Composite powder having caco 3@zno core-shell structure and preparation method therefor

Abstract

Disclosed in the present invention is a composite powder having a CaCO3@ZnO core-shell structure, the composite powder comprising a nano calcium carbonate core and a zinc oxide shell, wherein the weight of the zinc oxide is 5-15% of the weight of the nano calcium carbonate. The composite powder having a CaCO3@ZnO core-shell structure of the present invention has good dispersibility, has whiteness greater than 95, a uniform zinc oxide coating and a very low content of zinc oxide, and has a good application effect in rubber, thereby achieving the aims of being low cost, having high efficiency and being environmentally friendly.

Description

CaCO3@ZnO core-shell composite powder and its preparation method Technical Field

[0001] This application relates to the field of calcium carbonate preparation technology, specifically to a CaCO3@ZnO core-shell structured composite powder and its preparation method. Technical Background

[0002] As the "food" of modern industry, mineral resources play a vital role in its development. Carbonate minerals are among the most valuable mineral resources for industrial applications, occupying a crucial position in my country's industrial system, especially the mining and application of calcium carbonate. Calcium carbonate is an inorganic compound composed of three different elements: C, O, and Ca, with the molecular formula CaCO3. It possesses stable physicochemical properties and is a major component of limestone, calcite, marble, dolomite, chalk, coral, and shells. my country's calcium carbonate resources are mainly distributed in North China, Sichuan, Anhui, Yunnan, Guangxi, and Guizhou, with widespread distribution and abundant reserves. Due to its excellent and unique physicochemical properties, wide availability, and low price, calcium carbonate is widely used in industrial production, especially high-value-added heavy calcium carbonate and light (nano) calcium carbonate products, which are widely used in the rubber, plastics, papermaking, and coating industries. With the rapid development of the papermaking, coating, plastics, and rubber industries, the market demand for calcium carbonate products is increasing, and calcium carbonate production and consumption are showing a rapid growth trend. Currently, the competitive field of calcium carbonate products is mainly concentrated in the fields of light calcium carbonate and nano calcium carbonate. Surface modified nano calcium carbonate, as one of the most technologically advanced nano calcium carbonate products, is a key focus of industrial layout in various countries.

[0003] Zinc oxide, a white powder with the chemical formula ZnO, is an important branch of the inorganic zinc salt series. It is a crucial basic chemical raw material and new material indispensable for national economic development, widely used in ceramics, electronics, pharmaceuticals, chemicals, rubber, coatings, and textiles. my country's zinc oxide market is enormous, with demand showing a stable growth trend. Rubber is the largest downstream application of zinc oxide, accounting for approximately 60%, and is one of the main drivers of the zinc oxide industry's development. Currently, there is no product that can completely replace zinc oxide used in rubber, and the rubber industry will remain the largest downstream demand sector for zinc oxide in the coming years. However, the zinc oxide industry is resource-intensive. The production process consumes a large amount of zinc resources while generating significant amounts of wastewater, waste gas, and waste residue, causing environmental pollution. Faced with multiple challenges such as resource scarcity, environmental pressure, and rising production costs, pursuing a low-zinc, high-efficiency, energy-saving, and environmentally friendly approach is an inevitable trend for the zinc oxide industry.

[0004] Studies have shown that constructing a core-shell composite material of calcium carbonate (CaCO3@ZnO) with calcium carbonate as the core and nano-zinc oxide as the shell can not only reduce production costs and increase the added value of calcium carbonate, making it a high-end product, but also play the same role as solid ZnO particles, achieving the goals of environmental protection, zinc reduction, and high efficiency.

[0005] Patent CN117342594A discloses a method for preparing core-shell structured calcium carbonate with UV resistance. Using alkali metal hydroxides and zinc salts as raw materials, a CaCO3@ZnO core-shell structured composite powder is prepared via a sol-gel method. This method is simple and can obtain a core-shell structured product with the calcium carbonate surface completely and uniformly coated with nano-zinc oxide. The coating effect is good, the product has a regular morphology, good dispersibility, high whiteness, and excellent UV resistance. When the coating amount of nano-zinc oxide reaches 20%, the UV absorption intensity of the prepared CaCO3@ZnO core-shell structure can reach the same level as pure nano-ZnO. However, this method uses solutions such as anhydrous ethanol and methanol as reaction reagents, resulting in high production costs and making industrial-scale production difficult.

[0006] Huang Xincheng et al. used a liquid-phase precipitation method to detect the effect of hydroxyapatite generated on the surface of CaCO3 on Zn. 2+ The adsorption process facilitated the assembly of ZnO and CaCO3, preparing ZnO / CaCO3 composite powder. When the ZnO to CaCO3 composite ratio was 1:2 and calcined at 300-350℃, the resulting composite powder, when applied to styrene-butadiene rubber (SBR), exhibited a faster vulcanization rate, reaching up to 0.247 s⁻¹, using the same proportions. -1 ZnO is used in relatively small quantities and has good economic prospects. The ZnO / CaCO3 composite powder prepared by this method is micron-sized, while nano-sized zinc oxide filler is used in high-end rubber and plastic products. In addition, the ZnO particles in this method are adsorbed on the surface of calcium carbonate. The affinity between ZnO and calcium carbonate is poor, and the ZnO particles are easy to fall off, resulting in poor coating effect (Huang Xincheng, Chen Xuemei; Preparation of ZnO / CaCO3 composite material and its application in styrene-butadiene rubber vulcanization [J]. Journal of Materials Science and Engineering, 1673-2812(2022)01-0070-07).

[0007] Chinese patent CN106279762A discloses an ammoniacal method for preparing core-shell zinc oxide powder. This method uses calcium carbonate as a template, controlling the reaction temperature to allow zinc carbonate to slowly grow on the calcium carbonate surface. Finally, calcination yields core-shell zinc oxide powder with a layer of flake-like zinc oxide coating the calcium carbonate surface. The prepared core-shell zinc oxide powder exhibits good dispersibility and processability in vulcanized rubber, effectively promoting rubber vulcanization and improving tensile strength, elongation, and tear strength while maintaining good sulfur modulus data. However, the particle size of this core-shell zinc oxide powder is between 2 and 15 μm, classifying it as a micron-sized material, making it unsuitable for use in high-end rubber and plastic products. Furthermore, the Zn / Ca weight ratio in this method ranges from 2 / 8 to 7 / 3, resulting in a large amount of ZnO used, along with significant amounts of ammonia and ammonium bicarbonate, which is environmentally unfriendly and fails to achieve the goals of low zinc content, high efficiency, and environmental friendliness.

[0008] Chinese patent CN106752106B discloses a high-brightness, UV-resistant, and anti-aging functional filler nano-calcium carbonate, its preparation method, and its uses. In the final stage of nano-calcium carbonate preparation, precise control is achieved over various parameters, including reaction system concentration, termination pH, reaction temperature, dispersant formulation, and coating agent selection, resulting in high-performance, multi-purpose nano-calcium carbonate with a particle size of 80nm-200nm, a whiteness exceeding 92, a zinc oxide coating content of 4%, no agglomeration, and UV-resistant and anti-aging properties. However, the nano-calcium carbonate obtained by this method has a low whiteness, affecting the quality of the calcium carbonate and failing to meet the requirements for high-quality calcium carbonate.

[0009] Chinese patent CN101412818A discloses an industrial preparation method for nano-calcium carbonate for antibacterial and antifungal silicone rubber. The method involves adding silicate and zinc salts to carbonized nano-calcium carbonate slurry, introducing kiln gas, and controlling the reaction temperature. Under the synergistic effect of the silicate and zinc salt components, they hydrolyze into silica sol and zinc hydroxide, respectively, which uniformly coat the surface of the nano-calcium carbonate. This forms a core-shell structure of nano-calcium carbonate, with nano-calcium carbonate as the core and a uniformly coated layer of weather-resistant silica and antibacterial and antifungal nano-zinc oxide as the shell. This product can be used as a functional filler for silicone rubber, exhibiting good thixotropic properties while also possessing antibacterial, antifungal, and weather-resistant functions. However, the maximum whiteness value of this product is only 93. To use it as high-quality calcium carbonate, further improvements in production technology and increasing product whiteness are still needed.

[0010] Chinese patent CN113000058A discloses a method for preparing and applying nano-zinc oxide / calcium carbonate composite powder. Two methods, in-situ chemical composite and mechanical composite, were used to prepare the nano-zinc oxide / calcium carbonate composite. The prepared product can be used in rubber as an aid in rubber vulcanization to improve the tensile strength and elongation of the rubber. Under visible light irradiation, the product also exhibits superior photocatalytic activity compared to pure nano-zinc oxide. However, due to the poor affinity between zinc oxide and calcium carbonate, it is difficult to uniformly coat the calcium carbonate surface with zinc oxide using only simple in-situ chemical composite or mechanical composite methods. This results in poor interfacial bonding between composite particles, low stability, and easy detachment of ZnO, thus affecting the overall performance of the product.

[0011] Chinese patent CN111606351B discloses a zinc oxide-coated calcium carbonate nanomaterial and its preparation method. Using nano-calcium carbonate particles as the core and urea as the precipitant, CaCO3@Zn(OH)2 is first prepared using a hydrothermal method under high temperature and high pressure, followed by high-temperature calcination to obtain CaCO3@ZnO core-shell composite nanoparticles. The obtained CaCO3@ZnO core-shell composite nanoparticles have a completely covered surface of plaque-like zinc oxide, exhibiting good coating effect. However, the CaCO3@ZnO core-shell composite nanoparticles prepared by this method have poor dispersibility and are prone to agglomeration. Furthermore, the method uses urea as the precipitant, resulting in a slow reaction, long preparation cycle, high energy consumption, and the requirement to place the reactants in a sealed high-temperature and high-pressure reaction vessel, making large-scale production difficult.

[0012] The CaCO3@ZnO core-shell structured materials prepared by the disclosed processes have limitations such as low powder whiteness and poor dispersibility. Therefore, researching and developing composite powders that effectively combine CaCO3 and ZnO to possess the properties of zinc oxide, achieving the goals of low zinc content, high efficiency, and environmental friendliness, while simultaneously increasing the added value of nano-calcium carbonate and making nano-calcium a high-end product, is an important direction for the development of the entire calcium carbonate and zinc oxide industries. Summary of the Invention

[0013] To address the aforementioned problems, this application provides a CaCO3@ZnO core-shell structured composite powder, which solves the problems of poor dispersibility and low whiteness of CaCO3@ZnO core-shell structured composite powder prepared by existing technologies.

[0014] To achieve the above objectives, this application adopts the following technical solution:

[0015] A CaCO3@ZnO core-shell structured composite powder, comprising a nano-calcium carbonate core and a zinc oxide shell coating its surface; wherein the weight of zinc oxide in the CaCO3@ZnO core-shell structured composite powder is 5% to 15% of the weight of nano-calcium carbonate.

[0016] Preferably, in the CaCO3@ZnO core-shell composite powder, the weight of zinc oxide is 10% to 15% of the weight of nano-calcium carbonate.

[0017] Preferably, in the CaCO3@ZnO core-shell composite powder, zinc oxide is deposited on the surface of calcium carbonate in the form of particles with a particle size of 10-20 nm.

[0018] Preferably, in the CaCO3@ZnO core-shell composite powder, the particle size of zinc oxide is 10-15 nm.

[0019] Preferably, the CaCO3@ZnO core-shell composite powder further contains stearic acid, which coats the outer surface of the CaCO3@ZnO core-shell composite powder.

[0020] Preferably, the preparation method of the CaCO3@ZnO core-shell structured composite powder includes the following steps:

[0021] (1) Prepare calcium hydroxide slurry, and then introduce a mixed gas containing carbon dioxide into it to cause a carbonation reaction. When the pH value of the system is 8.0 to 9.0, add soluble zinc salt and soluble carbonate to the system, stir the reaction, and obtain a mixed slurry.

[0022] (2) Remove impurities and moisture from the mixed slurry obtained in step (1) to obtain CaCO3@ZnCO3 powder;

[0023] (3) The CaCO3@ZnCO3 powder obtained in step (2) is calcined to obtain CaCO3@ZnO core-shell structured composite powder.

[0024] Preferably, in step (1), the solid content of calcium hydroxide in the calcium hydroxide slurry is 8.0-15.0%.

[0025] Preferably, in step (1), the carbonation reaction temperature is 18–25°C, and the flow rate of the carbon dioxide-containing mixed gas is 1–4 m³ / s. 3 / h, with a carbon dioxide volume concentration of 15-25%.

[0026] Preferably, in step (1), the stirring speed is 800-1200 r / min.

[0027] Preferably, in step (1), the soluble zinc salt is one of zinc acetate dihydrate, zinc citrate, zinc chloride, zinc sulfate, and zinc nitrate; and the soluble carbonate is one of sodium carbonate, potassium carbonate, ammonium carbonate, and ammonium bicarbonate.

[0028] Preferably, the amount of soluble zinc salt added is calculated based on the weight of the generated ZnO being 5% to 15% of the weight of nano-calcium carbonate; the amount of soluble carbonate added is calculated based on just enough to completely react with the soluble zinc salt.

[0029] Preferably, in step (1), the pH value of the system is adjusted to 7.0 to 8.5 during the stirring process.

[0030] Preferably, the stirring time is 2 to 4 hours.

[0031] Preferably, an acid or base is added as a pH adjuster to regulate the pH of the system.

[0032] Preferably, the acid is hydrochloric acid, and the base is either sodium hydroxide or potassium hydroxide, both with a concentration of 0.1–1.0 mol / L.

[0033] Preferably, the method for removing impurities and moisture in step (2) is to perform pressure filtration and drying.

[0034] Preferably, the drying method is as follows: drying is carried out in a forced-air drying oven at a temperature of 110-150°C for 12-24 hours.

[0035] Preferably, in step (3), the heating rate of calcination is 3 to 10 °C / min, and the temperature is maintained at 300 to 450 °C for 1 to 5 hours.

[0036] Preferably, in step (3), the CaCO3@ZnO core-shell composite powder is surface modified with stearic acid as a modifier, and the amount of stearic acid is 3.0 to 4.0% of the weight of nano-calcium carbonate; the modification temperature is 90 to 95°C and the time is 30 to 60 min.

[0037] Preferably, the surface modification treatment is carried out in a high-speed mixer.

[0038] Compared with the prior art, the advantages and beneficial effects of this application are as follows:

[0039] (1) The CaCO3@ZnO core-shell structured composite powder of this application has uniform zinc oxide coating, good dispersibility, and whiteness greater than 95. Moreover, the zinc oxide content in the composite powder is very low, only 5% to 15% of the weight of nano calcium carbonate, but it has a good application effect in rubber. In particular, when the zinc oxide content is 10% to 15% of the weight of nano calcium carbonate, it can play an application effect comparable to that of nano zinc oxide, achieving the purpose of low cost, high efficiency and environmental protection.

[0040] (2) The preparation method of this application combines carbonation and precipitation. In the initial stage of the carbonation reaction, linear intermediates of nano-calcium carbonate are mainly generated. As the reaction time progresses, the linear intermediates grow continuously. At the end of the reaction, the linear intermediates break instantly into cubic or spherical nano-calcium carbonate. The pH value of the carbonation system is very close to the end of the reaction when it reaches 8.0 to 9.0. This application chooses to add zinc salt and carbonate at this pH value, that is, before the linear intermediates break, so that the generated ZnCO3 precipitate can be deposited on the surface of the broken cubic or spherical nano-calcium carbonate and coated, preventing the nanoparticles from agglomerating due to their high specific surface energy, thereby obtaining CaCO3@ZnO core-shell structured composite powder material with good dispersibility.

[0041] (3) In order to make ZnO uniformly distributed on the surface of nano-calcium carbonate and obtain CaCO3@ZnO core-shell structure composite powder with good coating effect, this application controls the surface charge between nano-calcium carbonate and ZnCO3 by adjusting the pH value of the reaction system in the range of 7.0 to 8.5 during the process of coating nano-calcium carbonate with ZnCO3, thereby increasing the binding energy between them, so that ZnCO3 is more uniformly coated on the surface of nano-calcium carbonate, and effectively controlling the coating layer. Attached Figure Description

[0042] Figure 1 is a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared by treatment 1;

[0043] Figure 2 shows a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared by treatment 2;

[0044] Figure 3 shows a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared by treatment 3;

[0045] Figure 5 shows a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared by treatment 4.

[0046] Figure 4 shows a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared by treatment 5;

[0047] Figure 6 shows a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared by treatment 6;

[0048] Figure 7 shows a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared by treatment 7;

[0049] Figure 8 shows a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared by treatment 8;

[0050] Figure 9 shows a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared by treatment 9;

[0051] Figure 10 shows a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared by treatment 10;

[0052] Figure 11 is a scanning electron microscope image of commercially available nano zinc oxide purchased in Comparative Example 1;

[0053] Figure 12 shows a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared in Comparative Example 2;

[0054] Figure 13 shows a scanning electron microscope image of the CaCO3@ZnO core-shell composite powder prepared in Comparative Example 3. Detailed Implementation

[0055] To better illustrate this application, specific implementation examples are provided. These implementation examples fall within the scope of protection of this application but do not limit the scope of protection of this application.

[0056] Example 1

[0057] A method for preparing CaCO3@ZnO core-shell composite powder includes the following steps:

[0058] (1) After preparing a calcium hydroxide slurry with a solid content of 8.0–15.0%, it is pumped into a carbonization tower. Under the conditions of 18–25℃ and stirring at a speed of 800–1200 r / min, carbon dioxide with a volume concentration of 15–25% and a flow rate of 1–4 m³ / min is introduced. 3 A mixture of carbon dioxide and air is introduced at a rate of / h, causing calcium hydroxide to react with carbon dioxide to form CaCO3. When the carbonation reaction proceeds to a system pH of 8.0–9.0, soluble zinc salt and soluble carbonate are added. The amount of soluble zinc salt added is calculated based on the weight of the generated ZnO being 5–15% of the weight of the nano-calcium carbonate, and the amount of soluble carbonate added is just enough to ensure the complete reaction of the soluble zinc salt. The mixture is stirred for 2–4 hours to allow the soluble zinc salt and soluble carbonate to react fully, generating ZnCO3 that coats the surface of CaCO3, resulting in a mixed slurry.

[0059] (2) After the mixed slurry from step (1) is filtered by pressure, it is dried in a forced-air drying oven at 110-150℃ for 12-24h to obtain CaCO3@ZnCO3 powder;

[0060] (3) Place the CaCO3@ZnCO3 powder obtained in step (2) in a muffle furnace, set the heating rate to 3-10℃ / min, heat to 300-450℃ and hold for 1-5h to obtain CaCO3@ZnO core-shell structure composite powder with zinc oxide coated with nano calcium carbonate.

[0061] In this embodiment, referring to the preparation method of CaCO3@ZnO core-shell composite powder provided above, different treatment groups were set up (as shown in Table 1) with the combination of added soluble zinc salt and soluble carbonate and the pH value of the added node system as variables, in order to investigate the effect of adding different combinations of soluble zinc salt and soluble carbonate at different system pH values ​​during the carbonation reaction on the product performance.

[0062] Table 1. Setup of each processing group in Example 1

[0063] Example 2

[0064] A method for preparing CaCO3@ZnO core-shell composite powder includes the following steps:

[0065] (1) After slaked quicklime to form a calcium hydroxide slurry with a solid content of 8.0–15.0%, it is pumped into a carbonation tower. The slurry is then stirred at 800–1200 r / min at a temperature of 18–25℃, with a carbon dioxide volume concentration of 15–25% and a flow rate of 1–4 m³ / min. 3 A mixture of carbon dioxide and air is introduced per hour; when the carbonation reaction reaches a system pH of 8.0–9.0, the gas flow is stopped, and soluble zinc salt and soluble carbonate are added. The amount of soluble zinc salt added is calculated based on the weight of the generated ZnO being 5–15% of the weight of the nano-calcium carbonate, and the amount of soluble carbonate added is just enough to ensure complete reaction of the soluble zinc salt. The mixture is stirred for 2–4 hours, during which acid or alkali is added as a pH adjuster to control the system pH to 7.0–8.5, resulting in a mixed slurry. The acid added is hydrochloric acid, or the alkali added is either sodium hydroxide or potassium hydroxide, with a concentration of 0.1–1.0 mol / L.

[0066] (2) The mixed slurry from step (1) is filtered by pressure and dried in a forced-air drying oven at 110-150℃ for 12-24h to obtain CaCO3@ZnCO3 powder;

[0067] (3) Place the CaCO3@ZnCO3 powder obtained in step (2) in a muffle furnace, set the heating rate to 3-10℃ / min, heat to 300-450℃ and hold for 1-5h to obtain CaCO3@ZnO core-shell structure composite powder with zinc oxide coated with nano calcium carbonate.

[0068] In this embodiment, referring to the preparation method of CaCO3@ZnO core-shell composite powder provided above, the same combination of soluble zinc salt and soluble carbonate as in treatment groups 1-3 of Example 1 was selected, and the pH value of the added node system was adjusted. Different treatment groups were set up (as shown in Table 2) with the type of pH adjuster added and the pH value of the adjusted system as variables to examine the effect of adjusting the pH value of different systems on product performance.

[0069] Table 2. Setup of each processing group in Example 2

[0070] Example 3

[0071] The CaCO3@ZnO core-shell composite powders prepared in Examples 1-3 were placed in a high-speed mixer, and the composite powders were surface modified with stearic acid as a modifier. The amount of stearic acid used was 3.0-4.0% of the weight of the nano-calcium carbonate; the modification temperature was 90-95℃, and the time was 30-60 min.

[0072] In this embodiment, referring to the preparation method of CaCO3@ZnO core-shell structured composite powder provided above, different treatment groups were set up (as shown in Table 3) with modification temperature, modification time, and amount of stearic acid as variables, to compare with the products prepared by treatments 1 to 3 in Example 1, and to examine the effect of modification on product performance.

[0073] Table 3. Setup of each processing group in Example 3

[0074] Example 4

[0075] The CaCO3@ZnO core-shell composite powders prepared in Examples 2, 6-8 were placed in a high-speed mixer. The composite powders were surface modified with stearic acid as a modifier. The amount of stearic acid was 3.0-4.0% of the weight of the nano-calcium carbonate. The modification temperature was 90-95℃ and the time was 30-60 min.

[0076] In this embodiment, referring to the preparation method of CaCO3@ZnO core-shell structured composite powder provided above, different treatment groups were set up (as shown in Table 3) with modification temperature, modification time, and amount of stearic acid as variables, to compare with the products prepared by treatments 6-8 in Example 2, and to examine the effect of modification on product performance.

[0077] Table 4. Setup of each processing group in Example 4

[0078] Comparative Example 1

[0079] Commercially available nano zinc oxide products.

[0080] Comparative Example 2

[0081] Core-shell structured nanomaterials of zinc oxide-coated calcium carbonate prepared by CN 111606351B.

[0082] Comparative Example 3

[0083] Nano-zinc oxide / calcium carbonate composite powder prepared by CN113000058A.

[0084] I. Product Performance Testing Experiment

[0085] 1. The zinc oxide particle size, whiteness, and dispersibility of the CaCO3@ZnO core-shell composite powders prepared by treatments 1 to 16 and the products of comparative examples 1 to 3 were determined according to the following methods.

[0086] The dispersibility of the composite powder is determined by observing the scanning electron microscope (SEM) image. The more clustered the calcium carbonate particles are, the worse the dispersibility, and vice versa. Similarly, at least 50 zinc oxide particles are selected from the SEM image for point measurement, and the average value is taken to obtain the particle size of zinc oxide.

[0087] The whiteness of the CaCO3@ZnO core-shell composite powders prepared by treatments 1-16 and the products of comparative examples 1-3 was tested using a whiteness meter.

[0088] 2. The measurement results are shown in Table 5.

[0089] Table 5. Performance of products obtained from each treatment. Note: "Zinc oxide coating amount" refers to the percentage of the weight of zinc oxide in the composite powder relative to the weight of nano-calcium carbonate.

[0090] As shown in Table 5 and the scanning electron microscope images:

[0091] (1) Figure 12 shows a scanning electron microscope image of commercially available nano-zinc oxide with a particle size of 25-35 nm. Due to the small particle size and large surface energy, the zinc oxide particles adhere to each other, forming clusters with poor dispersibility. Under the process conditions of this application, soluble zinc salt and soluble carbonate were added to processes 1-3 at a pH of 8.0-9.0 to prepare composite powders. The zinc oxide content was 5%-15% of the weight of nano-calcium carbonate, the specific gravity was small, and the whiteness was above 95.1, which was comparable to the whiteness of the pure nano-zinc oxide product of Comparative Example 1. The generated zinc oxide was deposited on the surface of calcium carbonate in the form of particles, with uneven distribution and no complete coating layer (Figures 1 to 3). In addition, some zinc oxide was adsorbed on the surface of calcium carbonate in the form of independent nucleation. The coating effect was similar to that of the comparative example. The nano-zinc oxide / calcium carbonate composite powder prepared in treatment 3 (Figure 13) is similar; however, in treatments 4 and 5, adding zinc salt and carbonate too early or too late will lead to poor dispersibility of CaCO3@ZnO core-shell structure composite powder (Figures 4 and 5). This is because if added too early, the linear intermediate has not grown to the point of being able to break before being coated, and it is impossible to form cubic or spherical nano-calcium carbonate, and the composite powder will form clusters; if added too late, the linear intermediate has already broken, and the broken nano-calcium carbonate will agglomerate due to the high surface energy, affecting the coating effect.

[0092] (2) pH adjusters were used in treatments 6-8 to regulate the pH of the system. Compared with treatments 1-3, the ZnCO3 particles were smaller and more uniformly coated on the surface of the nano-calcium carbonate, resulting in higher whiteness and better dispersibility of the product (Figures 6 to 8). The pH value of the system has a great influence on the performance of the CaCO3@ZnO core-shell composite powder. If the pH value of treatment 9 is too low, the calcium carbonate will react with the acid, leading to corrosion and dissolution of the calcium carbonate (Figure 9). If the pH value of treatment 10 is too high, the particle size of the generated zinc oxide will increase, affecting the performance (Figure 10). This is because the basic properties of zinc oxide, mainly the particle specific surface area and structure, have a great influence on the rubber processing. The activation effect of zinc oxide on the vulcanization system mainly depends on its specific surface area. That is, the smaller the particle size and the larger the specific surface area, the better the activation effect.

[0093] II. Product Application Effect Test Experiment

[0094] The products of each treatment group and comparative examples 1 to 3 were mixed on an open mill for about 30 minutes according to the formulation in Table 6. The vulcanization characteristics of the rubber compound at 160℃ were determined using an MDR-2000 vulcanizing apparatus according to GB / T9869-1997. The tensile strength, elongation at break, tear strength and other mechanical properties were tested according to standard GB / T528-2009.

[0095] Table 6 Formulations for Rubber Application Experiments

[0096] Table 7. Vulcanization data of each product in styrene-butadiene rubber.

[0097] Table 8. Mechanical property data of each product applied in styrene-butadiene rubber.

[0098] Nano-zinc oxide, as a vulcanization accelerator, promotes the vulcanization of rubber and plays an important role in rubber applications. Tables 7 and 8 show that when the CaCO3@ZnO core-shell structured composite powder prepared by treatments 1–3 is applied to styrene-butadiene rubber, the mechanical properties and vulcanization properties of the rubber improve with increasing ZnO content, specifically manifested in improved scorch time (t). 10 As the vulcanization time (t) increases, the vulcanization time (t) 90 Shortening, torque (M) H -M L With increased zinc oxide content, the tensile strength, elongation at break, and tear strength of the rubber are all improved. Furthermore, at the same content, the more uniform the zinc oxide distribution on the surface of nano-calcium carbonate, the better the coating effect, and the superior vulcanization and mechanical properties of the rubber (treatment 6-8).

[0099] The particle size of zinc oxide and the dispersibility of the CaCO3@ZnO core-shell composite powder also affect its performance in rubber applications. For example, the CaCO3@ZnO core-shell composite powder prepared in treatment 10 has generally poor dispersibility and a larger zinc oxide particle size, resulting in a worse application effect compared to treatment 8. Similarly, the dispersion of the CaCO3@ZnO core-shell composite powder in the rubber matrix and its compatibility with the rubber matrix also affect its application performance. The application effects of stearic acid-modified CaCO3@ZnO core-shell composite powders in treatments 11–13 and 14–16 are better than those in treatments 1–3 and 6–8 (unmodified CaCO3@ZnO core-shell composite powders). This is because stearic acid modification can reduce the interaction between particles and the adhesion between polymers, allowing the CaCO3@ZnO core-shell composite powder to be well dispersed in rubber. Furthermore, after surface modification with stearic acid, the hydrophilicity of the CaCO3@ZnO core-shell composite powder is eliminated, greatly increasing its compatibility with the rubber matrix.

[0100] The data in the table also show that, under the same coating amount, the CaCO3@ZnO core-shell composite powder (treatment 7) prepared by the method of this application has superior performance compared to the CaCO3@ZnO core-shell composite powder prepared by patents CN 111606351B (comparative example 2) and CN113000058A (comparative example 3). Furthermore, when the zinc oxide content in the product of this application is 10% of the weight of nano-calcium carbonate, its application effect is superior to commercially available nano-zinc oxide.

[0101] The above results show that the CaCO3@ZnO core-shell composite powder prepared by combining carbonation and precipitation methods has good dispersibility and high whiteness. After modification with stearic acid, when the ZnO content in the core-shell composite powder is 10-15% of the weight of nano-calcium carbonate, it can replace nano-zinc oxide in rubber and has better performance.

[0102] The above description, in conjunction with specific / preferred embodiments, provides a further detailed explanation of this application and should not be construed as limiting the specific implementation of this application to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of this application, and all such substitutions or modifications should be considered within the scope of protection of this application.

Claims

1. A CaCO3@ZnO core-shell structured composite powder, wherein the core-shell structured composite powder comprises a nano-calcium carbonate core and a zinc oxide shell coating its surface, wherein the weight of zinc oxide in the core-shell structured composite powder is 5% to 15% of the weight of nano-calcium carbonate.

2. The CaCO3@ZnO core-shell structured composite powder as described in claim 1, wherein: In the core-shell composite powder, zinc oxide is deposited on the surface of calcium carbonate in the form of particles with a particle size of 10-20 nm.

3. The CaCO3@ZnO core-shell structured composite powder as described in claim 1, wherein: The core-shell composite powder also contains stearic acid, which coats the outer surface of the core-shell composite powder.

4. The method for preparing the CaCO3@ZnO core-shell structured composite powder as described in claim 1 or 2, comprising the following steps: (1) Prepare calcium hydroxide slurry, and then introduce a mixed gas containing carbon dioxide into it to cause a carbonation reaction. When the pH value of the system is 8.0 to 9.0, add soluble zinc salt and soluble carbonate to the system, stir the reaction, and obtain a mixed slurry. (2) Remove impurities and moisture from the mixed slurry obtained in step (1) to obtain CaCO3@ZnCO3 powder; (3) The CaCO3@ZnCO3 powder obtained in step (2) is calcined to obtain CaCO3@ZnO core-shell structured composite powder.

5. The method for preparing CaCO3@ZnO core-shell structured composite powder as described in claim 4, wherein: In step (1), the solid content of calcium hydroxide in the calcium hydroxide slurry is 8.0-15.0%.

6. The method for preparing CaCO3@ZnO core-shell structured composite powder as described in claim 4, wherein: In step (1), the carbonation reaction is carried out at a temperature of 18–25 °C.

7. The method for preparing CaCO3@ZnO core-shell structured composite powder as described in claim 4, wherein: In step (1), the soluble zinc salt is one of zinc acetate dihydrate, zinc citrate, zinc chloride, zinc sulfate, and zinc nitrate; the soluble carbonate is one of sodium carbonate, potassium carbonate, ammonium carbonate, and ammonium bicarbonate.

8. The method for preparing CaCO3@ZnO core-shell structured composite powder as described in claim 4, wherein: In step (1), the pH of the system is adjusted to 7.0 to 8.5 during the stirring process.

9. The method for preparing CaCO3@ZnO core-shell structured composite powder as described in claim 4, wherein: In step (3), the heating rate of calcination is 3-10℃ / min, and the temperature is maintained at 300-450℃ for 1-5 hours.

10. The method for preparing CaCO3@ZnO core-shell structured composite powder according to any one of claims 4 to 9, wherein: In step (3), the CaCO3@ZnO core-shell structure powder is surface modified with stearic acid as a modifier. The amount of stearic acid used is 3.0 to 4.0% of the weight of the nano-calcium carbonate. The modification temperature is 90 to 95°C and the time is 30 to 60 min.

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