Yuan Lei's Little Knowledge | True Density, False Density and Bulk Density of Powder

Release time:

2024-01-29 09:34

True density (true specific gravity)

The true density is relative to the bulk density of the particle group, and refers to the actual mass of the solid matter per unit volume of the material in an absolutely dense state, that is, the density after removing the internal pores or the gaps between the particles.

True density is the most basic physical parameter of powder materials, and it is also a parameter that must be used to determine other physical properties such as micropowder particle distribution. The value of true density depends on the chemical composition and purity of the material, and its value directly affects the quality, performance and use of the material, which is of great significance to its determination.

Formula for calculating true density of pattern: ρ = m/v

ρ-true density m-mass of sample v-volume of sample


False density (false specific gravity, apparent density)

Apparent density refers to the ratio of mass to apparent volume of a material. The apparent volume is the solid volume plus the closed pore volume plus the open pore volume.

Apparent density refers to the natural state of the material (dry state stored in the air for a long time)

Apparent density = M (solid)/V (solid closed pore open pore)


Bulk density

(1) Bulk density of powder

Bulk density is the mass per unit volume measured by filling dust or powder freely in a container just after filling.

The bulk density of the powder occupies a very important position in the use of the powder, because the bulk density of various powders is not the same, the water absorption and specific surface area of the coating is not the same, the resulting porosity of the coating is not the same, directly affect the performance of the coating. The bulk density is measured with a bulk density tester.

The bulk density of the powder is mainly due to the size of the powder or the number of days is different, the bulk density can be divided into loose bulk density and tap bulk density.

(2) The following is the approximate calculation method of bulk density:

Bulk density refers to the quality of powder in the natural accumulation state.

Density p = Mass M/Volume V

Volume V = True Volume V1 (Void V2 Air V3)

It can be seen from the above that in addition to the real physical density of the powder, the bulk density with a certain structural porosity is formed because of the porosity between the air and the powder.The larger the void ratio between the powders is, the larger the volume of the formed powder is, so the smaller the bulk density is.

(3) the size of the bulk density and the relationship between the film cover:

When the bulk density of the powder used in the coating is smaller, the larger the volume of the powder used, and the greater the porosity of the coating film formed after the volatilization of water between the powders, the stronger the dry cover of the coating film. At the same time, the volume of the powder, the higher the oil absorption, the film's weather resistance and scrub resistance and so on all the performance also have an impact.

Therefore, the various properties of the comprehensive powder, the rational use of the characteristics of various powders, in order to reduce the cost of coating production, improve the application performance of the coating.


Density, packing, volume, mass, material, apparent, pore, void, not the same

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