What technique involves mixing powders to achieve uniform particle size?

The technique that involves mixing powders to achieve a uniform particle size is known as trituration. This process typically requires grinding and mixing substances together, frequently using a mortar and pestle, to break down larger particles into finer particles and promote a consistent texture throughout the mixture. Trituration is especially critical in pharmaceutical formulations where uniformity is essential for dose accuracy and overall effectiveness of the medication.

In contrast, the other techniques mentioned serve different purposes. Filtration is a method used to separate solids from liquids or gases based on particle size but does not involve mixing. Spatulation pertains to the blending of powders but is more about spreading and incorporates air to lighten the mixture rather than achieving uniform particle size through grinding. Evaporation involves the conversion of a liquid into vapor, which does not relate to mixing powders. Therefore, trituration is the most appropriate answer for achieving uniform particle size in powdered materials.