Preparation Of Cerium-Based Rare Earth Polishing Powder For Optical Lens

Among the polishing compositions currently used in the glass industry,those based upon cerium typically perform the best.A variety of processes for the manufacture or preparation of such compositions are known.For example,it has been proposed to prepare cerium-based polishing compositions by precipitating ceric hydroxide,by means of ammonia,from a rare earth nitrate solution in which the cerium has been preliminarily oxidized.In spite of the fact that ceria based polishing powders are used worldwide,there is still the need to improve production routes and the polishing performance of the powders especially in terms of stock removal rate for the lens,etc.At present,cerium based polishing powder is usually prepared by precipitation roasting method with rare earth chloride as raw material in the market.The rare earth polishing powder prepared by this method has uniform composition,good consistency of particle size and crystal shape.The products are commonly used for polishing optical glass,photomask and LCD.But this method is complex and difficult to control.How to prepare rare earth polishing powder suitable for optical field has become a hot research topic.Accordingly a major objective of the present investigation is the provision of an improved process for the preparation of polishing compounds with a high stock removal rate.The ceria based polishing composition according to the current project can be produced by a process,comprising?a?suspending an inorganic cerium salt or cerium hydroxide with a cerium content calculated as cerium oxide in the range of 50%-100%based on total rare earth oxide?TREO?in an aqueous medium thereby obtaining an aqueous suspension,?b?treating said aqueous suspension with an acid or a salt of an acid selected from the group of HF,H₃PO₄ and H₂SO₄,thereby obtaining a solid suspended in said aqueous medium,?c?separating said solid from said aqueous medium,and?d?calcining the separated solid at a temperature between 950.degree.C.and grinding the calcined solid to grain sizes in the range of 0.5?mThe purpose of this paper is to develop a process to produce the rare earth polishing powder which could be used for lens,spherical surface polishing and to study the polishing mechanism,the effective methods to improve their stock removal rate?SRR?,or the polishing performance to reduce the scratch.The paper reveals that the hydroxyl introduced from Ce?OH?₄ highly elevated the stock removal rate.The hardness of the powder is a function of the specific surface area which is determined by calcination temperature and time.To secure narrow particle distribution,the carbonate the precursor of the rare earth oxyfluoride is a critical factor.One means of accomplishing this uniform particle size is parallel flow precipitation by which the kernel cations are surrounded in the same environment.Using mathematic software Mathematic 11.The function of temperature vs specific surface area was established.Namely,F_SSA=26199/T–2775/T^1/2+636/T^1/3The present research also amends the classic equation exported by Preston,introduces the specific surface into the formulas as following:SRR=**/A^1/3As such the specific surface and the stock removal rate have an invers relationship...