Rare earth garmet sintered compact

#This invention relates to a sintered compact of a polycrystalline rare earth garnet, which is used as a laser material such as YAG laser and an optical material such as a mirror and a prism, and a manufacturing method thereof. YAG is an abbreviation of yttrium aluminum garnet having a composition of Y3Al5O12.

#It was proposed to use a polycrystalline sintered compact such as YAG as an optical material for a scintillator. For example, Greskovich et al. (U.S. Pat. No. 5,013,696) disclosed presintering a rare earth oxide mold, which has the composition of 67 mol % Y2O3, 3 mol % Eu2O3, and 30 mol % Gd2O3, in a hydrogen atmosphere at 1625 deg C. for 4 hours followed by HIP (hot isostatic pressing) at 1650 deg C. for 1 hour in an Ar atmosphere of 170 MPa and finally, re-sintering at 1850 deg C. for 2 hours in a wet hydrogen atmosphere (U.S. Pat. No. 5,013,696).

#The rare earth oxide sintered compact obtained by presintering has a density ranging from 97% to 99% of a theoretical density and the sintered compact subjected to HIP becomes more compact to reduce the number of pores. The sintered compact subjected to HIP shows not prominent increase of an average crystallite diameter as reported in that the average crystal crystallite diameter after HIP ranges from 2 to 4 μm. Resintering increases the average crystallite diameter of the sintered compact to 25 or more micrometers and squeezes bubbles by using grain growth and clearness of the sintered compact increases. The sintered compact after resintering was reported as having the light loss coefficient of 2.93 cm−1.

#FIG. 1 is a figure a showing characteristic of an average crystallite diameter of a sintered compact prepared by subjecting a preliminary sintered compact to HIP processing at a temperature ranging from 1350 deg C. to 1850 deg C. for 5 hours in 147 MPa Ar.

#FIG. 2 is a figure a showing characteristic of an average crystallite diameter of a sintered compact prepared by subjecting a preliminary sintered compact to HIP processing at 1450 deg C. for 0.5 to 100 hours in 147 MPa Ar.

#FIG. 3 is a figure a showing characteristic of an average crystallite diameter of a sintered compact prepared by subjecting a preliminary sintered compact to HIP processing at 1800 deg C. for 0.5 to 100 hours in 147 MPa Ar.

#Material Powder

#Fifteen liter of 0.5 mol/liter high purity yttrium chloride aqueous solution is blended with 25 liter of 0.5 mol/liter high purity aluminum chloride aqueous solution to make a mixture solution of YAG composition. The mixture solution of YAG composition was dripped into 40 liter of 2 mol/liter ammonium hydrogen carbonate aqueous solution, of which an ammonium water was used for adjusting the pH to 8.2, in a rate of 1.5 liter/minute. At this time, both of the mixture solution of YAG composition and the ammonium hydrogen carbonate aqueous solution were kept at 32 deg C. A minimum value of pH during dripping was 7.0, and pH reached 7.95 being a constant value about 3 hours after dripping. Following dripping the mixture solution was cured at 32 deg C. for 48 hours and, then, filtration and washing were repeated 6 times resulting in yielding a YAG precursor. The obtained YAG precursor was subjected to burning at 1200 deg C. for 5 hours in air and pulverized to prepare a material powder. A BET area/weight ratio value of this powder was 14.6 m2/g and the average grain diameter (secondary grain diameter) measured by the laser scattering method was 0.22 μm. On the other hand, aggregated grains having diameter of 2 or larger μm were not observed.

#Molding