WO2019058185A1

WO2019058185A1 - Fabrication of sound absorbing layers

Info

Publication number: WO2019058185A1
Application number: PCT/IB2018/053552
Authority: WO
Inventors: Zahra MAZROUEI-SEBDANI; Akbar Khoddami
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-09-19
Filing date: 2018-05-21
Publication date: 2019-03-28
Anticipated expiration: 2020-03-19

Abstract

L'invention concerne un procédé de fabrication d'une couche absorbante acoustique. Le procédé peut comprendre la synthèse d'une poudre d'aérogel, la préparation d'une pâte de revêtement remplie d'un aérogel par mélange de l'aérogel synthétisé avec une pâte de revêtement, et l'application de la pâte de revêtement remplie d'un aérogel sur un substrat. La pâte de revêtement remplie d'un aérogel peut comprendre en outre un liant, un agent régulateur de la viscosité, et/ou un agent retardateur de flamme.The invention relates to a method of manufacturing an acoustic absorbing layer. The process may include synthesizing an airgel powder, preparing a coating paste filled with an airgel by mixing the synthesized airgel with a coating paste, and applying the filled coating paste. of an airgel on a substrate. The airgel-filled coating paste may further comprise a binder, a viscosity regulator, and / or a flame retardant.

Description

FABRICATION OF SOUND ABSORBING LAYERS

TECHNICAL FIELD

[0001] The present disclosure generally relates to sound insulators, and particularly to a method for fabricating sound absorbing layers.

BACKGROUND ART

[0002] Noise is generally defined as an unpleasant sound that may harm human ears. Noise may be reduced by utilizing sound-absorbing materials. Sound-absorbing materials generally have porous structures and size and number of pores in the porous structures may significantly affect their sound absorption properties.

[0003] Among different porous materials used in noise controlling applications, silica aerogels are excellent acoustic insulators. Aerogels are sol-gel materials that are dried in such a way as to avoid pore collapse, leaving an intact solid nanostructure in a material that is 90- 99% air by volume. Aerogels, known as frozen smoke or air-glass, may include nanoparticles with typical dimensions of less than 10 nm and pore sizes of less than 50 nm. The high porosity of the aerogel materials makes them excellent sound insulators. The propagation of an acoustic wave in an aerogel is attenuated in both amplitude and velocity because the wave energy is progressively transferred from the gas to the aerogel solid network.

[0004] However, aerogels are brittle and fragile materials. One approach to tackle this drawback is using a continuous nonwoven fiber batting to further reinforce the aerogels. While nonwoven fabrics are known as good sound absorbers at high frequency, they are less effective at low and middle frequencies where human sensitivity to noise is higher. Thus, introduction of fiber assemblies to the aerogel structures not only may reinforce fragile aerogel structures but also may improve acoustical behavior of the nonwovens especially at low frequencies. For example in aerogels with blanket-type forms, micron and submicron inorganic or organic fibers are added to a silica sol as a reinforcement, and these flexible blanket-type forms are prepared via a direct gelation of silica on the fibers. However, pure silica systems are mechanically too weak, blankets are dusty, and purely organic derived materials are flammable. Therefore there is a need for new inorganic-organic composites and/or hybrids that could address the above-mentioned problems and allow for production of superior sound insulators particularly from mechanical and thermodynamic points of view. SUMMARY OF THE DISCLOSURE

[0005] This summary is intended to provide an overview of the subject matter of the present disclosure, and is not intended to identify essential elements or key elements of the subject matter, nor is it intended to be used to determine the scope of the claimed implementations. The proper scope of the present disclosure may be ascertained from the claims set forth below in view of the detailed description below and the drawings of exemplary embodiments.

[0006] In one general aspect, the present disclosure is directed to a method for fabrication of a sound absorbing layer. The method may include synthesizing an aerogel powder, preparing an aerogel -filled coating paste by mixing the synthesized aerogel with a coating paste, and coating a substrate with the aerogel-filled coating paste.

[0007] According to one or more implementations, preparing an aerogel-filled coating paste by mixing the synthesized aerogel with a coating paste may include adding the synthesized aerogel to the coating paste in an amount between 0 and 10 wt. % based on a total weight of the aerogel-filled coating paste.

[0008] According to one or more implementations, the coating paste may further include 0.5 to 3 wt. % of a thickening agent, 2 to 10 wt. % of a binder, and 0.0 to 1 wt. % of a pigment.

[0009] According to some implementations, preparing an aerogel-filled coating paste by mixing the synthesized aerogel with a coating paste may include mixing the synthesized aerogel with a coating paste. The coating paste may include 2 to 10 wt. % of a binder, 1 to 5 wt. % of a viscosity adjustment agent, and 5 to 10 wt. % of a flame retarding agent. The aerogel -filled coating paste may include 1 to 15 wt. % of the synthesized aerogel.

[0010] According to an implementation, the binder may be selected from the group consisting of acrylates, cyanoacrylates, methacrylate epoxide, ethylene vinyl acetate, urea, polyamides, polyesters, polyethylene, polystyrenes, polyurethanes, polyvinyl acetates, polyvinyl alcohols, and silicone.

[0011] According to an implementation, the viscosity adjustment agent may include a filler with a chemical base comprising one of polymeric fibers, calcium carbonate, sodium carbonate, or inorganic like silica, titania, alumina, zinc oxides.

[0012] According to another implementation, the flame retarding agent includes a flame- retardant material with a chemical base may include one of ammonium salts, boric acid and/or borax, phosphorous- and nitrogen-containing chemicals, halogen-containing chemicals, zirconate and titanate salts, and mixtures thereof.

[0013] According to one or more implementations, preparing an aerogel-filled coating paste by mixing the synthesized aerogel with a coating paste may include vigorous stirring of the mixture at 600 rpm to 1100 rpm for 5 to 45 minutes.

[0014] According to one or more implementations, coating a substrate with the aerogel-filled coating paste may include submerging the substrate in the aerogel-filled coating paste. According to an implementation, coating the substrate with the aerogel-filled coating paste may further include drying the coated substrate at ambient pressure, and curing the dried coated substrate at an elevated temperature.

[0015] According to some implementations, drying the coated substrate at ambient pressure may include drying the coated substrate at ambient temperature for 2 to 24 hours. According to other implementations, drying the coated substrate at ambient pressure may further include drying the coated substrate at ambient pressure and at a temperature of approximately 50 °C to 120 °C for 2 to 15 minutes.

[0016] According to some implementations, curing the dried coated substrate at an elevated temperature may include curing the substrate at an elevated temperature of approximately 150 °C to 200 °C.

[0017] According to one or more implementations, synthesizing the aerogel powder may include preparing a silicic acid solution by passing a sodium silicate solution through an ion- exchange resin to remove sodium ions, subjecting the silicic acid solution to a gelation process by adjusting pH of the silicic acid solution between 4.5 and 5.5 to obtain a hydrogel, exchanging water content of the hydrogel with an alcohol by washing the hydrogel with the alcohol to obtain an alcogel, exchanging the alcohol of the alcogel with an organic solvent by washing the alcogel with the organic solvent to obtain an organogel, modifying the organogel by incubating the organogel with one of trimethylsilyl chloride (TMCS)-n-hexane, TMCS- cyclohexane, TMCS -heptane, hexamethyldisiloxane (HMDS)-n-hexane, HMDS- cyclohexane, and HMDS -heptane mixtures, drying the modified organogel to obtain a dried aerogel, and grinding the dried aerogel to obtain the aerogel powder.

[0018] According to some implementations, preparing a silicic acid solution may include passing a sodium silicate solution with a concentration between 10 wt. % and 30 wt.% through an ion-exchange resin. [0019] According to some implementations, subjecting the silicic acid solution to a gelation process to obtain a hydrogel may include mixing an ammonia solution with a concentration between 1 wt. % and 10 wt. % with the collected silicic acid.

[0020] According to some implementations, exchanging water content of the hydrogel with an alcohol may include washing the hydrogel with an alcohol including one of propan-2-ol, methanol, ethanol, propanol, butanol, hexanol, and mixtures thereof.

[0021] According to some implementations, exchanging the alcohol of the alcogel with an organic solvent may include washing the alcogel with an organic solvent including one of n- hexane, cyclohexane, heptane, octane, benzene, toluene, xylene, and mixtures thereof.

[0022] According to some implementations, drying the modified organogel at ambient pressure may include air drying the modified aerogel at room temperature for a duration of at least 2 hours and then drying the modified gel at an elevated temperature between 50 °C and 230 °C for approximately 1 hour.

[0023] In another general aspect, the present disclosure is directed to an aerogel-filled coating paste that may include 1 to 15 wt. % of an aerogel 2 to 10 wt. % of a binder, 1 to 5 wt. % of a viscosity adjustment agent, and 5 to 10 wt. % of a flame retarding agent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawing figures depict one or more implementations in accord with the present teachings, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements.

[0025] FIG. 1A illustrates a method for fabrication of a sound absorbing layer, according to one or more implementations of the present disclosure;

[0026] FIG. IB illustrates an implementation of synthesizing an aerogel powder, according to one or more implementations of the present disclosure;

[0027] FIG. 1C illustrates an implementation of coating a substrate with an aerogel-filled coating paste, according to an implementation of the present disclosure;

[0028] FIG. 2 shows a logarithmic graph of sound absorption coefficient of a coated nonwoven fabric for different sound frequencies, as described in connection with EXAMPLE 1;

[0029] FIG. 3A illustrates a scanning electron microscope (SEM) image of a nonwoven fabric before being coated; [0030] FIG. 3B illustrates an SEM image of the nonwoven fabric of FIG. 3A now coated with an aerogel -filled paste as described in detail in connection with EXAMPLE 1;

[0031] FIG. 4 shows contact angle of a water droplet on a surface of a coated nonwoven fabric, according to an implementation of the present disclosure as described in connection with EXAMPLE 1;

[0032] FIG. 5 shows a logarithmic graph of sound absorption coefficient of a coated nonwoven fabric for different sound frequencies, as described in connection with EXAMPLE 2; and

[0033] FIG. 6 shows contact angle of a water droplet on a surface of a coated nonwoven fabric, according to an implementation of the present disclosure as described in connection with EXAMPLE 2.

DESCRIPTION OF EMBODIMENTS

[0034] In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent that the present teachings may be practiced without such details. In other instances, well known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings.

[0035] The following detailed description is presented to enable a person skilled in the art to make and use the methods and devices disclosed in exemplary embodiments of the present disclosure. For purposes of explanation, specific nomenclature is set forth to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that these specific details are not required to practice the disclosed exemplary embodiments. Descriptions of specific exemplary embodiments are provided only as representative examples. Various modifications to the exemplary implementations will be readily apparent to one skilled in the art, and the general principles defined herein may be applied to other implementations and applications without departing from the scope of the present disclosure. The present disclosure is not intended to be limited to the implementations shown, but is to be accorded the widest possible scope consistent with the principles and features disclosed herein. [0036] The following disclosure describes techniques and methods for fabrication of sound absorbing layers by applying or otherwise coating aerogels over substrates, such as woven or nonwoven fabrics and thereby imparting the sound-absorbing properties of the aerogels to the substrate. The disclosed methods may include synthesizing an aerogel powder from non- expensive and available precursors such as sodium silicate via simple sol-gel methods where the drying step is carried out at ambient pressure. The disclosed methods may further include, coating the synthesized aerogel over the substrate to fabricate a sound absorbing layer. The synthesized aerogel may be coated by first preparing a coating paste containing the aerogel and then coating the substrate with the coating paste.

[0037] FIG. 1A illustrates a method 100 for fabrication of a sound absorbing layer, according to one or more implementations of the present disclosure. The method 100 may include a step 101 of synthesizing an aerogel powder; a step 102 of preparing an aerogel- filled coating paste by mixing the synthesized aerogel with a coating paste, such as a textile printing paste; and a step 103 of coating a substrate with the aerogel-filled coating paste.

[0038] FIG. IB illustrates an implementation of the step 101 of synthesizing an aerogel powder. Referring to FIG. IB, the step 101 may include a step 111 of preparing a silicic acid solution by passing a sodium silicate solution through an ion-exchange resin to remove sodium ions; a step 112 of subjecting the silicic acid solution to a gelation process to obtain a hydrogel; a step 113 of exchanging water content of the hydrogel with an alcohol to obtain an alcogel; a step 114 of exchanging the alcohol of the alcogel with an organic solvent such as n-hexane, cyclohexane, or heptane to obtain an organogel; a step 115 of modifying the organogel by incubating the organogel with one of trimethylsilyl chloride (TMCS)-n-hexane, TMCS-cyclohexane, TMCS -heptane, hexamethyldisiloxane (HMDS)-n-hexane, HMDS- cyclohexane, and HMDS -heptane mixture; a step 116 of drying the modified organogel to obtain a dried aerogel; and an optional step 117 of grinding the dried aerogel to obtain the aerogel powder.

[0039] Referring to FIG. IB, according to one or more implementations, the step 111 of preparing a silicic acid solution may include passing a sodium silicate solution with a concentration between 10 wt. % and 30 wt.% through an ion-exchange resin, such as Amberlite IR 120 H resin, or Purolite to remove sodium ions. According to an implementation, passing the sodium silicate solution through the ion-exchange resin may include passing the sodium silicate solution through a resin-filled column and then collecting the prepared silicic acid solution from the column.

[0040] Referring to FIG. IB, according to one or more implementations, the step 112 of subjecting the silicic acid solution to a gelation process to obtain a hydrogel may include mixing a pH adjusting solution, such as an ammonia solution with a concentration between 1 wt.% and 10 wt.% with the collected silicic acid to adjust the pH of the mixture at a value between 4.5 and 5.5. According to an implementation, the step 112 may further include aging the obtained hydrogel for 1 to 5 hours.

[0041] Referring to FIG. IB, according to one or more implementations, the step 113 of exchanging water content of the hydrogel with an alcohol to obtain an alcogel may include washing the hydrogel with an alcohol, such as propan-2-ol, methanol, ethanol, propanol, butanol, or hexanol.

[0042] Referring to FIG. IB, according to one or more implementations, the step 114 of exchanging the alcohol of the alcogel with an organic solvent such as n-hexane, cyclohexane, heptane, octane, benzene, toluene, or xylene to obtain an organogel may include washing the alcogel with the organic solvent solution.

[0043] Referring to FIG. IB, according to one or more implementations, the step 115 of modifying the organogel may include incubating the organogel with a modifying mixture, such as a TMCS-n-hexane mixture. According to some implementations, the modifying mixture may be one of TMCS-cyclohexane, TMCS -heptane, HMDS-n-hexane, HMDS- cyclohexane, or HMDS -heptane.

[0044] Referring to FIG. IB, according to one or more implementations, the step 116 of drying the modified organogel to obtain a dried aerogel may include drying the modified organogel at ambient pressure. In an implementation, drying the modified organogel at ambient pressure may include air drying the modified aerogel at room temperature for a duration of at least 2 hours and then drying the modified gel at an elevated temperature between 50 °C and 230 °C for approximately 1 hour.

[0045] Referring to FIG. IB, according to one or more implementations, the step 117 of grinding the dried aerogel to obtain the aerogel powder may include subjecting the dried aerogel to a ball milling process. In an example, the dried aerogel may be gently grinded in a ball mill with for example two zirconia balls at 150 rpm for 120 minutes. [0046] Referring back to FIG. 1A, according to an implementation, the step 102 of preparing an aerogel-filled coating paste may include mixing the prepared aerogel with a coating paste with a concentration of at most 10 wt.% based on the total weight pf the aerogel -filled coating paste. In an implementation, the coating paste may include 0.5 to 3 wt. % of a thickening agent, 2 to 10 wt. % of a binder, and 0.0 to 1 wt. % of a pigment. According to some implementations, mixing the prepared aerogel with the coating paste may include vigorous stirring of the mixture at 600 rpm to 1100 rpm for 5 to 45 minutes to obtain a homogeneous aerogel-filled paste.

[0047] According to an implementation, the homogeneous aerogel-filled paste may include 1 to 15 wt. % of the aerogel, 2 to 10 wt. % of a binder, 1 to 5 wt. % of a viscosity adjustment agent, and 5 to 10 wt. % of a flame retarding agent.

[0048] In an implementation, the binder may have a chemical base comprising one of acrylates, cyanoacrylates, methacrylate epoxide, ethylene vinyl acetate, urea, polyamides, polyesters, polyethylene, polystyrenes, polyurethanes, polyvinyl acetates, polyvinyl alcohols, and silicone. In another implementation, the viscosity adjustment agent may be a filler with a chemical base comprising one of polymeric fibers, calcium carbonate, sodium carbonate, or inorganic like silica, titania, alumina, zinc oxides.

[0049] According to an implementation, the flame retarding agent may be a flame-retardant material with a chemical base comprising one of ammonium salts, boric acid and/or borax, phosphorous- and nitrogen-containing chemicals, halogen-containing chemicals, zirconate and titanate salts, and mixtures thereof. In an example, the flame retarding agent may be added to the aerogel-filled coating paste and in another example, the flame retarding agent may be added as a flame retarding finishing on the coated substrate.

[0050] Referring to FIG. 1, according to one or more implementations, the step 103 of coating the substrate with the aerogel-filled coating paste may include a coating method comprising one of pad-dry, pad-cure, pad-dry-cure, knife over roll coating-dry, knife over roll coating-cure, knife over roll coating-dry-cure, knife over screen coating-dry, knife over screen coating-cure, knife over screen coating-dry-cure, foam coating-dry, foam coating-cure, foam coating-dry-cure, screen printing-dry, screen printing-cure, screen printing-dry-cure, rotary printing-dry, rotary printing-cure, rotary printing-dry-cure. In an implementation, the substrate may be a nonwoven or a woven fabric that may be made of organic or inorganic polymers. For example the substrate may be a polymer fabric made of a polymer such as polyester, polypropylene, polyamides, cotton, wool, and mixtures thereof.

[0051] FIG. 1C illustrates an implementation of the step 103 of coating the substrate with the aerogel-filled coating paste. Referring to FIG. 1C, the step 103 may include a step 131 of submerging the substrate in the aerogel -filled coating paste; a step 132 of squeezing excess aerogel-filled coating paste out of the substrate; a step 133 of drying the coated substrate at ambient pressure; and a further step 134 of curing the dried coated substrate at an elevated temperature.

[0052] Referring to FIG. 1C, according to an implementation, the step 131 of submerging the substrate in the aerogel -filled coating paste may include passing the substrate through a bath of the hydrogel-filled coating paste with a speed of 1 to 5 m/min. According to another implementation, the step 132 of squeezing excess aerogel-filled coating paste out of the substrate may include utilizing a padding process with an average pressure between 1 and 5 bar.

[0053] Referring to FIG. 1C, in an implementation, the step 133 of drying the coated substrate at ambient pressure may include drying the coated substrate at ambient temperature for 2 to 24 hours. In another implementation, drying the coated substrate at ambient pressure may include drying the coated substrate at ambient pressure and at a temperature of approximately 50 °C to 120 °C for 2 to 15 minutes.

[0054] Referring to FIG. 1C, in an implementation, the step 134 of curing the dried coated substrate at an elevated temperature may include curing the substrate at an elevated temperature of approximately 150 °C to 200 °C.

EXAMPLE 1

[0055] In this example, a sound absorbing layer is synthesized pursuant to the teachings of the present disclosure. Approximately 2 g of a silica aerogel synthesized from water-glass is added into 100 g of a foam-derived paste that contains 10 g of a urethane binding agent. The silica aerogel and the foam-derived paste are mixed in a mechanical stirrer under vigorous stirring for several minutes to form a homogenous aerogel filled-paste. In this example, for coating the aerogel-filled paste on a polyester nonwoven fabric with 1 mm thickness, pad- dry-cure method is used. The polyester nonwoven fabric was immersed in the homogenous aerogel filled-paste and subsequently, two-roll padder with the speed of 1 m/min. The fabric is then dried at ambient temperature and cured for 5 min at 150 °C. The pressure of the padding process is 2 bar.

[0056] FIG. 2 shows sound absorption coefficient of the coated nonwoven fabric of EXAMPLE 1 for different sound frequencies. Referring to FIG. 2, the sound absorption coefficient of the coated nonwoven fabric increases with an increase in the frequency. The highest sound absorption coefficient of 0.35 is obtained in a frequency of approximately 5000 Hz.

[0057] FIG. 3A illustrates a scanning electron microscope (SEM) image of the nonwoven fabric before being coated and FIG. 3B illustrates an SEM image of the same nonwoven fabric coated with the aerogel -filled paste as was described in detail in connection with EXAMPLE 1.

[0058] FIG. 4 shows contact angle of a water droplet 401 on a surface 402 of the coated nonwoven fabric. Referring to FIG. 4, contact angle 403 is approximately 110.1° and contact angle 404 is approximately 111.4°. An average contact angle of approximately 110.8° is obtained for the surface 402 of the coated nonwoven fabric of EXAMPLE 1, which indicates the hydrophobicity of the surface 402 of the coated nonwoven fabric.

EXAMPLE 2

[0059] In this example, a sound absorbing layer is synthesized pursuant to the teachings of the present disclosure. Approximately 4 g of a silica aerogel synthesized from water-glass is added into 100 g of a foam-derived paste that contains 5 g of a urethane binding agent and 10 g of a fluorocarbon water repellent material. The silica aerogel and the foam-derived paste are mixed in a mechanical stirrer under vigorous stirring for several minutes to form a homogenous aerogel filled-paste. In this example, for coating the aerogel-filled paste on a polyester nonwoven fabric with 3 mm thickness, knife-over-screen method is used. The fabric is then cured for 5 min at 170 °C.

[0060] FIG. 5 shows sound absorption coefficient of the coated nonwoven fabric of EXAMPLE 2 for different sound frequencies. Referring to FIG. 5, the sound absorption coefficient of the coated nonwoven fabric increases with an increase in the frequency. The highest sound absorption coefficients of 0.6-0.7 is obtained in a frequency range of approximately 2500-5000 Hz. [0061] FIG. 6 shows contact angle of a water droplet 601 on a surface 602 of the coated nonwoven fabric. Referring to FIG. 6, contact angle 603 is approximately 110.1° and contact angle 604 is approximately 111.4°. An average contact angle of approximately 110.8° is obtained for the surface 402 of the coated nonwoven fabric of EXAMPLE 2, which indicates a higher hydrophobicity of the surface 602 of the coated nonwoven fabric of EXAMPLE 2 in comparison to the hydrophobicity of the surface 402 of the coated nonwoven fabric of EXAMPLE 1 (labeled in FIG. 4).

[0062] While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that subject matter disclosed herein may be implemented in various forms and examples, and that the teachings may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all applications, modifications and variations that fall within the true scope of the present teachings.

[0063] Unless otherwise stated, all measurements, values, ratings, positions, magnitudes, sizes, and other specifications that are set forth in this specification, including in the claims that follow, are approximate, not exact. They are intended to have a reasonable range that is consistent with the functions to which they relate and with what is customary in the art to which they pertain.

[0064] The scope of protection is limited solely by the claims that now follow. That scope is intended and should be interpreted to be as broad as is consistent with the ordinary meaning of the language that is used in the claims when interpreted in light of this specification and the prosecution history that follows and to encompass all structural and functional equivalents. Notwithstanding, none of the claims are intended to embrace subject matter that fails to satisfy the requirement of Sections 101, 102, or 103 of the Patent Act, nor should they be interpreted in such a way. Any unintended embracement of such subject matter is hereby disclaimed.

[0065] Except as stated immediately above, nothing that has been stated or illustrated is intended or should be interpreted to cause a dedication of any component, step, feature, object, benefit, advantage, or equivalent to the public, regardless of whether it is or is not recited in the claims.

[0066] It will be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study, except where specific meanings have otherwise been set forth herein. Relational terms such as "first" and "second" and the like may be used solely to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, as used herein and in the appended claims are intended to cover a non-exclusive inclusion, encompassing a process, method, article, or apparatus that comprises a list of elements that does not include only those elements but may include other elements not expressly listed to such process, method, article, or apparatus. An element proceeded by "a" or "an" does not, without further constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0067] The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is not intended to be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various implementations. Such grouping is for purposes of streamlining this disclosure, and is not to be interpreted as reflecting an intention that the claimed implementations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed implementation. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separately claimed subject matter.

[0068] While various implementations have been described, the description is intended to be exemplary, rather than limiting and it will be apparent to those of ordinary skill in the art that many more implementations are possible that are within the scope of the implementations. Although many possible combinations of features are shown in the accompanying figures and discussed in this detailed description, many other combinations of the disclosed features are possible. Any feature of any implementation may be used in combination with or substituted for any other feature or element in any other implementation unless specifically restricted. Therefore, it will be understood that any of the features shown and/or discussed in the present disclosure may be implemented together in any suitable combination. Accordingly, the implementations are not to be restricted except in light of the attached claims and their equivalents. Also, various modifications and changes may be made within the scope of the attached claims.

Claims

WHAT IS CLAIMED IS:

1. A method for fabrication of a sound absorbing layer, the method comprising: synthesizing an aerogel powder; preparing an aerogel-filled coating paste by mixing the synthesized aerogel with a coating paste; and

coating a substrate with the aerogel-filled coating paste.

2. The method according to claim 1, wherein preparing an aerogel-filled coating paste by mixing the synthesized aerogel with a coating paste includes adding the synthesized aerogel to the coating paste in an amount between 0 and 10 wt. % based on a total weight of the aerogel-filled coating paste.

3. The method according to claim 2, wherein the coating paste further comprises 0.5 to 3 wt. % of a thickening agent, 2 to 10 wt. % of a binder, and 0.0 to 1 wt. % of a pigment.

4. The method according to claim 1, wherein preparing an aerogel-filled coating paste by mixing the synthesized aerogel with a coating paste includes mixing the synthesized aerogel with a coating paste, the coating paste comprising 2 to 10 wt. % of a binder, 1 to 5 wt. % of a viscosity adjustment agent, and 5 to 10 wt. % of a flame retarding agent, the aerogel-filled coating paste comprising 1 to 15 wt. % of the synthesized aerogel.

5. The method according to claim 4, wherein the binder is selected from the group consisting of acrylates, cyanoacrylates, methacrylate epoxide, ethylene vinyl acetate, urea, polyamides, polyesters, polyethylene, polystyrenes, polyurethanes, polyvinyl acetates, polyvinyl alcohols, and silicone.

6. The method according to claim 4, wherein the viscosity adjustment agent includes a filler with a chemical base comprising one of polymeric fibers, calcium carbonate, sodium carbonate, or inorganic like silica, titania, alumina, zinc oxides.

7. The method according to claim 4, wherein the flame retarding agent includes a flame- retardant material with a chemical base comprising one of ammonium salts, boric acid and/or borax, phosphorous- and nitrogen-containing chemicals, halogen-containing chemicals, zirconate and titanate salts, and mixtures thereof.

8. The method according to claim 1, wherein preparing an aerogel-filled coating paste by mixing the synthesized aerogel with a coating paste includes vigorous stirring of the mixture at 600 rpm to 1100 rpm for 5 to 45 minutes.

9. The method according to claim 1 , wherein coating a substrate with the aerogel-filled coating paste includes submerging the substrate in the aerogel-filled coating paste.

10. The method according to claim 9, further comprising:

drying the coated substrate at ambient pressure; and

curing the dried coated substrate at an elevated temperature.

11. The method according to claim 10, wherein drying the coated substrate at ambient pressure includes drying the coated substrate at ambient temperature for 2 to 24 hours.

12. The method according to claim 11, further comprising drying the coated substrate at ambient pressure and at a temperature of approximately 50 °C to 120 °C for 2 to 15 minutes.

13. The method according to claim 10, wherein curing the dried coated substrate at an elevated temperature includes curing the substrate at an elevated temperature of approximately 150 °C to 200 °C.

14. The method according to claim 1, wherein synthesizing the aerogel powder comprises:

preparing a silicic acid solution by passing a sodium silicate solution through an ion-exchange resin to remove sodium ions;

subjecting the silicic acid solution to a gelation process by adjusting pH of the silicic acid solution between 4.5 and 5.5 to obtain a hydrogel;

exchanging water content of the hydrogel with an alcohol by washing the hydrogel with the alcohol to obtain an alcogel;

exchanging the alcohol of the alcogel with an organic solvent by washing the alcogel with the organic solvent to obtain an organogel;

modifying the organogel by incubating the organogel with one of trimethylsilyl chloride (TMCS)-n-hexane, TMCS-cyclohexane, TMCS -heptane, hexamethyldisiloxane (HMDS)-n-hexane, HMDS-cyclohexane, and HMDS -heptane mixtures;

drying the modified organogel to obtain a dried aerogel; and

grinding the dried aerogel to obtain the aerogel powder.

15. The method according to claim 14, wherein preparing a silicic acid solution includes passing a sodium silicate solution with a concentration between 10 wt. % and 30 wt.% through an ion-exchange resin.

16. The method according to claim 14, wherein subjecting the silicic acid solution to a gelation process to obtain a hydrogel includes mixing an ammonia solution with a concentration between 1 wt.% and 10 wt.% with the collected silicic acid.

17. The method according to claim 14, wherein exchanging water content of the hydrogel with an alcohol includes washing the hydrogel with an alcohol comprising one of propan-2-ol, methanol, ethanol, propanol, butanol, hexanol, and mixtures thereof.

18. The method according to claim 14, wherein exchanging the alcohol of the alcogel with an organic solvent includes washing the alcogel with an organic solvent comprising one of n- hexane, cyclohexane, heptane, octane, benzene, toluene, xylene, and mixtures thereof.

19. The method according to claim 14, wherein drying the modified organogel at ambient pressure includes air drying the modified aerogel at room temperature for a duration of at least 2 hours and then drying the modified gel at an elevated temperature between 50 °C and 230 °C for approximately 1 hour.

20. An aerogel-filled coating paste, comprising 1 to 15 wt. % of an aerogel 2 to 10 wt. % of a binder, 1 to 5 wt. % of a viscosity adjustment agent, and 5 to 10 wt. % of a flame retarding agent.