Low-temperature aqueous suspension composition for inhibiting hydration reaction and powder molded body manufactured using same

Abstract

The present invention relates to a composition and a powder molded body prepared from the composition, wherein, in preparing a suspension of powder that undergoes a hydration reaction upon contact with water or moisture, the hydration reaction is minimized by performing a grinding-mixing process at a low temperature, thus enabling the composition to form a stable aqueous suspension having a low viscosity enabling spraying or slip casting.

Description

Low-temperature aqueous suspension composition that inhibits hydration reaction and powder molded body prepared using the same

[0001] The present invention relates to a composition capable of forming a stable aqueous suspension having low viscosity suitable for spraying or slip casting by minimizing the hydration reaction during a grinding-mixing process at low temperature, in preparation of a powder suspension that undergoes a hydration reaction upon contact with water or moisture, and to a powder molded body prepared from the composition.

[0002] Molding methods for ceramic powder materials can be broadly classified into dry molding and wet molding methods. Dry ceramic molding methods, such as powder press molding, are widely used in ceramic manufacturing processes due to their excellent economic efficiency and mass production capabilities, as well as the advantages of being easy to make large molded bodies and easy to control quality. In addition, wet molding methods, such as slip casting or tape casting, are highly advantageous for manufacturing molded bodies of complex shapes or very thin plate-like bodies.

[0003] In manufacturing such a molded body, a common prerequisite step is the process of preparing a suspension of raw material powder. For example, in dry molding, a molded body is manufactured by press molding using granules prepared by spray-drying a suspension of raw material powder, and in wet molding, the molded body is manufactured by pouring the suspension directly into a porous mold or by applying it thinly onto a polymer film.

[0004] However, some ceramic raw material powders (MgO, CaO, BaO, AlN, etc.) have a problem in that they change into hydroxides with completely different crystal structures and chemical formulas due to hydration reactions when in contact with water or moisture. For example, magnesium oxide has a problem in that a hydration reaction of MgO + H2O = Mg(OH)2 occurs when it comes into contact with moisture or water, which makes it impossible to use water, which is the most commonly used solvent for preparing suspensions in the conventional ceramic spray drying process. To overcome this problem, existing technology adopts a method using non-aqueous suspensions that use alcohol-based solvents instead of water as the solvent for preparing suspensions.

[0005] However, in processes using non-aqueous suspensions containing organic solvents, explosion-proof (spray) dryers are used for safety during granule manufacturing—specifically to prevent explosions of suspensions composed of flammable organic solvents. These explosion-proof spray dryers are more expensive than those used in water-based (spray) drying processes. Furthermore, the cost of high-purity organic solvents, which are consumed in large quantities during mass production, is significantly higher than that of distilled water used in water-based processes. Moreover, since most organic solvents are hazardous to varying degrees depending on the type, water-based processes are preferable to non-aqueous ones whenever possible. Additionally, in the manufacture of ceramic powder bodies by slip casting, which is widely used in wet molding processes, production is very difficult using suspensions composed of organic solvents. Moreover, process control is extremely challenging, as workers are exposed to organic solvents for extended periods during drying, and the molded bodies have weak strength, leading to easy cracking.

[0006] Accordingly, the present invention has developed a stable aqueous suspension composition having low viscosity capable of spraying or slip casting and a process for manufacturing a powder molded body using the same by suppressing the hydration reaction through a grinding-mixing process at a low temperature when preparing an aqueous suspension of a raw material powder with hydration reactivity.

[0007] The present invention aims to produce a composition capable of forming a stable aqueous suspension of low viscosity that is suitable for spraying or slip casting, and a powder molded body produced from said composition, by minimizing the hydration reaction through a grinding-mixing process at a low temperature while preparing a powder suspension that undergoes a hydration reaction upon contact with water or moisture.

[0008] To achieve the above-mentioned purpose, the present invention provides a suspension composition comprising: an aqueous solvent; and one or more raw material powders selected from hydration-reactive metals, metal compounds, and non-metal powders, wherein the raw material powders are ground and mixed at a temperature of less than 25°C and the hydroxide content is within 20% by weight of the raw material powder.

[0009] In the present invention, the metal is one or more of Mg, Si, B, Al, and Ca; the metal compound is one or more of metal oxide, metal nitride, metal carbide, metal boride, metal silicide, and metal carbonate; and the nonmetal may be one or more of carbon, phosphorus, and sulfur.

[0010] In the present invention, the average particle size of the raw material powder may be 50 μm or less, and the specific surface area of ​​the raw material powder may be 150 m² / g or less.

[0011] In the present invention, the raw material powder may include lightly calcined magnesium oxide powder calcined at a temperature of 1000°C or lower.

[0012] In the present invention, the raw material powder may be included in an amount of 5 volume% or more relative to the total volume of the composition.

[0013] In the present invention, the viscosity of the suspension may be 5 Pa·S or less.

[0014] The suspension composition according to the present invention further comprises one or more water-resistant reactive agents selected from citric acid, tartaric acid, aminopolycarboxylate, polyphosphate, and eco-friendly chelating agents; the water-resistant reactive agent may be included in a range of 0.01 to 5 weight% relative to the weight of the raw material powder.

[0015] The suspension composition according to the present invention further comprises an aqueous solution of a basic compound; the aqueous solution of the basic compound is an aqueous solution of one or more of ammonia, calcium hydroxide, lithium hydroxide, potassium hydroxide, sodium hydroxide, and magnesium hydroxide; and the aqueous solution of the basic compound may be included in a range of 0.001 to 5 weight% relative to the weight of the raw material powder.

[0016] The suspension composition according to the present invention further comprises a dispersant or a surfactant; the dispersant or surfactant may be included in a range of 0.01 to 10 weight percent relative to the weight of the raw material powder.

[0017] In addition, the present invention provides granules formed from the above-described suspension composition, wherein the granules are spherical and the average particle size of the granules is 0.1 to 500 μm.

[0018] In addition, the present invention provides a molded body formed from the granules described above.

[0019] In addition, the present invention provides a method for preparing a suspension composition comprising the step of grinding and mixing the above-described solvent and raw material powder at a temperature of less than 25°C.

[0020] In the present invention, grinding and mixing may be one or more of ball milling, bead milling, attrition milling, planetary milling, high-energy milling, and ultrasonic treatment.

[0021] In addition, the present invention provides a method for manufacturing granules comprising the step of granulating the above-described suspension composition, wherein the granulation is one or more of spray drying, freeze drying, drying, crushing, and sieving.

[0022] In addition, the present invention provides a method for manufacturing a molded body comprising the step of molding the granules described above.

[0023] In addition, the present invention provides a method for manufacturing a sintered body comprising the step of making the granules described above into a granule form or a dry-molded powder molded body and sintering them to produce a dense ceramic sintered body.

[0024] In addition, the present invention provides a method for manufacturing a powder molded body, comprising the step of wet molding using the above-described suspension composition, wherein the wet molding is one or more of slip casting, pressure casting, solid casting, and tape casting.

[0025] The present invention has the advantage of enabling the mass production of hydration-reactive powder molded bodies in an environmentally friendly and low-cost economical manner through the preparation of a stable low-temperature aqueous suspension that suppresses the hydration reaction.

[0026] Figure 1 is a graph showing the hydration reaction rate over time during the mixing (slaking) process of an aqueous slurry containing 6 wt.% (1.8 vol.%) MgO.

[0027] Figure 2 is a graph showing the conversion rate of magnesium oxide to hydroxide according to hydration time, where A (●) is 36℃, B (△) is 46℃, and C (○) is 56℃.

[0028] Figure 3 is a scanning electron microscope image showing AlN and MgO granules prepared by the methods of (a) Example-1 and (b) Example-2, respectively, and a scanning electron microscope image of MgO granules prepared by the methods of (c) Example-2 and (d) Example-3 after sintering at 1350°C for 2 hours.

[0029] Figure 4 is the X-ray diffraction analysis pattern of AlN and MgO granules prepared by the method of (a) Example-1 and (b) Example-2.

[0030] Figure 5 is a graph showing the change in pH and viscosity of an aqueous MgO suspension according to ball-milling time.

[0031] Figure 6 shows Mg in an aqueous MgO suspension according to ball-milling time. 2+ and NH4 + This is a graph showing changes in ion concentration and viscosity.

[0032] The present invention will be described in detail below.

[0033] The present invention relates to a low-temperature aqueous suspension composition that inhibits hydration reactions. By adding a hydration-reactive raw material powder to an aqueous solvent at a high concentration and applying a process of grinding and mixing at a low temperature to inhibit the hydration reaction, the invention provides a stable suspension composition prepared such that the formation (content) of a hydrate (hydroxide) can be suppressed to within 20 weight% of the raw material powder. At this time, the grinding and mixing process may be performed at a low temperature, for example, less than 25°C, 20°C or less, 15°C or less, 12°C or less, or 10°C or less (0°C, 1°C, 3°C, or 5°C or more).

[0034] The suspension composition according to the present invention essentially comprises a solvent (water, etc.) and a raw material powder (MgO, AlN, etc.), preferably may additionally comprise a dispersant (surfactant), preferably may additionally comprise one of a water-resistant reactive agent (citric acid, etc.) and an aqueous solution of a basic compound (ammonia water, etc.), and optionally may additionally comprise a sintering aid (YF3, CaF2, TiO2, etc., 0.01 to 5 wt%), a sintering additive (La2O3, V2O5, etc., 0.01 to 1 wt%), and / or an antifoaming agent (0.001 to 0.1 wt%), etc.

[0035] The solvent is for forming a liquid vehicle and may be an aqueous solvent. The aqueous solvent may include one or more selected from various solvents including, for example, water (distilled water, etc.).

[0036] The solvent content is the remainder remaining after subtracting the total content of the remaining components, and may be, for example, 20 to 80 weight%, 25 to 70 weight%, or 30 to 60 weight% based on the total weight of the composition.

[0037] The raw material powder may be in the form of a powder as a main component of the suspension composition. The raw material powder may be one type (alone) or two or more types (combination) of a metal, a metal compound, or a non-metal powder.

[0038] The metal may be various metals (e.g., Fe, B, Al, Si, Mg, Co, Ni, Cu, Pd, Ag, In, Sn, Sb, Pt, Au, Ti, W, Ir, Mo, Nd, Ta, Ti, La, Ce, V, Cr, Zr, Pb, Bi, Li, Be, Na, Ca, Sr, Ba, Sc, Mn, Zn, Ga, Ge, Y, Nb, Ru, Rh, Sm, Gd), preferably Mg, Si, B, Al, Ca, etc.

[0039] Metal compounds can be ceramic powders such as, for example, metal oxides, metal nitrides, metal carbides, metal borides, metal silicides, metal carbonates, etc. Nonmetals can be, for example, carbon, phosphorus, sulfur, etc.

[0040] In particular, the raw material powder may be a hydration-reactive raw material powder that undergoes a hydration reaction upon contact with water or moisture, and specifically may be a hydration-reactive metal oxide such as MgO or a hydration-reactive metal nitride such as AlN.

[0041] The raw material powder may be composed of fine particles and may have an average particle size of, for example, 50 μm or less, 30 μm or less, 0.01 to 20 μm, 0.1 to 15 μm, or 1 to 10 μm. In addition, the raw material powder may have a specific surface area of, for example, 150 m² / g or less (0.1, 1, 10, 30, 50, 70, 100, or 120 m² / g or more).

[0042] The raw material powder may include lightly calcined magnesium oxide powder calcined at a temperature of 1000°C or lower. The lightly calcined raw material powder is an active powder made to have fine particle size and a large specific surface area by calcining at a low temperature, and has high reactivity and can be used to manufacture sintered bodies, etc.

[0043] The raw material powder may be included in a high concentration within the suspension composition. Specifically, the content of the raw material powder in the suspension may be, for example, 5 volume% or more, 10 to 60 volume%, 15 to 50 volume%, or 20 to 40 volume% relative to the total volume of the composition (solid content); and based on the total weight of the composition, it may be 20 to 80 weight%, 30 to 75 weight%, or 40 to 70 weight%.

[0044] The suspension may have a viscosity low enough to allow for spraying or wet molding, and the viscosity of the suspension may be, for example, 5 Pa·S or less, 2 Pa·S or less, 1 Pa·S or less, or 500 cP or less. The lower viscosity limit may be, for example, 1 cP, 2 cP, 3 cP, or 5 cP or more.

[0045] A hydration-resistant reactive agent (chelating agent) is intended to suppress hydration reactions that occur during processes such as grinding and mixing for the preparation of an aqueous suspension (slurry), and a hydration-resistant reactive suspension can be provided by using a hydration-resistant reactive agent. The hydration-resistant reactive agent may be used only for raw powders (such as MgO and AlN) that undergo hydration reactions, and may not be used for raw powders (such as SiC and BN) that do not undergo hydration reactions.

[0046] The hydration-resistant reactive agent is a chelating agent soluble in the above solvent, and may be, for example, one (alone) or two or more (combination) of citric acid, tartaric acid, aminopolycarboxylates, polyphosphates, and environmentally friendly chelating agents. As aminopolycarboxylates, for example, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), etc. may be used. As polyphosphates, for example, 1-hydroxyethylidene-1,1-diylbisphosphonic acid (HEDP), aminotrimethylethanolisphosphonic acid (ATMP), diethylenetriaminepentamethylenepentakisphosphonic acid (DTPMPA), etc. may be used. Examples of eco-friendly chelating agents that can be used include aspartic acid-N,N-diacetic acid (ASDA), glutamic acid-N,N-diacetic acid (GLDA), methylglycine diacetic acid (MGDA), ethylenediamine-N,N-disuccinic acid (EDDS), and iminodisuccinic acid (IDS).

[0047] The hydration-resistant reactive agent can dissolve in an aqueous solvent to form a liquid carrier. The content of the hydration-resistant reactive agent may be, for example, 0.01 to 5 wt%, 0.1 to 3 wt%, or 0.3 to 1 wt% relative to the weight of the raw powder; and based on the total weight of the composition, it may be 0.01 to 3 wt%, 0.05 to 2 wt%, or 0.1 to 0.5 wt%. The amount of hydroxide formed by the hydration reaction in the suspension may be suppressed by the hydration-resistant reactive agent to 20 wt% or less, 15 wt% or less, 10 wt% or less, or 5 wt% or less (0 wt% or more).

[0048] The aqueous solution of a basic compound is intended to suppress the increase in the concentration of metal cations that occurs during the grinding-mixing process of the raw material powder. The aqueous solution of a basic compound is a compound that can be dissolved in a solvent to provide hydroxyl ions, and may be, for example, an aqueous solution of one (alone) or two or more (combination) of ammonia, calcium hydroxide, lithium hydroxide, potassium hydroxide, sodium hydroxide, and magnesium hydroxide.

[0049] The content of the aqueous solution of the basic compound may be, for example, 0.001 to 5 weight%, 0.01 to 4.5 weight%, 0.1 to 4 weight%, or 1 to 3.5 weight% based on the weight of the raw powder; and based on the total weight of the composition, it may be 0.001 to 3 weight%, 0.01 to 2 weight%, or 0.1 to 1.5 weight%.

[0050] A dispersant or surfactant is used to smoothly disperse raw powder particles within a solvent or liquid carrier, and commercial water-based dispersants such as BYK-194N, SN-5468, and APCA can be used.

[0051] The content of the dispersant or surfactant may be, for example, 0.01 to 10 weight%, 0.1 to 5 weight%, or 0.5 to 3 weight% based on the weight of the raw powder; and based on the total weight of the composition, it may be 0.01 to 5 weight%, 0.1 to 3 weight%, or 0.5 to 2 weight%.

[0052] In addition, the present invention provides granules formed from the above-described suspension composition. The granules may preferably be spherical. The relative bulk density of the granules may be, for example, 25% or more (80% or less). The average particle size of the granules may be, for example, 0.1 to 500 μm, 1 to 300 μm, 3 to 100 μm, or 5 to 50 μm.

[0053] In addition, the present invention provides a molded body formed from granules. The powder molded body may be formed through dry molding (press molding, CIP molding, etc.) or wet molding (slip casting, tape casting, etc.).

[0054] Furthermore, the present invention provides a method for preparing a suspension composition comprising the step of grinding and mixing a solvent and a raw material powder at a low temperature. For example, by adding a hydration-reactive raw material powder to an aqueous solvent and performing a process of uniformly mixing or milling the prepared composition at a low temperature of less than 25°C, the hydration reaction can be minimized to produce a stable aqueous suspension (slurry) of low viscosity suitable for spraying or slip casting. Additionally, to control viscosity, hydroxyl ions (OH-) in the aqueous solvent - A step of adding an aqueous solution of a basic compound (e.g., ammonia water: NH4OH) containing ) can be added.

[0055] Various mixing methods can be used for grinding and mixing (i.e., milling) to prepare a suspension, such as ball milling, bead milling, attrition milling, planetary milling, high-energy milling, and ultrasonication.

[0056] In addition, the present invention provides a method for manufacturing granules comprising the step of granulating a suspension composition. Specifically, granules can be manufactured using various granulation methods including spray drying, freeze drying, drying, crushing, and sieving. For example, a hydration-reactive raw material powder can be introduced into an aqueous solvent and mixed or milled at a low temperature to create a suspension, and then atomized and dried to produce spherical granules; that is, granules can be manufactured by applying a process of spraying and drying a prepared suspension.

[0057] In addition, the present invention provides a method for manufacturing a molded body comprising the step of molding granules. Molding may be dry molding (press molding, CIP molding, etc.) or wet molding (slip casting, tape casting, etc.). For example, in dry molding, a molded body may be manufactured by press molding using granules prepared by methods such as spray drying a suspension of raw material powder, and in wet molding, the molded body may be manufactured by pouring the suspension directly into a porous mold or by thinly coating it onto a polymer film. In this way, a powder molded body may be manufactured by applying a wet molding process such as slip casting, or the granules may be dry-molded into a powder molded body, or used as a molded body in their granular state.

[0058] In addition, the present invention provides a method for manufacturing a sintered body comprising the step of manufacturing granules in their original granular form or in the form of a dry-molded powder body and sintering them to produce a dense ceramic sintered body.

[0059] In addition, the present invention provides a method for manufacturing a powder molded body comprising the step of wet molding using a suspension composition. Wet molding may be one or more of slip casting, pressure casting, solid casting, and tape casting.

[0060] In existing technology (for example, in the case of magnesium oxide), a suspension was prepared at room temperature without milling using heated or burnt raw material powder, and consequently, the particle size was large and the reactivity was low, making it impossible to produce a dense sintered body using it, so it was limited to applications such as refractories or water purification.

[0061] In contrast, the present invention uses a (active) raw material powder having a small particle size and a large specific surface area, optionally uses a water-resistant reactive agent (such as citric acid) and / or an aqueous solution of a basic compound (such as ammonia water), and prepares a suspension through a milling process at a low temperature, thereby having high reactivity (specific surface area / particle size), enabling spray drying, and making it useful for sintered ceramics, etc.

[0062] In the case of MgO, CaO, BaO, AlN, etc., which undergo a phase change into a hydroxide through a hydration reaction when in contact with water or moisture, during the grinding-mixing process (e.g., ball milling) for the preparation of an aqueous suspension (slurry), the hydration reaction occurs rapidly, and the amount of hydroxide in the slurry increases rapidly, causing the viscosity of the suspension to increase significantly, making it impossible to prepare a stable suspension.

[0063] In this invention, the preparation of an aqueous suspension of hydration-reactive powders is described, focusing on magnesium oxide (MgO, magnesia) and aluminum nitride (AlN). Magnesium oxide is prepared by converting magnesium oxide into MgO by heat-treating it with an alkali at a temperature between 500 and 2000°C, using magnesium hydroxide (Brucite, Mg(OH)2) produced from natural mines, magnesium carbonate (Magnesite: MgCO3, or Dolomite: CaMg(CO3)2), seawater magnesium hydroxide obtained by washing and drying magnesium hydroxide produced by substitution reaction of magnesium ions contained in seawater with a solution of slaked lime (Ca(OH)2), or synthetic magnesium hydroxide prepared by precipitating and separating it with other brine or a solution of magnesium salts such as magnesium chloride, magnesium nitride, magnesium acetate, and magnesium sulfide.

[0064] At this time, magnesia is classified into light-burned, hard-burned, and dead-burned magnesia depending on the calcination temperature. (1) Light-burned magnesia is an active MgO powder produced by calcining at a low temperature of about 500 to 1000°C to have fine particle size and a large specific surface area (surface area per unit weight of powder particles, m² / g). It is highly reactive and is used to manufacture MgO sintered bodies or as a filler in plastics, rubber, adhesives, etc. (2) Ignition-fired magnesia is magnesia calcined at a temperature between 1000 and 1500°C. During calcination, grain growth and partial sintering of MgO particles occur, resulting in a relatively small specific surface area and a fairly large particle size. Because it has low reactivity, it is used as a flame retardant, animal feed, or fertilizer. (3) Calcination-fired magnesia is calcined at a high temperature between 1500 and 2000°C. Due to the very large MgO particle size (127 μm (200 mesh) to 40 mm), it has a very small specific surface area and is therefore non-reactive. It does not hydroxylate or generate spontaneous heat, so it is used as a basic material for refractories. Because it has a very low surface area, high density, and is chemically inert, it has the highest melting temperature among all refractory oxides and is mainly used for refractory bricks.

[0065] Meanwhile, as shown in Table 1, the rate of hydration reaction upon contact with water varies significantly depending on the type of MgO. Lightly calcined MgO, which has a small particle size and a large specific surface area, undergoes a very rapid hydration reaction, whereas strongly calcined or lightly calcined MgO exhibits a very slow hydration reaction rate due to its large particle size and small specific surface area. Table 1 shows the hydration reaction rate of MgO according to calcination temperature.

[0066] Hydration Reaction Time (days) Light Calcination (800℃) Magnesia Ignition (1200℃) Magnesia Iron Calcination (1400℃) Magnesia 17 5.4% 6.5% 4.7% 31 00% 23.4% 9.3% 30 9 4.8% 32.8%

[0067] Figure 1 is a diagram showing the change in the hydration reaction rate over time when preparing a (heated) MgO aqueous suspension using slaking methods such as pump recirculation, turbine agitation, or stirring. As can be seen here, the hydration reaction is inhibited as the temperature decreases.

[0068] In contrast, lightly calcined MgO undergoes a very rapid hydration reaction. Figure 2 shows the results of investigating the degree of hydration reaction over time after dispersing 1.5 g of lightly calcined (900°C calcined) MgO powder in 9 ml of water (solid content 4.45 vol.%) in a Teflon container. As can be seen here, the hydration reaction occurs very rapidly even in a static state.

[0069] The reason this hydration reaction occurs is that in an aqueous solution, MgO + H2O = MgOH + (surface) + OH - Due to the (aqueous) reaction, MgOH on the surface of the MgO powder + is formed, and at the same time, in the aqueous solution, OH - As the concentration increases, the pH of the aqueous solution rises to approximately 10–12; simultaneously with this process, OH in the aqueous solution - ions on the surface of MgO particles MgOH + This is because Mg(OH)2 is formed on the surface as it combines with ions.

[0070] Therefore, in existing technologies, heated or decomposed MgO has always been used to minimize the hydration reaction when preparing industrially required aqueous MgO suspensions (for the production of castable refractories, fertilizers, and animal feed). Nevertheless, to further minimize the hydration reaction, a method has been reported to further suppress the hydration reaction by using a chelating agent such as lignin sulfonate or citric acid (CH2COOH-C(OH)COOH-CH2COOH, C6H8O7) in aqueous suspensions using heated or decomposed MgO, thereby forming a stable passivation layer attributable to chelate ions on the surface of MgO particles.

[0071] However, in order to manufacture MgO ceramic products based on polycrystalline magnesium oxide sintered bodies (e.g., heat dissipation fillers, heat dissipation substrates, active metal melt corrosion-resistant MgO crucibles, insulating ceramics, etc.), highly active magnesium oxide powder that densifies well during sintering must be used as a raw material. To this end, it is necessary to produce an MgO aqueous suspension consisting of fine particles through wet grinding and mixing of MgO powder. In a process that includes a process of reducing the size of powder particles by continuously ball-milling as in the present invention, rather than simply slacking the suspension as in conventional technology (i.e., a grinding-mixing process), continuous destruction of the Mg(OH)2 layer on the surface of the powder particles occurs due to impact, compression, or shear stress caused by the balls, or wear, and as new MgO surfaces are continuously exposed, the hydration reaction may not only continue but also accelerate during the ball-milling process. As a result, not only does the proportion of MgO in the aqueous solution continue to decrease, but the viscosity of the aqueous solution also continues to increase due to the formation of Mg(OH)2, eventually reaching a high viscosity stage where it is impossible to droplet the suspension.

[0072] For this reason, in order to suppress the rapid hydration reaction that may occur during the grinding-mixing process of MgO powder, according to a recent invention, when preparing an aqueous MgO suspension through a grinding-mixing (e.g., ball-milling) process, if a chelating agent, such as citric acid, is added in excess of 0.5 wt.% or more, a stable [nMgOH] with hydration resistance is formed on the surface of the MgO particles. + ·Cit n- It has been reported that the formation of a passivation layer can significantly inhibit the hydration reaction of MgO.

[0073] However, in the case of aluminum nitride, another representative material that undergoes a hydration reaction upon contact with water, as shown in Comparative Example 1, even when a chelating agent is used, if a grinding-mixing process is performed for more than 5 hours at room temperature, a stable aluminum nitride aqueous suspension cannot be prepared due to the hydration reaction AlN + 3H2O = Al(OH)3 + NH3. Furthermore, when preparing aqueous slurries (suspensions) in conventional ceramic processes, commercially available aqueous dispersants, such as polycarboxylic acid ammonium salt, which are most commonly used, do not provide dispersion stability when preparing aqueous suspensions of hydration-reactive powders. Instead, coagulation occurs, causing a problem where the viscosity of the suspension rises rapidly. This is presumed to be closely related to changes in the surface state of the powder particles due to the hydration reaction. Furthermore, suspensions using the aforementioned commercial dispersants have a problem in that the high viscosity of the suspension due to aggregation is not improved even when a chelating agent is added. Therefore, in order to prepare suspensions of hydrated reactive powders using some commercial water-based dispersants that are incompatible with chelating agents, it is necessary to develop other methods.

[0074] To solve this problem, the present invention aimed to produce a high-concentration aqueous highly active MgO or AlN powder suspension of 15 vol.% or more with or without the use of a chelating agent by delaying the hydration reaction rate through ball-milling at a low temperature of less than 25°C (preferably 15°C or less) and using an appropriate dispersant to prevent a decrease in dispersion stability due to the refinement of particle size. To this end, the present invention produced a high-concentration highly active MgO or AlN aqueous suspension with suppressed hydration reaction by performing a grinding-mixing process (e.g., a ball-milling process) involving a reduction in powder particle size at a low temperature of less than 25°C (preferably 15°C or less). This enabled the production of a stable high-concentration aqueous MgO or AlN suspension capable of droplet formation by suppressing the increase in viscosity of the suspension.

[0075] [Example-1 and Comparative Example-1]

[0076] To determine the effect of the grinding-mixing process temperature on the hydration reaction, an aqueous aluminum nitride suspension was prepared at low temperature (10°C) and room temperature (25°C), and the process is as follows. For the preparation of the composition, distilled water produced by reverse osmosis, AlN (1.5 μm, Kojundo Chemical Laboratory Co., Ltd.), YF3 (99.9%, Kojundo Chemical Co., Ltd., Japan), and CaF2 (98%, Duksan Pure Chemicals, Korea) were used as raw material powders, and BYK-194N (BYK-Chemie GmbH) was used as an aqueous dispersant to control the viscosity and dispersibility of the suspension, and BYK-012 (BYK-Chemie GmbH), a non-silicon-based antifoaming agent, was used. Citric acid (Duksan Pure Chemicals, Korea) was used as a chelating agent.

[0077] At this time, the overall composition of the prepared composition is as shown in Table 2. Accordingly, a polyethylene container with a volume of 500 ml was first filled about halfway with ZrO2 balls with a diameter of 10 mm, and raw materials were added in the ratios shown in the composition tables of Example-1 and Comparative-1 in Table 2. At this time, distilled water, a chelating agent, and a dispersing agent were added in order, and then ball milling was performed for about 1 minute to ensure they were uniformly mixed. After adding YF3, CaF2, and AlN powders to the liquid carrier prepared in this way according to the example and comparative example as presented in Table 2, ball milling was performed for 20 hours at a rotation speed of 180 rpm in a refrigerator where the temperature was maintained at 10°C for Example-1 and at room temperature (25°C) for Comparative-1. At this time, as indicated in the row "State after 20 hours of ball milling" of Table 2, when ball milling was performed at room temperature (Comparative Example-1), the container exploded and ruptured due to the temperature increase and ammonia gas caused by the rapid hydration reaction during ball milling, despite the addition of a chelating agent. On the other hand, when ball milling was performed at 10°C (Example-1), a stable AlN aqueous suspension with very low viscosity was maintained even after 20 hours. Table 2 shows the composition table of AlN suspensions for inhibiting hydration reactions (Unit: weight%).

[0078] Material Example-1 Comparative Example-1 Remarks Distilled water 37.08 37.08 Citric acid 0.29 0.29 Chelating agent Dispersant 0.66 0.66 BYK-194 NYF 32.34 2.34 Sintering aid CaF 21.17 1.17 Sintering aid AlN 58.44 58.44 Kojundo Chem. Lab. Antifoamer 0.02 0.02 BYK-012 Solid content 33.19 33.19 Unit: vol.% Ball-milling capability ○○ Immediately after batch mixing Ball-milling temperature 1025 Unit: ℃ State after 20 hours of ball milling Maintains low-viscosity, stable suspension Explosion due to hydration reaction during ball milling

[0079] The ball-milled suspension (slurry) of Example-1 was sprayed and dried using a laboratory spray dryer with hot air at approximately 150°C to produce spherical granules with a diameter of approximately 5 to 40 μm. Figure 3(a) is a scanning electron microscope image of the aluminum nitride granules prepared by the method of Example-1. Meanwhile, Figure 4(a) is an X-ray diffraction analysis graph of the AlN granules prepared in Example-1. Even after ball-milling for a long time (20 hours), no Al(OH)3 phase formation due to the hydration reaction was detected, confirming that the hydration reaction was significantly suppressed during the ball-milling process at low temperatures. This indicates that a stable AlN aqueous suspension with significantly suppressed hydration reactions at low temperatures can be produced. Furthermore, it was confirmed that even when a grinding-mixing process involving long-term ball-milling of the hydration-reactive raw material powder is performed, a stable suspension with a viscosity range that allows for droplet formation can be produced.

[0080] [Example-2]

[0081] In order to apply the effect of inhibiting the hydration reaction by low-temperature ball milling, which was confirmed during the preparation of an aluminum nitride aqueous suspension, to the preparation of a magnesium oxide aqueous suspension, an aqueous MgO suspension was prepared by the following process, and spherical granules were prepared using it. For the preparation of the composition, distilled water produced by reverse osmosis, MgO (ZH-V2, 98%, 8 μm, Jiangsu Zehui Magnesium New Material Technology Co., Ltd.), TiO2 (Extra Pure, Kosundo Chemicals Co., Ltd., Japan), La2O3 (Extra Pure, Duksan Pure Chemicals, Korea), V2O5 (0.3 μm, 99.9%, Kosundo Chemicals Co., Ltd., Japan) as raw powders, and BYK-194N (BYK-Chemie GmbH) was used as a dispersant to control the viscosity and dispersibility of the suspension. Citric acid (Duksan Pure Chemicals, Korea) was used as a chelating agent.

[0082] At this time, the overall composition of the prepared composition is as shown in Table 3. Accordingly, a polyethylene container with a volume of 500 ml was first filled approximately halfway with ZrO2 balls with a diameter of 10 mm, and the raw materials were added in the proportions indicated in the composition table of Example-2 in Table 3. At this time, distilled water, a chelating agent, and a dispersing agent were added in that order, and then ball milling was performed for about 1 minute to ensure uniform mixing. After adding TiO2, La2O3, V2O5, and MgO powders to the liquid carrier thus prepared as shown in Table 3, ball milling was performed for 24 hours at a rotation speed of 180 rpm in a refrigerator maintained at a temperature of 10°C. Table 3 shows the composition table of the MgO suspension for inhibiting hydration reaction (Unit: weight%).

[0083] Material Example-2 Example-3 Comparative Example-2 Remarks Distilled water 34.03 50.15 50.90 Citric acid 0.32 Chelating agent Dispersant (SN-5468) -0.88 0.91 Commercial aqueous dispersant Dispersant (BYK-194N) 1.22 - Commercial aqueous dispersant Ammonia water (28%) -1.48 - Basic compound TiO2 0.19 0.14 0.14 Sintering aid La2O 30.16 0.12 0.12 Sintering additive V2O 50.02 0.02 0.02 Sintering additive MgO 64.05 47.20 47.91 Raw material powder Solid content 33.70 20.15 20.62 Unit: vol.% Ball-milling capability ○○X Immediately after batch mixing Ball-milling temperature 10 10 - Unit: ℃ Mg(OH)2 content 4.7 7.8 - Content in granules: wt.%

[0084] The suspension of Example-2, after ball milling, was sprayed and dried with hot air at approximately 150°C using a laboratory spray dryer to produce spherical granules with a diameter of approximately 5 to 40 μm. Fig. 3(b) is a scanning electron microscope image of the magnesium oxide granules prepared by the method of Example-2, and Fig. 3(c) is a scanning electron microscope image of the magnesium oxide granules prepared by Example-2 after sintering at 1350°C for 2 hours. As can be seen here, it can be confirmed that spherical magnesium oxide granules and dense magnesium oxide sintered granules were successfully produced from a high-concentration active MgO aqueous suspension in which the hydration reaction was suppressed.

[0085] [Example-3 and Comparative Example-2]

[0086] Meanwhile, Figure 4(b) is an X-ray diffraction analysis graph of the MgO granules prepared in Example-2. As a result of analyzing the obtained diffraction pattern using the Rietveld method, it was confirmed that the hydration reaction was significantly suppressed during the ball-milling process, as the increase in the content of the Mg(OH)2 phase due to the hydration reaction was only 4.7% even after ball-milling for a long time (24 hours). In addition, it was confirmed that a stable suspension with a viscosity range capable of droplet formation could be produced even when a grinding-mixing process involving ball-milling the hydration-reactive raw material powder for a long time was performed.

[0087] Meanwhile, in the manufacturing process of aqueous ceramic suspensions, the most economical and widely used commercial dispersant is ammonium polycarboxylate (structure: ~~~X-NH4 + It is a dispersant containing ).

[0088] [Chemical Formula 1]

[0089]

[0090] When a water-based MgO powder suspension using the above dispersant is ball-milled, the Mg(OH)2 layer formed on the surface of the MgO particles by the hydration reaction, like the reaction in Reaction Scheme 1 during ball-milling, contains ammonium ions (NH4) in the aqueous solution originating from the dispersant. + Reacting with ), Mg 2+ As ions dissolve into the aqueous solution, Mg within the suspension increases with increasing ball-milling time. 2+ The ion concentration increases. As a result, the repulsive force between particles decreases, causing aggregation; consequently, viscosity continuously increases, making it difficult to prepare high-concentration suspensions.

[0091] [Reaction Equation 1]

[0092]

[0093] To verify this, as a model experiment, 1 wt% of the above-mentioned commercial dispersant was added to an Mg(OH)2 powder suspension relative to the powder, and the viscosity, pH, and Mg of the suspension were measured over time during ball-milling. 2+ , NH4 + Changes in the concentration of ions, etc., were measured using the ion chromatography method. Figure 5 shows the results, in which the viscosity of the suspension increases significantly with the passage of ball-milling time, and the pH of the suspension, i.e., [OH - ] It shows that the concentration shows almost no change. This means that the increase in viscosity of the suspension is unrelated to pH.

[0094] On the other hand, as can be seen in Fig. 6, (NH4 in the suspension + Even though there is no change in ion concentration) Mg 2+ It can be observed that the ion concentration tends to increase continuously along with the increase in viscosity. Therefore, to suppress the increase in viscosity of the suspension, Mg (due to the progress of ball milling) which causes a reduction in inter-particle repulsion 2+It can be seen that the increase in ion concentration must be suppressed.

[0095] Meanwhile, Mg following ball-milling 2+ The inhibition of the increase in ion concentration can be found in Reaction Scheme 1 above; by adding NH4OH into the suspension based on Le Chatelier's principle, the chemical equilibrium of Reaction Scheme 1 is shifted to the left, thereby reducing Mg 2+ It can inhibit the increase in ion concentration.

[0096] Even during the ball-milling process of the MgO aqueous suspension, since an Mg(OH)2 layer is continuously formed on the surface of the MgO particles, it is believed that a chemical reaction as shown in Reaction Equation 1 above will occur in the aqueous solution (same as with the Mg(OH)2 powder suspension). Therefore, judging that the results of the model experiment mentioned above can be applied in this case as well, the Mg generated during ball milling 2+ As a method to suppress the increase in ion concentration, it was hypothesized that artificially adding NH4OH into the suspension would shift the equilibrium of the chemical reaction to the left, thereby suppressing the reaction. As a result, during ball milling, Mg 2+ It is possible to suppress the increase in ions, and as a result, the decrease in repulsion between particles is reduced, thereby minimizing the increase in viscosity due to ball milling. By applying this principle to the preparation of a high-concentration aqueous MgO suspension by a low-temperature ball milling process, it was possible to prepare a high-concentration MgO aqueous suspension of 15 vol.% or higher.

[0097] The process for preparing a stable MgO aqueous suspension composition in which the hydration reaction is suppressed by the addition of a basic compound, and for preparing spherical granules using the same, is as follows. The reagents used to prepare the composition are similar to those in Example-2, except that the chelating agent (citric acid) was excluded; SN-Dispersant 5468 (Korea Sannopco Co., Ltd.) was used as an aqueous dispersant to control the viscosity and dispersibility of the suspension; and OH within the suspension - Ammonia water (30%, Samjeon Chemical Co., Ltd., Korea), a basic compound, was used as a source of ions.

[0098] At this time, the overall composition of the prepared composition is as shown in Table 3. Accordingly, a polyethylene container with a volume of 500 ml was first filled about halfway with ZrO2 balls with a diameter of 10 mm, and raw materials were added in the proportions shown in the composition tables of Example-3 and Comparative-2 in Table 3. At this time, distilled water and a dispersant were added in sequence first, and then ball milling was performed for about 1 minute to ensure they were uniformly mixed. In Example-3, ammonia water was additionally added. After adding TiO2, La2O3, V2O5, and MgO powders to the liquid carrier thus prepared according to the Examples and Comparative Examples as presented in Table 3, ball milling was performed for 23.5 hours at a rotation speed of 180 rpm in a refrigerator maintained at a temperature of 10°C. At this time, as indicated in the "Ball-milling feasibility" row of Table 3, in the case where ammonia water was not added (Comparative Example-2), even though all the dispersants were added, the suspension exhibited a very high viscosity from the beginning, to the extent that ball-milling was impossible due to the aggregation of powder particles. In contrast, in the case of Example-3, in which ammonia water, a basic compound, was added, the viscosity of the suspension was significantly lower, making ball-milling possible. Meanwhile, when viscosity adjustment was required for spray drying of the ball-milled suspension, 0.46 wt% of SN-Dispersant 5468 dispersant and 0.78 wt% of ammonia water were additionally added relative to the weight of the raw powder, and ball-milling was performed for an additional 20 minutes.

[0099] The suspension of Example-3, after ball milling, was sprayed and dried with hot air at approximately 150°C using a laboratory spray dryer to produce spherical granules with a diameter of approximately 5 to 40 μm. Figure 3(d) is a scanning electron microscope image of the magnesium oxide granules prepared by the method of Example-3 after sintering at 1350°C for 2 hours. As can be seen here, it can be confirmed that spherical magnesium oxide granules and dense magnesium oxide sintered granules were successfully produced from a high-concentration active MgO aqueous suspension in which the hydration reaction was suppressed.

[0100] Therefore, it was found that if a basic compound such as ammonia water is used in combination with a commercial dispersant, as in the method of the embodiment of the present invention, a stable high-concentration active MgO aqueous suspension with significantly suppressed hydration reaction at low temperatures can be prepared. Furthermore, it was confirmed that even when a grinding-mixing process involving ball-milling the hydration-reactive raw material powder for a long time is performed, a stable suspension within a viscosity range where droplet formation is possible can be prepared.

Claims

1. Aqueous solvents; and It includes one or more raw material powders among hydration-reactive metals, metal compounds, and non-metal powders, and The raw material powder is ground and mixed at a temperature below 25℃, and A suspension composition having a hydroxide content of 20% by weight or less of the raw material powder.

2. In Paragraph 1, The metal is one or more of Mg, Si, B, Al, and Ca; The metal compound is one or more of metal oxides, metal nitrides, metal carbides, metal borides, metal silicides, and metal carbonates; A suspension composition in which the nonmetal is one or more of carbon, phosphorus, and sulfur.

3. In Paragraph 1, A suspension composition having an average particle size of raw material powder of 50 μm or less and a specific surface area of ​​raw material powder of 150 m² / g or less.

4. In Paragraph 1, A suspension composition containing at least 5 volume% of the raw material powder relative to the total volume of the composition.

5. In Paragraph 1, A suspension composition having a viscosity of 5 Pa·S or less.

6. In Paragraph 1, Additionally comprising one or more water-resistant reactive agents among citric acid, tartaric acid, aminopolycarboxylate, polyphosphate, and eco-friendly chelating agents; A suspension composition containing a water-resistant reactive agent in a range of 0.01 to 5 weight percent relative to the weight of the raw material powder.

7. In Paragraph 1, Additionally comprising an aqueous solution of a basic compound; The aqueous solution of the basic compound is an aqueous solution of one or more of ammonia, calcium hydroxide, lithium hydroxide, potassium hydroxide, sodium hydroxide, and magnesium hydroxide; A suspension composition containing an aqueous solution of a basic compound in a range of 0.001 to 5 weight percent relative to the weight of the raw material powder.

8. In Paragraph 1, Additionally comprising a dispersant or surfactant; A suspension composition containing a dispersant or surfactant in a range of 0.01 to 10 weight percent relative to the weight of the raw material powder.

9. Granules formed from the suspension composition according to claim 1: Granules are spherical, and the average particle size of the granules is 0.1 to 500 μm.

10. A molded body formed from granules according to paragraph 9.

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