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Production methods and current situation of high purity alumina/aluminum oxide in China

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Production methods and current situation of high purity alumina/aluminum oxide 
               《crystal reports》   20120201   Yan xiao lu
 
Introduction 
 
Sapphire (Greek: σάπφειρος; sappheiros, "blue stone"[1]) is a gemstone variety of the mineral corundum, an
aluminium oxide (α-Al2O3).As an important technical crystal,it is widely applied in the field of science technology
,national defense,civilian industry.Over 100 companies invest in the growing of sapphire ingots in China these two 
years,and the new companies appear continuously.Even some foreign sapphire ingots growing companies from 
Tanwan,Ruassia,America came to China to build production base .The future of LED market belongs to China.
That followed,demand of high purity alumina will increase greatly.
 
 
 
production technology of high purity alumina home and abroad
 
Presently, main technology of producing high purity aluminum oxide are Crystallization method ,water-
soluble method,flame fusion method,Hydrolysis of Aluminum Alkoxide method.
 
 
 
1,Crystallization method include hot decompounding method of Ammonium Aluminum Sulfate and hot 
decompoundingmethod of Ammonium Aluminium carbonic acid.At present,many factories in Shang 
Dong,Shang Hai,Gui Zhou mainly adopt the method.Its disadvantage is that the purity is lower,saying 
99.99% in theory ,99.9% in fact because the impurities such as Fe,Ni,Ti,Zr and halogen can't be 
removed.Generally,the material only can be used to produce optical sapphires,can't satisfy high-end requirement.
 
 
 
2,water-soluble method,also be called Choline method,which is adopted by the biggest producer in China 
such as Shanghai Yiming Materials Tech. Co., Ltd ,Hebei Pengda New Material Technology Co., Ltd.The
material only can be used to produce industrial jewel and Low end sapphire.According to test ,the purity of 
aluminaproduced by the technology is only 99.95%-99.98%.Its disadvantage are that the technology process
can't purify again,the quality of the producedalumina is the same as the raw material;Secondly in order to 
speed up reaction between metal Al and purified water,the technology will cut metal alumina bark or block
into powder with metal knives ,which will take Fe,Ni,Ti,Zr these impurities to the material by knives,
while these impurities will strongly affect the quality of sapphire.In addition,in the process of locking 
block,they usually add adhesive in the material in order to enhance the density of block.However,these 
adhesive will degrade the quality of sapphire.Some of these sapphire can't be used on LED sapphire substrate,
only can be used on optical field.
 
 
 
3,flame fusion method,alumina crystalline granules is produced by the method.The disadvantage of the method 
is as follows:
  First, screen the high purity alumina powder from the roof through vibration screen,the screened powder 
will cool and consolidate on the core crystalline during falling after through oxyhydrogen flame with high 
temperature(the crystalline granules is half transparent,and more Taiwan customers are crazy with it,who 
think themselves its purity is relatively high and transparent.But,in fact,the purity is only 99.9% according 
to test.
  Second,Hydrogen goes to the furnace body through stainless steel tube which will bring some impurities
such as Fe,Ni,Cr,Ti and other metal impurities along ,which will be a part of sapphire.As melting temperature
of alumina is 2050°,while that of Fe,Ti,Cr,Mg is 2200 and evaporating temperature is over 4000°.And 
oxyhydrogen flame can only blow less light impurities on the surface,having no effect on the inside impurities.
  
  Third,according to the test report by authoritative experts,170 cubic hydrogen is needed to produce 1KG 
alumina crystalline granules,which will cost RMB150-230.In order to make profits,factories have to use low 
purity alumina (99.9% or 99.99%)instead of high purity ones.However,the transparent surface of such 
crystalline granules has cheated many people.
 
 
 
4.Hydrolysis of Aluminum Alkoxide method
 
Fig. 1 shows the manufacturing process of high purity alumina by aluminum alkoxide method.High purity 
Aluminum alkoxide is synthesizedfrom aluminum metal and alcohol,and hydrated alumina is produced by 
hydrolysis of alkoxide,and finally high purity alumina is obtained by calcination.
 
Al+3ROH /Al(OR)3+3/2H2
2Al(OR)3+4H2O /Al2O3·H2O+6ROH
Al2O3·H2O /Al2O3+H2O

 
Fig. 1  the manufacturing process of high purity alumina by aluminum alkoxide method
   Description of the technology process is as follows:
    1Firstly, as the reaction of block and alcohol is very fast ,use high purity alumina block and isopropyl alcohol 
or butanol or ethyl hydrate as materials instead of cutting metal alumina bark or block into powder with metal 
knives ,which will avoid ferric pollution taken by knives. 
    2)Secondly, to refine or purify, especially by distillation at 230-250℃ from aluminum iso-propoxide can collect
middle high purity aluminum iso-propoxide liquid, with getting rid of former and bottom distillation impurities, 
which is the most important procedure to distinct from other methods. The liquid is got by condensing of aluminum iso-propoxide steam. The method will leave impurities such as Fe, Ni, Si, and Cu in the bottom of the reactor.
    3)Thirdly, after distillation, to refine or purify further by ceramic membra(which is made by high purity alumina
of 99.999% purity) at 230℃ can remove other impurities like K,Na,Zn.
    4)Finally, use the high purity aluminium iso propoxide and high purity water as materials, after reaction, purifying by
ceramic membrane at 150-160℃ will remove other impurities further. Next wash and clean it with water.
    5)Then the powder is calcined under 5N nitrogen protection in the clean room.
    6)Then the block will repress under 1000 tons press,and isopress.And the blocks aren't added adhensives.We adopt 
advanced technology and the nature way by taking advantage of surface activity betwween nanoparticles and microparticles
of 5N high purity alumina powder to make blocks instead of adding adhensives in powder.
 
 
 
Production situation of high purity alumina in China
In China,most factories own small production capacity such as Yangzhou Crown New Material Co.,Ltd,Hong Fu Crystal 
Technology(Anhui) Co., Ltd.Dalian Rall Fine Ceramics Co., Ltd,Zibo Xinfumeng Chemicals Co., Ltd.,they can't satisfy
demand of sapphire production.But He Bei Peng Da Advance Materials Technology Co., Ltd has large production capacity
nearly 5000 tons per year,its production technology limits purity of alumina---Water-soluble method,which is mainly used
in the field of fluorescent lamp,can't widely used in LED.While xuan cheng jing rui new material co.,ltd adopts advanced 
method in the world---Hydrolysis of Aluminum Alkoxide method,,can meet needs of sapphire growing market.Whose 
production capacity can reach 2000tons.Production method depends the quality of high purity alumina.The future of high 
purity alumina will be xuan cheng jing rui new material co.,ltd.
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