Preparation method of pyrophosphate with smooth and compact morphology

Abstract

The invention relates to the technical field of functional materials, in particular to a preparation method of pyrophosphate with smooth and compact morphology, which comprises the following steps: by taking phosphoric acid as a phosphorus source and metal oxide powder as a metal source, mixing a phosphoric acid aqueous solution with the metal oxide powder, and performing pre-reaction under a stirring condition to obtain a blocky precursor product; the method comprises the following steps: adding a metal oxide into the pyrophosphate, calcining at a high temperature, crushing, grinding and screening to obtain the pyrophosphate with the required particle size and a solid solution of the pyrophosphate, the metal oxide is an oxide of divalent metals Ca, Mg, Fe, Co, Ni, Cu, Zn, Mn or Cd, the high-temperature calcining temperature is 700-1200 DEG C, and the high-temperature calcining time is 1-72 hours. The pyrophosphate prepared by the preparation method is regular in shape, smooth in surface and uniform in performance, and the preparation method is simple, low in cost, short in preparation period and suitable for batch production.

Description

Technical Field

[0001] The invention relates to a method for preparing pyrophosphate with smooth and dense morphology, and belongs to the technical field of functional materials. Background Art

[0002] Pyrophosphate has special thermal and optoelectronic properties and is widely used in production and life, such as fertilizer, catalyst, negative thermal expansion reinforcement, optoelectronic material, etc. In addition, if pyrophosphate has a smooth and dense morphology, it is more conducive to the realization of stable and high-quality downstream applications, and can effectively avoid the problem of holes in the preparation of composite materials. At present, the demand for the smoothness and density of pyrophosphate is also increasing.

[0003] Traditional synthesis methods are divided into wet method and solid phase sintering method. The wet process is complex, the cycle is long, and a large amount of harmful waste liquid will be generated, which is not conducive to industrial production and energy conservation and environmental protection. The solid phase sintering method usually uses diammonium hydrogen phosphate and metal oxide as raw materials for two-step calcination. The synthesis cycle is long, and ammonia will be released during the calcination process. In the large-scale preparation process, due to the excessive thickness of the powder accumulation, it is difficult to completely exhaust the ammonia in the first step of calcination, resulting in the continuous ammonia discharge in the second step of calcination, causing the powder to be loose and porous. Porous powders are prone to local defects when preparing composite materials, which damages the material properties. For example, the methods used in Chinese patent applications CN118588926A, CN118431440A, and CN115521140A all require two sinterings. At present, there is no method for preparing smooth and dense pyrophosphate that is very suitable for industrial application. Therefore, it is of great significance to develop a large-scale preparation of dense and smooth pyrophosphate powder. Summary of the invention

[0004] The present invention aims to solve the problems existing in the prior art and provides a method for preparing a pyrophosphate with a smooth and dense morphology. The pyrophosphate prepared by the preparation method has a smooth and dense morphology, a simple preparation process, is environmentally friendly, and is conducive to large-scale production. When used as a composite material additive, the problem of holes in the preparation of composite materials can be solved.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: a method for preparing a pyrophosphate with a smooth and dense morphology, the preparation method comprising: using phosphoric acid as a phosphorus source and metal oxide powder as a metal source, mixing an aqueous phosphoric acid solution with the metal oxide powder, and performing a pre-reaction under stirring conditions to obtain a block precursor product, and then calcining at a high temperature, crushing, grinding and screening to obtain a pyrophosphate with a desired particle size and a solid solution thereof.

[0006] Furthermore, the metal oxide is an oxide of a divalent metal such as Ca, Mg, Co, Ni, Cu, Zn, Mn or Cd.

[0007] Furthermore, the pyrophosphate and its solid solution are monobasic pyrophosphate formed by a single metal oxide and polybasic pyrophosphate solid solution formed by any combination of different metal oxides.

[0008] Furthermore, the mass concentration of phosphoric acid in the phosphoric acid aqueous solution is 50%-85%.

[0009] Furthermore, when the metal oxide is an oxide of Ca, Mg, or Mn, the mass concentration of phosphoric acid in the aqueous phosphoric acid solution is ≥50% and ≤60%; when the metal oxide is an oxide of Co, Ni, or Zn, the mass concentration of phosphoric acid in the aqueous phosphoric acid solution is >60% and ≤75%; when the metal oxide is an oxide of Cu or Cd, the mass concentration of phosphoric acid in the aqueous phosphoric acid solution is >75% and ≤85%.

[0010] Furthermore, the stoichiometric ratio of the metal oxide to the phosphoric acid is 1:(1-1.3).

[0011] Furthermore, the operation of mixing the phosphoric acid aqueous solution with the metal oxide powder is: adding the metal oxide powder into the phosphoric acid aqueous solution at one time and immediately starting stirring.

[0012] Furthermore, during the pre-reaction process, the temperature of the system is controlled at 10 to 80°C, the stirring speed is 120 to 300 rpm, and the stirring time is 10 to 60 min, so that the materials can be fully mixed and initially reacted. The materials are then stirred for another 10 to 60 min at a stirring speed of 60 to 150 rpm. The reaction releases a large amount of heat, the system temperature rises, and the dehydration reaction is accelerated.

[0013] Furthermore, during the pre-reaction process, stirring is performed continuously, heat is released during the reaction process, the amount of liquid phase gradually decreases, and the fluidity of the slurry gradually decreases. Stirring is stopped after the water vapor is completely evaporated to form a block precursor product.

[0014] Furthermore, the temperature of the high temperature calcination is 700-1200° C., and the time of the high temperature calcination is 1-72 hours.

[0015] Preferably, the temperature of the high-temperature calcination is 1000-1200° C., and the time of the high-temperature calcination is 1-12 hours.

[0016] The beneficial effects of the present invention are:

[0017] The preparation method of the present invention uses phosphoric acid and metal oxide as raw materials to calcine and synthesize pyrophosphate in one step. The preparation process is simple, the cycle is short, the cost is low, and it is environmentally friendly and conducive to large-scale production. The prepared pyrophosphate particles have regular, dense, smooth shapes and high purity. They can be used as composite material additives in the fields of aerospace, microelectronic devices, photoelectric catalysis, etc.

[0018] In the preparation method of the present invention, the fluidity of the slurry can be enhanced by using an aqueous solution of phosphoric acid (i.e., phosphoric acid diluted with water) as a raw material. The concentration of the phosphoric acid solution and the initial stirring temperature are controlled to slow down the reaction rate of the acid and the alkaline solid oxide, so that the raw materials react on the basis of full mixing, thereby improving the uniformity and purity of the product. Increasing the fluidity of the liquid phase is conducive to improving the flow mass transfer rate. During the reaction, the liquid phase penetrates into the pores of the particles to increase the density of the particles; in addition, with a higher calcination temperature, the pyrophosphate is slightly melted, so that the density and smoothness of the particle surface are further improved.

[0019] In the preparation method of the present invention, by controlling the phosphoric acid concentration and the pre-reaction temperature, the reaction rate is controlled, the phosphoric acid aqueous solution and the metal oxide powder are fully mixed, and the reaction and dehydration are gradually performed, so that monohydrogen phosphate crystal particles are finally formed in the reaction system, and then pyrophosphate is formed by high-temperature sintering. During the high-temperature sintering process, the final pyrophosphate product is formed on the basis of the monohydrogen phosphate crystal particles, so that the pyrophosphate has higher density and smoothness. The smooth and dense pyrophosphate can solve the problem of holes in the preparation of composite materials when used as a composite material additive in downstream applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The X-ray diffraction patterns and scanning electron microscope images of copper pyrophosphate of Example 1 and Comparative Example 1 are shown;

[0021] Figure 2 The X-ray diffraction pattern and scanning electron microscope image of the manganese pyrophosphate powder of Example 2;

[0022] Figure 3 The X-ray diffraction pattern and scanning electron microscope image of zinc pyrophosphate powder of Example 3;

[0023] Figure 4 The X-ray diffraction pattern and scanning electron microscope image of the cobalt pyrophosphate powder of Example 4;

[0024] Figure 5 The X-ray diffraction pattern and scanning electron microscope image of the calcium pyrophosphate powder of Example 5;

[0025] Figure 6 The X-ray diffraction pattern and scanning electron microscope image of the cadmium pyrophosphate powder of Example 6;

[0026] Figure 7 is Zn of Example 7 1.6 Mg 0.4 P2O7 powder X-ray diffraction pattern and scanning electron microscope image;

[0027] Figure 8 The X-ray diffraction pattern and scanning electron microscope image of the copper pyrophosphate powder of Comparative Example 2;

[0028] Fig. 9 The X-ray diffraction pattern and scanning electron microscope image of zinc pyrophosphate powder of Comparative Example 3;

[0029] Fig.10 The X-ray diffraction pattern and scanning electron microscope image of the copper pyrophosphate powder of Comparative Example 4;

[0030] Fig.11 The X-ray diffraction pattern and scanning electron microscope image of the copper pyrophosphate powder of Comparative Example 5 are shown. DETAILED DESCRIPTION

[0031] The specific implementation of the present invention is described in detail below. The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0033] A method for preparing a pyrophosphate with a smooth and dense morphology comprises the following steps: using phosphoric acid as a phosphorus source and metal oxide powder as a metal source, mixing an aqueous phosphoric acid solution with the metal oxide powder, and performing a pre-reaction under stirring conditions to obtain a block precursor product, and then calcining at a high temperature, crushing, grinding and screening to obtain the pyrophosphate and its solid solution with a desired particle size.

[0034] Specifically, the metal oxide is an oxide of a divalent metal such as Ca, Mg, Co, Ni, Cu, Zn, Mn or Cd.

[0035] That is, the molecular formula of the pyrophosphate is A2P2O7, and A is Ca, Mg, Co, Ni, Cu, Zn, Mn or Cd.

[0036] More specifically, the divalent metal oxides may be combined in any manner to form a multi-component solid solution of pyrophosphate.

[0037] Specifically, the mass concentration of phosphoric acid in the phosphoric acid aqueous solution is 50%-85%.

[0038] More specifically, when the metal oxide is an oxide of Ca, Mg, or Mn, the mass concentration of phosphoric acid in the aqueous phosphoric acid solution is ≥50% and ≤60%; when the metal oxide is an oxide of Co, Ni, or Zn, the mass concentration of phosphoric acid in the aqueous phosphoric acid solution is >60% and ≤75%; when the metal oxide is an oxide of Cu or Cd, the mass concentration of phosphoric acid in the aqueous phosphoric acid solution is >75% and ≤85%.

[0039] More specifically, when the metal oxides include two or more species forming a solid solution, the concentration of the phosphoric acid solution is selected as the weighted average value of each interval.

[0040] More specifically, the method for preparing the phosphoric acid aqueous solution is as follows: according to the phosphoric acid dilution requirements, concentrated phosphoric acid is slowly added into deionized water, and the solution is continuously stirred to obtain the phosphoric acid aqueous solution.

[0041] Specifically, the stoichiometric ratio of the metal oxide to the phosphoric acid is 1:(1-1.3).

[0042] Specifically, the operation when the phosphoric acid aqueous solution is mixed with the metal oxide powder is as follows: the analytical grade metal oxide powder is added to the phosphoric acid aqueous solution at one time and stirred immediately. The metal oxide is added to the phosphoric acid aqueous solution at one time for reaction, which is more conducive to the raw materials being mixed evenly and reacting according to the ratio, and finally obtaining a smooth and dense pyrophosphate. If the metal oxide is slowly added to the phosphoric acid aqueous solution in batches, solid precursor products may be preferentially generated in the reaction system, reducing the fluidity of the slurry, causing local uneven components, and not conducive to obtaining products with uniform quality. The stirring process must be continued, otherwise the slurry will be stratified due to density differences, resulting in uneven product components. In addition, if the stirring speed is too slow, the slurry is not easy to mix evenly, and it is difficult to obtain a target product with uniform quality in the end; if the stirring speed is too fast, the system will react violently, resulting in uncontrollable temperature of the entire system, too high system temperature, rapid formation of blocky substances in the system, and too fast water vapor discharge process, which will eventually lead to a decrease in the density and smoothness of the target product.

[0043] Specifically, during the pre-reaction process, the temperature of the early control system is 10-80°C, the stirring speed is 120-300 rpm, and the stirring time is 10-60min, so that the materials are fully mixed and initially reacted, and then stirred for another 10-60min, the stirring speed is 60-150 rpm, the slurry fluidity continues to decrease, and a large amount of heat is released, and the slurry is stirred until it becomes a viscous clay-like state, then the stirring is stopped, and it is allowed to stand for half a minute to form a block precursor product. If the temperature in the system is too low, it will affect the reaction process, and the water vapor cannot be discharged smoothly, which ultimately affects the preparation of the product; if the reaction temperature is too high, the reaction process is accelerated, the raw materials are difficult to fully mix, and the water vapor discharge speed is too fast, which ultimately affects the purity and smoothness of the target product. The temperature control of the pre-reaction process can be controlled by a water bath, but this is not a limitation of the technology of the present invention, and other conventional temperature control methods can also be used.

[0044] Preferably, during the pre-reaction process, the temperature of the system is controlled at 20-40°C, the stirring speed is 160-300 rpm, and the stirring time is 20-30 min; then the system is stirred for another 15-30 min at a stirring speed of 80-150 rpm.

[0045] More specifically, during the pre-reaction process, the stirring speed in the early stage is v, in units of revolutions per minute; the temperature of the system in the early stage is t, in units of °C; then v = V ± 15, V = 83exp (0.031t). The stirring speed and the temperature of the system are more conducive to efficiently obtaining high-quality target products by conducting experiments according to this relationship.

[0046] More specifically, the mixing process needs to be done in a well-ventilated environment and away from open flames.

[0047] More specifically, in order to facilitate the smooth discharge of water vapor in the later stage of the reaction, the height-to-diameter ratio of the slurry accumulation in the container should be less than 1 / 3.

[0048] Because heat accumulates in the later stage of the reaction, the reaction speed increases, and the fluidity of the slurry decreases due to the gradual drainage of the reaction. If the thickness of the material in the reaction container is too large, it is easy to cause the lower layer of material to be pressed. Under the action of air pressure, the material in the reaction container is easy to be flushed out, resulting in safety and pollution problems. If the ratio of material thickness to container diameter is controlled within 1 / 3, the exhaust in the later stage of the reaction is relatively smooth, and it is not easy to cause the material to be flushed out.

[0049] Specifically, the temperature of the high-temperature calcination is 700-1200° C., and the time of the high-temperature calcination is 1-72 hours.

[0050] Preferably, the temperature of the high-temperature calcination is 1000-1200° C., and the time of the high-temperature calcination is 1-12 hours.

[0051] Example 1

[0052] Analytical grade copper oxide powder was used as the metal source and phosphoric acid was used as the phosphorus source. The mass concentration of phosphoric acid in the phosphoric acid aqueous solution used in this embodiment was 85%, and the molar ratio of copper oxide powder to phosphoric acid was 1:1.1 (i.e., the molar ratio of Cu to P was 1:1.1).

[0053] Weigh copper oxide powder and phosphoric acid aqueous solution according to the molar ratio, add phosphoric acid aqueous solution into the crucible, then add copper oxide powder at one time, keep stirring in the fume hood to prevent the raw materials from stratifying, control the system temperature to 40°C, the stirring speed to 300 rpm, and the stirring time to 30 min. Then reduce the stirring speed to 150 rpm, continue stirring for 15 min, gradually discharge water vapor during the reaction, the slurry fluidity gradually decreases, and finally the material becomes viscous clay-like, let it stand for half a minute, and obtain a block product.

[0054] The block product was placed in a muffle furnace and calcined at 1000°C for 6 hours. After cooling, it was crushed and ground to obtain the target copper pyrophosphate product.

[0055] Example 2

[0056] Analytical grade manganese monoxide powder was used as the metal source and phosphoric acid was used as the phosphorus source. The mass concentration of phosphoric acid in the phosphoric acid aqueous solution used in this embodiment was 60%, and the molar ratio of manganese monoxide powder to phosphoric acid was 1:1.2.

[0057] Weigh manganese monoxide powder and phosphoric acid aqueous solution according to the molar ratio, add phosphoric acid aqueous solution into a crucible, and then add manganese monoxide powder all at once, continue stirring in a fume hood to prevent the raw materials from stratifying, control the system temperature to 30°C, and the stirring speed to 200 rpm. After stirring for 20 minutes, continue stirring at 100 rpm for 15 minutes. The material becomes a viscous clay. Let it stand for half a minute to obtain a block product.

[0058] The block product was placed in a muffle furnace and calcined at 1200°C for 5 hours. After cooling, it was crushed and ground to obtain the target manganese pyrophosphate product.

[0059] Example 3

[0060] Analytical grade zinc oxide powder was used as a metal source and phosphoric acid was used as a phosphorus source. The mass concentration of phosphoric acid in the phosphoric acid aqueous solution used in this embodiment was 65%, and the molar ratio of zinc oxide powder to phosphoric acid was 1:1.1.

[0061] Weigh zinc oxide powder and phosphoric acid aqueous solution according to the molar ratio, add phosphoric acid aqueous solution into a crucible, and then add zinc oxide powder all at once, continue stirring in a fume hood to prevent stratification of the raw materials, control the system temperature to 30°C, and the stirring speed to 200 rpm. After stirring for 20 minutes, continue stirring at 100 rpm for 20 minutes until the material becomes a viscous clay. Let it stand for half a minute to obtain a block product.

[0062] The block product was placed in a muffle furnace and calcined at 1100°C for 2 hours. After cooling, it was crushed and ground to obtain the target zinc pyrophosphate product.

[0063] Example 4

[0064] Analytical grade cobalt monoxide powder was used as a metal source and phosphoric acid was used as a phosphorus source. The mass concentration of phosphoric acid in the phosphoric acid aqueous solution used in this embodiment was 70%, and the molar ratio of cobalt monoxide powder to phosphoric acid was 1:1.1.

[0065] Weigh cobalt monoxide powder and phosphoric acid aqueous solution according to the molar ratio, add phosphoric acid aqueous solution into a crucible, and then add cobalt monoxide powder all at once, continue stirring in a fume hood to prevent the raw materials from stratifying, control the system temperature to 30°C, and the stirring speed to 200 rpm. After stirring for 20 minutes, continue stirring at 100 rpm for 15 minutes. The material becomes a viscous clay. Let it stand for half a minute to obtain a block product.

[0066] The block product was placed in a muffle furnace and calcined at 1100°C for 6 hours. After cooling, it was crushed and ground to obtain the target cobalt pyrophosphate product.

[0067] Example 5

[0068] Calcium oxide powder was used as a metal source and phosphoric acid was used as a phosphorus source. The mass concentration of phosphoric acid in the phosphoric acid aqueous solution used in this embodiment was 55%, and the molar ratio of calcium oxide powder to phosphoric acid was 1:1.2.

[0069] Weigh calcium oxide powder and phosphoric acid aqueous solution according to the molar ratio, add phosphoric acid aqueous solution into a crucible, and then add calcium oxide powder all at once, continue stirring in a fume hood to prevent stratification of the raw materials, control the system temperature to 20°C, and the stirring speed to 160 rpm. After stirring for 20 minutes, the raw materials are evenly mixed. Continue stirring at 80 rpm for 30 minutes until the material becomes viscous clay. Let it stand for half a minute to obtain a block product.

[0070] The block product was placed in a muffle furnace and calcined at 1200°C for 10 hours. After cooling, it was crushed and ground to obtain the target calcium pyrophosphate product.

[0071] Example 6

[0072] Analytical grade cadmium oxide powder was used as the metal source and phosphoric acid was used as the phosphorus source. The mass concentration of phosphoric acid in the phosphoric acid aqueous solution used in this embodiment was 85%, and the molar ratio of cadmium oxide powder to phosphoric acid was 1:1.1 (i.e., the molar ratio of Cd to P was 1:1.1).

[0073] Weigh cadmium oxide powder and phosphoric acid aqueous solution according to the molar ratio, add phosphoric acid aqueous solution into a crucible, and then add cadmium oxide powder all at once, continue stirring in a fume hood to prevent stratification of the raw materials, control the system temperature to 40°C, and the stirring speed to 300 rpm. After stirring for 30 min, continue stirring at 150 rpm for 30 min. The material becomes a viscous clay. Let it stand for half a minute to obtain a block product.

[0074] The block product was placed in a muffle furnace and calcined at 1000°C for 12 hours. After cooling, it was crushed and ground to obtain the target cadmium pyrophosphate product.

[0075] Example 7

[0076] Analytical grade zinc oxide and magnesium oxide powders were used as metal sources, phosphoric acid was used as a phosphorus source, the mass concentration of phosphoric acid in the phosphoric acid aqueous solution used in this embodiment was 63%, and the molar ratio of metal oxide to phosphoric acid was 1:1.1.

[0077] Weigh zinc oxide powder, magnesium oxide powder and phosphoric acid aqueous solution in a molar ratio of (1.6:0.4:2), first mix the zinc oxide and magnesium oxide powders evenly, add the phosphoric acid aqueous solution into a crucible, and then add the mixed oxide powders at one time, continue stirring in a fume hood to prevent the raw materials from stratifying, control the system temperature to 30°C, the stirring speed to 200 rpm, stir for 20 minutes, continue stirring at 100 rpm for 20 minutes, the material becomes a viscous clay, let it stand for half a minute, and obtain a block product.

[0078] The block product was placed in a muffle furnace and calcined at 1100 °C for 2 h. After cooling, it was crushed and ground to obtain Zn 1.6 Mg 0.4 P2O7 target product.

[0079] Comparative Example 1

[0080] Copper pyrophosphate powder was synthesized by conventional methods. The specific preparation method is as follows:

[0081] According to the stoichiometric ratio of 1:1, diammonium hydrogen phosphate and copper oxide were weighed in an agate mortar, and ground with alcohol for 10 minutes. The product was pre-calcined at 250°C for 6 hours to remove water and ammonia. The product was taken out of the muffle furnace and ground for 10 minutes, and then calcined at 800°C for 12 hours to obtain the target product copper pyrophosphate. The purity and morphology of the product were compared with the copper pyrophosphate prepared in Example 1.

[0082] Comparative Example 2

[0083] Copper pyrophosphate was prepared by the same method as in Example 1, except that in this comparative example, the calcination temperature was 600° C. (lower than the calcination temperature specified in the present invention). The specific preparation process is as follows:

[0084] Analytical grade copper oxide powder was used as a metal source and phosphoric acid was used as a phosphorus source. The mass concentration of phosphoric acid in the phosphoric acid aqueous solution used in this comparative example was 85%, and the molar ratio of copper oxide powder to phosphoric acid was 1:1.1 (i.e., the molar ratio of Cu to P was 1:1.1).

[0085] Weigh copper oxide powder and phosphoric acid aqueous solution according to the molar ratio, add phosphoric acid aqueous solution into a crucible, and then add copper oxide powder all at once, continue stirring in a fume hood to prevent stratification of the raw materials, control the system temperature to 40°C, and the stirring speed to 300 rpm. After stirring for 30 min, continue stirring at 150 rpm for 15 min. The material becomes viscous clay. Let it stand for half a minute to obtain a block product.

[0086] The block product was placed in a muffle furnace and calcined at 600°C for 6 hours. After cooling, it was crushed and ground to obtain the target copper pyrophosphate product.

[0087] Comparative Example 3

[0088] Zinc pyrophosphate was prepared by the same method as in Example 3, except that the mass concentration of phosphoric acid in the phosphoric acid aqueous solution used in this comparative example was 85% (higher than the concentration in Example 3). The specific preparation process is as follows:

[0089] Analytical grade zinc oxide powder was used as a metal source and phosphoric acid was used as a phosphorus source. The mass concentration of phosphoric acid in the phosphoric acid aqueous solution used in this embodiment was 85%, and the molar ratio of zinc oxide powder to phosphoric acid was 1:1.1.

[0090] Weigh zinc oxide powder and phosphoric acid aqueous solution according to the molar ratio, add phosphoric acid aqueous solution into a crucible, and then add zinc oxide powder all at once, continue stirring in a fume hood to prevent stratification of the raw materials, control the system temperature to 30°C, and the stirring speed to 200 rpm. After stirring for 20 minutes, continue stirring at 100 rpm for 20 minutes until the material becomes a viscous clay. Let it stand for half a minute to obtain a block product.

[0091] The block product was placed in a muffle furnace and calcined at 1100°C for 2 hours. After cooling, it was crushed and ground to obtain the target zinc pyrophosphate product.

[0092] Comparative Example 4

[0093] Copper pyrophosphate was prepared by the same method as in Example 1, except that the temperature of the system was controlled to be 100° C. (higher than the temperature specified in the present invention) in the early stage of this comparative example. The reaction was found to be very violent, and the reaction system quickly changed from a state with good fluidity to a block.

[0094] Comparative Example 5

[0095] Copper pyrophosphate was prepared by the same method as in Example 1, except that the stirring speed during the pre-reaction in this comparative example was 500 rpm (higher than the stirring speed specified in the present invention). The experiment found that the reaction was very violent, and the reaction system quickly changed from a state with good fluidity to a block.

[0096] The pyrophosphates prepared in the above examples and comparative examples were subjected to X-ray diffraction and scanning electron microscopy examinations.

[0097] Figure 1 The copper pyrophosphate characterization results of Example 1 and Comparative Example 1 are compared. Figure 1 It can be seen that the copper pyrophosphate prepared by the preparation method of the present invention and the traditional method are both pure phases. In Example 1 of the preparation method of the present invention, the copper pyrophosphate powder prepared with phosphoric acid as the raw material is denser, regular and smooth in morphology, while the powder prepared by the traditional method is loose and porous, and the surface is uneven. The two methods prepare the same amount of copper pyrophosphate powder, and the working hours consumed by Example 1 of the preparation method of the present invention is 1 / 3 of that of the traditional method. The present invention has lower cost, shorter cycle, is conducive to mass preparation, and the product morphology is denser and smoother.

[0098] Figure 2 The X-ray diffraction pattern and scanning electron microscope image of the manganese pyrophosphate powder prepared by the preparation method of the present invention in Example 2 are shown in FIG. Figure 2 It can be seen that the manganese pyrophosphate prepared by the preparation method of the present invention is a pure phase with dense particles and smooth morphology.

[0099] Figure 3 The following are the X-ray diffraction patterns and scanning electron microscope images of the zinc pyrophosphate powder prepared by the preparation method of the present invention in Example 3. Figure 3 It can be seen that the zinc pyrophosphate prepared by the preparation method of the present invention is a pure phase with dense particles and smooth morphology.

[0100] Figure 4 The X-ray diffraction pattern and scanning electron microscope image of the cobalt pyrophosphate powder prepared by the preparation method of the present invention in Example 4 are shown in FIG. Figure 4 It can be seen that the cobalt pyrophosphate prepared by the preparation method of the present invention is a pure phase with dense particles and smooth morphology.

[0101] Figure 5The X-ray diffraction pattern and scanning electron microscope image of the calcium pyrophosphate powder prepared by the preparation method of the present invention in Example 5 are shown in FIG. Figure 5 It can be seen that the calcium pyrophosphate prepared by the preparation method of the present invention is a pure phase with dense particles and smooth morphology.

[0102] Figure 6 The following are the X-ray diffraction patterns and scanning electron microscope images of the cadmium pyrophosphate powder prepared by the preparation method of the present invention in Example 6. Figure 6 It can be seen that the cadmium pyrophosphate prepared by the preparation method of the present invention is a pure phase, with dense particles and smooth morphology.

[0103] Figure 7 The Zn prepared by the preparation method of the present invention in Example 7 1.6 Mg 0.4 X-ray diffraction pattern and scanning electron microscope image of P2O7 powder. Figure 7 It can be seen that the Zn prepared by the preparation method of the present invention 1.6 Mg 0.4 The P2O7 solid solution is of the same structure as α-Zn2P2O7, and no other impurities are found. The particles are dense and the morphology is smooth.

[0104] In addition, the relationship between the stirring speed and temperature in the early stage of Examples 1 to 7 all meet v=V±15, V=83exp(0.031t), which is more conducive to obtaining high-quality target products with high efficiency. It is also found in the experiment that if the relationship between temperature and stirring speed does not meet the relationship conditions, the particle density and smooth morphology are also relatively good, but will be slightly inferior to the target product obtained according to the relationship conditions.

[0105] Figure 8 The X-ray diffraction pattern and scanning electron microscope image of the copper pyrophosphate powder of Comparative Example 2 are as follows: Figure 8 and Figure 1 Comparison of the scanning electron microscope images of copper pyrophosphate in Example 1 shows that if the sintering temperature is reduced, the morphology smoothness of the copper pyrophosphate will deteriorate. During the high-temperature sintering process of the preparation method of the present invention, a final pyrophosphate product is formed on the basis of monohydrogen phosphate crystal particles, so that the pyrophosphate has higher density and smoothness. It can be seen that the present invention cooperates high-temperature sintering with various process conditions to finally obtain a pyrophosphate with a smooth and dense morphology, and the pyrophosphate with a smooth and dense morphology can solve the problem of holes in the preparation of composite materials when used as a composite material additive in downstream applications.

[0106] Fig. 9 The X-ray diffraction pattern and scanning electron microscope image of zinc pyrophosphate powder of Comparative Example 3 are as follows: Fig. 9 and Figure 3From the comparison of the scanning electron microscope images of zinc pyrophosphate in Example 3, it can be seen that if a higher concentration of phosphoric acid aqueous solution is used to prepare zinc pyrophosphate, the raw materials will react rapidly upon contact, resulting in the raw materials reacting to obtain a block product without uniform mixing, which will eventually affect the purity of zinc pyrophosphate. It can be seen that metal oxides with different reactivity and a suitable concentration of phosphoric acid aqueous solution are more conducive to obtaining a pyrophosphate product with excellent performance.

[0107] Fig.10 The X-ray diffraction pattern and scanning electron microscope image of the copper pyrophosphate powder of Comparative Example 4 are as follows: Fig.10 and Figure 1 Comparison of the scanning electron microscope images of copper pyrophosphate in Example 1 shows that if the system is heated to a relatively high temperature at the initial stage of stirring, the reaction will be very violent, resulting in an uneven reaction and obtaining a bulk product, which will ultimately affect the purity and morphology of the copper pyrophosphate.

[0108] Fig.11 The X-ray diffraction pattern and scanning electron microscope image of the copper pyrophosphate powder of Comparative Example 5 are as follows: Fig.11 and Figure 1 From the comparison of the scanning electron microscope images of copper pyrophosphate in Example 1, it can be seen that if a higher stirring speed is used to prepare copper pyrophosphate, the reaction is very violent, resulting in uncontrollable temperature, and the raw materials are violently dehydrated to form block products without being fully mixed, which will ultimately affect the purity and morphological smoothness of the copper pyrophosphate.

[0109] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0110] For those skilled in the art, several modifications and improvements may be made without departing from the concept of the present invention, all of which belong to the protection scope of the present invention. The protection scope of the present invention shall be based on the attached claims.

Claims

1. A method for preparing a pyrophosphate having a smooth and dense morphology, characterized in that: The preparation method comprises the following steps: using phosphoric acid as a phosphorus source and metal oxide powder as a metal source, mixing a phosphoric acid aqueous solution with the metal oxide powder, and then pre-reacting under stirring conditions to obtain a block precursor product, and then calcining at high temperature, crushing, grinding and screening to obtain pyrophosphate and a solid solution thereof with a desired particle size.

2. A method for preparing a pyrophosphate having a smooth and dense morphology according to claim 1, characterized in that: The metal oxide is an oxide of a divalent metal such as Ca, Mg, Co, Ni, Cu, Zn, Mn or Cd.

3. The pyrophosphate and solid solution thereof according to claim 1, characterized in that: The product can be a monovalent pyrophosphate generated by a single metal oxide, or a polyvalent pyrophosphate solid solution formed by any combination of divalent metal oxides.

4. The method for preparing a pyrophosphate having a smooth and dense morphology according to claim 1, characterized in that: The mass concentration of phosphoric acid in the phosphoric acid aqueous solution is 50%-85%.

5. The mass concentration of the phosphoric acid aqueous solution according to claim 4, characterized in that: When the metal oxide is an oxide of Ca, Mg, or Mn, the mass concentration of phosphoric acid in the aqueous phosphoric acid solution is ≥50% and ≤60%; when the metal oxide is an oxide of Co, Ni, or Zn, the mass concentration of phosphoric acid in the aqueous phosphoric acid solution is >60% and ≤75%; when the metal oxide is an oxide of Cu or Cd, the mass concentration of phosphoric acid in the aqueous phosphoric acid solution is >75% and ≤85%.

6. The method for preparing a pyrophosphate having a smooth and dense morphology according to claim 1, characterized in that: The stoichiometric ratio of the metal oxide to the phosphoric acid is 1:(1-1.3).

7. The method for preparing a pyrophosphate having a smooth and dense morphology according to claim 1, characterized in that: The operation of mixing the phosphoric acid aqueous solution with the metal oxide powder is as follows: adding the metal oxide powder into the phosphoric acid aqueous solution at one time and immediately starting stirring.

8. The method for preparing a pyrophosphate having a smooth and dense morphology according to claim 1, characterized in that: During the pre-reaction process, the temperature of the system is controlled at 10-80°C, the stirring speed is 120-300 rpm, and the stirring time is 10-60 min, so that the materials can be fully mixed and initially reacted. The materials are then stirred for another 10-60 min at a stirring speed of 60-150 rpm, relying on the heat released by the reaction itself to promote the reaction and remove water vapor.

9. A method for preparing a pyrophosphate having a smooth and dense morphology according to claim 8, characterized in that: During the pre-reaction process, the stirring operation needs to be continued until the water vapor is completely volatilized and then stopped to form a block-shaped precursor product.

10. The method for preparing a pyrophosphate having a smooth and dense morphology according to claim 1, characterized in that: The temperature of the high-temperature calcination is 700-1200° C., and the time of the high-temperature calcination is 1-72 hours.

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