Because of profound applications of MoS2 crystals in electronics, their microscale oxidation is the subject of substantial interest. We report on oxidation of single MoS2 crystals, which were oxidized within a precision muffle furnace at a series of increasing temperatures up to 500 °C. Using electron dispersion X-ray spectroscopy (EDS) at ambient conditions, we observed an increase of oxide content with increasing heating temperature and obtained an apparent activation energy for the oxidation process of the order of 1 kcal/mol. This value is at least 8 times smaller than an activation energy for surface formation of MoO3 and according to the literature points rather to physisorbed oxygen species. Our Auger electron spectroscopy (AES) results also pointed out toward the physisorbed oxygen, similarly as our further heating studies within elevated relative humidity conditions. The Mo oxide leftovers on the sample were investigated using atomic force microscopy (AFM) and showed dendritic structures. Surface appearance of those dendrites, their fractal dimension between 1.61 and 1.66, and their surface distribution were reminiscent of the diffusion-limited aggregation (DLA) growth. On the basis of analysis of AFM topographs, we hypothesized that the DLA process was controlled by a surface diffusion of the initially physisorbed oxygen, which had to diffuse to reaction centers in order to facilitate the subsequent chemical conversion of MoS2 layers to volatile Mo oxides.

The paper presents various methods for quantitative description of material structures. The main focus is on direct methods of description based on image analysis. In particular, techniques for the estimation of the size, shape and spatial distribution of structural elements observed by different microscopic techniques are described. The application of these methods for the characterization of the structures of engineering materials is demonstrated on a stainless steel used in petrochemical installations. It is shown that the methods applied are useful for the assessment of service degradation of materials.

No abstract

No abstract

Monitorowanie uszkodzeñ w kompozytach metodami nieniszcz¹cymi MONITORING OF FAILURES IN THE COMPOSITES BY NON-DESTRUCTIVE METHODS Summary-A review of selected methods of non-destructive evaluation (NDE) for the monitoring of failures in composites based on ceramic or polymer matrices. The reasons of failures and the fillers actions related to them were discussed (Figs. 1-4). Acoustic emission as a variant of NDE methods has been characterized in details. An effort to classify the acoustic signals to find the load ranges relating to particular types of failures (Fig. 5, 6) has been taken up. Advantages of use of falck transform to evaluation of failures' progress at real time were illustrated (Fig. 7). Intelligent materials use for in situ monitoring of polymeric composite condition during its curing and exploitation (Fig. 8) was described.