particles to make concentrated 40 wt cerium oxide slurry while stirring at room temperature for 15 to 20 minutes the cerium oxide slurry was stirred or shaken thoroughly to increase the washing process efficiency then different centrifuge times and various rotating speed rotations per minute were selected to treat the cerium oxide slurry after centrifuging at different centrifuge times and rotating at various speeds the separation process started the supernatant solutions were removed and discarded the remaining cerium oxide particles were re dispersed in deionized water the washing centrifuge and separation process repeated to have multi passes the particle distributions were measured by light scattering technique to monitor the changes of the particle distributions the analytic results of the particle distributions revealed that very small sized less than 10 nm cerium oxide particle percentages were reduced which also led to the slight shift of mean particle size toward the increased mps direction the percentages of the very small cerium oxide particles were reduced in the ranges of more than 11 to 78 depending on the number of the passes treating the cerium oxide slurry the small particle fraction was reduced 11 2 27 8 50 6 and 78 3 corresponding to the wash pass 1 2 3 and 4 respectively compared to the control cerium oxide slurry the results were shown in table 5 further a new sti polishing composition was made by using the cerium oxide particles having reduced very small sized cerium oxide particles after 4 washes to replace the cerium oxide particles in the base control reference sti slurries.