CN1587187A - Lanthanum hafnate base transparent ceramics and its preparing method - Google Patents

Abstract

The invention relates to a lanthanum hafnate-based transparent ceramic and a preparation method thereof, belonging to the field of transparent ceramics. It is characterized in that the composition of the transparent ceramic is: La _2－2x RE _2x Hf ₂ O ₇ ; 0≤x<0.1, RE is Ce, Pr, Eu, Tm, Tb and other rare earth ions, and when x=0, it is pure lanthanum hafnate . The above materials can be prepared into transparent ceramics with good transparency by adopting hot pressing, hot isostatic pressing and sintering in vacuum and hydrogen. The transparent ceramic provided by the invention has high density and strong ability to absorb rays, and the maximum transmittance of the 1mm thick polished transparent La ₂ Hf ₂ O ₇ ceramic in the visible light band is greater than 70%; and other fields have potential application prospects.

Description

Lanthanum hafnate-based transparent ceramic and preparation method thereof

technical field

The invention relates to a lanthanum hafnate-based transparent ceramic and a preparation method thereof, belonging to the field of transparent ceramics.

Background technique

Since R.L. Coble first reported the successful preparation of translucent alumina ceramics (U.S.P. 3026210) in 1962, a new application field of ceramic materials has been opened up. After decades of development, people have been able to prepare transparent ceramics with excellent optical properties. The optical properties of some transparent ceramics have reached the level of single crystals, while their mechanical properties are significantly better than single crystals. Transparent ceramics have become an important optical material and have been applied in high temperature windows, radiation detection, laser media and other fields.

Has developed Yttralox: Nd (1973) [C.Greskovich, JPChernoch.J.Appl.Phys., 1973, 44 (10): 4599-4603.], YAG: Nd [A.Ikesue, T.Kinoshita, K .Kamata, et al., J.Am.Ceramic Soc., 1995, 78(4):1033-1037.], Y ₂ O ₃ :Nd (2001) [Ji.Lu, Ju.Lu, T.Murai, et al., Jpn.J Appl.Phys., 2001, 40(12A): L1277-1283.] and other laser ceramics, and (Y, Gd) ₂ O ₃ :Eu[USP4421671], Gd ₂ O ₂ S:Pr , Ce, F[Ito H, Yamada H, Yoshida M, et al, Jpn.J.Appl.Phys.1988, 27(8):L1371-1373], Gd ₃ Ga ₅ O ₁₂ :Cr, Ce[USP5318722] etc. flashing ceramics. At present, laser ceramics are still in the trial production stage, and some scintillation ceramics basically meet the performance requirements of medical X-CT, and gradually replace the original inorganic scintillation crystals and are widely used in medical X-CT detectors.

Lanthanum hafnate (La ₂ Hf ₂ O ₇ ) has high density, high effective atomic number and high ray absorption capacity, and various active ions have strong luminescence in lanthanum hafnate. Therefore, lanthanum hafnate (La ₂ Hf ₂ O ₇ ) can be used as a host material of high absorption heavy scintillators in the field of radiation detection. However, due to the high melting point of lanthanum hafnate (La ₂ Hf ₂ O ₇ ) (~2300°C), it is difficult to prepare large-sized single crystals by traditional crystal growth methods, which limits its application as scintillation crystals.

The ceramic sintering process through solid-state diffusion can prepare materials with cubic equal optical isotropy into transparent ceramics with excellent optical properties through a special sintering process at a temperature much lower than the melting point. Compared with single crystals, transparent ceramics also have the advantages of short preparation time, low cost, and the ability to prepare transparent ceramics with large sizes, complex shapes, and excellent mechanical properties. Lanthanum hafnate (La ₂ Hf ₂ O ₇ ) has a stable cubic pyrochlore structure below 2500K, and there is no birefringence, so it is possible to prepare it into transparent ceramics. Traditionally, solid-state reaction is generally used to prepare lanthanum hafnate (La ₂ Hf ₂ O ₇ ) powder, and it is difficult to obtain powder with high sintering activity; so far, there is no preparation of lanthanum hafnate (La ₂ Hf ₂ O ₇ ) into transparent ceramics. and other reports on optical materials. The highly sintered active lanthanum hafnate (La ₂ Hf ₂ O ₇ ) and its rare earth ion-doped powder synthesized by hot pressing, hot isostatic pressing, vacuum, hydrogen sintering process and combustion are prepared into transparent ceramics, The development of a new optically transparent ceramic material with high density and high radiation absorption leads to the object of the present invention.

Contents of the invention

The purpose of the present invention is to prepare a transparent lanthanum hafnate ceramic-based transparent ceramic by hot pressing, hot isostatic pressing, and sintering in vacuum and hydrogen.

The composition of transparent ceramics is: La _2-2x RE _2x Hf ₂ O ₇ ; 0≤x<0.1, RE is Ce, Pr, Eu, Tm, Nd, Yb, Tb and other rare earth ions, and when x=0, it is pure hafnium acid lanthanum.

The lanthanum hafnate transparent ceramic prepared by the present invention has a general formula: La _2-2x RE _2x Hf ₂ O ₇ ; 0≤x<0.1, RE is Ce, Pr, Eu, Tm, Nd, Yb, Tb and other rare earths Ions, x = 0 for pure lanthanum hafnate. The transparent ceramic has high density and ray absorption capacity, and has important application prospects in the fields of radiation detection and laser media.

_The powder used in the _present invention is _{a particle size of} 10- 100 nanometer powder.

The lanthanum hafnate transparent ceramic provided by the invention includes the powder heat treatment, molding and sintering processes of combustion synthesis. The sintering process is characterized by:

(1) The molding process can adopt dry pressing or isostatic pressing procedure, and the sintering process can adopt vacuum or hydrogen sintering or hot isostatic pressing sintering or hot pressing sintering;

(2) Keep warm at 1500-2000°C for 4-10 hours, and cool with the furnace.

Using glycine and ethylenediaminetetraacetic acid (EDTA) as fuel to prepare powder through combustion reaction, La ₂ Hf with good transparency was successfully prepared for the first time by sintering processes such as hot pressing, hot isostatic pressing, vacuum, and sintering in hydrogen ₂ O ₇ ceramics, the highest transmittance of the polished 1mm thick sample in the visible light band is higher than 70%. The obtained ceramic sintered body had a cubic pyrochlore structure. No porosity was detected in the microstructure of the ceramics, the grains were closely bonded, and the grain boundaries were very thin, which had typical microstructure characteristics of transparent ceramics. Doping rare earth ions such as Tb ³⁺ , Ce ³⁺ , Pr ³⁺ , Tm ³⁺ , Eu ³⁺ has strong light emission under ultraviolet or X-ray excitation.

La ₂ Hf ₂ O ₇ transparent ceramics provided by the present invention are characterized by:

(1) There are no pores in La ₂ Hf ₂ O ₇ transparent ceramics that can be detected by scanning electron microscopy, and the grain boundaries are closely combined and the grain boundaries are very thin.

(2) La ₂ Hf ₂ O ₇ transparent ceramics have high transmittance in the visible light band (380-780nm).

(3) La ₂ Hf ₂ O ₇ transparent ceramics have high density (>7.8g/cm ³ ) and high ray absorption capacity.

(4) Transparent ceramics doped with Tb ³⁺ , Ce ³⁺ , Pr ³⁺ , Tm ³⁺ , Eu ³⁺ rare earths have strong light emission under ultraviolet or X-ray excitation.

Description of drawings

Figure 1 is a polished transparent La ₂ Hf ₂ O ₇ ceramic sample with a diameter of 1.5 cm and a thickness of 1 mm, indicating that it is transparent in the visible light band.

Figure 2 is the transmittance curve of polished transparent La ₂ Hf ₂ O ₇ ceramics with a thickness of 1mm in the visible light band, the abscissa is the wavelength, and the ordinate is the transmittance.

Fig. 3 is the X-ray diffraction spectrum of the transparent La ₂ Hf ₂ O ₇ ceramic, which shows that it is a pure cubic pyrochlore La ₂ Hf ₂ O ₇ .

Figure 4 is the SEM photo of the fracture of transparent La ₂ Hf ₂ O ₇ ceramics, no porosity was detected, the grains were closely bonded, the grain boundaries were very thin, and it had typical microstructure characteristics of transparent ceramics.

Fig. 5 is (a) transmittance curve and (b) fluorescence spectrum of La ₂ Hf ₂ O ₇ : 1% Eu ³⁺ transparent ceramic. The abscissa in Figure 5(b) is the wavelength, and the ordinate is the luminous intensity.

Fig. 6 is (a) transmittance curve and (b) fluorescence spectrum of La ₂ Hf ₂ O ₇ : 1% Tb transparent ceramics.

Fig. 7 is (a) transmittance curve and (b) fluorescence spectrum of La ₂ Hf ₂ O ₇ : 1% Tm transparent ceramics.

Fig. 8 is (a) transmittance curve and (b) fluorescence spectrum of La ₂ Hf ₂ O ₇ : 1% Ce transparent ceramics.

Fig. 9 is (a) transmittance curve and (b) fluorescence spectrum of La ₂ Hf ₂ O ₇ :% 1.5Pr transparent ceramics.

Detailed ways

The substantive characteristics and remarkable progress of the present invention are further illustrated below through examples, but the present invention is by no means limited to the described examples.

Example 1

The powder prepared by combustion reaction of 0.02 mol of HfO(NO ₃ ) ₂ and La(NO ₃ ) ₃ with 0.054 mol of glycine was calcined at 800° C. for 2 hours to remove residual carbon and organic matters. The La ₂ Hf ₂ O ₇ powder synthesized by calcination and combustion is first subjected to isoaxial pressing, and then subjected to 180MPa isostatic pressing to form a molding density of 35%. The products formed by isostatic pressing are kept in a hydrogen atmosphere at 1850°C for 6 hours.

The transmittance curve of the obtained transparent ceramics is shown in Fig. 2(b). The performance is as follows:

Density (g/cm ³ ) ＞7.8

Crystal phase (X diffraction analysis) La ₂ Hf ₂ O ₇

Porosity (%) ＜0.1

380-780nm band maximum transmittance (%) ＞60

From the SEM fracture morphology analysis, it can be seen that the grain size distribution of La ₂ Hf ₂ O ₇ ceramics is uneven, basically composed of large grains with a diameter of ~1 and large grains with a diameter of ~5 μm, but the grains are closely arranged , the grain boundaries are very thin, and no pores can be observed under the scanning electron microscope, resulting in a transparent material, as shown in Figure 4(a).

Example 2

The powder prepared by combustion reaction of 0.02 mol of HfO(NO ₃ ) ₂ and La(NO ₃ ) ₃ with 0.054 mol of glycine was calcined at 800° C. for 2 hours to remove residual carbon and organic matters. The La ₂ Hf ₂ O ₇ powder synthesized by calcination and combustion is first subjected to isoaxial pressing, and then subjected to 180MPa isostatic pressing to form a molding density of 35%. The products formed by isostatic pressing are kept in a hydrogen atmosphere at 1750°C for 6 hours. The transmittance curve of the obtained transparent ceramics is shown in Figure 2(a), and the properties of the prepared transparent La ₂ Hf ₂ O ₇ ceramics are as follows:

Density (g/cm ³ ) ＞7.5

Crystal phase (X diffraction analysis) La ₂ Hf ₂ O ₇

Porosity (%) ＜0.1

380-780nm band maximum transmittance (%) ＞40

Example 3

The powder prepared by combustion reaction of 0.02 mol of HfO(NO ₃ ) ₂ and La(NO ₃ ) ₃ with 0.054 mol of glycine was calcined at 800° C. for 2 hours to remove residual carbon and organic matters. The La ₂ Hf ₂ O ₇ powder synthesized by calcination and combustion is first subjected to isoaxial pressing, and then subjected to 180MPa isostatic pressing to form a molding density of 35%. The products formed by isostatic pressing are kept in a hydrogen atmosphere at 1900°C for 6 hours. The transmittance curve of the obtained transparent ceramics is shown in Figure 2(c), and the properties of the prepared transparent La ₂ Hf ₂ O ₇ ceramics are as follows:

Density (g/cm ³ ) ＞7.5

Crystal phase (X diffraction analysis) La ₂ Hf ₂ O ₇

Porosity (%) ＜0.1

380-780nm band maximum transmittance (%) ＞60

Example 4

The powder prepared by combustion reaction of 0.02 mol of HfO(NO ₃ ) ₂ and La(NO ₃ ) ₃ with 0.054 mol of glycine was calcined at 800° C. for 2 hours to remove residual carbon and organic matters. The La ₂ Hf ₂ O ₇ powder synthesized by calcination and combustion is first subjected to isoaxial pressing, and then subjected to 180MPa isostatic pressing to form a molding density of 35%. The products formed by isostatic pressing are kept in a hydrogen atmosphere at 1850°C for 12 hours. The transmittance curve of the obtained transparent ceramics is shown in Figure 2(d), and the properties of the prepared transparent La ₂ Hf ₂ O ₇ ceramics are as follows:

Density (g/cm ³ ) ＞7.8

Crystal phase (X diffraction analysis) La ₂ Hf ₂ O ₇

Porosity (%) ＜0.1

380-780nm band maximum transmittance (%) ＞70

Example 5

The powder synthesized by combustion of 0.02 mol of HfO(NO ₃ ) ₂ and La(NO ₃ ) ₃ and 0.013 mol of ethylenediaminetetraacetic acid (EDTA) was calcined at 1000°C for 2 hours to remove residual carbon and organic matter. After calcination, the La ₂ Hf ₂ O ₇ powder synthesized by combustion is first subjected to isoaxial pressing, and then isostatically pressed at 180 MPa. The products formed by isostatic pressing are kept in a hydrogen atmosphere at 1850°C for 6 hours.

The prepared transparent La ₂ Hf ₂ O ₇ ceramics have good light transmittance, and the properties are as follows:

Density (g/cm ³ ) ＞7.8

Crystal phase (X diffraction analysis) La ₂ Hf ₂ O ₇

Porosity (%) ＜0.1

380-780nm band maximum transmittance (%) ＞40

From the analysis of SEM fracture morphology (Fig. 4(b)), it can be seen that the grain size distribution of La ₂ Hf ₂ O ₇ ceramics is uniform, and the grain size is ~4 μm, but the grains are closely arranged, and the grain boundaries are very thin. No pores were observed under the electron microscope, resulting in a transparent material.

Example 6

The powder prepared by combustion reaction of 0.02 mole of HfO(NO ₃ ) ₂ , 0.0198 mole of La(NO ₃ ) ₃ , 0.0002 mole of Eu(NO ₃ ) ₃ and 0.054 mole of glycine was calcined at 800°C for 2 hours to remove residual carbon and organic matter. After calcination, the La ₂ Hf ₂ O ₇ powder synthesized by combustion is first subjected to isoaxial pressing, and then isostatically pressed at 180 MPa. The products formed by isostatic pressing are kept in a hydrogen atmosphere at 1900°C for 6 hours. The prepared transparent La ₂ Hf ₂ O ₇ :1% Eu ceramics has a maximum transmittance in the 380-780nm band of >40%. The transmittance curve and fluorescence spectrum are shown in FIG. 5 .

Example 7

The powder prepared by combustion reaction of 0.02 mole of HfO(NO ₃ ) ₂ , 0.0198 mole of La(NO ₃ ) ₃ , 0.0002 mole of Tb(NO ₃ ) ₃ and 0.054 mole of glycine was calcined at 800°C for 2 hours to remove residual carbon and organic matter. Others are the same as embodiment 3. The prepared transparent La ₂ Hf ₂ O ₇ :1% Tb ceramic has a maximum transmittance in the 380-780nm band > 40%. The transmittance curve and fluorescence spectrum are shown in FIG. 6 .

Example 8

The powder prepared by combustion reaction of 0.02 mole of HfO(NO ₃ ) ₂ , 0.0198 mole of La(NO ₃ ) ₃ , 0.0002 mole of Tm(NO ₃ ) ₃ and 0.054 mole of glycine was calcined at 800°C for 2 hours to remove residual carbon and organic matter. Others are the same as embodiment 3. The prepared transparent La ₂ Hf ₂ O ₇ :1% Tm ceramic has a maximum transmittance in the 380-780nm band > 40%. The transmittance curve and fluorescence spectrum are shown in FIG. 7 .

Example 9

The powder prepared by combustion reaction of 0.02 mole of HfO(NO ₃ ) ₂ , 0.0198 mole of La(NO ₃ ) ₃ , 0.0002 mole of Ce(NO ₃ ) ₃ and 0.054 mole of glycine was calcined at 800°C for 2 hours to remove residual carbon and organic matter. Others are the same as embodiment 3. The maximum transmittance in the 380-780nm band of the prepared transparent La ₂ Hf ₂ O ₇ :1% Ce ceramics is >40%. The transmittance curve and fluorescence spectrum are shown in FIG. 8 .

Example 10

The powder prepared by combustion reaction of 0.02 mole of HfO(NO ₃ ) ₂ , 0.0197 mole of La(NO ₃ ) ₃ , 0.0003 mole of Pr(NO ₃ ) ₃ and 0.054 mole of glycine was calcined at 800°C for 2 hours to remove residual carbon and organic matter. Others are the same as embodiment 3. The prepared transparent La ₂ Hf ₂ O ₇ :1.5% Pr ceramic has a maximum transmittance in the 380-780nm band >40%. The transmittance curve and fluorescence spectrum are shown in FIG. 9 .

Claims (6)

1. A lanthanum hafnate ceramic-based transparent ceramic, characterized in that the ceramic composition is La _2-2x RE _2x Hf ₂ O ₇ ; 0≤x<0.1, RE is Ce, Pr, Eu, Tm, Nd, Yb, Tb and other rare earth ions. 2. The preparation method of a lanthanum hafnate ceramic-based transparent ceramic according to claim 1, wherein the La ₂ Hf ₂ O ₇ powder with a particle size of 10-100 nanometers synthesized by combustion is heat-treated and formed and sintering process. 3. According to the preparation method of a lanthanum hafnate ceramic-based transparent ceramic according to claim 2, it is characterized in that the forming process can adopt dry pressing or isostatic pressing procedure. 4. The preparation method of a lanthanum hafnate ceramic-based transparent ceramic according to claim 2, characterized in that the sintering process can be sintering under vacuum or hydrogen, hot isostatic pressing or hot pressing. 5. The preparation method of a lanthanum hafnate ceramic-based transparent ceramic according to claim 2, characterized in that the sintering condition is 1500-2000°C for 4-10 hours, followed by furnace cooling. 6. The preparation method of a lanthanum hafnate ceramic-based transparent ceramic according to claim 2, wherein the powder used is the use of organic fuels such as glycine, ethylenediaminetetraacetic acid (EDTA) and La(NO ₃ ) _3. HfO(NO ₃ ) ₂ , RE(NO ₃ ) ₃ combustion synthesized powder with a particle size of 10-100 nanometers.

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