Strain point

Fig. 6. Cooling cycle, where is the enamel layer and VA is steel, at (a) the upper no-strain point, where the enamel is molten, with no stress (b) after solidification of the enamel, where the porcelain is in tension (c) the lower no-strain point, where no stress is evident and (d) at room temperature, where...

One type of point defect that cannot be entirely eliminated from a solid compound is the substituted ion or impurity defect. For example, suppose a large crystal contains 1 mole of NaCl that is 99.99 mole percent pure and that the 0.01% impurity is KBr. As a fraction, there is 0.0001 mole of both K+ and Br ions, which is 6.02 X 1019 ions of each type present in the 1 mole of NaCl Although the level of purity of the NaCl is high, there is an enormous number of impurity ions that occupy sites in the lattice. Even if the NaCl were 99.9999 mole percent pure, there would still be 6.02 X 1017 impurity cations and anions in a mole of crystal. In other words, there is a defect, known as a substituted ion or impurity defect, at each point in the crystal where some ion other than Na+ or Cl- resides. Because K+ is larger than Na+ and Br is larger than Cl-, the lattice will experience some strain and distortion at the sites where the larger cations and anions reside. These strain points are frequently reactive sites in a crystal. 

Strain point Highest temperature from which the glass can be rapidly cooled without serious internal stress 1014 5 820 470... 

Figure 15.8 shows the temperature dependence of several glass compositions. Several temperatures are identified by viscosity the working temperature of a glass by 103 Pa s, the softening point by 4 x 106 Pa s, the anneal point by 2.5 x 1012 Pa s, and the strain point by 4 x 1013 Pa s. Glass objects are usually shaped... 

Silver metal usually is employed in the form of wires or foils. In contact with a melt that contains Ag(I), silver metal continuously reciystallizes, so that a wire of small diameter may eventually be converted to a fragile string of loosely joined crystals. The rate of the process depends on temperature, and also appears to proceed more rapidly at a kinked or otherwise strained point in the wire. 

ASTM C598-88, Standard Test Method for Annealing Point and Strain Point of Glass by Beam Bending , Annual Book of ASTM Standards, American Society for Testing and Materials, Philadelphia, PA. 

Strain Point ( 10145 poises) Anything above this temperature may... 

---