X-Message-Number: 4894
Date: Wed, 20 Sep 1995 22:58:05 -0700 (PDT)
From: Doug Skrecky <>
Subject: time machine construction

                     TIME MACHINE CONSTRUCTION
                        By Doug Skrecky
              (From April 1992 Canadian Cryonics News)

      A key requirement for long term storage of human remains is a secure
 container to insure that nothing goes amiss in the deceased's long
 journey to the future. Such a "time machine" would require a construction
 material that is impervious to both air and moisture, is resistent to
 mechanical stress and does not corrode. Plastics fail on the first count,
 borrosilicate glass and ceramics are brittle and so fail on the second
 count, and finally most but not all metals fail by corrosion due to
 ground water. For example aluminum and lead are dissolved in acid or
 alkaline solutions, copper and nickel are attacked by sulfides while
 steel simply rusts in aerated water. The only easily available metals
 which do not readily corrode are stainless steels, nickel alloys and
 titanium. 
     Stainless steels derive their corrosion resistance primarily from the
 incorporation of chromium, molybdenum and nitrogen. *1 Nickel is added to
 stainless steels in order to eliminate brittleness. *2 The primary
 vulnerability of stainless is to the chloride ion. In low chloride waters
 even inexpensive 18% chromium (type 304) steels average corrosion rates
 of less than 0.000025 millimeters per year. *3 At this rate it would take
 about 40,000 years to penetrate just 1 millimeter into the metal. 
 Unfortunately this situation changes dramatically when stainless is
 buried at sites close to the seashore as after just 4 years of burial
 type 304 plates were virtually perforated. *4
     Chromium alone is not enough to ensure that stainless steels will not
 corrode. Molybdenum and nitrogen must also be incorporated to achieve
 that. For instance outdoor atmospheric exposure of stainless steels for
 32 years at a rural test site yielded no evidence of corrosion. However
 when these same metals were tested at a sea shore beach front test site
 great differences were observed. Type 304 with no molybdenum rusted more
 than type 316 with 2% molybdenum, while type 216 with 2% molybdenum and
 0.33% nitrogen remained inert. *5
     Recent research has reduced the effective price of stainless steels
 by increasing their yield strength so that less metal is required. The
 most widely used high strength stainless alloy is duplex 2205, which
 contains 22% chromium, 3% molybdenum and 0.2% nitrogen. This alloy is
 roughly equal to type 216 in general corrosion resistance. *6 Further
 addition of another 3% chromium plus 2% copper results in a newer alloy
 called duplex 255, which is able to remain inert even in seawater, while
 yet being only slightly more expensive than type 316 stainless. *7 A
 bargain, indeed. 
     What about nickel alloys and titanium? Some bacteria have the nasty
 habit of attacking metal surfaces and this has produced some unexpected
 structural failures. When tested with bacteria type 316L was found to be
 quite resistant and corroded even less than the extremely expensive
 nickel base alloy Inconel 625. *8 However the situation is quite
 different with titanium as no cases of corrosion from ambient temperature
 seawater have ever been reported with this metal. The only known failures
 involve hydrogen induced embrittlement when titanium was joined to
 another corroding metal. *9 A titanium casket would thus have to be
 constructed solely of that metal. 
     Suitable materials for time machine construction are limited at
 present to titanium and some of the more highly alloyed stainless steels. 
 By using these materials in conjunction with permafrost burial there is a
 substantial probability that the body of the deceased will eventually
 attain to a posthumous fame thousands of years from now which would dwarf
 all others. 

 *1 "Effects of Alloy Composition and Microstructure on the Passivity of
 Stainless Steels" 376-389 Vol.42 No.7 1986 Corrosion
 *2 "Nickel Steels in Arctic Service" 46-49 October 1987 Materials
 Performance
 *3 "Long Term Corrosion Tests in Rondout Reservoir, New York" 27-33 May
 1978 Materials Performance
 *4 "The Galvanic Coupling of Some Stainless Steeks to Copper -
 Underground" 16-20 October 1975 Materials Performance
 *5 "Appearance and Corrosion of Stainless Steels in the Atmosphere" 47-54
 February 1988 Materials Performance
 *6 "Practical Guide to Using Duplex Stainless Steel" 57-62 January 1990
 Materials Performance
 *7 "Duplex Alloy 255 in Marine Applications" 63-67 October 1990 Materials
 Performance
 *8 "Ranking Alloys for Susceptibility to MIC - A Preliminary Report on
 High-MO Alloys" 55-57 January 1991 Materials Performance
 *9 "Use of Titanium in Petroleum Refining" 48-52 September 1990 Materials
 Performance


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