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Raman spectra of solid nitric acid hydrates (NAM, alpha- and beta-NAD, alpha- and beta-NAT, and NAP) are obtained in the low-frequency region 20-175 cm(-1) where phonon bands show characteristic patterns. This fingerprint information, intimately related to the structure and symmetry of the unit cell, is well suited for observation of phase changes in solid nitric acid hydrates and allows the distinction of mixtures of different hydrate phases. The low-frequency spectra are correlated with the spectra of the respective symmetric NO stretching vibration (1000-1080 cm(-1)), with literature data, and with X-ray diffraction patterns.
A catalytic spectrophotometric method for the determination of trace amounts of nitrite is proposed. In acidic solution, chlorpromazine (CP) is oxidized by nitric acid to form a red compound, which is further oxidized to a colorless compound. The reaction is accelerated by trace amounts of nitrite and can be followed by measuring the absorbance at 525 nm: nitrite ion is regenerated and multiplied by nitric acid. The absorbance of the reaction increased with an increase in the reaction time, reached a maximum and decreased rapidly. Since the time required for the absorbance to reach the maximum decreased with increasing nitrite concentration, this value was used as the measured parameter for the nitrite determination. Under the optimum experimental conditions (2.3 M nitric acid, 1.2 x 10(-5) M CP, 40 degrees C), nitrite can be determined in the range 0-100 microg l(-1). The relative standard deviations (n = 6) are 4.7 and 1.8% for 40 and 100 microg l(-1) nitrite, respectively. The detection limit of this method (3sigma) is 1.2 microg l(-1). This method was successfully applied to a determination of nitrite in natural water samples.
Sulfur dioxide, nitrogen dioxide, particulate sulfate and nitrate, gaseous nitric acid, ozone and meteorological parameters (temperature and relative humidity) were measured during the winter season (1999-2000) and summer season (2000) in an urban area (Dokki, Giza, Egypt). The average particulate nitrate concentrations were 6.20 and 9.80 microg m(-3), while the average gaseous nitric acid concentrations were 1.14 and 6.70 microg m(-3) in the winter and summer seasons, respectively. The average sulfate concentrations were 15.32 microg m(-3) during the winter and 25.10 microg m(-3) during the summer season. The highest average concentration ratio of gaseous nitric acid to total nitrate was found during the summer season. Particulate sulfate and nitrate and gaseous nitric acid concentrations were relatively higher in the daytime than those in the nighttime. Sulfur conversion ratio (Fs) and nitrogen conversion ratio (Fn) defined in the text were calculated from the field measurement data. Sulfur conversion ratio (Fs) and nitrogen conversion ratio (Fn) in the summer were about 2.22 and 2.97 times higher than those in the winter season, respectively. Moreover, sulfur conversion ratio (Fs) and nitrogen conversion ratio (Fn) were higher in the daytime than those in the nighttime during the both seasons. The sulfur conversion ratio (Fs) increases with increasing ozone concentration and relative humidity. This indicates that the droplet phase reactions and gas phase reactions are important for the oxidation of SO2 to sulfate. Moreover, the nitrogen conversion ratio (Fn) increases with increasing ozone concentration, and the gas phase reactions are important and predominant for the oxidation of NO2 to nitrate.
Injury to the triangular fibrocartilage complex (TFCC) is frequently implicated in the etiology of ulnar-sided wrist pain. This study examines the nervous anatomy of the TFCC using a nitric acid maceration technique and attempts to correlate this information with known tear patterns. Ten fresh frozen cadaveric specimens were studied in detail. Gross dissection of each upper-extremity specimen included removal of all flexor and extensor tendons. After identification and labeling with permanent color of the ulnar nerve, dorsal sensory branch of the ulnar nerve, posterior interosseous nerve, anterior interosseous nerve, and median nerve, an en bloc excision of the distal radioulnar region was performed. Digestion of the soft tissue was performed with nitric acid at sequential concentrations of 50% and 33% for 9 of 10 specimens. The digestion was halted by immersing the specimen in a mixture of 10% formaldehyde and 1% glycerine. After removal of bone, the specimens were fixed in paraffin, sectioned, and stained with hematoxylin and eosin. Nine of the 10 specimens were studied microscopically to determine the contribution of the grossly identified nerves to each zone of the triangular fibrocartilage complex as defined by Palmer's classification of acute TFCC tears. The anterior interosseous, median, and superficial radial nerves did not contribute to the innervation of the TFCC. The intraarticular course of the peripheral nerves could not be defined in the one specimen that was not digested with nitric acid. Nitric acid maceration is a rediscovered technique for identifying the nervous anatomy of soft tissues. The study showed that the triangular fibrocartilage complex is innervated by branches of the posterior interosseous, ulnar, and dorsal sensory ulnar nerves in a fairly consistent manner. Improved treatment of TFCC tears may result from an enhanced understanding of the supporting structures' innervation and mechanical function.
Improved ion-chromatographic approaches for measuring trace chloride in nitric acid are presented. Two columns, the IonPac Cryptand A1 and a higher-capacity Cryptand prototype, were tested and compared. Also, the use of a Continuously Regenerated Anion Trap Column (CR-ATC) was evaluated for its ability to purify electrolytically generated eluent. Nitric acid (70%) was used as the test matrix and chloride was used as the test analyte; prior to injection, the nitric acid was diluted to 0.7% for the A1 column and to 2.8% for the prototype column. Chloride could be quantified in only 20 min on either column; detection limits computed for 70% HNO3 (at 95% confidence, alpha = beta = 2.5%) were 1.8 and 1.5 ppm for the A1 and prototype columns, respectively. Results also showed that the CR-ATC was necessary for obtaining acceptable acid blanks.
A simple method to estimate the amounts of ultra-trace metal impurities in nitric acid reagents has been developed. The determination of sixty-four metals in nitric acid was accomplished by direct measurements of 0.1 M nitric acids accurately diluted with ultrapure water by ICP-MS. Though accurate metal concentration could not be obtained for all of the elements, we could effectively evaluate the nitric acid quality by comparing the ion counts of the samples, ultrapure water and standard metal solutions for a calibration prepared with Ultrapur nitric acid.
The airway effect of a 4-hr exposure (via a Plexiglas hood) to 1.6 ppm nitric acid vapor were evaluated in seven normal and seven allergic sheep, i.e., animals that have a history of reacting with bronchospasm to inhalation challenge with Ascaris suum antigen. The nitric acid vapor was generated by ultrasonic nebulization of a 2% nitric acid solution. Airway effects were assessed by measuring the change in specific pulmonary flow resistance before and after a standard inhalation challenge with 2.5% carbachol aerosol. Nitric acid exposure did not produce bronchoconstriction in either group. Pre-exposure increases in specific pulmonary flow resistance after carbachol inhalation were 68% (SD +/- 13%) and 82% (SD +/- 35%) for the normal and allergic sheep, respectively. Within 24 hr, the largest post exposure increased in specific pulmonary flow resistance for the normal and allergic sheep were 108% [SD +/- 51% (P less than .06)] and 175% [SD +/- 87% (P less than .02)], respectively. We conclude that a short-term exposure to nitric acid vapor at levels below the industrial threshold limit (2 ppm), produces airway hyperreactivity to aerosolized carbachol in allergic sheep.
OBJECTIVE: To study the composition, surface characteristics and response to removal torque of an implant surface subjected to hydrofluoric acid etching and posterior passivating with hydrofluoric and nitric acid. STUDY DESIGN: Twelve implants were initially selected and their physico-chemical characteristics were evaluated by means of energy-dispersive X-rays (EDS), scanning electron microscopy (SEM) and photoelectron spectroscopy (XPS). In addition, 24 implants - 12 measuring 8 mm and 12 measuring 10 mm in length - were implanted in 6 Beagle dogs. Twelve implants were removed after a recovery period of 6 weeks, followed by removal of the remaining 12 implants after 12 weeks, using a torque calibrator (Gauge Tonichi model BGT150CN-S) with a force registry range of 0-150 Ncm. RESULTS: EDS analysis of the surface chemical composition only revealed the presence of titanium in the etched surfaces. In the same way as with the surfaces of other dental implants, XPS analysis revealed traces of other elements present in the surface, fundamentally carbon. Following dual acid etching, the surface showed the roughness resulting from acid action, with a morphology that proved to be quite homogeneous. The roughness values obtained exceeded 1 mm. The mean removal torque values after 6 weeks were 79.7 Ncm for the 8 mm implants and 115 Ncm for the 10 mm implants. After 12 weeks, these values increased to 101.2 Ncm and 139.7 Ncm, respectively. CONCLUSIONS: Hydrofluoric and nitric acid etching affords optimum surface characteristics comparable to those of other surfaces. The recorded removal torque values raise the possibility of human clinical application for early or immediate loading procedures.
The interaction between gas-phase nitric acid and the graphite surface is taken as a simple model of interactions occurring at the surface of atmospheric soot particles. In particular, we study the heterogeneous processes that lead to the dissociation of the nitric acid and the production of nitrous acid. The atomistic details of the reaction mechanisms are reproduced by use of the new metadynamics method. The binding interactions of the HNO3 molecule and its fragments with the graphite surface are calculated, and the role of the surface in catalyzing the reaction is taken into account. From the reactive trajectory generated by the metadynamics, it is seen that the path goes through several different intermediate states. We analyze in detail the electronic structures and spin density distributions of the relevant products and report on the mechanisms and the main features of the transition regions relative to all the activated processes observed.
Although heterogeneous chemistry on surfaces in the troposphere is known to be important, there are currently only a few techniques available for studying the nature of surface-adsorbed species as well as their chemistry and photochemistry under atmospheric conditions of 1 atm pressure and in the presence of water vapor. We report here a new laboratory approach using a combination of long path Fourier transform infrared spectroscopy (FTIR) and attenuated total reflectance (ATR) FTIR that allows the simultaneous observation and measurement of gases and surface species. Theory is used to identify the surface-adsorbed intermediates and products, and to estimate their relative concentrations. At intermediate relative humidities typical of the tropospheric boundary layer, the nitric acid formed during NO2 heterogeneous hydrolysis is shown to exist both as nitrate ions from the dissociation of nitric acid formed on the surface and as molecular nitric acid. In both cases, the ions and HNO3 are complexed to water molecules. Upon pumping, water is selectively removed, shifting the NO(3-)-HNO3(H2O)y equilibria toward more dehydrated forms of HNO3 and ultimately to nitric acid dimers. Irradiation of the nitric acid-water film using 300-400 nm radiation generates gaseous NO, while irradiation at 254 nm generates both NO and HONO, resulting in conversion of surface-adsorbed nitrogen oxides into photochemically active NO(x). These studies suggest that the assumption that deposition or formation of nitric acid provides a permanent removal mechanism from the atmosphere may not be correct. Furthermore, a potential role of surface-adsorbed nitric acid and other species formed during the heterogeneous hydrolysis of NO2 in the oxidation of organics on surfaces, and in the generation of gas-phase HONO on local to global scales, should be considered.
OBJECTIVE: This work presents the results of clinical and radiological behaviour, for 2 years, of 290 implants treated with a first etching with HF and a second etching with HF and HNO3 acids and that were loaded 8 weeks after insertion. EXPERIMENTAL DESIGN: It is a prospective study on 290 implants placed in 56 patients with an age range from 28 to 81. The selection was previously made through radiological study with panoramic and tomographic radiographs, followed by the implantological treatment with prosthetic loading and clinical (15 days, 1, 3 , 6, 12, 18 and 24 months) and radiological control (12 and 24 months). RESULTS: During the healing period, 11 implants failed, resulting in a CSR of 96.21%. After prostheses placement at 2 months, 4 implants were retired, successfully remaining 275 implants. CONCLUSIONS: The following and favourable results after the prosthetic loading of 179 implants (CSR of 98.56%), attest that early loading may and must be applied, after rigorous planning and case selection.
A two-tiered, Teflon/nylon filterpack system was used to characterize spatial and temporal patterns of particulate nitrates and nitric acid vapors at two monitoring sites in the Rocky Mountains. Geometric means for particulate nitrates were 38.9 and 52.8 ng/m(3) for the upper and lower sites, respectively. For nitric acid, geometric means of 70.4 ng/m(3) for the upper site and 295 ng/m(3) for the lower site were observed. The relatively low concentrations found at these two sites are comparable to published values for these materials at other remote sites. Atmospheric concentrations of nitrates and nitric acid were correlated significantly at each site, and the total nitrate concentrations (NO(3)(-) plus HNO(3)) were correlated between sites. Comparisons between the two sites indicate that nitric acid concentrations were statistically greater at the lower elevation site, whereas nitrate concentrations were not significantly different. No general seasonal or annual pattern of nitrate or nitric acid concentrations were evident when comparable sampling periods were examined.
A laboratory study was performed to evaluate the transmission of nitric acid through different materials. Copper, stainless steel, sodium glass and chromium-plated stainless steel proved to be poor choices for the construction of size classifiers, transfer lines and filter holder plates of air sampling devices, as they adsorb significant amounts of nitric acid. Tubes made of Teflon or pyrex exhibited good HNO3 transmission but, unexpectedly, devices machined from Teflon rods (cyclones, manifolds) showed a noticeable sorption capacity. Moreover, the Teflon of different manufacturers behaved differently. The features of a sampling unit capable of accurate measurements of nitric acid and ammonium nitrate in the atmosphere are discussed.
We report theoretical studies on the complexation of uranyl nitrate and the dissolution of nitric acid in supercritical CO2 by TBP. According to quantum mechanical calculations, TBP (modeled by trimethyl phosphate TMP) displays stronger hydrogen-bonding interactions with HNO3 than with H2O, and this has been modeled in force-field calculations. Different combinations of water, TBP, and acid are compared in SC-CO2 and simulated by molecular dynamics (MD), demonstrating the importance of TBP and water concentrations. In MD simulations, which started from "random" mixtures of water, TBP, nitric acid, and uranyl nitrate, complexation of uranyl by TBP is observed and the yield increases with the TBP concentration. TBP molecules are also necessary to dissolve nitric acid in the supercritical phase. Indeed, without TBP, nitric acid alone self aggregates via hydrogen-bonding interactions. Adding water to this solution leads to the formation of water microdomains containing the acid and uranyl salts. The simulations show that a high TBP/nitric acid ratio is needed to fully dissolve the acid in the supercritical phase and to form CO2-philic UO2(NO3)2(TBP)2 complexes. The resulting hydrogen-bonding and solvation patterns are analyzed. The results are consistent with experimental observations and provide microscopic views of this important extraction system.
The acute toxicity of nitric acid to fingerling rainbow trout was measured in 7 day bioassays at 11 degrees C. The LC50 was about pH 4.0. Fish which died at low pH (3.0-4.0) exhibited classical symptoms of acid toxicity. Comparison of our results with other toxicity measurements suggests that nitric acid is intermediate in toxicity between H2SO4 and HCl at pH 3.0 and less toxic than either acid at pH 3.3 and above.
Although nitric acid is a component in some new bonding systems, the action of nitric acid as an etchant for the improvement of adhesion of bonding systems for resin composites to dentin and enamel has not been reported. A determination of the extent of etching on both dentin and enamel using 2.5% HNO3 solution at various application time periods was the purpose of this study. Extracted human molars were cleaned and sectioned so that flat samples of dentin and enamel would be produced. Surfaces were abraded with 320-grit aluminum-oxide paper, washed with distilled water for 10 s, and blown with air for 10 s. Duplicate samples of dentin and enamel were treated with a drop of 2.5% HNO3. Application periods varied by 10-second intervals, from 10 s up to 60 s. After being rinsed with distilled water and dried, the sections were routinely processed for observation by SEM. The micrographs of the treated surfaces showed various degrees of etching and erosion proportional to the length of application time. The 30-second application revealed a well-etched surface with minimal erosion.
Fluorescent properties of multi-walled carbon nanotubes (MWNTs) before and after concentrated nitric acid treatment were studied. The results show that both multi-walled carbon nanotubes (MWNTs) and treated multi-walled carbon nanotubes (t-MWNTs) could emit fluorescence; compared with MWNTs, fluorescence from t-MWNTs is stronger and fluorescent emission peak from t-MWNTs blue shifts slightly to short-wavelength. Luminescence from MWNTs could be related to the trapping of excitation energy at defect sites and the energy bandgap between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). Treating MWNTs with concentrated nitric acid could introduce more defects on MWNTs and make MWTNs trap more excitation energy, leading to a fluorescence enhancement of t-MWTNs; in addition, the energy bandgap between LUMO and HOMO increases with length decreasing of MWNT, and the shortening of MWNT caused by concentrated nitric acid treatment could make energy bandgap between LUMO and HOMO increase, resulting in a slight blue shift of fluorescent emission peak of t-MWTNs to short wavelength.