Mercury, critical temperature

Chemical Designations - Synonyms. Calochlor Corrosive mercury chloride Corrosive sublimate Mercury bichloride Mercury (II) chloride Mercury perchloride Chemical Formula-. HgClj Observable Characteristics(as shipped)-. Solid Color. White colorless Odor. None. Physical and Chemical Properties - Physical State at 15 X and 1 atm. Solid Molecular Weight-. 271.50 Boiling Point at I atm. 576, 302, 575 Freezing Point 531, 277, 550 Critical Temperature Not pertinent Critical Pressure Not pertinent Specific Gravity 5.4 at 20 °C (solid) Vapor (Gas) Specific Gravity Not pertinent Ratio of Specific Heats of Vapor (Gas) Not pertinent Latent Heat of Vaporization Not pertinent Heat of Combustion Heat of Decomposition Not pertinent. 

The phenomenon of superconductivity was discovered at the beginning of the twentieth century by the Dutch physicist H. Kamerlingh Onnes, during the first attempts to liquefy helium (which at atmospheric pressure boils at 4.2 K). After refining the technique of helium liquefaction, in 1911, Onnes attempted to measure the electrical resistance of metals at these extraordinary low temperatures, and realized that at 4 K the resistance of mercury, as well as that of other metals indicated in Figure 1, became too low to be measured. This change in electrical property became the indication of the new superconductive physical state. The temperature below which materials become superconducting is defined as the critical temperature, Tc. 

Fig. 5.10 The mass dependence of the critical temperature of the superconducting/resistive transition in isotopically enriched samples of mercury (Triangles Reynolds, C. A., et al. Phys. Rev. 78, 487 (1950). Circles Maxwell, E., Phys. Rev. 78, 477 (1950))...

In 1908, Kamerlingh Onnes succeeded in liquefying helium, and this paved the way for many new experiments to be performed on the behaviour of materials at low temperatures. For a long time, it had been known from conductivity experiments that the electrical resistance of a metal decreased with temperature. In 1911, Onnes was measuring the variation of the electrical resistance of mercury with temperature when he was amazed to find that at 4.2 K, the resistance suddenly dropped to zero. He called this effect superconductivity and the temperature at which it occurs is known as the (superconducting) critical temperature, Tc. This effect is illustrated for tin in Figure 10.1. One effect of the zero resistance is that no power loss occurs in an electrical circuit made from a superconductor. Once an electrical current is established, it demonstrates no discernible decay for as long as experimenters have been able to watch ... 

If the same process is followed for a temperature above the critical temperature, for instance, line 45 on Figure 2-3, the removal of mercury will cause pressure to decrease. However, there will not be a sudden change in the density of the substance. The vapor-pressure line will not be crossed. There is no abrupt phase change. 

Silicon tetrafluoride is a colorless, pungent, fuming gas at room temperature. The triple point is at —90.2° and 1318 mm.3 The critical temperature and pressure are —14.5° and 36.66 atm., respectively.5 The sublimation temperature3 at 1 atm. is —95.7°. The gas liquefies under pressure to form a colorless, mobile liquid. Distillation of the liquid can be used for purification.1,5 In the absence of moisture, pure silicon tetrafluoride does not attack glass, mercury, stopcock grease, or rubber. 

De Keen attempted to find the effect of pressure up to and above the critical point, on the specific heat. A steel cylinder enclosing the liquid was surrounded by a jacket of mercury vapour, and the time taken for heating through 50° compared with that when water was in the cylinder. The accuracy of this method is doubtful. He found that the specific heat decreased with increasing pressure near the critical point, and there was a sudden change of specific heat at the critical temperature. With ether ... 

As pointed out by Ettinger et al. (4), the trans N F is the less active isomer which is different from the active isomer by Its (1) vapor pressure (2) boiling point (3) heat of vaporization (4) critical temperature (5) melting point (6) mass spectral cracking pattern (7) NMR spectrum (8) infrared spectrum (9) heat of isomerization (10) reactivity with mercury and glass. 

While Onnes was experimenting on the liquefaction of helium in 1911, he found the resistance of mercury dropped dramatically from 0.08 at 4.2 K to less than 3 x 10 Q at 4 K over a temperature interval of 0.01 K (Figure 7.1). He named this phenomenon superconductivity. This behaviour is the most striking feature of superconducting materials, in which below a critical temperature, the electrical resistance suddenly drops to effectively zero. 

Table 11.7 lists the critical temperatures and critical pressures of a number of common substances. The critical temperature of a substance reflects the strength of its intermolecular forces. Benzene, ethanol, mercury, and water, which have strong intermolecular forces, also have high critical temperatures compared with the other substances listed in the table. 

Colorless gas. Repulsive odor, mp —37.6°. Sublimes at — 38,9°, Critical temperature 83°. d (solid —191°) 4.006 d (liq —10°) 2.499. Not as inert chemically as SeF( and SF, because the covalence maximum of tellurium is higher than 6. Slowly absorbed by water with hydrolysis to telluric acid, H6TeOt more quickly hydrolyzed by aq KOH. Does not attack glass when pure. Corrodes mercury. 

The most commonly used techniques involve measurement of vapour pressure up to the critical temperature. The sample is confined over mercury in a tube sealed at the upper end. The mercury can be pressurized using a dead-weight pressure tester and the pressure on the sample varied at will. The critical pressure can either be obtained by measuring the vapour pressure as a function of temperature up to a kelvin or so below the critical point and extrapolating to the critical temperature, or by measurement of the pressure at which the meniscus... 

Factors Affecting the Accuracy of the Measurement.—Mercury Vapour. Often mercury is used as a pressure transferring medium in apparatus used for determining critical properties. If a sample is confined over mercury at temperatures for which the vapour pressure is appreciable the measured pressure may be considerably different from the pressure which would be measured in the absence of mercury. Relatively little work has been undertaken on the effect of mercury having a catalytic effect on slow reactions which take place in the sample. Secondly, the partial pressure of mercury may differ considerably from the vapour pressure of mercury at the same temperature. The usual procedure for correcting for the mercury-vapour effect is to subtract the vapour pressure of mercury from the experimental measured pressure. Jepson and Rowlinson have questioned this procedure and Kay and co-workers have made measure-... 

Superconductors are materials that have the ability to conduct electricity without resistance below a critical temperature above absolute zero. The phenomenon of superconductivity was first seen in mercury at liquid helium temperatures. Great interest developed in this area in the late 1980s, when Muller and Bednorz discovered that even ceramic-like materials can exhibit superconductivity. C. W. Chu subsequently found yttrium barium copper oxide (YBCO) to be superconducting above liquid nitrogen temperatures. Indeed, various books are devoted to this subject. > In the following subsections we highlight representative force field applications that have aided the understanding of static and dynamic properties of superconductors. 

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