Showing papers on "Calcium oxide published in 2016"

Structure, Properties, and In Vitro Behavior of Heat-Treated Calcium Sulfate Scaffolds Fabricated by 3D Printing.

Abstract: The ability of inkjet-based 3D printing (3DP) to fabricate biocompatible ceramics has made it one of the most favorable techniques to generate bone tissue engineering (BTE) scaffolds. Calcium sulfates exhibit various beneficial characteristics, and they can be used as a promising biomaterial in BTE. However, low mechanical performance caused by the brittle character of ceramic materials is the main weakness of 3DP calcium sulfate scaffolds. Moreover, the presence of certain organic matters in the starting powder and binder solution causes products to have high toxicity levels. A post-processing treatment is usually employed to improve the physical, chemical, and biological behaviors of the printed scaffolds. In this study, the effects of heat treatment on the structural, mechanical, and physical characteristics of 3DP calcium sulfate prototypes were investigated. Different microscopy and spectroscopy methods were employed to characterize the printed prototypes. The in vitro cytotoxicity of the specimens was also evaluated before and after heat treatment. Results showed that the as-printed scaffolds and specimens heat treated at 300°C exhibited severe toxicity in vitro but had almost adequate strength. By contrast, the specimens heat treated in the 500°C–1000°C temperature range, although non-toxic, had insufficient mechanical strength, which was mainly attributed to the exit of the organic binder before 500°C and the absence of sufficient densification below 1000°C. The sintering process was accelerated at temperatures higher than 1000°C, resulting in higher compressive strength and less cytotoxicity. An anhydrous form of calcium sulfate was the only crystalline phase existing in the samples heated at 500°C–1150°C. The formation of calcium oxide caused by partial decomposition of calcium sulfate was observed in the specimens heat treated at temperatures higher than 1200°C. Although considerable improvements in cell viability of heat-treated scaffolds were observed in this study, the mechanical properties were not significantly improved, requiring further investigations. However, the findings of this study give a better insight into the complex nature of the problem in the fabrication of synthetic bone grafts and scaffolds via post-fabrication treatment of 3DP calcium sulfate prototypes.

Biodiesel Production from Castor Oil by Using Calcium Oxide Derived from Mud Clam Shell

Abstract: The catalytic potential of calcium oxide synthesized from mud clam shell as a heterogeneous catalyst for biodiesel production was studied. The mud clam shell calcium oxide was characterized using particle size analyzer, Fourier transform infrared spectroscopy, scanning electron microscopy, and BET gas sorption analyzer. The catalyst performance of mud clam shell calcium oxide was studied in the transesterification of castor oil as biodiesel. Catalyst characterization and transesterification study results of synthesized catalyst proved the efficiency of the natural derived catalyst for biodiesel production. A highest biodiesel yield of 96.7% was obtained at optimal parameters such as 1 : 14 oil-to-methanol molar ratio, 3% w/w catalyst concentration, 60°C reaction temperature, and 2-hour reaction time. Catalyst reusability test shows that the synthesized calcium oxide from mud clam shell is reusable up to 5 times.

Optimization of the activity of KOH/calcium aluminate nanocatalyst for biodiesel production using response surface methodology

Abstract: In this study, alumina and calcium aluminate were prepared through microwave combustion method (MCM) and then were modified by potassium hydroxide as solid base catalysts. The catalytic activities were evaluated in the transesterification reaction of canola oil. The characteristic properties of the samples determined by XRD, FTIR, TG, BET surface area, basicity by Hammett indicator, SEM and EDX showed that the alpha phase of alumina and monocalcium aluminate (CaAl2O4) were successfully synthesized by MCM. However, the samples showed less basicity and activity whereas these properties were meaningfully increased by KOH loading. Moreover, the surface area of monocalcium aluminate was increased from 38.9 to 48.1 m2/g by loading of potassium components. To obtain a catalyst with highest activity and basicity, the calcium oxide and potassium group precursor dosages on aluminum oxide were optimized using the response surface methodology (RSM). The optimal parameters obtained were calcium oxide/alumina molar ratio of 1.48:1 and 23 wt.% potassium hydroxide to CaO-Al2O3. The yield in the optimal condition was 96.7% (the predicted yield was 98.3%) where the transesterification reaction was performed in conditions of 65 °C, 3.5 wt.% catalyst, 12:1 molar ratio of methanol-to-oil and 4 h reaction time. The catalyst maintained its activity for at least three times.

Synthesis, Application, and Carbonation Behavior of Ca2Fe2O5 for Chemical Looping H2 Production

Abstract: Chemical looping hydrogen production uses the oxidation and reduction of metal oxides, typically iron, to produce hydrogen. This work focuses on the modification of iron oxide with calcium oxide to form an oxygen carrier containing dicalcium ferrite (Ca2Fe2O5), which presents favorable thermodynamics for achieving higher conversions of steam to hydrogen, compared to chemically unmodified iron oxide. Different methods of synthesis, viz. mechanochemical synthesis and coprecipitation, were used to produce Ca2Fe2O5, and their resulting performances were compared. Consistent with thermodynamic predictions, it was found that CO2, or steam, was sufficient to fully regenerate the reduced carriers to Ca2Fe2O5. The cyclic stability of the oxygen carriers were studied in fluidized bed reactors and by thermogravimetric analysis (TGA). Good stability of the materials was observed for up to 50 cycles, with no evidence of agglomeration, even up to 950 °C. The rate of deactivation was found to correlate with the purity o...

Mesoporous calcium oxide–silica and magnesium oxide–silica composites for CO2 capture at ambient and elevated temperatures

Abstract: Incorporation of basic metal species (oxides) such as magnesium oxide and calcium oxide into porous materials is a logical strategy for enlarging the uptake of acidic greenhouse gases such as CO2. This work reports the development of ordered mesoporous silica (OMS) with incorporated magnesium and calcium oxides for CO2 sorption at ambient and elevated temperatures. These materials were prepared by using the sol–gel method in the presence of the triblock copolymer Pluronic P123 in acidic medium followed by evaporation-induced self-assembly (EISA). The resulting magnesium oxide (MgO)- and calcium oxide (CaO)-OMS materials were used for CO2 sorption at low (0, 15 °C), ambient (25 °C), and elevated (120 °C) temperatures. Temperature programmed desorption (TPD) was used to measure the CO2 sorption capacities for the mesostructures studied at 120 °C. These sorbents exhibited relatively high adsorption capacity (0.63–2.61 mmol g−1) under low (0, 15 °C) and ambient conditions (25 °C, 1 atm) and remarkably high sorption uptake (3.11–4.71 mmol g−1) at 120 °C. The observed high CO2 uptake by CaO–SiO2 and MgO–SiO2 composites under ambient conditions is caused by enhanced physisorption of CO2 in micropores. Amazingly high CO2 uptake at elevated temperatures by OMS sorbents with incorporated CaO and MgO is mainly due to the chemisorption of CO2. The well-developed porous structure together with high surface area, basic surface properties and high thermal and chemical stabilities of CaO–SiO2 and MgO–SiO2 composites increase their prospects for high temperature capture of CO2 from industrial emissions.

Mechanochemically Activated, Calcium Oxide-Based, Magnesium Oxide-Stabilized Carbon Dioxide Sorbents

Abstract: Carbon dioxide capture and storage (CCS) is a promising approach to reduce anthropogenic CO2 emissions and mitigate climate change. However, the costs associated with the capture of CO2 using the currently available technology, that is, amine scrubbing, are considered prohibitive. In this context, the so-called calcium looping process, which relies on the reversible carbonation of CaO, is an attractive alternative. The main disadvantage of naturally occurring CaO-based CO2 sorbents, such as limestone, is their rapid deactivation caused by thermal sintering. Here, we report a scalable route based on wet mechanochemical activation to prepare MgO-stabilized, CaO-based CO2 sorbents. We optimized the synthesis conditions through a fundamental understanding of the underlying stabilization mechanism, and the quantity of MgO required to stabilize CaO could be reduced to as little as 15 wt %. This allowed the preparation of CO2 sorbents that exceed the CO2 uptake of the reference limestone by 200 %.

Marshall Stability and Flow of Lime-modified Asphalt Concrete

Abstract: The purpose of highway pavement is to provide smooth surface over which vehicles can move safely from one place to another. The two major types of pavement (flexible and rigid) have been mostly selected for the highway pavement to fulfil this function and they must be capable of transferring the wheel load to the subgrade such that its bearing capacity is not exceeded. However, the flexible pavements normally show defects like rutting, fatigue failure, low skid resistance and so on, causing the pavement to fail before its design life. Therefore, it is important to modify the asphalt concrete to make it more resistant to rutting and fatigue failure. Lime-modified asphalt has been observed to have better resistance to rutting, cracking and stripping, as well as having improved aging behavior. Therefore, this study looks at the Marshall properties of hydrated lime-modified asphalt mixture and the conventional asphalt. The conventional asphalt mixture was made using 10% mineral filler while for the lime-modified asphalt, the mineral filler was replaced with hydrated lime. The bitumen with penetration grade 60/70 was used and the content varied from 5.0 to 7.5%. Marshall stability and flow tests were carried out on the samples. The results show that the Marshall stability for the asphalt concrete with mineral filler ranges from 5.89 – 7.90 kN while that with hydrated lime ranges from 5.9 to 8.2 kN. The flow values for the asphalt concrete with mineral filler range from 2.3 mm – 3.3 mm, while that with hydrated lime range from 2.4 – 3.4 mm. The optimum bitumen content for both mixtures was found to be 6.5%. The stability and flow for the mixture with mineral filler were 7.9 kN and 3.3 mm, respectively, while for the mixtures with hydrated lime they were 8.2 kN and 3.4 mm, respectively. This indicates the replacement of the mineral filler with lime improves the stability of the mixtures, while there was slight increase in the flow of the mixture with hydrated lime. The slight increase in stability and flow values may be attributed to the complete replacement of the mineral filler with lime and the high lime content used in the study. More studies are being carried out to evaluate the Marshall properties for mixture with the mineral filler partially replaced with lime and for varying proportions of the lime content in the asphalt mixture.

Preparation and Characterization of Amorphous Silica and Calcium Oxide from Agricultural Wastes

Abstract: Rice husk ash and bagasse ash were agricultural wastes that provide an abundance of the silica (SiO2) source and the chicken eggshells and duck eggshells were important sources for calcium oxide (CaO). Therefore, in this study the rice husk ash and bagasse ash were used as raw materials for synthesis of silica powder, while chicken eggshells and duck eggshells were synthesized for the calcium oxide. The results from the XRD pattern clearly showed the structural formation of amorphous SiO2 and CaO phase. While the FTIR results indicated that the spectrums which displayed the characteristic peaks of the functional groups presenting in the SiO2 and CaO powder. However, the SEM images revealed that the particles agglomerated, various sizes and the particle size were found to be in micron level.

Design of Stable Cage-like CaO/CaZrO3 Hollow Spheres for CO2 Capture

Abstract: This paper aims to solve the problem of the reversibility in carbonation/calcination cycles of Ca-based materials. The CaO/CaZrO3 hollow sphere sorbents were prepared using colloidal carbon spheres as a template via the co-adsorption method. The hollow structure sorbents, which contained two kinds of metal ions, were observed by scanning electron microscopy and transmission electron microscopy images, and the components were obtained by X-ray diffraction and energy-dispersive X-ray analysis. The performances in CO2 capture at different absorption temperatures, calcination temperatures, molar ratios of Ca/Zr, and heating rates compared to calcium oxide were investigated employing the thermogravimetric analyzer. The results showed that the CaO/CaZrO3 sorbent could be fabricated using a trace Zr precursor and the specific prepared sorbent still could maintain a high capture capacity after exceeding a 12 000 min operation, which suggesting the approach that adsorbs both calcium and zirconium ions on the collo...

Using Low-Temperature Differential Scanning Calorimetry to Quantify Calcium Oxychloride Formation for Cementitious Materials in the Presence of Calcium Chloride

Abstract: Whereas many concrete pavements have exhibited service lives of 30 to 50 years, a portion of these pavements in regions that are exposed to snow, ice, and salt have shown premature distress at the joints. This distress has been observed to occur between 5 and 20 years and requires extensive repair of an otherwise well-functioning pavement. Although there are several potential mechanisms that can lead to this deterioration, a reaction can occur between calcium chloride coming from deicing salt (CaCl2) and the tricalcium aluminate (C3A) and/or calcium hydroxide (CH) in the cementitious matrix. This paper describes the development of a test method that can be used to evaluate the potential for a cementitious binder to react with the calcium chloride deicing salts to form calcium oxychloride (the reaction between CaCl2 and CH). The test method enables the quantity of calcium oxychloride to be determined for each binder system. The results indicate that the amount of calcium oxychloride can be reduced with the replacement of cement with supplementary cementitious materials (fly ash, slag, silica fume, etc.). It is anticipated that the proposed test method could be used to better understand the role of binder chemistry on the calcium oxide formation and to optimize the binder composition to reduce the calcium chloride formation to an acceptable level and ultimately reduce the risk for deterioration.

Effects of additives on the microstructure of clay

Abstract: Some soils under construction cause numerous problems in terms of geotechnical engineering. Clay soils cause significant problems in the construction of roads, airports, pavements and highways. Some soils contain mixed additives, such as lime, cement, fly ash and bitumen. In this study, the microstructures of uncured and cured lime/cement-stabilised clay samples are investigated. Compacted soil samples were evaluated by mercury intrusion porosimetry, X-ray diffraction, scanning electron microscopy (SEM) analyses and specific surface area analysis. The results indicated that the addition of lime and cement was effective in the treatment of compaction properties. The pore sizes in the SEM images vary with an increase in the percentage of lime and cement and an increase in curing time.

Development and evaluation of materials for thermochemical heat storage based on the CaO/CaCO3 reaction couple

Abstract: The current work relates to the development of synthetic calcium oxide (CaO) based compositions as candidate materials for energy storage under a cyclic carbonation/decarbonation reaction scheme. Although under such a cyclic scheme the energy density of natural lime based CaO is high (∼ 3MJ/kg), the particular materials suffer from notable cycle-to-cycle deactivation. To this direction, pure CaO and CaO/Al2O3 composites have been prepared and preliminarily evaluated under the suggested cyclic carbonation/decarbonation scheme in the temperature range of 600-800°C. For the composite materials, Ca/Al molar ratios were in the range between 95/5 and 52/48 and upon calcination the formation of mixed Ca/Al phases was verified. The preliminary evaluation of materials studied was conducted under 3 carbonation/decarbonation cycles and the loss of activity for the case of natural CaO was obvious. Synthetic materials with superior stability/capture c.f. natural CaO were further subjected to multi-cyclic carbonation/decarbonation, via which the positive effect of alumina addition was made evident. Selected compositions exhibited adequately high CO2 capture capacity and stable performance during multi-cyclic operation. Moreover, this study contains preliminary experiments referring to proof-of-principle validation of a concept based on the utilization of a CaO-based honeycomb reactor/heat exchanger preliminary design. In particular, cordierite monolithic structures were coated with natural CaO and in total 11 cycles were conducted. Upon operation, clear signs of heat dissipation by the imposed flow in the duration of the exothermic reaction step were identified.

Investigating the Effect of Catalyst Type and Concentration on the functional Group Conversion in Castor Seed Oil Alkyd Resin Production

Abstract: Significant scientific and economic benefits may be derived from investigating the best choice of catalyst in the alkyd resin synthesis. The effect of catalyst type and concentration on the production of alkyd resin using castor seed oil (CSO) was evaluated. Lithium hydroxide, lead (II) oxide, calcium carbonate, sodium hydroxide and calcium oxide were investigated. The fatty acid profile of the raw CSO was determined using GC-MS while structural elucidation of the CSO based alkyd resins was determined using FTIR spectrometry. The CSO modified alkyd resin produced has acid values of 5.0, 5.61, 7.0 8.24 and 11 for lithium hydroxide, lead (II) oxide, calcium carbonate, sodium hydroxide and calcium oxide respectively. The extent of reaction was 95%, 95%, 91%, 89% and 88% for lithium hydroxide, lead (II) oxide, calcium carbonate, sodium hydroxide and calcium oxide respectively at the reaction time of 150 minutes. The alcoholysis reaction completion time was fastest in LiOH followed by PbO, CaCO3, NaOH and CaO catalyst. Physico-chemical parameters of the oil and performance evaluation of the alkyd films suggest that they are sustainable materials for surface coating. LiOH shows excellent robustness to expanded process parameters.

Rapid transesterification of Jatropha curcas oil to biodiesel using novel catalyst with a microwave heating system

Abstract: We used a microwave heating system to increase Jatropha biodiesel yield, and to reduce both reaction time and energy consumption. The feasibility of converting natural and non-edible feedstocks including arcuate mussel shells and dolomitic rocks, into a novel high-performance, reusable, low-cost and heterogeneous catalyst for the synthesis of biodiesel was also explored. Arcuate mussel shells and dolomitic rocks were first ground and calcined at 900 °C for 2 h. After calcination, calcium oxide (CaO) or a mixed oxide of calcium and magnesium (CaO·MgO) was obtained as white powder, which was then chemically activated to improve the physical, chemical and surface properties, and catalytic activities of the catalysts. By heating CaO from waste shells in an excess dehydrated methanol under 65 °C at 8 h with nitrogen (N2) flow, calcium methoxide (Ca(OCH3)2) catalyst was prepared. The CaO from natural rocks was, however, turned into calcium glyceroxide complex, by combining with methanol and glycerol of the by-product. It was determined that calcium glyceroxide (Ca[O(OH)2C3H5]2) was formed during the transesterification and acted as the most active phase. Catalyst characterization was by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), and Brunauer-Emmett-Teller (BET) surface area and basic strength measurements. The reaction parameters, including reaction time, microwave power, methanol/oil molar ratio, catalyst dosage and catalyst reusability, were studied for fatty acid methyl esters (FAME) yield. The results indicated that Ca(OCH3)2 and Ca[O(OH)2C3H5]2 catalysts derived from waste shells and natural rocks showed good reusability, high energy efficient, environmental-friendly, low cost and facile route for the synthesis of biodiesel.