Buoyancy effect when weighing in air


All four degradation pathways, ie, biodegradation, oxidation, hydrolysis, and photodegradation, initially give intermediate products or fragments that may biodegrade further to some other residue, biodegrade completely and be removed from the environment entirely (being converted into biomass and carbon dioxide and/or methane, depending on whether it is an aerobic or anaerobic system) and ultimately mineralised, or remain unchanged in the environment. Mineralisation, usually a slow process for polymeric materials and fragments, refers to complete conversion of a polymer (or any organic compound) to carbon dioxide or methane, water, and salts it is used here loosely to indicate complete or total removal from the environment to carbon dioxide or methane, water, and biomass. In the cases where residues remain in the environment, they must be estabUshed as harmless by suitably rigorous fate and effect evaluations. Only biodegradation has the potential to remove plastic and polymers completely from the environment. Thus, when developing and designing polymers and plastics for degradation in the environment by other pathways, the final stage preferably should be complete biodegradation and removal from the environment, with ultimate mineralisation. In this way, the polymers ate essentially recycled through nature into microbial cells, plants, and higher animals (21), and thence back into chemical feedstocks. Therefore, an environmentally acceptable degradable plastic or polymer maybe defined as one which degrades by any of the above-defined mechanisms, ie, biodegradation, photodegradation, oxidation, or hydrolysis, to leave no barm fill residues in the environment (20). This definition has the advantage of not limiting the degree of degradation for a particular polymer but requiting sufficient testing for fragments and degradation products that ate incompletely removed from the environment to ensure that no long-term damage or adverse effects to the ecological system remain a possibility. Polymers and plastics meeting this definition should be completely acceptable for disposal in the appropriate environment anywhere in the world.  [c.473]

Splash filling may also affect flammability. Froth and mist created by splashing may be ignited at much less than the flash point of the bulk liquid (5-1.3.1). An opposite and previously unrecognized effect of splash filling is the associated dilution of vapor near the liquid surface via air entrainment and turbulence (5-1.4.1). When a tank is filled with a volatile liquid whose equilibrium vapor concentration exceeds the UFL, a large fraction of the vapor space remains flammable until sufficient evaporation has taken place. However, in the absence of turbulent mixing the UFL is very rapidly exceeded close to the evaporating liquid surface. Since ignition via bmsh discharges typically occurs within 10 cm of the surface, air dilution may create an ignition hazard above liquids that otherwise would quickly generate local vapor concentrations close to or above their UFLs. The probability of ignition of volatile liquids such as naphtha may therefore be increased by splash filling as opposed to bottom filling. The effect of vapor concentration on the frequency of ignition by bmsh discharges is discussed in 2-6.2.1.  [c.98]

The simplest mechanism for spin-spin couplings is described by tlie Fenui contact model. Consider two nuclei linked by a single electron-pair bond, such as H and F in the hydrogen fluoride molecule. The magnetic moment of H can be either up or down relative to as described earlier, with either possibility bemg almost equally probable at nonual temperatures. If the H is up then it will have a slight preferential attraction for the down electron in the bond pair, i.e. the one whose magnetic moment lies antiparallel to it, for magnets tend to pair in this way. The effect will be to impair the two electrons very slightly and, thus, to make tlie F nucleus more likely to be close to tlie up electron and thus slightly favoured in energy, if it is itself down . The net result is that the H and F nuclei gain slightly in energy when they are mutually antiparallel. The favourable and unfavourable arrangements are siinunarized as follows  [c.1450]

Sky rockets are tubes with a stick attached for guidance and stability and which contain a pressed black powder propellant. They rise high into the air when ignited and a burst of color or a report, an audible bang, is normally produced in the air. Alternatively, rockets may contain a different propellant that fires the device into the air with a simultaneous whistling effect. Mines are aerial items that use a black powder propelling charge to fire a burst of colored stars, whisties, or firecrackers into the air from a cardboard tube. A barrage of color and noise results. Small aerial shells are plastic or cardboard spheres that are similar in effect to the type used by professional operators at large displays. These devices are launched from a mortar tube by a black powder propelling charge. A time delay fuse bums as the sphere or canister tumbles into the air, and a burst of color is produced high in the air when a black powder bursting charge explodes, breaking the sphere open and igniting the stars that are mixed with the black powder.  [c.349]

The volume soflds of latex gloss paints are substantially lower than the volume soflds of alkyd gloss paints. The soflds of latex paints are commonly around 33% compared to around 67% for an alkyd paint. In order to apply the same dry film thickness, twice as much wet paint has to be apphed. The main factor controlling the wet film thickness initially apphed is the viscosity of the paint at the high shear rates experienced during bmsh apphcation. In order to apply a thicker wet film, latex paint should have a higher viscosity at high shear rate than is appropriate for an alkyd paint. For many years the high shear viscosity of most latex gloss paints was lower than that of a corresponding alkyd paint. The film thickness apphed is also affected by the judgment of the painter and the fact that the wet hiding of latex paints is substantially higher than the dry hiding. When the water (refractive index 1.33) evaporates from the film, the latex particles (refractive index approximately 1.5) coalesce. The number of interfaces for scattering light drops and, therefore, hiding decreases. This effect is augmented by the larger difference in refractive index between mtile Ti02 (refractive index 2.76) and water, which is the interface in the wet film, as compared to Ti02 and the latex polymer which is the interface in the dry film. The effect is large because a small change in a large refractive index difference makes a larger difference in light scattering than the same change where there is a smaller refractive index difference. Furthermore, in the wet paint the Ti02 scatters light more efficiently because of the lower volume concentration as compared to the dry film. There is a similar difference in alkyd paints but the effect is smaller because the volume change during drying is less.  [c.352]

XRD is the most widely used technique for general crystalline material characterization. Owing to the huge data bank available covering practically every phase of every known material (powder diffraction patterns), it is routinely possible to identify phases in polycrystalline bulk material and to determine their relative amounts from diffraction peak intensities. Phase identification for polycrystalline thin films, using standard equipment and diffraction geometries, is also possible down to thicknesses of 100 A. For completely random polycrystalline thin films relative amounts are also easily determined. Once preferred orientations occur (texturing) this gets more difficult, requiring the collection of much more data or the introduction of more sophisticated equipment with different diffraction geometries so that the orientations can be seen effectively. These diffraction geometries include Grazing Incidence XRD (GIXRD), in which case the X-ray probing depth is gready reduced. This has the effect of greatly improving surface sensitivity and allowing a depth profiling mode (50 A to microns) by varying the incidence angle. When coupled to a synchrotron radiation X-ray source (to produce an intense, parallel X-ray beam) monolayer sensitivity can be achieved by GIXRD. GIXRD can therefore be used for the extreme situation of surface structure, or epitaxial relationships at the interfaces of films, where atomic positions can be determined to an accuracy of 0.001 A in favorable cases.  [c.194]


Langes handbook of chemistry (1999) -- [ c.2 , c.83 ]