ELECTROCHEMICAL EFFECTS ON ROCK DRILLING.

Drilling tests were conducted on Sioux quartzite with AlCl//3, ZrCl//4, CaCl//2, and NaCl solution concentrations and on Westerly granite with AlCl//3 solution concentrations below, at, and above their respective ZPC concentrations using a 16-mm diamond impregnated coring bit. Results show that surface tension reducers are efficient in chemical crack propagation. However, when drilling is regarded as activated cracking that involves the catastrophic growth of microcracks into more destructive ones, it is then possible that the interfacial tension, or surface energy, must first go up to a critical tension before a rock fragment separates with a lowering of interfacial tension. This distinction between the kinetic process of drilling and the thermodynamic state of crack formation can explain why an increase in interfacial tension can facilitate drilling rate by lowering the energy barrier for rock fragmentation.