Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Protein – carbohydrate – lignin – plant matter of indeterminate...
Reexamination Certificate
1999-08-31
2001-06-05
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Protein, carbohydrate, lignin, plant matter of indeterminate...
C508S216000, C508S459000, C378S045000
Reexamination Certificate
active
06242392
ABSTRACT:
The invention relates to grinding aids for X-ray fluorescence analysis (XRF).
Sample preparation is very important in XRF. Correct analytical results can be obtained only with careful sample preparation. Metallic samples ought to be finely machined on one side, and possibly ground or polished. Organic and biological samples can be ashed. Oxide samples such as rocks, glasses, slags etc. can be powdered, ground to a uniform fineness and possibly compressed with a grinding aid or binder.
Determination of low concentrations of uranium, thorium and potassium via XRF is described in Chemical Geology 38, page 225, 1983. This entails adding a few drops of polyvinylpyrrolidone/methylcellulose binder to a finely ground, homogenized rock powder, and compressing in the form of tablets and analysing.
EP 0690302 describes a grinding aid composed of polyvinylpyrrolidone and microcrystalline cellulose.
In addition, tablets of Canada balsam and cellulose provided with a sugar coating are commercially available for sample preparation. These tablets are finely ground by the user together with the sample to be investigated, and compressed anew in the form of tablets with which the XRF is then carried out.
All known aids have considerable disadvantages. Tablets of polyvinylpyrrolidone and methylcellulose are not stable to fracture. Air conditioning is necessary for usage of the grinding aids composed of polyvinylpyrrolidone and microcrystalline cellulose because they are hygroscopic. Canada balsam in turn is tacky and therefore can be homogenized with cellulose and processed only with difficulty. In addition, the tablets must be sugar-coated in order to avoid adhesion during storage. This makes an additional production step necessary.
It is therefore an object of the present invention to provide grinding aids for XRF which do not have the disadvantages mentioned and whose production and usage are as simple as possible.
It has been found that grinding aids composed of binders such as cellulose, fillers such as lactose, and lubricants such as stearic acid have ideal properties for sample preparation for XRF. Grinding aids of this composition can be processed easily, are not tacky and are not hygroscopic.
The invention therefore relates to grinding aids which consist of a filler (2 to 50% by weight), of a lubricant (0 to 3% by weight) and of a binder (47 to 98% by weight).
A preferred embodiment comprises grinding aids consisting of lactose, stearic acid and microcrystalline cellulose.
A preferred embodiment comprises grinding aids in the form of powders or tablets.
The invention further relates to the use of a grinding aid according to the invention for sample preparation for X-ray fluorescence analysis.
The compositions according to the invention are ground with the sample in accordance with the usage of known compositions and are compressed to the final tablets which are then measured by XRF. General information on usage is to be found in K. H. Koch, K. D. Ohls, J. Flock, Steel Technology International, pages 293-298, Sterling Publications International, London, 1990 or K. H. Koch, K. D. Ohls, J. Flock, Rationalisierung der Multi-Elementanalytik durch Einsatz der RFA [Rationalization of Multielement Analysis by Use of XRF], Laborpraxis 14, pages 1022-1027, 1990.
In general, the dosage of the composition according to the invention does not differ from the dosage of conventional compositions. Typically, about 2 g of the grinding aid are added to 20 g of a sample.
Grinding aids ought, besides simple production and usage, to meet the following requirements:
Elevated temperatures during the grinding lead to increased adhesion of the mixture of grinding aid and sample in the grinding vessel. Accordingly, the temperature during the grinding should be kept as low as possible by the grinding aids so that the samples can be processed more rapidly in succession, since the grinding vessel does not need so long to cool.
To minimize particle size effects on the analysis, very fine grinding is necessary. The samples should therefore be ground very fine in the shortest possible time (evolution of heat).
After the grinding, it should be possible to remove the mixture of sample and grinding aid from the grinding vessel without residues. Hence grinding aids should prevent adhesion of the mixture of grinding aid and sample to the walls of the grinding vessel (scale formation).
The final tablet must have a certain minimum hardness in order not to be damaged during transfer from the press to the XRF and during the measurement.
The abovementioned requirements are taken into account by the individual components of the composition according to the invention. The compositions according to the invention for XRF preferably consist of a polysaccharide binder, of a sugar or sugar alcohol as filler and of a lubricant.
Binders which can be used for the grinding aid according to the invention are polysaccharides and polysaccharide derivatives, in particular starch (for example maize, rice, potato or wheat starch), modified starches (for example cold-soluble starch, hydroxy-ethylstarch), cellulose (cellulose powder, microcrystalline cellulose) or cellulose derivatives (methylcellulose, carboxymethylcellulose), particularly preferably microcrystalline cellulose.
Fillers used according to the invention are sugars or sugar alcohols, in particular lactose, mannitol, glucose or sucrose, particularly preferably lactose.
Lubricants are, according to the invention, in particular stearic acid, palmitic acid, stearyl, cetyl or myristyl alcohol, glycerol fatty acid esters (for example esters or mixed esters of palmitic or stearic acid with glycerol), polyethylene glycols or paraffin, particularly preferably stearic acid. Calcium hydrogen phosphate or salts of the abovementioned acids cannot be used as lubricants for grinding aids for XRF because they would falsify the result of the XRF.
The percentage composition of the components depends on the exact use, in particular the characteristics of the sample. The grinding aids according to the invention preferably comprise between 0 and 3% by weight of lubricant, particularly preferably between 1 and 2.5% by weight. The lubricant prevents scale formation in the grinding vessel at high speeds of rotation, so that fewer residues remain in the grinding vessel. On the other hand, the addition of lubricants influences the characteristics of the final tablet. The final tablet will be too soft if too much lubricant is added. For this reason, the content of lubricant in the grinding aid according to the invention must be carefully metered. With hard samples, contents of about 2% by weight result in final tablets of good quality. If, on the other hand, the samples are soft, a content of 0.5% by weight or less of lubricant may suffice. The skilled person aware of the differences in characteristics of the sample material is able suitably to vary the content of lubricant in the grinding aid according to the invention. Grinding aids according to the invention which comprise lubricants are also particularly suitable for soft samples when they are added in tablet form.
The filler content of the composition according to the invention is preferably between 2 and 50% by weight, particularly preferably between 5 and 20% by weight. As the content of filler increases it is often no longer possible to ensure tabletability of the final tablet. However, in some cases, it is also possible to use compositions with filler contents above 50% by weight; however, it is then necessary to add more grinding aid than usual to the sample, so that the detection limit of the analysis deteriorates.
The content of binder is adapted according to the two other components. With a preferred filler content of 5 to 20% by weight a content of up to 3% by weight of lubricant, the content of binder is typically 77 to 95% by weight.
Grinding aids composed of microcrystalline cellulose, lactose monohydrate and stearic acid have proved to be particularly preferred for many applications. The lactose content in this case is between 5 and
Hoffmann Frank
Martens Wolfgang
Wachsmann Manfred
Howard Jacqueline V.
Merck Patent Gesellschaft mit
Millen White Zelano & Branigan P.C.
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