Method for measuring chlorine content of fine powder-containing powder

Abstract

To provide a method for measuring the chlorine content of fine powder-containing powder capable of easily and accurately measuring the amount of chloride in the fine powder-containing powder by using a chlorine amount measuring meter utilizing a capillary phenomenon.SOLUTION: A method for measuring a chlorine content of a fine powder-containing powder, comprising the steps of: adding a water-reducing agent to a mixed liquid comprising a fine powder-containing powder and water and stirring the mixture, or adding a fine powder-containing powder to water containing a water-reducing agent in advance and then stirring the mixture to obtain a suspension; measuring a chlorine content of a liquid phase of the suspension using a chlorine content meter utilizing a capillary phenomenon; and calculating a chlorine content of the fine powder-containing powder from the obtained chlorine content of the liquid phase of the suspension.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the chlorine content of fine powder-containing powder, which can easily measure the chlorine content of powder containing fine powder, such as a cement mixture.

[0002] In this application, "fine powder" refers to powder with a particle size of 1 μm or less, and "fine powder-containing powder" refers to powder that contains such a quantity of fine powder that agglomerations of the fine powder clog the capillary portion of the measuring meter.

[0003] In this application, "cement admixture" refers to materials contained in cement other than cement clinker and gypsum, such as ground granulated blast furnace slag, fly ash, silica fume, ground limestone, coal ash, and silica powder, which are added during the finishing and mixing processes in cement production. Furthermore, this "cement admixture" also encompasses "admixtures" such as ground granulated blast furnace slag, fly ash, silica fume, ground limestone, coal ash, and silica powder, which are the same materials as the cement admixtures used as needed during concrete production. [Background technology]

[0004] One of the measures to reduce carbon dioxide emissions in the cement industry is to expand the use of blended cement, which replaces part of the cement clinker, which emits carbon dioxide during its production, with cement admixtures, thereby reducing carbon dioxide emissions.

[0005] One of the challenges in expanding the use of blended cement is the issue of quality control of cement admixtures. Because blended cement is a mixture of Portland cement and cement admixtures, the quality of the cement admixtures directly affects the quality of the blended cement. In other words, the quality of the cement admixtures must be controlled to a degree that does not cause quality problems when used in blended cement. However, because many cement admixtures are by-products, sufficient quality control is sometimes not possible.

[0006] For example, silica fume is a spherical particle with a particle size of about 0.1 μm that is generated during the refining process of ferrosilicon, metallic silicon, and zirconia in an electric furnace. However, since trichlorosilane (SiHCl3) is generally used in the refining process of polycrystalline silicon, the by-product silica fume is prone to contain chlorine, an undesirable component in cement-based materials.

[0007] Against this background, JIS A 6207 "Silica fume for concrete" stipulates an upper limit of 0.10% for the chlorine content of silica fume used as an admixture.

[0008] The chlorine content of cement admixtures such as silica fume is generally measured using briquettes in accordance with JIS R 5202 "Methods for chemical analysis of cement" or JIS R 5204 "Methods for X-ray fluorescence analysis of cement" Annex JE "Method for determining chlorine in cement by X-ray fluorescence analysis."

[0009] However, when using the instrumental analysis method JIS R 5204 "X-ray fluorescence analysis method for cement" for quality control of various cement mixtures, it is necessary to install X-ray fluorescence analyzers (XRF) and sample pretreatment equipment at ready-mix concrete plants that handle admixtures and local cement mixing bases that handle cement mixtures. Furthermore, there are many challenges involved in implementing this method, as analysts are required to have relevant knowledge and be familiar with how to operate it.

[0010] The Cantab (manufactured by Pacific Materials Corporation) is known as a simple method for measuring the amount of chlorine contained in fresh concrete. The Cantab is a simple meter for measuring the amount of chlorine in a liquid phase, utilizing capillary action (dry chemistry) based on the Mohr method, in which silver nitrate reacts with chloride ions to produce silver chloride. Its application is not limited to mixing water for fresh concrete; for example, Patent Document 1 describes the measurement of the amount of chlorine in soil, and Patent Document 2 describes the measurement of solute concentration in a suspension containing chlorine.

[0011] However, the present inventors have found that when a Cantab is used to measure the amount of chlorine in a silica fume suspension in order to measure the chlorine content of the silica fume, the capillary portion of the Cantab may become clogged, making it impossible to perform the measurement. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-167567 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-71015 Summary of the Invention [Problem to be solved by the invention]

[0013] The object of the present invention is to provide a method for easily and accurately measuring the chlorine content of fine powders such as cement admixtures using a chlorine content meter utilizing capillary action, such as a Cantab. [Means for solving the problem]

[0014] As a result of intensive research into the above-mentioned problems, the inventors have found that adding a water-reducing agent to a suspension of powder containing fine powders makes it possible to measure the chlorine content of a suspension of powder containing fine powders accurately and in a short time without clogging the capillary part of the chlorine content meter, and have completed the inventions [1] to [5] below.

[0015] [1] A step of adding a water-reducing agent to a mixture of fine powder-containing powder and water and stirring the mixture, or adding fine powder-containing powder to water that has already contained a water-reducing agent and then stirring the mixture to obtain a suspension; Next, a step of measuring the amount of chlorine in the liquid phase of the suspension using a chlorine amount measuring meter that utilizes capillary action on the suspension or the supernatant of the suspension; Finally, the method for measuring the chlorine content of the fine-powder-containing powder comprises a step of calculating the chlorine content of the fine-powder-containing powder from the amount of chlorine in the liquid phase of the obtained suspension. [2] The method for measuring the chlorine content of a fine-powder-containing powder according to [1] above, wherein the water-reducing agent is one or more selected from the group consisting of polycarboxylic acids, lignin sulfonic acid, naphthalene sulfonic acid formaldehyde condensates, melamine sulfonic acid formaldehyde condensates, and salts thereof. [3] A method for measuring the chlorine content of a fine-powder-containing powder according to [1] or [2] above, wherein the mass ratio c / p of the water-reducing agent (c) to the fine-powder-containing powder (p) is 0.005 to 0.08, and the mass ratio ((w+c) / p) of the water (w), water-reducing agent (c) and fine-powder-containing powder (p) in the suspension is 1 to 7 (however, the mass of the water-reducing agent (c) is the mass of the product). [4] The method for measuring the chlorine content of a fine-powder-containing powder according to [1] above, wherein the stirring time of the suspension is 45 to 240 seconds. [5] The method for measuring the chlorine content of a fine-powder-containing powder according to [1] above, wherein the fine-powder-containing powder is silica fume, ground granulated blast furnace slag, fly ash, ground limestone, coal ash, or silica powder. [Effects of the Invention]

[0016] The present invention makes it possible to use a chlorine content measuring meter that utilizes capillary action, which could not be used for powders containing fine particles in the past, and therefore makes it possible to easily determine the chlorine content of powders in which most of the chlorides contained are water-soluble. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram showing an example of a chlorine amount measuring meter that utilizes capillary action. DETAILED DESCRIPTION OF THE INVENTION

[0018] The method for measuring the chlorine content of the fine-powder-containing powder of the present invention will be described in detail below.

[0019] The fine-powder-containing powders for which the chlorine content is measured using the present invention are those in which the aggregates of fine particles with a particle size of 1 μm or less clog the capillary tube of the measuring meter. Examples of such powders include silica fume, ground granulated blast furnace slag, fly ash, ground limestone, coal ash, and some cement admixtures such as silica powder.

[0020] An example of a chlorine content meter that utilizes capillary action and is used in the present invention is the Cantab (manufactured by Pacific Materials Corporation). A schematic diagram of the Cantab is shown in Figure 1. The Cantab is a thin rectangular plastic piece with a long, thin T-shaped capillary tube inside, and is graduated from 0 to 10 in 0.2 increments. Silver dichromate is added to the vertical part of the capillary tube, and a humidity indicator is added to the horizontal part of the capillary tube.

[0021] When the Cantab is placed in a solution containing dissolved chloride, the solution rises up the vertical part of the capillary tube due to capillary action. The chloride ions dissolved in the solution react with the silver dichromate in the vertical part of the capillary tube to produce pale yellow silver chloride. When the solution reaches the top of the vertical part of the capillary tube, the humidity indicator in the horizontal part of the capillary tube turns blue, indicating the end of the measurement. The measurer can read the scale at the tip of the pale yellow colored area in the vertical part of the capillary tube and use the conversion table attached to the Cantab to determine the amount of chlorine in the liquid phase being measured.

[0022] The water used in the present invention may be tap water or the like without any restrictions, but from the viewpoint of the accuracy of chlorine measurement, it is preferable that the water is as chlorine-free as possible, and specifically, it is preferable to use distilled water, ion-exchanged water, or pure water.

[0023] When using water containing chlorine, such as tap water, the value obtained by subtracting the amount of chlorine in the water from the amount of chlorine measured by the chlorine meter can be used as the amount of chlorine in the liquid phase to be measured.

[0024] The water-reducing admixture used in the present invention is a chemical admixture specified in JIS A 6204 "Chemical admixtures for concrete" and is not particularly limited as long as it can prevent blockage of the capillary portion of a chlorine content meter that utilizes capillary action, and examples thereof include one or more selected from polycarboxylic acids, lignin sulfonic acid, naphthalene sulfonic acid formaldehyde condensates, melamine sulfonic acid formaldehyde condensates, and salts thereof.

[0025] Among these water-reducing agents, polycarboxylic acids or their salts are preferred, such as homopolymers, copolymers, or salts thereof containing one or more monomers selected from unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and maleic anhydride.

[0026] The other monomers constituting the copolymer include one or more selected from polyalkylene glycol acrylates, polyalkylene glycol methacrylates, polyalkylene glycol vinyl ethers, and the like.

[0027] The water-reducing admixture may be added to water and then mixed with the fine-powder-containing powder, or may be added directly to the suspension of water and the fine-powder-containing powder.

[0028] It is believed that the addition rate of the water-reducing agent can prevent blockage of the capillary portion of the chlorine content meter in most cases if it is near the standard addition rate of the water-reducing agent as a product, but the mass ratio c / p of the fine powder-containing powder (p) to the water-reducing agent as a product (c) is preferably 0.005 to 0.08, more preferably 0.005 to 0.06, and particularly preferably 0.005 to 0.04.

[0029] The amount of water (w) used, expressed as the mass ratio ((w+c) / p) of the total amount of water (w) and water-reducing agent (c) as a product to the fine powder-containing powder (p), is preferably 1 to 7, more preferably 2 to 6, and particularly preferably 3 to 5. If the amount of water used is within the above range, the dilution ratio of the suspension is optimized, making it possible to measure the amount of chlorine using a chlorine meter that utilizes capillary action.

[0030] The liquid to be measured by the chlorine content meter utilizing capillary action is a suspension obtained by stirring and mixing the above-mentioned fine powder-containing powder, water-reducing agent and water, or the supernatant liquid of the suspension.

[0031] Naturally, the filtrate obtained by suction or pressure application to the suspension may also be used as the measurement object.

[0032] The stirring time for the suspension is 45 to 240 seconds, preferably 60 to 180 seconds. This stirring time stabilizes the measured value of a chlorine amount measuring meter that utilizes capillary action. The stirring method is not particularly limited, but mixing can be performed using a stirrer or a stirring rod, for example.

[0033] The chlorine content measurement method used in the chlorine amount meter is not particularly limited as long as it is a method that can determine the amount of chlorine in the liquid phase by utilizing capillary action, but an example is the Mohr method, in which a specific color change occurs due to the reaction between chloride ions and silver nitrate. The above-mentioned Cantab is an example of a chlorine amount meter based on the Mohr method.

[0034] The chlorine content of the powder can be calculated from the measurement value of the chlorine amount meter that utilizes capillary action using the following formula (1). T(ppm)=(((w+c)×Kw×K') / p)×10 4 ···(1) Here, the symbols in formula (1) represent the following: p: mass of powder sample (g) w: mass of water (g) c: Mass of the water-reducing agent as a product (g) K: Measured amount of chlorine in the liquid to be measured (%) K': Chlorine content of water (%) T: Chlorine content of powder sample (%) [Example]

[0035] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0036] 1. Materials and standards (1) Powder containing fine powder Seven silica fume samples (made in China) containing fine particles were prepared. The chlorine content measured by X-ray fluorescence analysis (XRF) in accordance with JIS R 5204 "Method for X-ray fluorescence analysis of cement" was 420 ppm to 1020 ppm. All of the silica fume samples had an average particle size of 0.3 μm or less and a specific surface area of ​​15 m2 measured by the BET method. 2 / g or more.

[0037] (2) Water-reducing agent and water The following water-reducing agents and water were used: Water reducing agent: Polycarboxylic acid water reducing agent (Mastergranium SP8SV manufactured by Pozzolith Solutions Co., Ltd.) Water: Distilled water

[0038] (3) Chlorine content measuring meter The chlorine amount measuring meter used was a Cantab low concentration model (manufactured by Pacific Materials Co., Ltd.). The method of using Cantab was in accordance with the method described in the product catalog. Regarding the conversion table attached to Cantab, which is used to calculate the amount of chlorine in the liquid phase from the reading (measurement value) of Cantab, "For concrete" was used for measuring the suspension, and "Solution, for fine aggregate" was used for measuring the supernatant liquid of the suspension.

[0039] (4) Test level All test levels are shown in Table 1. For the comparative test with and without the use of a water-reducing agent, two silica fume samples with chlorine contents (measured by XRF; the same applies below) of 420 ppm and 1020 ppm were used. In addition, seven silica fume samples with chlorine contents of 420 ppm, 540 ppm, 610 ppm, 740 ppm, 810 ppm, 950 ppm (suspension), and 1020 ppm were used for a comparative test between direct measurement of the suspension and measurement of the supernatant of the suspension. In addition, for comparative tests when the rate of addition of water-reducing agent was changed, silica fume with a chlorine content of 420 ppm was used.

[0040] 2. Steps for obtaining a suspension (1) Procedure for preparing a suspension containing a water-reducing agent 0.75 g of water-reducing agent was added to 99.25 g of distilled water to obtain 100 g of a mixed liquid with a water-reducing agent addition rate of 0.75%, to which 25 g of the specified silica fume was added, and the mixture was stirred and mixed for 60 seconds using a stirrer to obtain a suspension.

[0041] (2) Preparation procedure for supernatant The container containing the suspension was covered with a lid and allowed to stand for 10 minutes in a place not exposed to direct sunlight, after which the supernatant was collected by suction with a dropper.

[0042] (3) Procedure for preparing a suspension that does not contain a water-reducing agent 25 g of a predetermined silica fume was added to 100 g of distilled water, and then the mixture was stirred and mixed for 60 seconds using a stirrer to obtain a suspension.

[0043] 3. A process for measuring the amount of chlorine in the liquid phase of the suspension (1) Measurement using a chlorine meter Three Cantabs were inserted into each of the suspension and supernatant liquid placed in the container. After confirming that the humidity indicator at the horizontal part of the narrow tube of the Cantab had turned blue, the Cantab was removed. The time from inserting the Cantab until the temperature indicator changed color is shown in Table 1 as "Cantab measurement time." The time required for the Cantab measurement is an index showing the effect of the present invention, and the Cantab catalog states that the typical time is about 10 minutes.

[0044] (2) Reading the chlorine meter The pale yellow discoloration of the vertical part of the capillary tube of the three Cantabs was read, and the amount of chlorine in the liquid phase was calculated for each of the three from the conversion table attached to the Cantab. Note that the conversion table for "Concrete" was used for the suspension, and the conversion table for "Solution, for fine aggregate" was used for the supernatant liquid of the suspension.

[0045] (3) Amount of chlorine in the liquid phase The average value of the chlorine amounts in the three liquid phases obtained for one sample was taken as the chlorine amount in that liquid phase.

[0046] 4. Calculating the chlorine content of the fine powder (1) Measurement using a chlorine meter The chlorine content of each silica fume was calculated by substituting the amount of chlorine in the obtained liquid phase into the above formula (1). In the calculation, K' for the chlorine content (%) of water in formula (1) was set to 0. The chlorine contents of the obtained silica fume are shown in Table 1 together with the values ​​obtained by X-ray fluorescence analysis (considered to be true values).

[0047] [Table 1]

[0048] With regard to the ratio A / B shown in Table 1, which is the ratio of the chlorine content (A) of silica fume obtained from the Quantab measurement value to the chlorine content (B) of silica fume measured by X-ray fluorescence analysis, Examples 1 to 14, which used a water-reducing agent, all had an accuracy of 0.75 or higher, while Comparative Examples 1 and 2, which did not use a water-reducing agent, had values ​​of 0.55 or lower.

[0049] The time required for the Cantab measurement was 20 minutes or less in Examples 1 to 14, whereas it was 49 minutes or more in the comparative example.

[0050] Thus, the present invention makes it possible to use a chlorine content measuring meter that utilizes capillary action for powders containing fine particles, and provides a method for easily determining the chlorine content of powders.

Claims

1. A step of adding a water-reducing agent to a mixture of fine-powder-containing powder and water and stirring the mixture, or adding fine-powder-containing powder to water that has already contained a water-reducing agent and then stirring the mixture to obtain a suspension; Next, a step of measuring the amount of chlorine in the liquid phase of the suspension using a chlorine amount measuring meter that utilizes capillary action on the suspension or the supernatant of the suspension; Finally, the method for measuring the chlorine content of the fine-powder-containing powder comprises a step of calculating the chlorine content of the fine-powder-containing powder from the amount of chlorine in the liquid phase of the obtained suspension.

2. A method for measuring the chlorine content of a fine-powder-containing powder as described in claim 1, wherein the water reducing agent is one or more selected from polycarboxylic acids, lignin sulfonic acid, naphthalene sulfonic acid formaldehyde condensates, melamine sulfonic acid formaldehyde condensates, and salts thereof.

3. A method for measuring the chlorine content of a fine-powder-containing powder according to claim 1 or claim 2, wherein the mass ratio c / p of the water-reducing agent (c) to the fine-powder-containing powder (p) is 0.005 to 0.08, and the mass ratio ((w+c) / p) of the water (w), water-reducing agent (c) and fine-powder-containing powder (p) in the suspension is 1 to 7 (however, the mass of the water-reducing agent (c) is the mass of the product).

4. 2. The method for measuring the chlorine content of a fine-powder-containing powder according to claim 1, wherein the stirring time of the suspension is 45 to 240 seconds.

5. 2. The method for measuring the chlorine content of a fine-powder-containing powder according to claim 1, wherein the fine-powder-containing powder is silica fume, ground granulated blast furnace slag, silica fume, limestone powder, coal ash, or silica powder.

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