Effect environmental

Environmental E )i ecti. tn Toughened CeranUc6 - Norman L. Hecht (University of Dayton) 

During the past six months (October 1989 to March 1990), evaluations of one SiC and two Si N ceramics continued. The tensile strength of GTE s PY6 was measured from temperatures of 20 C to 1400 C, and the tensile stress rupture (static fatigue) behavior of Norton/TRW NT-154 and Hexoloy SA was investigated. In addition, the effect of thermal aging in air on the flexural strength of Hexoloy SA, NT-154, and PY6 was also investigated. 

The tensile strength measurements of PY6 were made using button-head cylindrical specimens on an Instron Electro-Mechanical Test 

Carborundum Hexoloy SA Cold formed (injection molded or isostatic pressing) and pressureless sintered a-SiC with additions of B and C. 

Carborundum Hexoloy ST Cold formed and pressureless sintered a-SiC and TiB  

Environmental factors may also affect the fatigue behavior of materials. A few brief comments will be given relative to two types of environment-assisted fatigue failure thermal fatigue and corrosion fatigue. 

The environmental effects of using drugs and additives in animal diets are 

Dietary additives can affect the microbiota that are associated with the faeces of animals and degradation of the faeces may be impaired because of the influence of the excretory products on insects, microbes and fungi. The microbiota in the soil and waste material may be affected, thus altering the fertility of the pasture and sustainability of other wildlife. These microbiota can be used as dietary ingredients for animals, so inhibition of their production would be an unsatisfactory consequence of dietary additives.  

Relatively high levels of copper in pig diets can improve nutritional performance due to the antimicrobial effects in the gastrointestinal tract. However, if land is fertilized with dung from pigs and subsequently grazed by sheep, the sheep may suffer copper toxicity because of their increased susceptibility to copper compared with pigs. Similarly, pig diets would be unacceptable for sheep because of the high levels of copper therein. 

Ibanez, C. A. Herrara, L. A. Velasquez and P. Hehel, Animal Feed Sci. TechnoL, 1993,42,165. 

Drugs and Dietary Additives, Their Use in Animal Production 

The environmental effects of nuclear power are discussed in detail in Section 6.7 of the IAEA Guidebook Introduction of Nuclear Power , and the IAEA publication Nuclear Power, the Environment and Man, as well as in other Agency publications. 

Polymers are sensitive to several environmental effects. Polar or nonpolar solvents or irradiation with ultraviolet light can significantly decrease the 

Polymers may react with different organic or inorganic solvents. Generally, polar solvents may permeate polar polymers and nonpolar solvents nonpolar polymers. For example, pmma has a limited solubility for alcohol and polyamide (pA, nylon) for water. 

If solvents penetrate a. polymer and weaken the intermolecular bonds, they also ease the formation of crazes. On the one hand, the solvent reduces the surface energy, facilitating the formation of free surfaces needed to initiate and propagate crazes. On the other hand, the reduced bond strength reduces the force needed to draw chain molecules out of the bulk material to form fibrils. Crazes formed by this mechanism may, 

The increase in volume by swelling can also reduce the strength of a component. If the amount of dissolved solvent is different in different parts, the volume increase is non-uniform, and residual stresses may be induced. If, for example, the solvent diffuses out of the surface region, it is under tensile stress and thus sensitive to tensile loads. 

One way to protect polymers from solvents is copolymerisation. For example, polystyrene can be attacked by the nonpolar solvent benzene. Copolymerisation with a polar group (for example acrylonitrile) stops the nonpolar 

The way in which the environment can attack the resin and the reinforcement is discussed in broad outline. The effects of moisture, corrosion, abrasion, wear and weathering on properties are considered in turn. There is considerable variability amongst materials so it is possible to design components which can successfully withstand their operating environment. 

The environment in the form of a gas, liquid or particles can attack the resin and the reinforcement in various ways. Possible ways include  

As the reinforcement s role is to boost the resin properties, it is important that the surface be resin rich to protect the fibres from the influence of the environment. 

Most data are derived for a single influence and the effect of combining more than one influence has then to be determined, e.g. combining temperature, loading and exposure to abrasive particles to characterize the environmental effects on a pump housing. 

In addition, results of tests on small samples may not be representative of large panels because of the differing ratio of surface to volume. In practice, it is generally found that the small scale tests tend to give conservative results. 

The rate of an enzymatic reaction is affected by a number of environmental factors such as solvent, ionic strength, temperature, pH and presence of inhibitor/activator. Some of these effects are described below  

1 Presence of inhibitors inhibition kinetics. The kinetic study of an enzymatic reaction in the presence of inhibitors is one of the most important diagnostic procedures for enzymologists. The inhibition (reduction in the rate) of an enzyme reaction is one of the major regulatory devices of living cells and offers great potential for the development of pharmaceuticals. An irreversible inhibitor forms the stable enzyme complex or modifies the enzyme to abolish its activity, whereas a reversible inhibitor (I) forms dynamic complex(es) in equilibrium with the enzyme (E) or the enzyme substrate complex (EA), by reducing the rate of the enzymatic reaction  

It is assumed that the inhibitor complex El cannot combine with the substrate and the EAI complex cannot be decomposed to form the product, therefore establishes an equilibria for the formation of the inhibitor complexes. 

The general rule for writing the rate equation according to the equilibrium treatment of enzyme inhibition kinetics for the forward direction is as follows  

TABLE 11.6 Reversible inhibition patterns of enzyme reactions 

The so-called polarizable continuum model (PCM) offers a unified and well sound framework for the evaluation of all these contributions both for isotropic and anisotropic solutions. In PCM, the solute molecule (possibly supplemented by some strongly bound solvent molecules, to include short-range effects such as hydrogen bonds) is embedded in a cavity formed by the envelope of spheres centered on the solute atoms. The procedures to assign the atomic radii and to form the cavity have been described in detail together with effective classical approaches for evaluating K vand , 

The core of the model is then the dehnition of the Q matrix, which in the mostrecent implementations of PCM depends only on the electrostatic potentials, takes into the proper account the part of the solute electron density outside the molecular cavity, and allows the treatment of conventional, isotropic solutions, ionic strengths, and anisotropic media such as liquid crystals. Furthermore, analytical first and second derivatives with respect to geometrical, electric, and magnetic parameters have been coded, thus giving access to proper evaluation of structural, thermodynamic, kinetic, and spectroscopic solvent shifts. 

Composite materials must survive in the environment to which they are subjected at least as well as the conventional materials they replace. Some of the harmful environments encountered include exposure to humidity, water immersion, salt spray, jet fuel, hydraulic fluid, stack gas (includes sulfur dioxide), fire, lightning, and gunfire as well as the combined effects of the space environment. 

Tsai listed and quantitatively discussed specific degradation mechanisms for environmental exposure [6-40]  

Degradation of the fiber-matrix interface resulting in loss of adhesion and interfacial bond strength. 

Permeability of the matrix material to corrosive agent such as water 

Normal viscoelastic dependence of matrix modulus and strength on time and temperature. 

There are two basic categories of acceptance standards performance standards and product specifications. Performance standards focus on the ability of a material, component or assembly to resist the loads or environmental effects of its intended application. Product specifications focus on aspects of material quality, which may affect strength, appearance and durability. In some instances it may be possible to use existing standards directly with newly developed products and materials in other cases it may be necessary to modify existing standards or develop new standards to assure equitable evaluation. Consensus committees comprising producer, consumer, and user groups develop performance standards, which are used to evaluate the engineering performance of wood-based panels, such as hardboard, MDF and particleboard. This standard was used because no standard exists for the evaluation of woodfibre-plastic panel materials. 

A variety of material property and engineering tests were performed, including bending modulus of rupture (MOR), bending modulus of elasticity (MOE), tension strength, shear strength, thermal expansion, moisture absorption, hardness, and fastener withdrawal. 

Some of the common standards used are ASTM D1037-94 [92], ASTM D2718-90 [93], ASTM D2719-89 [94], ASTM D3043-87 [95], ASTM D3044-76 [96], ASTM D3500-90 [97] and ASTM D3501-76 [98]. 

The author would like to thank Professor Dr. N.G. Kandil, Head of Chemistry, Faculty of Girls, Ain Shams University, Cairo, for the help provided during the writing of this chapter. 

Wittig, Kunststoffe im Automobilbau, VDI-Verlag, Dusseldorf, Germany, 1994. 

Due to the rapid increase in necessary computer resources as the size of the system under study enlarges, explicit calculations of entire biomolecules are out of the question. But this does not mean that the smaller model systems chosen for inquiry must be examined in a complete vacuum. It is possible to surround the system of interest with a number of other entities. Judicious choice of the surroundings can capture the essence of how the full biomolecule may influence the proton transfer within the H-bond of interest. 

As one would anticipate, the dependence of electronic properties of photochromic chromophores upon environment is more pronounced in solvents, where hyp-sochromic or bathochromic shifts of the absorption and fluorescence spectra were observed and are strongly influenced by the polarity of solvent molecules [28]. Chromophore properties are also influenced by the physical properties of the matrix, such as viscosity, conductivity, pH, solubiHty, or phase-transition temperatures [29, 30]. For example, the reversible Hght-induced insolubiHty of polystyrene with pendant azobenzene in cyclohexane induced by irradiation was attributed to the reduction in solvent-polymer interactions, as the azobenzene chromophore transforms from the less polar trans form to the more polar cis form [30]. 

Williams [137] had found earlier that the addition of paraffin or French chalk acted as a diluent to lead azide and lowered the detonation velocity in powder layers (30% paraffin decreased the velocity from over 2000 m/sec to 

The hydrolysis of lead azide has been studied by Todd et al [138], who found it to be a complex process involving a sequence of hydroxyazides in which the hydroxyl-to-azide ratio gradually increases. If carbon dioxide is also present, basic lead carbonate and normal lead carbonate can be formed. This difference in final product is important since basic lead azide is explosive whereas basic lead carbonate is not. 

Deflagration in powders and pellets is influenced by the various factors listed on page 431. The heats of decomposition and the reaction kinetics are known for several azides. However, the effects of confinement and sample dimensions are only understood qualitatively. Suggestions have been made for the role of particle size, particle surface area, interstitial gases, and the streaming of products, but further investigation is needed. 

The results for propagation in single crystals of /3-lead azide are interesting. Reaction fails if the crystal thickness falls below 17 fxm [133]. For crystals of thickness greater than this and up to 215 /mn the deflagration velocity increases. In the range 215 /rm to about 2 mm the velocity remains constant at 

Propagation is thought to occur by decomposition in the solid phase with with the reaction proceeding from layer to layer. The plateau velocity ( 2.9 km/sec) is the velocity of sound in the crystal. This will be the maximum velocity for heat conduction until the pressures in the reaction front are sufficient to build up a shock wave and, eventually, full detonation conditions (for crystals 2 mm diameter). Chaudhri and Field explain the initial velocity/crystal thickness results in terms of heat losses from the reaction front. 

For irreversible (non-equilibrium) sensors that utilize activated reaction ter-action mechanisms, sensitivity usually increases as a result of increased reaction rates at higher temperatures. This type of response behavior is illustrated in Ing-ure 5.5 for the reaction of a Pt-olefin-complex with ethyl acrylate [92d]. In contrast to the steady decrease in sensitivity for the reversible sensor, die SAW response rate (in Hz/min) increases with temperature. Thus, depending on the type of coating-analyte interactions being utilized, the sensor sensitivity can be improved by selecting an operating temperature consistent with the predominant response mechanism. 

Another significant environmental factor for vapor-phase applications is humidity. The ubiquitous nature of water vapor requires development of means to exclude or correct for interferences from water [92a,b]. Careful selection of coating materials, for example, can minimize the effect of water vapor on the sensor response. Alternatively, a coating with appropriate sensitivity to water can be used in the development of correction algorithms [93]. Other instrumental or system approaches, such as preconcentrators or sensor arrays with pattern recognition [94a-c], will be discussed in Section 5.5 and in Chapter 6. 

Traditionally, regulatory and compliance testing requires gravimetric determination of, for example, fuel mass emissions. Instruments utilizing collecting or in situ measurement techniques are used for the analysis of various particle parameters for nonregulatory purposes. 

The health effects of particulate matter (a complex mixture of solids and liquids) emissions are not yet well understood but are recognized as major contributors to health problems. Biological activity of particulate matter may be related to particle sizes and/or particle composition. Furthermore, it has generally been concluded that exposure to particulate matter may cause increased morbidity and mortality, such as from cardiovascular disease. Long-term exposure to particulate emissions is also associated with a small increase in the relative risk of lung cancer. 

Since the Claus process by itself removes only about 90% of the hydrogen sulfide in the gas stream, the Beavon process (Speight, 1993, p. 268), SCOT (Shell Claus Off-Gas Treating) process (Speight, 1993, p. 316 Hydrocarbon Processing, 

or the Wellman-Lord process (Speight, 1993, p. 327) is often used to recover additional sulfur. The Claus process consists of partial combustion of the hydrogen sulfide-rich gas stream (with one-third the stoichiomefiic quantity of air), followed by reacting the resulting sulfur dioxide and unbumed hydrogen sulfide in the presence of a bauxite catalyst to produce elemental sulfur. 

In the SCOT process, the sulfur compounds in the Claus tail gas are converted to hydrogen sulfide by heating and passing it through a cobalt-molybdenum catalyst with the addition of a reducing gas. The gas is then cooled and contacted with a solution of diisopropanolamine (DIPA) that removes all but trace amounts of hydrogen sulfide. The sulfide-rich diisopropanolamine is sent to a stripper, where hydrogen sulfide gas is removed and sent to the Claus plant. The diisopropanolamine is returned to the absorption column. 

Domestic Animals. Although domestic animals can be affected directly by air pollutants, the main concern is chronic poisoning as a result of ingestion of forage that has been contaminated by airborne pollutants. Pollutants important in this connection are 

Materials and Structures. Building materials have become soiled and blackened by smoke, and damage by chemical attack from acid gases in the air has led to the deterioration of many marble statues in western Europe. Metals are also affected by air pollution for example, S02 causes many metals to corrode at a faster rate. Ozone is known to oxidize rubber products, and one of the effects of Los Angeles smog is cracking of rubber tires. Fabrics, leather, and paper are also affected by S02 and sulfuric acid, causing them to crack, become brittle, and tear more easily. 

Atmospheric Effects. The presence of fine particles (0.1-1.0 mm in diameter) or N02 in the atmosphere can result in atmospheric haze or reduced visibility due to light scattering by the particles. The major effect of atmospheric haze has been degradation in visual air quality and is of particular concern in areas of scenic beauty, including most of the major national parks such as Great Smoky Mountain, Grand Canyon, Yosemite, and Zion Parks. 

Acidic Deposition. Acidic deposition is the combined total of wet and dry deposition, with wet acidic deposition being commonly referred to as acid rain. Normal uncontaminated rain has a pH of about 5.6, but acid rain usually has a pH of less than 4.0. In the eastern United States, the acids in acid rain are approximately 65% sulfuric, 30% nitric, and 5% other, whereas in the western states, 80% of the acidity is due to nitric acid. 

Many lakes in northeastern North America and Scandinavia have become so acidic that fish are no longer able to live in them. The low pH not only directly affects fish but also contributes to the release of potentially toxic metals, such as aluminum, from the soil. The maximum effect occurs when there is little buffering of the acid by soils or rock components. Maximum fish kills occur in early spring due to the acid shock  

For a deeper understanding of photophysical processes it is sometimes very useful to study the influence of the environment. The results of some such studies will be briefly mentioned in the following sections. 

Exposure of TijAl or TigAl-base alloys to oxygen at higher temperatures leads to oxidation on the one hand and to oxygen dissolution in the alloy on the other (Rowe, 1990 Kim and Froes, 1990 Froes etal., 

Oxidation resistance would be expected if a protective AljOj, layer could be formed by selective oxidation. However, AI2O3 is only slightly more stable than TiO and the activity of Ti is much higher than that of Al in TijAl (Meier and Pettit, 

Thus TiO is the stable oxide in contact with TijAl and further oxidation leads to the formation of Ti02, i.e. rutile. The thermodynamics of the system Ti-Al-0 and the equilibrium conditions for the formation of the various oxide phases have been studied in detail (Rahmel and Spencer, 1991 Pajunen and Kivilahti, 1992 Li etal., 1992 Zhang etal., 1992b Saunders and Chandrasekaran, 1992). 

According to these thermodynamic considerations, the observed oxidation behavior is complex leading to a layered oxide scale structure with Ti02 on the outside and oxides with higher metal contents underneath, including AljOj (Khobaib and 

In spite of these successes the qc2 Hoy components are not yet flying (Froes et al., 1991), i.e. they are not yet implemented 

In solution vibrational relaxation is extraordinarily fast, and usually, thermal equilibrium is reached before emission or other photophysical or photochemical processes can come into play. In low-pressure vapors, however, time intervals between collisions will be large enough for other processes to be able to compete with vibrational relaxation. Hot reactions in excited states and particularly in the ground state, with the molecule excited to a 

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Rehbinder and co-workers were pioneers in the study of environmental effects on the strength of solids [144], As discussed by Frumkin and others [143-145], the measured hardness of a metal immersed in an electrolyte solution varies with applied potential in the manner of an electrocapillary curve (see Section V-7). A dramatic demonstration of this so-called Rehbinder effect is the easy deformation of single crystals of tin and of zinc if the surface is coated with an oleic acid monolayer [144]. 

The use of NMR spectroscopy to characterize copolymer microstructure takes advantage of this last ability to discern environmental effects which extend over the length of several repeat units. This capability is extremely valuable in analyzing the stereoregularity of a polymer, and we shall have more to say about it in that context in Sec. 7.11. 

The left-hand side of Equation (8.15) involves the difference between two electron binding energies, E — E. Each of these energies changes with the chemical (or physical) environment of the atom concerned but the changes in Ek and E are very similar so that the environmental effect on Ek — E is small. It follows that the environmental effect on E -h Ej, the right-hand side of Equation (8.15), is also small. Therefore the effect on is appreciable as it must be similar to that on There is, then, a chemical shift effect in AES rather like that in XPS. 

There is no official or universally accepted definition of what constitutes a "microemulsion." In fact, for several years, some leading scientists in microemulsion research considered the term to be an unnecessary and even an unfortunate one. Nevertheless (Table 1), during the years from about 1975 to 1980 the word ascended from obscurity to ubiquity. By the end of 1996 there were 13 widely available Knglish-language books (1 9) with the word "Microemulsion" in their tides (10). About 70 more books on surfactants are in print, of which those on industrial appHcations (9,11—18), and environmental effects (19—21) are of particular interest here. 

Office of Mobile Sources, Analysis of the Economic and Environmental Effects of Methanol as an Automotive Euel, U.S. Environmental Protection Agency, Ann Arbor, Mich., Sept. 1989. 

D. Layton and co-workers. Conventional Weapons Demilitarisation, A Health and Environmental Effects Data Base Assessment Explosives and Their Co-Contaminants, UERL-21109, Livermore National Lab., University of California, Livermore, Dec 1987. 

Possible negative environmental effects of fertilizer use are the subject of iatensive evaluation and much discussion. The foUowiag negative effects of fertilizer usage have been variously suggested (113) a deterioration of food quaUty the destmction of natural soil fertility the promotion of gastroiatestiaal cancer the pollution of ground and surface water and contributions toward the destmction of the ozone layer ia the stratosphere. 

HSDB National Library of Medicine s Toxicology Information Program toxicology and the environmental effects of chemicals... 

Environmental Concerns. Few data on the environmental effects of the nitroparaffins are available. However, they are known to be of low toxicity to the fathead minnow (109). Based on their uv spectra, the nitroparaffins would be expected to undergo photolysis in the atmosphere. The estimated half-life of 2-nitropropane in the atmosphere is 3.36 h (110). Various values have been determined for the half-life of nitromethane, but it is similar to 2-nitropropane in persistence (111). Reviews of the available data on the environmental effects of nitromethane and 2-nitropropane have been pubhshed by the U.S. Environmental Protection Agency (112,113). 

Health and Environmental Effects Profile forlSHtromethane U.S. Environmental Protection Agency, Cincinnati, Ohio, 1985. 

The U.S. domestic capacity of ammonium perchlorate is roughly estimated at 31,250 t/yr. The actual production varies, based on the requirements for soHd propellants. The 1994 production ran at about 11,200 t/yr, 36% of name plate capacity. Environmental effects of the decomposition products, which result from using soHd rocket motors based on ammonium perchlorate-containing propellants, are expected to keep increasing pubHc pressure until consumption is reduced and alternatives are developed. The 1995 price of ammonium perchlorate is in the range of 1.05/kg. Approximately 450 t/yr of NH ClO -equivalent cell Hquor is sold to produce magnesium and lithium perchlorate for use in the production of batteries (113). Total U.S. domestic sales and exports for sodium perchlorate are about 900 t/yr. In 1995, a solution containing 64% NaClO was priced at ca 1.00/kg dry product was also available at 1.21/kg. 

Environmental Effects of Plasticizers. Measurement of the effect of phthalates on environmental species is difficult because standard test methods are not designed to deal with poorly water-soluble substances. Eor this reason a number of early studies are flawed and their results should be disregarded in favor of more recent investigations where these difficulties have been overcome. 

Plastics testing encompasses the entire range of polymeric material characterizations, from chemical stmcture to material response to environmental effects. Whether the analysis or property testing is for quaUty control of a specific lot of plastic or for the determination of the material s response to long-term stress, a variety of test techniques is available for the researcher. 

The chronic aquatic effects which relate silver speciation to adverse environmental effects were studied on rainbow trout eggs and fry. The maximum acceptable toxicant concentration (MATC) for silver nitrate, as total silver, was reported to be 90—170 ng/L (43). Using fathead minnow eggs and fry, the MATC, as total silver, for silver thiosulfate complexes was reported as 21—44 mg/L, and for silver sulfide as 11 mg/L, the maximum concentration tested (27). 

Free ionic silver readily forms soluble complexes or insoluble materials with dissolved and suspended material present in natural waters, such as sediments and sulfide ions (44). The hardness of water is sometimes used as an indicator of its complex-forming capacity. Because of the direct relationship between the availabiUty of free silver ions and adverse environmental effects, the 1980 ambient freshwater criterion for the protection of aquatic life is expressed as a function of the hardness of the water in question. The maximum recommended concentration of total recoverable silver, in fresh water is thus given by the following expression (45) in Fg/L. 

J. S. Matfice, Environmental Effects of Cooling Systems, Technical Report Series 202, International Atomic Energy Agency, Vieima, 1980, pp. 12—26, 148-167. 

Environmental effects, including effect on methanogenic and nitrifying bacteria, persistence in the environment, and projections of possible HabiUty to relevant ecosystems. 

J. S. Dmry and co-workers, Keview of the Environmental Effects of Pollutants TT Beyllium, ORNE/EIS-87, EPA-600/1-78-028, Oak Ridge National Laboratory, Oak Ridge, Term., 1978, pp. 38—76. 

The electrical characteristics of ceramic materials vary gteady, since the atomic processes ate different for the various conduction modes. The transport of current may be because of the motion of electrons, electron holes, or ions. Electrical ceramics ate commonly used in special situations where reftactoriness or chemical resistance ate needed, or where other environmental effects ate severe (see Refractories). Thus it is also important to understand the effects of temperature, chemical additives, gas-phase equilibration, and interfacial reactions. 

A substantial body of information on the toxicological and environmental effects of chlotinated paraffins has been compiled over the past 20 years, and research is still continuing ia both areas. 

An important concern in photofinishing and in industrial photography is the environmental effect of effluents discharged by laboratories that process large quantities of color films. Further concerns are the limited suppHes of clean water available for processing in many areas and the high cost of energy to provide clean air and water at required temperatures. The completely self-contained instant films avoid all of these problems. 

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