The response of sputter deposited Fe-15Cr and Fe-25Cr alloys to a rapid potential increase in the passive region was studied using two in situ methods: electrochemical quartz crystal microbalance and inductive coupled plasma-atomic emission spectroscopy (ICP-AES). Both methods indicated an increase in the dissolution rate of iron following the potential change; the total amount of material dissolved being higher for the Fe-15Cr alloy. For both alloys, about 10% of the total dissolved material was Cr. This result compared well with experiments on a 430 stainless steel. ICP-AES is shown to be useful for the in situ determination of partial currents of metal dissolution using solution analysis in a flow cell. 相似文献
Two acoustic emission (AE) parameters, event count rate (ER) and the skewness of the peak amplitude distribution (PAD), were found to correlate with mechanical and damage mechanisms in unidirectional Kevlar-epoxy composites loaded in tension. The ER of the AE reached a local maximum at about 0.3σcu (σcu= composite tensile strength), a minimum at about 0.6–0.7σcu, and increasing ER rates were noted as failure stress approached, with a peak at final failure.Along with our proposed approach to evaluate the PAD as a tool for characterizing processes, damage mechanisms and failure modes, the third statistical moment of the PAD, the skewness, was found to be able to distinguish between various mechanisms. From the beginning of loading until completion of the fibre straightening process, 0.6–0.7σcu, the value of the skewness steadily decreased, and then gradually increased to final failure. This behaviour is explained by a model based on the non-elastic mechanisms which contribute to the monitored AE. At final failure, the PAD's skewness value was affected by macroscopic failure modes. When this mode comprises fibre fracture with little matrix and interface splitting, the skewness decreased; when fibre failure was accompanied by matrix and interface splitting, its value changed slightly or even increased. 相似文献
A exhaust system consisting of a close-coupled Pd technology 32 in3 lightoff converter and Pt/Rh technology 170 in3 underfloor converter was vehicle-aged for 56000 miles on a vehicle equipped with a 3.8 l engine. Following this aging, the converters were taken off the vehicle and cut into 1″ thick sections along their axis and characterized for lightoff and warmed-up activity using a laboratory reactor to simulate vehicle exhaust. Each section was also analyzed for the quantity of oil additive poisons (phosphorus and zinc) deposited. Following this initial characterization, the phosphorus and zinc deposits were removed, and the sections were characterized again for lightoff and warmed-up activity. This procedure was used to qualitatively determine the relative contribution of oil additive poisoning and thermal sintering to the total activity deterioration as a function of axial position in the catalyst monoliths.
Analysis of the lightoff converter as taken from the vehicle showed a dramatic axial gradient in the lean and stoichiometric lightoff and warmed-up (600°C) performance for HC, CO and NOx, with most of the deterioration having taken place in the forward-most 1″ section of the converter, which was consistent with the gradient in the deposition of phosphorus (P) and zinc (Zn) in this converter. Comparison of these data sets with those obtained after removal of the P and Zn poisons indicates that most of the total deterioration of lean HC and CO activity can be attributed to P and Zn poisoning of the forwardmost 1″ section. When tested under stoichiometric conditions, most of the deterioration of HC activity is attributable to P and Zn poisoning, while most of the deterioration of CO and NOx activity is attributable to thermal deterioration. A similar activity and poison deposition gradient was detected in the underfloor converter, but to a smaller extent. 相似文献