CA1227811A - Ceramic foam cement - Google Patents

Abstract

Abstract of the Disclosure Apparatus for filtering solid particulates from sus-pension in fluid streams (especially carbon particulates from exhaust gas of diesel engines) comprising a honeycomb filter with thin porous walls defining cells extending therethrough, with the transverse cross-sectional shapes of the cells forming a repeating pattern of geometric shapes without interior corner angles of less 30° and with alternate cells forming an inlet group and an outlet group. The inlet group is open at the inlet face and closed adjacent the outlet face. The outlet group is closed adjacent the inlet face and open at the outlet face Each cell of each group shares cell walls only with cells of the other group.
The walls may have a volume of substantially uniform interconnected open porosity and a mean pore diameter of the pores forming the open porosity lying within the area defined by the boundary lines connecting points 1-2-3-4 in FIG. 8 of the drawings.
Further described are impervious, unglazed, sintered ceramic products of primarily cordierite crystal phase, exhibiting low coefficients of thermal expansion and having analytical molar composition of about 1.7-2.4 RO ? 1.9-2.4 A1203 ? 4.5-5.2 SiO2, as well as a foamable particulate cement capable of forming sintered cordierite foamed ceramic masses, consisting essentially, by weight, of 1-40% cordierite grog, 99-60% ceramic base material and foaming agent, such as SiC, useful as materials for the apparatus.

Description

Frost 9-,6, 17 7 1, 4 One PARTICULATE FILTER AND MATERIEL FOR PRODUCING TOE SAME

Removal of solid particulate from fluids - gazes and/or liquids - in which the particulate are suspended is commonly done by use of filters. Generally filters are made of porous solid materials in the form of articles or masses with a plurality of pores extending there through (which may be interconnected) and hove small cross-sectional size or minimum diameter such that the filters are: if) permeable to the fluids, which flow through the filters from their inlet surface to their outlet surface, and (2) capable of restraining most or all of the particulate, as desired, from passing completely through the filters with the fluid.
Such pores constitute what is termed "open porosity" or "accessible porosity". The restrained particulate are collected on the inlet surface and/or within the pores of the f titer while the fluid continue to pass through those collected particulate and the filter. The minimum cross-sectional size of each of some or all of the pores can be larger than the size of some or all of the particulate, but only to the extent that significant or desired amounts of the particulate become restrained or collected on and/or within the filters during filtration of the fluids flowing through the filters. As the mass of collected particulate increases, the flow rate of the fluid through the filter usually decreases to an undesirable level. At that point, the filter is either discarded as a disposable/replaceable element or regenerated by suitably removing the collected particles off Andre out of the filter so that it can be reused.

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Four general main considerations for useful filters are:
(1) filter efficiency: the amount of suspended portico-fates of concern in a given volume of fluid thaw are removed from what volume of fluid as it passes through the jilter (usually expressed as a weight percentage of the total particles of concern originally in that given volume of fluid prior to passing into the filter,

(2) flow rate: the volume of the fluid per unit of 10 time that passes through the filter and collected portico-fates or, in a closed continuous feed system, the back pressure or increased pressure created in such system upstream from the filter by the presence of the filter and - particulate collected thereon in comparison to what the pressure therein would have been in the absence of the filter,

(3) continuous operating tome: the cumulative time of continued service of the filter before filter efficiency and/or flow rate/back pressure become unacceptable so as to necessitate replacement and/or regeneration of the filter;
and I compact structure: smallest space~sa~ing volume and configuration of the filter for attaining the best combination of filter efficiency, flow ratetback pressure and continuous operating time.
or filtration of fluids at elevated temperatures, consideration must also be given to the filters having adequate mechanical and chemical durability under the pro-veiling conditions of temperature within the filter and chemical reactivity of the fluids and suspended particulate coming into contact with the filter.

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The considerations noted above, especially the four general main ones, appear to be accommodated in varying degrees, but in less than fully satisfactory ways, by the following examples of prior art filters or incomplete filter suggestions:
US. Patents 2,884,0~1, 2,952,333 and 3,242,649 thus-irate filters of the type made of pleated thin porous sheets of filter material whose layers are interleaved with corrugated or crimped spacers with the parallel corrugations or crisps thereof extending substantially perpendicular to the folds of the pleated sheets. In essence, fluid enters a complete layer or column of cells defined by a spacer and then passes - through only the filter sheets on each side thereof (but not through corrugation or crimp segments of a spacer separating adjacent cells in that spacer) to effect filtration. More over, the corrugations involve cell-like passages whose transverse cross-sections have sinusoidal geometric shapes having smell interior angle "ccrnersi' of substantially less than 30.
British Patent Specification 848,129 shows another form of thy pleated-type filters wherein, instead of being interleaved with corrugated spacers, the thin porous sheets of filter aerial are Impressed with spacer dimples to maintain spacing between the pleats.
US. Patent 3,346,121 discloses thin porous-walled honeycomb filters ox corrugated layer structure having crosswise oppositely indented portions that block end portions of the channels or passages in an alternating pattern within each layer (but not necessarily from layer to layer to cause fluid therein to pass through the porous walls to effect filtration of the fluid. The corrugation pattern is such that the channels or cells have transverse, SLY
cro~s-sectional, geometric shapes with numerous instances of corners formed by small interior angles substantially less than 30 Moreover, the layered structure involves numerous portions, where the layers adjoin each other, which are of double and sometimes triple layer or wall thickness.
US. Patent 3,533,753 describes catalyst bodies with layered networks of intersecting "capillary" channels which can function as a filter body for combustion exhaust gas dust or sediment Ed particles, which can be diesel engine exhaust soot or particulate as noted in US. Patent 4,054,417.
US. Patent 3,637,353 discloses a tubular packed bed of granular catalyst with fluid-flow interstices for filtering - particulate from exhaust gases generated by diesel engines.
: US. Patent 4,054,417 also suggests making the disk closed diesel exhaust filters of known materials used in heat exchangers for turbine engines or in monolith catalytic converters for automotive vehicles ego. as disclosed in I- US. Patent 3,112,184 as a corrugated structure and in US.
Patent 3,790,654 as an extruded structure) as alternatives to and in a manner similar to the material in US. Patent 3,533,753 it with fluid flow passing into r through and out of Avery channel.
Research report EPA-600t~;77-056 of the U~5O Environ-mental Protection Agency suggests thaw several commercially available thin-porous-walled ceramic monoliths of honeycomb appearance, Roth corrugated and extruded, are potential filters for diesel exhaust particulate. However, the only illustrated arrangement given Hereford is the alternate layer cross-flcw design of a corrugatedl~nolith, with small mterior corner angles less to 30 in transverse cross section, wherein the exhaust gas passes through only those thin walls between ~22~

layers of cells or passages. This report Allah suggests the suitability of porous bonded mycosis of ceramic fibers for filters of diesel exhaust particu].ates.
British Patent Specification 1,440,184 discloses that porous bonded sheets of refractory metal oxide fibers can be formed into corrugated or embossed honeycomb structures for use in filtration of hot waste gases containing particulate matter and of molten metal prior to casting. As in cases noted above, the transverse cross-section of the corrugated embossed or structures contain numerous small interior angle corners much less than 30.

US. Patents 3,893,~17 and 3,962,081 describe ceramic . foam filters for removing entrained solids or inclusion particulate from molten metals as whose metals pass through the foam structure.
US. Patents 4,041,591 and 4,041,592 disclose thin-walled, honeycombed, multiple-fluid-flow-path bodies with all cells or passages parallel such that fluid entering each of the passages can continue through and pass out of the open exit end thereon without passing through any cell wall.
Alternate selected columns or layers of cells have their ends sealed for advantageous separate manifolding to fluid -- conduits. An optional use indicated for these bodies is in filtration and osmosis when porous materials are used to form thy honeycombed body so that some of the fluid flowing in a first set of cell can past into an adjacent alternate set of cells through the thin porous walls between them while a remaining portion of the fluid with a hither concern-traction of an undesirable or separable constituent can continue through and pass out of the open exit end of the first set of cells. Examples of the latter use are reverse AL
osmosis filtration and ultrafiltration of saline or Impure water to produce potable or purified water, in which cases the surfaces of the porous walls de~ininy the first jet of cells are lined with suitable selectively permeable membranes.

Summary of the Invention A new filter body has now been conceived for removing solid particulate from suspension in fluids and which is believed to provide a superior combination of satisfaction, especially with regard to all four main considerations noted above. When fabricated of inorganic (especially ceramic) material having incipient melting point above the elevated temperature of fluids to be filtered, the superior combination of satisfaction includes regard to adequate mechanical and chemical durability under the prevailing filtration conditions with such hot fluids The new filter body is based on a thin-porous-walled honeycomb structure with its cells or passages being mutually parallel and extending longitudinally there through between inlet and outlet end faces. It is uniquely characterized by the entirety of all cell walls constituting effective filters directly between adjacent inlet and outlet cells such that there are no small interior angle ~30) corners in the transverse cross-sectior.~l geometric shapes of the culls that inhibit - full effective access to such filters by the fluid due to fluid flow patterns and particulate accumulation patterns effected by such shapes with small angle corners. When viewed from each of the inlet and outlet end faces of the filter, alternate groups of cell ends are open and close in a checkered or checkerboard pattern, with the outlet end face pattern being the opposite of the inlet end face pattern l~Z7~

In particular, the invention it an apparatus for filtering solid particulate from suspension in fluid streams (e.g. hot gases or liquids) and which comprises a filter of honeycomb structure having a matrix of thin porous walls defining a plurality of cells extending long-tudinally and mutually parallel there through between inlet and outlet end faces of the structure. Generally, the walls are not greater than about 1.5 mm (preferably maximum ox about 0.635 mm) thick. The walls contain substantially uniform randomly interconnected open porosity of a volume and size sufficient to enable the fluid to flow completely through the walls and to restrain most or all of the part-curates from passing completely through the walls. Generally the open porosity is at least about 25~ (preferably at least about 35%) by volume formed by pores with a mean pore diameter determined by conventional mercury-intrusion porosimetry) of at least about lam preferably at least about 3.5~m)~
The transverse cross-sectional shapes of the cells form a - substantially uniformly repeating pattern of geometric shapes without interior angles of less than 30 (preferably less than 45). Thy inlet group of the cells is open at the inlet end face and closed adjacent to the outlet end face. The outlet - group of the cells it closed to adjacent the inlet end face and open at the outlet end face. Each cell ox the inlet group shares cell walls only with cells of the outlet group. Each cell of the outlet group shares cell walls only with cells of the inlet group.
The walls within each of a plurality of transverse sectors (e.g. annular or pie/wedge shaped) of the structure or throughout the structure should beneficially have sub-staunchly uniform thickness for substantially uniform ~2Z7~

filtration within the entirety respectively of such sectors or whole structure to maximize continuous operating time.
Transverse cross-sectional cell density within the structure should be generally at least about 1.5 cells/cm2 (preferably at least about 7.75 cells/cm2) for maximizing filter surface area within a compact structure.
According to a further embodiment of the present invention, the volume of interconnected open porosity in the walls and the mean pore diameter of the pores forming the open porosity lie uniquely within the area defined by - the boundary line connecting points 1 2-3-4 in FIG. 8 (and preferably connecting points 1-5-6-4 in that same figure).
; Such porosity and pore diameters are determined by convent tonal mercury-intrusion porosimetry.
The walls within each of a plurality of transverse sectors (e.g. annular or pie/wedge shaped) of top structure or throughout the structure should beneficially have sub-staunchly uniform thickness for substantially uniform filtration within the entirety respectively of such sectors or whole structure to maximize continuous operating time.
Transverse cross-sectional cell density within the - structure should be generally at least about 1.5 cells/cm2 - (preferably at least about 7.75 cells/cm2) for maximizing filter surface area within a compact structure.

As a material for making these products, it has been found that sistered products characterized by full density, having a cordierite crystal structure and low thermal expansion coefficients, can be formed of manganese-containing mineral batch compositions which comprise narrower compost-tonal ranges than that disclosed in US. Patent 3,885,977.
It has further been discovered that the impervious I

manganese-containing cordierite centrical product can be more economically and more desirably manufactured where prereacted cordierite material comprise at least 50 White (especially 50-95 White) of the ceramic batch materials.
This material provides an impervious, unglazed, sistered manganese-containing ceramic product having its major and primary crystal phase being cordierite crystal structure, having a analytical molar composition ox about 1.7-2.4 ROW 1.9-2.4 AWOKE 4.5-5.2 Sue and made of mineral batch composition selected from:
(a) wholly raw ceramic material wherein ROW comprises, as mole. % of ROW about 55-95% Moo and 5-45% Moo, and (by at least about 50 White prereacted cordierite material and the balance whereof being raw ceramic material, and wherein ROW comprises, as mole % of ROW about 5-40% Moo and 60-95% Moo.
In toe case of invention products made of wholly raw ceramic material, the more desirable products have ROW
proportioned as about 74-90. mole % Moo and 10-26 mole Moo.
In the case of invention products made of mixtures of raw ceramic material and prereacted cordierite material,- the more desirable products have ROW proportioned as about 6-15 mole. % Moo and 85-94 mole % Moo Moreover, it is preferable to have to prereacted cordierite material be about 80-90 wt.% of the mineral batch composition.
For the most preferred Norm of the invention, its molar composition is about 1.9-2~1 ROW o 1.9-2.1 Aye o 4.9-5 1 Sue.
When desired, Moo on the above formulations can be partially replaced my other oxide such as No, Coo Leo and/or Chihuahuas in toe manner described in US. Patent 3,885,977 (column. 2, Lyons. Accordingly, recital herein of Moo ~Z7~

is intended to include such optional partial substitutions in the present invention.
The products of this invention not only stinter to impervious condition, but exhibit typical low coefficient of thermal expansion (CUTE) on the order of about 15-20 x 10-7/C (25-1000C). They are particularly applicable to the production of honeycomb structures by the methods of US. Patents 3,790,654, 3,899,326, 3,900,546 and 3,919,384, and to the manufac~llxe of ceramic cements for bonding or plugging of cordierite honeycomb structures with similar low Cues. In particular, the products of this invention in the form of honeycomb structures are useful in constructing industrial heat recovery wheels.
As a further aspect of this invention, a cement is provided for bonding the aforedescribed products.
It was found that a formable particulate ceramic cement capable of forming a sistered cordierite foamed ceramic mass can be made by seeding ceramic base material of controlled composition with cordierite grog of another 2C controlled composition and adding thereto a foaming agent in an effective amount to effect foaming of the cement upon firing to produce the foamed ceramic mass.
This cement consists essentially, by weight, of 1-40%
cordierite grog, 9q-60% ceramic base material and foaming agent. The vase material Lo raw ceramic material that has an analytical molar composition consisting essentially of about 1.7-2.4 MO 1.2-2.4 Aye 4.5-5.4 Sue wherein MO
comprises, as mole % of MO, bout 0-55% Moo and at least 45% Noah The grog is ceramic material that has been previously fired and commented, and thaw has an analytical molar composition consisting essentially of about 1.7-2.4 Skye ROW 1.9-2.4 Aye 4.5-5.2 Sue wherein ROW comprises, as mole of ROW Moo in an amount of I up to a mole % that is about 20 mole % lower than the mole ox MO that it Moo and the balance it substantially Moo. Minor portions ox Moo it either or both of MO and ROW can be replaced by equal molar amounts of other oxides such as No, Coo Foe and Shea as noted in USE Patent 3,885,977~
Foaming agent can be selected from a variety of substances that decompose to give of gas at about the foaming temperature of the cement, i.e. the temperature at which the grog and base material axe in - a softened condition adequate to be foamed by the gas.
Among such substances are compounds such as carbides, - carbonates, sulfates, etc., preferably of cations that are in the grog and/or base material. Silicon carbide it the preferred foaming agent and can be employed in any effective amount (usually at least 0.25 White) up to a ; practical amount of about 5% my weight of grog plus base material. Larger amounts can be employed without additional benefit, but they dilute the amount of ceramic in the foamed mass. Generally 1-2 wt.% tic (by weight of grog plus base material) is preferred.
To insure thorough cordierite crystallization in the foamed ceramic masses, it is advantageous for the grog in the cement to be at least 5 White and correspondingly for the base material to not exceed 95 White. Preferred pro-portions are 5-20 wt.% grog and 95-80 wt.% base material.
While the invention can broadly utilize base combo-sessions within the aforesaid molar composition range embracing both the stoichiometric cordierite area and the nonstoichrometric eutectic cordierite area, it is preferred ~'~Z7~

to use base compositions of the generally stoichiometric type having an analytical molar composition consisting essentially of about 1.7-2.4 MO 1.9-2.4 Aye 4.5-5.2 Sue wherein MO is as previously stated. Most preferably, such molar composition is about 1.8-2.1 MO 1.9-2.1 Aye

4.9-5.2 Sue and MO is wholly Moo.
The requisite minimum difference of about 20 mole for Moo in MO and ROW provides the grog with adequately higher melting point vise a vise melting point of the base material so as to insure proper cordierite crystallization seeding effect by the grog at foaming temperature. To enhance such effect, it is preferred to have MO of the base composition comprise not more than about 15 mole % Moo.
`- The most preferable grog has an analytical composition of about 1.8-2.1 ROW 1.9-2.1 Aye 4.9~5.2 Sue, and JO
comprises 8-12 mole % Moo and the balance go.
If desired, optional customary fluxes may be included ; in the cement in minor amounts up to 5 wt.% or so of the : .
: grog plus assay material. Such fluxes are illustratively disclosed in US. Patents 3,189,512 and 3,634tlll.

- The present invention also encompasses ceramic structures embodying the novel sistered cordierite foamed ceramic mass and the method providing suck mass in the structures. The structure broadly comprises at least two closely spaced cordierit~ ceramic surfaces hazing the mass in the space between and bonded to those surfaces. In the method, the cement it disposed between such surfaces, then the structure with the cement so disposed is fired to foaming temperature in the range of about 1160-1325C and thereafter cooled with to cement converted to the foamed ceramic mass. Preferably ~L2%78~L

the foaming temperature is in the range ox 1170-1250C, especially for attaining foamed ceramic mass that it sub Stan-tidally impervious to fluids. Lower temperatures Hall to develop an adequate foaming of the cement. Also, it it desirable to fire to the foaming temperature at an average fate of at least about 100C per hour (preferably at least about 200C per hour) to avoid the possible adverse effect of much slower (e.g. cry.) heating rates that may cause loss of foaming agent gas before the ceramic constituents lo of the cement are soft enough to be foamed.

grief Description of Drawn s FIG. 1 is a partially broken away, oblique view of a - preferred embodiment of a filter body according to the present invention.
FIG. 2 is a sectional view taken in each plane India acted by each of the line and arrows A-A and the line and arrows B-B of FIG. 1.
- FIGS. 3-6 inclusive are views of the end faces of four alternative embodiments of filter bodies according to the present invention, which bodies have different transverse cross-sectional cell geometries ox shapes.
FIG. 7 is a longitudinal sectional view through a filter apparatus according to the present invention for filtration of particulate from diesel engine exhaust gas.
FIG. 8 is a graphical representation of the combined open porosity and mean pore size of filters according to the present invention. It includes, as the best mode of carrying out the present generic invention with respect to filters in diesel engine exhaust conduits or systems, an indication of unique combinations of open porosity and mean pore size I

I

FOE 9 is a longitudinal sectional view through a ; filter chamber according to the present invention for filtration of particulate or entrained solids from molten metals.
IT. 10 is a schematic illustration of a rotatable heat exchanger or heat recovery wheel assembly with filter structure according to the present invention.
'-' : Detailed Description . .
The filter body 1 shown in FIG. 1 comprises a cellular or honeycomb structure (monolith) which has a matrix of intersecting, uniformly thin walls 2 defining a plurality of cells 3. The Silas extend longitudinally and mutually parallel through thy body 1 between the inlet end face 4 - and the outlet end face 5. Ordinarily the body 1 also has a peripheral wall or skin 6.. An inlet group of alternate cells 7 are open at the inlet end face 4 and are closed, : sealed or plugged with closure means 8 adjacent outlet end - face 5. Means 8 can be a seal nut or cement mass adhering to walls 2 and extending from face 5 a short distance inwardly Jo end face 2 of means 8. The other alternate cells 10 form an outlet group and are open at outlet end face S, but they are similarly closed adjacent inlet end face 4 by closure means 11, which likewise extend inwardly a short distance from face 4 to end face I of means 11. Thus, as viewed at I

end races 4 and 5, the alternating open and closed cells are in a checkered or checkerboard patkernO
Body 1, including means 8 and 11, can be mode ox any suitable materials such that walls 2 have the requisite interconnected open porosity therein and means 8, 11 are generally Impermeable to fluids. Such materials may include ceramics (generally crystalline), glass-ceramics, glasses, - metals, cermets, resins or organic polymers, papers or textile fabrics. (with or without fillers, etc. and come binations thereof. For walls 2 and skin 6, it is preferred to fabricate them from plastically formable and sinterable finely divided particles and/or short length fibers of substances that yield a porous sistered material after being fired to effect sistering thereof, especially ceramics, glass-ceramics, glasses, metals and/or swarms. As desired (besides volatizable plasticizers/binders for the formable particle batch or mixture, any suitable or conventional fugitive or combustible urinate additive can be dispersed within the formable and sinterable mixture so as to provide appropriate and adequate open porosity in the sistered material of walls 2. Moreover, the requisite open porosity can also be designed into walls 2 by raw material selection . as described in US. Potent.
The Cody 1 can be fabricated by any suitable technique.
It (without plugs 8 and 11~ is made preferably by extrusion of a sînterable mixture in the manner as disclosed in US.
Patents, 3,919,384 and 4,008,033. Such extruded green honeycomb body is then fired for effecting the sistered condition thereof in the manner as disclosed in US. Patent 30 3,8~9,3~6.
Plug means 8,11 can then ye formed in the sistered I

monolith 1 by injecting a sinterable or other suitable sealant mixture into the appropriate ends of the cells 3.
For example such mixture can be injected by moans ox a pressurized air actuated sealant gun whose nozzle can be positioned at the proper cell openings on the end faces 4,5 so as to extrude the mixture Unto and to plug the end portions of the cells. An appropriate assembly and post-toning of an array of sealant nozzles of such gun(s) can he used to inject the plug mixture simultaneously in a plurality or all of the alternate cells at Mach face 4,5 for efficient production. Upon subsequent f irking of the body 1 after -; having teen plugged with a sinterable or other heat-setting mixture, there results rigid if ted closure masses 8,11 which are adherently bonded to adjacent portions of walls 2.
These plugs 8,11 are substantially nonpermeable to the fluid to be pasted through filter 1.
If so desired, the monolith 1 need not necessarily be fired or sistered before injecting sealant mixture, especially ceramic cement, into the ends of the cells 3. For example, monolith 1 can be made of ceramic material having a firing - temperature thaw is substantially the same as or closely similar to the firing or foaming temperature of an appropri-lately selected ceramic cement. In that case, the cement can be injected into the cell ends while the monolith is in the - unfired or groaner state. Thereafter the green monolith with green cement plugs is fired to suitable temperature or temperatures within the appropriate range to effect sistering of toe monolith and of the cement (including foaming thereof if that it a characteristic of it JIG. 2 shows the pattern of fluid flow through filter 1 in Roth a vertical column ox cells 3 (in plane A-A of FIG.

~16-Z7~

1) and a horizontal column ox cells 3 (in plane B-B ox FIG.
1). Fluid flow is indicated by the lines 13 with arrows.
Thus, fluid 13 passes into inlet cells 7 from inlet end race I, but because of the blocking effect of end faces 9 of plugs 8, the fluid under some pressure then passes through the pores or open porosity in cell walls 2 at top, bottom and both sides of the cells 7 so as to respectively enter outlet cells 10 above, below and on Roth sides of each cell 7. While fluid 13 passes through the entirety of all cell walls 2, their porosity is such as to restrain particulate therein and thereon as a porous accumulation which may even fill up all of cells 7 before replacement of the filter 1).

, It can be seen that the entirety of all cell walls 2 act as filters for unique superior filter capability. The fluid 13 passing into cells 10 then flows out of these cells at the outlet end face 5, since the end faces 12 of plugs 11 adjacent the inlet end face 4 prevents the fluid from reversing direction. Also, plugs 11 prevent fluid 13 from directly entering cells I without first going into cells 7 and through walls 2.
While it is preferred to make the transverse cross-sectional geometry of the cells 3 to be squares as shown in FIG. 1, any other suite to geometries Jay be employed.
Examples of such other geometries are shown in FIGS. 3-6~ In FIG. 3, cells pa are in the transverse geometrical form of equilateral triangle, but they could also have the form of right triangles. FIG. 4 shows cells 3b with transverse cross-sectional geometry of rhomboids, which could optionally be made as rhombuses. Similarly, rectangles can form the transverse cell geometry instead of squares. A less easily manufactured transverse cell geometry is shown in FIG. 5, Sue which constitutes a repeating pattern of quadrilateral of cells 3c. In each of these polygonal shapes, intersecting walls 2 preferably form include angles what are not less than 60 to avoid the nonuniform accumulation of particulate in smaller angle corners and to enable proper complete plugging of the alternate cells adjacent end faces 4,5.
Also, it may be desirable for enhanced mechanical strength of the honeycomb filter bodies that the cell corners be filleted or slightly filled in with the same or similar material as forms cell walls 2. what latter concept can be extended to a presently lesser desirable form as shown in FIG. 6, wherein cell Ed have a circular transverse geometry.
. The walls 2 have a substantially uniform thickness throughout - in that they substantially uniformly vary from their thinnest . portions pa to their thicker (or maximum filleted) portions 2b. Another alternative to the latter one would be elliptical transverse cell geometry. If it is desired for certain purposes, the filter Cody can be made with a plurality of transverse sectors (eye. annular or pie/wedge shaped) whereby the transverse cell cross-sectional axes are larger in a sector or sectors than such areas are in another sectcx or other sectors. It is even conceivable that repeating patterns .-. of different transverse geometric cell shapes can be employed in different transverse sectors.
In all variations of the filter body with respect to transverse cell geometry, alternate cells are plugged adjacent each end face in a checkered style pattern such that those cells plugged at the inlet end face are open at toe outlet end face and vice versa. Also, the transverse cross-sectional areas of such cells are desirably sized to provide transverse cell densities in the range of about 2-93 12Z7~
cells/cm2. Correspondingly, it it desirable to make the thin walls with thickness in the range of about 0.05-1.27 mm.
One embodiment of the present invention is a filter apparatus for removing carbonaceous particulate from diesel engine exhaust gas so as to avoid air pollution by such paxticulates, which individually can tango in size from about 5 micrometers down to and below 0.05 micrometer. FIG.
7 shows an exemplary form of such apparatus, which comprises the filter body 1 held within a container or can 20. Body 1 10 is the same as. that shown in FIG. 1, with skin 6, inlet cells 7 extending from inlet end face 4 and blocked by plugs 8, and outlet cells 10 open at outlet end face 5. Can 20 is similar to a conventional type of can (see US. Patent 3,441,381) employed for mounting catalytic converter honey-- comb substrates in exhaust systems of internal combustion engines. The can 20 comprises two parts 21,22 respectively formed of filter-holding portions 23,24, conduit-connectors - 25,26, conical portions 27,28, respectively joining connectors ~5,26 to portions 23,24, and mating flanges 29,30 which are - 20 mechanically fastened together ego. by bolts and nuts not shown to keep the can properly assembled for use and so as to capahle.of being unfastened in order to open the can 20 for replacement ox filter body 1. Internal annular mounting mummers ox L shaped cross-section are respect lively fastened to portions 23,24 so as to respectively abut against faces 4,5 and. hold body 1 in its proper fixed axial position within can 20. To cushion body 1 against mechanical shock and vibration, it is ordinarily desirable to surround body 1 with a wrapping or mat 33 ox metal mesh, refractory fiber and thy like, which may fill the annular space between body 1 and portions 23,24. To minimize heat loss from body ~Z?d~8~

1 and excessive heating of portions 23,24, a layer of insulating material 34, such as glass or mineral wool mat, may also be wrapped around body 1.
Connectors 25,26 are suitably fastened (e.g. by welding or casketed mechanical coupling) to exhaust gas conduit of a diesel engine. While can 20 can be located in and form part of the exhaust gas conduit some distance downstream for the . engine exhaust manifold, it can desirably be located near or at the exit from the exhaust manifold. The latter arrangement facilitates regeneration of filter body 1 by utilizing the . higher temperature of the exhaust gas upon exiting the - exhaust manifold to cause, with excess air in the gas, the .: combustion of carbonaceous particulate restrained in body 1 to form further gaseous combustion products that can then pass on through and out of body 1 for emission through connector 25 to the tailpipe (not shown) fastened to connector 26. If desirable (especially when can 20 is located downstream along the exhaust conduit some distance from the exhaust - manifold, a combustion ignition device may be positioned in I 20 can 20, such as a glow plug in conical portion I or an electric heater within the central axis ox body 1 (similar to the device of US. Potent), and secondary air may be injected into can 20 upstream from body 1 to assist in regeneration of Cody 1 without removing it from can 20.
Additionally, catalyst substance can be placed on and in walls 2 ox Cody 1 (similar to catalytic converter honeycomb substrates) to facilitate regeneration of combustion in body 1.
In ordinary usage, frequent higher speed or rum of the diesel engine can contribute sufficient heat (e.g. 400-500C
or higher) to cause repetitive regeneration combustion of body 1 without rewiring the can 20 to be opened often for I

replacement of body 1. Nevertheless;, removed bodies 1 can be reverse flushed with air to how much of the particulate out of it into a collector bag and when fully regenerated by high temperature air passed through it before reinstalling in can 20.
In a further embodiment of the invention, the volume of interconnected open porosity and the mean diameter of the pores forming the open porosity lie within the area defined by the boundary lines connecting points 1-2-3-4 in FIG. 8 of the drawings..
. In a preferred embodiment, the walls are not more than about 1.5 mm thick, the volume of interconnected open porosity and the mean diameter of the pores forming the open porosity lie within the area defined by the boundary lines connecting point 1-5-6-4 in FIG. 8 of the drawings, and the structure for a transverse cross-sectional cell density of at least about 1.5 cells/cm2.
In further advantageous embodiments, the walls are not less than about 0.3 mm thick, even more preferably not more than about 0.635 mm thick, and the cell density is at least about 7.75 cells/cm2.
Dense cordierite swineherd structures for these and other I- products are achieved my the partial substitution of Moo for Moo in the cordierite crystal structure within controlled -. amounts. That substitution greatly increases the sinterability of thy cordierite watch materials my lowering and widening the sistering temperature range at which full density can be achieved. In general, the sistering of mineral batch come positions comprise of wholly raw ceramic materials to lull density occurred at about 1200-1300C, whereas mineral batch compositions containing prereacted cordierite material I
sistered to impervious conditions at about 1250-1410C.
Also, when prereacted cordierite material is included in the mineral batch composition, the minimum weight percent manganese oxide necessary to form the impervious product is about 0.6 wt.%, as compared to a minimum of about 12.6 White for the mineral batch composition with wholly raw ceramic materials.
Therefore, the benefits of utilizing the mineral batch compositions containing prereacted cordierite material are that a more refractory product is produced (similar to regular cordierite without manganese oxide) and that lesser amounts of m nganese oxide are required to effect full density. Furthermore, less firing shrinkage is generally experienced with the mineral batch compositions containing prereacted cordierite material.
Full density either is unattainable or cannot be reliably attained with mineral batch compositions which either have wholly raw batch material and too little molar proportion of Moo (i.e. less than 55 mote % of ROW), or which contain prereacted cordierite material in amounts which are too small it less than 50 wt.% of the mineral batch composition, or which contain at least about 50 White prereacted cordierite material while having a mole proper-lion of Moo outside the range of 5-40% of ROW The mineral batch composition of wholly prereacted cordierite material can be fired to full density at about 1410C, but it requires extra expense of thoroughly fine grinding of such batch material prior to shaping and firing it into impervious product.
Impervious sistered products of the invention may contain minor amounts of phases other than the primary cordierite phase as may occur within the molar compositional limits defined avow.

I
As used in the foregoing description of the tense cordierite ceramic of the present invention:
(a) "full density" and "impervious" mean the condition of a ceramic body whereby it exhibits leer than 1% by volume of open porosity as determined either by the conventional mercury porosimetry test or by the toiling water test for apparent porosity generally as defined in ASTM Designation C20-7Q effective January 22, 19~0, both of which give Essex-tidally the same results for products of the invention stated herein;
(b) "raw" means the condition of ceramic batch material which is not prereacted with another batch ingredient, but - which may have been individually calcined or fired without melting thereof or otherwise is unfired;
(c) "prereacted" means the condition of ceramic batch material which has been formed by reaction between two or more raw ,~aterïals with, at most, melting of only minor portions thereof; and (do "mineral batch composition" means a ceramic batch composition in which all of the ceramic material is raw and/or prereacted.

Examples Cordierite ceramic materials of the type disclosed in US. Patent 3,885,~77 and Alec are generally preferred for diesel particulate trap filters because, as was earlier found for their use as catalyst substrates in internal combustion engine exhaust systems, these material have properties that enable them to withstand and be durable under the thermal, chemical and physical conditions to which they are subjected in such systems including those of diesel ~LZ~78~1 engines. A series of filter honeycomb samples with square cross-section cells were extruded of cordierite batch come ; positions as set forth in TALE 1. Those samples were then dried and fired generally in accordance with the following typical firing schedule:

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80C to 1425C within about 60 hours.
told about 10 hours at 1~25C.

Cool 1425~C to room temperature within about 24 hours.

The walls of the as-fired samples had typical open porosity and mean pore diameters as set forth in TABLE 2, which varied among the samples with particular relation to vane-lion in the graphite (as burn-out material) and talc used in the batch compositions.

Open Porosity Mean Pore Diameter Samples volume % micrometers . A 35 4 B 44.5 9 C 41.3 10 D 48.0 11 - E 48.5 13 F 47~7 13 G 46.8 12 H 6~.6 11 I 65.8 15 : J 3~.8 35 X 37.2 35 L 36.7 23 M 44.7 22 N 54.6 6 Plugs were formed in the end portions of alternate cells, as previously descried, of the sistered samples by injecting a plastically formable ceramic cement into such cell ends with an air-operated sealant gun. The amount of I

I I

plugging cement injected into the cell ends was controlled by measuring the time that operative air pressure was applied to the sealant gun. By this means, the cement plugs were generally made with a depth or length into the cell from - an end face thereof in the range of about 9.5-13 mm.
A preferred plugging cement employed with the foregoing samples was the manganese-magnesium cordierite foam type of this invention. In particular, the preferred foam cement used in the above-noted samples had the batch composition lo in accordance with Sample 6 of TARE lo further below. The previously fired samples with the injected cement plugs ; were then fired generally in accordance with the following.
- The Mn-Mg cordierite grog in the cement batch was the dense cordierite containing manganese in accordance with the present invention In particular, the grog was made of the following batch composition (in weight of the total ceramic raw materials:
Sample A grog L-2Qo mesh 84.48 Georgia-Kaolin Xaopaque lo clay ZAPS 10) Lowe ED Baker MnCO3 power 4~15 - Penn. Glass Sand Mainsail silica UPS 5) 0.78 ` Pfizer MY ~6~28 talc UPS 20~ 0.59 Methyl cellulose ~inder/plasticizer4.0 Alkali Stewart extrusion aid 0.5 Distilled water plasticizer 26.0 This Mn-Mg cordierite grog was fired generally in accordance with the same firing schedule as for Sample A, except that the maximum temperature was 1405C instead of 1425C.
The previously fired samples with the injected cement plugs, as noted above, were fired generally in accordance with the following typical firing schedule:

~Z7~

Room temperature to 1210C within about 6 hours.
Hold about 30 minutes at 1210C.
Cool 1210C to room t~perature within about 18 hours.
The cement foamed during firing to develop good sealing to the cell walls and generally fluid impervious plugs. The foaming action counteracts normal drying and firing shrink-age of an otherwise non foaming ceramic cement.
While the previously mentioned foam cement is preferred for worming the plug, other suitable foaming and nonoaming ceramic cements may be used. Even non ceramic cements or sealants may be used if they are capable of being durable under exhaust system conditions of heat as well as chemical and physical abuse.
The filter samples made as described above, and having - various cell densities, wall thicknesses and external dimensions (diameter and length), were tested in the exhaust - system of a 1980 Oldsmobile 350 CID (cubic inch displacement) diesel V-8 engine operated with a water brake dynamometers at -- constant conditions ox spend and load. A dri~eshaft speed of lOOOrpm was used, which was equivalent to a vehicle road speed of 40mph ~64 km per ho A load of 100 ills (approx. 136 joylessly torque was used, which was equivalent to higher than basic vehicle road load at steady 40 mph (64 km per ho speed on a horizontally level road surface.
This higher than basic road load provided more realistic exhaust particulate volume per unit time with respect to the fact that actual or commonly experienced road loads are ordinarily higher than basic road loads because of phlox- -lions in acceleration and variations in road surfaces from toe revel condition. Thy engine was warmed up to normal operating temperature before beginning the tests of the ~.2Z~

filter samples.
The filter cans were located about 2.1 meter downstream from the engine exhaust manifold. Exhaust gas flow rate through each filter placed in the can (from only four engine cylinders) was approximately constant in the range of about 1.0-l.l cubic meters per minute. Back pressures callused by or pressure drops across) the filter samples were measured by water manometer and were monitored during the tests from an initial level up to the time they rose to 140 cm of water, at which time the test were discontinued because higher back pressure has been determined by the engine manufacturer to ye unacceptable for proper engine operation. Thus, when the pressure drop across the filter retches 14Q cm of water, the filter has attained its maximum effective filter capacity in a single operation in the noted system. The total time from the beginning of the test (with the exhaust gas started through the filter) until the filter Jack pressure becomes 140 cm of water is referred to as the Operating Tome of the filter.
- 20 Exhaust gas samples were taken downstream of the filter can. Without any filter in the can, the amount of part~culates in the total unfiltered exhaust gas (in terms of grams per mile or g~mi.~ were calculated from the amount of partlculates measured in an unfiltered gas sample. This amount of particulate - called the Baseline Particulate -was found to haze negligible variation over a range of back pressures exerted on the system up to 14~ cm of water. The Baseline Partïculates ranged between 0.17 gamin and 0.24 gamin in the various tests. With a filter in the can, the amount ox Residual Particulate in the total filtered exhaust gas (it terms of g~mi.~ were calculated from the amount --2g--` ~2;~'78~

of particulate measured in a filtered gas sample. The difference between the Baseline Particulate and the Residual Particulate as a percent of the Baseline Portico-fates is referred to as the calculated Filter Efficiency.
Incidentally, the Filter Efficiency in terms of the weight gain of the filter during a test (i.e. the gain over the initial untested filter weight) as a percent of the Baseline Particulate for the same test agreed closely with the above-noted calculated Filter Efficiency.
TABLE 3 sets forth the initial pressure drop, Operating Time and Filter Efficiency for a series of tested filter samples having a square cell density of 15.5 cells/cm2, external dimensions of about 9.3 cm diameter and 30.5 cm length, and wall thickness as indicated in that table. In most cases for a given wall thickness, two filters of the same sample honeycomb body were tested.

. .

:

Wall Thickness 0.432 0.635 .

', Sample B 30.2/14.2 35.0/34.5 39.8/34.5 Sample D 29.4/24.8 28.2 40.5/29.7 Sample H 24.6/20.9 20.0/16.. 3 30.1 Sample I - 11.6/10.0 Sample J 6.2/7.3 - 15.7/16.8 Sample K 8.1/8.0 9,5/9.9 17.4/17.6 Sample L 12.7 19.0/17.2 24.0/21.3 Sample M ho 0/11~ 7 29.0/23.7 23.4/21.7 Sample N 20.8/23.7 - 28.6/27.9 Operating Time (hours) -Sample C 2.01/2.20 2.39/2.04 1.18/1.48 Sample-D 3.40/3.8 3.17 1.89/2.3 Sample H 3.60/5.0 3,20/4.30 3.30 Smut I 4,50/4,90 Sample J 18.0~/16.6 - 5.90/4.30 Sample K 8.80/11.3 5.40/5.70 2.17/3.00 Sample 6.00 1.80/2.16 1.32/1.5;
Sample M 7.80/8.50 2.67/3.00 1.39/1.78 Sample N 3.5~/3060 3~00/3.30 2.40/2.60 I

Filter Efficie~y (~) Sample B - 91.3/95.0 Sample C 95.9/~6.0 95.8/97.8 97.0/~8.2 Sample D 94.6/95.3 96.0 94.6/95.0 Sample H 84~3/80.9 86.8/89.0 87.0 Sample I - 69.7/60.1 Sample J 51.2/41.~ 64.0/6Z.6 Sample K 57.5/46.4 66.8/62.3 78.1/77.6 : 10 Sample L 67.8 85.8/86.1 85.3/89.4 Sample M 66.8/70.3 87.0/84.9 88.4/87.6 Sample N ~6.3/96.2 98.0~97.0 98.3/98.8 -............... Preferred as the most practical filters, based on the foregoing tests, are those which have an average Filter Efficiency of at least 75% and a minimum average Operating Tome of three hours. The data of TABLE 3 show samples D, H.
and N to fit this preferred category, which is more generally defined in FIG. 8 by the area 1234 and by the most preferred area 1564 (represented my the undoer lines connecting those numbered points with coordinate values as follows):
.
: Coordinates Point pen Porosity mean Pore Dime or us 1 58.5 2 33.Q 20 3 5~-5 20 4 9Q.0 3~.5 15 62.Q 15 ~2~7~

Thus, the preferred category of filters or diesel exhaust systems have an optimum balance of open porosity and mean pore diameter.
The preceding test data also show a tendency for reduced Operat~lg Time when maximiz1n~ Filter Efficiency in filters of a given external size and cell density.
However, it has been found that Operating Time is directly proportional to the filter surface area. To avoid come promise of Filter Efficiency, Operating Tome can be increased 10 by increasing cell density and/or external size.
- The test data of TABLE 4 (derived from the same test previously described) illustrate the effect of increasing cell density and of increasing external size on Operating Time of the filters with wall thickness of 0.305 mm and a - diameter of about 9.3 cm. Typical initial Jack pressures of those filters with square cell densities of 31 and 46.5 cells/cm2 were respectively 14.1/lQ.5 and 15.7 cm of water. Live Sample D, Samples E and F also are within the preferred category of filters indicated by FIG. 8. While - I no actual test data was obtained for a Sample F filter with - more than 1 my of filter surface aria, it is evlden~ from the presented data that such larger Sample F filter would - have an Operating Time in excess of three hours.

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A further illustration of larger filter suffice area providing greater Operating Time I the test results with a Sample D filter having a square cell density of 15.5 cells/cm a diameter of about 14.4 cm, a length of about 30.5 cm and wall thickness of about 0.432 mm. Its jilter surface area was 3.03 my. The filter had an initial back pressure of 3~0 cm of water. It exhibited a Filter Efficiency of 79~ and an Operating Time of 23.1 hours.
The tested filter samples were examined for the con-10 diction of accumulated particulate that generally completely filled such filters. No significant differences in the amount of particulate were seen with respect to varying radial and axially positions in the filters These results are believed to be in significant part due to lack of lower angle corners in the geometric transverse square shapes of - the cell in those filter samples. Further, the packed densities of the accumulated particulate were estimated to be relatively constant throughout the filter samples -- being in the range of Owe g/cm3 for samples with about 20 9.3 cm diameter and 30.5 cm length and about Owe g/cm3 for the sample with about 14.4 cm diameter and 30.5 cm length.
-I Moreover, it was observed that the accumulation of - particulate in the filter samples has a restage effect on filter pressure drop. The first stage involves a fairly substantial steady rise in pressure drop. It is hollowed by a second stage during which the pressure drop rises at a much lower rate. Finally in a third stage (apparently when fluid flow paths through the accumulated particulate are being fully blocked), the rise in pressure drop accelerates 30 again to a much higher rate. All three stages can usually be observed in toe larger samples with 14.4 em diameter and ~LZ2~

.
30.5 cm length. however, the smaller samples often showed only either the first and second stages or the first stage before the pressure drop reached 140 cm of water.
The effects of lower cell density were demonstrated with Samples G of filters having square cell density of about 7.75 cells/cm2 and wall thickness of about 0.635 mm.
Their approximate external dimensions and jest results are set forth in TABLE 5. Those results show that lower cell density tends to decrease Operating Time because of lower filter surface area, but that such tendency can be offset by employing larger external dimensions As indicated in FIG.
8, Sample G is also within the preferred category of filters.

..' TUBULE

Diameter Length Filter Operating cm cm Effic eons Time-hours go 30.5 95.0 1.35 - 9.3 30.5 96.~ 1.73 14.4 I 93.3 14.7 A Sample A filter was also made with cell density of about 7.75 cells/cm2, wall thickness of about 0.635 mm, diameter of about 14.9 cm and length of about OWE cm. It had a fairly high initial pressure drop indicative of pro-voiding too little Operating Time. However, improved Operating Time could be obtained with Sample A filters by increasing cell density Andre external dimensions.

MOLTEN METAL FILTERS

Another embodiment of the present invention is a filter apparatus for removing entrained solid particulate from molten metal ego. aluminum prior to casting it into ~227~

a solid body or ingot and so as to avoid defects in the cast metal products caused by such particulate trapped herein.
Such particulate can be of the individual size order of 10-20 micrometers. FIG. 9 shows an exemplary form of such apparatus, which comprises the filter body 40 (of the type shown in FIGS. 1 and 21 held within a molten metal filtration chamber 41 (of the type discussed in US. Patent 4,024,056).
Chamber 41 comprises an inlet portion 42 and an outlet portion 43 separated by an intermediate refractory wall 44. Allah 44 - joins with a base portion 45 connected to and forming part of floor 46 of inlet portion 42. Portion 45 contains an aperture 47 for passage of molten metal from the inlet portion 42 into outlet portion 43. Filter 40 is interposed across aperture 47 such that the inlet face 48 of jilter 40 (which corresponds to inlet face end 4 of filter body 1 in FIGS . 1 and 2 ) faces upstream of the molten metal flow path - through aperture 47, viz. into inlet portion 42. Outlet portion 43 has a floor I which is lower than inlet floor 46 20 to facilitate flow of molten metal through aperture 47 via the filter 40. Conventional staling means 50 replaceable holds and seals filter 4Q within aperture 47 so that all of the molten metal passes through filter 40 from inlet portion 42 to outlet portion 43 and that, when it becomes substantially filled and clogged wit entrained solids, filter 40 can be readily replaced with a new like filter. Thus, unfiltered molten metal enters inlet portion 42 via pouring spout 51 and the filtered metal exits from filter 40 into outlet portion 43. Filter I has plugs 52 and 53 in alternate cell ends respectively adjacent to the inlet and outlet faces of the filter in the same manner as shown in FIGS . 1 and 2.

2~7~

As an example ox this embodiment of the present invent lion, a molten aluminum filtration chamber is employed in a modified form from that described above to contain a filter, between inlet and outlet portions of the modified chamber, which has a diameter of about 14.6 cm and a length of about 15.2 cm. The filter is like that of Sample C with square cell density of about 7.75 cells/cm and wall thickness of about 0.635 mm. Upon completion of a casting run, this filter is removed and discarded, and then replaced with a lo n w like filter.
Preferably the above-described filter is made of thermal shock resistant, micro cracked type of ceramics having good corrosion/erosion resistance to molten aluminum - in addition to the requisite porosity in the walls of the ; filter. Such ceramics include zirconia-spinel ceramics, aluminum titan ate based ceramics, etc., with a particularly desirable one being, by weight, 60% zircon phase and 40% magnesium acuminate spinet phase.

HEAT RECOVERY WISE

A further embodiment of the present invention is a heat exchange assembly involving a rotatable honeycomb heat recovery (or exchange wheel for absorbing heat from one fluid stream and Imparting such heat to another fluid stream. According to the present invention, the coven tonal heat recovery wheel is modified to additionally act as a filter ox particulate suspended in such fluids. FIG.
10 schematically shows the conventional assembly with the heat recovery wheel 60 in modified form (similar to filter Cody l of PHASE 1 and 21 Jo function as a filter as previously discord Wheel I rotates within and across two fluid I

flow paths within a heat exchange chamber and separated by conventional robing seal and duct structure 62. As shown, a first fluid passes sequentially through a pair of ducts - (as indicated by arrows) with the wheel 60 interposed between those ducts and their fluid flow paths. The cooler first fluid passes from one duct into the slowly rotating honeycomb wheel 60, absorbs heat from the wheel as it passes through . it and then continues as heated first fluid flowing through the second duct downstream of the wheel 60. A second fluid passes sequentially trough another pair of ducts (as India acted by arrows with the wheel 60 interposed between those ducts and their fluid flow paths. The hotter second fluid passes from one duct into the slowly rotating honeycomb wheel 60, gives up heat to the wheel as it passes through it and then continues as cooled second fluid flowing through the second duct downstream of the wheel 60. Thus, each of the faces 63 and 64 of wheel 60 alternately function as inlet and outlet faces as wheel 60 rotates between the first and second fluid' flow paths, which faces 63 and 64 are facing the fluid flow directions from and to the ducts. Wheel 60 - also constitutes the filter with thin cell walls 65 defining Jo two sets of alternate cells - cells 66 open at face 63 and the other cells closed adjacent face 63 by plugs 67. A
: reverse arrangement exists at and adjacent face 64.
eat recovery wheel 60 is typically employed for risque lying heat from a second fluid which is an exhaust gas of a combustion system, such as an internal combustion engine system or an industrial furnace system. By the last men-toned embodiment of the present invention, the filter heat recovery wheel 60 will remove particulate entrained in the second fluid. Then, as the wheel 60 rotates a sector of the ~L227~

wheel from the second fluid flow path to the first fluid flow path, air for the combustion system passes through the same sector of wheel 60, but in a direction opposite of the second fluid, to pick up heat from it (thereby becoming preheated air) and to blow the particulate collected in such sector of wheel 60 back through the combustion system to ye oxidized into gaseous species or a smaller particulate form. Moreover, the filter wheel 60 may also serve to filter particulate from incoming air and to exhaust such accumulated particulate with cooled exhaust gas from the combustion system.
; Although the impervious products of the invention can - be fabricated into a variety of forms by any of the usual or known ceramic forming techniques, a series of samples of the invention as noted in TABLES 6 and 8 were made in the preferred form of honeycomb structures by the previously noted method of extrusion and firing. The batch ceramic - materials were dry blended with (as White of the total ceramic materials therein) 4.Q~ methyl cellulose plasticizer/
winder and 0.5~ alkali Stewart extrusion aid. Those mixtures were plasticized with the water in a mix-muller, and further plasticized and desired by pre-extrusion into spaghetti-like masses. Then the fully plasticized and compacted batches were extruded in honeycomb green shapes, dried and fired.
TABLES 6 and 8 also set forth the analytical molar compositions as calculated from the batch ceramic materials.
TALE 7 sets forth the sistering temperatures, firing shrinkages and Cues for the Samples 1-4 of TABLE 6 made of mineral batch compositions with wholly raw ceramic materials and exiting less than 1% by volume of open porosity.

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Such temperatures were the approx~late lowest temperatures for full density.

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Sample Temperature C Shrunk C_ 1 1285 13.2 17.5 2 1300 19.7 19.7 3 1200 12.0 16.4 4 1200 19.4 18.4 In contrast to Samples 1-4, other similarly prepared samples with wholly raw ceramic materials, but not within this invention because of having molar proportions of Moo that were 50 mole % or less of ROW failed to develop full density at sinteriny temperatures that did not cause over-firing. For example, a sample with the analytical molar composition of about 0.8 Moo lo 2 Moo AYE 5 Sue (wherein Moo is 40 mole of ROW exhibited 47% by volume of open porosity after hying fired at sistering tempera-lure of 124QC.

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The Samples 5~9 in Table 8 illustrate the mineral batch compositions of the invention containing prereact~d cordierite material. Prereacted cordierite material #l is essentially the same as fired composition F in US. Patent 3,885,977, but in crushed and ground particulate form. Prereacted cordierite material #2 is essentially the same as fired Composition 804 in US. Patent 4,001,028, but in crushed and ground particulate form.
Table q sets forth the sistering temperatures, firing shrinkages and Cues for the Samples 5-9 of Table 8 exhibiting less than 1% by volume of open porosity. Such temperatures were the approximate lowest temperatures for full density.

..'' Sistering Firing CUTE x 10-7/C
Sample Temperature CShrinkage 25-1000C
1250 15.4 17.1 6 139Q 14.6 17.8 7 1400 16-18 16.7 8 1400 16-18 18.0 9 141~ 17.0 17.0 Other samples with either less than 50 wt.% prereacted cordierite or having Moo substantially outside the range of

5-40 mole % of ROW while also having at least 50 wt.% pro-- reacted cordierite cannot be reliably made with full density.
A series of formable particulate ceramic cement samples according to this invention were prepared by thoroughly mixing the watch materials as shown in Table 10 to form pastes of those samples.
The analytical molar composition of the combined raw base materials of clay, silica and MnCO for Samples 1-4 ~22~

and 6 was 1. 84 Moo 2. 04 Aye 5.11 Sue. Such combo-session for Sample 5 was 2. 36 Moo 1. 29 Aye 5 . 35 Sue .

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The Mn-Mg cordierite grog in the cement batches in Table 10 was a dense cordierite containing manganese of - the present invention. In particular, the grog was made of the following batch composition yin weight % of the total ceramic batch materials):
My Cordierite grog (95~-200 mesh) 84.48 Georgia-Kaolin Kapok 10 clay ZAPS 10) 10.00 waker reagent MnCO3 powder 4.15 Penn. Glass Sand Mainsail silica ZAPS 5) 0.78 - 10 Pfizer Jo ~6-28 talc ZAPS 20) 0.59 Methyl cellulose binder/plasticizer4.0 . i-Alkali Stewart extrusion aid 0.5 Distilled water plasticizer ~6.0 This Mn-Mg cordierite grog was fired generally in accord-ante with the following firing schedule:
- 80C to 1405C within about 60 hours.
Hold about 10 hours at 1405C.
Cool 1405C to room temperature within about 24 hours.
The My cordierite grog (in the batch for the My My cordierite grog) was made of the following batch composition yin weight % ox the total ceramic batch materials):
Georgia-Raslin ~ydrite MY clay UPS 9.7~ 25.15 George a-Kaolin Glomax LO clay UPS 1.9) 21.17 Pfizer MY 96-28 talc UPS 20~ 40.21 Alcoa A-2 alumina UPS 5.8~ 13.47 -Methyl cellulose binder/plasticizer4.0 Allele Stewart extrusion aid 0.5 Distilled water plasticizer 32.5 This My cordierite grog was fired generally in accordance with the same fifing schedule as for the Mug cordierite grog, except that the maximum temperature was 1425C.

- ~27~8~L

The analytical molar composition of Mn-Mg cordierite grog was 2.03 ROW 20.4 Aye 4.92 Sue wherein ROW con-sited of 9.7 mole 5 Moo and 90.3 mole % Moo.
Pieces of ceramic honeycomb monolith wore extruded in accordance with US. Patents 3,79Q,654 and 3,919,384 from the same batch composition as described for the Mn-Mg cordierite grog. Those extruded green honeycomb bodies w no then fused in the manner as disclosed in US. Patent 3,89~,326 and in accordance with the same firing schedule as described for the Mn-Mg cordierite grog. A series of pairs of these honeycomb pieces were cemented together by - applying the sample pastes described in TABLE 10 to the cordierite surfaces of these pieces that were to be joined and then pressing those paste-coated surfaces together. These assembled pairs of cemented pieces were dried in air at least 22-75C, then fired at about cry. to the foaming -I temperature set forth in TABLE 1, held at the foaming tempera-- lure for about one hour and thereafter cooled at furnace rate to at least 2~QC, at which time the foam cemented pieces were removed from the furnace for further cooling in ambient - air atmosphere. The coefficients of thermal expansion (CUTE) ox the foamed cement samples are set forth in TABLE 10, which - are closely similar to the typical CUTE of 18 x 10 icky (awoke for the pieces except the CUTE of Sample 5.
- All of those sistered foamed cement samples had a substantially wholly cordierite crystal structure.
Upon subjecting the foam cemented pieces to a cycling thermal shock test of SO cycles of heating from 250C to 800C in 3 minutes and then cooling back to 250C in 3 30 minutes, the foam cemented pieces with cement Samples 1-4 and 6 showed good resistance to thermal shock whereas the I

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.

foam cemented pieces with cement Sample 5 showed moderate resistance to thermal shock. However, cement Sample 5 should serve well with pieces having CUTE more closely similar to the CUTE of roamed Sample 5 so as to exhibit good nests-lance to thermal shock.
~oamahle cement Sample 6 has also been used to plug the end portions of cells in extruded ceramic honeycomb bodies made of the same and similar compositions and fired in the same manner as the My cordierite grog previously described.
In those cases, the Mn-Mg cordierite grog was US wt. % - 325 mesh, and the cement batch was formed with 2.0 woo % methyl cellulose and 70.0 White water to provide a paste that was injected into the cell ends, between the surfaces of opposed cell walls, by means of an air pressure operated sealant or caulking gun with an appropriately shaped nozzle. Those bodies with the green plugs were then fired generally in accordance with the following typical firing schedule:
Room temperature to 1210C within about 6 hours.
told about 30 minutes at 1210C.
Cool 1210~C to room temperature within about 18 hours.
The cement foamed during firing to develop a sistered cordite mass having good sealing to the cell walls and . . .
belong generally impervious to fluid.
The particle sizes of cordierite grog and Six or other ; foaming agent in the cement can be varied as desired. For example, the grog may be as coarse as -20 mesh. All mesh sizes herein are according to the US. Standard Sieve series.

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. A foamable particulate ceramic cement capable of forming a sintered cordierite foamed ceramic mass consisting essentially, by weight, of:
1-40% cordierite grog, 99-60% ceramic base material and an effective amount of a foaming agent to effect foaming of the cement upon firing to produce the foamed ceramic mass, the base material being raw ceramic material that has an analytical molar composition consisting essentially of about:
1.702.4 MO ? 1.2-2.4 A1203 . 4.5-5.4 SiO2 wherein MO comprises, as mole % of MO, about 0-55% MgO and at least 45% MnO, and the grog being ceramic material that has been previously fired and comminuted, and that has an analytical molar composition consisting essentially of about:
1.7-2.4 RO . 1.9-2.4 A1203 . 4.5-5.2 SiO2 wherein RO comprises, as mole % of RO, MnO in an amount of 0%
up to a mole % that is about 20 mole % lower than the mole % of MO that is MnO and the balance is substan-tially MgO.

2. Cement of claim l wherein the foaming agent is SiC
in an amount of at least 0.25% and up to about 5% by weight of grog plus base material.

3. Cement of claim 2 wherein the grog is a least 5 wt.%

and the base material is not more than 95 wt.%.

4. Cement of claim 2 wherein the analytical molar composition of the base material is about:
1.7-2.4 MO . 1.9-2.4 Al2O3 . 4.5-5.2 SiO2, the grog is 5-20 wt.%, the base material is 95-80 wt.%, SiC is at least 1 wt.%, and MO comprises not more than about 15 mole % MgO.

5. Cement of claim 4 wherein the analytical molar composition of the grog is about:
l.8-2.1 RO . 1.9-2.1 A12O3 . 4.9-5.2 SiO2, wherein RO comprises 8-12 mole % MnO and the balance MgO, and SiC is not more than 2 wt.%.

6. Cement of claim 5 wherein the analytical molar composition of the base material is about:
1.8-2.1 MO . 1.9-2.1 A12O3 . 4.9-5.2 SiO2 and MO is wholly MnO.

7. A ceramic structure comprising at least two closely spaced cordierite ceramic surfaces having a sintered cordierite foamed ceramic mass in the space between and bonded to those cement of claim 1.

8. A method of providing a sintered cordierite foamed ceramic mass between and bonded to at least two closely spaced cordierite ceramic surfaces of a ceramic structure, which method comprises:
disposing cement between the surfaces, firing the structure with the cement so disposed to foaming temperature in the range of about 1160-1325°C, and thereafter cooling the structure with the cement converted to the foamed ceramic mass;
wherein the cement referred to above is a foamable particulate ceramic cement capable of forming a sintered cordierite foamed ceramic mass consisting essentially, by weight, of:

1-40% cordierite grog, 99-60% ceramic base material and an effective amount of a foaming agent to effect foaming of the cement upon firing to produce the foamed ceramic mass, the base material being raw ceramic material that has an analytical molar composition consisting essentially of about:
1.7-2.4 MO 1.2-2.4 A12O3 . 4.5-5.4 SiO2 wherein MO comprises, as mole % of MO, about 0-55% MgO and at least 45% MnO, and the grog being ceramic material that has been previously fired and comminuted, and that has an analytical molar composition consisting essentially of about:
1.7-2.4 RO . 1.9-2.4 A12O3 . 4.5-5.2 SiO2 wherein RO comprises, as mole % of RO, MnO in an amount of 0%
up to a mole % that is about 20 mole % lower than the mole % of MO that is MnO and the balance is substan-tially MgO.

9. The method of claim 8 wherein the foaming temperature is in the range of 1170-1250°C.

10. The method of claim 8 or 9 wherein firing to foaming temperature is at an average rate of at least about 100°C.