Japan(Sumitomo),America,Germany,China (CrownRe Innovative Materials Inc.) main adopt the method thoughit 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 CNY 450-500 per kilogram. Their product is popular worldwide owing to high purity and quality. In China, CrownRe Innovative Materials Corp.-CIMC Group adopt the advanced production method since 2012 to produce high purity alumina. In the way, via 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 3 years to resolve the purity, technique, equipments. Now their technology is rather mature, and own their independent intellectual property rights. Practice proves that their product of CN-L100G,CN-L100K can grow big and superior sapphire wafer.
Now, CrownRe not only offer 99.999% Alumina for sapphire, but 99.9999% for much stricter sapphire application.
Presently, main technology of producing high purity aluminum oxide Al2O3 are Crystallization method, water-soluble method, flame fusion method and 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 simple 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.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 withmetal 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:
Firstly, 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 acturally the purity is just 99.9% after test.
Secondly, 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 cent degree, while that of Fe,Ti,Cr，Mg is 2200 cent degree and evaporating temperature is over 4000 cent degree. And oxyhydrogen flame can only blow less light impurities on the surface,having no effect on the inside impurities.
Thirdly,with the test report by authoritative experts,170 cubic hydrogen is needed to produce 1kg alumina crystalline granules,which will cost CNY150-230.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 lied to 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 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 cent degree 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 cent degree 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 cent degree 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.