Far infrared studies of the formation of potassium fluoride dihydrate in and its interaction with low molecular weight polytetrafluorethylene

The process of preparing low molecular weight polytetrafluorethylene by high temperature oxidation with potassium nitrate has been shown to lead to the formation of potassium fluoride in the polymer. This is found to absorb water vapour from the atmosphere forming its dihydrate KF.2H₂O, a crystalline substance which shows a complex many line spectrum in the far infrared. The observed spectrum of KF.2H₂O in the matrix differs in one major respect (the absence of a band at 73 cm^–1) from that of pure KF.2H₂O showing that there is some specific interaction between the dihydrate and its polymeric host.     

Definierter Einbau und optische Absorption von O 2 − - und O−−-Zentren in KCl-Kristallen

A method is described how to grow single crystals of potassium chloride with high concentrations of O ₂ ^? by strictly excluding spurious amounts of water, which would react to OH^?. Reducing treatment with F-centers transforms O ₂ ^? quantitatively into O^?? and anion vacancies. For both oxygen centers the absorption spectra in the UV contain several bands. All the O^??-bands can be interpreted as electron transfer from O^?? to the surrounding K⁺-ions considering different excited states of the potassium atom. Another band is due to the α-centers. Photochemical reaction at 20 °C yields F-centers and O^?-centers. The concentration of the O^??-centers (and of the original O ₂ ^? -centers) can be determined from the produced F-band.     

A Sensitive Fluorimetric Method for the Determination of Epinephrine

A sensitive fluorimetric method for the determination of epinephrine (E) is described in this paper. The experiments indicate that epinephrine can react with formaldehyde (HCHO) in an acid medium to form a condensation product, which can be oxidized by potassium hexacyanoferrate(III) (K₃[Fe(CN)₆]) in borax buffer (pH = 9.5). The reaction product can emit strong fluorescence. Ascorbic acid (AA) is used in order to consume excess potassium hexacyanoferrate and stabilize the fluorescent product. Under optimum conditions, a linear relationship has been obtained between the fluorescence intensity and the concentration of epinephrine in the range of 1.4×10^–9–2.1×10^–6 mol/l, and the detection limit is 2.4×10^–10 mol/l (4.3×10^–11 g/ml, S/N = 3). The method is applied for the determination of E in both actual sample and the synthetic sample with E and norepinephrine (NE) by using the coupling technique of synchronous fluorimetry and H-point standard addition method, and the results obtained are satisfactory.     

Na<Superscript>+</Superscript>/K<Superscript>+</Superscript> selectivity in the formation of ion pairs in aqueous solutions

The integral equations of liquids (RISM) and molecular dynamics method were used to calculate the mean force potential for the SO₃ and COO hydrophilic groups and the CH₃ hydrophobic group in the acetate, methyl sulfonate, and hydrosulfate anions, which form ion pairs with sodium and potassium cations in water. The carboxyl group selectively binds sodium ions from solutions containing Na⁺ and K⁺ ions, in spite of their equal charges, because the potassium ion experiences stronger steric hindrances near this group compared with sodium. The biophysical consequences of the revealed selectivity are discussed.     

Potassium and potassium oxide monolayers on the platinum (111) and stepped (755) crystal surfaces: A LEED,AES, and TDS study

The adsorption of potassium and the coadsorption of potassium and oxygen on the Pt(111) and stepped Pt(755) crystal surfaces were studied by AES, LEED, and TDS. Pure potassium adlayers were found by LEED to be hexagonally ordered on Pt(111) at coverages of θ = _K0.9–;1. The monolayer coverage was 5.4 × 10¹⁴K atoms/cm² (0.36 times the atomic density of the Pt(111) surface). Orientational reordering of the adlayers, similar to the behavior of noble gas phase transitions on metals, was observed. The heat of desorption of K decreased, due to depolarization effects, from 60 kcal/mole at θ_K <0.1, to 25 kcal/mole at θ_K = 1 on both Pt(111) and Pt(755). Exposure to oxygen thermally stabilizes a potassium monolayer, increasing the heat of desorption from 25 to 50 kcal/mole. Both potassium and oxygen were found to desorb simultaneously indicating strong interactions in the adsorbed overlayer. LEED results on Pt(111) further indicate that a planar K₂O layer may be formed by annealing coadsorbed potassium and oxygen to 750 K.     

Reductive conversion of hexavalent chromium in the preparation of ultra-fine chromia powder

By reducing potassium chromate with hydrogen and then calcining the obtained intermediate at high temperature, the ultra-fine chromia (Cr₂O₃) powder with a mean diameter of 0.3 μm was successfully prepared. Using scanning electron microscopy (SEM) and XRD, the chromia products were characterized. Through XPS, TG-DSC, FT-IR, XRD and chemical analysis, the reaction mechanism was explored. The results revealed that, the intermediate from reducing potassium chromate with hydrogen consists of Cr(OH)₃·nH₂O, CrOOH, KCrO₂ but the composition of the intermediate changes with the reduction temperature and time. Typically, the potassium content in the intermediate ranges approximately from 0.7% to 8% by weight and the chromium content from 50% to 57% by weight. It was also found that, just by calcining the intermediate in the presence of oxygen can the potassium in the intermediate be completely removed from the final chromia product.     

Bimodal dependence of light scattering/fluctuations on the concentration of aqueous solutions

Two concentration ranges (from 10^?5 to 10^?9 and from 10^?13 to 10^?18 M) corresponding to enhanced fluctuations of Rayleigh and Raman scattering of second-harmonic (527 nm) pulses of YVO₄:Nd³⁺ laser are found for aqueous solutions of antioxidant potassium phenosan. A correlation is revealed between the rise in elastic Rayleigh scattering intensity and its fluctuations and the shift of the center of OH Raman band of water toward the ice component characteristic frequency (3200 cm^?1). The development of phase-equilibrium instabilities is analyzed based on the model of fluctuations of the number of hydrogen bonds on the assumption of formation/destruction of ordered hydration layer of phenosan molecules in water.     

Rapid anisotropic diffusion of lithium in electrochromic thin films based on the hexagonal tungsten bronze structure

The chemical diffusion coefficient of lithium in oxidized potassium hexatungstate and reduced hexagonal potassium tungsten bronze films was measured by the galvanostatic transient method. Two-dimensional anisotropic diffusion was found in the hexagonal hexatungstates, while no appreciable anisotropy was observed in samples with the potassium hexagonal tungsten bronze structure. The chemical diffusion coefficients along the c-axis in thin films of the tungstates K_0.33WO_3.165 and K_0.3WO_3.15 (about 6000 Å thick) are about 10^?10 cm²/s, while those along the a-axis are about 10^?7 cm²/s. This latter value is about the same to those measured in a potassium hexagonal tungsten bronze single crystal of composition K_0.28WO₃ which was grown electrochemically. It is most likely that the presence of the additional oxygen atoms in the tunnels within the hexatungstate structure is responsible for the large decrease in the rate of motion of lithium along the c-axis that leads to the anisotropy in the macroscopic diffusion coefficient in this crystal structure.     

Experimental study of the energy dependence of the reaction rate coefficients of the reaction CH 3 + with N2O and NH3

The kinetics of the reaction of CH ₃ ⁺ ions with N₂O and NH₃ has been investigated in He and Ar buffers using Selected Ion Flow Drift Tube technique (SIFDT). Both studied reactions proceed with nearly collisional rate at near thermal energies. The rate coefficient of the reaction of CH ₃ ⁺ with N₂O is decreasing more than one order of magnitude (from 1.2×10^?9cm³s^?1 up to 8×10^?11cm³s^?1) with reactant ion/reactant neutral average centre-of-mass kinetic energy (E _r) increasing from near thermal up to 2 eV. The dominant product of this reaction is the isomer HCO⁺ (≥94%) and the minor product is CH₃O⁺. The reaction of CH ₃ ⁺ with NH₃ has two binary channels with the dominant product ion CH₂NH ₂ ⁺ (>70%) and the minor product ion NH ₄ ⁺ (≈10%) and three body association channel with product CH₃NH ₃ ⁺ (≈20% at 0.32 Torr). The rate coefficient of this reaction is decreasing nearly by one order of magnitude with increasingE _r from near thermal up to 0.8eV, forE _r>0.8 eV the rate coefficient increases with increasingE _r. The experimental results are interpreted in terms of a simple model assuming the reactions to proceed via the formation of long-lived collision complexes.     

Gas-phase vibrational spectroscopy and ab initio calculations of Rb(H2O)n and Rb(H2O)nAr cluster ions

The competition between ion–water electrostatic interactions and water–water hydrogen bonding in cluster ions depends on several factors, including charge density of the ion and temperature of the system. Infrared photodissociation spectra of Rb⁺(H₂O)_n=2–5 and Rb⁺(H₂O)_n=1–5Ar are presented here and compared to previous experiments involving potassium and cesium. The temperature, or internal energy, of hydrated rubidium cluster ions is controlled by varying the evaporative path available for cluster formation. Warmer clusters (with effective temperatures of 250–500 K) are formed by the evaporation of water, while colder clusters (40–120 K) can be formed by argon evaporation. Colder cluster ions tend to favor conformers with more hydrogen bonds compared to those cluster ions at warmer temperatures. Previous work from this laboratory has shown significant and dramatic differences between the spectra of hydrated potassium and cesium ions. With a charge density intermediate between that of K⁺ and Cs⁺, Rb⁺ plays an important role in bridging the gap in our previous studies.     

Framework and extra-framework aluminium in wet ion exchanged Fe-ZSM5 and the effect of steam during the decomposition of N2O

The role of extra-framework and framework aluminium in wet-ion exchanged Fe-ZSM5 has been studied using ²⁹Si NMR and ²⁷Al triple quantum magic angle spinning (3QMAS) NMR. A series of samples were studied, the parent material, the wet ion exchanged Fe-ZSM5 and Fe-ZSM5 that has been used in the decomposition of N₂O with varying reaction conditions. Various framework and extra-framework aluminium species have been identified. It was found that cationic Fe species prefer to replace the Brønsted acid protons in their charge balancing role at those aluminium sites associated with the largest quadrupolar product. The framework aluminium atoms that pertain to the smaller quadrupolar product, which are either charge balanced by extra-framework aluminium or a proton, are much less prone to exchange. In the catalytic decomposition of N₂O it seemed that water present in small amounts enhances the catalytic activity. However, water also decreases the long term stability and performance by dealuminating the zeolite framework. With a high amount of water present, Fe-ZSM5 was destabilised and catalytically inferior.     

In-depth study of the sulfur migration and transformation during hydrothermal carbonization of sewage sludge

This study investigated the effect of temperature on sulfur transformation behavior during the hydrothermal carbonization of raw sludge, water washed sludge and the corresponding filtrate solution at 110–235 °C. The different sulfur species in the various products were determined, primarily focusing on the sulfur species present in the aqueous product. At 110 °C, 31.9% of sulfur migrated to the aqueous product, primarily in the form of sulfone-S and sulfoxide-S. As the temperature increased to 160 °C, the hydrolysis of aliphatic-S and aromatic-S was enhanced, and the former species further transformed to other organic-S or SO₄²-S in the aqueous product. High temperature is beneficial to the formation of sulfate-S and thiophene-S/aromatic-S in the aqueous and hydrochar products, along with the release of H₂S and CH₃SH. This caused a retention of only 29.2% sulfur (i.e., sulfate-S) in the hydrochar at 235 °C, with a large amount of sulfur migrating to the aqueous product (51.1%), followed by the gas product (9.1%). Among all the sulfur species in raw sludge, aliphatic-S was the most thermally unstable. SO₄²-S and sulfur-containing gas were primarily formed from the decomposition of water-insoluble aliphatic-S, while part of thiophene-S/aromatic-S in aqueous products was generated from water-soluble sulfone-S and sulfoxide-S at high temperatures of ≥160 °C. The results indicate that 210 °C is the optimal temperature for preparing of sludge-based fuel during hydrothermal carbonization, and water washing pre-treatment is a good strategy for enhancing the removal of sulfur in hydrochar and reducing the release of sulfur-containing odorous gas.     

Carbon dioxide activation and alkali compound formation. I. Vibrational characterization of oxalate intermediates

The activation of CO₂ in thin potassium layers adsorbed on Cu(1 1 1) has been studied with time-evolved Fourier transform-infrared reflection absorption spectroscopy. The growth of thin layers by reactive evaporation of potassium in a CO₂ atmosphere permits control of the K:CO₂ stoichiometry, which strongly affects the selectivity in the formation of intermediates and the decomposition pathways of the layer. Layers grown in a CO₂ rich atmosphere exhibit the preferential growth of stoichiometric potassium oxalate K₂C₂O₄ (D_2h). The molecular identity of oxalate with D_2h symmetry is confirmed by vibrational spectra utilizing isotopic substitution methods (¹³CO₂ and C¹⁸O₂) and by the use of isotopic mixtures of CO₂/C¹⁸O₂ and CO₂/¹³CO₂. A comparison of the isotope data with theoretical calculations gives an estimated OCO bond angle in oxalate of 132°. Far-IR spectra obtained with synchrotron radiation indicate the equivalent interaction of all oxygen atoms with the potassium. A comparison of the vibrational data with theoretical ab initio calculations confirms the structural model of an oxalate species that is bulk coordinated with no strong directional bonding and all oxygen atoms equally interacting with potassium.At medium and low CO₂:K ratios, very complex vibrational spectra are observed, indicating the formation of an oxalate surface species with C_2v symmetry in addition to D_2h⁻ oxalate, CO₂⁻ and CO₂²⁻ species.     

Mössbauer study of the effect of potassium on iron oxide catalysts

One kind of catalyst used for dehydrogenation of ethylbenzene to styrene was investigated by⁵⁷Fe Mössbauer spectroscopy. The results show that the area ratioS _B /S _A of two Mössbauer subspectra of Fe_3-vO₄ produced after catalytic reaction depends on the amounts of potassium added to the catalysts. A tentative conclusion is that the effect of potassium in iron oxide catalysts could be related to the reduction of Fe³⁺ to Fe²⁺.     

Investigation of the temperature dependence for the spectra of supercooled water in the middle infrared

The temperature dependence of the bending ν₂, combination ν₂ + ν _L , and stretching (ν₁, ν₃, 2ν₂) absorption bands in the infrared spectra of supercooled water with a temperature-change step Δt from 2 to 2.5°C was studied using an advanced infrared Fourier spectrometer. It was found that the frequency of the maximum of the stretching absorption band (2700–3700 cm^?1) decreases with the reduction of the water temperature from ?0.5 to ?5.0°C. The frequency of the maximum of the combination absorption band (2130 cm^?1) increases with the reduction of the water temperature in a range from ?3.0 to ?5.0°C. The frequency of the maximum of the absorption band of bending oscillation (1640 cm^?1) is invariable with a reduction of the water temperature from ?0.5 to ?5.0°C.     

Spectroscopic Parameters of High Overtones of the Vibrations of Molecules

Based on the fundamental equation from the vibration theory of molecules and the operation of direct product of matrices and its properties for eigenvalues and eigenvectors, an equation of overtone vibrations for any high order has been obtained whose solution yields the matrices of vibration modes. Correlations determining changes in the structure parameters, just as expressions for the matrices of the coefficients of kinematic interaction and force constants, and for the parameters of vibrational-rotational interaction have been presented. Using the formulas obtained, the electro-optical parameters of water molecules H₂O and isotopes H₂ ¹⁷O and H₂ ¹⁸O have been calculated for overtones of up to the sixth order within the framework of the semiempirical quantum-chemical CNDO/2 method using the method of numerical differentiation by spline functions.     

Integrated chemical process for exothermic wave synthesis of high luminance YAG:Ce phosphors

In this paper, high-luminance yellow-emitting Y₃Al₅O₁₂:Ce³⁺ phosphor (YAG:Ce) microparticles were prepared in a solid flame using a 1.425Y₂O₃+2.5Al₂O₃+0.15CeO₂+k(KClO₃+urea)+mNH₄F precursor mixture (here k is the number of moles of the KClO₃+urea red-ox mixture, and m is the number of moles of NH₄F). The self-sustaining combustion process for the entire reaction sample was provided by the heat generated from the KClO₃+urea mixture. Parametric studies demonstrated that the maximum temperature in the combustion wave varied from 885 to 1200 °C for k=2.0-3.0 mole and m=0-1.5 mole. X-ray analysis results showed that the product obtained in the solid flame consisted of Y₃Al₅O₁₂:Ce³⁺ and KCl phases. Therefore, after dissolving potassium chloride in distillated water, pure-phase YAG:Ce phosphor powder was obtained. The as-prepared YAG:Ce phosphor particles had diameters of 10-25 μm and good dispersity and exhibited luminescence properties comparable to those of YAG:Ce phosphor powders prepared by conventional high-temperature processing.     

Intermolecular energy transfer from UO2+2 to Eu3+ in solutions

The quenching constants for the UO²⁺₂ ion fluorescence by the Eu³⁺ ion in H₂O, D₂O, potassium formate and acetic acid media were determined by measuring the decrease in intensity of the 5050 Å fluorescence peak and the lifetime of the UO²⁺₂ ion fluorescence. The energy transferred to the Eu³⁺ ion was found to be a small fraction of the energy lost by the UO²⁺₂ ion by the non-radiative processes. The variations of the quenching constants of the UO²⁺₂ ion and the fluorescence lifetimes were determined for different concentrations of potassium formate and acetic acid. These results indicate that the UO²⁺₂ ion forms inner sphere complexes with the two ligands mentioned.     

Growth, microhardness, dielectric and photoconductivity characterization of a highly polarizable NLO material: Sodium p-nitrophenolate dihydrate (NO2-C6H4-ONa.2H2O)

Sodium p-nitrophenolate dihydrate (NPNa.2H₂O) is a highly polarisable non linear optical material. It has a d_eff about 1.45 times than that of potassium titanyl phosphate. Single crystals of (NPNa.2H₂O) have been grown successfully by slow solvent evaporation having water and methanol as solvent. The structure of the crystal is verified by single X-ray analysis. Optical absorption shows that the crystal is highly transparent between 1500 and 300 nm. Microhardness of the crystal is found to increases with increase in load and the hardness number is found to be high for methanol grown crystal as compared to the water grown crystal. Electrical conductivity as evaluated from the cole-cole plot is found to be 1.26 × 10⁻⁵ mho m⁻¹. The dielectric constant of the crystal is low and independent at higher frequencies. The crystal has prominent photoconduction in the presence of trap energy levels formed by the Na⁺ ions. The SHG efficiency of the crystal is studied by performing Kurtz powder test and the results of scanning electron microscope analysis indicate that the major part of the crystal surface is free from inclusion and dislocation.     

Preparation and Sorption Properties of Cadmium Hexacyanocobaltate(III)

The preparation of cadmium hexacyanocobaltate (III), CdHCC, is discussed. The product has been prepared by reacting cadmium nitrate and potassium hexacyanocobaltate (III) in a volume ratio of 2:1. The effect of the monovalent cations, H⁺, Na⁺, K⁺, and NH₄ ⁺ on the percentage retention and of pH on the loading capacity of CdHCC for cesium have been investigated. It has been found that the equilibrium behavior and the loading capacity of CdHCC after being soaked overnight in M NaCl are significantly improved. A loading capacities of 10, 30, and 60 g Cs/kg CdHCC have been achieved from simulated PWR waste, MAW and solutions of pH 12, respectively. A comparison of the distribution coefficients for cesium in different media is made.