High-alumina cement

Hg Mercury, high alumina cement  [c.204]

High-alumina cement is fundamentally different from Portland cement. As its name suggests, it consists mainly of CA, with very little C2S or C3S. Its attraction is its high hardening rate it achieves in a day what Portland cement achieves in a month. The  [c.209]

High-alumina cement is very quick setting, but its acid resistance is only slightly better than Portland cement, and it is rapidly attacked by alkalis. Super-sulfated cement is used for liquors high in sulfates. It is resistant to acidic conditions down to a pH of 3.5 and has alkali resistance similar to Portland cement [50].  [c.103]

Little information is available about the corrosion of metals in concrete, although it seems likely that all Portland cements, slag cement and high-alumina cement behave similarly Concrete provides an alkaline environment and, under damp conditions, the metals behave generally as would be expected e.g. zinc, aluminium and lead will react, copper is unaffected, while iron is passivated by concrete.  [c.53]

High aluminum grade of 75% ferrosihcon containing 3—5% Al is used for the production of spheroidal iron. In gray iron apphcations, this inoculant is used to control and minimize the formation of carbides and decrease section sensitivity by refining graphite size and distribution. In ductile iron it is also effective in minimizing carbide formation while increasing nodule count.  [c.540]

Higb-alumina bricks are manufactured from raw materials rich in alumina, such as diaspore. They are graded into groups with 50, 60, 70, 80, and 90 percent alumina content. When well fired, these bricks contain a large amount of mulhte and less of the glassy phase than is present in firebricks. Corundum is also present in many of these bricks. High-alumina bricks are generally used for unusually severe temperature or load conditions. They are employed extensively in lime Idlns and rotary cement Idlns, in the ports and regenerators of glass tanks, and for slag resistance in some metallurgical furnaces their price is higher than that of firebrick.  [c.2471]

The presence of certain inorganic compounds in the hazardous waste and the mixing water can be deleterious to the setting and curing of the waste-containing concrete. Also, impurities such as organic materials, silt, clay or lignite may delay the setting and curing of common portland cement for as long as several days. Dust-like, insoluble materials passing through a No. 200 mesh sieve (74 X lO-Sm particle size) are undesirable, as they may coat the larger particles and weaken the bond between the particles and the cement. Soluble salts of manganese, tin, zinc, copper and lead may cause large variations in setting time and significant reduction in physical strength. In this regard, salts of zinc, copper and lead are the most detrimental. Other compounds such as sodium salts of arsenate, borate, phosphate, iodate and sulfide will retard setting of portland cement even at concentrations as low as a few tenths of a percent of the weight of the cement used. Wastes containing large amounts of sulfate (such as flue-gas cleaning sludges) not only retard the setting of concrete, but, by reacting to form calcium sulfoaluminate hydrate, cause swelling and spalling in the solidified waste-containing concrete. To prevent this reaction, a special low-alumina cement was developed for use in circumstances where wastes containing high sulfate levels are encountered.  [c.180]

Rhodium-platinum alloys containing up to 40% Rh are used in the form of wire or ribbon in electrical resistance windings for furnaces to operate continuously at temperatures up to 1 750°C. Such windings are usually completely embedded in a layer of high-grade alumina cement or flame-sprayed alumina to prevent volatilisation losses from the metal due to the free circulation of air over its surface. Furnaces of this type are widely employed for steel analysis, ash fusions and other high-temperature analytical procedures.  [c.941]

In 1989, 164,200 t of regular fused alumina abrasive and 30,630 t of high purity fused alumina were produced in the United States and Canada, valued at U.S. 62.3 and 19.4 million, respectively (20).  [c.11]

Hydrolysis. Aluminum alkoxides are hydrolysed using either water or sulfuric acid, usually at around 100°C. In addition to the alcohol product, neutral hydrolysis gives high quaUty alumina (see Aluminum compounds) the sulfuric acid hydrolysis yields alum. The cmde alcohols are washed and then fractionated.  [c.456]

Aluminum sulfate (hydrate) [17927-65-0, 57292-32-7] is commonly known as alum. [10043-01-3, 10043-67-1] (see Aluminum compounds, aluminum SULFATE AND ALUMs). The use of this material has been known for centuries (3). It is made by the leaching of aluminous ores, such as bauxite, with sulfuric acid. It is now weU known that alum forms various polymeric species when used (4). Their rate of formation and the species formed is controUed by the pH and the presence of other ions. Although its use has not grown rapidly over the past few years, it is stiU widely used in municipal wastewater treatment, drinking water treatment, and in the paper industry (5). The principal disadvantages of alum are that it lowers the pH of the system, which often necessitates addition of base, and it leaves soluble aluminum in the effluent. It is sold both as a solution or as a dry chemical. The former is easier to dispense but must be kept warm to prevent crystallisation. Grades lower in iron are used in papermaking and command a higher price than high iron grades used in waste treatment.  [c.31]

Small appHcations iaclude furnaces, hot water heaters, clothes dryers, and cooking stoves for residential iastallations. A high performance, natural gas fueled furnace usiag a pulse-combustioa process and operating at conditions resulting ia the coadeasatioa of the water vapor ia the combustioa products has an overall energy efficiency exceeding 90%. This technology has been successfully iacorporated iato many of the resideatial or small-scale appHcatioas (16). Large-scale appHcatioas iaclude the use of aatural gas to supply process heat ia the productioa of steel (qv), glass (qv), ceramics (qv), cement (qv), paper (qv), chemicals, alumiaum, processed foods, fabricated metal products, etc. Natural gas fueled, iadirect-fired metallic radiant tubes and ceramic radiant-tube burners have faciHtated the expanded use of natural gas for heat-treating appHcations (17). Natural gas is also used as a primary fuel for the production of electrical energy.  [c.174]

Coke. This is the residue left by the destmctive distillation (coking) of residua. Petroleum coke is employed for a number of purposes its principal use is ia the manufacture of carbon electrodes for aluminum refining, which requires a high purity carbon that is low ia ash and free of sulfur. In addition, coke is employed ia the manufacture of carbon bmshes, siHcon carbide abrasives, stmctural carbon (eg, pipes and Rashig rings), as weU as calcium carbide manufacture from which acetylene is produced. Coke produced from low quaHty cmde oil is mixed with coal and burned as a fuel. Flue gas scmbbiag is required. Coke is used ia fluidized-bed combustors or gasifiers for power geaeratioa.  [c.212]

Calcium aluminate cement (81) develops very high strengths at eady ages. It attains neady its maximum strength in one day, which is much higher than the strength developed by Pordand cement in that time. At higher temperatures, however, the strength drops off rapidly. Heat is also evolved rapidly on hydration and results in high temperatures long exposures under moist warm conditions can lead to failure. Resistance to corrosion in sea or sulfate waters, as well as to weak solutions of mineral acids, is outstanding. This cement is attacked rapidly, however, by alkah carbonates. An important use of high alumina cement is in refractory concrete for withstanding temperatures up to I500°C. White calcium aluminate cements, with a fused aggregate of pure alumina, withstand temperatures up to I800°C.  [c.296]

Concrete is a particulate composite of stone and sand, held together by an adhesive. The adhesive is usually a cement paste (used also as an adhesive to join bricks or stones), but asphalt or even polymers can be used to give special concretes. In this chapter we examine three cement pastes the primitive pozzolana the widespread Portland cement and the newer, and somewhat discredited, high-alumina cement. And we consider the properties of the principal cement-based composite, concrete. The chemistry will be unfamiliar, but it is not difficult. The properties are exactly those expected of a ceramic containing a high density of flaws.  [c.207]

Aluminum has high resistance to atmospheric conditions as well as to industrial fumes and vapors and fresh, brackish, or salt waters. Many mineral acids attack aluminum, although the metal can be used with concentrated nitric acid (above 82 percent) and glacial acetic acid. Aluminum cannot be used with strong caustic solutions.  [c.2450]

Transfer rale, BTU/(hr.) (sq. ft.) ( F), based on outside fin lube surface for 1" O.D. tubes with Vs" high aluminum fins spaced 11 per inch. The suggested number of tube layers cannot be accurately predicted for all services, in general, coolers having a cooling range up to 80°F. and condensers having a condensing range up to 50°F. are selected with 4 tube layers. Cooling and condensing services with ranges exceeding these values are generally figured with 6 tube layers. Courtesy Griscom-Russetl Co.  [c.37]

With many organic compounds, aluminium shows high corrosion resistance either in the presence or absence of water. The lower alcohols and phenols are corrosive when they are completely anhydrous —rarely encountered in practice —since repair of breaks in the natural protective oxide film on aluminium cannot take place in the absence of water. Amines generally cause little attack unless very alkaline.  [c.672]

Three types of hydraulic cement are in use, viz. Portland, supersulphated and high-alumina. Portland cement is satisfactory in solutions with a pH of 7 and upwards, high-alumina will withstand solutions of pH 5 5 and upwards but will be attacked by alkaline solutions greater than pH 9, while supersulphated cement is resistant to solutions of pH 3 and upwards and also to alkaline solutions. All these cements are resistant to solvent solutions. Another advantage in the use of high-alumina cements is that they will attain their maximum strength in about 24 h. If Portland cement is used for the foundations of acid plants, care should be taken to insulate it from the surrounding earth.  [c.910]

Calcium oxide. This reagent is commonly used for the drying of alcohols of low molecular weight its action is improved by preheating to 700-900° in an electric furnace. Both calcium oxide and calcium hydroxide are insoluble in the medium, stable to heat, and practically non-volatile, hence the reagent need not be removed before distillation. Owing to its high alkalinity, it cannot be used for acidic compounds nor for esters , the latter would undergo hydrolysis. Alcohols dried by distillation over quicklime are not completely dry the last traces of moisture may be removed by distillation over aluminium or magnesium amalgam or by treatment with a high toiling point ester and a little sodium (see Section 11,47,5 and 6).  [c.142]

Place a solution of 190 g. of sodium hydroxide in 750 ml. of water in a 2 litre beaker equipped with an efficient stirrer (1), cool in an ice bath to 10°, and add 150 g. of nickel - aluminium alloy in small portions, with stirring, at such a rate that the temperature does not rise above 25°. If excessive foaming is encountered, add 1 ml. of re-octyl alcohol. When all the alloy has been introduced (about 2 hours), stop the stirrer, remove the beaker from the ice bath, and allow the contents to attain room temperature. When the evolution of hy drogen becomes slow, heat the reaction mixture gradually (2) on a water bath until the evolution again becomes slow (about 8-12 hours) add distilled water to restore the original volume, stir the mixture, allow to settle, and decant the super-natent liquid. Transfer the nickel to a stoppered graduated cyhnder with the aid of distilled water, and decant the water again. Add a solution of 25 g. of sodium hydroxide in 250 ml. of water, shake to disperse the catalyst thoroughly, allow to settle, and decant the alkali solution. Wash the nickel by suspension in distilled water and decantation until the washings are neutral to litmus, then 10 times more to remove the alkali completely (25-40 washings are required) (3). Repeat the washing process three times with 100 ml. of rectified spirit (95 per cent. C HjOH) and three times with absolute alcohol. Store the catalyst in bottles which are completely filled with absolute alcohol and tightly stoppered the product is highly pyrophoric and must be kept under liquid at all times. The Raney nickel contained in this suspension weighs about 75 g.  [c.871]

The reflecting surfaces of the mirrors are specially coated, with alternate layers of high and low dielectric materials such as Ti02 and SiO, to give almost total reflection at the specific laser wavelength. The usual aluminium, silver or gold coatings are not sufflciently highly reflecting. One of the mirrors is coated so as to allow 1 to 10 per cent of the radiation to emerge as the laser beam.  [c.339]

There is an abundance of aluminum ores and alumina plants (see Aluminum and aluminum alloys Aluminum compounds, aluminum oxide), and less importandy to gallium production 2inc ores and plants (see Zinc and zinc alloys) these are the main sources of gallium. Gallium is found also in the production of germanium from germanium minerals. In certain coals, the due dust may contain 0.001—0.05 wt % Ga, sometimes as high as 1 wt % Ga (see Coal). Micas are also gallium-rich (up to 0.1%) and gallium extraction from a combined spodumene andlepidoHte deposit (Rernic Lake, Ontario, Canada) was considered (see Micas, natural and synthetic). Gallium has also been extracted from copper ores (Apex mine, St. George, Utah).  [c.158]

Catalytic Cracking. Although it has long been known that heating cmde oil fractions could break or crack the compounds into smaller molecules, the development of suitable catalysts and processing designs has made catalytic cracking the premier refinery process for changing the molecular stmcture of the cmde (see Catalysis). Catalytic cracking generates higher yields than thermal cracking as well as superior quaUty products. As of this writing, over 50% of the gasoline in the United States is obtained by catalytic cracking which uses a fluidized bed of powdered or small diameter catalysts that are continuously regenerated in an adjacent vessel called a regenerator (see Catalysts, regeneration Fluidization). The fluidized-bed catalytic cracking (FCC) process was first commercialized in 1942 by Standard Oil Co. (New Jersey) at its Baton Rouge refinery (29) using powdered siUca/alumina as a catalyst. Fluidized beds offered the abiUty to use powdered, high surface area catalysts, to operate continuously, to regenerate easily, and to use short contact times which increased yield and selectivity. Since 1942, many improvements have been made in process design, catalyst formulation, and the abiUty to handle heavier feeds (30—32). Catalysts of the 1990s are zeoHtes having highly controlled pore size and surface area (see Molecularsieves).  [c.184]

First, is die removal of impurities. Water, carbon dioxide, and sulfides are removed by scmbbing with monoethanol amine (see Alkanolamines) and diediylene glycol (see Glycols), followed by drying with alumina. Then the natural gas is concentrated in helium as the higher boiling hydrocarbons are liquefied and collected. Cmde helium, concentrated to perhaps 70% and containing nitrogen, argon, neon, and hydrogen, undergoes final purification at pressures up to 18.7 MPa (2700 psi). The crude material is chilled to 77 K in liquid nitrogen-cooled cods of a heat exchanger. Under the high pressure, the low temperature liquefies most of the remaining nitrogen and argon, allowing the helium together with last traces of nitrogen, neon, and hydrogen to separate. Evaporation of nitrogen reduces the temperature and nitrogen content of the helium before it passes into liquid-nitrogen-cooled adsorbers. Activated charcoal operating at liquid nitrogen temperatures or below is capable of adsorbing all nonhelium gases. Hence, passage through these adsorbers yields helium that exceeds 99.9999% in purity. Both concentration and purification steps require nitrogen refrigeration, which is obtained by expansion engines or turbines as well as by expansion valves.  [c.10]

Nonferrous M.etallurg. Lime and limestone are required in many strategic nonferrous metallurgical processes (22). All seawater, brine, or bittern processes for magnesium metal and magnesia manufacture require either high calcium or dolomitic quicklime (see Magnesiumand MAGNESIUM ALLOYS). In the Bayer process, lime is used for causticization and desilifica tion in the manufacture of alumina for reduction to aluminum metal (see Aluminum AND ALUMINUM alloys). Limestone is also used instead of lime in an alumina process adaptation called the sinter process. The second largest metallurgical use for lime is in the beneficiation of copper ore by flotation (qv), where it is used for neutralization and to maintain proper pH control (see Copper). Limestone serves as a flux in smelting copper, lead, zinc, ferrosiUcon, and antimony from their ores. Lime is the key reagent for recovering uranium from gold slimes in South Africa, and in Canada and the United States lime neutralizes acid wastewater in acid extraction of uranium from its ore. Lime also aids in the recovery of nickel and tungsten by chemical processes after smelting, in the flotation of gold and silver, and in the sintering of low carbon ferrochrome.  [c.178]

In most heat treatment processes for metal fabricated parts, nitrogen serves as a nonreactive, passive constituent of the furnace atmosphere. It can be used alone for the annealing of aluminum, copper, and some low carbon steels. Most often it is used in combination with other gases such as CO to produce reactive atmospheres for sintering, carburi2ing, and carbonitriding ferrous parts. Nitrogen reacts with some stainless steels and caimot be used in their heat treatment. At high temperatures, atomic nitrogen combines with iron to form finely divided nitrides, producing a hardened nitrided or carbonitrided surface layer (35).  [c.80]

Idemitsu Process. Idemitsu built a 50 t x 10 per year plant at Chiba, Japan, which was commissioned in Febmary of 1989. In the Idemitsu process, ethylene is oligomerised at 120°C and 3.3 MPa (33 atm) for about one hour in the presence of a large amount of cyclohexane and a three-component catalyst. The cyclohexane comprises about 120% of the product olefin. The catalyst includes sirconium tetrachloride, an aluminum alkyl such as a mixture of ethylalurninumsesquichloride and triethyl aluminum, and a Lewis base such as thiophene or an alcohol such as methanol (qv). This catalyst combination appears to produce more polymer (- 2%) than catalysts used in other a-olefin processes. The catalyst content of the cmde product is about 0.1 wt %. The catalyst is killed by using weak ammonium hydroxide followed by a water wash. Ethylene and cyclohexane are recycled. Idemitsu s basic a-olefin process patent (9) indicates that linear a-olefin levels are as high as 96% at C g and close to 100% at and Cg. This is somewhat higher than those produced by other processes.  [c.440]

High Purity Aluminum. The HaH-Hfiroult process caimot ensure aluminum purity higher than 99.9%. Techniques such as electrolytic refining and fractional crystallization are required to produce metal of higher purity. Development of an electrolytic refining process was begun in 1901 and made workable by 1919. The Hoopes process is based upon the use of a cell containing three Hquid layers, as depicted in Figure 6. Aluminum is electrochemically transported from the bottom alloy layer (anode) through an intermediate electrolyte layer to the high purity top layer (cathode). The bottom phase consists of impure aluminum plus an alloying agent (usually copper) to increase the density above that of the fused salt electrolyte. The composition of the electrolyte is selected to have a density less than the alloy layer but greater than pure alurninum. Electrical connection is made to the alloy through carbon or graphite blocks and graphite is used for the cathode connection. Aluminum is purified because metals more noble than aluminum are not oxidized and remain in the anodic layer. Metals less noble than aluminum are oxidized at the anode, but not reduced at the cathode. Hence impurities accumulate as chlorides or fluorides in the electrolyte.  [c.101]

If aluminum hydroxide is decomposed by heating at low temperature under vacuum or by rapidly heating at high temperature, a nearly amorphous (x-ray indifferent) phase known as rho alumina is produced which has the interesting property of recrystallizing (rehydrating) to boehmite or bayerite when mixed with water (17). This behavior is known as rehydration bonding and occurs to a significant degree in hot water at atmospheric pressure (18). Rho alumina can be formed from any of the aluminum hydroxides. The crystal stmctures are probably somewhat different depending upon which precursor (gibbsite or bayerite) is used, but this caimot be detected by x-ray and rehydration properties are similar. Some recrystallization to boehmite occurs in all of the activated aluminas under severe hydrothermal conditions and generally the degree to which this occurs decreases with increased crystalline order (higher activation temperature). The ease with which rho alumina rehydrates sets it apart from the other activated alumina phases.  [c.155]

Tabular alumina also offers advantages over other materials as an aggregate in castables made from calcium aluminate cement as the binder and in phosphate-bonded monolithic furnace linings in all thermal processing industries. Other appHcations include their use in electrical insulators, electronic components, and kiln furniture. AppHcations other than refractories and high AI2O2 ceramics include molten metal filter media (116), ground filler for epoxy and polyester resins (see Eillers), inert supporting beds for adsorbents or catalysts, and heat exchange media, among others.  [c.163]

Refined calcined alumina is commonly used in combination with high purity limestone [1317-65-3] to produce high purity calcium aluminate cement (CAC). The manufacture, properties, and appHcations of CAC from bauxite limestone, as weU as high purity CAC, has been described (104). High purity CAC sinters readily in gas-fired rotary kiln calcinations at 1600 —1700 K. CAC reactions are considered practically complete when content of free CaO is less than 0.15% andloss on ignition is less than 0.5% at 1373 K.  [c.163]

Calcium Aluminate Cements. Low purity calcium aluminate [12042-78-3] cements are obtained by sintering or fusing bauxite and lime in a rotary or shaft kiln. A high purity calcium aluminate cement, 2CaO 5AI2O2, capable of withstanding service temperatures of 1750°C can be prepared by the reaction of high purity lime with calcined or hydrated alumina (see Aluminum compounds).  [c.25]

A deposited thin film is a layei on a surface having piopeities that diffei from those of the bulk material (substrate) that has been formed by the addition of sohd material to the surface. Generally, the substrate material caimot be detected in the film, which can be an organic or inorganic material. This surface layer differs from surface conversion where the surface is chemically converted to another material, eg, anodization of aluminum (see Metal surface treatments Surface and interface analysis (Supplement)). The term thin film is generally appHed to layers that have thicknesses on the order of several micrometers or less. These films may be as thin as a few atomic layers. In many cases, thin films are formed by adding atoms or molecules to a substrate surface one at a time. Thicker layers are generally called coatings (qv). Although coatings can often be formed by the same processes that are used to form thin films, there are some coating processes (qv) that are not appHcable to forming thin films. For example, thermal spray coating processes, which melt small particles, accelerate them to high velocities, and splat-cool them on surfaces, are not appHcable to forming thin films.  [c.513]

See pages that mention the term High-alumina cement : [c.87]    [c.251]    [c.87]    [c.87]    [c.88]    [c.530]    [c.185]    [c.891]    [c.99]    [c.238]    [c.133]    [c.13]    [c.260]    [c.196]   
Chemistry of the elements (1998) -- [ c.251 ]