As an important inorganic compound, zinc oxide is widely used in many fields. Depending on the classification criteria, it can be categorized in several ways. Different types of zinc oxide exhibit varying properties, which determine their specific functions and applications. The following sections elaborate on the classifications, differences, and functions of various forms of zinc oxide.
1. Classification by Particle Size
(I) Ordinary Zinc Oxide
Ordinary zinc oxide typically has a particle size greater than 100 nanometers. It possesses certain hiding power and tinting strength and is widely used in traditional industries such as rubber, coatings, and ceramics.
In the rubber industry, it is an essential vulcanization activator. It enhances the vulcanization speed and cross-linking degree of rubber, thereby improving the physical and mechanical properties of rubber products, such as tensile strength and wear resistance. In coatings, it serves as a white pigment, offering strong hiding power and weather resistance.
(II) Nano Zinc Oxide
Nano zinc oxide has a particle size ranging from 1 to 100 nanometers. Due to its small size, surface effects, and quantum size effects, it exhibits unique properties.
In catalysis, its large specific surface area and high surface activity provide more active sites for chemical reactions, thereby accelerating reaction rates and improving catalytic efficiency. In sunscreen cosmetics, its excellent ultraviolet absorption and scattering capabilities offer effective protection from UV damage. Compared with traditional sunscreens, nano zinc oxide is thinner, more transparent, and less greasy.
In antibacterial applications, it interacts with bacterial cell membranes, disrupting their structure and causing cell death. It shows significant antibacterial effects against Escherichia coli, Staphylococcus aureus, and other bacteria.
2. Classification by production process
(I) Indirect zinc oxide
It is made from zinc ingots through high-temperature sublimation oxidation.
It has a high purity of 99.5% – 99.7%, a relatively large particle size, and a narrow distribution. It is commonly used in the rubber tire industry, which can effectively improve the vulcanization activity of rubber, enhance the adhesion between rubber and steel cord, and improve the strength and wear resistance of tires. In the electronics industry, it is also used to manufacture electronic components such as varistors because of its good electrical performance stability.
(II) Direct zinc oxide
It is mostly made from zinc ore through direct oxidation roasting and other processes.
It has a relatively low purity, generally 95% – 98%, and a relatively high impurity content. It is commonly used in the ceramic industry to reduce the sintering temperature of ceramics and improve the density and gloss of ceramics. In glass manufacturing, it can increase the transparency and chemical stability of glass.
(III) Wet chemical zinc oxide
It is prepared by chemical reactions in solutions, such as precipitation method, sol-gel method, etc.
The particle size and morphology can be precisely controlled, and the product has high purity, small and uniform particle size. It has obvious advantages in the preparation of high-performance electronic devices. For example, it can be used to prepare zinc oxide thin-film transistors, because of its small particle size and good uniformity, it can improve the performance and stability of the device. When preparing luminescent materials, the luminescent properties of zinc oxide can be precisely controlled by controlling the reaction conditions.
3. Classification by use
(I) Zinc oxide for rubber
It is a key active agent in the rubber vulcanization process. It can be combined with stearic acid, accelerators, etc. to form an active complex, accelerate the vulcanization speed, and improve the crosslinking density and physical and mechanical properties of the vulcanized rubber, such as tensile strength, tear strength, and wear resistance. It is widely used in the production of rubber products such as tires, hoses, and tapes.
(II) Zinc oxide for coatings
As a white pigment, it has good hiding power and tinting power, and can improve the whiteness and brightness of the coating.
At the same time, it can enhance the weather resistance, corrosion resistance and anti-powdering properties of the coating, and is suitable for architectural coatings, industrial coatings and other fields.
(III) Zinc oxide for medicine
It has astringent, antipruritic, and antibacterial effects.
It can be used to prepare external ointments, pastes, etc. to treat skin inflammation, eczema and other skin diseases. For example, the common zinc oxide ointment can protect the skin, reduce water evaporation, and promote wound healing.
(IV) Zinc oxide for feed
As a zinc source additive in animal feed, it provides animals with the zinc element required for growth.
Proper addition can promote animal growth and development, improve immunity, and enhance disease resistance. However, it should be used properly. High doses may cause intestinal damage to animals and environmental pollution. For example, adding a proper amount of zinc oxide to piglet diets can reduce the incidence of diarrhea, but high doses are restricted by regulations.
4. Effect of different process principles on product performance
(I) Indirect method
1. Process principle
The indirect method usually uses high-purity zinc ingots as raw materials. The zinc ingots are first heated to about 1000 °C to melt and evaporate into zinc vapor.
Subsequently, under high temperature conditions, the zinc vapor undergoes oxidation reaction with hot air or oxygen to generate zinc oxide. The chemical reaction equation is: 2Zn + O₂ → 2ZnO. In this process, the oxidation of zinc vapor is the key step. Factors such as reaction temperature and oxygen flow have an important influence on the generation and performance of zinc oxide.
2. Effect on product performance
The zinc oxide prepared by this method has a high purity of more than 99% and a low impurity content. It is suitable for fields with strict purity requirements, such as electronics and medicine.
The product particle size is relatively large, usually in the range of 0.1-10μm, with a narrow particle size distribution and good dispersibility, which is conducive to application in rubber, coatings and other fields, and can improve the uniformity and stability of the product. The crystal structure is relatively complete and the crystallinity is high, which makes it have good physical and chemical stability, and its performance changes little in harsh environments such as high temperature and high humidity.
(II) Direct method
1. Process principle
The direct method is based on zinc-containing raw materials such as zinc ore and zinc ash. Usually, the raw materials are mixed with reducing agents such as coke and then reduced and roasted at high temperature (1000-1300 °C).
The zinc-containing compound is reduced to zinc vapor, and the impurities in the raw materials will also react accordingly. The zinc vapor then enters the oxidation chamber and reacts with air or oxygen to form zinc oxide. This process involves complex reduction and oxidation reactions, and factors such as raw material composition, reducing agent dosage, and temperature have a great impact on product quality.
2. Impact on product performance
Because the raw materials contain impurities, the product purity is relatively lower than the indirect method, generally 95%-98%, but the purity can be improved by optimizing the process and subsequent treatment. It is suitable for fields that do not require extremely high purity, such as ceramics and glass.
The particle size and distribution of the product are greatly affected by the raw materials and process conditions. The particle size may be uneven, which requires fine control of the process to improve. The crystal structure may have defects due to impurities and rapid oxidation processes, affecting its electrical and optical properties.
It should be used with caution in some application scenarios with high performance requirements.
(III) Wet chemical zinc oxide
1. Process principle
The wet chemical method is a series of chemical reactions carried out in a solution system to prepare zinc oxide.
Common methods include precipitation method and sol-gel method. Taking the precipitation method as an example, zinc salts (such as zinc nitrate, zinc acetate) and precipitants (such as sodium hydroxide, ammonia water) are usually mixed in a solution. By controlling the reaction conditions (such as pH value, temperature, reaction time, etc.), zinc ions react with the precipitant to form zinc hydroxide precipitates. Subsequently, the precipitate is filtered, washed, dried and calcined to obtain a zinc oxide product. The chemical reaction equation is: Zn²⁺ + 2OH⁻ → Zn (OH)₂↓, Zn (OH)₂ → ZnO + H₂O (calcination).
The sol-gel method is to first hydrolyze and polycondense metal salts or metal alkoxides in an organic solvent to form a sol, then age them to form a gel, and finally dry and calcine them to obtain zinc oxide.
2. Impact on product performance
By precisely controlling the reaction conditions, the particle size, morphology and structure of the product can be precisely controlled.
For example, when preparing nano-scale zinc oxide, the particle size can be as small as a few nanometers to tens of nanometers, which has unique advantages in the fields of catalysis and antibacterial. The product has high purity. By selecting high-purity raw materials and appropriate washing and separation steps, impurities can be effectively removed to meet applications with high purity requirements. However, the organic reagents and complex reaction conditions introduced during the preparation process may cause product agglomeration and affect its performance. Measures such as adding dispersants and optimizing process conditions need to be taken to solve this problem.
About Epic Powder Machinery
Epic Powder Machinery is a leading manufacturer of advanced powder processing equipment, specializing in ultrafine grinding, classification, and surface modification systems. With decades of industry experience and European core technologies, Epic Powder provides customized solutions for zinc oxide and other fine materials, helping customers improve product performance, consistency, and production efficiency across industries such as electronics, rubber, ceramics, and pharmaceuticals.
