The digital microscope (VHX-2000, Keyence Corporation, Osaka, Japan) illustrated in Fig. 3 is a high resolution CCD camera-based system with a high intensity halogen lamp and image processing capabilities that integrates observation, recording and determination of measurement functions. The structural evaluation processes, after pressurization of samples, were carried out by software (VHX-2000) developed for imaging purposes. This investigation was performed with 20× and 400× objectives.