

Our detailed physical simulation model allows for an unprecedented and systematically improved prediction of melting points of alkali halides.

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.

Studies on the freezing of pure liquids I. Critical supercooling in molten alkali halides

1960 ◽  
Vol 259 (1298) ◽  
pp. 325-340 ◽  
Keyword(s):  
High Temperature ◽  
Critical Temperature ◽  
Melting Point ◽  
Alkali Halide ◽  
Alkali Halides ◽  
Solid Particles ◽  
High Supersaturation ◽  
Chamber Temperature ◽  
Reduced Temperature ◽  
Heater Coil

A high-temperature cloud chamber is described in which a bead of alkali halide is supported on a heater coil mounted in the roof. By passing the current through the coil the temperature of the bead may be momentarily raised by several hundred degrees, producing salt vapour at high supersaturation. Condensation ensues in the presence of the inert supporting gas, and clouds of droplets or solid particles appear depending on the chamber temperature. Light scattered from the clouds under strong illumination is examined with a telescope, and the presence of crystalline particles is detected by their capacity to scintillate, or ‘twinkle’. It is found that twinkling in clouds of alkali halides appears sharply as the temperature is lowered below the melting point, defining a critical temperature of solidification for each salt. Reasons are given for regarding this temperature as the freezing threshold of molten salt droplets, for which supercoolings of about 150 °C are indicated. A reduced temperature, given by the ratio of the freezing threshold to the melting point, has the value of approximately 0.8 for all the alkali halides examined.

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.

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.

A note on the melting-point of paraffins and fatty acids

1938 ◽  
Vol 34 (3) ◽  
pp. 459-464 ◽  
Author(s):  
E. B. Moullin
Keyword(s):  
Fatty Acids ◽  
Melting Point ◽  
Melting Temperature ◽  
Smooth Curve ◽  
Melting Points ◽  
Normal Paraffin ◽  
Simple Interpretation

The purpose of this note is to draw attention to a certain correspondence between the melting-points of normal paraffins and of fatty acids and to indicate a simple interpretation of this phenomenon. If the number of carbon atoms in a normal paraffin is plotted against the corresponding melting temperature, all the points in the diagram lie very close to a smooth curve drawn among them. If a similar diagram is made for the fatty acids, the points corresponding to an even number of carbon atoms lie on a curve of the same character as that found for paraffins. The points for an odd number of carbon atoms lie on a separate but similar curve, exemplifying the well-known alternation property.

scholarly journals An investigation of the dissociation pressures and melting points of the system Copper-cuprous oxide

1912 ◽  
Vol 87 (598) ◽  
pp. 524-534 ◽  
Keyword(s):  
Melting Point ◽  
Solid Solutions ◽  
Cuprous Oxide ◽  
Eutectic Temperature ◽  
Eutectic Point ◽  
Cooling Curve ◽  
Melting Points ◽  
Platinum Crucible ◽  
Dissociation Pressures

E. Heyn determined the melting points of mixtures of copper and cuprous oxide of compositions varying between 100 per cent. Cu and 88·24 per cent. Cu, 11·76 per cent. Cu 2 O. The results of his experiments are shown by the points marked + in fig. 1. These points fall on two curves intersecting at the eutectic point 1065° C., Cu 2 O 3·5 per cent., Cu 96·5 per cent. Heyn found that all his mixtures showed a halt in the cooling curve at this eutectic temperature, so that within the range of his experiments there is no evidence of the existence of solid solutions. C. N. Otin has lately published some experiments on the melting points of the system cuprous oxide-silica. He attempted to determine the melting point of cuprous oxide, but as some oxidation always took place in his experiments, and as he did not analyse the solid obtained (on account of having to remelt it to get it out of the platinum crucible), there is some doubt as to the actual composition of the substance of which he determined the melting point. The highest temperature at which he found a halt in the cooling curve was 1205° C.

PLASMA-ASSISTED VACUUM-COATING PROCESSES

1992 ◽  
Vol 06 (01) ◽  
pp. 1-24 ◽  
Author(s):  
GERHARD KIENEL
Keyword(s):  
Thin Films ◽  
Melting Point ◽  
Substrate Temperature ◽  
Important Variable ◽  
Coating Material ◽  
Melting Points ◽  
Coating Materials ◽  
Substrate Temperatures

For the properties of thin films produced in a vacuum the most important variable is the mobility of the particles in the course of condensation, which is dependent on the melting point of the coating material, the substrate temperature and the energy of the particles as they strike the substrate. Because of the generally higher particle energies in plasma-assisted processes, under comparable coating conditions lower substrate temperatures suffice than in the case of conventional evaporative coating. Especially with coating materials having higher melting points, compact films can be produced only if the particle energies are sufficiently high.

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