Heating and cooling cycles

A metal tumbler would not crack because its elastic limit must be exceeded considerably before it fails. However, repetitions of thermal stress, when some plastic flow occurs on both heating and cooling cycles, can result in either cracking or so much deformation that a part becomes unserviceable. 

Another important factor in the selection of a lead alloy is fatigue strength, which may arise from high-frequency vibration from pumps and stirrers or from differential expansion from heat and cooling cycles. The marked increase of fatigue strength obtained by alloying with copper, silver and tellurium can be seen from Table 3.25. 

If a graphite substrate is used, Reaction (2) produces niobium carbide which may remain incorporated in the metal deposit. Niobium absorbs hydrogen readily and, forthatreason, an inert atmosphere suchas argon is used in the heating and cooling cycles. 

The lithium salt solutions were prepared by adding the chosen salt (LiCl, LiBr, or LiNOj) to the N,N-dimethylacetamide followed by addition of the polysaccharide. Complete dissolution of the polysaccharide required several hours—often with heating and cooling cycles. 

D is heated, melting begins at 7, though is not complete. At 1, a system of composition D contains crystals of pure B in a melt of composition C. If this mixture is cooled, then a solid mixture of B and that represented by point C is obtained and subsequent heating and cooling cycles result in further decomposition of the compound represented by D. 

Energy efficiency. Temperature gradients are steady state and take place in space rather than in time, reducing the need for the expensive heating and cooling cycles common in batch equipment. 

Thermotropic LCs can be further divided into (a) enantiotropic materials, in which the LC phases are formed on both heating and cooling cycles, and (b) mesotropic materials, in which the LCs are stable only on supercooling from the isotropic melt. Mesotropic LCs have been further divided into three groupings as follows ... 

Experiments of this type (Figure 3.2) are usually carried out with the reactant solids in small boat placed in a tube in a horizontal tube furnace. The gas is passed over the reactants for a time to expel all the air from the apparatus, and then flows over the reactants during the heating and cooling cycles, exiting through a bubbler to maintain a positive pressure and prevent the ingress of air by back diffusion. 

Fig. 28. Plot of ln(I/I0) as a function of the temperature for the heating and cooling cycles of both polymers using the fixed elastic window method...

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