Direct hydrolysis is the reaction of aluminum with water directly, aluminum hydroxide, the hydrolysis process in fully enclosed organic lined environment,do not add any catalysts. This method can make the alumina 4N and 5N . At present,Guangzhou Kincaid is using this production method . Hydrolysis defect,industry insiders are unable to re- purification, the raw material is what level, made out of aluminum, that is,what level , can not go beyond the level of raw materials . However, the premise of this evaluation , the final powder product is only done so far,and if followed by the powder processed into high-density block of crystalline material,the purity can be improved beyond the level of material level .

Production of sapphire crystal main raw material consumed or broken crystal alumina powder . Domestic production of sapphire can be used to do a lot of low brightness substrate , which is lower quality , such as yellow crystals after irradiation color, cracked crystal,twins ,dislocation density ,etc. etc.,in addition to technology, the quality of raw materials have an important impact .
The current domestic production of high purity alumina popular technology in three ways: multiple crystallization,alkoxide solution,direct hydrolysis. Also divided into multiple crystallization of ammonium aluminum sulfate and ammonium aluminum carbonate pyrolysis pyrolysis . At present, Shandong,Shanghai,Guizhou and other places of the manufacturers,the majority of adopted this approach. Its drawback is that the metal ions and halogen element are difficult to remove,the purity can reach 4N,has basically been the limit;said from the purity of its flaws getting bigger,generally only used in flame fusion gems, to be directly used bigger size sapphire crystal material is difficult . But if the first use made of sapphire flame fusion debris, the equivalent first conducted a crystallization purification,can be used for growing large crystals,but still can not meet the high requirements.

Alkoxide solution also divided into aluminum isopropoxide France and choline France. Choline method which is currently the largest of 4N grade alumina production methods. Hebei factory using a choline law,but almost all of its products are sold to the phosphor industry went in the crystal industry did not seem to see their sight. Dalian has several plants are basically used for aluminum isopropoxide law,and product purity are generally superior choline law,the domestic industry more accustomed YAG crystal made of the material in this way .