Cryogenic liquids physical properties

Table 8.4 Physical properties of selected cryogenic liquids ...

Particles produced in the gas phase must be trapped in condensed media, such as on solid substrates or in liquids, in order to accumulate, stock, and handle them. The surface of newly formed metallic fine particles is very active and is impossible to keep clean in an ambient condition, including gold. The surface must be stabilized by virtue of appropriate surface stabilizers or passivated with controlled surface chemical reaction or protected by inert materials. Low-temperature technique is also applied to depress surface activity. Many nanoparticles are stabilized in a solid matrix such as an inert gas at cryogenic temperature. At the laboratory scale, there are many reports on physical properties of nanometer-sized metallic particles measured at low temperature. However, we have difficulty in handling particles if they are in a solid matrix or on a solid substrate, especially at cryogenic temperature. On the other hand, a dispersion system in fluids is good for handling, characterization, and advanced treatment of particles if the particles are stabilized. 

Not only do LCP exhibit superior performance under high temperatures, but are of the few plastic materials which perform well under cryogenic temperatures. For most plastics, there is a certain temperature between -50 C and -100°C where the physical properties reach a ductile-brittle transition point. Even under cryogenic temperatures as low as that of liquid nitrogen, the mechanical properties of LCP remain unaffected. 

Mechanical Properties. Table 2 shows the physical properties of Teflon PFA (28,29). At 20-25°C the mechanical properties of PFA, FEP, and PTFE are similar differences between PFA and FEP become significant as the temperature is increased. The latter should not be used above 200°C, whereas PFA can be used up to 260°C. Tests at liquid nitrogen temperature indicate that PFA performs well in cryogenic applications (Table 3). 

There is a great deal of information available on the physical and chemical properties of compressed gases and cryogenic liquids and the precautions to follow for their safe storage, transport, handling, and use. Years of experience with these products have resulted in numerous safety regulations, standards, guidelines, product and equipment specifications, and recommended practices and procedures. 

Because of their different physical and chemical properties, the various cryogenic liquids have their own peculiar requirements, some of which are discussed below. 

Table 5-1. Physical Properties of Cryogenic Liquids (Also see Table 5-3)...

Cyanate ester and phenolic triazine (PT). The cyanate ester resins have shown superior dielectric properties and much lower moisture absorption than any other structural resin for composites. The physical properties of cyanate ester resins are compared to those of a representative BMI resin in Table 2.33. The PT resins also possess superior elevated-temperature properties, along with excellent properties at cryogenic temperatures. They are available in several viscosities, ranging from a viscous liquid to powder, which facilitates their use in applications that use liquid resins such as filament winding and transfer molding. 

Generally, cryogenic propellants are listed at their normal boiling point, whereas the storable propellants are evaluated at 68 (293 K). Detailed information on the physical properties of the liquid propellants can be found in reference 52. To obtain a wide operating range and a large payload capacity, the desired physical properties are ... 

Liquid fluorine (atomic weight 18.9984) is a light yellow liquid having a normal boiling point of 85.24 K. At 53.5 K and 0.1013 MPa, liquid fluorine solidifies as a yellow solid, but upon subcooling to 45.6 K, it transforms to a white solid. Liquid fluorine is one of the most dense cryogenic liquids (density at the normal boiling point is 1506.8 kg/m ). See Appendix B for other physical properties of fluorine. 

In the field of cryogenics, as in many other phases of science and industry, the accurate measurement of temperature is a very critical matter. The measurement of temperature, however, is more difficult to accomplish than the measurement of many of the other physical properties of a substance. Unlike properties such as volume or length, temperature cannot be measured directly. It must be measured in terms of another property. Some of the physical properties that have been utilized include pressure of a gas, equilibrium pressure of a liquid with its vapor, electrical resistance, thermoelectric emf, magnetic susceptibility, volume of a liquid, length of a solid, refractive index, and velocity of sound in a gas. In addition, there are thermometers that respond to a temperature-dependent phenomenon rather than to a physical property. Included in this category are the optical pyrometer and the electrical noise thermometer. 

Vapor Pressure Thermometry. The pressure exerted by a saturated vapor in equilibrium with its liquid is a very definite function of temperature, and can be used to measure the temperature of the liquid. A number of useful fixed points for several cryogenic fluids are given in Table 8.3. With a good pressure-measuring device, the vapor pressure thermometer is an excellent secondary standard since its temperature response depends upon a physical property of a pure compound or element. Many expressions have been... 

PFA lacks the physical strength of PTFE at elevated temperatures but has somewhat better physical and mechanical properties than PEP above SOOT (149°C) and can be used up to SOOT (260°C). Like PTFE, PFA is subject to permeation by certain gases and will absorb selected chemicals. Refer to Table 2.23 for the absorption of certain liquids by PFA. Perfluoralkoxy also performs well at cryogenic temperatures. 

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