Atmosphere high temperature


This is an endothermic reaction accompanied by an increase in the number of moles. High conversion is favored by high temperature and low pressure. The reduction in pressure is achieved in practice by the use of superheated steam as a diluent and by operating the reactor below atmospheric pressure. The steam in this case fulfills a dual purpose by also providing heat for the reaction.  [c.44]

When a hot utility needs to be at a high temperature and/or provide high heat fluxes, radiant heat transfer is used from combustion of fuel in a furnace. Furnace designs vary according to the function of the furnace, heating duty, type of fuel, and method of introducing combustion air. Sometimes the function is to purely provide heat sometimes the furnace is also a reactor and provides heat of reaction. However, process furnaces have a number of features in common. In the chamber where combustion takes place, the heat is transferred mainly by radiation to tubes around the walls of the chamber, through which passes the fluid to be heated. After the flue gas leaves the combustion chamber, most furnace designs extract further heat from the flue gas in a convection section before the flue gas is vented to the atmosphere.  [c.188]

Reaction rates often may be improved by using more extreme operating conditions. More extreme conditions may reduce inventory appreciably. However, more extreme conditions bring their own problems, as we shall discuss later. A very small reactor operating at a high temperature and pressure may be inherently safer than one operating at less extreme conditions because it contains a much lower inventory. A large reactor operating close to atmospheric temperature and pressure may be safe for different reasons. Leaks are less likely, and if they do happen, the leak will be small because of the low pressure. Also, little vapor is produced from the leaking liquid because of the low temperature. A compromise solution employing moderate pressure and temperature and medium inventory may combine the worst features of the extremes. The compromise solution may be such that the inventory is large enough for a serious explosion or serious toxic release if a leak occurs, the pressure will ensure that the leak is large, and the high temperature results in the evaporation of a large proportion of the leaking liquid.  [c.263]

Certain curves, T = f(% distilled), level off at high temperatures due to the change in pressure and to the utilization of charts for converting temperatures under reduced pressure to equivalent temperatures under atmospheric pressure.  [c.332]

It is widely believed that gases are virtually ideal at a pressure of one atmosphere. This is more nearly tnie at relatively high temperatures, but at the nonnal boiling point (roughly 20% of the Boyle temperature), typical gases have values of pV/nRT that are 5 to 15% lower than tlie ideal value of unity.  [c.356]

The vapour pressures of the various hydrate systems increase with temperature (compare the figures for the three copper sulphate - water systems of equations (i), (ii) and (iii) at 25° and 50° already given). It follows, therefore, that the efficiency of desiccants decreases with rise of temperature and, indeed, at high temperatures certain desiccating agents may actually undergo dehydration. Thus the vapour pressures of some calcium chloride - water systems exceed atmospheric pressure at high temperatures, as can be seen from the following table.  [c.42]

Phenylethylene boils at 145-146° at atmospheric pressure, but the high temperature causes a considerable loss by polymerisation. It has been stated that the addition of about 0-1 per cent, by weight of hydroquinone considerably reduces the extent of polymerisation at atmospheric pressure.  [c.1024]

Type E thermoelements (Table 11.57) are very useful down to about liquid hydrogen temperatures and may even be used down to liquid helium temperatures. They are the most useful of the commercially standardized thermocouple combinations for subzero temperature measurements because of their high Seebeck coefficient (58 /xV/°C), low thermal conductivity, and corrosion resistance. They also have the largest Seebeck coefficient (voltage response per degree Celsius) above 0°C of any of the standardized thermocouples which makes them useful for detecting small temperature changes. They are recommended for use in the temperature range from —250 to 871°C in oxidizing or inert atmospheres. They should not be used in sulfurous, reducing, or alternately reducing and oxidizing atmospheres unless suitably protected with tubes. They should not be used in vacuum at high temperatures for extended periods of time.  [c.1216]

The Type K thermocouple (Table 11.59) is more resistant to oxidation at elevated temperatures than the Type E, J, or T thermocouple, and consequently finds wide application at temperatures above 500°C. It is recommended for continuous use at temperatures within the range — 250 to 1260°C in inert or oxidizing atmospheres. It should not be used in sulfurous or reducing atmospheres, or in vacuum at high temperatures for extended times.  [c.1216]

In arc processes, either d-c or a-c current is used to estabUsh and maintain an arc between the base metal and an electrode. The electrode itself may be consumed by melting and thus become part of the weld, acting as a filler metal, or it may be a nonconsumable material, eg, tungsten. In the latter case, the heat of the electric arc may simply be used to fuse adjacent base metal (autogenous welding), or a separate filler metal may be added. It is essential that the molten pool of material under the arc, as well as the adjacent solidified but still high temperature metal, be protected from oxygen, nitrogen, and other elements of the atmosphere, since these react with the metal to form oxides and other products that reduce the strength and toughness of a weld. Consequentiy, various forms of shielding are provided around the arc in the different processes.  [c.341]

Aluminum and Aluminum Alloys. Aluminum alloys are used wherever lightness or atmospheric corrosion resistance are requited, or where mildly corrosive fluids are involved. Typical appHcations for aluminum alloys include railroad tank cars and the skin on aircraft increasingly, aluminum is being used in the automotive industry. Aluminum alloys are classified as heat-treatable or nonheat-treatable. Strengths of commercially pure and nonheat-treatable alloys are developed by strain hardening and by alloying elements of which magnesium, manganese, and silicon are typical examples. The beneficial effects of strain hardening can be erased by the heat of the welding process thus, heat inputs ate kept low when welding these aluminum alloys. The alloying elements in heat-treatable aluminum alloys are dissolved in the aluminum at high temperature by a process known as solution heat treatment subsequent heat treatment precipitates these elements as microscopic particles of intermetaUic phases, which strengthen the alloy. The welding heat dissolves these particles at or neat the weld, thus reducing the strength properties can be restored by a post-weld heat treatment.  [c.347]

Fracture toughness of SiC tends to be lower than that of other stmctural ceramics leading to some concern about the appHcation of SiC in certain heat engines, such as turbine rotors which may be susceptible to impact from foreign objects (30). The yttria Hquid-phase sintered SiC is, however, reported to be comparable to other stmctural ceramics in fracture toughness. Erosion and corrosion characteristics have not been measured as extensively as other mechanical properties. Wear and coefficient of friction measurements have mostly been appHcation specific, but point out the importance of surface preparation and characterization. PubHshed erosion results show good resistance to angular particle or slurry erosion. Reaction-bonded SiC tends to be the most susceptible to erosive wear because of preferential wear of surface connected free siHcon grains (31). Reaction-bonded SiC also appears much less resistant to acids, alkaH, and high temperature combustion products than the single-phase sintered material (32). In contact with sodium sulfate, or acidic or basic coal slags from coal gasification, SiC tends to corrode slightly in a pitting reaction. In basic coal slag reactions at temperatures from 1000 to 1300°C, the reaction involves dissolution of the protective siHca oxidation layer followed by reaction with Fe or Ni to form low-melting point siHcides (33). Sintered siHcon carbide has also been shown to corrode at elevated temperature in hydrogen-containing atmospheres. The reaction appears to be a decarburization of the SiC, particularly at grain boundaries, resulting in siHcon rich regions and some grain fallout (34). Corrosion from sodium siHcate glass vapors and particulates has demonstrated that both sintered and reaction-bonded SiC corrode through passive oxidation foUowed by dissolution of the oxide coating. The siHcon component in reaction-bonded SiC was oxidized more rapidly than the SiC phase (35).  [c.321]

Nitrogen present in the fuel tends to produce other nitrogen oxides in addition to NO, which leads to higher exhaust concentrations of NO than would exist from the combustion-driven nitrogen fixation alone. NO reacts with O2 at a slow but steady rate in the atmosphere and thus NO ends up as NO2. Combustion chemistry and NO formation and control have been reviewed (100,101). NO formation in combustion may be reduced by maintaining low excess air (0.5% O2 or less in flue gas), employing two-stage combustion where the first stage is fuel-rich and reducing (high temperature) and the second stage is oxidising (1000—1100°C), flue gas recirculation, burner design, combustion chamber modifications, and burner placement. Combustion technology (qv) methods (102—112) are limited in their NO reduction capabiUties to ranges of 200—300 ppmv NO. Target emission levels for acid rain control are expected to be 80—100 ppmv of NO. Retro-fitting with low NO burners is one of the least expensive ways to achieve NO reduction. References 103 and 104 discuss low NO burner design. An overview of NO control from industrial sources has been presented (113) references 114—116 discuss NO control retrofit. Other control methods which are being developed for combustion NO emissions are selective catalytic reduction (SCR), Thermal Denox, and urea reduction (88,113—122).  [c.391]

No bag fabric can withstand tmly high temperature, therefore gas cooling is often practiced. The usual methods are indirect cooling, tempering with cold air, direct water spray cooling, or a combination of any of these. Indirect cooling may take place in radiation panels or ducts exposed to the atmosphere, in waste heat boilers, or in heat transfer devices such as finned heat exchangers and heat wheels. Tempering consists of mixing air from the atmosphere and the hot gas in a duct good mixing must be provided to ensure temperature equiUbration. Automatic temperature control can be quite precise and tempering can reduce the dewpoint of a hot, humid gas. The major disadvantage is that tempering increases the gas volume and hence the  [c.405]

Direct water spray cooling must be carried out with care. The spray chamber must be designed to ensure complete evaporation of all Hquid droplets before the gas enters the baghouse. Spray impinging on the chamber walls can result ia a dust mud iaside the chamber and any increase ia gas dewpoint may result in baghouse problems or atmospheric plume condensation. Spray nozzle wear can result in coarse or distorted spray and wetted bags, and water pressure failure can cause high temperature bag deterioration.  [c.406]

Oxidation. Aluminum alkyls are oxidised to the corresponding alkoxides using dry air above atmospheric pressure in a fast, highly exothermic reaction. In general, a solvent is used to help avoid localised overheating and to decrease the viscosity of the solution. By-products include paraffins, aldehydes, ketones, olefins, esters, and alcohols accidental introduction of moisture increases paraffin formation. To prevent contamination, solvent and by-products must be removed before hydrolysis. Removal can be effected by high temperature vacuum flashing or by stripping.  [c.456]

Although exact mechanisms have yet to be estabUshed, hermetic coatings (23) are being directly appHed to keep contaminants from reaching the fiber surface. Polymeric coatings may be permeated by atmospheric moisture. A number of materials, metals and carbon, may be appHed during the fiber drawing process, using vapor deposition. But only an amorphous carbon hermetic coating has been commercialized. These coatings are primarily intended to protect the fiber from corrosion by water, but also prevent hydrogen-induced loss increases. Accelerated testing at high temperature or high pressure have been used to predict effects on the fiber over its lifetime.  [c.258]

The chemical expansion method is most widely used for the manufacture of flexible PVC foam. The three general methods used to produce flexible vinyl foam (246) are (/) the pressure mol ding technique, which consists of the decomposition of the blowing agent and fusion of the plastisol in a mold under pressure at elevated temperatures, cooling the mold, removing the molded part, and post expansion at some moderate temperature (2) the one-stage atmospheric foaming method in which the blowing agent is decomposed in the hot viscosity range that Hes between the gelation and complete fusion of the plastisol and (J) the two-stage atmospheric foaming method in which the blowing agent is decomposed below the gelation of the plastisol, followed by heating at high temperature to fuse the foamed resin (247).  [c.420]

The process is carried at moderate (slightly above atmospheric) pressures, but at very high temperatures that reach a maximum of 1900°C. Even though the reaction time is short (0.6—0.8 s) the high temperature prevents the occurrence of any condensable hydrocarbons, phenols, and/or tar in the product gas. The absence of Hquid simplifies the subsequent gas clean-up steps.  [c.69]

Protective-Atmosphere Furnaces. These furnaces are used where the work caimot tolerate oxidation or where the atmosphere must provide a chemical or metallurgical reaction with the work. In some cases, mainly in high temperature appHcations, the atmosphere is required to protect the electric heating element from oxidation.  [c.135]

Chrome—nickel alloy heating elements that commonly ate used in low temperature furnaces are not suitable above the very low end of the range. Elements commonly used as resistors are either silicon carbide, carbon, or high temperature metals, eg, molybdenum and tungsten. The latter impose stringent limitations on the atmosphere that must be maintained around the heating elements to prevent rapid element failure (3), or the furnace should be designed to allow easy, periodic replacement.  [c.137]

Refractory selection becomes critical with high temperature radiation furnaces that have molybdenum or tungsten heating elements. Although these elements ate stable in vacuum or inert atmospheres, many appHcations requite a reducing atmosphere, often high in hydrogen content and very dry. In these cases, there is the possibility of reducing the oxides that make up refractory insulations. PubUshed data are available relating temperature and dew point at which hydrogen reduces the various oxides present in insulations (4). If this point is reached, the reduction process begins to destroy the insulation system of the furnace, thus limiting the maximum practical operating temperature to less than the capability of the heating element material (see Refractories).  [c.137]

This exothermic reaction has an energy release of 50 kj/g (12 kcal/g) of methane reacted. This energy can be released by raising the temperature of a methane—air mixture to its ignition temperature where the reaction becomes self-sustaining, produciag high temperature reaction products. At atmospheric pressure, the combustion reactions can be sustained ia methane—air mixtures for methane concentrations ranging from approximately 5.4 to 14 vol %. A methane—air mixture containing approximately 9.5% methane would be stoichiometricaHy balanced for CO2 and H2O (14). The adiabatic combustion temperatures for combustible methane—air mixtures are ia the range of 1950 to 2325 K depending on the specific conditions. The overall reaction of methane and oxygen can also be promoted at lower temperature through a series of steps usiag catalysts and electrolytic cells that result ia the direct conversion of the chemical energy to electrical energy without the use of an iatermediate heat engine and generator. Heat energy is also derived from fuel-ceU reactions and the overall energy utilization efficiencies of these units can exceed 80% (15) (see Combustion science and technology Fuel cells).  [c.174]

Effect of Temperature on Design. In gas separation processes high pressure equipment is needed to operate at temperatures considerably below atmospheric, whereas some heterogeneous gas reactions have to be carried out at high temperatures to make them economically feasible. Both high and low temperatures have an effect on the mechanical properties of metals. In general, the ductile properties, and in particular the toughness and impact strength, of most low alloy steels, decrease sharply as the temperature is reduced and care has to be taken over the choice of materials if low temperature embrittlement is to be avoided. On the other hand, the yield and tensile strength of steels decrease as the temperature increases and allowance has to be made for this in estimating the static strength of a thick-waHed cylinder at temperatures above ambient. Above about 350°C, creep starts to become an important factor with Ni—Cr—Mo steels of the sort used for high pressure appHcations, and the stresses in the wall of the vessel and its deformation are no longer independent of time. In addition to the effect of temperature on mechanical properties, temperature gradients, generated in the walls of vessels as a result of apphed heat or of heat Hberated by exothermic reactions proceeding within the vessel, cause thermal stresses which may need to be considered when estimating the stresses in a thick-waked cylinder subjected to both internal pressure and heat flux.  [c.85]

Polyglycols have low pour points and good viscosity— temperature characteristics, although at low temperatures these materials tend to become more viscous than some of the other synthesized bases. High temperature stability is fair to good and can be improved with additives. Thermal conductivity is high. Polyglycols are not compatible with mineral oils or additives that were developed for use in mineral oils, and may have considerable affect on paints and finishes. They have low solubility for hydrocarbon gases and for some refrigerants. Seal swelling is low, but care must be exercised in seal selection with the water-soluble types to be sure that the seals are compatible with water. The glycol fluid does have a tendency to adsorb moisture from the atmosphere.  [c.265]

The Texaco coal gasification system is an example of a high (>1300° C) temperature-(>2 MPa) pressure system used for raw-gas generation. Figure 4 gives a typical simplified processing sequence for coal gasification. Pulverized coal, shown Oto be most efficient, is used as the feedstock. Chemical equihbrium at elevated temperatures favors the formation of H2 and CO. Under high temperature conditions, methane formation is minimized, and no tars and oils are produced. Although hydrogen yield is slightly reduced, high pressure gasification results in significant power savings from elimination of raw gas compression. Low (700—800°C) temperature gasification processes, such as the Lurgi gasifier or BGC—Lurgi slagging gasifier, requite a more complex processing sequence. Considerable amounts of methane, tars, and oils are formed. Recovered methane must be sold or steam-reformed for more hydrogen production. Tar and oil can be used as boiler fuel or in other ways dictated by economics. The energy requirement of the Texaco pressurized gasification process is 108, 000 kJ/mol (25, 812 kcal/mol) H2, lower heating value (LHV). This corresponds to a thermal efficiency of 63.2% on a higher heating value (HHV) basis. This conversion efficiency is nearly 20% higher than that reported for atmospheric gasification systems (145). Typical synthesis gas composition from the Texaco gasification process using bituminous coal is 34% H2, 48% CO, 17% CO2, and 1% N2 + Ar.  [c.423]

Hydrochloric acid is found naturally in the gases evolved from volcanoes, particularly those in Mexico and South America. Its formation is attributed to the high temperature reaction of water with the salts found in seawater. The original atmosphere of the earth is considered to have contained water (qv), carbon dioxide (qv), and hydrogen chloride in the ratio of 20 3 1, giving an early ocean consisting of about 1A[ HCl, which dissolved the cmstal minerals, lea ding to the ocean salinity. Hydrogen chloride was also detected in the atmosphere of the planet Venus. The dissociation of HCl is considered the source of chlorine detected in the spectra of distant stars.  [c.437]

Atmospheric Conditions. In addition to complete combustion, wastes may be destroyed by treatment at high temperatures either without oxygen (qv) (pyrolysis), usiag limited oxygea (partial combustioa), or ia reactive atmospheres (gasiftcatioa), such as those containing steam (qv), hydrogea (qv), or carboa dioxide (qv).  [c.45]

At the high temperatures found in MHD combustors, nitrogen oxides, NO, are formed primarily by gas-phase reactions, rather than from fuel-bound nitrogen. The principal constituent is nitric oxide [10102-43-9] NO, and the amount formed is generally limited by kinetics. Equilibrium values are reached only at very high temperatures. NO decomposes as the gas cools, at a rate which decreases with temperature. If the combustion gas cools too rapidly after the MHD channel the NO has insufficient time to decompose and excessive amounts can be released to the atmosphere. Below about 1800 K there is essentially no thermal decomposition of NO.  [c.422]

Pack Diffusion. Pack diffusion or cementation processes are similar to pack carburizing, and are used to coat iron, nickel, cobalt, and copper with chromium, boron, zinc (Sheradizing), aluminum, siHcon, titanium, molybdenum, and other metals. It is possible to obtain a surface layer which contains 60% aluminum, but usual limits are 25% on iron-based alloys and 12% on nickel- or cobalt-based alloys. A pure aluminum overlay is never formed in this method, owing to the high temperature of the substrate, on which the deposited aluminum immediately alloys with the substrate. Aluminum is suppHed in the pack diffusion process from pure aluminum powder or a ferroalloy powder, aluminum oxide, and an aluminum haHde. Cleaned parts and the packing material react in a closed container at 820—1200°C, depending on the base metal, in a reducing atmosphere. The reaction deposits a high concentration of aluminum metal which subsequendy diffuses deeply into the substrate. The concentration of aluminum is 50—60% immediately after coating, dropping to 12—25% after the diffusion cycle (18,30).  [c.136]

Urea acts as a monobasic substance and forms salts with acids (4). With nitric acid, it forms urea nitrate, C0(NH2 )2 HNO3, which decomposes explosively when heated. SoHd urea is stable at room temperature and atmospheric pressure. Heated under vacuum at its melting point, it sublimes without change. At 180—190°C under vacuum, urea sublimes and is converted to ammonium cyanate, NH OCN (5). When soHd urea is rapidly heated in a stream of gaseous ammonia at elevated temperature and at a pressure of several hundred kPa (several atm), it sublimes completely and decomposes partially to cyanic acid, HNCO, and ammonium cyanate. SoHd urea dissolves inhquid ammonia and forms the unstable compound urea—ammonia, CO(NH2)2NH2, which decomposes above 45°C (2). Urea—ammonia forms salts with aLkaU metals, eg, NH2CONHM or CO(NHM)2. The conversion of urea is biuret is promoted by low pressure, high temperature, and prolonged heating. At 10—20 MPa (100—200 atm), biuret gives urea when heated with ammonia (6—7).  [c.298]

Nitrogen Oxides (NO ). Most of the NO is emitted as NO, which is then oxidi2ed to NO2 in the atmosphere (see eqs. 3 and 8). AH combustion processes (see Combustion science and technology) are sources of NO. At the high temperatures generated during combustion, some N2 is converted to NO in the presence of O2 and, in general, the higher the combustion temperature, the more NO produced. NO2 is one of the criteria pollutants as well as a precursor to O, so it was the target of successful U.S. emissions reduction strategies in the 1970s and 1980s. As a result, in 1987, all areas of the United States, excepting the Los Angeles/Long Beach area, were in compliance with the NAAQS for NO2. From 1980 to 1989 nationwide NO emissions and ambient concentrations declined 5% (4).  [c.372]

Propellants are mixtures of chemical compounds that produce large volumes of high temperature gas at controlled, predetermined rates, and can sustaia combustion without requiring atmospheric oxygen for the purpose. Principal applications are ia launching projectiles from guns, rockets, and missile systems. Propellant-actuated devices are used to drive turbiaes, move pistons, operate rocket vanes, start aircraft engines, eject pilots, jettison stores from jet aircraft, pump fluids, shear bolts and wires, and act as sources of heat ia special devices. Propellants are appHcable wherever a weU-controUed force must be generated for a relatively short period of time. SoHd propellants are compact, have a long storage life, and may be handled and used without exceptional precautions.  [c.32]

The remaining carbon transport mechanisms on earth are primarily physical mechanisms, such as the solution of carbonate sediments in the sea and the release of dissolved carbon dioxide to the atmosphere by the hydrosphere (6). The great bulk of carbon, however, is contained in the Hthosphere as carbonates in rock. These carbon deposits contain Htde or no stored chemical energy, although some high temperature deposits could provide considerable thermal energy, and all of the energy for a synfuel system must be suppHed by a second raw material, such as elemental hydrogen. These carbon deposits consist of hthospheric sediments and atmospheric and hydrospheric carbon dioxide. Together, these carbon sources comprise 99.9% of the total carbon estimated to exist on the earth. Fossil fuel deposits are only about 0.05% of the total, and the nonfossil energy-containing deposits make up the remainder, about 0.02%.  [c.10]

Argon bubbles are frequently used to stir iron and steel ladles to prevent stratification, to help remove dissolved gases, to remove potential inclusion by flotation (qv), and to control temperatures. Argon is used as an inert blanket in melting, casting, and annealing certain alloys. Helium and argon environments are used for high temperature refining and fabrication of specialty materials such as tirconium, niobium, tantalum, titanium, uranium, thorium, plutonium, and reactor-grade graphite. Some furnace bra2ing, soldering, and powder-metal sintering operations (97) use helium and argon atmospheres either alone or in mixtures with hydrogen when a reducing atmosphere is required. Jets of argon can be used to atomize molten reactive metals to produce metal powders (98). In some metallurgical reactions, argon or helium is used as a carrier to transport products to and from the reaction zone and as an inert diluent to modify reaction rates. Typical appHcations are the KroU process for making zirconium and titanium (99) and the submerged injection of pulverized reagents such as lime and calcium carbide into molten steel.  [c.15]

Alloy research in the 1950s concentrated on improving the oxidation resistance of the refractory metals. Efforts in the 1960s concentrated on developing oxidation-resistant coatings. The most successful coatings are disiUcides of the base metal, 2—5 mm thick, usually appHed by a high temperature pack cementation process. Aluminide coatings also have been appHed successfully. The aluminide and siUcide coatings form thin, impervious layers of alumina and siUca that protect against oxidation at temperatures from 1100 to 1500°C, depending on the substrate. In the case of molybdenum alloys, temperatures of less than 1093°C are required in order for useful life to exceed 10 h (53). At reduced oxygen pressures, such as are encountered during aerodynamic heating by reentry of aerospace vehicles, siUcide coatings break down and are not as protective as under normal atmospheric pressures of oxygen. Other coating systems have been based on noble metals and Ni—Cr alloys (56).  [c.127]

Molybdenum. Molybdenum is the most readily available and widely utili2ed refractory metal. Most engineering appHcations of this metal utili2e the high melting temperature, high strength and stiffness, resistance to corrosion in many environments, or high thermal and electrical conductivity. However, molybdenum must be coated if exposed to air above 535°C. The melting point of 2610°C, over 1000°C higher than for most high temperature superaHoys, permits molybdenum to be used in inert atmosphere furnace equipment. Furnace hardware and heat shields also perform well under extreme temperature conditions. The high thermal and electrical conductivity of molybdenum, as well as its inertness to molten glasses, permits it to be used for electrical heating or heat booster electrodes in commercial continuous glass making operations. Molybdenum also is used in a wide range of electronic and thermionic devices as well as crystal growing devices, x-ray tubes, magnetism and thyristors, and resistance weld electrodes. Other characteristics of molybdenum are its low thermal expansion, high stiffness, and the abiUty to take a high surface finish. Molybdenum is usehil for high temperature laser mirror components such as those to be used in fusion power systems (see Fusionenergy Lasers).  [c.127]

Polyamide. Nylon hoUow fibers are produced by Du Pont, Berghof GmbH, and many others. The development of hoUow fiber initially from nylon-6 or nylon-6,6 was a natural extension of technology estabUshed in the textile industry (see Polyamides, fibers). These materials were aimed toward the desalination of brackish water employing high pressure reverse osmosis. Fiber dimensions were 50—60 pm OD and 25—30 pm ID. Hydraulic permeabUity through these aUphatic nylon derivatives was very low. The second generation of asymmetric polyamide hoUow-fiber membranes developed for high pressure reverse osmosis consist of derivatives of aromatic polyamides (aramids) with improved water permeabUity and water (brackish and seawaters) separation. They ate the largest consumers of hoUow fibers. The fibers are spun from a solution of inorganic salts and DMA while a nitrogen stream is maintained through the nascent fiber bore. The extmsion is carried into a high temperature nitrogen atmosphere, resulting in solvent evaporation, and skin estabUshment in the outer zone is annealed. These fibers must be stored wet to retain the asymmetric morphology essential for high hydraulic permeabUity.  [c.154]

PeformingPxchanger. An advance in reforming technology is the commercialization of complementary and supplementary reforming technologies. Waste heat reforming, which refers to the direct use of high temperature process heat generated in an autothermal or primary reformer, can be used to provide part of the reforming energy input. Typically, the most advantageous scheme is to use a heat-exchange type of reformer, which has reforming catalyst in the tubes and the heat of reaction suppHed by exchange with process gas on the shell-side. A number of reforming exchanger designs have been commercialized ICl s gas-heated reformer (GHR) for the production of ammonia and Air Product s enhanced heat-transfer reforming (EHTR) for the production of hydrogen. The Kellogg Reforming Exchanger System (KRES) allows for elimination of the capital- and maintenance-intensive direct-fired primary reformer. Not only is hydrogen generation made more economical, but the amount of nitrous oxides that are released to the atmosphere are significantly reduced compared to conventional reforming. Some technologies, eg, Uhde s combined autothermal reformer (CAR), physically integrate autothermal and heat-exchange-based primary reforming duties in a single vessel.  [c.421]

The synthesis of this phosphor requires both a strongly reducing atmosphere and a high temperature. The starting materials are the rare-earth oxides Ce02 and Tb O, and Al(OH)2 and MgO or basic magnesium carbonate. The firing temperature must be higher than 1400°C and for the stabilization of the trivalent state of the rare-earth ions a strongly reducing atmosphere containing a high concentration of hydrogen is required. Any residual tetravalent oxidation state of the rare-earth ions is detrimental to phosphor performance. A remarkable property of the luminescence in this stmcture is the maintenance of high quantum efficiency of luminescence at temperatures as high as 500°C.  [c.290]

Upon exposure to the atmosphere, magnesium hydroxide absorbs moisture and carbon dioxide. Reactive grades are converted to the basic carbonate 5MgO 4CO2 XH20 over a period of several years. Grades that resist carbonization at high temperature and humidity have been reported (71).  [c.345]

Galvalume has been shown to have two to six times the life of an equivalent thickness of 2inc, including marine atmospheres. Eor high temperature oxidation resistance up to 700°C, Galvalume is equivalent to pure aluminum.  [c.131]

Carburizing and Nitriding. Several commonly used metallurgical surface treatments are appHed by gas-phase reactions in a reducing atmosphere for carburizing, and in a nitrogen atmosphere for nitriding. These treatments are used to increase the surface hardness of ferrous alloys by diffusion of carbon and nitrogen at high temperature. As for all processes, good cleaning is necessary prior to treatment. Selective treatment can be done by electroplating cyanide copper onto the areas of the parts which are not to be hardened. The copper is an excellent barrier to carbon and nitrogen, and is easily removed after hardening (13,14) (see Metal surface TliEATlffiNTS, case hardening).  [c.136]


See pages that mention the term Atmosphere high temperature : [c.216]    [c.215]    [c.389]    [c.330]    [c.580]    [c.131]    [c.134]   
Corrosion, Volume 2 (2000) -- [ c.4 , c.7 ]