Low-temperature high-pressure hydrogen storage cylinder

Abstract

The utility model provides a kind of low-temperature high-pressure hydrogen storage cylinder, including hydrogen storage inner bag, carbon fiber winding layer located hydrogen storage inner bag outside, shell and including first air inlet pipe, second air inlet pipe, first air outlet pipe, second air outlet pipe, the air inlet and outlet assembly of link cavity, vacuum heat insulation layer is equipped between shell and carbon fiber winding layer, flow valve is equipped at shell opening, link cavity is located in vacuum heat insulation layer, and it is equipped with air inlet chamber and air outlet chamber therein, flow valve, first air inlet pipe, air inlet chamber, second air inlet pipe and hydrogen storage inner bag are sequentially connected, hydrogen storage inner bag, first air outlet pipe, air outlet chamber, second air outlet pipe and flow valve are sequentially connected, and the connecting place of link cavity and first air inlet pipe, second air inlet pipe, first air outlet pipe, second air outlet pipe is all provided with heat insulation structure, solve the technical problem that hydrogen storage container in prior art cannot effectively block heat from outside to pass to the inside of inner bag.

Description

Technical Field

[0001] This utility model relates to the field of hydrogen storage equipment technology, and in particular to a low-temperature high-pressure hydrogen storage cylinder. Background Technology

[0002] Hydrogen is considered the ultimate energy source of the new century because of its high energy density, lack of CO2 production during combustion, and ability to be produced from renewable energy sources. Low-temperature high-pressure hydrogen storage is a technology that uses low temperature and high pressure to improve the storage density and efficiency of hydrogen. It combines the advantages of low-temperature liquid hydrogen storage and high-pressure gaseous hydrogen storage, increasing the density of stored hydrogen and reducing storage energy consumption.

[0003] Hydrogen storage containers are an important component of cryogenic and high-pressure hydrogen storage systems. However, how to prevent heat transfer between the outside and inside of the container and keep the cryogenic hydrogen inside the container warm remains a problem that needs to be solved in the field.

[0004] For example, Chinese Patent Application No. CN202021197613.6 discloses a high-pressure cryogenic hydrogen storage device, which reduces radiative and convective heat transfer between the inner liner and the outer container through cladding and vacuum interlayer. However, because the inner liner of this hydrogen storage device extends outward at the bottle opening, it is not completely isolated by the vacuum interlayer, resulting in the inability to effectively block heat transfer at the bottle opening. Chinese Patent Application No. CN201820172112.9 discloses a cryogenic high-pressure hydrogen storage cylinder. Although it completely isolates the inner liner within the outer shell through a vacuum insulation interlayer, it requires the transportation of cryogenic hydrogen through inlet and outlet pipes. The inlet and outlet pipes directly connect the outside of the outer shell to the inside of the inner liner. Furthermore, because the cryogenic hydrogen transportation pipes need to be made of metal, external heat can quickly enter the inner liner through the inlet and outlet pipes, failing to effectively block heat transfer. Utility Model Content

[0005] The purpose of this application is to provide a low-temperature, high-pressure hydrogen storage cylinder to solve the technical problem that existing hydrogen storage containers cannot effectively prevent heat from being transferred from the outside to the inside of the liner.

[0006] To achieve the above objectives, the embodiments of this application adopt the following technical solutions:

[0007] A low-temperature high-pressure hydrogen storage cylinder includes a hydrogen storage liner, a carbon fiber winding layer, an outer shell, and an inlet / outlet assembly. The carbon fiber winding layer covers and connects to the outside of the hydrogen storage liner. The outer shell is disposed on the outer layer of the carbon fiber winding layer and has a flow valve at its opening. A vacuum insulation layer is disposed between the carbon fiber winding layer and the outer shell. The inlet / outlet assembly includes a first inlet pipe, a second inlet pipe, a first outlet pipe, a second outlet pipe, and a connecting cavity.

[0008] The connecting cavity is located inside the vacuum insulation layer, and it is provided with an air inlet cavity and an air outlet cavity.

[0009] One end of each of the first and second air inlet pipes passes through the connecting cavity and communicates with the air inlet cavity. The other end of the first air inlet pipe is connected to an external hydrogen source through the flow valve, and the other end of the second air inlet pipe is connected to the interior of the hydrogen storage liner.

[0010] One end of each of the first and second gas outlet pipes passes through the connecting cavity and communicates with the gas outlet cavity. The other end of the first gas outlet pipe communicates with the interior of the hydrogen storage liner. The other end of the second gas outlet pipe is connected to an external hydrogen terminal through the flow valve.

[0011] The first air inlet pipe, the second air inlet pipe, the first air outlet pipe, and the second air outlet pipe are all connected to the connecting cavity through a heat insulation structure.

[0012] In the low-temperature high-pressure hydrogen storage cylinder described in the embodiments of this application, the heat insulation structure is a low-temperature resistant structural adhesive or a polytetrafluoroethylene O-ring.

[0013] In a cryogenic high-pressure hydrogen storage cylinder described in this application embodiment, both ends of the hydrogen storage liner are provided with openings, and both openings of the hydrogen storage liner are provided with sealing and support components. The sealing and support components include a sealing block, a fiberglass support ring, a pressure block, and several support rods.

[0014] The sealing block is located at the opening, with one end extending outward from the hydrogen storage liner as an extension end. The fiberglass support ring is threadedly connected to the extension end, and a plurality of support embedding grooves are spaced apart in the circumferential direction. A support rod is embedded in each of the support embedding grooves. The other end of the support rod overlaps with the outer shell through an overlap limiting groove provided on the outer shell. The pressure block is threadedly connected to the sealing block and pressed against the fiberglass support ring. The second air inlet pipe and the first air outlet pipe both pass through the pressure block and the sealing block.

[0015] In a cryogenic high-pressure hydrogen storage cylinder as described in the embodiments of this application, a plurality of the support embedding grooves are distributed at equal intervals along the circumference of the fiberglass support ring.

[0016] In the cryogenic high-pressure hydrogen storage cylinder described in the embodiments of this application, a silicone rubber pad is provided in each of the overlapping limiting grooves.

[0017] In a cryogenic high-pressure hydrogen storage cylinder as described in this application embodiment, an annular groove is provided on the inner side of the hydrogen storage liner around the opening, and an O-ring is provided in the annular groove. The sealing block is provided with a flange at one end inside the hydrogen storage liner, and the flange abuts against the O-ring.

[0018] In a cryogenic high-pressure hydrogen storage cylinder described in this application embodiment, the support rod includes a first support rod, a second support rod, and a partition bridge;

[0019] The two ends of the partition bridge are respectively connected to the first support rod and the second support rod. The other end of the first support rod is connected to the support embedding groove, and the other end of the second support rod is connected to the overlapping limiting groove.

[0020] In a cryogenic high-pressure hydrogen storage cylinder described in this application embodiment, the partition bridge is located on the side of the vacuum insulation layer close to the outer shell.

[0021] In the cryogenic high-pressure hydrogen storage cylinder described in this application embodiment, the material of the partition bridge is PA66.

[0022] In a cryogenic high-pressure hydrogen storage cylinder described in this application embodiment, the connecting cavity, the first inlet pipe, the second inlet pipe, and the carbon fiber winding layer are all covered with an aluminum film.

[0023] Compared with the prior art, the embodiments of this application have the following beneficial effects:

[0024] As can be seen from the above technical solution, the low-temperature high-pressure hydrogen storage cylinder provided in this application solves the problem of the inability to effectively block heat transfer points at the bottle opening by connecting the flow valve to the outer shell and completely surrounding the hydrogen storage liner with a vacuum insulation layer. By setting the first inlet pipe, the second inlet pipe, the first outlet pipe, and the second outlet pipe to be connected to the connecting cavity through the insulation structure, there are two "broken bridge" structures on the inlet and outlet pipes connecting the outside and the inside of the liner, which effectively reduces the heat transferred from the outside of the outer shell to the inside of the liner through the inlet and outlet pipes, thus solving the technical problem in the prior art that hydrogen storage containers cannot effectively block heat transfer from the outside to the inside of the liner. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. The drawings are not intended to be drawn to scale, and for clarity, not every component will be labeled in each drawing. The drawings described below are merely some embodiments of this application. Those skilled in the art can obtain other drawings based on these drawings without creative effort. Wherein:

[0026] Figure 1 This is a schematic diagram of the structure of an embodiment of this application.

[0027] Figure 2 for Figure 1 A magnified view of part A in the diagram.

[0028] Figure 3 for Figure 1 A magnified view of part B in the diagram.

[0029] Figure 4 This is a schematic diagram of the fiberglass support ring in an embodiment of this application.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1-Hydrogen storage inner liner, 2-Carbon fiber winding layer, 3-Outer shell, 4-Flow valve, 5-Vacuum insulation layer, 6-First inlet pipe, 7-Second inlet pipe, 8-First outlet pipe, 9-Second outlet pipe, 10-Connecting cavity, 11-Inlet cavity, 12-Outlet cavity, 13-Insulation structure, 14-Sealing block, 15-Fiberglass support ring, 16-Pressure block, 17-Support rod, 18-Support embedding groove, 19-Overlapping limiting groove, 20-O-ring seal, 21-Flange, 22-First support rod, 23-Second support rod, 24-Break-off bridge. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0033] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0034] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0035] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0036] The following disclosure provides many different embodiments or examples for implementing different structures of this application. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, various specific examples of processes and materials are provided in this application, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0037] Example

[0038] This application provides a cryogenic high-pressure hydrogen storage cylinder, such as... Figures 1 to 4As shown. A low-temperature, high-pressure hydrogen storage cylinder includes a hydrogen storage liner 1, a carbon fiber winding layer 2, an outer shell 3, and an inlet / outlet assembly. The carbon fiber winding layer 2 covers and connects to the outside of the hydrogen storage liner 1. The outer shell 3 is disposed on the outer layer of the carbon fiber winding layer 2, and a flow valve 4 is provided at its opening. A vacuum insulation layer 5 is provided between the carbon fiber winding layer 2 and the outer shell 3. The inlet / outlet assembly includes a first inlet pipe 6, a second inlet pipe 7, a first outlet pipe 8, a second outlet pipe 9, and a connecting cavity 10. The connecting cavity 10 is located inside the vacuum insulation layer 5, and has an inlet chamber 11 and an outlet chamber 12. One end of each of the first inlet pipe 6 and the second inlet pipe 7 is... The connecting cavity 10 is connected to the air inlet cavity 11. The other end of the first air inlet pipe 6 is connected to an external hydrogen source through the flow valve 4. The other end of the second air inlet pipe 7 is connected to the interior of the hydrogen storage liner 1. One end of each of the first air outlet pipe 8 and the second air outlet pipe 9 is connected to the air outlet cavity 12 through the connecting cavity 10. The other end of the first air outlet pipe 8 is connected to the interior of the hydrogen storage liner 1. The other end of the second air outlet pipe 9 is connected to an external hydrogen terminal through the flow valve 4. The first air inlet pipe 6, the second air inlet pipe 7, the first air outlet pipe 8, and the second air outlet pipe 9 are all connected to the connecting cavity 10 through the heat insulation structure 13.

[0039] Specifically, the heat insulation structure 13 is a low-temperature resistant structural adhesive or a polytetrafluoroethylene O-ring.

[0040] In this embodiment, the low-temperature resistant structural adhesive can be DW-3 low-temperature resistant adhesive, and the polytetrafluoroethylene (PTFE) O-ring can be a PTFE O-ring manufactured by Greene Tweed. In this embodiment, the vacuum insulation layer 5 completely encloses the hydrogen storage liner 1 and isolates it from the outer shell 3, preventing heat from being transferred to the hydrogen storage liner 1 at the bottle opening. Furthermore, in this application, the first air inlet pipe 6, the air inlet chamber 11, and the second air inlet pipe 7 constitute the "air inlet pipe" of the hydrogen storage container. Two "break bridges" are formed on the "air inlet pipe" through the heat insulation structure 13 at the connection between the first air inlet pipe 6 and the connecting chamber 10, and the heat insulation structure 13 at the connection between the second air inlet pipe 7 and the connecting chamber 10. The structure effectively reduces the heat entering the hydrogen storage liner 1 from the outer shell 3 through the "air inlet pipe". The "air outlet pipe" of the hydrogen storage container is composed of the first air outlet pipe 8, the air outlet chamber 12 and the second air outlet pipe 9. Through the heat insulation structure 13 at the connection between the first air outlet pipe 8 and the connecting chamber 10, and the heat insulation structure 13 at the connection between the second air outlet pipe 9 and the connecting chamber 10, two "broken bridge" structures are formed on the "air outlet pipe", which effectively reduces the heat entering the hydrogen storage liner 1 from the outer shell 3 through the "air outlet pipe" and improves the heat transfer barrier effect of the hydrogen storage container.

[0041] In some embodiments, both ends of the hydrogen storage liner 1 are provided with openings, and both openings of the hydrogen storage liner 1 are provided with sealing support assemblies. The sealing support assemblies include sealing blocks 14, fiberglass support rings 15, pressure blocks 16, and a plurality of support rods 17. The sealing blocks 14 are provided at the openings, with one end extending outward from the hydrogen storage liner 1 as an extension end. The fiberglass support ring 15 is threadedly connected to the extension end, and a plurality of support embedding grooves 18 are provided circumferentially at intervals. Each support embedding groove 18 is embedded with a support rod 17. The other end of the support rod 17 overlaps with the outer shell 3 through an overlapping limiting groove 19 provided on the outer shell 3. The pressure block 16 is threadedly connected to the sealing blocks 14 and pressed against the fiberglass support ring 15. The second air inlet pipe 7 and the first air outlet pipe 8 both pass through the pressure block 16 and the sealing blocks 14.

[0042] Specifically, the extension end is provided with an external thread, and the inner side of the fiberglass support ring 15 is provided with an internal thread. The fiberglass support ring 15 is threaded to the extension end through the internal and external threads. A plurality of support embedding grooves 18 are distributed at equal intervals along the circumference of the fiberglass support ring 15. The extension end is provided with a through hole at its center, and the through hole is also provided with an internal thread. The pressure block 16 is also provided with an external thread. The pressure block 16 is threaded to the sealing block 14 through the internal and external threads. As the pressure block 16 is screwed into the sealing block 14, the fiberglass support ring 15 is pressed and fixed. At the same time, the middle of the pressure block 16 and the middle of the sealing block 14 are also provided with through holes. The through holes of the sealing block 14 and the through holes on its extension end are connected. The through holes are used for the second air inlet pipe 7 and the first air outlet pipe 8 to pass through.

[0043] It should be noted that, in this embodiment, the overlapping limiting groove 19 is disposed at the end caps of both ends of the outer shell 3. The overlapping limiting grooves 19 at both ends of the outer shell 3 are arranged opposite each other, and the groove openings are opposite each other. The overlapping limiting grooves 19 arranged opposite each other at both ends of the outer shell 3 and the corresponding support rods 17 are used to achieve the centering and fixing of the hydrogen storage liner 1.

[0044] In some embodiments, a silicone rubber pad is provided in the overlap limiting groove 19. The silicone rubber pad can not only further block the heat on the outer shell 3 from being conducted to the hydrogen storage inner liner 1 through the support rod 17, but also improve the overlap stability of the support rod 17 and the overlap limiting groove 19.

[0045] In some embodiments, an annular groove is provided on the inner side of the hydrogen storage liner 1 around the opening, and an O-ring 20 is provided in the annular groove. A flange 21 is provided at one end of the sealing block 14 located inside the hydrogen storage liner 1, and the flange 21 abuts against the O-ring 20.

[0046] The O-ring 20 can be the same as the heat insulation structure 13 mentioned above, and is a polytetrafluoroethylene O-ring packaged by Greene Tweed. Since the hydrogen in the hydrogen storage liner 1 is in a high-pressure state, when it squeezes the sealing block 14 outward, the sealing block 14 squeezes the O-ring 20 to improve the sealing performance of the hydrogen storage liner 1.

[0047] In some embodiments, the support rod 17 includes a first support rod 22, a second support rod 23, and a partition bridge 24. The two ends of the partition bridge 24 are respectively connected to the first support rod 22 and the second support rod 23. The other end of the first support rod 22 is connected to the support embedding groove 18, and the other end of the second support rod 23 is connected to the overlapping limiting groove 19.

[0048] Specifically, the partition bridge 24 is made of PA66 and is located on the side of the vacuum insulation layer 5 close to the outer shell 3, away from the low-temperature region of the vacuum insulation layer 5.

[0049] The first support rod 22 and the second support rod 23 can be made of stainless steel. By setting the support rod 17 to be composed of the first support rod 22, the second support rod 23 and the partition bridge 24, a support structure similar to "broken bridge aluminum" is formed, so that the support rod 17 provides support to the hydrogen storage liner 1 while minimizing the heat transfer from the outer shell 3 to the hydrogen storage liner 1.

[0050] In some embodiments, the connecting cavity 10, the first air inlet pipe 6, the second air inlet pipe 7, and the carbon fiber winding layer 2 are all covered with an aluminum film. By setting the aluminum film, radiative heat transfer is reduced, and the heat preservation effect of this application is further improved.

[0051] In summary, the cryogenic high-pressure hydrogen storage cylinder provided in this application solves the problem of ineffective heat transfer at the cylinder opening by connecting the flow valve to the outer shell and completely surrounding the inner liner with a vacuum insulation layer. This effectively isolates the inner liner from the outer shell. Furthermore, by connecting the first inlet pipe, second inlet pipe, first outlet pipe, and second outlet pipe to the connecting cavity via an insulation structure, two "broken bridge" structures exist on both the inlet and outlet pipes connecting the outside and the inner liner. This effectively reduces heat transfer from the outer shell to the inner liner through the inlet and outlet pipes, thus solving the technical problem in existing hydrogen storage containers where heat cannot be effectively transferred from the outside to the inner liner.

[0052] The above provides a detailed description of a cryogenic high-pressure hydrogen storage cylinder provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A cryogenic high-pressure hydrogen storage cylinder, characterized in that, The device includes a hydrogen storage liner, a carbon fiber winding layer, an outer shell, and an inlet / outlet assembly. The carbon fiber winding layer covers and connects to the outside of the hydrogen storage liner. The outer shell is disposed on the outer layer of the carbon fiber winding layer and has a flow valve at its opening. A vacuum insulation layer is disposed between the carbon fiber winding layer and the outer shell. The inlet / outlet assembly includes a first inlet pipe, a second inlet pipe, a first outlet pipe, a second outlet pipe, and a connecting cavity. The connecting cavity is located inside the vacuum insulation layer, and it is provided with an air inlet cavity and an air outlet cavity. One end of each of the first and second air inlet pipes passes through the connecting cavity and communicates with the air inlet cavity. The other end of the first air inlet pipe is connected to an external hydrogen source through the flow valve, and the other end of the second air inlet pipe is connected to the interior of the hydrogen storage liner. One end of each of the first and second gas outlet pipes passes through the connecting cavity and communicates with the gas outlet cavity. The other end of the first gas outlet pipe communicates with the interior of the hydrogen storage liner. The other end of the second gas outlet pipe is connected to an external hydrogen terminal through the flow valve. The first air inlet pipe, the second air inlet pipe, the first air outlet pipe, and the second air outlet pipe are all connected to the connecting cavity through a heat insulation structure.

2. The cryogenic high-pressure hydrogen storage cylinder as described in claim 1, characterized in that, The thermal insulation structure is a low-temperature resistant structural adhesive or a polytetrafluoroethylene O-ring.

3. The cryogenic high-pressure hydrogen storage cylinder as described in claim 1, characterized in that, Both ends of the hydrogen storage liner are provided with openings, and both openings of the hydrogen storage liner are provided with sealing and support components. The sealing and support components include sealing blocks, fiberglass support rings, pressure blocks and several support rods. The sealing block is located at the opening, with one end extending outward from the hydrogen storage liner as an extension end. The fiberglass support ring is threadedly connected to the extension end, and a plurality of support embedding grooves are spaced apart in the circumferential direction. A support rod is embedded in each of the support embedding grooves. The other end of the support rod overlaps with the outer shell through an overlap limiting groove provided on the outer shell. The pressure block is threadedly connected to the sealing block and pressed against the fiberglass support ring. The second air inlet pipe and the first air outlet pipe both pass through the pressure block and the sealing block.

4. A cryogenic high-pressure hydrogen storage cylinder as described in claim 3, characterized in that, Several of the aforementioned support embedding grooves are distributed at equal intervals along the circumference of the fiberglass support ring.

5. A cryogenic high-pressure hydrogen storage cylinder as described in claim 3, characterized in that, Each of the overlapping limiting grooves is equipped with a silicone rubber pad.

6. A cryogenic high-pressure hydrogen storage cylinder as described in claim 3, characterized in that, An annular groove is provided on the inner side of the hydrogen storage liner around the opening, and an O-ring is provided in the annular groove. The sealing block is provided with a flange at one end inside the hydrogen storage liner, and the flange abuts against the O-ring.

7. A cryogenic high-pressure hydrogen storage cylinder as described in claim 3, characterized in that, The support rod includes a first support rod, a second support rod, and a partition bridge; The two ends of the partition bridge are respectively connected to the first support rod and the second support rod. The other end of the first support rod is connected to the support embedding groove, and the other end of the second support rod is connected to the overlapping limiting groove.

8. A cryogenic high-pressure hydrogen storage cylinder as described in claim 7, characterized in that, The partition bridge is located on the side of the vacuum insulation layer closest to the outer shell.

9. A cryogenic high-pressure hydrogen storage cylinder as described in claim 8, characterized in that, The material of the partition bridge is PA66.

10. A cryogenic high-pressure hydrogen storage cylinder as described in claim 1, characterized in that, The connecting cavity, the first air inlet pipe, the second air inlet pipe, and the carbon fiber winding layer are all covered with an aluminum film.

Images