WO2012078739A2 - Insulated units and methods for producing them - Google Patents

Abstract

A method for producing an insulated unit includes sealing an interior space of the unit, the interior space containing a particulate material and a gas, the gas being at a first temperature that is higher than a second temperature and a first pressure, wherein the first pressure is not generated by mechanical evacuation of the interior space, for instance by pumping gas from the interior space to draw a vacuum on the interior space; and cooling or allowing the gas to cool to the second temperature, thereby reducing the first pressure and compacting the particulate material. Also disclosed is an insulated unit.

Description

INSULATED UNITS AND METHODS FOR PRODUCING THEM

RELATED APPLICATIONS

[oooi] This application claims the benefit under 35 U.S.C. § 1 19(e) of U.S. Provisional Patent Application No. 61/421 ,538, filed on December 9, 2010, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[ 0002 ] Insulated windows and spandrel panels are increasingly used in residential and commercial buildings. Double pane, as well as triple pane, and even quadruple pane window units are available. In many existing insulated windows the internal space is filled with air. Sometimes the internal space is filled with a gas such as argon or krypton for better thermal resistance value. Insulated glass units and daylighting systems that employ particulate aerogel material also are becoming available.

[ 0003 ] Filling the internal cavity of such units with aerogel particles, however, continues to present challenges. "Settling" of the aerogel particles, for instance, can result in diminished insulating properties, uneven translucence, dust lines and/or losses in the esthetic appearance of the unit. Alterations in internal temperature, external air pressure, wind loads or rapidly changing loads and other conditions encountered during

transportation and/or use of the unit can cause expansion of the unit cavity, pushing adjacent panes away from one another and leading to a settling of particulate material which, in many cases, continues even after the unit returns to its relaxed state.

[ 0004 ] In one manufacturing approach that addresses settling, the internal cavity of a fenestration unit is expanded, for example, by pulling adjacent panes away from one another, and the unit is overfilled or overpacked with particulate matter. The unit is then stabilized, for instance, by use of a vacuum pump to remove gas, e.g., air, from the internal cavity, followed by sealing and/or other finishing steps. [ 0005] Mechanical evacuation also is employed to drive off moisture from aerogel particles in heated multiple plate panels, in order to reduce water condensation in the finished panel.

[ 0006] It is found, however, that mechanical pumping through a space packed with particulate material is laborious and that difficulties and problems encountered in achieving a desired pressure reduction are exacerbated in larger aerogel-filled units.

SUMMARY OF THE INVENTION

[ 0007] A need exists, therefore, for insulated units, e.g., glazing panels, and methods of fabricating such units that reduce or minimize these problems.

[ 0008 ] In one embodiment the invention is directed to a method for producing an insulated unit. The method includes: sealing an interior space of the unit, the interior space containing a particulate material and a gas, the gas being at a first temperature that is higher than a second temperature and a first pressure, wherein the first pressure is not generated by mechanical evacuation of the interior space; and cooling or allowing the gas to cool to the second temperature, thereby reducing the first pressure and compacting the particulate material.

[ 0009] In another embodiment, a method for producing an insulated unit comprises: heating a panel having an interior space; filling the interior space with a particulate material; sealing the panel; and cooling or allowing the sealed panel to cool, thereby reducing a pressure in the interior space and compacting the particulate material, wherein heated gas present in the interior space after filling with the particulate material is not evacuated by mechanical means.

[ o o i o] In a further embodiment, a method for producing an insulated panel comprises: heating a particulate material; filling an interior space of a panel with the particulate material; sealing the panel; and cooling or allowing the sealed panel to cool, thereby reducing a pressure in the interior space and compacting the particulate material, wherein heated gas present in the interior space after filling with the particulate material is not evacuated by mechanical means.

[ooii] In yet another embodiment, a method for producing an insulated panel comprises heating a particulate material, a panel or both; filling an interior space of the panel with the particulate material; sealing the panel; and cooling or allowing the sealed panel to cool, thereby reducing a pressure in the interior space and compacting the particulate material, wherein heated gas present in the interior space after filling with the particulate material is not evacuated by mechanical means.

[0012] Another aspect of the invention relates to an insulated unit. In one example, a glazing panel has an interior space that is free of mechanical reinforcements and is filled with an aerogel material; a surface area of at least 1 ft2; and a settling of the aerogel material determined by thermal cycling according to ASTM E2190 that is no greater than about ¼ of an inch.

[0013] The invention addresses the increased demand for energy conservation and "green" construction practices and/or materials, and has many advantages. For example, window units manufactured according to embodiments of the invention have excellent insulating and optical properties, have uniform appearance, present no or greatly reduced dust lines, and contain minimal contamination. Settling of particulate material is eliminated or minimized. In spandrel applications, units such as described herein can be glazed into the profiled system as a finished unit, eliminating the back pans, other insulating materials and labor required to fabricate and install them.

[0014] Aspects of the invention can be practiced in the absence of mechanical gas evacuation, eliminating difficulties encountered with pumping through particles packed in the unit cavity. Furthermore, fabrication techniques according to the invention can be easily integrated in existing manufacturing infrastructure and/or processes.

[0015] Panels filled according to the invention also allow for greater opportunity and time for proper sealing of the panels as the final internal pressure level achieved in the panels can be a function of how much the temperature drops, rather than of maintaining a vacuum produced through mechanical means.

BRIEF DESCRIPTION OF THE DRAWINGS

[ 0016] In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings:

[ 0017 ] FIG. 1 is a cross sectional view of a unit that can be filled with a particulate material.

[ 0018 ] FIG. 2 is a cross-sectional view of a filling apparatus including a dispensing device, and a unit being filled with particulate material.

[ 0019] FIG. 3 is a schematic representation of increasing the internal volume during the fabrication of an insulated unit.

[ 002 0 ] FIG. 4 is a schematic representation of a relaxed insulated unit produced by embodiments of the invention.

[ 0021 ] FIG. 5 is a schematic diagram of a sealed and finished insulated glass unit.

[ 0022 ] FIGS. 6A, 6B and 6C are schematic diagrams of arrangements that can be employed to seal the insulated unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[ 0023 ] The above and other features of the invention including various details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. [ 0024 ] The invention generally relates to insulated units such as, for example, insulated panels used in fenestration systems, roof coverings, e.g., skylights, smoke vents, roof hatches and so forth, spandrel units and other applications, and methods for producing such insulated units. In specific examples, the invention relates to insulated glazed panels or units (IGUs). The insulated units can be can be utilized in the construction industry, transportation, storage containers, refrigeration, green houses, manufacturing or processing stations and so forth.

[ 0025 ] Many embodiments of the invention pertain to an insulating unit that has an interior space, also referred to as a "gap" or "cavity", typically defined by adjacent panes. A unit can include two or more panes, and one or more interior spaces. Shown in FIG. 1 , for example, is insulated panel 10 having panes, 12a and 12b secured by frame 14, which includes frame member 16 and top frame member 18.

[ 0026 ] Panes 12a and 12b can be transparent, translucent or opaque and can be both made from the same or different materials. Suitable materials include glass, metals, stone, ceramics, plastics, e.g., polycarbonate, polyesters, acrylics, fiber-reinforced panels, laminated structures, and others. In many cases, the panes are flat and parallel or substantially parallel to one another and are held in a frame, as known, for instance, in double or triple pane window systems.

[ 0027 ] One or more pane surfaces can be coated, for instance, with an ultraviolet (UV) reflecting film, a dyed layer, a scratch-resistant material, or with other suitable coatings. Uncoated panes also can be utilized. In a specific implementation, the insulated unit, e.g., panel 10, includes a low-emissivity (Low-E) coating applied to one or more pane surfaces. A Low-E coating can be a very (e.g., microscopically) thin layer deposited directly on the pane surface and serving to reduce infrared (IR) radiation from a warm pane to a cooler pane, thus reducing the U-factor (susceptibility of the panel to transfer heat) of the unit. Typically, Low-E coatings are applied on an exterior pane surface when the insulated panel is designed for warm climates where the objective is to protect against the sun. For maintaining heat inside the house, units designed for colder climates typically employ Low- E coatings that are applied on the inside pane of glass. In an alternative approach to Low-E coatings films can be applied either directly to one of the glass panels or as an intermediate surface between the glass panels. These films, such as those available from Serious Materials, provide the desired reduction in infrared radiation, and in the case of a film that is used as an intermediate surface between the glass panes, provide a means to reduce the convective heat transfer between the panels of glass.

[ 0028 ] The panes are dimensioned to the particular application. In a specific example, the panes are sized for relatively large units and can have a surface of at least 3 square meters (m²). Aspects of the invention also can be practiced with panes having a smaller surface, e.g., less than about 0.1 m². In further examples the units have a surface area of at least 0.5, 1 , 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, m² or more.

[ 0029] For typical glass panes, the pane thickness can be within the range of from about 2 mm to about 10 mm. In polycarbonate systems, the pane thickness could be within the range of from about 1 mm to about 60 mm. Polyester panes typically have a thickness within the range of from about 1 mm to about 6 mm. Metal panes thickness can be within the range of from about 0.5 mm to about 6 mm. Within one system, the wall thickness can be the same for two or more walls, or can be different.

[ 0030 ] Frame 14 can be constructed from one or more materials such as, for example, metal, e.g., aluminum, stainless steel or magnesium, plastic materials, e.g., polyurethane foam, or other materials, for instance materials intended to limit the transfer of heat from one glass pane to the other.

[ 0031] Panes 12a and 12b define interior space 20 and can be separated by a spacer which, as known in the art, is the piece (made of metal or another suitable material) that separates and seals the unit. The distance between these two panes i.e., the gap width (W) can be dimensioned for a particular application. For example, the gap width can be within the range of from about 3 mm to about 200 mm, e.g., 10, 50, 75, 100, 1 50 or 175 mm. If more than two panes are employed, interior spaces between any two adjacent panes can have the same or a different gap width.

[ 0032 ] The interior space can be provided with one or more mechanical reinforcements (not shown in FIG. 1) also referred to herein as "internal" reinforcements. Examples include spacers (other than the spacer found at the periphery of the panes), e.g., rubber spacers, internal supports, inner walls (e.g., walls dividing the gap into channels), ribs, springs or other bracing devices. Positioned in the gap between adjacent walls, internal reinforcements can stabilize the overall system during manufacturing, distribution, installation and service life. In glass systems internal reinforcements can reduce the likelihood of breakage. In other cases, internal reinforcements can mitigate flimsiness in units constructed with thin plastic, e.g., polycarbonate, walls. Examples of insulated panel and glazing systems that have a channeled gap and inner walls are described, for example, in U.S. Patent No. 7,641 ,954, with the title Insulated Panel and Glazing System

Comprising the Same, issued on January 5, 2010 to Rouanet et al., the teachings of which are incorporated herein by reference in their entirety.

[ 0033 ] In specific examples, the insulated unit described herein is "internally un- reinforced", i.e., the system does not include an internal reinforcement such as described above.

[ 0034 ] At least one of the interior spaces of the insulated unit, e.g., space 20 of insulated unit 10 of FIG. 1 , contains a particulate material.

[ 0035] The aggregate particle size (i.e., particle size distribution) of the particulate material can be selected by considering parameters such as dust formation, unit dimensions, e.g., filling openings, packing efficiency, commercial availability and so forth. A suitable aggregate particle size can be within the range of from about 0.1 mm and about

10 mm. Insulated units described herein can utilize granular materials having a particle size of 0.5, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10 mm or higher. Combination of particles having different particle sizes (as specified, for instance, by classification, e.g., sieving) also can be employed.

[ 0036 ] In some embodiments, the particulate material is composed of chemically different particles.

[ 0037 ] The particulate material can be a porous material, e.g., a microporous or a nanoporous material. As used herein, the term "microporous" refers to materials having pores that are about 1 micron and larger. As used herein, the term "nanoporous" refers to a material having pores that are smaller than about 1 micron, e.g., less than 0.1 microns. In specific examples, the nanoporous material is an oxide of a metal, for instance, silicon, aluminum, zirconium, titanium, hafnium, vanadium, yttrium and others, and/or mixtures thereof.

[ 0038 ] In specific embodiments of the invention, the particulate material consists of, consists essentially of, or comprises aerogel. Aerogels are low density porous solids that have a large intraparticle pore volume and typically are produced by removing pore liquid from a wet gel. However, the drying process can be complicated by capillary forces in the gel pores, which can give rise to gel shrinkage or densification. In one manufacturing approach, collapse of the three dimensional structure is essentially eliminated by using supercritical drying. A wet gel also can be dried using ambient pressure, also referred to as non-supercritical drying process. When applied, for instance, to a silica-based wet gel, surface modification, e.g., end-capping, carried out prior to drying, prevents permanent shrinkage in the dried product. The gel can still shrink during drying but springs back recovering its former porosity.

[ 0039] Product referred to as "xerogel" also is obtained from wet gels from which the liquid has been removed. The term often designates a dry gel compressed by capillary forces during drying, characterized by permanent changes and collapse of the solid network.

[ 0040] For convenience, the term "aerogel" is used herein in a general sense, referring to both "aerogels" and "xerogels".

[ 004 1] Aerogels typically have low bulk densities (about 0.15 g/cm³ or less, in many instances about 0.03 to 0.3 g/ cm³), very high surface areas (generally from about 300 to about 1 ,000 square meters per gram (m²/g) and higher, for example from about 600 to about 1000 m²/g), high porosity (about 90% and greater, e.g., greater than about 95%), and a relatively large pore volume (e.g., about 3 milliliter per gram (mL/g), for example, about 3.5 mL/g and higher, for instance, 7 mL/g). Aerogels can have a nanoporous structure with pores smaller than 1 micron (μηι). Often, aerogels have a mean pore diameter of about 20 nanometers (ran). The combination of these properties in an amorphous structure gives the lowest thermal conductivity values (e.g., 9 to 16 mW/m-K, at a mean temperature of 37° C and 1 atmosphere of pressure) for any coherent solid material. Aerogels can be nearly transparent or translucent, scattering blue light, or can be opaque.

[ 0042 ] A common type of aerogel is silica-based. Aerogels based on oxides of metals other than silicon, e.g., aluminum, zirconium, titanium, hafnium, vanadium, yttrium and others, or mixtures thereof can be utilized as well.

[ 0043 ] Also known are organic aerogels, e.g., resorcinol or melamine combined with formaldehyde, dendritic polymers, and so forth, and the invention also could be practiced using these materials.

[ 0044 ] Suitable aerogel materials and processes for their preparation are described, for example, in U.S. Patent Application No. 2001/0034375 Al to Schwertfeger et al., published on October 25, 2001 , the teachings of which are incorporated herein by reference in their entirety.

[ 00 5 ] In many implementations, the aerogel employed is hydrophobic. As used herein, the terms "hydrophobic" and "hydrophobized" refer to partially as well as to completely hydrophobized aerogel. The hydrophobicity of a partially hydrophobized aerogel can be further increased. In completely hydrophobized aerogels, a maximum degree of coverage is reached and essentially all chemically attainable groups are modified.

[ 0046 ] Hydrophobicity can be determined by methods known in the art, such as, for example, contact angle measurements or by methanol (MeOH) wettability. A discussion of hydrophobicity in relation to aerogels is found, for example, in U.S. Patent No. 6,709,600 B2 issued to Hrubesh et al. on March 23, 2004, the teachings of which are incorporated herein by reference in their entirely.

[ 0047] Hydrophobic aerogels can be produced by using hydrophobizing agents, e.g., silylating agents, halogen- and in particular fluorine-containing compounds such as fluorine-containing alkoxysilanes or alkoxysiloxanes, e.g., trifluoropropyltrimethoxysilane (TFPTMOS), and other hydrophobizing compounds known in the art. Hydrophobizing agents can be used during the formation of aerogels and/or in subsequent processing steps, e.g., surface treatment.

[ 00 8 ] Silylating compounds such as, for instance, silanes, halosilanes,

haloalkylsilanes, alkoxysilanes, alkoxyalkylsilanes, alkoxyhalosilanes, disiloxanes, disilazanes and others are preferred. Examples of suitable silylating agents include, but are not limited to diethyldichlorosilane, allylmethyldichlorosilane, ethylphenyldichlorosilane, phenylethyldiethoxysilane, trimethylalkoxysi lanes, e.g., trimethylbutoxysilane, 3,3,3- trifluoropropylmethyldichlorosilane, symdiphenyltetramethyldisiloxane,

trivinyltrimethylcyclotrisiloxane, hexaethyldisiloxane, pentylmethyldichlorosilane, divinyldipropoxysilane, vinyldimethylchlorosilane, vinylmethyldichlorosilane,

vinyldimethylmethoxysilane, trimethylchlorosilane, hexamethyldisiloxane,

hexenylmethyldichlorosilane, hexenyldimethylchlorosilane, dimethylchlorosilane, dimethyldichorosilane, mercaptopropylmethyldimethoxysilane, bis{3- (triethoxysilyl)propyl}tetrasulfide, hexamethyldisilazane and combinations thereof.

[ 0049] Aerogel materials such as aerogel particles often include additives, for instance, fibers, opacifiers, color pigments, dyes, reactive binders and mixtures thereof. Silica aerogel, for example, can be prepared to contain fibers and/or one or more metals or compounds thereof. Specific examples include aluminum, tin, titanium, zirconium or other non-siliceous metals, and oxides thereof. Non-limiting examples of opacifiers include carbon black, titanium dioxide, zirconium silicate, and mixtures thereof. Additives can be provided in any suitable amounts, e.g., depending on desired properties and/or specific application.

[ 0050 ] Aerogel materials in particulate form include aerogel granules, pellets, beads, powders and so forth. Aerogel particles employed can have any particle size suitable for an intended application. For instance, the aerogel particles can be within the range of from about 0.01 microns to about 10.0 millimeters (mm) and can have, for example, a mean particle size in the range of 0.3 to 3.0 mm, e.g., 0.3, 0.5, 0.8, 1.0, 1.5, 2.0, 2.5 or 3.0 mm. Many implementations employ larger particles. Also suitable are aerogel particles having a particle size distribution (PSD) that promotes efficient packing.

[ 0051 ] Examples of commercially available aerogel materials in particulate form are those supplied under the tradename of Nanogel® by Cabot Corporation, Billerica, Massachusetts. Nanogel® aerogel granules have high surface area, are greater than about 90% porous and are available in a particle size ranging, for instance, from about 8 microns (μηι) to about 10 mm, e.g., 10 microns, 50 microns, 100 microns, 500, microns, 1 mm, 3 mm, 5 mm, 6 mm, or 7 mm. Specific grades of translucent Nanogel® aerogel include, for instance, those designated as TLD302, TLD301 or TLD100. As one example, a particulate layer of translucent Nanogel® aerogel particles, having a thickness of 25 mm, has a visible light transmission of about 53%, while layer made of translucent Nanogel® aerogel particles having a thickness of 50 mm, has a visible light transmission of about 26%. Also, light transmission through some types of Nanogel® aerogel can be diffused.

[ 0052 ] The interior space also can contain opaque aerogel. Spandrel areas, for instance, relate to opaque areas, as contrasted to the vision area of a curtain wall, which is formed by the use of spandrel panels which are either intrinsically opaque or are rendered opaque by various backing or coating materials. Spandrel units, also referred to as "spandrel panels" or "spandrels" can be employed to thermally isolate and/or conceal certain portions of the interior structure of a building. Often, spandrels are employed to conceal floor slabs, mechanical chase ways, vertical spans between floors and ceilings or between successive viewing closures, heating and air conditioning convectors and so forth.

Spandrel units also can be used in building zones where it is desired to maintain a degree of privacy, such as at the ground level of a building. Specific grades of IR-opacified Nanogel® aerogel that can be utilized include, e.g., those under the designation of RGD303 or CBTLD103; specific grades of opaque Nanogel® aerogel include, for instance, those designated as OGD303.

[ 0053 ] Aerogel materials in particulate form can also be derived from a monolithic aerogel or aerogel based composite, sheet, blanket and so forth. For example, pieces of such aerogel materials can be obtained by crushing, breaking down, chopping, comminuting or by other suitable techniques through which aerogel particles can be obtained from aerogel monoliths, composites, blankets, sheets and other such precursors.

[ 0054 ] Some specific examples of materials that can be processed to produce particles include aerogel-based composite materials, such as those including aerogel and fibers (e.g., fiber-reinforced aerogels) and, optionally, at least one binder. The fibers can have any suitable structure. For example, the fibers can be oriented in a parallel direction, an orthogonal direction, in a common direction or a random direction. There can be one or more types of fibers. The fibers can be different in terms of their composition, size or structure. In the composite, the one type of fibers can be in different dimensions (length and diameter) and their orientation can be different. For example long fibers are in plane aligned whereas smaller fibers are randomly distributed. Specific examples are described, for instance, in U.S. Patent No. 6,887,563, issued on May 3, 2005 to Frank et al., the teachings of which are incorporated herein by reference in their entirety. Other examples include at least one aerogel and at least one syntactic foam. The aerogel can be coated to prevent intrusion of the polymer into the pores of the aerogel, as described, for instance in International Publication No. WO 2007047970, with the title Aerogel Based Composites, the teachings of which are incorporated herein by reference in their entirety. In yet other examples, the aerogel can derive from a blanket, e.g., arrangements in which blanket sheets are laminated together to form a multilayer structures. Described in U.S. Patent No.

5,789,075, issued on August 4, 1998 to Frank et al., the teachings of which are

incorporated herein by reference in their entirety, are a cracked monoliths and these also can serve as suitable precursor in producing the self supporting rigid composite disclosed herein. Other suitable examples of aerogel material that can be used are fiber-web/aerogel composites that include bicomponent fibers as disclosed in U.S. Patent No. 5,786,059 issued on July 28, 1998 to Frank et al., the teachings of which are incorporated herein by reference in their entirety. The aerogel particles also can be derived from sheets or blankets produced from wet gel structures, as described, for instance, in U.S. Patent Application Publication Nos. 2005/0046086 Al , published March 3, 2005, and 2005/0167891 Al , published on August 4, 2005, both to Lee et al., the teachings of which are incorporated herein by reference in their entirety. Commercially, aerogel-type blankets or sheets are available, for example, from Cabot Corporation, Billerica, Mass. or from Aspen Aerogels, Inc., Northborough, Mass.

[ 0055 ] Combinations of aerogel particles also can be employed. For instance, the interior space can include two or more different types of aerogel materials, optionally having different particle sizes and/or light transmitting properties. For example, the mixture might include TLD 101 and TLD 302 Nanogel® aerogels. Aerogel particles also can be used in conjunction with other materials. If light transmission properties are important, aerogel particles can be combined with transparent or translucent non-aerogel material, for instance, glass microbeads or microspheres, such as those commercially available from 3M Corporation. Polymeric microspheres, e.g., expanded polystyrene or polypropylene beads, as well as other particulate materials, whether light-transmitting or opaque, also can be utilized. Examples of non-aerogel materials include silicon oxide and other metal oxides, e.g., alumina, aluminosilicate, perlite, or combinations thereof.

[ 0056] The particulate material can be obtained by combining aerogel and non-aerogel materials, blended in any proportion suitable to the application. Cost, insulating properties, light transmission, function of the unit within the overall construction are some of the factors that can be considered. Generally, the non-aerogel material can be present in the mixture in an amount anywhere from 0% to 99%. For instance, aerogel and non-aerogel materials can be blended in 20:80 to 80:20 ratios, e.g., 70: 30, 60:40, 50:50 or 40:60 or 30:70. Other relative amounts can be used.

[ 0057 ] In specific embodiments of the invention, the particulate material has one or more properties, as further described below.

[ 0058 ] For example, the particulate material can have a density less than about 0.5 g/cm³, for instance, less than about 0.3 g/cm³ or less than about 0.1 g/cm³. In some implementations, the particulate material has a void volume fraction of at least about 10%, e.g., least about 50%. In specific examples, the particulate material has a void volume % of at least about, 75, 80, 85 or 90%. [ 0059] In many cases, the particulate material has insulating properties. For instance, the particulate material can be a thermal insulator having an "R-value", which is a measure of thermal resistance to heat flow, of at least 2, e.g., 3, 5, 10, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36 or 38. In other examples, the particulate material has a thermal conductivity (k) value within the range of from about 12 to about 30, e.g., 15, 18, 20, 24 or 28, mW/m-K at a mean temperature of 37° C and 1 atmosphere of pressure. In some cases, the particulate material has a k value that decreases with load or compression as well as reduced pressure. Furthermore, compressible and springy particulate materials can act as a brace or reinforcement, providing support.

[ 0060] The particulate material can have acoustic insulating properties. For instance, it can slow down the speed of sound through the material, reducing noise, in particular in the lower nuisance frequency range.

[ 0061] The particulate material can have electrical insulating properties.

[ 0062 ] In some implementations, the particulate material has fire resistance or fire proofing properties, water resistance, hydrophobic properties and/or can withstand mold formation.

[ 0063 ] The particulate material can have a light transmission greater than 0% and in many cases is translucent. As used herein, the term "translucent" refers to a light transmittance (%T) of at least 0.5% when measured at visible light wavelengths. In specific implementations, the material has a %T of at least, 10% for a 0.25 inch thickness. In some aspects of the invention, the particulate material eliminates glare, allowing a soft, deep distribution of daylight.

[ 0064 ] One method for producing an insulated unit, e.g., a glazing or another type of insulated panel, includes gravity feeding of particulate material through a filling port. Shown in FIG. 2 is filling apparatus 30 including unit 32 having panes 12a and 12b and one or more top opening(s) for receiving particulate material from a dispensing device such as hopper 34. Shutter 36 can be employed to close or open access between the dispensing device and unit 32. The filling process can be enhanced by vibration, for instance by using vibrator assembly 38. Techniques that can be employed to facilitated the filling process are described, for instance in U.S. Patent No. 7,621 ,299, with the title Method and Apparatusor Filling a Vessel with Particulate Matter, issued to Rouanet et al. on November 24, 2009; and U.S. Patent Application Publication No. 2008/0302059, Du Plessis et al, published on December 1 1 , 2008 with the title Filling Fenestration Units, both of which are being incorporated herein by reference in their entirety.

[ 0065 ] Filling can be conducted in air or using a gas such as nitrogen or other inert gas.

Filing also can be conducted at reduced pressure, for instance by removing air from the internal volume prior to and/or during filling. Filling rates can depend on factors such as size opening size, gap volume, material employed, production parameters and other criteria. To increase the flow rate of a particulate material through an opening in a fully framed system, internal gases can be vented, e.g., through vent holes, located, for example, in frame 14.

[ 0066] Optionally, moisture can be removed from the particulate material prior to, during or after the filling operation. In one embodiment particulate aerogel material is dried prior to its introduction into the cavity, thereby reducing moisture content in the material and preventing condensation from forming within the finished insulated unit. Desiccants or other techniques designed to reduce moisture also can be employed.

[ 0067] Particulate materials have a tendency to settle, forming void regions that can diminish the overall insulating properties of the unit. In translucent systems, they can cause uneven light transmittance, with void regions propagating more light than remaining regions filled with insulator.

[ 0068 ] To reduce or minimize settling and the formation of voids, the inner volume can be "overfilled" or "overpacked". Overpacked systems can have a density at least as high as the tap density. For aerogel particles, overfilling is to a density higher than the tap density.

In systems filled with aerogel particles that are very light compared to the relatively heavy frame, the density can be considerably greater than the tap density, for instance about 105 to about 1 15% - 120% and higher of tap density. [ 0069] Overfilling can be accomplished, for example, by increasing the inner volume of the unit. Before, during or after the filling operation is started, one or both panes 12a and 12b can be pulled away from one another to expand the volume of interior space 20 and maximize filling. A convenient way to increase the interior volume is to use suction cups 40a and 40b. More than one suction cups can be applied to a single pane. Dead weights, exposing the outer face of one or both panes 12a and/or 12b to a pressure that is lower than the pressure in interior space 20 (and that is exerted at the inner face(s) of panes 12a and/or 12b), for example by using one or more vacuum chambers, as well as other approaches, as described, for example, in U.S. Patent Application Publication No.

2008/0302059, Du Plessis et al, published on December 1 1 , 2008 with the title Filling Fenestration Units, the teachings of which are incorporated herein by reference in their entirety. In FIG. 3, the shape of the expanded interior space, as forces A and B (which can be the same or different) are exerted at the outer surface of panes 12a and 12b, is shown by the solid line; the broken line illustrates the initial pane arrangement.

[ 0070 ] The extent of volume expansion can be determined by taking into consideration factors such as unit size, pane material, degree of overpacking desired, tolerances towards breakage and others. Optionally, to avoid excessive stress, mechanical restraints, e.g., external stops, can be employed to limit the expansion of the internal volume. The volume increase can be, for instance, 200 % or higher. A theoretical estimate showed that a 6 m x 3 m tempered glass 6 mm thick can be bend in the range of 20 cm before it breaks, resulting in a volume increase of around 800 %. To ensure integrity of a typical seal, a more modest volume increase may be employed.

[ 0071] The filling operation can be conducted in one or more than one stages, until the entire desired amount has been transferred to the insulated unit. In many cases, at least 90 percent of the interior space is filled with particulate material. In others, at least 95, 97, 99 or 100 percent of the interior space is filled. If panes 12a and 12b are pulled apart, as described above, 90, 95, 97, 99 or 100 percent of the expanded interior volume is filled with particulate material. [ 0072 ] In addition to the particulate material, the interior space of the unit, e.g., a glazing panel, contains a gas, for example air. Argon, krypton, or other gases or mixtures of gases also can be utilized. The gas can be present in the interior space before the filling operation begins or can be introduced during or after the particulate material or a portion thereof, has been added to the interior space.

[ 0073 ] The panel, the particulate material or both are heated using ovens, heating chambers, forced hot gas, heating coils, direct or indirect heat transfer, microwaves and/or other techniques known in the art.

[ 0074 ] Once the desired temperature, T_H, is reached, the panel, particulate material or both can be soaked (e.g., baked) at this temperature, for a period of time, selected, for example, to ensure an even heat distribution. Soak time can depend on the size of the panel, pane material, whether the panel is being heated while empty or after filling, and so forth. Suitable soak times can be within the range of from about a few minutes to several hours or more. A 2 foot by 5 foot glass panel, for example, can be baked prior to being filled at a temperature of 70°C for 4 hours. Heating and soaking can be conducted in stages, by ramping to an intermediate temperature and soaking the panel, the particulate material or both at that temperature, followed by further heating and soaking.

[ 0075 ] This desired temperature TH can be selected by considering the onset of heat damage or deterioration of materials employed to fabricate the panel, such as, for instance polymeric materials used in sealing the unit, adhesives used to affix the panes in the frame, frame components, the particulate material employed and so forth. Other factors that can be taken into account include cost, production efficiency, energy consumption during processing, intended use of the panel and so forth.

[ 0076] In many cases, T_H is less than about 100°C, for example, within the range of from about 65°C and about 95°C, e.g., 70°C, 75°C, 80°C or 85°C. A suitable T_H when heating a panel having a seal that includes poly-iso-butylene tape is about 70 °C. [0077 ] In one approach, the panel is heated prior to, during and/or after being filled with the particulate material. In another approach, the particulate material is heated before, during and/or after filling the interior space with particulate material. Alternatively or in addition, the gas also can be heated before, during or after being introduced into the panel or while present in the panel.

[ 0078 ] Without evacuating heated gas from the interior space by mechanical means, such as by pumping or other mechanical means for drawing a vacuum, the filled and heated unit is sealed, the gas within the unit being at an initial pressure Pj. In many cases P; is the atmospheric pressure. Other pressure values can be used, for instance pressures at which the gas behaves similarly to an ideal gas.

[ 0079] Sealing can be accomplished by closing the filling port(s), vent holes, and the like. In specific examples, the filling port is plugged using, for instance, a plug made of a suitable material, e.g., rubber, plastics (such as polyethylene and so forth, and shaped to mate with the filling port. The seal can be consolidated by using a suitable tape, such as, for instance, poly-iso-butylene (PIB) tape, or by applying a layer of hot melt butyl material, for example a hot melt butyl sealant designed for the sealed insulating glass industry. Hot melt butyl sealants also are available in tape form. Coatings of silicone, polyurethane, polysulfide, epoxy, and/or other materials or combinations of materials can be added (e.g., as a secondary seal), to provide the structural performance typical of insulated (glass) units. In one example, an insulated panel is plugged with a rubber or plastic (poly-isobutylene or polyethylene) plug followed by sealing all four sides of the unit with silicone or hot melt butyl sealant. In specific implementations, one or more of the materials employed to create the seal have permeability characteristics that minimize passage of air and/or moisture.

[ 0080 ] Examples of typical sealing materials in the construction of Insulated Gas Materials include silicones and butyl rubbers, with butyl rubbers often being utilized in applications where air and moisture permeation requirements are more stringent. Literature data for air permeation rates for butyl rubber are on the order of 0.14x10^"

9cm³*cm/(sec*cm²*cmHg). For silicone rubber systems, air permeation rates are on the order of 60xl O^"9cm³*cm/(sec*cm²*cmHg). Some differences are also found for moisture vapor transmission rates where butyl based sealants can be up to two orders of magnitude better than silicone systems.

[ 0081] Other sealing arrangements and/or materials can be utilized, e.g., as known in the art. Typically, the sealing operation produces a completely sealed unit.

[ 0082 ] The sealed panel is brought to a temperature T_c that is lower than T_H, the difference between T_H and Tc being ΔΤ. In many cases, Tc is the ambient temperature. Higher and lower values, compared to the ambient temperature, can be selected for T_c. The panel can be allowed to cool or can be cooled, for example, by placing it in a refrigerated environment or by other means, e.g., suitable to the overall manufacturing process.

[ 0083 ] If employed, forces that keep panes 12a and 12b apart, e.g., as exerted by suction cups 40a and 40b, or a low pressure environment at the outer surface of the pane(s), are removed, e.g., before or during the cooling process. For example, suction cups can be removed right before, during or right after the unit is sealed.

[ 0084 ] As the insulated unit is cooled, or allowed to cool, the pressure inside the panel is reduced, the particulate material becomes compacted and panes 12a and 12b relax towards one another, as shown by the solid line in FIG. 4, where the broken line indicates the expanded interior space. Panes 12a and 12b can relax to be parallel, or essentially parallel to one another. In many cases, any remaining outward bulge in the finished product has a maximum value no greater than about 2 mm. For instance, a 2 ft by 5ft panel with an outward bulge of about 6 mm during filling was found to relax almost completely after the cooling step, with a final deformation of only about 1 mm at the maximum point of the outward bulge. In specific implementations, the pressure within the insulated unit remains lower than ambient pressure during usage of the unit.

[ 0085] Shown in FIG. 5 is a partial cross sectional view of one finished unit, namely glazing panel 50, having panes 12a and 12b, which in this example are made of glass, and including particulate material 52. One or more surfaces of the insulated unit, in this case the inner surface of pane 12b is provided with Low-E coating 60. Spacer 54, typically made of aluminum, another metal or another suitable material, can be provided with a drying agent, e.g., a molecular sieve or another type of desiccant. Typically, spacer 54 includes a filling port for introducing particulate material 52 in the glazing panel. The filling port is plugged, e.g., as described above, and sealed using primary seal 56, made of rubber or another plastic material and backed by PIB tape. Secondary seal 58 utilizes one or more materials such as silicone, polyurethane, polysulfide, and so forth. Other sealing approaches, e.g., a layer of hot melt butyl material covering the plug, also can be utilized.

[ 0086] Several sealing designs are illustrated in FIGS. 6A, 6B and 6C. Shown in FIG. 6A, for instance, is sealing arrangement 70 including polyethylene plug 72, poly-iso- butylene tape 74, and silicone coating 76, which typically extends to edge of the glass 78. Sealing arrangement 80, shown in FIG. 6B, includes plug 82, made of poly-iso-butylene, poly-iso-butylene tape 84 and silicone coating 86, extending to edge of the glass 78.

Shown in FIG. 6C is sealing arrangement 88, including plug 90 made of polyethylene. Applied over plug 90 is hot melt butyl layer 92, which extends to edge of the glass 78.

[ 0087] To study the performance of a given panel with respect to settling and/or sealing approach, panels can be subjected to thermal cycling, e.g., for 50, 60, 70, 80, 90, 100 or more cycles between high and low temperatures, e.g., between 15 and 60°C, then observed for settling. In other examples, a panel can be subjected to vibration cycles (for instance, at least 1 ,000, 5,000, 8,000, 9,000, 10,000, 1 1 ,000, 1 1,800, 12,000 cycles or more), then assessed for settling. In many cases, it is found that an acceptable settling level is one inch or less, e.g., 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.25, 0.2, 0.1 inch or less. In some instances, no settling is observed.

[ 0088] Aspects of the invention also relate to insulated glazing panels filled with aerogel material. In one implementation, a glazing panel has an interior space that is free of mechanical reinforcements and is filled with an aerogel material; a surface area of at least 10 ft² and a settling of the aerogel material determined by thermal cycling testing between -20°C and 60°C that is no greater than about 1/4" (a quarter of an inch). One or more pane surfaces can be covered with a Low-E coating. In specific implementations, the aerogel material is hydrophobic.

[ 0089] In some implementations, the insulated unit has a measure of thermal resistance to heat flow, referred to herein as "R" value of at least 2, for instance within the range of from about 3 to 38, e.g., 3, 5, 10, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36 or 38.

[ 0090 ] The insulated unit can provide acoustic insulation. This can be expressed in terms of sound transmission coefficient or STC which is often used to assess acoustic insulation of floors, ceilings and other building units. Generally, higher STC values reflect better acoustic insulators. Insulated units described herein can have STC values in the range of from about 22 to about 44 or more.

[ 0091] In some aspects, glass and other window units fabricated as described above have a visible light transmission greater than 0%, in many cases greater than 0.5% and often up to 80% or higher. Also possible are units that have high ultraviolet (UV) reflectance, for instance a UV reflectance of at least 80%. Solar heat gain coefficients can be close to 0.0 and are often in the range of from about 0.21 to 0.73.

[ 0092 ] Insulated window units produced as described above can be tested by the following industry standards, e.g., ASTM-E744, ASTM E-2189, ASTM-2190 and/or other suitable testing techniques.

[ 0093 ] The invention is further illustrated through the non-limiting examples below.

EXEMPLIFICATION

Example 1

[ 0094 ] Experimental insulated glazing units (IGUs) with dimensions of 14" X 20" were fabricated from two panes of glass separated by an aluminum spacer. A hole was drilled into the aluminum spacer as a means for filling the panel with granular material, specifically Nanogel® type aerogel TLD302. This aerogel is characterized by having a bulk particle size range of 1.2-4.0mm. [ 0095 ] During filling, the panes were slightly pulled apart in order to allow for some overfill of the material. The filled panels were heated to 80°C for approximately 1 hour, in order to ensure that everything was up to temperature.

[ 0096] The "hot" IGUs were sealed according to one of the three sealing approaches illustrated in FIGS. 6A-6C to obtain four (4) panels per design. These were designated, respectively, as: experimental (or heated) Panels A (polyethylene plug with poly-iso- butylene tape, sealed with silicone), experimental (or heated) Panels B (poly-iso-butylene plug with poly-iso-butylene tape, sealed with silicone) and experimental (or heated) Panels C (with the hole being originally plugged with a polyethylene plug, after which all four sides of the IGU were sealed with hot melt butyl sealant).

[ 0097 ] Comparative IGUs were prepared and sealed as described above but without being heated. They were designated, respectively, as comparative (or unheated) Panels A, comparative (or unheated) Panels B and comparative (or unheated) Panels C.

[ 0098 ] Thermal cycling (15 to 60°C) for 50 cycles led to significant settling in all the "unheated" (comparative) panels and this settling was found to occur independently of the sealing approach (any of FIGS. 6A, 6B or 6C) being employed.

[ 0099] In contrast, cycling for 82 thermal cycles resulted in no observable settling for experimental (heated) Panels C (sealed with the hot melt butyl material), while some of the experimental panels A and B showed minor settling after 82 cycles.

[ o o i o o ] The results indicated that panels prepared according to embodiments of the invention exhibited less amounts of settling than did the comparative panels. In addition, the results suggested that techniques utilized to seal the panel may play a role in the level of settling observed with a finished product. It is believed that minimizing air transfer between the environment and the interior space of the panel can further reduce settling in panels obtained by practicing aspects of the invention.

Example 2 [ooioi] Experimental panels such as described above also were tested according to the procedures described in ASTM Standard E2190.

[00102] In this protocol, phase I (High Humidity Phase) includes maintaining the panel for two weeks at 139°F and 95%RH. Phase II (Accelerated Weathering Phase) involves 1 hour rise from ambient to 140°F; 1 hour at 140°F and 95%RH with UV light; 1 hour drop from 140°F to ambient; 1 hour drop from ambient to -20°F; 1 hour at -20°F; 1 hour rise from -20°F to ambient; repeated 252 times. In Phase III (High Humidity Phase) a panel is maintained for four weeks at 139°F and 95%RH.

[00103] The results were as follows. One experimental Panel A was tested and showed some settling during the thermal cycling phase. Two experimental Panels B were tested and showed some settling during the thermal cycling phase. Three experimental Panels C were tested and none showed settling during the thermal cycling phase. (One of these C Panels had previously been subjected to the 82 cycles described in Example 1).

[00104] The results indicated that experimental panels performed very well with respect to settling during thermal cycling and that settling levels can be further reduced by the sealing technique selected. It is believed that using sealing materials that have low permeability to air, moisture or both may further minimize settling.

Example 3

[00105] Minor levels of settling of about a quarter inch (1/4") were observed for two glass panels 2 ft by 2 ft, having a glass pane thickness of 6 mm. The panels were filled with aerogel designated as Nanogel® TLD302, from Cabot Corporation, while the panes were pulled slightly apart to allow for overfilling, then heated to a temperature

ofapproximately 80° C for 2 hours. The panels were sealed while hot, using poly-iso- butylene material and were subjected to ASTM E2190 testing to evaluate the integrity of the sealant. The test involved maintaining the units for 2 weeks at 60°C and 95% humidity and for nine (9) weeks of thermal cycling between -20°C to 60°C. On further investigation it was learned that the results observed could be attributed to the relatively poor construction technique employed.

[ 00106 ] While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

claimed is:

A method for producing an insulated unit, the method comprising:

sealing an interior space of the unit, the interior space containing a particulate material and a gas, the gas being at a first temperature that is higher than a second temperature and a first pressure, wherein the first pressure is not generated by mechanical evacuation of the interior space; and

cooling or allowing the gas to cool to the second temperature, thereby reducing the first pressure and compacting the particulate material.

The method of Claim 1, wherein the insulated unit is a glazing panel having two or more panes defining one or more interior spaces, at least one of the one or more interior spaces containing the particulate material.

The method of any of the preceding claims, wherein the unit includes at least one pane comprised of a material selected from the group consisting of glass, polymer, ceramic, metal, and any combination thereof.

The method of any of the preceding claims, wherein the insulated unit has an R value greater than about 2.

The method of any of the preceding claims, wherein the insulated unit has an R value from about 3 to about 38.

The method any of the preceding claims, wherein the insulated unit has one or more faces covered with a low emissivity coating.

The method of any of any of the preceding claims, wherein the particulate material is transparent or translucent.

8. The method of any of the preceding claims, wherein the particulate material is a porous or microporous material.

9. The method of any of the preceding claims, wherein the particulate material is a nanoporous material.

10. The method of any of the preceding claims, wherein the particulate material is an aerogel material.

1 1. The method of any of the preceding claims, wherein the particulate material

includes aerogel.

12. The method of any of the preceding claims, wherein the particulate material is hydrophobic.

13. The method of any of the preceding claims, wherein the first pressure is ambient pressure.

14. The method of any of the preceding claims, wherein the first temperature is at least 70° C.

15. The method of any of the preceding claims, wherein the interior space is sealed by plugging a filling port.

16. The method of any of the preceding claims, wherein means for sealing the interior space include a plug and poly-iso-butylene tape or hot melt butyl material.

17. The method of any of the preceding claims, wherein secondary means for sealing the interior space include a silicone, polysulfide, polyurethane or epoxy coating.

18. The method of any of Claims 1 -15, wherein sealing includes plugging all holes and applying hot melt butyl sealant on all four sides of the insulated unit.

19. The method of any of the preceding claims, wherein the unit is sealed with one or more sealing materials that have low permeability to air, moisture or both.

20. The method of any of the preceding claims, wherein the first pressure is reduced to a second pressure that remains lower than ambient pressure during usage of the insulated unit.

21 . The method of any of the preceding claims, wherein the insulated unit is a

fenestration unit, or a spandrel unit.

22. The method of any of the preceding claims, wherein the insulated unit is a roof covering selected from the group consisting of skylight, roof hatch and smoke vent.

23. The method of any of the preceding claims, further comprising heating the

particulate material, the unit, or both to the first temperature.

24. The method of any of the preceding claims, further comprising soaking the

particulate material, the unit, or both at a soaking temperature that is higher than the second temperature.

25. The method of any of the preceding claims, further comprising soaking the

particulate material, the unit, or both for a period of time sufficient to ensure that the particulate material, the unit, or both have reached the desired temperature.

26. The method of any of the preceding claims, further comprising:

expanding the interior space; and

filling the expanded interior space with particulate material.

The method of any of the preceding claims, wherein the interior space is expanded by pulling adjacent panes defining the interior space away from one another.

28. The method of any of the preceding claims, wherein the interior space is expanded by maintaining the interior space at a pressure higher than a pressure exerted on at least one outer face of the unit.

29. The method of any of the preceding claims, wherein the interior space is expanded and at least approximately 90% of the volume of the expanded interior space is filled with particulate material.

30. An insulated unit produced by the method of any of the preceding claims and

having a settling of the particulate material that is less than about 1 inch as determined by ASTM E2190.

31. A glazing panel having:

an interior space that is free of mechanical reinforcements and is filled with an aerogel material;

a surface area of at least 1 ft²; and

a settling of the aerogel material determined by thermal cycling according to ASTM E2190 that is no greater than about 1/4 of an inch.

32. The glazing panel of Claim 31 , wherein the aerogel material is hydrophobic.

33. The glazing panel of Claims 31 or 32, having at least one face covered with a low emissivity coating.

34. The glazing panel of any of Claims 31 through 33, comprising a frame made of a material selected from the group consisting of aluminum, plastic, polyurethane foam and any combination thereof.

35. The glazing panel of any of Claims 3 1 through 34, having an R value of at least about 2.

36. The glazing panel of any of Claims 31 through 34, having an R value from about 3 to about 38.

37. A method for producing an insulated panel, the method comprising:

heating a panel having an interior space;

filling the interior space with a particulate material;

sealing the panel; and

cooling or allowing the sealed panel to cool, thereby reducing a pressure in the interior space and compacting the particulate material, wherein heated gas present in the interior space after filling with the particulate material is not evacuated by mechanical means.

38. The method of Claim 37, wherein the panel is heated before, during and/or after filling the interior space with the particulate material.

39. The method of Claims 37 or 38, further comprising expanding the interior space prior to filling.

40. The method of any of Claim 39, wherein at least approximately 90 % of the

expanded interior space is filled with the particulate material.

41. A method for producing an insulated panel, the method comprising:

heating a particulate material;

filling an interior space of a panel with the particulate material;

sealing the panel; and

cooling or allowing the sealed panel to cool, thereby reducing a pressure in the interior space and compacting the particulate material, wherein heated gas present in the interior space after filling with the particulate material is not evacuated by mechanical means.

42. The method of Claim 41, wherein heating the particulate material is conducted before, during and/or after filling the interior space of the panel.

43. The method of Claims 41 or 42, further comprising expanding the interior space prior to filling.

44. The method of Claim 43, wherein at least approximately 90% of the volume of the expanded interior space is filled with the particulate material.

45. A method for producing an insulated panel, the method comprising:

heating a particulate material, a panel or both;

filling an interior space of the panel with the particulate material;

sealing the panel; and

cooling or allowing the sealed panel to cool, thereby reducing a pressure in the interior space and compacting the particulate material, wherein heated gas present in the interior space after filling with the particulate material is not evacuated by mechanical means.

46. The method of Claim 45, wherein filling the interior space of the panel is conducted before, during or after heating the particulate material, the panel or both.

47. The method of Claim 45 or 46, further comprising expanding the interior space prior to filling.

48. The method of Claim 47, wherein at least approximately 90% of the volume of the expanded interior space is filled with the particulate material.