Ceramic Selection

The Right Ceramic for Your Particular Application

If you need hermetic seals for specific applications, the technical information, guidelines and tips throughout the next several pages will help you select seal designs that are most efficient and competitively-priced. These data have been derived from the experiences of Specialty Seal Group engineering and production staff over more than 50 years of service to customers in a wide variety of industries.

After you have worked with us to establish the parameters for your seals, Specialty Seal Group’s state-of-the art capabilities in CAD design, CNC machining, sealing technology, mass spectrometer leak testing, and plating finishes will yield accurate, cost-effective results.

Typical Parameters of Ceramics in SSG Seals


  #9095  #9297 
Tensile Strength PSI   18,500  28,500
Compression Strength PSI  280,000  350,000
Modulus of Elasticity PSI
 42.45 x 106 46.09 x 106 
Flexural Strength PSI 46,500 49,500
Impact Resistance, Charpy
6.5-6.8 7.0-7.6
Specific Gravity, Bulk
3.58 3.72
Thermal Conductivity - cal/cm2/cm/25°C
Hardness, MOHS Scale
9 +
9 +
Water Absorption
0 0
Porosity, Helium Mass Spectrometer
Vacuum Tight
Vacuum Tight
Firing Temperature °C
Coefficient of Thermal Expansion > 25-700°C, cm/cm/°C
7.8 x 106
7.9 x 106


Dielectric Strength V/mil  1/4" Thick 220  230
Dielectric Constant  106
9.25  9.60
K @25°C
 108 9.25 9.60

9.15 9.36
Dielectric Loss Factor 25°C 105 .0007 <.0001

 106 .0006 .0005




Volume Resistivity Ohms/cm3
6.00 x 1013
2.00 x 1014

 6.00 x 1010
 1.2 x 1010 

Typical Composition


Composition, Alumina Content, Nominally  AL203 - 92% AL203 - 92%

 Si02 - Balance  Si02 - Balance

 Mg0 - Balance Mg0 - Balance 

Ca0 - Balance Ca0 - Balance
    Cr203 - Balance

NOTE: All data tests completed to ASTM standards. Results are average for specimen tested and should be - but are not guaranteed to be - applicable to parts made of the material.

Cost vs. Alumina Content

As a rule, ceramic cost increases as the purity of raw Al2O3 increases. Specialty Seal Group excels at providing the strongest ceramic-to-metal seals and metallized ceramics with the lowest cost per alumina content possible.

Typically, 92-96% of Al2O3 ceramics prepared with Specialty Seal Group’s proprietary metallization process provide high performance where reliability and strength are critical. In addition, Specialty Seal Group ceramics promote increased thermal conductivity, chemical resistance and dielectric strength. H2SO4 and HCl, for examples, will not attack a ceramic, eliminating the probability of corrosion in a number of applications.

Those factors, along with alumina’s high temperature tolerance and high compressive strengths, make it the ceramic material of choice.