Density

    Particle size, along with density, is also an important characteristic that determines the properties of powders. Density, as you are aware, is defined as the mass per unit volume. However, for powders, density isn’t uniquely defined by the term alone. There are generally two types of density for powders: the primary property called “particle density” and the secondary property known as “bulk density” or “powder density,” which refers to the density of the assembly of particles.

    Particle Density

    Particle density refers to the density obtained by dividing the mass of each particle by its volume. However, due to the presence of surface irregularities and internal voids in particles, particle density is classified into three types based on the definition of particle volume.
    • True Density
    True density is the density of particles calculated by considering only the volume of the material that forms the particles, excluding any internal voids. It represents the density of pure particles without other components. To measure it accurately, particles need to be finely ground until there are no internal voids left.
    • Particle Density
    Particle density is the density of particles calculated by including the internal voids as part of the particle volume. Since the volume is evaluated to include the space occupied by internal voids compared to the actual volume of the particle, particle density tends to be smaller than true density.
    • Particle Density
    Apparent particle density refers to the density of particles that includes both internal voids and surface pores in the particle volume. It takes into account both internal voids and surface pores more significantly than particle density. Therefore, apparent particle density is generally smaller than particle density.
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    Powder Density

    Powder density refers to the density determined by filling a container with powder and measuring the mass of the filled powder. This is called “bulk density.” Due to the presence of gaps between the filled powder particles, bulk density is generally smaller than particle density.
    • Loose (Bulk) Density
    The loose density, also known as bulk density, is the density measured when the powder is gently filled into a container. Because of the presence of numerous gaps between the loosely filled powder particles, this state results in a lower density value.
    • Tapped Density
    Tapped density, also known as compacted bulk density, is the density measured after applying a certain amount of vibration to a container filled with powder to fill the gaps between particles, and then refilling the container. The gaps between the powder particles are filled through the application of vibration. The presence of these gaps is influenced by factors such as particle geometry and surface properties, including adhesion forces.
    • Compressibility
    Compressibility is a secondary property that defines the ratio of the change between tapped density and loose density. It provides insights into the flow characteristics of the powder. Higher compressibility indicates poor flowability, while lower compressibility indicates better flowability.
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