Showing papers on "Calcium oxide published in 1997"

Lime modification of clay soils for construction expediency.

Abstract: Lime modification has the potential to reduce greatly the delays to construction projects caused by wet weather. The initial consumption of lime (ICL) test, currently used as an indicator of how much lime to use, is shown to produce results that can be both inconsistent and excessively conservative. Interpretation based on the full pH against lime addition curve is suggested. Changes in plasticity with both time after mixing and lime content are examined for four British clays, comprehensive Atterberg limit testing being shown to be adequate for design. The points at which full modification occurs are interpreted from these changes and complement well those determined by the modified ICL test. Changes in plasticity caused by smaller lime additions are shown to be adequate in many cases to improve site workability. (A)

Surface modification of titanium in calcium-ion-containing solutions

Abstract: The surface of titanium was modified in calcium-ion-containing solutions to improve bone conductivity. Three kinds of aqueous solutions for the modification were prepared using calcium nitrate, calcium chloride, and calcium oxide. The pH values of the solutions were 3.9, 7.4, and 12.6, respectively. At first, anatase powder was immersed in the solutions for 7 days to confirm the effect of the solutions on the modification. As a result, calcium titanate was formed on the anatase powder, indicating that the titanium surface was possibly modified by the solutions. Titanium plates were then immersed in the solutions at ambient temperature for 7 days, washed by deionized water, and dried. X-ray photo-electron spectroscopy of surface-modified titanium revealed that the surface-modified layer contained calcium hydroxide and/or calcium titanate. The surface-modified layer in which titanium was modified was thickest in this order: calcium oxide, calcium chloride, and calcium nitrate solutions. Apatite was formed on the surface-modified titanium in Hanks' solution while apatite was undetected on unmodified titanium. Therefore, the surface modification of titanium may improve bone conductivity. The amount of apatite corresponded to the thickness of the surface-modified layer and the amount of calcium in the layer. © 1997 John Wiley & Sons, Inc.

Catalyzed decomposition of N2O on metal oxide supports

Abstract: The catalytic decomposition of N 2 O using metal oxides supported on silica, magnesium oxide, calcium oxide and hydrotalcite-like supports was studied. CoO is much more active than CuO and Fe 2 O 3 when supported on silica. A conversion of 95% was achieved using CoO on SiO 2 at 1500 h −1 GHSV, 500°C and 50,000 ppm feed N 2 O. However, the use of higher flow rates resulted in lower conversions. We found that when supporting CoO on MgO, a much more active catalyst is attained. A conversion of 95% was achieved using this catalyst at 40,000 h −1 , 500°C, 100,000 ppm N 2 O feed. This is a significant improvement over any catalyst currently in the literature. The activity of this catalyst was decreased by calcination at 1000°C. XPS and XRD studies revealed that higher temperature calcination led to an inactive crystalline phase. The active catalyst displayed a less crystalline phase involving the support and the metal oxide. Other oxide combination catalysts were found to be less active than theCoO/MgO catalyst. Based on our findings, a modification of the reactions proposed for N 2 O decomposition is suggested.

Metal-ceramic composite coatings, materials, methods and products

Abstract: Metal-ceramic composite coatings provide refractory anti-corrosion flexible enamel coated products. Frit is made of silicon dioxide, sodium or potassium oxide, boron oxide, calcium oxide and zinc oxide, with possible other components. The frit is wet milled with clay and bentonite as a suspending agent, magnesium carbonate and sodium nitrates as electrolyte, boric acid a buffer, and water. Finely divided aluminum is blended after milling. A substrate is coated with the frit aluminum and clay mixture, which is heated and fused. The metal component coats the substrate and provides galvanic protection. The resulting coating is flexible and deforms with the substrate without delaminating or chipping. The coating is prepared by crushing, sieving, mixing and melting the frit components. The melt is tested by pulling, cooling and feeling a thread. The melt is fritted by pouring into water. The frit is dried, ground and sieved, and then wet milled with water, clay, bentonite and pH adjustors. Fine metal powder is added, and flowability is adjusted with water for spraying. Metal panels are cleaned and spray coated. The coating is dried, and then fired or baked, to provide the metal-ceramic composite flexible corrosion prevention coating.

Destructive Adsorption of Chlorinated Hydrocarbons on Ultrafine (Nanoscale) Particles of Calcium Oxide. 3. Chloroform, Trichloroethene, and Tetrachloroethene

Abstract: As a one-step approach to the safe destruction of chlorocarbons, the reactions of trichloroethene, chloroform, and tetrachloroethene with ultrafine particles of calcium oxide have been studied. Calcium oxide prepared by an aerogel/hypercritical drying method (AP-CaO) is generally superior to conventionally prepared (CP-CaO) and vastly superior to commercially available (CM-CaO) samples, although in higher temperature reactions with C2Cl4 CP-CaO exhibited higher capacity but slower reaction kinetics. The main reaction products of CaO with C2HCl3 were CaCl2, H2O, CO and C; with CHCl3 were CaCl2, H2O and CO and with C2Cl4 were CaCl2, CaCO3, and C. Reaction temperatures were 300−500 °C, and optimum temperatures were found. If temperatures were too low, reaction efficiencies were low and if too high, efficiencies could also go down due to graphite formation which could block reactive sites.

Bonded aggregate composition and binders for the same

Abstract: Bonded aggregate compositions such as concrete, concrete repair products, high temperature refractories, high temperature insulation and fire resistant insulation are made from an aqueous solution of phosphoric acid and a separate, storable dry mixture of suitable aggregate, monocalcium phosphate, and calcium in the form of calcium aluminate cement or calcium oxide. The proportion of wet to dry constituents is variable so as to select the working time and strength of the aggregate composition, typically on the order of ten to fifteen minutes. The mixture of the preferred dry constituents, and the binder to be mixed with the aggregate to yield the preferred dry mixture, are also disclosed. The binder system is particularly advantageous in that the same set of binder constituents can readily be employed with a variety of aggregates, reducing the cost of providing a variety of aggregate compositions due to the ready availability of the raw materials and obviating the need to stock different binders for different aggregate compositions. Cost is additionally reduced through the use of less purified, and therefore less expensive constituents.

Evaluation of Resilient Modulus for Lime- and Cement-Stabilized Synthetic Cohesive Soils

Abstract: The effects of deviator stress, molding moisture content, stabilizer type and content, curing period, and soil type on the resilient modulus (Mr) of lime- and cement-stabilized cohesive soils were investigated by using Hydrite R (kaolinite) and sodium bentonite (montmorillonite) blends. It was found that Mr increases with decreasing deviator stress, increasing lime and cement content, and extended curing period. Moisture variations around optimum had little effect on Mr with higher lime contents. Multiple regression analyses and Student's t-tests indicated that all the factors investigated were significant and could be related to Mr by predictive regression equations. For a given stabilizer type and content, the low-plasticity clay (CL) soil produced the best results. The cement-stabilized CL soil normal cured for 28 days produced the highest Mr value. However, cement stabilization was not found to be very effective for the high-plasticity clay (CH) soil. Mineralogical composition has a marked effect on t...

Hydraulically-bonded monolithic refractories containing a calcium oxide free binder comprised of a hydratable alumina source and magnesium oxide

Abstract: This invention relates to cement-free refractories exhibiting high green strength, improved corrosion resistance, and improved magnesium oxide hydration resistance useful as refractory castables for steel ladles, slag contact areas, ladle sidewalls and bottoms, and the like and as precast refractory shapes, such as well blocks, nest blocks, and the like. More particularly, this invention is directed hydraulically-bonded monolithic refractories containing a calcium oxide-free binder comprised of a hydratable alumina source and magnesium oxide and which exhibit high green strength, improved corrosion resistance, improved magnesium oxide hydration resistance, and controllable work and set times.

Hydrothermal synthesis of xonotlite whiskers by ion diffusion

Abstract: Xonotlite, a calcium silicate hydrate, has been industrially produced as a main constituent for heat insulating material [1, 2], building material [1, 3] and artificial wood [1, 4], because of its high stability at high temperature and fibrous crystal form. It is usually prepared from a suspension of silica and calcium hydroxide by hydrothermal treatment [5– 10]. Formation mechanism of xonotlite crystals from the suspension is complicated, because various intermediate reaction products are formed in the reaction processes. For example, calcium hydroxide reacts with low-quartz particles to form calcium-rich CSH (low crystalline calcium silicate hydrates) in the first stage of the reaction. Compositional change in CSH to equivalent Ca=Si ratio leads to crystallization of tobermorite which transforms to xonotlite by further hydrothermal treatment [5]. The size of the xonotlite crystals thus prepared is limited because of formation from these intermediate products. Kunugida et al. [11] pointed out that direct preparation of xonotlite, not through intermediate products such as CSH and tobermorite, was important for preparation of long fibre xonotlite. They obtained long fibre xonotlite crystals with maximum length 2 mm at 350 8C in the continuoustype autoclave by the two processes, in-situ mixing and rapid heating of raw materials. They reported that recrystallization of xonotlite also lengthened the crystals. We consider that continuous crystal growth provides elongation of xonotlite crystals under conditions where xonotlite is stable. We report here the preparation of xonotlite whiskers at 250 8C using a continuous supply of calcium and silicate ions in a multichamber autoclave where silica and calcium hydroxide are separately placed. The multichamber autoclave used in this study is shown in Fig. 1. It was made of stainless steel with total inner volume 50 cm3 and had two separate chambers each with volume 12.5 cm3. Two kinds of silica sources were used; silica gel (Wakogel C-300, Wako Pure Chem. Ind., Japan, 200–300 mesh) and low-quartz powder (SiO2 99.5 wt %, Al2O3 0.2 wt %) consisting of coarse grains from 20–150 im in diameter, produced by crushing silica stone (from Fukushima Prefecture, Japan) and classifying from the water suspension by gravitational sedimentation. Calcium source was a pellet of calcium oxide produced by calcination of calcium carbonate (reagent grade, Wako Pure Chem. Ind., Japan) at 1100 8C for 3 h. After placing the silica and calcium source (0.5 g each) at the bottom of each chamber, decarbonated distilled water (30 cm3) was poured slowly into the autoclave so not to suspend the raw materials. The silica source was brought into contact with the calcium source via the water; thus, ion species dissolved from the two sources diffuse to each other in the autoclave to produce calcium silicate hydrates. Platinum plates were placed in the autoclave (Fig. 1) to collect the reaction products formed by ion diffusion. These operations were performed in a glove box purged of carbon dioxide with nitrogen gas. The autoclave was heated at 250 8C for 2 to 72 h in an electric oven without temperature gradient; it took about 1 h to heat the autoclave to 250 8C. At the conclusion of the hydrothermal treatment, the autoclave was cooled down to room temperature by a cold air blow, and dried in vacuum after removal of the water. The reaction products, precipitated on the platinum plates, were observed by scanning and transmission electron microscope equipped with an energy dispersive X-ray spectrometer and identified by X-ray powder diffraction. When silica gel was used as a silica source, a large quantity of ribbon-like crystals were obtained after 2 h at 250 8C (Fig. 2a). X-ray diffraction showed that they were low crystalline tobermorite

Particulate urea with finely divided inorganic material incorporated for hardness nonfriability and anti-caking

Abstract: A particulate urea product having improved hardness, nonfriable and anti-caking properties and which is useful for either direct application to the soil or as an intermediate product for the subsequent incorporation with other fertilizer materials into solid bulk blends. The product consists of an admixture of urea and a finely divided inorganic material selected from the group consisting of calcium oxide, calcium hydroxide, cement and fly ash and is in particulate form, some examples of which are granules or prills.

Novel preparation method of macroporous lime from limestone for high-temperature desulfurization

Abstract: In order to develop a highly active calcium oxide high-temperature desulfurization sorbent, macroporous calcium oxides were directly prepared from limestone. This method is composed of two steps: swelling of the limestone in the gas phase followed by drying and calcination of the swelled samples. The swelling was found when limestone was exposed to a vapor of aqueous acetic acid. The swelling of the sample resulted from an increase of calcium acetate formation in the sample. It was then converted to macroporous calcium oxides by heating the sample to 850 °C. The reactivity of the macroporous calcium oxide for the removal of SO2 or H2S under coexisting H2O vapor was higher than that of the calcined raw limestone. In particular, its SO2 removal capacity and oxidative character of CaS to CaSO4 and CaO were greatly improved by the swelling method.

Method for fixing co2 with alkaline earth metallic silicate

Abstract: PROBLEM TO BE SOLVED: To obtain silica as fine spherical silica in large quantities at a low cost as well as to fix CO2 by suspending powder contg. calcium silicate or magnesium silicate in water, blowing CO2 or CO2 -contg. gas and causing reaction in a fluidized state. SOLUTION: Calcium silicate is a general name for compds. each having a compsn. in which calcium oxide bonds to silicon dioxide. Magnesium silicate is a general name for compds. each having a compsn. in which magnesium oxide bonds to silicon dioxide. The particle size of powder of a material contg. at least one of calcium silicate and magnesium silicate is preferably made as small as possible so as to increase the surface area and the pref. particle size is <=50 mesh. By the above-mentioned method, CO2 is efficiently fixed and a large amt. of fine spherical silica is obtd. at a low cost. The photograph is a microscopic photograph of the produced silica having 0.1-0.5μm particle diameter.

Production of calcium hydroxide

Abstract: PURPOSE:To obtain the powdery calcium hydroxide which is hardly stickable and consolidatable at the time of transportation and storage in a pipe and a tank by adding a surfactant, liquid alcohol and water to calcium oxide and bringing this calcium oxide into a slaking reaction. CONSTITUTION:An aq. soln. prepd. by dissolving the surfactant (e.g.: sodium polyacrylate) in water in such a manner that the amt. of addition to raw material quicklime attains 0.05 to 1.0wt.% at the time of the slaking reaction is added to an aq. alcohol soln. contg. 5 to 60vol.% concn. of methanol and/or ethanol and further, fresh water is added to the soln. mixture at need, by which slaking water is prepd. While this slaking water is kept stirred in a slaking machine, the slaking water is added at 32 to 80 pts.wt. per 100 pts.wt. quicklime to the quicklime to effect the slaking reaction. The resulted calcium hydroxide is discharged after the unequal slaking is eliminated while the calcium hydroxide is kept stirred in a maturing machine. The alcohol and the excess water evaporate from the upper part of the maturing machine, but the fine powder of the calcium hydroxide entrained in steam is removed by a dust collector and thereafter, the alcohol is recovered in a recovering column and is cyclically used.

Flame retardant high temperature polyphthalamides having improved thermal stability

Abstract: The thermal stability of flame retardant, high temperature polyamides containing an organohalogen flame-retardant such as brominated polystyrene in combination with an antimony compound such as sodium antimonate during molding and similar melt fabrication operations is markedly improved when further combined with a minor amount of calcium oxide. The thermal stability of these compositions are much improved over analogous flame retardant polyamides formulated with magnesium oxide and/or zinc oxide.

Production of transparent yttrium oxide sintered body

Abstract: PROBLEM TO BE SOLVED: To provide a method capable of producing a transparent yttrium oxide sintered body at a lower cost than a conventional method and free from the necessity for severely controlling production conditions. SOLUTION: An yttrium compound which becomes yttrium oxide powder by pyrolysis or yttrium oxide powder of <=0.5 μm in an average particle size of primary particles is mixed with a calcium compound which becomes calcium oxide by pyrolysis or calcium oxide powder in a range of 100 ppm or 4% based on the yttrium oxide, and the resultant powdery mixture is processed into a formed body. The obtained formed body is baked at a temperature in the range of 1400-2000 deg.C under an atmosphere whose nitrogen partial pressure is controlled.

Method and packaging utilizing calcium cyanamide for soil treatment

Abstract: Processes and structures for using calcium cyanamide fertilizer in a manner to greatly enhance its most effective oil treatment form prior to its application. Dry, dusty granules and fines of calcium cyanamide are placed directly into tanks of liquid for transformation or within biodegradable bags through which water can freely flow. The bags are submerged in a tank of water. The insoluble calcium oxide and carbon components thereof remain as solid residuals within the bags. Hydrolysis occurs and the solution is biocidal and ready for immediate application. The solution can be sprayed or irrigated onto a targeted soil area with conventional dispersal equipment. The remaining non-dissolved material in the bags can be dispersed on and into the plant crop soil. Additives of other fertilizers into the above solution can be used to enhance effectiveness. When the calcium cyanamide is placed directly into the liquid, the mixture will become slurry-like.

Reactivity of Metal Oxide Sorbents for Removal of Sulfur Compounds from Coal Gases at High Temperature and Pressure

Abstract: Hot-gas desulfurization for the integrated gasification combined cycle (IGCC) process has been investigated to effectively remove hydrogen sulfide with various metal oxide sorbents at high temperatures and pressures. Metal oxide sorbents such as zinc titanate oxide, zinc ferrite oxide, copper oxide, manganese oxide, and calcium oxide were found to be promising sorbents in comparison with other removal methods such as membrane separation and reactive membrane separation. The removal reaction of H2S from coal gas mixtures with zinc titanate oxide sorbents was conducted in a batch reactor. The main objectives of this research are to formulate promising metal oxide sorbents for removal of hydrogen sulfide from coal gas mixtures, to compare reactivity of a formulated sorbent with a sorbent supplied by the Research Triangle Institute at high temperatures and pressures, and to determine effects of concentrations of moisture contained in coal gas mixtures, and to determine effects of concentrations of mo...

Method for the preparation of acid-resistant calcium silicate

Abstract: A novel method is proposed for the preparation of a calcium silicate powder particularly useful as a filter aid in the filtration of an acidic aqueous liquid by virtue of the extremely high acid resistance of the calcium silicate powder. The inventive method comprises a hydrothermal reaction of a blend of a silica-containing material and calcium oxide or hydroxide in a specified molar ratio under specified reaction conditions to form calcium silicate, which is then subjected to a heat treatment at 800°-1200° C. for 0.5-2 hours. An improvement can be obtained in the clarity of the filtrate obtained by the filtration using the calcium silicate powder prepared by the inventive method as a filter aid when the hydrothermal reaction for the preparation thereof is conducted in an aqueous solution of potassium hydroxide in a specified concentration.

Calcium aluminate based catalyst and use of the catalyst

Abstract: Shaped units suitable for use as a catalyst, e.g. for the decomposition of hypochlorite, comprise a compacted particulate mixture of at least one oxide of a Group VIII metal M selected from nickel and cobalt, a calcium aluminate cement, and alumina and/or magnesia, said shaped units having (after ignition in air at 900 °C) a content of said Group VIII metal oxide of 10 to 50 % by weight (expressed as the divalent oxide, MO), a calcium oxide content of 1 to 10 % by weight, an alumina content by weight that is at least four times the weight of calcium oxide, a total content of alumina plus magnesia of at least 40 % by weight, a silica content of less than 1 % by weight, and said shaped units having a pore volume in the range 0.2 to 0.5 ml/g and having a pore size distribution such that from 5 to 25 % of the total pore volume is in the form of pores of diameter in the range 15 to 35 nm, at least 30 % of the total pore volume is in the form of pores of diameter greater than 35 nm, and 10 to 20 % of the total pore volume is in the form of pores of diameter greater than 1500 nm.

Production of slaked lime

Abstract: A method of producing an aqueous suspension of calcium hydroxide which comprises passing a gaseous flow incorporating particles of calcium carbonate through a calcining furnace thermally to decompose the calcium carbonate, delivering a flow of the decomposition products formed in the furnace comprising calcium oxide particles suspended in gas comprising carbon dioxide to a vessel wherein the calcium oxide particles are contacted with water to produce an aqueous suspension of calcium hydroxide and separating the aqueous suspension from the said gas.

Hydration Kinetics of Lime

Abstract: Hydration rate of calcium oxide has been investigated for a suspended single pellet into an atmosphere of air with a controlled humidity using a computer aided thermo-gravimetric technique. It has been found that the hydration reaction takes place on a sharp, well defined interface between the product layer and the unreacted core. A theoretical model for this reaction, that takes into account the sample swelling, was derived and employed to estimate the values for the rate constant and the effective diffusivity of the water vapor in the Ca(OH) 2 layer. These results suggest that gas mass transfer, pore diffusion and chemical reaction were all contributing resistances in the model. The calcination temperature and the water vapor partial pressure are the two most important variables that affect the hydration rate of lime. The higher the calcination temperature, the lower the hydration rate and the higher the water vapor partial pressure, the higher the hydration rate. The hydration temperature was found to play also a very important role in the phenomena involved.

Apparatus and integrated process for reclaiming paper mill sludge and producing useful products therefrom

Abstract: Paper mill sludge is reclaimed and useful products produced therefrom. A predetermined amount of paper mill sludge is continuously discharged from a storage reservoir onto a mixer/conveyor to create a first reactant stream. A predetermined amount of calcium oxide is input into the first reactant stream from a calcium oxide reservoir. The calcium oxide and paper mill sludge are mixed as they travel along the mixer/conveyor to form a first intermediate mixture. After a time period sufficient to allow for the reaction of the calcium oxide and paper mill sludge, a predetermined amount of diatomite is added to the reactant stream from a diatomite storage reservoir. The first reactant stream, now comprising the first intermediate mixture of paper mill sludge and calcium oxide combined with diatomite, forms a useful, environmentally safe product.

冷熱生成型CaO/H2O/Ca(OH)2系ケミカルヒートポンプにおける性能向上の検討

Abstract: CaO/H2O/Ca(OH)2反応系ケミカルヒートポンプにおける冷凍モードでの性能向上を目的として, ガラス製冷熱生成ケミカルヒートポンプ装置を試作し, 装置工学的な観点から実験的検討を行なった.特に, 反応器内の熱・物質移動状態に着目して, 装置形状および作動温度条件の冷熱生成特性への影響の検討を行なった.その結果, 1) 多段反応粒子トレーと反応器内側壁とのすき間が約2.5倍に拡大されて粒子層間距離と等しくなることにより, 水蒸気が反応器全体により均一に供給されて冷熱生成速度および生成冷熱量が増加することがわかった.2) 装置を横型から縦型にして水蒸気流入口を反応器上部から下部へ変更することにより, 反応器内への水蒸気流入状態が向上し, 特に初期反応が促進されることが確認された.3) 反応器側熱交換媒体温度の違いにより粒子の平衡圧力および反応活性が変化し, これらのバランスが生成冷熱温度および冷熱生成速度に大きく影響することがわかった.

Stabilization of Shallow Slope Failures with Lime Piles

Abstract: Lime piles essentially consist of boreholes filled with lime. They have been used to stabilize slopes in many countries worldwide but have not been adopted as a standard means of stabilization in any country. The literature on the subject makes several claims about the way lime piles stabilize the soil. However, the reported results of experimental work are in some cases contradictory and are too few to facilitate appropriate engineering judgment of the stabilizing mechanisms. Research at Loughborough University, United Kingdom, has investigated the use of quicklime piles in the context of stabilization of shallow slope failures in clay slopes. The stabilizing mechanisms observed in a series of laboratory and field investigations are (a) increased strength of an annular zone of clay surrounding the pile caused by lime-clay reaction, (b) clay dehydration, (c) generation of negative pore-water pressure, (d) over-consolidation of the soil in the shear plane, and (e) pile strength. The idea of lateral consoli...

Gypsum-based modelling material especially for dentistry

Abstract: A mineral modelling material based on alpha calcium sulphate hemihydrate, with a light reflection-free surface and more than 50% reflection in the 800-1800 nm range, for optical measurement and scanning of the model by an IR laser, comprises: (i) 70-95% alpha hemihydrate; 0-20% accompanying components (e.g. beta hemihydrate, anhydrate and calcium oxide); (ii) 0.5-2% water-soluble salts (e.g. potassium sulphate, potassium sodium tartrate and sodium citrate); (iii) 0.5-2% calcium sulphate dihydrate; (iv) 0-30% filler (e.g. calcium carbonate or silicon dioxide); (v) 0.2-3% organic component (e.g. melamine resin); and (vi) 2-10% inorganic pigment with a refractive index of at least 2.5 (e.g. titanium dioxide, chromium (III) oxide or iron (III) oxide).

Hydraulic cement with an accelerated development of high strength

Abstract: The invention consists in a method for the manufacture of calcium sulfoaluminate based cements, which consists in the formation of a clinker by the burning of the raw materials at a temperature above 1200 °C, so that the clinker so produced has a high content in calcium sulfoaluminate, tricalcium silicate and dicalcium silicate, and, during or prior to the grinding of the resulting mixture, adding, to the clinker so produced and together with the basic components previously mentioned, optimum amounts of calcium oxide or hydroxide and calcium sulfate so as to activate said clinker. During said grinding a temperature of approximately between 100 and 125 °C shall be ensured, as well as sufficient time to convert gypsum into the hemihydrate, thus ensuring that the calcium sulfate present in the product so obtained will be in a condition to react rapidly during the hydration of the cement, resulting in the formation of etringite, requiring a pH of above 12 in order to do this.