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Rectangular fluidised beds are commonly used in industry, e.g. circulating fluidised bed (CFB) boilers. Apparently, no one has tried to imagine rectangular fluidised beds by electrical capacitance tomography (ECT). The purpose of this paper is to design a rectangular ECT sensor to understand the behaviour of a rectangular CFB riser.

A rectangular sensor with eight electrodes is adopted to obtain the capacitance data. The sensitivity map is simulated to calculate the grey level of pixels for visualisation using the linear back‐projection algorithm.

Experiments showed that the position of the objects in the riser can be obviously indicated and the central region of the object(s) has significantly higher grey level than other regions in the images using the rectangular ECT sensor.

It has a limitation in providing a higher resolution image.

The results obtained by the rectangular ECT sensor show that it is promising to study the characteristics of flow non‐uniformity in the fast fluidisation regime of CFB.

Without using square and circular ECT sensors, this is the first time a rectangular ECT sensor has been developed to study the unique problems of the characteristics of flow non‐uniformity in a rectangular CFB riser.

The purpose of this study is to investigate the corrosion resistance of superalloys subjected to ultrasonic impact treatment (UIT). The passive film growth on the superalloys’ surface is analyzed to illustrate the corrosion mechanism.

Electrochemical tests were used to investigated the corrosion resistance of GH4738 superalloys with different UIT densities. The microstructure was compared before and after the corrosion tests. The passive film characterization was described by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) tests.

The compressive residual stress and corrosion resistance of the specimens significantly increased after UIT. The order of corrosion resistance is related to the UIT densities, i.e. 1.96 s/mm² > 1.71 s/mm² > 0.98 s/mm² > as-cast. The predominant constituents of the passive films are TiO₂, Cr₂O₃, MoO₃ and NiO. The passive film on the specimen with 1.96 s/mm² UIT density has the highest volume fraction of Cr₂O₃ and MoO₃, which is the main reason for its superior corrosion resistance.

This study provides quantitative corrosion data for GH4738 superalloys treated by ultrasonic impact. The corrosion mechanism is explained by the passive film’s characterization.