Processing of Ceramics - User contributions [en]

3D-printing-paste

2022-04-03T20:44:44Z

Tschlordt: /* How to prepare the paste */

==Introduction==

Solid Freeform Fabrication uses many different techniques. One is the freeforming of extruded strands of ceramic pastes, which exhibits some important features:

* No excess material needed
* Coextrusion is possible
* Waterborne feedstocks are common
* Nowadays there are lots of cheap extrusion devices on the market
* High density/low porosity and thus high strengths are feasible

==Requirements for the feedstock==
* A high solids loading to counteract shrinkage and cracking due to drying, sintering or binder burn-out
* Well dispersed particles to ensure a constant flow and to avoid flaws due to agglomerates
* Entrapped air should be minimized to avoid pores in the ceramic
* Solvent migration and sedimentation of particles must be prevented to ensure constant flow and storage stability
* Suitable rheology for the applied process to ensure shape retention and sufficient merging of the filaments
* Suitable particle size and distribution for the applied nozzle dimensions
* A binder phase that is easy to drain, dry or burn out
* Suitable solidification kinetics
* Suitable interface properties for adhesion and fusion of filaments
* Sufficient green strength, either to be obtained by the binder or the particle size distribution.

Most preparation routes for RC and FEF feedstocks follow the same principle.

The first step to obtain a feedstock is preparing a homogeneous dispersion having a high solids loading (mostly about 50 vol%).
The particles are dispersed in the medium (mostly water) by agitation with shakers, ball mills, planetary mills or ultrasonic probes until particle separation is achieved.
When using wide particle size distributions,
the smaller particles facilitate the slip and rearrangement of the bigger particles during extrusion, which is favorable for flow through small orifices.
The results are feedstocks of higher solids loading, lower viscosity and an overall drop of extrusion pressure.
It must be noted that increasingly high particle concentrations are accompanied by severe changes of the rheological properties,
i.e. yield stresses develop and frequency-dependent sol-gel transitions occur, thus small changes in solids loading and processing might have large effects on the result.
A polymeric viscosifier or binder is added to prevent sedimentation, reagglomeration and solvent migration to ensure consistent extrusion and to provide green strength.
After complete dissolution of the viscosifier the suspension can be degassed using vacuum or centrifugation. If a colloidal gel shall be applied to EFF the slurry is coagulated by adding salts, pH-modifiers or charged polymers such as Polyethylene-Imine.

==Recipe examples of an alumina and a carbon black paste:==

{| class="wikitable"
|-
! Component !! Alumina paste !! Mass Percent !! Carbon black paste !! Mass percent
|-
| Powder species || CT3000SG || 78-79 || Luvomaxx N990|| 64
|-
| Dispersant || Darvan C-N || 0.4 || Darvan 670|| 0.3
|-
| Solvent || Water || 19-20 || Water || 30
|-
| Thickener || Bermocoll E230/320 FQ/PEG || 0.4|| PEG 10 kDa|| 3.4
|-
| Coagulant || Ammonium-acetate || 1.5-2.6 || Ammonium-acetate || 3.2
|}
[[File:PSD.png|thumb|Particle size distributions]]

To achieve lower sintering shrinkage due to higher particle packing, bimodal/trimodal powders can be used, which are readily available on the market.

==How to prepare the paste==

* Mix water and dispersant in a PE-bottle. Make sure to find the proper dispersant amount, which correlates with the surface area of the powder. Better use a slight excess, as the surace area might increase during milling.
* Add grinding media (zirconia or alumina, 3 - 20 mm diameter, some big spheres are useful)
* Add the powder successively and shake between additions. Use decreasing additions, i.e. 50%, 25%, 12,5% ...
* Put in a shaker für several hours.
* Add thickener
* Put in shaker for several hours until there are no remaining lumps.
* Prepare a lid for the PE-Bottle with a sieve in it, so the milling balls can be separated from the slurry
* Now add the coagulant as an aqueous solution and stir the paste. The stiffness of the paste can be tuned by the amount and valency of the salt. A centrifugal planetary mixer is optimum to mix and remove air bubbles.

3D-printing-paste

2022-04-03T20:38:15Z

Tschlordt: /* How to prepare the paste */

==Introduction==

Solid Freeform Fabrication uses many different techniques. One is the freeforming of extruded strands of ceramic pastes, which exhibits some important features:

* No excess material needed
* Coextrusion is possible
* Waterborne feedstocks are common
* Nowadays there are lots of cheap extrusion devices on the market
* High density/low porosity and thus high strengths are feasible

==Requirements for the feedstock==
* A high solids loading to counteract shrinkage and cracking due to drying, sintering or binder burn-out
* Well dispersed particles to ensure a constant flow and to avoid flaws due to agglomerates
* Entrapped air should be minimized to avoid pores in the ceramic
* Solvent migration and sedimentation of particles must be prevented to ensure constant flow and storage stability
* Suitable rheology for the applied process to ensure shape retention and sufficient merging of the filaments
* Suitable particle size and distribution for the applied nozzle dimensions
* A binder phase that is easy to drain, dry or burn out
* Suitable solidification kinetics
* Suitable interface properties for adhesion and fusion of filaments
* Sufficient green strength, either to be obtained by the binder or the particle size distribution.

Most preparation routes for RC and FEF feedstocks follow the same principle.

The first step to obtain a feedstock is preparing a homogeneous dispersion having a high solids loading (mostly about 50 vol%).
The particles are dispersed in the medium (mostly water) by agitation with shakers, ball mills, planetary mills or ultrasonic probes until particle separation is achieved.
When using wide particle size distributions,
the smaller particles facilitate the slip and rearrangement of the bigger particles during extrusion, which is favorable for flow through small orifices.
The results are feedstocks of higher solids loading, lower viscosity and an overall drop of extrusion pressure.
It must be noted that increasingly high particle concentrations are accompanied by severe changes of the rheological properties,
i.e. yield stresses develop and frequency-dependent sol-gel transitions occur, thus small changes in solids loading and processing might have large effects on the result.
A polymeric viscosifier or binder is added to prevent sedimentation, reagglomeration and solvent migration to ensure consistent extrusion and to provide green strength.
After complete dissolution of the viscosifier the suspension can be degassed using vacuum or centrifugation. If a colloidal gel shall be applied to EFF the slurry is coagulated by adding salts, pH-modifiers or charged polymers such as Polyethylene-Imine.

==Recipe examples of an alumina and a carbon black paste:==

{| class="wikitable"
|-
! Component !! Alumina paste !! Mass Percent !! Carbon black paste !! Mass percent
|-
| Powder species || CT3000SG || 78-79 || Luvomaxx N990|| 64
|-
| Dispersant || Darvan C-N || 0.4 || Darvan 670|| 0.3
|-
| Solvent || Water || 19-20 || Water || 30
|-
| Thickener || Bermocoll E230/320 FQ/PEG || 0.4|| PEG 10 kDa|| 3.4
|-
| Coagulant || Ammonium-acetate || 1.5-2.6 || Ammonium-acetate || 3.2
|}
[[File:PSD.png|thumb|Particle size distributions]]

To achieve lower sintering shrinkage due to higher particle packing, bimodal/trimodal powders can be used, which are readily available on the market.

==How to prepare the paste==

* Mix water and dispersant in a PE-bottle. Make sure to find the proper dispersant amount, which correlates with the surface area of the powder. Better use a slight excess, as the surace area might increase during milling.
* Add grinding media (zirconia or alumina, 3 - 20 mm diameter, some big spheres are useful)
* Add the powder successively and shake between additions. Use decreasing additions, i.e. 50%, 25%, 12,5% ...
* Put in a shaker für several hours.
* Add thickener
* Put in shaker for several hours until there a no remaining lumps.
* Prepare a lid for the PE-Bottle with a sieve in it, so the milling balls can be separated from the slurry
* Now add the coagulant as an aqueous solution and stir the paste. The stiffness of the paste can be tuned by the amount and valency of the salt. A centrifugal planetary mixer is optimum to mix and remove air bubbles.

3D-printing-paste

2022-04-03T20:37:05Z

Tschlordt: /* Recipe examples of an alumina and a carbon black paste: */

==Introduction==

Solid Freeform Fabrication uses many different techniques. One is the freeforming of extruded strands of ceramic pastes, which exhibits some important features:

* No excess material needed
* Coextrusion is possible
* Waterborne feedstocks are common
* Nowadays there are lots of cheap extrusion devices on the market
* High density/low porosity and thus high strengths are feasible

==Requirements for the feedstock==
* A high solids loading to counteract shrinkage and cracking due to drying, sintering or binder burn-out
* Well dispersed particles to ensure a constant flow and to avoid flaws due to agglomerates
* Entrapped air should be minimized to avoid pores in the ceramic
* Solvent migration and sedimentation of particles must be prevented to ensure constant flow and storage stability
* Suitable rheology for the applied process to ensure shape retention and sufficient merging of the filaments
* Suitable particle size and distribution for the applied nozzle dimensions
* A binder phase that is easy to drain, dry or burn out
* Suitable solidification kinetics
* Suitable interface properties for adhesion and fusion of filaments
* Sufficient green strength, either to be obtained by the binder or the particle size distribution.

Most preparation routes for RC and FEF feedstocks follow the same principle.

The first step to obtain a feedstock is preparing a homogeneous dispersion having a high solids loading (mostly about 50 vol%).
The particles are dispersed in the medium (mostly water) by agitation with shakers, ball mills, planetary mills or ultrasonic probes until particle separation is achieved.
When using wide particle size distributions,
the smaller particles facilitate the slip and rearrangement of the bigger particles during extrusion, which is favorable for flow through small orifices.
The results are feedstocks of higher solids loading, lower viscosity and an overall drop of extrusion pressure.
It must be noted that increasingly high particle concentrations are accompanied by severe changes of the rheological properties,
i.e. yield stresses develop and frequency-dependent sol-gel transitions occur, thus small changes in solids loading and processing might have large effects on the result.
A polymeric viscosifier or binder is added to prevent sedimentation, reagglomeration and solvent migration to ensure consistent extrusion and to provide green strength.
After complete dissolution of the viscosifier the suspension can be degassed using vacuum or centrifugation. If a colloidal gel shall be applied to EFF the slurry is coagulated by adding salts, pH-modifiers or charged polymers such as Polyethylene-Imine.

==Recipe examples of an alumina and a carbon black paste:==

{| class="wikitable"
|-
! Component !! Alumina paste !! Mass Percent !! Carbon black paste !! Mass percent
|-
| Powder species || CT3000SG || 78-79 || Luvomaxx N990|| 64
|-
| Dispersant || Darvan C-N || 0.4 || Darvan 670|| 0.3
|-
| Solvent || Water || 19-20 || Water || 30
|-
| Thickener || Bermocoll E230/320 FQ/PEG || 0.4|| PEG 10 kDa|| 3.4
|-
| Coagulant || Ammonium-acetate || 1.5-2.6 || Ammonium-acetate || 3.2
|}
[[File:PSD.png|thumb|Particle size distributions]]

To achieve lower sintering shrinkage due to higher particle packing, bimodal/trimodal powders can be used, which are readily available on the market.

==How to prepare the paste==

* Mix water and dispersant in a PE-bottle. Make sure to find the proper dispersant amount, which correlates with the surface are of the powder. Better use a slight excess, as the surace area might increase during milling.
* Add grinding media (zirconia or alumina, 3 - 20 mm diameter, some big spheres are useful)
* Add the powder successively and shake between additions. Use decreasing additions, i.e. 50%, 25%, 12,5% ...
* Put in a shaker für several hours.
* Add thickener
* Put in shaker for several hours until there a no remaining lumps.
* Prepare a lid for the PE-Bottle with a sieve in it, so the milling balls can be separated from the slurry
* Now add the coagulant as an aqueous solution and stir the paste. The stiffness of the paste can be tuned by the amount and valency of the salt. A centrifugal planetary mixer is optimum to mix and remove air bubbles.

3D-printing-paste

2022-04-03T20:36:18Z

Tschlordt: /* How to prepare the paste */

==Introduction==

Solid Freeform Fabrication uses many different techniques. One is the freeforming of extruded strands of ceramic pastes, which exhibits some important features:

* No excess material needed
* Coextrusion is possible
* Waterborne feedstocks are common
* Nowadays there are lots of cheap extrusion devices on the market
* High density/low porosity and thus high strengths are feasible

==Requirements for the feedstock==
* A high solids loading to counteract shrinkage and cracking due to drying, sintering or binder burn-out
* Well dispersed particles to ensure a constant flow and to avoid flaws due to agglomerates
* Entrapped air should be minimized to avoid pores in the ceramic
* Solvent migration and sedimentation of particles must be prevented to ensure constant flow and storage stability
* Suitable rheology for the applied process to ensure shape retention and sufficient merging of the filaments
* Suitable particle size and distribution for the applied nozzle dimensions
* A binder phase that is easy to drain, dry or burn out
* Suitable solidification kinetics
* Suitable interface properties for adhesion and fusion of filaments
* Sufficient green strength, either to be obtained by the binder or the particle size distribution.

Most preparation routes for RC and FEF feedstocks follow the same principle.

The first step to obtain a feedstock is preparing a homogeneous dispersion having a high solids loading (mostly about 50 vol%).
The particles are dispersed in the medium (mostly water) by agitation with shakers, ball mills, planetary mills or ultrasonic probes until particle separation is achieved.
When using wide particle size distributions,
the smaller particles facilitate the slip and rearrangement of the bigger particles during extrusion, which is favorable for flow through small orifices.
The results are feedstocks of higher solids loading, lower viscosity and an overall drop of extrusion pressure.
It must be noted that increasingly high particle concentrations are accompanied by severe changes of the rheological properties,
i.e. yield stresses develop and frequency-dependent sol-gel transitions occur, thus small changes in solids loading and processing might have large effects on the result.
A polymeric viscosifier or binder is added to prevent sedimentation, reagglomeration and solvent migration to ensure consistent extrusion and to provide green strength.
After complete dissolution of the viscosifier the suspension can be degassed using vacuum or centrifugation. If a colloidal gel shall be applied to EFF the slurry is coagulated by adding salts, pH-modifiers or charged polymers such as Polyethylene-Imine.

==Recipe examples of an alumina and a carbon black paste:==

{| class="wikitable"
|-
! Component !! Alumina paste !! Mass Percent !! Carbon black paste !! Mass percent
|-
| Powder species || CT3000SG || 78-79 || Luvomaxx N990|| 64
|-
| Dispersant || Darvan C-N || 0.4 || Darvan 670|| 0.3
|-
| Solvent || Water || 19-20 || Water || 30
|-
| Thickener || Bermocoll E320 FQ || 0.4|| PEG 10 kDa|| 3.4
|-
| Coagulant || Ammonium-acetate || 1.5-2.6 || Ammonium-acetate || 3.2
|}
[[File:PSD.png|thumb|Particle size distributions]]

To achieve lower sintering shrinkage due to higher particle packing, bimodal/trimodal powders can be used, which are readily available on the market.

==How to prepare the paste==

* Mix water and dispersant in a PE-bottle. Make sure to find the proper dispersant amount, which correlates with the surface are of the powder. Better use a slight excess, as the surace area might increase during milling.
* Add grinding media (zirconia or alumina, 3 - 20 mm diameter, some big spheres are useful)
* Add the powder successively and shake between additions. Use decreasing additions, i.e. 50%, 25%, 12,5% ...
* Put in a shaker für several hours.
* Add thickener
* Put in shaker for several hours until there a no remaining lumps.
* Prepare a lid for the PE-Bottle with a sieve in it, so the milling balls can be separated from the slurry
* Now add the coagulant as an aqueous solution and stir the paste. The stiffness of the paste can be tuned by the amount and valency of the salt. A centrifugal planetary mixer is optimum to mix and remove air bubbles.

3D-printing-paste

2022-04-03T20:34:22Z

Tschlordt: /* Recipe examples of an alumina and a carbon black paste: */

==Introduction==

Solid Freeform Fabrication uses many different techniques. One is the freeforming of extruded strands of ceramic pastes, which exhibits some important features:

* No excess material needed
* Coextrusion is possible
* Waterborne feedstocks are common
* Nowadays there are lots of cheap extrusion devices on the market
* High density/low porosity and thus high strengths are feasible

==Requirements for the feedstock==
* A high solids loading to counteract shrinkage and cracking due to drying, sintering or binder burn-out
* Well dispersed particles to ensure a constant flow and to avoid flaws due to agglomerates
* Entrapped air should be minimized to avoid pores in the ceramic
* Solvent migration and sedimentation of particles must be prevented to ensure constant flow and storage stability
* Suitable rheology for the applied process to ensure shape retention and sufficient merging of the filaments
* Suitable particle size and distribution for the applied nozzle dimensions
* A binder phase that is easy to drain, dry or burn out
* Suitable solidification kinetics
* Suitable interface properties for adhesion and fusion of filaments
* Sufficient green strength, either to be obtained by the binder or the particle size distribution.

Most preparation routes for RC and FEF feedstocks follow the same principle.

The first step to obtain a feedstock is preparing a homogeneous dispersion having a high solids loading (mostly about 50 vol%).
The particles are dispersed in the medium (mostly water) by agitation with shakers, ball mills, planetary mills or ultrasonic probes until particle separation is achieved.
When using wide particle size distributions,
the smaller particles facilitate the slip and rearrangement of the bigger particles during extrusion, which is favorable for flow through small orifices.
The results are feedstocks of higher solids loading, lower viscosity and an overall drop of extrusion pressure.
It must be noted that increasingly high particle concentrations are accompanied by severe changes of the rheological properties,
i.e. yield stresses develop and frequency-dependent sol-gel transitions occur, thus small changes in solids loading and processing might have large effects on the result.
A polymeric viscosifier or binder is added to prevent sedimentation, reagglomeration and solvent migration to ensure consistent extrusion and to provide green strength.
After complete dissolution of the viscosifier the suspension can be degassed using vacuum or centrifugation. If a colloidal gel shall be applied to EFF the slurry is coagulated by adding salts, pH-modifiers or charged polymers such as Polyethylene-Imine.

==Recipe examples of an alumina and a carbon black paste:==

{| class="wikitable"
|-
! Component !! Alumina paste !! Mass Percent !! Carbon black paste !! Mass percent
|-
| Powder species || CT3000SG || 78-79 || Luvomaxx N990|| 64
|-
| Dispersant || Darvan C-N || 0.4 || Darvan 670|| 0.3
|-
| Solvent || Water || 19-20 || Water || 30
|-
| Thickener || Bermocoll E320 FQ || 0.4|| PEG 10 kDa|| 3.4
|-
| Coagulant || Ammonium-acetate || 1.5-2.6 || Ammonium-acetate || 3.2
|}
[[File:PSD.png|thumb|Particle size distributions]]

To achieve lower sintering shrinkage due to higher particle packing, bimodal/trimodal powders can be used, which are readily available on the market.

==How to prepare the paste==

* Mix water and dispersant in a PE-bottle. Make sure to find the proper dispersant amount, which correlates with the surface are of the powder. Better use a slight excess, as the surace area might increase during milling.
* Add grinding media (zirconia or alumina, 3 - 20 mm diameter, some big spheres are useful)
* Add the powder successively and shake between additions. Use decreasing additions, i.e. 50%, 25%, 12,5% ...
* Put in a shaker für several hours.
* Add thickener
* Put in shaker for several hours.
* Prepare a lid for the PE-Bottle with a sieve in it, so the milling balls can be separated from the slurry
* Now add the coagulant as an aqueous solution and stir the paste. A centrifugal planetary mixer is optimum to mix and remove air bubbles.

3D-printing-paste

2022-04-03T20:31:52Z

Tschlordt: /* Recipe examples of an alumina and a carbon black paste: */

==Introduction==

Solid Freeform Fabrication uses many different techniques. One is the freeforming of extruded strands of ceramic pastes, which exhibits some important features:

* No excess material needed
* Coextrusion is possible
* Waterborne feedstocks are common
* Nowadays there are lots of cheap extrusion devices on the market
* High density/low porosity and thus high strengths are feasible

==Requirements for the feedstock==
* A high solids loading to counteract shrinkage and cracking due to drying, sintering or binder burn-out
* Well dispersed particles to ensure a constant flow and to avoid flaws due to agglomerates
* Entrapped air should be minimized to avoid pores in the ceramic
* Solvent migration and sedimentation of particles must be prevented to ensure constant flow and storage stability
* Suitable rheology for the applied process to ensure shape retention and sufficient merging of the filaments
* Suitable particle size and distribution for the applied nozzle dimensions
* A binder phase that is easy to drain, dry or burn out
* Suitable solidification kinetics
* Suitable interface properties for adhesion and fusion of filaments
* Sufficient green strength, either to be obtained by the binder or the particle size distribution.

Most preparation routes for RC and FEF feedstocks follow the same principle.

The first step to obtain a feedstock is preparing a homogeneous dispersion having a high solids loading (mostly about 50 vol%).
The particles are dispersed in the medium (mostly water) by agitation with shakers, ball mills, planetary mills or ultrasonic probes until particle separation is achieved.
When using wide particle size distributions,
the smaller particles facilitate the slip and rearrangement of the bigger particles during extrusion, which is favorable for flow through small orifices.
The results are feedstocks of higher solids loading, lower viscosity and an overall drop of extrusion pressure.
It must be noted that increasingly high particle concentrations are accompanied by severe changes of the rheological properties,
i.e. yield stresses develop and frequency-dependent sol-gel transitions occur, thus small changes in solids loading and processing might have large effects on the result.
A polymeric viscosifier or binder is added to prevent sedimentation, reagglomeration and solvent migration to ensure consistent extrusion and to provide green strength.
After complete dissolution of the viscosifier the suspension can be degassed using vacuum or centrifugation. If a colloidal gel shall be applied to EFF the slurry is coagulated by adding salts, pH-modifiers or charged polymers such as Polyethylene-Imine.

==Recipe examples of an alumina and a carbon black paste:==

{| class="wikitable"
|-
! Component !! Alumina paste !! Mass Percent !! Carbon black paste !! Mass percent
|-
| Powder species || CT3000SG || 78-79 || Luvomaxx N990|| 64
|-
| Dispersant || Darvan C-N || 0.4 || Darvan 670|| 0.3
|-
| Solvent || Water || 19-20 || Water || 30
|-
| Thickener || Bermocoll E320 FQ || 0.4|| PEG 10 kDa|| 3.4
|-
| Coagulant || Ammonium-acetate || 1.5-2.6 || Ammonium-acetate || 3.2
|}
[[File:PSD.png|thumb|Particle size distributions]]

==How to prepare the paste==

* Mix water and dispersant in a PE-bottle. Make sure to find the proper dispersant amount, which correlates with the surface are of the powder. Better use a slight excess, as the surace area might increase during milling.
* Add grinding media (zirconia or alumina, 3 - 20 mm diameter, some big spheres are useful)
* Add the powder successively and shake between additions. Use decreasing additions, i.e. 50%, 25%, 12,5% ...
* Put in a shaker für several hours.
* Add thickener
* Put in shaker for several hours.
* Prepare a lid for the PE-Bottle with a sieve in it, so the milling balls can be separated from the slurry
* Now add the coagulant as an aqueous solution and stir the paste. A centrifugal planetary mixer is optimum to mix and remove air bubbles.

3D-printing-paste

2022-04-03T20:20:33Z

Tschlordt: /* Recipe examples of an alumina and a carbon black paste: */

==Introduction==

Solid Freeform Fabrication uses many different techniques. One is the freeforming of extruded strands of ceramic pastes, which exhibits some important features:

* No excess material needed
* Coextrusion is possible
* Waterborne feedstocks are common
* Nowadays there are lots of cheap extrusion devices on the market
* High density/low porosity and thus high strengths are feasible

==Requirements for the feedstock==
* A high solids loading to counteract shrinkage and cracking due to drying, sintering or binder burn-out
* Well dispersed particles to ensure a constant flow and to avoid flaws due to agglomerates
* Entrapped air should be minimized to avoid pores in the ceramic
* Solvent migration and sedimentation of particles must be prevented to ensure constant flow and storage stability
* Suitable rheology for the applied process to ensure shape retention and sufficient merging of the filaments
* Suitable particle size and distribution for the applied nozzle dimensions
* A binder phase that is easy to drain, dry or burn out
* Suitable solidification kinetics
* Suitable interface properties for adhesion and fusion of filaments
* Sufficient green strength, either to be obtained by the binder or the particle size distribution.

Most preparation routes for RC and FEF feedstocks follow the same principle.

The first step to obtain a feedstock is preparing a homogeneous dispersion having a high solids loading (mostly about 50 vol%).
The particles are dispersed in the medium (mostly water) by agitation with shakers, ball mills, planetary mills or ultrasonic probes until particle separation is achieved.
When using wide particle size distributions,
the smaller particles facilitate the slip and rearrangement of the bigger particles during extrusion, which is favorable for flow through small orifices.
The results are feedstocks of higher solids loading, lower viscosity and an overall drop of extrusion pressure.
It must be noted that increasingly high particle concentrations are accompanied by severe changes of the rheological properties,
i.e. yield stresses develop and frequency-dependent sol-gel transitions occur, thus small changes in solids loading and processing might have large effects on the result.
A polymeric viscosifier or binder is added to prevent sedimentation, reagglomeration and solvent migration to ensure consistent extrusion and to provide green strength.
After complete dissolution of the viscosifier the suspension can be degassed using vacuum or centrifugation. If a colloidal gel shall be applied to EFF the slurry is coagulated by adding salts, pH-modifiers or charged polymers such as Polyethylene-Imine.

==Recipe examples of an alumina and a carbon black paste:==

{| class="wikitable"
|-
! Component !! Alumina paste !! Mass Percent !! Carbon black paste !! Mass percent
|-
| Powder species || CT3000SG || 78-79 || Luvomaxx N990|| 64
|-
| Dispersant || Darvan C-N || 0.4 || Darvan 670|| 0.3
|-
| Solvent || Water || 19-20 || Water || 30
|-
| Thickener || Bermocoll E320 FQ || 0.4|| PEG 10 kDa|| 3.4
|-
| Coagulant || Ammonium-acetate || 1.5-2.6 || Ammonium-acetate || 3.2
|}
[[File:PSD.png|thumb|Particle size distributions]]

3D-printing-paste

2022-04-03T20:18:04Z

Tschlordt: /* Recipe examples of an alumina and a carbon black paste: */

==Introduction==

Solid Freeform Fabrication uses many different techniques. One is the freeforming of extruded strands of ceramic pastes, which exhibits some important features:

* No excess material needed
* Coextrusion is possible
* Waterborne feedstocks are common
* Nowadays there are lots of cheap extrusion devices on the market
* High density/low porosity and thus high strengths are feasible

==Requirements for the feedstock==
* A high solids loading to counteract shrinkage and cracking due to drying, sintering or binder burn-out
* Well dispersed particles to ensure a constant flow and to avoid flaws due to agglomerates
* Entrapped air should be minimized to avoid pores in the ceramic
* Solvent migration and sedimentation of particles must be prevented to ensure constant flow and storage stability
* Suitable rheology for the applied process to ensure shape retention and sufficient merging of the filaments
* Suitable particle size and distribution for the applied nozzle dimensions
* A binder phase that is easy to drain, dry or burn out
* Suitable solidification kinetics
* Suitable interface properties for adhesion and fusion of filaments
* Sufficient green strength, either to be obtained by the binder or the particle size distribution.

Most preparation routes for RC and FEF feedstocks follow the same principle.

The first step to obtain a feedstock is preparing a homogeneous dispersion having a high solids loading (mostly about 50 vol%).
The particles are dispersed in the medium (mostly water) by agitation with shakers, ball mills, planetary mills or ultrasonic probes until particle separation is achieved.
When using wide particle size distributions,
the smaller particles facilitate the slip and rearrangement of the bigger particles during extrusion, which is favorable for flow through small orifices.
The results are feedstocks of higher solids loading, lower viscosity and an overall drop of extrusion pressure.
It must be noted that increasingly high particle concentrations are accompanied by severe changes of the rheological properties,
i.e. yield stresses develop and frequency-dependent sol-gel transitions occur, thus small changes in solids loading and processing might have large effects on the result.
A polymeric viscosifier or binder is added to prevent sedimentation, reagglomeration and solvent migration to ensure consistent extrusion and to provide green strength.
After complete dissolution of the viscosifier the suspension can be degassed using vacuum or centrifugation. If a colloidal gel shall be applied to EFF the slurry is coagulated by adding salts, pH-modifiers or charged polymers such as Polyethylene-Imine.

==Recipe examples of an alumina and a carbon black paste:==

{| class="wikitable"
|-
! Component !! Alumina paste !! Mass Percent !! Carbon black paste !! Mass percent
|-
| Powder species || CT3000SG || 78-79 || Luvomaxx N990|| 64
|-
| Dispersant || Darvan C-N || 0,4 || Darvan 670|| 0,3
|-
| Solvent || Example || Example || Example || Example
|-
| Polymer || Example || Example || Example || Example
|-
| Coagulant || Example || Example || Example || Example
|}
[[File:PSD.png|thumb|Particle size distributions]]

3D-printing-paste

2022-04-03T13:37:56Z

Tschlordt: /* Recipe examples of an alumina and a carbon black paste: */

==Introduction==

Solid Freeform Fabrication uses many different techniques. One is the freeforming of extruded strands of ceramic pastes, which exhibits some important features:

* No excess material needed
* Coextrusion is possible
* Waterborne feedstocks are common
* Nowadays there are lots of cheap extrusion devices on the market
* High density/low porosity and thus high strengths are feasible

==Requirements for the feedstock==
* A high solids loading to counteract shrinkage and cracking due to drying, sintering or binder burn-out
* Well dispersed particles to ensure a constant flow and to avoid flaws due to agglomerates
* Entrapped air should be minimized to avoid pores in the ceramic
* Solvent migration and sedimentation of particles must be prevented to ensure constant flow and storage stability
* Suitable rheology for the applied process to ensure shape retention and sufficient merging of the filaments
* Suitable particle size and distribution for the applied nozzle dimensions
* A binder phase that is easy to drain, dry or burn out
* Suitable solidification kinetics
* Suitable interface properties for adhesion and fusion of filaments
* Sufficient green strength, either to be obtained by the binder or the particle size distribution.

Most preparation routes for RC and FEF feedstocks follow the same principle.

The first step to obtain a feedstock is preparing a homogeneous dispersion having a high solids loading (mostly about 50 vol%).
The particles are dispersed in the medium (mostly water) by agitation with shakers, ball mills, planetary mills or ultrasonic probes until particle separation is achieved.
When using wide particle size distributions,
the smaller particles facilitate the slip and rearrangement of the bigger particles during extrusion, which is favorable for flow through small orifices.
The results are feedstocks of higher solids loading, lower viscosity and an overall drop of extrusion pressure.
It must be noted that increasingly high particle concentrations are accompanied by severe changes of the rheological properties,
i.e. yield stresses develop and frequency-dependent sol-gel transitions occur, thus small changes in solids loading and processing might have large effects on the result.
A polymeric viscosifier or binder is added to prevent sedimentation, reagglomeration and solvent migration to ensure consistent extrusion and to provide green strength.
After complete dissolution of the viscosifier the suspension can be degassed using vacuum or centrifugation. If a colloidal gel shall be applied to EFF the slurry is coagulated by adding salts, pH-modifiers or charged polymers such as Polyethylene-Imine.

==Recipe examples of an alumina and a carbon black paste:==

{| class="wikitable"
|-
! Component !! Alumina paste !! Mass Percent !! Carbon black paste !! Mass percent
|-
| Powder species || Example || Example || Example || Example
|-
| Dispersant || Example || Example || Example || Example
|-
| Solvent || Example || Example || Example || Example
|-
| Polymer || Example || Example || Example || Example
|-
| Coagulant || Example || Example || Example || Example
|}
[[File:PSD.png|thumb|Particle size distributions]]

3D-printing-paste

2022-04-03T13:33:54Z

Tschlordt: /* Requirements for the feedstock */

File:PSD.png

2022-04-03T13:32:58Z

Tschlordt:

Particle size distribution for collidal gels

3D-printing-paste

2022-04-03T13:20:22Z

Tschlordt: Created page with "==Introduction== Solid Freeform Fabrication uses many different techniques. One is the freeforming of extruded strands of ceramic pastes, which exhibits some important featur..."

Processing Slurries for Tape Casting

2022-04-03T13:01:43Z

Tschlordt: /* Slip components and their influence */

== General==
The production of a ceramic slip is, depending on the application, a very multifaceted undertaking, as it is a very complex system consisting of many components. The main component, i.e. the ceramic or metallic powders, are mixed with organic or aqueous solvents as well as binders and additives. The slurry produced is then processed on a Tape casting bench. In the Doctor Blade process, the slurry is applied to a steel strip or plastic carrier tape by means of a doctor blade. In a further process step, the tape thus obtained is first dried, possibly converted, and then fed into a sintering process. The thickness of the tape thus obtained varies between 10 µm and 1.5 mm and could be reduced or increased as required. Applications include battery and capacitor technology as well as catalyst carriers or heat exchanger technology.

== Slip components and their influence ==
'''Prerequisites:'''

All slurry components must be selected in such a way that they do not (chemically) react with each other. The compatibility of the individual reactants must also be maintained.

Furthermore, the reactant/solvent systems must be considered critically. For example, methyl cellulose can be dissolved in water only. A low-polarity solvent cannot be used. Polyvinyl butyrate (PVB), on the other hand, can be dissolved in ethanol with a low water content. If the water content exceeds the solubility of the binder, it would precipitate.

'''Starting components:'''
=== Powder===
Oxides, metallic nitrides and metal powders are used as slurry starting powders. Since the physical properties (surface area, particle size and particle shape) of the powders are of great importance, the powders are first characterized.
===Solvents===
The physical properties (surface tension, dielectric constant, melting point, boiling point, viscosity) of the solvents used have a high influence on the slip production / processing. Besides water, alcohols (ethanol, butanol, isopropanol) or ketones (acetone), organic solvents (toluene, xylene) or hexane and trichloroethylene or can be used. (The solvents can be used pure or as azeotropic mixtures). The drying speed of the films depends crucially on the solvent used.
===Binder===
The binder combines the components into a homogeneous mixture and can also influence the permeability or impermeability of the films. Examples of water-based binders are methyl cellulose, polyvinyl alcohol (PVA) or alginates. Other possible solvents for the binder are polymers (polyvinyl butyral (PVP), polymethylacrylates (PMMA), polyvinyl pyrolidone (PVP), etc.).
===Disperser===
The use of a disperser provides steric and electrostatic stabilization to the slurry. Steric stabilization is used for solvent-based systems and electrostatic stabilization for water-based systems.
===Plasticizer===
A plasticizer (polyethylene glycol, glycerol, triethylene glycol di-(2-ethylhexannoate), phthalate ester, etc.) is added to the slurry to give the green films flexibility.
===Pore-forming agents===
For the production of porous films, so-called pore-forming agents are added to the slurry. In addition to polymethyl acrylate, graphite powder and commercially available starch are suitable for this purpose.
===Additives===
The addition of very small amounts (approx. 0.01 - 1 wt.%) of additives increases the processability of the slurry and at the same time reduces defective or faulty areas in the tape.

Additives are further differentiated according to their influence on the physical and chemical properties of the slip. Thus, in addition to wetting/dispersing additives and rehological additives, there are also defoamers, driers, catalysts and preservative additives.

Several additives can also be used in a slurry, but the number should be kept to a minimum.

Products from BYK, Tego, Zschimmer & Schwarz and Münzig have proved particularly successful in this respect.

==General formulation and performance==
The table below gives a typical example for an alumina-based slurry.
{| class="wikitable"
|-
! Components !! Function !! Weight % !! Weight in g
|-
| Al2O3 || Matrix (Powder) || 68.3 || 1250
|-
| Ethanol || solvent || 7.2 || 132
|-
| Methylketon (MEK) || Solvent || 13.4 || 256
|-
|Polyvinylbutyral (PVB 98)||Binder||4||75
|-
|Polyetylenglykol (PEG 400)||Plastificizer||3||56
|-
|Triethylenglykohl-di-(2- ethylhexannoat) (3G8)||Plastificizer||3||56
|-
|Disperbyk BYK 220S|| Disperser|| 0.34|| 6,25
|-
|Al2O3 Millingballs Ø 5mm|| || || 625
|}

In order to obtain a homogeneous slurry, the components are filled into a mixing jar or bottle with grinding balls and processed in a tumbling mixer at a medium rotational speed.

The mixing container should occupy at least half, but not more than 75% of the container volume. The ratio of balls to powder should ideally be 1:2.

First, the balls, solvent and dispersant are weighed and mixed thoroughly. Only then is the matrix powder added. After 6 hours in the tumbling mixer, the powder agglomerates should normally be broken up and a homogeneous mixture should have formed. The mixing time mentioned varies depending on the particle size of the matrix powder used. (The Martoxid aluminum oxide (MR 70) used here had a measured particle size value of d50= >5µm. At this stage of the slurry production, a new particle size determination is now carried out. Depending on the binder addition, an increase in viscosity of the slurry could occur, which makes homogeneous mixing difficult or can only be compensated by increasing the energy input. Only then, the binder is added. The batch is now tumbled for additional two hours. The plasticizer is then added to the lump-free mixture and the mixture is tumbled for another hour. Finally, the grinding balls are removed from the slurry with a sieve. The slurry must now be degassed with a vacuum pump, as bubbles could have formed processing. Finally, the slurry should rest for another 48 hours before it can be used.

==Film influencing factors ==
Whether the films produced meet the desired properties or strength requirements depends on the following factors:
===Preparation of the slip===
===Ratio of slurry density/density of cast film===
===Gap height of the casting shoe===
===Gap length/width doctor blade===
===Hydrostatic pressure in the casting shoe===
===Slip viscosity, belt speed, ventilation===
===Sintering parameters===
[[File:Img 2482-1.mp4|thumb]]