In recent years, the emergence of various new types of zinc oxide, such as active zinc oxide, nano-zinc oxide, organic zinc, etc., but as the variety increases, the market often appears counterfeit products, some manufacturers for price competition and profit , Selling some adulterated zinc oxide, but also means more and more concealed, not only the visual appearance can not be discerned, even if the rubber companies have a test method is also a headache, because this type of fake goods by the national standard test method to analyze the purity of zinc oxide, testing The results can often be passed "smoothly." Enterprises that use such unqualified zinc oxide often cause the vulcanizate to become unsaturated, not only degrade the performance and quality of the rubber product, but also cause blooming, and some light-colored products change. Color often finds no reason, which makes technicians very annoyed and also brings economic and reputational losses to the company.
Zinc oxide is an important activator for rubber, and it also serves as a crosslinker, colorant, etc. for halogen-containing rubber (CR, XIIR). Nowadays, as long as the quality of zinc oxide is raised, people are puzzled and even doubt the reliability of the national standard test method to evaluate the purity of zinc oxide. Here is to point out: Why do you want to measure the purity of zinc oxide? How does purity affect rubber? When zinc oxide contains a certain amount of impurities, such as: iron, lead, copper will make rubber products discoloration, cadmium can prevent the activation of zinc oxide on some accelerators, copper and manganese can damage the aging properties of rubber products, especially The purity of zinc oxide is not enough, and it also affects the degree of rubber vulcanization. Therefore, the determination of the purity of zinc oxide is a meaningful analysis item. For a long time, the main products are indirect or direct zinc oxide.
Why does the national standard test method fail to identify true and false? This may be a "mystery" that many corporate managers and technicians do not understand. Where are the problems? In analytical chemistry, the determination of the content of unknown substances should first be qualitatively analyzed before quantitative analysis can be performed. So for zinc oxide, it is a known material, and it should be directly quantified by the national standard method. However, some zinc oxide is adulterated and becomes an “unknown object” (I wonder if it is adulterated.) Authenticity), the method of measuring purity can not be used for qualitative analysis. When directly applying the national standard method, there must be a precondition: that is, zinc oxide is produced by the formal process method (such as indirect method or direct method, etc.) instead of "man-made". Zinc oxide doped with other substances, otherwise there will be interference with the analysis, and quantitative errors will occur, so the method of accusing the country of marking purity is not, it is really a bit embarrassing. Because commonly adulterated zinc oxide often contains salts such as calcium and magnesium or other metal oxides, when using the national standard to analyze the purity of zinc oxide, it is based on the principle of complexation reaction of EDTA standard solution with zinc ions, within a certain range of pH values. For titration and quantification, the solution of adulterated zinc oxide, in addition to containing zinc ions, often contains a variety of metal ions such as calcium, magnesium, and other metal ions, and EDTA (not recognized) will be mixed with these "artificial" Some of the metal ions that were brought in falsely occur together with a complex chemical reaction. The final results are all included in the total zinc oxide content. Therefore, the adulterated zinc oxide becomes a “qualified product”, and some are even better than the “first grade product”. (99.7%) purity is even higher.
In previous years, a company was afraid of buying counterfeit goods and purchased zinc oxide at a high price of 17,000 yuan per ton. The purity of the product's target was very high, and it was believed to be very reliable. The results were found by the laboratory's qualitative tests: they were still adulterated by (a few) adulteration. Zinc oxide, so, so far there may be many companies still kept in the dark, spent high prices but bought low-quality raw materials.
At present, there are two types of products in the market: one is the regular production of genuine zinc oxide (including defective zinc oxide produced due to poor processes), and the other is “man-made” zinc oxide doped with other substances. Solve it? We believe that as with the melamine-produced artificial milk powder, it must be qualitative (differential) true and false, and then the authentic zinc oxide quantitative purity, the analysis of data is reliable, but the fake goods do not quantitative detection (due to analysis interference, the results appear error). Therefore, the qualitative work before quantification of zinc oxide is the key. Today, there are many instruments for qualitative metal element analysis, such as commonly used analytical instruments such as plasma emission spectroscopy (ICP) and atomic absorption spectrometry (AAS), which can be qualitative and quantitative, but The price is more expensive and it is still difficult to spread. General companies do not have these detection methods. Some testing units are also very tricky to adulterate zinc oxide, which makes many companies feel puzzled about the quality of zinc oxide coming into the plant, and it is very helpless, which also encourages the circulation of fake products in the market.