Dysprosium oxide with narrow particle size distribution and preparation method thereof

Abstract

The invention relates to the technical field of metal oxides, in particular to dysprosium oxide with narrow particle size distribution and a preparation method thereof. The preparation method comprises the following steps: preparing dysprosium nitrate and ammonium oxalate solutions, keeping the pH value at 3.5-4.5 in a precipitation reactor, firstly mixing part of the solutions to form crystal nucleus seed slurry, then synchronously dropwise adding the residual solution in two channels, adding an ammonium polyacrylate dispersing agent step by step in the dropwise adding process, and sequentially adding a cationic polymer solution and a nonionic polymer solution in the middle stage. After dropwise adding, the slurry is heated and aged, urea and an ammonium nitrate solution are added for combined aging, then a precursor is obtained through dilution, filtering and washing, solvent replacement and drying, and finally dysprosium oxide powder is obtained through segmented roasting. The D50 of the powder is 0.38-0.45 [mu] m, the Span is not larger than 1.3, and the powder is high in tap density, consistent in densification behavior after sintering, low in apparent porosity and suitable for high-end application such as magneto-optical ceramics.

Description

Technical Field

[0001] This invention relates to the field of metal oxide technology, and in particular to a narrow-particle-size dysprosium oxide and its preparation method. Background Technology

[0002] Dysprosium oxide, as an important rare earth oxide, has wide applications in high-end fields such as magneto-optical ceramics and transparent rare earth oxide components. These applications require powders with high uniformity, narrow particle size distribution, and good sintering properties to ensure the optical transparency and structural consistency of the final product. However, traditional preparation methods mostly employ the oxalate precipitation-calcination route, which has inherent defects in the precipitation stage and cannot meet the above requirements.

[0003] During oxalate precipitation, the mixing of ammonium oxalate and dysprosium salt solutions easily generates localized instantaneous supersaturation peaks, causing nucleation and crystal growth to occur concurrently rather than in a controllable stepwise manner. This concurrent behavior makes it difficult to achieve uniform formation of dysprosium oxalate precursor particles, resulting in the coexistence of fine and coarse particles, forming a wide particle size distribution or even a bimodal distribution. Simultaneously, dysprosium oxalate particles have high surface energy, making them prone to bridging and flocculation in the precipitation environment. Particles adhere to each other through physical or chemical interactions, forming aggregates that are difficult to disperse.

[0004] The aforementioned wide particle size distribution and agglomeration issues further lead to low powder bulk density, inconsistent shrinkage behavior during molding and sintering, and a narrow densification window. During sintering, residual pores are difficult to expel, resulting in increased apparent porosity of the final dysprosium oxide ceramic and a significant decrease in optical properties such as internal transmittance. Although existing technologies attempt to improve this by adjusting precipitation parameters or adding dispersants, they often cannot simultaneously control supersaturation and particle surface conditions, resulting in limited improvement.

[0005] For example, simply adjusting the dropping rate or pH value can only locally alleviate supersaturation fluctuations, but cannot fundamentally suppress the concurrent nucleation and growth; while the addition of a single dispersant is prone to insufficient dispersion or even the introduction of impurities due to uneven adsorption or improper dosage. These limitations result in poor uniformity of dysprosium oxide powder prepared by existing methods, making it difficult to support the performance consistency requirements of high-end applications. Therefore, a new approach that can synergistically control precipitation kinetics and surface modification is urgently needed. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose a narrow particle size distribution dysprosium oxide and its preparation method, in order to solve the problem that in the existing oxalate precipitation method for preparing dysprosium oxide, the high local instantaneous supersaturation leads to simultaneous nucleation and growth, particle bridging and flocculation, resulting in a wide particle size distribution and severe agglomeration. This causes fluctuations in powder bulk density and sintering densification behavior, making it difficult to meet the stringent requirements of powder uniformity and narrow distribution for applications such as magneto-optical ceramics.

[0007] To achieve the above objectives, the present invention provides a method for preparing dysprosium oxide with a narrow particle size distribution, comprising the following steps:

[0008] (1) Preparation of dysprosium nitrate solution;

[0009] (2) Preparation of ammonium oxalate solution, dispersant modifier solution, cationic polymer solution, nonionic polymer solution, urea solution and ammonium nitrate solution;

[0010] (3) In the precipitation reactor, the pH of the system is kept constant at 3.5-4.5. After adding the dispersant modifier solution, a portion of the dysprosium nitrate solution and a portion of the ammonium oxalate solution are mixed to form a dysprosium oxalate crystal seed pulp. Then, the remaining dysprosium nitrate solution and the remaining ammonium oxalate solution are added symmetrically and synchronously through two feed pipes to cause dysprosium oxalate precipitation in the system. During the drop addition, the pH of the system is kept constant by adjusting with ammonia water. The dispersant modifier solution is added stepwise during the drop addition. The cationic polymer solution is added in the middle of the drop addition, followed by the nonionic polymer solution. The seed pulp is formed by mixing 1%-10% of the total dysprosium nitrate solution and the total ammonium oxalate solution and stirring for 3-10 minutes.

[0011] (4) After the dripping is completed, the slurry is heated and aged at a constant temperature. During the aging process, urea solution is added and the pH of the system is kept constant. Then ammonium nitrate solution is added and kept warm. Then deionized water is added to dilute and the aging continues.

[0012] (5) The precipitate was filtered, washed, solvent replaced and dried to obtain the dysprosium oxalate precursor;

[0013] (6) The dysprosium oxalate precursor is calcined to obtain dysprosium oxide with a narrow particle size distribution.

[0014] Preferably, in step (1), dysprosium oxide is reacted with 65% nitric acid to prepare dysprosium nitrate solution, and the mass ratio of deionized water, 65% nitric acid and dysprosium oxide is (250-350):(160-240):(45-55).

[0015] Preferably, in step (2), the ammonium oxalate solution is prepared by dissolving ammonium oxalate monohydrate in deionized water, and the mass ratio of the ammonium oxalate monohydrate to the deionized water is (50-70): (930-950).

[0016] Preferably, the dispersant modifier solution in step (2) is an aqueous solution of ammonium polyacrylate with a concentration of 1wt% to 2wt%, prepared from polyacrylic acid and ammonia; the weight-average molecular weight of the polyacrylic acid is 300,000 to 600,000.

[0017] Preferably, the cationic polymer solution in step (2) is an aqueous solution of polydiallyldimethylammonium chloride with a concentration of 0.3wt% to 0.5wt%.

[0018] Preferably, the nonionic polymer solution in step (2) is an aqueous solution of polyethylene glycol or an aqueous solution of polyvinylpyrrolidone, with a concentration of 4wt% to 6wt%.

[0019] Preferably, in step (2), the concentration of the urea solution is 8wt% to 10wt%; and the concentration of the ammonium nitrate solution is 8wt% to 10wt%.

[0020] Preferably, in step (3), the dispersant modifier solution is added in a stepwise manner. The stepwise addition includes: first adding the first part of the dispersant modifier solution, then adding the second part of the dispersant modifier solution at a constant rate 10 minutes after the start of the dual-channel synchronous dripping, and adding the third part of the dispersant modifier solution in the middle and later stages of the dual-channel synchronous dripping; the first part of the dispersant modifier solution accounts for 30% to 35% of the total mass of the dispersant modifier solution, the second part of the dispersant modifier solution accounts for 45% to 55% of the total mass of the dispersant modifier solution, and the remainder is the third part of the dispersant modifier solution.

[0021] Preferably, the isothermal aging in step (4) is as follows: after the dripping is completed, the slurry is heated to 60°C and the stirring is adjusted to 500 rpm for isothermal aging; urea solution is added within 2 min and aged at 60°C for 120 min; during the aging process, the pH of the system is maintained at 4 using 65 wt% nitric acid.

[0022] Preferably, the addition of ammonium nitrate solution and heat preservation in step (4) is as follows: under the condition of maintaining 60°C and stirring, ammonium nitrate solution is added to the blade shear zone within 1 minute and kept warm for 10 minutes.

[0023] Preferably, in step (4), adding deionized water for dilution and continuing aging is: adding deionized water for dilution within 5 minutes and continuing aging for 30 minutes.

[0024] Preferably, in step (5), the pore liquid is washed three times with deionized water and once with anhydrous ethanol to replace the water with ethanol.

[0025] Preferably, step (6) involves calcining in an air atmosphere according to the following segmented heating program: heating to 350°C at 2°C / min and holding for 2 hours, heating to 550°C at 3°C / min and holding for 1 hour, heating to 800°C at 5°C / min and holding for 3 hours, followed by furnace cooling.

[0026] Furthermore, the present invention provides a narrow-particle-size dysprosium oxide powder, which is obtained by the above-described method for preparing narrow-particle-size dysprosium oxide powder.

[0027] Preferably, the D50 of the narrow-particle-size dysprosium oxide powder is 0.38 to 0.45 μm, and the Span is not greater than 1.3, where Span = (D90 - D10) / D50.

[0028] The beneficial effects of this invention are:

[0029] This invention utilizes ammonium polyacrylate to disperse and modify dysprosium oxalate precursor particles. Combined with a dual-channel simultaneous dropwise precipitation strategy at constant pH, this effectively inhibits particle bridging flocculation and secondary agglomeration. Ammonium polyacrylate, acting as a dispersant, forms a stable adsorption layer on the surface of dysprosium oxalate. By enhancing electrostatic repulsion and steric hindrance, it lowers the attraction barrier between particles, maintaining the dispersion stability of the precursor particles during precipitation and aging, thereby obtaining powder with a more concentrated particle size distribution.

[0030] The synergistic effect of constant pH control and dual-channel synchronous dropping avoids local supersaturation peaks, allowing the precipitation process to be dominated by crystal growth and reducing random nucleation. This balanced precipitation environment ensures the uniformity of dysprosium oxalate particle formation, weakening the tendency for particle size distribution broadening from the source and providing a uniform precursor basis for subsequent calcination.

[0031] Sequential surface composite treatment, by introducing components such as polydiallyldimethylammonium chloride and polyethylene glycol, performs staged surface modification during particle growth, further passivating surface defect sites and reducing the tendency for hard agglomeration during aging. This treatment enhances the wettability and stability of the particle surface, allowing the powder to maintain a soft agglomerated structure after drying and calcination, which is beneficial for densification during sintering.

[0032] The combined aging sequence, including urea addition aging, ammonium nitrate short pulse, and rapid dilution, promotes rearrangement or dissolution-redeposition processes on the particle surface by regulating ionic strength and intermolecular interactions. This aging method further narrows the particle size distribution without sacrificing dispersibility, reduces the risk of irreversible flocculation, and makes it easier for dysprosium oxide powder to expel pores during sintering.

[0033] The overall technical solution, through multi-step synergy, improves the tap density and sintering densification behavior of dysprosium oxide powder, resulting in a final product with higher bulk density and optical transmittance. The controllable surface charge state and stable isoelectric point of the powder ensure its dispersibility over a wide pH range, providing a high-performance raw material foundation for applications such as magneto-optical ceramics. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0035] Figure 1 The figures show the zeta potential curves of Embodiment 1 and Comparative Examples 1-4 of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0037] This invention provides a narrow-particle-size dysprosium oxide and its preparation method. The overall approach employs a route of dysprosium nitrate solution – constant supersaturation addition of oxalate for precipitation – dispersion modification and sequential surface composite control – combined aging – controlled calcination. This addresses the problem of random nucleation and particle bridging flocculation caused by localized instantaneous supersaturation during oxalate precipitation, leading to broadened particle size distribution or even bimodal distribution. The result is dysprosium oxide powder with more concentrated particle size, narrower distribution, and more controllable agglomeration. This technical route utilizes ammonium polyacrylate to disperse and modify the dysprosium oxalate precursor particles, combined with simultaneous dual-channel addition at constant pH and controlled aging and crystal transformation to achieve the desired technical effect.

[0038] The method provided by the present invention preferably includes the following steps:

[0039] (1) Prepare dysprosium nitrate solution; (2) Prepare ammonium oxalate solution and various auxiliary agent solutions; (3) Establish seed pulp under constant pH conditions and carry out dual-channel synchronous drop precipitation. At the same time, during the precipitation and aging process, add ammonium polyacrylate dispersant, polydiallyldimethylammonium chloride diluent and polyethylene glycol solution stepwise according to the established strategy, and age by urea addition aging + ammonium nitrate short pulse + rapid dilution combination aging; (4) Filter, wash, solvent replacement and drying to obtain dysprosium oxalate precursor; (5) Segmented heating calcination to obtain narrow particle size distribution dysprosium oxide.

[0040] (I) Preparation of dysprosium nitrate solution

[0041] In the dysprosium nitrate solution preparation steps provided by the present invention, the preferred dysprosium source is the reaction of dysprosium oxide with nitric acid to obtain the dysprosium nitrate solution. Specifically, deionized water, nitric acid with a mass fraction of 65%, and dysprosium oxide are used for preparation and dissolution reaction.

[0042] In the dysprosium nitrate solution provided by this invention, the preferred mass ratio of deionized water, nitric acid with a mass fraction of 65%, and dysprosium oxide is (250-350):(160-240):(45-55). A more preferred ratio is 300:100:50.

[0043] In the dissolution reaction provided by the present invention, the heating temperature is preferably 50-70°C, more preferably 60°C; the stirring reaction time is preferably 40-80 min, more preferably 60 min.

[0044] In the dysprosium nitrate solution provided by this invention, it is preferable to add deionized water after dissolution to adjust the total solution volume to match the total volume of the ammonium oxalate solution, so that the subsequent seed preparation and dripping amounts can be strictly connected and the measurement accuracy maintained. This total volume matching helps to maintain a stable stoichiometric relationship between oxalate and dysprosium ions, reducing the cumulative effects of measurement deviation, supersaturation fluctuations, and particle size broadening from the source.

[0045] Without altering the subsequent oxalate precipitation-calcination to oxide conversion main route, the dysprosium source can also be dysprosium nitrate hydrate directly dissolved in deionized water to form a dysprosium nitrate solution, in order to reduce the exothermic fluctuations of the acid dissolution step; however, the acid dissolution method using dysprosium oxide is preferred.

[0046] In the dysprosium nitrate solution provided by this invention, a small amount of organic complexing agent can be selectively added to temporarily complex some dysprosium ions and reduce the activity of free dysprosium ions, thereby further weakening the local supersaturation peak at the moment of dropwise mixing. The complexing agent can specifically be one or more of citric acid, tartaric acid, malic acid, and lactic acid; its addition amount is preferably controlled at 0.5% to 5% relative to the molar amount of dysprosium ions, more preferably 1% to 3%, to avoid excessive complexation leading to incomplete precipitation or increased washing burden. This parameter affects the activity of free dysprosium ions, thereby affecting the nucleation rate and crystal growth ratio, which is beneficial for further convergence of particle size distribution.

[0047] (II) Preparation of ammonium oxalate solution and auxiliary agent solution

[0048] In the precipitant system provided by the present invention, the preferred source of oxalate is ammonium oxalate monohydrate dissolved in deionized water to obtain an ammonium oxalate solution.

[0049] In the ammonium oxalate solution provided by this invention, the preferred mass ratio of ammonium oxalate monohydrate to deionized water is (60±10):(940±10), more preferably 60:940. The concentration of ammonium oxalate directly affects the supersaturation level of the dropping mixing zone: too high a concentration will lead to increased instantaneous nucleation, resulting in the coexistence of fine powder and agglomeration; too low a concentration will lead to insufficient precipitation driving force, prolonged crystal growth time, and increased particle size tail.

[0050] In the dispersion modification system provided by the present invention, the dispersion modifier is preferably ammonium polyacrylate, which can be prepared by fully swelling and dispersing polyacrylic acid in water and then neutralizing it with ammonia water.

[0051] In the dispersant modifier provided by this invention, the weight-average molecular weight of polyacrylic acid is preferably 200,000 to 800,000, more preferably 300,000 to 600,000. Molecular weight affects the thickness of the adsorption layer and steric hindrance: if the molecular weight is too low, the steric hindrance is insufficient and bridging flocculation is likely to occur; if the molecular weight is too high, the solution viscosity increases and mass transfer is restricted, which may cause local flocculation.

[0052] Without introducing alkali metal impurities, the dispersant modifier can also be replaced by ammonium polymethacrylate, ammonium polymaleate, or other carboxyl-containing ammonium salt polycarboxylic acid dispersants; however, ammonium polymethacrylate is preferred in order to obtain more stable adsorption and charge repulsion under the acidity and alkalinity conditions of this system.

[0053] In the surface composite control system provided by this invention, a diluted polydiallyldimethylammonium chloride solution and a polyethylene glycol solution are preferably used, and added in a predetermined order during the precipitation stage (the diluted polydiallyldimethylammonium chloride solution is added first, followed by the polyethylene glycol solution). This sequential addition is used to control the surface composite during particle formation: the former provides cationic polymer action, and the latter provides spatial stabilization of nonionic segments, thereby reducing the tendency of defect site adhesion and aging hard agglomeration.

[0054] In the aging control step provided by this invention, urea solution and ammonium nitrate solution are preferably configured, and the process is carried out in the sequence of urea addition aging + ammonium nitrate short pulse + rapid dilution after the addition is completed. This sequence promotes surface rearrangement or dissolution-redeposition process by changing the intermolecular interaction and ionic strength environment, while reducing the risk of irreversible flocculation through rapid dilution, thereby further converging the particle size distribution and reducing the tendency for hard agglomeration without sacrificing dispersion stability.

[0055] (III) Constant pH dual-channel synchronous dripping + stepwise addition of dispersant modifier

[0056] In the dysprosium oxalate precipitation step provided by this invention, a preferred strategy is to establish a seed paste, use dual-channel synchronous dropping, and maintain constant pH control during the dropping process: First, a small amount of dysprosium nitrate solution and ammonium oxalate solution are used to form dysprosium oxalate crystal nuclei as a seed paste. Then, the remaining dysprosium nitrate solution and ammonium oxalate solution are symmetrically fed through two feed pipes and added synchronously. During the dropping process, ammonia water is used to adjust the pH of the system to a constant 4. The seed paste ensures that subsequent precipitation primarily focuses on crystal growth, reducing random nucleation. The dual-channel synchronous dropping and maintenance of constant pH reduce localized instantaneous supersaturation, suppressing the coarse particle tails and widening of the distribution caused by concurrent nucleation and growth from the source.

[0057] In the dropwise precipitation provided by this invention, the pH is preferably kept constant between 3.5 and 4.5, more preferably between 3.8 and 4.2. This parameter affects the distribution of oxalate species and the solubility balance of dysprosium oxalate, thereby affecting the ratio of nucleation rate to crystal growth rate: too low a pH can easily lead to insufficient precipitation driving force and incomplete growth; too high a pH can easily cause precipitation to be too fast, increase the local supersaturation peak, and broaden the particle size distribution.

[0058] In the dual-channel synchronous dripping method provided by this invention, the two feed streams are preferably arranged symmetrically and metered synchronously. The dripping rate is preferably 15-25 g / min, more preferably 20 g / min. The dripping rate affects the instantaneous supersaturation of the mixing zone: too high a rate or asynchronous rate will cause local concentration spikes, inducing additional nucleation and bridging flocculation; too low a rate will reduce production efficiency and prolong particle growth time, which may aggravate secondary agglomeration.

[0059] In the seed pulp preparation provided by this invention, it is preferable to use 1% to 10% of total dysprosium nitrate solution and total ammonium oxalate solution for seed preparation, more preferably 5% of each, and maintain stirring for 3 to 10 minutes. This ratio affects the initial number of crystal nuclei and the degree of dominance of subsequent growth: too few crystal nuclei will lead to increased re-nucleation in the subsequent dropwise stage; too many crystal nuclei will lead to a smaller average particle size and increased surface energy, and an increased risk of agglomeration.

[0060] In the precipitation process provided by this invention, the ammonium polyacrylate dispersant modifier is preferably added in stages, throughout the seed establishment and growth stages: first, the first part of the dispersant modifier solution is added; then, 10 minutes after the start of dual-channel dropwise addition, the second part of the dispersant modifier solution is added at a constant rate; and finally, the third part of the dispersant modifier solution is added again in the middle and later stages. This staged addition allows the newly generated dysprosium oxalate to continuously acquire an adsorption layer on its surface, enhancing electrostatic repulsion and steric hindrance between particles, inhibiting bridging flocculation and secondary agglomeration, thereby facilitating stable dispersion and further narrowing the particle size distribution.

[0061] (iv) Sequential surface composite treatment + combined aging sequence

[0062] In the precipitation mid-stage treatment step provided by this invention, it is preferable to increase the stirring intensity when the dual-channel droplet addition reaches the mid-stage, and add the diluted polydiallyldimethylammonium chloride solution along the outer edge of the liquid surface vortex, followed by the addition of the polyethylene glycol solution at the same position. This sequential addition helps reduce the adhesion of defect sites on the particle surface and the tendency for subsequent hard agglomeration during aging, thereby obtaining a more stable soft agglomerate structure and more controllable consistency.

[0063] In the post-dropleting treatment steps provided by this invention, a preferred aging sequence is a combination of urea addition aging + ammonium nitrate short pulse + rapid dilution: after dropleting, the temperature is raised and maintained at a constant temperature for aging; urea solution is added within a short time and aging continues while maintaining pH with nitric acid; then ammonium nitrate solution is rapidly added and briefly kept warm, followed immediately by rapid addition of deionized water for dilution and continued aging. This sequence promotes surface rearrangement / dissolution-redeposition through phased changes in ionic strength and intermolecular interactions, while reducing the risk of irreversible flocculation through rapid dilution, thereby further converging particle size distribution and reducing hard agglomeration.

[0064] (v) Filtration and washing - solvent replacement - drying - segmented calcination

[0065] In the solid-liquid separation and drying steps provided by this invention, preferably, dysprosium oxalate filter cake is obtained by vacuum filtration after cooling, washed multiple times with deionized water to remove soluble ions, and then washed with anhydrous ethanol to achieve the displacement of pore liquid from water to ethanol. Finally, it is dried at medium temperature in a vacuum drying oven to obtain the dysprosium oxalate precursor. The number of water washes, ethanol displacement, and vacuum drying conditions collectively affect the residual salt level and capillary force during the drying process: ethanol displacement can reduce surface tension and mitigate the risk of hard agglomeration caused by drying shrinkage, thus helping to maintain the soft agglomerate structure of the precursor.

[0066] In the calcination step provided by this invention, the dysprosium oxalate precursor is preferably spread in a corundum crucible and calcined in an air atmosphere according to a segmented heating program. After cooling, it is ground and sieved to obtain dysprosium oxide with a narrow particle size distribution. The segmented heating and moderate heating rate can avoid local sintering, necking, and hard agglomeration caused by excessively rapid decomposition of oxalate, thereby helping to maintain a concentrated particle size distribution and powder dispersibility.

[0067] The present invention will be described more fully below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0068] Example 1:

[0069] Dysprosium oxide was sourced from Yiyang Hongyuan Rare Earth Co., Ltd.; ammonium oxalate was sourced from Sigma-Aldrich ammonium oxalate monohydrate, catalog number 221716; polyacrylic acid was sourced from Shanghai Maclean Biochemical Technology Co., Ltd., catalog number P815683, with a weight-average molecular weight of approximately 450,000; polydiallyl dimethyl ammonium chloride was sourced from Sigma-Aldrich polydiallyl dimethyl ammonium chloride aqueous solution, catalog number 409022, with a concentration of 20 wt% and a weight-average molecular weight of approximately 300,000; polyethylene glycol was sourced from Shanghai Maclean Biochemical Technology Co., Ltd., catalog number P815609, with a weight-average molecular weight of approximately 6,000.

[0070] S1. Weigh 300g of deionized water and add it to a beaker. Add 200g of 65wt% nitric acid under stirring. After the temperature of the mixture drops below 30℃, add 50g of dysprosium oxide. Heat to 60℃ and maintain stirring for 60min. Then add 450g of deionized water and continue stirring for 10min to obtain a dysprosium nitrate solution.

[0071] S2. Weigh 60g of ammonium oxalate monohydrate and add it to 940g of deionized water. Stir at 25℃ for 30min to obtain an ammonium oxalate solution. Weigh 1g of polyacrylic acid and add it to 99g of deionized water. Stir at 25℃ for 60min to allow it to fully swell and disperse. Then add 1g of 25wt% ammonia water and continue stirring for 10min to obtain an ammonium polyacrylic acid dispersion modifier solution. Weigh 2g of 20wt% polydiallyldimethylammonium chloride aqueous solution and add it to 98g of deionized water. Stir for 10min to obtain a diluted polydiallyldimethylammonium chloride solution. Weigh 5g of polyethylene glycol and add it to 95g of deionized water. Stir at 60℃ for 20min to obtain a polyethylene glycol solution. Weigh 10g of urea and add it to 90g of deionized water. Stir for 10min to obtain a urea solution. Weigh 10g of ammonium nitrate and add it to 90g of deionized water. Stir for 10min to obtain an ammonium nitrate solution.

[0072] S3. Add 600g of deionized water and 10g of 65wt% nitric acid to a jacketed glass reactor. Start stirring at 900rpm and maintain the temperature at 25℃. Add 20g of ammonium polyacrylate dispersant solution, then adjust the pH of the reactor to 4 using 5wt% ammonia. Subsequently, add 50g of dysprosium nitrate solution and 50g of ammonium oxalate solution, maintaining stirring for 5min to form fine dysprosium oxalate crystal nuclei as seed pulp. Feed 950g of dysprosium nitrate solution and 950g of ammonium oxalate solution symmetrically through two feed pipes at a simultaneous dripping rate of 20g / min. During the dripping process, use... A 5wt% ammonia solution was used to adjust the pH of the solution to maintain a constant 4. Ten minutes after the start of the dual-channel dropping process, 30g of ammonium polyacrylate dispersion modifier solution was fed through the third feed pipe at a rate of 1g / min. When the simultaneous feeding of 700g of dysprosium nitrate solution and 700g of ammonium oxalate solution was completed in step S3, the simultaneous feeding was paused. The stirring speed was increased to 1100 rpm, and 100g of diluted polydiallyldimethylammonium chloride solution was added along the outer edge of the liquid surface vortex at a rate of 10g / min. After the addition was completed, stirring was continued, and 100g of polyethylene glycol solution was added. The liquid was added at the same position at a rate of 10 g / min, followed immediately by the addition of 10 g of ammonium polyacrylate dispersion modifier solution, and the simultaneous feeding of the remaining dysprosium nitrate solution and ammonium oxalate solution continued until all the dysprosium nitrate solution and ammonium oxalate solution were added. After the addition was completed, the slurry was heated to 60°C and the stirring was adjusted to 500 rpm for constant temperature aging. 100 g of urea solution was added along the blade shear zone within 2 min and the aging was maintained at 60°C for 120 min. During the aging process, the pH was maintained at 4 using 65 wt% nitric acid. Subsequently, while maintaining 60°C and stirring, 100 g of urea solution was added... ammonium nitrate solution was rapidly added to the blade shear zone within 1 minute and kept at that temperature for 10 minutes. Immediately afterwards, 400 g of deionized water was added within 5 minutes for rapid dilution and aging continued for 30 minutes. After cooling to 25°C, dysprosium oxalate filter cake was obtained by vacuum filtration. The cake was washed three times with deionized water and then once with anhydrous ethanol, and vacuum filtration was continued for 10 minutes to complete the replacement of pore liquid from water to ethanol. The filter cake was then spread flat on a glass tray and placed in a vacuum drying oven and dried at 80°C and a vacuum of -0.08 MPa for 12 hours to obtain the dysprosium oxalate precursor.

[0073] S4. The dysprosium oxalate precursor was placed in a corundum crucible and spread out. It was then calcined in air according to the following procedure: the temperature was increased to 350°C at 2°C / min and held for 2 hours; the temperature was increased to 550°C at 3°C / min and held for 1 hour; the temperature was increased to 800°C at 5°C / min and held for 3 hours. The furnace was then cooled to room temperature. After cooling, the mixture was ground in an agate mortar and passed through a 200-mesh sieve to obtain dysprosium oxide with a narrow particle size distribution.

[0074] Example 2:

[0075] The difference between Example 2 and Example 1 is that the step S3, "subsequently adding 50g of dysprosium nitrate solution and 50g of ammonium oxalate solution, maintaining stirring for 5 minutes to form fine dysprosium oxalate crystal nuclei as seed paste; and feeding 950g of dysprosium nitrate solution and 950g of ammonium oxalate solution symmetrically through two feed pipes and adding them simultaneously at 20g / min", is adjusted to "subsequently adding 10g of dysprosium nitrate solution and 10g of ammonium oxalate solution, maintaining stirring for 3 minutes to form fine dysprosium oxalate crystal nuclei as seed paste; and feeding 990g of dysprosium nitrate solution and 990g of ammonium oxalate solution symmetrically through two feed pipes and adding them simultaneously at 20g / min"; the other conditions are the same as in Example 1.

[0076] Example 3:

[0077] The difference between Example 3 and Example 1 is that the step S3, "subsequently adding 50g of dysprosium nitrate solution and 50g of ammonium oxalate solution, maintaining stirring for 5 minutes to form fine dysprosium oxalate crystal nuclei as seed paste; and symmetrically feeding 950g of dysprosium nitrate solution and 950g of ammonium oxalate solution through two feed pipes and simultaneously adding dropwise at 20g / min", is adjusted to "subsequently adding 100g of dysprosium nitrate solution and 100g of ammonium oxalate solution, maintaining stirring for 10 minutes to form fine dysprosium oxalate crystal nuclei as seed paste; and symmetrically feeding 900g of dysprosium nitrate solution and 900g of ammonium oxalate solution through two feed pipes and simultaneously adding dropwise at 20g / min"; the remaining conditions are the same as in Example 1.

[0078] Example 4:

[0079] The difference between Example 4 and Example 1 is that the constant pH of the addition and aging process in step S3 is adjusted from 4 to 3.8 (achieved through ammonia / nitric acid linkage control); the other conditions are the same as in Example 1.

[0080] Example 5:

[0081] In this embodiment, the polyvinylpyrrolidone used is a product of Shanghai Maclean Biochemical Technology Co., Ltd., product number P816206, with a weight-average molecular weight of approximately 8000.

[0082] The difference between Example 5 and Example 1 is that the polyethylene glycol solution added in step S3 is replaced with an aqueous solution of polyvinylpyrrolidone (the total mass of the solution is the same as the method of addition); the other conditions are the same as in Example 1.

[0083] Comparative Example 1:

[0084] The difference between Comparative Example 1 and Example 1 is that in step S3, instead of first adding a small amount of dysprosium nitrate solution and ammonium oxalate solution to form fine dysprosium oxalate crystal nuclei as seed pulp, and then feeding the remaining dysprosium nitrate solution and ammonium oxalate solution symmetrically through two feed pipes and adding them dropwise simultaneously, and using ammonia water to adjust the solution to maintain a constant pH of 4 during the dropwise addition, instead, 1000g of ammonium oxalate solution obtained in step S2 is added to the reactor all at once, and then 1000g of dysprosium nitrate solution obtained in step S1 is added dropwise into the reactor at 20g / min under stirring conditions, and the pH is no longer maintained at a constant pH of 4 using 5wt% ammonia water during the dropwise addition; the other conditions are the same as in Example 1.

[0085] Comparative Example 2:

[0086] The difference between Comparative Example 2 and Example 1 is that in step S3, the ammonium polyacrylate dispersion modifier solution is not added in stages, such as adding 20g first, adding 30g at 1g / min after the first 10 minutes of dual-channel dripping, and then adding another 10g in the middle and later stages. Instead, the ammonium polyacrylate dispersion modifier solution is added all at once at the beginning of step S3, with a total addition amount of 60g. No additional ammonium polyacrylate dispersion modifier solution is added in the subsequent dripping and middle and later stages. The other conditions are the same as in Example 1.

[0087] Comparative Example 3:

[0088] The difference between Comparative Example 3 and Example 1 is that in step S3, the sequential surface composite treatment of pausing synchronous feeding in the middle of the dual-channel droplet addition and adding polydiallyldimethylammonium chloride diluent followed by polyethylene glycol solution is not performed. That is, when the synchronous feeding of 700g dysprosium nitrate solution and 700g ammonium oxalate solution is completed in the dual-channel droplet addition in step S3, the synchronous feeding is not paused, and polydiallyldimethylammonium chloride diluent and polyethylene glycol solution are not added; the other conditions are the same as in Example 1.

[0089] Comparative Example 4:

[0090] The difference between Comparative Example 4 and Example 1 is that: after the addition of urea in step S3, the combined aging sequence of urea addition aging + ammonium nitrate short pulse + rapid dilution is not used. Instead, after the addition of urea, the slurry is heated to 60°C and the stirring is adjusted to 500 rpm for constant temperature aging for 160 min. During the aging process, the pH is maintained at 4 with 65 wt% nitric acid. Urea solution and ammonium nitrate solution are not added during the aging process, and deionized water is not used for rapid dilution. The other conditions are the same as those in Example 1.

[0091] Performance testing:

[0092] Powder particle size distribution: Weigh 0.20g of powder and add it to 200mL of deionized water. After pre-dispersing with magnetic stirring at 600rpm for 2min, disperse it with ultrasonication (power 200W) for 2min. Add the dispersion to the wet circulation tank of the laser particle size analyzer. Set the circulation flow rate to 6.0L / min and the pump speed to 40%. Before the test, use deionized water to subtract the background. During the test, set the refractive index to 1.80 and the absorptivity to 0.10. Collect data for 60s for each test and automatically invert to obtain D10, D50, and D90. Calculate Span = (D90-D10) / D50.

[0093] Tapped density: Weigh 50.0g of powder into a 100mL graduated cylinder, install it in a tapped density meter, set the number of tapping cycles to 3000, read the volume after tapping and calculate the tapped density.

[0094] Zeta potential and isoelectric point: The zeta potential was tested according to GB / T 32671.2-2019, and the isoelectric point was determined according to GB / T 44149-2024. A 1 mmol / L ammonium nitrate aqueous solution was prepared as the background electrolyte solution. 0.050 g of powder was weighed and added to 100 mL of the background electrolyte solution. The mixture was magnetically stirred at 600 rpm for 5 min and then ultrasonically dispersed (power 200 W) for 2 min. The pH of the dispersion was adjusted to 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, and 11.0 respectively with 65 wt% nitric acid and 5 wt% ammonia. After standing at a constant temperature of 25℃ for 3 min, the supernatant was taken for electrophoretic light scattering test. Each pH point was tested 3 times and the average zeta potential was taken. The pH corresponding to the zero crossing of the zeta potential was taken as the isoelectric point.

[0095] Sintering densification behavior: 5.00g of powder was weighed and placed into a φ20mm cemented carbide mold, unidirectionally dry-pressed at a pressure of 200MPa for 60s, and demolded to obtain a circular green body. The green body was placed in an air atmosphere box furnace, heated to 600℃ at 5℃ / min and held for 1h to remove adsorbed / residual organic matter, then heated to 1700℃ at 10℃ / min and held for 4h, and then cooled to room temperature with the furnace to obtain the sintered body. Linear shrinkage: The diameter of the circular body before and after sintering was measured with vernier calipers, and the linear shrinkage was calculated as (diameter before sintering - diameter after sintering) / diameter before sintering × 100%. Bulk density and apparent porosity: The bulk density and apparent porosity of the sintered body were determined according to the Archimedes method in GB / T 25995-2010.

[0096] Internal transmittance: GB / T 7962.12-2010 determines the internal transmittance of sintered bodies. The sintered discs obtained from the sintering densification behavior test were polished on both sides with 800#, 1200#, and 2000# silicon carbide sandpaper, and then polished to a mirror finish with 1μm diamond suspension. The sample thickness was adjusted to 1.00 mm using a thickness gauge and the thickness value was recorded. The internal transmittance at λ=532nm and λ=1064nm was measured using a UV-Vis-NIR spectrophotometer.

[0097] The test results are shown in Table 1.

[0098] Table 1 Performance Test Results

[0099] project D10 / μm D50 / μm D90 / μm Span <![CDATA[Tap density / g·cm -3 > isoelectric point pH Sintering linear shrinkage rate / % <![CDATA[Sintered bulk density / g·cm -3 > Apparent porosity / % Intraspectral transmittance (532nm) / % Intraspectral transmittance (1064nm) / % Example 1 0.24 0.40 0.58 0.85 2.91 9.3 19.6 7.77 ≤0.5 62.5 73.4 Example 2 0.18 0.45 0.75 1.27 2.74 9.2 18.8 7.71 ≤0.5 58.7 71.0 Example 3 0.21 0.38 0.60 1.03 2.65 9.3 19.4 7.75 ≤0.5 61.0 72.6 Example 4 0.25 0.42 0.62 0.88 2.98 9.3 19.0 7.73 ≤0.5 60.2 72.0 Example 5 0.23 0.41 0.64 1.00 2.82 9.2 18.9 7.72 ≤0.5 59.3 71.5 Comparative Example 1 0.15 0.65 1.35 1.85 2.32 8.7 17.4 7.59 2.1 44.8 60.3 Comparative Example 2 0.17 0.60 1.18 1.68 2.41 8.9 17.8 7.62 1.8 47.5 62.0 Comparative Example 3 0.20 0.50 0.92 1.44 2.56 9.0 18.2 7.66 1.2 52.6 66.1 Comparative Example 4 0.19 0.52 0.97 1.50 2.52 9.0 18.0 7.65 1.4 50.8 65.0

[0100] Data Analysis:

[0101] From Table 1 and Figure 1 Data from the embodiments show that the dysprosium oxide powder prepared by this invention exhibits relatively small D10, D50, and D90 values ​​and a low span, while maintaining a high tap density. As the pH increases, the Zeta potential continuously decreases and reaches an isoelectric point around pH 9, indicating that the surface charge state of the powder is adjustable with pH and the dispersion modification effect is stable. Furthermore, the sintering linear shrinkage and sintering bulk density increase simultaneously, while the apparent porosity decreases, resulting in high internal transmittance at both 532 nm and 1064 nm. The possible reasons are as follows: by establishing seed pulp, synchronously adding through dual channels, and controlling constant pH, local instantaneous supersaturation is reduced and the precursor is mainly grown as crystals, thus inhibiting the coarse particle tail caused by random nucleation from the source; in addition, the segmented addition of ammonium polyacrylate dispersant modifier, the sequential surface composite treatment of polydiallyldimethylammonium chloride and polyethylene glycol (or polyvinylpyrrolidone), and the combined aging sequence of urea addition, ammonium nitrate short pulse and rapid dilution can weaken the tendency of dysprosium oxalate particles to bridge flocculate and hard agglomerate, forming a more stable soft agglomerate structure, so that it can still maintain dispersibility after subsequent filtration and washing, solvent replacement, drying and segmented calcination, and more easily remove pores and obtain more complete densification during the sintering process.

[0102] From Table 1 and Figure 1 The data from Example 1 and Comparative Example 1 show that when a small amount of dysprosium nitrate solution and ammonium oxalate solution are not used to form fine dysprosium oxalate crystal nuclei as seed paste, and ammonia water is no longer used to maintain a constant pH during the dropwise addition process, the powder particle size distribution is more easily broadened, which adversely affects the compaction and subsequent densification, and leads to a decrease in transmission performance after sintering. Combined with... Figure 1It is evident that under these conditions, the Zeta potential curve is more likely to approach zero in the pH range near the isoelectric point, resulting in a narrower dispersion stability window and making particles more prone to aggregation and structural locking. This may be due to the superposition of localized instantaneous supersaturation and pH fluctuations during the dropwise addition process, leading to simultaneous nucleation and growth, and an uneven particle surface state, making it difficult to form a stable charge repulsion and adsorption layer. Consequently, after drying and calcination, these particles are more likely to transform into hard aggregates and residual pore sources. Therefore, the establishment of seed pulp and constant pH control are not independent but jointly determine the controllability and dispersion stability of the precipitation process.

[0103] From Table 1 and Figure 1 The data from Example 1 and Comparative Example 2 show that when the ammonium polyacrylate dispersant modifier solution is added all at once at the beginning of the droplet addition without being added in stages, it is difficult to balance the convergence and packing properties of the powder particle size distribution, the sintering densification trend is weakened and the transmission performance is reduced. Figure 1 Further analysis shows that Comparative Example 2 exhibits insufficient increase in absolute Zeta potential or decreased stability within the critical pH range, indicating that a single addition is more likely to cause localized adsorption supersaturation and charge neutralization, inducing early flocculation and solidification. This structural defect is difficult to completely rearrange during subsequent aging and washing processes, ultimately manifesting as obstructed pore expulsion during calcination and sintering. These results demonstrate that the staged addition of ammonium polyacrylate dispersant, synchronized with the dropwise addition process, can continuously inhibit agglomeration and maintain the stability of the dispersion system at different stages, thus amplifying the effect in conjunction with constant pH control.

[0104] From Table 1 and Figure 1 The data from Example 1 and Comparative Example 3 show that when the synchronous feeding in the middle section of the dual-channel droplet addition is paused and the sequential surface composite treatment of polydiallyl dimethyl ammonium chloride dilution and polyethylene glycol solution is added, although a certain degree of particle size control can still be achieved, the synergistic improvement in particle size distribution convergence, packing, and sintering densification is insufficient, and the transmission performance decreases accordingly. Combined with... Figure 1 It can be inferred that without sequential surface composite treatment, the charge regulation and adsorption layer construction on the particle surface are incomplete, resulting in weaker stability of the Zeta potential curve over a wider pH range and a greater likelihood of re-agglomeration near the isoelectric point. This may be because sequential surface composite treatment helps to passivate and regulate the wetting of defect sites on the particle surface in stages, weakening short-range attraction between particles and inhibiting the evolution of soft agglomeration into hard agglomeration. When this step is missing, subsequent washing and drying are more likely to form irreversible adhesive structures, which can then be transformed into sintering pore sources. Therefore, sequential surface composite treatment plays a crucial supporting role in the dispersion stabilization-densification-transmission chain.

[0105] From Table 1 and Figure 1The data from Example 1 and Comparative Example 4 show that when the combined aging sequence of urea addition aging, ammonium nitrate short pulse and rapid dilution is removed, the overall performance of powder particle size distribution and stacking behavior decreases, the apparent porosity after sintering is difficult to further reduce, and the transmission performance is also affected. Figure 1 The results indicate that the stable range of the Zeta potential curve narrows or approaches zero more easily under these conditions, reflecting that the surface state and ionic environment were not effectively reorganized during the aging process, making the particles more prone to re-agglomeration and hardening in subsequent treatment stages. This may be because the combined aging sequence, through a continuous process of slow-release regulation, short-term perturbation, and rapid dilution in the later stages of precipitation, promotes the rearrangement of the adsorbed layer on the particle surface and weakens the adhesion caused by local ionic strength, thereby reducing the probability of hard agglomeration formation. Removing this sequence makes it easier to retain unfavorable agglomeration structures, ultimately limiting densification and transmission enhancement. These results demonstrate a synergistic effect between the combined aging sequence, the initial dispersion modification, and the sequential surface composite treatment.

[0106] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing dysprosium oxide with a narrow particle size distribution, characterized in that, Includes the following steps: (1) Preparation of dysprosium nitrate solution; (2) Preparation of ammonium oxalate solution, dispersant modifier solution, cationic polymer solution, nonionic polymer solution, urea solution and ammonium nitrate solution; (3) In the precipitation reactor, the pH of the system is kept constant at 3.5 to 4.

5. After adding the dispersant modifier solution, a portion of the dysprosium nitrate solution and a portion of the ammonium oxalate solution are mixed to form dysprosium oxalate crystal seed pulp. Then, the remaining dysprosium nitrate solution and the remaining ammonium oxalate solution are added symmetrically and synchronously through two feed pipes to cause dysprosium oxalate precipitation in the system. During the drop addition, the pH of the system is kept constant by adjusting with ammonia water, and the dispersant modifier solution is added step by step during the drop addition. The cationic polymer solution is added during the middle stage of the dropwise addition, followed by the nonionic polymer solution; the seed pulp is formed by mixing 1% to 10% of total dysprosium nitrate solution and total ammonium oxalate solution and stirring for 3 to 10 minutes. (4) After the dripping is completed, the slurry is heated and aged at a constant temperature. During the aging process, urea solution is added and the pH of the system is kept constant. Then ammonium nitrate solution is added and kept warm. Then deionized water is added to dilute and the aging continues. (5) The precipitate was filtered, washed, solvent replaced and dried to obtain the dysprosium oxalate precursor; (6) The dysprosium oxalate precursor is calcined to obtain dysprosium oxide with a narrow particle size distribution.

2. The method for preparing narrow-particle-size dysprosium oxide according to claim 1, characterized in that, In step (1), dysprosium oxide is reacted with 65% nitric acid to prepare dysprosium nitrate solution, and the mass ratio of deionized water, 65% nitric acid and dysprosium oxide is (250-350):(160-240):(45-55); in step (2), ammonium oxalate solution is prepared by dissolving ammonium oxalate monohydrate in deionized water, and the mass ratio of ammonium oxalate monohydrate to deionized water is (50-70):(930-950).

3. The method for preparing narrow-particle-size dysprosium oxide according to claim 1, characterized in that, In step (2), the dispersant modifier solution is an aqueous solution of ammonium polyacrylate with a concentration of 1wt% to 2wt%, prepared from polyacrylic acid and ammonia; the weight-average molecular weight of the polyacrylic acid is 300,000 to 600,000.

4. The method for preparing narrow-particle-size dysprosium oxide according to claim 1, characterized in that, In step (2), the cationic polymer solution is a polydiallyldimethylammonium chloride aqueous solution with a concentration of 0.3wt% to 0.5wt%; the nonionic polymer solution is a polyethylene glycol aqueous solution or a polyvinylpyrrolidone aqueous solution with a concentration of 4wt% to 6wt%; the urea solution has a concentration of 8wt% to 10wt%; and the ammonium nitrate solution has a concentration of 8wt% to 10wt%.

5. The method for preparing narrow-particle-size dysprosium oxide according to claim 1, characterized in that, In step (3), the dispersant modifier solution is added in a stepwise manner. The stepwise addition includes: first adding the first part of the dispersant modifier solution, then adding the second part of the dispersant modifier solution at a constant rate 10 minutes after the start of the dual-channel synchronous dripping, and adding the third part of the dispersant modifier solution in the middle and later stages of the dual-channel synchronous dripping; the first part of the dispersant modifier solution accounts for 30% to 35% of the total mass of the dispersant modifier solution, the second part of the dispersant modifier solution accounts for 45% to 55% of the total mass of the dispersant modifier solution, and the remainder is the third part of the dispersant modifier solution.

6. The method for preparing narrow-particle-size dysprosium oxide according to claim 1, characterized in that, The constant temperature aging in step (4) is as follows: after the dripping is completed, the slurry is heated to 60°C and the stirring is adjusted to 500 rpm for constant temperature aging; urea solution is added within 2 min and aging is maintained at 60°C for 120 min. During the aging process, the pH of the system is maintained at 4 using 65 wt% nitric acid; the addition of ammonium nitrate solution and heat preservation in step (4) is as follows: under the condition of maintaining 60°C and stirring, ammonium nitrate solution is added to the blade shear zone within 1 min and heat preservation is maintained for 10 min; the addition of deionized water for dilution and continued aging in step (4) is as follows: deionized water is added within 5 min for dilution and continued aging is maintained for 30 min.

7. The method for preparing narrow-particle-size dysprosium oxide according to claim 1, characterized in that, In step (5), the pore liquid is washed three times with deionized water and once with anhydrous ethanol to replace the water with ethanol.

8. The method for preparing narrow-particle-size dysprosium oxide according to claim 1, characterized in that, Step (6) involves calcining in an air atmosphere according to the following segmented heating program: heating to 350°C at 2°C / min and holding for 2 hours, heating to 550°C at 3°C / min and holding for 1 hour, heating to 800°C at 5°C / min and holding for 3 hours, followed by furnace cooling.

9. A narrow-particle-size dysprosium oxide, characterized in that, It is obtained by the method for preparing narrow-particle-size dysprosium oxide according to any one of claims 1-8.

10. The narrow-particle-size dysprosium oxide according to claim 9, characterized in that, The narrow-particle-size dysprosium oxide powder has a D50 of 0.38–0.45 μm and a Span of no more than 1.3, where Span = (D90 - D10) / D50.

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