METHODS OF MANUFACTURING GREEN BODIES AND SUBSTRATES

Abstract

A method of manufacturing a green body, the method comprising: providing: a third composition comprising a second substrate material, a third polymer, a fusing agent, and a third solvent; forming the third composition into a structure wherein the third composition forms a third layer; and contacting the third layer with a fourth solvent in which the third polymer is insoluble to precipitate said polymer, thereby forming a green body.

A substrate is further manufactured by: arranging a plurality of green bodies to form an assembly of green bodies;
fusing the green bodies in the assembly together, thereby forming a precursor substrate; and sintering the precursor substrate, thereby forming a substrate.

Claims

1. A method of manufacturing a green body, the method comprising: providing: a third composition comprising a second substrate material, a third polymer, a fusing agent, and a third solvent; forming the third composition into a structure wherein the third composition forms a third layer; and contacting the third layer with a fourth solvent in which the third polymer is insoluble to precipitate said polymer, thereby forming a green body.

2. A method of manufacturing a green body, the method comprising: providing: a first composition comprising a first polymer and a first solvent, wherein the first polymer is soluble in the first solvent, a third composition comprising a second substrate material, a third polymer, a fusing agent, and a third solvent, wherein the third polymer is soluble in the first solvent and the third solvent; forming the first composition and the third composition into a multilayer structure wherein the first composition forms a first layer and the third composition forms a third layer; and contacting the multilayer structure with a fourth solvent in which the first polymer and third polymer are insoluble to precipitate said polymers, thereby forming a green body.

3. A method of manufacturing a green body, the method comprising: providing: a first composition comprising a first polymer and a first solvent, wherein the first polymer is soluble in the first solvent, a second composition comprising a first substrate material, a second polymer and a second solvent, wherein the second polymer is soluble in the first solvent and the second solvent, and a third composition comprising a second substrate material, a third polymer, a fusing agent, and a third solvent, wherein the third polymer is soluble in the first solvent and the third solvent; forming the first composition, the second composition and the third composition into a multilayer structure wherein the first composition forms a first layer, the second composition forms a second layer, and the third composition forms a third layer and the second layer is adjacent to the third layer; and contacting the multilayer structure with a fourth solvent in which the first polymer, second polymer, and third polymer are insoluble to precipitate said polymers, thereby forming a green body.

4. The method of claim 3, wherein the first polymer is immiscible with at least one of the second polymer and the third polymer.

5. The method of claim 3, wherein the second polymer and the third polymer are the same.

6. The method of claim 1, wherein the fusing agent is miscible with the third polymer.

7. The method of claim 3, wherein the first substrate material and/or the second substrate material each independently comprises one or more of: a ceramic, cordierite, zirconia, yttrium-stabilised zirconia, titania, silicon carbide, clay, alumina, stainless steel, FeCr alloys, alloys of iron, alloys of aluminium, aluminium titanate, sintered metals, or a zeolite.

8. The method of claim 3, wherein the second layer is adjacent to the first layer and is adjacent to the third layer in the multilayer structure

9. The method of claim 1, wherein the (multilayer) structure is formed by moulding or extrusion.

10. The method of claim 1, wherein the (multilayer) structure is formed as a (multilayer) hollow fibre.

11. A method of manufacturing a substrate, the method comprising the steps of: manufacturing a green body according to claim 1; arranging the green body with a plurality of green bodies to form an assembly of green bodies; fusing the green bodies in the assembly together, thereby forming a precursor substrate; and sintering the precursor substrate, thereby forming a substrate.

12. The method of claim 11, wherein the assembly comprises green bodies having different shapes and/or sizes.

13. The method of claim 11, wherein the green bodies are fused by heating the assembly or by contacting the assembly with a fifth solvent.

14. The method of claim 11, further comprising removing the first polymer from the green body, the assembly, or the precursor substrate.

15. The method of claim 11, further comprising heating the precursor substrate to remove organic polymers from the precursor substrate prior to sintering.

16. The method of claim 15, wherein the precursor substrate is heated to a temperature of from 300 to 800? C.

17. The method of claim 11, wherein the precursor substrate is sintered at a temperature of at least 1000? C.

18. A green body obtained by the method of claim 1.

19. A method of manufacturing a filter, the method comprising manufacturing a substrate according to claim 11 and blocking at least some macro-channels in the substrate.

20. A method of filtering, the method comprising manufacturing a filter according to claim 19 and passing a composition through the filter.

21. The method of claim 20, wherein the composition comprises a liquid, preferably wherein the liquid comprises water.

22. A filter comprising a substrate according to claim 18.

23. A method of manufacturing a catalytic convertor, the method comprising manufacturing a substrate according to claim 11 and depositing a catalytic species or precursor thereof on the substrate.

24. A method of catalytic conversion of pollutants, the method comprising manufacturing a catalytic convertor according to claim 23 and passing a pollutant composition through the catalytic convertor.

25. A catalytic convertor comprising a substrate according to claim 18.

26. A method of manufacturing an exhaust system, the method comprising: manufacturing a filter and incorporating the filter into an exhaust system; and/or manufacturing a catalytic convertor and incorporating the catalytic convertor into an exhaust system, wherein the filter is manufactured by a method comprising manufacturing a substrate according to claim 11 and blocking at least some macro-channels in the substrate and wherein the catalytic convertor is manufactured by a method comprising manufacturing a substrate according to claim 11 and depositing a catalytic species or precursor thereof on the substrate.

27. A method of manufacturing a product including an internal combustion engine, the method comprising manufacturing an exhaust system according to claim 26 and incorporating the exhaust system into a product including an internal combustion engine.

28. A substrate obtained by the method of claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0288] For a better understanding of the invention, and to show how example embodiments may be carried into effect, reference will now be made to the accompanying drawings in which:

[0289] FIG. 1 shows a photograph of a cross section of a hollow fibre substrate manufactured according to the method of the fifth aspect of the invention.

[0290] FIG. 2 shows a photograph of a cross section of a substrate manufactured according to the fifth aspect of the invention.

EXAMPLES

Example 1

1. Preparation of Extrusion Feeds

1.1 Bore Fluid

[0291] Dimethicone (polydimethylsiloxane) with a viscosity between 5 and 500 cSt was transferred to an air-tight reservoir and degassed under vacuum for about 1 hour.

1.2 First Composition

[0292] 20 wt % polycaprolactone (PCL) with a weight average molecular weight of 55,000 g/mol was mixed with 80 wt % n-methyl-2-pyrrolidone (NMP) and stirred at about 60? C. for 3 hours under vacuum. The solution was then transferred to an air-tight reservoir.

1.3 Second Composition

[0293] 44.85 wt % aluminium oxide (alumina) with a particle size between 0.1 and 1 ?m was added to 43.60 wt % dimethylsulfoxide (DMSO) and 0.34 wt % Cithrol DPHS dispersant (PEG-30 dipolyhydroxystearate). The materials were then mixed at high shear (4000 rpm) at about 40? C. for about 4 hours. After mixing at high shear 11.21 wt % polyethersulfone (PES, Mw=58,000 g/mol) was added and stirring was continued at about 2000 rpm. The mixed suspension was then transferred to a gas tight reservoir and vacuum was applied until no bubbles could be seen at the surface.

1.4 Third Composition

[0294] 39.88 wt % aluminium oxide (alumina) with a particle size between 0.1 and 1 ?m was added to 39.88 wt % dimethylsulfoxide (DMSO) and 0.30 wt % Cithrol DPHS dispersant. The materials were then mixed at high shear (4000 rpm) at about 40? C. for about 4 hours. After mixing at high shear 9.97 wt % polyethersulfone (PES, Mw=58,000 g/mol) and 9.97 wt % bisphenol-A-diglycidyl ether (Epon 828, Mn=700 g/mol) were added and stirring was continued at about 2000 rpm. The mixed suspension was then transferred to a gas tight reservoir and vacuum was applied until no bubbles could be seen at the surface.

2. Extrusion

[0295] The extrusion feed reservoirs were pressurized to about 50 kPa (0.5 bar) to supply material to progressive cavity pumps for the first composition, the second composition and the third composition and to syringe pumps for the bore fluid.

[0296] The four extrusion feeds were pumped to an extrusion die. The flow rates were 13 mL/min, 3 mL/min, 10 mL/min, 4 mL/min for the bore fluid, the first composition, the second composition, and the third composition, respectively. The fluids were pumped through four concentric internal nozzles in the die and exited the die through a single outlet immersed in a water tank. The fluids exited the die in the form of a cylinder with concentric layers, the order of the layers being the bore fluid, the first composition, the second composition, and the third composition from innermost to outermost.

[0297] Contact with the water caused the four fluids exiting the die to solidify, forming a solid, polymer/ceramic, flexible mixed matrix tube (hollow fibre) with an outer diameter of about 3.5 mm and an inner diameter of about 2 mm. The hollow fibre was drawn from the water and lengths of fibre were cut therefrom and deposited into another container of water.

3. Post Extrusion Fibre Processing

[0298] The collected fibres were soaked in water for about 12 hours with agitation to remove the remaining solvent from the hollow fibre green body. A small portion of the end of the fibres was removed to expose the first layer (precipitated from the first composition), which formed a continuous polymer layer separated from the second layer (precipitated from the second composition). The first layer was removed manually by pulling one end. After removal of the first layer, the fibres were soaked in water and surfactant (15-30% anionic surfactants and 5-15% non-ionic surfactants) with agitation to remove traces of the dimethicone (bore fluid). The fibres were then dried at a temperature between 30? C. and 80? C.

4. Assembly

[0299] Dry fibres were placed vertically on a template consisting of 5 mm long pins arranged so that the outer surfaces of the fibres were in contact and the fibres were arranged in a hexagonal close packed configuration. For a final substrate diameter of 85 mm (post-sintering), 1040 fibres having a total diameter of 115 mm were arranged on the template and 3 silicone rubber bands with a diameter of about 100 mm were placed around the outside of the assembly of fibres. After the bands were in place the assembly was removed from the template. The assembly was placed in a preheated oven at 150? C. for 2 hours. After heating, the assembly was allowed to cool to room temperature and the silicone bands were removed. The result was a fused precursor substrate.

5. Heat Treatment

[0300] The precursor substrate was heated in a furnace according to the following steps.

[0301] Step 1: The precursor substrate was heated from 20? C. to 250? C. at a rate of 0.5? C./min.

[0302] Step 2: The substrate was held at 250? C. for 1 hour to control exothermic reactions in the substrate.

[0303] Step 3: The substrate was heated from 250? C. to 440? C. at a rate of 0.5? C./min.

[0304] Step 4: The substrate was held as 440? C. for 15 hours to remove the Epon 828 and to partially remove the polyethersulfone.

[0305] Step 5: The substrate was heated from 440? C. to 540? C. at a rate of 0.5? C./min, during which time the remaining polyethersulfone was removed.

[0306] Step 6: The substrate was heated from 540? C. to 1350? C. at a rate of 5? C./min.

[0307] Step 7: The substrate was held at 1350? C. for 4 hours to sinter the substrate.

[0308] Step 8: The substrate was cooled from 1350? C. to 20? C. at a rate of 5? C./min to obtain a cooled, sintered substrate.

[0309] FIG. 1 shows a cross section of the wall of a sintered hollow fibre made by the above method. It can be seen that the follow fibre contains two layers: an outer layer with narrower micro-channels precipitated from the third composition, and an inner layer with wider micro-channels (ranging from 20 ?m to 100 ?m in width) precipitated from the second composition.

[0310] FIG. 2 shows a cross section of the sintered substrate made by the above method. The junction between three hollow fibres is shown. It can be seen that the layer precipitated from the third composition has merged such that the hollow fibres are fused together. Although not shown, the fused region of the hollow fibres also contains micro-channels.

[0311] FIGS. 1 and 2 were obtained from a Phenom ProX desktop scanning electron microscope. The detector type was backscatter, with an accelerating voltage of 10 kV.

Example 2

[0312] Steps 1 to 3 were carried out as for Example 1.

4. Substrate Skin Fabrication

[0313] A portion of the third composition was poured into a mould with length, width, height of 115 mm, 80 mm and 3 mm respectively. The mould had 5 sides, i.e. the top side of the mould was open. The mould containing the suspension was then immersed in water to solidify the suspension, the mould and solidified suspension were left in water until all suspension solvent had been removed. The solidified suspension was removed from the mould and dried at 30? C. for 3 hours to produce a green sheet of polymer/ceramic material.

[0314] The sheet was heated at 100? C. for 10 minutes so that it became soft and pliable after which it was wrapped around a 115 mm diameter cylinder and allowed to cool. On cooling the sheet retained the cylindrical shape of the cylinder.

5. Assembly

[0315] Dry fibres were placed vertically on a template consisting of 5 mm long pins arranged so that the outer surfaces of the fibres were in contact and the fibres were arranged in a hexagonal close packed configuration. For a final substrate diameter of 85 mm (post-sintering), 1040 fibres having total diameter of 115 mm were arranged on the template and the cylindrical sheet made in step 4 was placed around the fibres to form an assembly. 3 silicone rubber bands with a diameter of about 100 mm were placed around the assembly. After the bands were in place the assembly was removed from the template. The assembly was placed in a preheated oven at 150? C. for 2 hours. After heating, the assembly was allowed to cool to room temperature and the silicone bands were removed. The result was a fused precursor substrate.

6. Heat Treatment

[0316] The assembly was heat treated as described in Example 1 to obtain a cooled, sintered substrate.

[0317] Although a few preferred embodiments have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

[0318] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0319] All of the features disclosed in this specification (including any accompanying claims), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0320] Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0321] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.