CA1219821A - Shipping container for storing materials at cryogenic temperatures - Google Patents

Abstract

SHIPPING CONTAINER FOR STORING MATERIALS
AT CRYOGENIC TEMPERATURES
Abstract A container for shipping transportable materials at cryogenic temperatures including a vessel which opens to the atmosphere and contains a micro-fibrous structure for holding a liquefied gas such as liquid nitrogen in adsorption and capillary suspension. The micro-fibrous structure structure comprises a core permeable to liquid and gaseous nitrogen and an adsorption matrix composed of randomly oriented inorganic fibers surrounding the core as a homogeneous body in stable confinement.

Description

~Z~98Zl SHIPPING CONTAINER FOR STORING MATERIALS AT
CRYOGENIC TEMPERATURES
Thi8 invention relate6 to container~ for storing materials at cryogenic temperatures and more particularly to an open to atmosphere ~hipping containeL adapted to hold a supply of liquid nitrogen for refrigerating a ~tored biological product during transportation from one location to another over a relatively long time period.
Backaround of ~hi6 Invention The shipment of heat-sensitive bio-systems, as for instance ~emen, vaccines, cultures of bacteria and viruses at optimal temperature levels between about 78K and lOOK, poses a 6eries of difficulties. Th~ vials or "straws~', in which the biologicals are hermetically sealed, mu~t be kept continuously at near liquid nitrogen temperature to preserve the viability of the biological product.
But since the boiling point of liquid nitrogen at ambient pre6~ure is 77.4K (-320.4F) the cryogen holding vessel (refrigerator) must remain open to the atmosphere to vent the boiled-off gas and thus avoid a dangerou~ pressure build-up in6ide. Fo~
this reason open-to-atmosphere liquid nitrogen ve6~els are used for refrigeration. It is obvious that 6uch vessel6 must be kept upright at all times to prevent 6pillage of the cryogen. This condi~ion i8 difficult to control during a long shipment unless an attendant accompanies the ves~el on the trip which is rarely a feasible option.

~Z19~32~

To overcome the difficulties a6sociated with the shipment of biologicals at cryogenic temperature a fihipping container was developed in which the liquid nitrogen i8 retained in a solid porous mass by adsorption, capillarity and absorption. Based upon this development a patent is6ued to R. F. O'Connell et al. in 1966 as U.S.
Patent No. 3.238~002. The shipping containe~
described in this patent is of a double-walled con6truction to provide a vacuum space around the inner vessel which hold6 the liquid nitrogen. The vacuum space is filled with a multilayer in~ulation to reduce heat t~ansfer by radiation. An adsorbent and a getter are part of the system to maintain vacuum integrity. The inner vessel is filled with the solid porous mas6 which, when saturated with liquid nitrogen, will hold the cryogen by adsorption, and capillarity as well as by ab60rption, similar to a sponge "holding" water. In the center of the porous filler core one or more voids are provided to hold the vials containing the biologicals.
The solid components of the porous mass described in V.5. Patent 3,238,003 are silica (~and), quick-lime, and a small amount of inert heat resistant mineral fibers such as asbestos. The porous mass i8 formed ~tarting with an aqueous filurry of the filler components which is poured into a mold and then baked in an autoclave under precisely controlled equilibrium conditions of pressure and temperature.

~Z~91~Zl The components undergo a chemical reaction ~orming a porous ma~s of calcium silicate~, reinforced by inert fibers. The evaporated water leaves inside the dried out 601 id structure microscopic void~, of complex geometry, sometimes referred to as "poresl', which comprise on the average 89.5% of the appacent ~olid volume. Since the resulting mass is incompressible the mold must either provide the mas6 with a shape confor~ing to the inner vessel of the stocage container or it muct be machined to size. The porous mass is filled with liquid nitrogen by submerging it in a liquid nitrogen bath until it i8 ~aturated. The filling operation for a conventional two liter container housing a sand-lime pocous mass matrix take6 about twenty-fouL hours.
The baked sand-lime porous mass i8 intrinsically hydrophilic. Because of this property moisture must be periodically driven out of the porous mass matrix to prevent the accumulation of trapped water. If this i& not done, the trapped water will turn into ice crystals every time it is exposed to liquid nitrogen and eventually will crack the brittle microstructure of the filler. This ~ay be preYented by periodically heating the porou6 structure to above 100C after several fill and wacm up cycles.
Although the ingcedients used in manufacturing the sand-lime pocous ma~ are relatively inexpensive (deionized water, sand, quick-lime and inert fibers, as for example asbesto6~ the finishing operations in handling a ~ Z:19~21 solid porous ma6s are very expensive due to the high labor co6ts involved and the elaborate safety precautions required. It is noe economically feasible to cast the porous filler in a cryogenic holding vessel. Elaborate safety precautions are indispensable when handling substances like asbe~tos fibers and noxiou6 dust. In addition, the thermal energy co~t is very high for the manufacturing procesc of the sand-lime filler ma6s.
Alternative sy~tems for retaining liquid nitrogen in a container through a combination of adsorption, absoeption and capillarity have in the past being investigated by those skilled in the art. The u~e of high porosity blocks, artificial stone~, bricks and light papers made from cellulose fibers such a~ towels and bathroom tissues have been studied and, in general have been dismissed as inferioL compared to the use of the sand-lime porous mass matrix due primarily to their low porosity.
The average porosity of the sand-lime porous matrix is 89.5% whereas the porosity of a matrix fabricated from any of the aforementioned materials is below 60%. More recently block in~ulation material composed of hydrous calcium silicate has been used as the adsorption matrix. Such material is closer in porosity to the sand-lime porou~ ma~6 composition but al~o has ~ost of the shortcomings of the sand-lime porous mass composition. The porosity of the filler matrix determines for a gi~en size shipping container its liquid nitrogen capacity.
The porosity and rate of evaporation are the most important characteristic~ of a liquid nitrogen ~torage container for trangporting a product at cryogenic temperature~. A ~torage container using a sand-lime porous ma~6 matrix has an average 5 day holding time based on an evaporation rate of .33 liters per day and a liquid capacity of 1.6 liter6.
Accordingly, the act has long sought a less expen6ive and much more efficient liquid nitrogen adsorption sy~tem as an alternative to the 6torage sy~tems in present use.
Obiects of the Invention It i8 therefore, ~he principle object of the present invention to provide a low cost refrigerated container for transporting bio-systems at cryogenic temperatures.
It is another object of the pre~ent invention to provide a refrigerated container for shipping a bio-system over a long holding period during which time the bio-system is sustained in ~uspended animation at cryogenic temperatures.
It i8 yet another object of the present invention to provide a low cost refrigerated container having a liquid nitrogen adsorption matrix which has a high average holding capacity and i6 intrinsically hydro-neutral.
A still furthec object of the pre6ent invention i~ to pzovide a refrigerated con~ainer having a liquid nitrogen adsorption matrix which ha6 a higher ad60rptivity than state of the art liquid nitrogen adsorption matrices and which will fill to capacity in a sub~tantially reduced time period.

Summary of the Invention The present invention provides a structure for holding a liquified gas such as liquid nitrogen in adsorption and capillary suspension comprising a core permeable to liquid and/or gaseous nitrogen having a cavity extending therethrough and a liquified gas adsorption matrix composed of a mass of randomly oriented microfiber particles having a diameter in a range of between 0.03 to 8 microns in relatively close engagement with one another surrounding said core as a homogeneous body.
Brief Description of the Drawings Further objects and advantages of the present invention will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings of which:
Figure 1 is a front elevational view, in section, of the shipping container of the present invention;
Figure 2 shows a preferred insertion technique for forming the micro-fibrous adsorption matrix within the inner vessel of the cryogenic shipping container of ~19821 Figure 1 before the bottom end of the inner vessel is attached;
Figure 3 is a partial view of Figure 2 showing the inner vessel after the fibrous adsorption matrix has been formed and the bottom end attached; and Figure 4 is a perspective view of the micro-fibrous adsorption structure of Figure 1 formed as a self-supported structure by an alternate manufacturing process.
Description of the Preferred Embodiment The invention is illustrated in the preferred embodiment of Figure 1 which shows a shipping container 10 having a self supporting outer shell 12 surrounding an inner vessel 13. The inner vessel 13 is suspended from the outer shell 12 by a neck tube 14.
The neck tube 14 connects the open neck 15 of the inner vessel 13 to the open neck 16 of the outer shell 12 and defines an evacuable space 17 separating the outer shell 12 and the inner vessel 13. A neck tube core 18 is removably inserted into the neck tube 14 to reduce heat radiation losses through the neck tube 14 as well as to prevent foreign matter from entering into the inner vessel 13 and to preclude moisture vapors from - iZlg~21 buildîng up highly objectionable frost and ice barriers inside the neck tube 14. The neck tube core 18 should fit loosely within the neck tube 14 to provide sufficient clearance space between the neck tube 14 and the neck tube core 18 for assuring open communication between the atmosphere and the inner vessel 13.
The evacuable space 17 is filled with insulation material 19 preferably composed of low emissivity radiation barriers, like aluminum foil, interleaved with low heat conducting spacers or metal coated nonmetallic flexible plastic sheets which can be used without spacers. Typical multilayer insulation systems are taught in U.S. Patent Nos: 3,009,600, 3,018,016, 3,265,236, and 4,055,268. A plurality of frustoconical metal cones 20 may be placed around the neck tube 14 in a spaced apart relationship during the wrapping of the insulation in order to improve the overall heat exchange performance of the storage container 10 following the teaching of U.S. Patent No. 3,341,052.
To achieve the required initial vacuum condition in the evacuable space 17, the air in the evacuable space 17 is pumped out through a conventional evacuation spud 31 using a conventional pumping system not shown. After the evacuation has lZ198~ -g been completed the spud 21 is hermetically sealed under vacuum in a manner well known in the art using, for example, a sealing plug and cap ~not ~hown).
An adsorbent Z2 is located in the vacuum space 17 to maintain a lo~ ab601ute pres6ure of typically le~s then 1 X 10-4 torr. The ad60rbent 22 may be placed in a retainer 23 formed between the shoulder 24 and the neck 15 of the inner vessel 13.
The retainer 23 ha6 a ~ealable opening 25 through which the adsorbent 22 i~ inserted. The ad~orbent 22 is typically an activated charcoal or a zeolite sueh as Linde 5A which i~ available from the Union Carbide Corporation. A hydrogen getter 26 ~uch as palladium oxide (PdO) or silver zeolite may also be included in the vacuum ~pace 17 foc removing residual hydrogen molecules. To those skilled in the art it is apparent that other locations. as well as methods of placement of the adsorbent and the hydrogen qetter, are feasible.
The inner vessel 13 contains a micro-fibrou6 6tructure 27 for holding liquid nitrogen by adsorption and capillary 6uspension.
The micro-fibrou6 structure 27 Gomprise~ a permeable cylindrical core 28 and a liquid nitrogen ad60rption matrix 30 composed of a homogeneous mass of randomly oriented ~hort particles of inorganic fibers e.g.
qlass quartz or eeramic of very 6mall diameter. The micro-fibrous structure 27 is shown in longitudinal cross section in Figure 2 at the manufacturing stage. The upper cylindrical portion 32 of the inner ve6sel 13, hermetically ~ealed between and 1;i~19~21 permanently attached to the neck tube 14, as well as the permeable cylindrical core 28 are placed in a loosely fitting relationship over a columnar extension 38 of a suppo t device 39. The cylindrical portion 32 with the attached necktube 14 are placed for this operation upside-down, that is, the unattached nec~tube end is facing downwards.
The open space between the tubular core 28 and the inner surface of the cylinarical portion 32 i6 filled with an aqueou6 micro-fibrous slurry 40 of inorganic fibers pceferably glas~ poured from a mixing vat (not shown) at such a rate that the water 41 rom the in-pouring slurry 40 is free to flow through the opening6 29 in the core 28 as well as down thsough pas6ages 42 in the columnar support 3æ, leaving the moist semi-solid micro-fibrous glass re6idue to form the homogeneou6 body of the ad60rption matrix 30. The slurry influx i6 stopped when the level of the body 30 reaches the rim 34.
The matrix 30, con6isting of a qua6i-infinite number of randomly oriented inorganic micro-fiber particles, typically about 3mm to lOmm in length, i8 then, her~etically sealed in6ide the inner vessel 13 by welding the bottom 33 around the circumference of 34, a6 ~hown in the partial cro6s-6ectional view of Figure 3. A curved bottom plate 33 is used to provide an ullage 43 between the matrix 30and the bottom en~ of the inner vessel 13 to enable the liquid nitrogen to readily permeate the matrix 30 axially as well as radially. The re6idual moi6ture in the matrix 30 can be removed by the application of moderate heat trai6ing the temperature to about ~19~Z~

Cl~ ~OCE,~ se 70C) and by simultaneou~ application of a ~E~
6l vacuum of about 20 to 150 torr.
However, to those skilled in the art it i~
apparent that other processe6 can be u~ed foc the manufacture of the matrix 30. One of them, very similar to the one described above, would consist for example, of a long cylindrical mold made up of two longitudinal hemi-cylindrical halves that could be separated from each other for easy removal of the molded product. The inside diameter of the mold would be the same as the inside diamete~ 11 of the inner vessel 13 in Figure 1. The permeable core would be an appropriate tubing, matching in length the hemi-cylindrical mold. The void between the inside of the mold and the outside of the permeable core would be filled with an aqueous micro-fibrous slurry and treated afterwards in a similar fashion as the individual matrix shown in Figure 2. The end product of such an operation would be a long cylindrical semi-fini~hed micrQ-fibrous adsorptive body 30 surrounding a permeable core 2a which would then be cut into pieces of appropriate length to form a structure 27 a~ shown in Figure 4 corresponding exactly to the structure 27 of Figure 1. Since the microfibrou~ structure 27 is the same identical reference characters have been used in describing the alternate method~ of manufacture.
The pre-fabricated and pre-cu~ structure 27 of Figure 4 would then be in6erted into the upper cylindrical section 32 of the inner vessel 13 of Figure 1. The open bottom would then be closed u~ing a curved bottom plate 33 which may be welded ~2~98;Z1 around the periphery 34 as explained earlier in connection with Figure 3 leaving an ullage 43 between the bottom plate 33 and the structure 27.
This ullage 39 may readily be avoided leaving no open space 43 if 80 desired.
Although one does not ordinarily as60ciate glass with characteristic6 ~uch as 6pongine66 and poro6ity, it has been di6covered in accordance with the present invention that reasonably compacted glass fiber6 possess high capacity for holding liquid nitrogen by adsorption and capillary suspension provided the gla66 fibers in forming the web are of very small diameter. The liquid nitrogen is held in the micro-fibroufi matrix 30 by molecular adsorption to the enormous aggregate area of the micro fiber6, as well as by capillary su6pen~ion made possible by the microscopic intra-fibrous voids between individual fibers. It i6 therefore of importance that the diameters of the glass fibers be as small as pos~ible with the preferred range from .03 to 8 microns. The body of micro-fiber qlass particles ~hould preferably be formed without using any rigidizing binder6 or cemen~6. The structural 6tability of the felt-like body is effected primarily by intra-fibrou6 friction. Substantially binderless inorganic micro fibers in diameter~
ranqing from 0.3 to 8 micron are commercially available from e.g., the ~anville Corporation and Subsidiaries, Denver, Colorado and Owen6-Corning, Toledo, Ohio. The glass fiber6 u6ed in this invention are composed of boro6ilicate glass with the glas6 fibers ranging from .5 to .75 microns in diameter.

lZ19~1 The core 2a is preferably of tubular geometry having a central void 31 into which the biological product is to be placed during shipment.
It should be understood that the invention is not li~ited to a ~inqle void 31. ~ultiple voids 31 may be readily formed using muleiple cores 2~ and arranged in any desired pattern or geometry. The core 28 can be of any material composition, e.g., metal or plastic that will remain structually ~table and retain its form after being repeatedly subjected to cold shocks at liquid nitrogen temperature~. To maintain the lowest po~sible temperature within the cavity 31 the core 28 must be permeable to the nitrogen gas that boil~ off from the liquid nitrogen stored in the glass fiber matrix 30. The permeability of the core can be provided by forming the core 2~ fLom a perforated sheet rolled into a tube or using a porou6 sintered tube without apparent hole6. Where perforations are u~ed, ehe holes 29 in the wall of the core 28 must be small enough to prevent any loose fiber particles from passing across the core wall 28 into the storage cavity 31 containing the biological product.
The storage container 10 of Figure 1 is preferably assembled starting with the inner ve6sel assembly 13 of a two piece construction, having an upper cylindrical section 32 with an open end bottom 34, a lower section 33, and then neck tube 14 permanently attached by way of the open neck 15 to the cylindrical section 32, employing any acceptable joining method.

;l9~3Zl The adsorption/storage system 27, comprisinq the homogeneous micro-fibrous matrix 30 and the permeable core 28, in coaxial alignment with the neck tube 14, make up the inner container as6embly 13.
The outer shell 12 is al80 of a two piece construction with an upper cylindrical section 35 and a lower bottom ~ection 36. The inner ves~el 13 i8 inserted into the upper section 35 before the two sections are joined to each other. Where a wrapped compo~ite insulation system is used, the inner ve6sel i~ first wrapped with the layers of insulation preferably using the hea~ exchange cones 20 before the inner ves~el 13 is inserted into the upper 6ection 35. The adsorbent 22 is placed in~ide the ad~orbent retainer 23 before the insulation is applied. The upper 6ection 35 may have ccimped end 37 to facilitate attachment of the lower section 36. Before the two sections 35 and 36 are velded together to from a unitary structure, the getter composition 26 i6 placed inside the vacuum space 17. Instead of circumferential crimping as shown in 34 and 37 of Figure 1 other means of alignment of mating cylindcical components can be u~ed, e.g. bute welding with a back-up ring or tack welding in a jig.
The liquid capacity of the micro-fibrous matrix with randomly oriented fiber par~icles is determined by the apparent volume of the matrix and its "porosity". The design volume being 2,400 cm and the "porosity" of the microfibrous adsorption medium having a mean value of 92%, the mean liquid capacity of such a cryogenic ~torage container is ~2198Z~

found to be 2,400 cm x 0.92 = 2,208 cm or about 2.2 liters.
This then is the design figure for the amount of liquid nitrogen to be held within the micro-fibrous matrix by ad~orption and capillarity without deainage or ~pillage.
In service, the liquid nitrogen, held in the matrix, keeps evaporating due to the unavoidable heat inflow from ambient resulting from the temperature gradient between ambient and liquid nitrogen. Eventually all ~he cryogen is bound to boil off completely, leaving the &torage compartment for the temperature sensitive product without refcigeration. Considering this ci~cumstance, which in essence is a race between the hold time of the storage container and the shipping time of the product, the rate of evaporation is the most important characteristic of a shipper-refrigerator.
The evaporation rates of containers of this invention have a mean value of 0.084 liter/day.
This low evaporation rate makes it possible to achieve a mean holding time of:

2.2 liters . 26 days 0.084 liter/day compared to 5 day~ for the state-of-the-art shipper~. In other words, a shipper/refrigerator of this invention will provide the required near liquid nitrogen temperature inside its seorage compartment to maintain bio-systems in the state of suspended animation thcoughout a maximum of 26 days of transportation, regardless whether the shipper is standing upright. laying on the ~ide. or even Up6 ide-down.
The invention as de6cribed in accordance with the preferIed embodiment 6hould not be construed as limited to a specific configuration for the core and adsorption matrix in definin the micro-fib~ous structure. For example, the core may have a plurality of voids defined, for example.
within a ~ubular framework with the void~ separated by partitions extending from a solid control po~t to the outer tubula~ wall of the core. In such case only the outer tubular wall of the core must be permeable to ga~eou~ nitrogen.

Claims (28)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A shipping container for transporting materials at cryogenic temperatures having a micro-fibrous structure with randomly oriented fiber particles adapted for holding a liquefied gas such as liquid nitrogen in adsorption and capillary suspension within the interior of the container, said micro-fibrous structure comprising a core permeable to gaseous and/or to liquid nitrogen, with said core being disposed in said container and having at least one void adapted for the removable placement of the transportable materials; and a liquefied gas adsorption matrix composed of a mass of very small diameter substantially non-porous inorganic fibers in a range from 0.03 to 8 microns in diameter with the fibrous particles surrounding said core as a homogeneous body having an outside diameter conforming to the diameter of the shipping container.

2. A shipping container as claimed in claim 1 further comprising an inner vessel containing said micro-fibrous structure, an outer shell surrounding said inner vessel and spaced apart therefrom to define an evacuable space therebetween with said inner vessel being open to the atmosphere and insulation material occupying said evacuable space.

3. A shipping container as claimed in claim 2 wherein said inner vessel and outer shell each have an open neck and further comprising a neck tube connecting the open neck of said outer shell to the open neck of said inner vessel.

4. A shipping container as claimed in claim 3 wherein said insulation material is composite multilayered insulation composed of a radiant heat reflecting component and a low heat conducting component disposed in relation to the radiant heat reflecting component so as to minimize the transfer of heat across evacuable space.

5. A shipping container as claimed in claim 1, wherein said micro-fibrous structure surrounding said core is in the form of a felt-like homogeneous body composed of an extremely large number of randomly oriented inorganic microfiber particles in relatively close engagement with one another.

6. A shipping container as defined in claim 5 wherein said inorganic fibers are composed of borosilicate glass.

7. A storage container as defined in claim 5 wherein said inorganic fibers are composed of quartz.

8. A shipping container as claimed in claim 5 wherein said insulation material consists essentially of finely divided particles of agglomerate sizes, less than about 420 microns, of low heat conducting substances such as perlite, alumina, and magnesia, with or without admixture of finely divided radiant heat reflecting bodies having reflecting metallic surfaces of sizes less than about 500 microns.

9. A shipping container as claimed in claim 5 wherein said core is of a hollow tubular construction with said void being defined by the hollow space in said core.

10. A shipping container as defined in claim 9 wherein said core has a multiple number of small perforated openings of a suitable geometric configuration and size.

11. A shipping container as defined in claim 9 wherein said core is of an intrinsically permeable structure having inherent micro-passages throughout its body.

12. A container for shipping transportable materials at cryogenic temperatures comprising:
an inner vessel having an open end; an outer shell having an open end; access means connecting said open end of said outer shell to said open end of said inner vessel such that said inner vessel is suspended from said outer shell in a spaced apart relationship for defining an evacuable space therebetween; insulation means disposed within said evacuable space; and a microfibrous structure located within said inner vessel for holding liquid nitrogen by adsorption and capillary suspension, said micro-fibrous structure comprising a gas permeable core having a void disposed in said inner vessel in alignment with said access means, with said access means providing ingress and egress to said void for removably inserting said transportable materials and a liquid nitrogen adsorption matrix composed of randomly oriented very small diameter substantially non-porous inorganic fibers in a range from 0.03 to 8 microns in diameter with the fibrous particles surrounding said core in form of a stable homogeneous body with an outside diameter conforming to the inside diameter of said inner vessel.

13. A structure for holding a liquified gas such as liquid nitrogen in adsorption and capillary suspension comprising a core permeable to liquid and gaseous nitrogen having a cavity extending therethrough and a liquified gas adsorption matrix composed of a mass of an extremely large number of randomly oriented microfiber particles having a diameter in a range of between 0.03 to 8 microns in relatively close engagement with one another surrounding said core as a homogeneous body.

14. A structure as defined in claim 13 wherein said microfiber particles are selected from the class consisting of glass, quartz and ceramic.

15. A shipping container as claimed in claim 3, wherein said micro-fibrous structure surrounding said core is in the form of a felt-like homogeneous body composed of an extremely large number of randomly oriented inorganic microfiber particles in relatively close engagement with one another.

16. A shipping container as defined in claim 15 wherein said inorganic fibers are composed of borosilicate glass.

17. A storage container as defined in claim 15 wherein said inorganic fibers are composed of quartz.

18. A shipping container as claimed in claim 15 wherein said insulation material consists essentially of finely divided particles of agglomerate sizes, less than about 420 microns, of low heat conducting substances such as perlite, alumina, and magnesia, with or without admixture of finely divided radiant heat reflecting bodies having reflecting metallic surfaces of sizes less than about 500 microns.

19. A shipping container as claimed in claim 15 wherein said core is of a hollow tubular construction with said void being defined by the hollow space in said core.

20. A shipping container as defined in claim 19 wherein said core has a multiple number of small perforated openings of a suitable geometric configuration and size.

21. A shipping container as defined in claim 19 wherein said core is of an intrinsically permeable structure having inherent micro-passages throughout its body.

22. A shipping container as claimed in claim 4 wherein said micro-fibrous structure surrounding said core is in the form of a felt-like homogeneous body composed of an extremely large number of randomly oriented inorganic microfiber particles in relatively close engagement with one another.

23. A shipping container as defined in claim 22 wherein said inorganic fibers are composed of borosilicate glass.

24. A storage container as defined in claim 22 wherein said inorganic fibers are composed of quartz.

25. A shipping container as claimed in claim 22 wherein said insulation material consists essentially of finely divided particles of agglomerate sizes, less than about 420 microns, of low heat conducting substances such as perlite, alumina, and magnesia, with or without admixture of finely divided radiant heat reflecting bodies having reflecting metallic surfaces of sizes less than about 500 microns.

26. A shipping container as claimed in claim 22 wherein said core is of a hollow tubular construction with said void being defined by the hollow space in said core.

27. A shipping container as defined in claim 26 wherein said core has a multiple number of small perforated openings of a suitable geometric configuration and size.

28. A shipping container as defined in claim 26 wherein said core is of an intrinsically permeable structure having inherent micro-passages throughout its body.