Lu Kun-Quan

STRUCTURAL STUDY OF IRON IN PHOSPHATE-GLASSES

Abstract In the present paper, EXAFS and Mossbauer spectroscopies have been used to study the structure of iron in Fe 2 O 3 P 2 O 5 glasses, Na 2 OFe 2 O 3 P 2 O 5 glasses and the samples which are obtained from heat-treated iron metaphosphate glass. The results indicate that ferric and ferrous ions are present in the phosphate glasses, and Fe 3+ ions are coordinated with both four and six oxygens, but Fe 2+ ions are only in six-coordination. The proportion of each kind of iron ion to the total iron ions changes with a composition of the glasses and heat treatment conditions of the samples. The coordination number of Fe 3+ ions in an iron phosphate glass is lower than in the iron phosphate crystal with the same composition.

Extended X-ray-absorption fine structure of mixed-coordination systems

Abstract An analysis method of the extended x-ray absorption fine structure (EXAFS) for mixed-coordination systems (MCS) is provided to determine structure parameters of the same type of atoms located at different coordination sites and proportion of them. Its demonstrated that if the effects of different sites on EXAFS amplitudes are ignored, the coordination numbers gotten from EXAFS analyzing must be wrong mostly. The method has been well tested by analyzing a known structure Gd 3 Ga 5 O 12 (GGG) crystal in which the Ga atoms have two different coordination sites. Li 2 O-ZnO-GeO 2 glass system is also analyzed by means of the EXAFS method for MCS. Two different coordination sites for Ge atoms in the glasses. are found and the occupancies of them and the structure parameters are determined.

Local structure of Ge in binary oxide glasses by EXAFS

The coordination number and distances around a Ge atom in binary oxide glasses BiO1.5-GeO2 and PO2.5-GeO2 have been measured by EXAFS. The results show that Ge-O tetrahedron network in GeO2 rich BiO1.5-GeO2 glass is much like that in amorphous GeO2, but that in PO2.5-GeO2 glass it is more disordered.

Harmonic effect on EXAFS amplitude

The effect on amplitude of EXAFS from harmonic caused by high order diffraction of crystal monochromator is discussed. The general expression and calculated results are presented. It is shown that the harmornic decreases the amplitude of EXAFS and the amount of decrease is related to such factors as intensity ratio of harmonic to fundamental, thickness and absorption coefficient of specimen. K edge EXAFS spectra with and without harmonic for different thickness copper foils have been measured respectively, and the distortion of single shell EXAFS amplitudes have been extracted. The measured results are consistent with calculated ones. Consequently, a method to correct the harmonic effect on EXAFS amplitude is proposed.

Abnormal Viscosity of Al Electro-Rheology Fluid

The viscosity of the mixture of metal particles Al and silica oil is studied under different ac electric field at room temperature. The viscosity increases with rising field until a maximum (about two times of that at zero field) at about 2.5 MV/m and a tendency of decrease appears after this critical field. Microscope observation shows that this special behavior corresponds to the formation and destruction of fiber structure in Al electro-rheology fluids.

Properties of Molten Potassium Niobate System

The density and surface tension of the K2O-Nb2O5 molten system between 50 and 56 mol% K2O melts were measured from 1080 to 1180°C. The concentration of K2O from 50 to 56 mol% in melt not only caused the density of melt to decrease, but also induced the surface tension to decrease. Both composition gradient and the temperature coefficient of density exist extremum within this composition range. These properties are possibly employed to explain why the KNbO3 crystal should be grown at the composition from 52 to 54 mol% K2O at above 1150°C.

Torsion Pendulum Method in Viscosity Measurement of Melts

In this paper we present the results of our preliminary study on the improvements of torsion pendulum in order to make it suitable for the viscosity measurement of melt at high temperature. The amplitude features of conventional torsion pendulum and our method have been compared at room temperature and at high temperature, respectively. The relationship between the damping factor and the kinematical viscosity is derived and discussed. The viscous properties of molten KNbO3 and molten Li2B8O13 at high temperatures in air are measured with this method.

On the Spatial Configuration of the Mitotic Spindle

An experimental simulation using electrorheological (ER) fluid is developed to investigate the spatial configuration of the mitotic spindle. In the presence of two different kinds of electric field, the structures of particle arrangement in ER fluid are similar to the configuration of the mitotic spindle of the animal and plant cells respectively.

Phase content and atomic structure determination in two-phases systems by EXAFS

A method of EXAFS analysis to determine phase content and local structure surrounding same type atoms in different phase of a mixed phases system is proposed. A general expression of χ(κ) function for a two phases system is presented. To verify the method, the EXAFS of some specimens were measured and analyzed. The results agreed well with expected ones.