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Impurities And Detection Methods Of Diamond Micropowder

May 11,2023

Most diamond micro powders in China use single crystal diamond from I-type materials as raw materials, but I-type materials have high impurity content and low strength, and can only be used for low-end product demand in the market. A few domestic diamond powder manufacturers use single crystal diamond of type II or III materials as raw materials to produce diamond powder, which has a much higher processing efficiency than ordinary diamond powder and can meet high-end market demand.

Diamond powder has high hardness and good wear resistance, and is widely used in cutting, grinding, drilling, polishing and other fields. With the development and progress of science and technology, the demand for diamond powder in the market is increasing, and the quality requirements are also increasing. For diamond powder, the amount of impurities in diamond powder directly affects the product quality and usage performance of the powder.

Type of impurity
The impurities in diamond powder refer to the non carbon components in diamond powder, which can be divided into external impurities and internal impurities of the particles. The external impurities of particles are mainly introduced from raw materials and production processes, including silicon, iron, nickel, as well as elements such as calcium, magnesium, cadmium, etc; The impurities inside the particles are introduced during the diamond synthesis process, mainly including iron, nickel, cobalt, manganese, cadmium, copper, etc. The impurities in diamond micro powder can affect the surface properties of the micro powder particles, making the product difficult to disperse. Impurities such as iron and nickel can also produce varying degrees of magnetism in the product, which has an impact on the application of ultrafine powders.

Two impurity detection methods
There are many methods to detect the impurity content of diamond powder, including gravimetry, atomic emission spectrometry, atomic absorption spectroscopy, etc. Different detection methods can be selected according to different requirements in application.

Gravimetric method
The gravimetric method is suitable for the analysis and detection of total impurity content (excluding volatile substances burning at the burning temperature). The main equipment includes muffle furnace, Analytical balance, porcelain crucible, dryer, etc. The inspection method for impurity content in the micro powder product standard is the high-temperature loss on ignition method: sample according to regulations and weigh the sample to be tested into a constant weight crucible. Place the crucible containing the sample to be tested in a muffle furnace and burn it at 1000 ℃ until it reaches constant weight (the temperature allows ± 20 ℃). The weight of the residue is the impurity mass, and the weight percentage is calculated.

Atomic emission spectrometry, atomic absorption spectroscopy

Atomic emission spectrometry and atomic absorption spectroscopy are suitable for qualitative and quantitative analysis of trace elements.
(1) Atomic emission spectrometry: It is an analytical method that uses the characteristic radiation line generated by the electronic transition from the excited state to the ground state to qualitatively or quantitatively analyze elements by using the atoms of various chemical elements under external energy excitation. Atomic emission method can analyze about 70 elements. In general, it is used for component determination with a content below 1% to accurately measure the ppm level trace elements in diamond powder. This method is the earliest and most developed optical analysis method. Atomic emission spectroscopy has played an important role in the qualitative and quantitative analysis of various materials in modern times. It has the advantages of simultaneous detection of multiple elements, fast analysis speed, low detection limit, and high accuracy.
(2) Atomic absorption spectroscopy: when the radiation emitted by a specific light source passes through the atomic vapor of the element to be measured, it is absorbed by its ground state atoms. The element analysis can be carried out by measuring the absorption degree.
Atomic absorption spectroscopy and atomic absorption spectroscopy can complement each other and cannot replace each other.

▲ A high frequency inductively coupled plasma emission spectrometer

Three factors affecting impurity measurement values

The influence of sampling quantity on test values

In practical operation, it was found that the sampling amount of diamond powder has a significant impact on the test results. When the sampling amount is 0.50g, the average deviation of the test is relatively large; When the sampling volume is 1.00g, the average deviation is small; When the sampling amount is 2.00g, although the deviation is also small, the testing time increases and the efficiency decreases. Therefore, blindly increasing the sampling amount during measurement may not necessarily improve the accuracy and stability of the analysis results, but also significantly prolong the operation time and reduce work efficiency.

The Effect of Microparticle Size on Impurity Content
The finer the particle size of diamond powder, the higher the impurity content in the powder. The average particle size is 3 μ During the production of fine diamond powder, due to its fine particle size, some acid-base insoluble substances mixed in the raw material are difficult to separate, and therefore precipitate into the fine-grained powder, resulting in an increase in impurity content. Furthermore, the finer the particle size, the more processes involved in the manufacturing process, and the more impurities brought in from the outside, such as dispersants, settling solutions, dust pollution in the production environment, and other impurities.
In the research on impurity content testing of micro powder samples, we found that over 95% of coarse grained diamond micro powder products have impurity content below 0.50%, while over 95% of fine grained micro powder products have impurity content below 1.00%. Therefore, in the quality control of micro powder, it is stipulated that 3 μ The impurity content of fine powder should be less than 1.00%; three μ The impurity content of coarse micro powder should be less than 0.50%; And the impurity content data in the standard should be retained to two decimal places after the decimal point. Because with the advancement of micro powder manufacturing technology, the impurity content in micro powder will gradually decrease, and a large portion of coarse micro powder has impurity content below 0.10%. If only one decimal place is retained, its quality cannot be effectively distinguished.

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