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Thermiculite® 870

Thermiculite® 870 is a high temperature sealing material designed for low stress sealing in solid oxide fuel cells. It is based on the mineral vermiculite and contains no organic components.


Thermiculite® 870 is specifically designed for use in solid oxide fuel cells (SOFC) and solid oxide electrolysers (SOE) and has a high degree of compression combined with good sealing under low applied surface stresses.

Thermiculite® 870 contains only two minerals, vermiculite and steatite. There are no organic materials or other elements (such as phosphorous or sulphur) that would contaminate SOFC or SOE cell chemistry.

Gasket Test Data:

For some SOFC designs a softer, more compressible sealing material is required. TH870 is significantly more compressible under low loads, e.g. 1MPa. TH870 is around ten times more compressible than TH866.
Figure 1 (below) shows load vs defection for TH870 compared to TH866.

At a stress of 1 MPa TH870 compresses 0.22mm whereas TH866 gasket only compresses 0.02mm under the same load.


Thermiculite® 870 is available in sheet form:
Standard sheet size: 450mm x 350mm
Standard thicknesses: 0.5mm, 0.7mm and 1.0mm*

*Please note that these nominal thicknesses are provided as a guide. As the material is very soft the measured thicknesses may differ slightly due to compression during measurement.

Special thicknesses between 0.3mm and 1.0mm are available on request.

Flexitallic can provide a gasket cutting service, ideally a .dxf file of the gasket shape would be provided by the customer.

Flexitallic will review the dimensions and design and advise if cutting is feasible and provide a quote.
Sample material available on request.

Health & Safety

For further Health and Safety information please see the relevant Material Safety Datasheets or contact Flexitallic UK Ltd.
Thermiculite® 870 also seals at least as effectively as TH866, but at much lower applied loads. This is the case at ambient and elevated temperatures. Figure 2 (below) shows an 80 hour leakage test at ambient temperature.

Table 1 

shows the effect of gasket thickness on leak rate for TH870 gaskets. It is recommended that the thinnest material is chosen after taking account of other requirements e.g. flange surface imperfections, spacing requirements between cells or for the gasket to compensate for tolerances throughout the stack.

TABLE 1. Leak Rate Variation with Gasket Thickness.
(700°C, 1 MPa Gasket Stress, He Test Pressure 100 mbar)
TH870 Thickness
Leak rate after 100 hours
Table 2

shows the leak rate of TH870 at elevated temperature at three different gasket stresses. For a given temperature the leakage rate reduces as gasket stress is increased. A representative 120 hour leakage plot is shown in figure 3 (on the following page).

A representative 120 hour leakage plot is shown in figure 3

TABLE 2. TH870 Leak Rate Variation with Gasket Stress and Temperature.
(0.7mm Gasket Thickness, He Test Pressure 100 mbar)
Leak Rate (ml/min/m)

1 MPa
3 MPa
5 MPa