Showing papers on "Ammonia published in 1986"

Zinc-oxide thin-film ammonia gas sensors with high sensitivity and excellent selectivity

Abstract: A sensor with a high sensitivity and an excellent selectivity for ammonia gas was prepared by using sputtered ZnO thin films. The sensor exhibited an increase of resistance for exposure to ammonia gas whereas it exhibited a decrease of resistance for exposure to many other gases such as inflammable and organic gases. The resistance change and the selectivity of the sensor were enhanced by doping group III metal impurities such as Al, In, and Ga. The lower limit of the detection for ammonia gas was about 1 ppm at a working temperature of 350 °C.

Ammonia synthesis on molybdenum nitride

Abstract: Ammonia synthesis on unsupported Mo/sub 2/N powders was studied at atmospheric pressure between 557 and 717 K. Turnover rates based on titration of sites by CO decreased by a factor of 25 as the particle size of Mo/sub 2/N went from 12 to 3 nm. This confirms the structure sensitivity of the rate of ammonia synthesis. Strong inhibition of the rate by ammonia was observed. It is attributed to large values of the binding energy of nitrogen to the catalyst surface.

Growth yields of methanotrophs

Abstract: The growth yield ofMethylococcus capsulatus (Bath) on methane was dependent on the availability of copper in the growth medium In nitrate mineral salts medium the carbon conversion efficiency increased by 38%, concomitant with the transition from soluble to particulate methane monooxygenase, after transfer from low to high copper medium An increase in growth efficiency was also observed with ammonia as nitrogen source but not when methanol replaced methane as carbon source The high growth efficiency is attributed to a reduced NADH requirement for methane oxidation This could only arise if methanol dehydrogenase was capable of electron transfer, either directly or indirectly to the particulate methane monooxygenase (MMO) The carbon conversion efficiency from methanol with nitrate as nitrogen source was as high as theoretically predicted It is suggested that the previously low yields of methanotrophs grown on methanol resulted from the use, as nitrogen source, of ammonia which was oxidised by the MMO still present under these growth conditions

Urea Transformations and Fertilizer Efficiency in Soil

Abstract: Publisher Summary This chapter discusses urea transformations and fertilizer efficiency in soil. Urea has less tendency to coalesce and compact than ammonium nitrate, is less corrosive than other nitrogen fertilizers, and is suitable as a carrier for a number of herbicides. Much of the urea in the United States is applied as urea ammonium nitrate solution prepared by combination of urea with ammonium nitrate. Although urea is frequently equivalent to other nitrogenous fertilizers poor crop responses to urea have frequently been observed. The rapid hydrolysis of urea in the soil can result in high soil pH values and high ammonium ion concentrations, which are conducive to the accumulation of ammonia. The major problems observed in urea fertilization are the loss of volatile ammonia gas and ammonia toxicity to germinating seedling. This chapter discusses environmental, chemical, and physical soil conditions, which must be considered in regard to controlling urea transformations in the field. It also elaborates studies that have directly measured urea transformations in the field or under simulated field conditions. New classes of urease inhibitors that may improve the efficiency of urea under field conditions are also described.

Kinetics and effect of nitrogen source feeding on production of poly-β-hydroxybutyric acid by fed-batch culture

Abstract: A kinetic study of the production of poly-β-hydroxybutyric acid (PHB) by a fed-batch culture of Protomonas extorquens showed that a nitrogen source was necessary even in the PHB production phase. The effect of ammonia feeding on PHB production was consequently investigated. The nitrogen source (ammonia water) was supplied at a low constant feeding rate after the growth phase in which cell mass concentration reached 60 g/l. Feeding with a small quantity of ammonia resulted in a more rapid increase in intracellular PHB content than was the case without ammonia feeding. Excessive feeding of ammonia, however, caused not only degradation of accumulated PHB but also reduction of microbial PHB synthetic activity.

Ammonia synthesis over iron single-crystal catalysts: the effects of alumina and potassium

Abstract: They have investigated the effects of potassium and aluminum oxide on the synthesis of ammonia from nitrogen and hydrogen over model iron single-crystal catalysts at 20-atm reactant pressure. Elemental potassium does not remain on a Fe(100) surface under reaction conditions but a small amount of potassium can be stabilized by coadsorption with oxygen. The presence of the stabilized K + O has no effect on the rate of ammonia synthesis. Substantially more potassium can be stabilized at higher temperatures on Fe(100), Fe(111), and Fe(110) surfaces by coadsorption with aluminum oxide. The cooperative interaction between the potassium and oxidized aluminum seems to be due to compound formation. There is an inverse relationship between the rate of reaction and amount of aluminum oxide and potassium present on all three iron surfaces investigated.

A model of ammonia volatilization from applied urea. I. Development of the model

Abstract: SUMMARY Urea application to soil raises the pH and ammonium concentration, thus providing ideal conditions for ammonia volatilization. A mechanistic model is presented, which combines the process of ammonia volatilization with the simultaneous transformation and movement of urea and its products in soil, for predicting the concentration profiles of urea, ammoniacal-nitrogen and soil pH, and ammonia losses, following application of urea. The model consists of continuity equations describing the diffusion and reaction of urea, ammoniacal-nitrogen and soil base; it takes into account the volatilization of ammonia and the concurrent acidification of the soil surface; and considers a variable PCo2 profile due to soil respiration and urea hydrolysis. The derivation of the continuity equations and their boundary conditions, calculations of ammonia volatilization, and appropriate methods for numerical solutions are described.

Ammonia synthesis by means of plasma over MgO catalyst

Abstract: Ammonia synthesis from H2-N2 mixed gas was studied at room temperature in a glow-discharge plasma in the presence of metals or metal oxides. Magnesia (MgO) and calcia (CaO), which are oxides with solid basicity, revealed catalytic activity in the plasma synthesis of ammonia, although they are catalytically inactive in industrial ammonia synthesis. The acidic oxides (Al2O3, WO3, and SiO2-Al2O3) lead to the consumption of the reactant, i.e., the H2-N2 mixed gas. No ammonia was isolated. Metal catalysts showed higher activity than the above basic oxides. They have, however, different activities. The reaction was faster over the active materials than over sodium chloride (NaCl) or glass wool or in a blank reactor without any catalyst.

Catalyst for the reduction of oxides of nitrogen

Abstract: A catalyst for the selective reduction of nitrogen oxides to nitrogen in the presence of ammonia in the form of composite bodies formed from a mixture of zirconia (5 to 50% by weight), a zeolite (50 to 90%), a bond material (0 to 30%), and, optionally, a promoter selected from oxides of vanadium and copper in the amount of at least 0.1% by weight.

Vibrationally state‐selected reactions of ammonia ions. II. NH+3(v)+CH4

Abstract: The effects of vibrational excitation of the ammonia ν2 inversion mode on the reaction of NH+3(X,v=0 to 9) with methane have been measured in a tandem quadrupole mass spectrometer over the center‐of‐mass collision energy range 1.5 to 10 eV. The hydrogen abstraction channel is enhanced by nearly a factor of 2 at nine quanta of vibrational energy relative to the v=0 level of the ion. Added vibration in the ammonia ion umbrella‐bending mode facilitates the transition to the NH+4 product ion geometry. Protonated methylamine is formed at lower kinetic energies by attack of the ion at the methane carbon center, but with increasing vibrational excitation of the ammonia ion, the protonated methylamine decomposes by 1,2‐elimination of molecular hydrogen and by C–N bond scission.

Gaseous ammonia and ammonium ions in the free troposphere

Abstract: Ammonia, the most important alkaline compound commonly found in the atmosphere, has a key role in aerosol chemistry. Gaseous ammonia is released at the Earth's surface primarily through the decomposition of organic material and, due to its extremely large solubility in water and reactivity with acid aerosol components, is efficiently removed by interaction with aqueous and acid aerosols. While the presence of ammonium ions (NH4+) in aerosols and rain water is well established, there have been few studies of gaseous ammonia and its abundance is not well established, particularly in the free troposphere1. This is probably due to the difficulty in developing sufficiently sensitive analytical methods, which are not affected by interference of ammonium-containing aerosols. Due to its large proton affinity or gas-phase basicity, ammonia vapour is expected to react also with atmospheric gaseous positive ions leading to gaseous NH4+ ‘core ions’. Detection of the gaseous NH4+ core ions, which have not yet been observed in the free atmosphere, may provide sensitive means of detecting atmospheric ammonia vapour2,3,4. We report here on the first measurements of this ion in the free atmosphere at altitudes from 4,000 to 8,000 m. Ammonia vapour abundances inferred from these data are very low suggesting efficient heterogeneous ammonia removal and very low ammonia saturation pressures over aerosols.

Effects of various nitrogen fertilizers on emission of nitrous oxide from soils

Abstract: Field studies of the effects of different N fertilizers on emission of nitrous oxide (N20) from three Iowa soils showed that the N2O emissions induced by application of 180 kg ha−1 fertilizer N as anhydrous ammonia greatly exceeded those induced by application of the same amount of fertilizer N as aqueous ammonia or urea. On average, the emission of N2O-N induced by anhydrous ammonia was more than 13 times that induced by aqueous ammonia or urea and represented 1.2% of the anhydrous ammonia N applied. Experiments with one soil showed that the N2O emission induced by anhydrous ammonia was more than 17 times that induced by the same amount of N as calcium nitrate. These findings confirm indications from previous work that anhydrous ammonia has a much greater effect on emission of N2O from soils than do other commonly used N fertilizers and merits special attention in research relating to the potential adverse climatic effect of N fertilization of soils.

Electron-transfer reactions in nitrogen fixation. Part 2. The electrosynthesis of ammonia: identification and estimation of products

Abstract: Protonation of trans-[W(N2)2(Ph2PCH2CH2PPh2)2] with toluene-p-sulphonic acid gives the hydrazido cation trans-[W(NNH2)(p-MeC6H4SO3)(Ph2PCH2CH2PPh2)2]+. Reduction of this cation at a Hg-pool electrode in a tetrahydrofuran electrolyte under N2(1 atm) affords free ammonia with regeneration of the parent dinitrogen complex in excellent yield. Protonation of the regenerated product allows the system to be cycled and this can be performed in one vessel, the cathode compartment of the electrolysis cell.

Hydrogenation during thermal nitridation of silicon dioxide

Abstract: The incorporation of nitrogen and hydrogen during nitridation of SiO2 was studied over the temperature range of 800–1000 °C and for ammonia pressures of 1, 5, and 10 atm. The nitrogen content of the nitrided films was determined with Rutherford‐backscattering spectrometry and elastic‐recoil detection. Nitrogen in‐depth profiles were obtained applying Auger analysis combined with ion sputtering. Hydrogen profiles in the films were measured using nuclear‐reaction analysis. Both the nitrogen and hydrogen incorporation were found to increase with temperature in this range. A higher ammonia pressure primarily increases nitridation of the bulk of the oxide films. Depending on the nitridation conditions, up to 10 at.% of hydrogen may be incorporated. As distinct from the nitrogen profiles, the hydrogen in‐depth profiles are essentially flat. The concentration of hydrogen in the films, however, was always found to be smaller than that of nitrogen: measured H/N ratios varied between 0.25 and 0.85, the smaller valu...

Influence of pH and Ammonia Salts on Ammonia Toxicity and Water Balance in Young Channel Catfish

Abstract: Eight static 24-h median lethal tests were conducted with 16-g channel catfish Ictalurus punctatus at water temperatures of about 21°C. Tests were performed at four acidities with ammonium chloride and with ammonium sulfate. When compared on the basis of un-ionized ammonia nitrogen (NH3-N), ammonium chloride solutions were more toxic than ammonium sulfate solutions. Median lethal concentrations (24-h LC50s) at pH 8.8, 8.0, 7.2, and 6.0 were, respectively, 1.91, 1.45, 1.04, and 0.74 mg NH3-N/L for ammonium chloride, and 2.24, 1.75, 1.16, and 0.81 mg NH3-N/L for ammonium sulfate. Ionized ammonia (NH 4) was not lethal at concentrations up to 1,787 mg NH 4-N/L. Slopes of the probit regressions of NH3-N concentration versus mortality increased with decreases in pH and were nearly vertical at pH 6.0. Hematocrits of channel catfish exposed to lethal ammonia solutions also increased with decreases in pH, indicating an effect on osmoregulation. Plasma osmolality and red blood cell diameters did not change...

Ammonia loss from surface applied urea-acid products

Abstract: Ammonia (NH3) losses from soils occur only under alkaline conditions; therefore, adequate acidification could prevent NH3 loss. In acid soils this alkaline condition will exist only as a micro-environment around the decomposing CO(NH2)2 granule. The objective of this experiment was to examine the degree of NH3 loss reduction that occurs when acids are placed with surface applied CO(NH2)2. Phosphoric acid, H2SO4, HCl and HNO3 were used with surface applied CO(NH2)2 in a laboratory experiment to examine resultant NH3 loss under very extreme NH3 loss conditions. Calcium and magnesium chloride salts were added to urea:phosphoric acid to compare the relative effectiveness of acid and Ca + Mg salts for control of NH3 loss. Little depression of NH3-N loss was found from CO(NH2)2 containing H3PO4 and H2SO4 when the sand contained free CaCO3. However, when CO(NH2)2:H3PO4 (UP) mixtures were applied as 17-19-0 on neutral and acid sands, NH3 losses were reduced. Molar ratios less than 1:1 (28-12-0, 35-7-0) resulted in NH3 losses similar to those from CO(NH2)2 alone even in acid soils. The 110 g N m−2 as 17-19-0 reduced relative NH3-N loss and pH in acidified and neutral soils more effectively than 11 g N m−2. Ammonia losses are determined by chemical reactions occurring under the individual CO(NH2)2 granules; therefore, the use of the high 110 g N m−2 rates in this research. The 17-19-0 reduced soil pH and retarded the rate of CO(NH2)2 hydrolysis with consequent reduction in NH3 loss. Ammonia loss was reduced only slightly at 11 g N m−2 from 17-19-0 even in acid soils. Ammonia loss was reduced from 70 to 30% of applied N by applications of HNO3 and HCl with the CO(NH2)2. The HNO3 and HCl react with CaCO3 in a calcareous soil to produce CaCl2 and Ca(NO3)2 which are known to reduce NH3 loss from surface applied CO(NH2)2. However, a dry product of HNO3 · CO(NH2)2 is explosive and can not be used as a general fertilizer. Calcium chloride or MgCl2 combined with CO(NH2)2:H3PO4 reduced NH3 loss more at 110 g N m−2 than at 11 g N m−2. Calcium chloride reduced NH3 loss more effectively than MgCl2. The CaCl2 and MgCl2 salts were more effective than H2SO4 or H3PO4 in reducing NH3 losses except when (e.g., 17-19-0) mixtures were added to neutral or acidic sands.

Model of temperature dependence of a vanadia-alumina catalyst for nitric oxide reduction by ammonia: fresh catalyst

Abstract: On etudie la competition entre les reactions d'oxydation de NH 3 par NO et de reduction de NO par O 2

Nitrate-Ammonium Ratio Required for pH Homeostasis in Hydroponically Grown Soybean

Abstract: Imsande, J. 1986. Nitrate-ammonium ratio required for pH homeostasis in hydroponically grown soybean.—J. exp. Bot. 37: 341-347. Plant acid-base homeostasis is achieved when the mmoles of hydroxyl ions produced in the plant equal the mmoles of protons. Reduction of nitrate to ammonia is the major source of hydroxyl ions whereas ammonium uptake-assimilation and the metabolism of neutral sugars to organic acids are the primary sources of protons. Soybean [Glycine max (L.) Merr.] plants were grown hydroponically on medium supplemented with 3 0 mol m 3 nitrogen provided as various combinations of KN03 and NH4NO3. Plant growth consumed essentially all available nitrogen in each case; however, only in flasks supplemented with approximately 1-8 mmoles of KN03 plus 0-6 mmole of NH4N03 was the pH of the medium unchanged. Thus, for every mmole of nitrogen assimilated, approximately 0-6 mmole of dissociable protons must have been produced by the conversion of neutral sugars to carboxylic acids. Also, it was shown that a plant obtaining all of its nitrogen from nitrate must neutralize or excrete approximately 0-5 mmole of hydroxyl ion d~ Conversely, the plant deriving all of its nitrogen from dinitrogen must excrete or neutralize at least 0-8 mmole of hydrogen ion d~1 whereas the plant deriving all of its nitrogen from ammonium must excrete or neutralize approxi mately 2-1 mmoles of hydrogen ion d-1. Nevertheless, plants grown on medium supplemented with 2-4 mol m-3 nitrate plus 0-6 mol m-3 ammonium did not achieve a higher growth rate than plants grown on 3-0 mol m-3 nitrate.