bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gallium and Gallium Compounds
Authors: Sabot Jean Louis , Lauvray Hubert 
Published: July 2004

AbstractGallium is a scarce but not a rare element. It is found most commonly in association with its immediate neighbors in the Periodic Table, ie, zinc, germanium, and aluminum. The concentration of gallium in the earth's crust, 10–20 g/t (10–20 ppm), is comparable to that of lead and arsenic. There is an abundance of aluminum ores and alumina plants, and less importantly to gallium production zinc ores and plants; these are the main sources of gallium. The physical properties of gallium, especially its thermal properties, are exceptional. It is easily supercooled. In accordance with its normal potential, gallium is chemically similar to zinc and is somewhat less reactive than aluminum. A minor amount of gallium is extracted as a by‐product from the zinc industry. The significant amount of primary gallium is recovered from the alumina industry. The main source is the sodium aluminate liquor from Bayer‐process plants that produce large quantities of alumina.A large part of the wastes from the gallium arsenide industry is recovered for both economical and environmental reasons. Several processes are effective and are being used to recover both the gallium either as a metal, a salt, or a hydroxide for recycling, and the arsenic in some form for recycling or disposal. Gallium either comes from mining sources or is recycled from scrap.Gallium has complete miscibility in the liquid state with aluminum, indium, tin, and zinc. No compounds are formed.Numerous intermetallic gallium–transition element compounds have been reported. The toxicity of metallic gallium or gallium salts is very low. Gallium is used in the production of electronics and magnets, in medicine, as a petroleum industry catalyst, and in the solar reactions experiment.
Coal Conversion Processes, Gasification
Authors: Shadle Lawrence J. , Berry David A. , Syamlal Madhava 
Published: July 2004

Abstract
Coal gasification is presented in terms of the chemistry of coal conversion and the product gas characteristics, the historical development of coal gasifiers, variations in the types and performance of coal gasifiers, the configuration of gasification systems, and the status and economics of coal gasification. In many ways, coal gasification processes have been tailored to adapt to the different types of coal feedstocks available. Gasification technology is presented from a historical perspective considering early uses of coal, the first practical demonstration and utilization of coal gasification, and the evolution of the various processes used for coal gasification. The development of the gasification industry is traced from its inception to its current status in the world economy. Each type of gasifier is considered focusing on the process innovations required to meet the changing market needs. Complete gasification systems are described including typical system configurations, required system attributes, and aspects of the industry's environmental and performance demands. The current status, economics of gasification technology, and future of gasification are also discussed.
Gas, Natural
Authors: Woodcock Kermit E. , Gottlieb Myron 
Published: July 2004

Abstract
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

AbstractColor 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

AbstractA 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

AbstractHeat 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

Abstract
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

AbstractGermanium 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

Abstract
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

AbstractMetallic 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

Abstract
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

Abstract

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

AbstractHafnium, 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

AbstractHardness 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 ConversionsDespite 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

AbstractHeat 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.