Showing papers on "Calcium oxide published in 1994"

Development of some calcium phosphate cements from combinations of α-TCP, MCPM and CaO

Abstract: From previous studies it is known that alpha-tertiary calcium phosphate (α-TCP), monocalcium phosphate monohydrate (MCPM) and calcium oxide form cements upon mixing combinations of them with water. In this study some formulations were optimized with respect to the particle size of the constituents, their molar ratio, amounts of hydroxyapatite or beta-tertiary calcium phosphate (β-TCP) added and the water/powder ratio. Three suitable products were obtained. Product 1 had a relatively short setting time and might be suitable as a dental cavity liner or for filling parodontological pockets or for filling alveolar cavities to prevent alveolar ridge resorption. Products 2 and 3 may be more suitable for orthopaedic purposes. Their compressive strength being 35 and 12 MPa, respectively, after soaking for 1 day in Ringer's solution at 37°C. Product 1 reaches its full strength within 4 h, whereas products 2 and 3 take about 12 h and 10 h, respectively.

Chemical equilibria between silicon and slag melts

Abstract: The equilibria between silicon and slags of the systems CaO-SiO2, Na2O-SiO2, and CaO-SiO2-Y with Y being A12O3, MgO, TiOx, B2O3, and Na2O have been investigated in silica crucibles. The calcium content under silica-saturated CaO-SiO2 slag is 262 parts per million (ppm) at 1500 °C. The aluminum and magnesium contents increase with increasing alumina or magnesium oxide contents, respectively, reaching about 1800 ppm Al at silica/mullite or about 390 ppm Mg at silica/protoenstatite saturation. Boron has a distribution ratio [B]/(B2O3) of 0.18. The sodium content under silica-saturated Na2O-SiO2 slag is 25 ppm at 1500 °C. In contrast, the titanium content of the silicon, if Y is TiOx, and (Ti) is in the percent range, is highand varies with the titanium content of the slag according to [wt Pct Ti] = 2.7 √(wt pctTi). In other experiments, it is shown that metallurgical grade (MG) silicon can be purified from aluminum, magnesium, and calcium by treatment with suitable silicate slags.

Optimization of a calcium orthophosphate cement formulation occurring in the combination of monocalcium phosphate monohydrate with calcium oxide

Abstract: In a previous study it has been found that mixtures of monocalcium phosphate monohydrate MCPM and calcium oxide CaO set upon mixing with water. In this study it was found that the optimum composition for such a mixture is a Ca/P molar ratio of 1.35_+0.02. The milling procedure for preparation of the powder of this cement was also optimized. The optimum water/powder ratio appeared to be 0.53___0.01. Amounts of precipitated hydroxyapatite up to 7% by weight increased the compressive strength and the diametral tensile strength of the cement. The maximum values found for these properties were 6 and 1.6 MPa, respectively. Finally, it was found that the cement obtained its maximum strength within 5 h but this diminished upon further soaking in Ringer's solution at 37°C until after 10 weeks of soaking the strength was decreased to 62% of the maximum value.

Process and Additives for the Ladle Refining of Steel

Abstract: A process of refining steel in a ladle using solid granules or briquettes made from recycled LMF slag and raw materials to make a desulfurizing addition, a slag conditioner or synthetic refining slag is described. The preferred recycled LMF slag material generally comprises of 35% to about 65% CaO; 10% to about 35% Al 2 O 3 ; 1% to about 10% SiO 2 ; 3% to about 15% MgO; 0.3% to about 10% FeO; 0.1% to about 5% MnO; 0% to about 0.5% P 2 O 5 ; and 0.1% to about 0.5% S. The ladle refining additive comprises from about 10% to about 90% of a recycled ladle metallurgy furnace slag and the balance of raw materials selected from the group consisting of: a calcium oxide source; soda ash; fluorspar; borax; calcium carbonate; aluminum source; calcium aluminate; alumina source; metallic calcium, magnesium, sodium and their oxides, fluorides and carbides; and mixtures of all of the foregoing.

Removal Of H2S from Coal Gas Using Limestone: Kinetic Considerations

Abstract: The calcium carbonate contained in limestone becomes thermodynamically capable of sorbing hydrogen sulfide from high-pressure coal gas at temperatures above 600 C, typically well below the calcination temperature. Limestone can be used more effectively as a sorbent for hydrogen sulfide in high-temperature gas-cleaning applications if it is prevented from undergoing calcination since calcium oxide may sinter rapidly. For large (millimeter) sized particles typically used in gas cleaning, sintering of uncalcined limestone was found to be insignificant in the temperature range 750--900 C. Poor conversion of the solid upon reaction with H[sub 2]S is caused by sintering of the CaS product layer, which can be seen from scanning electron microscopy photographs. Sintering of CaS is rapid in an atmosphere that contains CO[sub 2], but is slow under N[sub 2] or H[sub 2]. The kinetics of CaS sintering under CO[sub 2] was determined for the temperature range 750--900 C.

Microwave dielectric ceramic composition

Abstract: The present invention is characterized in that in order to obtain a microwave dielectric ceramic composition having a high dielectric constant (e) and a large Q value and having a temperature coefficient (τf) which is close to zero, calcium oxide and strontium oxide, sodium oxide or lead oxide which are mixed with each other in an adjusted ratio are added to lithium oxide, samarium oxide and titanium oxide.

Process for the preparation of calcium aluminates from aluminum dross residues

Abstract: The present invention is concerned with a process for the preparation of sintered calcium aluminates that can generally be used as a protective cover for liquid metals, and particularly steel, the process comprising the steps of mixing calcium oxide, or its precursor, particles and aluminum dross residue, such as NOVALTM; calcining the resulting mixture; maintaining a calcining temperature of 1200 °C or higher for approximately 5 minutes or more which is sufficient to form a friable sintered product rich in calcium aluminates; and recovering the sintered product after cooling. Optionally, calcium fluoride, or other fluoride can be added to the starting mixture, if it is not already contained in the dross residue.

Method for the stabilization and detoxification of waste material

Abstract: A process for the treatment of waste material. The process includes the steps of combining the waste material with a treatment composition to form crystal growth structures and adsorb the waste material within the crystal growth structures thereby stabilizing the waste-material. The treatment composition includes natural zeolite seed, crystalline quartz, aluminum trihydrate, sodium carbonate or sodium hydroxide, dolomitic calcium oxide or calcium oxide or dolomitic limestone, and potassium hydroxide or potassium carbonate. The zeolite seed may be selected from the group consisting of clinoptilolite, chabazite, heulandite, phillipsite or mordenite and mixtures thereof.

Ferrite and ferrite core for power supply

Abstract: PURPOSE: To cut down power loss in a high-frequency region by a method wherein specific amounts of silicon oxide, calcium oxide, tin oxide and/or titanium oxide, niobium oxide. zirconium oxide are contained in the material of ferrite. CONSTITUTION: As for the main components, mangenese oxide, zinc oxide and iron oxide are contained and as for the sub components, silicon oxide, calcium oxide, tin oxide and/or titanium oxide, niobium oxide and zirconium oxide are contained. At this tiem, the contents of mangnese oxide in the main contents is 30-41mol% in terms of MnO, 6-16mol% of zinc oxide in terms of ZnO. On the other hand, the weight ratio of the sub components to the main components is 50-250-ppm of silicon oxide in terms of SiO 2 , 200-1500ppm of calcium oxide in terms of CaO, not exceeding 4000ppm of tin oxide in terms of SnO 2 , not exceeding 3000ppm of titanium oxide in terms of TiO 2 and the total of the tin oxide and titanium oxide exceeds 3000ppm. COPYRIGHT: (C)1995,JPO

Determination of original free lime content of weathered iron and steel slags by thermogravimetric analysis

Abstract: Iron and steel slags are often used as subbase materials in the construction of highways. Previous studies have suggested that the free lime (CaO) in these subbases is responsible for the deposition of calcium carbonate (tufa) in many highway drains. Clogging of these drains leads to the deterioration of highways. Previous work has shown that if the total original CaO in slags exceeds 1%, the slags will readily produce tufa. Therefore, to classify the tufa-producing potential of these slags, it is necessary to determine the total original CaO. Thermogravimetry (TG) methods were employed and most of the TG plots indicated two major changes in weight loss--dehydroxylation of Ca(OH)2 and dissociation of carbonates. From these changes in weight loss the percentage of CaO was calculated. These calculated percentages of CaO from the TG plot plus the results from the "sugar test" determine the total original percentage of CaO. Five groups are recognized according to the calculated total percentage of CaO: 0%, 3.5 to 5%, 8 to 9%, 10 to 12%, and 24 to 25%. Air-cooled blast furnace slag (0% CaO) is the only slag that should be used as a subbase in highway construction, whereas all others are considered to be harmful and could lead to the formation of tufa. TG methods and the sugar test are excellent and economical ways to characterize the original CaO in slags and the susceptibility of the slags to precipitate CaCO3 in subdrains of highways.

Aluminum nitride sintered body having a metallized coating layer on its surface

Abstract: An aluminum nitride sintered body has a metallized layer on its surface. The metallized layer contains tungsten, aluminum oxide and calcium oxide. Preferably, the metallized layer contains 40 to 96 percent by weight of a metal, 0.4 to 25 percent by weight of an aluminum oxide and 3 to 35 percent by weight of calcium oxide. In a method of forming a metallized layer on the surface of the aluminum nitride sintered body, such body is first formed by firing. Then, a metal paste of tungsten containing powder of calcium oxide and powder of aluminum oxide is provided. The metal paste is coated on the surface of the aluminum nitride sintered body which is then fired with the metal paste in an inert atmosphere.

Glass-ceramic composite

Abstract: The invention provides a glass-ceramic composite with sufficient strength and other excellent properties suitable for IC packages or multilayer substrates. The glass-ceramic composite of the invention includes crystallized glass and at least either of alumina and mullite at the ratio by weight of eighty through fifty-five to twenty through forty-five. The crystallized glass includes cordierite as primary crystals and contains 40 to 52 percent by weight of silicon dioxide or SiO2, 27 to 37 percent by weight of aluminum oxide or Al2 O3, 11 to 13 percent by weight of magnesium oxide or MgO, 2 to 8 percent by weight of diboron trioxides or B2 O3, 2 to 8 percent by weight of calcium oxide or CaO, and 0.1 to 3 percent by weight of zirconium oxide or ZrO2.

Deep-slope stabilization using lime piles

Abstract: Lime piles have been successfully used in practice in several countries worldwide but their mechanism of operation has not been adequately explained The literature on the subject has been briefly reviewed and a list of suggested stabilizing processes has been compiled Programs of experimental work to investigate each process are described and the results are presented Lime piles, which usually consist of columns of quicklime placed in pre-formed holes in clay soils, draw in water during hydration and expand No lateral consolidation of the surrounding clay occurs, however, because of the stoichiometry of the hydration reaction The water loss in the surrounding clay causes an increase in undrained shear strength The associated pore water pressure reduction, or suction, caused by the hydration reaction is shown to be significant in the short term to increase the stability of the slope and in the long term by overconsolidation of the shear plane Migration of calcium and hydroxyl ions from the piles has been shown to be limited to less than 30 mm (12 in), as might be expected from considerations of clay liners The pile itself is shown to have significant strength The laboratory work has heen supported by the initial findings of a program of field trials

Characterization of base and subbase iron and steel slag aggregates causing deposition of calcareous tufa in drains

Abstract: Tufaceouslike materials are observed clogging pavement drains along highways in northeastern Ohio. These materials have also been found in catch basins and spillways. Previous studies suggest that the original free lime (CaO) in slags used as subbase materials is responsible for the deposition of the tufa. To characterize these slags, X-ray diffraction, energy dispersive X-ray, surface area measurements, CaO solubility in anhydrous ethylene glycol ("sugar test"), and other physicochemical tests were conducted on air-cooled blast furnace (ACBF), open-hearth (OH), and basic oxygen furnace (BOF) slags. ACBF iron slag is composed of crystalline akermanite (Ca2MgSi2O7). Results of the sugar test indicate that this slag does not contain any residual or easily available free lime. The ACBF sample exhibited the lowest surface area and therefore is the least reactive with CO2-charged waters. The OH and BOF slags, however, exhibit the presence of CaO or its weathering equivalents such as Ca(OH)2 and CaCO3. All these steel slags exhibit a high tufa-generating potential. Analysis of the physicochemical tests of these steel slags indicates that they are composed mainly of Beta-dicalcium silicate (larnite), calcium ferrites, wustite (FeO), free lime (CaO), periclase (MgO), portlandite [Ca(OH)2], and calcite (CaCO3). These slags also exhibit high surface areas and are more reactive with CO2-charged waters. Most highway departments require that steel slags be aged or cured for at least 6 months before they are used. Sugar tests conducted on samples obtained from different horizontal depths (up to 10 ft) in a stockpile showed that the CaO (free lime) content increases with increasing depth into the stockpile. Evidently some of the free lime is encapsulated by insoluble silicates or is in occluded pores and has not come in contact with CO2-charged porewater. Therefore, aging of slags by exposure to weathering does not necessarily decrease the free lime content enough to prevent the formation of tufa. It is concluded that the presence of CaO, MgO, Ca(OH)2, and CaCO3 in slags is critical in determining their tufa potential for use as base and subbase aggregates.

Porous granular composite material of calcium oxide and its production

Abstract: PURPOSE:To stabilize activity of porous material of calcium oxide having high activity by coating the surface of calcium oxide with a calcium carbonate layer. CONSTITUTION:A porous laminar granular composite material of calcium oxide comprising porous particles of highly active calcium oxide having >=5m /g specific surface area and >=1mm particle diameter and a coated layer of calcium carbonate formed on the surface of the calcium oxide is obtained by the following two methods. (A) Calcium hydroxide powder or calcium carbonate powder having =1mm particle diameter, burnt under normal pressure at 400-950 deg.C for 30 minutes to 2 hours and further burnt in a carbon dioxide gas atmosphere at 400-700 deg.C to give 10% carbonization ratio. (B) Calcium hydroxide having 10-300mum average particle diameter is blended with 5-25wt.% water and granulated. The granules are heated at 390-480 deg.C for >=5 minutes and heating is stopped at 480 deg.C. The prepared porous material of highly active calcium oxide is heated to 400-700 deg.C and brought into contact with about 3% carbon dioxide gas to form a coating film of calcium carbonate.

Formation of calcium chromate hydroxylapatite on the surface of a calcium-doped lanthanum chromite sintered body

Abstract: Sintered bodies of highly sinterable calcium-doped lanthanum chromites with chromium deficiency have been found to deteriorate and form calcium chromate hydroxyl apatite on their surfaces when exposed to high-temperature water-containing atmospheres. Microstructure analysis, composition measurement, and phase identification were performed on the surface of the samples after annealing in various conditions. The mechanism of the surface deterioration is thus deduced: traces of liquid phase which are formed in the sintering process migrate to the external surface and then react with water vapour to yield an apatite-type compound. Electrical conductivity has also been measured. The poorly conductive nature of the surface will cause some problems when the subject materials are used as high-temperature electronic conductors.

Surface segregation of calcium oxide in wustite and its effects on the reduction

Abstract: The segregation of calcium oxide to the surface of wustite was investigatedin situ by Auger electron spectroscopy at temperatures in the range of 973 to 1223 K. Calcium oxide indicated a strong tendency to segregate, with the molar fractions at the surface being 10 to 1000 times the molar fractions in the bulk (X CaO bulk ). The segregation isotherms showed maxima at intermediate molar fractions in the bulk (X CaO bulk = 0.003 or 0.005). The enthalpy change for the segregation increased from −43.3 to −5.20 kJ/mol with increasing X CaO bulk . The main driving force of the segregation may be the relaxation of the strain energy generated around calcium ions. Calcium oxide also segregates at the surface of iron in contact with the wustite. By the segregation of calcium oxide, the surface energies of wustite and iron may decrease whereas the wustite/iron interfacial energy may increase. The enhancement of the reduction of wustite by calcium oxide is concluded to essentially occur by the good and continuous direct contact of wustite surface with reducing gases owing to the suppression of new iron nucleus and owing to the contraction of the wustite/iron-nuclei interfacial area compared with the free-surface area of wustite in order to decrease the total energy.

Spark plug insulator for use in internal combustion engine

Abstract: In a spark plug insulator for use in an internal combustion engine, a sintered body has boron nitride and a metal oxide, the boron nitride of the sintered body being 80% or greater by weight, and the sintered body having a thermal expansion coefficient of less than 5.0×10- 6 /°C. The metal oxide is selected alone or in combination from the group consisting of magnesium oxide, calcium oxide, silicon oxide, boron oxide, yttrium oxide and aluminum oxide.

Effective utilization of excess sludge

Abstract: PURPOSE:To develop the effective utilization by which excess sludge of food factories and night soil or sewerage treatment plants can be recycled. CONSTITUTION:When quick lime (calcium oxide) is added to the excess sludge, the quick lime reacts highly exothermically with water in the sludge to form calcium hydroxide (slaked lime). As a result various microorganisms in the sludge is completely killed and the sludge is partly hydrolyzed by the high alkalinity and temperature. Thereafter by adding straws, sawdust, and further tuff loam and leaf mold to the sludge and by fermenting the mixture, a completely aged organic manure can be produced. At the time of applying the manure to vegetables, excellent growth promotion of the vegetables without any adverse effect on them resulting from any applied amount of the manure can be attained. On the other hand sulfuric acid is added to the excess sludge and the resulting sludge is neutralized with an aqueous suspension of slaked line and then sawdust is added to it. The mixture is sufficiently blended while stirring. At the time of using the mixture thus produced as a culture medium of Cortinellus shiitake (mushroom) and Pholiota nameko (mushroom), the growth of the hyphae of the mushrooms is remarkably promoted and also good yields and qualities of Cortinellus shiitake and Pholiota nameko can be attained.

Laboratory evaluation of the addition of lime treated sand to hot-mix asphalt

Abstract: Moisture damage to hot-mix asphalt (HMA) is a major problem. Hydrated lime has been shown to be an effective additive for reducing moisture damage susceptibility of HMA. Among the currently used methods for addition of hydrated lime to HMA aggregate, the one most often used is to add the lime to the entire aggregate stream. A recent field trial has shown that it is feasible to add hydrated lime to only the sand fraction in amounts that are equivalent to the desired concentration on the total aggregate basis. This would allow set up of a central facility for adding lime to the sand fraction of an HMA aggregate. The lime/fine aggregate mixtures could then be transported to an HMA plant and mixed with the remaining aggregate fraction. This concept is investigated in the laboratory using three aggregate combinations, two methods of conditioning specimens for moisture susceptibility testing (AASHTO T283 and ASTM D4867), two methods of lime addition, and three lime concentration levels. A statistical analysis of the data indicates that the two methods of lime addition (lime to fine aggregate and lime to total aggregate) produce asphalt mixtures that are equivalent in reduced moisture damage susceptibility. Other statistical comparisons indicate that (a) the greatest reduction in moisture susceptibility of the mixtures studied occurred from increasing the lime content from 0.5 to 1.0% (total dry aggregate basis), with less effect resulting from a 1.0 to 1.5% increase; (b) both the AASHTO T283 and ASTM D4867 procedures can be used to evaluate moisture susceptibility, but it appears that the specific aggregate combination will determine which procedure is most severe for a particular mixture; and (c) the addition of lime in the form of a slurry was in most cases better than the addition of lime to a moist aggregate. On the basis of recent field trials and the data obtained in the investigation, it appears that the addition of lime to the fine aggregate fraction of HMA aggregates, followed by subsequent mixing with the remainder of the aggregate stream, is an innovative process that has the potential for reducing capital costs sometimes associated with lime addition, without compromising the beneficial effects of lime addition for reduced moisture damage susceptibility of HMA.

Molten Steel Pouring Nozzle

Abstract: A molten steel pouring nozzle having, along the axis thereof, a bore through which molten steel flows. At least part of an inner portion of the molten steel pouring nozzle, which inner portion forms the bore, is formed of a refractory consisting essentially of: zirconia clinker comprising calcium zirconate : from 40 to 64.9 wt.%, where, a content of calcium oxide in the zirconia clinker being within a range of from 8 to 35 weight parts relative to 100 weight parts of the zirconia clinker, graphite : from 10 to 35 wt.%, and calcium silicate: from 25.1 to 50 wt.%, where, a content of calcium oxide in the calcium silicate being within a range of from 40 to 54 weight parts relative to 100 weight parts of the calcium silicate.

Stabilization of calcium-based slurries for sox reduction by in-furnance injection

Abstract: More reliable removal of sulfur oxides (SO x ) from combustion effluents by in furnace injection is achieved by stabilizing slurries of calcium carbonate (limestone), calcium oxide (lime) and calcium hydroxide (hydrated lime) for extended periods of time and during in-furnace injection. The slurries are stabilized by a stabilization system comprising a generally hydrophobic surfactant having an HLB of less than about 8 and a more hydrophilic surfactant having an HLB of at least about 8, wherein the HLB values of the hydrophobic and the hydrophilic surfactants differ by at least about 3.

Calcium carbide prodn. from calcium oxide and carbonaceous cpd. - derived from crushed plastics waste in presence of granular calcium oxide by pyrolysis and calcination

Abstract: Calcium carbide is produced by reacting calcium oxide with a carbon-contg. component in an electric arc furnace, said component being produced from crushed plastic waste which, in the presence of granular CaO and in a rotary kiln, undergoes: (a) pyrolysis at 400-800 deg.C; and (b) calcination of the resultant CaO-pyrolytic coke mixt. at 1000-1300 deg.C. Thermoplastic waste, namely polythene, polypropylene and polystyrene, contg. 70-85 wt.% C is crushed to obtain particles of max. size 20 nm, pref. 1-10 mm.. Granular CaO, particle size max. 10 mm, pref. max. 5 mm, in the form of calcined lime or anhydrous calcium hydroxide is heated to 80-400 deg.C prior to pyrolysis. Environmentally-friendly and virtually complete utilisation of waste plastic. A carbon-contg. component for calcium carbide mfr. is produced from low-cost raw materials. The exhaust gases produced by pyrolysis are high purity and may be used for power generation.