Reaction binding

Reaction bonding is a material-specific process from the field of ceramic materials in which a metal reacts with a gas. All of these reactions are exothermic in nature, releasing energy. The best known is reaction- bonded silicon nitride ( RBSN ), in which the metallic silicon forms the corresponding nitride with a nitrogen atmosphere (pure nitrogen or ammonium compounds can be used). RBSN is a purely synthetic material that does not occur naturally in the earth's crust.

Further representatives of this process are reaction- bound silicon carbide (RSiC), reaction- bound aluminum oxide RBAO, reaction-bound mullite RBM, reaction- bound magnesium oxide (RBMO), etc. All of these reaction products are of particularly high chemical purity.

The increase in volume during the thermal reaction is characteristic of the reaction bonding, whereby the sintering shrinkage can be partially compensated. Due to the exothermicity during production, only small-format components can be bound by reactions. In the case of larger dimensions, the thermal stresses are then too great if the temperature is improperly controlled and lead to the formation of cracks in the sintered body. To avoid this, only low heating rates (approx. 0.5 - 1 K / min) are possible, which is typical and characteristic of reaction binding.

The areas of application range from technical ceramics to use as a refractory material.

The RBAO procedure

RBAO is the abbreviation for R eAction B onded A luminum O xide (reaction-bonded alumina). The forerunner of this process was the direct melt oxidation (DMO process: direct melting oxidation). A porous body is infiltrated with a metal melt and then oxidized. With the RBAO, the metal aluminum and aluminum oxide are crushed in suitable mills to grain sizes in the 1 µm range. Alcohols or oils are used as grinding liquids in order to avoid premature oxidation of the metal phase. After the batch has dried, the bodies are ideally isostatically pressed, oxidized and sintered at up to 1600 ° C. The flexural strength is slightly higher than that of classic corundum ceramics due to the fine-grain structure.

The modification RBM

Reaction-bound mullite (RBM) is a further modification of the RBAO process, in which aluminum and additionally silicon, or silicon carbide, or zircon (zirconium silicate) and corundum are used as raw materials. When using SiC, it is possible to produce a "zero shrinkage ceramic"; the sintering shrinkage is compensated for by the oxidation of the SiC and the associated increase in volume. Attention must be paid to complete oxidation of the SiC (small grain sizes, intensive processing, temperature control, etc.), otherwise a residual proportion of SiC remains, which can have a strength-reducing effect.

Individual evidence

↑ Holz, D .: "Production and characterization of reaction-bound Al2O3 ceramics (RBAO - process) using the example of the system Al2O3 / ZrO2, dissertation 1994, TUHH. VDI Verlag Düsseldorf (progress reports VDI: series 5, basic and materials; 367)
↑ Holz, D .; Röger, M .: "Mechanical Properties of Reaction-Bonded Al2O3 / ZrO2 Composites", Ceram. Closely. Sci. Proc. Vol 15, No. 5 (1994) 651-658.
↑ Scheppokat, S .: "Reaction-bound mullite with zero shrinkage based on the precursor system Al / Al2O3 / SiC", dissertation 1999, TUHH. VDI Verlag Düsseldorf, (progress reports VDI: series 5, basic and materials; 552).
↑ Holz, D .: "Production and characterization of reaction-bound Al2O3 ceramics (RBAO - process) using the example of the system Al2O3 / ZrO2, dissertation 1994, TUHH. VDI Verlag Düsseldorf (progress reports VDI: series 5, basic and materials; 367).

swell

Klaus Irrgang: Temperature measurement practice with resistance thermometers and thermocouples , Vulkan-Verlag, Essen
W. Bergmann: Werkstofftechnik , Carl-Hanser-Verlag, Munich 1987, ISBN 3446141286
DE Garcia, J. Wendorff: "Fast firing of reaction-bonded aluminum oxide RBAO composites" in Journal of Materials Science (Volume 30, Issue 20, pp 5121-5124) January 1995

[1] Holz, D .: "Production and characterization of reaction-bound Al2O3 ceramics (RBAO - process) using the example of the system Al2O3 / ZrO2, dissertation 1994, TUHH. VDI Verlag Düsseldorf (progress reports VDI: series 5, basic and materials; 367)

[2] Holz, D .; Röger, M .: "Mechanical Properties of Reaction-Bonded Al2O3 / ZrO2 Composites", Ceram. Closely. Sci. Proc. Vol 15, No. 5 (1994) 651-658.

[3] Scheppokat, S .: "Reaction-bound mullite with zero shrinkage based on the precursor system Al / Al2O3 / SiC", dissertation 1999, TUHH. VDI Verlag Düsseldorf, (progress reports VDI: series 5, basic and materials; 552).

[4] Holz, D .: "Production and characterization of reaction-bound Al2O3 ceramics (RBAO - process) using the example of the system Al2O3 / ZrO2, dissertation 1994, TUHH. VDI Verlag Düsseldorf (progress reports VDI: series 5, basic and materials; 367).