A container is provided which can be designed to heat its outer surface to sterilize it, or to heat its inner surface and any contents therewithin. In a container that self sterilizes its outer surface, the container includes a combustible layer of thermite-type pyrotechnic material which can be ignited to generate considerable heat, and a thin casing around the combustible layer which is of highly thermally conductive materials such as aluminum which can be heated to a high temperature by the ignited combustible layer. A buffer layer which may be of metal, lies within the combustible layer, and a layer of insulation such as Teflon lies within the buffer layer to insulate the contents of the container from the heat

Yang, L. C.

English

NASA Technical Reports Server

United States Patent 4,193,388 
[4s] Mar. 18, 1980 
[54] PORTABLE HEATABLE CONTAINER 
[76] Inventor: Robert A. Frwh, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Lien C. Yang, La 
Canada, Calif. 
[21] Appl. No.: 897,831 
[22] Filed: Apr. 19, 1978 
[51] Int. C l . 2  ................................................. F24J 1/00 
[52] US. Cl. ..................................... 126/263; 149/15; 
149/37; 220/429 
[58] Field ob $ear& .................. 126/263, 262; 149/15, 
149/37,40,102/90; 426/113,521; 220/3.1,426, 
429,444,451; 422/1 
[561 References Cited 
U.S. PATENT DOCUMENTS 
2,531,548 11/1950 Bennett .................................. 149/15 
2,606,547 8/1952 Stofel ................................... 126/262 
2,683,449 7/1954 Katz ..................................... 126/263 
Primary Examiner-Carroll B. Dority, Jr. 
Assirtant Examiner--Lee E. Barrett 
Attorney, Agent, or Firm-Monte F. Mon; John R. 
Manning; Wilfred Grifka 
A container is provided which can be designed to heat 
its outer surface as to sterilize it, or to heat its inner 
surface and any contents therewithin. In a container 
that self sterilizes its outer surface, .the container in- 
cludes a combustible layer of thermit-type pyrotechnic 
material which can be ignited to generate considerable 
heat, and a thin casing around the combustible layer 
which is of highly thermally conductive materials such 
as aluminum which can be heated to a high temperature 
by the ignited combustible layer. A buffer layer which 
may be of metal, lies within the combustible layer, and 
a layer of insulation such as Teflon lies within the buffer 
layer to insulate the contents of the container from the 
heat. The thicknesses of the thermit-type charge of the 
combustible layer and of the casing are chosen so that 
the amount of heat from the charge heats the casing to 
a temperature which is only moderately high to avoid 
melting the casing. 
1571 ABSTRACT 
2 Claims, 4 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19800012324 2020-03-21T02:29:09+00:00Z
U.S. Patent Mar. 18, 1980 4,193,388 
4,193,388 
1 
PORTABLE HEATABLE CONTAINER 
ORIGIN OF THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
(72 Stat. 435; 42 USC 2457). 
BACKGROUND OF THE INVENTION 
A portable, self heating container has important uses. 
For example, programs for exploration of the planets 
have required that precautions be taken to prevent any 
potentially hazardous organisms from contaminating 
the Earth between the time when the sample is brought 
to the Earth on a space vehicle and the time when the 
sample is brought to a control laboratory on the Earth. 
A container is required whose outer surface is sterilized 
at some point prior to entering the Earth's atmosphere, 
but without administering excessive heat to the contents 
of the container that would damage the enclosed speci- 
men. Such a container must be efficient, of low weight, 
simple, and pose no hazard to the spacecraft. A similar 
type of container would be useful in passing a container 
into or out of a biologically hazardous laboratory (such 
as where recombinant DNA experiments are con- 
ducted). 
A container which can heat the inside walls of the 
container and/or the contents therein, is also useful in a 
variety of situations, as in providing sterilizing facilities 
for field hospitals and other emergency situations, 
where a lightweight device is necessary which can 
rapidly apply high sterilizing temperatures. 
SUMMARY OF THE INVENTION 
In accordance with one embodiment of the invention, 
a container is provided which can apply considerable 
heat, and yet which is of low weight and simple design. 
The container includes a layer of a combustible charge 
such as thermit type pyrotechnic which is held between 
a pair of container walls that can withstand at least 
moderately high temperatures, and with the combusti- 
ble material extending around substantially the entire 
container in a thin layer. When the combustible material 
is ignited, it generates considerable heat, which can 
sterilize the outside of the container, the inside of the 
container, or the contents of the container, depending 
on the construction of the container. 
In one container structure wherein the outside of the 
container must be sterilized without excessively heating 
the contents of the container, the thermit-type charge 
lies between a thin outer casing and a thicker structural 
and buffer layer, and an insulative layer is provided 
withii the structural layer. The thickness of the thermit- 
type layer is chosen so that it produces sufficient heat to 
heat the thin casing to a moderately high temperature, 
so that all outer surface portions are heated to at least 
230" C. to assure destruction of all potential microor- 
ganisms, and yet to not create so much heat as to melt 
the thin outer casing. The structural layer lying within 
the thermit-type charge is thick enough to absorb con- 
siderable amounts of heat to avoid reaching a very high 
temperature, and the insulator serves to minimize the 
transfer of heat to the contents of the container so that 
the inner walls of the container are maintained at a 
temperature below loo" C. 
In another container, the thermit-type layer lies near 
a thin inside casing or wall of the container to heat it, so 
as to sterilize the inside of the container and/or heat the 
contents of the container. 
The novel features of the invention are set forth with 
particularity in the appended claims. The invention will 
be best understood from the following description when 
read in conjunction with the accompanying drawings. 
BRIEF DESCRIPTION O F  THE DRAWINGS 
FIG. 1 is a sectional view of a container constructed 
in accordance with one embodiment of the present 
invention. 
FIG. 2 is an enlarged view of the area 2-2 of FIG. 1. 
FIG. 3 is a view taken on the line 3-3 of FIG. 1. 
FIG. 4 is a sectional side view of a container con- 
structed in accordance with another embodiment of the 
invention. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 illustrates a cannister or container 10 which is 
designed to hold a specimen or other goods G, and to 
sterilii  its exterior stdace without excessively heating 
the goods. The particular container is designed to avoid 
25 contamination of the Earth by any microorganisms on 
the container, when it is used to bring a specimen from 
another planet to the Earth and then to a secured labo- 
ratory where the container can be opened and the speci- 
men examined. The outside of the container must be 
30 heated to a considerable temperature such as above 230" 
C. at every location of the outside surface, without 
heating the goods to 100" C. 
The container includes two similar parts lOA, 10B 
that are bolted together by fasteners 12. Each container 
35 half includes a substantially uniformly thin layer of 
combustible material 14 such as thennit-type pyrotech- 
nic which can react and self-sustainedly create heat 
without the need for additional oxygen or the like. A 
thin casing 16 surrounds the thennit layer and forms the 
40 outside of the container. A structural-buffer member or 
layer 18 in the form of a container lies within the ther- 
mit-type material 14, and an insulator 20 lies within the 
structural layer. An electrical squib igniter 22 is utilized 
to ignite a small quantity of pyrotechnic powder 24, 
As the combustible layer 14 reacts, it creates heat 
which is transferred to the casing 16 and structural layer 
18 that lie on opposite sides of the combustible layer. 
The heat raises the temperature of all portions of the 
50 casing surface 16s to a moderately high temperature 
such as above 230' C. for all surface areas of the casing 
for a short period of time, typically several minutes, to 
destroy any microorganisms on the casing surface. The 
thickness of the combustible layer 14, in relation to the 
55 heat capacity of the casing 16, is chosen so that the 
casing 16 will be heated to the required temperature, 
but not to such a high temperature that it will melt. Of 
course, about half of the heat generated by the ignited 
combustible layer 14 will be applied to the structural 
60 layer 18 to raise its temperature. However, the struc- 
tural layer 18 is designed to have a greater heat capacity 
than the thin casing 16, so that the structural layer 18 
will not be heated to as high a temperature as the casing. 
The insulator layer #) is also provided to minimize the 
65 amount of heat transfer from the structural layer 18 to 
the inner surface 20s of the container and the goods G 
within the container. Instead, after the combustible 
layer 14 has been fully combusted to raise the tempera- 
5 
15 
2o 
45 which secondarily ignites the thermit-type layer 14. 
4,193,388 
3 
ture of the casing 16, and after the temperature of the 
casing 16 then drops, much of the heat from the struc- 
tural layer 18 will be transferred into the interior of the 
cannister. The thin casing will soon drop in temperature 
after having been raised to the sterilizing temperature, 
so that heat from inner parts of the container can be 
conducted out to the environment. Thus, the amount of 
the heating of the inside of the container is minimized 
by conducting heat away from the cannister and by 
distributing the limited amount of heat generated by the 
combustible layer to the large heat capacity structure 
formed by the structural member 18 and the insulator 
20. 
In order to facilitate the opening and closing of the 
container, the casing 16 is provided with a pair of 
flanges 26 which can be bolted together. Each of the 
flanges is formed with a groove 28 that is filled with the 
combustible charge 14, to heat the flange and the fas- 
tener 12 thereon to assure sufficient heating of the 
flanges to raise them to the required temperaGre. The 20 
two halves lOA, 10B of the container can be identical, 
with both of them formed to receive a squib 22 and with 
the two squibs being initiated simultaneously. 
A container of the type shown in FIG. 1 can be con- 
structed using aluminum for the casing 16 and structural 25 
layer 18, to minimize the weight of the container. The 
container was designed with an aluminum casing 16 of 
one-eighth inch thickness, a combustible layer 14 of 
thermit (a mixture of finely divided metallic zirconium 
and one or more oxides such as barium chromate or iron 30 
oxide) of a substantially uniform thickness of about two 
millimeters or about 0.080 inch, an aluminum structural 
layer 18 of onequarter inch thickness, and a Teflon (or 
rubber, formed plastic, glass, etc. ) insulative layer 20 of 
one-quarter inch thickness. The outside diameter of the 35 
container was about four inches and the height was 
about one foot so that the combustible portion at the 
end of the container had a diameter or length and width 
of much more than ten times its thickness (actually, 
about fifty times its thickness). The combustible layer 40 
portion 14w at the side walls of the container, had a 
circumferential length of about one foot, which is also 
much more than ten times the thickness of the layer. 
The container can be formed using aluminum tubing, 
and the thermit-type powder can be poured into the 
container space between the casing 16 and structural 
layer 18 and compacted using an arc-shaped tamper just 
slightly thinner than the annular space. The ends of the 
cylindrical container can be formed by merely laying 
layers of the material on one another and welding them 
to the cylindrical container portions, the flanges 26 
being similarly welded in place. 
The combustible layer 14 is preferably constructed of 
a composition which reacts without the significant re- 
Pease of gas, so that no venting is required. A propaga- 
tion speed of the ignition will be on the order of 0.2 to 
1.0 centimeters per second. It is estimated that the pow- 
der reacts in the temperature range of 800"-1,000" C. 
The pyrotechnic column 24 which connects the electri- 
cal squib to the thermit can be formed of a boron based 
pyrotechnic powder. 
In many applications, heating of a container surface is 
necessary at the inside of the container rather than the 
outside. For example the inside of a container intended 
to carry a material which must not be contaminated 
may have to be first sterilized. Also, there are applica- 
tions where the contents of a container must be heated, 
such as to sterilize instruments in a field hospital or to 
45 
50 
55 
60 
65 
4 
begin the operation of a fuel cell that must start at a high 
temperature. FIG. 4 illustrates a container 30 con- 
structed in accordance with another embodiment of the 
invention, which can provide in-the-field heating at the 
inside of a portable container. The container 30 includes 
a combustible layer 32 of a themit-type material which 
is trapped between a casing 34 forming the innner wall 
of the container, and a structural buffer layer 36 sur- 
rounding the combustible layer. An insulator layer 38 
can be provided around the structural layer 36, and a 
protective outer layer 40 can be provided around the 
insulator. When the combustible layer 32 is ignited as by 
an electrically ignitible squib 22 and pyrotechnic col- 
umn 24, the combustible layer creates heat which heats 
the inner casing 34. The heat can sterilize the inner 
casing where this is desired, and can heat goods lying 
within the inner casing where this is desired. Where 
only the casing needs to be heated, a thin thermit layer 
can be utilized. Where goods within the inner casing 32 
must be heated, such as implements to be sterilized or a 
quantity of water to be turned into steam, a somewhat 
thicker layer of thermit-type material may be utilized. 
The casing 34 may be constructed of a very high tem- 
perature-resistant material such as stainless steel, to 
enable considerable heat transfer without melting. The 
surrounding structural layer 36 serves as a structure to 
hold the container together and as a heat-isolating 
buffer for absorbing heat from the thermit layer to mini- 
mize the temperature at which it and the insulating 
layer 38 is raised. The insulating layer 38 prevents the 
outside of the container from reaching a very high tem- 
perature. 
The container 30 can be constructed with a cylindri- 
cal portion 30A and an end portion 30B, which can be 
easily assembled and disassembled. In many applica- 
tions, the combustible layer 32 extends around substan- 
tially the entire container to completely sterilize the 
outer or inner surface thereof. However, where it is 
desired only to heat goods within the container, it is 
possible to utilize the thermit layer so it extends around 
only a portion of the container. 
Thus, the invention provides a container of relatively 
simple design, and which can be highly portable, which 
can heat its outside or inside. Uniform distributed heat- 
ing can be obtained by a thin layer of a combustible 
material such as a thermit-type pyrotechnic which can 
be held at one side by a casing that is to be heated by the 
thermit type charge layer. The thickness of the casing 
and of the thermit layer are chosen so that the casing is 
heated to the desired temperature but is not overheated. 
The casing is preferably constructed of a highly ther- 
mally conductive material such as aluminum or copper, 
so that a large portion of the heat generated by the 
combusted thermit type material is absorbed by the 
casing. Although a casing of steel can be utilized, a 
material of higher thermal conductivity than steel, such 
as aluminum or copper provides more effective trans- 
ference of heat to the casing. The side of the combusti- 
ble layer opposite the casing, can be formed of a thick 
layer of material which can withstand high tempera- 
tures, so that this layer will not be raised to as high a 
temperature as the casing. An insulative layer can lie on 
a side of the thick isolating layer which is opposite the 
thermit, so that the side (inside or outside) of the con- 
tainer opposite the casing is not excessively heated. 
Although particular embodiments of the invention 
have been described and illustrated herein, it is recog- 
nized that modifications and variations may readily 
5 
4,193,388 
6 
occur to those skilled in the art, and consequently it is 
intended that the claims be interpreted to cover such 
modifications and equivalents. 
What is claimed is: 
1. A cannister apparatus which can self sterilize its 5 
outside surface while avoiding excessive heating of 
goods within the cannister, comprising: 
walls forming a container for surrounding the goods; 
a layer of combustible material surrounding said con- 
tainer walls to lie over substantially all areas of said 10 
container; and 
a layer of insulation lying within said container to 
insulate the goods from heat generated by the com- 
bustible material. 
15 
2. A cannister apparatus which can self sterilize its 
outside surface while avoiding excessive heating of 
goods within the cannister, comprising: 
walls forming a container for surrounding the goods; 
a layer of combustible material surrounding said con- 
tainer walls to lie over substantially all areas of said 
container, and 
a casing surrounding said container but spaced there- 
from, said combustible material lying in the space 
between said container and casing, and said com- 
bustible material being of a type and thickness to 
heat the outside of said casing to at least about 230' 
C. to sterilize it. 
I * * * * '  
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Portable heatable container

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