Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
2001-11-30
2003-05-13
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C051S307000, C423S263000
Reexamination Certificate
active
06562092
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of producing a stock material for cerium-based abrasives comprising cerium oxide as the main ingredient, and also to a cerium-based abrasive of excellent grinding characteristics, produced from the above stock material.
EARLIER TECHNOLOGY
Cerium-based abrasives have been used for grinding various glass materials. Recently, in particular, their applicable areas have been expanding, as they are used for grinding glass materials for electric and electronic devices, e.g., glass as magnetic recording medium for hard disks or the like and glass substrates for liquid crystal displays.
A cerium-based abrasive is composed of cerium oxide (CeO
2
) particles as the main ingredient and abrasive particles of another rare-earth metal oxide. It is classified into two general categories, high-cerium and low-cerium, by a proportion of a cerium oxide content to a total rare-earth oxide (hereinafter referred to as TREO) content. The methods of producing these types are not much different. More concretely, the method starts with crushing the stock material followed by chemical treatment (wet treatment) for each type. The chemical treatment methods include fluorination, i.e., incorporation of a fluorine component to secure high grindability for the cerium-based abrasive, and treatment with a mineral acid to remove an alkaline metal, e.g., sodium, for prevention of abnormal growth of the particles during a roasting process. The wet-treated stock material is subjected to filtration, drying, roasting at high temperature to sinter the stock particles with each other, crushing again and classification, to produce an abrasive of desired particle size and particle size distribution.
The stock material for cerium-based abrasives has been frequently concentrated bastnaesite, a naturally occurring mineral substance obtained by beneficiation of the rare-earth ore by the name of bastnaesite. More recently, the abrasives are produced more frequently from carbonate of cerium-group rare-earth (hereinafter sometimes referred to as the carbonate of rare-earth) or oxide of cerium-group rare-earth (hereinafter sometimes referred to as the oxide of rare-earth). The carbonate of rare-earth is a chemically treated bastnaesite ore or chemically treated relatively-cheap China's complex ore, which an increased rare-earth metal content, and the oxide of rare-earth is obtained through roasting the carbonate of rare-earth.
The cerium-based abrasive produced from the carbonate of rare-earth as the stock material may sometimes have insufficient grindability. On the other hand, it is pointed out that the cerium-based abrasive produced from the oxide of rare-earth as the stock material tends to leave behind fine scratches on the ground surface, although excellent in grindability.
SUMMARY OF THE INVENTION
The present invention is developed to solve the above problems. It is an object of the present invention to provide a cerium-based abrasive having sufficient grindability and, at the same time, little leaving behind fine scratches on a ground surface. It is another object of the present invention to provide a stock material for the above abrasive.
The inventors of the present invention have investigated the processes of producing a cerium-based abrasive for each type of the stock material, noting that the abrasive will have different grinding characteristics by stock material, as discussed above. As a result, they have found that carbonate of rare earth as the stock material has a disadvantage that it is not sintered smoothly during roasting process. Insufficient sintering leads to insufficient grain growth, with the result that it is difficult to prepare a stock material of an adequate particle size and hence to secure sufficient grindability of the resultant abrasive.
On the other hand, it is also found that since an oxide of rare earth sinters smoothly during the roasting process, sintering proceeds unevenly when the oxide of rare earth is used as a stock material, with the result that part of the particles grows excessively. In this case, the abrasive from such a stock material, although excellent in grindability, tends to suffer quality dispersion and leave behind fine scratches on the ground surface, e.g., that of glass.
The inventors of the present invention have found, after having extensively studied while noting difference in properties between the carbonate and oxide of rare earth, that there is a relationship between grindability of a cerium-based abrasive and loss on ignition of the stock material, reaching the present invention.
A first aspect of the invention relates to a stock material for cerium-based abrasives, used for producing cerium-based abrasives, characterized in that it simultaneously contains a carbonate and an oxide of cerium-based rare earth and has a loss on ignition of 0.5 to 25% by weight on a dry basis, when heated at 1000° C. for 1 hour.
Loss on ignition (hereinafter also referred to as LOI) is a loss of weight of the sample heated at high temperature. A stock material for cerium-based abrasives (hereinafter referred to as merely stock material) having a higher LOI means that the final product loses more weight from the stock before roasting, to decrease productivity. It is known that LOI of the carbonate of rare earth is high at around 30% and that of the oxide of rare earth is low at around 0.5%. Therefore, LOI can serve as an index which indirectly indicates carbonate/oxide ratio for the present invention. LOI for the present invention is the level determined when the sample is heated at 1000° C. for 1 hour, based on the consideration that temperature of 1000° C. will give the level applicable as the most stable index, because the carbonate of rare earth is experimentally confirmed to have a stable LOI level when heated at 500° C. or higher. The method of determining LOI is specified in JIS-K-0067 (1992, Japanese Standards Association).
The stock material of the present invention for cerium-based abrasives has an LOI of 0.5 to 25% on a dry basis, determined by heating the sample at 1000° C. for 1 hour, preferably 1.0 to 25%, more preferably 1.0 to 20%. The stock material having an LOI in the above range for production of cerium-based abrasives secures a higher roasting productivity than the carbonate of rare earth, and, at the same time, prevents uneven sintering, which may occur when the oxide of rare earth is used, thereby allowing the sintering process to proceed more uniformly. As a result, it gives a better cerium-based abrasive both in grindability and grinding precision. More uniform sintering improves classification efficiency, contributing to improved productivity. The stock material thus produced has a lower LOI than the carbonate of rare earth, making the stock lighter by that, and reducing the stock material cost, including transportation cost.
In particular, the abrasive from a stock material having an LOI of 5.0 to 25%, more preferably 5.0 to 20%, has a higher grinding precision and leaves behind less scratches on the ground surface, e.g., that of glass. These advantages make the abrasive suitable for secondary grinding (abrasion for finishing) ofhighly functional glass, e.g., glass substrates for optical disks and magnetic disks. On the other hand, the abrasive from an abrasive atock having an LOI of 0.5 to 5.0%, more preferably 1.0 to 5.0%, is particularly excellent in grindability, and suitable for purposes that require high-speed grindability, e.g., primary grinding of the above-described highly functional glass.
In accordance with the Preferred Embodiments of the present invention, cerium oxide preferably accounts for 40% by weight or more of TREO, more preferably 50% by weight or more. The abrasive comprising cerium oxide in the above range can realize better grindability.
Next, one of the preferable methods of producing the stock material as the first aspect of the invention for abrasives is described.
A second aspect of the invention relates to a method of producing a stock material comprising, as main ingre
Ito Terunori
Uchino Yoshitsugu
Yamasaki Hidehiko
Marcheschi Michael
Mitsui Mining & Smelting Co. Ltd.
Rothwell Figg Ernst & Manbeck
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