Sludge slurry for direct ink writing and preparation method and application thereof

Abstract

The invention provides sludge slurry for direct ink writing (DIW) as well as a preparation method and application of the sludge slurry. According to the preparation method of the ceramic product, the sludge is firstly heated to obtain the sludge powder which is small in particle size and excellent in dispersity and meets the ceramic sintering requirement; then regulating and controlling the solid phase content or adding a composite additive of polyvinyl alcohol (PVA) and glycerol to prepare sludge slurry with rheological properties adaptive to the DIW process; and finally, printing and forming the sludge slurry by utilizing a DIW technology, and carrying out subsequent sintering to obtain pottery products. The method effectively solves the problems of low efficiency and high secondary pollution risk of traditional sludge treatment, realizes conversion of sludge into high-value products, has both environmental benefits and economic benefits, and provides a brand new technical path for resource utilization of sludge in waterworks.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment and additive manufacturing technology, and particularly relates to a sludge slurry for direct ink writing (DIW), its preparation method and application. Background Technology

[0002] With the acceleration of urbanization, the amount of sludge produced by waterworks is increasing year by year, and sludge treatment and resource utilization have become important challenges in the field of solid waste. Traditional sludge treatment technologies (such as landfill, composting, and incineration) have problems such as low efficiency, high risk of secondary pollution, and insufficient resource recovery rate, making it difficult to meet the needs of sustainable development. Therefore, exploring new, efficient, and environmentally friendly sludge treatment technologies is of urgent practical significance.

[0003] Direct Ink Writing (DIW) technology in additive manufacturing (3D printing) offers a new direction for the resource utilization of solid waste due to its advantages such as strong material adaptability, high process controllability, and significant cost-effectiveness. DIW technology uses a nozzle to deposit slurry layer by layer according to CAD model instructions. The core requirement is that the slurry must possess both good flowability (ensuring smooth extrusion) and early strength (ensuring stacking stability). Existing research has confirmed that industrial solid waste (such as red mud, fly ash, and waste garnet) can be used to prepare 3D printed building materials, but research on the application of waterworks sludge in the DIW field still has significant gaps.

[0004] Waterworks sludge is mainly composed of inorganic minerals such as clay and iron and aluminum oxides (primarily SiO2, Al2O3, and Fe2O3). After proper pretreatment, it can acquire properties similar to ceramic raw materials. However, there is currently no method for converting waterworks sludge into ceramic products using DIW (Distillation-Washing) technology. Summary of the Invention

[0005] This invention provides a sludge slurry for direct ink writing, its preparation method, and its application, in order to solve the defects of traditional sludge treatment and realize the transformation of sludge into high-value ceramic products.

[0006] The present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a sludge slurry for direct ink writing, comprising the following steps:

[0008] The sludge is heated and then ground to obtain sludge powder.

[0009] The sludge powder is added to water and stirred to obtain a sludge slurry; wherein the mass fraction of the sludge powder in the sludge slurry is 62-66%;

[0010] Alternatively, PVA can be added to water to obtain a PVA aqueous solution;

[0011] Add glycerol to the PVA aqueous solution and stir to obtain a mixture;

[0012] Add the sludge powder to the mixture and stir to obtain sludge slurry;

[0013] The PVA aqueous solution contains 5-12.5% ​​PVA by mass.

[0014] The mass ratio of the PVA aqueous solution to glycerol is (90~100):(1.5~2), and the mass fraction of sludge powder in the sludge slurry is 62~66%.

[0015] Preferably, the sludge is heated at 300~350℃ for 1~2 hours, then ground and passed through a 200~300 mesh sieve to obtain sludge powder.

[0016] Preferably, the sludge powder comprises the following phases by mass fraction: illite 45%~55%, chlorite 18%~23%, albite 8%~13%, and quartz 15%~20%.

[0017] Preferably, the sludge powder is added to water and stirred at a rate of 500-600 r / min for 6-10 min to obtain sludge slurry.

[0018] Preferably, PVA is added to water and stirred at 80-90 °C to obtain a PVA aqueous solution;

[0019] Add the sludge powder to the mixture and stir at a rate of 500-600 r / min for 5-10 min to obtain sludge slurry.

[0020] Secondly, the present invention also provides a sludge slurry for direct ink writing, which is prepared by the preparation method described above.

[0021] Thirdly, the present invention also provides a sludge slurry prepared by the preparation method described above, or the application of the sludge slurry in the preparation of ceramic products.

[0022] Fourthly, the present invention also provides a method for preparing a ceramic product, comprising the following steps:

[0023] The sludge slurry is loaded into the cartridge of a direct ink writing device and printed to obtain a sludge blank.

[0024] The sludge blanks are sintered to obtain ceramic products;

[0025] The sludge slurry is prepared by the preparation method described in any one of claims 1 to 5 or the sludge slurry described in claim 6.

[0026] Preferably, the printing parameters controlled when printing the sludge preform are as follows:

[0027] The printhead diameter of the direct ink writing device is 0.4~2.6 mm, the printing pressure is 0.1~0.5MPa, and the printhead movement speed is 5~20 mm / s.

[0028] Preferably, in the step of sintering the sludge blank, the sintering process parameters are as follows:

[0029] The sludge preform is heated from room temperature to 600-610 ℃ at a rate of 5-6 ℃ / min and held for 2-3 h. Then, it is heated to 1100-1200 ℃ at a rate of 3-4 ℃ / min and held for 3-4 h.

[0030] The preparation method and application of the sludge slurry for direct ink writing of the present invention have the following advantages compared with the prior art:

[0031] 1. The present invention provides a method for preparing sludge slurry for direct ink writing, wherein the sludge is first heated to obtain sludge powder with fine particle size, excellent dispersibility and meeting the requirements of ceramic sintering; then, by adjusting the solid content or adding a composite additive of polyvinyl alcohol (PVA) and glycerol, a sludge slurry with rheological properties adapted to the DIW process is prepared.

[0032] 2. The ceramic product preparation method of this invention transforms sludge into high-value pottery products, completely solving the secondary pollution problem caused by traditional landfill and incineration, and realizing the "reduction, harmlessness, and resource utilization" of sludge, which is in line with the concept of green and sustainable development. The raw material cost of sludge is extremely low, and additives such as PVA and glycerin are inexpensive. The energy consumption of the DIW process is lower than that of traditional ceramic forming processes. The pottery products prepared can be used in decoration, gardening, industrial auxiliary fields, etc., and have high market value, creating new profit growth points for sludge treatment companies. This invention is the first to use heat-treated waterworks sludge for DIW printing. Through the synergistic effect of solid content control and PVA-glycerin composite additives, the rheological properties of the slurry are precisely optimized, filling the application gap of sludge in the DIW field and providing a referable technical path for the resource utilization of similar solid wastes. The parameters of the entire process (pretreatment-slurry preparation-printing-sintering) are clear and the operation is simple. By adjusting the nozzle diameter, printing parameters and sintering temperature, products of different shapes and precisions can be prepared to meet diverse market demands. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the process for preparing the ceramic product of the present invention;

[0035] Figure 2 This is a schematic diagram illustrating the mechanism by which the PVA-glycerol composite additive of the present invention regulates the rheological properties of sludge slurry;

[0036] Figure 3 This is a graph showing the relationship between the viscosity of the PVA aqueous solution and the mass fraction of PVA in the PVA aqueous solution in Example 3.

[0037] Figure 4 Viscosity curves of the sludge slurry prepared in Example 2 and the sludge slurry prepared in Example 3 with PVA mass fractions of 5%, 7.5%, and 12.5% ​​in PVA aqueous solution, respectively;

[0038] Figure 5 The shear stress curves are those of the sludge slurry prepared in Example 2 and the sludge slurry prepared in Example 3 with PVA mass fractions of 5%, 7.5%, and 12.5% ​​in the PVA aqueous solution.

[0039] Figure 6 The image shown is a scanning electron microscope (SEM) image of the sludge powder obtained in step S1 of Example 2. Figure 6 a) and energy dispersive spectroscopy (EDS) analysis plot ( Figure 6 (b)

[0040] Figure 7 To obtain photographs of sludge blanks of different shapes by printing according to the method in Example 4;

[0041] Figure 8 To obtain photographs of ceramic products of different shapes by printing according to the method in Example 4;

[0042] Figure 9 The images show photos of sludge slurries prepared using only glycerol in Comparative Examples 1 and 2, and the sludge blanks and ceramic products printed using them. Detailed Implementation

[0043] To facilitate understanding of the present invention, a more comprehensive description of the invention will be provided below in conjunction with specific embodiments. Preferred embodiments of the invention are given in the specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0044] The order in which the embodiments are described below is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0045] The present invention provides a method for preparing sludge slurry for direct ink writing, employing two methods, which can be selected according to actual printing needs; wherein, the preparation method of scheme A includes the following steps:

[0046] S1. Heat the sludge and then grind it to obtain sludge powder;

[0047] S2. Add sludge powder to water and stir to obtain sludge slurry; wherein the mass fraction of sludge powder in the sludge slurry is 62~66%;

[0048] The preparation method of Scheme B includes the following steps:

[0049] S1. PVA is added to water to obtain a PVA aqueous solution;

[0050] S2. Add glycerol to the PVA aqueous solution and stir to obtain a mixture;

[0051] S3. Add sludge powder to the mixture and stir to obtain sludge slurry;

[0052] The PVA mass fraction in the PVA aqueous solution is 5-12.5%.

[0053] The mass ratio of PVA aqueous solution to glycerol is (90~100):(1.5~2), and the mass fraction of sludge powder in the sludge slurry is 62~66%.

[0054] For scheme A, sludge powder is directly added to water and stirred to obtain sludge slurry; when the mass fraction of sludge powder in the sludge slurry is 62% (i.e., when the solid content is 62wt%), the viscosity of the sludge slurry is 48. Pa·s, modulus of 1.65 × 10⁻⁶ Pa·s 5 Pa has good fluidity, but its shape stability after stacking is average; when the mass fraction of sludge powder in the sludge slurry is 66%, the viscosity of the sludge slurry is 49. Pa·s, modulus is 7.53 × 10⁻⁶. 5 Pa has excellent shape stability, but its fluidity is reduced. If the mass fraction of sludge powder in the sludge slurry exceeds 66%, the sludge slurry is prone to agglomeration, which can easily cause nozzle clogging or line breakage during printing. Therefore, the mass fraction of sludge powder in the sludge slurry should be controlled within the range of 62-66 wt%.

[0055] For scheme B, a sludge slurry is prepared using a PVA (polyvinyl alcohol)-glycerol (glycerol) composite additive; (Reference) Figure 2 As shown, PVA, as a polymeric binder, forms a three-dimensional network structure in the slurry through its long-chain molecules. This physically wraps around sludge particles, inhibiting particle sedimentation and improving slurry stability and viscosity. Glycerol molecules contain multiple hydroxyl groups (-OH), which can form a hydrogen bond network with the hydroxyl groups on the surface of sludge particles or PVA molecules, weakening the electrostatic repulsion between particles and improving slurry dispersibility and flowability. The two work synergistically to regulate the rheological properties of the sludge slurry. Experiments have shown that when the mass fraction of PVA in the PVA aqueous solution exceeds the range of 5~12.5 wt%, the viscosity of the sludge slurry will be too low or too high, making it difficult to maintain the shape or extrude normally during printing. When the concentration of PVA aqueous solution is 10 wt%, the viscosity of the slurry at stability (approximately 50 Pa·s) is the highest. At this point, the viscosity and shear stress reach the optimal balance, ensuring smooth extrusion from the nozzle and ensuring the shape stability of the printed lines. This is the optimal additive concentration.

[0056] In some embodiments, the sludge is heated at 300~350°C for 1~2 hours, then ground and passed through a 200~300 mesh sieve to obtain sludge powder.

[0057] In some embodiments, the sludge powder comprises the following phases by mass fraction: illite 45%~55%, chlorite 18%~23%, albite 8%~13%, and quartz 15%~20%.

[0058] In some embodiments, the dewatered sludge from the waterworks is crushed and placed in a muffle furnace for constant temperature heat treatment at 300~350℃ for 1~2 hours. During the heat treatment, the natural organic matter (such as humus) in the sludge is fully decomposed, while avoiding excessive sintering of inorganic minerals. After cooling, the heat-treated sludge is ground in a planetary ball mill for 30-60 minutes and passed through a 200-300 mesh standard sieve to obtain sludge powder. Heat treatment can effectively decompose organic pollutants in sludge, improve the crystallinity and dispersibility of powder, and the loss on ignition is ≤8.1%, which meets the requirements of ceramic sintering process. The sludge powder has the following characteristics: Particle size distribution: The proportion of particles with a diameter less than 0.074μm (by mass) reaches 88.06%, which belongs to ultrafine powder. The absolute value of the Zeta potential is about 77mV, and the dispersion performance in aqueous solution is excellent. Composition and phases: The main components are SiO2 (mass fraction 50.49%), Al2O3 (mass fraction 20.38%), and Fe2O3 (mass fraction 5.62%). The main phases are illite (mass fraction 50.61%), chlorite (mass fraction 20.65%), albite (mass fraction 10.83%), and quartz (mass fraction 17.91%).

[0059] In some embodiments, sludge powder is added to water and stirred at a rate of 500-600 r / min for 6-10 min to obtain sludge slurry.

[0060] In some embodiments, PVA is added to water and stirred at 80-90°C at a rate of 500-600 r / min for 1-2 h to obtain an aqueous PVA solution.

[0061] In some embodiments, glycerol is added to an aqueous PVA solution, and the mixture is stirred at 500-600 r / min for 5-30 min at 60-70°C to obtain a mixture.

[0062] In some embodiments, sludge powder is added to the mixture and stirred at a rate of 500-600 r / min for 5-10 min to obtain sludge slurry.

[0063] The present invention provides a method for preparing sludge slurry for direct ink writing. First, the sludge is heated to obtain sludge powder with fine particle size, excellent dispersibility and meeting the requirements of ceramic sintering. Then, by adjusting the solid content or adding a composite additive of polyvinyl alcohol (PVA) and glycerol, a sludge slurry with rheological properties adapted to the DIW process is prepared.

[0064] Based on the same inventive concept, the present invention also provides a sludge slurry for direct ink writing, which is prepared by the above-described preparation method.

[0065] Based on the same inventive concept, the present invention also provides a sludge slurry prepared by the above-described preparation method or the application of the above-described sludge slurry in the preparation of ceramic products.

[0066] Based on the same inventive concept, the present invention also provides a method for preparing a ceramic product, comprising the following steps:

[0067] S1. Load the sludge slurry into the cartridge of the direct ink writing device and print to obtain a sludge blank;

[0068] S2. Sinter the sludge blank to obtain ceramic products;

[0069] The sludge slurry is prepared by the above-mentioned preparation method.

[0070] The method for preparing ceramic products of the present invention involves loading prepared sludge slurry into the cartridge of a direct ink writing device, starting the device according to a preset CAD model (such as a decorative plate, a small flowerpot, etc.), adjusting the printing pressure and the nozzle movement speed, and depositing the sludge layer by layer along the path, so that the sludge slurry is deposited layer by layer on the printing platform until the entire blank is printed, and a sludge blank is obtained; the sludge blank is sintered and cooled to room temperature to obtain a ceramic product.

[0071] In some embodiments, the printing parameters controlled when printing the sludge preform are as follows:

[0072] The printhead diameter of the direct ink writing device is 0.4~2.6 mm, the printing pressure is 0.1~0.5 MPa, and the printhead movement speed is 5~20 mm / s.

[0073] In some embodiments, the sintering process parameters in the step of sintering the sludge blank are as follows:

[0074] The sludge preform is heated from room temperature (20~25℃) to 600~610℃ at a rate of 5~6℃ / min and held for 2~3 h. Then, it is heated to 1100~1200℃ at a rate of 3~4℃ / min and held for 3~4 h.

[0075] In some embodiments, the printed sludge blank is placed in a ventilated area to air dry naturally for 24 hours to remove surface moisture; then it is placed in a programmed temperature sintering furnace and sintered according to the following temperature program: room temperature → 600~610 ℃: heating rate 5~6 ℃ / min, holding for 2 hours, the purpose of which is to remove residual moisture and PVA in the blank (to avoid rapid decomposition of organic matter at high temperature, which would cause the blank to crack); 600~610 ℃ → 1100~1200 ℃: heating rate 3~4 ℃ / min, holding for 3~4 hours, so that the inorganic minerals in the blank are fully sintered to form a dense structure; 1100~1200 ℃ → room temperature: cooling with the furnace to avoid sudden temperature drop that would cause the blank to crack.

[0076] Performance indicators of sintered pottery products: Water absorption rate: 0.41%, which meets the water absorption rate requirements (≤0.5%) of "fine porcelain" in the "Method for Determination of Water Absorption Rate of Daily-use Ceramics" (GB / T 3299-2011); Shrinkage rate: 19.71%, with uniform volume shrinkage and no obvious deformation; Microstructure: SEM characterization shows that the internal pores of the product are evenly distributed, highly dense, and have excellent water resistance.

[0077] Further reference Figure 1 As shown, it illustrates the preparation method of ceramic products. After heat treatment of sludge at 300°C, sludge slurry is prepared. The sludge slurry is then printed using DIW technology to obtain sludge blanks, which are then fired to obtain ceramic products.

[0078] The ceramic products of this invention can be decorative plates, small flower pots, etc., and can be used in decoration, gardening, industrial auxiliary fields, etc., with high market value, creating new profit growth points for sludge treatment enterprises.

[0079] The method for preparing ceramic products according to this invention involves first heating sludge to obtain sludge powder with fine particle size, excellent dispersibility, and meeting the requirements for ceramic sintering; then, by adjusting the solid content or adding a composite additive of polyvinyl alcohol (PVA) and glycerol, a sludge slurry with rheological properties suitable for the DIW process is prepared; finally, the sludge slurry is printed into shape using DIW technology, and subsequently sintered to obtain ceramic products. This invention effectively solves the problems of low efficiency and high risk of secondary pollution in traditional sludge treatment, realizing the transformation of sludge into high-value products, combining environmental and economic benefits, and providing a new technical path for the resource utilization of sludge from waterworks.

[0080] The present invention has the following advantages:

[0081] Significant environmental benefits: This invention transforms sewage sludge from waterworks into high-value ceramic products, completely solving the secondary pollution problems caused by traditional landfilling and incineration, and realizing the "reduction, harmlessness, and resource utilization" of sewage sludge, which is in line with the concept of green and sustainable development.

[0082] Significant economic benefits: The raw material cost of sludge is extremely low, and additives such as PVA and glycerin are inexpensive. The energy consumption of the DIW process is lower than that of traditional ceramic forming processes. The pottery products produced can be used in decoration, gardening, industrial auxiliary fields, etc., and have high market value, creating new profit growth points for sludge treatment companies.

[0083] Highly innovative technology: For the first time, heat-treated waterworks sludge was used for DIW printing. By controlling the solid content and working synergistically with PVA-glycerol composite additives, the rheological properties of the slurry were precisely optimized, filling the gap in the application of sludge in the DIW field and providing a referable technical path for the resource utilization of similar solid wastes.

[0084] High process controllability: The parameters of the entire process (pretreatment-slurry preparation-printing-sintering) are clear and the operation is simple. By adjusting the nozzle diameter, printing parameters and sintering temperature, products of different shapes and precision can be prepared to meet diverse market demands.

[0085] The following specific embodiments further illustrate the sludge slurry for direct ink writing of the present invention, its preparation method, and its application. This section further illustrates the content of the present invention in conjunction with specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0086] In the following examples, the PVA specifically refers to polyvinyl alcohol 767382, Mw9000-10000, purchased from Maclean's Reagents.

[0087] Example 1

[0088] This embodiment provides a method for preparing sludge slurry for direct ink writing, including the following steps:

[0089] S1. After heating the sludge at 300℃ for 1 hour, grind it for 30 minutes and pass it through a 200-mesh sieve to obtain sludge powder. The sludge powder has the following characteristics: Particle size distribution: The proportion of particles with a diameter less than 0.074μm (by mass) reaches 88.06%, which belongs to ultrafine powder, and the absolute value of the Zeta potential is 77mV; Composition and phases: The main components are SiO2 (mass fraction 50.49%), Al2O3 (mass fraction 20.38%), and Fe2O3 (mass fraction 5.62%), and the main phases are illite (mass fraction 50.61%), chlorite (mass fraction 20.65%), albite (mass fraction 10.83%), and quartz (mass fraction 17.91%).

[0090] S2. Add sludge powder to water and stir at 500 r / min for 6 min to obtain sludge slurry; wherein, when the mass fraction of sludge powder in the sludge slurry is 62% (i.e., when the solid content is 62 wt%), the viscosity of the sludge slurry is 48 Pa·s and the modulus is 1.65 × 10⁻⁶. 5 Pa; When the mass fraction of sludge powder in the sludge slurry is 66%, the viscosity of the sludge slurry is 49 Pa·s, and the modulus is 7.53 × 10⁻⁶ Pa. 5 Pa.

[0091] Example 2

[0092] This embodiment provides a method for preparing sludge slurry for direct ink writing, including the following steps:

[0093] S1. After heating the sludge at 300℃ for 1 hour, grind it for 30 minutes and pass it through a 200-mesh sieve to obtain sludge powder. The sludge powder has the following characteristics: Particle size distribution: The proportion of particles with a diameter less than 0.074μm (by mass) reaches 88.06%, which belongs to ultrafine powder, and the absolute value of the Zeta potential is 77mV; Composition and phases: The main components are SiO2 (mass fraction 50.49%), Al2O3 (mass fraction 20.38%), and Fe2O3 (mass fraction 5.62%), and the main phases are illite (mass fraction 50.61%), chlorite (mass fraction 20.65%), albite (mass fraction 10.83%), and quartz (mass fraction 17.91%).

[0094] S2. Add PVA to water and stir at 80℃ and 500 r / min for 1 h to obtain a PVA aqueous solution; the mass fraction of PVA in the PVA aqueous solution is 10%.

[0095] S3. Add 1.5g of glycerol to 90g of PVA aqueous solution, and stir at 500r / min for 15min at 60℃ to obtain a mixture;

[0096] S4. Add 160g of sludge powder to the mixture and stir at 500r / min for 5min to obtain sludge slurry (the mass fraction of sludge powder in the sludge slurry is 63.4%).

[0097] Example 3

[0098] The method for preparing sludge slurry for direct ink writing provided in this embodiment is the same as that in embodiment 2, except that the mass fraction of PVA in the PVA aqueous solution in step S2 is adjusted to 0%, 5%, 7.5%, 12.5%, and 15%, respectively, while the remaining process parameters are the same as those in embodiment 2.

[0099] Figure 3The relationship between the viscosity of the PVA aqueous solution and the mass fraction of PVA in the PVA aqueous solution is shown in Example 3; from Figure 3 It can be seen that the viscosity of the PVA aqueous solution increases with the increase of the PVA mass fraction, and the growth is approximately exponential. Since the sludge slurry needs to have a certain viscosity and fluidity during printing, experimental research has found that the slurry with a PVA mass fraction in the PVA aqueous solution in the range of 5% to 12.5% ​​can meet the requirements of DIW printing.

[0100] Figure 4 Viscosity curves of the sludge slurry prepared in Example 2 (PVA aqueous solution with PVA mass fraction of 10%) and the sludge slurry prepared in Example 3 with PVA aqueous solutions of 5%, 7.5%, and 12.5% ​​respectively;

[0101] Figure 5 The shear stress curves are for the sludge slurry prepared in Example 2 (PVA aqueous solution with a PVA mass fraction of 10%) and the sludge slurry prepared in Example 3 with PVA aqueous solutions containing PVA mass fractions of 5%, 7.5%, and 12.5%, respectively.

[0102] Figures 4-5 5wt% PVA, 7.5wt% PVA, and 12.5wt% PVA represent the sludge slurry prepared in Example 3 with PVA mass fractions of 5%, 7.5%, and 12.5% ​​in the PVA aqueous solution, respectively; 10wt% PVA represents the sludge slurry prepared in Example 2 with PVA mass fraction of 10% in the PVA aqueous solution.

[0103] Shear rate-viscosity and shear stress curves of sludge slurry with different PVA contents are shown in Figures 4 and 5. The results show that the slurry viscosity gradually decreases with increasing shear rate, exhibiting a significant shear thinning phenomenon, which meets the requirements of the DIW printing process. Figure 4Meanwhile, the viscosity and shear stress of the slurry initially increased and then decreased with increasing binder mass fraction. The viscosity of the slurry with 10 wt% PVA addition was the highest at stability (approximately 50 Pa·s). This is because PVA molecules disperse in the slurry to form a network structure, effectively reducing system viscosity and improving flowability and printability. Furthermore, the introduction of PVA significantly enhances the stability of the slurry by inhibiting particle sedimentation and agglomeration, ensuring uniformity during storage and use, making it more suitable for DIW printing technology. Experiments showed that when the PVA content exceeded the range of 5–12.5 wt%, the slurry viscosity was either too low or too high, making it difficult to maintain the shape or extrude normally during printing. The slurry with 10 wt% exhibited the best overall performance in terms of viscosity and shear stress, hence this addition amount was selected for subsequent experiments. The amount of PVA aqueous solution added needs to balance the slurry printing performance and the final performance of the sintered ceramic, achieving process optimization and product quality improvement through a balance between the two.

[0104] Figure 6 The image shown is a scanning electron microscope (SEM) image of the sludge powder obtained in step S1 of Example 2. Figure 6 a) and energy dispersive spectroscopy (EDS) analysis plot ( Figure 6 (b)

[0105] from Figure 6 As can be seen from the scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses, the microstructure, elemental composition, and mineral phase characteristics of the sludge powder are highly consistent. SEM images show that the sample exhibits a sheet-like, multi-layered stacked structure, while EDS analysis indicates that O, Al, and Si elements constitute the highest proportions. The SEM-EDS analysis results corroborate the phase analysis results of the sludge powder, providing important experimental support for the application of sludge in 3D printing.

[0106] Example 4

[0107] This embodiment provides a method for preparing a ceramic product, including the following steps:

[0108] S1. Sludge slurry was prepared according to the method in Example 2. The sludge slurry was loaded into the barrel of a direct ink writing device and printed to obtain a sludge blank (specifically a decorative disc blank). The printing parameters controlled when printing the sludge blank were: the nozzle diameter of the direct ink writing device was 2.0 mm, the printing pressure was 0.25 MPa, the nozzle moving speed was 12 mm / s, the layer thickness was 0.25 mm, and a decorative disc blank with a diameter of 15 cm was printed.

[0109] S2. The sludge blank is naturally dried at room temperature (25 ℃) for 24 h, then heated from room temperature to 600 ℃ at a rate of 5 ℃ / min, held for 2 h, then heated to 1150 ℃ at a rate of 3 ℃ / min, held for 3 h, and cooled to obtain the ceramic product (specifically a decorative plate).

[0110] The ceramic product prepared in Example 4 has a water absorption rate of 0.38%, a shrinkage rate of 19.5%, a smooth surface, and no cracks or deformation.

[0111] Example 5

[0112] This embodiment provides a method for preparing a ceramic product, including the following steps:

[0113] S1. Sludge powder was prepared according to the method in Example 1;

[0114] S2. Add 160 g of sludge powder to 90 g of water and stir at 500 r / min for 6 min to obtain sludge slurry (the mass fraction of sludge powder in the sludge slurry is 64%).

[0115] S3. Load the sludge slurry into the cartridge of the direct ink writing device and print to obtain a sludge blank (specifically a small flower pot blank); the printing parameters controlled when printing the sludge blank are: the nozzle diameter of the direct ink writing device is 1.0mm, the printing pressure is 0.35MPa, the nozzle moving speed is 8mm / s, the layer thickness is 0.3mm, and a small flower pot blank with a height of 8cm is printed;

[0116] S2. The sludge blank is naturally dried at room temperature (25 ℃) for 24 h, then heated from room temperature to 600 ℃ at a rate of 5 ℃ / min, held for 2 h, then heated to 1100 ℃ at a rate of 3 ℃ / min, held for 3 h, and cooled to obtain the ceramic product (specifically a small flower pot).

[0117] The ceramic product prepared in Example 5 has a water absorption rate of 0.40%, a shrinkage rate of 19.8%, and good mechanical properties, and can withstand a weight of 5 kg without breaking.

[0118] Following the method described in Example 4, sludge blanks of different shapes were obtained by printing using nozzles of different diameters, as shown in the photographs below. Figure 7 As shown in Figures a, b, c, and d, where a is a sludge blank printed using a nozzle with a diameter of 2.6 mm, b is a sludge blank printed using a nozzle with a diameter of 2.3 mm, c is a sludge blank printed using a nozzle with a diameter of 2.0 mm, and d is a sludge blank printed using a nozzle with a diameter of 1.7 mm.

[0119] In slurry extrusion printing, the nozzle diameter is a key parameter for controlling the quality of printed lines and the precision of the forming. For example... Figure 7 As shown, the printing effect of sludge slurry with a solid content of 64 wt% is best when the nozzle diameter is 2.0 mm, with continuous and uniform lines, smooth surface and no obvious deformation. The 2.0 mm diameter nozzle can achieve the best forming accuracy and line uniformity while ensuring the fluidity of the slurry, and ensure the structural stability and surface smoothness of the preform.

[0120] Following the method described in Example 4, ceramic products of different shapes were printed, as shown in the photographs below. Figure 8 As shown in Figures a, b, c, d, e, and f. Compared to other 3D printing methods, the core advantage of direct-write printing technology lies in its ability to dynamically adjust the properties of the printing paste, thereby optimizing the quality of printed parts and achieving integrated molding of complex structures. Figure 8 The paper showcases various complex-shaped components fabricated by direct-write printing. The paper presents the green and sintered parts of a cube and a vase, respectively. The forming results demonstrate that direct-write printing technology can accurately form from regular geometric shapes (such as cubes) to irregular structures (such as vases), verifying its compatibility with complex models.

[0121] Comparative Example 1

[0122] This comparative example provides a method for preparing a ceramic product, including the following steps:

[0123] S1. Add 1.5g of glycerol to 90g of water and stir at 500r / min for 15min at 60℃ to obtain a mixture; add 160g of sludge powder (prepared in the same way as in Example 1) to the mixture and stir at 500r / min for 5min to obtain sludge slurry;

[0124] S2. Load the sludge slurry into the barrel of the direct ink writing device and print it to obtain a sludge blank. The printing parameters controlled when printing the sludge blank are: the nozzle diameter of the direct ink writing device is 2.0 mm, the printing pressure is 0.25 MPa, the nozzle moving speed is 12 mm / s, and the layer thickness is 0.25 mm.

[0125] S3. The sludge blank is naturally dried at room temperature (25 ℃) for 24 h, then heated from room temperature to 600 ℃ at a rate of 5 ℃ / min, held for 2 h, then heated to 1150 ℃ at a rate of 3 ℃ / min, held for 3 h, and cooled to obtain the ceramic product.

[0126] Comparative Example 2

[0127] This comparative example provides a method for preparing a ceramic product, including the following steps:

[0128] S1. Add 15g of glycerol to 90g of water and stir at 500r / min for 15min at 60℃ to obtain a mixture; add 160g of sludge powder (prepared in the same way as in Example 1) to the mixture and stir at 500r / min for 5min to obtain sludge slurry.

[0129] S2. Load the sludge slurry into the barrel of the direct ink writing device and print it to obtain a sludge blank. The printing parameters controlled when printing the sludge blank are: the nozzle diameter of the direct ink writing device is 2.0 mm, the printing pressure is 0.25 MPa, the nozzle moving speed is 12 mm / s, and the layer thickness is 0.25 mm.

[0130] S3. The sludge blank is naturally dried at room temperature (25 ℃) for 24 h, then heated from room temperature to 600 ℃ at a rate of 5 ℃ / min, held for 2 h, then heated to 1150 ℃ at a rate of 3 ℃ / min, held for 3 h, and cooled to obtain the ceramic product.

[0131] Figure 9 To prepare sludge slurry using only glycerin (without glycerol) in Comparative Examples 1 and 2, and to use it to print ceramic products; specifically, Figure 9 In Comparative Example 1, a represents the sludge blank obtained by printing, and c represents the final ceramic product prepared in Comparative Example 1. Figure 9 In Comparative Example 2, b represents the sludge blank obtained by printing, and d represents the final ceramic product prepared in Comparative Example 2.

[0132] Figure 9 Experiments have shown that products printed using only glycerin in 3D printing are prone to deformation and cracking, as glycerin has a small molecular weight and poor adhesion.

[0133] It is understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0134] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method for preparing sludge slurry for direct ink writing, characterized in that, Includes the following steps: The sludge is heated and then ground to obtain sludge powder. The sludge powder is added to water and stirred to obtain a sludge slurry; wherein the mass fraction of the sludge powder in the sludge slurry is 62-66%; Alternatively, PVA can be added to water to obtain a PVA aqueous solution; Add glycerol to the PVA aqueous solution and stir to obtain a mixture; Add the sludge powder to the mixture and stir to obtain sludge slurry; The PVA aqueous solution contains 5-12.5% ​​PVA by mass. The mass ratio of the PVA aqueous solution to glycerol is (90~100):(1.5~2), and the mass fraction of sludge powder in the sludge slurry is 62~66%.

2. The method for preparing sludge slurry for direct ink writing as described in claim 1, characterized in that, The sludge is heated at 300-350℃ for 1-2 hours, then ground and passed through a 200-300 mesh sieve to obtain sludge powder.

3. The method for preparing sludge slurry for direct ink writing as described in claim 1, characterized in that, The sludge powder comprises the following phases by mass fraction: illite 45%~55%, chlorite 18%~23%, albite 8%~13%, and quartz 15%~20%.

4. The method for preparing sludge slurry for direct ink writing as described in claim 1, characterized in that, The sludge powder is added to water and stirred at a rate of 500-600 r / min for 6-10 min to obtain sludge slurry.

5. The method for preparing sludge slurry for direct ink writing as described in claim 1, characterized in that, PVA is added to water and stirred at 80-90℃ to obtain a PVA aqueous solution; Add the sludge powder to the mixture and stir at a rate of 500-600 r / min for 5-10 min to obtain sludge slurry.

6. A sludge paste for direct ink writing, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 5.

7. The application of the sludge slurry prepared by any one of claims 1 to 5 or the sludge slurry of claim 6 in the preparation of ceramic products.

8. A method for preparing a ceramic product, characterized in that, Includes the following steps: The sludge slurry is loaded into the cartridge of a direct ink writing device and printed to obtain a sludge blank. The sludge blanks are sintered to obtain ceramic products; The sludge slurry is prepared by the preparation method described in any one of claims 1 to 5 or the sludge slurry described in claim 6.

9. The method for preparing the ceramic product as described in claim 8, characterized in that, The printing parameters controlled when printing the sludge preform are as follows: The printhead diameter of the direct ink writing device is 0.4~2.6 mm, the printing pressure is 0.1~0.5 MPa, and the printhead movement speed is 5~20 mm / s.

10. The method for preparing the ceramic product as described in claim 8, characterized in that, In the step of sintering the sludge blank, the sintering process parameters are as follows: The sludge preform is heated from room temperature to 600-610 ℃ at a rate of 5-6 ℃ / min and held for 2-3 h. Then, it is heated to 1100-1200 ℃ at a rate of 3-4 ℃ / min and held for 3-4 h.

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