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Zirconium oxide ceramic is a new type of high-tech ceramic. It has high strength, high hardness, high temperature resistance, acid and alkali corrosion resistance and high chemical stability. It also has scratch resistance, no signal shielding and excellent heat dissipation performance. The appearance is good and so on, so it becomes a new type of mobile phone body material after plastic, metal and glass. At present, the application of zirconia ceramics in mobile phones is mainly two parts of the backboard and the fingerprint identification cover.

According to statistics, in 2015, plastic and metal materials in the field of consumer electronics parts accounted for more than 90% of shipments, while zirconia ceramics accounted for less than 1%. Although some media have predicted that "zirconia ceramics are expected to surpass metal and glass to become the mainstream material of the third-generation mobile phone body", there are multiple factors in the reality that limit the zirconia ceramics to become the mainstream mobile phone body material.

High technical barriers

The back cover of zirconia ceramic mobile phone adopts precision ceramic processing technology, and its material preparation and processing technology is very complicated. A ceramic back cover mainly goes through nine steps from powder to finished product, including powder preparation, rubberizing, cover forming, degumming, sintering, CNC machining, polishing/punching, inspection and laser/PVD coating. According to the upstream and downstream of the supply chain, it is mainly divided into three sections: the most upstream raw material powder preparation; the midstream briquette forming and high temperature sintering; and the downstream CNC polishing/grinding.

Nano zirconia powder is the main raw material for the back cover of mobile phone ceramics. The technical barriers of the most upstream zirconia ceramic powder in the back cover industrial chain are the highest. At present, most nano-scale high-end powder preparation technologies are in the hands of a few countries such as Japan, Germany and Germany, among which the high-end zirconia powder for ceramic back cover is used. At present, the strong manufacturers include Japan TOSOH, Kyocera, China Sanhuan Group, and China Ceramics and Oriental Zirconium.

The preparation technology of zirconia ceramic powder is the key to the preparation of precision parts of mobile phones. The quality of powder directly affects the inherent quality and performance of finished products. High purity, ultrafine particle size, narrow particle size distribution and good dispersion performance are important basis for evaluating the quality and performance of ceramic powders. At present, the preparation methods commonly used for zirconia ceramic powders include chemical precipitation method, hydrothermal method, and sol-gel method.

In the big problem of zirconia powder agglomeration, Gan Xuexian et al. investigated the final depolymerization effect by designing different grinding equipment and process parameters. The zirconia powder with d50=1.355μm was taken as the research object. When the vertical ball mill, the vertical bead mill and the horizontal sand mill were respectively used as the grinding equipment, the φ2mm zirconia balls were used as the grinding medium, and the m medium was: After the material of m material=5:1 is ground for 15h, the particle size of the zirconia slurry after grinding is detected. The results show that: (1) The grinding effect of the horizontal sand mill is optimal, and the d50 of the zirconia slurry after grinding is 0.303μm; (2) When the horizontal sand mill is used as the grinding equipment, the ratio of medium to material (m medium: m material) is 4:1, the solid content (w) of the slurry is 45%, and the linear velocity is 10m· S-1, the grinding time is 25h, the grinding effect is the best.

In the powder formula, in order to enhance the toughness and other properties of the powder sintered product, it is necessary to add a modified material to the zirconia powder. The modified additive mainly includes rare earth elements such as lanthanum to ensure the insulation of the formula powder. Another part of additives such as magnesium, manganese, vanadium, tungsten, etc., is mainly used to ensure the temperature stability and reliability of the formula powder. In this step, the incorporation of the modified additive and the incorporation ratio are the key to the formula powder, and the process requirements are extremely high. These need to be accumulated over a long period of time, which is a major manifestation of technical barriers.

In addition to the high technical barriers, the corresponding equipment investment barriers are also very high. The high capital investment barriers for tunnel furnaces for zirconia ceramic sintering, CNC machines for grinding and grinding machines, etc., have severely restricted the scale and industrialization of high-end zirconia ceramics. According to rough statistics, the annual production capacity of global nano-zirconia powder is about 40,000 tons, more than half of which are low-end and medium-end powders, which cannot be used to make mobile phone back covers; even if there are more than 10,000 tons of high-end powders, Not all of them will be used in the production of mobile phone back covers, as some high-end powders will be used for sensors, fuel cells and more. The capacity bottleneck of high-end zirconia powder also restricts the production capacity of ceramic mobile phone backplanes. It is almost impossible for zirconia ceramics to become the mainstream mobile phone body material in the short term.

Outstanding cost issue

The high-end zirconia powder used to make ceramic mobile phone parts accounts for about 30% of the total cost. The world's best quality TOSOH powder (Tosoh) powder has exceeded 1 million / ton, and domestic powders such as Chinese porcelain materials are also needed. About 300,000 / ton, according to each ceramic back cover needs to use powder 100g to calculate, the price of the powder is 30-100 yuan, combined with the production yield, the overall cost will be higher. Therefore, the unit price of the ceramic backing plate is roughly estimated to be about 200 yuan. According to an industry insider: "Ceramic materials are basically the high-end mobile phones in the high-end mobile phone, because the price is too high, the basic one is more than 200 yuan, if you do some decoration and coloring, you have to More expensive. At present, it is mainly focused on some small batches of high-end flagship market."

In addition to the cost issue, the problems of long processing time and low yield of ceramic appearance parts are also prominent. Since zirconia ceramics have a high Mohs hardness, it takes a long time in fine processing such as polishing and polishing. At the same time, due to the many production processes of ceramic appearance parts, and the yield of each link is interlocking, it is very easy to cause bottlenecks and the overall yield cannot be improved. These factors have severely restricted the production capacity of zirconia ceramics.