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Showing papers on "Calcium oxide published in 1991"


Journal ArticleDOI
TL;DR: In this article, the authors examined the potential for burning various industrial wastes combined with lime, in certain proportions, to produce a byproduct having cementing characteristics similar to ordinary portland cement (OPC).
Abstract: Using a geotechnical viewpoint, this paper proposes a potential, partial solution to solve some of the problems posed by increasing amounts of certain types of sludgy industrial waste. The primary objective of this study is to examine the potential for burning various industrial wastes combined with lime, in certain proportions, to produce a by-product having cementing characteristics similar to ordinary portland cement (OPC). It is found that the percentages of main cementitious compounds in this new cement-like stabilizer are comparable to those of OPC. The by-product also shows promise for use in stabilizing a loam soil. The contribution of ettringite to strength development is discussed. It is found that this new type of additive can be used to stabilize loam soil for subgrade purposes.

140 citations


Journal Article
TL;DR: In this paper, an evaluation of the soil-lime system for two soils typical of the highly expansive soils existing in Irbid city in northern Jordan is presented, where the lime was added to the soils at 0 to 9 or 12%.
Abstract: Heave and settlement of clayey soils pose a difficult problem to civil engineers. Several methods are usually suggested to control this problem. The most common method is the addition of stabilizing agents, such as lime. An evaluation of the soil-lime system for two soils typical of the highly expansive soils existing in Irbid city in northern Jordan is presented. The lime was added to the soils at 0 to 9 or 12%. The soil-lime specimens were cured for 1 hr, 7 days, and 28 days, after which they were subjected to laboratory tests. The properties obtained were the grain size distribution, consistency limits, chemical composition, swell potential, swell pressure, compression and rebound indices, rate of swell and consolidation, immediate settlement, and primary consolidation as percent of total settlement. Generally, lime is found to be most effective in stabilizing heave and settlement of expansive clays.

123 citations



Patent
22 Jul 1991
TL;DR: The calcium carbonate is prepared by slaking quicklime in an aqueous medium, carbonating and neutralizing the suspension of slaked lime formed in step (a) using a gas comprising carbon dioxide; and separating the precipitated calcium carbonates formed in stage (b) from the aquatic medium in which it was suspended as mentioned in this paper.
Abstract: The calcium carbonate is prepared by: (a) slaking quicklime in an aqueous medium; (b) carbonating and neutralising the suspension of slaked lime formed in step (a) using a gas comprising carbon dioxide; and (c) separating the precipitated calcium carbonate formed in step (b) from the aqueous medium in which it is suspended. There is added 0,01 % to 15 % by weight based on the weight of dry calcium oxide, of a reagent having one or more active hydrogen atoms (or a salt thereof), to the aqueous medium in which the quicklime is slaked in step (a).

103 citations


Patent
25 Mar 1991
TL;DR: In this article, a process for pathogen reduction in waste where dewatered sludge having a solids content in the range of 10-60% is mixed with an additive selected from the group consisting of calcium oxide or calcium carbonate group.
Abstract: A process for pathogen reduction in waste where dewatered sludge having a solids content in the range of 10-60% is mixed with an additive selected from the group consisting of calcium oxide or calcium carbonate group. Hydration to calcium hydroxide occurs with an attendant release of heat. The pH of the sludge is then elevated and the heat of the hydration reaction is retained resulting in effective neutralization of pathogens. Apparatus is also disclosed.

81 citations


Patent
30 May 1991
TL;DR: A metastable complex of calcium, citrate and malate is disclosed in this article, which is a mixture of calcium carbonate, calcium hydroxide or calcium oxide with citric and malic acids in aqueous solution.
Abstract: A metastable complex of calcium, citrate and malate is disclosed. This material is highly bioavailable, and is soluble in both neutral and acid solutions. The salt is prepared by the reaction of calcium carbonate, calcium hydroxide or calcium oxide with citric and malic acids in aqueous solution. The reaction mixture is dried at a temperature of less than 100 °C, and the resultant solid is a metastable solid. The solid can be ground to reduce the particle size for easier tabletting or adding to foods and beverages. Preferred salts are neutral and acidic salts which can be expressed by molar ratios.

72 citations


Book ChapterDOI
TL;DR: In this paper, the soft soil is mixed in situ either with unslaked lime (CaO) or with cement using a tool shaped like a giant dough mixer, as illustrated in Figure 24.1.
Abstract: The behavior of very soft clay or silt can be improved with lime or cement columns. In this soil stabilization method, the soft soil is mixed in situ either with unslaked lime (CaO) or with cement using a tool shaped like a giant dough mixer, as illustrated in Figure 24.1. Other materials can be used, such as gypsum (Holm et al., 1983a), fly-ash and furnace slag (Nieminen, 1978), hydroxyaluminum (Bryhn et al., 1983), and potassium chloride (Eggestad and Sem, 1976).

70 citations


Journal Article
TL;DR: In this article, concrete slabs uncovered at neolithic archaeological sites in southern Galillee were described, showing that Roman concrete and the Greek emplechton had their precursors in lime/pozzolan-bound mortar and plaster.
Abstract: The article describes concrete slabs uncovered at neolithic archaeological sites in southern Galillee. It shows that Roman concrete and the Greek emplechton had their precursors in lime/pozzolan-bound mortar and plaster. The binding properties of concrete were discovered early in human history. Burnt limestone was slaked in contact with moisture or rain, and the resulting powder was then found to have binding properties. Polished concrete floors have been excavated in Jericho. Neolithic lime preparation is described, as well as the laboratory investigation of excavated samples.

50 citations


Journal ArticleDOI
TL;DR: In this paper, the authors propose Ca(OH)2/CaO-2/CAO-1/Ca(OH), CaO-3, CaO -2/CO-4/Ca-O-5/CA-6, Ca-O -3/Ca
Abstract: 高度熱エネルギー有効利用の観点から, ヒートポンプ用要素反応として基本的に優れた特徴を有するCa(OH)2/CaO系可逆反応を利用したケミカルヒートポンプにおいて, その性能向上に対して検討課題の1つとなっている固体反応層の伝熱性能の向上に主眼をおき, 本ヒートポンプの性能向上のための実験的検討を行った.その結果, エネルギーを要しないパッシブな伝熱促進である反応器内試料充填層に銅プレートフィンを挿入する方法を適用することにより比較的簡単に蓄熱密度を下げることなく, 反応層内の温度分布をなくしつつ反応器の熱入出力速度を大幅に高め得ることが確認された.

41 citations


Patent
08 Oct 1991
TL;DR: Alumina-zirconia lapping abrasives containing at most 30% tetragonal zirconium and optionally containing at least one oxide selected from the group consisting of yttrium oxide, calcium oxide, magnesium oxide, titanium oxide and other rare earth oxides in the form of solid solutions as mentioned in this paper.
Abstract: Alumina-zirconia lapping abrasives containing at most 30% tetragonal zirconia and optionally containing at least one oxide selected from the group consisting of yttrium oxide, calcium oxide, magnesium oxide, titanium oxide and other rare earth oxides in the form of solid solutions, which are obtainable and preferably obtained by fusing alumina-zirconia abrasive materials, quenching fused materials to obtain an ingot, crushing the ingot and subjecting the crushed ingot to a heat treatment at a higher temperature than the phase transition temperature of zirconia

38 citations


Patent
21 Oct 1991
TL;DR: In this article, a method for preparing smectite clay alkaline earth metal hydroxide and carbonate composite materials is described, which uses low amounts of the clay added to water to which is added calcium oxide or calcium hydroxides.
Abstract: A method for preparing smectite clay alkaline earth metal hydroxide and carbonate composite materials is described. The method uses low amounts of the clay added to water to which is added calcium oxide or calcium hydroxide. Optionally the calcium carbonate is formed in situ by exposure to air or to carbon dioxide in the solution. The product is dried to form the composite material which is used to remove SO x from flue gases.

Journal ArticleDOI
TL;DR: In this paper, a model describing the chemical kinetics of the sulphation of calcium oxide has been developed in terms of elementary chemical reaction mechanisms, which predicts that the rate-determining reaction at low tempeatures is the disproportionation of calcite and/or the reaction between calcium oxide and sulphur trioxide.

Journal Article
TL;DR: In this paper, the effects of water leaching on the engineering and physical properties of a lime-treated expansive clay in north-central Texas were determined. And the results indicated that leaching does have a detrimental impact on the physical properties.
Abstract: The effects that continuous water leaching has on the engineering and physical properties of a lime-treated expansive clay in north-central Texas were determined. Seventy laboratory-prepared lime-treated clay samples were subjected to continuous accelerated leaching for periods of 45 and 90 days in large-diameter, flexible-wall leach cylinders. The soils' physical properties were measured before and after leaching, then graphically and statistically analyzed for significant changes. Results indicated that leaching does have detrimental impact on the physical properties of lime-treated expansive clays. The property changes are related to lime content and initial moisture content. Permeability of all samples increased dramatically with the addition of lime. 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 of leaching were minimized or eliminated. Changes to properties upon leaching varied depending on their compaction water content relative to the optimum.

Journal Article
TL;DR: Barium hydroxide and barium chloride were applied to sulfate-rich soils before lime application to increase the bearing strength and decrease the percent swell of the treated soils.
Abstract: Some sulfate-bearing soils stabilized with calcium hydroxide (lime) have developed heave over periods of time. This heave is thought to result from reactions of soluble sulfates, calcium hydroxide, and free aluminum in the soil or groundwater, or both, to form ettringite (3CaO.Al2O3.3CaSO4.32H2O), a highly water-expansive mineral. Laboratory testing, using the California bearing ratio (CBR) method, has indicated increased bearing strength values and decreased swell when barium hydroxide or barium chloride was added to sulfate-rich soils before lime application. A California soil containing sodium sulfate had increased strength values when either barium compound was used with lime as compared with specimens with lime only. A barium hydroxide treatment followed by lime application to a Texas soil containing sodium sulfate was successful, showing increased CBR values and a decrease in percent swell. Potential volume change tests were conducted on a Colorado soil and the California and Texas soils using lime only and lime added to soils treated with barium hydroxide or barium chloride. The barium hydroxide plus lime treatment showed a marked decrease in swell pressure when compared with lime-only treatment. The mix of barium chloride plus lime decreased in swell pressure, but not as significantly as the mix of barium hydroxide plus lime. The presence of ettringite in the treated soils was determined using scanning electron microscopy. Ettringite formation was not detected in the California or Colorado soils for either combination of barium hydroxide or barium chloride plus lime. The Texas soil contained an abundance of ettringite in the mix of barium chloride plus lime, and it was present, but sparse, in the mix of barium hydroxide plus lime.

Journal Article
TL;DR: In this paper, the strength and stress-strain characteristics of a cohesive soil in natural and lime-treated states were investigated and compared and the experimental results indicated that increasing the percent lime increases grain size, calcium ions, and the pH value, whereas it decreases the plasticity index, sodium ions and dispersion, and furthermore, the unconfined compressive strength and the undrained angle of internal friction increased because of the addition of lime and curing time.
Abstract: Strength and stress-strain characteristics of a cohesive soil in natural and lime-treated states were investigated and compared. For this purpose, a cohesive soil from a semiarid region in Jordan was selected and subjected to various laboratory tests. The experimental program involved three levels of treatment (3, 6, and 9%) with hydrated lime and a range of curing times (0, 7, 14, 21, and 28 days). The experimental results indicated that increasing the percent lime increases grain size, calcium ions, and the pH value, whereas it decreases the plasticity index, sodium ions, and dispersion. The compaction characteristics of the soil studied were not significantly affected by lime. Furthermore, the unconfined compressive strength and the undrained angle of internal friction increased because of the addition of lime and curing time. The undrained cohesion decreased with lime treatment up to 3% and increased for lime content greater than 3%. The lime treatment strength ratio (LSR), defined as the ratio of the unconfined compressive strength of a treated specimen to an untreated one, was introduced. Greater values of LSR indicate that lime is more effective in stabilizing the soil as far as strength is concerned. For the soil studied, LSR increased both with lime percentage and curing time. In addition, the undrained modulus increased significantly for values of LSR between 1.0 and 2.0. For LSR greater than 2.0, the increment in undrained modulus was much smaller.

Patent
20 Aug 1991
TL;DR: A calcium phosphate type glass-ceramic which comprises from 64 to 72% by weight of phosphorus oxide in terms of P2 O5, from 13 to 20% of CaO, from 6 to 13% of strontium oxide and from 3 to 15% of Lanthanum oxide was selected from the group consisting of aluminum oxide, cerium oxide, and lanthanum oxides.
Abstract: A calcium phosphate type glass-ceramic which comprises from 64 to 72% by weight of phosphorus oxide in terms of P2 O5, from 13 to 20% by weight of calcium oxide in terms of CaO, from 6 to 13% by weight of strontium oxide in terms of SrO, and from 3 to 15% by weight in total of at least one member selected from the group consisting of aluminum oxide, cerium oxide and lanthanum oxide respectively in terms of Al2 O3, Ce2 O3 and La2 O3, a molar ratio of (CaO+SrO)/P2 O5 being 0.78-0.86.

Journal ArticleDOI
TL;DR: In this paper, the reactivity of pure and sodium-promoted calcium oxide catalysts toward the oxidative coupling of methane at 640°C has been investigated, and the deactivation of both pure and promoted catalysts demonstrated that the presence of calcium oxide was necessary for both catalysts to be active.

Journal ArticleDOI
TL;DR: Sorbents for SO2 removal from humidified simulated flue gas have been prepared from CaO-fly ash slurries using a pressure hydration technique, and the sorbents were characterized by measuring thermogravimetrically the SO2 uptake from flue gases, and by X-ray diffraction, surface area, particle size, and optical microscopy studies as mentioned in this paper.

Journal ArticleDOI
M. Rashid Khan1, K. Seshadri
TL;DR: In this paper, low-temperature coal pyrolysis liquids produced in the presence or absence of additives (calcium oxide and Genstar, a dolomitic material) were separated by adsorption chromatography.

Patent
27 Jun 1991
TL;DR: An additive for use in the desulfurization of molten iron is disclosed in this article, which comprises a granular mixture of metallic magnesium, calcium oxide and a small amount of a hydrocarbon-containing material which provides a volatile gas producing component to the mixture.
Abstract: An additive for use in the desulfurization of molten iron is disclosed. The additive comprises a granular mixture of metallic magnesium, calcium oxide and a small amount of a hydrocarbon-containing material which provides a volatile gas producing component to the mixture. The hydrocarbon-containing material is preferably coal, carbon black, wood flour or a high density polyethylene. The additive is intended to be pneumatically injected into the melt in a stream of nonoxygenated carrier gas.

Patent
05 Mar 1991
TL;DR: A sintered, composite ceramic material if formed of a plurality of titanate and aluminate compounds that cooperate to produce improved dielectric properties is presented in this paper, where the material exhibits an oxide composition generally characterized by the formula (MgO).sub.a (CaO),sub.c (Al.sub.f) and sub.d wherein a,b,c, and d are mole fractions and a+b+c+d=1.
Abstract: A sintered, composite ceramic material if formed of a plurality of titanate and aluminate compounds that cooperate to produce improved dielectric properties, including a dielectric constant between about 10 and 25, preferably between 14 and 21, and a temperature coefficient less than 15 ppm per °C., preferably less than 10 ppm per °C. The material exhibits an oxide composition generally characterized by the formula (MgO).sub.a (CaO).sub.f (TiO.sub.2).sub.c (Al.sub.2 O.sub.3).sub.d wherein a,b,c, and d are mole fractions and a+b+c+d=1 and further wherein a is between about 0.36 and 0.47 mole fraction, b is between about 0.023 and 0.03, c is between about 0.386 and 0.50 and d is between about 0.05 and 0.23. The material is formed by a process that comprises first calcining a mixture formed of a suitable calcium oxide powder, a suitable magnesium oxide powder, and a suitable titanium oxide powder to form a titanate powder. The titanate powder is mixed with aluminum oxide powder, compacted and sintered to form a dense, integral body.

Patent
06 Jun 1991
TL;DR: In this article, a process for treating contaminated sludges such as municipal sewage sludge, industrial waste sludge and riverbottom sludge with calcium oxide (CaO) and/or calcium carbide (CaC 2 ) with reclaiming and recycling of calcium oxide from the reaction materials is presented.
Abstract: A process for treating contaminated sludges such as municipal sewage sludge, industrial waste sludge and riverbottom sludge with calcium oxide (CaO) and/or calcium carbide (CaC 2 ) with reclaiming and recycling of calcium oxide (CaO) from the reaction materials. The process is also applicable for dechlorinating PCB contaminated sludges.

Patent
James Minn1
21 Nov 1991
Abstract: Rosin esters having improved viscosity stability are prepared by heating a mixture of rosin and a polyol in the presence of a catalyst mixture of 0.1% to 0.6% by weight calcium bis(ethyl 3,5-di-t-butyl-4-hydroxybenzyl phosphonate) and 0.02 to 1.0% by weight of a second calcium compound selected from calcium carbonate, calcium oxide and a calcium salt of an aliphatic carboxylic acid, all percentages being based on the weight of rosin.

Journal ArticleDOI
01 Jan 1991
TL;DR: In this paper, it was shown that CaO may be used to absorb sulphur species in situations where the combustion is either fuel-rich or fuel-lean, when sulphur exists as H2S or SO2, respectively.
Abstract: Calcium oxide is commonly used to remove sulphur dioxide formed during the combustion of coal in fluidized beds. However, during fuel-rich stages of combustion, the predominant sulphur species present is hydrogen sulphide; thus a knowledge of the sulphidation of CaO, i.e. CaO+H2S→CaS+H2O, is necessary. This reaction has been investigated at temperatures from 873 to 1173 K using thermogravimetric analysis and infra-red spectroscopy. The results indicate that the formation of CaS does not follow straightforward first order kinetics, but instead inhibition occurs at higher concentrations of H2S. The system was modelled by applying Langmuir-Hinshelwood kinetics to the scheme: CaO+H2S→Ca(OH)(SH)→CaS+H2O. The rate constants of the two steps were derived to be 4.1×10−6 m/s and 5.0×10−7 mol/m2 s, respectively. Thus the rate constant for the first step is three times larger than that for the reaction between CaO and SO2, which has a value of 1.4×10−6 m/s. Both steps in the reaction between H2S and CaO were found to have negligible activation energies. The overall conclusion is that CaO may be used to absorb sulphur species in situations where the combustion is either fuel-rich or fuel-lean, when sulphur exists as H2S or SO2, respectively. Both rich and lean regions exist in a fluidized bed burning coal.

Journal Article
TL;DR: In this article, the authors investigated the shear strength properties of a kaolin clay stabilized with hydrated lime or phosphoric acid and found that the added acid to the clay increases its cohesion and its angle of internal friction.
Abstract: Consolidation and shear strength properties of a kaolin clay stabilized with hydrated lime or phosphoric acid were investigated. Consolidation test results indicated that lime or phosphoric acid treatments cause a chemically induced preconsolidation effect of the normally consolidated kaolin clay. The overconsolidation behavior caused by chemical addition is influenced by the type and amount of chemicals and the applied original preconsolidation pressure. Lime or phosphoric acid also decreases the rebound compressibility index of kaolin clay. Consolidated, undrained, shear box tests indicate that the addition of lime or phosphoric acid to clay increases its cohesion and its angle of internal friction and that the strength gain of chemically treated clay is improved and accelerated by consolidation with aging. These findings encourage consideration of chemical treatment as a possible alternative for the control of settlements of kaolin clayey soils.

Patent
17 Jul 1991
TL;DR: In this paper, the authors present coal combustion additive and its use, which requires that total ash content must be lower than 40% of the total weight of the coal mixture and that the filler must be a mineral or mineral slag contg.
Abstract: The present invention refers to a coal combustion additive and its use. The said coal combustion additive contains solid sulfur components, catalytic oxidation components and filler. The said solid sulfur components are minerals or mineral slags contg. calcium oxide and magnesium oxide, the said catalytic oxidation components are minerals or mineral slags contg. ferrous oxide and mangnese dioxide, the said filler is mineral or mineral slag contg. silicon dioxide and aluminium oxide. The total content of the above mentioned oxides accounts for 69% or more of the total weight. The present coal combustion additive requires that total ash content must be lower than 40%.

Journal ArticleDOI
TL;DR: In this paper, the kinetics of the reaction between calcium oxide and sulfur dioxide in a gas stream simulating flue gas were studied in a differential, fixed bed setting, and the reaction was shown to be stable.


Patent
09 Oct 1991
TL;DR: Alumina-zirconia lapping abrasives containing tetragonal zirconium at a rate of 30% or less and optionally containing at least one oxide selected from the group consisting of yttrium oxide, calcium oxide, magnesium oxide, titanium oxide and other rare earth oxide in the form of solid solution as discussed by the authors.
Abstract: Alumina-zirconia lapping abrasives containing tetragonal zirconia at a rate of 30% or less and optionally containing at least one oxide selected from the group consisting of yttrium oxide, calcium oxide, magnesium oxide, titanium oxide and other rare earth oxide in the form of solid solution, which are produced by fusing alumina-zirconia abrasive materials, quenching fused materials to obtain an ingot, crushing the ingot and subjecting the crushed ingot to a heat treatment at a higher temperature than the phase transition temperature of zirconia.

Patent
05 Jun 1991
TL;DR: In this article, the subject composition is obtained by mixing an aggregate (preferably garnet) with a hydraulic cement [preferredably composed of 20-25wt.% sodium oxide] and an aqueous synthetic resin emulsion containing an acrylic resin.
Abstract: PURPOSE:To obtain the subject composition, capable of sufficiently being compatible with the surface to be coated, bonding thereto and exhibiting excellent compressive strength, abrasion and water resistance and suitable for floor and wall coating materials, etc., by mixing an aggregate with a hydraulic cement and acrylic resin-containing aqueous synthetic resin emulsion. CONSTITUTION:The objective composition obtained by mixing an aggregate (preferably garnet) with a hydraulic cement [preferably composed of 20-25wt.% silicon dioxide, 8-12wt.% aluminum oxide, 0.09-0.11wt.% ferric oxide, 59-65wt.% calcium oxide, 0.8-1.0wt.% magnesium oxide and 0.09-0.11wt.% sodium oxide] and an aqueous synthetic resin emulsion containing an acrylic resin.