Explosion hazards of ion exchange resin mixed with perchloric acid

On January 21, 2003, an explosion occurred while ion exchange resin (IER) was being used to separate impurities from uranium solution. To clarify the cause of the accident and go/no-go criteria of the explosion, elemental analysis of the IER, DSC analysis, and SIKAREX analysis (a screening tool for runaway reactions) were performed. Finally, experiments on the same scale as the accident were conducted in an explosion chamber. When HClO₄ was added to IER-NO₃, the IER violently exploded without any heating nor metal ions such as uranium. It was confirmed that the accident was caused by an incorrect procedure in the chemical process. From the standpoint of explosion safety, IER-NO₃ in particular should be kept away from perchloric acid in the laboratory.     

Behaviour in solution of piezoelectric quartz crystals coated with poly(vinylpyridines). Application to the determination of copper(II)

Poly(2-vinylpyridine) or poly(4-vinylpyridine) coated on a piezoelectric quartz crystal adsorbed copper, thus decreasing the oscillation frequency. The bound copper could be removed by EDTA solution. Poly(4-vinylpyridine) is recommended to determine copper (5–35 μM) in a maleate buffer at pH 6.6 flowing over the coated crystal for 5 min. Iron(III) and cadmium interfered.     

Observation and evaluation of proton diffusion in porous media by the pH-imaging microscope using a flat semiconductor pH sensor.

The diffusion of protons in porous media was observed and evaluated using a pH-imaging microscope with a flat semiconductor. Small particles were packed on the sensing surface of the flat sensor, followed by the addition of a lactic acid droplet on the top of the packed particle layer. The pH distribution accompanied by the diffusion of lactic acid was visualized at the bottom of the layer using the flat sensor. The difference in the diffusion property was confirmed depending on the particle type. The effective diffusion coefficients of the lactic acid in some porous media were estimated by combining the experimental results and mathematical calculation.     

Practical preparation of benzyloxyacetic acids

An efficient and practical method for the preparation of benzyloxyacetic acids is described. The procedure involves the reaction of readily available chloroacetic acid with benzyl alcohol in the presence of powdered KOH providing a safer alternative to the known literature procedures, which completely eliminates the use of pyrophoric bases such as sodium hydride and sodium metal.     

Origin of ion beam mixing effects on morphological features in solid-phase titanium silicide formation

The origin of the ion beam mixing effect, which causes the formation of smooth silicide films, is investigated for the Ti/Si solid-phase silicidation reaction. Ge ion beam mixing of a conventional Ti/c-Si structure with an oxide-contaminated interface shows an obvious effect when the implant conditions are such that the Ti/Si interface is amorphized. On the other hand, silicidation without ion mixing for Ti/a-Si and Ti/c-Si structures with oxide-free interfaces, prepared by sequential deposition in UHV, results in smooth and rough film surfaces, respectively. This strongly suggests that the ion beam mixing effect primarily comes from the amorphization of the Si substrate surface rather than the destruction of the interfacial oxide film.     

Efficient optical near-field energy transfer along an Au nanodot coupler with size-dependent resonance

We confirmed that the light intensity (λ=785 nm) scattered from an isolated hemispherical Au nanoparticle was resonantly enhanced at a diameter of 200 nm and a height of 50 nm, as observed experimentally using a collection-mode near-field optical microscope. The experimental results agreed with the calculated results using Mie’s theory. Furthermore, we observed resonant energy transfer of the optical near-field energy along a chain of Au nanoparticles. The magnitude of the transferred energy increased resonantly at the size of resonant light scattering for an isolated Au nanoparticle (200 nm diameter with 240 nm center-to-center separation). PACS 42.82.Et; 73.20.Mf; 78.67.Bf     

Preparation of a cycloheptane ring from a 1,2-diketone with high stereoselectivity

Treatment of 1,6-dialkylhexa-1,5-diene-3,4-diones with bis(iodozincio)methane gave zinc alkoxides of cis-5,6-dialkylcyclohepta-3,7-diene-1,3-diol in good yields at room temperature. The reaction proceeded with high stereospecificity. Bis(iodozincio)methane converted the diketone into the cis-divinylcyclopropane-1,2-diol stereoselectively; this diol transformed into the corresponding cycloheptane derivative stereospecifically via Cope rearrangement.     

Sulfur-rich CpCo(dithiolene) complexes: Isostructural or non-isostructural couples of CpCo(III) with CpNi(III) dithiolene complexes

Eight new sulfur-rich [CpCo(dithiolene)] complexes were synthesized from [Zn(dmit)₂]²⁻ as a starting material. The structures, electrochemical behavior and electronic absorption spectra of the sulfur-rich [CpCo(S₂C₂S₂Y)] complexes could be compared with the early data of analogous Ni complexes. [CpCo(pddt)] (Y = -(CH₂)₃-), [CpCo(dpdt)] (Y = -CH₂C(CH₂)CH₂-), [CpCo(bddt)] (Y = -(CH₂)₄-), [CpCo(dtdt)] (Y = -CH₂SCH₂-) and [CpCo(poddt)] (Y = -CH₂C(O)CH₂-) crystallized in all isostructural with the corresponding paramagnetic [CpNi(dithiolene)] complexes, but [CpCo(dmid)] (Y = CO), [CpCo(dddt)] (Y = -(CH₂)₂-) and [CpCo(F₂pddt)] (Y = -CH₂CF₂CH₂-) crystallized in non-isostructural with them. These molecules are associated with intermolecular short S?S contacts in the crystals. [CpCo(F₂pddt)] did not show any remarkable S?S contacts but indicated interesting fluorine segregation and Cp?Cp face-to-face interactions. Redox potentials of [CpCo(dithiolene)] complexes were obtained with the cyclic voltammetry measurements and dimerized by electrochemical oxidations. Electronic absorption spectra of [CpCo(dithiolene)] complexes showed visible absorption in the range of 585-701 nm as lowest energy wavelengths (? = 9800-11,800 M⁻¹ cm⁻¹) in solutions, and they were higher energy than those of [CpNi(dithiolene)] complexes (near-IR).     

Numerical solutions to the time-dependent Bloch equations revisited

The purpose of this study was to demonstrate a simple and fast method for solving the time-dependent Bloch equations. First, the time-dependent Bloch equations were reduced to a homogeneous linear differential equation, and then a simple equation was derived to solve it using a matrix operation. The validity of this method was investigated by comparing with the analytical solutions in the case of constant radiofrequency irradiation. There was a good agreement between them, indicating the validity of this method. As a further example, this method was applied to the time-dependent Bloch equations in the two-pool exchange model for chemical exchange saturation transfer (CEST) or amide proton transfer (APT) magnetic resonance imaging (MRI), and the Z-spectra and asymmetry spectra were calculated from their solutions. They were also calculated using the fourth/fifth-order Runge-Kutta-Fehlberg (RKF) method for comparison. There was also a good agreement between them, and this method was much faster than the RKF method. In conclusion, this method will be useful for analyzing the complex CEST or APT contrast mechanism and/or investigating the optimal conditions for CEST or APT MRI.     

CO2 absorption of perovskites as seen by positron lifetime spectroscopy

The CO₂ absorption of several ABO₃ type perovskites was studied by positron lifetime spectroscopy. The longer positron lifetime was associated with positrons trapped by A site vacancies. The evaluated positron lifetime data indicated the relative stability of the crystal structure of Sr(Co_0.5Fe_0.5)O_3−δ against Ca doping at low Ca concentrations. Oxygen desorption and CO₂ absorption/desorption could also be followed by positron lifetime spectroscopy. It was shown that the concentration of oxygen vacancies has a large effect on positron lifetime data through the electron density of A site vacancies.