Circumferential crack detection of small diameter tubes is a difficult problem to solve in eddy current testing. The three-dimensional simulation model is established through electromagnetic field simulation software to analyze the eddy current field distribution of the traditional bobbin probe and transverse cylindrical probe in small diameter tubes. The results show that the circumferential crack has a more marked disturbance to the eddy current field generated by the latter. Based on the simulation research, a new type of probe based on transverse excitation is designed to detect the artificial circumferential crack of the specimen with the designed probe, which can effectively detect the circumferential crack and has a potentially high sensitivity to the narrower natural circumferential crack.

Hydrophobic modification of Fischer-Tropsch synthesis catalyst can inhibits water gas shift(WGS) reaction and regulates product distribution. Herein, a series of hydrophobic Fe 2 O 3 @SiO 2 -xHDTMS (Hexadecyltrimethoxysilane, HDTMS. x represents the amount of HDTMS.) catalysts with various HDTMS content were synthesized for Fischer-Tropsch synthesis to light hydrocarbons. The Fe 2 O 3 @SiO 2 -xHDTMS catalysts were characterized by X-ray diffractometer(XRD), scanning electron microscope(SEM), transmission electron microscope(TEM), fourier transform infrared spectrometer(FT-IR) and contact angle measuring instrument(CAMI). After HDTMS modification, the hydrophobicity of the catalyst is significantly improved, the selectivity of the catalyst to CO 2 is significantly reduced due to the inhibition of WGS reaction, and the selectivity of hydrocarbon products is significantly improved. This indicates that HDTMS is very suitable as a silanizer for hydrophobic modification of Fischer-Tropsch synthesis catalysts. With the increase of HDTMS content, the hydrophobicity of the catalyst always increased, but the selectivity of CO 2 in Fischer-Tropsch synthesis products decreased first and then increased, and the selectivity of hydrocarbons increased first and then decreased, indicating that the content of HDTMS has a significant impact on the hydrophobicity and catalytic performance of the catalyst.

The direct synthesis of light olefins from syngas via Fischer-Tropsch synthesis reaction is a promising technology for direct synthesis of olefins from syngas. The key is to improve the selectivity of light olefins through the regulation of product distribution. In this work, the hydrophobic Fe@Si catalyst was prepared by room temperature solid state method-Stöber-silylation method, and then the catalyst was combined with SAPO-34 molecular sieves with different contents to prepare Fe@Si/S-34 composite catalysts. The effects of SAPO-34 molecular sieve content on the physicochemical properties of the catalysts were investigated by X-ray diffraction, scanning electron microscopy, N2 adsorption-desorption, NH3 temperature programmed desorption and water contact angle measurement. The results showed that the content of SAPO-34 molecular sieve has significant influence on the surface area, pore volume, acidity and hydrophobicity of the catalysts. With the increase of SAPO-34 molecular sieve content, the specific surface area and total pore volume of the catalyst increased, the weak acid and medium-strong acid sites increased, and the hydrophobicity weakened. The catalytic performance evaluation results showed that the Fe@Si/S-34 composite catalyst decomposed C5+ hydrocarbons into light hydrocarbons, significantly reduced the selectivity of C5+ products and increased the selectivity of C2～C4 hydrocarbons. Appropriate SAPO-34 molecular sieve could significantly improve the selectivity of C2～C4 olefins. When the mass ratio of Fe@Si catalyst to SAPO-34 is 2, the C2～C4 olefin selectivity of Fe@Si/S-34 catalyst is the highest, the conversion of CO is 80.0%, the selectivity of CO2 in the product is 8.9%, and the selectivity of C2～C4 olefins is 31.1%. In this study, the hydrophobicity of Fe@Si catalyst and the cracking activity of SAPO-34 molecular sieve for C5+ hydrocarbon were coupled together to inhibit the water-gas shift (WGS) reaction, reduce the CO2 selectivity and obtain higher C2～C4 olefin selectivity, which provided a new strategy for the development of catalysts for Fischer-Tropsch synthesis to olefins.

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