Analysis method for fumed silica

Abstract

Provided is a method for analyzing fumed silica, which makes it possible to improve the accuracy of analysis of fumed silica, particularly analysis by a combustion method, to a level that has not been achieved before. [Solution] A sample of fumed silica is compacted using a fumed silica compaction jig that includes, for example, a cylindrical cylinder 1, a base 2 forming the bottom surface of the cylinder, and a cylindrical piston rod 3 that can be fitted into the cavity of the cylinder, preferably to a compacted body with a bulk density of 150 g / L or more, and the obtained compacted body is then subjected to analysis.

Description

[Technical Field]

[0001] The present invention relates to a novel method for analyzing fumed silica, and more particularly to a method for analyzing fumed silica that enables the accuracy of fumed silica analysis, particularly analysis by a combustion method, to be improved to a level of accuracy that was previously unattainable. [Background technology]

[0002] Fumed silica is lightweight, and the amount of sample that can be placed in a measurement cell with limited volume is small, making it difficult to perform high-precision analysis.Furthermore, fumed silica is very prone to scattering, and if placed in an open state in an autosampler, the powder will scatter due to vibration, making it difficult to measure properly.

[0003] Therefore, when analyzing fumed silica, a method has been proposed in which fumed silica is analyzed as a formed body filled in a resin or an inorganic substance (see Non-Patent Document 1), and a method has been proposed in which fumed silica is analyzed as a dispersion liquid dispersed in a solvent such as water or alcohol (see Non-Patent Document 2).

[0004] However, the above method cannot be applied to analysis by combustion, particularly organic elemental analysis, due to the carbon contained in the resin component and the presence of a solvent.

[0005] Furthermore, even if attempts are made to compact fumed silica having a high bulk density using a commercially available tablet press, which is a method commonly used in the analysis of powder collected for analysis, in which the powder is placed in a cylindrical cylinder and a piston is pressed into it, the bulk density is barely increased due to powder leakage, and the current situation is that it is not possible to sufficiently improve analytical accuracy. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Journal of the Mineralogical Society of Japan (March 1976), Vol. 12, Special Issue, pp. 3-7. [Non-patent document 2] Kobelniks (1994) Vol. 3, pages 5-8 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the present invention aims to provide an analytical method that can analyze bulky fumed silica collected as a sample for analysis with high accuracy. [Means for solving the problem]

[0008] The inventors of this invention have conducted extensive research to solve the above problems and have established a compaction technique using a specific jig. As a result, they have succeeded in increasing the bulk density of small amounts of fumed silica collected for analysis by compaction using fumed silica alone, without using a binder or other medium, thereby achieving the aforementioned objective and completing the present invention.

[0009] In other words, the present invention provides a method for analyzing fumed silica, characterized by compacting fumed silica collected as a sample, and then subjecting the resulting compacted body to analysis. The compaction is preferably carried out so that the bulk density of the fumed silica becomes 150 g / L or more.

[0010] In the present invention, the volume of the compact to be subjected to the analysis is generally 0.1 to 1 ml.

[0011] Furthermore, the present invention can be suitably applied when the analysis is performed by a combustion method that is undesirable due to the presence of binders, etc. The analytical method of the present invention is also effective in X-ray fluorescence analysis. The compressed body of the present invention can be obtained by a jig for compacting fumed silica, which is characterized in that it includes a cylindrical cylinder, a base that forms the bottom surface of the cylinder, and a cylindrical piston rod that can be fitted into the hollow portion of the cylinder, and the distance (s) between the inner wall surface of the cylinder and the outer wall surface of the piston rod that face each other when the piston rod is fitted into the cylinder is set to be 0.10 mm or more and 0.20 mm or less at a temperature of 25°C. In the consolidation jig, the material of the cylinder is preferably a material having a larger coefficient of thermal expansion than the piston rod.

[0012] In the analysis of the fumed silica, the fumed silica is preferably compressed using the compression jig. [Effects of the Invention]

[0013] Increasing the bulk density of fumed silica alone has never been considered for small amounts of fumed silica used for analysis, and this is the first time it has been proposed by the present invention. Furthermore, by compacting the fumed silica used for analysis, the amount charged into the measurement cell can be increased, thereby dramatically improving analytical accuracy. Furthermore, fumed silica compacted to the above bulk density remains stable and does not return to its original bulk. For example, even when using an autosampler, the sample fumed silica is not likely to fly off due to vibrations or wind during operation, providing the advantage of excellent operability. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing one embodiment of a consolidation jig of the present invention; FIG. [Figure 2] 1 is a cross-sectional view of one embodiment of a consolidation jig of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The fumed silica targeted by the analytical method of the present invention is a general term for silica obtained by gas-phase synthesis, and a typical example is silica obtained by flame hydrolysis using silane compounds as raw materials. More specifically, this includes silica obtained by supplying silicon tetrachloride together with a gas containing hydrogen and oxygen to a burner and reacting it at a temperature of about 1000°C.

[0016] The fumed silica that is the subject of the analytical method of the present invention also includes fumed silica that has been modified by reacting the silanol groups on the surface of the fumed silica with various silylating agents.

[0017] The fumed silica obtained by the above method is generally 20 to 500 m 2 / g and the primary particle diameter is about 5 to 50 nm.

[0018] In the present invention, the fumed silica to be analyzed may be fumed silica obtained from the above-mentioned production process, or fumed silica as a product that has been subjected to volume reduction treatment and stored in a tank or packaging bag.

[0019] The fumed silica obtained in the manufacturing process has a low bulk density of about 20 g / L, and the fumed silica that has been subjected to the volume reduction treatment and stored also has a bulk density that does not exceed 100 g / L and still has a low bulk density.

[0020] To analyze the fumed silica, an appropriate amount of the fumed silica is taken as a sample.

[0021] The analytical method of the present invention is characterized in that the fumed silica collected as the sample is compacted to form a compact, and then the resulting compact is subjected to analysis.

[0022] The above-mentioned compact is a mass of individual particles that does not have flowability, and has a high bulk density. However, the compact does not need to be self-supporting, and may be one that collapses when handled. A suitable bulk density of the compact is 150 g / L or more, particularly 250 g / L or more. The higher the bulk density of the compact, the better, but the upper limit is about 1000 g / L, preferably about 600 g / L, taking into consideration the durability of the jig, which will be described later.

[0023] Furthermore, when the above-mentioned compacted material is to be used for analysis, it may be used as is, or it may be broken down and filled into a separately prepared analytical container. The amount of compacted material to be used for analysis should be in accordance with the volume of the analytical container, but 0.1 to 1 ml is common.

[0024] In the present invention, analytical methods suitable for the fumed silica compact are those that require a relatively large amount of sample, such as carbon analysis, nitrogen analysis, sulfur analysis, combustion-gas chromatography analysis, combustion-ion chromatography analysis, and other solid-state combustion analysis such as organic element analysis, as well as fluorescent X-ray analysis. In particular, in analyses using the combustion method, the compact of the present invention allows analysis to be performed in a pure fumed silica state without using additives such as binders, thereby preventing the inclusion of inhibitors in the combustion gas and enabling accurate analysis.

[0025] In these analyses, by providing fumed silica as a compact, it is possible to analyze a large amount of fumed silica in a limited sample volume, thereby dramatically improving the analytical accuracy of the above analyses. In addition, when measuring a sample having a low bulk density of about 20 g / L obtained from a manufacturing process, when measuring a sample made of a compacted body compacted to 200 g / L, the analytical accuracy (detection limit) is improved by a factor of 10, by simple calculation.

[0026] In the present invention, it is preferable to use the following specific compaction jig to obtain a compacted fumed silica body. The inventors have conducted extensive research on the structure of conventional tablet presses having a piston rod and a cylinder, and have succeeded in developing a compaction jig having a structure that can effectively compact fumed silica.

[0027] The following description will be given with reference to the accompanying drawings, but the present invention is not limited to the accompanying drawings.

[0028] The present invention relates to a jig for compacting fumed silica, comprising a cylindrical cylinder 1, a base 2 forming the bottom surface of the cylinder, and a cylindrical piston rod 3 that can be fitted into the cavity of the cylinder, characterized in that the distance (s) between the inner wall surface of the cylinder and the outer wall surface of the piston rod, which face each other when the piston rod 3 is fitted into the cylinder 1, is set to be 0.10 mm or more and 0.20 mm or less at a temperature of 25°C.

[0029] The cylindrical cylinder 1 may have any inner cylinder shape, and the cylindrical shape preferably has a perfectly circular cross section. The shape of the piston rod 3 is columnar, and may be determined to match the shape of the inner cylinder of the cylinder.

[0030] The inner diameter of cylinder 1 is not particularly limited, but is generally in the range of 10 to 50 mm based on the volume of the sample usually taken. The outer diameter of piston rod 3 should be determined by considering the distance (s) between the inner wall surface of the cylinder and the outer wall surface of the piston rod when the piston rod 3 is fitted into cylinder 1. The length of cylinder 1 is generally 20 to 80 mm, and the length of piston rod 3 is preferably set to be slightly longer, specifically about 10 to 30 mm, to facilitate removal from cylinder 1 after compaction.

[0031] The distance (s) is calculated by dividing the outer diameter of the piston rod by the inner diameter of the cylinder measured at 25°C, and multiplying this by 1 / 2. If the distance (s) is smaller than 0.10 mm, the piston rod is likely to stick when inserted into the cylinder. If the distance (s) is larger than 0.20 mm, the fumed silica will leak out from between the cylinder and the piston rod, preventing compaction. The distance (s) is more preferably 0.10 to 0.15 mm.

[0032] Furthermore, since the compaction jig of the present invention has an extremely narrow gap (s) compared to tablet presses conventionally used for analysis, it is preferable that the inner diameter of the cylinder 1 and the outer diameter of the piston rod 3 are formed with high precision. Specifically, it is preferable that the error in the inner circumference of the cylinder and the outer circumference of the piston rod be ±0.05 or less, preferably ±0.03 or less, over their entire surfaces.

[0033] It is also preferable that the inner peripheral surface of the cylinder and the outer peripheral surface of the piston rod are as smooth as possible, and that each be finished to an Ra of 0.30 μm or less.

[0034] The materials for each component are not particularly limited, but metals are preferred because they have high strength, excellent dimensional stability, and the ability to prevent organic contamination. In this regard, metals such as stainless steel, copper, brass, and aluminum are preferred in terms of processability. The cylinder 1 and piston rod 3 may be made of the same material. However, to prevent the gap (s) from decreasing due to temperature changes during use and the piston rod 3 from sticking when inserting or extracting the cylinder 1, it is preferable to use a material for the cylinder 1 with a thermal expansion coefficient equal to or higher than that of the piston rod 3. For example, the cylinder 1 may be made of copper, and the piston rod 3 and base 2 may be made of stainless steel (e.g., SUS430). The advantage of using copper as the cylinder material is that it is easier to process than other metals. Therefore, by using copper for a cylinder whose inner surface is relatively difficult to process, the precision of the inner surface processing can be improved.

[0035] In the present invention, densification of fumed silica using a fumed silica densification jig can be carried out by setting a base 2 on a cylinder 1, filling the cylinder with fumed silica collected as a sample, and then inserting and pressing down a piston rod 3, as shown in Figure 2. The piston rod 3 can be pressed down using a known press device, for example, a hydraulic press. The resulting densified body 4 can be removed by pulling out the piston rod 3 and removing the cylinder 1 from the base 2.

[0036] Furthermore, the densification process may be carried out multiple times by adding fumed silica in stages. It is also preferable to carry out the densification process at a temperature of approximately 25°C.

[0037] In the present invention, the compacted body 4 obtained by compaction can be used as is, or broken up and filled into a measuring container for analysis. [Example]

[0038] The present invention will be further illustrated by the following examples, but the invention is not limited thereto.

[0039] In the examples, the bulk density of fumed silica was determined by the following method.

[0040] An empty measuring cylinder was placed on a top-pan balance and tared, then the sample (powder) was placed in the measuring cylinder, which was then removed from the balance. After leaving it to stand for 30 minutes, the scale on the measuring cylinder was read (silica volume: L). Next, the measuring cylinder containing the sample was placed back on the balance and its weight was measured (silica weight: g). From the above measurements, the bulk density was calculated using the following formula:

[0041] Bulk density (g / L) = Silica weight (g) / Silica volume (L) For samples that were compacted, the silica volume (L) was calculated from the dimensions of the compact after compaction, and the weight (g) of the compact was measured. From the measured values, the bulk density was calculated using the following formula.

[0042] Bulk density (g / L) = Silica weight (g) / Silica volume (L)

[0043] Examples 1 and 2; Comparative Examples 1 and 2 A consolidation jig (see Figure 1) was created with the dimensions and materials shown in Table 1 below.

[0044] [Table 1]

[0045] Fumed silica (specific surface area 119 m) was sampled from a silo at a fumed silica manufacturing plant. 2 The material (1 / g, bulk density 50g / L) was filled to about 80% of its height into a cylinder 1 set on the base 2 of the compaction jig, a piston rod 3 was inserted, and the piston rod 3 was pressed down by a 10MPa hydraulic press to compact the material. After that, the piston rod 3 was withdrawn, the cylinder 1 was removed from the base 2, and the compacted body 4 obtained was taken out and its bulk density was measured.

[0046] The compact obtained by the above method was filled into a test vessel (approximately 1 mL) of a carbon analyzer (manufactured by Sumika Chemical Analysis Center, model number SUMIGRAPH NC-TR22), and the carbon concentration of the fumed silica was measured by the combustion method. The analytical lower limit of the carbon concentration in the above measurement is shown in Table 2.

[0047] [Table 2]

[0048] In Comparative Example 1, the piston rod could not be lowered, and sufficient compaction could not be achieved. In Comparative Example 2, which is equivalent to a commercially available tablet press, when the piston rod was lowered to perform compaction, almost all of the fumed silica in the cylinder was blown out through the gap between the piston rod and the cylinder, resulting in sample loss and making measurement impossible. [Explanation of symbols]

[0049] 1 cylinder 2 Piston Rods 3. Pedestal 4. Compacted body

Claims

1. A method for analyzing fumed silica, characterized by compacting fumed silica collected as a sample to form a compacted body, and then subjecting the resulting compacted body to analysis.

2. 2. The method for analyzing fumed silica according to claim 1, wherein the densification is carried out so that the bulk density of the fumed silica becomes 150 g / L or more.

3. 2. The method for analyzing fumed silica according to claim 1, wherein the volume of the compacted body subjected to the analysis is 0.1 to 1 ml.

4. 2. The method for analyzing fumed silica according to claim 1, wherein the analysis is performed by a combustion method.

5. 2. The method for analyzing fumed silica according to claim 1, wherein the analysis is performed by fluorescent X-ray analysis.

6. A jig for consolidating fumed silica, comprising: a cylindrical cylinder; a base constituting the bottom surface of the cylinder; and a cylindrical piston rod that can be fitted into a hollow portion of the cylinder, wherein a distance (s) between an inner wall surface of the cylinder and an outer wall surface of the piston rod that face each other when the piston rod is fitted into the cylinder is set to be 0.10 mm or more and 0.20 mm or less at a temperature of 25°C.

7. 7. The consolidation jig according to claim 6, wherein the material of the cylinder has a thermal expansion coefficient greater than that of the piston rod.

8. 7. The method for analyzing fumed silica according to claim 1, wherein the fumed silica is densified using the densification jig of claim 6.

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