The pressure of hydrothermal system is increased based on the traditional hydrothermal synthesis to prepare nano-barium ferrite at the reaction temperature of 180℃ under different magnetic field.Using XRD,SEM and TEM methods,the phase composition and micro structure of the nano-barium ferrite powder obtained under different initial pressure(l.0atm,1.5atm and 2.0atm) is discussed.All the powder prepared under different initial pressure is mainly composed of BaFe_(12)O_(19).But the morphology of the products is different.Flake BaFe_(12)O_(19)is obtained under the 10T magnetic field when the initial pressure is 1.5atm and 2.0atm.Moreover,the degree of crystallinity of hydrothermal products is also improved by the application of magnetic field and additional high pressure.Hexagonal flake grains of BaFe_(12)_(19) with excellent crystallization have been prepared under 6T magnetic field,when the initial pressure reached 2.0atm,some of the rod-like BaFe_(12)O_(19) self-organized to form ordered forked structure through oriented attachment due to the multiple influence of pressure and magnetic field on crystal face energy.It can be found that the additional high pressure will disturb the influence of the magnetic field on one-dimensional growth.And the phenomenon of oriented attachment can be regarded as the intermediate state between the one-dimensional rod and two-dimensional sheet.
Coatings containing Fe-Si particles were electrodeposited on 3.0wt% Si steel sheets under magnetic fields. The effects of magnetic flux density （MFD）, electrode arrangement and current density on the surface morphology, the silicon content in the coatings and the cathode current efficiency were investigated. When a magnetic field was applied parallel to the current and when the MFD was less than 0.5 T, numerous needle-like structures appeared on the coating surface. With increasing MFD, the needle-like structures weakened and were transformed into dome-shaped structures. Meanwhile, compared to results obtained in the absence of a magnetic field, the silicon content in the coatings significantly increased as the MFD was increased for all of the samples obtained using a vertical electrode system. However, in the case of an aclinic electrode system, the silicon content decreased. Furthermore, the cathode current efficiency was considerably diminished when a magnetic field was applied. A possible mechanism for these phenomena was discussed.
Coatings containing Fe-Si or Si particles were electrodeposited on 3.0%（mass fraction） Si steel sheets. The surface morphology, the cross-section and the silicon content of coating have been investigated, respectively. It was found that the number of particles on the coating surface and cross-section significantly decreased with increasing silicon content in the applied particles, leading to a decrease of the silicon content of coatings. About 10.2% silicon content of coatings deposited with Fe-30%Si particles can be obtained, whereas that for Si particles was only 2.9% at a particle concentration of 100 g/L and current density of 2 A/dm2. This is mainly attributed to the conductivity of applied particles. High conductivity can promote the co-deposition of the particles. With increasing silicon content in the particles, their conductivity decreased sharply, resulting in the decrease of silicon content of coatings. Present work may initiate a new method to modify the particle content of the composite coatings via changing the conductivity of the particles during the composite electrodeposition. In this paper, a possible mechanism was proposed to explain the phenomena.
LONG Qiong ZHONG Yunbo ZHENG Tianxiang LIU Chunmei
Using XRD,TEM and VSM methods,the phase,morphology and magnetic property of iron hydroxide oxide(FeOOH) which has been prepared by low-temperature neutralization reaction under different magnetic fields were analyzed.It can be found that the magnetic field had a great influence on the product.Acicular goethite(α-FeOOH) was synthetized without magnetic field.When the magnetic flux density was increased to 0.1T,γ-FeOOH was obtained.If the magnetic field intensity was raised to 0.5T,the product was all composed of δ-FeOOH.Moreover,the crystallization of FeOOH was greatly influenced by magnetic field as well.Thermodynamic calculation results show that the magnetic free energy of chemical reaction reached to more than hundreds KJ/mol when the magnetic field is applied.It meaned that the application of magnetic field was conducived to producing the products with higher susceptibility.Even under the low magnetic field,due to the stability of the reaction products was broken by the magnetic field,the magnetic free energy was also effective.
