Construction of E-pH diagram and experimental study on wet synthesis of FePO4 as the precursor of cathode materials

The preparation of FePO4 as a precursor by co-precipitation method is widely used, Due to the lack of the guidance of thermodynamic theory, The prepared FePO4 often contains impurity phase, which leads to unsatisfactory performance of LiFeO4. The E-pH diagram of Fe-P-H2O system at the temperature of 25℃ were drawn through the basic E-pH principle with a number of thermodynamic data. According to the E-pH Diagram, the pH value is approximately 2.5, and the FePO4 with less impurity can be prepared by adding proper oxidant. Base on the above mentioned condition, a simple verification experiment was carried out. The results showed that the prepared iron FePO4 had fewer impurities, which provided a theoretical basis for preparing high-performance LiFeO4.

Кристаллохимия и магнитные свойства гексаферрита BaFe-=SUB=-12-=/SUB=-O-=SUB=-19-=/SUB=- при гетеровалентном замещении железа цирконием

Samples of BaFe12O19 M-type barium hexaferrite with partial iron substitution by zirconium ions (concentration up to 10 at.%) have been synthesized and investigated. Studies of crystal features, phase composition, and magnetic properties were carried out using X-ray diffraction, Mössbauer spectroscopy, and VSM respectively. The presence of limited heterovalent isomorphism by the 2Fe3+ → Zr4+ + Fe2+ mechanism was shown. The limit of heterovalent isomorphic substitution by zirconium ions in barium hexaferrite (x = 0.6) was established. It was noted that additional sextets in the Mössbauer spectra of barium hexaferrite can be formed during the localization of Zr4+ ions predominantly in the 12k and 4f2 positions due to the frustration of the magnetic structure. The correlation between the chemical composition (concentration of zirconium ions), impurity phase formation, the peculiarities of the distribution of substituents over oxygen coordination, and the magnetic properties was established.

Size Effect of Fe3O4 Nanoparticles on Magnetism and Dispersion Stability of Magnetic Nanofluid

It is well known that magnetic nanofluids are widely applied in various fields ranging from heat transfer to miniature cooling, and from damping to sealing, due to the mobility and magnetism under magnetic field. Herein, the PFPE-oil based magnetic nanofluids with superior magnetization and dispersion stability were obtained via regulating reaction temperature. The structures of particles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The size effects of particles on the magnetism and coating effect of particles, and on the stability and saturation magnetization of the fluids were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM) and density instrument, respectively. The results indicate that the impurity phase FeOOH only appear in the sample prepared at 18°C and the average size of Fe3O4 nanoparticles reduces from 120 to 20 nm with raising reaction temperature. The saturation magnetization of Fe3O4 particles increases firstly and then reduces with increasing particle size, which is affected by the thickness of magnetic dead layer and impurity phase FeOOH. The Fe3O4 particles could be chemically coated by PFPE-acids, and the coated mass is a little affected by particle size. The stability of the nanofluids lowers while the saturation magnetization increases firstly and then decrease with increasing particle size. At reaction temperature of 60°C, Fe3O4 particles of 25 nm and the nanofluids with superior stability and saturation magnetization were obtained. Our results indicate that the control of nanoparticles size by regulating reaction temperature can be a useful strategy for preparing magnetic nanofluids with desirable properties for various potential applications.

Structure and magnetic characterization of Sr-doped BiFeO3 prepared by sol–gel method

Multiferroic nanocrystalline Bi[Formula: see text]Sr[Formula: see text]FeO3 ([Formula: see text], 0.05, 0.1) samples were synthesized using the sol–gel method and characterized by powder X-ray diffraction, Mössbauer spectroscopy and SQUID system. The small-angle X-ray diffraction analysis showed that the sample underwent phase transition from rhombohedral to pseudo-cubic structure with the enhancement of Sr content. In addition, impurity peaks gradually diminished, indicating that content of impurities of samples reduced. Furthermore, it can be determined that there is only Fe[Formula: see text] in all the samples and impurity phase that existed in the samples was Bi[Formula: see text]FeO[Formula: see text] by fitting Mössbauer spectra. It is further confirmed that Bi[Formula: see text] Sr[Formula: see text]FeO3 samples were generated by oxygen vacancy equilibrium valence state when Sr[Formula: see text] ions replaced Bi[Formula: see text] ions. The change of quadrupole splitting indicated that a low concentration of Sr[Formula: see text] ions diffused homogeneously in the sample. Magnetization measurement showed that the magnetization of the sample increased gradually with the substitution of Bi[Formula: see text] by nonequivalent Sr[Formula: see text] ions, which can be ascribed to the decrease of grain size and the increase of oxygen vacancy and specific surface in the samples.

Effect of Reaction Time on the Coercivity of Barium Ferrite Synthesized by Hydrothermal Process

The barium ferrite BaFe12O19 with c-plane anisotropy, which possessed relative high saturation magnetization and low coercivity, had been synthesized by hydrothermal method with different reaction time of 5 h, 8 h,11 h,14 h, and 17 h. The X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and vibrating sample magnetometer (VSM) were used to study the phase composition, microstructure and magnetic properties of barium ferrite, respectively. The results showed the intensities of the peak were enhanced and there was no impurity phase. With the prolonging of the reaction time to 11 h, 14 h and 17 h, the grain size increased, and the equivalent diameter was about 1 μm, and the thickness was about 100 nm. When the reaction time was 17 h，the coercivity of barium ferrite was 1104 Oe. The reduction of coercivity was ascribed to the increase of particle size and the reduction in magnetic anisotropy.

Гомогенизационный отжиг и магнитные свойства образца фазы Лавеса GdNi-=SUB=-2-=/SUB=-

The paper shows the effect of homogenization annealing on the ferromagnet-paramagnet phase transition in the GdNi2 alloy. In the cast sample, at the Curie point, a temperature hysteresis is observed, which in an external magnetic field of 13.5 T can be at least 3 degrees. The data of scanning electron microscopy of the electropolished samples showed a decrease in the impurity phase of GdNi and practically no temperature hysteresis of the phase transition in the annealed GdNi2 sample. The value of the isothermal change entropy DSm = - 18.931 J/(kg*K) for an annealed sample of the GdNi2 alloy at the Curie point of 75 K in a magnetic field of 13.5 T.

SYNTHESIS OF MAGNESIUM PHOSPHATES IN A POLYMERIC MATRIX

Изучена зависимость фазового состава наноразмерных фосфатов магния (MgNHPO·6HO, Mg(HPO), MgHPO·3HO, Mg(PO)•22HO) с размером кристаллитов 13-54 нм от условий осаждения из водных растворов в присутствии поливинилового спирта и его смеси с поливинилпирролидоном. В полимерной матрице дополнительно образуется примесная фаза MgOHCl. Наличие средних и двузамещенных фосфатов магния в пленках поливинилового спирта и поливинилового спирта/поливинилпирролида ингибируют их термическую деструкцию. The dependence of the phase composition of nanoscale magnesium phosphates (MgNHPO·6HO, Mg(HPO), MgHPO·3HO, Mg(PO)•22HO) with 13-54 nm crystallite size on the conditions of precipitation from aqueous solutions in the presence of the polyvinyl alcohol and its mixture with polyvinylpyrrolidone was studied. In the polymer matrix an additional impurity phase MgOHCl is formed. The presence of medium and disubstituted magnesium phosphates in polymer films of polyvinyl alcohol and polyvinyl alcohol/polyvinylpyrrolidone inhibit their thermal destruction.