Specific heat in the NH4NO3-HNO3-H2O system

The specific heat has been measured in this ternary system. A theoretical study has been made of the effects of temperature and of the electrolyte concentrations (NH₄NO₃ and HNO₃) on the specific heat.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 1, pp. 90–91, January, 1985.     

Calculation of Phase Equilibria in the Th(NO3)4-HNO3-H2O System at 25°C

Pitzer's binary parameters of thorium nitrate were calculated from critically selected published data on the water vapor pressure in the Th(NO₃)₄-H₂O system at 25°C. From data on the water vapor pressure in the Th(NO₃)₄-HNO₃-H₂O ternary system, the Pitzer's ternary parameters were calculated at 25°C. The branch of thorium nitrate hexahydrate crystallization in the ternary system was calculated in the region from 0 to 15 m HNO₃ using complete set of Pitzer's binary and ternary parameters. The calculation results coincide with the experimental data on the solubility.     

Chemical etching of (100) GaAs in the (NH4)2Cr2O7-H2SO4-N H4Cl-H2O system

The etching solution containing ammonium dichromate, sulphuric acid and ammonium chloride in water solution allows for the investigation of the influence of individual active components and their concentration on the etching reaction with GaAs. The influence of these agents on etching as well as the temperature and stirring were examined. The etching rate increases with increasing Cl^– ion concentration, increases and subsequently decreases with the increasing of H⁺ ion concentration and remains constant in the wide range of oxidant anion concentration. The effect of stirring on etching rate allows us to estimate regions dominated by diffusion kinetics. The activation energy in the wide range of parameters is constant and equal to 60 kJ mol^–1. Microscopic observations reveal surfaces of various morphologies: smooth; covered with round hills; or with a network of veins. Various profiles of grooves arranged in various directions are revealed due to the preferential characteristic of etching; these profiles are also influenced by the mask material.     

Synthesis and structural study of new potassium uranyl selenates K2(H5O2)(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)4 and K3(H3O)[(UO2)2(SeO4)4(H2O)2](H2O)5

Single crystals of new uranyl selenates K₂(H₅O₂)(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₄ (1) and K₃(H₃O)[(UO₂)₂(SeO₄)₄(H₂O)₂](H₂O)₅ (2) were prepared by isothermal evaporation at room temperature. The crystal structure of 1 was solved by the direct method [C2/c, a = 17.879(5), b = 8.152(5), c = 17.872(5) Å, β = 96.943(5)°, V = 2585.7(19) ų, Z = 4] and refined to R ₁ = 0.0449 (wR ₂ = 0.0952) for 2600 reflections with |F _o| ≥ 4σ _F . The structure of 2 was solved by the direct method [P2₁/c, a = 17.8377(5), b = 8.1478(5), c = 23.696(1) Å, β = 131.622(2)°, V = 2574.5(2) ų, Z = 4] and refined to R ₁ = 0.0516 (wR ₂ = 0.1233) for 4075 reflections with |F _o| ≥ 4σ _F . The structures of 1 and 2 are based on [(UO₂)₂(SeO₄)₄(H₂O)₂]^4? layers. The charge of the inorganic layer is compensated by potassium and oxonium ions arranged in the interlayer space. Each K ion is surrounded by seven O atoms belonging to uranyl selenate layers and water molecules, so that it binds with each other the adjacent uranyl selenate structural elements.     

Specific Features of Anodic Dissolution of Copper in H2SO4 + H2O and H2SO4 + CuSO4 + H2O Systems

We investigate anodic dissolution of copper in H₂SO₄ + H₂O and H₂SO₄ + H₂O + CuSO₄ systems, which model solutions for the electrochemical production of copper (+2) sulfate. Ultimate densities of anodic current in the temperature range 20–80°C for a voltage up to 8 V were found. We show that a concentration of copper ions ( Cu²⁺) of 1.5–2.0 moles/liter in the anolyte is the limiting one in the electrochemical production of solutions of copper (+2) sulfate.     

Sellmeier Coefficients for the Birefringence and Refractive Indices of ZnGeP(2) Nonlinear Crystal at Different Temperatures

Birefringence (B(f)), refractive indices, and their temperature derivatives (dB(f)/dT) determine the temperature characteristics of nonlinear-optical laser devices. The birefringences at different temperatures are analyzed critically by use of a new physically meaningful Sellmeier equation for what is to the author's knowledge the first time the birefringences at different operating temperature from 14 to 500 K and wavelength for ZnGeP(2) nonlinear crystal have been found. This equation is based on the average electronic absorption gap in the UV region and the lattice absorption gap at the IR region. In this model the fitting accuracy is better than the experimental accuracy of ?0.0001 at different temperatures. The refractive indices are estimated at different temperatures from the room-temperature values, the thermo-optic coefficients, and the smoothed values of birefringence. The Sellmeier coefficients for refractive indices that are used to characterize the currently available nonlinear-optical devices satisfactorily are then evaluated. These optical constants are essential in characterizing the parametric short-pulse generation in the mid-IR region.     

Dielectric properties of K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3

Dielectric constant (ɛ), dielectric loss (tan δ) and conductivity (σ) for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ have been measured over the frequency range 100 Hz — 100 kHz and in temperature range 30°C — 400°C. The values of static dielectric constant at room temperature are 7.67 and 4.80 for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ respectively. The plots of log σ against reciprocal temperature at different frequencies of these samples merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0.67 eV and 1.98 eV for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ respectively.     

Geometric isomerism of layered complexes of uranyl selenates: Synthesis and structure of (H3O)[C5H14N]2[(UO2)3(SeO4)4(HSeO4)(H2O)] and (H3O)[C5H14N]2[(UO2)3(SeO4)4(HSeO4)(H2O)](H2O)

New uranyl selenates with organic cations (H₃O)[C₅H₁₄N]₂[(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)] (I) and (H₃O)[C₅H₁₄N]₂[(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)](H₂O) (II) were synthesized by evaporation of aqueous solutions and studied. Compound I has monoclinic symmetry, space group C2/c, a = 16.7572(13), b = 11.7239(12), c = 19.0490(13) Å, β = 98.875(6)°, V = 3697.6(5) ų, Z = 4. The crystal structure was solved by the direct method and refined to R ₁ = 0.085 for 2868 reflections with |F _hkl | ≥ 4σ|F _hkl |. Compound II has monoclinic symmetry, space group P2₁/n, a = 10.8252(10), b = 19.0007(10), c = 18.6463(15) Å, β = 100.324(7)°, V = 3773.2(5) ų, Z = 4. The crystal structure was solved by the direct method and refined to R ₁ = 0.084 for 5721 reflections with |F _hkl | ≥ 4σ|F _khl |. The structures of I and II are based on layered complexes [(UO₂)₃(SeO₄)₄(HSeO₄)(H₂O)]^3? formed by combination of uranyl pentagonal bipyramids and selenate tetrahedra. H₃O⁺ cations, water molecules, and protonated methylbutylamine cations are located in the interlayer space. Geometric isomerism of two-dimensional complexes [(UO₂)₃(SeO₄)₅(H₂O)] in the structures of uranyl selenates was found and described.     

Solid solutions between ettringite, Ca6Al2(SO4)3(OH)12·26H2O, and thaumasite, Ca3SiSO4CO3(OH)6·12H2O

A series of solid solution phases between ettringite, Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O, and thaumasite, Ca₃SiSO₄CO₃(OH)₆·12H₂O, have been prepared and analysed by X-ray powder diffraction and full pattern fitting. Solid solutions were shown to exist with both the ettringite structure (space group P31c) and the thaumasite structure (space group P6₃, c-axis halved). A possible discontinuity was identified, characterised by a gap in the a-dimension of the solid solution phases produced. This discontinuity is believed to correspond to a switch between the ettringite space group and the thaumasite space group. It is suggested that any discontinuity in the solid solution is caused by differences in the hydrogen bonding of the two structures.     

DC electrical conductivity of CoSiF6·6H2O and (NH4)2SO4

D.C. electrical conductivity of single crystals of (NH₄)₂SO₄ and CoSiF₆·6H₂O have shown conductivity jump near their respective structural transition temperature. Activation energy of (NH₄)₂SO₄ has been found to be consistent with the earlier data. However, CoSiF₆·6H₂O has given prolonged aging effect due to dipolar relaxation and formation of space charge polarisation.σ _true andP _max have been measured.P _max has shown a negative maximum at the transition point. Activation energy of ZnSiF₆·6H₂O has been found to be comparable with CoSiF₆·6H₂O.     

Role of U(VI) complexes in the chemiluminescent reaction U(IV) + O3 in H2SO4 solution

Data on the effect of U(VI) on the reaction U(IV) + O₃ in H₂SO₄ solution are analyzed. The chemiluminescence enhancement is caused by the formation of a complex of an excited U(VI) ion with an unexcited U(VI) ion, so-called excimer. The decomposition of the excimer to two U(V) ions and H₂O₂ is followed by the reaction of U(V) with ozone, giving rise to the excited U(VI) ion. Thus, a chain reaction develops.     

Dumbbell-like PtPd-Fe(3)O(4) Nanoparticles for Enhanced Electrochemical Detection of H(2)O(2)

Dumbbell-like Pt(x)Pd(100-x)-Fe(3)O(4) nanoparticles (NPs) were synthesized and studied for electrocatalytic reduction and sensing of H(2)O(2). In 0.1 M phosphate buffered saline (PBS) solution, the 4-10 nm Pt(x)Pd(100-x)-Fe(3)O(4) NPs showed the Pt/Pd composition-dependent catalysis with Pt(48)Pd(52)-Fe(3)O(4) NPs having the best activity. The Pt(48)Pd(52)-Fe(3)O(4) NPs were tested for H(2)O(2) detection, and their H(2)O(2) detection limit reached 5 nM, which was suitable for monitoring H(2)O(2) generated from Raw 264.7 cells. These dumbbell-like PtPd-Fe(3)O(4) NPs are the most sensitive probe ever reported and can be used to achieve real-time quantitative detection of H(2)O(2) in biological environment for biological and biomedical applications.     

Simulation Experiments on On-Line Isolation of Element 106 (Seaborgium,Sg) and Study of Its Chemistry in H2SO4 and H2SO4/HF Solutions

Model experiments with W and Mo were performed to simulate on-line ion-exchange isolation of element 106 (seaborgium, Sg) from H₂SO₄ and H₂SO₄/HF solutions. Short-lived isotopes of W and Mo were prepared by Sm(²⁴ xMg,xn)W nuclear reaction performed on a U-400 cyclotron. Molybdenum isotopes were prepared on an MT-25 microtron (Flerov Laboratory of Nuclear Reactions, JINR, Dubna) by fission of ²³⁵U with photoneutrons. The feasibility of isolation and chemical study of ²⁶⁵Sg in the course of its preparation and of identification of this radionuclide by long-lived daughter product, ²⁵³Fm, was demonstrated. The correlation of ion-exchange properties of W, Hf, Sr, and REE (TPE) under static and on-line conditions was revealed.     

Behavior of Np(V) in HCOOH Solutions Containing H2O and HClO4

Radiochemistry - Spectrophotometry has been used to examine the kinetics of Np(V) disproportionation in HCOOH solutions containing H2O and HClO4 at temperatures of 20–45°C. The reaction...     

Separation of H(2)SO(4) + CuSO(4) mixture by diffusion dialysis

Diffusion dialysis of aqueous solution of H(2)SO(4) + CuSO(4) has been investigated in a two-compartment cell with an anion-exchange membrane Neosepta-AFN. The experiments have proved that sulfuric acid permeates well through the membrane used, while cupric sulfate is efficiently rejected. This operation is very effective at high acid concentrations and low concentrations of cupric sulfate. Furthermore, it has been found that even at the highest concentration of CuSO(4), the rejection coefficient is higher than 0.965. The flux of CuSO(4) calculated from the time dependences of the CuSO(4) concentration is negatively influenced by increasing acid concentration.     

Magnetic behavior of Mn(NH4)2(SO4)2 · 6H2O in its Curie region in fields directed along theb-axis

The intensity of magnetization and the isentropic magnetic susceptibility of Mn(NH₄)₂(SO₄)₂ · 6H₂O have been determined along 13 isentropes (between 0.620 and 2.825 cal mole^–1 deg^–1) in fields up to 1670 Oe directed along theb-axis of a spherical single crystal. Eleven of the isentropes originated, in zero field, within the Curie region of the salt. Field increments of 10 to 15 Oe were used below 170 Oe, with larger steps above this. All isentropes originating within the Curie region show a common (high) susceptibility at zero field. In each case the susceptibility then drops sharply at a small field characteristic of the particular entropy. The drop in susceptibility was used to define the boundaries of the Curie region (critical fieldvs entropy). The change of temperature with magnetic field was determined along the isentropes and examples are given.