Yttrium oxide powder's use

Rare earth is an extremely important strategic resource, which plays an irreplaceable role in industrial production. Automobile glass, nuclear magnetic resonance, optical fiber, LCD screen and so on cannot do without the addition of rare earth.  Among them, yttrium (Y) is one of the rare earth metal elements, is a gray metal.  But because it is more content in the crust, so the price is relatively cheap, and widely used, in the current social production is mainly used in the state of yttrium alloy and yttrium oxide.  

Yttrium oxide's uses

Yttrium oxide (Y2O3) is one of the most important yttrium compound, it does not dissolve in water and alkali, soluble in acid, appearance is white crystalline powder (crystal structure of cubic crystal system) has good chemical stability and vacuum and low volatility and high heat resistance, corrosion resistance, high dielectric, and the advantages of transparent (infrared), therefore has been applied in many fields.

1. Synthesis of yttrium stabilized zirconia powder  

As pure ZrO2 is cooled from high temperature to room temperature, the following phase transition will occur: cubic phase (C)→ tetetic phase (T)→ monoclinic phase (M), and the T → M phase transition will occur at 1150℃ accompanied by volume expansion of about 5%.  But if the ZrO2 t - m phase transition point stability to room temperature, in the load generated by the stress induced when t - m phase transition, due to the phase change of volume effect and can absorb a large number of fracture, which makes material showed abnormally high fracture energy, which makes material showed abnormally high fracture toughness, phase transformation toughening, high toughness, high abrasion resistance.  

In order to realize the phase transformation toughening of zirconia, it is necessary to add a certain stabilizer and under certain firing conditions, the high temperature stable phase - tetragonal metastable to room temperature tetragonal phase, which is the stabilizing effect of stabilizer on zirconia.  Y2O3 is the most studied zirconia stabilizer developed so far. Y-tzp sintered material has excellent mechanical properties at room temperature, high strength, good fracture toughness, and the grain size of the material in the collective is small and uniform, so it has received more attention.  

2. Sintering aid  

The sintering of many special ceramics requires the participation of sinter aid, the role of sinter aid can be generally divided into the following parts: forming solid solution with sinter;  Prevent crystal transformation;  Inhibit grain growth;  It produces the liquid phase.  For example, in the sintering of alumina, MgO is often added as the microstructure stabilizer in the sintering process, which can refine grains, greatly reduce the difference of grain boundary energy, weaken the anisotropy of grain growth and inhibit the discontinuous grain growth.  Due to the high temperature volatility of MgO, in order to achieve good results, yttrium oxide is often mixed with MgO, Y2O3 can play a role in refining grains and promoting the densification of sintering.  

3. Synthesis of YAG powder  

Yttrium aluminum garnet (Y3Al5O12) is a man-made compound, no natural minerals, colorless, Mohs hardness can reach 8.5, melting point is 1950℃, insoluble in sulfuric acid, hydrochloric acid, hydrofluoric acid nitrate, etc. The high temperature solid phase method is the traditional method to prepare YAG powder. According to the ratio obtained in the binary phase diagram of yttrium oxide and alumina, the two powders are mixed and roasted at high temperature, and YAG powder is formed through the solid state reaction between oxides.  In the reaction of alumina and yttrium oxide at high temperature, the intermediate phase YAM and YAP are formed, and finally YAG is formed.  

There are many applications of YAG. For example, its Al-O bond size is small and its bond energy is high. This high bond energy can precisely match the high vacuum energy of fluorescent materials, that is, keep its optical properties stable under the impact of higher electrons.  YAG can become phosphor by doping Ce3+, Eu3+ and other trivalent rare earth ions.  In addition, YAG crystal has good transparency, very stable physical and chemical properties, high mechanical strength and good thermal creep resistance. It is a kind of laser crystal material with wide application and ideal performance.

4. Transparent ceramics  

Yttrium oxide has always been the focus of research in the field of transparent ceramics. It belongs to the cubic crystal system, and has the homogeneity of each axis of optical properties. Compared with the heterotropy of transparent alumina, the image is less distorted, so it is gradually paid attention to and developed by high order lenses or military optical Windows.  The main characteristics of its physical and chemical properties are:  

(1) High melting point, good chemical and photochemical stability, wide optical transparency range (0.23 ~ 8.0μm);  

(2) At 1050 nm, the refractive index is up to 1.89, which makes it have more than 80% theoretical transmittance;  

(3) Y2O3 has enough to accommodate most of the emission levels of trivalent rare earth ions, large conductance to valence band gap, through the doping of rare earth ions, to achieve effective cutting of luminescence performance, so as to achieve its application of multi-functional;  

(4) The maximum phonon cutoff frequency is about 550 cm -- 1. The low phonon energy can suppress the probability of radiative transition and improve the probability of radiative transition, thus improving the quantum efficiency of luminescence.  

(5) High thermal conductivity, about 13.6 W/(m·K), high thermal conductivity as a solid laser dielectric material is very important.  

The melting point of Y2O3 is about 2690℃, and the normal temperature sintering temperature is about 1700~1800℃.  If you want to make transparent ceramics, it is best to adopt hot pressing sintering.  Because of excellent physical and chemical properties, Y2O3 transparent ceramics are widely used and potential development, mainly including: missile infrared window and sphere cover, visible and infrared lens, high pressure gas discharge lamp, ceramic scintillator and ceramic laser and other fields.