SELF-FUSING SILICONE TAPE FOR SENSING HYDROGEN AND HYDROGEN SULFIDE GAS LEAKS

Abstract

A gas-sensing pigment incorporated in a thin film indicator or tape that changes color upon exposure to hydrogen or hydrogen sulfide. The gas-sensing pigment is compounded together with a silicone polymer to produce a self-fusing silicone tape having a tensile strength of at least 700 psi, a tear resistance of at least 85 psi, and ultimate elongation of at least 300%. The gas-sending pigment includes chemochromic metal oxide particles of a tungsten oxide or a molybdenum oxide, and a catalyst having platinum, palladium, rhodium, nickel, or silver. The catalyst coating is applied to each metal oxide particle as nanoparticles of less than 30 nanometers in diameter, and the microparticles of chemochromic metal oxide material are less than 200 microns or 100 microns in diameter.

Claims

1. A self-sealing silicone tape having a tensile strength of at least 700 psi, a tear resistance of at least 85 psi, and ultimate elongation of at least 300%, comprising: a silicone polymer embedded with a mixture of (a) microparticles of chemochromic metal oxide particles selected from the group consisting of a tungsten oxide and a molybdenum oxide, coated with (b) nanoparticles of a catalyst selected from the group consisting of platinum, palladium, rhodium, nickel and silver; wherein the microparticles of chemochromic metal oxide material have a range of sizes less than 200 microns in diameter, and the catalyst nanoparticles have a range of sizes less than 30 nanometers in diameter.

2. A film comprising a polymer embedded with a mixture of (a) microparticles of chemochromic metal oxide particles selected from the group consisting of a tungsten oxide and a molybdenum oxide, and (b) nanoparticles of a catalyst selected from the group consisting of platinum, palladium, and rhodium; wherein the microparticles of chemochromic metal oxide material have a range of sizes less than 200 microns in diameter; wherein the metal oxide macroparticles are coated with catalyst nanoparticles having a range of sizes less than 30 nanometers in diameter.

3. The film of claim 2, wherein each metal oxide macroparticle has a discontinuous coating of catalyst nanoparticles.

4. The film of claim 3, wherein the catalyst is selected from the group consisting of platinum, palladium, rhodium, nickel, and silver.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Understanding of the present invention will be facilitated by consideration of the following detailed description of the preferred embodiments of the invention taken in conjunction with the accompanying illustrations, in which like numerals refer to like parts, and wherein:

[0016] FIG. 1A, FIG. 1B show images of a portion of a self-fusing tape product incorporating a hydrogen gas sensor and a catalyst, in accordance with an embodiment of the invention;

[0017] FIG. 2A and FIG. 2B show images of the self-fusing gas leak indicating tape product applied to a piping fitting before 2A and after 2B exposure to leaking hydrogen gas according to embodiments of the present invention.

[0018] FIG. 3 shows a spectrographic response curve of the change in relative light transmittance of the tape product as it is exposed to hydrogen gas according to embodiments of the present invention;

[0019] FIG. 4A, FIG. 4B, FIG. 4C are plan views and FIG. 4D is a perspective exploded view illustrating different patterns of carbon thread dependent on the tensile strength and modulus of elasticity desired self-fusing tape with an embedded carbon fiber according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020] It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding, while eliminating, for the purpose of clarity, many other elements found in the self-fusing hydrogen indicating tape with or without an embedded carbon fiber technology, methods of using the same and its manufacture. Those of ordinary skill in the art may recognize that other elements and/or steps may be desirable in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein.

[0021] In one non limiting embodiment the invention includes a self-sealing silicone tape product having one or more strips of silicone rubber tape and embedded in the silicone chemochromic metal oxide particles of tungsten oxide or molybdenum oxide, and a catalyst of metallic platinum or silver. Notably, the catalyst coating is applied to each microscopic metal oxide particle, as nano-scale metallic particles.

[0022] More particularly, the hydrogen gas indicating tape is made of a silicone polymer, which is highly permeable to hydrogen gas and hydrogen sulfide gas. Hydrogen gas or hydrogen sulfide gas from a leak can readily permeate into the silicone tape and react with the indicator pigment dispersed therein. The silicone resin used in the tape is a matrix which contains the dispersed chemically reactive indicating pigment powder and catalyst. The silicone matrix provides protection for the pigment from handling and from the weather, while still allowing the gases such as hydrogen and hydrogen sulfide to diffuse into the tape where the hazardous gas chemically reacts with the pigment to produce the telltale color change.

[0023] The pigment is a fine powder of a metal oxide to which a suitable catalyst is applied to facilitate the reaction between the metal oxide powder and the hazardous gas. By way of example and not limitation, the metal oxide is tungsten oxide or molybdenum oxide and the catalyst is metallic platinum or silver. The catalyst is a coating applied to each microscopic metal oxide particle as very fine, nano-scale metallic particles. The hazardous gas reacts with the metal oxide to chemically reduce it. Whereas the metal oxide itself is nearly colorless, the partially reduced oxide is highly colored blue or black.

[0024] In another embodiment the invention includes a method of making a self-sealing silicone tape that changes color in the presence of hydrogen or hydrogen sulfide, including the steps of: mixing a reinforced silicone polymer and nanoparticles of metal catalyst material with powder microparticles of chemochromic metal oxide material; and coating the powder microparticles of chemochromic material with the nanoparticles of the metal catalyst material by one of ginding or milling the nanoparticles of metal catalyst material with the microparticles of chemochromic metal oxide material.

[0025] In one embodiment of the invention the nanoparticles of the catalyst material are sized in a range of 2 nanometers to 30 nanometers. In another embodiment of the invention the nanoparticles of the catalyst material are sized in a range of 31 nanometers to a tens of nanometers. In yet another embodiment of the invention the microparticles of chemochromic metal oxide material are sized in a range of 10 to 200 microns in diameter.

[0026] With respect to other embodiments of a self-sealing silicone indicator tape used in the invention a catalyst material can be selected from the group of platinum, palladium, rhodium, nickel, combinations of these metals, or alloys of these materials with other metals.

[0027] More particularly, the silicone self-sealing tape incorporates a hydrogen sensor coating, including powder particles of chemochromic, transition metal oxide with a catalyst to create chemochromic powder pigments for use in paints, inks, dyes, and other emulsions that can be spread on surfaces to function as hydrogen detectors. A further embodiment of the present invention may include a chemochromic powder pigment silicone self-sealing tape that incorporates a powder particles of a transition metal oxide and a catalyst that is coated on or attached to surfaces of the transition metal oxide powder particles. Each of the foregoing hydrogen sensing coatings are as described in the related U.S. Pat. No. 9,422,160, entitled Visual Hydrogen Sensors Using Chemochromic Metal Oxide Microparticles Superficially Coated With Catalyst.

[0028] FIG. 1A is an illustration of a self-sealing silicone indicator tape used by way of example and not limitation in a high pressure hydrogen facility, known as a Hydrogen Fueling Station Gas Management Panel. This type of equipment is shipped and thereafter utilized in hydrogen fueling stations to calibrate hydrogen delivery pumps. As the equipment is moved during shipment, it undergoes vibration and stresses which can loosen fittings and cause leaks. Wrapping the potential leak sites with the indicator tape provides a quick and simple way to visually check for leaks at the new destination.

[0029] By way of example and not limitation FIG. 1A shows the tape as initially applied. FIG. 1B shows the tape after the system has been pressurized with hydrogen and a dark spot has formed on the tape indicating a hydrogen leak. The test illustrated in FIG. 1A and FIG. 1B is one of a number of ongoing tests of the hydrogen indicating tape being conducted at the US Department of Energy's National Renewable Energy Laboratory (NREL) in their Safety Sensor Testing Laboratory (see, Passive Leak Detection Using Commercial Hydrogen Colorimetric Indicator, Kevin Hartmann, et al, prepared under Task No. HT12.7210, National Renewable Energy Laboratory NREL, U.S. Department of Energy Office of Energy Efficiency & Renewable Energy. Report available from the National Renewable Energy Laboratory at www.nrel.gov/publications. September 2016.).

[0030] By way of example and not limitation, FIG. 2A and FIG. 2B show the self-sealing silicone indicator tape applied to a fitting before and after exposure to a hydrogen leak, respectively.

[0031] FIG. 3 shows a spectrographic response curve 15 of the change in tape relative light transmittance “T” along the vertical axis, as it is exposed to hydrogen gas according to embodiments of the present invention. Also shown is the corresponding visual color change 10 before and change 20 after exposure to hydrogen. Experiments have determined that a decrease of as small as 10% to 20% in the relative light transmittance is readily observable to the naked eye.

[0032] In FIG. 4A, 4B, 4C, 4D, a carbon fiber thread as illustrated as reference 105a, 105b, 105c, in multiple strands may be incorporated in the silicone self-fusing indicator tape 100 to provide added lengthwise tensile strength. The fiber-reinforcement tape may be particularly hard to tear or cut to the needed length. To facilitate tearing the tape into useful length, the tape may be perforated across its width at periodic distances along its length. Of course, if the tape is reinforced with carbon thread, the perforations will have to cut through all of the carbon fibers.

[0033] As further illustrated in FIG. 4D, the tape 100 incorporates two opposing elongated strips of silicone rubber 115a, 115b and interposes therein the carbon fiber, such as embodied in thread 105a, which by way of example and not limitation has a transverse spatial pattern, such that the thread increases the tensile strength and increases the tear resistance of the tape 100, while maintaining the elastic limit of the strips of self-fusing tape themselves. The incorporation of the carbon fiber in itself increases the tear resistance of the tape product, since the carbon fiber thread is virtually impossible to break.

[0034] The embodiments shown as “S”, triangular or a “Z” pattern in FIG. 4B, 4C are by way of example and not limitation, cross sectional views illustrate different pattern of carbon thread 105b and 105c, dependent on the desired tensile strength and modulus of elasticity.

[0035] In certain industrial applications, a coloration may be added to the tape as a whole or as a marking along the length of the tape to provide additional information to the user and/or to increase its visibility in the field. The tape may be color coded with additional pigment or dye to indicate which hazardous gas it is intended to detect. Fluorescent pigment or dye may be added to the tape to enhance its visibility, as by way of example in the dark.

[0036] A self-fusing silicone suitable for the top layer of silicone tape and the bottom layer of silicone tape should endeavor to meet the requirements for operating at a continuous temperature between −64° C. to +260° C.; having a tensile strength of 700 psi minimum (ASTM-d-412 standard testing), thickness tolerances +/−0.002 inches, width +/−0.0625 inches; ultimate elongation 300% minimum (ASTM d-412 standard testing); and a tear resistance 85 psi.

[0037] An apparatus for manufacturing self-sealing silicone tape having a carbon fiber includes: a multilayered silicone tape that changes color in the presence of hydrogen or hydrogen sulfide, that changes color in the presence of hydrogen or hydrogen sulfide, a bobbin for the insertion of a spool having carbon thread for feeding a continuous strand of thread into an oscillating mechanism for moving the thread strand transverse to the motion of a top layer of silicone tape and a bottom layer of silicone tape that serve to encapsulate the carbon fiber thread for producing a desired spatial pattern that increases the tear resistance of the tape product, while insuring the elastic limit of the strips of the tape is maintained, each such spool of silicon tape supplied by bobbins, whereby when the carbon thread is embedded between the layers of silicone tape and a heat mechanism to supply a contact heat required to fuse the interior surfaces of the layer of silicone tape thereby encapsulating the carbon fiber thread. Methods of constructing and operating spools of silicon tape supplied by bobbins in the manner described are well known to those skilled in the art of manufacturing tape products.

[0038] A method of manufacturing silicone tape product that serves as an indicator tape that changes color in the presence of hydrogen or hydrogen sulfide, and that encapsulates the carbon fiber thread includes, providing an apparatus to embed a carbon thread between the two elongated strips of self-fusing silicone rubber tape, oscillating carbon thread as it enters a nib in a pattern that increases the tear resistance while insuring the elastic limit of the strips tape is maintained, heating the two elongated strips until the surfaces are permanently joined to encapsulate the carbon thread.

[0039] While the present invention has been described with reference to the illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art in reference to this description. It is expressly intended that all combinations of those elements that perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention.