January 26, 2020

New green technology for joint production of fine alumina powder of different purity

Abstract aluminum and ammonium salts combined with new technology the production of fine alumina green production, the production process proposed principle, has been described how the raw materials recycling and recovery, the plasma activation analysis and neutron mass The purity of alumina was analyzed by scanning electron microscopy.

Keywords fine powder, alumina, green production

CLC number TQ133.1

A NEW COMBINED PROCESS FOR PRODUCTION OF FINE ALUMINA POWDERS

MA Chicheng ZHOU Xuexi ZHU Tun

(Inst. Chem. me tall., Chinese Academy of Sciences, Beijing 100080, China)

ABSTRACT A new combined process for production of fine alumina powders ofnanometer size is studied. The flow of the produced alumina was analyzed by neutro nactivation and plasma spectrometery, and the particle size of thealumina was characterized by TEM.

KEY WORDS Fine powder, Alumina, Green production

1 Introduction

Alumina is a widely used ceramic powder material, which not only plays an important role in structural ceramics, but also has been widely used in bioceramics and functional ceramics, especially in catalyst carriers, integrated circuit substrate materials and light transmission. Materials and other fields are popular [1]. Different applications require alumina of different purity. The purity of high-purity alumina is above 99.99%, and the single crystal can be applied in the fields of laser materials and window materials. It is used in the production of abrasives and engineering ceramics. With the development of high technology, the research on alumina has become more and more intensive, and its purity, particle size and particle shape have been put forward higher requirements. Research on ultra-fine alumina materials has caused more and more More attention. At present, most of the domestically produced alumina adopts ammonium sulfate ammonium pyrolysis method. This method controls the pH and recrystallization of the solution to separate the impurities, and the purity is further increased. When the thermal decomposition is heated to 900 ° C, Only 90% of sulfur trioxide [2] is removed, and complete desulfurization requires further heating or holding for several hours. Complete conversion to γ-Al2O3 requires higher temperature and high energy consumption.

A new non-polluting process to achieve green production of alumina.

The requirements for green production are: the production uses non-toxic raw materials; it is carried out under non-toxic reaction conditions; it has "atomic economy", ie

The reaction has high selectivity, few by-products, and even “zero emissions”; the product is environmentally friendly [3]. In the green production process of alumina, ammonium bicarbonate and aluminum salt are non-toxic and harmless common industrial raw materials. In the process of production and thermal decomposition, due to the absorption and utilization of ammonia and carbon dioxide, there is no discharge of three wastes. The produced alumina is harmless to the environment. This paper studies the new process of fine alumina production-aluminum carbonate method to produce alumina. Green new process. Because of the different production of alumina products in the same production process, it is also called joint production process.

2 Principles and processes

The ammonium aluminum carbonate pyrolysis method [4] is to use ammonium hydrogencarbonate and aluminum salt to synthesize the precursor aluminum ammonium carbonate, and then thermally decompose it.

The liquid phase production method to alumina includes synthesis and thermal decomposition. The advantage of this method is that the produced powder has high purity and particle size.

Small. Its typical reaction can be expressed by the following formula

G421-1.gif (903 bytes)

(1)

G421-2.gif (1263 bytes)

(2)

G421-3.gif (1177 bytes)

(3)

The principle production process of the new process is shown in Figure 1. During the production process, the purity of the product is affected by the purity of the aluminum salt and ammonium bicarbonate. After the aluminum salt is purified, it can be reacted with the high-purity ammonium hydrogencarbonate solution to obtain high-purity alumina. Precursor, in this process, the concentration of ammonium bicarbonate in the mother liquor drops due to the reaction, and is added to the required concentration of ammonium bicarbonate to re-enter the cycle to achieve the internal circulation of the reaction medium. The process is characterized by: accumulation of impurities in the solution Below the upper limit of the product requirements, the desired concentration of ammonium bicarbonate can still be added to the mother liquor to prepare alumina with a slightly lower purity. Similarly, when the purity of the product is not required, a lower grade alumina can be produced. After the remaining solution, redistribute and recover water, ammonia and carbon dioxide. The (NH4)2SO4 in the residual liquid can be evaporated and recovered. The water, carbon dioxide and ammonia generated by decomposition during thermal decomposition enter the absorption tower to recover pure carbonic acid. Ammonium hydrogen, re-enter the cycle. The new process can prepare alumina products of different purity without changing the reactor, so that the raw materials can be utilized to the maximum extent and the production cost can be reduced without

Table 1 - Content of major impurities in alumina

Table 1 ~ The main impurities in alumina (×10{-6)

Al 2 O 3 (%) Si Na Mg Cu Fe Ti
25 99.995 <5 <5 <1 <3 <5 <2
26 99.995 <5 <5 <3.9 <3 <5 <2
AKS-G 1) 99.995 10 10 5 2 15

Note: 1) Sumitomo chemicalCO., LTD, Japan.

T421.gif (2117 bytes)

Figure 1 Process flow chart of alumina green production
Fig.1 The flowsheet of manufacture of alimina powder

3 Results and discussion

The purity of the precursors and products was determined by plasma mass spectrometry and neutron activation. The results are shown in Table 1. The alumina [5] was prepared by decomposing the precursor aluminum ammonium carbonate (), and the sample was subjected to differential heat and thermogravimetric analysis after drying at a lower temperature than the lower one. From the position of the difference heat peak in the figure, it can be seen that the sample begins to decompose at about time, and a significant endothermic peak appears at 224 ° C, indicating that the decomposition reaches a maximum at this time, and the decomposition basically ends at 280 ° C. After that, the sample weight loss becomes quite equivalent. Slowly, there is no obvious endothermic peak and exothermic peak on the DTA curve, which indicates that the decomposition reaction is basically finished after 280 ° C. It can be seen from Fig. 2 that the loss of the precursor is about 63%, which is lower. Thermal decomposition is completed at temperature.
The sample was sampled at 700 ° C for 2 h, and the particle size analysis was carried out by scanning electron microscopy [6] . The average particle size of γ-Al 2 O 3 was known .
The average degree is less than 1 μm. The specific surface of γ-Al 2 O 3 is determined by BET method to be 300 m 2 /g. The obtained sample is spray granulated.
To spherical alumina particles with a particle size of 30 to 50 μm (see Figure 3), as a raw material for producing alumina single crystals, it can also be used as a large ratio table.
Chemical and petroleum catalysts and catalyst carriers with good surface and fluidity. The main properties of γ--Al2O3 before and after granulation are shown in Table 2.

Table 2 Main properties of γ-Al 2 O 3 before and after granulation
Table 2 The main characteristics of γ-Al 2 O 3 particlesbefore and after
Granulation

Sample
No.
Particle size (nm) Specific surface area
(m2/g)
Particlesize 1) (μm) Loose bulk density 1) (g/cm 3 ) Packed bulk density 1)
(g/cm 3 )
25 <20 296 30~50 0.43 0.52
26 <20 309 30~50 0.43 0.52
AKS-G 10 120~170 30~50 0.3 to 0.5 0.35~0.55

Note: 1) After granulation.

T422-1.gif (2685 bytes)

Figure 2 Differential thermal and thermogravimetric curves of AACH
Fig.2 TG and DTA curves of AACH precipitated

T422-2.gif (8823 bytes)

Figure 3 γ- Al 2 O 3 after granulation
Fig.3 The images of Granulated
γ -Al 2 O 3

The process has been semi-industrial test, the particle size and purity of the produced alumina have reached the requirements of high purity and fineness, and samples are provided to many users at home and abroad for experimental research and satisfactory results.
The advantages of this production process are: (1) less process, compact equipment and less investment. (2) The use of readily available non-toxic industrial raw materials, production safety and low cost. (3) Synthesize in a closed reactor to avoid the loss of ammonia and carbon dioxide, absorb and return ammonia, carbon dioxide and water obtained by decomposition and drying, and make full use of raw materials to reduce environmental pollution.

4 Conclusion

The process has a green design for the combined production of alumina with ammonium bicarbonate and aluminum salts, which reduces energy consumption and does not cause environmental pollution.
Dyeing, maximizing the use of raw materials. The particle size and purity of the produced alumina meet the requirements, and the alumina flow after spray granulation
Good sex, bigger than the surface.

*Key Projects of the Chinese Academy of Sciences (95-1-201)
About the author: Ma Chiwei: Male, 29 years old, master's degree, researcher, inorganic materials and chemical engineering
Author: Institute of Chemical Metallurgy Chinese Academy of Sciences, Beijing 100080

references
1
Shepperd LMRecent Development and Outlook for Electro nic Ceramics Ind. , 1993 , 5(6) : 83-89
2 beautiful pigeons. High purity alumina preparation technology. Functional Materials, 1993, 24(2): 187-191
3 Zhu Qingshi. Green chemistry progress. University Chemistry, 1997, 6(12): 7
4
Kato.S., Iga T., Hatano S. et al. Effects of Synthetic Co nditions of NH 4 AL(OH) 2 CO 3 on Sinterability of Aluimina by Thermal Decomposition.Yoggyo-Kyokai-Shi , 1976 , 84(6 ) : 255-258
5 Ma Chi. Synthesis and thermal decomposition of heteromorphic ammonium aluminum carbonate. Master's thesis of the Institute of Chemical Engineering and Research, Chinese Academy of Sciences, 1997
6
Ma Chicheng, Zhou Xuexi, Zhu Tun. Preparation of Alumina Powder with Special Morphology. In: proc.the 12th KACG Tech.Meeting and the 4th Korea-Japan EMGS.Keun Ho Auh Ed.SEOUL:The Korean Association of CrystalGrowth , 1997 . 3-5

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