Solid-Phase Synthesis of Calcium Carbide in a Plasma Reactor..
Solid Phase Synthesis of Calcium Carbide in a Plasma Reactor
AjerschSolid-phase synthesis of calcium carbide in a plasma reactor.
Except hollow SiO2, hollow CaCO3 particles have also been prepared by w/o emulsion template method. For example, D. Walsh and co-workers) reported a facile and high yield approach to produce spherical particles of crystalline CaCO3 (vaterite) with an elaborate sponge-like micro architecture. J. A. Thomas and co-workers) also prepared CaCO3 microcapsules for the encapsulation of organic and inorganic substrates using a liquid emulsion system. They prepared the emulsion by mixing a solution of 3.0 M sodium carbonate (Na2CO3) which contains the materials to be encapsulated within the oil membrane phase. The two phases were mixed together until a homogeneous macro-emulsion was formed. This w/o emulsion was then added to a solution of calcium chloride (CaCl2) or calcium nitrate (Ca(NO3)2). Based on work by Nakahara), this method allows calcium ions (Ca2+) to diffuse across the oil membrane into internal aqueous droplets that contains the materials to be encapsulated. Carbonate ions (CO32−) in the internal aqueous phase react with the diffused Ca2+ at the o/w interface and solid CaCO3 in the metastable vaterite form precipitates at the interface, encapsulating the materials dispersed in this phase. The vaterite spheres are prone to transformation to the more stable calcite polymorphy, which would destroy the capsules. In order to prevent this transformation and stabilize the vaterite, L-glutamic acid, a known inhibitor of calcite crystallization was added to the aqueous phase prior to precipitation. After decantation and centrifugation, hollow vaterite spheres inside with desired substance were obtained.
Calcium carbide was successfully synthesized by carbothermal reduction of lime with coke at 1973 K for 1.5 h. The effect of potassium carbonate as additive on the composition and morphology of the product was investigated using X-ray diffraction and scanning electron microscope. Addition of potassium carbonate increased the yield of calcium carbide. The sample in the presence of potassium carbonate generated acetylene gas of 168.3 L/kg, which was 10% higher than that in the absence of potassium carbonate. This result confirmed the catalytic effect of potassium carbonate on the synthesis of calcium carbide. A possible mechanism of the above effects was that the additive, which was melted at the reduction temperature, dissolved CaO and so promoted the contact between CaO and carbon, which was essential for the solid-solid reaction to form calcium carbide.
Solid-Phase Synthesis of Calcium Carbide in a Plasma Reactor
An emulsion is defined as a heterogeneous system, consisting of at least two immiscible liquid or phase. Since emulsion is thermodynamically unstable, rearrangement from droplet into two bulks liquid is ready to occur with a net reduction of interfacial area, which is energetically favourable. So the surfactants or polymer, which can stabilize emulsion are necessary to use in the emulsion system. The emulsion template method is a process to fabricate hollow particles by localizing the reaction on the surface of emulsion and forming a solid shell. After removal of the emulsion template by calcination or solvent dissolution, hollow particles are obtained. The emulsion template is generally classified into two types. One is water-in-oil (w/o) templates which have oil continuous phase with water droplets. Another is oil-in-water (o/w) templates which have water continuous phase with oil droplets. The formation of these two kinds of emulsion is determined by the weight ratio of water and oil. High weight ratio of oil lead to the formation of w/o templates while high weight ratio of water result in the formation of o/w templates. The choice of which kinds of templates is determined by the reactants and reactions.
Solid-Phase Synthesis of Calcium Carbide in a ..
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Oriental Journal of Chemistry is a peer reviewed quarterly research journal of pure and applied chemistry
Indira Gandhi Centre for Atomic Research, Kalpakkam
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