Crystalline Nitrate Research Articles

MOLECULAR RELAXATION IN BINARY SYSTEMS NaNO3 – NaNO2, KNO3 – KNO2

In the present study, the molecular relaxation processes in crystalline sodium nitrate NaNO3, crystalline sodium nitrite NaNO2, crystalline potassium nitrate KNO3, crystalline potassium nitrite KNO2, and in solid binary salt systems sodium nitrate – sodium nitrite NaNO3 – NaNO2 and potassium nitrate - potassium nitrite KNO3 – KNO2 were studied with the Raman spectroscopic methods. We have found that the relaxation time of the fully symmetric vibration of n1 (A) of the molecular nitrate anion NO3– in the solid binary salt systems “nitrate – nitrite” NaNO3 – NaNO2 or KNO3 – KNO2 is lower than in the individual crystalline nitrate NaNO3 or KNO3, respectively. It is shown that the increase in the rate of intramolecular relaxation is explained by the presence in the binary system of an additional relaxation mechanism of the vibrationally excited states of the nitrate ion NO3–. This relaxation mechanism of the nitrate ion NO3– in a binary system is associated with the excitation of a lower-frequency vibration of another anion (nitrite ion NO2–) and the "birth" of a lattice vibration (phonon). The frequency of this phonon is equal to the difference in the vibration frequencies of the nitrate ion NO3– and nitrite ion NO2–. It is established that the condition for the realization of such a relaxation mechanism is that the difference in the frequency of these oscillations of the nitrate ion NO3– and nitrite ion NO2– must correspond to the region of a sufficiently high density of states of the phonon spectrum of the solid binary salt system under study. The maximum frequency of the phonon spectrum of the system is determined by its Debye temperature. For ionic salt systems, the Debye temperature is always higher than 200 K, and often more than 300 K. Therefore, in the solid binary salt systems, the proposed relaxation mechanism is almost always relevant.Forcitation:Aliev A.R., Akhmedov I.R., Kakagasanov M.G., Aliev Z.A., Amirov A.M. Molecular relaxation in the binary systems NaNO3 – NaNO2, KNO3 – KNO2. Izv. Vyssh.Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 23-30

Thermodynamic properties of calcium-ammonium nitrate decahydrate

Abstract The functions of formation at T = 298.15 K of calcium-ammonium nitrate decahydrate, 5Ca(NO3)2·NH4NO3·10H2O, have been computed on the basis of experimental results obtained in this work. Single-phase crystalline calcium-ammonium nitrate decahydrate has been synthesized and checked by chemical analysis, thermogravimetry, differential scanning calorimetry, powder X-ray diffraction, and infrared spectroscopy. The enthalpy of dissolution of the decahydrate in water at T = 298.15 K was measured in a sealed swinging calorimeter with an isothermal jacked. The low-temperature heat capacity of the solid has been measured by vacuum adiabatic calorimetry in the temperature range (7 to 338) K. The temperature, enthalpy, and entropy of fusion of the crystalline hydrate have been determined via differential scanning calorimetry at high pressure. A second-order solid-solid transition for the substance in the temperature range (300 to 330) K has been detected by methods of adiabatic calorimetry and differential scanning calorimetry.

An ab initio study of the vibrational properties of alkaline-earth metal nitrates and their crystallohydrates

The vibrational frequencies and corresponding intensities have been calculated ab initio for the center of the Brillouin zone of crystalline magnesium, calcium, strontium, and barium nitrates; magnesium nitrate hexahydrate; and calcium nitrate tetrahydrate. The calculation has been performed within the electron- density functional theory using the PBE exchange-correlation functional in the basis of localized atomic orbitals with the aid of the CRYSTAL14 software. The calculated values and the experimental IR and Raman spectral data on strontium and barium nitrates are shown to be in satisfactory agreement. The frequencies of normal long-wavelength vibrations in the nitrates become red-shifted with an increase in the cation atomic mass. The occurrence of several peaks due to the vibrations of hydrogen atoms in water molecules with different dynamic charges is predicted in the IR spectrum of hexahydrate magnesium in the frequency range above 3430 cm–1.

Structure and electronic properties of MNO3 (M: Li, Na, K, NH4) under pressure: DFT-D study

The structural and electronic properties of crystalline nitrates have been investigated within the framework of density functional theory including van der Waals interactions. Pressure behavior of nitrates has been investigated using semiempirical dispersion correction scheme DFT-D. The optimizations of the crystal structures have been done with full relaxation of the atomic positions and lattice parameters under the experimentally determined crystal symmetries. The pressure dependences of geometrical parameters, band gaps, densities of states, charge distributions, overlap populations and atomic charges are computed. The predicted results agree well with the available experimental data.

Ab initio study on optical properties of glycine sodium nitrate: a novel semiorganic nonlinear optical crystal

The electronic structure, and linear and nonlinear optical susceptibilities of crystalline glycine-sodium nitrate (GSN) has been studied using the full potential linear augmented plane wave method within density-functional theory.

ChemInform Abstract: Understanding Automotive Exhaust Catalysts Using a Surface Science Approach: Model NOx Storage Materials

AbstractReview: 56 refs.

Understanding Automotive Exhaust Catalysts Using a Surface Science Approach: Model NOx Storage Materials

The structure–reactivity relationships of model BaO-based NOx storage/reduction catalysts were investigated under well controlled experimental conditions using surface science analysis techniques. The reactivity of BaO toward NO2, CO2, and H2O was studied as a function of BaO layer thickness [0 < θBaO < 30 monolayer (ML)], sample temperature, reactant partial pressure, and the nature of the substrate the NOx storage material was deposited onto. Most of the efforts focused on understanding the mechanism of NO2 storage either on pure BaO, or on BaO exposed to CO2 or H2O prior to NO2 exposure. The interaction of NO2 with a pure BaO film results in the initial formation of nitrite/nitrate ion pairs by a cooperative adsorption mechanism predicted by prior theoretical calculations. The nitrites are then further oxidized to nitrates to produce a fully nitrated surface. The mechanism of NO2 uptake on thin BaO films (<4 ML), BaO clusters (<1 ML) and mixed BaO/Al2O3 layers are fundamentally different: in these systems initially nitrites are formed only, and then converted to nitrates at longer NO2 exposure times. These results clarify the contradicting mechanisms presented in prior studies in the literature. After the formation of a nitrate layer the further conversion of the underlying BaO is slow, and strongly depends on both the sample temperature and the NO2 partial pressure. At 300 K sample temperature amorphous Ba(NO3)2 forms that then can be converted to crystalline nitrates at elevated temperatures. The reaction between BaO and H2O is facile, a series of Ba(OH)2 phases form under the temperature and H2O partial pressure regimes studied. Both amorphous and crystalline Ba(OH)2 phases react with NO2, and initially form nitrites only that can be converted to nitrates. The NO2 adsorption capacities of BaO and Ba(OH)2 are identical, i.e., both of these phases can completely be converted to Ba(NO3)2. In contrast, the interaction of CO2 with pure BaO results in the formation of a BaCO3 layer that prevents to complete carbonation of the entire BaO film under the experimental conditions applied in these studies. However, these “carbonated” BaO layers readily react with NO2, and at elevated sample temperature even the carbonate layer is converted to nitrates. The importance of the metal oxide/metal interface in the chemistry on NOx storage-reduction catalysts was studied on BaO(<1 ML)/Pt(111) reverse model catalysts. In comparison to the clean Pt(111), new oxygen adsorption phases were identified on the BaO/Pt(111) surface that can be associated with oxygen atoms strongly adsorbed on Pt atoms at the peripheries of BaO particles. A simple kinetic model developed helped explain the observed thermal desorption results. The role of the oxide/metal interface in the reduction of Ba(NO3)2 was also substantiated in experiments where Ba(NO3)2/O/Pt(111) samples were exposed to CO at elevated sample temperature. The catalytic decomposition of the nitrate phase occurred as soon as metal sites opened up by the removal of interfacial oxygen via CO oxidation from the O/Pt(111) surface. The temperature for catalytic nitrate reduction was found to be significantly lower than the onset temperature of thermal nitrate decomposition.

NO 2 uptake under practically relevant conditions on BaO/Pt(1 1 1)

The formation of nitrites and nitrates (Ba(NO x ) 2) under practically relevant conditions ( P NO 2 up to 1.0 Torr and T = 500 K) and their thermal decomposition on BaO (>20 monolayer equivalent (MLE))/Pt(1 1 1) were studied using temperature programmed desorption (TPD), infrared reflection absorption (IRA), and X-ray photoelectron (XP) spectroscopies. The exposure of BaO to 1.0 × 10 −8 Torr NO 2 at 500 K leads to the formation of a Ba(NO x ) 2 layer with small, disordered crystalline nitrate clusters. Under these conditions ( P NO 2 = 1.0 × 10 − 8 Torr and T = 500 K) only the top portion of the BaO layer converts to Ba(NO x ) 2 and the nitrites in this Ba(NO x ) 2 layer stay without converting completely to nitrates even after 100 min of NO 2 exposure. In the thermal decomposition of Ba(NO x ) 2, first nitrites decompose, releasing NO and then the decomposition of nitrates occurs via two pathways releasing NO 2 and NO + O 2. At 500 K and P NO 2 ≥ 1.0 × 10 − 7 Torr , first NO 2 reacts with BaO to form small disordered crystalline Ba(NO 3) 2 particles and then these particles agglomerate to form large, well-ordered (bulk-like) crystalline nitrates as the NO 2 exposure increases. The thermal decomposition of these well-ordered, bulk-like crystalline nitrate aggregates occurs in two steps releasing NO 2 and NO + O 2 in each step in two different temperature regions. NO 2 pressure ≥1.0 × 10 −5 Torr is required for the complete oxidation of initially formed nitrites to nitrates and the full nitration of the BaO layer at 500 K sample temperature.

Evolution of microstructure during the thermal processing of aluminum-modified titania and aluminum/vanadium co-modified titania gels

Sol-gel materials of aluminum-modified TiO2 of nominal composition 5.7 wt% and 10.8 wt% aluminum and aluminum/vanadium co-modified TiO2 of nominal composition 5.7Al–3.5V wt% have been prepared by evaporation of aqueous colloidal sols obtained by the hydrolysis of aqueous solutions of titanium chloride with the appropriate amount of vanadyl oxalate and/or aqueous aluminum nitrate using aqueous ammonia followed by peptization of the resulting hydrated solids using nitric acid. The nature of the sol-gel materials and the behavior upon calcination at temperatures up to 1373 K have been investigated using x-ray fluorescence, x-ray powder diffraction, transmission electron microscopy, and electron diffraction. At 333 K, all the gels comprise small (approximately 5 ± 1 nm) particles of anatase together with traces of brookite and highly crystalline ammonium nitrate. The particle size changes little on thermal treatment at 573 K, but increases significantly at higher temperatures and is accompanied by transformation to rutile. Aluminum-modified gels stabilize the anatase phase from 923 K in unmodified TiO2 to 1023 K in the 6Al/TiO2 gel and 1173 K in the 11Al/TiO2 gel. The alumina in the co-modified gel has a dominating effect on stabilizing the anatase phase until 973 K. Only rutile is present at high temperatures, except for small amounts of phase-separated α-Al2O3 (Corundum). No substitutional incorporation of Al3+ ions in the tetragonal rutile lattice occurs at high temperatures.

Physicochemical characterization of the decomposition course of hydrated ytterbium nitrate: thermoanalytical studies

Yb(NO 3) 3·6H 2O was used as a parent compound for the formation of Yb 2O 3 at up to 800 °C in atmosphere of air. Thermal processes occurring during the decomposition course were monitored by means of differential thermal analysis (DTA), thermogravimetry (TG), and the gaseous decomposition products were identified by mass spectrometry (GC–MS). The intermediates and final solid products were characterized by IR-spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that, Yb(NO 3) 3·6H 2O decomposes completely through 11 endothermic mass loss processes. The dehydration occurs through the first six steps at 95, 145, 165, 175 and 200 °C, forming crystalline nitrate Yb(NO 3) 3, which decomposes to YbO 0.5(NO 3) 2 at 250 °C. The latter, decomposes to non-stoichiometric unstable intermediate YbO 0.75(NO 3) 1.5 at 335 °C, which decompose immediately to a stable and crystalline YbONO 3 at 365 °C, then to a non-stoichiometric unstable intermediate Yb(O) 1.25(NO 3) 0.5 at 470 °C. Finally, Yb 2O 3 was formed at 510 °C. The decomposition course and surface morphology were supported and followed by SEM and textural studies ( S BET).The final product Yb 2O 3 at 600 °C has a large irregular sheet shaped particles containing a large pores, voids and cracks and has S BET=45 m 2/g. The gaseous decomposition products are water vapor, nitric acid and nitrogen oxides (NO, NO 2 and N 2O 5). The activation energy (Δ E in kJ/mol) was calculated non-isothermally for each thermal processes.

Optical Spectra of the Photolysis Products of Potassium Nitrate

As has been shown in [1], peroxonitrite ion, the peroxide isomer of the nitrate ion, is generated during the photolysis of crystalline potassium nitrate and is an important intermediate in the photolysis of crystalline nitrates [2, 3]. Peroxonitrite [1, 3] and nitrite [4] absorb light in the UV spectral region. To date, information about the absorption spectrum induced in crystalline nitrates by light of λ = 253.7 nm is incomplete and concerns only wavelengths longer than 300 nm [5]. The data on the absorption spectrum of KOONO produced in the photolysis of KNO 3 in an argon matrix by 193nm light [6] are ambiguous, because paramagnetic products absorbing in this spectral range may be generated under these conditions [7]. The objective of this work was to identify absorption bands in photolyzed potassium nitrate crystals. For this purpose, we studied the buildup kinetics for the products of photolysis of crystalline potassium nitrate at 253.7 nm and their photoannealing by spectrophotometry and their thermal annealing by chemical analysis. Potassium nitrate crystals were grown by slow evaporation of saturated aqueous solutions. The triply recrystallized reagent-grade salt was used. Typical crystal size was 1 〈 0.5 cm and their thickness varied from 0.0050 to 0.2000 cm. The concentration of nitrite and peroxonitrite ions was determined after dissolution of the samples as described in [8]. The crystals were irradiated by unfiltered light from a BUV-30 low-pressure mercury lamp at ambient temperature. The photolysis products were photoannealed with light from a DRT-1000 medium-pressure mercury lamp filtered through a BS-4 light filter absorbing light at wavelengths shorter than 300 nm. The light of a DB30 lamp passed through this filter does not cause the annealing of photoinduced optical absorption.

Formation and characterization of samarium oxide generated from different precursors

Sm(NO 3) 3·6H 2O and Sm 2(C 2O 4) 3·10H 2O were used as precursors for the formation of Sm 2O 3. Thermal processes involved in the decomposition course of both salts up to 800 °C in air were monitored by nonisothermal gravimetry and differential thermal analysis. Intermediates and final solid products were characterized by IR-spectroscopy, X-ray diffraction and scanning electron microscopy. The results showed that Sm(NO 3) 3·6H 2O decomposes completely through nine endothermic mass loss processes. The dehydration occurs through the first four steps at 90, 125, 195, and 240 °C, culminating in a crystalline nitrate monohydrate, which subsequently decomposes to Sm(OH)(NO 3) 2 at 355 °C. The latter decomposes rapidly to form a stable and crystalline SmO(NO 3) at 460 °C, through nonstoichoimetric unstable intermediates. Finally Sm 2O 3 forms at 520 °C. For the oxalate, the dehydration occurs in five steps: the anhydrous oxalate is thermally unstable and immediately decomposes to Sm 2O 3 at 645 °C through two unstable intermediates. The crystalline oxide obtained from the nitrate contains larger pores than the oxide obtained from the oxalate, as indicated from scanning electron microscopy (SEM) results.

Radical-Recombination Luminescence of the Uranyl Nitrate Complex in the Adsorbed State

We have investigated the luminescence of uranyl nitrate molecules on the surface of powdery SiO2 upon excitation by UV light (PhL) and hydrogen atoms (radical-recombination luminescence (RRL)). It has been found that the PhL and RRL spectra have a clearly defined vibrational structure. The luminescence peaks of the adsorbed UO2 2− ion are characterized by a systematic longwave shift from the same peaks of crystalline uranyl nitrate (by 230–430 cm−1 at 130 K). Moreover, in the adsorption centers the vibration frequencies of UO2 2− are 20–80 cm smaller than in crystalline salt and the RRL bands are 150–350 cm−1 (130 K) wider than the corresponding PhL bands.

Thermal genesis course and characterization of praseodymium oxide from praseodymium nitrate hydrate

Pr(NO 3) 3·6H 2O was used as a precursor to produce PrO 1.833 at 600°C in an atmosphere of static air. Thermal processes occurred were monitored by means of thermogravimetry, differential thermal analysis and mass spectrometry. IR-spectroscopy and X-ray characterized the intermediates and final solid products. The results showed that, Pr(NO 3) 3·6H 2O decomposes through 11 endothermic weight loss processes. Five dehydration steps occurred at 130, 180, 200, 230 and 250°C, leading to the formation of crystalline nitrate monohydrate, Which decomposes to Pr(NO 3) 2 at 340°C. The latter, decomposes to PrO 1.833 at 465°C, via four different intermediates PrO(NO 3) at 430°C, and nonstoichiometric unstable, PrO 0.25(NO 3) 2.5 at 362°C; Pr(O) 0.5(NO 3) 2 at 382°C and Pr(O) 0.75(NO 3) 1.5 at 400°C. The gaseous decomposition products identified by mass spectroscopy were water vapor and nitrogen oxides (NO, NO 2 and N 2O 5). The activation energy was determined nonisothermally for the thermal processes monitored throughout the decomposition course. The final product PrO 1.833 has a surface area of 46.3 m 2/g.

Thermal genesis course and characterization of lanthanum oxide

La(NO 3) 3·6H 2O was used as a precursor to produce La 2O 3 at 650°C in an atmosphere of air. Thermal processes occurred were monitored by means of thermogravimetry, differential thermal analysis, and gas-mass spectrometry. Infrared (IR)-spectroscopy, X-ray diffractometry and scanning electron microscopy characterized the intermediates and final solid products. The results showed that, La(NO 3) 3·6H 2O decomposes through nine endothermic weight loss processes. Five dehydration steps occurred at 90, 105, 150, 175 and 215°C, leading to the formation of crystalline nitrate monohydrate, which decomposes to La(OH)(NO 3) 2 at 410°C. The latter, decomposes to La 2O 3 at 640°C, via two different intermediates; LaO(NO 3) at 440°C, and non-stoichiometric unstable, La(O) 1.5(NO 3) 0.5 at 570°C. The gaseous decomposition products as identified by gas-mass spectroscopy were water vapor, nitric acid and nitrogen oxides (NO, NO 2 and N 2O 5). The final product La 2O 3 has a large crystalline containing pores, voids and cracks, with a surface area of 23 m 2 g −1. Also it possessed Lewis acidic and basic sites, as indicated by Pyridine adsorption.

Influence of temperature and concentration of water on lanthanum nitrate dissolution and crystallization

The curves of heating and cooling crystalline lanthanum nitrate were registered and numerical differentiation was carried out. The first derivatives of kinetic curves expressed as the temperature function make it possible to carry out comparative studies of dissolution and crystallization. Superposition of relative water concentration scale on the third derivative of heating and cooling curves make the analysis of stoichiometry and mechanism of hydration changes possible in the solid phase and saturated solutions.

Physicochemical characterization of the decomposition course of hydrated holmium nitrate. Thermoanalytical studies

Ho(NO 3) 3·5H 2O (HoNit) was used as a parent compound for the formation of Ho 2O 3 at up to 800°C in atmosphere of air. Thermal processes occurring during the decomposition course were monitored by means of differential thermal analysis (DTA), thermogravimetry (TG) and gas-mass spectroscopy. The intermediates and final solid products were characterized by infrared (IR) spectroscopy, X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that, HoNit decomposes completely through eight endothermic weight losses processes. The dehydration occurs through the first four steps at 120°, 140°, 205° and 240°, forming crystalline nitrate monohydrate, which decomposes to Ho(OH)(NO 3) 2 at 265°C. The latter, decomposes immediately to form a stable and crystalline HoO(NO 3) at 368°C, then to nonstoichiometric unstable intermediates; Ho(O) 1.25(NO 3) 0.5 at 500°C. Finally, Ho 2O 3 was formed at 560°C. The decomposition course and surface morphology were supported and followed by SEM. The final product Ho 2O 3 at 600°C has large crystalline with irregular sheet-shaped particles containing large pores, voids and cracks. The gaseous decomposition products as identified by gas-mass spectroscopy are water vapor, nitric acid and nitrogen oxides (NO, NO 2 and N 2O 5).

Theoretical study of the influence of structure on the vibrational spectra of crystalline nitrates of substituted glucopyranosides

On the basis of a normal coordinate analysis of molecules of 2,3-, 2,6-, 3,6- di- O-nitro-methyl- β-D-glucopyranosides and 2,3,6-tri- O-nitro-methyl- β-D-glucopyranoside, a study has been made of the influence of the nitrogroup location and degree of hydroxyl-group substitution on the complex structure of analytically important nitrogroup vibration bands in the IR spectra of samples of monosaccharide nitrates.

Standard heats of solution of yttrium and rare earth metal nitrate hydrates in water

Heats of solution of yttrium and lanthanoid metal nitrate hydrates (Ln(NO 3) 3· nH 2O: Ln  La-Lu; n = 1–6) in water were measured at 298.15 K. A linear relationship was found between the heats of solution ΔH S and water contents n per mole of nitrate for all the nitrates. When the heats of solution of anhydrous crystalline nitrate are plotted against the reciprocal of the ionic radii of trivalent lanthanoid ions, they tend to decrease from lanthanum to gadolinium and to increase from gadolinium to lutetium, with a few exceptions. The values of the slope of the line ΔH S/ n tend to increase from lanthanum to praseodymium, to be kept at an approximately constant value from praseodymium to thulium, and then to decrease from thulium to lutetium. These results were discussed on the basis of the lattice energy of crystalline nitrates and the hydration structure of trivalent lanthanoid ions in aqueous solution.

Electrical properties near the structural phase transition of crystalline caesium nitrate

Abstract The a.c. conductivities along the c axis of caesium nitrate have been measured in the frequency range from 3 Hz to 100 kHz at temperatures between room temperature and 274·3°C. The a.c. conductivities show a different frequency dependence in the phases II and I. The temperature dependence of the conductivities shows a discontinuous jump, on increasing the temperature, at the structural phase transition point.