Investigation of the Phase Transition Mechanism in LiFePO4 Cathode Using In Situ Raman Spectroscopy and 2D Correlation Spectroscopy during Initial Cycle.

The phase transition of the LiFePO4 and FePO4 in Li-ion cell during charging-discharging processes in the first and second cycles is elucidated by Raman spectroscopy in real time. In situ Raman spectroscopy showed the sudden phase transition between LiFePO4 and FePO4. Principal component analysis (PCA) results also indicated that the structural changes and electrochemical performance (charge-discharge curve) are correlated with each other. Phase transition between LiFePO4 and FePO4 principally appeared in the second charging process compared with that in the first charging process. 2D correlation spectra provided the phase transition mechanism of LiFePO4 cathode which occurred during the charging-discharging processes in the first and second cycles. PCA and 2D correlation spectroscopy are very helpful methods to understand in situ Raman spectra for the Li-ion battery.

Surface reaction of LiCoO2/Li system under high-voltage conditions by X-ray spectroscopy and two-dimensional correlation spectroscopy (2D-COS).

We studied the surface reactions of a LiCoO(2)/Li cell under high-voltage conditions using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and two-dimensional correlation spectroscopy (2D-COS). 2D XPS correlation spectra show that Li(2)CO(3) is formed first by decomposition of the organic solvents, and then polycarbonate, which is formed by polymerization of the electrolytes, is produced on the cathode surface of the LiCoO(2)/Li system under high-voltage conditions. XAS measurements also confirm that the solid electrolyte interface (SEI) layer is formed on the LiCoO(2) electrode by decomposition of the organic solvents. The thickness of the SEI layer is less than 100 Å.

Effects of the polarizability and packing density of transparent oxide films on water vapor permeation.

The tin oxide and silicon oxide films have been deposited on polycarbonate substrates as gas barrier films, using a thermal evaporation and ion beam assisted deposition process. The oxide films deposited by ion beam assisted deposition show a much lower water vapor transmission rate than those by thermal evaporation. The tin oxide films show a similar water vapor transmission rate to the silicon oxide films in thermal evaporation but a lower water vapor transmission rate in IBAD. These results are related to the fact that the permeation of water vapor with a large dipole moment is affected by the chemistry of oxides and the packing density of the oxide films. The permeation mechanism of water vapor through the oxide films is discussed in terms of the chemical interaction with water vapor and the microstructure of the oxide films. The chemical interaction of water vapor with oxide films has been investigated by the refractive index from ellipsometry and the OH group peak from X-ray photoelectron spectroscopy, and the microstructure of the composite oxide films was characterized using atomic force microscopy and a transmission electron microscope. The activation energy for water vapor permeation through the oxide films has also been measured in relation to the permeation mechanism of water vapor. The diffusivity of water vapor for the tin oxide films has been calculated from the time lag plot, and its implications are discussed.

Fourth brachymetatarsia treated with distraction osteogenesis.

BACKGROUND: This study investigated metatarsal lengthening by distraction osteogenesis for fourth brachymetatarsia in 22 metatarsals (16 patients). METHODS: From May 1997 to May 2000, lengthening was performed with a monoexternal fixator, and distraction was started at a rate of 0.5 mm per day after a latency period of approximately 7-10 days. RESULTS: The average gain in length was 16.5 mm (range, 13-21 mm), equivalent to an increase of 39% (range, 28-51%), and the average healing index was 72.9 days/cm (range, 51.7-95.7 days/cm). The American Orthopaedic Foot and Ankle Society (AOFAS) average score for lesser toe was 86.3 (range, 47-100). The most common residual complication was subluxation of metatarsophalangeal (MTP) joint in five cases, with partial or total stiffness of the MTP joint. These complications happened in the group of metatarsals excessively lengthened more than 40% and made the AOFAS score poorer. The other complications were three cases of angular deformity in the lengthened bone, and two cases of pin-tract infection. CONCLUSION: Although distraction osteogenesis is an effective method to address fourth brachymetatarsia, stiffness or subluxation of the MTP joint was not uncommon. To avoid complications that can happen as a result of excessive lengthening, careful preoperative radiographic measurement to calculate the optimal amount of lengthening may help us to avoid overlengthening and the complications that accompany it.