Humidity sensitive irreversible phase transformation of an open-framework Zinc phosphate and its water-assisted high proton conduction properties

Open-framework zinc phosphate (NMe4)(ZnP2O8H3) undergoes irreversible phase transformation. Structural transformation with α (NMe4.Zn[HPO4][H2PO4] the low-temperature phase) and β (NMe4.ZnH3[PO4]2 the high-temperature phase) (Tc=149 °C) and conduction properties were investigated by...

First-principles study on properties of Sn-doped LiCoO2 for Li-ion batteries

The key for the application of LiCoO2 as lithium-ion battery electrode under high voltage is to suppress the irreversible phase transformation from the layered to the spinel/rocksalt structure during cycling....

Microstructure and Phase Transformation Behavior of Ni-Mn-Fe High-Temperature Shape Memory Alloys

The microstructure and phase transformation behavior of Ni-Mn-Fe high-temperature shape memory alloys including Ni40+xFe10Mn50-x (x = 0, 10) were investigated. The results show that both two alloys exhibit single fcc γ phase annealed at 900°C for 1 day. When these quenched alloys are again annealed at 500°C for 20 days, they almost exhibit main tetragonal θ martensite. The microstructural evolutions are consistent with the results of phase transformation measurements. It is clearly found that there is an irreversible phase transformation around 480°C ~ 570°C, which is associated with the formation of tetragonal θ martensite from γ phase. Afterwards, the reversible martensitic transformation occurs during heating and cooling with very high transformation temperature.

ARAGONITE TO CALCITE TRANSFORMATION STUDY BY XRD AND ESR STUDIES OF Mn2+ IN FRESHWATER SNAIL SHELLS: P. CANALICULATA LAMARCK

Electron spin resonance spectroscopy (ESR) was used to study the Mn 2+ ions in snails of P. canaliculata lamarck (PCL). All these shells are abundant in Thailand. Fractions of aragonite and calcite phase in the shells have been approximately determined by ESR. The PCL shell was ground into fine powders and then four samples were separately annealed for 2 h in air at 400°C, 450°C, 500°C and 600°C, respectively. The phase transition from aragonite to calcite was monitored by X-ray diffractometer (XRD) and electron spin resonance spectrometer (ESR). Our results show that unheated PCL sample is mainly made of aragonite with only a small fraction of calcite. Annealing of the PCL powder sample at the temperature more than 450°C has resulted in the irreversible phase transformation from aragonite to calcite. The analysis of their ESR spectra has shown that Mn 2+ ions partially substituted Ca 2+ in the lattices. Finally, the spin Hamiltonian parameters for Mn 2+ distributed in both aragonite and calcite were evaluated. Our detailed ESR spectral analyses of PCL show that Mn 2+ ions enter Ca 2+ sites during a biomineralization process. Typical simulated ESR parameters of PCL-500 of Mn 2+ at a uniaxial site of calcite are gx=gy=2.078(1), gz=1.999(1), Ax=Ay=87.0 G, Az=89.00 G and D=115 G, respectively. It is thus possible to gain some insight of manganese incorporation into the fresh water shells during the biomineralization process.

ELECTRON SPIN RESONANCE STUDIES OF Mn2+ IN FRESHWATER SNAIL SHELLS: S. INGALLSIANA, P. AMPULLACEA, P. CANALICULATA LAMARCK AND FOSSILIZED SNAIL SHELL

We have studied paramagnetic Mn 2+ ions present in the shells of today's univalve freshwater snails, Sinotaia ingallsiana (FS), Pila ampullaceal (PA), Pomacea canaliculata lamarck (PCL) and the fossilized freshwater snail (FFS), Viviparus which are abundant in Thailand. The FS, PA and AG shells in our study were ground into fine powder. A set of seven samples was each then separately annealed for 2 hours in air atmosphere at 300°C, 400°C, 450°C, 500°C, 550°C, 600°C and 900°C, respectively, while the FFS powder was characterized as received. The FS, PA and PCL shells mainly consist of aragonite and a fraction of calcite. The heat treatments higher than 450°C of the FS, PA and PCL powder samples resulted in an irreversible phase transformation from aragonite to calcite. However, it is found that the FFS shell is mainly made of calcite, with a minor fraction of aragonite. The crystal structure of high temperature annealed FS, PA and PCL samples are quite similar to that of FFS, which indicates that the metamorphosis (aragonite → calcite) in the FFS shell had occurred but not yet completed, although they remained under the pressure and temperature of the Earth's crust over millions of years. Our detailed ESR spectral analyses of FS, PA, PCL and FFS show that Mn 2+ ions enter Ca 2+ sites during a biomineralization process. Typical simulated ESR parameters of FS-500 of Mn 2+ at a uniaxial site of calcite are gx=gy=2.078±0.001, gz=2.002±0.001, Ax=Ay=87.50±1.00 G , Az=89.00±1.00 G and D=115±1 G , respectively. It is surprising to find that the ratio of Mn 2+ concentration present in FFS to those in FS, PA and PCL shells evaluated from ESR spectra is as much as 10:1. It is thus possible to gain some insight of manganese incorporation into the freshwater shells during the biomineralization process.