SILICON CARBIDE JOINING. FINAL TOPICAL REPORT

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Future energy systems will be required to fire lower-grade fuels and meet higher energy conversion efficiencies than today's systems. The steam cycle used at present is limited to a maximum temperature of 550 C because above that, the stainless steel tubes deform and corrode excessively. To boost efficiency significantly, much higher working fluid temperatures are required. Although high-temperature alloys will suffice for the construction of these components in the near term, the greatest efficiency increases can be reached only with the use of advanced structural ceramics such as silicon carbide (SiC). However, SiC does not melt, but instead sublimes at ... continued below

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6 pages

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Creator: Unknown. October 1, 1998.

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Description

Future energy systems will be required to fire lower-grade fuels and meet higher energy conversion efficiencies than today's systems. The steam cycle used at present is limited to a maximum temperature of 550 C because above that, the stainless steel tubes deform and corrode excessively. To boost efficiency significantly, much higher working fluid temperatures are required. Although high-temperature alloys will suffice for the construction of these components in the near term, the greatest efficiency increases can be reached only with the use of advanced structural ceramics such as silicon carbide (SiC). However, SiC does not melt, but instead sublimes at temperatures over 2000 C. Therefore, it is not possible to join pieces of it through welding, and most brazing compounds have much lower melting points, so the joints lose strength at temperatures much lower than the maximum use temperature of the SiC. Since larger objects such as heat exchangers cannot be easily created from smaller ceramic pieces, the size of the SiC structures that can presently be manufactured are limited by the size of the sintering furnaces (approximately 10 feet for sintered alpha SiC). In addition, repair of the objects will require the use of field-joining techniques. Some success has been had by causing silicon and carbon to react at 1400--1500 C to form SiC in a joint (Rabin, 1995), but these joints contain continuous channels of unreacted silicon, which cause the joints to corrode and creep excessively at temperatures below 1260 C (Breder and Parten, 1996). The objective of this work conducted at the Energy & Environmental Research Center (EERC) is to develop a patentable technique for joining large SiC structures in the field. The key to developing a successful technique will be the use of reactive joining compounds to lower the joining temperature without leaving continuous channels of unreacted compounds that can weaken the joint at temperatures below 1260 C or serve as conduits for transport of corrodents. In addition, the method of heating the joint to cause the reaction bonding must be applicable to structures that are large in two dimensions, which precludes the use of furnaces for heating the samples. Special efforts will be made in this project to transfer the developed technologies to the materials industry via licensing agreements through the EERC Foundation.

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6 pages

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OSTI as DE00007938

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  • Other Information: PBD: 1 Oct 1998

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  • Report No.: DE--FC21-93MC30097--41
  • Grant Number: FC21-93MC30097
  • DOI: 10.2172/7938 | External Link
  • Office of Scientific & Technical Information Report Number: 7938
  • Archival Resource Key: ark:/67531/metadc738153

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • October 1, 1998

Added to The UNT Digital Library

  • Oct. 19, 2015, 7:39 p.m.

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  • April 15, 2016, 1:29 p.m.

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SILICON CARBIDE JOINING. FINAL TOPICAL REPORT, report, October 1, 1998; Morgantown, West Virginia. (digital.library.unt.edu/ark:/67531/metadc738153/: accessed November 17, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.