Abstract
The valorisation of agricultural waste into value-added materials presents a sustainable path for waste management and resource conservation. Rice husk (RH) contains a high percentage of silica, which, when transformed into Rice Husk Ash (RHA), presents an opportunity for multiple industrial applications, including reinforcement in metal matrix composites. The present study investigates the effect of milling time on nanoparticles formation during mechanical milling of rice husk ash. Rice husk ash were produced by combusting rice husks at 600°C, followed by ball milled for durations ranging from 10 to 50 hours to yield rice husk ash nanoparticles. The synthesized nanoparticles were characterized to evaluate their properties. Fourier Transform Infrared (FTIR) spectroscopy confirmed removal of organic components of the rice husk and formation of silica after thermal treatment, as evidenced by the absence of organic functional groups and presence of Si-O-Si vibration bands. X-Ray Fluorescence (XRF) analysis indicated SiO₂ as the major oxide component (~ 60wt.%), alongside other inorganic compounds. Particle size analysis using Dynamic Light Scattering (DLS) showed a clear trend of size reduction with increased milling time, achieving a Z-average size of 95.8 nm after 50 hours, with a particle distribution within the 17–70 nm range. Scanning Electron Microscopy (SEM) revealed agglomerated nanoparticles with irregular morphology, and Energy-Dispersive X-ray (EDX) analysis confirmed a composition rich in silicon and oxygen. The findings affirm that mechanical milling is an effective method for converting rice husk, an abundant agricultural waste, into rice husk ash nanoparticles suitable for applications in composite materials and other industrial sectors.

Key words: Rice husk ash; Nanoparticles; Mechanical milling; Milling time; Agricultural waste