The coulometric titration of tetraphenylborate ion with electrogenerated silver ion and a biamperometric end-point : Application to the determination of potassium and polyethyleneglycols

Microequivalent amounts of TPB in a 40% acetone generating electrolyte were titrated with coulometrically generated silver ions. With a biamperometric endpoint, samples of 0.1–4 μeq of NaTPB were determined with a precision with 1%. The technique was applied to the determination of potassium in potassium chloride alone and in mixtures with other salts.The overall accuracy ranged from -3 to -7% for samples of 4 μeq to 1 μeq of potassium, respectively. Artificial serum samples gave somewhat discordant results, because of difficulty in removing all interfering protein. A method was developed, for the determination of 0.1–1.0 mg of PEG 600 to 4000 with excess TPB in the presence of barium ions. With reasonable care errors may be held to within 5%.     

Studies of intrinsic luminescence in KCl

Measurements have been made of the luminescence intensity, lifetime, emission spectra, and thermoluminescence associated with self-trapped exciton states in KCl, at temperatures of 7°K and above. These results indicate the presence of another exciton-like state in addition to the well-known state that decays by emission at 2.32 eV. Thermoluminescence glow peaks and spectra are correlated with F + V_k and F + H recombination processes.     

A Bichromatic Incidence Bound and an Application

We prove a new, tight upper bound on the number of incidences between points and hyperplanes in Euclidean d-space. Given n points, of which k are colored red, there are O _d (m ^2/3 k ^2/3 n ^(d−2)/3+kn ^d−2+m) incidences between the k red points and m hyperplanes spanned by all n points provided that m=Ω(n ^d−2). For the monochromatic case k=n, this was proved by Agarwal and Aronov (Discrete Comput. Geom. 7(4):359–369, 1992).     

On the nucleation of cementite on bainitic ferrite–austenite interphase boundaries

Among all possible variants of the Isaichev orientation relationship between cementite and ferrite, a single major cementite variant has been observed to appear in bainite. Interphase boundary nucleation of cementite on ferrite–austenite semi-coherent interfaces is considered a plausible reason for this observation. With the aid of known crystallographic relations and habit planes of the ferrite–cementite, ferrite–austenite and austenite–cementite phases, a model for cementite nucleation has been proposed. The interphase-boundary nucleus is assumed to form on a semi-coherent ferrite–austenite interface and to possess ferrite–cementite and austenite–cementite habits as two main facets of the nucleus. It is shown that interphase cementite nucleation will be viable if the energies of all facets of the nucleus are in the semi-coherent range.     

Reactions of CFBr studied by laser-induced fluorescence

Laser-induced fluorescence has been used to study reactions of CFBr radicals in a discharge-flow system. Arrhenius expressions of (1.9 ± 0.6) ξ 10^?12 exp(?762± 92/T) and (1.4 ± 0.3) ξ 10^?12 exp(?533 ± 62/T) cm³ molecule ^?1s^?1 for their reactions with Cl₂ and Br₂ respectively. Upper limits were obtained for the rate of reaction of CFBr with O₂ and F₂CCFBr.     

The palladium electrode in aqueous and nonaqueous titrimetry

Two modifications of the palladium-hydrogen electrode of Schwing and Rogers have been made and tested. A new form of “generation” electrode with a vertical palladium diaphragm and fast constant speed circulation has been devised. This form of electrode responds rapidly and has been used in a variety of acid-base titrations in aqueous and nonaqueous systems.     

Defect dynamics observed by NMR of quadrupolar nuclei in gallium nitride

Hexagonal and cubic polytypes of bulk gallium nitride powders are characterized by 69,71Ga and 14N MAS NMR at 11.7 T. The (corrected) 71Ga chemical shifts are 333.0 and 357.5 ppm, respectively; the corresponding 14N chemical shifts are -301.8 and -297.0 ppm (all shifts referenced to 1 M gallium nitrate). The 69,71Ga nuclear quadrupole coupling constants (NQCC) in the hexagonal form are axially symmetric and agree with previous single-crystal determinations. The 71Ga MAS NMR satellite pattern envelope of the cubic form has a large Gaussian half-height width of 297 kHz, due to nonzero NQCC values induced by defects. The 14N MAS NMR spinning sideband pattern of the cubic form has a Lorentzian envelope half-height width of 17.5 kHz for the same reason. A sample containing both phases shows an unexpected marked loss of the 71Ga MAS NMR satellite transition intensity expected for the hexagonal phase. Static 71Ga-selective Hahn spin-echo measurements at the perpendicular edge of the powder pattern for the hexagonal form in this sample show a large reduction in T2, especially at higher temperatures. The partial destruction of both spin-echoes and rotational echoes is due to a chemical-exchange type process involving sites having different NQCC values.     

The effect of carbonization heating rate on charcoal and active carbon yields

Amperometric glucose sensors have been assembled by immobilizing glucose oxidase on Nucleopore polycarbonate membranes via glutaraldehyde crosslinking. To eliminate electrochemical interferences, novel blocking membranes were used that are permeable to hydrogen peroxide, making them interference free, highly stable, reproducible, and with extended linearity for glucose up to 50 mM. Author to whom all correspondence and reprint requests should be addressed.