What Are The Factors That Affect The Polishing Performance Of Rare Earth Polishing Powder?

The characterization of polishing powder can be summarized in two parts, namely chemical properties and physical properties. The physical properties of rare earth polishing powder include particle size, hardness, specific surface area, suspension, crystal structure, and crystal form. Studies have shown that the activity of polishing powder mainly depends on its chemical composition, crystal structure, crystal shape, and particle breakage rate.
In the past, it was generally believed that the higher the purity of CeO2, the stronger the polishing ability, and the better the polishing effect, but this is not always the case. When the purity of CeO2 reaches a certain level, grade is no longer the determining factor, and increasing grade has almost no effect on the improvement of polishing performance.
The influence of CeO2 content
The CeO2 content has a significant impact on the polishing ability of rare earth polishing powder. In practice, it has been found that when the content of CeO2 exceeds 40%, the polishing effect will be significantly enhanced. Continuing to increase the content of CeO2, the improvement in effect is no longer significant. When it increases to around 80%~85%, it is only about 15% higher than the polishing powder with a CeO2 content of 40%. It can be seen that the influence of purity is not the absolute factor. For polishing powder, simply pursuing high purity is meaningless.
The influence of other rare earth elements
The chemical composition of rare earth polishing powder mainly includes lanthanum, cerium, praseodymium, neodymium, fluorine, iron, oxygen and other chemical elements, among which the most important component is cerium oxide. Other rare earth elements mainly exist in the lattice of cerium oxide in a solid solution manner, playing a role in changing the crystal morphology, structure and polishing performance.
In rare earth polishing powder, other rare earth elements play a positive role in the polishing ability of the polishing powder, because other rare earth elements change the crystal structure between fluorite and hexagonal systems without changing the crystal structure of cerium oxide. For example, face centered cubic Pr6O11 has the same structure as CeO2 and is also suitable for polishing; Some rare earth oxides have almost no polishing ability, but can form solid solutions with CeO2 within a certain range without changing the crystal structure of CeO2, causing the crystal structure to change between fluorite and hexagonal systems.
Doping different rare earth elements into CeO2 will change the calcination temperature, refine the grains, cause lattice distortion, and form oxygen vacancies, which is beneficial for improving polishing ability.
The influence of non rare earth impurities
In addition to rare earth impurities, there are also many non rare earth impurities in the chemical composition of rare earth polishing powder, such as oxygen, sulfur, fluorine, silicon, iron, calcium and other chemical elements. Some non rare earth impurities such as fluorine, sulfur and other elements can change the crystal structure, color and polishing performance of the polishing powder. There are also impurities such as mechanical impurities and some hard particles in the polishing powder, which can cause mechanical damage and scratches on the surface of the polished workpiece. Even if the content of these impurities is less than 0.001%, they can scratch the glass.
In addition, rare earth carbonates also contain a small amount of CaO, which can reduce the polishing ability of the polishing powder. Therefore, the content of CaO should usually not exceed 1%.
The impact of fluoride
Fluorine is a common constituent element in cerium based rare earth polishing powder. The addition of fluorine can change the crystal structure of the polishing powder and improve its polishing ability; At the same time, fluorine components can react with the glass being ground, thereby improving the smoothness and effectiveness of grinding; In addition, adding fluorine can also act as a co solvent, reducing the reaction temperature and increasing the grain size, but the amount of fluorine added must be controlled within an appropriate range.
Another important function of fluorine doping is to generate HF during the polishing process, which erodes the existing silicon oxide film on the glass surface and generates a new layer of silicon oxide film, resulting in high smoothness and transparency of the glass.
Due to the harm caused by F element to the environment, people are paying more and more attention to fluoride free rare earth polishing materials, and have conducted in-depth research. Especially in some glass cold processing enterprises in Western European and American countries, fluoride free cerium based rare earth polishing powder has become a necessary product in the processing process.