| Recently high transparent ceramic laser materials have received great attentionsince the quality of ceramic laser materials has been improved dramatically usingnano-crystal technology and non-press vacuum sintering method. High transparentpolycrystalline Nd:YAG ceramic is a promising material as a very good substitutecandinate to YAG single crystal for Nd:YAG ceramics are potential advancedstructural materials in view of their high creep and oxidation resistance at hightemperatures and theirsuitable heat conductivity. The study of Nd:YAG ceramics hasbeen extensively attented at present.The factor of effect on purified phase powder during the co-precipitation hasbeen discussed in the paper. The sintering technics and the properties of Nd:YAGceramics sintered by different doped MgO ratio's powders have been systemiclyinvestigated. The best ratio MgO and sintering technics have been obtained. Inexperiment, with the different concentration of ammonium hydrogen carbonate asprecipitant, with the different concentration of mixed solution of aluminum nitrateand yttrium nitrate as mother solution, with different dripping speed, under thedifferent temperatures, the different precursors were acquired. Then the precursorswere calcined at above 1100℃for 2h, and the different powders were gotten. Basedabove study and the optimization condition, aluminum nitrate and yttrium nitrateneodymium nitrate accroding to the ratio of Nd0.06Y3-0.06Al5O12(Nd-dopedconcentration is 2%) have been mixed as the mother solution. The different weightratio of 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt% MgSO4·7H2O be put into the mothersoltion as sintering additive. After the precursors have been calcined, one of the precipitates turned into the form of sintering additive MgO and the different ratios ofdoped MgO powders have been obtained. Many pellets with the dimension ofφ20mm×2mm were formed by isostatic pressing under 200MPa. Then these pelletswere sintered at 1800℃for 10 hours and 1780C for 20 hours, respectively, in avacuum-sintering furnace (Pressure=5.6×10-2 Pa). After that, these specimens weretreated by HIP at 1650℃for 2 hours under 200 MPa of argon gas pressure.The phase of these powders was mainly measured by means of XRD. At onetime, a part of precursors were qualitatively analyzed by FI-IR. The results show that,whether generating the major phase powder of YAG, the concentration of mixedsolution and precipitant solution are dominant factors. And environmentaltemperature and dripping speed effect on the phase purity of powder. The XRD andthe TG-DSC were used to analyze the phase and the transform temperature of YAG.The results show that the precursor has transformed into YAG phase at 900℃, but alittle Y2O3 phase. The precursor has completely transformed into YAG phase until1000℃. The appearance of pure phase powders with good dispersedness,non-agglomerate, size of narrow range with average size of 60 nm was observed byTEMMorphology of the surface and fracture of the specimens with 0.1wt%,0.2wt%, 0.3wt%, 0.4wt% different doped ratios MgO were observed by SEM.Therusluts show that the specimen with 0.2wt% MgO as sintering additive is the best inthem. There are nearly no pores in the cramics and impurity and the second phase inthe clearn grain boundaries aren't observed. The average grain size of Nd:YAGceramic is about 7μm. there are many large-size pores in Nd:YAG ceramic withoutsintering additive MgO. Many of them gather in the grain boundaries trijunction.The average grain size of the Nd:YAG ceramic is about 200μm. So it is especiallyimportant for making high-quality Nd:YAG ceramics to be added into appropriateMgO as sintering additive. Microstructure of ceramic and densification areconnected with the sintering temperature, holding time and the additives in thesintering process. If the temperature was too high, it is easy for grains to developabnormally and increase many pores in inner grains. It is extremely difficult for thepores to be eliminated from the Nd:YAG ceramic even though the one was treated by the HIP. Compared with sintering experiment, the results show that it is the bestcondition for sintering Nd:YAG ceramics at 1780℃for 20 hours. The opticaltransmittance of each specimen (Disk specimens ofφ15mm×1mm andmirror-polished on both surfaces) was measured over the wavelength region from400nm to 1200nm using an ultraviolet spectrophotometer (model SHIMADZUuv-2100). The maximum optical transmittance of the Nd:YAG ceramics is about50% in the infrared light wavelength region. However, the maximum opticaltransmittance of the specimens increases to 76% in the infrared light wavelengthregion after the specimen was treated by the HIP although a few pores in innergrains can be observed in the surface of the specimens.Generally speaking, some important results are obtained either in preparation ofnano-sized powder and sintering additive amount or sintering technics. Some of theresults are creative and useful, which can be a part of fabirication of high transparentceramic in future.
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