Sintering of the Cold Isostatic Pressed (CIP) Alumina Ceramics
Using a Submillimeter
Waves Gyrotron
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K. 'Sako, S. Tani, K. Kuwayama,
S. Mitsudo,T.
Idehara!"#$,R. Ito,
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Research Center for Development of Far Infrared Region, University of Fukui, 3-9-1 Bunkyo 910-0017, Fukui, Japan910-0017
3-9-1
E-mail : sudiana75@yahoo.com

Due to obtain better characteristics of alumina ceramics we have investigated submillimeter waves sintering
effect to alumina. Sintering was done by using a submillimeter waves (SMMW) gyrotron. Alumina samples
were pressed by using cold isostatic pressing before sintering. Density of sintered samples were measured
by using Archimedes method. The densification of SMMW sintered samples then compared to samples
sintered by millimeter waves (MMW) from previous results. The CIP treated samples sintered by SMMW
show a higher densification than MMW ones. In other hand the samples without CIP treatment show thatthe samples sintered by SMMW have a lower densification than MM ones. To explain the results, amicrostructure evaluation using SEM was performed.

1. Introduction
Frequency of electromagnetic radiation is
one of the main roles for determining material
properties after heating[1-3]. To investigate
effect of highly frequency waves to alumina
properties, a high purity alumina was preparedand sintered. Alumina samples sintered bymillimeter waves (MMW) for samples without
and with CIP treatment show a significant
difference both on their density and hardness[1]. Preliminary research using alumina
ceramics without CIP treated samples reported
that densification of samples alumina sinteredusing MMW is higher than sintered by using
submillimeter waves (SMMW)[2]. In this study,
densification ofthe CIP treated alumina
sintered by using SMMW are reported.
2. Experiment
The raw material for the experiment was anα alumina powder (AES-11C; Sumitomo
Chemical Co. Ltd., 99.8 % purity, 400 nm inaverage particle size, and 7-8 m2/g of specificsurface area) as a starting samples. Powder
compacts were prepared by slip casting method.
Ammonium salt of poly(methacrylic) acid (NH4+-PMAA; Aron A6114, Molecular Weight 6000,
Toagousei Co. Ltd., Japan) is added into theslurry to prevent agglomeration of suspended
aluminaparticles.
Toremovehard
agglomerates prior to compaction, the powders
were ball mixed in an alumina jar for 22 hours.
A cylindrical samples of 20 mm x 5 mm wereobtained then followed by cold isostaticpressing (CIP) at 150 MPa. Pre sintering wasdone for all samples by heating at 600 0C inelectric furnace (FUA-112DB; Johnson Scie.
Equipment Corp.) after dried at roomtemperature about 12 hours in air. After presintering, samples then sintered by using asubmillimeterwaves
gyrotronmaterial
processing system (SMMW-MPS) in ResearchCenter for Development of Far Infrared Region,
University of Fukui, Japan. The SMMW-MPS
are consisted of a 300 GHz, 3.5 kW, CW
gyrotron. The whole system is shown in fig.1.

PFig. 1 Whole system of submillimeter wave
gyrotron material processing system
The sintering was done starting from final
temperature 1100 oC to 1700 oC. After reaching
final temperature, the temperature was kept
about 20 minutes. Densities of the finalsintered samples were measured by using theArchimedes method. To characterized themicrostructure of samples a scanning electron
microscope(SEM) (Hitachi S-2600HS, Hitachi
High Tech. Corp., Japan ) was performed.
Before SEM, the specimens are coated with Pt
using ion sputtering Hitachi C-1030.

3. Result and Discussion
Density dependence to final sintering
temperature was evaluated and plotted. The
density of CIP treatment samples sintered by
MMW from previous result in [1] are alsoplotted in the graph as shown in fig. 2. Thegraph shows that samples with submillimeterwaves heating have a better densification thanmillimeter waves ones. The highest relative
density achieved for SMMW heating is about
99.1 % of theoretical density (TD). From that
result we can conclude that for CIP samples thesubmillimeter waves heating is more effective
for densification than millimeter waves ones.

Fig. 3 SEM photograph of CIP treated alumina
green sample ( D=58.2 % TD).

Fig. 4 SEM photograph of not CIP treated alumina
green sample ( D=55.5 % TD)

Fig. 2 Relative density of CIP alumina sintered bymillimeter and submillimeter waves
This is agreed to previous results by Sano,et al.
on [1], that CIP alumina sintered by 83 GHz
showing a significant higher densities andbending strengths than that sintered by thelower frequency, 30 GHz. To understanding theresults a microstructure evaluation for thegreen samples after pre sintering was done.
The relative density of green alumina sample
for the CIP treated samples is 58.2 %, with thedensity difference to without CIP green sample
is 2.7% of theoretical density. The differences of
microstructure of CIP and without CIP treatedgreen samples may be the one reason that thesubmillimeter waves heating have better
densification than millimeter ones for CIP
treated ones as shown in fig. 3 and 4.

4. Conclusion
Densification of CIP treated alumina sinteredby submillimeter waves shown higher
densification than millimeter ones. The
differences of microstructures of the green
samples as shown on SEM photograph results
may be the one reason of that densification
behavior.
References[1] S. Sano, et al., J. Materials Science Letters, 19,(2000), 2247 – 2250.
[2] S. Mitsudo, et al., FIR Center Report-105, (2010).
[3] Y. Makino, et al., J. Advances in Microwave &Radio Frequency Processing,8, (2006),570–576.