RELATED APPLICATIONS

[001] The present invention claims priority to Singapore patent application no. 10202250970K filed on 12 Sept 2022 and no. 10202251617T filed 3 Nov 2022, the disclosures of which are incorporated in their entireties.

FIELD OF INVENTION

[002]The invention relates to the art of additive manufacturing. More particularly, the invention relates to a slurry having properties that include a high solid loading and low viscosity, and its involvement in a method for additive manufacturing.

BACKGROUND OF THE INVENTION

[003] The application of additive manufacturing for ceramics continues to generate significant interest. In particular, modern manufacturing of ceramics is still costly and delicate due to its brittleness. Current conventional production methods involve high-cost machining of green bodies to a desired shape and size, contributing to up to 80% of the total manufacturing cost as it requires specially developed tools and drill bits.

[004] Regarding ceramics, alumina is a structural ceramic that possesses several attractive properties such as high-temperature resistance, corrosion resistance, biocompatibility, and high hardness. These properties are beneficial and sought after over a wide range of applications including automobiles, marine, and medicine. Notwithstanding these advantages, producing complex or advance alumina components, is both time-consuming and costly.

[005] On the contrary, additive manufacturing may potentially bypass these demanding requirements to produce a near-net-shape part. Though challenging, numerous attempts on additive manufacturing of ceramics have been made by use of different technologies, including selective laser sintering (SLS) and selective laser melting (SLM). Other techniques such as direct ink writing and the use of ultrasound to manipulate the location of materials to form unique shapes have also been developed to fabricate ceramic parts.

[006] Stereolithography methods such as digital light processing (DLP) are popular due to their ease of use and lower costs. Conventionally, stereolithography is a mature additive manufacturing technology used to fabricate polymer parts.

[007] In this process, ultra-violet (UV) light cures selected regions of the photocurable suspension to form a 3D part. By infusing the photosensitive resin with ceramic particles, it is possible to modify the process to enable the fabrication of ceramic green bodies. However, it has been reported that the success of printing a ceramic part heavily relies on the quality of the UV-curable suspension.

[008] To obtain a defect-free ceramic part, it is desirable that the ceramic suspension has characteristics such as low viscosity, well-dispersed, and colloidally stable. In addition, the ceramic suspension should contain a high solid loading to ensure a high sintered density. Hence, there are complex challenges in additive manufacturing of ceramic parts using ceramic suspensions.

[009] It is noted that the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory suggests that colloidal stability of a UV-curable slurry depends on the balance of attractive and repulsive forces around the suspended particles. The manipulation of these forces can be accomplished by (i) adding or removing surface hydroxyl ( — OH) groups to create a double-layer repulsion force, (ii) controlling the pH value of the slurry, and (iii) steric repulsion.

[0010] It has been suggested that pH value of a slurry affects the dispersion quality of the powder. As the pH value increases, surface charges tend to change from a positive state to an uncharged state at the isoelectric point (IEP), and then to a negative state. This is achieved through surface modification by the adsorption of carboxylic acids. However, since the IEP of untreated alumina is in the range of about 8 — 9, surface charge changes by manipulating the pH with one carboxylate group may not be strong enough to overcome the attractive forces. Moreover, a single substitution of surface groups may not change surface charges according to the ligand exchange model. [0011] Steric repulsion offers means to prevent flocculation within a slurry. Steric stabilization has been indicated to improve dispersion quality through manipulating the interparticle interaction. However, is has been demonstrated that excessive use of dispersants adversely affected viscosity. Not only that, the different types of dispersant results in different sedimentation response.

[0012] There are a number of disclosed technologies over the prior art that may relate to slurries for use in additive manufacturing. Among them is US6117612A, issued to the University of Michigan, which discloses a process to prepare a photocurable ceramic resin for use in additive manufacturing. In particular, the constituents of the photocurable resin are stated to comprise photopolymerizable monomers (which may be collectively referred to as photopolymer), dispersant, photoinitiator, and sinterable particles. However, its slurry has a tedious preparation process, as it is required that mixing is done using a ball mill mixer with incremental addition of the constituents. As such, a duration of 20 to 40 hours is required for its photocurable resin to be prepared.

[0013] Accordingly, it would be desirable to have a slurry, more particularly, a photocurable ceramic-based resin, which improves upon the existing prior art and has a high solid loading, low viscosity, and low sedimentation rate. In addition, it is also desirable that the ceramic suspension has a hassle-free preparation process.

SUMMARY OF INVENTION

[0014] The present invention seeks to provide a slurry, more specifically, a photocurable ceramic-based resin, which has a high solid loading and low viscosity. To achieve this objective, the invention provides a slurry composed of ceramic-based particles that is appropriately dispersed with a dispersant that adsorbs to the surface of said particles. Furthermore, one or more steps of duration-based mixing are performed in the slurry’s preparation process to ensure homogeneous mixing between the slurry’s constituents between steps.

[0015] Advantageously, the present invention provides a slurry that requires a short preparation time of around 15 to 30 minutes. [0016] Advantageously as well, the present invention enables relatively lesser amounts of some constituents of the slurry while maintaining a reasonable solid loading.

[0017] Advantageously as well, the present invention provides a slurry that remains substantially stable over a duration where a product undergoes 3D printing or after it is 3D printed. More specifically, a 3D product may still be printed out through light-based curing technologies using the slurry even if the slurry was unused and stored for a period of time.

[0018] Advantageously as well, the present invention enables a quicker process time in providing on-demand preparation of the slurry and 3D printing of a product.

[0019] Advantageously as well, the present invention provides a slurry that may have sinterable particles in a concentration of up to 55% in volume percentage with respect to solid content while exhibiting low viscosities of substantially less than about 5 Pa- s at a shear rate of about 30 s ¹ . More specifically, the present invention provides a slurry that have sinterable particles in a concentration of up to 45% in volume percentage with respect to solid content with a dispersant of about in a concentration of up to 2% in weight percentage with respect to solid content, which enables the slurry to have a low viscosity of substantially about 0.52 Pa- s at a shear rate of about 30 s ¹ .

[0020] Advantageously as well, the present invention provides a ceramic-based slurry having alumina platelets which enables it to be involved in a method for additive manufacturing that produces final 3D products having nacre-like structures. In particular, a recoating system in a commercial 3D printer aligns alumina platelets to print the nacre-like structures. Nacre, otherwise known as the brick-and-mortar structure, is inspired by the mollusc shell and is among the toughest material in nature.

[0021] In one embodiment, the present invention provides a slurry, more particularly, a photocurable resin, for use in additive manufacturing. In another embodiment, the present invention provides a method of additive manufacturing involving the slurry.

[0022] The invention intends to provide a slurry for use in additive manufacturing, comprising a first constituent, being a photomonomer or photopolymer, a second constituent, being a dispersant, a third constituent, being sinterable particles, and a fourth constituent, being a photoinitiator. The second constituent adsorbs to surfaces of the third constituent through at least one mode of adsorption as they mix.

[0023] Preferably, the second constituent is selected from any one of polyacrylic-based dispersants, polyvinylpyrrolidone-based dispersants, polyoxyethylene-based glycol-based dispersants, polyester-based dispersants, or lipid-based dispersants.

[0024] Preferably, the second constituent is any one of polyester phosphoric acid ester dispersant or oleic acid dispersant.

[0025] Preferably, the third constituent is selected from any one of ceramic-based powders, polyamide-based powders, or metallic-based powders.

[0026] Preferably, the sinterable particles that is selected from the ceramic-based powders comprising any one of alumina powder, alumina platelets, silica-derivative powder, or zirconia powder.

[0027] Preferably, the second constituent is present within the slurry at a concentration ranging from about 1 - 5% in weight percentage with respect to solid content.

[0028] Preferably, the fourth constituent is present within the slurry at a concentration ranging from about 0.3 - 1% in a weight percentage with respect to solid content.

[0029] Preferably, the third constituent is present within the slurry at a concentration ranging from about 35 - 55% in a volume percentage with respect to solid content.

[0030] The invention further intends to provide a method for additive manufacturing, comprising the steps of preparing a slurry having a first constituent, being a photomonomer or photopolymer, a second constituent, being a dispersant, a third constituent, being sinterable particles, and a fourth constituent, being a photoinitiator, coating a vat with the slurry, lowering a platform into the vat for the platform to be in contact with the slurry, exposing light to the slurry for forming a printed part, and raising the platform to separate the printed part therefrom. The slurry has its second constituent adsorbed to surfaces of its third constituent through at least one mode of adsorption as they are mixed during preparation. [0031] Preferably, the method further comprises the steps of preparing the first constituent and the second constituent, mixing the first constituent with the second constituent to obtain a first intermediate mix, adding the third constituent into the first intermediary mix, mixing the first intermediary mix with the third constituent to obtain a second intermediate mix, adding a fourth constituent into the second intermediary mix, and mixing the second intermediary mix with the fourth constituent to obtain the slurry.

[0032] Preferably, regarding the method, the second constituent is selected from any one of polyacrylic-based dispersants, polyvinylpyrrolidone-based dispersants, polyoxyethylenebased glycol-based dispersants, polyester-based dispersants, or lipid-based dispersants.

[0033] Preferably, regarding the method, the second constituent is a polyester phosphoric acid ester dispersant or oleic acid dispersant.

[0034] Preferably, regarding the method, the third constituent is selected from any one of ceramic-based powders, polyamide-based powders, or metallic-based powders.

[0035] Preferably, regarding the method, the sinterable particles that is selected from the ceramic-based powders comprises any one of alumina powder, alumina platelets, silicaderivative powder, or zirconia powder.

[0036] Preferably, regarding the method, the second constituent is present within the slurry at a concentration ranging from about 1 - 5% in weight percentage with respect to solid content.

[0037] Preferably, regarding the method, the fourth constituent is present within the slurry at a concentration ranging from about 0.3 - 1% in a weight percentage with respect to solid content.

[0038] Preferably, regarding the method, the third constituent is present within the slurry at a concentration ranging from about 35 - 55% in a volume percentage with respect to solid content.

[0039] Preferably, the method further comprises the steps of performing debinding upon the printed part, performing sintering upon the printed part, and cooling the printed part. [0040] Preferably, the step of performing debinding upon the printed part is performed at a combination of temperatures that include a first temperature of about 162 °C, a second temperature of about 438 °C, a third temperature of about 543 °C, and a fourth temperature of about 620 °C.

[0041] Preferably, wherein the step of performing sintering upon the printed part further comprises the steps of heating the printed part to a fifth temperature ranging from about 1700 °C and heating the printed part for a duration of about 120 minutes.

[0042] One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the advantages mentioned, as well as those inherent therein. The embodiments described herein are not intended as limitations on the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] To facilitate an understanding of the invention, there are illustrated in the accompanying drawings the preferred embodiments, from an inspection of which when considered in connection with the following description, the invention, its construction, and operation and many of its advantages would be readily understood and appreciated.

[0044] FIG. 1 illustrates a first flowchart describing the steps of a method of additive manufacturing provided by the present invention.

[0045] FIG. 2 illustrates a diagrammatic flow of a first preparation process of a slurry provided by the present invention.

[0046] FIG. 3 illustrates a second flowchart describing the steps of the first preparation process of the slurry provided by the present invention.

[0047] FIG. 4 illustrates a third flowchart describing the steps of a second preparation process of the slurry provided by the present invention. [0048] FIG. 5 illustrates a graph of temperature against time that illustrates the heating performed upon a printed part for it to undergo debinding, sintering, and subsequent cooling of the printed part.

[0049] FIGS. 6 to 7 are photographs showing spreadability of the slurry whereby different types of dispersants are used as the second constituent.

[0050] FIG. 8 illustrates a graph of sedimentation rate against time in days illustrating the sedimentation rates of various slurries each having different concentrations of the second constituent and/or the third constituent.

[0051] FIGS. 9 to 10 are graphs of slurry viscosity of various slurries against slurry shear rate. In particular, FIG. 9 presents plots of slurries having a second constituent that is DISPERBYK-103 dispersant, whereas FIG. 10 presents plots of slurries having a second constituent that is oleic acid dispersant,

[0052] FIG. 11 illustrates a graph of contact angle of a droplet of different slurries against time, with each slurry having different concentrations of the second constituent and/or different concentrations of the third constituent, whereby the second constituent is DISPERBYK-103 dispersant.

[0053] FIGS. 12 to 15 each illustrate a droplet from the different slurries and its corresponding contact angle at about t = 10 seconds.

[0054]FIG. 16 illustrates a graph derived from a thermogravimetric analysis (TGA) of a printed part, which was printed from a slurry having a third constituent that is alumina-based.

[0055]FIG. 17 illustrates a graph derived from a Fourier-transform infrared spectroscopy (FTIR) analysis of one or more printed parts, which were printed from different slurries.

[0056] FIGS. 18 to 20 are illustrations of chemical reactions pertaining to the esterification of the second constituent, and its possible modes of adsorption with the third constituent.

[0057] FIG. 21 illustrates a magnified photograph of a final 3D product printed using a slurry having a third constituent that is alumina platelets. [0058] FIGS. 22 to 24 are photographs of an example final 3D product printed using a slurry having a third constituent that is alumina powder. In particular, FIG. 22 is a photograph of the the final 3D product, FIG. 23 is a magnified photograph of the printed part, and FIG. 24 is a magnified photograph of the slurry.

[0059] FIGS. 25 to 26 are photographs of an example final 3D product printed using a slurry having a third constituent that is zirconia powder. In particular, FIG. 25 is a photograph of the final 3D product, and FIG. 26 is a magnified photograph of the final 3D product.

DETAILED DESCRIPTION OF THE INVENTION

[0060] The present invention relates to a method of additive manufacturing. According to the concept of the invention, a slurry with high solid loading and low viscosity is prepared, and it is subsequently used by a printing unit to produce a printed part which is in the form of a green part. The method further involves subsequent post-processing of the printed part for it to undergo debinding and sintering to become a final 3D product.

[0061] The invention will now be described in greater detail, by way of example, with reference to the figures.

[0062] FIG. 1 illustrates a first flowchart describing an A-series of steps pertaining to the method of additive manufacturing provided by the present invention. It is noted that the steps described in this flowchart are not to be interpreted as non-limiting, and minor modifications to the steps (e.g., additions, omissions, or swaps) are permissible by a skilled person without substantial deviation from as described.

[0063] First, in step SAI, the step of preparing a slurry comprising a first constituent, a second constituent, a third constituent, and a fourth constituent is performed. Preferably, all of these constituents have been evenly mixed for formation of the slurry. In particular, the first constituent is photomonomer or photopolymer, the second constituent is a dispersant, the third constituent is sinterable particles, and the fourth constituent is a photoinitiator. [0064] Next, in step SA2, the step of providing a printing unit with a file having three- dimensional information of a product is performed. Preferably the printing unit is a three- dimensional printer based on digital light processing (DLP) technology. Most preferably, the printing unit is a CeraFab 8500 from Lithoz GmbH.

[0065] Next, in step SA3, the step of programming the printing unit is performed. Preferably, the settings of the printing unit are programmed to include a total number of layers parameter, i, necessary for printing of the product.

[0066] Next, in step SA4, the step of coating a vat with the slurry prepared in step SAI is performed. Preferably, the step of coating is performed by use of a scraper blade.

[0067] Next, in step SAS, the step of lowering a platform of the printing unit into the vat is performed. Preferably, the platform is lowered for it to be in contact with the slurry.

[0068] Following step SAS is step SA6, which is a decision step where it is determined whether or not a current layer number n = 0. Should this be the case, step SA6 proceeds to step SA7. Else, step SA6 proceeds to step SA8.

[0069] In step SA7, since it was determined that the current layer number n = 0, hence, the step of exposing the entirety of the slurry to electromagnetic radiation is performed. In particular, the slurry may be exposed to electromagnetic radiation from the base of the vat. Preferably, the electromagnetic radiation in which the slurry is exposed to is part of the ultraviolet spectrum. Most preferably, the slurry receives frequencies from the electromagnetic spectrum that are at about 450 nm. With this, an adhesion layer is formed on the platform.

[0070] In step SA8, since it was determined that the current layer /? (), hence, it is determined that the current layer number n is between 1 and the total number of layers i, i.e. 1< n < i.

[0071] Following step SA8 is step SA9. Here, in step SA9, the step of exposing the entirety of the slurry to electromagnetic radiation is performed. Similar to step SA7, the slurry may be exposed to electromagnetic radiation from the base of the vat. In particular, the electromagnetic radiation exposure is based on a current geometry of the part to be printed. Preferably, the electromagnetic radiation in which the slurry is exposed to is part of the ultraviolet spectrum. Most preferably, the slurry receives frequencies from the electromagnetic spectrum that are at about 450 nm. With this, an adhesion layer is formed on the platform.

[0072] Following step SA7 or SA9 is step SA10. Here, in step SA9, the step of separating the platform from the vat is performed.

[0073] Following step SA10 is step SA11. Here, in step SA11, the step of raising the platform is performed.

[0074] Following step SA11 is step SA12, which is a decision step whereby it is determined whether or not current layer number n is equivalent to the total number of layers i. Should this be the case, step SA12 proceeds to step SA14. Else, step SA12 proceeds to step SA13.

[0075] In step SA13, since it was determined that a current layer number n is not equivalent to the total number of layers i, the current layer current n has not reached the total number of layers i. Hence, the current layer number n is incremented by a predetermined value, preferably being a value of 1. With this, step SA13 loops back to step SA4 and continues therefrom so that printing of a subsequent layer of the printed part may be done. Preferably, each layer is printed with thicknesses of substantially 25 pm, or any other permissible thickness.

[0076] In step SA14, since it was determined that a current layer number n is equivalent to the total number of layers i, accordingly, it is regarded that the printed part has now been produced. Preferably, this produced printed part corresponds to a green part.

[0077] Following step SA14 is step SA15. Here, in step SA15, the step of removing residual slurry from the printed part is performed. Preferably, the printed part is rinsed in alcohol, which may be by way of example, ethanol, to remove the residual slurry.

[0078] Following step SA15 is step SA16. Here, in step SA16, the step of heating the printed part from SA15 at a combination of temperatures for it to undergo debinding is performed. In particular, the temperatures in which the printed part is heated for it to undergo debinding include a first temperature Ti being of about 162 °C, a second temperature T2 being of about 438 °C, a third temperature T3 being of about 543 °C, and a fourth temperature T4 being of about 620 °C. [0079] In particular, step SA16 may be comprised of multiple sub-steps. In a first sub-step, the printed part is heated from room temperature to the first temperature Ti at a predetermined rate. In a second sub-step, it is put under the first temperature Ti for a predetermined period. In a third sub-step, the printed part is heated from the first temperature Ti to the second temperature T2 at a predetermined rate. In a fourth sub-step, it is put under the second temperature T2 for a predetermined period. In a fifth sub-step, the printed part is heated from the second temperature T2 to the third temperature T3 at a predetermined rate. In a sixth sub-step, it is put under the third temperature Ti for a predetermined period. In a seventh sub-step, the printed part is heated from third temperature T3 to the fourth temperature T4 at a predetermined rate. In an eighth sub-step, the printed part is heated at a constant manner under the fourth temperature T4 for a predetermined period.

[0080] Following step SA16 is step SA17. Here, in step SA16, the step of heating the printed part from SA14 further to a fifth temperature T5 for it to undergo sintering is performed. In particular, the fifth temperature T5 is about 1700 °C.

[0081] In particular, step SA17 may be comprised of multiple sub-steps. In a first sub-step, the printed part is heated from the fourth temperature T4 to the fifth temperature T5 at a predetermined rate. In a second sub-step, the printed part is heated at a constant manner under the fifth temperature T5 for a predetermined period.

[0082] Following step SA17 is the final step, step SA18. Here, in step SA18, the step of cooling the debinded and sintered printed part is performed. In particular, the printed part is cooled down from the fifth temperature T5 to room temperature at a predetermined rate. With this, the method of additive manufacturing as provided by the present invention is complete, and a debinded, sintered, and cooled printed part is the final 3D product of this method.

[0083] FIG. 2 and FIG. 3 in conjunction illustrate a first preparation process of the slurry provided by the present invention, which may be regarded as an extension to step SAI previously described in FIG. 1. In particular, FIG. 2 illustrates a diagrammatic flow of its preparation process. In particular, FIG. 3 illustrates a second flowchart describing a B-series of steps pertaining to the first preparation process of the slurry. It is noted that the steps described in this flowchart are not to be interpreted as non-limiting, and minor modifications to the steps (e.g., additions, omissions, or swaps) are permissible by a skilled person without substantial deviation from as described.

[0084] First, in step SB1, a first constituent, preferably being a photomonomer or a photopolymer, and a second constituent, preferably being dispersant, are provided or prepared.

[0085] Next, in step SB2, the first constituent and the second constituent are poured into a container and mixed, preferably by use of a planetary mixer. In particular, the first constituent and the second constituent are mixed in this manner for a duration of about 4 - 6 minutes, but most preferably about 5 minutes. This produces a first intermediate mix.

[0086] Next, in step SB3, a third constituent, preferably being sinterable particles, is dried. More specifically, the third constituent is dried in an oven at temperatures of about 80 °C to remove excess moisture that may be present therein.

[0087] Next, in step SB4, the dried third constituent is added into the first intermediate mix.

[0088] Next, in step SB5, the first intermediate mix and the sinterable particles are mixed, preferably by use of a planetary mixer. In particular, the first intermediate mix and the third constituent are mixed in this manner for a duration of about 4 - 6 minutes, but most preferably about 5 minutes. This produces a second intermediate mix.

[0089] Next, in step SB6, a fourth constituent, preferably being photoinitiator, having been provided or prepared, is added into the second intermediate mix.

[0090] Finally, in step SB7, the second intermediate mix and the fourth constituent are mixed, preferably by use of a planetary mixer. In particular, the second intermediate mix and the fourth constituent are mixed in this manner for a duration of about 4 - 6 minutes, but most preferably about 5 minutes. This produces the slurry that may be involved in subsequent steps within the method of additive manufacturing as provided by the present invention.

[0091] FIG. 4 is a second flowchart describing a C-series of steps pertaining to a second preparation process of the slurry, which may be regarded as an extension to step SAI previously described in FIG.l. It is noted that the steps described in this flowchart are not to be interpreted as non- limiting, and minor modifications to the steps (e.g., additions, omissions, or swaps) are permissible by a skilled person without substantial deviation from as described.

[0092] First, in step SCI, a second constituent, preferably being dispersant, and a fifth constituent, preferably being alcohol, are provided or prepared.

[0093] Next, in step SC2, the second constituent and the fifth constituent are poured into a container and vortex mixed. This produces a third intermediate mix.

[0094] Next, in step SC3, the third intermediate mix is ball-milled for its powder agglomerates to be broken up. Preferably, the third intermediate mix is ball-milled for a period of time, most preferably about 6 hours.

[0095] Next, in step SC4, a third constituent, preferably being sinterable particles, is dried. More specifically, the third constituent is dried in an oven at temperatures of about 80 °C to remove excess moisture that may be present therein.

[0096] Next, in step SC5, the dried third constituent is added into the third intermediate mix.

[0097] Next, in step SC6, the third intermediate mix and the sinterable particles are mixed. Preferably, this step is performed by use of a magnetic stirrer and under a temperature of about 75 °C. This produces a fourth intermediate mix. This step promotes adsorption of the second constituent to the third constituent.

[0098] Next in step SC7, the fourth intermediary mix is oven-dried by being heated above a vaporisation point of the fifth constituent for its removal from the fourth intermediate mix, thereby producing a modified fourth intermediate mix. Should the fifth constituent be an alcohol that is ethanol, the fourth intermediary mix is dried by being heated above 80 °C.

[0099] Next, in step SC8, a first constituent, preferably being photomonomer or photopolymer, is added into the modified fourth intermediary mix.

[00100] Next, in step SC9 a fourth constituent, preferably being photoinitiator, is added into the modified fourth intermediary mix. [00101] Finally, in step SCIO, the modified fourth intermediary mix, the first constituent, and the fourth constituent are mixed. This produces the slurry that may be involved in subsequent steps within the method of additive manufacturing as provided by the present invention.

[00102] The slurry provided by the present invention, which comprises a first constituent, a second constituent, a third constituent, and a fourth constituent shall now be described.

[00103] The first constituent is preferably a photomonomer or photopolymer. It may be, by way of example, acrylate-based photomonomers or photopolymers, glycol-based photomonomers or photopolymers, epoxy-based photomonomers or photopolymers, or any other substance that is cured through photopolymerization under exposure to energy sources such as ultraviolet radiation, X-rays, electron beams, or visible light.

[00104] Most preferably, the first constituent is 1, 6-hexanediol diacrylate (HDD A) photomonomer or photopolymer.

[00105] The second constituent is preferably a dispersant. It may be, by way of example, polyacrylic-based dispersants, polyvinylpyrrolidone-based dispersants, polyoxyethylenebased glycol-based dispersants, polyester-based dispersants, lipid-based dispersants, or any other substance that promotes mixture between constituents during the preparation process for the dispersion stability of the slurry.

[00106] In one embodiment of the slurry, the second constituent is a polyester phosphoric acid ester (DISPERBYK-103) dispersant.

[00107] In another embodiment of the slurry, the second constituent is an oleic acid dispersant.

[00108] The third constituent is preferably sinterable particles. It may be, by way of example, ceramic-based powders, ceramic-based platelets, polyamide-based powders, metallic-based powers, or any other powder-like or platelet-like substance that forms the base material of an additively manufactured 3D product. Most preferably, the third constituent is ceramic- based, and as such, it may be alumina platelets, alumina powder, zirconia powder, or silicaderivative powder. Moreover, the ceramic-based powder may or may not be derived from biological organisms.

[00109] The fourth constituent is preferably photoinitiator. It is preferably commercially obtained, and may be, but shall not be limited to BAPO, Ivocerin, or TPO-L. Moreover, the photoinitiator may be chosen from any one of Norish type-1 photoinitiators, Norish type-2 photoinitiators, or any other chemicals that releases free radicals under the exposure of the aforementioned energy sources such as azobisisobutyronitrile, benzoyl peroxide, 2,2- Dimethoxy-2-phenyl acetophenone, or camphorquinone.

[00110] Most preferably, the fourth constituent is a BAPO photoinitiator as it has an absorption spectrum of up to about 440 nm with a peak absorbance of between about 371 nm to about 400 nm. This indicates its suitability with the printing unit that is based on DLP technology.

[00111] Regarding the slurry prepared by the steps described in FIG. 2 and FIG. 3, it may have, by way of example, a first constituent being HDDA photomonomer or photopolymer, a second constituent being DISPERBYK-103 dispersant, a third constituent being particles of either one of alumina platelets, alumina powder, zirconia powder, or silica-derivative powder, and a fourth constituent being BAPO photoinitiator.

[00112] Regarding the slurry prepared by the steps described in FIG. 4, it may have, by way of example, a first constituent being HDDA photomonomer or photopolymer, a second constituent being oleic acid dispersant, a third constituent being particles of either one of alumina platelets, alumina powder, zirconia powder, or silica-derivative powder, and a fourth constituent being BAPO photoinitiator.

[00113] In particular, for slurry preparation as described in FIGS. 2 and 3, the preparation of the slurry with the dried third constituent is to take place under room temperature conditions, which may include temperatures ranging from about 20 °C - 25 °C.

[00114] In particular, for slurry preparation as described in FIGS. 2 and 3, the step of mixing was done through the use of a planetary mixer. However, it is noted that the step of mixing may be done through a household mixing machine, an industrial mixing machine, or any kind of machine that is capable of mixing one or more constituents.

[00115] In particular, for slurry preparation as described in FIGS. 2 to 4, a substantially 5- minute duration for performing mixing is most preferred as it ensures a homogeneous distribution between each constituent at each step of mixing.

[00116] FIG. 5 illustrates a graph of temperature against time. More specifically, it illustrates the heating and cooling performed upon a printed part from SA14 or SA15 for the printed part to become a final 3D product.

[00117] In particular, FIG. 5 illustrates the temperatures and the temperature changes in which debinding of the printed part takes place, which is preferably in accordance with the descriptions of step SA15 as previously described. As shown in FIG. 5, between each temperature Ti, T2, T3, T4, the printed part is heated at a predetermined rate of preferably 5°C/minute. As shown in FIG. 5 as well, for each temperature Ti, T2, T3, T4, the heated part is heated in a constant manner for a predetermined duration of about 25 minutes. Alternatively, for each temperature Ti, T2, T3, T4, the heated part is heated in a constant manner at different predetermined durations.

[00118] In particular, FIG. 5 illustrates the temperatures and the temperature changes in which sintering of the printed part takes place, which is preferably in accordance with the descriptions of step SA16 as previously described. As shown in FIG. 5, between the intervals of temperatures T4 and T5, the printed part is heated at a predetermined rate of preferably 5°C/minute. As shown in FIG. 5 as well, at temperature T5, the heated part is heated for a predetermined duration of about 120 minutes (or about 2 hours).

[00119] In particular, FIG. 5 illustrates the temperatures and the temperature changes in which cooling of the printed part takes place, which is preferably in accordance with the descriptions of step SA17 as previously described. As shown in FIG. 5, the printed part is cooled from temperature Ts to room temperature at a predetermined rate of preferably 5°C/minute. [00120] From hereon, one or more qualitative or quantitative evaluations shall be carried out to validate the properties of the slurry used in the method for additive manufacturing. The properties validated include the slurry’s spreadability, rheological behaviour, colloidal stability, and droplet contact angle. For these validations, the slurry may be prepared according to the first preparation process described in FIGS. 2 and 3, or the second preparation process described in FIG. 4. It is to be noted that parameters defined or determined in these evaluations are not meant to be interpreted as limitations to the scope of the invention.

[00121] From hereon, it is to be noted that descriptions of concentrations of a constituent within a slurry may be given either in weight percentage with respect to solid content (denoted “wt.%”), or in volume percentage with respect to solid content (denoted “vol.%”). Solid content may refer to an amount of solid material relative to a total volume of the slurry.

[00122] From hereon as well, it is to be noted that for simplicity, the notation for the slurry composition in the following descriptions may be written as “third constituent weight percentage_second constituent weight percentage & type”.

[00123] For example, a slurry having a third constituent with a concentration of 45 vol.% and without a second constituent, shall be written to have a notation of Untreated, 45_0.

[00124] For example, a slurry having a third constituent with a concentration of 45 vol.% and a second constituent being BYK103 with a concentration of 1 wt.%, shall be written to have a notation of 45_1B.

[00125] For example, a slurry having a third constituent with a concentration of 45 vol.% and a second constituent being oleic acid with a concentration of 1 wt.%, shall be written to have a notation of 45_1OA.

[00126] FIG. 6 and FIG. 7 collectively illustrates an observatory comparison of spreadability between two different slurries, each having a different type of dispersant used as the second constituent.

[00127] In particular, FIG. 6 illustrates the slurry having a second constituent being a DISPERBYK-103 dispersant. More specifically, the slurry has the third constituent at a concentration of 45 vol.% and has the second constituent (DISPERBYK-103 dispersant) at a concentration of 1% wt., thereby notated as 45_1B.

[00128] In particular, FIG. 7 illustrates a slurry having a second constituent being an oleic acid dispersant. More specifically, the slurry has the third constituent at a concentration of 35 vol.% and has the second constituent (oleic acid dispersant) at a concentration of 1% wt., thereby notated as 35_1B.

[00129] As observed in FIG. 6 and FIG. 7, after both slurries have been spread by a spreading tool, the slurry 45_1B having the DISPERBYK-103 dispersant has a smoother spread compared to the slurry 35_1B having the oleic acid dispersant.

[00130] FIG. 8 presents a graph describing colloidal stability of slurries. More specifically, FIG. 8 presents a graph of sedimentation rate against time in days for various slurries, each having different concentrations of the second constituent and/or the third constituent.

[00131] As shown in FIG. 8, the slurry notated as 45_1B settled at a sedimentation rate that is substantially more than about 3% of the volume within an initial period of about 1 day (about 24 hours). After about four days (or about 96 hours), its sedimentation rate was reduced to a steady rate that is substantially less than about 1%.

[00132] As shown in FIG. 8, the slurry notated as 45_2B had considerable stability within an initial period of the first day (about 24 hours). However, after that, its sedimentation rate began settling at a steady rate that is substantially less than about 1%. It is to be noted such behaviour is desirable as homogeneity of the slurry is required at least throughout the duration of a print job.

[00133] As shown in FIG. 8, the slurry notated as 45_3B appeared the most stable without any visible sedimentation over the whole observation period after rapidly settling in the initial period of about 1 day (about 24 hours).

[00134] As shown in FIG.8, the slurry notated as 5O_1B settled gradually at a sedimentation rate that is substantially up to about 1% on the second day (or from about 24 hours onwards). After that, its sedimentation rate continued to reduce for the remaining observation period. [00135] FIGS. 9 and 10 are graphs describing rheological properties of one or more slurries. More specifically, FIGS. 9 and 10 are graphs of slurry viscosity against slurry shear rate.

[00136] The graph of FIG. 9 presents plots of slurries having different concentrations of the second constituent and/or different concentrations of the third constituent, whereby the second constituent is DISPERBYK-103 dispersant.

[00137] The graph of FIG. 10 presents plots of slurries having different concentrations of the second constituent and/or different concentrations of the third constituent, whereby the second constituent is an oleic acid dispersant.

[00138] The rheological property data of the slurries as presented in FIG. 9 and FIG. 10 were obtained by use of a rheometer. Preferably, the rheometer is a HAAKE MARS III rheometer from Rheology Solutions Pte. Ltd. These data were collected under an ambient temperature of about 25 °C and at shear rates ranging from 0 to about 120 s ¹ . Furthermore, for collection of the data, a parallel plate set-up was used, which preferably has a gap of about 0.4 mm.

[00139] As shown in FIGS. 9 and 10 an inverse relationship is exhibited, indicating that the slurries at least conform to a non-Newtonian fluid with sheer-thinning behaviour. More specifically, this inverse relationship is most apparent when the second constituent (dispersant) is present in a concentration that is of at least 1% wt. Moreover, based on a comparison between the graphs of FIGS. 9 and 10, slurries having a second constituent being a DISPERBYK-103 dispersant overall exhibited a viscosity lower than slurries having a second constituent being an oleic acid dispersant.

[00140]As shown in FIGS. 9 and 10, the slurry notated as 45_2B exhibited the lowest viscosity compared to the other slurries. It had a viscosity of about 0.52 Pa-s at a shear rate of about 30 s’ ¹ .

[00141] As shown in FIGS. 9 and 10, the slurry notated as 45_/CM_cxhibitcd the highest viscosity compared to the other slurries. It had a viscosity of about 9.94 Pa-s at a shear rate of about 30 s’ ¹ . [00142] As shown in FIGS. 9 and 10, the slurry notated as 45_3B exhibited a viscosity of about 1.31 Pa-s at a shear rate of about 30 s ¹ , thereby showing that a further increase in dispersant concentration may not necessarily result in a decreased slurry viscosity.

[00143] As shown in FIGS. 9 and 10, the slurry notated as 5O_1B exhibited a viscosity that is substantively similar to the slurry notated as 45_1B.

[00144] As shown in FIGS. 9 and 10, the slurry notated as 55_1B exhibited a viscosity of about 3.3 Pa- s at a shear rate of about 30 s ¹ . This indicates a further increase in concentration of the third constituent (sinterable particles) may result in an increased slurry viscosity.

[00145] In particular, as shown in FIG. 10, for slurries dispersed with a second constituent being oleic acid dispersant, the slurry notated as 35_1OA had exhibited the lowest achievable viscosity compared to the other slurries shown in FIG. 10. It had a viscosity of about 2.94 Pa-s at a shear rate of about 30 s ¹ . For comparison, the slurry is notated as 55_2B in FIG. 9 exhibited a substantively similar viscosity, with it having a viscosity of about 3.47 Pa-s at the shear rate of about 30 s ¹ .

[00146] Based on FIGS. 9 and 10, it is deemed that having a second constituent being a DISPERBYK-103 dispersant would be effective in preparing a low-viscosity slurry having a high concentration of a third constituent. Furthermore, FIGS. 9 and 10 showed that the DISPERBYK-103 dispersant offered a better dispersion efficacy compared to the oleic acid dispersant.

[00147] FIGS. 11 illustrates a graph of contact angle of a droplet of different slurries against time, with each slurry having different concentrations of the second constituent and/or different concentrations of the third constituent, whereby the second constituent is DISPERBYK-103 dispersant.

[00148] FIGS. 12 to 15 are intended to be an extension of FIG. 11, wherein each of them illustrates a droplet from the different slurries and its corresponding contact angle at about t = 10 seconds.

[00149] For evaluation of contact angle, one or more slurries were prepared. A droplet from each slurry was deposited onto a flat surface for a contact angle representative of the slurry to be measured. Preferably, the contact angles of the droplets were evaluated by use of a contact angle test machine, most preferably an LR-SDC-80 Optical Contact Angle Tester. More specifically, the slurries were evaluated to determine presence of a self-levelling behaviour. After a droplet of the slurry was deposited on a Fluorinated Ethylene Propylene (FEP) film, contact angle measurements for each slurry droplet were performed for a period of time ranging from 0 to about 10 s, at an interval of about 1 s.

[00150] As shown in FIGS. 11, the droplet of each slurry stabilised after about 2 seconds. This steep initial reduction of contact angle exhibited by each slurry sample implies that these slurry samples readily spread on an FEP film.

[00151] Furthermore, based on FIG. 11, among the prepared slurries, the slurry notated as 45_2B is inferred to exhibit the best wettability, as its droplet has a contact angle of about 42.93 ° after about 10 seconds.

[00152] The following assessments will utilise a slurry denoted as 45_2B as it had exhibited a reasonably high solid loading with a low viscosity.

[00153] FIG. 16 illustrates a graph derived from a thermogravimetric analysis (TGA) of a printed part, which was printed from a slurry having a third constituent that is alumina-based.

[00154] The thermogravimetric (TGA) analysis was performed to determine thermolysis response of the slurry at temperatures ranging from about 25 °C to about 1000 °C, with a heating rate of about 5 °C/min in air. Preferably, the TGA analysis was performed by use of the STARe Excellence Thermal Analysis Software by Mettler-Toledo International Inc.

[00155] As shown in FIG. 16, the TGA plot (solid line) of the printed part reveals about four weight loss regions. The first weight loss region may be between temperatures of about 124 °C and 193 °C, the second weight loss region may be between temperatures of about 384 °C and 425 °C, the third weight loss region may be between temperatures of about 436 °C and 450 °C, and the fourth weight loss region may be between temperatures of about 511 °C and 575 °C. The temperatures of 124 °C, 384 °C, 436 °C, and 511 °C are referred to as onset temperatures (Ton), and may be denoted as T _on .i, T _on .2, T _on .3, and T _on .4, respectively.

[00156] As shown in FIG. 16, the TGA plot (solid line) of the printed part further indicates that the thermal decomposition of the printed part was completed at about 620 °C. The settlement of the TGA plot at about 76% suggests that the residue solid content is approximately about 76 wt.%.

[00157] As shown in FIG. 16, the first derivative of the TGA plot (dotted line) of the printed part reveals about four temperatures in which the fastest rate of mass loss occurred (Ta), which include the temperatures at about 163 °C, at about 418 °C, at about 438 °C, and at about 543 °C, and they may be denoted as Ta,i, Ta, 2, Ta, 3, and Ta, 4, respectively.

[00158] As shown in FIG. 16, one or more debinding temperatures may be derived therefrom to construe a multi-stage debinding profile. These temperatures include the Ta temperatures of about 163 °C, at about 438 °C, and at about 543 °C, and the temperature of about 620 °C where thermal decomposition of the printed part is complete.

[00159] As shown in the inset graph of FIG. 16, the second weight loss region, which may be between temperatures of about 384 °C and 425 °C, has an endset that is close to Ta, 3. Moreover, the third weight loss region that is between temperatures of about 436 °C and 450 °C may be regarded as a continuation of the second weight loss region. Hence, Ta, 2 was deemed excludable from the debinding profile.

[00160] Based on the graph of FIG. 16, the graph of FIG. 5 was derived therefrom. Accordingly, the graph of FIG. 5 had adopted the multi-stage debinding profile that includes the temperatures of about 163 °C, at about 438 °C, and at about 543 °C, and the temperature of about 620 °C. With this, a complete decomposition of the printed part during the debinding process, and retainment of the shape of the printed part, are ensured.

[00161] FIG. 17 illustrates a graph derived from a Fourier-transform infrared spectroscopy (FTIR) analysis of one or more printed parts, which were printed from different slurries. In particular, each slurry has different concentrations of the second constituent and/or different concentrations of the third constituent, whereby the second constituent is DISPERBYK-103 dispersant, and the third constituent is alumina-based sinterable particles.

[00162] Fourier-transform infrared spectroscopy (FTIR) allows for the assessment of surface characteristics of the particles of the third constituent before it was mixed with dispersant and after it was mixed with the dispersant. Measurements were made at wavenumbers ranging from about 400 cm ¹ to about 4000 cm ¹ . Preferably, the FTIR analysis was performed by using the Cary 600 Series FTIR spectrometer by Agilent Technologies, Inc.

[00163] Based on the graph of FIG. 17, the third constituent (sinterable particles) may exhibit new peaks after being mixed with the second constituent (dispersant).

[00164] As shown in FIG. 17, after mixing, there is a broad peak ranging from about 3250 cm to about 3750 cm ¹ , which corresponds to the presence of -OH group on the third constituent (sinterable particles) or second constituent (dispersant).

[00165] As shown in FIG. 17, after mixing, there are new peaks at about 1457 cm ¹ , at about 2869 cm ¹ , at about 2900 cm ¹ , and at about 2935 cm ¹ , which may be attributed to the CH bending and stretching vibration of the methyl solvent used in the second constituent (dispersant).

[00166] As shown in FIG. 17, after mixing, there is also a peak at about 1635 cm ¹ , which indicates an adsorption through Lewis acid sites. However, an increase in dispersant concentration may shift this peak to about 1643 cm ¹ .

[00167] As shown in FIG. 17, after mixing, there is also a peak at about 1731 cm ¹ , which is inferred to be associated with the carbonyl (C=O) stretching vibration of an aromatic compound aldehyde.

[00168] As shown in FIG. 17, after mixing, there is also a peak at about 1353 cm ¹ , which is inferred to be attributed to O-H bending vibration.

[00169] FIGS. 18 to 20 are illustrations or chemical reactions pertaining to the esterification of the second constituent, and its possible modes of adsorption with the third constituent. Preferably, the second constituent is a DISPERBYK-103 dispersant, and the third constituent is alumina-based sinterable particles.

[00170] According to the datasheet of DISPERBYK-103, it has phosphated polyester. It is known in the art that phosphated polyester is synthesised from a condensation reaction between a carboxylic acid having phosphate, and a polyol. For the presentation of the chemical reactions between DISPERBYK-103 dispersant as the second constituent and the third constituent, a chemical similar to DISPERBYK-103, namely phosphonobutane 1,2,4 tricarboxylic acid, was used as an example substitute to illustrate the esterification and adsorption modes of the DISPERBYK-103 dispersant onto the particle surfaces of the third constituent.

[00171] FIGS. 18 illustrates esterification that takes place between one end of the phosphonobutane 1,2,4 tricarboxylic acid having phosphate, and a polyol having the -OH group. The product from the esterification reaction is a phosphated polyester terminated with a carboxylic group on its other end, with water being liberated as a by-product.

[00172] FIGS. 19 illustrates a first example adsorption mode that may take place between the second constituent (phosphated polyester terminated with a carboxylic group, which mimicks DISPERBYK-103 dispersant) and the third constituent (alumina-based sinterable particles). Upon mixing, the surface -OH group of the third constituent may react and form a covalent ester linkage with the carboxylic end of the polyester, with a molecule of water being liberated as a by-product. Since the concentration of the second constituent is relatively low, it is unlikely that the amount of liberated water molecules is substantial enough to dilute the slurry and reduce its viscosity.

[00173] FIGS. 20 illustrates a second example adsorption mode that may take place between second constituent (phosphated polyester terminated with a carboxylic group, which mimicks DISPERBYK-103 dispersant) and the third constituent (alumina-based sinterable particles). The second example adsorption mode involves protonation of the C=O group to act as a Lewis base or formation of a Lewis acid at the -OH end of the third constituent.

EXAMPLES

[00174] Examples are provided below to illustrate the aspects and embodiments of the present invention. These examples are not intended in any way to limit the disclosed invention, which is limited only by the claims.

Example 1:

[00175] A final 3D product composed from alumina platelets was produced by the method of additive manufacturing provided by the invention. Preferably, the slurry prepared within the additive manufacturing method as provided by the invention was prepared according to the steps illustrated in FIGS. 2 and 3.

[00176] The slurry has a composition wherein the first constituent (photomonomer, HDD A) is present at a concentration ranging from about 35 - 45 vol.%, the second constituent (dispersant, DISPERBYK-103) is present at a concentration ranging from about 1 - 5 wt.%, the third constituent (sinterable particles, alumina platelets preferably RonaFlair®) is present at a concentration ranging from about 35 - 55 vol.%, and the fourth constituent (photoinitiator, BAPO) is present at a concentration ranging from about 0.3 - 1 wt.%.

[00177] Preferably, the second constituent is present at a concentration of about 2 wt.%, and the third constituent is present at a concentration of about 45 vol.%.

[00178] Preferably, the alumina platelets have a rated particle size of d50, or a particle size that is substantially less than about 10.5 pm. Preferably as well, the alumina platelets have a density of about 3.94 g/cm ³ .

[00179] FIG. 21 illustrates a magnified photograph of a printed part of Example 1 obtained by use of a scanning electron microscope. As shown, the use of alumina platelets as the third constituent enables a nature-inspired structure known as nacre to be substantially manufactured. Nacre has a highly aligned high aspect ratio of minerals bonded together by an organic material to produce a structure that is considered the toughest material in nature. The microstructure of the nacre may be similar to brick held in place by mortar. Due to the scrapping action of the recoating blade of the printing unit, this results in the printed parts having an organised microstructure. As shown in FIG. 21, aligned platelets are clearly observed in the SEM image. Moreover, areas of sintering are clearly seen in FIG. 21.

Example 2:

[00180] A final 3D product composed from alumina powder was produced by the method of additive manufacturing provided by the invention. Preferably, the slurry prepared within the additive manufacturing method as provided by the invention was prepared according to the steps illustrated in FIGS. 2 and 3.

[00181] Preferably, the slurry has a composition whereby the first constituent (photomonomer, HDDA ) is present at a concentration ranging from about 35 - 45 vol.%, the second constituent (dispersant, DISPERBYK-103) is present at a concentration ranging from about 1 - 5 wt.%, the third constituent (sinterable particles, alumina powder) is present at a concentration ranging from about 35 - 55 vol.%, and the fourth constituent (photoinitiator, BAPO) is present at a concentration ranging from about 0.3 - 1 wt.%.

[00182] Most preferably, the second constituent is present at a concentration of about 2 wt.%, and the third constituent is present at a concentration of about 45 vol.%.

[00183] Preferably, the alumina powder has a particle size that is substantially 500nm. Preferably as well, the alumina powder has a density of about 2.4 m ² /g. Preferably as well, the alumina powder has a purity of about 99.9%.

[00184] FIG. 22 is a photograph of an example 3D product printed using a slurry having a third constituent that is alumina powder. FIG. 23 is a magnified photograph of the said printed part obtained by the use of a scanning electron microscope.

[00185] The final 3D product of Example 2 shown in FIG. 22 indicates that products with one or more complex features and geometries, e.g., teeth, etc., may also be printed with the formulation. The microstructure of the final 3D product of Example 2, as shown in FIG. 23, suggests that the debinding and sintering profiles established from the evaluations above were adequate.

[00186] FIG. 24 is a photograph of the prepared slurry of Example 2, obtained by the use of a scanning electron microscope. As shown, there is no clear indication of particle agglomeration, which suggests the suspension is homogeneous.

Example 3:

[00187] A final 3D product composed from zirconia powder was produced by the method of additive manufacturing provided by the invention. Preferably, the slurry prepared within the additive manufacturing method as provided by the invention was prepared according to the steps illustrated in FIGS. 2 and 3.

[00188] Preferably, the slurry has a composition whereby the first constituent (photomonomer, HDDA) is present at a concentration ranging from about 35 - 45 vol.%, the second constituent (dispersant, DISPERBYK-103) is present at a concentration ranging from about 1 - 5 wt.%, the third constituent (sinterable particles, zirconia powder pref erably Alfa Aesar) is present at a concentration ranging from about 35 - 55 vol.%, and the fourth constituent (photoinitiator, BAPO) is present at a concentration ranging from about 0.3 - 1 wt.%.

[00189] Most preferably, the second constituent is present at a concentration of about 2 wt.%, and the third constituent is present at a concentration of about 45 vol.%.

[00190] FIG. 25 is a photograph of an example 3D product printed using a slurry having a third constituent that is zirconia powder. FIG. 26 is a magnified photograph of the said printed part obtained by use of a scanning electron microscope.

[00191] Preferably, the zirconia powder has a particle size that is substantially less than about 1 pm. Preferably as well, the zirconia powder has a purity of about 99.5%.

[00192] The final 3D product of Example 3 shown in FIG. 25 indicates that products such as dental implants may be printed with the formulation. Zirconia is a widely used ceramic with several key properties, such as superior toughness, strength, and fatigue resistance. When stress occurs on the surface, a crystalline modification opposes the propagation of cracks, hence improving its properties. The microstructure of the final 3D product of Example 2, as shown in FIG. 26, suggests that the debinding and sintering profiles established from the evaluations above were adequate.

Example 4:

[00193] A final 3D product composed from a silica-based biomaterial was produced by the method of additive manufacturing provided by the invention. In particular, a slurry was prepared according to the steps as illustrated in FIGS. 2 and 3. Examples of silica-based biomaterial may be sourced from natural silica or derived from biological organisms.

[00194] Preferably, the slurry has a composition whereby the first constituent (photomonomer, HDDA ) is present at a concentration ranging from about 35 - 45 vol.%, the second constituent (dispersant, DISPERBYK-103) is present at a concentration ranging from about 1 - 5 wt.%, the third constituent (sinterable particles, silica-based biomaterial in powderform) is present at a concentration ranging from about 35 - 55 vol.%, and the fourth constituent (photoinitiator, BAPO) is present at a concentration ranging from about 0.3 - 1 wt.%. [00195] Most preferably, the second constituent is present at a concentration of about 2 wt.%, and the third constituent is present at a concentration of about 45 vol.%.

[00196] Thus concludes the examples described.

[00197] With this, the details pertaining to the slurry for additive manufacturing, and the method of additive manufacturing, provided by the present invention, have been sufficiently described. The method of additive manufacturing has been shown to enable a final 3D product to be produced from a slurry with a solid loading up to about 55 vol.%, low viscosity of below or about 1 Pa-s, and a low sedimentation rate.

[00198] The present disclosure includes as contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the scope of the present invention.