Ozone layer problem


Anaerobic ponds are loaded such that anaerobic conditions prevail throughout the Hquid volume. One of the major problems with anaerobic ponds is the generation of odors. The odor problem can frequentiy be eliminated by the addition of sodium nitrate at a dosage equal to 20% of the appHed oxygen demand. An alternative is the use of a stratified facultative lagoon, in which aerators are suspended 3 meters below the Hquid surface in order to maintain aerobic surface conditions, with anaerobic digestion occurring at the lower depths.  [c.189]

Magnesium has an ignition temperature of 623°C and a burning temperature of around 1982°C. The burning temperature is variable it depends on the rate of heat dissipation, rate of burning, and other factors. Magnesium, burning with a blinding white flame, melts as it bums and the burning Hquid metal drops to lower levels, igniting all combustible materials in its path. Burning stops if oxygen is prevented from teaching the metal or if the metal is cooled to a point below its ignition temperature. Whereas magnesium does not have the highest heat of combustion of the metals, none of the other metals have been successfully used as air-combustible incendiaries. Some metals may be alloyed with magnesium without affecting its ignitabiUty. The alloyed metal has the strength to withstand distortion, whereas pure magnesium does not. In massive form, magnesium is difficult to ignite. This problem is overcome by packing a hoUow core in a bomb with thermite [8049-32-9]. This results in an easily ignited mixture that suppHes its own oxygen and bums at a very high temperature.  [c.400]

ICPMS offers a high-sensitivity method for the direct analysis of organic solvents. The large amount of carbon present introduces some problems unique to ICPMS. The need to transport ions direcdy from the plasma source into the mass spectrometer, and the small orifice needed to accomplish this, means that plu ng is a problem. This is avoided by adding oxygen to the plasma, converting it from a reducing environment to an oxidizing one. Carbon dioxide is formed from the carbon. Other modifications include operating the spray chamber at a lower temperatures  [c.628]

An even more complicated nomenclature problem arises with the closely related all-oxygen cryptands. These compounds do not utilize nitrogen as the three-chain junction. Most examples of this class of compounds have utilized pentaerythritol or glycerol as the junction. This naturally imparts a somewhat lower flexibility to the molecule than would be present in the nitrogen-containing cases. Structures of two such molecules are illustrated below.  [c.5]

The product from a new plant was purified in a vacuum distillation column. Soon after startup the column developed a high-pressure drop. It was opened up for inspection, and the lower trays were found so full of solid that the pressure drop had caused them to buckle. Analysis showed that the solid was a polymer of the product traces of the reaction catalyst were present and had presumably caused the polymerization. The obvious solution was to remove the traces of catalyst before distillation this would have been expensive, so changing the operating conditions was tried first. Lower throughput was tried, then lower boil-up. Next on the list was a lower pressure, which would give lower temperatures. It proved impossible to lower the pressure, though the vacuum system should have been able to pull a harder vacuum. Was there a leak of air into the plant A pressure test showed that there was, in the seal of the bottoms pump. When this was repaired the polymerization problem disappeared. Oxygen as well as traces of catalyst were needed for polymerization. The pump seal was padded with nitrogen so that if it leaked again only nitrogen would enter the column.  [c.350]

Ozone IS a molecule formed from binding together three oxygen atoms. Gaseous ozone readily absorbs selected frequencies of ultraviolet radiation because ozone molecules have a resonant frequency in the ultraviolet region of the electromagnetic spectrum. A natural concentration of ozone exists twenty to thirty kilometers above Earth s surface. Ozone molecules absorb nearly all ultraviolet radiation from the sun having a wavelength less than about 0.3 micrometers. Accordingly, the natural ozone layer protects humans from harmful effects such as skin cancer. Human-made products migrating into the ozone layer can react with ozone molecules and convert them to other forms that do not absorb ultraviolet radiation. Chlorinated fluorocarbons, CFCs for short, once commonly used m refrigerators and aerosol spray cans, were found to be depleting the ozone, and in 1978 were banned from use m aerosol sprays. Banning the use of CFCs has not totally solved the ozone depletion problem.  [c.1224]

Since a protective layer separates the primary reactants, further growth of the layer involves two essential steps (a) surface reactions at the metal/oxide and oxide/oxygen interfaces and (b) transport of material through the oxide. The rate of growth will be controlled by whichever of these two steps is the slower. If the layer is thin enough, a surface reaction must control the rate. Indeed, during the initial stages of oxide formation step (b) is absent. As the layer thickens, step (b) may be distinguished as a definite process which ultimately controls the rate. When this stage is reached, the surface reactions, by which both metal and oxygen are incorporated into the oxide, proceed to near equilibrium. The products of these reactions are then transported through the oxide by a driving force derived from the free energy change in the oxidation reaction. The first problem is to decide the nature of these reaction products.  [c.254]

Luluff used depends on the nature of the system under investigation. For example, in the fir.-.l-row elements the 2p valence orbitals approach closer to the nucleus than the com-[la ruble 3p orbitals in the second-row elements (the latter are repelled by the lower 2p stales). Thus elements such as silicon or sulphur usually have softer pseudopotentials I ban their first-row equivalents carbon and oxygen. Everything else being equal, a higher aitiiff is consequently required for the latter and hence more plane waves in the expansion lie. more reciprocal lattice vectors, G). Note that in the plane wave expansion the basis fii.nctions are not associated with particular atoms but are defined over fhe whole cell Ubis also removes the problem of basis-set superposition errors as an additional benefit), rill coefficients fl, k+G are obtained by following the usual density functional scheme an initial guess is made of the electron density variation p(r), the Kohn-Sham and overlap matrices are constructed, diagonalisation gives the eigenfunctions and eigenvectors (and thus the coefficients a) from which the Kohn-Sham orbitals can be constructed and hence Ibe density for the next iteration.  [c.175]

Ba.ttenes, Polymer electrolytes based on PEO have been widely reviewed (r53—r58,rl77). The prospect of using a thin-layer, flexible battery for apphcations ranging from cellular phones to electric vehicles has led to several patents and research papers in this field. Typically, a salt such as potassium iodide, lithium triflate, or lithium perchlorate is complexed with PEO in a methylene chloride solvent. The solution complex is cast into thin films and the solvent is evaporated. The complex has been characterized it is beheved that the 7C2 hehcal stmcture of PEO allows an ideal stmcture for ion transport and leads to effective use as a battery. The dissociation of the anion—cation pair in the PEO salt complex has been attributed to the oxygen atoms, which form a cage around the cation and lead to ionic conductivity. The crystallinity of PEO at room temperature has limited the use of this technology to batteries that are used at temperatures higher than 65°C, the melting point of PEO. Research in the 1990s focuses on modifying the complex or the PEO molecule to overcome the crystallinity problem (see Batteries).  [c.345]

Entrained-Flow Gasifier. The entrained-flow gasifier consists of a plug-flow system in which the fine coal particles concurrentiy react with steam and oxygen. Residence time is a few seconds. These systems operate at high temperatures, well above ash slagging conditions, in order to assure good carbon conversion and provide a mechanism for removal of ash as molten slag. Entrained-flow gasifiers are utilized in the Shell coal gasification process, Texaco coal gasification process, Dow coal gasification process by Destec, and Prenflo by Kmpp-Koppers (7). The short residence time required in entrained gasifiers can result in potentially high throughputs at elevated pressures. Entrained gasifiers have high feedstock flexibiUty. The agglomerating tendency and fines content of feed coal that greatiy limit the operation of the moving-bed and fluid-bed gasifiers are not a problem in entrained gasification. Entrained gasifiers, which can use 100% of the mine output, have a small coal inventory that results in rapid start-up, shutdown, and load-foUowing characteristics. Entrained gasifiers have greater turndown capacity than do fluid-bed gasifiers, and the product gases contain no tars and light oils, thus faciUtating heat recovery and requiring less gas cleaning and purification. Also, the product gas contains much lower quantities of other impurities, such as mercaptans, ammonia (qv), carbon disulfide (qv), carbonyl sulfide, and thiophene (qv), than does that of other types of gasifiers. Treatment of the wastewater from the gas cleaning operation is therefore simpler for entrained-flow gasifiers.  [c.269]

AppHcation of latex paints direcdy over a 2inc-rich primer essentially eliminates the penetration problem. The latex polymer particles are large compared to the primer pores, and after coalescence the viscosity of the polymer is so high that it does not penetrate into the pores. The water and oxygen permeabiHty of latex paints is generally higher than that of solvent-based paints. Thus it is especially desirable to incorporate platelet pigments such as mica and leafing aluminum. Use of vinyHdene chloride—acrylate ester copolymer latexes has been recommended because of the lower water permeabiHty (174). Field performance using latex paints over 2inc-rich primers in such appHcations as highway bridges has been reported to equal solvent-home paint performance (124,125).  [c.358]

Aeration Systems These systems control the design of aeration tanks. Aeration equipment has two major functions mixing and oxygen transfer. Diffused-aeration equipment employs either a fixed-speed positive-displacement blower or a high-speed turbine blower for readily adjustable air volumes. Air diffusers can be located along one side of the aeration tank or spread over the entire bottom of the tank. They can be either fine-bubble or coarse-bubble diffusers. Fine-bubble diffusers are more efficient in oxygen transfer but require more extensive air-cleaning equipment to prevent them from clogging as a result of dirty air. MecnanicaJ-surface-aeration equipment is more efficient than diffused-aeration equipment but is not as flexible. Economics has dictated the use of large-power aerators, but tank configuration has tended to favor the use of greater numbers of lower-power aerators. Oxidation ditches use horizontal rotor-type aerators. Mixing is a critical problem with mechanical-surface aerators since they are a  [c.2220]

In deaerated neutral salt solutions anodic polarisation of chromium-free steel tends to lower the rate of hydrogen entry, as the fall in pH due to ferrous ion hydrolysis is relatively limited, and cannot compensate for the increase in potential. However, in aerated solution the ferrous ion can be oxidised to ferric in solution by dissolved oxygen, and as ferric hydroxide is much less soluble than ferrous hydroxide the pH can fall much lower. (This reaction is a serious problem when trying to measure the solution pH in cracks and crevices, and much of the early work which shows very acid pH values in cracks in carbon steels is now known to be incorrect because this reaction was allowed to occur between extracting the crack solution and measuring its pH.) In addition to lowering the surface pH, it seems possible that the precipitated film of ferric hydroxide/oxide also presents an ohmic resistance, and may thereby allow the surface potential to become lower than that measured in the bulk solution. It seems probable that the combination of these two effects was responsible for the increase in permeation current observed for anodic polarisation by Barth and Troiano. Many steels contain small, but significant concentrations of chromium, and it should be appreciated that chromium concentrations of around l<7o can markedly increase the tendency for local acidification, owing to the much stronger tendency for chromium ion hydrolysis.  [c.1239]

Zinc diecastings complex baths and undercoats Diecastings are made from zinc with up to 8[c.351]


See pages that mention the term Ozone layer problem : [c.1099]    [c.591]    [c.231]    [c.565]    [c.349]    [c.40]    [c.275]   
Chemistry of Organic Fluorine compounds II (1995) -- [ c.1092 ]