Sealing and External Sterilization of a Sample Container
- Tuesday, 25 November 2008
This method would enable safe transport of a biologically hazardous sample.
A method of (1) sealing a sample of material acquired in a possibly biologically contaminated (“dirty”) environment into a hermetic container, (2) sterilizing the outer surface of the container, then (3) delivering the sealed container to a clean environment has been proposed. This method incorporates the method reported in “Separation and Sealing of a Sample Container Using Brazing” (NPO-41024), NASA Tech Briefs, Vol. 31, No. 8 (August 2007), page 42. Like the previously reported method, the method now proposed was originally intended to be used to return samples from Mars to Earth, but could also be used on Earth to transport material samples acquired in environments that contain biological hazards and/or, in some cases, chemical hazards.
To recapitulate from the cited prior article: the process described therein is denoted “S3B” (separation, seaming, and sealing using brazing) because sealing of the sample into the hermetic container, separating the container from the dirty environment, and bringing the container with a clean outer surface into the clean environment are all accomplished simultaneously with an inductive-heating brazing operation. At the beginning of the process, the sample container is the inner part of a double-wall container, and the inner and outer parts of the double- wall container are bonded together at a flange/braze joint at the top. By virtue of this configuration, the inside of the sample container is exposed to the dirty environment while the outer surface of the sample container is isolated from the dirty environment.
During the S3B process, a lid that is part of a barrier assembly between the dirty and clean environments becomes brazed onto the sample container, and the sample container with the lid attached becomes separated from the outer part of the double-wall container and is pushed into the clean environment. The brazing material is chosen to have a sufficiently high melting temperature (typically >500 °C) so that the brazing process sterilizes the outer surface of the lid/wall seam region of the newly created hermetic container. The outer surface of the inner container is covered with a layer of thermal-insulation material to prevent heat damage of the sample during brazing. Alternatively, in an application in which there is no concern about biological contamination, it could be feasible to substitute a lower-melting-temperature solder for the brazing material.
The method now proposed goes beyond what was reported previously by providing for container-design modifications and additional process steps to ensure cleanliness and delivery of a hermetically enclosed dirty sample to a clean environment. Implementation of the proposed method in the original intended Mars-to-Earth application would entail the use of dedicated machinery in a multistep augmented version of the previously reported S3B process that would result in sealing of the sample in a magazine and (see figure) and placement of the magazine in the nose cone of a spacecraft. Modified versions of the machinery and process, without provision for placement in a nose cone, could be devised for terrestrial applications. One feature of the outer-space process that might be useful in some terrestrial applications would be coating the outer surface of the magazine with a pyrotechnic paint, which would be ignited to insure sterilization before releasing the magazine into the clean environment.
The method as now proposed also provides additional options to choose materials and process conditions to suit specific applications. These options include the following:
- The sample container and the lid could be made of a nonmetallic material, in which case a mixture of plastic and metallic particles could serve as an appropriate lower-melting-temperature alternative to a brazing material. The metallic particles would render the mixture amenable to inductive heating, so that the plastic component could be melted to make or break a seal.
- During brazing or during the cool-down after brazing, expansion or contraction, respectively, of the gas inside the sample container could push the brazing material away from the desired braze joint. One way to limit expansion and contraction to a harmlessly low level would be to line the inside of the sample container with a thermally insulating material.
- Instead of trying to limit the aforementioned expansion and contraction, one could fabricate the sample container with a small breathing hole to accommodate the expansion and contraction. The hole would be sealed in a small, localized brazing operation after the main S3B brazing operation.
This work was done by Yoseph Bar-Cohen, Mircea Badescu, Xiaoqi Bao, Stewart Sherrit, and Ayoola Olorunsola of Caltech for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
Refer to NPO-45610, volume and number of this NASA Tech Briefs issue, and the page number.