The diffusion condition for which there is some net accumulation or depletion of diffusing species. The diffusion flux is dependent on time.

• 扩散过程中,扩散组元存在净堆积或净亏空的扩散过程是非稳定态扩散。也可以描述为:扩散通量与时间有关的扩散过程是非稳定态扩散。