Thermal expansion of the metals

An even number of tube passes is desireable because then input and output of the tube-side fluid occur on the same end of the exchanger. This allows the other end of the exchanger to "float" in response to thermal expansion of the metal, which can otherwise be a serious problem when the shell changes temperature during startup or shutdown. 

Spectral data showed a partial resolution of interband and plasmon absorption with increasing of reaction temperature. This phenomenon was caused by the thermal expansion of the metal phase which red-shifted the plasmon absorption band. 

An epitaxial effect based on similar lattice parameters (McMillan 1979) presented a theoretical explanation for the favorable nucleating action of metals. Furthermore, mechanical strain was present at the substrate-glass interface, producing a high interfacial energy, as the coefficients of thermal expansion of the metal and the new nucleus were substantially different. As a result, catalyzation of nucleation could also be expected. 

Thermal Properties. Refractories, like most other soHds, expand upon heating, but much less than most metals. The degree of expansion depends on the chemical composition. A diagram of the thermal expansion of the most common refractories is shown in Figure 1. 

Where a chrect fusion of glass-to-metal or metal oxide is obtained (sometimes termed the wetting of metal by glass) two types of seal can result—one matched, the other mismatched, depending on how the relative coefficients of thermal expansion of the glass and the metal compare. 

A typical measurement was performed as follows. The feeder was lowered into the crucible and the sample solution (seawater) was allowed to flow under an inert atmosphere with the suction on. A constant current was applied for a predetermined time. When the pre-electrolysis was over, the flow was changed from the sample to the ammonium acetate washing solution, while the deposited metals were maintained under cathodic protection. Ammonium acetate was selected for its low decomposition temperature, and a 0.2 ml 1 1 concentration was used to ensure sufficient conductivity. At this point the feeder tip was raised to the highest position and the usual steps for an electrothermal atomic absorption spectrometry measurement were followed drying for 30 s at 900 C, ashing for 30 s at 700 °C, and atomization for 8 s at 1700 °C, with measurement at 283.3 nm. The baseline increases smoothly with time as a consequence of an upward lift of the crucible caused by thermal expansion of the material. 

Table IV.—Coeff. of Thermal Expansion of the Alkali Metals.

Thermal variations. A solid propellant grain may be exposed to temperature extremes ranging from conditions of low temperature in the upper atmosphere, to tropical heat. The grain must not be too brittle at low temperature nor too soft at high temperature. The problem can be aggravated by case-bonding since different coefficients of expansion of the metal-case and the propellant can produce a very harmful effect. 

This factor may be calculated for room temperature and atmospheric pressure from tabulated sums of ionic radii obtained from X-ray data (Shannon and Prewitt, 1969, 1970). However, it must be recognized that the thermal expansions and the compressibilities of the (A-O) and (M-O) bonds are different, which makes t both pressure and temperature dependent. In the case of a transition-metal atom M, the thermal expansion of the (A-O) bond is the larger, which makes... 

The principle that is the basis for bicomponent fibers usually is likened to that which underlies the bicomponent metal strips often used in temperature controllers. With the latter, differential-thermal expansion of the two joined components results in a bending of the thermal element. With fibers, moisture usually is the agent that acts upon the two side-by-side portions. Differential swelling or shrinkage causes the fiber to be brought into... 

Such excellent or at least adequate capillary behaviour is also typical of the process variant known as eutectic bonding in which the transient creation of a liquid phase is caused by the interdiffusion of two chemically different metal alloy component materials. In the laboratory variant process known as partial transient liquid phase bonding, (Shalz et al. 1992), a coated interlayer is used for ceramic-ceramic or ceramic-metal joints. In this process the interlayer is a ductile metal or alloy whose surface is coated with a thin layer of a lower melting temperature metal or alloy, for example Ni-20Cr coated with 2 microns of Au. The bonding temperature is chosen so that only the coating melts and the ductility of the interlayer helps to accommodate mismatches in the coefficient of thermal expansion of the component materials. 

Thermal expansion is an important property of transition metal carbides. " They are practically never used in pure form but mostly in composite materials with matrices of other materials (metals). Upon thermal load, the difference in the thermal expansion coefficients of the carbide phase and the matrix may cause degradation of the composite. Generally, the thermal expansion of transition metal carbides is higher than that of the pure metal component. Table 1 gives average thermal expansion coefficients of various carbides. For WC, the thermal expansion has even been measured at various pressures. ... 

These are mostly used to heat round-bottom flasks at temperatures above 100°C. The oil bath, containing the heating fluid, is usually a non-ferrous metal or Pyrex dish and heated on a stirrer hot plate, and the temperature of the bath is measured with a thermometer. The oil bath should never be more than half-full, to allow a margin of safety for thermal expansion of the oil, and stirred with a magnetic flea to ensure even heating. The equipment used in a typical oil bath is shown in Fig. 5.12b. 

The size of the metal rods or hoops in unlined wood tanks is determined partly by calculations related to the hydraulic load imposed by the contents, but may be modified by dictates of past experience. As noted previously, the chemically-resistant masonry lining on the walls and the bottom may impose additional loads on the walls requiring more tie rods or hoops. The tank designer should be aware of the possibility of loads on the structure caused by the irreversible growth characteristics and the thermal expansion of the chemically-resistant masonry. The accidental soaking and consequent swelling of the dry wood shell may also be a factor to allow for. 

Thicker platinum layers are used extensively for temperature sensors, for example, deposited on ceramic substrates. Compared to other thin film metals, such as gold, silver, or nickel, platinum has a low thermal expansion coefficient, thus minimizing stress problems due to the differential thermal expansions of the various membrane layers. 

Improvements have been made in the support arrangement of the ceramic monolith within the metal container. A felt like blanket capable of withstanding high temperatures is now used to a great extent. It is composed of ceramic fiber in a vermiculite base. The material is capable of holding the monolith securely in place despite substantial differences in thermal expansion of the ceramic and the metal can. (FIGURE 7)... 

---