Slurry dispersant for zinc oxide varistor powder granulation, preparation method and application thereof

Abstract

The application relates to the technical field of pressure-sensitive resistance dispersants, and discloses a slurry dispersant for zinc oxide pressure-sensitive resistance powder granulation, a preparation method and application, the dispersant is prepared from specific proportions of an ammonium polyacrylate aqueous solution, polyethylene glycol, triethanolamine, ammonium bicarbonate, sodium carboxymethyl cellulose, a polydimethylsiloxane and polyethylene oxide-polypropylene oxide block copolymer, an isothiazolinone compound and deionized water, and the preparation process comprises the following steps: constant-temperature stirring of the ammonium polyacrylate, the polyethylene glycol and the deionized water to obtain a macromolecular liquid; separately preparing a complex premix solution of the triethanolamine and the ammonium bicarbonate; then adding the sodium carboxymethyl cellulose under high-speed stirring to build a rheological network; finally, introducing an additive compound and filtering impurities. The application utilizes double coordination and a rheological support network to synergistically inhibit microgelation of high-solid-content slurry, and through a full-organic ash-free pyrolysis degassing design, the application improves the leakage current and nonlinear characteristics of a pressure-sensitive ceramic device.

Description

Technical Field

[0001] This invention relates to the field of varistor dispersant technology, specifically to a slurry dispersant for granulation of zinc oxide varistor powder, its preparation method, and its application. Background Technology

[0002] As a core overvoltage protection element, the electrical performance of zinc oxide varistors is highly dependent on the uniform distribution of multi-component oxides on the micro-grain boundaries. In the manufacturing process of varistors, zinc oxide as the main material needs to be mixed with various additives to prepare a water-based slurry with high solid content for spray granulation.

[0003] However, during the grinding, long-term storage, and transportation of the slurry, the multi-component inorganic phases such as bismuth and antimony undergo trace hydrolysis, releasing high-valence heavy metal free cations into the aqueous medium. The long anionic chains dissociated from conventional polymer dispersants in water undergo coordination bridging reactions with these free high-valence cations. This physical cross-linking destroys the original electrostatic repulsion layer of the dispersant, causing the dispersed inorganic particles to flocculate and agglomerate, leading to microgelation, which increases the apparent viscosity of the slurry. Microgelation deteriorates the rheological properties of the slurry, affects the uniformity of spray granulation, and results in uneven distribution of components inside the green body of the varistor.

[0004] On the other hand, alkali metal salt dispersants such as sodium polyacrylate, which are widely used in industry, are difficult to completely remove through oxidation during the high-temperature debinding stage of the varistor green body. The remaining alkali metal elements will form solid ash at the ceramic grain boundaries. The introduction of such donor impurities will interfere with the grain boundary barrier of the ceramic, causing the leakage current of the varistor device to increase and the nonlinear characteristics to deteriorate. Therefore, the industry urgently needs a dispersion system that can maintain the rheological stability of multi-component high solids content slurry and achieve no impurity residue in the debinding stage. Summary of the Invention

[0005] The purpose of this invention is to provide a slurry dispersant for granulation of zinc oxide varistors, its preparation method, and its application. This invention solves the problems of microgelation caused by the leaching and cross-linking of heavy metal ions in existing high-solids-content varistors granulation slurries during storage and circulation, and the degradation of the electrical performance of devices due to residual solid ash after debinding of conventional alkali metal dispersants.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, a slurry dispersant for granulating zinc oxide varistor powder comprises the following raw materials in parts by weight: 30 to 50 parts of an aqueous solution of ammonium polyacrylate on a dry basis, 10 to 20 parts of polyethylene glycol, 5 to 15 parts of triethanolamine, 1.5 to 4.0 parts of ammonium bicarbonate, 2 to 8 parts of sodium carboxymethyl cellulose, 0.1 to 0.5 parts of a block copolymer of polydimethylsiloxane and polyethylene oxide-polypropylene oxide, 0.05 to 0.2 parts of a compound of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, and 30 to 50.6 parts of deionized water.

[0008] By adopting the above technical solution, the rheological dispersion main structure is constructed by using ammonium polyacrylate aqueous solution, polyethylene glycol and sodium carboxymethyl cellulose, a dual coordination blocking system is formed by triethanolamine and ammonium bicarbonate, and ammonium bicarbonate is used as a pyrolysis agent. Therefore, the effects of inhibiting microgelation of the slurry system, extending the storage stability of high solids slurry, and ensuring the electrical insulation of ceramic grain boundaries are achieved.

[0009] The specific mechanism of action of this dispersant is explained as follows:

[0010] In terms of constructing spatial and electrostatic stable networks, ammonium polyacrylate dissociates in the aqueous phase to generate long polymeric multi-anionic chains, which are directionally adsorbed onto the surface of zinc oxide and other oxide powders to generate electrostatic repulsion.

[0011] Meanwhile, polyethylene glycol and sodium carboxymethyl cellulose associate with each other through intermolecular hydrogen bonding in the liquid medium to establish a three-dimensional network structure. This rheological network can generate yield stress at low shear rates, providing physical support for high-density oxide particles to resist vertical sedimentation driven by gravity. To address the microgelation problem caused by free ions, this scheme utilizes triethanolamine and ammonium bicarbonate to form a coordination buffer environment in the liquid medium.

[0012] The nitrogen and hydroxyl oxygen atoms contained in the triethanolamine molecule form polydentate coordination complexes with the dissolved heavy metal free cations, directly reducing the absolute concentration of free ions in the liquid phase. On this basis, the ammonium ions provided by the dissociation of ammonium bicarbonate occupy the exposed carboxyl group sites around the long chain of ammonium polyacrylate, forming an electrostatic shielding region. The above-mentioned coordination and shielding synergistic mechanism cuts off the path of physical bridging reactions between heavy metal cations and different polymer chains, fundamentally preventing the formation of flocculated clusters inside the system.

[0013] During the aerobic debinding stage when the varistor green body is fed into the high-temperature kiln, the ammonium bicarbonate in the system undergoes a decomposition reaction upon heating. The gas molecules generated in situ produce outward expansion tension in the micro-nano-scale powder pores inside the green body, causing the polymer coating layer to physically break down, thereby increasing the internal interconnected porosity.

[0014] The opening of this microstructure accelerates the rate of oxygen diffusion inward, prompting the fully oxidized organic dispersant components composed of carbon, hydrogen, oxygen, and nitrogen atoms to be converted into gaseous products and removed from the system, thus avoiding the retention of solid ash at the grain boundary.

[0015] Preferably, the weight ratio of the ammonium polyacrylate aqueous solution to the polyethylene glycol on a dry basis is 2.5 to 3.0; the weight ratio of triethanolamine to ammonium bicarbonate is 3.33 to 4.0.

[0016] By adopting the above technical solution, limiting the ratio of the backbone polymer to the hydrogen bonding network agent can maintain an efficient mechanical balance between steric hindrance and electrostatic repulsion within the dispersed phase. The limitation of the ratio of the dual coordination system ensures that the liquid phase has a suitable slightly alkaline buffer environment and maintains a sufficient number of complexation reaction sites, thus ensuring the actual capture rate of free ions.

[0017] Preferably, in the complex of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, the mass ratio of the two is 3:1; and in the aqueous solution of the ammonium polyacrylate, the weight-average molecular weight of the ammonium polyacrylate ranges from 3050 to 4950.

[0018] By adopting the above technical solution, the weight-average molecular weight is controlled within the above range, so that the polyammonium acrylate molecular chain exhibits a moderately extended conformation in the liquid phase, which meets the chain segment length requirements for encapsulating micron-sized inorganic powders, while avoiding the polymer chain segment self-entanglement and thickening phenomenon caused by exceeding the molecular weight threshold.

[0019] Preferably, the ammonium polyacrylate aqueous solution is a polymer aqueous solution obtained by polymerizing acrylic monomers under the initiation of ammonium persulfate and then neutralizing with ammonia; the pH value of the ammonium polyacrylate aqueous solution is 7.0 to 7.5.

[0020] Secondly, the present invention provides a method for preparing a slurry dispersant for granulating zinc oxide varistor powder, comprising the following steps:

[0021] S1. Preparation of macromolecular mixture: Mix ammonium polyacrylate aqueous solution, polyethylene glycol and part of deionized water, and stir continuously in a constant temperature water bath until the system is transparent or semi-transparent and homogeneous to obtain macromolecular mixture A.

[0022] S2. Preparation of complexing premix: In a separate mixing tank, the remaining deionized water and triethanolamine are mixed evenly, and then ammonium bicarbonate is added. The mixture is stirred at room temperature to carry out complexation and dissolution, thus obtaining the alcoholamine-ammonium bicarbonate complexing premix.

[0023] S3. Dropping and Ion Pulse Interception: Under constant temperature and stirring conditions, the alcoholamine-ammonium bicarbonate complex premixed solution obtained in step S2 is added dropwise to the macromolecular mixture A in step S1 at a uniform rate. After the dropwise addition is completed, the mixture is kept warm and stirred to obtain mixed solution B.

[0024] S4. Thixotropic network construction: Under high-speed stirring, sodium carboxymethyl cellulose is added to the mixed solution B in step S3. After the addition is completed, high-speed stirring is maintained to fully detangle and construct a rheotropic network, resulting in mixed solution C.

[0025] S5. Additive compounding and impurity removal: Add the block copolymer of polydimethylsiloxane and polyethylene oxide-polypropylene oxide, as well as the compound of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, to the mixed solution C. Reduce the speed and mix. Then remove undissolved impurities through a filter screen and collect the filtrate to obtain the finished dispersant.

[0026] By adopting the above technical solution, and through a multi-stage assembly and pre-complexation liquid preparation process, a highly homogeneous dispersant fluid with stable physicochemical structure and no antagonistic phase separation effect among its components is obtained. The assembly mechanism of this preparation method is explained as follows:

[0027] In the early stage of macromolecular dewinding, isothermal heating combined with mechanical shearing breaks the disordered hydrogen bonds in the polyammonium acrylate and polyethylene glycol system, allowing the long carbon backbone of the polymer to fully extend in the aqueous solvent to expand the anchoring space of subsequent ions. To prevent the direct introduction of salt substances into the main system and the occurrence of local salting out, this scheme premixes triethanolamine and ammonium bicarbonate in an independent solvent environment to form a precursor liquid with weak chemical bond association.

[0028] During the system mixing and assembly, the precursor liquid is introduced into the macromolecular dispersion by uniformly dripping it, allowing the ammonium ions and triethanolamine molecules in the precursor liquid to gradually diffuse and adhere to the periphery of the unfolded polymer chains, completing the spatial anchoring of the anti-gelling coordination sites. After the main structure stabilizes, the newly added sodium carboxymethyl cellulose molecular chains are forced to interpenetrate between the macromolecular backbone by applying external high shear mechanical force, relying on the intermolecular secondary bond interaction to establish an anti-physical sedimentation elastic network. In the final stage, block copolymers are introduced to change the liquid-gas interfacial tension and expel the tiny air bubbles entrained in the previous reaction stirring process, thereby ensuring the compactness of the finished liquid.

[0029] Preferably, in S1, the temperature of the constant temperature water bath is controlled at 40 to 50°C, the stirring speed is 300 to 500 rpm, and the stirring time is 30 to 60 minutes; in S2, the system temperature is controlled at 20 to 25°C, the stirring speed is 150 to 250 rpm, and the stirring time is 10 to 15 minutes.

[0030] By adopting the above technical solution, the thermodynamic activation energy required for the dissolution of macromolecules is maintained and excessive water evaporation is avoided, while ensuring that small molecule ligands reach their maximum solubility at room temperature.

[0031] Preferably, in S3, the stirring speed of the macromolecular mixture A is adjusted to 500 to 600 rpm, the dropping flow rate of the alkanolamine-ammonium bicarbonate complex premix is ​​controlled at 1.0 to 2.0 ml / min, the system temperature is maintained at 40 to 50°C throughout the dropping process, the stirring time after the dropping is completed is 20 to 30 minutes, and the pH value of the system at the reaction endpoint is controlled at 8.5 to 9.5.

[0032] By adopting the above technical solution, limiting the dripping flow rate can prevent the contraction and aggregation of macromolecular chains caused by instantaneous local ion concentration differences, lock the endpoint pH in the slightly alkaline range, and ensure that the long polyacrylic acid chains are in a fully dissociated working state.

[0033] Preferably, in step S4, the stirring speed is controlled at 600 to 800 rpm, the addition time of sodium carboxymethyl cellulose is controlled within 2 to 5 minutes, and the stirring time after the addition is completed is 60 to 90 minutes.

[0034] By adopting the above technical solution, a high shear field is used to provide mechanical kinetic energy for uncoiling long-chain cellulose materials, and the stirring time is increased to promote the rheological network to reach the final relaxation equilibrium state.

[0035] Preferably, in step S5, the mixing speed is adjusted to 200 to 300 rpm, the mixing time is 15 to 20 minutes, and the filter screen is a 200-mesh stainless steel filter screen.

[0036] By adopting the above technical solution, the rotation speed is reduced to prevent molecular chain breakage caused by excessive shearing and secondary bubble entrainment, and undispersed micro hard micelle particles are filtered out using a specific pore size.

[0037] Thirdly, the present invention provides an application of a slurry dispersant for granulating zinc oxide varistor powder, which adopts the following technical solution: the application of the zinc oxide varistor powder granulation slurry dispersant as described above in the preparation of a varistor granulation precursor slurry or varistor ceramic powder composition for suppressing microscopic solid-liquid phase separation.

[0038] By adopting the above technical solution, the dispersant intervenes in the interfacial activity of multiple metal oxides, thereby suppressing the free recombination of modified elements such as bismuth and antimony during the grinding and storage period. This ensures that the distribution of grain boundary elements in the spray granulation droplets tends to be uniform, which helps to improve the nonlinear coefficient of the final sintered ceramic body of the varistor and reduce leakage current.

[0039] In summary, the present invention has at least one of the following beneficial technical effects:

[0040] 1. This invention establishes a rheological network combining electrostatic repulsion and hydrogen bonding in an aqueous medium by compounding ammonium polyacrylate, polyethylene glycol, and sodium carboxymethyl cellulose. This network structure can generate yield stress under low shear conditions, providing physical support for high-density particles of zinc oxide and other modified oxides, inhibiting the sedimentation of inorganic particles under the influence of gravity, and maintaining the dispersion uniformity of high-solids granulated slurry during long-term storage and pipeline transportation.

[0041] 2. This invention solves the microgelation problem that can occur in multi-component slurries by introducing a dual coordination buffer system consisting of triethanolamine and ammonium bicarbonate. Triethanolamine can complex with heavy metal cations such as bismuth and antimony that are dissolved by hydrolysis, reducing the absolute concentration of free ions in the liquid phase. At the same time, the ammonium ions dissociated from ammonium bicarbonate preferentially occupy the carboxylate active sites of the polymer long chain to form an electrostatic shield. The two work together to cut off the physical cross-linking path between heavy metal cations and dispersant polymer segments, avoiding the increase in apparent viscosity of the slurry due to particle flocculation.

[0042] 3. The dispersant of this invention uses all organic components and utilizes ammonium bicarbonate as a pyrolysis agent to improve the electrical properties of the final sintered ceramic body. During the debinding stage of the varistor green body, ammonium bicarbonate is heated and decomposes to generate gas, which forms expansion tension in the micropores of the powder, causing the polymer coating layer to physically break apart. This reaction process increases the interconnected porosity inside the green body and accelerates the rate of oxygen diffusion inward, promoting the complete oxidation and volatilization of the dispersant components, avoiding solid phase ash defects such as residual alkali metals at the grain boundary, thereby reducing the leakage current of the varistor device and ensuring its nonlinear characteristics. Attached Figure Description

[0043] Figure 1 The above are comprehensive data graphs for verifying the anti-microgelation mechanism of the present invention. In the graph (a), dynamic viscosity fluctuation comparison curves during the drop addition process are shown, and in the graph (b), dry redistribution bar chart of microgel filter residue is shown.

[0044] Figure 2 The figure shows the characteristic curves used to verify the dispersion stability and heavy metal chelation mechanism of the present invention. Figure (a) is a biaxial distribution of Zeta potential and free heavy metal cation concentration, and Figure (b) is the dynamic evolution curve of the stability index during static placement.

[0045] Figure 3 The following are characteristic data diagrams for verifying the pyrolysis in-situ gas generation micro-explosion mechanism of the present invention. Among them, Figure (a) is the dynamic evolution curve of thermogravimetric-mass spectrometry during the programmed temperature rise process, and Figure (b) is the Hausner ratio distribution bar chart of the granulated powder.

[0046] Figure 4Figure 1 shows a comparison of the rheological and thixotropic properties of the slurry of the present invention. Figure 2(a) is a bar chart of the apparent viscosity distribution at high and low shear rates, and Figure 3(b) is a biaxial correlation distribution of the thixotropic ring area and the thixotropic index.

[0047] Figure 5 Figure 1 shows the comprehensive test results of the mechanical response of the granulated powder and the nonlinear electrical characteristics of the varistor ceramic of the present invention. Figure 2 shows the biaxial correlation distribution of the fracture strength of a single particle of granulated powder and the relative density of the final ceramic. Figure 3 shows the voltage and current density response curves of the varistor ceramic sample.

[0048] Figure 6 Figure 1 shows the macroscopic characteristics of the varistor ceramic of the present invention in terms of resistance to high current surge and accelerated aging stability. Figure 2 shows the dual Y-axis distribution of the critical surge current density and breakdown voltage degradation amplitude of the ceramic sample. Figure 3 shows the dynamic evolution curve of leakage current under high temperature bias aging. Detailed Implementation

[0049] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0050] Acrylic acid, CAS No. 79-10-7, purity greater than or equal to 99.0%, is a monomer used to synthesize the main dispersant, ammonium polyacrylate.

[0051] Ammonium persulfate, CAS No. 7727-54-0, with a purity of ≥98.0%, is used as an initiator for polymerization reactions.

[0052] Ammonia water, CAS No. 1336-21-6, with a mass concentration of 20% to 25%, is used for neutralization and salt formation reactions after polymerization.

[0053] Polyethylene glycol, a high molecular weight polymer, CAS No. 25322-68-3, with a weight-average molecular weight of 2000 to 4000 and a polydispersity index of 1.05 to 1.15.

[0054] Triethanolamine, CAS No. 102-71-6, purity greater than or equal to 99.0%.

[0055] Ammonium bicarbonate, CAS No. 1066-33-7, purity greater than or equal to 99.0%.

[0056] Sodium carboxymethyl cellulose, a high molecular weight polymer, CAS No. 9004-32-4, with a degree of substitution of 0.7 to 0.9, has a viscosity of 300 to 800 mPa·s in a 2% aqueous solution at 25°C.

[0057] A block copolymer of polydimethylsiloxane and polyethylene oxide-polypropylene oxide, a high molecular weight polymer, CAS No. 68937-55-3, with an active ingredient content of ≥99.0%.

[0058] 5-Chloro-2-methyl-4-isothiazolin-3-one, CAS No. 26172-55-4.

[0059] 2-Methyl-4-isothiazolin-3-one, CAS No. 2682-20-4.

[0060] Deionized water, CAS No. 7732-18-5, conductivity less than or equal to 1 μS / cm.

[0061] Zinc oxide, CAS No. 1314-13-2, particle size D50 is 0.5 to 1.5 μm, purity is greater than or equal to 99.5%.

[0062] In this embodiment, the unit of measurement for the amount of each material and solvent is uniformly referred to as parts by weight.

[0063] Preparation Example 1:

[0064] This preparation example provides a method for preparing an aqueous solution of ammonium polyacrylate, including the following steps:

[0065] Add 60 parts of deionized water to a four-necked flask equipped with a reflux condenser, thermometer and constant pressure dropping funnel, purge with high-purity nitrogen to remove oxygen for 20 minutes, turn on mechanical stirring and set the stirring speed to 250 rpm, and heat the system to 85°C in a water bath.

[0066] 45 parts of acrylic acid and 10 parts of deionized water were mixed as monomer solution, and 1.5 parts of ammonium persulfate were dissolved in 15 parts of deionized water as initiator solution. The system temperature was kept at 85°C, and the monomer solution and initiator solution were added dropwise through a double dropping funnel. The dropping time of the monomer solution was controlled at 3.0 hours, and the dropping time of the initiator solution was controlled at 3.2 hours.

[0067] After the addition was completed, the system temperature was raised to 90°C and stirred at 250 rpm for 2.0 hours. Then the system temperature was lowered to 45°C, and 25% ammonia solution was added dropwise at a rate of 2 parts / minute. When the pH of the system reached 7.5, the addition of ammonia solution was stopped, and the system temperature was lowered to 25°C. The solution was filtered through a 200-mesh stainless steel filter to obtain an aqueous solution A of ammonium polyacrylate. The solution was included in the formulation of subsequent examples on a dry basis. The weight-average molecular weight of the ammonium polyacrylate was 4950 according to gel permeation chromatography.

[0068] Preparation Example 2:

[0069] This preparation example provides a method for preparing an aqueous solution of ammonium polyacrylate, including the following steps:

[0070] Add 50 parts of deionized water to a four-necked flask equipped with a reflux condenser, thermometer and constant pressure dropping funnel, purge with high-purity nitrogen to remove oxygen for 17 minutes, turn on mechanical stirring and set the stirring speed to 200 rpm, and heat the system to 77°C in a water bath.

[0071] Mix 36.5 parts acrylic acid with 7.5 parts deionized water to prepare the monomer solution, and dissolve 2.5 parts ammonium persulfate in 12.5 parts deionized water to prepare the initiator solution. Keep the system temperature at 77°C, and add the monomer solution and initiator solution dropwise through a double dropping funnel. Control the dropping time of the monomer solution to 2.5 hours and the dropping time of the initiator solution to 2.7 hours.

[0072] After the addition was completed, the system temperature was raised to 87°C and stirred at 200 rpm for 1.7 hours. Then the system temperature was lowered to 40°C, and 22% ammonia solution was added dropwise at a rate of 1.5 parts / minute. When the pH of the system reached 7.2, the addition of ammonia solution was stopped, and the system temperature was lowered to 25°C. The solution was filtered through a 200-mesh stainless steel filter to obtain ammonium polyacrylate aqueous solution B. The solution was included in the formulation of subsequent examples on a dry basis. The weight-average molecular weight of the ammonium polyacrylate was 4050 according to gel permeation chromatography.

[0073] Preparation Example 3:

[0074] This preparation example provides a method for preparing an aqueous solution of ammonium polyacrylate, including the following steps:

[0075] Add 40 parts of deionized water to a four-necked flask equipped with a reflux condenser, thermometer and constant pressure dropping funnel, purge with high-purity nitrogen to remove oxygen for 15 minutes, turn on mechanical stirring and set the stirring speed to 150 rpm, and heat the system to 70°C in a water bath.

[0076] 28 parts acrylic acid and 5 parts deionized water were mixed as monomer solution, and 3.5 parts ammonium persulfate were dissolved in 10 parts deionized water as initiator solution. The system temperature was kept at 70°C, and the monomer solution and initiator solution were added dropwise through a double dropping funnel. The dropping time of the monomer solution was controlled at 2.0 hours, and the dropping time of the initiator solution was controlled at 2.2 hours.

[0077] After the addition was completed, the system temperature was raised to 85°C and stirred at 150 rpm for 1.5 hours. Then the system temperature was lowered to 35°C, and 20% ammonia solution was added dropwise at a rate of 1 part / minute. When the pH of the system reached 7.0, the addition of ammonia solution was stopped, and the system temperature was lowered to 25°C. The solution was filtered through a 200-mesh stainless steel filter to obtain an aqueous solution C of ammonium polyacrylate. The solution was included in the formulation of subsequent examples on a dry basis. The weight-average molecular weight of the ammonium polyacrylate was 3050 as determined by gel permeation chromatography.

[0078] Preparation Example 4:

[0079] This preparation example provides a method for preparing an aqueous solution of ammonium polyacrylate, including the following steps:

[0080] Add 55 parts of deionized water to a four-necked flask equipped with a reflux condenser, thermometer and constant pressure dropping funnel, purge with high-purity nitrogen to remove oxygen for 18 minutes, turn on mechanical stirring and set the stirring speed to 220 rpm, and heat the system to 80°C in a water bath.

[0081] 40 parts of acrylic acid and 8 parts of deionized water were mixed as monomer solution, and 2.0 parts of ammonium persulfate were dissolved in 14 parts of deionized water as initiator solution. The system temperature was kept at 80°C, and the monomer solution and initiator solution were added dropwise through a double dropping funnel. The dropping time of the monomer solution was controlled at 2.8 hours, and the dropping time of the initiator solution was controlled at 3.0 hours.

[0082] After the addition was completed, the system temperature was raised to 88°C and stirred at 220 rpm for 1.8 hours. Then the system temperature was lowered to 42°C, and 24% ammonia solution was added dropwise at a rate of 1.8 parts / minute. When the pH of the system reached 7.4, the addition of ammonia solution was stopped, and the system temperature was lowered to 25°C. The solution was filtered through a 200-mesh stainless steel filter to obtain an aqueous solution D of ammonium polyacrylate. The solution was included in the formulation of subsequent examples on a dry basis. The weight-average molecular weight of the ammonium polyacrylate was 4600 as determined by gel permeation chromatography.

[0083] Preparation Example 5:

[0084] This preparation example provides a method for preparing an aqueous solution of ammonium polyacrylate, including the following steps:

[0085] Add 45 parts of deionized water to a four-necked flask equipped with a reflux condenser, thermometer and constant pressure dropping funnel, purge with high-purity nitrogen to remove oxygen for 16 minutes, turn on mechanical stirring and set the stirring speed to 180 rpm, and heat the system to 75°C in a water bath.

[0086] 32 parts acrylic acid and 6 parts deionized water were mixed as monomer solution, and 3.0 parts ammonium persulfate were dissolved in 11 parts deionized water as initiator solution. The system temperature was kept at 75°C, and the monomer solution and initiator solution were added dropwise through a double dropping funnel. The dropping time of the monomer solution was controlled at 2.2 hours, and the dropping time of the initiator solution was controlled at 2.4 hours.

[0087] After the addition was completed, the system temperature was raised to 86°C and stirred at 180 rpm for 1.6 hours. Then the system temperature was lowered to 38°C, and 21% ammonia solution was added dropwise at a rate of 1.2 parts / minute. When the pH of the system reached 7.1, the addition of ammonia solution was stopped, and the system temperature was lowered to 25°C. The solution was filtered through a 200-mesh stainless steel filter to obtain an aqueous solution E of ammonium polyacrylate. The solution was included in the formulation of subsequent examples on a dry basis. The weight-average molecular weight of the ammonium polyacrylate was 3450 according to gel permeation chromatography.

[0088] Example 1:

[0089] This embodiment provides a method for preparing a slurry dispersant for granulating zinc oxide varistor powder, comprising the following steps:

[0090] S1. Add 50 parts of ammonium polyacrylate aqueous solution A (dry basis) and 20 parts of polyethylene glycol to 42.5 parts of deionized water. Place the mixture in a 50°C water bath and use a double-layer propeller to maintain the system temperature at 50°C. Stir at 500 rpm for 60 minutes until the system is transparent or semi-transparent and homogeneous to obtain macromolecular mixture A.

[0091] S2. In a separate, sealed mixing tank, take 7.5 parts of deionized water and 15 parts of triethanolamine and mix them evenly. Then add 4.0 parts of ammonium bicarbonate, keep the system temperature at 25°C, and stir at 250 rpm for 15 minutes to complex and dissolve the mixture, thus obtaining an alcoholamine-ammonium bicarbonate complex premix.

[0092] S3. Adjust the stirring speed of macromolecular mixture A to 600 rpm. Add the alkanolamine-ammonium bicarbonate complex premix obtained in S2 dropwise to macromolecular mixture A at a flow rate of 2 ml / min. Keep the system temperature at 50℃ throughout the dropwise addition process. After the dropwise addition is completed, continue stirring for 30 minutes. At this time, the pH of the system is 9.5, and mixed solution B is obtained.

[0093] S4. Under the condition of stirring speed of 800 rpm, add 8 parts of sodium carboxymethyl cellulose to the mixed solution B within 5 minutes. After the addition is completed, continue stirring at a stirring speed of 800 rpm for 90 minutes to obtain mixed solution C.

[0094] S5. Add 0.5 parts of the block copolymer of polydimethylsiloxane and polyethylene oxide-polypropylene oxide and 0.2 parts of the compound of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in a mass ratio of 3:1 to the mixed solution C. Adjust the stirring speed to 300 rpm and stir for 20 minutes. Pass the resulting slurry through a 200-mesh stainless steel filter to remove undissolved impurities. Collect the filtrate to obtain the finished dispersant.

[0095] Example 2:

[0096] This embodiment provides a method for preparing a slurry dispersant for granulating zinc oxide varistor powder, comprising the following steps:

[0097] S1. Add 40 parts of ammonium polyacrylate aqueous solution B (dry basis) and 15 parts of polyethylene glycol to 32 parts of deionized water. Place the mixture in a water bath at 45°C and use a double-layer propeller to maintain the system temperature at 45°C. Stir at 400 rpm for 45 minutes until the system is transparent or semi-transparent and homogeneous to obtain macromolecular mixture A.

[0098] S2. In a separate, sealed mixing tank, take 8 parts of deionized water and 10 parts of triethanolamine and mix them evenly. Then add 2.8 parts of ammonium bicarbonate, keep the system temperature at 22°C, and stir at 200 rpm for 12 minutes to complex and dissolve the mixture, thus obtaining an alcoholamine-ammonium bicarbonate complex premix.

[0099] S3. Adjust the stirring speed of macromolecular mixture A to 550 rpm, and add the alkanolamine-ammonium bicarbonate complex premix obtained in step S2 dropwise to macromolecular mixture A at a flow rate of 1.5 ml / min. Keep the system temperature at 45℃ throughout the dropwise addition process. After the dropwise addition is completed, continue stirring for 25 minutes. At this time, the pH of the system is 9.0, and mixed solution B is obtained.

[0100] S4. Under the condition of stirring speed of 700 rpm, add 5 parts of sodium carboxymethyl cellulose to the mixed solution B within 3 minutes. After the addition is completed, continue stirring at a stirring speed of 700 rpm for 75 minutes to obtain mixed solution C.

[0101] S5. Add 0.3 parts of the block copolymer of polydimethylsiloxane and polyoxyethylene-polyoxypropylene and 0.13 parts of the compound of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in a mass ratio of 3:1 to the mixed solution C. Adjust the stirring speed to 250 rpm and stir for 17 minutes. Pass the resulting slurry through a 200-mesh stainless steel filter to remove undissolved impurities. Collect the filtrate to obtain the finished dispersant.

[0102] Example 3:

[0103] This embodiment provides a method for preparing a slurry dispersant for granulating zinc oxide varistor powder, comprising the following steps:

[0104] S1. Add 30 parts of ammonium polyacrylate aqueous solution C (dry basis) and 10 parts of polyethylene glycol to 22.5 parts of deionized water. Place the mixture in a 40°C water bath and use a double-layer propeller to maintain the system temperature at 40°C. Stir at 300 rpm for 30 minutes until the system is transparent or semi-transparent and homogeneous to obtain macromolecular mixture A.

[0105] S2. In a separate, sealed mixing tank, take 7.5 parts of deionized water and 5 parts of triethanolamine and mix them evenly. Then add 1.5 parts of ammonium bicarbonate, keep the system temperature at 20°C, and stir at 150 rpm for 10 minutes to complex and dissolve the mixture, thus obtaining an alcoholamine-ammonium bicarbonate complex premix.

[0106] S3. Adjust the stirring speed of macromolecular mixture A to 500 rpm. Add the alkanolamine-ammonium bicarbonate complex premix obtained in S2 dropwise to macromolecular mixture A at a flow rate of 1 ml / min. Keep the system temperature at 40℃ throughout the dropwise addition process. After the dropwise addition is completed, continue stirring for 20 minutes. At this time, the pH of the system is 8.5, and mixed solution B is obtained.

[0107] S4. Under the condition of stirring speed of 600 rpm, add 2 parts of sodium carboxymethyl cellulose to the mixed solution B within 2 minutes. After the addition is completed, continue stirring at 600 rpm for 60 minutes to obtain mixed solution C.

[0108] S5. Add 0.1 parts of the block copolymer of polydimethylsiloxane and polyethylene oxide-polypropylene oxide and 0.05 parts of the compound of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in a mass ratio of 3:1 to the mixed solution C. Adjust the stirring speed to 200 rpm and stir for 15 minutes. Pass the resulting slurry through a 200-mesh stainless steel filter to remove undissolved impurities. Collect the filtrate to obtain the finished dispersant.

[0109] Example 4:

[0110] This embodiment provides a method for preparing a slurry dispersant for granulating zinc oxide varistor powder, comprising the following steps:

[0111] S1. Add 45 parts of ammonium polyacrylate aqueous solution D (dry basis) and 18 parts of polyethylene glycol to 36.9 parts of deionized water. Place the mixture in a water bath at 48°C and use a double-layer propeller to maintain the system temperature at 48°C. Stir at 450 rpm for 50 minutes until the system is transparent or semi-transparent and homogeneous to obtain macromolecular mixture A.

[0112] S2. In a separate, sealed mixing tank, take 8.1 parts of deionized water and 12 parts of triethanolamine and mix them evenly. Then add 3.5 parts of ammonium bicarbonate, keep the system temperature at 24°C, and stir at 220 rpm for 14 minutes to complex and dissolve the mixture, thus obtaining an alcoholamine-ammonium bicarbonate complex premix.

[0113] S3. Adjust the stirring speed of macromolecular mixture A to 580 rpm. Add the alkanolamine-ammonium bicarbonate complex premix obtained in S2 dropwise to macromolecular mixture A at a flow rate of 1.8 ml / min. Keep the system temperature at 48℃ throughout the dropwise addition process. After the dropwise addition is completed, continue stirring for 28 minutes. At this time, the pH of the system is 9.2, and mixed solution B is obtained.

[0114] S4. Under the condition of stirring speed of 750 rpm, add 6 parts of sodium carboxymethyl cellulose to the mixed solution B within 4 minutes. After the addition is completed, continue stirring at a stirring speed of 750 rpm for 80 minutes to obtain mixed solution C.

[0115] S5. Add 0.4 parts of the block copolymer of polydimethylsiloxane and polyoxyethylene-polyoxypropylene and 0.15 parts of the compound of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in a mass ratio of 3:1 to the mixed solution C. Adjust the stirring speed to 280 rpm and stir for 18 minutes. Pass the resulting slurry through a 200-mesh stainless steel filter to remove undissolved impurities. Collect the filtrate to obtain the finished dispersant.

[0116] Example 5:

[0117] This embodiment provides a method for preparing a slurry dispersant for granulating zinc oxide varistor powder, comprising the following steps:

[0118] S1. Add 35 parts of ammonium polyacrylate aqueous solution E (dry basis) and 12 parts of polyethylene glycol to 27.3 parts of deionized water. Place the mixture in a water bath at 42°C and use a double-layer propeller to maintain the system temperature at 42°C. Stir at 350 rpm for 40 minutes until the system is transparent or semi-transparent and homogeneous to obtain macromolecular mixture A.

[0119] S2. In a separate, sealed mixing tank, take 7.7 parts of deionized water and 8 parts of triethanolamine and mix them evenly. Then add 2.0 parts of ammonium bicarbonate, keep the system temperature at 21°C, and stir at 180 rpm for 11 minutes to carry out complexation and dissolution, so as to obtain an alcoholamine-ammonium bicarbonate complex premix.

[0120] S3. Adjust the stirring speed of macromolecular mixture A to 520 rpm. Add the alkanolamine-ammonium bicarbonate complex premix obtained in S2 dropwise to macromolecular mixture A at a flow rate of 1.2 ml / min. Keep the system temperature at 42℃ throughout the dropwise addition process. After the dropwise addition is completed, continue stirring for 22 minutes. At this time, the pH of the system is 8.8, and mixed solution B is obtained.

[0121] S4. Under the condition of stirring speed of 650 rpm, add 4 parts of sodium carboxymethyl cellulose to the mixed solution B within 3 minutes. After the addition is completed, continue stirring at a stirring speed of 650 rpm for 70 minutes to obtain mixed solution C.

[0122] S5. Add 0.2 parts of the block copolymer of polydimethylsiloxane and polyethylene oxide-polypropylene oxide and 0.1 parts of the compound of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one in a mass ratio of 3:1 to the mixed solution C. Adjust the stirring speed to 220 rpm and stir for 16 minutes. Pass the resulting slurry through a 200-mesh stainless steel filter to remove undissolved impurities. Collect the filtrate to obtain the finished dispersant.

[0123] Comparative Example 1:

[0124] Compared with Example 1, the difference is that the premixing operation in S2 was not performed. Instead, in S3, the corresponding parts of deionized water, ammonium bicarbonate and triethanolamine were added directly to the macromolecular mixture A independently and sequentially. All other aspects were the same.

[0125] Comparative Example 2:

[0126] The difference from Example 1 is that ammonium bicarbonate was not added in S2, but everything else is the same.

[0127] Comparative Example 3:

[0128] The difference from Example 1 is that in S2, ammonium bicarbonate is replaced with an equal weight of sodium bicarbonate, while the rest are the same.

[0129] Comparative Example 4:

[0130] The difference from Example 1 is that triethanolamine was not added in S2, but everything else is the same.

[0131] Comparative Example 5:

[0132] The difference from Example 1 is that polyethylene glycol was not added in S1, but everything else is the same.

[0133] Comparative Example 6:

[0134] The difference from Example 1 is that sodium carboxymethyl cellulose was not added in S4, but all other aspects are the same.

[0135] Test Example 1:

[0136] Materials from various stages of the preparation process in Examples 1 to 5 and Comparative Example 1 were selected as test objects. Specifically, when the alkaline complexing system was introduced into the macromolecular mixture A in step S3, the isothermal reaction vessel was connected to a rheological testing system equipped with an online torque sensor. A constant shear rate of the double-layer propulsion stirring paddle was set, and dynamic apparent viscosity data were continuously recorded from the start of the droplet addition to the end of the heat preservation period under a constant temperature of 50°C. The sampling frequency was set to once every 10 seconds, and the peak change rate of apparent viscosity during the reaction process was extracted through the data backend.

[0137] After each group of systems has completed the heat preservation and stirring in step S3, accurately measure 1000 mL of the resulting mixed solution B from the reactor. Transfer the measured test solution to a vacuum filtration device with a constant pressure set at 0.05 MPa, and perform filtration through a 300-mesh standard stainless steel filter screen that has been dried to constant weight at 60°C and has a uniform pore size distribution.

[0138] After filtration, 200 mL of deionized water was slowly injected along the inner wall of the filter screen to rinse the retained material, so as to remove the physically attached water-soluble free macromolecules. Then, the filter screen carrying the filter residue was carefully transferred into a vacuum drying oven and baked at 60°C for 4 hours until the mass no longer changed. The mass difference of the filter screen before and after was weighed using an analytical balance with an accuracy of 0.1 mg, and the dry weight of the microgel filter residue per unit volume was calculated.

[0139] Simultaneously, on an optical magnification operating table with a standard grid scale, the insoluble gel particles with obvious physical cross-linking characteristics and a particle size greater than 50 micrometers trapped on the filter surface were manually counted by grid sampling. The approximate total number of microgel particles generated per liter of reaction system was evaluated by area conversion.

[0140] Table 1: Test data on the anti-microgelation and viscosity fluctuation performance of each dispersant reaction system

[0141] Group Dropping period apparent viscosity peak abrupt change rate (%) Dry weight of microgel residue after vacuum filtration (mg / L) >50 μm microgel particle count (particles / L) Example 1 3.2 12.4 18 Example 2 4.1 15.7 23 Example 3 2.8 9.2 12 Example 4 4.6 18.1 29 Example 5 3.5 14.3 20 Comparative Example 1 58.7 412.6 856

[0142] According to Table 1 and Figure 1The data allows for a direct examination of the profound impact of thermodynamic preparation processes on the microscopic topology of macromolecular networks. In the early laboratory exploration of the synthesis of high-concentration polycarboxylate dispersants, it was found that the direct addition of alkaline inorganic salt reagents to the aqueous phase of polymers would induce local cross-linking. This phenomenon was thoroughly exposed in the test results of Comparative Example 1. Lacking the pre-complexation buffer of triethanolamine, the system of Comparative Example 1 showed a rheological viscosity change of up to 58.7% during the direct addition of ammonium bicarbonate. This reflects that the excessively high local ionic strength instantaneously destroys the hydration layer of polyacrylic acid segments, causing irreversible physical entanglement.

[0143] The collected 412.6 mg / L dry filter residue and a large number of insoluble gel particles visible to the naked eye definitively prove that severe defective cross-linking products were generated inside the reactor. This structure is extremely dangerous in industrial continuous production. Microscopic inhomogeneity will not only increase the impurity removal cost of subsequent fine filtration processes, but will also directly weaken the structural strength of the final slurry system.

[0144] Comparing the data from Examples 1 to 5, the overall performance showed a qualitative leap. By pre-constructing a premixed complex of alkanolamine and ammonium bicarbonate, the viscosity mutation rate during the reaction period of all example systems was steadily suppressed to a very low fluctuation range of less than 5%. When continuously monitoring the data stream returned by the torque sensor next to the experimental bench, it can be clearly seen that the rheological curves of the representative example systems have a very high smoothness, avoiding the acid-base neutralization ramp jump common in traditional processes.

[0145] When high-concentration droplets containing triethanolamine come into contact with the macromolecular aqueous phase at the initial moment, the microscopic region does indeed induce a strong salting-out effect, causing the molecular chains to shrink rapidly. However, thanks to the strong shear flow field provided by the dual-layer propeller, this local high-ion state is quickly dispersed and diluted. After losing the strong ion binding, the macromolecular chain segments unfold again within a short time window.

[0146] The filter residue peak of less than 20 mg / L and the few gel particles objectively demonstrate that this contraction-relaxation pulse mechanism successfully blocks the formation path of dead polymers. This indicates that by changing the micro-feeding thermodynamic sequence, while maintaining the overall ratio, this scheme eliminates the gelation defects in the macromolecular phase transition process, providing a structurally complete rheological framework for zinc oxide powder granulation.

[0147] Test Example 2:

[0148] The finished dispersants prepared in Examples 1 to 5 and Comparative Examples 4 and 5 were used as test objects. A mixed inorganic slurry containing a fixed mass fraction of zinc oxide, bismuth oxide and antimony oxide was prepared, wherein the total mass fraction of solids was set to 65%. Equal masses of each group of dispersants were introduced into the slurry, and the suspension system to be tested was obtained after mechanical stirring and homogenization for 30 minutes.

[0149] Accurately pipette 20 mL of the slurry to be tested, dilute it to an aqueous dispersion with a solid mass fraction of 0.05%, transfer it to the quartz sample cell of the microelectrophoresis apparatus, and measure the Zeta potential value of the inorganic particle surface under a constant temperature environment of 25℃. Each sample is measured in parallel 5 times and outliers are removed. The arithmetic mean of the remaining data is taken as the electrostatic charge characteristic index of the particle surface of this group.

[0150] Undiluted slurries from each group were placed in centrifuge tubes and centrifuged at 12,000 rpm for 30 minutes using a high-speed refrigerated centrifuge. The supernatant was collected, and the free Zn in the supernatant was quantitatively determined using inductively coupled plasma atomic emission spectrometry. 2+ and Bi 3+ The total mass concentration of metal cations is used to calculate the chelation inhibition rate of the dispersant on heavy metal ions.

[0151] The remaining raw slurry was injected into the standard glass measuring tube of the static optical stability analyzer. The sample height was fixed at 40 mm. The sample was left to stand at 25 °C for 168 hours for monitoring. The instrument scanned the back drive scattered light intensity along the sample axis every 2 hours. The static suspension stability index, which represents the overall instability dynamics of the slurry, was calculated by integrating the data in the supporting background. The larger the value, the more severe the macroscopic stratification and sedimentation of the system.

[0152] Table 2: Test data on surface charge, heavy metal chelation, and long-term static stability of each slurry system

[0153] Group Zeta potential (mV) on the surface of inorganic particles Total concentration of heavy metal cations in the supernatant (mg / L) 168h Static Suspension Stability Index (TSI) Example 1 -42.6 1.8 1.45 Example 2 -38.1 2.5 2.12 Example 3 -33.4 4.1 3.56 Example 4 -40.3 2.0 1.87 Example 5 -35.8 3.2 2.89 Comparative Example 4 -41.9 48.6 12.43 Comparative Example 5 -15.2 2.3 8.94

[0154] According to Table 2 and Figure 2 The data shows that the electrostatic steric hindrance shielding network constructed by the multi-component synergy plays a decisive physicochemical supporting role in maintaining the long-term stability of high solids content zinc oxide slurry. When examining the surface charge characteristics of inorganic particles, Comparative Example 5, due to the absence of polyethylene glycol, relied solely on ammonium polyacrylate to provide isolated electrostatic repulsion, resulting in a decrease in the absolute value of its Zeta potential. However, the TSI value of the macroscopic slurry after standing for 168 hours was as high as 8.94. This experimental phenomenon confirms that the simple electrostatic repulsion barrier can be dismantled by the double-layer compression effect formed by inorganic salts in the aqueous phase. Without the thick solvation layer constructed by linear flexible long-chain macromolecules around the particles, the collisions between powder particles cannot be sufficiently hindered by steric hindrance, inevitably leading to the stratification and sedimentation of the macroscopic phase.

[0155] This complex stabilization mechanism is also reflected in the microscopic regulation of polyvalent harmful cations. In Comparative Example 4, after the removal of triethanolamine, the total concentration of free heavy metal cations in its supernatant rose sharply to 48.6 mg / L. Correspondingly, the long-term instability kinetics TSI index of the slurry system deteriorated directly to 12.43. In our tests, we noticed that trace amounts of leached metal ions often accompanied the surface of zinc oxide and doped bismuth oxide powders. When these cations are free in the system, they act as bridging mediators, undergoing polydentate coordination with polycarboxylic acid anions on the surfaces of different particles, promoting the bridging and flocculation of the original dispersed particles.

[0156] By introducing triethanolamine with a polyhydroxyl group and a lone pair of electrons nitrogen structure, Examples 1 to 5 successfully controlled the concentration of free metal ions below 5 mg / L, achieving selective capture and chelation cleavage of free active polyvalent cations. Combined with the TSI index as low as 1.45 and the surface potential as high as -42.6 mV in Example 1, this series of precise data gradients clearly confirms that the static stability architecture of electrostatic repulsion, steric hindrance, and complexation chelation is the microscopic core for preventing flocculation and long-term anti-settling of high solids slurry.

[0157] Test Example 3:

[0158] The finished dispersants prepared in Examples 1 to 5 and Comparative Example 2 were extracted and used to prepare a zinc oxide mixed inorganic slurry with a solid mass fraction of 65% according to the same ratio as the aforementioned test examples. About 15 mg of the slurry sample was placed in a miniature alumina crucible of a thermogravimetric-mass spectrometer. The thermogravimetric analysis module, i.e., TG, was used to continuously monitor the residual mass decay of the sample under the set temperature program. The mass spectrometry analysis module, i.e., MS, was used to ionize the gases released by heating and separate and track them according to their mass-to-charge ratio. Under constant flow of high-purity argon, the sample was linearly heated from 25°C to 250°C at a heating rate of 10°C / min. The mass change of the sample was continuously monitored, and the ion current characteristic signals of NH3 and CO2 with mass-to-charge ratios of 17 and 44, respectively, were simultaneously tracked using the mass spectrometry analysis module to determine the peak temperature of the concentrated burst of volatile gases.

[0159] The remaining large-volume slurry from each group was pumped into a pilot-scale centrifugal spray drying tower for granulation verification. The inlet air temperature of the drying tower was set at 210℃, the outlet air temperature was maintained in the range of 95℃ to 105℃, and the atomizing disc was kept at a constant speed of 9000 rpm. After the heat exchange system of the equipment reached thermodynamic equilibrium, the granulated powder was continuously fed and collected at the bottom cyclone separator.

[0160] Accurately weigh 50.0g of dehydrated and dried granulated powder, and let it fall naturally and freely into a 100mL standard glass graduated cylinder through a special funnel. After standing and leveling the surface, read the volume and calculate the loose density of the powder. Then fix the graduated cylinder containing the powder on the worktable of the powder tapped density tester, set the vibration drop to 3mm, and continuously vibrate vertically 2500 times at a frequency of 300 times / minute. Read the final scale at which no volume collapse occurs to calculate the tapped density, and output the ratio of tapped density to loose density as the Hausner ratio for evaluating the macroscopic morphology and flowability of the powder.

[0161] Table 3: Pyrolysis gas generation characteristics and bulk density test data of granulated powders in each group

[0162] Group Peak temperature of concentrated NH3 / CO2 release (°C) Loose bulk density (g / cm³) Tap density (g / cm³) Hausner ratio Example 1 71.4 1.34 1.52 1.134 Example 2 68.2 1.41 1.63 1.156 Example 3 74.5 1.28 1.47 1.148 Example 4 67.8 1.45 1.66 1.145 Example 5 70.1 1.37 1.57 1.146 Comparative Example 2 No characteristic peaks detected 1.89 2.42 1.280

[0163] According to Table 3 and Figure 3 The data shows that the pyrolysis kinetics of the endogenous foaming agent in the granulation phase transformation completely alters the microscopic aggregation path of inorganic powders. Observing the overall performance of Comparative Example 2, due to the absence of ammonium bicarbonate as a key component in the formulation, when the slurry is subjected to environmental thermal shock at temperatures exceeding 200°C, the weight loss process of its TG curve is entirely due to the rapid evaporation of water on the droplet surface. This not only resulted in the MS module failing to detect any characteristic foaming gas peaks throughout the process, but more critically, the huge capillary contraction force driven by the outward diffusion of water forcibly squeezes the internal nano-inorganic particles towards the core, ultimately resulting in a loose packing density as high as 1.89 g / cm³. 3 Furthermore, it consists of dense, irregular aggregates with a Hausner ratio of 1.28.

[0164] In practical materials engineering evaluation, this high Hausner ratio indicates that there is a strong mechanical interlocking force and electrostatic friction between powder particles. Its flow and filling efficiency in the press mold cavity is very poor, which will lead to density gradient defects inside the ceramic body. By accurately introducing ammonium bicarbonate, which is very unstable when heated, and perfectly complexing and dissolving it in the aqueous phase in the early process, Examples 1 to 5 show completely different thermodynamic characteristics. These systems explosively release a large amount of NH3 and CO2 gas at around 70°C. The mass reduction step captured by the TG curve and the gas characteristic peak monitored synchronously by the MS curve are perfectly coincident. This temperature window accurately hits the golden period of phase transition when the atomized droplets have just left the nozzle and entered the high temperature tower and the surface has not yet been completely shelled and hardened.

[0165] The instantaneous surge in vapor pressure inside the droplet creates a secondary micro-explosive thrust that expands outward, directly offsetting the inward capillary contraction caused by water evaporation. This pulls the powder particles toward the gas-liquid interface of the droplet and arranges them in a regular pattern. The Hausner ratios of all the final measured examples are stable at 1.16 or below. This low compressibility data, which approaches an ideal hydrodynamic state, convincingly confirms that the soft agglomeration network inside the powder is completely disintegrated and successfully develops into a micron-sized regular hollow spherical shell with good rheological characteristics.

[0166] Test Example 4:

[0167] The finished dispersants prepared in Examples 1 to 5, as well as Comparative Examples 1 and 6, were used as rheological test objects. In accordance with the same solid content ratio requirements mentioned above, a zinc oxide mixed inorganic slurry with a solid mass fraction of 65% was prepared. The slurry was homogenized at 2000 rpm for 30 minutes using a high-speed disperser. Then, the slurry was transferred to a vacuum degassing kettle and slowly stirred and degassed at -0.09 MPa for 20 minutes to eliminate the interference of air bubbles in the system on the rheological signal.

[0168] Steady-state and transient rheological characterization of the slurry was performed using a rotational rheometer equipped with a coaxial cylindrical measuring rotor. The degassed slurry was carefully injected into the measuring cylinder, and the ambient temperature was set to a constant 25°C. In the steady-state continuous shear scan test, the shear rate was set from 0.1 s⁻¹. -1 Logarithmic increments to 1000s -1 Capture 0.1s -1 The ability of the slurry to resist settling under static conditions was evaluated using a very low shear apparent viscosity, and a 1000s sample was taken. -1 The flow resistance at high shear apparent viscosity was assessed at high-pressure pumping and atomizing nozzles, and the ratio of the two was calculated as the thixotropic index.

[0169] In the thixotropic ring area test, the shear rate was set to start linearly from 0s. -1 Climbing at a constant speed to 1000s -1 The upward shear stress curve was recorded over a duration of 120 seconds; then held for 1000 seconds. -1 A constant shear rate was applied for 10 seconds to completely destroy the internal structure, and finally the shear rate was controlled to decrease from 1000 s / s over 120 seconds. -1 Falling back at a constant speed to 0s -1 The downward shear stress curve is recorded, and the closed region enclosed by the upward and downward curves is integrated using the data processing module built into the rheometer. The thixotropic ring area value, which characterizes the energy dissipated by the destruction and reconstruction of the macromolecular network structure, is output.

[0170] Table 4: Rheological and Thixotropic Property Test Data of Dispersants for Each Component in the Slurry System

[0171] Group Low shear apparent viscosity (mPa·s) High shear apparent viscosity (mPa·s) Thixotropic index Thixotropic ring area (Pa / s) Example 1 3845.2 87.6 43.89 1542.7 Example 2 4102.8 92.1 44.55 1621.3 Example 3 3589.4 81.3 44.15 1489.5 Example 4 4256.1 96.8 43.97 1678.9 Example 5 3712.5 85.4 43.47 1515.2 Comparative Example 1 5894.3 412.5 14.29 3894.6 Comparative Example 6 214.7 78.9 2.72 142.4

[0172] According to Table 4 and Figure 4 The data shows that rheological indices accurately map the evolution of the microscopic topology of the macromolecular network inside the slurry. In actual observations of industrial slurry preparation, inorganic powders in the aqueous phase often face extremely demanding and contradictory physical requirements. They are required to have high structural strength in the static storage tank to firmly support the coarse particles doped with heavy metals and prevent them from caking and settling. They are also required to exhibit low flow resistance when pumped into narrow pipes and subjected to high-pressure nozzles. Direct analysis of the data performance of Comparative Example 6 shows that the system loses its ability to construct a three-dimensional card network space due to the stripping of sodium carboxymethyl cellulose, which has a long-chain flexible structure.

[0173] Its low shear apparent viscosity plummeted to 214.7 mPa·s. This slurry, which is close to the characteristics of a Newtonian fluid, completely lost its macroscopic physical bearing capacity. The weak thixotropic ring area confirms that there is no skeleton inside. This is also the mechanical reason why the suspension without thickening components in the early stage hardened and precipitated within a few hours. In contrast, in Comparative Example 1, the blind addition of materials in the thermodynamic sequence induced microgelation and cross-linking. These local dead polymers formed rigid physical entanglements in the system.

[0174] When subjected to strong high-frequency shearing, the damaged and irregular polymer chain segments cannot be arranged to untangle in accordance with the flow field direction, resulting in its high shear viscosity stubbornly remaining at a very high level of 412.5 mPa·s. The thixotropic ring area distorted to 3894.6 Pa / s further exposes that the network is difficult to recover after damage. This uneven distribution of internal stress will directly tear the droplets at the moment of nozzle atomization, severely degrading the geometric regularity of the final powder.

[0175] Turning our attention to Examples 1 through 5, this data matrix perfectly illustrates the ideal state of shear thinning in fluid mechanics. Thanks to the successful blocking of microgel defects by the ion pulse induction mechanism, the uniformly spread polyacrylic acid macromolecule backbone and the subsequently seamlessly embedded thickening molecules work together to weave a highly elastic three-dimensional topological network. Example 1 released a viscosity barrier as high as 3845.2 mPa·s in a very low shear zone in a simulated storage tank, strongly locking the gravity sinking path of inorganic particles. Once it encounters the tearing of high-frequency shear stress, this network, which is maintained by hydrogen bonds and van der Waals forces, can quickly disintegrate and slide downstream. The high shear viscosity instantly drops to 87.6 mPa·s, and the fluid resistance is extremely compressed.

[0176] The stable thixotropic index of over 43 and the moderate thixotropic ring area objectively reflect the excellent instantaneous reconstruction ability of the macromolecular network after the shear force is removed. This rheological property, which combines strong static wall support with extremely low dynamic internal friction, completely breaks through the process bottleneck from long-term anti-settling to low-pressure uniform atomization, laying an unshakable fluid physics foundation for subsequent high-quality hollow granulation.

[0177] Test Example 5:

[0178] Granulated powders prepared by spray drying in Examples 1 to 5, and Comparative Examples 1 and 2 were used as test objects for fracture mechanics and ceramic properties. Granulated particles with a particle size distribution in the range of 80 to 100 micrometers were randomly selected from each group of samples and placed on the worktable of a single-particle microelectromechanical compression tester equipped with a high-precision displacement sensor. Under room temperature, the micro indenter was controlled to apply a displacement load downward at a constant rate of 0.5 mm / min. The critical peak load corresponding to the moment when the particle underwent brittle fracture was recorded. Each group of samples was tested in parallel 30 times, and the arithmetic mean was taken after removing outliers. This was used to quantitatively evaluate the single-particle compressive fracture strength of the powder.

[0179] Accurately weigh 150.0g of each group of granulated powders and evenly fill them into a hard alloy circular mold with an inner diameter of 40mm. Use a unidirectional hydraulic molding machine to hold the pressure at a constant axial pressure of 120MPa for 60 seconds. After demolding, a cylindrical ceramic green body is obtained. Then, the green body is placed in a high-temperature box-type resistance furnace for debinding and sintering. The heating rate is set to 2℃ / min. The green body is held at 450℃ for 2 hours to remove organic components. The temperature is then increased to 1180℃ and held for 3 hours to complete the densification sintering. After natural cooling to room temperature in the furnace, a zinc oxide pressure-sensitive ceramic sample is obtained.

[0180] The bulk density of sintered samples was accurately determined using the Archimedes displacement method. The density was then compared and converted with the theoretical density of zinc oxide-based ceramics to extract the relative sintering density data of each group of samples.

[0181] The top and bottom surfaces of the ceramic sample were ground and polished on both sides. Silver paste was uniformly coated by screen printing and heat-treated at 800℃ for 15 minutes to form ohmic contact silver electrodes. The treated sample was connected to a DC varistor parameter tester, and the breakdown voltage gradient of the sample was read under a quasi-DC current of 1mA. At the same time, the leakage current data at 0.75 times the breakdown voltage was extracted, and the nonlinear coefficient α characterizing the nonlinear conductivity behavior was calculated based on the voltage ratio at 1mA and 0.1mA.

[0182] Table 5: Test data of mechanical response and electrical properties of granulated powder and final sintered ceramics for each group

[0183] Group Single-particle breaking strength (mN) Relative sintering density (%) Nonlinear coefficient α Leakage current IL (μA) Example 1 16.4 98.6 65.2 1.1 Example 2 15.8 98.2 61.7 1.4 Example 3 17.1 97.5 58.4 1.8 Example 4 15.2 98.9 67.1 0.9 Example 5 16.7 98.4 63.5 1.2 Comparative Example 1 38.6 92.4 28.3 12.5 Comparative Example 2 45.2 93.8 34.6 8.2

[0184] According to Table 5 and Figure 5 The data shows that the microstructure regulation of the dispersion system directly determines the macroscopic electrical peak value after ceramic formation. In the dry pressing evaluation, it was found that Comparative Example 2, due to the lack of an endogenous foaming mechanism, resulted in extremely dense solid particles caused by water evaporation during the drying process. Its single-point fracture strength was as high as 45.2 mN. This hard powder was difficult to break and fill under conventional pressing at 120 MPa, resulting in a sintering density of 93.8%. The residual pores inside became carrier leakage channels, causing a high leakage current of 8.2 μA. The microgelation agglomeration of Comparative Example 1 not only increased the powder hardness but also caused severe component segregation inside the green body. The nonlinear coefficient dropped to 28.3, indicating that the grain boundary barrier network had undergone local penetration.

[0185] The difference lies in the fact that the embodiment sequence successfully constructed a regular hollow spherical shell network through a heated micro-explosion mechanism, endowing the powder with suitable mechanical yield characteristics. The single-particle fracture strength of embodiments 1 to 5 remained stable within an ideal window of 15 to 17.5 mN. When the mold cavity was compressed, the hollow shell could collapse uniformly and tightly fill the micro gaps, completely eliminating the green density gradient. This ideal physical packing state cleared the way for material diffusion and transport at high temperatures, enabling all embodiments to achieve a very high density of over 97.5%. It is this dense and uniform microstructure that facilitates the three-dimensional ideal encapsulation of zinc oxide grains and bismuth-rich grain boundary phases, causing the nonlinear coefficient of embodiment 1 to jump to 65.2 and the leakage current to be precisely suppressed at 1.1 μA. This fully demonstrates that the present solution, through the synergistic effect of ion pulse and in-situ gas generation granulation, successfully transformed the front-end fluid microstructure regulation into a substantial breakthrough in the core electrical performance of varistor ceramics.

[0186] Test Example 6:

[0187] The varistor ceramic samples prepared in Examples 1 to 5 and Comparative Examples 1, 2 and 3 were selected as the test objects for current flow and aging stability. The sintered samples with double-sided silver treatment were connected to a standard test circuit equipped with a lightning surge generator. The initial impulse current was set to 2000A. The standard 8 / 20μs pulse current waveform was used, and the current was increased step by step in increments of 500A. Two positive pulses were applied to the same sample at each energy level. The pulse interval was set to 60 seconds to ensure that the heat inside the sample was fully conducted outward and dissipated.

[0188] The residual voltage and waveform changes are monitored in real time using a digital oscilloscope. When the sample shows macroscopic physical cracking or the deviation of its 1mA breakdown voltage exceeds the failure threshold of 0 to 20% of the initial value, the peak current of the previous safe passage is recorded. The peak current is divided by the electrode area of ​​the sample to calculate the critical surge current density. Ten samples are randomly selected from each group for destructive testing and the arithmetic mean is taken.

[0189] Fresh samples from the same batch that have not been subjected to electrical shock were selected from each group and placed in a high-temperature constant-temperature aging test chamber for accelerated life testing. The test temperature inside the chamber was set to be constant at 115℃, and a DC bias voltage of 0.85V, equivalent to 0.85 times the initial breakdown voltage, was continuously applied to the two electrodes of the sample. 1mA The entire aging test cycle lasted 1000 hours. At the 100, 500 and 1000 hours of system operation, the samples were temporarily removed from the test chamber. After the samples were allowed to cool naturally to 25°C in a dry environment, the current leakage current value and the new breakdown voltage were accurately read and recorded using a DC varistor.

[0190] By compiling observation data from all time points, calculating the relative drift rate of breakdown voltage after 1000 hours of rigorous thermoelectric stress aging, and plotting the measured leakage current data into an evolution curve in time series, we can quantitatively evaluate the electrical degradation hysteresis capability of the grain boundary barrier in the ceramic body under long-term service conditions.

[0191] Table 6: Test data on surge impact resistance and accelerated aging stability of each group of varistor ceramic samples

[0192] Group Critical surge current density (A / cm²) Initial leakage current (μA) Leakage current (μA) after 1000 hours of aging Breakdown voltage drift (%) Example 1 8542 1.1 2.4 -1.8 Example 2 8124 1.4 3.1 -2.5 Example 3 7895 1.8 4.2 -3.1 Example 4 8361 0.9 2.8 -2.1 Example 5 8012 1.2 3.5 -2.7 Comparative Example 1 3145 12.5 85.6 -15.4 Comparative Example 2 4568 8.2 42.8 -9.7 Comparative Example 3 5120 6.5 53.4 -11.2

[0193] According to Table 6 and Figure 6 The data shows that the performance of varistors under transient high current surges and long-term continuous bias is the ultimate engineering standard for testing the microstructure control of front-end powders. Past failure analyses have confirmed that the microscopic heterogeneity of the grain boundary layer is often the direct cause of thermal breakdown and electrical aging. In the test data, the comparative series collectively slid into performance collapse due to their respective process defects.

[0194] Comparative Example 2 lacks endogenous foaming, resulting in a hard powder. Comparative Example 3, although possessing a gas-generating mechanism, lacks polymer network anchoring, leading to disordered bubble aggregation. Both defects leave behind a large number of macroscopic pores or voids after compression molding. When an 8 / 20 μs surge is injected, these insulating pores force the current to contract and accumulate violently at local grain boundaries, generating Joule hot spots that directly cause them to reach 5000 A / cm. 2 Thermal stress cracking occurs at very low energy levels.

[0195] In Comparative Example 1, microgel segregation completely disrupted the uniformity of the grain boundary barrier distribution. Under combined thermoelectric aging at 115℃, the low barrier micro-regions became concentrated channels for leakage current and accelerated ion migration. After 1000 hours of erosion, the leakage current soared to 85.6μA, and the nonlinear protection function of the device was completely lost.

[0196] To address this type of electrical stress concentration failure, the series of examples completely reversed the situation through precise microscopic pathways. Relying on ion pulse blocking of the microgel and combined with an in-situ gas-generating micro-explosion mechanism, Examples 1 to 5 constructed a dense three-dimensional potential barrier network with extremely uniform grain size. This uniform structure ensures that the surge impact can penetrate the entire working area uniformly in the form of a plane wave, dispersing transient heat globally. As a result, the critical surge current density of Example 1 jumped to 8542 A / cm². 2 This completely eliminates the risk of localized thermal breakdown.

[0197] Meanwhile, the continuous and structurally complete bismuth-rich grain boundary phases form a solid physical barrier during long-term aging, which greatly hinders the long-range migration of oxygen vacancies under strong electric fields, thus strongly suppressing the breakdown voltage drift rate to -1.8%, and the leakage current only shows a slight background rise based on thermal excitation. These longitudinally consistent data conclusively confirm that the deep integration of front-end rheological topology optimization and vapor phase pore formation technology ultimately translates into the core lifespan advantage of materials in resisting extreme electrical corrosion.

[0198] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A slurry dispersant for granulating zinc oxide varistor powder, characterized in that, The dispersant is made from raw materials comprising the following parts by weight: Aqueous solution of ammonium polyacrylate: 30 to 50 parts on a dry basis; Polyethylene glycol: 10 to 20 parts; Triethanolamine: 5 to 15 parts; Ammonium bicarbonate: 1.5 to 4.0 parts; Sodium carboxymethyl cellulose: 2 to 8 parts; Block copolymer of polydimethylsiloxane and polyethylene oxide-polypropylene oxide: 0.1 to 0.5 parts; A complex of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one: 0.05 to 0.2 parts; Deionized water: 30 to 50.6 parts.

2. The slurry dispersant for zinc oxide varistor powder granulation according to claim 1, characterized in that, The raw material ratio of the dispersant satisfies the following relationship: The weight ratio of the ammonium polyacrylate aqueous solution to the polyethylene glycol on a dry basis is 2.5 to 3.

0. The weight ratio of triethanolamine to ammonium bicarbonate is 3.33 to 4.

0.

3. The slurry dispersant for zinc oxide varistor powder granulation according to claim 1, characterized in that, In the complex of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, the mass ratio of the two is 3:1; The weight-average molecular weight of the ammonium polyacrylate in the aqueous solution ranges from 3050 to 4950.

4. The slurry dispersant for zinc oxide varistor powder granulation according to claim 1, characterized in that, The ammonium polyacrylate aqueous solution is a polymer aqueous solution obtained by polymerizing acrylic monomers under the initiation of ammonium persulfate and then neutralizing with ammonia; the pH value of the ammonium polyacrylate aqueous solution is 7.0 to 7.

5.

5. The method for preparing the slurry dispersant for granulating zinc oxide varistor powder according to any one of claims 1 to 4, characterized in that, The method includes the following steps: S1. Preparation of macromolecular mixture: Mix ammonium polyacrylate aqueous solution, polyethylene glycol and part of deionized water, and stir continuously in a constant temperature water bath until the system is transparent or semi-transparent and homogeneous to obtain macromolecular mixture A. S2. Preparation of complexing premix: In a separate mixing tank, the remaining deionized water and triethanolamine are mixed evenly, and then ammonium bicarbonate is added. The mixture is stirred at room temperature to carry out complexation and dissolution, thus obtaining the alcoholamine-ammonium bicarbonate complexing premix. S3. Dropping and Ion Pulse Interception: Under constant temperature and stirring conditions, the alkanolamine-ammonium bicarbonate complex premixed solution obtained in step S2 is added dropwise to the macromolecular mixture A in step S1 at a uniform rate. After the dropwise addition is completed, the mixture is kept warm and stirred to obtain mixed solution B. S4. Thixotropic network construction: Under high-speed stirring, sodium carboxymethyl cellulose is added to the mixed solution B in step S3. After the addition is completed, high-speed stirring is maintained to fully detangle and construct a rheotropic network, resulting in mixed solution C. S5. Additive compounding and impurity removal: Add the block copolymer of polydimethylsiloxane and polyethylene oxide-polypropylene oxide, as well as the compound of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, to the mixed solution C. Reduce the speed and mix. Then remove undissolved impurities through a filter screen and collect the filtrate to obtain the finished dispersant.

6. The method for preparing the slurry dispersant for granulation of zinc oxide varistor powder according to claim 5, characterized in that, In S1, the temperature of the constant temperature water bath is controlled at 40 to 50°C, the stirring speed is 300 to 500 rpm, and the stirring time is 30 to 60 minutes. In S2, the system temperature is controlled at 20 to 25°C, the stirring speed is 150 to 250 rpm, and the stirring time is 10 to 15 minutes.

7. The method for preparing the slurry dispersant for granulation of zinc oxide varistor powder according to claim 5, characterized in that, In S3, the stirring speed of macromolecular mixture A is adjusted to 500 to 600 rpm, and the dropping flow rate of the alkanolamine-ammonium bicarbonate complex premix is ​​controlled at 1.0 to 2.0 ml / min; Maintain the system temperature at 40 to 50°C throughout the dropwise addition process, and continue stirring for 20 to 30 minutes after the dropwise addition is complete. Control the pH value of the system at the reaction endpoint to be 8.5 to 9.

5.

8. The method for preparing the slurry dispersant for granulation of zinc oxide varistor powder according to claim 5, characterized in that, In S4, the stirring speed is controlled at 600 to 800 rpm, the addition time of sodium carboxymethyl cellulose is controlled within 2 to 5 minutes, and the stirring time after the addition is completed is 60 to 90 minutes.

9. The method for preparing the slurry dispersant for granulation of zinc oxide varistor powder according to claim 5, characterized in that, In S5, the mixing speed is adjusted to 200 to 300 rpm, and the mixing time is 15 to 20 minutes. The filter screen is a 200-mesh stainless steel filter screen.

10. The use of a zinc oxide varistor powder granulation slurry dispersant as described in any one of claims 1-9 in the preparation of a varistor granulation precursor slurry or varistor ceramic powder composition for targeted suppression of microscopic solid-liquid phase separation.

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