Decomposition Of HNO3 Research Articles

Kinetics and Mechanism of Thermal and Catalytic Decomposition of Hydroxylammonium Nitrate (HAN) Monopropellant

AbstractHydroxylammonium nitrate (HAN) monopropellant with its low sensitivity, volatility and toxicity, not only promises a safer substitute to hydrazine but also offers a higher specific impulse and a positive oxygen balance. This study primarily explores the decomposition mechanism and underlying kinetics for a newly developed cerium oxide‐based catalyst. The chemical kinetics involved in the thermal and catalytic decomposition was examined through an isoconversional method using thermogravimetric analysis (TG) data. The activation energy (Ea) was evaluated using differential isoconversional method (Friedman's method) and advanced integral isoconversional method (Popescu‐Ortega's method). To find frequency factor, compensation effect method (ACE) and intercept method (A0) were used. Advanced integral method could not provide realistic kinetic parameters while differential method predicted values similar to reported values for thermal decomposition. The values obtained for thermal decomposition were found matching with reported values obtained by other techniques which validated the methodology adopted. The reaction mechanism for both thermal and catalytic decomposition were proposed based on evolved gas analysis. The mechanism proposed was able to describe the variable kinetic parameters extracted from isoconversional method. Overall Ea of thermal decomposition of HAN was ∼95 kJ/mol. The decomposition over ceria‐based catalyst was distributed over three stages namely inception, peak and decay with Ea of ∼33 kJ/mol, ∼170 kJ/mol and ∼130 kJ/mol, respectively. Under identical conditions, iridium‐based catalyst show two decomposition stages with Ea of ∼65 kJ/mol and ∼120 kJ/mol while final stage being evaporation of HNO3. The ceria catalyst favoured N2 formation, increased decomposition of HNO3 and enhanced decomposition enthalpy.

Theoretical Study on the Mechanism for the Formation of Nitro Compounds in Red Oil

The mechanisms involved in reactions between methane, n-hexane, n-butanol, cyclohexane, and nitric acid were explored by density functional theory calculations. All the calculations in gas phase and n-tributyl phosphate (TBP) solvent were performed at the B3LYP/6–311++G ∗ ∗ and CCSD(T)/6–311++G ∗ ∗ levels of theory. The results showed that TBP has an important effect on the reactions between nitric acid and alkanes or butanol. The reactions were considered as that the radicals (·NO2 and ·NO3 radicals are formed via the HNO3 decomposition under irradiation) initiate the H-atom depletion of the reactants (R), and the produced radicals in red oil combine with ·NO2 radical to form the nitro compounds spontaneously. The rate constants of reactions R + ·NO2 and R + ·NO3 differ substantially, the rate constants of the latter being much larger than those of the former. In the reactions of R + ·NO3, the transition states and products are 20 kJ/mol and 100 kJ/mol or more stable than the reactants, respectively, but the reactions of R + ·NO2 need to overcome energy barriers over 25 kJ/mol. The formations of products mainly depend on the reactions of R + ·NO3. For the same type of alkanes (either chain or cyclic ones), the lower the relative stabilities of carbon-centered radicals are, the more reactive the alkanes are. Cyclohexane is the most competitive species, followed by n-butanol, n-alkanes, and methane which are the least competitive.

A numerical and experimental study of the decomposition pathways of guanidinium nitrate

The thermal decomposition behaviour of guanidinium nitrate (GN), an energetic material, was analysed using a combined experimental and computational approach. Simultaneous thermogravimetric analysis, Fourier transform infrared spectroscopy and mass spectrometry (TG-FTIR-MS) experiments were carried out at three different heating rates under closed and open crucible conditions. A two-stage decomposition process was observed, and the major gases evolved were found to be NH3, N2O, NO2 and CO2. Quantum mechanics based ab initio computations were performed to evaluate the possible decomposition pathways available for GN. Results indicate that decomposition of GN is not initiated in the condensed phase as the guanidinium cation and the nitrate anion are highly stable. The most likely mechanism involves isomerization of GN followed by a proton transfer in the gas phase to yield nitric acid and guanidine. These products then further react to form nitroguanidine (NQ) and H2O. NQ dissociates via several competing pathways to yield NH3, N2O, H2O and CO2. HNO3 decomposition can help explain NO2 formation. The residue left towards the end of TG can be attributed to dimerization and trimerization reactions of cyanamide.

Thermal dissociation cavity attenuated phase shift spectroscopy for continuous measurement of total peroxy and organic nitrates in the clean atmosphere.

A thermal dissociation cavity attenuated phase shift spectroscopy (TD-CAPS) instrument was developed for measuring total peroxy nitrates (PNs) and organic nitrates (ONs) concentrations in the clean atmosphere. This instrument is easy to operate and can be applied to continuous measurement of PNs and ONs. A continuously measurable system is convenient to perform observations, especially in remote areas. Three lines (NO2, PNs, and ONs lines) were used for thermal dissociation. The NO2 line contains a quartz tube that is not heated, while the PN and ON lines contain quartz tubes that are heated at 433 K and 633 K, respectively. The concentrations of NO2, NO2 + PNs, and NO2 + PNs + ONs can be obtained from the NO2, PN, and ON lines, respectively. The lower limit values of the detection limit (3σ) for PNs and ONs were estimated to be 21 parts per trillion by volume with an integration time of 2 min. PNs were selectively thermally decomposed in the PNs line and formed NO2 quantitatively. In the ONs line, both PNs and ONs were thermally decomposed to produce NO2 quantitatively, but partial decomposition of HNO3 at 633 K interfered with the ONs measurement. Therefore, a HNO3 scrubber is required before the ONs line. Continuous observations were conducted with the TD-CAPS instrument in a remote area, and the instrument performed well for obtaining PNs and ONs concentrations.

Theoretical investigation of the mechanism of nitroxyl decomposition in aqueous solution

Nitroxyl (HNO) is a species that has been proposed recently to play different roles in nitrosative stress processes. HNO decomposition in aqueous solution leading to N2O is a fast reaction that competes with many biochemical reactions in which HNO may be involved. Since molecular determinants of this reaction are still not fully understood, we present in this work an exhaustive analysis of the mechanism in terms of electronic-structure calculations as well as state of the art hybrid quantum mechanics/molecular mechanics molecular dynamics simulations. We characterized the reaction mechanism and computed free energy profiles for the reaction steps using an umbrella sampling procedure. We propose a first dimerization step followed by an acid-base equilibria. Afterwards, the product is formed from two main pathways involving cis-hyponitrous acid (cis-HONNOH) and its conjugate basis as intermediate. Our calculations show preference for the anionic pathway under physiological conditions and allow us to rationalize the results in terms of a molecular description of specific interactions with the solvent. These interactions turn out to be determinant in the stabilization of transition states and, thereby, modifying the free energy barriers. We predict a strong pH-dependence of the overall kinetics of N2O formation, related with the fraction of reactive species available in solution. Finally, we suggest experimental procedures which could validate this mechanism.

Evaluation of sample preparation methods for the determination of As, Cd, Pb, and Se in rice samples by GF AAS

This study presents a comparative evaluation of three different methods for sample preparation in rice for As, Cd, Pb, and Se determination by graphite furnace atomic absorption spectrometry (GF AAS). Raw and cooked white rice, parboiled rice, and brown rice samples were studied with the following procedures: i) HNO3 decomposition in open system with cold finger, ii) HNO3 decomposition in ultrasonic bath, and iii) alkali solubilization with TMAH. The sample preparation using reflux system was optimized and the best conditions were: 750mg of sample, 10mL of HNO3, 120°C (heating), and 90min in the digester block. In rice samples, medium concentrations of 12.0±4.0 and 177.0±64.0ngg−1 for Cd and Pb were found, respectively, while for As and Se, the concentrations were below the limit of detection of the studied methods. After cooking, samples presented a maximum decrease of 61% in Cd concentration. The method validations were assured by analysis of certified reference material (NIST 1568a), and results were in accordance with the certified values. The recovery test was carried out and results ranged between 80 and 115% for all analytes in the rice samples, before and after cooking. All evaluated procedures presented accurate and precise results; however, the decomposition with reflux system proved to be more effective, simple and secure. Such characteristics are necessary for the application in routine analysis with medium detection limits of 77.2; 1.0; 35.5 and 192.1ngg−1 for As, Cd, Pb and Se, respectively.

Studies on supercritical hydrothermal syntheses of uranium and lanthanide oxide particles and their reaction mechanisms

In order to develop preparation method of raw metal oxide particles for low decontaminated MOX fuels by supercritical hydrothermal (SH) treatments, we have investigated behavior of aqueous solutions dissolving U(VI), Ln(III) (Ln: lanthanide = Ce, Pr, Nd, Sm, Tb), Cs(I), and Sr(II) nitrate or chloride compounds under SH conditions (temperature = 400–500 °C, pressure = 30–40 MPa). As a result, it was found that Ln(NO3)3 (Ln = Ce, Pr, Tb) compounds produce LnO2, that Ln(NO3)3 (Ln = Nd, Sm) compounds are hardly converted to their oxides, and that LnCl3 (Ln = Ce, Pr, Nd, Sm, Tb), CsNO3, and Sr(NO3)2 do not form their oxide compounds. Furthermore, HNO2 species were detected in the liquid phase obtained after treating HNO3 aqueous solutions containing Ln(NO3)3 (Ln = Ce, Pr, Tb) under SH conditions, and also NO2 and NO compounds were found to be produced by decomposition of HNO3. From these results, it was proposed that the Ln oxide (LnO2) particles are directly formed with oxidation of Ln(III) to Ln(IV) by HNO3 and HNO2 species in the SH systems. Moreover, the uranyl ions were found to form U3O8 and UO3 depending on the concentration of HNO3. From these results, it is expected that the raw metal oxide particles for low decontaminated MOX fuels are efficiently prepared by the SH method.

Optimum condition to fabricate 5–10 nm SiO2/Si structure using advanced nitric acid oxidation of Si method with Si source

A low temperature (≦120 °C) fabrication method to form relatively thick SiO2/Si structure with a Si source has been developed using the advanced nitric acid oxidation of Si (NAOS) method, and the formation mechanism has been investigated. The reaction mechanism consists of direct oxidation of Si, dissolution of Si sources, and surface reaction of the dissolved Si species. The dissolved Si species is present in HNO3 solutions as mono-silicic acid and reacts with oxidizing species formed by decomposition of HNO3 on an ultrathin SiO2 layer (i.e., 1.4 nm) produced by the direct oxidation of Si substrates with HNO3 solutions. To achieve a uniform thickness of SiO2 layer with a smooth surface, HNO3 solutions with concentrations higher than 60 wt. % are needed because the dissolved Si species polymerizes in HNO3 solutions when the concentration is below 60 wt. %, resulting in the formation of SiO2 particles in HNO3, which are deposited afterwards on the SiO2 layer. In spite of the low temperature formation at 120 °C, the electrical characteristics of the advanced NAOS SiO2 layer formed with 68 wt. % HNO3 and subsequent post-metallization anneal at 250 °C are nearly identical to those of thermal oxide formed at 900 °C.

Magnetic Properties and Interplay between Nanographene Host and Nitric Acid Guest in Nanographene-Based Nanoporous Carbon

Abstract Magnetic properties of nanoporous carbon consisting of a 3D disordered network of nanographite domains are investigated in relation to the host–guest interaction with guest nitric acid molecules possessing significant oxidizability. An individual nanographite domain consists of a stack of 3–4 nanographene sheets, the edges of which have the localized spins of nonbonding edge states. The adsorption of HNO3 induces a two-step reduction in the edge-state spin concentration due to the charge-transfer interaction and is accompanied with the decomposition of HNO3 into the magnetic NO molecules, which are dimerized to form nonmagnetic (NO)2 with an enthalpy of ≈35 kJ mol−1 at low temperatures. The electronic activities of the edge state play an important role in the decomposition effect, and the NO spins are coupled to the edge-state spins through exchange interaction. The NO molecules can be removed by vacuum heat-treatment above 200 °C, however the nitrogen-containing functional groups strongly incorporated on the nanographene sheets cannot be removed even at such high temperature.

Magnetism of HNO3-adsorbed nanoporous network of nanographene sheets

Nonbonding π-electron states (edge-state) localized at the graphene edges are the origin of electronic/chemical activities of nanographene, and the localized spin of this edge state gives unconventional magnetic features to nanographene. The magnetic properties of nanoporous carbon consisting of a 3D disordered network of nanographite domains (each consists of a stack of 3–4 nanographene sheets) are investigated in relation to the host-guest interaction with nitric acid molecules possessing significant oxidizing power. The adsorption of HNO3 molecules induces a two-step reduction in the edge-state spin concentration due to the charge transfer from nanographene to HNO3 molecules; charge transfer with the exterior nanographene sheets of the nanographite domain in the first step, and subsequent intercalation into the interior nanographene sheets in the second step. Besides the charge transfer reaction, it is found that the paramagnetic NO molecules are produced owing to the decomposition of HNO3 and they are dimerized to form nonmagnetic (NO)2 at low temperatures. This finding suggests that the chemically active nanographene having edge states plays an important role in enhancing charge transfer and the concomitant decomposition of the guest HNO3 molecules.

Measurement of HONO, HNCO, and other inorganic acids by negative-ion proton-transfer chemical-ionization mass spectrometry (NI-PT-CIMS): application to biomass burning emissions

Abstract. A negative-ion proton-transfer chemical ionization mass spectrometric technique (NI-PT-CIMS), using acetate as the reagent ion, was applied to the measurement of volatile inorganic acids of atmospheric interest: hydrochloric (HCl), nitrous (HONO), nitric (HNO3), and isocyanic (HNCO) acids. Gas phase calibrations through the sampling inlet showed the method to be intrinsically sensitive (6–16 cts/pptv), but prone to inlet effects for HNO3 and HCl. The ion chemistry was found to be insensitive to water vapor concentrations, in agreement with previous studies of carboxylic acids. The inlet equilibration times for HNCO and HONO were 2 to 4 s, allowing for measurement in biomass burning studies. Several potential interferences in HONO measurements were examined: decomposition of HNO3·NO3− clusters within the CIMS, and NO2-water production on inlet surfaces, and were quite minor (≤1%, 3.3%, respectively). The detection limits of the method were limited by the instrument backgrounds in the ion source and flow tube, and were estimated to range between 16 and 50 pptv (parts per trillion by volume) for a 1 min average. The comparison of HONO measured by CIMS and by in situ FTIR showed good correlation and agreement to within 17%. The method provided rapid and accurate measurements of HNCO and HONO in controlled biomass burning studies, in which both acids were seen to be important products.

Role of nitrous acid decomposition in absorber and bleacher in nitric acid plant

The stringent statutory regulation for clean environment makes the absorber and the bleacher in the nitric acid plant two very important equipments. The NOx finally released to the atmosphere from the absorber, is based on the mathematical calculations of the nitric acid and nitrous acid concentration profiles along the length of the absorber. The present work focuses on the role of HNO 2 decomposition in the absorber and the bleacher in the nitric acid plant. The decomposition of HNO 2 is a heterogeneous reaction resulting into the formation of nitric acid and desorption of nitric oxide. At high nitric acid concentration (40–50 wt.%), the reversibility of HNO 2 decomposition due to NO oxidation with nitric acid is important. The model for bleacher column is presented, which takes into account the de-colorization of the product acid from the absorption column and makes it free from the nitrous acid. The model for the bleacher also takes into account the decomposition and oxidation of HNO 2 with dissolved oxygen. The models proposed for absorber and bleacher are validated from the data collected from a mono-pressure nitric acid plant as well as the data present in open literature.

Effect of radiation and heating on acid products of acetic acid radiolysis in concentrated nitrate solution

Radiolysis and thermolysis of glyoxalic, glycolic, and succinic acids in aqueous nitrate and nitrate-nitric acid solutions were studied. The radiolysis of the acids occurs with the participation of nitric acid radical species, precursors of stable NO 2 − ions. Thermolysis of nitrate-nitric acid solutions of acids involves rapid decomposition of HNO3, intensifying the decomposition of the organic acids owing to their reaction with NO2, major product of HNO3 thermolysis. Accumulation of NO 2 − ions in irradiated and heated (150°C) solutions, with an increase in pH, was detected.

Production of nanosized graphite powders from natural graphite by detonation

A detonation method for preparing nanosized graphite powders from natural graphite is described. The process initiated by a detonator in an explosion vessel features quick release of energy, decomposition of HNO 3 graphite intercalation compounds and the smashing action due to the detonation. The products were soot-like deposits on the inner walls of the vessel, and were studied by XRD, SEM, TEM, BET, energy dispersive X-ray spectroscopy, and Raman spectroscopy. The results show that the as-made graphite powders have a perfect sheet-like structure, and vary in the two-dimensional plane at the micron scale and in thickness at the nanoscale. The specific surface area of the nanosized graphite is six times higher than that of the raw graphite. This technique may offer a low-cost, energy saving and efficient approach to the preparation of nanosized graphite powders.

Nitric acid oxidation of silicon at ∼120°C to form 3.5-nm SiO2∕Si structure with good electrical characteristics

3.5-nm-thick SiO2 layers can be formed at 120 °C by immersion of Si in 40 wt % nitric acid (HNO3) followed by immersion in an azeotropic mixture (i.e., 68 wt % HNO3). The former immersion produces a 1.1-nm SiO2 layer with a low atomic density of 2.19×1022∕cm2, where the layer acts as a catalyst for the decomposition of HNO3. The latter immersion results in a 3.5-nm SiO2 layer with a higher atomic density of 2.22×1022∕cm2. When the postmetalization annealing treatment at 250 °C in hydrogen is performed on the ⟨Al∕3.5-nmSiO2∕Si(100)⟩ metal-oxide semiconductor diodes, interface states are passivated and a low leakage current density (e.g., 8×10−4A∕cm2 at the forward gate bias of 1.5 V) is achieved.

Dynamics and chemistry of vortex remnants in late Arctic spring 1997 and 2000: Simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS)

Abstract. High-resolution simulations of the chemical composition of the Arctic stratosphere during late spring 1997 and 2000 were performed with the Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations were performed for the entire northern hemisphere on two isentropic levels 450 K (~18 km) and 585 K (~24 km). The spatial distribution and the lifetime of the vortex remnants formed after the vortex breakup in May 1997 display different behavior above and below 20 km. Above 20 km, vortex remnants propagate southward (up to 40°N) and are "frozen in'' in the summer circulation without significant mixing. Below 20 km the southward propagation of the remnants is bounded by the subtropical jet. Their lifetime is shorter by a factor of 2 than that above 20 km, owing to significant stirring below this altitude. The behavior of vortex remnants formed in March 2000 is similar but, due to an earlier vortex breakup, dominated during the first 6 weeks after the vortex breakup by westerly winds, even above 20 km. Vortex remnants formed in May 1997 are characterized by large mixing ratios of HCl indicating negligible, halogen-induced ozone loss. In contrast, mid-latitude ozone loss in late boreal spring 2000 is dominated, until mid-April, by halogen-induced ozone destruction within the vortex remnants, and subsequent transport of the ozone-depleted polar air masses (dilution) into the mid-latitudes. By varying the intensity of mixing in CLaMS, the impact of mixing on the formation of ClONO2 and ozone depletion is investigated. We find that the photochemical decomposition of HNO3 and not mixing with NOx-rich mid-latitude air is the main source of NOx within the vortex remnants in March and April 2000. Ozone depletion in the remnants is driven by ClOx photolytically formed from ClONO2. At the end of May 1997, the halogen-induced ozone deficit at 450 K poleward of 30°N amounts to ~12% with ~10% in the polar vortex and ~2% in well-isolated vortex remnants after the vortex breakup.

Weak impact of mixing on chlorine deactivation during SOLVE/THESEO 2000: Lagrangian modeling (CLaMS) versus ER‐2 in situ observations

During the second and third segment of the SOLVE campaign in February and March 2000, the Arctic polar vortex began to be disturbed by planetary waves and upper stratospheric warming events. The perturbations of the vortex were associated with transport of air from low and middle latitudes into the polar region. Filaments with a lifetime exceeding two weeks were generated in regions of strong baroclinicity and peeled off the vortex edge.The Chemical Lagrangian Model of the Stratosphere (CLaMS) is used for the interpretation of filamentary structures in chemical tracer fields measured on board the ER‐2 during the March flights across the edge of the polar vortex. Both the mixing and the impact of mixing on the chemistry are considered. The isentropic version of CLaMS is initialized on 10 February at four isentropic levels: θ = 400, 425, 450, and 475 K. A comparison of the measured CH4/Halon‐1211 correlation curves and time series with corresponding CLaMS results obtained for spatial resolution of about 45 km indicates weak mixing between vortex and midlatitude air without pronounced anomalous mixing events. Thus the Arctic vortex in the altitude range 400–475 K was well isolated during the considered period without significant mass exchange across the vortex edge. The mixing intensity in CLaMS is controlled by the finite time Lyapunov exponent λ measuring the deformation rate of the horizontal wind and switching on mixing in the flow regions where λ exceeds a critical value λc. The CLaMS simulations suggest a temporally and spatially inhomogeneous mixing in the lower stratosphere with a lateral (across the wind) effective diffusion coefficient of the order 103 m2 s−1. The amount of ClONO2 formed due to chemistry induced by mixing of the activated vortex air with NOx‐rich midlatitude air does not exceed 3%. The impact of mixing on the accumulated ozone loss is less than 1%. The ClONO2 collar observed during the flight on 11 March can be understood as a result of deactivation of ClOx through the NOx produced owing to the chemical decomposition of HNO3 without a significant contribution of mixing with NOx‐rich midlatitude air.

A Kinetic Study of the Decomposition of Spent Sulfuric Acids at High Temperature

Chemical industry produces and uses high sulfuric acid volumes, and many processes generate high spent acid (ASS) volumes. The use of ASS as starting materials contributes to the protection of the environment. Should this alternative not be implemented, ASS volumes could represent high amounts of wastes. The thermal oxidative cracking process starts with ASS to produce commercial grade sulfuric acids. The presence of organic and mineral pollutants in spent acids can greatly influence the conversion yield, and this study addresses this point. The thermal decomposition of sulfuric acid is studied in a high-temperature plug flow reactor; the influence of temperature, oxygen concentration, and sample concentration on SO2 formation has been quantified. It is shown that the two last parameters have only a small influence on sulfur dioxide yield. Temperature is the main factor because of its influence on the kinetics of the conversion of SO3 to SO2. The second part of the study is related to the influence of the presence of contaminants: nitric acid and butanol. It is shown that the decomposition of HNO3 enhances SO3 conversion to SO2, the decomposition of the hydrocarbon also increases sulfur dioxide yield.

Nitric Acid Uptake and Decomposition on Black Carbon (Soot) Surfaces: Its Implications for the Upper Troposphere and Lower Stratosphere

The uptake and decomposition of HNO3 on black carbon (soot) surfaces were investigated in order to evaluate the proposal that HNO3 decomposition on aircraft-generated soot aerosols may alter the NOx/NOy partitioning in the upper troposphere and lower stratosphere. The experimental measurements were performed by using a fast flow-tube reactor coupled to a quadrupole mass spectrometer. Black carbon samples used as surrogate material for aircraft soot in this study included Degussa FW2 (an amorphous carbon black comprising medium oxides), graphite, hexane soot, and kerosene soot. The measurements of uptake were performed by varying P(HNO3) in the range of 5 × 10-7 to 5 × 10-4 Torr at 220 and 295 K. The results are summarized as follows. Significant HNO3 decomposition was observed on FW2 at 295 K with P(HNO3) ≥ 1 × 10-4 Torr, while it did not occur at 220 K. Similar HNO3 decomposition behavior on graphite was also observed under the condition of P(HNO3) ≥ 10-4 Torr and T = 295 K, although the extent of the decomposition was much smaller than that on FW2. The decomposition of HNO3 on soot produced NO, NO2, H2O, oxidized soot surface, and some unidentified volatile products. To explain the observed decomposition behavior at higher partial pressures of HNO3, a bimolecular HNO3 decomposition mechanism on soot surfaces was proposed. However, HNO3 immediately decomposed on an FW2 surface at 503 K even at lower partial pressure (∼10-6 Torr). On flame-deposited hexane and kerosene soot film, no HNO3 decomposition was observed up to P(HNO3) = 5 × 10-4 Torr. Moreover, the uptake and desorption of HNO3 were reversible at 295 K and irreversible at 220 K. Adsorbed HNO3 molecules on hexane soot film were saturated to a monolayer coverage at P(HNO3) ∼ 2 × 10-4 Torr according to Langmuir adsorption isotherm; further increase in P(HNO3) resulted in multilayer adsorption. Under the experimental conditions (P(HNO3) = 5 × 10-7 Torr and T = 220 K), the uptake of HNO3 was found to involve purely physical adsorption without showing any sign of irreversible decomposition over all black carbon samples. Subsequent heating of the sample following the uptake at 220 K desorbed most of the adsorbed HNO3 molecules. Physical adsorption of HNO3 was found to take place on the surface of concentrated H2SO4-coated soot at 230 K, but decomposition of HNO3 took place at 296 K. Finally, the present results suggest that the HNO3 decomposition on soot aerosols through a direct gas−solid interaction, which was proposed as a possible NOy-reactivation mechanism in the atmospheric modeling of upper troposphere and lower stratosphere, should be dismissed.

Evaluation of digestion methods for multi-elemental analysis of organic wastes by inductively coupled plasma mass spectrometry

Abstract The influences of digestion methods on ICP-MS measurements for Be, V, Ga, Sb, La, and Bi in organic fertilizers were evaluated. The dry ashing method, the 6 M HCl reflux method and the HNO3 decomposition method in a pressurized vessel were inappropriate because of their low extractability for the metals. The HNO3-HClO4 digestion method and the aqua regia digestion method were unsuitable for V. The results obtained by ICP-MS after the HNO3-HClO4-HF digestion method agreed well with those obtained by atomic absorption spectrometry. The recoveries of the other 29 metals and semimetals, Li, Sc, Co, Ni, As, Rb, Sr, Y, Mo, Ag, Cd, Cs, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Tl, Pb, Th, and U, by this digestion were fairly satisfactory. Therefore, the HNO3-HClO4-HF digestion method was found to be suitable for the multi-elemental analysis of various metals and semimetals in organic fertilizers by ICP-MS.