Preparation method of high-temperature crystal face isolation type anti-cold-welding indirect method zinc oxide and product thereof

Abstract

The invention discloses a preparation method of high-temperature crystal face isolation type anti-cold welding indirect method zinc oxide and a product thereof, and belongs to the technical field of inorganic powder preparation. The core of the method is as follows: the airflow temperature is controlled at 350-550 DEG C in a high-temperature flue behind an outlet of an oxidizing chamber for indirect zinc oxide production and before cloth bag dust collection, and inorganic modifier precursors such as silicate ester, borate or zircon salt are continuously introduced into the high-temperature flue to form aerosol. The modifier is subjected to in-situ decomposition or reaction at high temperature, a high-temperature-resistant inorganic isolation layer is deposited on the surface of newly generated zinc oxide crystal grains, the isolation layer can physically isolate the crystal grains before cold welding fusion, and hard agglomeration is prevented from being formed from the source. And collecting dust by a cloth bag and cooling to obtain a high-dispersity zinc oxide product. The method is simple in process and easy to integrate with an existing production line, the obtained product is free of high-temperature hard agglomeration, high in looseness and good in dispersity, the chemical property of a zinc oxide body is not affected, and the method is suitable for continuous clean production of high-end zinc oxide.

Description

Technical Field

[0001] This invention belongs to the field of inorganic powder material preparation and surface modification technology, specifically involving a preparation method for in-situ crystal plane isolation of indirect zinc oxide under high temperature conditions to suppress grain cold welding and prevent hard agglomeration, and a zinc oxide product with high looseness and excellent dispersibility obtained by this method. Background Technology

[0002] Indirect zinc oxide is an important industrial raw material widely used in rubber, ceramics, coatings, electronics, and chemicals. Its traditional production process typically involves melting, evaporating, oxidizing, and subsequently cooling and collecting metallic zinc. At the outlet stage of the oxidation furnace (chamber), the generated primary zinc oxide grains are at high temperatures (typically 300-600℃). At this high temperature, the highly reactive zinc oxide grains, during collisions and contact, readily undergo "cold welding" or sintering through diffusion and rearrangement of surface atoms, forming strong, chemically bonded hard agglomerates. These hard agglomerates are not only difficult to disperse using conventional mechanical forces in subsequent processes, but also significantly reduce the specific surface area of ​​the final product, affecting its dispersibility, uniformity, and reactivity in the application system, ultimately impairing its performance.

[0003] To address the problem of powder agglomeration, existing technologies typically involve physical or chemical modification of the collected zinc oxide at room temperature, such as adding surfactants, coupling agents, or mechanical grinding. However, these methods are all "post-processing" and cannot intervene in or prevent the grain cold welding process that already occurs in the high-temperature zone at the furnace outlet. Therefore, hard agglomerates have already formed, and subsequent modification often only involves secondary treatment on their surface, with limited effectiveness. Furthermore, most organic modifiers are unable to withstand high temperatures and decompose and fail in the high-temperature zone, while inorganic high-temperature modification is rarely specifically applied to suppress the source of agglomeration during the high-temperature synthesis stage of zinc oxide.

[0004] Therefore, developing a novel preparation method that can effectively isolate grains and prevent the formation of cold-welded hard agglomerates during the initial high-temperature stage of zinc oxide formation is of great practical significance and technical value for improving the product quality of indirect zinc oxide and expanding its high-end applications. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a method for preparing zinc oxide via a "high-temperature crystal plane isolation type anti-cold welding" indirect method. This method involves introducing a specific inorganic modifier in situ into the high-temperature zone at the outlet of the oxidation chamber, causing it to form a high-temperature resistant physical isolation layer on the surface of newly formed zinc oxide grains. This effectively blocks the cold welding fusion of the grains, fundamentally preventing the formation of hard agglomerates.

[0006] The technical solution adopted in this invention is as follows: A method for preparing high-temperature crystal plane isolation type cold-resistant indirect zinc oxide, characterized by comprising the following steps: S1. Controlling the Reaction Temperature and Zone: In the indirect zinc oxide production process, the reaction zone is confined to the high-temperature flue gas duct after the oxidation chamber outlet and before the bag filter. The airflow temperature within this zone is precisely controlled and stabilized between 350°C and 550°C. This temperature range is a critical window period to ensure effective reaction of the modifier and to prevent severe cold welding of the zinc oxide grains.

[0007] S2. Introducing inorganic modifier: In the high-temperature flue described in step S1, a pre-prepared inorganic modifier precursor solution or suspension is continuously and uniformly introduced through an atomizing nozzle or by carrier gas, so that it rapidly forms an aerosol in the high-temperature gas flow.

[0008] S3. In-situ Formation of a Crystalline Isolation Layer: The inorganic modifier aerosol injected in step S2 rapidly undergoes thermal decomposition, hydrolysis (utilizing trace amounts of water vapor in the flue gas), or reaction with gas flow components at a high temperature of 350-550℃. The generated active components (such as SiO2, B2O3, ZrO2, ZrP, etc.) are instantly adsorbed and deposited on the surface of the flowing, high-temperature zinc oxide grains. By controlling the process parameters, these inorganic materials form a continuous or discontinuous, nano- to submicron-scale dense or loose isolation film on the surface of the zinc oxide grains; this is the "crystalline isolation layer." This isolation layer physically separates adjacent zinc oxide grains, blocking direct lattice contact and atomic diffusion paths between grains.

[0009] S4. Collection and Post-processing: The zinc oxide gas-solid mixture, after surface isolation treatment, is carried by the airflow into the downstream bag filter for collection. Because the grains are separated by the isolation layer, high-temperature cold welding will not occur even during the dust accumulation process. The collected powder is then naturally cooled to room temperature within the system to obtain the final product.

[0010] Preferably: In step S1, the airflow temperature in the high-temperature flue is controlled to be between 380°C and 500°C.

[0011] In step S2, the inorganic modifier is selected from substances that can decompose or react at high temperatures to generate stable oxides or inorganic salt films, preferably one or a mixture of several of silicate compounds, borate compounds, zirconium salts (such as zirconium oxychloride, zirconium nitrate) or zirconium phosphate precursors.

[0012] In step S2, to promote aerosol formation and uniform dispersion, the inorganic modifier precursor can be dissolved in volatile solvents such as alcohols to prepare a solution before being atomized and sprayed in.

[0013] In step S4, the total amount of the inorganic modifier, based on the effective components, is 0.1 wt% to 0.7 wt% of the final zinc oxide product mass.

[0014] Another objective of this invention is to provide a high-dispersion zinc oxide product prepared by the above method. This zinc oxide product consists of primary grains and an inorganic insulating layer on their surface. Its characteristics include: the absence of hard agglomerates formed by high-temperature cold welding and chemical bonding between the primary grains; extremely high dispersion of the powder, with a tap density significantly lower than that of indirect zinc oxide produced under the same conditions without high-temperature insulating treatment; and excellent dispersibility in application systems. Beneficial effects

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Source Suppression, Fundamental Solution: This invention breaks through the traditional approach of post-treatment at room temperature, placing the modification process at a critical high-temperature stage after zinc oxide grain formation and before cold welding. The in-situ formed isolation layer physically blocks grain fusion, fundamentally solving the problem of hard agglomeration caused by high-temperature cold welding, thus achieving "prevention first."

[0016] 2. Strong process adaptability and simple operation: This method cleverly utilizes the high-temperature flue in the existing indirect production process as a reactor, eliminating the need for complex high-temperature reaction equipment. The introduction of modifiers can be seamlessly integrated with the existing production process, making it suitable for continuous large-scale production.

[0017] 3. Long-lasting and stable modification effect: The selected inorganic isolation layer materials (such as silicon oxide, boron oxide, zirconium oxide, etc.) have extremely high thermal stability and chemical inertness. They will not decompose, melt or migrate within the subsequent processing and use temperature range, and can maintain the isolation effect for a long time.

[0018] 4. High product purity and superior performance: The modification process does not introduce organic impurities, eliminating organic residue issues and ensuring the chemical purity of the zinc oxide product. The prepared zinc oxide powder has high looseness and good flowability, making it easy to disperse uniformly in matrices such as rubber and ceramics, fully leveraging its functionality and enhancing the performance of composite materials.

[0019] 5. Minimal impact on the main properties: The inorganic isolation layer is extremely thin and used in very small quantities, without altering the core chemical composition, crystal structure, and basic physicochemical properties (such as purity and activity) of zinc oxide, ensuring the product's applicability in traditional application areas. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the method of the present invention.

[0021] Figure 2Microscopic morphology of zinc oxide (loose single particles) prepared in Example 1.

[0022] Figure 3 The image shows the microstructure of zinc oxide (with severe hard agglomeration) prepared by the conventional indirect method for Comparative Example 1. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the embodiments of this invention will be described in detail below. The following examples are used to illustrate this invention, but are not intended to limit the scope of this invention.

[0024] Example 1 In a conventional indirect zinc oxide production line, a precision atomizing nozzle is installed at the high-temperature flue outlet after the oxidation chamber. The gas temperature in the flue at this point is monitored and controlled at approximately 400 ± 10 °C. A 5% (w / w) tetraethyl orthosilicate-ethanol solution is prepared as a modifier. This solution is continuously and stably injected into the high-temperature flue using a metering pump, with the injection rate controlled so that the amount of tetraethyl orthosilicate (based on SiO2) added is approximately 0.3 wt% of the estimated zinc oxide yield. The solution is instantaneously atomized, evaporated, and decomposed in the high-temperature gas flow, and the generated nano-SiO2 is deposited on the surface of the hot zinc oxide grains. The treated gas-solid mixture is then subjected to subsequent baghouse dust collection and natural cooling to obtain zinc oxide product A. Testing shows that the tap density of this product is approximately 25% lower than that of the untreated product. Figure 2 The results showed that zinc oxide product A, observed under a scanning electron microscope, did not contain significant hard agglomerates; it mainly consisted of dispersed primary or soft agglomerate particles.

[0025] Example 2 In another production line, the temperature of the high-temperature flue gas reaction zone is controlled at approximately 480°C. Trimethyl borate is injected into the high-temperature flue gas in gaseous form via a nitrogen carrier, with the injection amount equivalent to approximately 0.15 wt% of the zinc oxide production (B₂O₃). Trimethyl borate decomposes at high temperature, forming a boron-containing insulating layer on the zinc oxide surface. The resulting product B also exhibits excellent bulkiness.

[0026] Example 3 The temperature of the high-temperature flue was controlled at 520℃. An aqueous solution of zirconium oxychloride (ZrOCl2·8H2O) was atomized and sprayed into the flue using compressed air. The solution rapidly dried and decomposed at high temperature, forming a ZrO2 isolation layer on the zinc oxide surface. The amount of ZrO2 added was approximately 0.5 wt% of the zinc oxide. The resulting product C exhibits high-temperature stability and is particularly suitable for applications requiring subsequent high-temperature processing.

[0027] Comparative Example 1 Without any high-temperature modification, zinc oxide, after being produced from the oxidation chamber, passes through the same high-temperature flue and bag filter dust collection process as usual to obtain product D. This product suffers from severe agglomeration and has a high tap density. Figure 3The scanned electron microscope revealed a large number of fused, hard aggregates.

Claims

1. A method for preparing high-temperature crystal plane isolation type cold-resistant indirect zinc oxide, characterized in that, Includes the following steps: In the high-temperature flue between the oxidation chamber outlet and the bag filter in the indirect zinc oxide production process, the airflow temperature is controlled at 350°C to 550°C. Inorganic modifier precursors are continuously introduced into the high-temperature flue to form an aerosol in the airflow. The inorganic modifier precursors react in situ on the surface of zinc oxide grains at the high temperature to form an inorganic isolation layer, thereby preventing high-temperature cold welding between grains. After bag filter dust collection and cooling, zinc oxide product is obtained.

2. The method according to claim 1, characterized in that, The inorganic modifier precursor is selected from one or more combinations of silicate compounds, borate compounds, thermally decomposable zirconium salts, and zirconium phosphate precursors.

3. The method according to claim 1, characterized in that, The silicate ester compound is methyl orthosilicate, ethyl orthosilicate, or polyethyl orthosilicate; the borate ester compound is trimethyl borate or triethyl borate; the thermally decomposable zirconium salt is zirconium oxychloride, zirconium nitrate, or ammonium zirconium carbonate.

4. The method according to claim 1, characterized in that, The inorganic modifier precursor is introduced into the high-temperature flue in the form of a solution or suspension via atomization, or in the form of a gas via a carrier gas.

5. The method according to claim 1, characterized in that, The total amount of the inorganic modifier precursor, based on the effective component mass of the inorganic isolation layer ultimately formed on the zinc oxide surface, is 0.1 wt% to 0.7 wt% of the zinc oxide product mass.

6. The method according to claim 1, characterized in that, The airflow temperature inside the high-temperature flue is controlled to be between 380°C and 500°C.

7. The high-looseness zinc oxide product prepared by the method according to any one of claims 1 to 6, characterized in that, The primary grains of the zinc oxide product are coated with an inorganic isolation layer, and there are no hard agglomerates formed between the grains due to high-temperature cold welding.

8. The zinc oxide product according to claim 7, characterized in that, The inorganic isolation layer comprises one or more of silicon oxide, boron oxide, zirconium oxide, and zirconium phosphate.

9. The zinc oxide product according to claim 7, characterized in that, The zinc oxide product has a lower tap density and higher dispersibility than zinc oxide produced under the same conditions without high-temperature isolation treatment.

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