Porous structure for filters and the like and method for producing the same

Abstract

A method for manufacturing a porous structure made for use in a particle filter includes a step of bonding a plurality of glass bubbles to each other and a step of breaking the plurality of glass bubbles. The gaps within the individual broken glass bubbles open into each other to form cavities that extend into the porous structure.

Description

Description of Related Applications

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 to Chinese Patent Application No. 202210837119.9, filed on July 15, 2022, the content of which is relied upon and incorporated herein by reference in its entirety.

Technical Field

[0002] The present disclosure broadly relates to filter materials, and more particularly to a porous structure made from broken hollow glass bodies and usable for filters.

Background Art

[0003] Since the Industrial Revolution, the amount of CO2 in the atmosphere has been steadily increasing due to fossil fuel combustion technologies such as coal-fired power plants and gasoline / diesel vehicles. With such an increase in CO2, concerns about global warming have grown, and countries have recognized the need to suppress CO2 emissions and / or recover CO2.

[0004] To counteract its harmful effects, CO2 can be reduced and / or captured directly from the air or at a V-source (e.g., a power plant) before it is released into the environment.

[0005] Over the past few decades, ceramic honeycomb wall-flow filters have been developed and incorporated into engine aftertreatment systems to capture particulate matter from the exhaust gases of diesel and gasoline engines. These filters are generally cordierite-based and are designed to withstand high temperatures (800°C or higher) and high thermal shocks. For capturing CO2 from flue gas ambient air, such characteristics are not necessary, and it is desirable to develop low-cost honeycomb filters with characteristics and performance optimized for CO2 capture applications.

[0006] Small glass bubbles, also known as "microspheres" of microballoons or hollow glass, are commercially available from Dennert Poraver GmbH, 3M, Zhongke Yali Technology, Ltd., Fibre Glast Developments Corp., Potters Industries LLC, etc. Such glass bubbles may be used as fillers in composite materials such as concrete.

[0007] Glass bubbles can be characterized by "diameter", where in this case the diameter refers to the diameter when the volume of the glass bubble is arranged in a perfect spherical shape. However, in reality, glass bubbles will have a shape like, for example, a potato and will only be approximately spherical. The size of the glass bubbles may be selected and characterized based on the diameter. In this case, "D50" corresponds to the 50% passing point of the glass bubbles having the diameter of the D50 value, with half of a group having a diameter larger than the D50 value and the other half having a diameter smaller than the D50 value. Similarly, measured according to ASTM standards by mercury intrusion, "d50" corresponds to the 50% pore diameter of the porous structure, and d10 corresponds to the 10% passing point. Therefore, the ratio of df = (d50 - d10) / d50 provides insight into the pore size distribution (the smaller the ratio, the narrower the pore size distribution).

[0008] Glass bubbles are generally brittle, and conventional methods teach ways to prevent the destruction of glass bubbles so as to maintain the closed internal cavities of the glass bubbles and maintain the relatively low mass-to-volume relationship that the glass bubbles would provide. When the integrity of the glass bubbles is maintained, the glass bubbles may be incorporated into composite materials for buoyant load-bearing structures such as surfboards and supports for ocean drilling equipment. SUMMARY OF THE INVENTION

[0009] Despite the conventional uses of glass bubbles, the Applicants have found that glass bubbles can be arranged and processed to produce a particularly efficient porous structure with an open porosity, such as for filters. A structure with an open porosity can be formed by tightly packing glass bubbles together, bonding the glass bubbles to each other, and breaking (e.g., destroying, bursting, crushing, opening, exposing) the glass bubbles. The gaps within individual glass bubbles are open to each other, forming porous cavities that interconnect throughout the overall structure and may be open to its surface. Such a structure can be particularly useful for filters or can be used for other purposes, such as providing a glass framework infiltrated with a polymer.

[0010] According to some embodiments, the porous structure comprises a plurality of glass bubbles containing at least 7.3 mass% of Na2O, and the glass bubbles are sintered together such that adjacent glass bubbles are directly physically bonded to each other, more than 50% of the glass bubbles are broken, the gaps defined within the individual broken glass bubbles are open to each other, forming a porous structure and cavities extending to its surface, the porous structure has a porosity of at least 50% by volume and contains at least 10% by volume of MgO.

[0011] According to some embodiments, the porous structure comprises glass bubbles containing at least 10% by volume of MgO and at least 10 mass% of Na2O. According to some embodiments, the porous structure comprises glass bubbles made from a glass having at least 20 mass% of Na2O. According to some embodiments, the porous structure comprises a glass having 10% to 15% by volume of MgO and 15% to 30% by mass of Na2O. According to some embodiments, the porous structure comprises glass bubbles made from a glass containing 10% to 20% by mass of Na2O.

[0012] According to some embodiments of the porous structure, more than 60% of the glass bubbles are broken. According to some embodiments, the porous structure has a porosity of at least 55% by volume, for example, a porosity of at least 60% by volume, a porosity of at least 70% by volume, or a porosity of at least 75% by volume. According to some embodiments, the porous structure has a porosity of at least 60% to 95% by volume. According to some embodiments, the porous structure has a porosity of at least 65% and 85% or less by volume.

[0013] According to some embodiments, at least some of the glass of the glass bubbles is devitrified such that the glass contains crystals. According to some embodiments, the porous structure consists mostly of glass by mass. According to some embodiments, the porous structure contains more than 50% glass by mass. According to some embodiments, the porous structure is more than 50% crystalline by mass.

[0014] According to some embodiments, the porous structure contains at least 90% glass by mass. According to some embodiments, the porous structure contains less than 75% amorphous phase glass by mass.

[0015] According to some embodiments, the porous structure has a cellular honeycomb shape with a wall thickness of 10 mils (about 254 micrometers) or less and a cell density of 400 cells per square inch (about 62 cells / cm 2 ) or less.

[0016] According to some embodiments, a method of manufacturing a porous structure for a particulate filter is adding an MgO source to a plurality of glass bubbles containing Na2O, heating and bonding the plurality of glass bubbles to each other, wherein the glass bubbles have a D50 particle size of at least 1 micrometer but 100 micrometers or less, and the plurality contains at least 1000 glass bubbles, and breaking at least some of the glass bubbles at a temperature between 500 °C and 800 °C. including In the aggregate, the broken glass bubbles that are combined form a porous structure, and the porous structure contains at least 10% by mass of Na2O and at least 10% by mass of MgO. The gaps within the individual broken glass bubbles are open to each other, forming a porous structure and cavities that extend to its surface.

[0017] According to some embodiments, a method for manufacturing a porous structure for a particulate filter comprises a step of adding an MgO source to a plurality of glass bubbles containing Na2O, a step of heating and bonding the plurality of glass bubbles to each other, wherein the glass bubbles have a D50 particle size of at least 1 micrometer but 100 micrometers or less, and the plurality contains at least 1000 glass bubbles, and a step of breaking at least some of the glass bubbles at a temperature between 500 °C and 800 °C, including In the aggregate, the broken glass bubbles that are combined form a porous structure, and the porous structure contains glass including at least 10% by volume of MgO and at least 7.3% by mass of Na2O. The gaps within the individual broken glass bubbles are open to each other, forming a porous structure and cavities that extend to its surface.

[0018] According to some embodiments of the method, the heating step is performed at a peak temperature of less than 900 °C.

[0019] According to some embodiments, a method for manufacturing a porous structure for a particulate filter comprises a step of adding an MgO source to a plurality of glass bubbles containing Na2O, a step of heating and bonding the plurality of glass bubbles to each other, wherein the glass bubbles have a D50 particle size of at least 1 micrometer but 100 micrometers or less, and the plurality contains at least 1000 glass bubbles, and a step of breaking at least 50% of the glass bubbles at a temperature between 500 °C and 800 °C (for example, between 600 °C and 770 °C), including In the aggregate, the broken glass bubbles that are combined form a porous structure, and the porous structure includes glass containing at least 10% by volume of MgO and at least 10% by mass of Na2O (for example, at least 15% by mass of Na2O). The gaps within the individual broken glass bubbles are open to each other, forming a porous structure and cavities that extend to its surface.

[0020] According to some embodiments of the method, the broken glass bubbles that are combined form a porous structure, and the porous structure includes at least 20% by mass of Na2O and 10% to 15% by mass of MgO.

[0021] According to some embodiments, the method includes a step of devitrifying at least some of the glass of the glass bubbles to form crystals. According to some embodiments, the step of breaking includes a step of flowing the amorphous glass of the glass bubbles against the crystals.

[0022] According to some embodiments, the step of heating is such that adjacent glass bubbles sinter to each other. According to some embodiments, the step of breaking is performed simultaneously with the step of heating.

[0023] According to some embodiments, the method further includes a step of cooling a plurality of glass bubbles such that the adjacent broken glass bubbles physically bond directly to each other.

[0024] According to some embodiments, the method may further include a step of extruding an unfired material containing glass bubbles and an organic binder before the step of heating. Most of the glass bubbles remain intact after the extrusion step. According to some embodiments, the extrusion step includes extruding thousands of glass bubbles bonded to each other with an organic binder. According to some embodiments, the heating step burns off or chemically changes most of the organic binder by mass.

[0025] According to some embodiments, the glass bubbles have a D50 particle size of at least 1 micrometer but 100 micrometers or less, for example, at least 5 micrometers but 25 micrometers or less, or at least 10 micrometers but 20 micrometers or less.

[0026] According to some embodiments of the method, the heating step is such that adjacent glass bubbles sinter together. According to some embodiments, the breaking step is performed simultaneously with the heating step.

[0027] According to some embodiments, the method of manufacturing a porous structure further includes a step of cooling a plurality of glass bubbles, and adjacent broken glass bubbles physically bond directly to each other.

[0028] According to some embodiments, the method of manufacturing a porous structure further includes a step of extruding a green material containing glass bubbles and an organic binder before the heating step, and most of the glass bubbles remain intact after the extruding step.

[0029] According to some embodiments, the method of manufacturing a porous structure includes a step of extruding thousands of glass bubbles bonded to each other with an organic binder.

[0030] According to some embodiments of the method of manufacturing a porous structure, the heating step burns off most of the organic binder by mass or chemically changes it.

[0031] Another exemplary embodiment is a method of manufacturing a porous structure, the method comprising the steps of extruding a green material comprising glass bubbles and an organic binder, such that most of the glass bubbles remain intact after the extrusion step, then breaking most of the glass bubbles after the extrusion step, and bonding a plurality of the glass bubbles together. The broken and bonded glass bubbles form a porous structure in an aggregate. In some embodiments, the glass bubbles have a D50 size of at least 1 micrometer, such as at least 5 micrometers and less than or equal to 50 micrometers, or from 5 micrometers to 25 micrometers during the extrusion step, but less than 100 micrometers. In some embodiments, the porous structure comprising broken glass bubbles has a pore size distribution (d50 - d10) / d50 of less than 0.8 after the breaking step. In some embodiments, the glass bubbles have a hydrostatic crushing strength of at least 1000 psi (about 6.9 MPa) during the extrusion step. In some embodiments, most of the glass bubbles have a density of at least 0.1 g / cm 3 but less than 1.5 g / cm 3 during the extrusion step. In some embodiments, the glass of the glass bubbles is soda lime, borosilicate, and / or aluminum silicate during the extrusion step.

[0032] Still other exemplary embodiments include, in a method of manufacturing a porous structure, extruding a green material comprising glass bubbles and an organic binder, wherein most of the glass bubbles remain intact after the extrusion step, heating the glass bubbles to at least the softening temperature of the amorphous glass of the glass bubbles, a step of rupturing most of the glass bubbles after the extrusion step, the step including expanding the gas within the glass bubbles to rupture the glass bubbles, and a step of bonding the glass bubbles to each other, wherein the heating step is such that adjacent glass bubbles sinter to each other at a temperature, for example, from 550° C. to 870° C., for example, from 550° C. to 800° C., or from 550° C. to 700° C. The ruptured and bonded glass bubbles form a porous structure in an aggregate, and the gaps within the individual ruptured glass bubbles open into each other and extend into the porous structure to form voids extending to its surface. In some such embodiments, the extruded green material floats in water, while the porous structure including the ruptured and bonded glass bubbles sinks.

[0033] In some embodiments, the porous structure includes a plurality of glass bubbles. The glass bubbles are sintered to each other such that adjacent glass bubbles are physically bonded directly to each other. Most of the glass bubbles are ruptured, and the gaps defined within the individual ruptured glass bubbles open into each other and extend into the porous structure to form voids extending to its surface. The porous structure has a porosity of at least 50% by volume. In some such embodiments, at least some of the glass of the glass bubbles is devitrified such that the glass contains crystals. In some embodiments, the porous structure is, by mass, mostly glass (including devitrified glass), such as at least 90% of glass, and / or less than 75% of the porous structure is, by mass, an amorphous phase. In some embodiments, the porous structure has a porosity of at least 65% and 85% or less by volume.

[0034] In other embodiments, the porous structure is, by mass, mostly (e.g., at least 90%) a plurality of fractured glass bubbles sintered together such that adjacent glass bubbles are physically bonded directly to each other. The gaps defined within the individual fractured glass bubbles open into each other and extend into the porous structure to form voids that extend to its surface. In some such embodiments, the porous structure has a web thickness of 9 mils (about 0.23 mm) or less, preferably 8 mils (about 0.20 mm) or less, more preferably 6 mils (about 0.15 mm) or less, and at most 300 cells per square inch (about 46.5 cells / cm 2 ), preferably at most 200 cells per square inch (about 31.0 cells / cm 2 ) and has a cellular honeycomb shape. Other embodiments include a filter comprising such a porous structure, further comprising a coating supported by the porous structure, the coating being capable of being made to block and / or attract target particles (i.e., a particle filter), and a housing at least partially surrounding the porous structure and the coating.

[0035] Still other embodiments include an extrusion batch material for manufacturing a porous structure, the extrusion batch material including a plurality of glass bubbles, where the glass bubbles have a D50 size of at least 1 micrometer and 100 micrometers or less, and the glass bubbles have a hydrostatic crushing strength of 1000 psi (about 6.9 MPa) or more. The extrusion batch material further includes a binder and has a specific gravity with respect to water of less than 1.0. In some embodiments, the extrusion batch material further includes a pore former such as an organic pore former (e.g., starch). In some embodiments, the glass bubbles have a D50 size of at least 5 micrometers and 50 micrometers or less. In some embodiments, the glass bubbles have a D50 size of at least 10 micrometers and 25 micrometers or less, or at least 10 micrometers and 20 micrometers or less.

[0036] Still other embodiments include a porous structure that can be a substrate or body for a filter (e.g., a honeycomb), or can serve other purposes such as a support for a liquid electrolyte or a framework for infiltrating a polymer. The structure includes a plurality of glass bubbles having a D50 size of less than 100 micrometers. The glass bubbles are sintered together such that adjacent glass bubbles are physically bonded directly to each other. Most of the glass bubbles are broken, and the gaps defined within the individual broken glass bubbles open into each other and extend throughout the structure to form cavities that extend to its surface. In some embodiments, at least some of the glass of the glass bubbles is devitrified such that the glass contains crystals.

[0037] Additional features and advantages are described in the following detailed description, some of which will be readily apparent to those skilled in the art from that description or will be recognized by practicing the embodiments as described in the written description and its claims and the accompanying drawings. It is to be understood that both the foregoing general description and the following detailed description are exemplary only and are intended to provide an overview or framework for understanding the nature and characteristics of the claims.

Brief Description of the Drawings

[0038] The accompanying drawings, which are included to provide a further understanding and are incorporated in and constitute a part of this specification, illustrate one or more embodiments and, together with the detailed description, serve to explain the principles and operation of the various embodiments. Therefore, the present disclosure will be more fully understood from the following detailed description when interpreted in conjunction with the accompanying drawings.

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DETAILED DESCRIPTION OF THE INVENTION

[0039] Before returning to the following detailed description and drawings that describe the exemplary embodiments in detail, it should be understood that the technology of the present invention is not limited to the details or methodologies described in the detailed description or shown in the drawings. For example, features and attributes related to an embodiment shown in one of the drawings or described in text with respect to one of the embodiments can be similarly applied to other embodiments shown in other drawings or described elsewhere in the text, as will be understood by those skilled in the art.

[0040] Referring to FIG. 1, the porous structure 210 may be used in the filter 110 or in another manner. The porous structure 210 is generally a "honeycomb" in that it includes elongated passages 212 that extend at least in part through the porous structure 210, such as linearly extending from the outer surface 214 (e.g., face) of the porous structure 210 to or near the opposite outer surface of the porous structure 210. In some embodiments, some or all of the elongated passages 212 are not plugged, and fluid can flow through the elongated passages 212. In still other embodiments, the porous structure may be porous but may not include elongated passages 212.

[0041] According to an exemplary embodiment, the elongated passages 212 may have a relatively high aspect ratio, such as length to width or length to diameter, where the length L is directed along the flow path of the elongated passages 212 between the openings on the outer surface 214 provided by the elongated passages 212 of the outer surfaces 214 of the porous structure 210 that are opposite each other, as shown in FIG. 1. According to an exemplary embodiment, the elongated passages 212 are elongated such that the aspect ratio, defined as the length of the elongated passages 212 to the widest cross-sectional dimension of each elongated passage 212 that is perpendicular to the length L, of at least some (e.g., most, or >90%, or all) of the passages is at least 10, at least 20, at least 50, at least 100, and / or 50,000 or less.

[0042] FIG. 1 shows a porous structure 210 having a substantially cylindrical shape, although other shapes are conceivable, such as a cube, box, sheet, and more complex shapes. For example, referring now to FIG. 2, the porous structure 310 is a sheet surrounded by substantially straight lines, which may be used as a substrate for a filter or for other applications. In some embodiments, the structure 310 of FIG. 2 is an essentially glass foam sheet having a substantially uniform density and a non-uniform pore distribution and having no elongated passages. This foam may be highly porous, coated, and / or partially or completely filled with a liquid material (e.g., an electrolyte), a solid material (e.g., a dielectric), or otherwise.

[0043] According to an exemplary embodiment, the structure 310 is highly porous and its pores (e.g., cavities, gaps, spaces between structures) are open to each other such that a fluid can enter and pass through the structure 310 through the pores. However, the structure 310 may be semi-permeable in some such embodiments, allowing only certain fluids and / or smaller particles to pass through the structure 310 while trapping or blocking others.

[0044] Structures such as the porous structures 112, 210 and structure 310 of FIGS. 1-2 may include and / or may be at least partially formed from a plurality of glass bubbles (e.g., hollow microspheres, see, e.g., glass bubbles 512, 512' of FIG. 5), where "plurality" may include more than 100, such as more than 1000. In some such embodiments, the glass bubbles have a D50 size of at least 1 micrometer (μm) and 1000 μm or less, such as at least 5 μm, at least 25 μm, and / or 500 μm or less, such as 250 μm or less, 100 μm or less, according to ASTM standards such as D4284-12. In some such embodiments, the porous structure containing the glass bubbles has a pore size distribution df = (d50 - d10) / d50 of less than 0.8, such as less than 0.4, less than 0.2, less than 0.1, less than 0.06, etc. In some such embodiments, most of the glass bubbles (as described below, before being broken) have a density of at least 0.1 g / cm 3 , such as at least 0.3 g / cm 3 , and / or less than 1.5 g / cm 3 , such as less than 0.7 g / cm 3 , where the density is the mass per volume including the internal foam volume.

[0045] According to the exemplary embodiments, the porous structures 210, 310 are, from the perspective of mass, at least 70% of the mass, for example, at least 80%, and at least 90%, etc., mostly glass or devitrified glass (glass ceramic, ceramic). Such a majority of the structures 210, 310 formed from glass or devitrified glass of glass bubbles would be unexpected or counterintuitive to those skilled in the art. Because those skilled in the art would predict that such structures are particularly brittle and / or not coherent at all. However, in some possible applications, the porous spaces of the porous structures 210 and the structure 310 may later be at least partially filled with other materials (for example, sorbents for CO2 capture), while the porous structures 210 and the structure 310 are coherent for the most part for the method of manufacturing such structures as taught herein.

[0046] Figs. 3-4 show the "unfired" (for example, before firing, before sintering) structures 410, 510. More specifically, the unfired structure 410 in Fig. 3 may be the outer wall of a porous structure such as a honeycomb porous structure as shown in Fig. 1. On the other hand, the unfired structure 510 in Fig. 4 may be the inner wall or web of a porous structure such as a honeycomb body.

[0047] The unfired structure can be formed from an extruded batch material. According to the exemplary embodiments, the unfired structures 410, 510 include glass bubbles 412, 512 held within binders 414, 514 (for example, organic binders, or binders that are mostly organic). It is preferred that the glass bubbles are hollow and have thin walls. Thereby, the glass bubbles rupture when heated, and a highly porous structure is obtained. In some embodiments, the batch material may include glass bubbles with a particle size of 3 to 100 micrometers having a particle distribution of (D90 - D10) / D90 less than 2, such as less than 1.5, or less than 1. According to some embodiments, Df of the particle distribution Df = (D50 - D10) / D50 is less than 2, such as less than 1.5, or less than 1.

[0048] According to an exemplary embodiment, the batch density (e.g., "wet batch" density) is less than 1.5 g / cm 3 and, for example, less than 1.0 g / cm 3 and less than 0.5 g / cm 3 and less than 0.3 g / cm 3 According to an exemplary embodiment, the unfired materials and batch materials of FIGS. 3-4 float (i.e., have a specific gravity of less than 1 compared to water), but the completed porous structure after firing and / or bursting of the glass bubbles may sink.

[0049] In some embodiments, the unfired materials 410, 510 may further include a slip agent and / or a lubricant, such as oil. Sodium stearate or other firing aids may be added to the batch. In some embodiments, the binder may include methylcellulose. In some embodiments, the batch may further include an organic pore former, such as a pore former such as starch (e.g., corn starch, pea starch). According to an exemplary embodiment, the glass bubbles 412, 512 may be "independent type" compositions with respect to the inorganic components (more than 90% by mass of the inorganic compounds in the batch, or more than 95% by mass of the skeleton (i.e., filled inorganic particles)). In other embodiments, the batch may further include a second inorganic material having a softening temperature higher than that of the glass bubbles, such as clay, talc, silica, alumina, minerals, synthetic oxides, other types of glass or ceramic particles and / or bubbles.

[0050] In some embodiments, particularly elastic glass bubbles 412, 512 are used, such as those having an average hydrostatic crushing strength of at least 1000 psi (about 6.9 MPa), for example, at least 2000 psi (about 13.8 MPa), at least 3000 psi (about 20.7 MPa) (see Measuring Isostatic Pressing Strength of Hollow Glass Microspheres by Mercury-injection Apparatus by Yun and Shou, Key Engineering Materials, Vol. 544, pp. 460-465 (2013)). Also, the speed and pressure through the corresponding extruder will vary depending on the size of the glass bubbles, their material, and the extrusion device. In some embodiments, the extrusion pressure is in the range of less than 2500 psi (about 17.2 MPa), for example, less than 2000 psi (about 13.8 MPa), and / or at least 500 (about 3.45 MPa) psi.

[0051] According to the exemplary embodiments, the glass bubbles 412, 512 in the binders 414, 514 are being extruded (e.g., biaxially) at speeds and pressures that maintain the integrity of most (e.g., greater than 50%, greater than 75%, greater than 90%) of the glass bubbles 412, 512. As shown in FIGS. 3-4, most of the glass bubbles 412, 512 appear to be completely intact. That being said, in other possible embodiments, the extrusion speed and pressure may maintain the integrity of at least 25%, or at least 20%, although not most, of the glass bubbles, such as less than 50%. By maintaining the integrity of the glass bubbles 412, 512, the glass bubbles can occupy a relatively large volume of the space within the unfired structures 410, 510 that have gaps between and within the glass bubbles 412, 512.

[0052] Extruding the unfired structures 410, 510 can be particularly efficient for forming through-holes (e.g., the elongated passages 212 as shown in FIG. 1) in a porous structure such as the honeycomb of FIG. 1, or other regular features in each of the unfired structures 410, 510. However, in other conceivable embodiments, such structures containing glass bubbles in the binder may be shaped or processed by molding, tape casting, or other means, whereby the integrity of the glass bubbles 412, 512 will be better maintained or otherwise. In yet other conceivable embodiments, structures having shapes completely different from the shapes of the porous structures 112, 210, such as the structure 310, may be extruded or otherwise formed.

[0053] The glass bubbles 412, 512 may comprise glass (e.g., soda-lime glass, borosilicate, aluminosilicate glass, or other glass). The glass of the glass bubbles 412, 512 may be completely or partially amorphous, crystalline, polycrystalline, etc., e.g., a two-phase glass-ceramic. In some embodiments, the glass of the glass bubbles 412, 512 may be amorphous prior to the heating step and may then devitrify and / or crystallize. For clarity, as used herein, "glass" includes devitrified glass containing crystals such as amorphous glass, glass-ceramics, and crystalline phases. In at least some conceivable embodiments, the glass bubbles 412, 512 may contain and / or be formed from other materials such as synthetic minerals, polymers, ceramics, fly ash / cenospheres, metals, etc.

[0054] According to the exemplary embodiments, the green structures 410, 510 are heated (e.g., fired in a furnace, laser heated). The heating may burn off, carbonize, chemically convert, or otherwise affect the binders 414, 514. According to the exemplary embodiments, the green structures 410, 510 are heated to at least the softening temperature of the glass of the glass bubbles 412, 512. However, the glass bubbles 412, 512 are not overheated, such as slightly exceeding the liquidus temperature. If overheated, the glass bubbles 412, 512 would completely lose their cohesiveness or structure. The peak heating temperature depends on the material and the required porosity of the resulting structure (e.g., honeycomb filter) and may be at least 500 °C, at least 550 °C, at least 600 °C, at least 700 °C, and / or 1025 °C or less, e.g., 1020 °C or less, e.g., 1000 °C or less, e.g., 900 °C or less, e.g., 870 °C or less, or 850 °C or less. The peak heating temperature may be, for example, between 500 °C and 1000 °C, between 550 °C and 900 °C, between 550 °C and 870 °C, between 550 °C and 850 °C, between 575 °C and 870 °C, between 575 °C and 850 °C, or between 600 °C and 770 °C depending on the material. The peak heating temperature may be, for example, between 600 °C and 900 °C, between 600 °C and 875 °C, between 600 °C and 870 °C, or between 600 °C and 850 °C. In some embodiments, the peak heating temperature will sinter the glass bubbles together. In conceivable embodiments, the glass bubbles 412, 512 may have other softening temperatures. After firing, the resulting structure has a porosity (by volume) of greater than 50%, e.g., 55% or more, or 60% or more, or between 60% and 90%. The Applicants have found that lower peak heating temperatures result in beneficial low shrinkage rates s (s ≤ 10%, further ≤ 5%) and high porosities while saving costs as energy consumption is reduced.

[0055] According to an exemplary embodiment, the state and handling of the unfired structures 410, 510 during heating are such that the adjacent glass bubbles 412, 512 physically interact with each other, for example, they sinter, weld, or melt into each other, but do not completely lose their individual structures. In other words, in at least some of such embodiments, the state and handling are such that the glass bubbles 412, 512 do not completely liquefy and / or do not completely lose their structure, and instead, in the aggregate, the resulting structure is cohesive and rigid as the glass bubbles are joined to each other.

[0056] Furthermore, according to such an exemplary embodiment, the state and handling of the unfired structures 410, 510 during heating are such that many (e.g., most, >60%, >70%, >75%, >80%, >90%, >95%, or >99%) of the glass bubbles 412, 512 may burst or break due to the expansion of the internal gas and / or devitrification or other means. In some of such embodiments, the glass bubbles 412, 512 are heated to a temperature such that the glass bubbles 412, 512 lose their integrity and the glass of the glass bubbles 412, 512 is pulverized or broken in other ways. In other conceivable embodiments, the glass bubbles may be broken by microwaves, sound waves, or other phenomena.

[0057] Breaking the glass bubbles 412, 512 may seem counterintuitive to those skilled in the art who may rely on the glass bubbles to provide buoyancy and / or prevent the inflow of materials through or into the gaps within the glass bubbles. However, the Applicants have discovered that, as disclosed herein, by breaking the glass bubbles 412, 512 of the structure, the gaps between the glass bubbles 412, 512 are maintained and / or may further expand and join to each other.

[0058] The unfired structures 410, 510 may be cooled to a temperature that is at least 100°C lower than the temperature to which the unfired structures 410, 510 were heated, such as, for example, less than 100°C, less than 50°C, etc. During cooling, the adjacent glass bubbles 412, 512 may not be very spherical at this point, but are physically bonded to each other, and / or remain so, such as being directly or indirectly bonded by an intermediate binder. In some such embodiments, the cooling step includes holding at a temperature that is higher than room temperature (e.g., the annealing point of the glass of the glass bubbles), but lower than the heating temperature. The holding may be performed in some embodiments in a step of gradually increasing, or in other embodiments, in the form of a very stepwise temperature decrease within a specific temperature range, both of which can form crystals in the material of the glass bubbles 412, 512, and / or promote relaxation of residual stress by slow cooling.

[0059] In some embodiments, during heating, the glass bubbles may be heated from the ambient temperature to a first temperature (e.g., a fixed temperature and / or a temperature within a limited range) at a first residence time, such as when the first temperature is from 300 °C to 400 °C and / or when the first residence time is at least 1 minute, such as from 1 to 10 hours. In some embodiments, the first residence time is 4 - 6 hours. In some of such embodiments, the temperature is then raised from the first temperature to a second temperature at a second residence time, such as when the second temperature is higher than 400 °C, such as from 550 °C to 900 °C, 500 °C and 800 °C, 550 °C to 800 °C, or even from 550 °C to 700 °C, and the second residence time is also at least 1 minute, such as from 1 to 10 hours. In some embodiments, the second residence time is 1 - 3 hours, for example, about 2 hours. This process beneficially results in a lower shrinkage, for example, at a rate s such as s < 10%, or even s ≤ 5%, and helps reduce crack formation in the final structure during cooling. It is preferred that the second temperature is the peak heating temperature. The parameter s is used to measure shrinkage or dimensional changes during firing, where s=(L 未焼成体 -L 焼成体 ) / L 未焼成体 , where L 未焼成体 is the length of the green body (the unfired structure before firing), and L 焼成体 is the length of the resulting porous structure after firing (i.e., after being exposed to the second (peak) heating temperature).

[0060] According to some embodiments, a method for manufacturing a porous structure is adding an MgO source to a plurality of glass bubbles containing Na2O, heating and bonding the plurality of glass bubbles together, wherein the glass bubbles have a D50 particle size of at least 1 micrometer but 100 micrometers or less, and the plurality contains at least 1000 glass bubbles, and A step of breaking at least some (e.g., >50%, or >55%, or >60%) of the glass bubbles at a temperature between 500 °C and 800 °C (e.g., between 550 °C and 750 °C, or between 550 °C and 700 °C, or between 600 °C and 750 °C), comprising In the aggregate, the combined and broken glass bubbles form a porous structure, and the porous structure includes glass bubbles containing at least 10% by volume of MgO and at least 10% by mass of Na2O. The gaps within the individual broken glass bubbles are open to each other, forming voids that extend to the porous structure and its surface.

[0061] According to some embodiments, the heating step is performed at a peak temperature of less than 900 °C, e.g., ≤870 °C, ≤800 °C, or ≤770 °C.

[0062] According to some embodiments, the porous structure includes glass bubbles containing at least 10% by volume of MgO and at least 15% by mass of Na2O, and the gaps within individual broken glass bubbles are open to each other, forming cavities that extend into the porous structure and its surface. According to some embodiments, the combined and broken glass bubbles form a porous structure, and the porous structure includes glass bubbles containing from at least 10% to 15% by volume of MgO and from 7.3% to 30% by mass of Na2O. According to some embodiments, the combined and broken glass bubbles form a porous structure, and the porous structure includes glass bubbles containing from at least 10% to 15% by volume of MgO and from 8% to 30% by mass of Na2O. According to some embodiments, the combined and broken glass bubbles form a porous structure, and the porous structure includes glass bubbles containing from at least 10% to 15% by volume of MgO and from 8.5% to 25% by mass of Na2O. According to some embodiments, the combined and broken glass bubbles form a porous structure, and the porous structure includes glass bubbles containing from at least 10% to 15% by volume of MgO and from 9% to 20% by mass of Na2O. According to some embodiments, the combined and broken glass bubbles form a porous structure, and the porous structure includes glass bubbles containing from at least 10% to 15% by volume of MgO and from 10% to 20% by mass of Na2O. According to some embodiments, the combined and broken glass bubbles form a porous structure, and the porous structure includes glass bubbles containing from at least 10% to 15% by volume of MgO and from 20% to 30% by mass of Na2O.

[0063] Referring now to FIGS. 5, 8, and 10, structures 410' and 510' are related to unfired (unburned) structures 410 and 510. More specifically, the structure 410' of FIG. 8 may be an outer or inner wall of a porous structure, and the structure 510' of FIG. 10 may be an inner or outer wall or web of a porous structure such as a honeycomb as shown in FIG. 1. However, the structures 410' and 510' are not "unfired" structures. Instead, the shells or skins of the glass bubbles 412' and 512' are bonded to each other, and the glass bubbles 412' and 512' are broken. In this case, the internal volumes of the glass bubbles 412' and 512' are exposed, the spaces between the glass bubbles 412' and 512' are opened and interconnected with each other, spreading to the structures 410' and 510' and forming cavities 416' and 516' (serpentine paths) extending on their surfaces. According to an exemplary embodiment, glass bubbles having a high crystallinity at the softening temperature of glass bubbles such as those containing more than 50% SiO2 and / or CaSiO3 by mass promote the change process from internal pores to open and connected pores as described below. The components of the exemplary glass composition include (by mass) more than 44% SiO2, at least 0.2% CaO, less than 1% and at least some Al2O3, 0 to 0.1% Fe2O3, and more than 7.3% by mass (e.g., more than 8%, more than 8.5%, or more than 9%, more than 9.5%, or more than 10%) Na2O. In some embodiments, the amount of Na2O in the glass bubbles is 12% or more, 15% or more, 18% or more, 20% or more, 25% or more, or 30%, or between them (e.g., 8% - 30%, 8% - 25%, 8 - 20%, 9.5% to 25%, or 9.5% to 20%). In some embodiments, the glass bubbles contain MgO. Some exemplary compositions of the glass bubbles are given in Table 1.

[0064]

Table 1

[0065] More specifically, FIG. 5 shows the morphological changes of HGMS (honeycomb made of hollow glass microspheres) during heat treatment of glass microbubbles corresponding to glass example A containing only 7% by mass of Na2O (i.e., less than 7.3% by mass of Na2O) when Mg oxide was not added to the batch. FIG. 5 shows the morphological changes of glass bubbles over different heating temperatures. As shown in FIG. 5, when the glass microbubbles were heated to 670° C., most of the glass microbubbles appeared to be completely intact. When the peak temperature rose to about 770° C., some broken microbubbles and some crystallization were observed, and the shrinkage parameter s increased to 12.6%. As the temperature continued to rise, a larger amount of microbubbles burst (opened). At about 900° C., the broken microbubbles formed interconnected pores, resulting in a porosity between about 57% and about 75% in structure 410'. When the peak temperature was raised to about 1000° C., more microbubbles burst, and the highest porosity of 77 - 80% of the resulting structure 410' was achieved at a temperature of about 1020° C. For example, FIGS. 5 and 6 show that when the microbubble composition contained 7% by mass of Na2O, a porosity of at least 67% (e.g., between about 67.5% and about 75% at firing temperatures between 770° C. and 1000° C.) could be achieved. At higher temperatures (e.g., >1000° C.), the resulting glass structure began to agglomerate, further shrank, and formed a dense body while losing most of its porosity. At temperatures higher than 900° C., significant shrinkage was observed as measured by parameter s, while minimal shrinkage was observed when the temperature was lower than 770° C. (e.g., between about 670° C. and 770° C.). That is, in this example, significant shrinkage (as evident by the increase in the value of parameter s) was observed when the peak temperature was raised above 770° C. FIG. 5 also shows that when the peak temperature was raised to 1170° C., due to the softening of the molten phase, the resulting structure formed a denser body with fewer pores, the walls between the pores became thicker, and the porosity p of the glass structure decreased to about 51%.

[0066] Figure 6 further shows the change in the microstructure shown in Figure 5 with respect to temperature. As described above, in this example, no Mg source was added to the batch. More specifically, Figure 6 shows the effect of the firing temperature on the honeycomb morphology change and indicates the presence of the crystal phase. Figure 6 shows that at the peak temperature of 670 °C, the porosity of structure 410’ was about 56.3% and the central pore diameter was 7 μm. At 770 °C, more microbubbles opened and the porosity p increased to about 67.8%. At a temperature of 770 °C, the central pore diameter was 7.3 μm, but the shrinkage rate s of the resulting porous structure 410’ increased to 12.6%.

[0067] In this embodiment, the porosity p continued to increase between 800 °C and 1000 °C while more microbubbles opened. At a temperature of 1020 °C, the microbubbles completely opened, the porosity reached a maximum value of 77.3%, and the central pore diameter increased to 22.7 μm. However, at this peak temperature (1020 °C), the porosity was high and the shrinkage rate s was also high, that is, about 18.5%. Finally, when the temperature rose to 1170 °C, the porosity decreased to 51.1% due to densification. As the peak heating temperature increased from 770 °C to 1000 °C, an increasing tendency to crystallize more was observed, and a decrease in porosity was observed during densification that occurred at temperatures above 1020 °C. Also, when the peak temperature rose to 1170 °C, the shrinkage rate s increased to about 28.7%, which is not desirable.

[0068] However, it was unexpectedly found that adding an Mg source to the batch containing microbubbles (such that the resulting structure has at least 10 vol% MgO) allows the glass bubbles to be sintered and ruptured at a lower peak temperature (e.g., <900 °C, ≦870 °C, ≦850 °C, or ≦800 °C), while reducing the shrinkage of structure 410’ and increasing the porosity of the structure. This low peak temperature helps to reduce the shrinkage rate s to less than 10%, and further to <5%, while maintaining a high porosity of >50%, >55%, or even more than 60%.

[0069] More specifically, as the amount of Na2O in the glass microbubbles increases, for example, to 9.5 mass% or more (e.g., 10 mass% or more, 12 mass% or more, 15 mass% or more, or 20 mass% or more), the structure based on the glass microbubbles softens at a gradually lower temperature. However, if there is not a significant amount of magnesium (Mg) present, the softened glass rapidly melts and forms a dense body with a relatively low porosity. This is not desirable. For example, if there is not a significant amount of MgO in the batch (<1 mass% of MgO, or <2 mass% of MgO), when the amount of Na2O in the glass microbubbles increases to 10 mass% and then to 20 mass%, the glass melts at a gradually lower temperature and forms a dense body with a low or zero porosity.

[0070] For example, FIG. 7 shows the comparative HGMS morphological changes when the microbubbles contain a large amount of sodium (the glass composition of Example E, 18.7 mass% of Na2O) and substantially no Mg. As the peak temperature increases, the HGMS glass structure softens at 470 °C, and the softening continues until about 520 °C, and then a highly fluid phase is formed. At temperatures between 520 °C and 570 °C, the glass microbubbles rapidly melt, and the resulting structure loses its porosity and becomes a dense body. This is not desirable. For example, after the glass structure was heated to a peak temperature of 570 °C, no pores were observed on the surface of this dense body. Furthermore, no crystallization was detected. This study has shown that a large amount of sodium in the glass leads to melting of the glass at a lower temperature, shrinkage of the glass-based structure, and minimization or disappearance of crystallization and porosity in the resulting structure.

[0071] The present applicants have surprisingly found that when a magnesium source containing a substantial amount of magnesium is added to a batch containing glass microbubbles containing a larger amount of sodium, the shrinkage of the structure is minimized and the porosity of the structure is significantly increased. For example, when the microbubbles contain a larger amount of Na2O (e.g., at least 7.3 wt%, at least 8 wt%, at least 9 wt%, at least 9.5 wt%, or more than 10 wt%, or more than 12 wt%, or more than 15 wt%), adding at least 10% by volume of magnesia to the structure can significantly increase the porosity of the resulting structure while maintaining a low peak firing temperature (e.g., 900 °C or lower, or ≤ 850 °C, or ≤ 800 °C). In some embodiments, the peak firing temperature is between 500 °C and 900 °C, e.g., between 600 °C and 900 °C, between 500 °C and 850 °C, between 600 °C and 850 °C, between 600 °C and 750 °C, between 500 °C and 750 °C, or between 600 °C and 700 °C. The porosity of the resulting structure is, for example, at least 60%.

[0072] Table 2 below shows batch compositions with 10% to 15% by volume (i.e., 44.3 wt% to 55.8 wt%) of MgO added to form a porous structure (200 / 8 honeycomb) having a porosity of 60 - 78%. The pore diameter and its size distribution were different under different heating temperatures between 620 °C and 870 °C. More specifically, Table 2 shows that when the glass microbubbles corresponded to the glass composition of Example E (18.7 wt% Na2O), adding 10% by volume of MgO (i.e., 44.3 wt% of MgO) to the batch resulted in a porosity of 69% when the glass batch was fired at a peak temperature of 620 °C, and a porosity of 63% when the structure containing glass bubbles was fired (heated) at a peak temperature of 870 °C. Further, Table 2 also shows that when 15% by volume (55.8 wt%) of MgO was added to the batch (instead of 10% by volume of MgO), a porosity of about 76 - 78% was obtained when the glass batch was fired at a peak heating temperature between 620 °C and 670 °C.

[0073]

Table 2

[0074] Figure 8 shows the morphological changes of the honeycomb in one exemplary embodiment. In this embodiment, the batch contains glass microbubbles containing 10% by volume of MgO (i.e., 44.3% by mass of MgO) and the glass composition of Example E (18.7% by mass of Na2O). When Mg is added to this batch, crystallization and the release / rupture of a large number of microbubbles are promoted at a temperature between 620°C and 770°C, while minimizing the shrinkage of the structure obtained when the batch is exposed to a higher temperature (e.g., >870°C). Figure 9 shows the XRD (X-ray diffraction) results indicating that the highly porous substrate structure of Figure 8 contains a crystalline phase including MgO, Na2MgSiO4, and forsterite.

[0075] In another embodiment, when 15% by volume of MgO (i.e., 38.7% by mass of MgO) is added to a batch containing microbubbles formed by a glass composition containing 15.8% by mass of Na2O, a porosity of more than 60% is obtained when the glass batch is fired at a peak heating temperature between 550°C and 700°C. For example, Table 3 and Figure 10 show that when glass microbubbles corresponding to the glass composition of Example F (15.8% by mass of Na2O) are used in the batch and 15% by volume of MgO (38.7% by mass of MgO) is added to the batch, a porosity of 65.3% is obtained when the batch is fired at a peak temperature of 580°C. Table 3 also shows that when 15% by volume of MgO is added to this batch, a porous structure with a porosity of 66% is obtained when the batch is fired at a peak temperature of 620°C, and a porosity of approximately 65% is obtained when the batch is fired at a peak temperature of 670°C. For this firing temperature, the shrinkage parameter s of the porous structure was <12%.

[0076]

Table 3

[0077] Figure 10 shows the morphological changes of honeycombs when batches containing 15% by volume of MgO and glass microbubbles of the glass composition of Example F (30% by mass of Na2O) are fired at various temperatures. More specifically, Figure 10 shows that when a large amount of Mg is added to the batch, crystallization and the release / rupture of a large amount of microbubbles are promoted at temperatures between 520 °C and 670 °C. When the batch is exposed to higher temperatures, the shrinkage of the resulting structure is also minimized. Figure 11 shows XRD results indicating that the highly porous substrate structure produced by firing a batch containing microbubbles of 15% by volume of MgO and the glass composition of Example F contains a crystalline phase including MgO, diopside, and forsterite.

[0078] According to some embodiments, the porous structure comprises a plurality of glass bubbles, and the glass bubbles are sintered to each other such that adjacent glass bubbles are physically bonded directly to each other, more than 50% of the glass bubbles are broken, the gaps defined within the individual broken glass bubbles are open to each other, forming voids extending to the porous structure and its surface, the porous structure has a porosity of at least 50% by volume and contains at least 8% by mass of Na2O and at least 10% by volume of MgO.

[0079] According to some embodiments, the porous structure contains at least 8.3% by mass of Na2O and at least 10% by volume of MgO. According to some embodiments, the porous structure contains at least 8.3% by mass of Na2O and at least 10% by volume to 60% by mass of MgO. According to some embodiments, the porous structure contains at least 8.5% by mass of Na2O and at least 10% by volume to 60% by mass of MgO.

[0080] Table 4 below summarizes the compositions of various exemplary embodiments of the porous structure.

[0081]

Table 4

[0082] Referring to FIGS. 5, 8, and 10, the inner walls formed between the pores in the porous structure are particularly thin and, in some contemplated embodiments, such as when particularly small glass bubbles are used, may be, for example, less than 1 millimeter (mm) thick, less than 500 micrometers (μm) thick, less than 100 μm thick, less than 50 μm thick, less than 10 μm thick, or less than 5 μm thick, as described below.

[0083] As can be seen from FIGS. 8 and 10, in at least some embodiments, the glass of the glass bubbles 412', 512' devitrifies and forms crystals. In FIGS. 5, 8, and 10, the devitrified glass appears as a light gray. As disclosed herein, gradually heating and holding can promote crystal growth, thereby strengthening the resulting structures 410', 510'. The unfired material will include amorphous glass bubbles, but the processed structure after firing may be a glass-ceramic having a crystallinity of more than 45% by mass (for example, at least 50% by mass, for example, 64% by mass crystallinity). In some embodiments, the porous structure (after firing) consists mostly of glass (including devitrified glass), such as at least 90% by mass being glass. In some of such embodiments, the porous structure consists of less than 55% by mass of the amorphous phase.

[0084] The porosity of the resulting structures 410’ and 510’ will be particularly high due to the cavities 416’ and 516’ formed by the broken glass bubbles 412’ and 512’ and / or the gaps left behind after the binder (see the binders 414 and 514 in FIGS. 3 - 4) has burned out. The Applicants believe that the techniques disclosed herein provide a high porosity (see ASTM D6761 - 07) of at least 40% by volume, at least 50% by volume, at least 55% by volume, at least 60% by volume, at least 65% by volume, at least 70% by volume, at least 80% by volume, etc. According to some exemplary embodiments, the porous structure 0 has a porosity of at least 65% and up to 85% by volume.

[0085] FIGS. 5, 8, and 10 show the microstructure and surface features according to at least some exemplary embodiments, but the porous structure has, within its outer surface (e.g., the outer surface having an opening on the outer surface 214), a total volume of at least 1 cubic centimeter (cm 3 ), e.g., at least 2 cm 3 , at least 10 cm 3 , at least 50 cm 3 , and / or up to 2000 cm 3 , e.g., up to 1000 cm 3 . In other embodiments, the volume can be much larger, such as for filters with a large frontal area.

[0086] In a possible embodiment, the processes and techniques disclosed herein are used in honeycomb filters such as diesel engine particulate filters. The glass bubbles are at least 50 cells per square inch (about 6.45 cm 2) For example, at least 100 cells per square inch, at least 200 cells per square inch, at least 300 cells per square inch, and / or 10 mils (i.e., one-thousandth of an inch) (about 0.254 mm) or less, for example, 8 mils (about 0.203 mm) or less, 7 mils (about 0.178 mm) or less, 6 mils (about 0.152 mm) or less, 5 mils (about 0.127 mm) or less web thickness, for example, in terms of web thickness expressed in cells per square inch / mil, about 200 / 8, 400 / 7, 400 / 6, 400 / 5, 400 / 4, 400 / 3, 400 / 2, 300 / 7, 300 / 6, 300 / 5, 300 / 4, 300 / 3, 300 / 2, 200 / 7, 200 / 6, 200 / 5, 200 / 4, 100 / 8, 100 / 7, 100 / 6, 100 / 5, 50 / 8, 50 / 7, 50 / 6, etc., are selected to have a crushing strength sufficient to promote the extrusion of a honeycomb body having a cell shape that is at least as dense as, less than, or approximately that value, and a sufficiently small shape.

[0087] At least some of such embodiments have a cylindrical shape with a diameter of at least 4 inches (about 102 mm), for example, at least 6 inches (about 152 mm), at least 8 inches (about 203 mm), at least 12 inches (about 305 mm), at least 24 inches (about 610 mm), and / or 64 inches (about 1630 mm) or less, for example, 36 inches (about 813 mm) or less. Others of such embodiments have a cross-sectional shape that is substantially square, rectangular, or other polygonal with sides of at least 4 inches (about 102 mm), for example, at least 6 inches (about 152 mm), at least 8 inches (about 203 mm), at least 12 inches (about 305 mm), at least 24 inches (about 610 mm), and / or 64 inches (about 1630 mm) or less, for example, 36 inches (about 813 mm) or less. Other conceivable embodiments have other sizes or shapes. Such shapes will promote low pressure drop, high dust loading, and high filtration efficiency.

[0088] According to some embodiments, the porous structure comprises a plurality of glass bubbles containing at least 10% by mass of Na2O comprising, (i) the glass bubbles are sintered together such that adjacent glass bubbles are physically bonded directly to each other, (ii) more than 50% of the glass bubbles are broken, (iii) the gaps defined within the individual broken glass bubbles are open to each other, forming a porous structure and cavities extending to its surface, and (iv) the porous structure has a porosity of at least 50% by volume and contains at least 10% by volume of MgO.

[0089] According to some embodiments, the porous structure contains at least 20% by mass of Na2O and at least 10% by volume of MgO, for example, 15% to 30% by mass of Na2O and 10% to 15% by volume of MgO. According to some embodiments of the porous structure, at least 50% of the glass bubbles are broken. According to some embodiments of the porous structure, at least 60% of the glass bubbles are broken. According to some embodiments of the porous structure, at least 50% of the glass bubbles are broken. For example, in some embodiments, more than 60% of the glass bubbles are broken, and the porous structure contains at least 20% by mass of Na2O and at least 10% by volume of MgO.

[0090] According to some embodiments, the porous structure comprises a plurality of glass bubbles, comprising, (i) the glass bubbles are sintered together such that adjacent glass bubbles are physically bonded directly to each other, (ii) more than 50% of the glass bubbles are broken, (iii) the gaps defined within the individual broken glass bubbles are open to each other, forming a porous structure and cavities extending to its surface, and (iv) the porous structure has a porosity of at least 50% by volume and contains at least 10% by volume of MgO. According to some embodiments, the porous structure contains at least 8.5% by mass of Na2O and at least 10% by mass of MgO. According to some embodiments, the porous structure contains at least 8.3% by mass of Na2O and at least 10% by mass of MgO. According to some embodiments, the porous structure contains at least 8.3% by mass of Na2O and up to 60% by volume of MgO.

[0091] According to some embodiments, the porous structure has a porosity of at least 55% by volume, for example, a porosity of at least 60%, at least 65%, at least 70%, at least 75%, or at least 80% by volume.

[0092] For example, the porous structure may have a porosity of 60% to 95% by volume, for example, at least 65% and 85% or less by volume.

[0093] According to some embodiments of the porous structure, at least some of the glass of the glass bubbles has devitrified such that the glass contains crystals. According to some embodiments of the porous structure, the porous structure is mostly made of glass by mass, for example, contains at least 80 or 90% glass by mass. In some embodiments, the porous structure contains less than 75% of an amorphous phase glass.

[0094] According to some embodiments, the porous structure has a cellular honeycomb shape with a wall thickness of 10 mils (about 254 micrometers) or less and a cell density of 400 cells per square inch (about 62 cells / cm 2 ) or less.

[0095] In some embodiments, a method of manufacturing a porous structure made for use in a filter has a step of breaking a plurality of glass bubbles (e.g., at least 100, at least 1000, at least 10,000 glass bubbles) at a relatively low sintering temperature, for example, 870 °C or lower, 850 °C or lower, preferably 800 °C or lower (e.g., 750 °C or lower, or 500 °C to 725 °C, 500 °C to 700 °C, 550 °C to 725 °C, or even 550 °C to 700 °C), and a step of joining the plurality of glass bubbles together. The broken and joined glass bubbles form a porous structure in an aggregate, and the gaps within the individual broken glass bubbles open to each other and spread into the porous structure to form voids extending to its surface. In some of such embodiments, the breaking step includes a step of expanding the gas within the glass bubble to rupture the glass bubble. In other of such embodiments, the breaking step includes devitrification of the glass of the glass bubble, in which case the glass bubble ruptures due to the movement of the amorphous glass with respect to the softened and devitrified glass. In other of such embodiments, the method includes a step of heating the plurality of glass bubbles to at least the softening temperature of the amorphous glass of the glass bubble. The heating step may be such that adjacent glass bubbles sinter to each other at a sintering temperature of 500 °C to 770 °C (e.g., 550 °C to 750 °C, or 550 °C to 700 °C). The breaking step may be performed simultaneously during the heating step. In some embodiments, the method includes a step of cooling the plurality of glass bubbles such that adjacent glass bubbles physically bond directly to each other. Depending on the timing and temperature of the heating step and / or the cooling step, at least some of the glass of the glass bubble may devitrify such that crystals form. The applicant believes that devitrification will help rupture the glass bubble, such as by limiting the shrinkage of the glass bubble under negative core pressure.

[0096] In some such embodiments, a method of manufacturing a porous structure includes extruding a green material comprising glass bubbles and an organic binder before the heating step. Most of the glass bubbles remain intact after the extrusion step. In some such embodiments, the heating step burns off or chemically changes most of the organic binder, by mass, from the porous structure. During the heating step, the glass bubbles are heated at an elevated temperature from ambient temperature to a first temperature for a first dwell time, and then the temperature is raised from the first temperature to a second temperature for a second dwell time. The first temperature may be in the range of 300 °C to 400 °C, and the first dwell time may be in the range of 1 to 10 hours. In some such embodiments, the second temperature may be between 550 °C and 900 °C (e.g., 550 °C to 700 °C), and the second dwell time may be from 1 to 10 hours (e.g., 4 to 6 hours). In at least some of those embodiments, the second temperature is above 400 °C and below the softening point of the amorphous glass of the glass bubbles, and the second dwell time is from 1 to 10 hours (e.g., 1 to 3 hours).

[0097] According to some embodiments, a firing process for breaking / open glass bubbles includes a step of heating the glass bubbles. The glass bubbles are heated at a first dwell time to a first temperature (e.g., a fixed temperature and / or a temperature within a limited range) from ambient temperature, such as when the first temperature is at least 200 °C, e.g., 300 °C to 400 °C (for burning off the binder and other inorganic components), and / or when the first dwell time is at least 1 minute, e.g., 1 hour to 10 hours. In some such embodiments, the temperature is then raised from the first temperature to a second temperature for a second dwell time, such as when the second temperature is above 400 °C, e.g., 500 °C to 750 °C, and the second dwell time is also at least 1 minute, e.g., 1 hour to 10 hours (which helps to promote crystallization).

[0098] According to some embodiments, a method of manufacturing a porous structure for a particulate filter is The step of adding an MgO source to a plurality of glass bubbles containing Na2O, The step of heating a plurality of glass bubbles and bonding them to each other, wherein the glass bubbles have a D50 particle size of at least 1 micrometer but 100 micrometers or less, and the plurality contains at least 1000 glass bubbles, and The step of breaking at least some of the glass bubbles at a temperature between 500 °C and 800 °C (for example, between 600 °C and 770 °C, or between 600 °C and 750 °C), including, In the aggregate, the bonded and broken glass bubbles form a porous structure, the porous structure contains at least 10% by mass of Na2O and at least 10% by volume of MgO, and the gaps within the individual broken glass bubbles are open to each other, forming cavities extending to the porous structure and its surface.

[0099] According to some embodiments of this method, the heating step is performed at a peak temperature of less than 900 °C.

[0100] According to some embodiments, a method for manufacturing a porous structure for a particle filter is The step of adding an MgO source to a plurality of glass bubbles containing Na2O, The step of heating a plurality of glass bubbles and bonding them to each other, wherein the glass bubbles have a D50 particle size of at least 1 micrometer but 100 micrometers or less, and the plurality contains at least 1000 glass bubbles, and The step of breaking at least 50% (for example, 60% to 99%) of the glass bubbles at a temperature between 500 °C and 800 °C (for example, between 600 °C and 770 °C), including, In the aggregate, the bonded and broken glass bubbles form a porous structure, the porous structure contains glass bubbles containing at least 10% by volume of MgO and at least 7.3% by mass of Na2O (for example, at least 8% by mass of Na2O, at least 9% by mass of Na2O, or at least 10% by mass of Na2O), and the gaps within the individual broken glass bubbles are open to each other, forming cavities extending to the porous structure and its surface.

[0101] According to some embodiments, a method of manufacturing a porous structure for a particle filter comprises: adding an MgO source to a plurality of glass bubbles containing Na2O; heating and bonding the plurality of glass bubbles together, the glass bubbles having a D50 particle size of at least 1 micrometer but not more than 100 micrometers, and the plurality containing at least 1000 glass bubbles; and rupturing at least 50% (e.g., 60% - 99%) of the glass bubbles at a temperature between 500°C and 800°C. The method includes: In the aggregate, the bonded and ruptured glass bubbles form a porous structure, the porous structure containing (i) at least 15% by mass of Na2O and (ii) at least 10% by volume of MgO, and the gaps within the individual ruptured glass bubbles open into each other to form a porous structure and cavities extending to its surface.

[0102] According to some embodiments, the rupturing step includes rupturing at least 50% of the glass bubbles at a temperature between 500°C and 870°C, between 500°C and 800°C, between 500°C and 770°C, between 600°C and 770°C, or between 600°C and 750°C. According to some embodiments, the rupturing step includes rupturing at least 60% of the glass bubbles at a temperature between 500°C and 770°C, or between 600°C and 750°C. According to some embodiments, the rupturing step includes rupturing from 60% to 99.5% of the glass bubbles at a temperature between 500°C and 770°C, or between 600°C and 750°C.

[0103] According to some embodiments of the method of manufacturing a porous structure, the bonded and ruptured glass bubbles form a porous structure, the porous structure containing glass bubbles with 10% to 15% by volume of MgO and at least 8.5% by mass of Na2O, e.g., glass bubbles containing 10 to 15% by volume of MgO and 9.5% to 30% by mass of Na2O.

[0104] According to some embodiments of a method for manufacturing a porous structure, broken bonded glass bubbles form a porous structure, and the porous structure contains 10% to 60% by mass of MgO and at least 8% by mass of Na2O (for example, 8.5% to 30% by mass of Na2O).

[0105] According to some embodiments, the method for manufacturing a porous structure further includes a step of devitrifying at least some of the glass of the glass bubbles to form crystals. According to some embodiments, the porous structure has a crystallinity of at least 50%. According to some embodiments, the porous structure has a crystallinity of at least 60%. According to some embodiments, the porous structure has a crystallinity of 60% to 95%. According to some embodiments, the breaking step includes a step of flowing the amorphous glass of the glass bubbles against the crystals.

[0106] The construction and arrangement of the porous structures, assemblies, and structures, as shown in various exemplary embodiments, are for illustrative purposes only. Although only a few embodiments are described in detail in this disclosure, many modifications (e.g., the sizes, dimensions, structures, shapes and ratios of various elements, the values of parameters, mounting arrangements, use of materials, color, changes in orientation) can be made without substantially departing from the novel teachings and advantages of the subject matter described herein. Some elements shown as integrally formed may be made from a number of parts or elements, the positions of the elements may be reversed or otherwise changed, and the nature and number of individual elements or positions may be varied or different. The order or sequence of any process, logical algorithm, or method steps may be changed or rearranged according to alternative embodiments.

[0107] Without departing from the scope of the technology of the present invention, other substitutions, modifications, changes, and omissions may be made to the designs, operating conditions, and arrangements of the various exemplary embodiments.

[0108] Hereinafter, the preferred embodiments of the present invention will be described item by item.

[0109] Embodiment 1 A porous structure comprising a plurality of glass bubbles containing at least 7.3% by mass of Na2O wherein the glass bubbles are sintered together such that adjacent glass bubbles are directly physically bonded to each other more than 50% of the glass bubbles are broken the gaps defined within each broken glass bubble open into each other to form voids extending across the porous structure and its surface the porous structure having a porosity of at least 50% by volume and containing at least 10% by volume of MgO.

[0110] Embodiment 2 The porous structure according to Embodiment 1, comprising glass bubbles made from a glass containing at least 10% by volume of MgO and at least 10% by mass of Na2O.

[0111] Embodiment 3 The porous structure according to Embodiment 2, comprising glass bubbles made from a glass having at least 20% by mass of Na2O.

[0112] Embodiment 4 The porous structure according to Embodiment 1, comprising glass bubbles made from a glass having 15% to 30% by mass of Na2O, the porous structure containing 10% to 15% by volume of MgO.

[0113] Embodiment 5 The porous structure according to Embodiment 1, comprising a glass having 10% to 20% by mass of Na2O, the porous structure containing 10% to 15% by volume of MgO.

[0114] Embodiment 6 The porous structure according to any one of Embodiments 1 to 5, wherein more than 60% of the glass bubbles are broken.

[0115] Embodiment 7 The porous structure according to any one of Embodiments 1 to 5, wherein the porous structure has a porosity of at least 55% by volume.

[0116] Embodiment 8 The porous structure according to Embodiment 7, wherein the porous structure has a porosity of at least 60% by volume.

[0117] Embodiment 9 The porous structure according to Embodiment 8, wherein the porous structure has a porosity of at least 70% by volume.

[0118] Embodiment 10 The porous structure according to Embodiment 9, wherein the porous structure has a porosity of at least 75% by volume.

[0119] Embodiment 11 The porous structure according to any one of Embodiments 1 to 8, wherein the porous structure has a porosity of 60% to 95% by volume.

[0120] Embodiment 12 The porous structure according to any one of Embodiments 1 to 9, wherein the porous structure has a porosity of at least 65% and 85% or less by volume.

[0121] Embodiment 13 The porous structure according to Embodiment 1, wherein at least some of the glass of the glass bubbles is devitrified so that the glass contains crystals.

[0122] Embodiment 14 The porous structure according to any one of Embodiments 1 to 10, wherein the porous structure is mostly made of glass by mass.

[0123] Embodiment 15 The porous structure according to any one of Embodiments 1 to 10, wherein the porous structure contains more than 50% glass by mass.

[0124] Embodiment 16 The porous structure according to any one of Embodiments 1 to 10, wherein more than 50% is crystalline by mass.

[0125] Embodiment 17 The porous structure according to any one of Embodiments 1 to 10, wherein the porous structure contains at least 90% glass by mass.

[0126] Embodiment 18 The porous structure according to any one of Embodiments 1 to 10, wherein the porous structure contains less than 75% amorphous phase glass by mass.

[0127] Embodiment 19 The porous structure according to any one of Embodiments 1 to 10, having a cell-like honeycomb shape with a wall thickness of 10 mils (about 254 micrometers) or less and a cell density of 400 cells per square inch (about 62 cells / cm 2 ).

[0128] Embodiment 20 In a method for manufacturing a porous structure for a particle filter, A step of adding an MgO source to a plurality of glass bubbles containing Na2O, A step of heating and bonding the plurality of glass bubbles to each other, the glass bubbles having a D50 particle size of at least 1 micrometer but 100 micrometers or less, and the plurality containing at least 1000 of the glass bubbles, and A step of breaking at least some of the glass bubbles at a temperature between 500 °C and 800 °C, Including, In the aggregate, the bonded and broken glass bubbles form a porous structure, the porous structure containing at least 7.3% by mass of Na2O and at least 10% by mass of MgO, and the gaps in the individual broken glass bubbles are open to each other to form voids extending to the porous structure and its surface.

[0129] Embodiment 21 The method for producing a porous structure for a particulate filter according to Embodiment 20, wherein the heating step is performed at a peak temperature of less than 900°C.

[0130] Embodiment 22 In a method for producing a porous structure for a particulate filter, a step of adding an MgO source to a plurality of glass bubbles containing Na2O, a step of heating and bonding the plurality of glass bubbles to each other, the glass bubbles having a D50 particle size of at least 1 micrometer but 100 micrometers or less, and the plurality including at least 1000 of the glass bubbles, and a step of breaking at least 50% of the glass bubbles at a temperature between 500°C and 800°C, comprising In the aggregate, the bonded and broken glass bubbles form a porous structure, the porous structure containing at least 15% by mass of Na2O and at least 10% by mass of MgO, and the gaps within the individual broken glass bubbles are open to each other to form voids extending to the porous structure and its surface.

[0131] Embodiment 23 The method for producing a porous structure for a particulate filter according to Embodiment 20 or 22, wherein in the aggregate, the bonded and broken glass bubbles form a porous structure, the porous structure containing at least 20% by mass of Na2O and 10% to 15% by mass of MgO.

[0132] Embodiment 24 The method for producing a porous structure for a particulate filter according to Embodiment 20 or 22, wherein in the aggregate, the bonded and broken glass bubbles form a porous structure, the porous structure containing 20% to 30% by mass of Na2O and 10% to 15% by mass of MgO.

[0133] Embodiment 25 The method according to Embodiment 20 or 22, further comprising a step of devitrifying at least some of the glass of the glass bubbles to form crystals.

[0134] Embodiment 26 The method according to embodiment 25, wherein the step of breaking includes a step of flowing the amorphous glass of the glass bubbles onto the crystal.

[0135] Embodiment 27 The method according to embodiment 22, wherein the step of heating is such that adjacent glass bubbles sinter to each other.

[0136] Embodiment 28 The method according to embodiment 27, wherein the step of breaking is performed simultaneously with the step of heating.

[0137] Embodiment 29 The method according to embodiment 26 or 27, further comprising a step of cooling the plurality of glass bubbles so that the adjacent broken glass bubbles are directly physically bonded to each other.

[0138] Embodiment 30 Before the step of heating, the method further includes a step of extruding an unfired material containing the glass bubbles and an organic binder, and most of the glass bubbles remain without being broken after the step of extruding, according to embodiment 17, 19, 24, or 26.

[0139] Embodiment 31 The method according to embodiment 30, wherein the step of extruding includes a step of extruding thousands of the glass bubbles bonded to each other with the organic binder.

[0140] Embodiment 32 The method according to embodiment 27 or 28, wherein the step of heating burns off most of the organic binder by mass or chemically changes it.

[0141] Embodiment 33 The method according to embodiment 17 and 19, wherein the glass bubbles have a D50 particle size of at least 1 micrometer but 100 micrometers or less.

[0142] Embodiment 34 The method according to embodiments 17 and 19, wherein the glass bubbles have a D50 particle size of at least 5 micrometers but 25 micrometers or less.

[0143] Embodiment 35 The method according to embodiments 17 and 19, wherein the glass bubbles have a D50 particle size of at least 10 micrometers but 20 micrometers or less.

Description of Reference Numerals

[0144] 110 Filter 112, 210, 310 Porous Structure 212 Elongated Passage 214 Outer Surface

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