Effects of surface abrasion and impurity levels on stress-induced Dauphine twinning in alpha quartz

Abstract

Two crystals of synthetic quartz were suitably prepared to study the effects of abrasion flaws and impurity content on the levels of stress required to induce Dauphine twinning. Four sample lots representing three surface treatments and two impurity levels were studied. One lot, designated as a control, was prepared from a crystal of low purity. Two lots prepared from the same crystal were abraded on one face with SiC grinding media, one with 15- mu particles and the other with 50- mu particles. Two stages of stress-induced Dauphine twinning are observed, namely nucleation and switchover. Raw data was collected in the form of applied load as read from a strip chart recorder attached to the stressing device. Contact areas of the specimens were determined and stress levels were calculated. These were ranked from lowest to highest and the standard form of the Weibull model was used to plot the data. A Newman-Keuls range test was used to estimate the significance of the difference between mean twinning stresses for all groups for nucleation and switchover. Initial results indicate that surface flaws and impurity concentration affect the stress level /required for twin nucleation and are factors in determining switchover stresses. >