Sintering aid and sintering additive composition for producing high-density magnesium oxide, and low-temperature sintering method

Abstract

The present invention relates to a sintering aid and a sintering additive composition for producing high-density magnesium oxide, and a low-temperature sintering method. The present invention provides a ceramic composition for sintering a magnesium oxide raw material powder molded body, the ceramic composition containing: a magnesium oxide raw material; and a sintering aid. The sintering aid is at least one titanium-based composite compound selected from among a metal oxide, a metal hydroxide, a metal carbonate, a metal sulfide, a metal chloride, a metal fluoride, and a metal organic material containing both titanium (Ti) and other metal elements in the chemical formula thereof.

Description

Composition of sintering agents and sintering additives for the production of high-density magnesium oxide and low-temperature sintering method

[0001] The present invention relates to a composition of sintering aids for low-temperature sintering for sintering a magnesium oxide (MgO) powder compact (including granules) to a high density of 95% or more at a temperature of 1,600°C or lower, and sintering additives (additives added in small amounts for the purpose of promoting densification during sintering of a powder compact) and sintering additives (additives added in small amounts for the purpose of suppressing grain growth or improving various physical properties such as thermal conductivity, in addition to the purpose of densification during sintering of a powder compact).

[0002] In particular, the present invention relates to a sintering agent and additive for low-temperature sintering, which are characterized in that they can realize a magnesium oxide sintered body having a high density and fine grain structure by suppressing grain growth (grain growth) that always occurs along with densification during sintering heat treatment.

[0003] In the present invention, sintering and firing are used interchangeably.

[0004] Generally, magnesium oxide (MgO; magnesia) is produced by reacting magnesium chloride (MgCl2) in seawater with quicklime (CaO) to produce magnesium hydroxide (Mg(OH)2), which is then calcined to convert it into MgO and manufactured in powder form. Among the metal oxides used in large quantities industrially, magnesium oxide not only has the highest melting point (2,852℃), but also has high corrosion resistance against alkaline metals and basic environments, making it an important material useful as a refractory material for various crucibles. It is also used as an insulating filler for industrial cables as a non-conductor. In addition, it is widely used as a pH adjuster, rubber additive, pharmaceuticals, and other exhaust desulfurization, insolubilization of heavy metals in soil, and water purification due to its weak alkalinity.

[0005] Meanwhile, magnesium oxide, in addition to its high heat resistance, has the highest thermal conductivity (>40 W / mK) and high insulation (1×10) among oxide materials for its price, along with high-temperature corrosion resistance. 17 Ω·cm) and has a relatively small specific gravity (3.58 g / cm3), so its recent applications in crucibles for heat treatment of highly corrosive materials, electronic circuit boards (PCB; Printed Circuit Board), heat dissipation substrates, and heat dissipation fillers are greatly anticipated.

[0006] However, for application in these fields, high-density sintering of the magnesium oxide raw material powder molded body is crucial. If the magnesium oxide sintered body does not achieve high density, it will lack sufficient mechanical strength and can easily be damaged by external forces during use. Furthermore, the large number of internal pores can reduce thermal conductivity and easily cause insulation breakdown when high voltage is applied.

[0007] For this reason, a high-temperature firing process, firing at temperatures above 1,600°C, has been adopted to achieve high density in magnesium oxide powder compacts. However, high-temperature firing heat treatment has been problematic due to high process costs, such as high energy costs, the use of expensive high-temperature electric furnaces, and increased time required per operation due to increased heating and cooling times. To improve these issues, efforts have been made to lower the sintering temperature by adding small amounts of sintering aids that promote densification. A representative example is a report that the firing temperature could be lowered to below 1,500°C by adding a small amount of TiO2 to magnesium oxide raw powder.

[0008] In particular, Korean Patent Nos. 10-2143817 and 10-2205178 reported that by adding 0 to 0.5 wt% of TiO2 and 0 to 0.5 wt% of Nb2O5 to magnesium oxide and firing at 1,300 to 1,400°C for 2 hours, dense magnesium oxide ceramics having a relative density of 95% or more could be manufactured. However, according to the MgO-TiO2 phase diagram (Fig. 1), a eutectic liquid phase with a composition of 61 mol% TiO2 is formed at 1,605°C, and according to the Nb2O5-TiO2 phase diagram (Fig. 2), a eutectic liquid phase with a composition of 50 to 60 mol% TiO2 is formed at approximately 1,435°C. Therefore, in the ternary system of MgO-TiO2-Nb2O5, the liquid phase formation temperature must be lower than the eutectic liquid phase formation temperature of the binary system, which is 1,300 to 1,400°C or lower. That is, at the sintering heat treatment temperature (1,300 to 1,400°C) performed in the above literature and patent, it is believed that a small amount of liquid phase is formed at the grain boundary during the sintering heat treatment, and grain growth occurs actively along with material movement.

[0009] However, when grain growth occurs actively during sintering, pores at the grain boundaries are captured inside the grains, making pore shrink much more difficult (compared to pores at the grain boundaries), which leads to a decrease in the density of the sintered body. In this way, the large number of pores captured inside the grains is very difficult to shrink even with additional heat treatment such as HIP (Hot Isostatic Pressing), making it difficult to apply to places that require high dielectric breakdown strength, such as electronic circuit boards. In addition, rapid grain growth during sintering causes an increase in the size (d) of the grains within the sintered body, which results in the strength σ of the sintered body, as shown in Equation 1 below. f There is a problem that the performance is greatly reduced. And, this prediction is also confirmed by actual experimental results (Fig. 3).

[0010] [Mathematical Formula 1]

[0011] σ f = σ O + K / √d

[0012] The flexural strength of magnesium oxide ceramics is generally significantly lower than that of alumina (approximately 400 MPa) or zirconia (approximately 900 MPa), at only about 150–200 MPa. Therefore, there is a need to develop a sintering aid composition for low-temperature firing that suppresses grain growth during magnesium oxide firing, thereby achieving high strength and high density.

[0013] The purpose of the present invention is to provide a sintering agent and a sintering additive composition capable of producing a high-density magnesium oxide sintered body having a relative density of 95% or more and an average particle size of 30 ㎛ or less at a low temperature of 1,600°C or less, and a method for low-temperature sintering of high-density magnesium oxide using the same.

[0014] The present invention provides a ceramic composition for sintering a magnesium oxide raw material powder molded body to achieve the above-described object: a magnesium oxide raw material; and a sintering aid; a ceramic composition comprising at least one titanium-based composite compound sintering aid selected from oxides, hydroxides, carbonates, sulfides, chlorides, fluorides, and metal organic compounds of metals containing titanium (Ti) and other metal elements together in the chemical formula.

[0015] In the present invention, the magnesium oxide raw material may include at least one selected from magnesium oxide, hydroxide, and carbonate.

[0016] In the present invention, the sintering agent may include at least one selected from MgTiO3, Mg2TiO4, MgTi2O5, LaTiO3, and ScTiO3.

[0017] The composition according to the present invention may additionally include, as a first sintering additive, one or more non-titanium sintering additives selected from oxides, hydroxides, carbonates, sulfides, chlorides, fluorides, and metal organic compounds of metals that do not contain titanium in their chemical formulas.

[0018] In the present invention, the first sintering additive may include at least one selected from La2O3 and Sc2O3.

[0019] In the present invention, the liquid phase formation temperature of the sintering agent and the melting temperature of the first sintering additive can each independently exceed 1,600°C.

[0020] In the present invention, the sintering agent and the first sintering additive can each be independently introduced with a particle size of 1 μm or less.

[0021] In the present invention, the sintering aid and the first sintering additive can each be independently added in a range of 0.01 to 5 wt% based on the weight of the magnesium oxide raw material converted into magnesium oxide.

[0022] In the present invention, the sintering temperature of the magnesium oxide raw material powder molded body made of a ceramic composition may be 1,600°C or lower.

[0023] In the present invention, the relative density after sintering of the magnesium oxide raw material powder molded body made of a ceramic composition may be 95% or more.

[0024] In the present invention, the average size of the particles in the magnesium oxide sintered body manufactured from the ceramic composition may be 30 μm or less.

[0025] The composition according to the present invention may additionally include, as a second sintering additive, a non-titanium sintering additive capable of forming a second phase by reacting with the magnesium oxide base material.

[0026] In the present invention, the second sintering additive may include Al2O3.

[0027] The composition according to the present invention may further include at least one of a TiO2 sintering agent; and at least one third sintering additive selected from oxides, hydroxides, carbonates, sulfides, chlorides, and fluorides of Sc, La, Ce, Hf, Ru, Co, Ni, Cu, Zn, Mo, W, Al, Li, V, B, Mn, Sn, Sb, Nb, Y, and Si.

[0028] In the present invention, the magnesium oxide raw material powder molded body is an integral molded body manufactured by a ceramic molding method using a ceramic composition; it may include a granule, a press or cold isostatic pressing molded body, an extrusion or injection molded body, and a filament molded body.

[0029] In addition, the present invention provides a sintering method for manufacturing magnesium oxide using the ceramic composition for sintering a magnesium oxide raw material powder molded body as described above, comprising: a first step of preparing a liquid carrier by dissolving a dispersant in an aqueous or non-aqueous solvent; a second step of preparing a composition by adding a sintering aid and a magnesium oxide raw material of a desired composition ratio to the prepared liquid carrier; a third step of preparing a suspension by uniformly mixing the prepared composition; a fourth step of preparing the prepared suspension into granules or a powder molded body by applying a drying process; and a fifth step of sintering the prepared granules or powder molded body by heat treatment.

[0030] The method according to the present invention may further include one or more of the following steps: a step of additionally adding at least one additive selected from a binder and a plasticizer to a solvent in the first step; a step of additionally adding a sintering additive to a liquid carrier in the second step; a step of reducing the particle size by milling at least one of the sintering aid and the sintering additive before adding in the second step; and a step of performing spray drying as a drying process in the fourth step.

[0031] The sintering agent and additive composition for low-temperature sintering according to the present invention has the advantage of being able to realize a magnesium oxide sintered body having a high density and fine particle structure by suppressing grain growth during sintering heat treatment.

[0032] Figure 1 is a MgO-TiO2 phase diagram.

[0033] Figure 2 is a Nb2O5-TiO2 phase diagram.

[0034] Figure 3 is a graph showing the particle size correlation of the fracture strength of MgO sintered bodies at room temperature.

[0035] Figure 4 is a graph showing the effect of particle size on the thermal conductivity of MgO specimens, where black circles (●) are MgO specimens hot-pressed at 1,100°C for 0.5 hours; white circles (○) are MgO specimens pressure-sintered at 1,600°C for 5 hours and then HIPed at temperatures between 1,500 and 1,600°C for 0.5 hours.

[0036] Figure 5 is a graph showing changes in particle size and apparent density of a magnesium oxide sintered body according to the amount of Al2O3 added.

[0037] Figure 6 is a scanning electron microscope photograph of the microstructure of a magnesium oxide ceramic obtained by firing a powder molded body using MgO as a magnesium oxide raw material at 1,350°C for 2 hours.

[0038] Figure 7 is a scanning electron microscope photograph of the microstructure of a magnesium oxide ceramic obtained by firing a powder molded body using Mg(OH)2 as a magnesium oxide raw material at 1,350°C for 2 hours.

[0039] Hereinafter, the present invention will be described in detail with reference to the attached drawings.

[0040] The present invention relates to a ceramic composition for sintering a magnesium oxide raw material powder molded body (a high-density magnesium oxide low-temperature sintering composition). The ceramic composition according to the present invention essentially comprises a magnesium oxide raw material; and a sintering aid, and may preferably further comprise a sintering additive to improve the physical properties of the sintered body.

[0041] Magnesium oxide raw material powder molded body refers to an all-in-one molded body manufactured by various ceramic molding methods using ceramic composition powder; it may include granules, press or cold isostatic pressing molded bodies, extrusion or injection molded bodies, and filament molded bodies.

[0042] The magnesium oxide raw material may be at least one selected from the group consisting of an oxide (MgO), a hydroxide (Mg(OH)2), and a carbonate (MgCO3) of magnesium (Mg), preferably magnesium oxide or magnesium hydroxide, and more preferably magnesium oxide.

[0043] The sintering aid is characterized by being a titanium-based composite compound sintering aid containing titanium (Ti) and other metal elements, i.e., two or more metal elements, in its chemical formula. The other metal elements may be, for example, at least one selected from among Mg, Sc, La, Ce, Hf, Ru, Co, Ni, Cu, Zn, Mo, W, Al, Li, Ca, Sr, Ba, Y, Zr, Nb, Si, Sn, Pb, Mn, B, and V, preferably at least one selected from among Mg, Sc, and La, and more preferably Mg.

[0044] The titanium-based composite compound sintering aid may be a compound of two or more metals containing titanium (Ti) and another metal element in the chemical formula, and specifically, may be at least one selected from oxides, hydroxides, carbonates, sulfides, chlorides, fluorides, and metal organic compounds of two or more metals, and preferably may be oxides of two or more metals. The sintering aid may be used singly or in combination of two or more.

[0045] Specifically, the titanium-based composite compound sintering agent may be at least one selected from MgTiO3, Mg2TiO4, MgTi2O5, LaTiO3, and ScTiO3, preferably MgTiO3 or Mg2TiO4, and more preferably MgTiO3.

[0046] The titanium-based composite compound sintering aid may have a liquid phase formation temperature higher than the sintering temperature. The liquid phase formation temperature may be the temperature at which a liquid phase is formed during sintering, as described above. Specifically, the liquid phase formation temperature of the titanium-based composite compound sintering aid may exceed 1,600°C, and preferably may be 1,650°C or higher. The upper limit of the liquid phase formation temperature may be, for example, 3,000°C, 2,500°C, or 2,000°C or lower.

[0047] The titanium-based composite compound sintering aid may be introduced into the composition after reducing the particle size through milling or the like. Specifically, the titanium-based composite compound sintering aid may be introduced with a particle size of 1 μm or less, preferably 0.8 μm or less. The lower limit of the particle size may be, for example, 0.1 μm or 0.2 μm or more.

[0048] The titanium-based composite compound sintering agent can be added in an amount of 0.01 to 5 wt%, preferably 0.05 to 3 wt%, and more preferably 0.1 to 1 wt%, based on the weight of the magnesium oxide raw material converted to magnesium oxide.

[0049] The sintering additive is characterized in that it is a non-titanium sintering additive that does not include titanium (Ti) in its chemical formula and includes a metal element other than titanium. The metal element other than titanium may be, for example, at least one selected from Sc, La, Ce, Hf, Ru, Co, Ni, Cu, Zn, Mo, W, Al, Li, Ca, Sr, Ba, Y, Zr, Nb, Si, Sn, Pb, Mn, B, and V, and preferably at least one selected from Sc, La, and Al.

[0050] The non-titanium sintering additive may be at least one selected from oxides, hydroxides, carbonates, sulfides, chlorides, fluorides, and metal organic compounds of metals other than titanium, and preferably may be an oxide of a metal other than titanium.

[0051] The sintering additives may be used alone or in combination of two or more. For example, one of the first sintering additive, the second sintering additive, and the third sintering additive may be used alone or in combination of two or more.

[0052] The first sintering additive may be at least one selected from the non-titanium sintering additives described above, and preferably at least one selected from La2O3 and Sc2O3.

[0053] The first sintering additive may have a melting temperature (mp) higher than the sintering temperature. Specifically, the melting temperature of the first sintering additive may exceed 1,600°C, and preferably may be 2,000°C or higher. The upper limit of the melting temperature may be, for example, 3,000°C or lower, or 2,500°C or lower.

[0054] The first sintering additive may be introduced after reducing the particle size through milling or the like before being introduced into the composition. Specifically, the first sintering additive may be introduced with a particle size of 1 μm or less, preferably 0.9 μm or less. The lower limit of the particle size may be, for example, 0.1 μm or 0.2 μm or more.

[0055] The first sintering additive may be added in a range of 0.01 to 5 wt%, preferably 0.05 to 3 wt%, and more preferably 0.1 to 1 wt%, based on the weight of the magnesium oxide raw material converted into magnesium oxide.

[0056] The second sintering additive may be a non-titanium sintering additive capable of forming a second phase by reacting with the magnesium oxide matrix, and specifically, the second sintering additive may be Al2O3. When the second sintering additive is additionally used together with the first sintering additive, grain growth can be further suppressed, thereby further reducing the grain size of the sintered body, compared to when the first sintering additive is used alone.

[0057] The second sintering additive may have a melting temperature (mp) higher than the sintering temperature. Specifically, the melting temperature of the second sintering additive may exceed 1,600°C, and preferably may be 1,900°C or higher. The upper limit of the melting temperature may be, for example, 3,000°C or lower, or 2,500°C or lower.

[0058] The second sintering additive may be added after reducing the particle size through milling or the like before being added to the composition. Specifically, the second sintering additive may be added with a particle size of 1 μm or less, preferably 0.5 μm or less. The lower limit of the particle size may be, for example, 0.1 μm or more.

[0059] The second sintering additive may be added in an amount of 0.1 to 10 wt%, preferably 0.5 to 7 wt%, and more preferably 1 to 4 wt%, based on the weight of the magnesium oxide raw material converted into magnesium oxide.

[0060] In addition, the ceramic composition may further include at least one of a TiO2 sintering aid; and one or more third sintering additives selected from oxides, hydroxides, carbonates, sulfides, chlorides, and fluorides of Sc, La, Ce, Hf, Ru, Co, Ni, Cu, Zn, Mo, W, Al, Li, V, B, Mn, Sn, Sb, Nb, Y, and Si.

[0061] In addition to the magnesium oxide raw material, sintering aid, and sintering additives described above, the ceramic composition may further include a solvent, a dispersant, and other additives. The solvent and dispersant may be included essentially in the ceramic composition, and the additives may be optionally included as needed.

[0062] The solvent may be an aqueous or non-aqueous solvent, and specifically may be water, alcohol (ethyl alcohol, etc.), etc. The content of the solvent may be 20 to 50 wt%, preferably 30 to 40 wt%, based on 100 wt% of the ceramic composition.

[0063] As a dispersant, a commonly used dispersant can be used, and specifically, a polycarboxylic acid ammonium salt (aqueous) or a high molecular weight copolymer phosphoric acid ester salt (non-aqueous) having an affinity group, for example, commercially available SN-Dispersant 5468 (Sannopco Korea Ltd.) or DISPERBYK-145 (BYK-Chemie GmbH), etc. can be used. The content of the dispersant can be 0.01 to 5 wt% for an aqueous solvent and 0.01 to 5 wt% for a non-aqueous solvent, based on 100 wt% of the ceramic composition.

[0064] Other additives may include one or more binders, plasticizers, etc. The content of other additives may be 0.01 to 5 wt% based on 100 wt% of the ceramic composition.

[0065] The content of the magnesium oxide raw material may be 50 to 80 wt%, preferably 55 to 70 wt%, of 100 wt% of the ceramic composition.

[0066] The content of the sintering agent may be 0.01 to 5 wt%, preferably 0.05 to 3 wt%, and more preferably 0.1 to 1 wt%, based on 100 wt% of the ceramic composition.

[0067] The content of the first sintering additive may be 0.01 to 5 wt%, preferably 0.05 to 3 wt%, and more preferably 0.1 to 1 wt%, based on 100 wt% of the ceramic composition.

[0068] The content of the second sintering additive may be 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 4 wt%, based on 100 wt% of the ceramic composition.

[0069] The sintering temperature of the magnesium oxide raw material powder molded body composed of a ceramic composition may be 1,600°C or lower, preferably 1,550°C or lower, and more preferably 1,500°C or lower. The lower limit of the sintering temperature may be, for example, 1,200°C or 1,300°C.

[0070] The relative (apparent) density of the sintered magnesium oxide raw powder molded body composed of a ceramic composition may be 95% or more, preferably 96% or more, and more preferably 97% or more. The upper limit of the density may be 100% or 99% or less. The relative (apparent) density may be measured by the Archimedes method using xylene or the like as a medium.

[0071] The average particle size of the high-density magnesium oxide sintered body manufactured from the ceramic composition may be 30 μm or less, preferably 20 μm or less, and more preferably 15 μm or less. The lower limit of the particle size may be, for example, 1 μm, 2 μm, or 3 μm or more. The particle size can be obtained by measuring the sizes of a large number of particles (10 or more) using a microscope (SEM) or the like, and then averaging the measurements.

[0072] In addition, the present invention provides a low-temperature sintering method for producing high-density magnesium oxide (a method for producing high-density low-temperature fired magnesium oxide ceramic) using the ceramic composition for sintering the above-described magnesium oxide raw material powder molded body.

[0073] Specifically, the sintering method according to the present invention:

[0074] The first step is to prepare a liquid vehicle by dissolving a dispersant in an aqueous or non-aqueous solvent;

[0075] A second step of preparing a composition by adding a sintering agent and magnesium oxide raw material of the desired composition ratio to the prepared liquid carrier;

[0076] The third step is to prepare a suspension by uniformly mixing the prepared composition;

[0077] Step 4: Manufacturing the prepared suspension into granules through a drying process and preparing the granules as is or as a powder molded body; and

[0078] It may include a fifth step of heat-treating and sintering the prepared granule or powder molded body.

[0079] In addition, the sintering method according to the present invention:

[0080] In the first step, a step of additionally adding one or more additives (organic additives) selected from binders and plasticizers to the solvent, if necessary;

[0081] Step 2: Adding a sintering additive to the liquid carrier;

[0082] In the second step, a step of reducing the particle size by milling at least one of the sintering agent and the sintering additive before injection; and

[0083] Step 4: A step of performing various suspension drying processes, including spray drying, as a drying process;

[0084] One or more additional steps may be included.

[0085] According to literature studies, in magnesium oxide sintering, small additions of TiO2 can create cationic vacancies, such as magnesium vacancies V", as depicted in Scheme 1 below. MgIt is known that the density of the sintered magnesium oxide body can be greatly increased by greatly increasing the concentration of magnesium oxide to promote material movement, and at the same time, the sintering temperature can be lowered.

[0086] [Reaction Formula 1]

[0087] TiO2→ Ti" Mg + V" Mg + 2O x O

[0088] However, in methods such as Korean Patent Nos. 10-2143817 and 10-2205178, which use TiO2 and Nb2O5 as sintering aids and additives for low-temperature sintering of magnesium oxide, it is expected that a ternary eutectic liquid phase of MgO-TiO2-Nb2O5 will be formed at a sintering temperature of approximately 1,300 to 1,400°C. This is because a eutectic liquid phase is formed between MgO-TiO2 at 1,605°C (see Fig. 1), and a eutectic liquid phase is formed between Nb2O5-TiO2 at approximately 1,435°C (see Fig. 2). In general, it is well known in the field of ceramic materials that a ternary eutectic liquid phase is formed at a lower temperature than a binary eutectic liquid phase formation temperature.

[0089] Therefore, in the present invention, in order to make the liquid phase formation temperature higher than the sintering temperature by the sintering agent and additives, the source of Ti is not TiO2, but a titanium-based complex compound such as MgTiO3 (liquid phase formation temperature 1,660°C) or Mg2TiO4 (liquid phase formation temperature 1,760°C), and instead of Nb2O5 having a melting temperature of 1,512°C, a non-titanium-based sintering additive having a melting temperature much higher than this, such as La2O3 (mp=2,315°C) and Sc2O3 (mp=2,485°C), is used, thereby forming a MgO-MgTiO3-La2O3 (MgO-MgTiO3-Sc2O3) system or a MgO-Mg2TiO4-La2O3 (MgO-Mg2TiO4-Sc2O3) system. It was determined that the temperature of eutectic liquid phase formation in a ternary system could be increased by forming a backbone. In this way, by suppressing particle growth during sintering heat treatment, a magnesium oxide ceramic sintered body composed of finer particles could be manufactured.

[0090] In addition, in order to maximize the suppression of grain growth that occurs during sintering, the principle of 'suppression of grain boundary migration by second phase particles dispersed within the microstructure', a well-known theory in the field of ceramic materials, was applied to the magnesium oxide sintering heat treatment process. That is, when an additive that can react with magnesium oxide to form a second phase, such as a small amount of Al2O3, is added, as shown in Reaction Scheme 2 below, the small amount of added alumina (Al2O3) reacts with magnesium oxide (MgO) to form spinel (MgAl2O4) second phase particles dispersed within the matrix.

[0091] [Reaction Formula 2]

[0092] Al2O3+ MgO = MgAl2O4

[0093] The spinel secondary particles formed in this way are dispersed and distributed at the grain boundaries and inside the magnesium oxide particles. By greatly suppressing (pinning, dragging) the movement of the grain boundaries for grain growth that occurs during the sintering heat treatment, a high-density sintered body composed of very fine magnesium oxide particles can be obtained.

[0094] High-density dense magnesium oxide has recently been attracting much attention as a heat-dissipating filler material. This requires the production of a powder composed of spherical dense particles with a diameter of approximately 5 to 150 μm along with high thermal conductivity. The technology of the present invention can also be applied to this field, and as can be seen in Examples 5 and 7, the thermal conductivity is judged to be equivalent to or superior to that of Comparative Example 2, which used TiO2 and Nb2O5 as a sintering aid and additive, respectively. It is well known that in polycrystalline materials, the thermal conductivity increases as the particle size increases. Therefore, although a smaller particle size may be slightly disadvantageous in terms of thermal conductivity, as can be seen in Fig. 4, there is no significant change in the particle size range of 30 μm or less. Moreover, Examples 5 and 7, despite having a significantly reduced particle size compared to Comparative Example 2, exhibit comparable or slightly superior thermal conductivity.

[0095] Meanwhile, care must be taken when comparing and interpreting the measured thermal conductivity. The thermal conductivity of the sample manufactured in the present invention was measured by the LFA (Laser Flash Analysis) method. When a laser is incident on one side of a specimen with a thickness L, the temperature of the corresponding side rapidly increases, and the temperature change of the opposite side is measured over time, and half of the time (t) when the temperature reaches its maximum is measured. 1 / 2 ), the thermal diffusivity (α = 0.1388 (L 2 / t 1 / 2 )) is determined. However, in actual measurement conditions, it is difficult to satisfy the insulation condition, and the amount of heat incident by the laser is lost over time. In addition, thermal conductivity (K) is determined by thermal diffusivity (α), specific heat of the specimen (C p ), and by the density (ρ) of the specimen, K = αC pIt is given by the equation ρ. However, in addition to thermal diffusivity, it is difficult to accurately measure the specific heat of a specimen, so an approximate value is usually used. Consequently, even for the same specimen, measured values ​​may vary depending on the measuring institution or measuring device. Therefore, when interpreting thermal conductivity values, it is preferable to compare them relative to a reference specimen rather than the absolute value.

[0096] Hereinafter, the present invention will be described in more detail by way of examples.

[0097] [Comparative Example 1 and Examples 1 to 4]

[0098] The process for demonstrating the grain growth inhibition effect according to the formation of secondary phase (spinel) particles formed during sintering heat treatment of magnesium oxide is as follows. The composition was manufactured using 99.95% pure ethyl alcohol and magnesium oxide (MgO) powder (Daejung Chemicals & Metals Co., Ltd.), 95% pure TiO2 (Rutile) with a particle size of 1 ㎛ or less and 99.9% pure Nb2O5 powder (Kojundo Chem. Lab. Co., Ltd.), 0.2 ㎛ particle size Al2O3 (AKP-50, Sumitomo Co.), and DISPERBYK-145 (BYK-Chemie GmbH) as a dispersant.

[0099] At this time, the entire composition of the manufactured composition is as shown in Table 1, and accordingly, first, ZrO2 balls with a diameter of 10 mm were filled about halfway in a polyethylene container with a volume of 250 ml, 34.5 g of ethyl alcohol and 0.33 g of a dispersant (DISPERBYK-145) were added, and then ball milled for about 1 minute (for uniform mixing of the dispersant and ethyl alcohol). In addition, 0.14 g of titanium oxide powder, 0.12 g of niobium oxide powder were added to the manufactured vehicle liquid, and 0 to 2.0 g of aluminum oxide powder were added differently depending on the example, and 64.86 to 62.89 g of magnesium oxide were added differently depending on the example, and then ball milling was performed for 24 hours.

[0100] Table 1 shows a comparative example and a composition table of examples for the effect of inhibiting magnesium oxide grain growth according to the formation of secondary phase (spinel) particles (unit weight %).

[0101] Material Comparison Example-1 Example-1 Example-2 Example-3 Example-4 Remarks Ethyl alcohol 34.5 34.5 34.5 34.5 34.5 Dispersant 0.33 0.33 0.33 0.33 0.33 BYK-145 TiO 2 0.14 0.14 0.14 0.14 0.14 Nb 2 O 5 0.12 0.12 0.12 0.12 0.12 Al 2 O 3 0.00 0.03 0.20 0.67 2.00 MgO 6 4.8 6 6 4.8 6 6 4.22 6 2.89

[0102] After ball milling, the slurry was poured into a beaker and dried on a hot plate at approximately 60 to 80°C while stirring. Afterwards, it was placed in an electric oven at 60°C and dried overnight to ensure complete drying. The completely dried powder cake was ground and sieved through a No. 100 sieve to produce granular powder for press molding. This was filled into a 20 mm diameter carbide mold and uniaxially pressed at a pressure of 100 MPa to produce a disk-shaped powder compact. The produced powder compact was then loaded into an electric furnace and sintered at 1,350°C for 2 hours at a heating rate of 5°C / min. During the heating, the temperature was maintained at 500°C for 30 minutes, then increased to the final firing temperature, and the cooling was performed at a rate of 10°C / min.

[0103] For each sintered body corresponding to Comparative Example 1 and Examples 1 to 4, the apparent density was measured using the Archimedes method using xylene as a medium. After the density measurement, the specimens were ground with 400 and 1,000 sandpaper for microstructural observation, and then polished in the order of 6 ㎛ and 1 ㎛ diamond abrasives. After the polishing, the specimens were thermally etched at 1,325°C for 30 minutes and then observed under a scanning electron microscope. The measurement results are summarized in Table 2.

[0104] Table 2 shows the results of comparative and exemplary property measurements on the effect of inhibiting magnesium oxide grain growth due to the formation of secondary phase (spinel) particles (thermal conductivity was measured using the Laser Flash Analysis method, and hardness and toughness were measured using the Vickers Indentation method).

[0105] MaterialAl2O3Addition amount(weight%)Apparent density(%)Particle size(㎛)Hardness(GPa)Toughness(MPa·m) 1 / 2 ) Thermal Conductivity (W / mK) Comparative Example - 10.009 7.827 5.52.848.4 Example - 10.039 8.525 NANA Example - 20.209 8.723 NANA 45.5 Example - 30.679 9.225 NANA Example - 42.009 9.685.93±0.765.12±0.4943.6

[0106] In addition, the change in particle size in the magnesium oxide sintered body according to the amount of Al2O3 added is shown in Fig. 5 (a) and (b). Fig. 5 (a) shows the amount added as a linear value, and Fig. 5 (b) shows the amount added as a logarithmic value. Comparing the above examples and comparative examples, it was found that when the amount of sintering additive Al2O3, which reacts with magnesium oxide to form a secondary phase (spinel), is added in an amount of about 1 wt% or more, grain growth is significantly suppressed.

[0107] [Comparative Example 2 and Examples 5-8]

[0108] In addition to the grain growth inhibition effect due to the formation of secondary phase (spinel) particles formed during sintering heat treatment by adding Al2O3 as confirmed in the above Comparative Example-1 and Examples-1 to 4, the process for demonstrating the low-temperature densification and grain growth inhibition effect of the titanium-based composite compound sintering aid and the non-titanium-based sintering additive on magnesium oxide is as follows. In the manufacture of the composition, 99.95% pure ethyl alcohol, MgO powder (Daejung Chemicals Co., Ltd.) as a magnesium oxide raw material, MgTiO3 (99%, Thermo Fisher Scientific) as a titanium-based composite compound sintering aid, La2O3 (Extra Pure, Duksan Pure Chemicals) and Sc2O3 (Green Resource Co., Ltd.) powders as non-titanium-based sintering additives, Al2O3 (AKP-50, Sumitomo Co.) powder with a particle size of 0.2 μm as a sintering additive for forming a spinel secondary phase, and DISPERBYK-145 (BYK-Chemie GmbH) as a dispersant were used.

[0109] At this time, the entire composition of the manufactured composition is as shown in Table 3, and ZrO2 balls with a diameter of 10 mm were filled about halfway in a polyethylene container with a volume of 250 ml, and ethyl alcohol and a dispersant (DISPERBYK-145) were added, and then ball milled for about 1 minute (for uniform mixing of the dispersant and ethyl alcohol). Here, sintering aids, sintering additives, and magnesium oxide were added according to the comparative examples and examples in the ratios shown in Table 3, and then ball milled for 24 hours. Meanwhile, in order to refine the sintering aid and additive powder particles, each of them was ball milled for 24 hours using ZrO2 balls before addition, and then the slurry was dried and the obtained powder was used as the sintering aid and additive powder. Through this milling, the average particle size of MgTiO3 could be reduced from 1.46 ㎛ to 0.61 ㎛, La2O3 from 1.17 ㎛ to 0.21 ㎛, and Sc2O3 from 10.01 ㎛ to 0.84 ㎛.

[0110] Table 3 shows comparative examples and a composition table of examples regarding the effects of low-temperature calcination titanium-based composite compound sintering agents and non-titanium-based sintering additives on magnesium oxide (MgO) raw materials (unit: weight %).

[0111] Material Comparison Example-2 Material Example-5 Example-6 Example-7 Example-8 Ethyl alcohol 33.95 Ethyl alcohol 34.1 34.1 34.1 34.1 Dispersant 0.32 Dispersant 0.33 0.33 0.33 0.33 TiO 2 0.14 MgTiO 3 0.29 0.29 0.29 0.29 Nb 2 O 5 0.12 La 2 O 3 0.17 0.17 Sc 2 O 3 0.17 0.17 Al 2 O 3 1.95 1.95 MgO 6 5.48 MgO 6 5.1 16 5.1 16 3.16 6 3.16

[0112] After ball-milling, the slurry was poured into a beaker and dried on a hot plate at approximately 60 to 80°C while stirring. Afterwards, it was placed in an electric oven at 60°C and dried overnight to ensure complete drying. The completely dried powder cake was ground and sieved through a No. 100 sieve to produce granular powder for press molding. This was filled into a 20 mm diameter carbide mold and uniaxially pressed at a pressure of 100 MPa to produce a disk-shaped powder compact. The produced powder compact was then loaded into an electric furnace and sintered at 1,350°C for 2 hours at a heating rate of 5°C / min. During the heating process, the slurry was held at 500°C for 30 minutes before being heated to the final firing temperature, and the cooling was performed at a rate of 10°C / min.

[0113] For each sintered body corresponding to Comparative Example 2 and Examples 5 to 8, the apparent density was measured using the Archimedes method using xylene as a medium. After the density measurement, the specimens were ground with 400 and 1,000 grit sandpaper for microstructural observation, and then polished with 6 ㎛ and 1 ㎛ diamond abrasives in that order. After the polishing, the specimens were thermally etched at 1,325°C for 30 minutes and then observed under a scanning electron microscope. The results of these observations and measurements are summarized in Fig. 6 and Table 4.

[0114] Table 4 shows comparative examples and the results of property measurement of examples regarding the effects of low-temperature calcination titanium-based composite compound sintering agents and non-titanium-based sintering additives on magnesium oxide (MgO) raw materials.

[0115] Material Sintering agent and additive Apparent density (%) Particle size (㎛) Note: Thermal conductivity (W / mK) Comparative example - 2 TiO2 + Nb2O5 97.97 27 46.27 Example - 5 MgTiO3 + La2O3 97.67 14 48.35 Example - 6 MgTiO3 + Sc2O3 96.67 12 39.83 Example - 7 MgTiO3 + La2O3 + Al2O3 98.86 6 45.57 Example - 8 MgTiO3 + Sc2O3 + Al2O3 97.69 4 42.57

[0116] Comparing the above examples with the comparative examples, when a titanium-based composite compound sintering aid (MgTiO3) was used instead of the existing TiO2 as a source of the Ti component that functions to promote densification, and a high-melting-point La2O3 or Sc2O3 non-titanium sintering additive was used instead of the existing low-melting-point sintering additive Nb2O5, it can be seen that the densification behavior is equivalent to that when the existing TiO2+Nb2O5 sintering aid and additive are used, but the particle size is reduced to less than 1 / 2. In addition, it can be confirmed that the particle size is reduced to about 1 / 5 to 1 / 7 when the Al2O3 sintering additive is additionally used. In other words, it was found that the titanium-based sintering aid and non-titanium sintering additive significantly suppress grain growth while showing equivalent low-temperature sintering densification behavior.

[0117] [Comparative Example 3 and Examples 9-10]

[0118] The above Comparative Example 2 and Examples 5 to 8 are examples of cases where MgO powder was used as a magnesium oxide raw material, and the following Comparative Example 3 and Examples 9 to 10 are processes for showing the low-temperature densification and grain growth inhibition effects of a titanium-based composite compound sintering aid and a non-titanium-based sintering additive when magnesium hydroxide (Mg(OH)2) powder was used as a magnesium oxide raw material, as follows. The compositions were prepared using distilled water, Mg(OH)2 powder (Daejung Chemicals & Metals Co., Ltd.) as a magnesium oxide raw material, MgTiO3 (99%, Thermo Fisher Scientific) pre-ground by ball-milling as a titanium-based sintering aid, La2O3 (Extra Pure, Duksan Pure Chemicals) and Sc2O3 (Green Resource Co., Ltd.) powders pre-ground by ball-milling as non-titanium-based sintering additives, and SN-Dispersant 5468 (Sannopco Korea Ltd.) as a dispersant.

[0119] At this time, the entire composition of the manufactured composition is as shown in Table 5, and ZrO2 balls with a diameter of 10 mm were filled about halfway in a polyethylene container with a volume of 250 ml, distilled water and a dispersant (SN-Dispersant 5468) were added, and ball milling was performed for about 1 minute. Here, sintering aids, sintering additives, and magnesium hydroxide were added according to comparative examples and examples in the ratios shown in Table 5, and ball milling was performed for 24 hours.

[0120] Table 5 shows a comparative example and an example composition table regarding the effect of a titanium-based composite compound sintering agent and a non-titanium-based sintering additive on magnesium hydroxide (Mg(OH)2) raw material (unit weight %).

[0121] Material Comparison Example-3 Material Example-9 Example-10 Distilled water 35.99 Distilled water 35.97 35.97 Dispersant 4.11 Dispersant 4.11 4.11 TiO 2 0.124 MgTiO 3 0.186 0.186 Nb 2 O 5 0.105 La 2 O 3 0.105 Sc 2 O 3 0.105 Mg(OH) 259.67 Mg(OH) 259.63 59.63

[0122] After ball-milling, the slurry was poured into a beaker and dried on a hot plate at approximately 110°C while stirring. Afterwards, it was placed in an electric oven at 60°C and dried overnight to ensure complete drying. The completely dried powder cake was ground and sieved through a No. 100 sieve to produce granular powder for press molding. This was filled into a 20 mm diameter carbide mold and uniaxially pressed at a pressure of 100 MPa to produce a disk-shaped powder compact. The produced powder compact was then loaded into an electric furnace and sintered at 1,350°C for 2 hours at a heating rate of 5°C / min. During the heating, the temperature was maintained at 500°C for 30 minutes, and then the temperature was increased to the final firing temperature. The cooling was performed at a rate of 10°C / min.

[0123] For each sintered body corresponding to Comparative Example 3 and Examples 9 to 10, the apparent density was measured using the Archimedes method using xylene as a medium. After the density measurement, the specimens were ground with 400 and 1,000 grit sandpaper for microstructural observation, and then polished with 6 ㎛ and 1 ㎛ diamond abrasives in that order. After the polishing, the specimens were thermally etched at 1,325°C for 30 minutes and then observed under a scanning electron microscope. The results of these observations and measurements are summarized in Fig. 7 and Table 6.

[0124] Table 6 shows comparative examples and the results of property measurement of examples regarding the effects of titanium-based composite compound sintering agents and non-titanium-based sintering additives on magnesium hydroxide (Mg(OH)2) raw materials.

[0125] Material Sintering Preparation and Additives Apparent Density (%) Particle Size (㎛) Comparative Example - 3 TiO2 + Nb2O5 95.3620 Example - 9 MgTiO3 + La2O3 94.4615 Example - 10 MgTiO3 + Sc2O3 95.7512

[0126] Comparing the above examples with comparative examples, it can be seen that even when magnesium hydroxide (Mg(OH)2) was used as the raw material powder, similarly to when magnesium oxide (MgO) was used as the raw material powder, when a titanium-based composite compound sintering aid (MgTiO3) was used as the source of the Ti component and a high-melting-point La2O3 or Sc2O3 non-titanium-based sintering additive was used, the densification behavior was equivalent to that when the existing TiO2+Nb2O5 sintering aid and additive were used, but the particle size was reduced by about half.

Claims

1. As a ceramic composition for sintering a magnesium oxide raw material powder molded body: Magnesium oxide raw material; and As a sintering aid; a ceramic composition comprising at least one titanium-based composite compound sintering aid selected from among oxides, hydroxides, carbonates, sulfides, chlorides, fluorides, and metal organic compounds of metals containing titanium (Ti) and other metal elements in the chemical formula.

2. In paragraph 1, Magnesium oxide raw material is a ceramic composition comprising at least one selected from the group consisting of oxides, hydroxides, and carbonates of magnesium.

3. In paragraph 1, A ceramic composition comprising at least one sintering agent selected from MgTiO3, Mg2TiO4, MgTi2O5, LaTiO3, and ScTiO3.

4. In paragraph 1, A ceramic composition further comprising, as a first sintering additive; at least one non-titanium sintering additive selected from oxides, hydroxides, carbonates, sulfides, chlorides, fluorides, and metal organic compounds of metals not containing titanium in their chemical formulas.

5. In paragraph 4, A ceramic composition comprising a first sintering additive and at least one selected from La2O3 and Sc2O3.

6. In paragraph 4, A ceramic composition wherein the liquid formation temperature of the sintering agent and the melting temperature of the first sintering additive independently exceed 1,600°C.

7. In paragraph 4, A ceramic composition in which the sintering aid and the first sintering additive are each independently introduced with a particle size of 1 ㎛ or less.

8. In paragraph 4, A ceramic composition in which the sintering aid and the first sintering additive are each independently added in a range of 0.01 to 5 wt% based on the weight of the magnesium oxide raw material converted to magnesium oxide.

9. In paragraph 1, A ceramic composition having a sintering temperature of 1,600°C or less for a magnesium oxide raw material powder molded body made of a ceramic composition.

10. In paragraph 1, A ceramic composition having a relative density of 95% or more after sintering of a magnesium oxide raw material powder molded body composed of a ceramic composition.

11. In paragraph 1, A ceramic composition having an average particle size of 30 ㎛ or less in a sintered magnesium oxide body manufactured from the ceramic composition.

12. In paragraph 1, A ceramic composition further comprising a non-titanium sintering additive capable of forming a second phase by reacting with a magnesium oxide base material as a second sintering additive.

13. In paragraph 12, The second sintering additive is a ceramic composition containing Al2O3.

14. In paragraph 1, TiO2 sintering agent; and At least one third sintering additive selected from oxides, hydroxides, carbonates, sulfides, chlorides, and fluorides of Sc, La, Ce, Hf, Ru, Co, Ni, Cu, Zn, Mo, W, Al, Li, V, B, Mn, Sn, Sb, Nb, Y, and Si; A ceramic composition further comprising at least one of the following:

15. In paragraph 1, Magnesium oxide raw material powder molded body is an integral molded body manufactured by a ceramic molding method using a ceramic composition; a ceramic composition including granules, press or cold isostatic pressing molded bodies, extrusion or injection molded bodies, and filament molded bodies.

16. A sintering method for manufacturing magnesium oxide using a ceramic composition for sintering a magnesium oxide raw material powder molded body according to Article 1: The first step is to prepare a liquid carrier by dissolving a dispersant in an aqueous or non-aqueous solvent; A second step of preparing a composition by adding a sintering agent and magnesium oxide raw material of the desired composition ratio to the prepared liquid carrier; The third step is to prepare a suspension by uniformly mixing the prepared composition; Step 4: Applying a drying process to the prepared suspension to manufacture granules or prepare a powder molded body; and A sintering method comprising a fifth step of heat-treating and sintering a prepared granular or powder molded body.

17. In paragraph 16, A step of additionally adding one or more additives selected from a binder and a plasticizer to the solvent in the first step; Step 2: Adding a sintering additive to the liquid carrier; In the second step, a step of reducing the particle size by milling at least one of the sintering agent and the sintering additive before injection; and A step of performing spray drying as a drying process in the fourth step; A sintering method comprising one or more additional steps.

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