alkali agent

Abstract

The alkali agent of the present application is characterized in that it contains magnesium oxide particles having a crystallite diameter of 80 nm to 300 nm and a BET specific surface area of 0.1 m 2 / g to 1.2 m 2 / g, and a MgO content of 95.0% by mass or more. (The MgO content is a value obtained by adding the contents (% by mass) of MgO, CaO, SiO2, Fe2O3, and Al2O3, which are obtained by converting the contents of Mg, Ca, Si, Fe, and Al, which are detected by fluorescence X-ray measurement, into MgO, CaO, SiO2, Fe2O3, and Al2O3, respectively, and taking the total as 100.)

Description

Technical Field

[0001] This invention relates to alkali agents. Background Technology

[0002] Sometimes it is necessary to modify and maintain the alkalinity of environments such as water and soil (alkaline agents). Such alkaline agents are also used in fertilizers, coatings, etc. For example, Patent Document 1 describes a soil-modifying material that, when combined with a base material and a pH adjuster, suppresses the soil-modifying effects of magnesium oxide or calcium oxide. Additionally, Patent Document 2 describes a coated steel with a non-water-soluble coating film having alkali metal concentration zones formed on the surface of a steel material with a specific composition.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-044110

[0006] Patent Document 2: Japanese Patent Application Publication No. 2015-151571 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] From the perspective of environmental modification, alkali agents, as the source of modification effects, have a moderate dissolution rate, which can be expected to maintain the effect for a long time. However, the dissolution rate of the alkali agents themselves has not received much attention and has not been sufficiently studied to date.

[0009] Therefore, the object of the present invention is to provide an alkali agent with a moderate dissolution rate and the ability to maintain a stable effect over a long period of time.

[0010] Methods for solving problems

[0011] The alkali agent of the present invention is characterized in that it contains magnesium oxide particles, wherein the microcrystal diameter of the magnesium oxide particles is 80 nm to 300 nm and the BET specific surface area is 0.1 m². 2 / g~1.2m 2 / g, with an MgO content of over 95.0% by mass.

[0012] The effects of the invention

[0013] According to the present invention, an alkali agent with a moderate dissolution rate and capable of maintaining a stable effect over a long period of time can be provided. Detailed Implementation

[0014] The inventors conducted in-depth research and found that magnesium oxide particles with a crystallite diameter and BET specific surface area within a specified range and containing a specified amount of magnesium oxide have a suitable dissolution rate, thus completing this invention.

[0015] The embodiments of the present invention will be described in detail below.

[0016] The alkali agent of the present invention contains magnesium oxide particles (MgO particles) with crystallite diameter and BET specific surface area within a specified range. The MgO particles contain magnesium oxide accounting for more than 95% by mass, and impurities may also be present.

[0017] The crystallite diameter of the MgO particles in this invention is 80 nm to 300 nm. By keeping the crystallite diameter within the range of 80 nm to 300 nm, moderate solubility can be ensured. MgO particles tend to dissolve faster the smaller the crystallite diameter. The crystallite diameter of the MgO particles is preferably 85 nm to 275 nm, more preferably 90 nm to 250 nm. The crystallite diameter is a value obtained by processing the MgO(002) surface peaks in the XRD pattern using analytical software. Typically, a particle is a polycrystalline material composed of multiple single crystals, and the crystallite diameter represents the average size of the single crystals in the polycrystalline material.

[0018] As described below, the MgO particles in this invention are obtained from sintered magnesium oxide bodies formed by sintering magnesium compounds, and the crystallite diameter can be controlled by the sintering temperature. Magnesium oxide is mostly produced through the thermal decomposition of magnesium compounds used as raw materials. After the formation of fine crystals, crystal growth occurs according to the sintering temperature. The crystallite diameter of the MgO particles can also be adjusted by the impurity content. Si and the like tend to promote crystal growth, especially in sintered magnesium oxide bodies with an MgO content of 99% by mass or less. Furthermore, the crystallite diameter of the MgO particles can be reduced by pulverizing the sintered magnesium oxide body.

[0019] In addition, the BET specific surface area of ​​MgO particles is specified as 0.1 m². 2 / g~1.2m 2 / g. This ensures adequate solubility. The preferred BET specific surface area of ​​the MgO particles is 1.0 m². 2 / g or less, more preferably 0.8m 2 / g or less, more preferably 0.6m 2 / g or less. Furthermore, the BET specific surface area of ​​the MgO particles is preferably 0.15m². 2 / g or more, more preferably 0.25m 2 / g or more.

[0020] The BET specific surface area of ​​MgO particles can be controlled by the firing temperature of the sintered magnesia body. There is a tendency for a lower BET specific surface area at higher firing temperatures. Alternatively, the BET specific surface area can be increased by pulverizing the sintered magnesia body. Furthermore, by classifying the sintered and / or pulverized magnesia body, particles with a predominantly arbitrary BET specific surface area can be selected.

[0021] In this invention, the MgO particles, except for their crystallite diameter and BET specific surface area which are within specified ranges, have an MgO content of 95% by mass or more. Therefore, they can be dissolved by alkali at a moderate rate, maintaining a stable effect over a long period. The MgO content is preferably 99.0% by mass or less in the MgO particles, more preferably 95.5% to 98.5% by mass, and even more preferably 96.0% to 98.0% by mass.

[0022] The MgO content in MgO particles is the MgO content when the total content (mass%) of the five elements Mg, Ca, Si, Fe and Al detected by fluorescence X-ray determination is converted into MgO, CaO, SiO2, Fe2O3 and Al2O3 respectively is set to 100.

[0023] In the determination of the alkali dissolution rate, a MgO suspension prepared by dispersing 50 mg of MgO particles in 100 mL of ion-exchanged water and 0.05 mol / L sulfuric acid were used. The pH of the MgO suspension was maintained at 3 by adding sulfuric acid dropwise using a potentiometric titration device, and the amount of sulfuric acid required to maintain the pH was calculated. Specifically, the dissolution rate test value X, as shown in the following equation (2), can be used for evaluation.

[0024] X=m / t (2)

[0025] (In the above formula (2), m is the endpoint sulfuric acid mol / MgO mol for the dissolution test to maintain the pH of the MgO suspension at 3, and t is the titration time (seconds).)

[0026] If the dissolution rate test value X obtained in this way is 0.00035 or less, it has a moderate dissolution rate and can function for a long time. More preferably, the dissolution rate test value X is 0.00025 or less, and even more preferably 0.00020 or less. The lower limit of the dissolution rate test value X is not particularly limited, but it is preferably 0.00003 or more, more preferably 0.00005 or more, and even more preferably 0.00010 or more.

[0027] MgO particles may contain impurities such as Ca, Si, Fe, and Al. Impurities can be evaluated using the S / M ratio shown in equation (1) below.

[0028] S / M = XRF(S) / XRF(M) (1)

[0029] XRF(S) and XRF(M) represent the SiO2 content (S) and MgO content (M) respectively, when the five elements Mg, Ca, Si, Fe, and Al detected by fluorescence X-ray determination are converted into MgO, CaO, SiO2, Fe2O3, and Al2O3 respectively, and the total content (mass%) is set to 100.

[0030] When the S / M ratio is 0.004 to 0.040, the stability is improved, and the moisture resistance tends to be maintained even when the surface is subjected to a large load during crushing and grading. It is speculated that the heterogeneous phase (Si-Mg compound) formed during the sintering of the magnesium oxide sintered body delays the internal penetration of deterioration caused by moisture absorption, etc. The S / M ratio is preferably 0.006 to 0.035, more preferably 0.007 to 0.020.

[0031] The 50% volumetric cumulative particle size (D50) of MgO particles is preferably 1 μm to 200 μm. Maintaining a D50 within this range allows for a suitable dissolution rate. There is a tendency for D50 to increase with higher firing temperatures. Furthermore, D50 can be reduced by pulverizing the fired sintered magnesia body. Additionally, D50 can be adjusted to any range by classifying the fired and / or pulverized magnesia sintered body. A more preferred D50 for MgO particles is 10 μm to 150 μm, and even more preferably 20 μm to 100 μm.

[0032] The ratio of the 50% volumetric cumulative particle size (D50) to the crystallite diameter (D50 / crystal diameter) of MgO particles is preferably in the range of 100 to 600. It is believed that the smaller the (D50 / crystal diameter) ratio, the higher the probability that the fracture surface of the crystal structure is exposed on the particle surface, and the lower the stability, such as moisture resistance. A ratio in the range of 100 to 600 can improve moisture resistance. The preferred (D50 / crystal diameter) ratio is 150 to 550, more preferably 200 to 500.

[0033] The moisture resistance of MgO particles can be evaluated based on the mass gain rate in a humidification test. When maintained in an atmosphere of 50°C and 85% humidity for 120 hours, the mass gain rate is preferably 2% or less. More preferably, the mass gain rate is 1.5% or less, and even more preferably 1.0% or less.

[0034] The alkali agent of the present invention can be obtained by pulverizing magnesium oxide sintered body and classifying it as needed.

[0035] Magnesium oxide sintered bodies can be obtained by sintering magnesium compounds such as magnesium hydroxide, magnesium carbonate, magnesium chloride, magnesium nitrate, and magnesium sulfate. Magnesium hydroxide can be precipitated by the reaction of magnesium salts in seawater with calcium hydroxide. Magnesium carbonate can be magnesite ore.

[0036] The magnesium compound is preferably calcined in the atmosphere at a temperature of 1300°C to 2800°C. At temperatures below 1300°C, the crystallite diameter tends to be smaller than a specified range, while the BET specific surface area tends to be larger than a specified range, easily resulting in a material with an excessive dissolution rate. Conversely, at temperatures above 2800°C, the crystallite diameter tends to be larger than a specified range, while the BET specific surface area tends to be smaller than a specified range, easily resulting in a material with insufficient function as an alkali agent. A calcination temperature of 1400°C to 2400°C is more preferred. The calcination time is preferably set to 10 minutes to 10 hours.

[0037] The composition of MgO particles, including the MgO content, can be adjusted during the firing of the sintered magnesia body. Specifically, this can be controlled by the selection of the magnesium compound used as the firing raw material and the use of additives corresponding to impurities such as Si. Considering manufacturing efficiency, it is preferable to adjust the composition by selecting and combining magnesium compounds, taking into account the amount of impurities in the magnesium compound used as the raw material.

[0038] The Si content can be adjusted by any additive. There are no particular limitations on the additives; examples include silica fume, silica sand, and sodium silicate. Commercially available magnesium compounds can be used, but magnesium compounds with adjusted compositions can also be produced using known methods. It should be noted that if a magnesium oxide sintered body meeting the specified conditions can be obtained, this magnesium oxide sintered body can also be used.

[0039] When sintered magnesium oxide contains a large number of coarse particles, it can be crushed into a particle size that is easy to process. Examples of crushing devices include hammer crushers, roller crushers, jaw crushers, impact crushers, disc mills, rolling ball mills, vibrating ball mills, pin mills, bead mills, jet mills, and cyclone mills. Such devices can be used individually or in combination of two or more.

[0040] After pulverization, classification can remove coarse and / or fine powders, resulting in an optimal particle size distribution. The classification method is not particularly limited; vibrating screens, air classifiers, cyclone classifiers, etc., can be used individually, or in combination of two or more methods.

[0041] The magnesia sintered body can be subjected to the pulverization and / or grading processes described above as needed to adjust it to a specified particle size. The pulverization and grading processes can be appropriately combined according to the magnesia sintered body, and there are no particular restrictions on the order or number of times. The grading and pulverization processes can be performed either first, or the pulverization process can be performed after the grading process on the magnesia sintered body that has undergone the pulverization process.

[0042] When the particle size of the magnesium oxide sintered body meets the desired properties, it can be used without performing the crushing and grading processes.

[0043] MgO particles that meet the requirements of crystallite diameter, BET specific surface area, and MgO content can be effectively used as the alkali agent of this invention. Because of their moderate dissolution rate, they can maintain a stable effect over a long period, making the material of this invention suitable for use as an alkali agent.

[0044] Example

[0045] The present invention will now be described in detail based on the embodiments, but these do not limit the purpose of the present invention. Furthermore, the present invention is not limited to these embodiments.

[0046] <Making of Magnesium Oxide>

[0047] Magnesium compounds, used as raw materials, are prepared to be magnesium hydroxide obtained by reacting seawater with slaked lime. The composition of magnesium hydroxide is determined based on impurities from the slaked lime, the presence or absence of impurity removal processes, and additives.

[0048] Magnesium hydroxide was sintered to produce sintered magnesium oxide, which was then pulverized and classified to manufacture MgO particles as examples and comparative examples. During the manufacture of MgO particles, the sintering temperature and pulverization / classification were controlled such that the crystallite diameter and BET specific surface area were as shown in Table 1. The sintering temperature and the presence or absence of pulverization / classification are shown in Table 1. Pulverization 1 used an impact crusher and a cyclone mill, classification used sieving and air screening, and pulverization 2 used a cyclone mill.

[0049] The crystallite diameter, BET specific surface area, constituent components, and cumulative volumetric diameter of the obtained MgO particles were determined. The evaluation methods for each are described below.

[0050] <Crystal diameter>

[0051] First, the XRD pattern was determined using an X-ray diffraction apparatus (Bruker AXS NEW D8 ADVANCE) under the following conditions.

[0052] X-ray source: CuKα (Ni filter)

[0053] Tube voltage: 40kV

[0054] Tube current: 40 mA

[0055] Detector: One-dimensional semiconductor high-speed detector LynxEye

[0056] Divergent slit: 0.30 degrees

[0057] Step size: 0.015 degrees

[0058] Counting time: 0.65 seconds / step

[0059] For the obtained XRD pattern, using analysis software (DIFFRAC.EVA V.3.2 manufactured by Bruker AXS), the crystallite diameter was calculated. The MgO (002) plane peak in the XRD pattern was specified, and the value calculated as the crystallite diameter based on the half-value width was used.

[0060] <BET specific surface area>

[0061] Using a specific surface area meter (MONOSORB manufactured by YUASA IONICS), as a pretreatment, after degassing at 180 °C for 10 minutes, the measurement was carried out using the BET single-point method.

[0062] <Determination of contained components>

[0063] The contained components of MgO particles were determined by the glass bead method using lithium tetraborate as the melting material through a fluorescence X-ray analyzer (Supermini 200 manufactured by Rigaku). In the quantitative analysis of the detected characteristic X-rays, a standard curve prepared from magnesia refractories for fluorescence X-ray analysis (JRRM401 - 410) of the Refractories Society standard substances was used.

[0064] The SiO2 content rate and MgO content rate when the total content rates (mass %) of the five elements Mg, Ca, Si, Fe, and Al detected by fluorescence X-ray determination were converted to MgO, CaO, SiO2, Fe2O3, and Al2O3 and set to 100 were denoted as XRF(S) and XRF(M), respectively. Using the obtained XRF(S) and XRF(M), the S / M ratio was calculated by the following formula (1).

[0065] S / M = XRF(S) / XRF(M) (1)

[0066] The obtained results were summarized in Table 1 below together with the crystallite diameter and BET specific surface area.

[0067] <Volume cumulative particle size (D50)>

[0068] The particle size distribution based on volume was determined by using a laser diffraction particle size distribution measuring device (MICROTRAC MT3300EX MicrotracBEL Co., Ltd.) with a wavelength of 780 nm, and the average of three repeated measurements was used to obtain the 50% volumetric cumulative particle size D50.

[0069] The results obtained are summarized together with D50 / crystal diameter in Table 2 below.

[0070] [Table 1]

[0071]

[0072] [Table 2]

[0073]

[0074] The MgO particles in the examples all had crystallite diameters of 80 nm to 300 nm and a BET specific surface area of ​​0.1 m². 2 / g~1.2m 2 The MgO content was 95% by mass or higher. In contrast, the MgO particles in Comparative Example 1 had a crystallite diameter of less than 80 nm, and the MgO particles in Comparative Examples 2 and 3 had a BET specific surface area exceeding 1.2 m². 2 / g.

[0075] For the MgO particles of the examples and comparative examples, dissolution and moisture resistance were evaluated. The methods are as follows.

[0076] <Dissolution Rate Test>

[0077] First, 50 mg of MgO particles were dispersed in 100 mL of ion-exchanged water to prepare a MgO suspension. Using an automatic potentiometric titration apparatus (Kyoto Electronics Industry, AT-510 model), 0.05 mol / L sulfuric acid was added dropwise while stirring the MgO suspension to maintain the pH of the MgO suspension at 3. The amount of sulfuric acid required to maintain the pH (CS(1)) (sulfuric acid mol / MgO mol) was calculated. The endpoint of the determination was defined as 1 hour after the start of the determination, or the moment when all the MgO in the suspension was consumed based on the amount of sulfuric acid consumed. The time from the start of the determination to the endpoint was taken as the titration time (seconds).

[0078] The same method was used to measure 100 mL of ion-exchanged water to determine the sulfuric acid consumption (CS(0)) (sulfuric acid mol / MgO mol). The sulfuric acid consumption (CS(0)) (sulfuric acid mol / MgO mol) at the end time of the magnesium oxide suspension was subtracted from the sulfuric acid consumption (CS(1)) (sulfuric acid mol / MgO mol) at the end time of the blank to determine the (end-point sulfuric acid mol / MgO mol) based on the magnesium oxide powder.

[0079] Let m be the (endpoint sulfuric acid mol / MgO mol) obtained in this way, and let t be the titration time (seconds). The test value of dissolution rate X is calculated by the following formula (2).

[0080] X=m / t (2)

[0081] If the dissolution rate test value X is below 0.00035, then it has a suitable dissolution rate.

[0082] <Wet Resistance Test>

[0083] 20g of MgO particles were placed and weighed in a glass weighing bottle and kept in a constant temperature and humidity bath at 50°C and 85% for 120 hours. Then, the MgO particles were removed from the bath and their mass (M(1)) was measured. The mass of the MgO particles before holding (M(0)) was used, and the weight gain rate was calculated using the following formula. If the weight gain rate is less than 2%, sufficient moisture resistance is achieved.

[0084] Quality increase rate = ((M(1)-M(0)) / M(0))×100(%)

[0085] The results obtained are summarized together with the experimental values ​​of dissolution rate in Table 3 below.

[0086] [Table 3]

[0087]

[0088] The MgO particles in the example have a crystallite diameter of 80 nm to 300 nm and a BET specific surface area of ​​0.1 m². 2 / g~1.2m 2 Within the range of / g, it exhibits a moderate dissolution rate. In contrast, Comparative Example 1, with MgO particle crystallite diameters as small as less than 80 nm, has a BET specific surface area exceeding 1.2 m². 2 In Comparative Examples 2 and 3, where the concentration was / g, the dissolution rate became too fast. Without meeting either the crystallite diameter or the BET specific surface area, the device could not maintain its functionality over a long period.

Claims

1. Use of magnesium oxide particles having a crystallite diameter of 80 nm to 300 nm, a BET specific surface area of 0.12 m2 / g to 1.2 m2 / g, a MgO content of 95.0 mass% or more, and a 50% volume cumulative particle diameter D50 of 1 μm to 200 μm in an alkaline agent. 2 2 g, a MgO content of 95.0 mass% or more, and a 50% volume cumulative particle diameter D50 of 1 μm to 200 μm in an alkaline agent.​ The MgO content is a value when the contents of Mg, Ca, Si, Fe, and Al, which are detected by fluorescent X-ray measurement, are converted into MgO, CaO, SiO2, Fe2O3, and Al2O3, respectively, and the total of the contents is set to 100, and the unit of the content is mass %.

2. The use of magnesium oxide particles in an alkaline agent according to claim 1, wherein, The S / M ratio represented by the following formula (1) of the magnesium oxide particles is 0.004 to 0.040, S / M = XRF(S) / XRF(M) (1) XRF(S) and XRF(M) are the SiO2 content and the MgO content, respectively, when the contents of Mg, Ca, Si, Fe, and Al, which are detected by fluorescent X-ray measurement, are converted into MgO, CaO, SiO2, Fe2O3, and Al2O3, respectively, and the total of the contents is set to 100, and the unit of the content is mass %.

3. The use of magnesium oxide particles in an alkaline agent according to claim 1, wherein, The ratio of the 50% volume cumulative particle size D50 of the magnesium oxide particles to the crystallite diameter, that is, D50 / crystallite diameter, is 100 to 600.

4. The use of the magnesium oxide particles in an alkaline agent according to claim 1, wherein, The elution rate test value X represented by the following formula (2) of the magnesium oxide particles is 0.00003 or more and 0.00035 or less, X = m / t (2) In the above formula (2), m is sulfuric acid at the end point of the elution test in which the pH of the MgO suspension is maintained at 3, and the unit of the end point of the sulfuric acid is mol / MgO mol, and t is the titration time, and the unit thereof is s.

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