Nanotech 2010

The Use of Taguchi Method to Determine Factors Affecting the size of fine attapulgite particles generated by rapid expansion supercritical solution with and without cosolvents

I. Asghari, F. Esmaeilzadeh
Shiraz University, IR

Keywords: attapulgite, nanoparticle, rapid expansion of supercritical solution, drilling mud, Taguchi method


The presence of fine particles tends to increase viscosity. Besides the solid load particle properties, especially the specific surface area, have a pronounced impact on the suspension’s viscosity. Attapulgite is used as a viscosifier in saltwater drilling fluids where bentonite becomes ineffective. Attapulgite is made up of thin, rod-shapped particles that behave differently from bentonite platelets. It is a very effective viscosifier in saltwater fluids and saturated brines.The smaller powder of attapulgite because of the higher specific surface area needs more water to be wet than the coarser one. Under the same solid content, the smaller particles cause the higher viscosity of the slurry. Nanoparticle can be obtained from a great variety of processes. On the Whole, there are only two approaches known for the nanomaterial fabrication: Bottom-up and top-down methods. The bottom-up approach deals with the controlled assembly of atomic and molecular aggregates into larger systems. Whereas the top-down approach deals with the reduction in structure sizes of microscopic elements to the nanometer scale by applying specific machining and etching techniques like: lithography, cutting, etching, grinding, etc. SCF technology replaces organic solvents in a number of chemical processes, including nanoparticle fabrication, food processing, chemical manufacturing, extraction, dry cleaning, etc. There are several methods in SCF technology like RESS (rapid expansion supercritical solution), PGSS (particle from gas-saturated solutions), GAS (gas anti-solvent process) PCA (precipitation from compressed antisolvent) and etc. RESS is a very attractive process as it is simple and relatively easy to implement at least at small scale when a single nozzle can be used. The RESS-process enables the micronization of thermally labile materials and the formation of particles of less than 500 nm in diameter. Our current research is aimed towards an improved understanding of the relationship between process parameters and particle characteristics and to explore new areas of application for nanoscale particles. The RESS apparatus was set up and the new type of nozzle were designed and fabricated to achieve ultrafine nanosize particles.The Schematic diagram of the used nozzle can be seen below. The experiments were carried out to investigate the effect of extraction temperature (308–328 K) and pressure (15–20MPa), spray distance (1-5 cm), nozzle diameter (450-1200 µm) and cosolvents on the size and morphology of the precipitated attapulgite particles. Precipitated attaoulgite particles were analyzed their size by scanning electron microscopy (SEM) .Before the SEM analysis, the process either original samples must be coated by a sputter-coater . Taguchi method creates an orthogonal array to accommodate these requirements. The selection of a suitable orthogonal array depends on the number of control factors and their levels. Taguchi design is preferred because it reduces the number of experiments significantly. With the selection of L18 orthogonal array, using five mentioned parameters and their levels, shown in Table 1, the number of experiments required can be drastically reduced to 18. It means that 18 experiments with different combinations of the factors should be conducted in order to study the main effects, which in the classical combination method using full factorial experimentation would require 35 = 243 number of experiments to capture the influencing parameters. These control factors include temperature, pressure, nozzle diameter, spraying distance, and cosolvents. All control factors have three levels. For the Taguchi design and subsequent analysis, the software named as Qualitek-4 (version 14.02.0) was used.
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