Transparent suspension and its use

Abstract

To provide a method for making small particle-containing suspension transparent that can be applicable to analysis of flow of small particle such as mud or red blood cell-containing suspension.SOLUTION: Provided is a transparent suspension, which is a suspension in which synthetic quartz particles are suspended in liquid, and in which the average particle diameter of the particles is 0.3 to 30 μm and the content ratio of coarse particles of 25 μm or more is 0.6% or less, and the liquid has the same refractive index as the particles.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a transparent suspension and its use.

Background Art

[0002] Even if transparent particles are used, a liquid in which solid particles are suspended has extremely low visibility due to the difference in refractive index between the particles and the liquid. In order to grasp the flow phenomenon inside the suspension, measuring instruments such as a laser Doppler velocimeter (LDV) and an ultrasonic velocity profiler (UVP) are required. Despite these measuring instruments being very expensive, the laser measuring instrument can only grasp a maximum of three velocity components in one point in three directions, and the ultrasonic measuring instrument can only grasp two velocity components in one dimension in two directions.

[0003] In order to grasp the flow field of the internal flow of the suspension, the velocity in two dimensions in two directions or three dimensions in three directions can be measured by using a particle image velocimeter (PIV). In order to utilize such a measurement method by image capture, it is important that the transparency of the suspension is high.

[0004] In recent years, a refractive index matching technique for making a solid transparent by matching the refractive indices of a solid and a liquid has been studied. For example, Patent Document 1 discloses a three-dimensional flow field visualization device for observing the flow of a liquid by circulating a liquid whose refractive index is adjusted to approximate that of a transparent model in an internal passage of the transparent model. In the liquid for refractive index change for the three-dimensional flow field visualization device, the liquid is a mixture of methylphenyl silicone oil and dimethyl silicone oil, or a mixture of methylphenyl silicone oil and ethanol, and the refractive index is adjusted by mixing at a predetermined ratio. In the example section of this document, the case where silicone rubber is used as the transparent model material and an aqueous glycerin solution is used as the first liquid and the second liquid is described.

[0005] Furthermore, the use of fused silica as a solid is being considered. For example, Non-Patent Document 2 reports that when liquid paraffin with refractive indices varied in 0.001 increments from 1.453 to 1.461 is used with fused silica (refractive index: 1.458), the transmittance is high in the refractive index range of 1.457 to 1.459. Non-Patent Document 3 also reports an example using 1-2 mm fused silica particles. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2005-300515 [Non-patent literature]

[0007] [Non-Patent Document 1] Yassin A. Hassan, EE Dominguez-Ontiveros, Flow visualization in a pebble bed reactor experiment using PIV and refractive index matching techniques, Nuclear Engineering and Design (2008) 238:3080-3085. [Non-Patent Document 2] Kazuya Ito, Tokyo City University, Faculty of Engineering Research Annual Report 2017, Basic Research on Visualization Technology for Understanding Phenomena Caused by Interactions between Ground and Structures, https: / / www.eng.tcu.ac.jp / report / archives2017 / report15 [Non-Patent Document 3] Daiki Takano et al., Reproduction experiment of chemical injection process using refractive index matching visualization technology for granular materials, 50th Proceedings of the Japanese Geotechnical Society (2015), E-14. [Non-Patent Document 4] Se´bastien Wiederseiner, Nicolas Andreini, Gael Epely-Chauvin, Christophe Ancey, Refractive-index and density matching in concentrated particle suspensions: a review, Exp Fluids (2011) 50:1183-1206 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In previous research, when considering PIV (Particle Infiltration Ventilation), it is believed that the practical limit for the number of interface surfaces between particles and liquid is approximately 350 in the depth direction (Non-Patent Literature 4).

[0009] Furthermore, for applications in the analysis of mud and red blood cell flow, a suspension of small particles on the scale of several tens of micrometers is required, but no such suspension exists that is sufficiently transparent. [Means for solving the problem]

[0010] The present invention provides the following: [1] A suspension of synthetic quartz particles in a liquid, The average particle size is 0.3 to 30 μm, and the proportion of coarse particles 25 μm or larger is 0.6% or less. The liquid has the same refractive index as the particles. A transparent suspension. [2] The suspension according to 1, wherein the average particle size of the particles is 0.3 to 10 μm, and the proportion of coarse particles of 20 μm or larger is 0.1% or less. [3] The suspension according to 1 or 2, wherein the particle concentration is 1 to 60%. [4] A suspension according to any one of items 1 to 3, wherein the liquid comprises liquid paraffin. [5] A method for producing a clear suspension, comprising the following steps: A step of suspending particles made of synthetic quartz, having an average particle diameter of 0.3 to 30 μm and a content ratio of coarse particles of 25 μm or more of 0.6% or less, in a liquid having the same refractive index as the particles by a rotating and revolving stirrer under vacuum or reduced pressure. [6] A method for clarifying a suspension of micro-order sized particles, characterized by using particles made of synthetic quartz, having an average particle diameter of 0.3 to 30 μm and a content ratio of coarse particles of 25 μm or more of 0.6% or less, and suspending them in a liquid having the same refractive index as the particles by a rotating and revolving stirrer under vacuum or reduced pressure.

Advantages of the Invention

[0011] According to the present invention, the suspension can be clarified at a high level.

[0012] According to the present invention, even when using a visualization model with a complex shape or when installing a model in a suspension, the internal flow can be visualized without distortion.

[0013] By using the suspension of the present invention, it is possible to realize the visualization of the internal flow of the suspension and the flow phenomenon around the model, which have been impossible in the past.

Brief Description of the Drawings

[0014] [Figure 1] The state of the suspension of synthetic quartz. Synthetic quartz particles with an average particle diameter of 3 μm were suspended in a liquid with a matching refractive index at each concentration to prepare a suspension. Each of the prepared suspensions was placed in an acrylic container with a depth of 40 mm, and photographed under a white light source with graph paper as the background. The grid interval of the graph paper is 5 mm. In order from the left, the volume concentrations of the suspensions are 50%, 35%, 20%, and 5%. [Figure 2] The state of refractive index matching between the beaker and the suspension [Figure 3] Microscopic photograph of natural quartz particles used for comparison [Figure 4] The state of a suspension (volume concentration 5%) of natural quartz particles with an average particle diameter of 13 μm [Figure 5]The state of a suspension of synthetic quartz particles with a volume concentration of 50% that has only been subjected to manual stirring

Mode for Carrying Out the Invention

[0015] The present invention relates to a transparent suspension in which synthetic quartz particles are suspended in a liquid.

[0016] [Synthetic quartz particles] In the suspension of the present invention, particles made of synthetic quartz are used. The quartz particles used for soil preparation are fused quartz made from natural quartz, but in the present invention, particles made of highly homogeneous synthetic quartz that is manufactured from silicon tetrachloride or the like and contains no impurities or bubbles at an extremely high level are used, so that the suspension can be made transparent at a high level even at a high concentration.

[0017] The synthetic quartz particles used in the suspension of the present invention are preferably those of low α and high purity produced by a gas-phase reaction using silicon tetrachloride as a raw material.

[0018] The average particle diameter of the synthetic quartz particles used in the suspension of the present invention is  0.3 to 30 μm, preferably 0.3 to 10 μm, more preferably 0.3 to 3.5 μm, and even more preferably 1 to 3 μm. Regarding the present invention, when indicating the average particle diameter of the particles, unless otherwise specified, the value is the average diameter measured and calculated on a volume basis by a standard measurement method and standard in the art, for example, by the laser diffraction / scattering method.

[0019] In the suspension of the present invention, it is preferable to use particles of a grade in which larger particle sizes have been cut. Such grades are commercially available for use as underfill materials, etc., and are referred to as fine-cut grades. If larger particle sizes (coarse particles) are included, the amount of air bubbles in the suspension increases, and even if the refractive index of the particles and the liquid are matched, the suspension becomes cloudy due to the air bubbles, making it difficult to achieve a high level of transparency. The inventors have found that when using synthetic quartz particles of a normal grade for solid sealants, liquid sealants, etc., which contain large particle sizes and coarse particles, it is difficult to achieve a high level of transparency in high-concentration suspensions.

[0020] Specifically, the synthetic quartz used in the suspension of the present invention should, in any case, have an average particle diameter of 0.6% or less, preferably 0.1% or less, and more preferably 0.01% or less, in which case the content of particles with a particle diameter of 25 μm or more is 0.6% or less.

[0021] Preferably, the synthetic quartz used in the suspension of the present invention has an average particle size of 20 μm or larger, and in all cases, the proportion of coarse particles of 20 μm or larger is 0.1% or less, preferably 0.01% or less, and more preferably 0.00%.

[0022] More preferably, the synthetic quartz used in the suspension of the present invention should have an average particle size of 0.2% or less, preferably 0.02% or less, and more preferably 0.01%, in all cases, that contains coarse particles of 10 μm or larger.

[0023] More preferably, the synthetic quartz used in the suspension of the present invention has an average particle size of 5 μm or larger, and in all cases, the proportion of coarse particles of 5 μm or larger is 10% or less, preferably 1% or less, and more preferably 0.05% or less.

[0024] In relation to the present invention, when indicating the proportion of coarse particles in the suspension, the values ​​are given as those measured using a wet sieve, unless otherwise specified.

[0025] In a preferred embodiment, the synthetic quartz used in the suspension of the present invention has an average particle size of 1 to 10 μm and contains 0.6% or less of coarse particles of 25 μm or larger. Examples of commercially available synthetic quartz of this type include EXCELLICA® Fine Cut Grade, UF-305, UF-310, UF-320, UF-345, and UF-725 (Tokuyama Corporation).

[0026] In a particularly preferred embodiment, the synthetic quartz used in the suspension of the present invention has an average particle size of 1 to 5 μm and contains 0.2% or less of coarse particles of 10 μm or larger. Examples of such synthetic quartz include EXCELLICA® Fine Cut Grade, UF-305, UF-310, and UF-320.

[0027] In the suspension of the present invention, it is preferable to use synthetic quartz with an internal transmittance of 90.0% or more, preferably 92.0% or more, more preferably 94.0% or more, and even more preferably 95.0% or more, in the range of 260 nm to 700 nm.

[0028] The refractive index of the synthetic quartz used in the present invention is not particularly limited, but it is preferably in the range of 1.43303 to 1.52120 when measured under the measurement conditions based on the Japanese Industrial Standard JIS B 7071-1:2015, Method for Measuring the Refractive Index of Optical Glass.

[0029] [Liquid (Suspension Medium)] In the suspension of the present invention, a liquid having the same refractive index as the suspended particles is used as the suspension medium. By using a transparent liquid with a refractive index corresponding to the suspended synthetic quartz particles as the suspension medium, a highly concentrated suspension can be made transparent to a high degree.

[0030] The liquid used in the suspension of the present invention is not limited as long as it is transparent and has the same refractive index as the particles used. For example, examples of liquids that can be used include liquid paraffin, silicone oil (e.g., 200 Fluid (Dow Corning), 550 Fluid (Dow Corning), 556 Fluid (Dow Corning), 710 Fluid (Dow Corning)), matching fluid for Calzil RI, d-limonene, methylsalicylic acid, diethyl phthalate, p-cymene, isopropyl alcohol, water, glycerin, zinc iodide solution, sodium iodide aqueous solution, potassium thiocyanate solution, ammonium thiocyanate solution, sodium thiocyanate solution, kerosene, silicone oil mixture, mineral oil, turpentine, solvent naphtha, soybean oil, olive oil, castor oil, tung oil, cassia oil, dibutyl phthalate, tetralin, benzyl alcohol, ethyl alcohol, methylnaphthalene, chloronaphthalene, and mixtures of any of these. One preferred example is liquid paraffin. Liquid paraffin is well known to those skilled in the art and is available for use as a raw material for cosmetics and toiletries, as a resin additive for polystyrene foam and food containers, in the production of lithium-ion battery membranes, pharmaceuticals, and reagents for genetic analysis.

[0031] It is preferable to use high-purity liquid paraffin in the suspension of the present invention. High purity means that the content of polycyclic aromatic hydrocarbons, sulfur compounds, sulfuric acid admixtures, lead, arsenic, free acids, and free alkalis is low. As the liquid paraffin used in the suspension of the present invention, it is possible to use one that has passed or conforms to at least one of the purity tests specified in the Food Additives Standards, the Japanese Pharmacopoeia, and the Quasi-Drug Raw Material Standards.

[0032] In a preferred embodiment, the liquid paraffin used is one that passes the purity tests consisting of (1) to (6) below. (1) Free acids and free alkalis: Measure 10 mL of this product and add approximately 10 mL of hot water and phenolphthalein reagent. When one drop of the solution is added and shaken vigorously, the solution does not turn red. However, when 0.20 mL of 0.02 mol / L sodium hydroxide solution is added to this solution and shaken, the solution turns red. (2) Lead: Less than 1 μg / g as Pb (3) Arsenic: As 3 μg / g or less (4) Sulfur compounds: Weigh out 4.0 mL of this product, add 2 mL of ethanol (99.5%), add 2 drops of a clear solution saturated with lead(II) oxide in a sodium hydroxide solution (1→5), shake frequently, and after heating at 70°C for 10 minutes and then allowing to cool, the solution should not turn dark brown. (5) Polycyclic aromatic hydrocarbons: Take 25 mL of this product into a 25 mL graduated cylinder and transfer it to a 100 mL separatory funnel. Next, take 25 mL of hexane for UV absorption spectroscopy into the same graduated cylinder and transfer it to the separatory funnel, and shake well. Add 5 mL of dimethyl sulfoxide for UV absorption spectroscopy, shake vigorously for 2 minutes, and then let stand for 15 minutes. Transfer the lower layer to a 50 mL separatory funnel, add 2 mL of hexane for UV absorption spectroscopy, shake vigorously for 2 minutes, and then let stand for 2 minutes. Transfer the lower layer to a 10 mL stoppered centrifuge tube and centrifuge at 2500-3000 rpm for about 10 minutes, and place the supernatant into a tightly stoppered cell to use as the test solution. Separately, when 25 mL of hexane for ultraviolet absorption spectroscopy is mixed with 5 mL of dimethyl sulfoxide for ultraviolet absorption spectroscopy, and the solution is prepared in the same manner as the preparation of the test solution, the absorbance at wavelengths of 260-350 nm is immediately measured using the solution as a control, and the value does not exceed 0.10. (6) Sulfuric acid coloring solution: Measure 5 mL of this product, place it in a Nessler tube, add 5 mL of sulfuric acid for sulfuric acid coloring solutions (94.5-94.9%), heat in a water bath for 2 minutes, and then immediately shake vigorously up and down for 5 seconds. Repeat this procedure four more times, and the color of the liquid paraffin layer will not change. The color of the sulfuric acid layer will not be darker than the color of the solution obtained by mixing 3.0 mL of iron(III) chloride colorimetric standard stock solution, 1.5 mL of cobalt(II) chloride colorimetric standard stock solution, and 0.5 mL of copper(II) sulfate colorimetric standard stock solution in a Nessler tube.

[0033] The liquid paraffin used in the suspension of the present invention may have a refractive index of 1.453 to 1.461.

[0034] In relation to the present invention, when the refractive index of a liquid is said to be the same as that of the particles, unless otherwise specified, it means that the refractive index of the liquid is ±0.010, preferably ±0.005, more preferably ±0.002, and even more preferably ±0.001 of that of the particles.

[0035] [concentration] The particle concentration in the suspension can be set as appropriate, but for example, it can be 1% or more, preferably 5% or more, more preferably 20% or more, and even more preferably 30% or more. The upper limit of the particle concentration can also be set as appropriate, but for example, it can be 60% or less, preferably 59% or less, more preferably 57% or less, and even more preferably 55% or less. In relation to the present invention, when indicating the concentration of the suspension, the value (%) is a value calculated based on the mass of the particles and the mass of the suspension, unless otherwise specified.

[0036] [Manufacturing method] The present invention also provides a method for producing a clear suspension, comprising the following steps: A process of suspending particles made of synthetic quartz, having an average particle diameter of 0.3 to 30 μm and containing 0.6% or less of coarse particles of 25 μm or larger, in a liquid having the same refractive index as the particles, using a rotating / revolving agitator under vacuum or reduced pressure.

[0037] When a high-concentration suspension is prepared using small-particle sizes on the order of mm or less, a large number of microbubbles inevitably end up in the suspension. In such cases, even if the mixture is stirred for a long time under atmospheric pressure, the bubbles cannot be effectively removed. Furthermore, according to our research, even when using an ultrasonic cleaner, which is a type of degassing method, it was not possible to effectively degass the bubbles trapped between the particles in the high-concentration suspension.

[0038] In this invention, a rotating and revolving agitator is used under vacuum or reduced pressure. By simultaneously rotating and revolving under vacuum or reduced pressure conditions, fluid is generated, and bubbles are released at the gas-liquid interface. This allows even highly concentrated suspensions to have permeability.

[0039] In this invention, conventional rotating and revolving agitators can be used. An example is the EME rotating and revolving vacuum agitator and defoamer.

[0040] In this invention, the rotational speed during stirring by the rotating / revolving agitator can be appropriately set by those skilled in the art. For example, it can be set to 400 rpm to 2000 rpm. If the rotational speed is too slow, there is a concern that aggregated particles may form. On the other hand, if the rotational speed is too fast, there is a concern that particles will wear down due to collisions with each other.

[0041] Furthermore, in this invention, the ratio of the rotation speed to the revolution speed during stirring by a rotation-revolution agitator can be appropriately set by those skilled in the art. It is sufficient as long as the suspension is stirred and the particles do not wear each other out. The rotation speed can be, for example, 0.4 to 0.6 times the revolution speed. If the rotation speed is too slow, it is possible that aggregated particles will exist because vertical convection will not occur. On the other hand, if the rotation speed is too fast, the speed of the swirling flow and vertical convection will increase, raising concerns that particles will wear out due to collisions with each other.

[0042] In this invention, the angle θ of the rotation axis with respect to the revolution axis during stirring by the rotation-revolution agitator can be appropriately set by a person skilled in the art. For example, it can be set to 30° to 60°. If the inclination angle θ of the rotation axis is small, particles tend to settle at the bottom of the container, and if the inclination angle θ is large, it becomes impossible to maintain a sufficient amount of suspension in the container.

[0043] In this invention, stirring by a rotating / revolving agitator is preferably performed under reduced pressure, and more preferably in a vacuum atmosphere. This is because air bubbles mixed into the suspension can be effectively removed. When using a vacuum atmosphere, from the viewpoint of effectively removing air bubbles, the maximum achievable vacuum can be set to, for example, 1.0 kPa or less, and more preferably to 0.67 kPa or less.

[0044] When stirring with a rotating / revolving agitator, there is a concern that the temperature of the suspension may rise due to friction between particles. This is especially noticeable when the suspension is highly concentrated. To suppress the temperature rise, the rotation speed and pressure should be adjusted.

[0045] In this invention, the stirring time using the rotating / revolving agitator can be 1 to 30 minutes, preferably 5 to 15 minutes, including the time for switching from an atmospheric environment to a vacuum environment during the process. If the stirring time is too short, there is a possibility that bubbles will not be sufficiently removed. On the other hand, if the stirring time is too long, there is a concern that particles will wear down due to collisions with each other.

[0046] The stirring by the rotating / revolving agitator described above is useful as a method for clarifying suspensions of micro-sized particles. Therefore, the present invention also provides a method for clarifying suspensions of micro-sized particles, characterized by using particles made of synthetic quartz having an average particle diameter of 0.3 to 30 μm and a content of coarse particles of 25 μm or more of 0.6% or less, and suspending them in a liquid having the same refractive index as the particles using a rotating / revolving agitator under vacuum or reduced pressure.

[0047] [Characteristics of the suspension] The suspension of the present invention is transparent. A suspension is transparent if what is on the other side of it can be seen through it. For example, if the suspension in question is placed in a transparent container with a depth of 40 mm and photographed under a white light source with 5 mm grid paper as the background, and the grid can be seen, then the suspension can be said to be transparent. A suspension in which small particles made of synthetic quartz are suspended in a liquid having the same refractive index as the particles can be achieved by thoroughly removing air bubbles from the suspension by stirring it with a rotating / revolving agitator under vacuum or reduced pressure when suspending the particles.

[0048] According to the inventors' research, a 5% suspension contains approximately 700 particles in the depth direction, and a 50% suspension contains approximately 7,000 particles in the depth direction, allowing for transparency to be maintained far beyond previous studies (see Non-Patent Literature 4). As a result, it becomes possible to visualize the inside of high-concentration suspensions, which was previously impossible.

[0049] [Use of suspensions] The transparent suspension obtained by the present invention can be used in various fields related to fluids. Many fluids contain particles. Typical examples of fluids containing particles include geophysical fluids such as avalanches, debris flows, mudslides, and pyroclastic flows; industrial fluids such as excavation mud and concrete; cosmetics, pharmaceuticals, and food products; blood, animal cell culture media, microbial culture media, and fermentation liquids (sake, wine, beer, soy sauce, etc.). The present invention can be used to understand the behavior of such suspensions.

[0050] This invention, when used in combination with conventional image processing techniques, allows for the visualization of the internal state of a suspension flow. The highly transparent suspension of this invention can be applied to conventional optical techniques such as particle image velocimetry (PIV), particle tracking velocimetry (PTV), laser Doppler velocimetry (LDV), and laser-induced fluorescence (LIF). Such combinations can be implemented at an affordable cost, are versatile, and offer high accuracy.

[0051] While combining model suspensions with optical techniques may be feasible with conventional suspensions when the number of fluid-solid and solid-fluid interfaces to be analyzed is small, it becomes difficult with conventional suspensions when the number of interfaces increases significantly. For example, attempting to visualize a 10cm thick sample composed of 1mm particles requires passing through at least 200 interfaces. Even slight mismatches in refractive index at each interface can accumulate, causing image distortion and affecting flow rate measurements. However, by using the suspension provided by this invention, which exhibits high transparency even at high concentrations, analysis of depths that were difficult to analyze with conventional techniques can be achieved. [Examples]

[0052] [Preparation of a suspension of synthetic quartz particles 1] Synthetic quartz particles were mixed with a liquid of the same refractive index (liquid paraffin, Moresco White P-55) using a V-mini 300 self-rotating vacuum stirring and defoaming mixer (EME self-rotating stirring and defoaming device, manufactured by EME) to prepare suspensions with concentrations (quartz particle mass (g) / solution mass (g)) of 50%, 35%, 20%, and 5%. The refractive index was confirmed using a refractometer (PAL-RI, Cat. No. 3850, Atago Co., Ltd.). Each of the prepared suspensions was placed in an acrylic container with a depth of 40 mm and photographed under a white light source with a 5 mm grid paper background.

[0053] Synthetic quartz particles used in the experiment Product Name: EXCELLICA (Registered Trademark) UF-310, Tokuyama Corporation Raw materials and manufacturing method: Low-alpha, high-purity synthetic spherical silica produced by gas-phase reaction using silicon tetrachloride as the raw material. Average particle size: 3.0μm Particle size distribution (wet sieve): 45μm or more 0.00%, 25μm or more 0.00%, 20μm or more 0.00%, 10μm or more 0.10% Impurities: Fe 6.0 ppm, Al 0.5 ppm, U 0.1 ppb or less, Na + 1ppm or less, Cl - 1ppm or less

[0054] Figure 1 shows photographs of each suspension obtained by transmitted light imaging using a white light source. Even at a volume concentration of 50%, the white light was transmitted, and the grid could be observed without distortion. At this time, there are approximately 14,000 interface surfaces between the particles and the liquid in the depth direction, and we were able to confirm visibility performance far exceeding that of previous studies.

[0055] [Table 1]

[0056] With a close-packing concentration of approximately 60% for soil and a hemacrit level of approximately 50% for blood flow, it covers a wide range of applications for various high-concentration suspensions.

[0057] To confirm whether the suspension has sufficient permeability even when using a curved container for visualization or when a model is placed within the visualization area, a 5% volume concentration suspension was placed in a synthetic quartz beaker. Furthermore, the beaker was placed in a liquid with a refractive index matching that of the synthetic quartz, and the resulting image is shown in Figure 2. When the area above the liquid surface is viewed through the beaker, the grid and numbers are distorted. On the other hand, in the area below the liquid surface, the refractive index of the liquid / suspension inside and outside the beaker matches that of the beaker, and the grid can be seen without distortion. From the above, it can be seen that this technology is fully applicable even when using a curved container for visualization or when a model is placed within the visualization area.

[0058] [Preparation of a suspension of natural quartz particles] To demonstrate the importance of high-quality quartz particles, a suspension of particles made from natural quartz was prepared and observed using transmitted light imaging. As with synthetic quartz, the refractive indices of the particles and the liquid were matched.

[0059] Natural quartz particles used in the experiment: K13 (Manufacturer: Carlo Bernasconi AG) Average particle size: 13 μm (wet-type laser diffraction particle measurement, measuring device: Malvern Mastersizer) Microscopic images of the natural quartz particles used are shown in Figure 3.

[0060] Figure 4 shows photographs of each suspension obtained by transmitted light photography. Although the impurity content of the natural quartz particles is less than 2%, the suspension is completely cloudy, and not only is the lattice invisible, but almost no light is transmitted. This is due to variations in particle quality, and it is necessary to maintain a uniform refractive index by reducing impurities in the particles as much as possible.

[0061] [Preparation of a suspension of synthetic quartz particles 2] A suspension with a volume concentration of 50% was prepared in the same manner as in Preparation 1 above, except that manual stirring was not performed. This suspension was scooped out with a spoon and transmitted light imaging was performed.

[0062] Figure 5 shows the state of the obtained suspension. Because the quartz particles were extremely fine, a large number of microbubbles were introduced into the suspension during manual stirring, causing it to become cloudy. Furthermore, these microbubbles could not be removed by further manual stirring or conventional methods such as ultrasound.

[0063] Based on the above, it is possible to achieve higher levels of transparency even in high-concentration suspensions by (1) making the particle size as uniform as possible, (2) minimizing the inclusion of impurities in the particles, and (3) completely removing air bubbles. [Industrial applicability]

[0064] This invention is expected to be used in a variety of fields, including fluid dynamics, civil engineering, materials science, medicine, cosmetics, and food.

[0065] By using the suspension prepared with this technology and applying existing optical measurement techniques, it becomes possible to visualize the internal flow of the suspension and the flow phenomena around the model, which were previously considered impossible.

Claims

1. A suspension in which synthetic quartz particles are suspended in a liquid, The average particle size is 0.3 to 30 μm, and the proportion of coarse particles 25 μm or larger is 0.6% or less. The liquid has the same refractive index as the particles. A transparent suspension that does not contain enough air bubbles to cause cloudiness.

2. The suspension according to claim 1, wherein the average particle diameter of the particles is 0.3 to 10 μm, and the content of coarse particles of 20 μm or more is 0.1% or less.

3. The suspension according to claim 1 or 2, wherein the particle concentration is 1 to 60%.

4. The suspension according to any one of claims 1 to 3, wherein the liquid comprises liquid paraffin.

5. A method for producing a clear suspension, including the following steps: A process of suspending particles made of synthetic quartz, having an average particle diameter of 0.3 to 30 μm and containing 0.6% or less of coarse particles of 25 μm or larger, in a liquid having the same refractive index as the particles, using a rotating / revolving agitator under vacuum or reduced pressure.

6. A method for clarifying a suspension of micro-order-sized particles, characterized by using particles made of synthetic quartz having an average particle diameter of 0.3 to 30 μm and containing 0.6% or less of coarse particles of 25 μm or more, and suspending the particles in a liquid having the same refractive index as the particles using a rotating / revolving agitator under vacuum or reduced pressure.

Images