Vacuum Materials

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Vacuum Materials

 

materials used in vacuum equipment and instruments. The basic requirements of vacuum materials are a low vapor pressure at operating temperatures and the possibility of easy outgassing. In addition, vacuum materials for vacuum-instrument casings must have low gas permeability. Vapor pressure, gassing, and gas permeability are the primary features of vacuum materials that determine the upper limit of the attainable vacuum and the possibility of maintaining it over an extended period of time. Other requirements of vacuum materials are specified according to the type of application. For example, materials for vacuum tubes must have sufficient strength at high temperatures and be good insulators or, conversely, good conductors.

Table 1. Inorganic construction materials
 Temperature at vapor pressure of 1.3 MN/m2(10-5 mm Hg) (°C)Temperature coefficient of linear expansion in internal from ) 0° to 100°C (α × 107) (°C-1)Melting point (°C)
Metals   
Aluminum...............841238658
Copper...............9341651083
Iron...............10831191535
Molybdenum...............1955552625
Nickel...............8561331452
Palladium...............11571161554
Platinum...............1585901773.5
Silver...............751189960.5
Tantalum...............2402652996
Titanium (iodide)...............133681 (20°-200°C)1725
Tungsten...............2564443410
Zirconium (iodide)...............183654 (20°-200°C)1845
    
Alloys   
L-68 brass...............184938
Fernico (Covar)...............45-55 (20°-300°C)1450
Monel...............1371250
Nichrome...............1251400
    
Stainless steel   
1Kh18N9(Ela-1)...............1601400
1Kh18N9T (Ela-1T)...............1601450
    
Miscellaneous materials   
Electrographite...............21298-18 (linear)3800-3900
Fused quartz...............51700
Glass...............30-120
Mica (muscovite)...............301300
    
Ceramics   
Alumina...............46-70 (20°-100°C)2000
Magnesia...............70-80 (20°-100°C)1600

Vacuum materials are divided into the following basic groups: construction materials, getters (gas absorbers), vacuum oils, and materials used as pressure fluids for pumps and vacuum gauges (for example, mercury), pastes, lubricants, lacquers, and cements. Some properties of the more important vacuum construction materials are presented in Tables 1, 2, and 3.

Table 2. Organic construction materials
 Gas separation rate at 20°CCoefficient of gas permeability at 20° C
 Table 2. Organic construction materialsTable 2. Organic construction materialsTable 2. Organic construction materials
   HeliumNitrogenHeliumNitrogen
NK natural-base rubber...............(5-8) × 10-6(4-6) × 10-61.3 × 10-162.3 × 10-171.3 × 10-72.3 × 10-8
SKN-26 synthetic nitrile-base rubber...............(3-4) × 10-5(2-3) × 10-55.2 × 10-172.5 × 10-185.2 × 10-82.5 × 10-9
SKN-40 synthetic nitrile-base rubber...............(3-4) × 10-5(2-3) × 10-53.6 × 10-123.9 × 10-183.6 × 10-83.9 × 10-9
SKTV-1 polyvinylsiloxane-base rubber...............(1-3) × 10-5(1-2) × 10-5 (250°C)2.0 × 10-15 (25°C)2.0 × 10-6 (25°C)
Fluoroplast-4 (Teflon)...............(4-7) × 10-7(3-5) × 10-7 (150°C-250°C)2.3 × 10-168.4 × 10-182.3 × 10-78.4 × 10-9
Polyethylene...............(7-13) × 10-7(5-10) × 10-72.5 × 10-172.5 × 10-182.5 × 10-82.5 × 10-9
Polyethyleneterephthalate...............(3-7) × 10-8(2-5) × 10-87.2 × 10-182.7 × 10-207.2 × 10-92.7 × 10-11
Polyethylenepolyamine-strengthened ED-5 epoxide resin...............(3-7) × 10-4(2-5) × 10-4 (60°C)1.0 × 10’-171.0 × 10-8

Metals are used in the manufacturing of housings, pumps, valves, casings, electrodes, and gas absorbers. Glass is the basic material for flasks, pipes, tubes, and so on. Tubes and wires are made from synthetic materials (polyethylene, polyterafluorethylene, polyamide, and others) and cured rubber. Vacuum lubricants and pastes serve to seal detachable and fixed connections. Lacquers are used for sealing scratches and coating surfaces, and cements are used for tube bases.

Table 3. Vacuum lubricants, pastes, lacquers, and cements
 Vapor pressure at 20°CFusing temperature (°C)Maximum operating temperature (°C) 
 (N/m2)(mm Hg)Purpose (use)
Lubricants     
High-vacuum...............10-410-6-40 to +200Sealing valves and ground joints
Lucricil...............10-310-540
Ramsay...............10-210-430
Apiezone...............10-110-3 (at 200°C)4330
Apiezone...............10-510-1047Seating of force-fit joints
      
Pastes     
Picein...............10-510-740Sealing ground-glass and polished metal joints
Denison...............10-310-560 
Rubber-beeswax compound10-1 to 10-210-3 to 10-460 
Apiezone...............10-110-345; 85Sealing fixed connections
Mendeleev...............50 
Khotinskii cement...............10-110-340For tube bases
Glyptal varnish...............3 × 10-22 × 10-4200Sealing abrasions and coating surfaces

REFERENCES

Bälitskii, A. V. Tekhnologiia izgotovleniia vakuumnoi apparatury, 2nd ed. Moscow-Leningrad, 1966.
Lebedinskii, M. A. Elektrovakuumnye materialy, 2nd ed. Moscow-Leningrad, 1966.

E. N. MARTINSON and E. G. PLESHCHENKO

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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