The color of matter is the result of its reflection. White light is mixed light, by all sorts of color light mix by certain proportion and become. If a substance appears yellow in a white light environment (such as nano-zinc oxide), it is because the object absorbs some or all of the blue light. The color of a substance is due to its selective absorption of light at different wavelengths.
Different colors of light have different wavelengths, and different substances absorb different wavelengths of color. Matter can only selectively absorb radiative light that is equal to the sum of the energy changes of its molecules in vibration, rotational and electronic motions. In other words, even if the same substance is at different energy levels, it will have different colors. Zinc oxide, for example, is yellow at high temperatures and lighter at lower temperatures, both in normal form and in nano form. The reason is that at different temperatures, the molecular energy of zinc oxide and the transition energy of electron energy are different, so the absorption of various colors of light is different.
Direct or indirect zinc oxide of coarse particles is ionic crystal. In general, zinc and oxygen atoms exist as ionic bonds. Because of its coarse size, each particle contains a considerable number of oxygen and zinc atoms, and the Numbers of both are the same (see formula ZnO, 1:1). But for nano-zinc oxide, the particles are so thin that the number of unbonded atoms on the surface of the particles increases. In other words, nano-zinc oxide can no longer be regarded as an ideal crystal with an infinite number of ideal crystal faces, and there will be disordered intercrystalline structure and crystal defects on its surface. The presence of these atoms on the surface, which are different from the central part, gives them a strong ability to react with other things, which is what we usually call activity.
Studies have shown that there are at least three states of oxygen in nano-zinc oxide: lattice oxygen (located inside the particles), surface adsorption oxygen and hydroxyl oxygen (–OH), and the amount of zinc in the particles is greater than the amount of oxygen, not 1:1. This is completely different from normal zinc oxide. The surface of nano-zinc oxide has oxygen vacancy and many suspended bonds, which is easy to react with other atoms. This is also the basic principle of nano-zinc oxide as active agent in rubber and catalyst.
Because nanometer zinc oxide and common zinc oxide the above – mentioned difference. The change energy levels of the molecular and electron energies of the particles are different, therefore, the color is different. Common zinc oxide is white, while nano-zinc oxide is yellowish.
For nano-zinc oxide, there are adsorption oxygen and hydroxyl oxygen on the surface of its particles, and the quantity of these two oxygen species will change with time, such as the adsorption of water and the re-adsorption and stripping of oxygen in the air. Changes in the amount of these two types of oxygen will inevitably lead to changes in the molecular and electron energy levels in the particles, as well as different absorption of light. Therefore, the color of nano-zinc oxide becomes lighter.
Pure nano zinc oxide, its color is pure micro yellow, appears very bright color.
When nano-zinc oxide contains impurities, such as iron, manganese, copper, cadmium and so on to a certain extent, the color of zinc oxide will have the feeling of earthy color in the micro yellow, that is because the oxides of iron, manganese, copper, cadmium and so on are all colored substances, after mixing with each other, several colors are mixed, showing the white soil. However, the color change of nano-zinc oxide (or activated zinc oxide, light zinc oxide) with time change will be covered by the earth color, which makes the color appear to change very little. When the impurities in nano-zinc oxide are higher, the color will become deeper, and it is impossible to observe the color change with time.
As mentioned before, the color of matter is caused by its selective absorption of external light. As a result, when we compare the color of zinc oxide, it is best to look for it in an outdoor light. When you compare different environments, you get different results, which also shows the interesting nature of light reflection.
Nanometer zinc oxide is obtained by calcining alkali zinc carbonate. In this process, if the basic zinc carbonate does not completely decompose, the color of the nano-zinc oxide will appear white, because the basic zinc carbonate is pure white. In addition, production in the south and north, or in wet rainy days and dry weather, can also affect color. Because nano-zinc oxide can react with wet air and carbon dioxide to form basic zinc carbonate, the reverse reaction of calcining process occurs. How much the change affects product quality is difficult to determine, since basic zinc carbonate is also catalytic and suitable for use in the desulfurizer and rubber industries. In the feed industry, basic zinc carbonate has the same function as zinc oxide, which is also a feed additive. At the same time, in the feed industry, we are mainly concerned about whether the content of heavy metals meets the standard requirements.