CN102649576A - Preparation process for flaky alumina with great diameter-thickness ratio - Google Patents

Abstract

The invention discloses a preparation process of flaky alumina with a large ratio of diameter to thickness. A molten salt is added to alumina powder, a template agent is added, and a shaping agent is added and mixed evenly. Put the mixture into a crucible with a cover, react at the set temperature, wash away the soluble salt with hot water, and then dissolve the impurity phase in the sample with hydrofluoric acid solution, wash and dry to obtain flaky alumina . In the method, regular and large-diameter-thick-ratio flaky alumina is obtained by adding a template agent and a shaping agent. The method has the characteristics of simple process and easy industrial production. The flaky aluminum oxide prepared by the invention can be used as a reinforcing phase of a composite material, a high-grade grinding material, a base material of a pearlescent pigment and a filler of a polymer material.

Description

A preparation process of flaky alumina with large ratio of diameter to thickness

technical field

The invention relates to a method for preparing flaky alumina with a large diameter-to-thickness ratio. The prepared flaky alumina can be used as a reinforcing phase for composite materials, a high-grade grinding material, a base material for pearlescent pigments, and a filler for polymer materials.

Background technique

The crystal form of flaky alumina is α-A1 ₂ O ₃ (corundum type), with a larger diameter (5-50 μm) and a smaller thickness (0.10-0.50 μm), complete crystalline α-A1 ₂ O ₃ particles It is in a regular hexagonal shape. Flaky alumina has high melting point, high hardness, high mechanical strength and easy dispersion. It can be used as a reinforcing phase for metal, ceramic and glass-based composite materials to improve the elastic modulus, Toughness and strength [Journal of the European Ceramic Society 19(1999) 335–339, Journal of the European Ceramic Society 25(2005) 1541–1550, Ceramics International 30(2004) 785–791]. It was found that the reinforcement with flake alumina Compared with ceramic matrix composites reinforced with granular alumina, the fracture toughness of ceramic matrix composites is higher. Because of the bridging effect of flake alumina in the matrix, the toughness of the material can be improved [Journal of Physics and Chemistry of Solids 69 (2008) 1521 –1524]. The thickness scale of flaky alumina is nanoscale or close to nanoscale, and the radial scale is micron scale, which combines the dual characteristics of nano-powder and micro-powder, reflecting good adhesion and moderate The surface activity of the powder can effectively combine with other active groups, and it is not easy to agglomerate. The powder itself is almost colorless and transparent, and has a significant shielding effect and the ability to reflect light; therefore, flake alumina can also be used for pearlescent pigments , cosmetics, automotive topcoats, fillers and abrasives [Journal of Process Engineering, 2004, 4 (Supplement): 279-283, Coating Industry, 2004, 34 (1): 59-63].

The main method for preparing flaky alumina is also the molten salt method. Yang Ying et al [Journal of Process Engineering, 2004, 4 (Supplement): 279-283] use aluminum sulfate as raw material, compound sulfate (Na ₂ SO ₄ +K ₂ SO ₄ ) is molten salt, supplemented with additional additives (such as phosphate, titanium dioxide or silicon dioxide, etc.), and a flaky alumina with a thickness of 200-400nm is synthesized. Zhang Qianying et al [Journal of Materials Research, 2008, 22(2): 205-208] also used aluminum sulfate as raw material to prepare Al(OH) ₃ precursor by sol-gel method in Na ₂ SO ₄ -K ₂ α-Al ₂ O ₃ powder was synthesized in SO ₄ molten salt, and the effects of Na ₃ PO ₄ ·12H ₂ O and TiOSO ₄ additives on the morphology of αAl ₂ O ₃ were studied. The phosphate ions in the additive Na ₃ PO ₄ 12H ₂ O adsorbed on the surface of the crystal can inhibit the growth of alumina crystals in the thickness direction, and reduce the agglomeration and interlaced growth between powders, and obtain no agglomeration and good dispersion After adding TiOSO ₄ , the entry of titanium ions will increase the concentration of aluminum vacancies, thereby changing the growth rate of each crystal face of the crystal and promoting the formation of a more regular shape, thereby preparing a regular shape, uniform size, Agglomerated flaky α-Al ₂ O ₃ . Zhu et al [CeramicsInternational34 (2008) 1729–1733] calcined Al(OH) ₃ at 500°C to obtain porous alumina, and used it as a precursor to prepare flaky alumina in NaCl–KCl molten salt. Calcined at 900℃ for 4h, the flake alumina with an average particle size of 2.4μm was obtained, but the ratio of diameter to thickness was small. Lee et al [Materials Science and Engineering A 466 (2007) 79–83] used γ-Al2O3 as raw material and Na ₂ SO ₄ as molten salt to study the influence of microwave sintering on the morphology of flaky alumina. The particle size distribution of the flaky alumina prepared by sintering is uniform, but the ratio of diameter to thickness is small.

From the above research, it is found that aluminum salts can be used as raw materials to obtain flaky alumina with a large diameter-to-thickness ratio, but the cost of using aluminum salts as a raw material is relatively high, and it is difficult to obtain flaky alumina with a large diameter-to-thickness ratio using alumina as a raw material. .

Contents of the invention

The purpose of the present invention is to provide a kind of aluminum oxide as raw material, adding template agent and shaping agent to the raw material, which can promote the growth of alumina into a regular sheet, and obtain a sheet with a large diameter-to-thickness ratio (diameter-to-thickness ratio greater than 60). The preparation process of alumina can significantly reduce the preparation cost.

To achieve the above object, the present invention is achieved by taking the following technical solutions:

A process for preparing flaky alumina with a large diameter-to-thickness ratio, characterized in that it comprises the following steps:

(1) Add template agent, molten salt and shaping agent to alumina powder, and then mix evenly. The template agent is one of kaolin, graphite, calcite and mica, and the amount added is 0.01-5% of the mass of alumina powder %, the added amount of the molten salt is 100-300% of the mass of the alumina powder, and the added amount of the shaping agent is 0.01-5% of the mass of the alumina powder;

(2) React the homogeneously mixed material at a temperature of 800-1200°C for 1-4 hours to obtain a reaction product;

(3) Soak the reaction product in water at 40-100°C for 3-24h, filter and wash, then soak in hydrofluoric acid solution with a temperature of 20-60°C and a mass concentration of 10%-40% for 1-10h, filter , washing and drying to obtain flaky alumina with a large diameter-to-thickness ratio.

In the above scheme, the molten salt described in step (1) is sodium sulfate, potassium sulfate, sodium chloride, sodium phosphate, sodium hydrogen phosphate, sodium pyrophosphate, potassium chloride, sodium sulfate with a molar ratio of 1:1 and One of potassium sulfate, sodium chloride and potassium chloride with a molar ratio of 1:1.

The shaping agent described in step (1) is one of titanium dioxide, zinc oxide, tin oxide, iron oxide and silicon oxide.

The waste water after soaking and washing the reaction product in the step (3) with hydrofluoric acid solution is treated with limestone and then discharged, and the generated waste residue is used as a raw material for cement.

The advantage of the present invention is that alumina is used as a raw material, and flake-like substances are added as templates, which can promote the nucleation and growth of flake alumina, and obtain flake alumina with a large diameter-thickness ratio (diameter-thickness ratio greater than 60). Adding a shaping agent to the raw material can promote the growth of alumina into a regular hexagon, and at the same time make the particle size of the flaky alumina powder uniform.

Description of drawings

Fig. 1 is a photo of the micromorphology of the flaky alumina with large diameter-thickness ratio prepared in Example 6 of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with specific examples.

Table 1 lists the first step process conditions of 10 examples numbered 1-10: according to the different examples in Table 1, determine the type and amount of template agent, molten salt, and shaping agent.

Table 1. Ratio of Raw Materials

Table 2 lists the process conditions of the second and third steps of the embodiment in Table 1: put the mixture into a crucible with a cover, determine the sintering temperature and time according to the different embodiments in Table 2, and obtain the reaction product. And determine the water washing temperature and time of the reaction product, pickling temperature, acid concentration and time, and obtain flaky alumina after drying.

Table 2 Preparation process conditions of flaky alumina

Table 3 shows the diameter-thickness ratio of the flaky alumina in the examples of the present invention.

Table 3 Diameter-thickness ratio of flaky alumina

Example number Diameter of flake alumina (μm) The maximum diameter-thickness ratio of flake alumina 1 20 40 2 30 45 3 25 40 4 35 45

5 40 43 6 30 60 7 28 48 8 36 48 9 38 46 10 28 42

It can be seen from Table 3 that the diameter-thickness ratio of the flaky alumina prepared by the method of the present invention is controllable, and it can be seen from Fig. 1 that the surface of the alumina flake is smooth and regular in shape.

Claims (4)

1. the tabular alumina preparation technology that the radius-thickness ratio value is big is characterized in that, comprises the steps:

(1) in aluminum oxide powder, adds template; Fused salt and shaping agent; Mix then, said template is a kind of in kaolin, graphite, calcite and the mica, and add-on is the 0.01-5% of aluminum oxide powder quality; The add-on of said fused salt is the 100-300% of aluminum oxide powder quality, and the add-on of said shaping agent is the 0.01-5% of aluminum oxide powder quality;

(2) with the material that mixes under 800-1200 ℃ the temperature reaction 1-4h after, obtain reaction product;

(3) with the water logging bubble 3-24h of reaction product with 40-100 ℃; After filtering, washing; Use temperature to soak 1-10h as the hydrofluoric acid solution of 10%-40%, obtain the big tabular alumina of radius-thickness ratio value after filtration, washing, the drying as 20-60 ℃, mass concentration.

2. the tabular alumina preparation technology that radius-thickness ratio value as claimed in claim 1 is big; It is characterized in that the fused salt described in the step (1) is that sodium sulfate, vitriolate of tartar, sodium-chlor, sodium phosphate, sodium hydrogen phosphate, trisodium phosphate, Repone K, mol ratio are a kind of in 1: 1 sodium sulfate and vitriolate of tartar, the mol ratio sodium-chlor that is 1: 1 and the Repone K.

3. the tabular alumina preparation technology that radius-thickness ratio value as claimed in claim 1 is big is characterized in that, the shaping agent described in the step (1) is a kind of in titanium oxide, zinc oxide, White tin oxide, red stone and the silicon oxide.

4. the tabular alumina preparation technology that radius-thickness ratio value as claimed in claim 1 is big; It is characterized in that; Described in the step (3) with the waste water after the hydrofluoric acid solution washing by soaking reaction product, handle the back discharging with Wingdale, the waste residue of generation is as the raw material of cement.

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