What is the purpose of using a sieve in powder preparation?

The purpose of using a sieve in powder preparation is primarily to achieve a uniform particle size. When powders are sieved, they are passed through a mesh that allows particles of a certain size to pass through while retaining larger particles. This process helps in refining the particle size distribution, ensuring that the powder has consistent characteristics, which is crucial in various applications such as pharmaceuticals, food production, and cosmetics. Uniform particle size can enhance the flowability of powders, improve their mixing, and facilitate even distribution in formulations, thereby affecting the final product's quality and performance. Other options do not align with the primary function of a sieve in this context. For example, melting powders or adding moisture are processes unrelated to the mechanical separation of particles, and increasing weight does not directly correlate with the purpose of sieving.