| Summary: | This study developed a micro-electrical discharge machining (micro-EDM) system for producing TiO<sub>2</sub> nanocolloids. When a proportional–integral–derivative controller designed using the Ziegler–Nichols method was adopted to control the interelectrode gap, TiO<sub>2</sub> nanocolloids were obtained from spark discharges generated between two titanium wires immersed in deionized water. For a pulse on time–off time of 40–40 μs and a colloid production time of 100 min, TiO<sub>2</sub> nanocolloids were produced that had an absorbance of 1.511 at a wavelength of 245 nm and a ζ potential of −47.2 mV. They had an average particle diameter of 137.2 nm, and 64.2% of particles were smaller than 91.28 nm. The minimum particles were spherical. The characteristics of colloids confirmed that the micro-EDM system can produce TiO<sub>2</sub> nanocolloids with excellent suspension stability. The colloid production method proposed in this study has the advantages of low equipment cost and no dust diffusion in the process environment. These advantages can improve the competitiveness of the electric spark discharge method for high-quality TiO<sub>2</sub> nanoparticle production. The colloids produced in this study did not contain elements other than titanium and oxygen, and they may prevent secondary environmental pollution.
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