bluuebunny/crossref_metadata_2025 huggingface dataset:
Gas, Natural
Authors: Woodcock Kermit E. , Gottlieb Myron
Published: July 2004

Natural gas is a mixture of naturally occurring hydrocarbon and non‐hydrocarbon gases found in porous geologic formations beneath the earth's surface. Methane is a principal constituent and the mixture may contain higher hydrocarbons such as ethane, propane, butane, and pentane. Gases such as carbon dioxide, nitrogen, hydrogen sulfide, various mercaptans, and water vapor along with trace amounts of other inorganic and organic compounds can also be present. Natural gas is found in a variety of geological formations including sandstones, shales, and coals. Worldwide natural gas reserves have continued to increase as the demand for gas has increased and exploration efforts have expanded. Natural gas production on a worldwide basis has also continued to increase. The composition of natural gas at the wellhead depends on the characteristics of the reservoir and is highly variable with respect to both the constituents present and the concentrations of these constituents. Natural gas obtained at the wellhead usually undergoes some type of treatment or processing prior to its use for safety, economic, or system and material compatibility reasons. Gases are odorless, but for safety reasons, natural gas is odorized before distribution to provide a distinct odor to warn users of possible gas leaks in equipment.

Natural gas is used as a fuel and source of heat throughout the industrialized countries for a broad range of residential, commercial. Both natural gas and natural gas liquids are used as feedstocks in the chemical industry. Production takes place both at onshore installations and on offshore platforms which service wells drilled to provide access to reservoirs located below the floor of the ocean.
Gemstone Treatment
Authors: Nassau Kurt
Published: July 2004

Color and clarity are two of the attributes that give gemstones used in jewelry value. Gemstones deficient in either color or clarity can be enhanced. Almost worthless material can at times be converted into valuable‐appearing gemstones. An estimated two‐thirds of all colored gemstones used in jewelry have been treated. Accordingly, the identification of the use of treatments and the disclosure of enhancements to the purchaser are important.

Some treatments are practiced so widely that untreated material is essentially unknown in the jewelry trade. The heating of pale Fecontaining chalcedony to produce red‐brown carnelian is one of these.

The stability of a particular treatment is also important. The enhancement should survive during normal wear or display conditions.

Heat and irradiation treatments are the major processes to enhance gemstones. A trained gemologist, is needed for identification of treated gems.
Polyamides, General
Authors: Weber Joseph N.
Published: July 2004

A general overview of polyamide technology is presented, with emphasis on commercial practice and technology developed since 1980. The article includes coverage of nomenclature; history; economic, health, and environmental aspects; and physical properties, including crystallinity, solubility, and piezoelectric effects. There is an extensive discussion of chemical properties including methods of preparation (direct amidation, reaction of acid chlorides, and ring‐opening polymerization of lactams via hydrolytic, anionic, and cationic processes); chemical reactions (acidolysis, aminolysis, alcoholysis, ammonolysis, transamidation, transesteramidation, and grafting); and degradation reactions (hydrolysis, thermal degradation, thermooxidation, photodegradation and photooxidation, biodegradation, and mechanodegradation). The manufacturing practices for most commercial nylons that are presented include monomer production for nylon‐6,6, nylon‐6, nylon‐4,6, nylon‐6,9, nylon‐6,10, nylon‐6,12, nylon‐11, nylon‐12, nylon‐12,12, and nylon‐13,13. Nylon‐6,6 and nylon‐6 are compared in detail. There are also discussions of copolyamides, mixed aliphatic–aromatic, and wholly aromatic polyamides. Extensive tables are presented which list CAS Registry Numbers, physical properties, and world‐wide manufacturers of most polyamides.
Geothermal Energy
Authors: Duchane David
Published: July 2004

Heat emanating from within the earth is one source of geothermal energy. This vast repository of energy is generated from the decay of natural radioisotopes and heat from the molten core of the earth.

Natural sources of geothermal fluids for heating and bathing have been utilized since prehistoric times. The useful applications of hydrothermal resources depend on the temperature of the extracted fluid. Relatively low temperature fluids can be effectively applied for purposes such as greenhouse heating, fish farming, and especially space heating. Waters at higher temperatures can be used for a variety of industrial processes. All direct uses of geothermal energy require that the point of application be essentially co‐located with the source of the hot water. Transportation of hot fluid over more than a few kilometers is impractical. The energy can, however, be converted to electricity. It is then possible to apply the power generated by hydrothermal energy in a variety of ways and at distant locations. The efficiency of electrical generation is directly related to the thermal quality of the resource. To successfully compete with the multitude of energy sources available, geothermal energy must be available and retrievable in both a convenient and an economical manner. Conditions have only been met using high grade geothermal resources in the form of hot water and steam and these particular hydrothermal resources are limited. Most of the world's accessible geothermal energy is found in rock that is hot but dry. Although research and development have demonstrated success in extracting thermal energy on a limited basis, the vast hot dry rock resource has not yet been shown to be an economically feasible source of energy on a scale large enough for practical use.
Geotextiles
Authors: Suits L. David
Published: July 2004

A geotextile, a subset of geosynthetics, is defined as any permeable textile material used with foundation soil, rock, earth, or any other geotechnical engineering‐related material, as an integral part of a synthetic project, structure, or system.

The varied uses of geotextiles include drainage, dissimilar materials separation, erosion control, environmental protection, highway pavement rehabilitation, as component materials for geocomposites used in a variety of applications. Within each of these categories of use there exist numerous types of installations using the geotextiles. Polymers used in the manufacturing process in decreasing order of use include polypropylene, polyester, polyamide (nylon), polyethylene, and others to a much lesser extent. Geotextiles may be woven, nonwoven, or knitted. Woven and nonwoven geotextiles are the most common types presently in use in geotechnical engineering. Geotextiles are a relatively new concept for solving problems in geotechnical engineering. They have gained wide use as not only an economical solution to these problems, but in many instances as the only viable solution to a complex engineering problem.
Germanium and Germanium Compounds
Authors: Thomas Dennis W. , Mahmood Tariq , Lindahl Charles B.
Published: July 2004

Germanium is a semiconducting metalloid element found in Group 14 (IVA), Period 4 of the Periodic Table. Although it looks like a metal, it has a diamond cubic crystal structure and is fragile like glass. Its electrical resistivity is about midway between that of metallic conductors and good electrical insulators. The first significant use was in solid‐state electronics, and, using germanium, the transistor was invented. The entire modern field of semiconductors owes it development to the early successful use of germanium. Germanium is used for optical fiber production, as polymerization catalysts, in infrared optics, in electronic and solar applications, and in other miscellaneous markets. Germanium usually occurs widely dispersed in minerals. Most germanium production has been from zinc smelters and copper smelters.

Germanium also occurs in significant concentrations in many coals around the world. Germanium is quite stable in air up to 400°C, where slow oxidation begins. The metal resists concentrated acid and alkali. Many Ge alloys have been prepared and studied.

No mineral is mined solely for its germanium content. Almost all of the Ge recovered worldwide is a by‐product of other mining. Germanium compounds generally have a low order of toxicity.
Ceramics, Glass Structure and Properties
Authors: Phifer Carol
Published: July 2004

Inorganic glasses are important ceramic materials and glasses share many of the desirable properties of crystalline ceramics even though they lack long‐range order. The structure of glasses is not completely random, however. Glasses do have short‐range order in the arrangement of anions around cations.

Glasses, less thermodynamically stable than crystals, must be “captured” in a metastable state, and this is typically accomplished by rapid cooling of a liquid.

The simplest inorganic glasses are composed of only one element: B, C, P, As, S, or Se. Glassy selenium in thin‐film form has been used extensively in the photocopying industry. Inorganic glasses containing more than one element can be broadly categorized according to the type of anion. There are two main categories: chalcogenide glasses and halide glasses. Several criteria for predicting which compounds form glasses have been proposed. The best known guidelines are those originally presented for oxide glasses and known as Zachariasen Rules.

The most striking and useful characteristic of common silicate glass is its transparency to visible light. This transparency results from the absence of grain boundaries and delocalized electrons, which tend to scatter and absorb light. There are many applications in which glass is used as an electrical insulator. One example is glass‐to‐metal seals. Moreover, other glasses are useful as a result of ionic or electronic conductivity. Glasses are good thermal insulators, making them ideal materials for windows in buildings. The thermal conductivity of a glass increases markedly as it is crystallized to form a glass–ceramic. The thermal conductivity of an aerogel is exceptionally low.

Glass processing techniques include melt processing, sol–gel processing, vapor‐phase processing, and thin‐film techniques. Silicate glass is a familiar, ubiquitous material, used in beverage containers, window panes, and automobile windshields. Increasingly, however, unusual glasses are being employed in high technology applications, such as optical fibers for telecommunications, graded‐refractive‐index glasses, nonlinear optical glasses, acousto‐optic glasses, fast‐ion conducting glasses, glass–ceramics, and glass microspheres.
Glassy Metals
Authors: Shiflet Gary J.
Published: July 2004

Metallic glasses do not occur naturally but are produced by various techniques, the oldest of which is by cooling molten metals so rapidly that the atoms do not get to form regular crystalline structures. The atoms are frozen in random or nonrepeating atomic patterns similar to those found in organic glasses. By metallic it is meant that the amorphous material is composed primarily, but not necessarily exclusively, of metallic elements that exhibit the properties of metals, such as electrical or magnetic behavior.

Primarily through modification of the chemistries, glasses have been produced that can truly be considered bulk, even exceeding 1 cm in all dimensions. Besides rapid solidification into thin ribbons or flakes, there exists a wide range of techniques to produce metallic glass. Methods available include chemical means, mechanical alloying, vaporization, and solid‐state reactions.

Interest is maintained in these materials because of the combination of mechanical, corrosion, electric, and magnetic properties. However, it is their ferro‐magnetic properties that lead to the principal application of glassy metals. The soft magnetic properties and remarkably low coercivity offer tremendous opportunities for this application.

A limitation of metallic glass is that it exists in metastable form, which means that it tends to crystallize if heated with sufficient thermal energy to allow the kinetics of crystallization, ie, both nucleation and growth, to occur.

To form an amorphous, ie, glassy metal alloy from the liquid stat means that the crystallization step must be avoided during solidification. Traditionally, production of metallic glasses requires rapid heat removal from the material which normally involves a combination of a cooling process that has a high heat‐transfer coefficient at the interface of the liquid and quenching medium, and a thin cross section in at least one‐dimension. Processes not dependent on rapid solidification include plastic deformation, mechanical alloying, and diffusional transformations.

Along with magnetic and mechanical behavior, high corrosion resistance is one of the most desirable properties of metallic glasses.

The magnetic properties of glassy metals provide the only commercial use in bulk quantities.
Groundwater Monitoring
Authors: Miller Carol J.
Published: July 2004

Groundwater monitoring is a necessary component in any investigation of subsurface contamination. It can be used to provide information on groundwater flow as well as groundwater quality concerns. Groundwater monitoring utilizes the skills of Civil Engineers, typically those specializing in geotechnical and environmental engineering. It involves the placement of monitoring wells for aquifer applications, and the use of suction lysimters and tensiometers in the unsaturated zone. Key issues involved in the design of monitoring well strategies include: site hydrogeology (flow rate and direction), subsurface material characterization (permeability, porosity, dispersivities, and organic content), contaminant characteristics, and potential remediation schemes. Design decisions include selection of monitoring tools, materials, location (placement), and analytical models for data analysis.
Gums
Authors: Baird John K.
Published: July 2004

The term
gums
denotes a groups of industrially useful polysaccharides or their derivatives that hydrate in hot or cold water to form viscous solutions, dispersions, or gels.

Gums are used in industry because their aqueous solutions or dispersions possess suspending and stabilizing properties. In addition, gums may produce gels or act as emulsifiers, adhesives, flocculants, binders, film formers, lubricants, or friction reducers, depending on the shape and chemical nature of the particular gum. Considerable research has been carried out to relate the structure and shape (conformation) of some gums to their solution properties. Gums fall into a category of specialty chemicals called thickeners and stabilizers. This market is dominated by starch, starch derivatives, and cellulosics.

Natural gums include agar (extracted from marine alagae); algin (from brown seaweed); carrageenan (from red seaweeds). Botanical gums represent a family of polysaccharides obtained from a wide variety of plant sources. They are divided into exudates gums, seed gums, and gums obtained by the extraction of plant tissue. Several microbial gums have been produced, but only a few, e.,g, xanthan, gellan, etc., have current application.
Hafnium and Hafnium Compounds
Authors: Nielsen Ralph H.
Published: July 2004

Hafnium, Hf, is in Group 4 (IVB) of the Periodic Table, as are the lighter elements zirconium and titanium. Hafnium is a heavy gray‐white metallic element never found free in nature. It is always found associated with the more plentiful zirconium. The two elements are almost identical in chemical behavior.

Hafnium is obtained as a by‐product of the production of hafnium‐free nuclear‐grade zirconium. Hafnium is used in nuclear control rods, nickel‐based superalloys, nozzles for plasma arc metal cutting, and high temperature ceramics.

Hafnium is a hard, heavy, somewhat ductile metal having an appearance slightly darker than that of stainless steel. Hafnium's aqueous chemistry is characterized by a high degree of hydrolysis, the formation of polymeric species, a very slow approach to true equilibrium, and the multitude of complex ions that can be formed. Hafnium is a highly reactive metal.

Most hafnium compounds have been of slight commercial interest aside from intermediates in the production of hafnium metal. However, hafnium oxide, hafnium carbide, and hafnium nitride are quite refractory and have received considerable study as the most refractory compounds of the Group 4 (IVB) elements.
Hardness
Authors: Crooks Ronald D.
Published: July 2004

Hardness is a measure of a material's resistance to deformation. Here hardness is taken to be the measure of a material's resistance to indentation by a tool or indenter harder than itself. This seems a relatively simple concept until mathematical analysis is attempted; the elastic, plastic, and elastic recovery properties of a material are involved, making the relationship quite complex. Further complications are introduced by variations in elastic modulus and frictional coefficients.

As a consequence, numerous practical applications of indentation hardness are in use and others are being developed. Many types of hardness tests have been devised. The most common in use are the static indentation tests, eg, Brinell, Rockwell, and Vickers. Dynamic hardness tests involve the elastic response or rebound of a dropped indenter, eg, Scleroscope. Although indentation hardness tests are usually classified as non‐destructive, they do in fact leave a permanent indentation on the surface of the workpiece.

Hardness Conversions

Despite variations in hardness test procedures and the variations in physical properties of the materials tested, hardness conversions from one test to another are possible.
Heat Stabilizers
Authors: Mesch Keith A.
Published: July 2004

Heat stabilizers protect polymers from the chemical degrading effects of heat or uv irradiation. These additives include a wide variety of chemical substances, ranging from purely organic chemicals to metallic soaps to complex organometallic compounds. By far the most common polymer requiring the use of heat stabilizers is poly(vinyl chloride) (PVC). However, copolymers of PVC, chlorinated poly(vinyl chloride) (CPVC), poly(vinylidene chloride) (PVDC), and chlorinated polyethylene (CPE), also benefit from this technology. PVC is the most important class of halogenated polymers requiring these chemical additives.

In normal operations, PVC resin is intimately mixed with the desired ingredients under high intensity shear mixing conditions to result in a homogeneous dry powder compound. The heat stabilizers can be either liquids or powders and are added early in the blending cycle to afford stabilizing action during this operation. Preheating the resin to about the glass‐transition temperature facilitates the adsorption of the liquid additives giving the final compound better powder flow properties and decreasing the bulk density. Post‐compounding operations, eg, extrusion pelletizing, can increase the overall heat history of the polymer, thus necessitating slightly higher levels of heat stabilizers to compensate for this.

Organotin‐based heat stabilizers are the most efficient and universally used PVC stabilizers. These are all derivatives of tetravalent tin. The second most widely used class of stabilizers are the mixed metal combinations. These products predominate in the flexible PVC applications in the United States. The commercially important alkali and alkaline‐earth metals used in these stabilizer systems are based on the salts and soaps of calcium, zinc, magnesium, barium, and cadmium. Other organic compounds, such as phosphites, epoxides, polyols, andβ‐diketones, can also be added to enhance the performance further. Antimony mercaptan stabilizers are also used.
Automated Instrumentation, Hematology
Authors: Zelmanovic David , Garcia Roque A. , Turrell John
Published: July 2004

Hematology analyzers provide information about blood cells and their constituents. The three basic blood cell types are erythrocytes or red blood cells, leukocytes or white blood cells, and thrombocytes or platelets. Hemoglobin is the principal nonaqueous component of red blood cells. Its physiological importance gives it the status of a primary hematological constituent. The aperture impedance principle of blood cell counting and sizing, also called the Coulter principle, exploits the high electrical resistivity of blood cell membranes. In the aperture impedance method, in its simplest form, a d‐c current flows between the electrodes. The resistive cells reduce the current as the cells pass through the aperture, and the current drop is sensed. Aperture impedance counters are flow cytometers, as are all current automated cell counters. Flow cytometers measure cells as the cells flow hydraulically, one at a time, through sensing zones. Aperture impedance counters provide cell volume information as well as cell counts. The light‐scattering principle of cell counting is based on the observation that microscopic particles, such as blood cells, scatter into small (0–15°) angles, most of the visible light incident upon them. This principle is used to count red blood cells, white blood cells, and platelets. The basic single‐angle interval light‐scattering method cannot accurately measure individual red blood cell or platelet volumes, but it can provide mean red cell volume (MCV) and mean platelet volume (MPV). A sphered cell's volume and the hemoglobin concentration can both be accurately determined from Mie Scattering Theory calculations by making simultaneous measurements of light‐scatter intensity over two suitably chosen angle interval. Two suitable angle intervals for red cells are 2–3°, known as low angle scatter (SL), and 5–15°, high angle scatter (SH). Cytochemical techniques can be combined with light‐scattering and absorption measurements to provide five‐part Diffs. Cytochemistry concerns the chemical reactions of cell components. Various method combinations can be used to produce five‐part Diffs including d‐c/r‐f aperture impedance plus light scattering; two‐angle interval light‐scattering plus depolarized light scattering; light scattering plus cytochemistry; and d‐c/r‐f aperture impedance plus cytochemistry. Flow cytometric methods produce five‐part Diffs that are generally more precise and accurate than manual Diffs. However, manual methods can provide more information. Most automated hemoglobinometry methods are derivatives of the manual ICSH reference method, in which the blood sample is diluted in a reagent to lyse the RBC membrane, releasing hemoglobin into solution, ferricyanide present in the diluent diffuses into the hemoglobin molecule yielding methemoglobin, and cyanide diffuses into methemoglobin's interior and reacts with heme to yield cyanmethemoglobin (HiCN), which is measured spectrophotometrically.
Hemicellulose
Authors: Thompson Norman S.
Published: July 2004

Hemicellulose, a poorly utilized component of arborescent plants, is a complex mixture of polysaccharides, each exhibiting polydispersity, polymolecularity, and polydiversity to varying extents. Hemicellulose is defined in this article as the noncellulosic polysaccharides that make up the cell wall structure of vegetable material, but other definitions based on solvent behavior also occur in the literature. The most common polysaccharides included in all definitions are xylans, arabinogalactans, and pectic materials of varying compositions found in gymnosperms and angiosperms, glucomannans found in gymnosperms and dicotyledons but seldom, if at all in monocotyledons, and β‐D‐glucans found only in monocotyledons. Xylans and glucomannans are the primary hemicellulose components of fibers and tracheids of arborescent plants, but other unique hemicellulose components may occur in significant quantities in other parts of the plant. The intimate association of hemicellulose with lignin and cellulose makes it difficult to isolate without unwanted degradation. Some mixtures of hemicellulose components cannot be separated in a quantitative manner. The utilization of hemicellulose components is complicated by their complexity and because of the transformations that they have undergone in many manufactured products. They affect the products in which they are present, being harmful in dissolving pulps and a mixed blessing in paper products, and are generally a beneficial components of foods.
High Pressure Technology
Authors: Bett K. E.
Published: July 2004

The growth in the use of high pressure by the chemical industry during the twentieth century, leading to the discovery of polyethylene by ICI in the early 1930s, is described briefly. At that time, the pressures required for the large‐scale production of low density polyethylene (LDPE) were well beyond the normal design practices for continuously operating plants and the development of the process in both the United States and Europe posed formidable problems. This led to a number of different modifications to the high pressure procedure used by ICI.

The basic principles governing the design of thick‐walled cylinders to withstand static high internal pressure are reviewed. It is shown how these principles together with the results of much work carried out since the 1940s, particularly that directed toward increasing the fatigue strength of cylinders subjected to pulsating internal pressure, were used to develop both stirred and tubular reactors, reciprocating compressors, initiator pumps, etc, for use in the production of LDPE at pressures up to about 345 MPa.

Most of the article is devoted to the design of continuous chemical plants; some attention is given to the problems of designing equipment for isostatic compaction which is operated as a batch process.
High Temperature Alloys
Authors: Stoloff Norman S.
Published: July 2004

High temperature alloys are combinations of metals used specifically for their heat resisting properties. Applications in the aircraft, automotive, power generation, and space‐related industries include use in steam and gas turbine engines, as cutting tools, and as various spacecraft parts.

The alloys most often used at high temperatures include steels, superalloys, refractory metal alloys, and new materials such as aligned eutectics and intermetallic compounds. These alloys, their properties and surface stability, mechanical behavior, and the strengthening mechanisms employed are discussed.

Various plain carbon and low alloy steels are employed as are modified stainless steels. Superalloys may have nickel, cobalt, or iron–nickel bases. The nickel‐base superalloys are most often used for high temperature structural applications in air. The Group 6 (VIB) metals and their alloys and various new materials are often employed as cutting tools and in spacecraft.
High Purity Gases
Authors: Whitlock Walter H. , Ezell Edward F. , Hwang Shuen‐Cheng
Published: July 2004

High purity industrial gases are routinely delivered in large quantities having purities exceeding 99.999% (>5 nines pure). Other commodity materials, whether in liquid or solid form, much less typically have purity exceeding 99.9%. There are many applications for gases where purity even higher than 99.999% is required. To service these applications, the technology for manufacturing and delivering high purity gases has developed into a multibillion dollar business worldwide. Japan and the United States have the majority of the market.

There is no universally accepted definition of what purity levels correspond to high purity. A good working definition of high purity is gases having certain individual impurities held to levels <0.1 ppm.

The technology for manufacturing and delivering high purity gases has largely developed to support the manufacture of advanced semiconductor materials needed as part of the overall process of manufacturing integrated circuits. Purity requirements in some of these high performance materials have reached the point where impurity concentrations in the starting gases of 1 part in 10
12
have been related to reduced yields and poor performance in the resulting integrated circuits. Depending on a volume, high purity gases can be delivered using either bulk systems, where a plant‐wide distribution system is integrated with central gas storage facilities, or cylinders, where a short local distribution system is supplied from a single high pressure cylinder.

Gases used in the manufacture of semiconductor materials fall into three principal areas: the inert gases, used to shield the manufacturing processes and prevent impurities from entering; the source gases, used to supply the molecules and atoms that stay behind and contribute to the final product, and the reactive gases, used to modify the electronic materials without actually contributing atoms or molecules.
Histamine and Histamine Antagonists
Authors: Janssens Monique M.‐L. , Timmerman Hendrik , Leurs Robert
Published: July 2004

Histamine, endogenously formed by decarboxylation of histidine, is stored preformed and released during allergic, reactions. Histamine is also responsible for gastric acid secretion, functions as a neurotransmitter in the brain, and may have a physiological role in the cardiovascular system. The actions of histamine are mediated through H1, and H3receptors. The H1receptor mediates most of histamine's effects in allergic diseases and H1receptor antagonists are used in the treatment of such diseases as allergic rhinitis and urticaria. Classical H1antagonists, primarily all substituted ethylamines, cause sedation, whereas second‐generation H1antagonists do not. Both types of H1antagonists are described. The most important effect mediated through H2receptors is gastric acid secretion. H2agonists and antagonists are described. The antagonists are available for the treatment of peptic ulcer disease and esophageal reflux. The H3receptor is present in the brain and in peripheral tissues modulating the release of a variety of neurotransmitters. H3agonists and antagonists are described. No clear therapeutic indications have been reported for H3ligands.
Hollow‐Fiber Membranes
Authors: Moch Irving
Published: July 2004

Hollow‐fiber membranes were invented in the 1960s. In the ensuing decades much research and development effort has transpired with the result that these fibers have become exceedingly important to industry, academia, and government in such fields as desalination of water, wastewater reclamation, medicine, agriculture, gas separation, and pervaporation. Commercial opportunities annually exceed several hundred million dollars. The hollow‐fiber membranes are usually the base technology within a significantly larger system.

This article briefly discusses the history and theory of hollow‐fiber membrane technology. Methods of manufacture are reviewed together with processing techniques employed to enhance various aspects of performance. Hollow‐fiber membranes are composed of many different materials of construction. The generic compositions are cited and specific end use applications noted. Lastly, the work to date has identified many areas where future prospects for hollow‐fiber membranes are the brightest. A number of these future growth areas are discussed together with which industrial corporations are in the forefront of the new developments.
Holography
Authors: Honh John H.
Published: July 2004

Holograms are capable of storing and displaying the optical waves scattered by an object wholly in a way that is completely unique from photographs which are, at best, accurate but flat projections. A hologram is essentially an interferometric, record of a wavefront so that the whole character of the wave, its amplitude, and phase, is captured. This article describes the fundamentals of optical holography, beginning with a discussion of the holographic principle and concluding with descriptions of important applications in the areas of displays, interferometry, data storage, and information processing. The large variety of hologram formats, materials, and techniques available to the holographer is explored in some detail with mathematical expressions that model the optical behavior of specific types of holograms given whenever appropriate.
Hydrogen Energy
Authors: Billings Roger E.
Published: July 2004

Billings, Roger E. (International Academy of Science). Hydrogen energy is expected to play an important role in the energy of the twenty‐first century in part because of increased concerns about environmental pollution, depleting fossil fuel resources, and advances in utilization technologies.

Costs of hydrogen production and hydrogen storage appear to be the limiting steps. Hydrogen can be utilized in a variety of energy applications including as a fuel for the internal combustion engine. Hydrogen can be safely stored at ambient pressures as powdered metal hydride. Testing of hydrogen‐fueled prototype vehicles has demonstrated higher utilization efficiencies for hydrogen than for conventional fossil fuels. Hydrogen has also been utilized as a fuel for household appliances originally manufactured to operate on natural gas.

Hydrogen can be efficiently converted into electricity by means of a hydrogen fuel cell. Such a device can generate electric power for stationary applications or for electric vehicles. Hydrogen fuel cells are two to three times more efficient than conventional internal combustion engines.
Hydroxy Dicarboxylic Acids
Authors: Blair Gary T. , DeFraties Jeffrey J.
Published: July 2004

Malic acid and tartaric acid are two hydroxy dicarboxylic acids of commercial significance. Thiomalic acid and derivatives of malic and tartaric acid are discussed briefly. For malic and tartaric acids, physical and chemical properties, manufacturing process, commercial significance, health and safety properties, and primary applications, including food, pharmaceutical, and industrial, are reviewed. The primary chemical reactions are summarized; chelation and corrosion are discussed. The primary chemical reactions are summarized; chelation and corrosion are discussed. The commercial production procedures for malic acid and tartaric acid are summarized. Compendial specifications (Food Chemicals Codex, National Formulary) for malic acid and tartaric acid are listed.
Hydrogen Peroxide
Authors: Eul W. , Moeller A. , Steiner N.
Published: July 2004

Hydrogen peroxide is a strong oxidizing agent commercially available in aqueous solution over a wide concentration range. Its many uses involve its varied chemistry and are based on oxidations, reductions, substitutions, molecular additions, and decompositions. Product from hydrogen peroxide decomposition are the environmentally benign oxygen and water. Manufacture and use, especially in industrial bleaching applications, are on the rise, fueled by environmental concerns and econological pressure to replace chlorine‐based bleaching with the cleaner peroxide chemistry.

Manufactured primarily in large, strategically located anthrahydroquinone autoxidation processes, the primary use for hydrogen peroxide is in bleaching wood pulp. Hydrogen peroxide is also produced electrolytically. The various manufacturing processes are discussed. Safe use and handling require adherence to approved procedures and use of proper protective equipment.
Hydrogen Chloride
Authors: Hisham Mohamed W. M. , Bommaraju Tilak V.
Published: July 2004

Hisham, Mohamed W. M. and Bommaraju, Tilak V., (Occidental Chemical Corp.). Hydrogen chloride, a gas at ambient temperature and pressure, is very soluble in water. Hydrogen chloride can be produced by direct reaction of the elements, by reaction of metal chlorides and acids, and as a by‐product from many chemical manufacturing processes such as those for chlorinated hydrocarbons. Over 90% of the hydrogen chloride produced in the United States is as a by‐product from various chemical processes. HCl is produced as a by‐product in the manufacture of chlorofluorohydrocarbons, aliphatic and aromatic hydrocarbons, production of high surface area silica, and the manufacture of phosphoric acid and esters of phosphoric acid. Crude by‐product HCl is generally contaminated with impurities of the process. A wide variety of techniques are employed to treat the HCl streams to obtain either anhydrous HCl or hydrochloric acid. Technologies have been developed for burning or pyrolyzing waste organics and recovering the chlorine values as hydrogen chloride.

Hydrogen chloride and its aqueous solution, muriatic acid, find application in many industries. In general, anhydrous HCl is consumed for its chlorine value, whereas aqueous hydrochloric acid is often utilized as a nonoxidizing acid, in metal‐cleaning operations, chemical manufacturing, petroleum well activation, and the production of food and synthetic rubber. Most of the HCl produced is consumed captively either in integrated operations, eg, chlorinated methane plants, or in separate HCl‐consuming operations at the same location.
Hydrocarbon Oxidation
Authors: Hobbs Charles C.
Published: July 2004

Hydrocarbon oxidation has long been a significant source of organic chemicals. Both vapor‐ and liquid‐phase reactions are of interest; they are believed to involve free‐radical chain mechanisms. Modern understanding of these reactions has developed over the last half of the twentieth century. Although sharp disputes are frequent, significant agreement on underlying principles is apparent.

Vapor‐phase oxidations can be conveniently divided into low, middle, and high temperature ranges. Fundamental changes in mechanisms occur over these regions. The direct oxidation of methane to methanol, formaldehyde, and/or C2products has received intense study, but no viable processes have yet been developed. Most other studies in this area are directed toward fuel utilization and pollution abatement.

Liquid‐phase oxidations of aliphatics have declined in importance as sources of bulk chemicals. However, the oxidation of butane to acetic acid, and of isobutane tot‐butylhydroperoxide (to produce propylene oxide), and of cyclohexane to cyclohexanol and cycohexanone (to produce adipic acid and nylon), remain important industrial processes. Oxidations of alkylaromatics continue to be important industrially. The oxidation ofp‐xylene to terephthalic acid and cumene to phenol are dominant routes to these products. The potential for producing fine chemicals by such oxidations is developing rapidly.
Aluminum Oxide (Alumina), Hydrated
Authors: Misra Chanakya
Published: July 2004

The term alumina hydrates or hydrated aluminas is used in industry and commerce to designate aluminum hydroxides. These compounds are true hydroxides and do not contain water of hydration. The most well‐defined crystalline forms are the trihydroxides, Al(OH)
3
: gibbsite, bayerite, and nordstrandite. In addition, two aluminum oxide–hydroxides, AlO(OH), boehmite and diaspore, have been clearly defined. The terms gelatinous alumina or alumina gel cover a range of products in which colloidal hydrated alumina is the predominant solid phase. Structural order varies from x‐ray indifferent (amorphous) to some degree of crystallinity. Apart from the crystalline forms, aluminum hydroxide often forms a gel. Gel products have considerable technical use. Aluminum hydroxides are technically the most widely used members of the alumina chemicals family. The most important source of aluminum hydroxides is the bauxite refining plant (Bayer process) for alumina production. Several commercial grades of aluminum hydroxide are produced. Hydroxide grades can be surface‐treated to modify dispersion behavior and rheological properties. Aluminum hydroxides are minimally absorbed by the body. Death upon ingestion occurs from intestinal blockage rather than systemic aluminum toxicity. In recognition of the possible adverse effects of long‐term exposure to alumina dusts, threshold limit values have been established by the ACGIH. Aluminum hydroxide and aluminum hydroxide oxide are reported in EPA TSCA inventory.
Hydrides
Authors: Eggeman Tim
Published: July 2004

Sullivan, Edward A. (Morton International). Hydrides may be divided into two groups: simple and complex. The simple or binary hydrides may be ionic, covalent, or interstitial as are most of the transition metal hydrides. The important properties, methods of manufacture, safe handling, and important uses of the commercial binary hydrides and certain hydrogen storage alloys are reviewed. Alkali metal, alkaline‐earth, and Group 4, 5, 13, and 14 hydrides find use in a variety of industries among which are the electronics, pulp and paper, dyeing, and clay industries.

The most important complex hydrides are the borohydrides and alumino‐hydrides. The important alkali metal salts of these hydrides are described. Complex hydrides are used principally in the synthesis of organic compounds effecting specific and nonspecific reductions. Alkoxyborohydrides, cyanoborohydride, acyloxyborohydrides, and alkoxy‐aluminohydrides, are also discussed.
Imines, Cyclic
Authors: Scherr G. , Steuerle U. , Fikentscher R.
Published: July 2004

This article describes aziridines with particular emphasis on the parent compound ethyleneimine. The physical and chemical properties of ethyleneimine, such as aminoethylation, synthesis of heterocycles, and polymerization, are discussed. Current industrial production methods, economic aspects, analytical and test methods, storage and toxicology, and safe handling procedures for ethyleneimine are described. The wide‐ranging applications of ethyleneimine derivatives, including the paper industry, extraction and complexing, additives, fixing, textile finishing, flocculation, electroplating, medicine, membranes and osmosis, and tertiary crude oil extraction are reviewed.
Immunoassay
Authors: Taylor Richard F.
Published: July 2004

Immunoassay, a diagnostic and measurement method which utilizes antibodies to detect and quantify specific analytes (antigens), is characterized by high analyte specificity, high sensitivity (routinely detecting ng to pg analyte levels), and rapid data output. It is amenable to a variety of formats, from single immunoassays carried out manually, to fully automated instruments capable of performing multiple assays on the same or different analytes. Immunoassay quantification methods are based on immunoprecipitation, such as agglutination assays, or on specific indicator reagents linked to antibody or antigen reagents used in the immunoassay. These include radioisotopes for radioimmunoassay, enzymes for enzyme‐linked immunoassay, fluorophores for fluorescence immunoassay, and chemiluminescent labels for chemiluminescent immunoassay. Immunoassay technology is continuing to evolve and applications are reaching beyond traditional clinical settings to industry and the environment. Immunoassays are also serving as the basis for newer measurement technologies including hybrid immunoassay–nucleic acid probe assays and immunobiosensors.
Incinerators
Authors: Diemer R. Bertrum , Ellis Thomas D. , Silcox Geoffrey D. , Lighty JoAnn S. , Pershing David W.
Published: July 2004

Many industrial manufacturers, municipalities, and most medical facilities use thermal destruction by incineration to dispose of wastes. Increased research has led to greater understanding of thermal destruction processes and the systems required to meet environmental regulations such as those of the U.S. Environmental Protection Agency governing the design and operation of incinerators. Incineration systems and theoretical phenomena for the destruction of liquid, solid, and gaseous wastes are described. Methods for establishing the appropriate technology are discussed. Evaluation of combustion mechanisms and the products of combustion, along with equipment needed to remove atmospheric pollutants, are described.
Inclusion Compounds
Authors: Weber Edwin
Published: July 2004

Inclusion compounds may be classified into three main categories: complexes, cavitates, or clathrates. Typical examples for each class of inclusion compounds are the crown complexes, the calix–cavitates, and the hydroquinone clathrates. All of these compounds have in common the ability to incorporate into the cavities of their own molecules, or within their lattices, other molecules of suitable size, spatially to enfold them, that is to hold them, mostly by physical imprisonment.

Materials having the attribute of inclusion have given rise to what is called host–guest chemistry, a typical feature of which is accommodation of a complementary guest species into a concave host framework involving a molecular recognition process such as imaged by the complementarity of a lock and a key. Logically, a new broad area of chemistry grew up on this basis starting in the 1970s. It is called supramolecular chemistry and means the chemistry beyond the molecule. This article surveys the various types of inclusion compounds and their applications.
Indium and Indium Compounds
Authors: Chagnon Mark J.
Published: July 2004

Indium, indium alloys, and indium compounds exhibit a wide range of diverse properties. For example, the metal retains plasticity at cryogenic temperatures and many compounds with the metalloids are semiconducting. Applications vary from the use of the metal in the control rods of nuclear reactors, to that of alloys as solders, and of indium trioxide as an electrically conductive film for glass and plastic.

Indium is referred to as a minor metal and is basically a by‐product of the zinc and lead‐zinc industries. Properties are described. Uses and production are discussed. Expanded economic data is given. Indium metal poses little or no environmental risks but some forms may pose dangers to the environment.
Indole
Authors: Sundberg Richard J.
Published: July 2004

Indole is an electron‐rich heteroaromatic nitrogen heterocycle which is isolated from coal‐tar distillate. The chemistry of indole is dominated by electrophilic substitution reactions which occur primarily at the 3‐position. Organometallic derivatives, especially lithium compounds, permit reactions at other ring positions. Substituted indoles are usually prepared from benzene derivatives having a nitrogen substituent. Indole derivatives appear prominently in nature, usually as metabolites of tryptophan. Examples include plant alkaloids and fungal metabolites. Synthetic derivatives of indole have been extensively explored as pharmaceuticals; the nonsteroidal antiflammatory drug indomethacin is the most widely used example.
Industrial Hygiene
Authors: Lynch Jeremiah
Published: July 2004

Industrial hygiene is defined as the anticipation, recognition, evaluation, and control of those environmental factors or stresses arising in or from the workplace that may cause sickness, impaired health or well‐being, or significant discomfort and inefficiency among workers or among the citizens of the community. The practice of industrial hygiene starts with an awareness of the hazardous nature of chemical, physical, and biological agents, and of the processes which give rise to opportunities for people to be exposed to these agents. The skill of industrial hygienists includes this recognition ability, the skill to make and interpret complex measurements of conditions, and the ability to identify risk reduction measures which may range from changes in work practices to modifications of the physical plant. All of this is performed in continuous interactions with workers, management, regulatory agencies, the public, and other professionals such as physicians and safety professionals. The techniques of industrial hygiene undergo continuous improvement resulting from the work of the practitioners and from research in toxicology, epidemiology, risk assessment, analytical chemistry, engineering, and other disciplines.