Why a Coffee Carafe Should Not Be Used in Cryogenic Applications
Philip Bennewirtz 1 * and Michal Meissner 2 1 KGW-Isotherm GmbH , 76185 Karlsruhe , Germany 2 FEI Company , 627 00 Brno , Czech Republic
*
p.bennewirtz@
kgw-isotherm.de
Abstract: Proper procedures for various types of liquid nitrogen Dewars are described. To ensure the safety of employees, only components made for cryogenic applications should be used. The functionality and condition of these components should be regularly monitored. Damaged components must be replaced immediately. None of the Dewar manufacturers or electron microscope manufacturers can guarantee the personal safety and proper functionality of their devices if coffee carafes or consumer beverage fl asks are used or if appropriate Dewars are used incorrectly.
Introduction
On the Internet we recently become aware of an article [ 1 ] in which coffee carafes were touted as a cheap and safe alternative to store liquid gases instead of conventional Dewar flasks. Because that article points out the “improvement of workplace safety” in the article title, we would like to outline a few important details that one should consider when choosing or buying a cryogenic vessel.
Glass Liquid Nitrogen Vessels
Coffee servers have the same basic functionality as Dewar flasks. They isolate the inserted liquid from the ambient temperature as long and as well as possible to maintain a stable temperature. Coffee carafes are produced, as the name suggests, for coffee, tea, or other hot or cold beverages. The materials used in the production of a coffeepot must be suitable for their use, a temperature range from −20°C to +100°C. A Dewar flask for laboratory use must resist the temperatures of extremely hot fluids up to +200°C as well as extremely cold fluids such as liquid nitrogen, as cold as −196°C. Dewar flasks dedicated for cryogenic applications are manufactured according to the accepted standards, for example, German DIN standard 12492, US ASTM E1379-90, or in the near future DIN EN ISO 16496. Such documents are setting high standards in the quality of materials and their processing. Unlike a coffee carafe, the specified minimum wall thickness for a Dewar flask must be precisely adhered to because of the high thermal loads. In addition, all Dewar vessels should be pressure-calculated and made from high-quality materials like borosilicate 3.3 glass according to DIN/ISO 3585, which is a typical material used for Dewar manufacturing ( Figure 1 ).
In the case that a coffee carafe is made of glass, they usually use the so-called soft glass, that is, glass with a high thermal expansion coefficient. Similar to metals, different glass types should be used depending on the expected application field.
Stainless Steel Liquid Nitrogen Vessels Besides vacuum-insulated glass Dewar fl asks, there are also vacuum-insulated cryogenic vessels made of stainless
30
Figure 1 : Cryogenic LN 2 Dewar. A Dewar dedicated for cryogenic applica- tions and manufactured from high-quality materials according to the relevant standards is recommended for use with transmission electron microscopes. Note the polystyrene cap that was placed on the top of the Dewar fl ask.
steel or aluminium, common in the cryogenics industry. In Europe, these fl asks or containers have to be manufactured according to the “Directive on Pressure equipment 97/23/EG” or be manufactured according to the AD data sheets (AD data sheets are Codes of Practice on Pressure Vessels). For the manufacture of these fl asks or containers, only appropriate standard materials, designated for use in this extreme temper- ature range, can be used. T erefore, proper attention should be paid when choosing the equipment for any cryogenic application.
doi: 10.1017/S1551929515001145
www.microscopy-today.com • 2016 January
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68