Showing papers on "Calcium oxide published in 1990"

Hydrothermal Preparation of Calcium Hydroxyapatite Powders

Abstract: Calcium hydroxyapatite powders were prepared by hydrothermal reactions of calcium pyrophosphate and calcium oxide. Primary particles of the hydroxyapatite obtained were spherical with diameters less than 0.2 μm, and small prismatic crystals were rarely observed in some fields. The effects of temperature, pressure, and soaking time on the structural features of the resultant powders were also studied by means of XRD and SEM and were smaller than expected for the ranges investigated.

Solid dielectric capacitor and method of manufacture

Abstract: A monolithic capacitor having a dielectric ceramic body cosintered with at least two base metal electrodes. The ceramic body is composed of a major ingredient expressed by the formula, (Ba.sub.k-x-y M.sub.x L.sub.y)O.sub.k TiO.sub.2 where M is either or both the magnesium and zinc, L is either or both of calcium and magnesium, and k, x and y are numerals in specified ranges. To this major ingredient is added a minor proportion of a first additive ingredient and a second additive ingredient. The first additive ingredient is at least either of dichromium trioxide and aluminum oxide. The second ingredient is a mixture of boric oxide or lithium oxide, silicon dioxide and at least one metal oxide selected from among barium oxide, strontium oxide, calcium oxide, magnesium oxide and zinc oxide. For the fabrication of capacitors the mixture of the above major ingredient and additives in finely divided form are formed into moldings of desired shape and size, each with at least two electrodes buried therein. The moldings and electrodes are cosintered in a reductive or neutral atmosphere at temperatures of less than 1200 degrees C. and then are reheated at a lower temperature in an oxidative atmosphere.

Stabilization of clay soils with lime

Abstract: Clay soil can be stabilized by the addition of a small percentage by weight of lime, the latter enhancing many of the engineering properties of the soil. Clay soils containing montmorillonite respond more rapidly to lime stabilization than do those in which kaolinite is the predominant clay mineral. Lime stabilization produces an improved foundation material and so the technique has been used for highway, railroad and airport construction to improve subgrades and sub-bases. Generally the amount of lime needed to modify a clay soil varies from 1% to 3% whereas that required for cementation varies from 2% to 8%. When lime is added to clay soils, calcium ions are combined initially with or adsorbed to clay minerals. This leads to an increase in the plastic limit of the clay and generally to a decrease in its liquid limit. The optimum lime additive for maximum increase of the plastic limit of the soil is referred to as the lime fixation point. Lime added in excess of the fixation point is used in the cementation process and gives rise to an increase in soil strength. The initial increase in strength has been attributed to the formation of poorly ordered cementitious products which surround the clay minerals. However, the development of long-term strength appears to be due to the gradual crystallization of structurally ordered new minerals from the initial disordered reaction products. Stabilization of clay soils with lime leads to an increase in their optimum moisture content and is accompanied by a decrease in their maximum dry density. In addition, the permeability of most clay soils is enhanced by the addition of lime, as is their resistance to frost activity.(A)

M40 motorway banbury iv contract - lime stabilisation

Abstract: This paper describes the problems encountered with the use of lime stabilisation in the M40 Motorway Banbury IV contract in England, and alerts highway engineers to a mechanism of lime stabilisation which has not been generally appreciated. The problems on Banbury IV appeared to occur only where the road ran over lower lias rock; they emerged at the end of the winter after the lime-stabilised element of the capping layer was constructed during Spring and Summer 1989. It was found that the carriageway had lifted by up to 150mm; the lime-stabilised layer had softened, was moister than expected, and its thickness had increased from 250mm to 400mm. The unexpected heave of the lime-stabilised material, found here and during very recent American research, emphasises the need for detailed chemical and laboratory studies of both soil and ground water in any project considering the use of lime stabilisation; conventional test methods are sometimes insufficient. The results show that the heave is caused by ettringite/thaumasite formation. In order for this to occur, the following conditions are necessary: a) high pH conditions; b) a sufficient clay mineral content giving an adequate supply of alumina, silica and carbonates; c) the presence of sulphates; d) the correct temperature conditions; and e) availability of sufficient water. These conditions were present on Banbury IV. The Department of Transport is now considering the implications for specifying lime stabilisation. (TRRL)

Stabilization characteristics of class f fly ash

Abstract: Stabilized fly ash is a mixture of fly ash and lime, or fly ash and cement, compacted at optimum moisture content and cured to form a product-like soil-lime or soil-cement. Limited past applications and engineering properties of stabilized class F fly ash are discussed. A research study was undertaken to establish the physical, chemical, compaction, strength, and durability characteristics of class F fly ash stabilized with lime, cement, or lime/cement combinations. Two ashes obtained from West Virginia power plants were included in the laboratory testing program. It was found that although the ashes are quite different in properties, both ashes can be successfully stabilized to produce pozzolanic mixtures of adequate strength and durability for use as base or liner, with the addition of a proper amount of stabilizer and by allowing the mixture to cure for a sufficiently long period. Cement stabilization, in general, produced better strength and durability than lime stabilization for a given stabilizer content for curing periods up to 56 days. Freeze-thaw cycles caused substantial strength losses, and wet-dry cycles resulted in strength gains. Vacuum saturation with water and an acetic acid solution produced intermediate effects. Very good correlations were found between freeze-thaw and water vacuum saturation tests.

A kinetic investigation of the calcium/calcium oxide system: non-Arrhenius behavior of the reaction calcium(1S) + nitrous oxide over the temperature range 250-898 K and a study of the reaction calcium oxide + oxygen atoms

Abstract: A study is presented of the reaction Ca({sup 1}S) + N{sub 2}O over the temperature range 250-898 K. Above 500 K there is a clear upward curvature in the Arrhenius plot, and the best description of the temperature dependence of the rate constant over the experimental temperature range is given. Such behavior is explained by vibrationally excited N{sub 2}O enhancing the reaction at high temperatures. This rate coefficient expression, and the chemiluminescence cross section obtained in a previous study of the title reaction in a beam-scattering experiment, are used to estimate photon yield of 12.5%. This yield is shown to be about half that predicted by a statistical consideration of the densities of states in the reactant electronic channels.

Permeability and leachate characteristics of stabilized class f fly ash

Abstract: A 2-year laboratory investigation of the permeability and leachate characteristics of stabilized fly ash has been completed at West Virginia University. Two class F fly ashes rom coal-fired power plants in West Virginia were amended with either lime, cement, or bentonite. Stabilized specimens were permeated in either rigid- or flexible-wall permeameters. Permeant liquids included distilled water, highly concentrated organic solutions, and acidic solutions. Effluents from the permeability tests were collected periodically during the tests and analyzed for toxic elements. Results from the study indicate, for the ashes tested, permeabilities near 1.0E-06 cm/sec can readily be obtained when 15% (by weight) of lime or cement is added to the fly ash. Much lower permeabilities (1.0E-08 cm/sec) can be obtained by substituting bentonite in place of the lime or cement. Addition of lime or cement appears to stabilize the fly ash with respect to toxic elements being leached from the ash. Bentonite may not be as successful at fixing the elements onto the fly ash. In conclusion, difficulty in using fly ash as a liner material probably does not lie in the ability to obtain low permeability nor in fixing the toxic elements from leaching but rather in combining those two properties into one material. Permeability can be decreased to acceptable values through the addition of bentonite, but some ability to fix elements from leaching may be lost. In addition, ashes from different plants and from different operating periods, as found in this study, can have markedly different properties. To use a particular ash in a liner application, ash must be tested for its behavior to ensure that the correct properties are used in design of the particular liner.

Oxidative coupling of methane over CaO-MgO mixed oxide

Abstract: Mixed oxide catalyst prepared by co-precipitating magnesium oxide and calcium oxide showed an excellent activity for the oxidative coupling of methane. The high performances were presumed to arise from the high basicity of the mixed oxide.

Moisture-absorbent compositions

Abstract: A moisture-absorbent composition contains 100 parts by weight of thermoplastic resin and 5 to 400 parts by weight of at least one among the group consisting of magnesium sulfate (represented generally by MgSO₄ . nH₂O (0 ≦n≦ 3), aluminum oxide, calcium oxide, silicon oxide, zeolite, barium oxide, and cobalt chloride. A moisture-­absorbent molded item is formed of this composition in a shape of a film, a sheet, a plate, a bag, a pellet, or a container. The molded item may be used as a cushion insert, etc. which requires moisture absorption proper­ties. A moisture-absorbent composition and an molded item made of the composition are provided with an indi­cator function, by specifying the amount of anhydrous cobalt chloride.

Thermal Dehydration of Calcium Hydroxide. 2. Surface Area Evolution

Abstract: The evolution of the specific surface area associated with the thermal decomposition of calcium hydroxide has been studied experimentally and described by kinetic models utilizing two different solids: commercial calcium hydroxide (So = 83 m2g-') and calcium hydroxide reagent (So = 187 m2g-') The surface area was observed to vary linearly with the fraction decomposed during the dehydration period Sintering phenomena have been experimentally measured by treating calcium oxide samples (So = 46 m2g-'), obtained after dehydration of calcium hydroxide under constant conditions, at temperatures in the range 500-900 "C for periods of time up to 24 h A previously developed model, German and Munir (1976), fits the experimental results well if the surface area decreases to less than 55% of the initial value An empirical kinetic model, where the surface area is linearly related to the heating time, correlates the experimental data, when AS/So L 55% Simulated curves using the obtained kinetic models and parameters, for the specific surface during dehydration and sintering, agree well within the experimental results

Property changes in lime treated expansive clays under continuous leaching. final report

Abstract: This report is the result of a study to determine what effect continuous water leaching has on the engineering, physical, and chemical properties of three lime treated expansve clays in north central Texas. Seventy laboratory prepared lime treated clay samples were subjected to continuous accelerated leaching for 45 and 90 days in large diameter, flexible wall leach cylinders. Constants during the leach testing were types of soil used, flow pressure, curing conditions, and compaction effort. Variables were lime content, initial moisture content, and duration of the leach cycle. The soil's physical and chemical properties were measured before and after leaching then graphically and statistically compared. Physical properties tested included permeability, Atterberg limits, linear shrinkage, swell properties, unconfined compression stength, and differential thermal analysis properties. Chemical properties measured were soil pH, pore-water cation extractions, and exchange complex cation extractions. Extractions were tested for calcium, sodium, magnesium, and potassium cations. Additionally, the leachate passing through the soil was collected and monitored for changes in pH and cation concentrations. Results indicate that leaching does have a detrimental impact on the properties of lime treated expansive clay. The changes in the soil's physical and chemical properties are related to lime content and moisture content during compaction. The permeability of all samples tested increased dramatically with the addition of lime, and it is speculated that permeability plays a key function in determining the amount of physical and chemical change that occurs during leaching. Maximum detrimental changes generally occurred at lime contents at or less than the lime modification optimum. At lime contents at or above the lime stabilization optimum, the detrimental effects were minimized. An estimation technique to correlate laboratory leach results to field predictions of calcium removal and soil pH declination is presented. Field samples of known lime specifications were used to validate the technique with limited success.

Kinetics of the high-temperature reaction of sulfur dioxide with calcium oxide particles using gas-phase Fourier transform infrared spectroscopy

Abstract: The reaction of SO 2 with CaO particles (size ∼ 4 μm), at temperatures between 100 and 1000°C, in both the presence and absence of O 2 , has been investigated by using gas-phase FTIR spectroscopy of SO 2 . By analyzing the time dependence of the fractional capture of SO 2 up to 1 min at each temperature, it is concluded that diffusion through the product layer is the controlling step for this reaction at all temperatures investigated

Substrate used for fabrication of thick film circuit

Abstract: An insulating substrate is used for fabrication of a thick film circuit and comprises a foundation (1) of alumi­num nitride and a surface film structure (2) provided on the foundation, in which the foundation contains at least one oxidizing agent selected from the group consisting of an yttrium oxide and a calcium oxide ranging from 0.1 % to 10 % by weight for enhancing a stiffness of the foundation, and in which the surface film structure is of the multi-­level surface film structure having a lower surface film (3) of an aluminum oxide rapidly grown on the foundation in the presence of the oxidizing agent and an upper surface film (4) containing a silicon oxide and a substance select­ed from the group consisting of a zirconium oxide, a tita­nium oxide and a boron oxide for enhancing the resistivity against a firing operation.

Soil stabilization in pavement structures

Abstract: Five soil samples were selected to represent the subgrade soils commonly stabilized by lime or cement in NCDOT highway construction. The five soils are classified by the AASHTO symbols A-4, A-4, A-5, A-6, and A-7-5 and were labelled as samples DOT-1 to DOT-5. Laboratory tests measured the CBR, resilient modulus, and unconfined compressive strength on samples compacted in the laboratory at three different water contents for each soil. The five soils were compacted without any additive to measure the soil properties for unstabilized soil. The five soils were then mixed with 3%, 4%, and 5% lime before compacting and with 8%, 10%, and 12% cement before compacting. The lime stabilized soils showed the greatest improvement when mixed with 4% lime as the resilient modulus for four of the samples increased by 3 to 5 times. The A-7-5 soil only increased by 1.5 times. The resilient modulus for the cement stabilized soils increased more but without an optimum cement level for all five soils. For soils DOT-1 to DOT-4 the resilient modulus increased by a factor of 5 to 7 times when mixed with cement. The measured resilient moduli were used in a layered elastic analysis to infer the structural layer coefficients by using the resilient vertical strain in the subgrade as a criterion. The structural layer coefficients for lime stabilized soils varied from 0.06 to 0.18 for base course resilient moduli of 30,000 to 40,000 psi. The structural layer coefficients for the cement stabilized soils were determined from the unconfined compressive strengths and varied from 0.12 to 0.18.

Metallurgical flux compositions

Abstract: A metallurgical flux composition comprising calcium oxide, alumina, magnesium oxide and silica contains 22-35% by weight magnesium oxide and has a weight ratio of calcium oxide to magnesium oxide of from 0.6:1 to 2.5:1. The preferred composition contains 28-42% by weight calcium oxide, 13-21% by weight alumina, 22-35% by weight magnesium oxide and 3-8% by weight silica, preferably has a calcium oxide to magnesium oxide weight ratio of from 0.8:1 to 1.9:1 and preferably has a calcium oxide to silica weight ratio of from 6.0:1 to 7.5:1. The flux composition is particularly useful as a tundish cover in the continuous casting of steel.

Steam gasification of naphthalene. Catalyst : calcium oxide

Abstract: The catalyzed steam gasification of naphthalene was studied using a fixed bed reactor and a commercial calcium hydroxide as the catalyst raw material. The kinetics of the reaction were investigated by variation of reaction temperature, residence time and naphthalene/steam ratio. A reaction mechanism and the corresponding rate equation are presented

Physical Chemistry of the Reduction of Calcium Oxide with Aluminum in Vacuum

Abstract: The physical chemistry of "aluminothermic" reduction of calcium oxide in vacuum is analyzed. Basic thermodynamic data required for the analysis have been generated by a variety of experiments. These include activity measurements in liquid AI-Ca alloys and determination of the Gibbs energies of formation of calcium aluminates. These data have been correlated with phase relations in the Ca-AI-0 system at 1373 K. The various stages of reduction, the end products and the corresponding equilibrium partial pressures of calcium have been established from thermodynamic considerations. In principle, the recovery of calcium can be improved by reducing the pressure in the reactor. However,, the cost of a high vacuum system and the enhanced time for reduction needed to achieve higher yields makes such a practice uneconomic. Aluminum contamination of calcium also increases at low pressures. The best compromise is to carry the reduction up to the stage where 3CaO-Al,O, is formed as the product. This corresponds to an equilibrium calcium partial pressure of 31.3 Pa at 1373 K and 91.6 Pa at 1460 K. Calcium can be extracted at this pressure using mechanical pumps in approximately 8 to 15 hr, depending on the size and the fill ratio of the retort and porosity of the charge briquettes.

Composition for sealing chromium, arsenic and other harmful metals in waste

Abstract: PURPOSE: To make toxic metals in a waste product harmless by compounding individual specific amounts of an anion adsorbent, a reducing agent and a fixative consisting of a calcium oxide and a magnesium oxide, thereby preparing a composition for encapsulating the toxic metals. CONSTITUTION: The composition for encapsulating chrome and other toxic metals is prepared by compounding at least one <=30 wt.% anion adsorbent, <=35 wt.% reducing agent and 5 to 15 wt.% fixative consisting of the calcium oxide and the magnesium oxide. Concrete examples of the anion adsorbent are selected from a group of SORBOPLUS (R)-TM or HydroSORB'A' (R). Concrete example of the reducing agent are ferrous sulfate, sodium hydrogensulfite, sodium sulfite, etc. Further, concrete examples of the fixative are Portland cement, lime, hiln dust, POZZALIME (R), etc.

Removal of SOx and NOx gases from flue gas by dry absorption using an absorbent

Abstract: A process is disclosed in which a flue gas from a coal fired burner is treated in a dry phase to remove both NOx and SOx which includes SO2 and SO3. This invention provides for use of an absorbent comprising of fly ash, calcium oxide and a hydrated sulfate of calcium to remove the SO2 and/or SO3 component while also incorporating either a high carbon ash, ash derived from a high-vanadium residual oil, iron oxide or iron oxides to remove NOx. Process conditions comprise a temperature in the range of 200° C. to 450° C.

Bordeaux mixtures and process for preparing them

Abstract: The subject of the invention is a Bordeaux mixture and the process for its manufacture. The process according to the invention comprises the steps of preparing a mixture essentially consisting of copper(II) sulphate, a calcium compound chosen from calcium oxide and calcium hydroxide and a polymer of a carboxylated vinyl compound and of grinding, in the wet state, the mixture thus prepared.

Removal of sulfur from petroleum coke with lime

Abstract: The sulfur in petroleum pitches and cokes can be converted to calcium sulfate instead of sulfur dioxide during combustion when calcium oxide or calcium carbonate is added to the molten pitch before burning.

Thermochemistry of calcium oxide and calcium hydroxide in fluoride slags

Abstract: Calcium oxide activity in binary CaF2-CaO and ternary CaF2-CaO-Al2O3 and CaF2-CaO-SiO2 slags has been determined by CO2-slag equilibrium experiments at 1400 °C. The carbonate ca-pacity of these slags has also been computed and compared with sulfide capacity data available in the literature. The similarity in trends suggests the possibility of characterizing carbonate capacity as an alternative basicity index for fluoride-base slags. Slag-D2O equilibrium experi-ments are performed at 1400°C with different fluoride-base slags to determine water solubility at two different partial pressures of D2O, employing a new slag sampling technique. A novel isotope tracer detection technique is employed to analyze water in the slags. The water solubility data found show higher values than the previous literature data by an order of magnitude but show a linear relationship with the square root of water vapor partial pressure. The activity of hydroxide computed from the data is shown to be helpful in estimating water solubility in in-dustrial electroslag remelting (ESR) slags.

Flame retardant tape for cable

Abstract: PURPOSE:To give fire stread preventive performance and to extend function maintenance time by either impregnating a base material with resin composition which contains ceramic fiber, metallic hydrate, and binder as essential constituent ingredients or applying it to both sides or single side of the base material. CONSTITUTION:Resin composition which contains ceramic fiber, metallic hydrate, and binder as essential constituent ingredients is either applied to single side on both sides of a base material or impregnated. For the metallic hydrate, for example, aluminum hydroxide, magnesium hydroxide, dawsonite, aluminate calcium oxide, gypsum dehydrate, calcium hydroxide, boric acid zinc, borax, kaolin clay, metaboric acid barium, or the like is used. For the ceramic fiber, for example, alumina-silica fiber, alumina fiber, silica fiber, rocker wool, glass fiber, zirconia fiber, silicon corbide fiber, silicon nitride fiber, or the like is used.

Process for overbasing sulfonates comprising two separate additions of calcium oxide

Abstract: In an overbased sulfonate process calcium hydroxide is formed in situ. The entire water charge and 30 to 50% of the calcium oxide is added. The temperature exotherm is observed. When the temperature ceases to rise, the remaining calcium hydroxide is added with temperature adjustment and carbonation is begun.