Failure analysis chemical method

Polarization probes. Polarization methods other than LPR are also of use in process control and corrosion analysis, but only a few systems are offered commercially. These systems use such polarization techniques as galvanodynamic or potentiodynamic, potentiostatic or galvanostatic, potentiostaircase or galvanostaircase, or cyclic polarization methods. Some systems involving these techniques are, in fact, used regularly in processing plants. These methods are used in situ or in the laboratory to measure corrosion. Polarization probes have been successful in reducing corrosion-related failures in chemical plants. 

It is evident that chemical composition is of fundamental importance in determining the character and quality of a refractory. A low content of basic impurities in siliceous materials and of acid ones in basic refractories is obviously desirable from the standpoint of heat resistance and for this purpose chemical analysis is of great importance in determining the causes of success or failure. In refractories used at temperatures close to their softening point the presence of impurities amounting only to 1 or 2 per cent may cause failure. The chemical analysis of refractory materials requires careful work and the modern analytical methods proposed by Hillebrand, the Geophysical Laboratory of the Carnegie Institution, Mellor, and others should be employed. 

Failure of parts, irrespective of plastic t5 e, is an inevitable fact of the operation of chemical plants. Fluoropolymers are no exception in spite of their excellent chemical, thermal, and mechanical properties. These plastics form the processing surfaces of equipment where they are exposed to the most aggressive and corrosive chemicals. The repeated exposure of fluoroplastics to these chemicals, in addition to other factors, can affect the integrity and surface quality of the parts. The chapters dealing with properties and part fabrication techniques of fluoropolymers should be consulted extensively. An understanding of the limitations of fluoropolymers and flaws created by fabrication methods is required for successful failure analysis of parts. 

Electrocatalytic reactions occur on catalyst surfaces. The catalyst surface structure and chemically bonded or physically absorbed substances on the catalyst surface exert strong influences on catalyst activity and efficiency. X-ray photoelectron spectroscopy (XPS) (also known as electron spectroscopy for chemical analysis (ESCA), auger emission spectroscopy (AES), or auger analysis) is a failure analysis technique used to identify elements present on the surface of the sample. For instance, this can be used to identify Pt and carbon surface chemical species that may present histories of chemical reactions or contamination in the catalyst layer. AES and XPS can also provide depth profiles of element analysis. Wang et al. [41] studied XPS spectra of carbon and Pt before and after fuel cell operation. They observed a significant increase in O Is peak value for each oxidized carbon support, the result of a higher surface oxide content in the support surface due to electrochemical oxidation. However, sample preparation in AES and XPS analysis is critical because these methods are very sensitive to a trace amount of contaminants on sample surfaces, and detect as little as 2-10 atoms on the sample surface. 

The features of these layers were validated by Pauschitz et al. [79,21] using a series of systematic but comprehensive experiments. The formation of these layers and their failure mechanisms are presented in Fig. 6.16 schematically [79]. Their presence can explain all the observed behaviour of elevated temperature sliding wear of metallic materials [20]. Furthermore, by carrying out systematic chemical analysis of the worn surface and the wear debris it is possible to identify the various types of layers that form during elevated temperature wear. Further, systematic study by optical interferometer can also identify the types of layers that form and their failure mechanisms. By using both methods a complete failure analysis of the worn surface can be carried out without destroying the wearing sample. 

Hazard and risk analysis is a vast subject by itself and is extensively covered in the literature [22]. In order to plan to avoid accidental hazards, the hazard potential must be evaluated. Many new methods and techniques have been developed to assess and evaluate potential hazards, employing chemical technology and reliability engineering. These can be deduced from Fault Tree Analysis or Failure Mode Analysis [23], In these techniques, the plant and process hazard potentials are foreseen and rectified as far as possible. Some techniques such as Hazards and operability (HAZOP) studies and Hazard Analysis (HAZAN) have recently been developed to deal with the assessment of hazard potentials [24]. It must be borne in mind that HAZOP and HAZAN studies should be properly viewed not as ends in themselves but as valuable contributors to the overall task of risk management... 

Ion beams provide useful information either as a diagnostic tool or as a precision etching method in adhesion research. The combination ISS/SIMS method used along with other techniques such as SEM provides a powerful tool for elemental analysis of surface composition. These results, as well as earlier work in this laboratory, indicate that the surface composition can be significantly different from the bulk due to contamination, selective chemical etching and segregation. These same techniques also provide an analysis of the mode of failure in adhesive joints. Many failures classified as "adhesive" on the basis of visual inspection are frequently mixed mode failures or failures at a new interface containing elements of both adhesives and adherend. 

True method development calls upon the technical expertise of the analytical department and more specifically the project analytical chemist to assess the nature of the chemical entity under investigation and the matrix in which it is present. Success or failure in method development is directly attributable to the analyst s overall technical competence and breadth of knowledge in various analytical techniques. Technically challenging analysis problems are usually handled by more senior members of the laboratory staff or those possessing advanced education and training. 

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