Ammonia-generating agent and method for producing ammonia-generating agent

Abstract

[Problem] To provide an ammonia-generating agent with which it is possible to stably generate ammonia and a method for producing an ammonia-generating agent. [Solution] Provided according to one embodiment of the present invention is an ammonia-generating agent that generates ammonia by contact with water molecules. The ammonia-generating agent contains boron nitride having a crystallinity of 90% or less.

Description

Ammonia generator and method for producing the ammonia generator

[0001] The present invention relates to an ammonia generating agent and a method for producing an ammonia generating agent.

[0002] Silicon nitride (Si ３ N ４ Silicon nitride is a material that has excellent strength, hardness, toughness, heat resistance, corrosion resistance, and thermal shock resistance, and is therefore used in components of various structures. In addition to these properties, silicon nitride is also known to have antibacterial and biocompatible properties (Patent Documents 1 and 2). According to the inventors' research, the antibacterial properties of silicon nitride are due to the ammonia (NH ３ ) is the effect of

[0003] When silicon nitride comes into contact with water, ammonia is generated in the liquid phase from the initial stage, and at this time, silicon oxide (SiO ２ This silicon oxide reacts with water to form silicic acid (Si(OH) ４ ) and dissolves in the liquid phase. As a result, the surface of the silicon nitride is exposed, and ammonia is generated again. However, because the rate of silicic acid generation from silicon oxide is very slow, the surface of the silicon nitride becomes less exposed over time. As a result, the amount of ammonia generated decreases over time, and the antibacterial properties also decrease.

[0004] To solve these problems, there is a need for the development of compounds that can stably generate ammonia for a longer period of time. Such compounds are expected to be used not only as antimicrobial agents such as antibacterial agents, but also in various fields that utilize ammonia.

[0005] Special table 2015-516239 publication Special table 2020-512072 publication

[0006] In view of the above circumstances, the present invention provides an ammonia generating agent capable of stably generating ammonia, and a method for producing the ammonia generating agent.

[0007] According to one aspect of the present invention, there is provided an ammonia generating agent that generates ammonia upon contact with water molecules. The ammonia generating agent contains boron nitride having a crystallinity of 90% or less.

[0008] According to this embodiment, ammonia can be generated stably.

[0009] 1 is a graph showing the relationship between the abundance ratio of ammonia in a liquid phase and pH.

[0010] Hereinafter, embodiments of the present invention will be described. Various features shown in the following embodiments can be combined with each other. The ammonia generating agent of the present invention generates ammonia upon contact with water molecules. Here, the water molecules may be liquid water or gaseous water vapor. Furthermore, the water or water vapor may contain other substances to the extent that they do not adversely affect the generation of ammonia.

[0011] Ammonia has the effect of inhibiting the growth of various microorganisms and killing them. The following describes an example in which an ammonia generator is used as an antimicrobial agent. Examples of target microorganisms include gram-negative bacteria such as Escherichia coli, Vibrio cholerae, Salmonella, Shigella, Vibrio parahaemolyticus, Pseudomonas aeruginosa, and Salmonella typhi; gram-positive bacteria such as Staphylococcus aureus, Staphylococcus epidermidis, Mycobacterium tuberculosis, Streptococcus hemolyticus, Enterococcus faecalis, Clostridium botulinum, Clostridium tetani, and Bacillus cereus; viruses such as influenza virus, feline cassilis virus, and COVID-19; oomycetes; and amoeba.

[0012] This ammonia generator contains boron nitride with low crystallinity. It is generally known that boron nitride is insoluble in cold water and water at room temperature, and slightly soluble in boiling water. As a result of extensive research into boron nitride, the inventors have found that boron nitride with low crystallinity dissolves in water at room temperature. Based on this unexpected phenomenon, the inventors have completed the present invention. Here, the degree of crystallinity of boron nitride can be expressed by the crystallinity degree or graphitization index (G.I.).

[0013] The crystallinity of boron nitride is about 90% or less, preferably about 88% or less, and more preferably about 86% or less. The crystallinity of boron nitride is preferably about 50% or more, more preferably about 60% or more, and even more preferably about 70% or more. The crystallinity of boron nitride can be adjusted within the above range, for example, to about 50% or more and 90% or less. This allows the solubility of boron nitride in water molecules to be sufficiently increased. Note that boron nitride having a crystallinity below the above lower limit is difficult to produce.

[0014] The crystallinity in this specification is a value measured by wide-angle X-ray scattering. Specifically, wide-angle X-ray scattering is performed on boron nitride powder, and a one-dimensional profile (diffraction data) is created from the measurement results using data analysis software. Then, based on the explanatory data, the crystallinity (%) can be calculated using the following formula: Crystallinity (%) = [peak area indicating crystalline region / (peak area indicating crystalline region + peak area indicating amorphous region)] × 100

[0015] The graphitization index of boron nitride is about 1.5 or more, preferably about 2 or more, more preferably about 2.5 or more, even more preferably about 3 or more, and particularly preferably about 3.5 or more. The graphitization index of boron nitride is preferably about 7 or less, more preferably about 6.5 or less, and even more preferably about 6 or less. The graphitization index of boron nitride can be adjusted within the above range, for example, to about 1.5 or more and about 7 or less. This makes it possible to sufficiently increase the solubility of boron nitride in water molecules. Note that boron nitride having a graphitization index exceeding the above upper limit is difficult to produce.

[0016] The graphitization index in this specification is also known as an index value indicating the degree of crystallinity of graphite (see, for example, J. Thomas, et. al., J. Am. Chem. Soc. 84, 4619 (1962)). The graphitization index can be calculated based on a spectrum obtained by measuring primary particles of boron nitride by powder X-ray diffraction. First, in the X-ray diffraction spectrum, the integrated intensities (i.e., the area surrounded by each diffraction peak and its baseline) (in any unit) of the diffraction peaks corresponding to the (100), (101), and (102) planes of the primary particles of boron nitride are calculated, and these are designated S100, S101, and S102, respectively. The calculated area values ​​are used to calculate the value of [(S100 + S101) / S102], thereby determining the graphitization index.

[0017] Furthermore, the higher the oxygen content of boron nitride, the more likely it is that its crystallinity will decrease. Specifically, the oxygen content in boron nitride is preferably about 0.5 atomic % or more, more preferably about 0.7 atomic % or more, and even more preferably about 0.9 atomic % or more. The oxygen content of boron nitride is preferably about 1.5 atomic % or less, more preferably about 1.3 atomic % or less, and even more preferably about 1.1 atomic % or less. The oxygen content of boron nitride can be adjusted within the above range, for example, to about 0.5 atomic % or more and 1.5 atomic % or less. This can further reduce the crystallinity and / or graphitization index of boron nitride, and as a result, can further increase the solubility of boron nitride in water.

[0018] The content of boron nitride in the ammonia generating agent is preferably about 80% by mass or more, more preferably about 85% by mass or more, even more preferably about 90% by mass or more, particularly preferably about 95% by mass or more, and may be 100% by mass. This makes it possible to sufficiently increase the amount and rate of ammonia generation upon contact with water molecules. Note that components other than boron nitride (boron nitride with low crystallinity) contained in the ammonia generating agent include, for example, boron nitride, silicon nitride, aluminum nitride, etc. with high crystallinity. By using these components in combination, it is possible to adjust the amount and rate of ammonia generation upon contact with water molecules of the ammonia generating agent. The case where boron nitride and silicon nitride are used in combination as the ammonia generating agent will be described in detail later.

[0019] The shape of the ammonia generating agent is not particularly limited, and examples thereof include particulate, granular, pellet, block, sheet, and fibrous forms. Among these, the ammonia generating agent is preferably particulate. A particulate ammonia generating agent has an increased specific surface area, so that a sufficient contact area with water molecules can be secured. As a result, the amount and rate of ammonia generation can be further increased.

[0020] In this case, the volume average particle diameter of the ammonia generating agent (primary particles) is preferably about 10 μm or less, preferably about 7.5 μm or less, and more preferably about 5 μm or less. The volume average particle diameter of the ammonia generating agent is preferably about 0.5 μm or more, more preferably about 1 μm or more, and even more preferably about 1.5 μm or more. The volume average particle diameter of the ammonia generating agent can be adjusted within the above range, for example, to about 0.5 μm or more and 10 μm or less. This makes it possible to prevent the ammonia generating agent from agglomerating while further increasing its specific surface area.

[0021] Here, the volume average particle size is the particle size (D) of 50% of the cumulative passing fraction (cumulative passing fraction) from the small particle size side in the volume-based particle size distribution obtained by measurement in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - laser diffraction and scattering method". ５０ ) refers to

[0022] The BET specific surface area of ​​the ammonia generator is 10 m ２ / g or more, and ２ / g or more is more preferable, and ２ The BET specific surface area of ​​the ammonia generating agent is more preferably about 50 m / g or more. ２ / g or less, and ２ / g or less is more preferable, and ２ The BET specific surface area of ​​the ammonia generating agent can be adjusted within the above range, and is preferably about 10 m / g or less. ２ / g or more 50m ２ This makes it possible to more reliably increase the contact area between the ammonia generating agent and water molecules.

[0023] Here, the BET specific surface area refers to a value measured by the BET single-point method using nitrogen gas in accordance with JIS Z 8830:2013 "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption."

[0024] When boron nitride is used as an ammonia generating agent, the following reaction occurs on the surface of the ammonia generating agent and its surroundings when the agent comes into contact with water (i.e., is immersed in water): (A) 2BN + 6H ２ O ⇒ 2B (OH) ３ +2NH ３ (B) NH ３ +H ２ O ⇔ NH ４ ＋ +OH － (C) B(OH) ３ +OH － ⇔ B (OH) ４ －

[0025] When the ammonia generating agent comes into contact with water, ammonia (NH ３ ) is generated, and then ammonium ions (NH ４ ＋ ) is generated. This causes the pH of the liquid phase around the ammonia generating agent to increase. In addition, boric acid (B(OH) ３ or H ３ BO ３ ) is deposited on the surface of boron nitride. This deposited boric acid is converted into tetrahydroxyborate anions (B(OH)) according to reaction formula (C). ４ － ) and dissolves in water.

[0026] In a high pH environment, the reaction of reaction formula (C) occurs rapidly, removing boric acid from the surface of the boron nitride, smoothly exposing the surface of the boron nitride to the liquid phase. This causes the reaction of reaction formula (A) to occur again. In this way, the reaction of reaction formula (A) and the reactions of reaction formulas (B) and (C) occur repeatedly, resulting in the rapid generation of ammonia and ammonium ions over a long period of time.

[0027] In the above reaction formula (A), the conversion of ammonia to ammonium occurs depending on the pH of the liquid phase. Figure 1 is a graph showing the relationship between the abundance ratio of ammonia in the liquid phase and pH. As shown in Figure 1, the abundance ratio of ammonia in the liquid phase increases significantly, with a pH of approximately 9.2 as the inflection point.

[0028] When 0.5 g of the ammonia generator is immersed in 10 g of water for 30 hours, the ammonia concentration in the liquid phase is 0.15 mmol / dm ３ It is preferable that the concentration is about 0.18 mmol / dm or more. ３ More preferably, it is about 0.21 mmol / dm or more. ３ It is more preferable that the ammonia generating agent has a concentration of 0.3 mmol / dm or more. This allows the ammonia generating agent to exhibit a high antimicrobial effect. ３This ensures high safety for the living body when the ammonia generating agent is buried in the living body or used to process components to be returned to or administered to the living body.

[0029] It is preferable that the concentration of ammonia in the liquid phase is sufficiently high from the initial stage when the immersion of the ammonia generating agent in water is started. Specifically, when 0.5 g of the ammonia generating agent is immersed in 10 g of water for 7 hours, the concentration of ammonia in the liquid phase is 0.1 mmol / dm ３ It is preferable that the concentration is about 0.15 mmol / dm or more. ３ More preferably, it is about 0.2 mmol / dm or more. ３ This allows the ammonia generator to exhibit good antimicrobial effects from the initial stage of use.

[0030] When 0.5 g of the ammonia generator is immersed in 10 g of water for 800 minutes, the pH of the liquid phase is preferably about 8 or higher, more preferably about 8.3 or higher, and even more preferably about 8.6 or higher. In this case, the ammonia generator generates ammonia over a long period of time, thereby maintaining a high level of antimicrobial effect. The upper limit of the pH of the liquid phase is preferably slightly lower than the pH at the inflection point where the ratio of ammonia in the liquid phase changes significantly when boron nitride is immersed in water. In this case, it is possible to prevent the ammonia concentration in the liquid phase from becoming too high. Therefore, when the ammonia generator is buried in a living organism or used to treat a component to be returned to or administered to a living organism, high safety for the living organism can be more reliably ensured.

[0031] It is preferable that the pH of the liquid phase does not fluctuate significantly from the initial stage when the ammonia generator is immersed in water. Specifically, when 0.5 g of the ammonia generator is immersed in 10 g of water for 200 minutes, the pH of the liquid phase is preferably about 8 or higher, more preferably about 8.3 or higher, and even more preferably about 8.6 or higher. This allows the ammonia generator to maintain a high ammonia concentration in the liquid phase from the initial stage of use, thereby enabling the antimicrobial effect to be exhibited satisfactorily.

[0032] When 0.5 g of the ammonia generator was immersed in 10 g of water for 300 minutes, the boron concentration in the liquid phase (pH 9) was 0.01 mol / dm ３ It is preferable that the concentration is about 0.03 mol / dm or more. ３ More preferably, it is about 0.05 mol / dm or more. ３ The concentration of boron in the liquid phase is preferably 0.1 mol / dm or more. ３ or less. If the boron concentration in the liquid phase is within the above range, it can be considered that the surface of the boron nitride is sufficiently exposed to the liquid phase. Therefore, the ammonia generator generates ammonia for a long period of time, and can maintain a high antimicrobial effect. The pH of the liquid phase may be adjusted with a pH adjuster such as an aqueous hydrogen chloride solution (hydrochloric acid) or nitric acid.

[0033] Such an ammonia generating agent (i.e., boron nitride particles with low crystallinity) can be produced, for example, as follows. One embodiment of a method for producing an ammonia generating agent comprises a first step of preparing a mixture, a second step of obtaining amorphous boron nitride, a third step of adjusting the crystallinity of the boron nitride, and a fourth step of post-treating the boron nitride after the crystallinity has been adjusted. First, in the first step, a mixture is prepared that contains a boron-containing compound and a nitrogen-containing compound (hereinafter, the "boron-containing compound" and the "nitrogen-containing compound" may be collectively referred to as "starting materials"), and a sintering aid, such as an alkali metal compound and / or an alkaline earth metal, that promotes the conversion of the starting materials to boron nitride during firing.

[0034] Next, in the second step, the mixture is fired at a first firing temperature in an inert atmosphere such as nitrogen, helium, or argon, and / or an ammonia atmosphere, to obtain amorphous boron nitride. Then, in the third step, the obtained amorphous boron nitride is further fired at a second firing temperature in an inert atmosphere such as nitrogen, helium, or argon, and / or an ammonia atmosphere, to adjust the crystallinity of the boron nitride. Finally, in the fourth step, the obtained boron nitride is washed with a washing solution to remove impurities, and then dried.

[0035] The mixture may contain other components in addition to the starting materials and sintering aids, as necessary, within the scope of the present invention. Examples of other components include simple substances and compounds. Specific examples of the simple substances and compounds include reducing substances such as carbon. Examples of boron-containing compounds include boric acid, boron oxide, and borax, with boric acid being preferred. Examples of nitrogen-containing compounds include cyandiamide, melamine, and urea, with melamine being preferred. The boron-containing compound and the nitrogen-containing compound may each be used alone or in combination of two or more of the above compounds.

[0036] The molar ratio of boron atoms to nitrogen atoms contained in the starting materials does not necessarily have to be fixed at 5:5. The molar ratio of boron atoms to nitrogen atoms can be appropriately changed, preferably within a range of about 2:8 or more and about 8:2 or less, more preferably within a range of about 3:7 or more and about 7:3 or less, depending on their reactivity and yield. The sintering aid may be mixed with amorphous boron nitride instead of the starting materials, or may be mixed with both the starting materials and amorphous boron nitride. That is, prior to the third step, a sintering aid that promotes the conversion of the starting materials to boron nitride may be mixed with the starting materials and / or amorphous boron nitride.

[0037] Examples of sintering aids include oxides or carbonates of alkali metals such as lithium, sodium, and potassium, and oxides or carbonates of alkaline earth metals such as calcium and strontium. The content of the sintering aid is preferably 0.9 parts by mass or more and 20 parts by mass or less per 100 parts by weight of the starting material or amorphous boron nitride. The compounds used as sintering aids may be used alone or in combination of two or more types.

[0038] The first firing temperature is preferably about 600° C. or higher and 1300° C. or lower, and more preferably about 800° C. or higher and 1200° C. or lower. By setting the first firing temperature to the above lower limit or higher, it is possible to promote the conversion of the mixture into amorphous boron nitride, and to reduce the amount of unreacted starting materials (e.g., boron-containing compounds, etc.). On the other hand, by setting the first firing temperature to the above upper limit or lower, it is possible to prevent the B that contributes to the formation of boron nitride from being released. ２ O ３ This can prevent the reduction of oxides and sintering aids such as those mentioned above, and promote grain growth and crystallization of boron nitride.

[0039] The second firing temperature is preferably about 1500°C or higher and 2200°C or lower, more preferably about 1600°C or higher and 1900°C or lower, and even more preferably about 1700°C or higher and 1800°C or lower. By setting the second firing temperature within the above range, excessive grain growth of boron nitride can be suppressed while the crystallinity of the amorphous boron nitride is easily increased. The first and second firing temperatures may be held constant or may be changed continuously or discontinuously. There are no limitations on the heating rate during heating and the cooling rate during cooling.

[0040] The holding time at the first firing temperature (first firing time) is preferably about 0.5 hours or more, and more preferably about 1 hour or more. By holding the first firing temperature for the above period, conversion to amorphous boron nitride can be promoted and the amount of remaining starting materials (e.g., boron-containing compounds, etc.) can be reduced. As a result, grain growth and crystallization of boron nitride can also be promoted. The holding time at the second firing temperature (second firing time) is preferably about 2 hours or more, and more preferably about 4 hours or more. By holding the second firing temperature for the above period, firing can proceed insufficiently, and grain growth and crystallization of boron nitride can be promoted.

[0041] If the amorphous boron nitride obtained in the second step has the desired crystallinity and / or graphitization index, the third step may be omitted. There are no particular limitations on the container for storing the mixture and amorphous boron nitride, etc., and the firing apparatus (e.g., a heating apparatus, etc.). For example, a container made of boron nitride can be used as the container. For example, a firing furnace using an electric heater can be used as the heating apparatus. The above-described method for producing boron nitride may further include steps of heating, cooling, humidifying, drying, and washing, within the scope of the object of the present invention, from the preparation of the mixture to the completion of firing the mixture.

[0042] Since boron nitride with enhanced crystallinity is generally extracted in the form of a block-shaped solid (lump), it is preferable to pulverize this. That is, in one embodiment of the method for producing an ammonia generator, it is preferable to include a step of pulverizing the boron nitride lump between the third step and the fourth step. By such pulverization, the average particle size, etc. of the boron nitride can be adjusted. For example, a glow mill, a jet mill, a super micron mill, etc. can be used as the pulverizer. When using, for example, a jet mill to pulverize boron nitride, the feed rate can be increased and the pulverization pressure can be set to an appropriately low condition. By setting such conditions, the average particle size of the obtained boron nitride can be made appropriate.

[0043] The crushed boron nitride may contain impurities other than boron nitride or water-soluble boron compounds (hereinafter, these may be collectively referred to as "impurities, etc."). Therefore, it is preferable to remove the impurities, etc. by washing with a washing liquid, followed by solid-liquid separation and drying to finally obtain boron nitride. As the washing liquid, an aqueous solution containing an acidic substance, an organic solvent, or a mixture of an organic solvent and water can be suitably used. Examples of acidic substances include inorganic acids such as hydrochloric acid and nitric acid. Examples of organic solvents include water-soluble organic solvents such as methanol, ethanol, propanol, isopropanol, and acetone.

[0044] In order to avoid secondary contamination with impurities, it is preferable to use water having an electrical conductivity of about 1 mS / m or less as the diluent for solid-liquid separation after washing. From the viewpoints of cost and waste liquid treatment, it is better to use a small amount of diluent for solid-liquid separation. However, if the amount is too small, impurities and the like will remain in the boron nitride. Therefore, the amount of diluent per kg of boron nitride is preferably about 300 times or less, more preferably about 250 times or less, and even more preferably about 200 times or less. When solid-liquid separation is performed after washing and then drying is performed, the method of solid-liquid separation is not particularly limited, and for example, decantation, a suction filter, a pressure filter, a rotary filter, a sedimentation separator, or a device combining these can be used.

[0045] There are no particular limitations on the method for drying the boron nitride powder after solid-liquid separation. Usable drying devices include, for example, a tray dryer, a fluidized bed dryer, a spray dryer, a rotary dryer, a belt dryer, or a combination thereof. The ambient temperature inside the dryer is preferably about 30°C or higher and 300°C or lower, and more preferably about 30°C or higher and 200°C or lower. Washing, solid-liquid separation, and drying may each be performed once, or may be performed multiple times using the same method or a combination of different methods.

[0046] As described above, the ammonia generating agent may use a combination of boron nitride and silicon nitride. That is, the ammonia generating agent may contain boron nitride and silicon nitride. Here, when silicon nitride is used as the ammonia generating agent, the following reaction occurs on the surface and its periphery due to contact with water (immersion in water). (X) Si ３ N ４ +6H ２ O ⇒ 3SiO ２ +4NH ３ (Y) NH ３ +H ２ O ⇔ NH ４ ＋ +OH － (Z) SiO ２ +2H ２ O ⇔ Si(OH) ４

[0047] When the ammonia generating agent comes into contact with water, ammonia (NH ３ ) is generated, and then ammonium ions (NH ４ ＋ ) is generated. This causes the pH of the liquid phase around the ammonia generating agent to increase. In addition, silicon dioxide (SiO ２ ) is deposited on the surface of the silicon nitride. This deposited silicon dioxide is converted into silicic acid (Si(OH)) according to reaction equation (Z). ４ ) and dissolves in water.

[0048] In a high pH environment, the reaction of reaction formula (Z) occurs, removing silicon dioxide from the silicon nitride surface, exposing the silicon nitride surface to the liquid phase. This causes the reaction of reaction formula (X) to occur again. In this way, the reaction of reaction formula (X) and the reactions of reaction formulas (Y) and (Z) occur repeatedly, generating ammonia and ammonium ions.

[0049] However, the reaction of reaction formula (Z) takes several days. Therefore, when silicon nitride is used as the ammonia generating agent, ammonia is generated in a short period of time, but the amount of ammonia generated decreases due to the deposition of silicon dioxide on the surface of the silicon nitride. After several days have passed, the surface of the silicon nitride is again exposed to the liquid phase, generating ammonia in a short period of time, and then the amount of ammonia generated decreases in the same manner as above. In other words, when silicon nitride is used as the ammonia generating agent, the concentration of ammonia in the liquid phase periodically increases.

[0050] The alpha conversion rate of silicon nitride is preferably about 85% or more, more preferably about 90% or more, even more preferably about 95% or more, and may be 100%. By using silicon nitride with such an alpha conversion rate, the periodicity of the increase in the ammonia concentration in the liquid phase can be made clearer. Therefore, by using boron nitride and silicon nitride in combination as an ammonia generator, ammonia can be generated stably over a long period of time and the amount of ammonia generated can be periodically increased. An ammonia generator having such properties is suitable for applications requiring antimicrobial properties (antibacterial properties, antiviral properties, etc.).

[0051] In this case, the mass ratio of boron nitride to silicon nitride is preferably about 1:9 or more and 9:1 or less, more preferably about 3:7 or more and 8:2 or less, and even more preferably about 4:6 or more and 7:3 or less. This allows ammonia to be generated stably over a long period of time, and the effect of periodically increasing the amount of ammonia generated is fully exhibited. The ammonia generating agent and the method for producing the ammonia generating agent of the present invention have been described above, but the ammonia generating agent and the method for producing the ammonia generating agent of the present invention are not limited to the above embodiments. For example, when the ammonia generating agent is used for purposes other than as an antimicrobial agent (e.g., for recovering as much ammonia as possible), there are no particular restrictions on the lower limit of the crystallinity, the upper limit of the graphitization index, etc. Furthermore, the ammonia generating agent may be provided in each of the following aspects.

[0052] (1) An ammonia generating agent that generates ammonia upon contact with water molecules, the ammonia generating agent containing boron nitride having a crystallinity of 90% or less.

[0053] (2) An ammonia generating agent that generates ammonia upon contact with water molecules, the ammonia generating agent containing boron nitride having a graphitization index of 1.5 or more.

[0054] (3) The ammonia generating agent according to (1) or (2) above, wherein the oxygen content in the boron nitride is 0.5 atomic % or more.

[0055] (4) The ammonia generating agent according to any one of (1) to (3) above, wherein the content of the boron nitride in the ammonia generating agent is 80 mass % or more.

[0056] (5) The ammonia generating agent according to any one of (1) to (4) above, wherein the ammonia generating agent is in a particulate form and has a volume average particle diameter of 10 μm or less.

[0057] (6) In the ammonia generating agent according to any one of (1) to (5) above, the BET specific surface area of ​​the ammonia generating agent is 10 m ２ / g or more.

[0058] (7) In the ammonia generating agent according to any one of (1) to (6) above, when 0.5 g of the ammonia generating agent is immersed in 10 g of water for 30 hours, the concentration of ammonia in the liquid phase is 0.15 mmol / dm ３ This is the ammonia generator.

[0059] (8) The ammonia generating agent according to any one of (1) to (7) above, wherein when 0.5 g of the ammonia generating agent is immersed in 10 g of water for 800 minutes, the pH of the liquid phase is 8 or higher.

[0060] (9) In the ammonia generating agent according to any one of (1) to (8) above, when 0.5 g of the ammonia generating agent is immersed in 10 g of water for 300 minutes, the concentration of boron in the liquid phase (pH 9) is 0.01 mol / dm ３This is the ammonia generator.

[0061] (10) The ammonia generating agent according to any one of (1) to (9) above, further containing silicon nitride.

[0062] (11) The ammonia generating agent according to (10) above, wherein the silicon nitride has an alpha conversion rate of 85% or more.

[0063] (12) The ammonia generating agent according to any one of (1) to (11) above, wherein the ammonia generating agent is used as an antimicrobial agent.

[0064] (13) A method for producing an ammonia generating agent according to any one of (1) to (12) above, comprising: a first step of preparing a mixture containing a boron-containing compound and a nitrogen-containing compound as a starting material; a second step of firing the mixture at a first firing temperature in an inert atmosphere and / or an ammonia atmosphere to obtain amorphous boron nitride; a third step of firing the amorphous boron nitride at a second firing temperature in an inert atmosphere and / or an ammonia atmosphere to adjust the crystallinity of the boron nitride; and a fourth step of performing post-treatment on the boron nitride after the crystallinity adjustment.

[0065] (14) In the method for producing an ammonia generating agent described in (13) above, prior to the third step, a sintering aid that promotes conversion of the starting material to boron nitride is mixed with the starting material and / or the amorphous boron nitride.

[0066] (15) The method for producing an ammonia generating agent according to (13) or (14) above, further comprising a step of pulverizing the agglomerates of boron nitride between the third step and the fourth step. Of course, the method is not limited to this.

[0067] Finally, while various embodiments of the present disclosure have been described, they are presented as examples and are not intended to limit the scope of the invention. The novel embodiments may be embodied in various other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. Such embodiments and modifications are intended to be included within the scope and spirit of the invention, as well as within the scope of the inventions and their equivalents as defined in the claims.

[0068] The present invention will be described in more detail below using the following examples and comparative examples, but the present invention is not limited to the following examples.

[0069] 1. Production of Ammonia Generator (Example 1) First, as starting materials, 200 g of boric acid powder (manufactured by Kanto Chemical Co., Inc., purity: 99.8% by mass or more) and 180 g of melamine powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity: 99.0% by mass or more) were weighed and mixed for 10 minutes using an alumina mortar. The produced powder mixture (mixed powder) was then placed in a small vibration humidifying dryer (manufactured by Chuo Kakoki Co., Ltd., "VH90") and dried for 6 hours at a temperature of 80°C and a relative humidity of 85% RH.

[0070] Next, the dried powder mixture was placed in a hexagonal boron nitride container (internal volume: 1.4 L), and this container was placed in an electric furnace (manufactured by Tokai Konetsu Kogyo Co., Ltd., "TV-200") with a furnace chamber volume of 16 L. Then, while supplying nitrogen gas into the furnace chamber at a flow rate of 16 L / min (volume at 25°C), the temperature was increased from room temperature at a heating rate of 10°C / min and held at 1000°C (first firing temperature) for 2 hours. Thereafter, heating was stopped and the mixture was allowed to cool naturally. When the temperature inside the furnace chamber had dropped to 100°C or below, the electric furnace was opened and amorphous boron nitride (before pulverization) was recovered.

[0071] Next, 100 parts by mass of the resulting amorphous boron nitride powder was blended with 10 parts by mass of calcium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity: 99.5% by mass or higher) as an auxiliary component, and the mixture was mixed in an alumina mortar for 10 minutes. The mixture was then placed in the electric furnace. While supplying nitrogen gas into the furnace at a flow rate of 16 L / min (volume at 25°C), the temperature was increased at a rate of 10°C / min until the maximum firing temperature reached 1750°C (second firing temperature), at which point the temperature was maintained for 4 hours. The heating was then stopped and the mixture was allowed to cool naturally. When the temperature dropped to 100°C or below, the electric furnace was opened and the boron nitride (before pulverization) was recovered.

[0072] The obtained boron nitride (before grinding) was then ground in a Super Micron Mill ("M52NC" manufactured by Hosokawa Micron Corporation) to obtain boron nitride powder. Boron nitride was fed into the Super Micron Mill at a feed rate of 10 kg / hour, and processing was carried out at a grinding pressure of 0.7 MPa. The ground boron nitride powder was recovered from a bag filter.

[0073] Next, to remove impurities and the like contained in the boron nitride powder obtained by pulverization, 40 kg of boron nitride was mixed with 20 L of 67 mass% diluted nitric acid and 390 L of water, and the mixture was stirred and washed at room temperature for 60 minutes. Subsequently, solid-liquid separation was performed using a continuous pressure filtration device ("RF-2.5" manufactured by Hiroshima Metal & Machinery Co., Ltd.), and before complete solid-liquid separation, 275 times the amount of water per 1 kg of boron nitride was added for dilution. Then, solid-liquid separation was completed. The powder after solid-liquid separation was dried in a dryer at 170°C for 12 hours to obtain the boron nitride powder (ammonia generator) of Example 1.

[0074] Example 2 A boron nitride powder (ammonia generating agent) of Example 2 was produced in the same manner as in Example 1, except that the auxiliary component added during the second firing was changed to sodium carbonate.

[0075] Comparative Example 1 A boron nitride powder (ammonia generating agent) of Comparative Example 1 was produced in the same manner as in Example 1, except that the maximum value of the second firing temperature was changed to 1900°C.

[0076] (Reference Example 1) First, the air in the vertical reactor was replaced with nitrogen gas, and then liquid ammonia and toluene were introduced. At this time, the liquid ammonia and toluene separated into upper and lower layers, respectively, in the vertical reactor. Next, a toluene solution containing silicon tetrachloride at a concentration of 20% by mass to 35% by mass, with the remainder being toluene, was slowly fed through a conduit attached to the vertical reactor into the stirred lower layer. Upon feeding the toluene solution, a white reaction product (silicon diimide) precipitated near the interface between the upper and lower layers. After the reaction was completed, the reaction solution in the vertical reactor was transferred to a filtration tank, and the product was filtered out. The filtered product was washed with liquid ammonia to purify the silicon diimide. Next, the silicon diimide was heated to approximately 1500°C in a nitrogen atmosphere and decomposed to obtain silicon nitride powder. This was used as the silicon nitride powder (ammonia generator) of Reference Example 1.

[0077] (Reference Example 2) First, a powder of silicon elemental material having a volume average particle size of 5 μm and a powder of silicon nitride having a volume average particle size of 0.1 μm were weighed out so that the molar ratio was 2:0.4. These powders were mixed in methanol for 12 hours using silicon nitride balls and a polyethylene container to obtain a slurry. Next, the obtained slurry was filtered and separated, and then vacuum dried at 100 ° C to obtain a premixed powder. Approximately 10 g of the premixed powder was filled into a porous refractory container, and then combustion synthesis was carried out in a nitrogen atmosphere at 10 MPa using a high-pressure container of a HIP apparatus.

[0078] The loaded powder was ignited by igniting a 20 mm diameter Ti pellet placed on top of the powder with a ribbon-shaped carbon heater for several seconds, using the heat generated by the self-combustion of Ti as it nitrided. The product produced by combustion was significantly agglomerated due to the high temperature during combustion synthesis. Furthermore, the particles contained in the product also showed grain growth. Next, approximately 100 g of the product was wet-milled in methanol for 72 hours using silicon nitride balls and a polyethylene container to obtain a slurry. This slurry was filtered and separated, and the resulting solid was vacuum-dried at 100°C to obtain silicon nitride powder.

[0079] Furthermore, this silicon nitride powder was pulverized using a planetary ball mill ("PM100" manufactured by Retsch). The pulverization time was 60 minutes. The pulverized silicon nitride powder was used as the silicon nitride powder (ammonia generator) of Reference Example 2.

[0080] 2. Measurement and Evaluation 2-1. Measurement of the Contents of Boron Nitride and Silicon Nitride in the Ammonia Generating Agent The contents of boron nitride and silicon nitride in the ammonia generating agent were measured using a gas substitution method (Micromeritics, Inc., "Dry Automatic Density Meter Accupyc II1340"). The true density of boron nitride is 2.26 g / cm ３ and the true density of silicon nitride is 3.17 g / cm ３ Therefore, the true density of the ammonia generating agent of this combination is 2.26 g / cm ３ 3.17g / cm or more ３ The ratio can be determined based on the true density value. Whether the ammonia generating agent contains components other than boron nitride and silicon nitride can be determined by analyzing the diffraction pattern of X-ray diffraction to reveal the presence of third or more components. The measurement results are shown in Table 1.

[0081] 2-2. Measurement of the alpha phase ratio of silicon nitride The alpha phase ratio of silicon nitride was measured by the following procedure. X-ray diffraction of silicon nitride was performed using an X-ray diffractometer (Rigaku Corporation, "Ultima IV") with CuKα radiation. The alpha phase was determined by the diffraction intensity I of the (102) plane. ａ１０２ and (210) plane diffraction intensity I ａ２１０ The β phase has a diffraction intensity of I ｂ１０１ and (210) plane diffraction intensity I ｂ２１０ Using these diffraction line intensities, the gelatinization rate was calculated by the following formula: Gelatinization rate (%) = (I ａ１０２ +I ａ２１０ ) / (I ａ１０２ +I ａ２１０ +I ｂ１０１ +I ｂ２１０ ) x 100 The measurement results are shown in Table 1.

[0082] 2-3. Measurement of Crystallinity The crystallinity of the ammonia generating agent (boron nitride powder) obtained in each Example and Comparative Example was calculated from the measurement results obtained by wide-angle X-ray scattering. Specifically, the ammonia generating agent obtained in each Example and Comparative Example was measured using a wide-angle X-ray scattering measurement device (Rigaku Corporation, "Ultima-IV"). Then, a one-dimensional profile (diffraction data) was created from the obtained measurement results using data analysis software, and the crystallinity (%) was calculated from the diffraction data based on the following formula: Crystallinity (%) = [peak area showing crystalline region / (peak area showing crystalline region+peak area showing amorphous region)] × 100. The measurement results are shown in Table 1.

[0083] 2-4. Measurement of Graphitization Index The graphitization index of the ammonia generating agent (boron nitride powder) obtained in each Example and Comparative Example was calculated from the measurement results obtained by powder X-ray diffraction. In the obtained X-ray diffraction spectrum, the integrated intensity of each diffraction peak corresponding to the (100), (101), and (102) planes of the primary particles of boron nitride (i.e., each diffraction peak) and its baseline were calculated (arbitrary units), and these were designated S100, S101, and S102, respectively. Using the area values ​​calculated in this way, the graphitization index was calculated based on the following formula: G.I. = (S100 + S101) / S102. The measurement results are shown in Table 1.

[0084] 2-5. Measurement of Oxygen Content First, 0.01 g of the ammonia generating agent obtained in each Example, Comparative Example, and Reference Example and 0.01 g of carbon powder were placed in an oxygen / nitrogen analyzer ("EMGA-920" manufactured by Horiba, Ltd.). Next, the temperature was increased from 20°C to 2400°C at a rate of 8°C / sec in a helium gas atmosphere. Then, the oxygen and nitrogen generated as the temperature increased were detected. The surface oxygen amount and the internal oxygen amount were determined from the respective peak areas resulting from the desorption of surface oxygen and internal oxygen, and the oxygen content was calculated based on the sum of these values. The measurement results are shown in Table 1.

[0085] 2-6. BET Specific Surface Area The BET specific surface area was measured for the ammonia generating agents obtained in each of the Examples, Comparative Examples, and Reference Examples. The BET specific surface area was measured by the BET single-point method using nitrogen gas in accordance with JIS Z 8830:2013 "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption." The measurement results are shown in Table 1.

[0086] 2-7. Particle size distribution The particle size distribution of the ammonia generators obtained in each of the Examples, Comparative Examples, and Reference Examples was measured by a laser diffraction / scattering method. The measurement was carried out in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - Laser diffraction / scattering method." In the particle size distribution (cumulative distribution) shown with the horizontal axis representing particle size [μm] on a logarithmic scale and the vertical axis representing frequency [volume %], the particle size at which the cumulative value from the smallest particle size reached 50% of the total was defined as the volume average particle size (D ５０ The measurement results are shown in Table 1.

[0087] 2-8. Measurement of ammonia concentration in the liquid phase 10 g of distilled water was placed in a 50 mL vial. 0.5 g of the ammonia generator obtained in each Example, Comparative Example, and Reference Example was placed in this vial and stirred for 30 seconds to obtain a dispersion. Thereafter, the lid of the vial was closed, and the dispersion was left to stand at room temperature (20°C). Then, after a predetermined time had elapsed, the liquid phase was sampled, and the ammonia concentration in the liquid phase was quantified using an ion chromatograph (manufactured by Thermo Fisher Scientific, "ICS-2100"). The measurement results are shown in Table 2.

[0088] 2-9. Measurement of pH of liquid phase 10 g of distilled water was placed in a 50 mL vial. 0.5 g of the ammonia generator obtained in each Example, Comparative Example, and Reference Example was placed in this vial and stirred for 30 seconds to obtain a dispersion. Thereafter, the lid of the vial was closed, and the dispersion was left at room temperature (20°C). Then, after a predetermined time had elapsed, the pH of the liquid phase was measured using a pH meter (manufactured by Mettler Toledo K.K., "FP20-Std-Kit"). The measurement results are shown in Table 3.

[0089] 2-10. Measurement of boron or silicon concentration in liquid phase 10 g of distilled water was placed in a 50 mL vial. 0.5 g of the ammonia generator obtained in each Example and Comparative Example was placed in this vial and stirred for 30 seconds to obtain a dispersion. Thereafter, the lid of the vial was closed, and the dispersion was left to stand at room temperature (20°C) for 300 minutes. After standing for 300 minutes, the boron concentration in the liquid phase at pH 9 was quantified using an ICP-MS device (Agilent Technologies, Inc., "Agilent 8800"). Furthermore, for the ammonia generators obtained in each Reference Example, the dispersion was left to stand at room temperature (20°C) for 3 weeks, and then the silicon concentration in the liquid phase at pH 9 was quantified in the same manner. The measurement results are shown in Table 1.

[0090] 2-11. Evaluation of antimicrobial activity Staphylococcus aureus was pre-cultured in BHI liquid medium to prepare a bacterial suspension (1 x 10 ５ CFU / mL or more 1×10 ６ CFU / mL or less) was prepared. 0.15 g of the ammonia generator obtained in each Reference Example and 1 mL of distilled water were placed in a microtube to obtain a 15 w / v% dispersion. After sterilization with ultraviolet light, 1 mL of the bacterial suspension was added to the microtube. After mixing for 5 minutes with a tube rotator at room temperature (approximately 20°C), the supernatant was collected and the bacterial survival rate was measured by WST-8 assay (absorbance 450 nm). The survival rate was also measured in the same manner when Staphylococcus epidermidis or Escherichia coli was used as the bacteria. The evaluation results are shown in Table 4. In Table 4, the survival rate results when no ammonia generator was used are shown in the "ref." column.

[0091]

[0092]

[0093]

[0094]

[0095] As shown in Table 4, the ammonia generators obtained in each Example and each Reference Example exhibited excellent antimicrobial properties. As shown in Table 2, the ammonia generators obtained in each Example, which released much more ammonia into the liquid phase than the ammonia generators obtained in each Reference Example at 0 hours, exhibited sufficiently high antimicrobial properties (see Table 4). In particular, the ammonia generators obtained in each Example released ammonia into the liquid phase over a long period of time (see Table 2) and maintained excellent antimicrobial properties (see Table 4).

[0096] Furthermore, the ammonia concentration in the liquid phase tends to increase again after about 48 hours for both the ammonia generating agents obtained in Reference Examples 1 and 2. Therefore, it is believed that when used in combination with the ammonia generating agents obtained in each Example at a predetermined mass ratio, ammonia can be generated stably over a long period of time and the amount of ammonia generated can be periodically increased.

Claims

1. An ammonia generator that generates ammonia upon contact with water molecules, the ammonia generator containing boron nitride having a crystallinity of 90% or less.

2. An ammonia generator that generates ammonia upon contact with water molecules, the ammonia generator containing boron nitride having a graphitization index of 1.5 or more.

3. The ammonia generator according to claim 1 or claim 2, wherein the oxygen content in the boron nitride is 0.5 atomic% or more.

4. The ammonia generator according to any one of claims 1 to 3, wherein the content of the boron nitride in the ammonia generator is 80% by mass or more.

5. The ammonia generator according to any one of claims 1 to 4, wherein the ammonia generator is in particulate form and has a volume average particle diameter of 10 μm or less.

6. In the ammonia generating agent according to any one of claims 1 to 5, the BET specific surface area of the ammonia generating agent is 10 m ２ / g or more, the ammonia generating agent.

7. In the ammonia generator according to any one of claims 1 to 6, when 0.5 g of the ammonia generator is immersed in 10 g of water for 30 hours, the concentration of ammonia in the liquid phase is 0.15 mmol / dm ３ or more. Ammonia generator.

8. The ammonia generator according to any one of claims 1 to 7, wherein when 0.5 g of the ammonia generator is immersed in 10 g of water for 800 minutes, the pH of the liquid phase is 8 or more.

9. In the ammonia generator according to any one of claims 1 to 8, when 0.5 g of the ammonia generator is immersed in 10 g of water for 300 minutes, the concentration of boron in the liquid phase (pH 9) is 0.01 mol / dm ３ or more. Ammonia generator.

10. The ammonia generator according to any one of claims 1 to 9, further containing silicon nitride.

11. The ammonia generator according to claim 10, wherein the α - conversion rate of the silicon nitride is 85% or more.

12. The ammonia generator according to any one of claims 1 to 11, wherein the ammonia generator is used as an antimicrobial agent.

13. A method for producing an ammonia generator according to any one of claims 1 to 12, comprising: a first step of preparing a mixture containing a boron - containing compound and a nitrogen - containing compound as starting materials; a second step of firing the mixture at a first firing temperature in an inert atmosphere and / or an ammonia atmosphere to obtain amorphous boron nitride; a third step of firing the amorphous boron nitride at a second firing temperature in an inert atmosphere and / or an ammonia atmosphere to adjust the crystallinity of the boron nitride; and a fourth step of performing a post - treatment on the boron nitride after adjusting the crystallinity.

14. In the method for producing an ammonia generating agent according to claim 13, prior to the third step, a sintering aid that promotes the conversion of the starting material into boron nitride is mixed with the starting material and / or the amorphous boron nitride. A method for producing an ammonia generating agent.

15. In the method for producing an ammonia generating agent according to claim 13 or claim 14, a step of pulverizing the mass of boron nitride is provided between the third step and the fourth step. A method for producing an ammonia generating agent.

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