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 decompounding
method 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,watersoluble 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.Its disadvantage are that the technology
process can't purify again,the quality of the produced alumina 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
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 synthesized from aluminum metal and alcohol,and hydrated alumina is produced by
hydrolysis of alkoxide,and finallyhigh purity alumina is obtained by calcination.
Fig. 1 the manufacturing process of high purity alumina by aluminum alkoxide method
Description of the technology process is as follows:
1)Firstly, 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 membrane(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 membraneat 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.
Japan(Sumitomo),America,Germany,China(Xuan cheng jing rui new material co.,ltd) main adopt the method though
it is dangerous and high-cost ?The only answer is high purity, which can make sure that the high purity
alumina will growing sapphire wafer with high quality. Its well known that impurities of 5N high purity alumina for
growing LED sapphire wafer must be controlled in the range (Fe <6ppm,Si<5ppm,Zr <1ppm,Cu <1ppm,K <1ppm,Na <1ppm).
Actually, the method is well controlledimpurity content .Presently, Sumitomo,in Japan, produces the largest quantity of 5N (99.999%)alumina with the way. Their capacity is 1000Tons per year and price is RMB 450500 per kilogram. Their product is popular worldwide
owing to high purity and quality. In China, xuan cheng jing rui new material co.,ltd,Hang Zhou wan jing new material co.,ltd adopt
the advanced method since 1996 to produce high purity alumina. In the way, though the companies take a lot of detours and the purity
is unqualified at first, they constantly make effort to explore technology and innovate. It takes nearly 6 years to resolve the purity,technique,
equipment.Now their technology is rather mature, and own their independent intellectual property rights. Practice proves that their product
of VK-L100G,VK-L100K can grow big and superior sapphire wafer.
production technology of High Purity Alumina for Sapphire waferPrevious
Sapphire ingots growed by our 5N high purity aluminum oxide
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