The concept of transparent ceramics
Transparent ceramics are ceramics that can transmit visible light. Ordinary polycrystalline ceramic materials are generally opaque because of their anisotropy, low-symmetry crystal structure system, extinction factors between grains, and absorption and scattering of visible light by internal impurities and pores.
The conditions for ceramics to achieve a certain degree of transparency
- Porosity: eliminate pores or make the porosity tend to 0;
- Surface processing finish: improve the surface finish by grinding and polishing;
- Reduce impurities;
- Crystal structure: choose isotropic cubic crystal system materials;
- Grain boundary structure: make the grain boundary structure as thin as possible, clean, and free of impurities and pores
- Grain size and additives: make the grain size much larger than the incident light wavelength;
- Raw materials and second-phase impurities: use high-purity, ultra-fine, and highly dispersed powder raw materials to avoid introducing impurities.
Types of transparent ceramics:
Transparent ceramic materials are mainly divided into two categories: oxide transparent ceramics and non-oxide transparent ceramics:
Oxide transparent ceramics
In addition to the most common alumina transparent ceramics, typical oxide transparent ceramics also include yttria transparent ceramics, magnesia transparent ceramics, yttrium aluminum garnet transparent ceramics, magnesium aluminum spinel transparent ceramics, transparent ferroelectric ceramics (PLZT), etc.
Non-oxide transparent ceramics
Non-oxide transparent ceramics include aluminum nitride transparent ceramics (not only have the advantages of AlN ceramics but also have good transparency), aluminum oxynitride transparent ceramics, α-Sialon transparent ceramics, and AlON transparent ceramics that are suitable as transparent ceramics through research.
Applications of transparent ceramics
Transparent ceramics are multifunctional materials that combine high transparency, corrosion resistance, strength, dielectricity, and thermal conductivity and have diverse applications.
- Lighting: alumina transparent ceramics, can not only effectively transmit visible light and infrared rays, but also have a large thermal conductivity, high-temperature strength, good thermal stability, and corrosion resistance, and can be used to make high-pressure sodium lamp tubes.
- Industry: transparent ceramics have light-transmitting and high-temperature-resistant properties, and can be used to make welding masks and human protection masks for nuclear tests. They are also widely used in various applications in pilots and mechanical, chemical, instrument, and electronic industries.
- Military: transparent ceramics are excellent transparent bulletproof materials in national defense and military. They can be used for radar antenna covers and infrared fairings of missiles and other aircraft. They can replace traditional multi-layer glass as transparent armor materials, improve transparency, reduce weight, enhance strength, and durability, have better anti-penetration and anti-scratch capabilities, and have better stealth performance.
- Medical field: Transparent ceramics can be used to make dental medical devices, such as orthodontic appliances. Yttrium aluminum garnet (YAG) is an excellent laser matrix, that has applications in medicine and high-energy physics, but improving transparency and light output is still the key technology of research.
Overall, transparent ceramics are a very promising new material with wide-ranging application prospects. With the continuous advancement of science and technology, the preparation technology and performance of transparent ceramic materials will be further improved and developed, and more fields will be able to utilize transparent ceramics in the future, making even greater contributions to the development of human society.
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