Expansion and contraction of solids

Hazardous situations can develop with changes in volume with temperature. The effect of temperature on gases and liquids is mentioned on pages 45 and 65, respectively. 

The thermal expansion and contraction of solids can also have safety implications. For a given material the amount of its linear expansion, or contraction, in one direction is directly related to temperature and its original size (i.e. length, diameter, circumference). Thus  

unacceptable stresses can arise in rigid construction materials in apparatus, equipment, piping, etc. if subjected to large temperature fluctuations. For example, conventional glass is prone to failure due to thermal shock. 

E 30 days of constant exposure cause no damage. Plastic may even tolerate exposure for years. 

G Little or no damage after 30 days of constant exposure to the reagent. 

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Dilatometer Basically it is a pyrometer equipped with instruments to study density as a function of temperature and/or time. It can measure the thermal expansion or contraction of solids or liquids. They also study polymerization reactions it can measure the contraction in volume of unsaturated compounds. It basically is a technique in which a dimension of a material under negligible load is measured as a function of temperature while it is subjected to a controlled temperature program. 

However, high electrolyte conductivity on its own does not necessarily guarantee low polarization in a solid state cell. Electrode/electrolyte inter-facial resistance must also be taken into account, and in contrast to the more familiar situation with conventional aqueous systems where the solid electrodes are uniformly wetted by the liquid electrolyte, the all-solid configuration of the cell may create non-uniform contact at the interfaces. Differential expansion and contraction of electrodes and electrolyte may lead to poor contact (and consequent high internal resistance due to low effective electrode/electrolyte interfacial area) or even to a complete open circuit during cell operation. The situation is even more serious with secondary cells, as illustrated schematically in Fig. 9.4, where the effects... 

A gas is defined as the state of matter distinguished from solid and liq uid states by very low density and viscosity, relatively great expansion and contraction with changes in pressure and temperature, and the ability to diffuse readily, distributing itself uniformly throughout any container... 

The contraction of solids on heating seems anomalous because it offends the intuitive concept that atoms will need more room to move as the vibrational amplitudes of the atoms increase. However, this argument is incomplete. Figure 11.9 plots schematically the variation of A with V at two temperatures, for both positive and negative thermal expansion. The volumes marked explicitly on the E-axis give the minima of each A vs. V isotherm. These are the equilibrium volumes at temperatures T and T2 respectively (J2 > 7j) and zero pressure. 

Empirical equations of the form T = aF + bD + c, expressing the relation between total solids (T), fat (F), and density (D), have been used for years. Such derivations assume constant values for the density of the fat and of the mixture of solids-not-fat which enter into the calculation of the coefficients (a, b, and c). Since milk fat has a high coefficient of expansion and contracts as it solidifies (note that the solid-liquid equilibrium is established slowly), the temperature of measurement and the previous history of the product must be controlled carefully (see Sharp and Hart 1936). Variations in the composition of... 

Two types of transformations can be very broadly distinguished. The first is the formation of a solid solution, in which solute atoms are inserted into vacancies (lattice sites or interstitial sites) or substitute for a solvent atom on a particular sublattice. Many types of synthetic processes can result in this type of transformation, including ion-exchange reactions, intercalation reactions, alloy solidification processes, and the high-temperature ceramic method. Of these, ion exchange, intercalation, and other so-called soft chemical (chimie douce) reactions produce no stmctural changes except, perhaps, an expansion or contraction of the lattice to accommodate the new species. They are said to be under topotactic, or topochemical, control. 

Fig. 3 An illustration of the zone refocusing mechanism (left) and its application to the separation of a mixture of phenylthio-hydantoin-amino acids (right). The broken line on the left-hand side represents the change in spot size due to the expansion and contraction stages in multiple development and the solid line depicts the expected zone width for a zone migrating the same distance in a single development.

Solid-state phase transitions often involve deformation of the unit cell along with rearrangements of the molecules inside the unit cell. Therefore a simple constant-pressure simulation which allows only isotropic expansion or contraction of the unit cell may not be able to reproduce all of the aspects of a solid-state phase transition. The technique of Parrinello and Rahman [160] introduces a time-dependent metric tensor in the Lagrangian of the system, which allows changes of both volume and shape of the xmit cells. As such, simple solid-state phase transitions can be directly simulated with this technique. However, this method cannot be used for solid phases with very different unit cells.[145] The orientational order-disorder transitions in the solid state in some cases occur with little change in the unit cell parameters or molecular rearrangements. These orientational transitions are suitable for the Parrinello-Rahman technique.[161]... 

Thermal conduction occurs primarily through the solid polymer it is the gas that provides thermal insulation. In closed-cell foams, restriction of convection Insulates further and choice of the gas, particularly fluorocarbons, produces the maximum insulating capacity. On the other hand, the gas in a closed-cell foam aggravates the coefficient of thermal expansion and contraction most seriously when it is used in refrigeration and condenses to a low-volume liquid. If the gas in a closed cell is a flame-retardant fluorocarbon rather than air, it may contribute to overall flame retardance of the polymeric material. 

When substances are heated and cooled, many students believe that the particles do likewise (Griffiths Preston, 1992 Lee et al., 1993). This belief correlates with the view that matter is continuous without space between particles. If a solid object contracts, students who believe that the particles are in contact have no way to explain this change other than to say the particles shrink because there is no free space between particles to diminish. From a students intuitive viewpoint, it is logical to say that particles expand and contract to explain the expansion and contraction seen at the macroscopic level. The scientific view insists that increased and decreased particle motion - kinetic particle jostling that is a function of energy content - accounts for expansion and contraction (Feynman, 1994). For the scientific view to be plausible, the student must see spaces between particles. 

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