Synthesis of Copper and Copper Oxide Fine Powders Using a High-Gravity Spinning Disk Reactor
Date Issued
2011
Date
2011
Author(s)
Chang, Ming-Hui
Abstract
Copper(II) oxide is an important ceramic material that has many applications, such as ice nucleating agent for artificial rain, coating on solar panel, p-type semiconductor, and high-temperature superconductor. Copper oxide nanoparticles can be dispersed into fluids to become nanofluids, which can enhance the thermal conductivity of fluids. Copper is one of the most important metals, which is wildly used in electric industry, electroplating, and semiconductor because of it is cheaper than other noble metals such as silver and gold. It can be also used as a catalyst.
There are many methods for preparing copper oxide nanoparticles, and the most common physical one is the gas-condensation method, in which copper raw material is evaporated by a high-temperature arc and then the vapor is condensed by contacting with cold liquid to become uniform nanoparticles. The chemical synthetic methods including sonochemical, sol-gel, hydrothermal, and solid-state method, are to synthesize copper oxide via various chemical reactions. For preparing fine particles of copper, besides the electroplating method, most chemical reduction methods using hydrazine and sodium borohydride as reducing agents, and formaldehyde is also used as reducing agent for the electroless copper deposition. Although these methods are available for producing copper oxide and copper particles, most of the synthesizing methods stay in the laboratory, and toxic organic compounds are usually used. Moreover, the problems associated with energy-consumption, time-consumption, and slow production rate make them difficult to apply in industry.
The high-gravity technique (HiGee) has been developing in recent years, and it can overcome the problems illustrated above. Two types of equipment, i.e., the rotating packed-bed reactor (RPBR) and spinning disk reactor (SDR), have been applied in this regard. As the packed-bed or disk is rotating, the high centrifugal force can be generated and thus a uniform and high supersaturation through micromixing is achieved. As a result, small and uniform particles can be obtained. Moreover, the short operating time and mass production rate are also advantageous to scale-up for industrial production. In our laboratory, powders of several chemicals including salts, drugs, and metals have been investigated, and they were all successfully micronized using high-gravity technique by applying crystallization theories and choosing optimal operating variables.
The aim of this research is to synthesize fine powder of copper oxide and copper using a spinning disk reactor. For synthesizing copper oxide, the precursors of copper oxide were first prepared in a continuous mode through a liquid-liquid reaction using copper(II) sulfate and sodium carbonate as reactant. Then, the precursor particles were calcined up to 500°C to obtain copper oxide nanoparticles. Among the effects of operating variables, smaller copper oxide particles were obtained under reactant concentrations lower than 0.1 M, rotation speed higher than 1000 rpm, flow rates of reactant solutions lower than 3.0 L/min, and pH of slurry around 6. As the reactant concentrations were both 0.1 M, rotation speed was 4000 rpm, and flow rates were both 3.0 L/min, a production rate of 34.6 kg CuO/day can be achieved. The volume mean size of the product particles was smaller than 65 nm and the primary particle size was 20-30 nm observed under a field emission gun scanning electron microscope. Finally, a CuO-water nanofluid was prepared using sodium hexametaphosphate as the dispersant. The effective thermal conductivity of the nanofluid prepared in this study was higher than that reported in literature and that by theoretical calculation. The best result in the improvement of thermal conductivity was 10.8% when the solid content was 0.4 vol.%.
For preparing copper fine powders, weak-reductant glucose or dilute nitric acid was used as the reducing agent. As glucose was used, the smallest copper particles were obtained under the temperature of 80°C, recycle time of 15 min, weight ratio of PVP/Cu=2. The concentrations of Cu(OH)2, NaOH, and glucose were 0.02 M, 1.0 M, and 0.1 M, respectively. The morphology of copper particles were polyhydral and the size was around 100-300 nm. Furthermore, the size of copper particle synthesized using an SDR was smaller than that using a stirred tank. As nitric acid was used as the reducing agent, continuous operating mode can be used, and the reaction can proceed at room temperature. Sodium hexametaphosphate was added for dispersing the reactant, Cu2O. Spherical copper particles with size around 100-300 nm can be obtained with PVP(polyvinylpyrrolidone) as the co-additive in a concentration of 1.1 g/L PVP, and the yield was 79.2 %. When the concentration of nitric acid was lower than 0.32 M, the yield of copper particles decreased because of the slower reaction rate. However, as the concentration of nitric acid was higher than 0.64 M, the copper oxide was obtained because of a higher oxidation ability. Finally, the waste solution containing copper(II) ions, which was produced from nitric reduction process, can be recycled to react with NaOH or Na2CO3 to produce copper oxide particles using the SDR.
Subjects
copper
copper oxide
high-gravity technique
spinning disk reactor
nanoparticles
Type
thesis
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