Thermally stimulated crystallization of (20−x)LiO2-80TeO2-xWO3 glass system

Tellurite glasses of the (20−x)LiO₂-80TeO₂-xWO₃ system were synthesized (x=0, 5, and 10) and annealed at different temperatures, and the crystallization kinetics was studied using XRD, FTIR spectroscopy, and DSC techniques. XRD data evidenced the amorphous state of as-quenched samples, while thermally treated samples showed the growth of crystalline phases. FTIR spectroscopy was used to observe the evolution of the vibrational mode assigned to the TeO₂ phases. The presence of γ-TeO₂, α-TeO₂, and α-Li₂Te₂O₅ crystalline phases was observed for the sample TL, x=0, while only the first and second phases were observed for TLW5 and TLW10 samples, x=5 and 10, respectively, suggesting that WO₃ enters the structure preferentially as glass former, inhibiting the growth of the phase α-Li₂Te₂O₅.     

Catalytic Etching of Platinoid Gauzes during the Oxidation of Ammonia by Air. Reconstruction of Surface of Platinoid Gauzes at 1133 K in Air,in Ammonia,and in an NH<Subscript>3</Subscript> + O<Subscript>2</Subscript> Reaction Medium

The structure, morphology, and chemical composition of the surface and near-surface layers of platinoid wires of polycrystalline gauzes, containing Pt (81 wt %), Pd (15 wt %), Rh (3.5 wt %), and Ru (0.5 wt %) after treatment at 1133 K in various media—in air, in ammonia, and after NH3 oxidation in air—are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS). A thin film is found on the surface of the initial gauze containing an oxide layer of Rh₂O₃ with a thickness of ~2 nm, on the surface of which an inhomogeneous graphite-like layer 10–50 nm thick is located. It is shown that the heat treatment of gauzes in air leads to the partial removal of the surface graphite-like film that forms the reticulated structure on the wire surface. The treatment of gauzes in an ammonia atmosphere leads to the complete removal of the graphite-like and oxide layers and to the growth of metal grains of ~10 μm. After the catalytic reaction of NH3 oxidation, a deep structural rearrangement of the surface layer of the wire takes place, as a result of which crystalline metal agglomerates of ~10 μm are formed. It is supposed that the reaction of NH3 molecules with oxygen atoms penetrated on the defects leads to the local increase of temperature, due to which the metal atoms emerge on the surface and form large crystalline agglomerates and pores in the region of the grain boundaries.     

The interaction of the theophylline metastable phase with water vapor

The conditions of hydration of the stable and metastable theophylline phases were determined. Two-phase metastable phase/monohydrate and stable phase/monohydrate equilibrium pressures were measured at 25, 30, and 35°C. The metastable phase began to react with water vapor at lower relative humidities than the stable phase. Processes that occurred with the metastable and stable theophylline phases over various water pressure ranges were considered. The metastable phase exhibited an unusual behavior at 25°C and relative humidity 47%. At constant water vapor pressure and temperature, theophylline was initially hydrated and then lost water and again became anhydrous. Two consecutive processes occurred in the system, the formation of theophylline monohydrate from the metastable phase and its decomposition to the stable phase. The ratio between the rates of these processes determined the content of the monohydrate at the given time moment.     

Voltammetric identification of insulin and its analogues using glassy carbon electrodes modified with polyarylenephthalides

Using chemometrics, we developed a voltammetric method for the identification and discrimination of pharmaceuticals containing insulin and its analogues from various manufacturers. Their electrochemical behavior on glassy carbon electrodes modified with polyarylenephthalide films is studied; analytical characteristics are evaluated; and the optimal conditions for recording the analytical signal and the nature of electrode processes are determined. Some examples of the voltammetric identification and recognition of pharmaceutical products containing insulin are given.     

Physicochemical foundations and optical parameters of the granulation process of NPK fertilizers based on ammonium sulfate

Physicochemical foundations of the granulation process of NPK fertilizers were studied. The effect of the composition of the starting components, type and amount of a binder, amount of the recycle, presence of a reinforcing additive in the mixture, temperature, and granulation duration on the yield and strength of the granulate was examined. The optimal parameters of the granulation of NPK fertilizers based on ammonium sulfate were determined.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

The mechanism of formation of light-scattering centers in sapphire crystals grown in gas atmospheres

The mechanism of the formation of light-scattering centers in sapphire crystals grown by horizontal directed crystallization in gas atmospheres reducing with respect to the Al₂O₃ melt was studied. The experimental regularities here significantly differ from those observed upon formation of other conventional defects in sapphire crystals (vacancy pores, gas bubbles, and so on). It is shown that the known formation mechanisms of macroscopic ≥1 mm) inclusions in crystals are not acceptable in this case. Using the model of bulk crystallization is proposed to describe the obtained regularities.