Density is a physical quantity that reflects the properties of matter. The properties of matter refer to a property that matter itself has but can be distinguished from each other. People often feel that substances with high density are "heavy" and substances with low density are "lighter". "Heavy" and "light" essentially refer to the magnitude of density. Density is a property of matter, it does not change with the change of mass and volume. The density of the same substance remains unchanged, it is only related to the type of matter and the state of matter. Different substances generally have different densities. The density of the substances is the same.

Various "density" terms and meanings in powder materials:

1. True Density refers to the actual mass of solid matter per unit volume of a material in an absolutely dense state, that is, the density after removing internal pores or voids between particles. The corresponding physical properties are apparent density and bulk density.

2. Tap Density is the density after vibration. Specifically, it is one of the important indicators of powder quality. Tap density measurement refers to putting a certain amount of powder into a container, vibrating regularly under certain conditions, compressing the gaps between particles as much as possible, and finally reaching the particle size. The gap between them cannot be narrowed. When the volume of the powder in the container no longer decreases, read the volume of the powder, and then divide the weight of the powder by this volume to obtain the tapped density.

Tap density is necessary for characterizing catalysts, foaming materials, insulating materials, ceramics, powder metallurgy and other industrial products, especially in the battery industry.

3. Apparent Density, also known as bulk density, is the density of powder when it is naturally packed. Specifically, it refers to the bulk density measured after the powder is freely filled in a standard container under specified conditions, that is, the powder is loosely packed. The mass per unit volume, expressed in g/cm3, is a technological property of the powder.

The bulk density is a comprehensive reflection of the various properties of the powder. It is very important for the stability of powder metallurgy, the production process of mechanical parts, and the control of product quality, and is also the basis for mold design.

There are many factors that affect the bulk density of powder, such as powder particle shape, size, surface roughness and particle size distribution. Usually these factors are significantly different due to the preparation method of the powder and its processing conditions. In general, powder bulk density decreases with decreasing particle size, increasing particle asphericity, and increasing surface roughness.

4. Apparent Density
It refers to the dry mass per unit volume of the material in its natural state (dry state stored in the air for a long time). Usually the apparent density refers to the apparent density of the material in the dry state, and other water content should be indicated. Most materials are porous substances with open pores that communicate with the outside and closed pores that do not communicate with the outside. The density of the material containing closed pores is called "apparent density".

5. Bulk Density
Bulk density is the mass per unit volume measured when dust or powder is freely filled in a container just after the filling is completed. Also called bulk density.

When filling powder, the density measured after a certain regular vibration or tap is called tap density.