True density alias true density, skeleton density information - Database & Sql Blog Articles

True density (true density, skeletal density): refers to the mass of the material in the absolute compact state, the actual volume of solid matter (excluding internal voids, ie, no open and closed pores and interparticle voids). The concept of true density is the same as density.

The formula is as follows:
Ρz=m/Vz
  ρz - the true density of the material, kg / m3 or g / cm3;
î—¥ î—¥ m - the quality of the material (dry to constant weight), kg or g;
î—¥ î—¥ Vz - material removal of open holes, closed cells and volume, m2 or cm3.

At present, China's existing national standards and industry standards such as: GB/T533-A, GB/T1033.1, GB/T6155, GB/T23561, YB/T5300, JB/T7984.3, GB/T 1713, GB/T8929 The GB/T1713, GB/T208, GB/T5071, QB/T1010, GB/T9966, GB/T18856, GB/T24203, GB/T8330, SL-237 and other standards all use the density bottle (pycnometer) method. In this method, the finer the material is ground, the more accurate the volumetric value of the material will be. When using the density bottle method to measure the density of porous materials (such as bricks, stones, etc.), the material will be ground into fine powder. Depending on the material, it is generally required to grind to about 80 mesh to 200 mesh. After drying, use Li. The bottle is measured for its absolute compact volume.

Testing the true density of materials using the density bottle method has some problems that affect the test results, such as:
1. Different samples need to use different wetting liquids to prevent dissolution and reaction with materials. For organic powders, organic solvents are often used, and materials that react with water, such as cement, can be organic such as kerosene or xylene. Liquid medium, etc.

2. The infiltrating liquid should be able to easily wet the surface of the internal pores of the material. If the selected wetting fluid is not appropriate, it will produce a situation that is not easy to infiltrate the surface, affecting the test results;

3. When testing powdery materials, when the powder is completely immersed in the liquid, the bubbles must be completely removed to determine the volume to be excluded. At this time, it is necessary to use boiling to remove the bubbles, and use a constant temperature water bath to remove the temperature and operate. It is not easy to do, it is easy to leak, and the calculation process is susceptible to operational errors;

4. Due to many operational steps, there are many problem nodes involved. Different operators have different proficiency and different methods, which will directly affect the accuracy of the experimental results.

Due to the above-mentioned defects in the density bottle method, a substitute analyzer with more accurate test results, more stable equipment, and simpler operation----the true density analyzer using the "gas replacement method" came into being. This type of analyzer uses helium instead of infiltrating liquid. Helium is an inert gas with small molecular diameter. It has the characteristics of easy diffusion, good permeability and good stability. It quickly penetrates into the internal pores of the material and cannot be measured by conventional methods. Material pores and irregular surface depressions can be quickly filled. The measured sample volume is closer to the true volume of the sample compared to the density bottle method, so that the true density value of the sample is closer to the true value. In addition, the true density analyzer using helium "gas replacement method" does not cause problems with the material reaction, does not cause corrosion to the equipment, has a high safety factor during use, and the sample can be directly recycled without being contaminated, which is beneficial to valuables. Recovery after sample testing. The instrument using this method is simpler to operate, the test time is shorter, the test result is accurate, and the repeatability is better. At present, it has been produced by domestic manufacturers and has been incorporated into the industry standards of some industries.

True density is an absolute concept, but in practice, the accuracy of true density values ​​is related to measurement methods, means, instruments and equipment. Since most materials contain open and closed cells, the material is generally broken. The purpose is to minimize the effect of the pores on the experimental results, so that the true density values ​​tested are as close as possible to the true values. However, this is not absolute. Taking calcined coke as a raw material for the production of carbon for aluminum as an example: when the calcined coke is produced and then enters the carbon production process, if the process requires the use of calcined coke fine powder, then after the calcined coke production In the true density test, the calcined coke is also ground; however, if the carbon production process directly uses the block-shaped calcined coke without grinding, then in the true density test after the calcined coke production, only the block is needed. The calcined coke is tested without further grinding. In short, the true density test is combined with the actual production requirements, in line with upstream and downstream production needs, unified test methods and standards.