25,,, Microwave Sintering of Electronic Ceramics Hideoki Fukushima, Goro Watanabe, Hiroyuki Mori, Masao Matsui ZnO PZT ZnO PZT Microwave heating offers advantages over conventional technologies such as rapid heating, internal heating and preferential heating. Microwave sintering of ceramics was performed using the heating control system and single mode cavity developed for this study. This study investigates the feasibility of the microwave sintering for electronic ceramics, e.g. ZnO varistors and PZT, in terms of densification, microstructure, mechanical and electric properties. ZnO varistors sintered by microwaves indicated higher nonlineality factors than those sintered by a conventional process using an electric furnace. PZT obtained by microwave sintering had a high strength due to its high density and small grain size compared with that obtained by conventional sintering. Furthermore, since the sintering reaction of PZT ceramics was accelerated by microwave radiation, they also had high electric properties. Thus, the microwave sintering is characterized by a low sintering temperature and a short soaking time and can be expected to sinter ceramics with both high strength and high electric properties. ZnO PZT 1980 R&D Vol. 30 No. 4 ( 1995. 12 )
26 ZnO PZT ( ) ( ) P P = 1 (1) 2 ε 0ε"ω E 2 Vs ε 0 ε" ( =ε r tanδ ) ( ε r : tanδ : ) ω EV s ε" ε" ε" ε" 1800 C 100 ε" 2 ( ) ( ) ( ) 2.45GHz Temperature dependence of dielectric loss factor of 92% alumina measured at 6GHz. R&D Vol. 30 No. 4 ( 1995. 12 )
27 6GHz 10 C 90% Al 2 O 3 AlN TiO 2 ZrO 2 ZnO PZT PLZT BaTiO 3 8 φ 6.6mm ( 300 C/min ) 5min Single mode rectangular cavity for microwave sintering. 6GHz 40W N 2 ZnO ZrO 2 Al 2 O 3 TiO 2 90% AlN AlN Y 2 O 3 AlN PZT BaTiO 3 PZT ZnO 620 C 840 C Major properties and chemical compositions of ceramic powder. Theoretical Powder Chemical composition Powder density size g/cm 3 wt% mm Al 2 O 3 3.99 0.2 > 99.99% AlN 3.26 1.8 N : 33.4%, O : 1.78% TiO 2 4.25 1 2 > 99.9% ZrO 2 * 5.90 0.3 Y 2 O 3 : 13.67% ZnO 5.78 <1.0 > 99.9% PZT 8.0 1 Pb(Nb 2/3 Ni 1/3 )O 3 Pb(Zr 0.33 Ti 0.67 )O 3 PLZT 7.8 1 2 Pb 0.92 La 0.08 (Zr 0.65 Ti 0.35 )O 3 BaTiO 3 6.0 1.1 > 99.7% * Stabilized zirconia Density of several ceramics after microwave sintering for 5min at 6GHz. R&D Vol. 30 No. 4 ( 1995. 12 )
28 1180 C 97% 1320 C ZnO 5 95% ZnO ZnO ( Bi 2 O 3 Co 2 O 3 MnO 2 Sb 2 O 3 Cr 2 O 3 ) ( φ 9 7mm ) α ZnO α ZnO Properties of ZnO varistors sintered by microwave and conventional process. Relation between temperature and density of ZnO sintered by microwave for 5min. Sintering Density Grain Breakdown Noncondition g/cm 3 µm V/mm α size voltage linearity Microwave 1150 C 5min 5.59 1 5 521 34 1150 C 10min 5.62 1 5 503 38 1350 C 5min 5.63 5 10 294 27 Conventional 1150 C 1h 5.67 5 10 300 22 1350 C 1h 5.62 5 15 54 4 (a) Microwave sintering for 5min (b) Conventional sintering for 1h Microstructure of ZnO varistors sintered at 1150 C. R&D Vol. 30 No. 4 ( 1995. 12 )
29 Co 2 O 3 MnO 2 ZnO ε" Sb 2 O 3 Sb 2 O 3 Co 2 O 3 MnO 2 PZT PZT SiC SiC SiC SiC PZT PZT PZT SiC PZT PZT SiC 2.45GHz ( SiC ) ( ) ( ) PZT φ16mmpzt PZT Single mode cavity and PZT sample covered with a couple of SiC. Dielectric properties of ceramic powders measured at 6GHz. PZT pellets sintered by microwave radiation of 2.45GHz. R&D Vol. 30 No. 4 ( 1995. 12 )
30 PZT PbTiO 3 -PbZrO 3 -Pb(Ni 1/3 Nb 2/3 )O 3 ( 0.16µm ) φ18mm CIP ( 170 C/min ) 5 20min PbO 300 C/h 4h X PZT 850 C 5min7.9g/cm 3 900 C 8.2g/cm 3 1100 C 5min 0.3%PbO 1000 C 1µm 1000 C 1.5µm 1100 C SEM Temperature dependence of density and evaporation loss for PZT ceramics. (a) Microwave sintering for 5min (b) Conventional sintering for 4h Microstructure of chemically etched surfaces of PZT sintered at 1000 C. R&D Vol. 30 No. 4 ( 1995. 12 )
31 X 900 C 5min 1050 C (002),(200) (103),(301) 950 C 4h 1200 C φ13mm 0.5mm kp ε r kp 1000 C 950 C kp ε r X-ray diffraction patterns of PZT after (a) microwave sintering for 5min and (b) conventional sintering for 4h. Average grain sizes of PZT sintered by microwave and conventional process. Sintering temperature dependence of electromechanical coupling factor Kp and dielectric constant ε r. R&D Vol. 30 No. 4 ( 1995. 12 )
32 ε r PZT ε r ( c/a ) X ε r 5µm ε ε r 1.5µm c/a 1µm c/a c/a ε r c/a 15% kp ε r Grain size dependence of bending strength of sintered PZT. Grain size dependence of dielectric constant ε r and crystal tetragonality (c/a). Relation between bending strength and displacement induced on electric field in PZT pellets. R&D Vol. 30 No. 4 ( 1995. 12 )
33 30% PZT MRS Am. Ceram. Soc. 1987 Microwave Processing Symposium 1) Sutton, W. H. : MRS Bulletin, 11(1993), 12 2),, (1994), 124, NTS 3) Metaxas, A. C. and Meredith, R. J. : Industrial of microwave heating, (1983), 54, 70, Peter Peregrinus, London 4),, :, -5 (1987), 743 5),,, :, -2(1988), 305 6) Fukushima, H., et al. : J. Mat. Res., -2(1990), 397 7),, :, - 1(1992), 75 8) Fukushima, H., et al. : Trans. Mat. Res. Soc. Jpn., (1994), 759 9),, :, (1992) 10),,, :, (1994), 435-6 11) Harmer, M. P. and Brook, R. J. : J. Brit. Ceram. Soc., (1981), 147 12), : (1994), 437 13) Toraya, H. : J. Appl. Cryst., (1986), 440 14) Clark, D. E., et al., eds. : Microwaves; Theory and Application in Material Processing, Ceramic Transactions, (1991) 15) Beatty, R. L., et al., eds. : Microwave Processing of Materials III, MRS Symp. Proc., (1992) Relation between bending strength and electric properties of sintered PZT. R&D Vol. 30 No. 4 ( 1995. 12 )
34 1955 1989 1957 1967 1942 1 1989 R&D Vol. 30 No. 4 ( 1995. 12 )