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Location:Home>Research>Research Divisions>Structural Ceramics Engineering Research Center>Transparent ceramics group>Research Fields

Research Fields

1. Transparent ceramics

Transparent ceramics exhibit enhanced thermal and mechanical properties with high transmittance in a wide range, which are being developed for many applications including lamp envelope, laser, scintillator, window, lens,  etc. Our objective is focused on the transparent ceramics with high transmittance in the visible and/or infrared range. Our research includes transparent/translucent alumina ceramics used on high pressure sodium lamps and ceramic metal halide lamps, yttrium oxide, yttrium aluminum garnet and aluminum oxynitride used in middle infrared range, and high refractive index transparent ceramics. Some of them have been industrialized.

1.1 Transparent/translucent alumina ceramic tubs used on high intensity discharge lamps

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Fig. 1. Translucent alumina ceramic tubs used on high pressure sodium lamps.

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Fig.2. Translucent alumina ceramic tubs (Five-piece set) used on ceramic metal halide lamps.

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Fig. 3. Translucent alumina ceramic tubs used on ceramic metal halide lamps.

1.2 Mid-infrared range transparent ceramics

Transparent Y2O3, YAG and AlON ceramics have high transmittance in the visible and mid-infrared range, and they can be used as high temperature observation window and mid-infrared detection device. AlON also has application on transparent body armor because of its high hardness.

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Fig. 4. Y2O3 transparent ceramic radome (Φ 80 mm × 5 mm).

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Fig. 5. YAG transparent ceramic radome (Φ 80 mm × 5 mm).

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Fig. 6. AlON transparent ceramic (Φ 100 mm × 5 mm).

1.3 High refractive index A2B2O7 transparent ceramics

RE2Zr2O7 and RE2Hf2O7 transparent ceramics with high optical quality have been successfully fabricated. The refractive index was higher than 2 at 633 nm. With the doping of rare earth ions, upconversion luminescence was achieved.

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Fig. 7. RE2Zr2O7 and RE2Hf2O7 transparent ceramics.

2. High heat conductivity aluminum nitride (AlN) ceramic materials

Aluminum nitride (AlN) is a ceramic material with higher thermal conductivity (3 ~ 10 times higher than that of Al2O3, and close to that of BeO), lower electrical conductivity, dielectric constant and dielectric loss. Besides, it has a thermal expansion coefficient which close to that of silicon and far less than that of BeO and Al2O3. Combined with its excellent electrical and mechanical properties as well as its non-poisonous character, AlN ceramic is considered as the ideal substrate material and electronic packages for high-frequency integrated circuits with higher power and higher density of components. They have broad application prospect in communication and microelectronic fields.

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Fig. 8. Aluminum nitride substrate (100×100×1 mm) and cooling fins.

3. Upconversion luminescence materials

Upconversion luminescence materials which can convert infrared radiation into visible light have a variety of potential applications. We select oxide system and fluoride as hosts and prepare oxide powders doping with rare earth elements by different methods, such as chemical coprecipitation, sol-gel combustion and so on. Upconversion luminescence was achieved in Y2O3, Lu2O3, YAG and NaYF4 materials.

3.1 Upconversion luminescence of transparent ceramics

The Upconversion luminescence of transparent ceramics have a variety of potential applications, such as compact short-wavelength upconversion laser, three dimensional display technology, molecular and cellular biological targets, optical fiber amplifier, two-photon excitation confocal microscope system, anti-counterfeiting field, and so on. 

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Fig. 9. The blue, green, orange and red emission of rare earth doped Y2O3 transparent ceramics (λex = 980nm).

3.2 Upconversion luminescence of rare earth doped NaYF4 nanocrystalline

Recently, with the development of preparation technology in the nanoparticles field, the research on upconversion luminescence attracted new attentions. NaYF4 has been considered as an ideal substrate material due to its high luminous efficiency. In our work, RGB (red, green, blue) NaYF4 nanocrystalline were prepared using chemical methods successfully. In addition, the products were surface modified with polymer and silicon dioxide respectively to improve properties.

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Fig. 10. (a) The Upconversion blue and green emission of NaYF4 nanocrystalline;

(b) NaYF4: Yb3+, Er3+ nanocrystalline surface-modified with SiO2

4. Fiber reinforcement oxide ceramic matrix composites

Carbon fiber-reinforced oxide ceramic matrix composites possess a much higher flexural strength up to 740 MPa. Through the optimizing of processing parameters, the bulk density of the composite can be tuned in the 1.952.04 g/cm3 range and the thermal expansion coefficient is only 0.69 × 10-6 /, exhibiting excellent thermal and mechanical shock resistance. In addition, the amorphization phenomenon of cristobalite under conventional process conditions was observed. That is to say, quartz fiber crystallization can transform into amorphous type when thermal heated at lower temperature in vacuum or reducing atmosphere.

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Fig. 11. The SEM of carbon fiber-reinforced quartz matrix composite.

5. New forming method

Forming is an important processing in the manufacture of ceramics as it affects the final quality of ceramic products. We focus our research interests and vigors on the innovation of ceramic forming techniques to make different products. Our work involves new reagents system for gelcasting, new porous molds for slip-cast, making ceramic foams by combination of forming and gelcasting method and so on.

5.1 Exploration of new curing system by gel injection molding

The mew gel injection curing system developed based on nucleophilic addition reaction enable the operation in air, which can solve the problem of oxygen polymerization in traditional gel injection process.

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Fig. 12 (a) Alumina ceramics, and (b) translucent alumina ceramic parts prepared by gel injection molding.

 

5.2 Porous alumina ceramics prepared by Foam Technique

Porous alumina ceramics are fabricated based on the mechanism that foaming agent can directly foam into micro bubbles in the gel system. The technology has been applied successfully.

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Fig. 13. (a) High purity alumina foam ceramic standard brick, thicker brick and 410 mm - long brick, and (b) their microstructure.

5.3 Oriented grain transparent alumina ceramics prepared with assistant of magnetic field

Oriented grain transparent alumina ceramics are prepared based on the mechanism that alumina particles can growth towards preferred orientation under the strong magnetic field. Oriented grain transparent alumina ceramics exhibit higher transparency compared to the traditional randomly oriented products.

 

Fig. 14. (a) Grain-oriented and (b) random-oriented Al2O3 ceramics.

 
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