□ Reporter Xie Shihan
Everyone is familiar with ceramics, but how many people have seen ceramics that are as transparent as glass? A few days ago, reporters visited Jiangsu Xiyi High-tech Materials Industry Technology Research Institute, the industrialization base of the Jiangsu Provincial Advanced Laser Technology and Emerging Industries Collaborative Innovation Center of Jiangsu Normal University. The new transparent ceramics in different application scenarios were eye-opening. "This is transparent ceramic composite armor. Even though it is very thin, it is stronger than tempered glass that is twice as thick. This transparent ceramic is as soft and thin as plastic wrap, and can be used in thin fluorescent ceramics and smart terminal protection exteriors. Screens, etc." Zhang Leru, deputy dean of the School of Physics and Electronic Engineering of Jiangsu Normal University and head of Jiangsu Xiyi High-tech Materials Industry Technology Research Institute.
Transparent ceramics are a wonderful combination of "light" function and ceramic carrier. Looking back on its development history of more than 60 years, from the initial "translucent" to the current complete transparency, its material systems and preparation methods have become increasingly rich, and the optical properties of the materials have been greatly improved. As a new generation of optical functional materials, transparent ceramics have great application potential in key fields such as solid lasers, protective armor, and solid-state lighting.
"Ceramics need to meet three extremely stringent conditions to become transparent. The first is that there must be no impurities, the second is that there cannot be any pores, and the third is that the interior of the ceramic must be absolutely uniform." Zhang Le picked up the table A ceramic tea cup introduced that the inside of traditional ceramic products is actually very rough and has many pores. If it is so difficult to become transparent, why do we still have to face the difficulty? Because compared to glass, transparent ceramics have obvious advantages. "First of all, the thermal conductivity of ceramics is as high as 5 times or more than that of glass. When light passes through the medium, it will inevitably produce losses. This loss will be converted into heat. The heat of the glass cannot be dissipated, so it is easy to explode, while transparent ceramics can It conducts heat very well. Secondly, ceramics are a typical representative of our country’s traditional culture, and we have inherent advantages in special-shaped structures, large-size ceramic firing technology, and defect control,” Zhang Le explained.
Ball milling, drying, degreasing and debinding, vacuum sintering, annealing... Every transparent ceramic product needs to go through 5-8 times of high-temperature sintering. Each sintering often takes more than ten hours. Problems may arise in any of these steps. This will lead to the complete scrapping of the product. For a long time, there has been a clear gap between my country and Japan, the United States, France and other countries in terms of high-performance transparent ceramic raw material powder and large-size uniform molding and sintering technology (equipment). To this end, 10 years ago, Jiangsu Normal University began to layout related technology research and development, trying to develop transparent ceramic products based on multi-dimensional extreme size (high aspect ratio, ultra-thin, large size) geometric configuration.
“Transparent ceramics have different forms for different application scenarios, but each form must take into account core issues such as heat dissipation during photoelectric conversion, which undoubtedly adds great difficulty to technology research and development.” After unremitting efforts, the team Finally conquered gel injection molding and water-based castingThese four key technologies for high-quality molding of transparent ceramics, extrusion molding and spray granulation, provide systematic solutions for the precision molding and innovative applications of multi-dimensional extreme size transparent ceramics. At present, relevant technologies and products have been promoted and applied in 12 companies including Fenghua Hi-Tech and Greer, with sales of nearly 1.9 billion yuan in the past two years.
In the past, if you wanted to prepare a high-quality laser ceramic, you had to use raw materials from Japan or France, equipment from Germany, and hot isostatic presses from the United States. Even the ball mills used needed to be imported from abroad. In order to solve the problem of "stuck neck" in raw materials and production equipment, in October 2019, Zhang Le led the team to cooperate deeply with many enterprises in the province to jointly tackle key problems. "How to improve the sintering activity of the powder while ensuring high-purity raw materials? How to ensure a uniform sintering thermal field? These are not only difficult points, but also the focus of our constant struggle." After more than four years of technical research, the team finally The core raw materials and key equipment required for the production of transparent ceramics have basically been domestically produced.
Adding different rare earth elements into transparent ceramic raw materials can be used in different scenarios. "By adding neodymium ions, we can make transparent laser ceramics; by adding cerium ions, we can make fluorescent ceramics with higher efficiency and better thermal stability." Shao Cen, head of the high-tech ceramics project team of the institute, said for example, the ones currently used in cars The core light conversion materials of LED headlights are mostly resin-based materials, which require a large heat dissipation system behind them. However, if you switch to a ceramic-based laser lighting source, even if a large amount of heat is generated during long-term operation, the ceramics fired at a high temperature of nearly 2,000 degrees Celsius will not suffer from problems such as blackening or explosion. Because of this, some high-end automobile laser headlights and high-power laser displays have begun to use fluorescent ceramic materials.
“The volume of product orders has increased significantly since this year, which gives us great confidence and more expectations.” Zhang Le said that in addition to continuing to expand market share in the civilian field, the team will focus on major national projects in the next step and carry out aerospace projects. Research and development of products such as sky laser ceramics and energy storage and light storage ceramics.
