Criteria for MC Formation

Equation (25.7) indicates that a metallic MC melts at a temperature of 1/4.185 (0.239) of the bulk T . Observations suggest that a metallic MC could be readily made at a temperature that is 20 6 K lower than its melting point, T, . Therefore, if one wants to make a MC of a certain specimen extendable at the ambient temperature (300 K), one has to work with the material whose T satisfies (300 -I- 20) X 4.185 = 1,343 K or a value close to this point. However, an extendable MC can hardly form at room temperature or above if the bulk T of a specific metal is below 300 x 4.185 = 1,260 K, such as Sn (505.1 K), Pb (600.6 K), and Zn (692.7 K). An extendable Ti-MC (with = 1,941 K) may form at 440 K, slightly lower than its Tm,i — 7) /4.185 = 462 K. Therefore, it is possible to make a specific MC by operating the MC at a carefully controlled range of temperamres. 

Au is favorable for such MC formation at the ambient temperature, whereas the well-known ductile metals of Ag = 1,235 K), A1 T = 933.5 K), and Cu — 1,356 K) are unlikely to form extendable MCs though they could form superplastic NWs at the ambient temperatures. Although the electronic structure may need to be considered in making an MC [10], the operating temperature would be most critical. The high extensibility is apparent in the temperature range that corresponds to the quasi-molten state that is much softer and highly extendable than the bulk. 

The T-BOLS correlation has enabled calibration of the length, strength, extensibility, and thermal stability of the Au-MC bond under the conditions with and without thermal and mechanical stimuli. Major findings are summarized as follows  

The analytical solution shows that the strain limit of a metallic bond in a MC under tension does not apparently vary with the mechanical stress or the strain rate but apparently with temperature in the form exp [AI T A.2—T). This relation governs the tendency for a metallic MC to form or break, and therefore, an MC of other elements could be made by operating it at properly controlled range of temperatures. However, as extrinsic factors, the stress field and the strain rate could be important in the experiments relating to MC elongation. 

Matching the calculated Au—Au distance to aU the insofar measured values indicates that the divergency in measurements originates from thermal and mechanical fluctuations and the extremely high extensibifity near the melting point. 

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