Methods to manufacture nano-alumina
Comparasion of these three methods
Each method both has its own advantages and disadvantages. Here they are.
|
Method |
Advantages |
disadvantages |
|
Solid phase method |
· Large yield · Simple equipment and process · Low cost and easy to realize industrial production |
· Purity and fineness do not meet the requirements · Non-uniform granularity and easy aggregation |
|
Liquid phase method |
· Easy to control chemical composition · High purity · The nano-powder has small particle size,narrow distribution, high stability, good dispersion and regular morphology |
· Complex operation · High cost |
|
Gas phase method |
· The nano-powder has small particle sizd,narrow distribution · Controllable average particle size and morphology · Not easy to aggregate and good dispersion |
· Low yield · High requirements for equipment · Difficult to collect |
How to manufacture alumina ceramic(step 1)
Description of step 1
In order to transform micron alumina powder into ceramics, the first step is to form. There are four main forming methods, which introduced one by one.
1.Dry-pressing shaping: Dry pressing is a relatively mature process. This forming method is a forming method that uses external force to increase internal friction and make particles connect because of internal friction, so as to maintain a certain shape[4].
2.Alumina Microinjection Molding Technology: After mixing alumina powder with adhesives, feeding is carried out. After feeding, the particles are re-broken. The particles are injected into the mold to form bio-culture[5].
3.Gelcasting: At the end of the twentieth century, researchers developed this kind of new molding process based on injection moulding[6].
4.Tape Casting: Also known as scraper forming method, it is suitable for the production of thin ceramic materials. Generally, adhesives, dispersants and plasticizers should be added to ceramic powder[7].
The development trend of alumina ceramics is to reduce the size of powders from micron to nano-level, because the grain size, grain boundaries and their combination are at the nano-level, and the number of grain boundaries is greatly increased, which can greatly improve the properties of materials and have an important impact on their electrical, thermal, optical and magnetic properties.
Description
To get nano-alumina, there are three sorts of methods based on from which phase we get it. These three method are Liquid method, Solid method and Gas phase method[1]
1.Liquid phase methodcan be classified into three specific methods and it is commonly used.
a.Precipitation:The appropriate precipitator is selected to react in the raw material solution to form insoluble precipitation such as hydroxide and sulfate, and then ultrafine compound powder is obtained by filtration, washing, drying and precipitate heating decomposition[2].
b.Sol-gel method: Using organic salts or inorganic salts as raw materials, hydrolysis and condensation reactions are carried out in organic medium, so that the solution is obtained by sol-gel process. The gel is heated or freeze-dried, and finally the ultrafine powder is obtained by calcination[2].
c.Microemulsion:One of the two immiscible solutions is dispersed in the form of micro droplets in the other phase to form an emulsion. The droplets in the emulsion are used as a micro reactor to produce oxide powder. The precipitation reaction takes place, and then the nano-alumina powder is obtained by washing, drying and calcining[3].
2.Solid phase method can be classified into two specific methods.
a.Mechanical attrition:Grinding raw materials into ultrafine powder by high energy ball mill.
b.Solid-state chemical reaction method:The reactants are mixed and grinded in a certain proportion, and then calcined. Ultrafine powders are prepared directly or re-crushed by solid-state reaction[2].
3.Gas phase method can be classified into three specific methods.
a.Combustion method:After mixing some substances which can produce intense chemical reactions evenly, ignition and combustion at a certain mixing place can be carried forward in the form of combustion wave until the reaction is completed by means of strong chemical reaction induction and propagation.
b.Vapor evaporation method:The raw material of alumina is heated and evaporated under the protection of inert gas, and then condensed in the gas medium to form ultrafine powder.
c.Chemical vapor deposition:Synthesis of Ultrafine Particles from Alumina Raw Materials by Gas Heating Decomposition and Chemical Reaction.
How to manufacture alumina ceramic(step 2)
Description of step 2
After obtaining the prototype of alumina, further sintering is needed to make the particles more closely bonded to form alumina ceramics. There are six main sintering processes of alumina ceramics.
1.Hot-pressing Sintering: Applying certain pressure while sintering will increase the diffusion rate of atoms[8-9], increase the driving force of sintering and shorten the time required under the condition of pressure.
2.Ultra-high Pressure intering: Ultra-high pressure sintering refers to sintering under higher pressure conditions. By this method, high-density and high-purity alumina ceramics can be successfully prepared without high temperature[10].
3.High Vacuum Sintering: Sintering under high vacuum.
4.Hot Isostatic Pressure Sintering: In the high temperature environment, the sintered green body is placed in the gas medium, so that the green body receives pressure in all directions, and the density of the ceramic material will be further improved.
5.Microwave Sintering: The material is heated by the loss of microwave in electromagnetic field, which is fast and compact.
6.Spark Plasma Sintering: Spark plasma sintering (SPS) is a process in which materials are heated to sintering temperature by means of instantaneous high temperature field generated by pulse energy, discharge pulse pressure and Joule heat.
Reference
[1]Wu Zhifu; Liang Liuqing; Yu Xiaoyou. Progress in preparation methods of nano-alumina [J] Industry and Technology Forum 2018-09-01
[2]Li Jinchang. Preparation of nano-alumina particles by mechanical method and its application in nano-electroless composite plating[D] South China University of Technology 2012-05-01
[3]Li Fang. What progress has been made in the preparation of nano-alumina ceramics?[J]Journal of Shanghai University of Engineering and Technology, Li Fang, 2008-09-15
[4]YinJianlong.Preparation and Sintering Properties of High Purity Alumina Ceramics [D] Dalian: Dalian Jiaotong University, 2013
[5]Zhou Gang; Fenglong Biao; Zhou Zhiyong; Xiao Jun; Li Xiaohui.Research progress of ceramic powder injection moulding technology and research progress[J] materials research and application 2018-06-15
[6]Peng He, Jiang Xianquan, Li Jing.Other research advances in injection moulding of alumina ceramics [J], functional materials, 2015, 21 (46): 21007-21011
[7]Chen Jianxin. Grinding and Polishing Technology of Alumina Ceramic Substrate [D] Guangzhou: Guangdong University of Technology, 2016
[8] GuyotP，AntouG， Pradeilles. Hot pressing and spark plasma sinteering of alumina：Discussion about an analytical modelling used for sintering mechanism determinnation［J］ ScrMetar，2014： 35-38
[9]Dai Jinshan. Sintering and Properties of High Purity Alumina Ceramics by Atmospheric Pressure and Hot Pressure [D] Jinan: Shandong University of Architecture, 2016
[10]Yang Lu, Jiang Shuwen, Wang Zhiqiang. Advances in Sintering Densification of special ceramics [J] Materials Report, 2014, 28 (4): 45-49