Jianzhong Jiang

On the akaganeite crystal structure, phase transformations and possible role in post-excavational corrosion of iron artifacts

Abstract The crystal structure of akaganeite and the akaganeite to hematite transition has been studied by means of conventional and synchrotron X-ray and neutron powder diffraction. The chemical formula of akaganeite can be written as FeO 0.833 (OH) 1.167 Cl 0.167 . The crystal structure does not contain free water. Heating below 200 °C will not alter the akaganeite structure. Initial water loss can be attributed to a large amount of adsorbed water due to a very small particle size; 0.15 μm by 0.03 μm. Chloride is released from the structure only in connection with the transformation to hematite. Due to its stability, the presence of akaganeite does not in itself posses a threat to iron artifacts, but it is rather a symptom of the presence of high concentrations of chloride in an acidic environment.

Gas-sensitive properties and structure of nanostructured ( - materials prepared by mechanical alloying

The gas-sensitive properties of nanostructured 94, 85, 71 and 7 mol% materials prepared by high-energy ball milling have been investigated in atmospheres containing alcohol, CO and gases. It has been found that the materials show a high sensitivity with a short response time to the alcohol gas and almost no sensitivity to the other two gases, CO and in the concentration ranges studied. Furthermore, the gas-sensitive behaviour of these materials in response to the alcohol gas has been discussed on the basis of the microstructure of the materials. It is found that the tin ion content in and tin ions on the surface of particles may play an important role in the enhancement of the gas sensitivity.

Evidence of icosahedral short-range order in Zr70Cu30 and Zr70Cu29Pd1 metallic glasses

Change in local atomic environment during crystallization of Zr-based glassy alloys was studied by extended x-ray absorption fine structure (EXAFS) spectroscopy. The formation of icosahedral quasicrystalline phase followed by crystallization of tetragonal CuZr2 has been observed in the Zr70Cu29Pd1 glassy alloy during annealing up to 850 K. On the other hand, the binary Zr70Cu30 alloy shows a single glassy to crystalline CuZr2 phase transformation. The local atomic environment of as-quenched Zr70Cu30 alloy is matched to an icosahedral local atomic configuration, which is similar to that of the as-quenched Zr70Cu29Pd1 alloy and the alloy annealed at 593 K containing icosahedral phase. Considering that the supercooled liquid region appears prior to crystallization in the Zr70Cu30 glassy alloy, the observed results support the theory claiming a strong correlation between the existence of local icosahedral short-range order and stability of the supercooled liquid state.

Magnetic structure evolution in mechanically milled nanostructured ZnFe2O4 particles

Nanostructured partially-inverted ZnFe2O4 particles have been prepared from bulk ZnFe2O4 by high-energy ball milling in an open container. The grain size reduction, cation site distributions, and the evolution of magnetic structures have been studied by x-ray diffraction with Rietveld structure refinements, transmission electron microscopy, and Mossbauer spectroscopy. It is found that a change of magnetic structure from an antiferromagnetic to a ferrimagnetic (or ferromagnetic) structure occurs in the milled samples. This change is correlated with the redistribution of the cations, Zn and Fe, in the A and B sublattices.

Trapping of cubic ZnO nanocrystallites at ambient conditions

Dense powder of nanocrystalline ZnO has been recovered at ambient conditions in the metastable cubic structure after a heat treatment at high pressure (15 GPa and 550 K). Combined x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) experiments have been performed to probe both long-range order and local crystallographic structure of the recovered sample. Within uncertainty of these techniques (about 5%), all the crystallites are found to adopt the NaCl structure. From the analysis of XRD and XAS spectra, the cell volume per chemical formula unit is found to be 19.57(1) and 19.60(3)u2009A3, respectively, in very good agreement with the zero-pressure extrapolation of previously published high-pressure data.

Pressure effects on Al89La6Ni5 amorphous alloy crystallization

The pressure effect on the crystallization of the Al89La6Ni5 amorphous alloy has been investigated by in situ high-pressure and high-temperature x-ray powder diffraction using synchrotron radiation. The amorphous alloy crystallizes in two steps in the pressure range studied (0–4 GPa). The first process, corresponding to simultaneous precipitation of fcc-Al crystals and the metastable bcc-(AlNi)11La3-like phase, is governed by a eutectic reaction. The second process corresponds to the transformation of a residual amorphous alloy into fcc-Al, Al11La3, Al3Ni, and as yet unidentified phase(s). The applied pressure strongly affects the crystallization processes of the amorphous alloy. Both temperatures first decrease with pressure in the pressure range of 0–1 GPa and then increase with pressure up to 4 GPa. The results are discussed with reference to competing processes between the thermodynamic potential barrier and the diffusion activation energy under pressure.

Crystallization in Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass under pressure

The effect of pressure on the crystallization behavior of the bulk metallic glass-forming Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy with a wide supercooled liquid region has been investigated by in situ high-pressure and high-temperature x-ray powder diffraction measurements using synchrotron radiation. In the pressure range from 0 to 3 GPa, the crystallization temperature increases with pressure having a slope of 19 K/GPa, which can be explained by the suppression of atomic mobility. This observation is opposite to the results of W.H. Wang, D.W. He, D.Q. Zhao, and Y.S. Yao [Appl. Phys. Lett. 75, 2770 (1999)], reporting a decrease of the crystallization temperature under pressure in a pressure range of 0–6 GPa for the bulk glass Zr41Ti14Cu12.5Ni9Be22.5C1 alloy. Compressibility with a volume reduction of approximately 22% at room temperature does not induce crystallization in the Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk glass alloy. This indicates that the densification effect induced by pressure in the pressure range i...

Elastic properties of Pd40Cu30Ni10P20 bulk glass in supercooled liquid region

In situ ultrasonic measurements for the Pd40Cu30Ni10P20 bulk glass in three states: Glassy solid, supercooled liquid, and crystalline, have been performed. It is found that velocities of both longitudinal and transverse waves and elastic moduli (shear modulus, bulk modulus, Young’s modulus, and Lame parameter), together with Debye temperature, gradually decrease with increasing temperature through the glass transition temperature as the Poisson’s ratio increases. The behavior of the velocity of transverse wave vs. temperature in the supercooled liquid region could be explained by viscosity flow, rather than the two different crystallization processes in the region, suggested in the literature. No decomposition was detected at a temperature only 5 K below the crystallization temperature.

Structure and red–ox chemistry of tin in SnO·NaPO3 pseudo-binary glasses

Thermal and spectroscopic investigations have been carried out on a number of binary

Microstructural evolution during high energy ball milling of Fe2O3-SiO2 powders

SnO–N_aPO_3