K. Y. Jiang

Mössbauer studies of iron oxide catalysts for the dehydrogenation of ethylbenzene to styrene

In-situ Mössbauer studies for dehydrogenation of ethylbenzene to styrene has been carried out. The results show that the formation of iron oxide is essentially Fe3O4 and there is no KFeO2 under the reaction condition. As a promoter, the existence of potassium is in favour of the electron exchange between Fe2+ and Fe3+ ions.

A study of the action of magnesium on iron oxide catalysts for dehydrogenation of ethylbenzene to styrene

Mössbauer study of the action of magnesium on iron oxide catalysts for the dehydrogenation of ethylbenzene to styrene has been carried out systematically. The presence of opportune amount of Mg enhances the stability and dispersivity of catalysts. Therefore Mg is one kind of useful structure promoter.

Mössbauer study on the coupling interaction of Fe-based nanocrystalline alloys

A two-phase system of Fe-based nanocrystalline alloys is here investigated. The nanocrystalline Fe69.5Cu0.5Cr4V5Si13B8 alloys, which consist of two magnetic phases: α-FeSi grains and an amorphous matrix, were prepared by annealing the amorphous ribbons. Mossbauer spectroscopy and magnetic measurements at elevated temperatures were carried out. The results show that the exchange coupling interaction exists between grains through the amorphous matrix, and obviously affect the soft magnetic properties of the nanocrystalline alloys. A phenomenological coupling model is applied to estimate the coupling intensity for samples annealed at different temperatures and the data can reasonably explain why the nanocrystalline alloys annealed at 540 °C hold the best soft magnetic properties.

Determination of the recoilless-fraction for57Fe in Fe3O4 by the Mössbauer Faraday effect

We have observed the Mössbauer Faraday effect in nonstoichiometric Fe3O4 by using a Mössbauer polarimeter. Experimental results demonstrated that electronic hopping above the Verwey temperature between Fe2+−Fe3+ ions on the octahedral sites is a localized phenomenon only and the recoilless fractions of57Fe nuclei in Fe3−vO4 (v=0.02) are 0.71 for A sites and 0.62 for B sites, respectively.

Mössbauer study of the effect of potassium on iron oxide catalysts

One kind of catalyst used for dehydrogenation of ethylbenzene to styrene was investigated by57Fe Mössbauer spectroscopy. The results show that the area ratioSB/SA of two Mössbauer subspectra of Fe3-vO4 produced after catalytic reaction depends on the amounts of potassium added to the catalysts. A tentative conclusion is that the effect of potassium in iron oxide catalysts could be related to the reduction of Fe3+ to Fe2+.

A Mössbauer Effect Study on the Structural Components in Potassium-Promoted Iron Oxide Catalysts for Dehydrogenation of Ethylbenzene

Potassium-promoted iron oxide catalysts for dehydrogenation of ethylbenzene to styrene belong to one kind of complex oxide catalysts with a spinel structure and they exhibit good catalytic properties. In this work, two series of potassium-promoted catalysts were prepared with different potassium-to-iron ratios and using different calcining temperatures. Mossbauer spectroscopy has been used to determine the optimal potassium amount and the lowest calcining temperature for spinel structure formation, and to detect other structural components in the catalysts. Information was obtained for K2CO3-promoted iron oxides which may prove useful for industrial applications of this type of catalysts.

Correlation between MI Effect and Transverse Anisotropy in Stress-Annealed Nanocrystalline Alloys: A Mössbauer Effect Study

In order to understand the correlation between the large and sensitive magneto-impedance (MI) effect in the tensile stress-annealed Fe-based nanocrystalline alloy Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 and the transverse magnetic anisotropy on a microscopic scale, a Mossbauer effect study has been carried out. A series of ribbon samples were subject to thermal annealing with tensile stress a up to 60 MPa. MI measurements showed that the effective field of transverse magnetic anisotropy H k increases with increasing σ. Analysis of Mossbauer spectra provided direct evidence that there is an increasing transverse magnetic structure with increasing σ in these tensile stress-annealed samples. This work confirms, on the microscopic scale, that the transverse magnetic anisotropy arises from stress-annealing and is essential for the giant magneto-impedance effect.

Moessbauer Study of Magnetic Structure in Fe-Based Nanocrystalline Alloys for MI Effect

The magneto-impedance effect in Fe-based nanocrystalline Fe73Cu1Nb1.5Mo2Si13.5B9 alloys has been observed. The results showed that the field dependence of the MI ratio was strongly influenced by the transverse magnetic structure in samples, which was demonstrated by Moessbauer spectroscopy.