JP6435515B2 - Firing equipment - Google Patents

Description

  The present disclosure relates to a firing apparatus capable of firing nitride materials including nitride phosphor powder inexpensively and safely.

  So far, phosphors have been used in various devices. Especially for display devices, the first application is considered to be used in a television using a cathode ray tube. In the cathode ray tube, an image is displayed by irradiating a phosphor with an electron beam accelerated by an electrostatic field and converting the kinetic energy into light of a specific wavelength band. In plasma display televisions, deep ultraviolet light obtained by plasma excitation of a gas containing a rare gas as a main component is converted into light of a specific wavelength band by a phosphor. These wavelength conversions are characterized by a very large energy difference between excitation and emission.

  On the other hand, in recent years, a display device using a light emitting diode as an excitation light source and using a method of further wavelength-converting light emitted from the phosphor by a phosphor has been put into practical use. For example, a white light emitting diode used for a backlight of a liquid crystal television emits yellow light using blue light as excitation light. Such a system is characterized in that the energy difference between excitation and fluorescence is very small.

  If the energy difference between excitation and fluorescence is small, the types of phosphors that can be used are very limited. This is determined by whether or not the absorption spectrum of the phosphor exists at a position that matches the excitation light wavelength. For example, cerium-doped yttrium aluminum garnet phosphor (YAG phosphor) is known as an excellent yellow phosphor, but has an absorption band in the blue 450 nm wavelength region but absorbs in the blue-violet 405 nm wavelength region. Since there is no belt, usage is limited.

  Many phosphors having divalent europium as the emission center have been put to practical use as phosphors having a broad absorption spectrum and exhibiting fluorescence in various colors. Europium is the most stable divalent element among the 14 lanthanoid elements. When europium is divalent, 4f electrons cannot be localized and are hybridized with 5d electrons. The 5d electrons are spatially expanded as compared with the 4f electrons, and are easy to hybridize with the orbits of the surrounding atoms. Therefore, the 5d electrons can have a broad excitation spectrum reflecting the band structure of the host material. The fluorescence wavelength is also strongly influenced by the band structure of the host material. As a result, excitation and fluorescence spectra can be designed by appropriate selection of the host material.

  In order to obtain fluorescence in a long wavelength visible light region such as green or red using divalent europium, it is generally necessary to use a host material having a narrow band gap. An effective method for narrowing the band gap of the host material is to use an oxide as an oxynitride or a nitride. Since nitrogen has a smaller electronegativity than oxygen, the band gap can be effectively narrowed. In addition, when the atom chemically bonded to europium is replaced from oxygen to nitrogen, the excitation and fluorescence spectra also change. In general, (oxy) nitride phosphors tend to have longer excitation and fluorescence spectra than oxide phosphors.

  In phosphors using divalent europium, blue phosphors include strontium / magnesium / silicon oxide (SMS) and barium / aluminum / magnesium oxide (BAM), which may not contain nitrogen. There are two common points. On the other hand, in the case of a green or red phosphor, the number of (oxy) nitride types increases considerably. For example, a calcium / aluminum / silicon nitride phosphor (CASN) or a silicon / aluminum oxynitride phosphor (sialon), which fluoresces in red or green. The phosphor disclosed in Patent Document 1 is a fluorescence spectrum of a beta sialon phosphor, and emits fluorescence in a green color having a peak wavelength of 530 nm.

JP 2012-62394 A

  However, as described in Patent Document 1, the (oxy) nitride phosphor described above needs to be heated at a high temperature (˜1500 ° C.) and a high pressure (1 atm or higher) in a nitrogen atmosphere. For this reason, the firing furnace is larger than a general electric furnace in ensuring pressure resistance, and as a result, the (oxy) nitride phosphor is more expensive than a general oxide phosphor.

  On the other hand, a firing method using ammonia as a nitriding agent has also been put into practical use. In this case, the (acid) nitride phosphor can be obtained by firing at a lower temperature or lower pressure. This method is a universal method used not only for phosphors but also for crystal growth of nitride semiconductors such as blue light emitting diodes and tantalum nitride used for photocatalysts. However, since dangerous high-pressure gas is used, a gas supply facility having a safety mechanism is necessary, and incidental facilities also contribute to an increase in cost.

  In view of the above problems, an object of the present invention is to provide an apparatus capable of firing not only a phosphor but also various oxynitride materials by using urea as a nitriding agent.

  In order to solve the above problems, a firing apparatus according to one aspect of the present invention is a firing apparatus for firing a raw material to form a fired product, and includes a furnace, a heater for heating the furnace, and water inside the furnace. It has the pipe | tube which introduce | transduces a nitriding agent, and the deoxidation member arrange | positioned inside the furnace, and a deoxidation member consists of a member which is more easily oxidized than a raw material. With this configuration, oxygen contained in water can be effectively removed by reaction with a member that is easily oxidized, while hydrogen contained in water is used for reducing the raw material. Furthermore, the oxynitride or nitride material can be fired at a lower temperature and lower pressure by causing the raw material to undergo a nitriding reaction with a nitriding agent in a strong reducing atmosphere.

  In the firing apparatus of the present invention, it is preferable that the deoxidizing member is made of at least one of carbon, aluminum, and titanium. According to this preferred configuration, the raw material that is less oxidized is effectively deprived of oxygen. As a result, the oxynitride or nitride material can be fired more effectively.

  In the firing apparatus of the present invention, the nitriding agent is preferably urea, a carbamide compound, a hydrazine compound, or an azide compound. According to this preferred configuration, the nitriding agent liberates ammonia or a highly reactive amino group during the thermal decomposition process. These nitrogen-containing compounds effectively nitride the raw material. Further, since these raw materials are much cheaper and safer than ammonia, the nitride material can be fired at low cost and safely.

  In the firing apparatus of the present invention, the furnace is preferably cylindrical and rotatable. According to this preferred configuration, since the raw material is evenly mixed with the nitriding agent, a uniform fired product can be obtained.

  In the firing apparatus of the present invention, it is preferable that the furnace further rotates when the fired product is formed by being heated by a heater.

  The firing apparatus of the present invention preferably further has a mechanism for supplying a nitriding agent onto the furnace, and the fired product is preferably dropped by gravity. According to this preferable configuration, an extrusion mechanism is not required for the baking apparatus. Therefore, the structure of the baking apparatus becomes simple and the nitride material can be fired at a lower cost.

  In the firing apparatus of the present invention, the nitriding agent is preferably introduced into the furnace as a liquid containing water. According to this preferable configuration, the raw material can be supplied into the furnace as a stable hydrate. In the furnace, the hydrate is thermally decomposed to perform a reducing action and a nitriding action, so that an efficient nitriding material can be fired. Further, since the mixing ratio of water and nitriding agent is stable, a uniform nitride material can be fired.

  A firing apparatus according to another aspect of the present invention is a firing apparatus for firing a raw material to form a fired product, and introduces a furnace, a heater for heating the furnace, and a nitriding agent containing water into the furnace. The furnace is made of a deoxidizing member, and the deoxidizing member is made of a member that is more easily oxidized than the raw material. With this configuration, oxygen contained in water can be effectively removed by reaction with a member that is easily oxidized, while hydrogen contained in water is used for reducing the raw material. Furthermore, the oxynitride or nitride material can be fired at a lower temperature and lower pressure by causing the raw material to undergo a nitriding reaction with a nitriding agent in a strong reducing atmosphere.

  According to the present invention, an oxynitride material can be realized at a lower pressure without having a highly toxic gas facility.

It is a structure sectional view of the calcination device in Embodiment 1 of the present invention. It is a structure sectional drawing of the baking apparatus in Embodiment 2 of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a cross-sectional view of the configuration of the firing apparatus according to the first embodiment of the present invention. In FIG. 1, a baking apparatus 100 includes a heater 101a and a heater 101b, a heat-resistant container 102 made of alumina, and a deoxygenation container 103. The heat-resistant container 102 is provided with a gas introduction hole 102a for introducing an inert gas into the inside and an exhaust hole 102b for exhausting to the side opposite to the gas introduction hole 102a. The deoxidation vessel 103 is provided inside the heat-resistant vessel 102, and a nitriding agent introduction pipe 104 is introduced into the deoxygenation vessel 103. The deoxygenation vessel 103 is provided with an exhaust hole 103b for exhausting air. In the present embodiment, the deoxygenation container 103 is made of graphite. The heater 101a and the heater 101b are disposed around the heat-resistant container 102 and heat the heat-resistant container 102.

  The nitriding agent introduction pipe 104 is for supplying the nitriding agent from the outside to the inside of the deoxidation vessel 103. A sample 106 is placed on a heat-resistant crucible 105 inside the deoxygenation container 103. Here, as an example, the sample 106 is obtained by adding a small amount of europium to an oxide of strontium and silicon, and the nitriding agent is so-called urea water (concentration 5M) in which urea is dissolved in water.

  First, urea water is supplied to the apparatus as a nitriding agent through the nitriding agent introduction pipe 104. The supply rate of urea water is 1 milliliter (mL / min) per minute. Further, nitrogen gas is supplied from the gas introduction hole 102a at a rate of 1 liter per minute (1 L / min). This is because the gas generated from the urea water is quickly discharged from the exhaust hole 102b. Next, the heater 101a and the heater 101b are energized to heat the heat-resistant container 102 and the inside thereof. The temperature is raised at a rate of 200 ° C. per hour (200 ° C./h) until the temperature inside the heat-resistant container reaches 1500 ° C. After the temperature inside the heat-resistant container 102 reaches 1500 ° C., the temperature is maintained for 4 hours while the urea water is being supplied. After the reaction, the temperature is lowered at a rate of 200 ° C./h and returned to room temperature. The supply of urea water is stopped when the temperature becomes 1000 ° C. or lower. After returning to room temperature, the sample 106 is taken out. The sample becomes a strontium oxynitride silicon phosphor (SSON) using europium as an activator by urea water, and exhibits fluorescence in red using, for example, blue light as excitation light.

  Here, the nitriding reaction mechanism of urea water will be described.

  When water is added to urea and the temperature is raised, the hydrolysis shown below occurs.

  That is, 2 mol of ammonia and 1 mol of carbon dioxide are produced for 1 mol of urea. This ammonia causes nitriding of the sample 106. Further, as a result of the raw material being placed in a reducing atmosphere by the deoxygenation vessel 103, the oxygen contained in the sample 106 is easily desorbed at a high temperature. As a result of ammonia nitriding where oxygen is desorbed, the sample is fired as nitride.

  On the other hand, there is an excess of water that is contained in urea water and that has not been used for the hydrolysis reaction of urea. Water generally tends to promote the oxidation of raw materials and weaken the reducing properties of the atmosphere. However, when the surface area of the deoxygenation container 103 is sufficiently larger than that of the sample 106, oxygen generated from water is used for oxidation of the deoxygenation container 103, so that a highly reducing atmosphere can still be maintained. In addition, hydrogen liberated from water further enhances reducing properties. Further, hydrogen combines with the oxygen of the sample 106 and has an effect of promoting deoxygenation, and has an effect of further promoting nitridation in the deoxygenation vessel 103.

  On the other hand, the same thing occurs with hydrazine water. In hydrazine water, the following decomposition reaction occurs.

  One mole of hydrazine generates excess oxygen gas while producing two moles of ammonia. Oxygen gas has a function of weakening the reducing property of the atmosphere and returning the generated nitride to oxide again. However, when the surface area of the deoxygenation container 103 is sufficiently larger than that of the sample 106, the oxygen gas is effectively removed and a high reducing atmosphere can be maintained.

  In addition, the above also occurs in a carbamide compound. For example, in the case of carbamide having the simplest molecular structure, the following decomposition reaction occurs.

  The atomic composition constituting carbamide is exactly the same as that of urea. Therefore, like urea, 1 mol of carbamide generates 2 mol of ammonia while generating 1 mol of carbon dioxide. These products produce exactly the same effect as when urea is used.

The above also occurs in the same manner with azide compounds. For example, in the case of sodium azide (chemical formula NaN ₃ ), which has been frequently used in automobile airbags in the past, the following decomposition reaction generally occurs.

As a result of the decomposition reaction, nitrogen gas is generated, which becomes a radical in an intermediate process. At that time, when an oxide to be reacted exists in the vicinity, a nitriding reaction occurs while desorbing oxygen of the oxide without becoming nitrogen gas. On the other hand, although sodium is precipitated, since the atmospheric boiling point of sodium is 880 ° C., when baked at a temperature higher than this temperature, sodium diffuses into the atmospheric gas, so there is almost no fear of being contained in the fired product. . When the fired product contains an alkali metal element such as sodium as a constituent element, it is also effective to use the alkali metal azide more positively as a nitriding agent. On the other hand, when it is desired to reduce the mixing of alkali metal elements as much as possible, it is also effective to use hydrogen azide (chemical formula N ₃ H) containing no alkali metal elements. In this case, hydrogen becomes a product, but due to its reducibility, there is an advantage that the nitriding reaction is further accelerated compared to sodium azide.

  The mechanism of nitriding using urea water, hydrazine, carbamide, and azide has been described above. The essence of this reaction is to use a less toxic nitrogen-containing compound and to nitride the raw material with ammonia generated from the decomposition reaction. It is also important to maintain a high reducing atmosphere with a deoxygenation vessel and promote deoxygenation of the raw material and nitriding agent. By these two actions, nitride can be efficiently fired at a lower temperature and at a normal pressure.

  Note that a deoxidation container 103 is provided in this embodiment mode. However, in the case where the heat-resistant container 102 is made of a material that easily reacts with oxygen such as graphite, the deoxygenation container 103 is not necessarily required. In this case, the heat-resistant container 102 also serves as the deoxygenation container 103.

  Moreover, although the deoxygenation container is described as a container in FIG. 1, it does not necessarily need to be a container. The main point is to maintain a reducing atmosphere, and the effect of the present invention is exhibited even if it is a plate shape or a rod shape as long as oxygen in the atmosphere can be effectively removed.

  In the present embodiment, the deoxygenation vessel 103 is made of graphite, but any material that can easily react with oxygen can be used instead. Examples include aluminum, titanium, and silicon. In particular, titanium is effective as a substitute for graphite because it has a high melting point and easily binds to oxygen. These oxides do not volatilize like carbon dioxide and remain as solids. For this reason, it is possible to create a reducing atmosphere more effectively by installing in the vicinity of the sample 106 as a powder rather than as a container.

  In the present embodiment, the heat-resistant crucible 105 is described, but it is more desirable if it is made of a material that does not release oxygen at a high temperature. In that case, materials, such as boron nitride and silicon carbide, are mentioned, for example.

The gas introduction hole 102a is provided for discharging the product gas after the reaction, and is not necessarily required in the present invention. Introducing an inert gas is preferable because it prevents ammonia from remaining in the furnace and improves the safety during sample removal.

  In addition, although it is the supply method of urea water, it is desirable to attach an extrusion pump in the upstream of the nitriding agent introduction pipe | tube 104, and to supply urea water, heating at about 50 degreeC. By increasing the temperature, it is possible to prevent the urea water from solidifying and to prevent clogging in the nitriding agent introduction pipe 104. Further, a method using a bubbler containing urea water may be used instead of the extrusion pump. In this case, for example, nitrogen gas is used as a bubbling gas, the bubbler temperature is raised as much as possible, water and urea are simultaneously taken into the nitrogen gas, and introduced into the furnace through the nitriding agent introduction pipe 104. . In this case, since a mechanism such as an extrusion pump is not required, the cost of the fired product can be reduced. Further, as a method for supplying urea water at a low cost, a solution such as a drip bag is filled and introduced into the furnace using dripping by gravity. In this case, neither an extrusion pump nor a bubbler container is required, and the supply system can be further simplified. Therefore, the cost of the fired product can be further reduced. In addition, although urea water was described here, the same effect is acquired even if this is hydrazine water.

(Embodiment 2)
Next, an embodiment in which urea nitriding technology is introduced into a rotary furnace will be described with reference to FIG.

  FIG. 2 shows a sectional view of the configuration of the firing apparatus according to the second embodiment of the present invention. In FIG. 2, the baking apparatus 200 includes a heater 201 a and a heater 201 b, a rotary furnace 202, and a deoxygenated structural material 203. The rotary furnace 202 has a wall 202a and a hollow portion 202b, and a deoxidized structural material 203 is disposed in the hollow portion 202b. The rotary furnace 202 has a cylindrical shape with the deoxidized structural material 203 as a central axis, and the product 208a, the product 208b, and the product 208c are placed inside the wall 202a.

  The heater 201 a and the heater 201 b are provided around the rotary furnace 202 and heat the rotary furnace 202.

  The rotary furnace 202 is installed with a slight inclination. That is, the wall 202a has a slight inclination. A nitriding reaction is performed in the hollow portion 202b. Further, a nitriding agent introduction pipe 204 and an inert gas introduction pipe 205 are connected to the hollow portion 202b. A sample 206 is put into the hollow portion 202b from above, and the inside of the furnace is sequentially reacted like a product 208a, a product 208b, and a product 208c, and the final reaction calcined product 207 comes out from below. It has a composition to come.

  First, the process starts by rotating the rotary furnace 202. The dimensions of the rotary furnace 202 are, for example, an inner diameter of 10 cm and a length of 2 m. When rotation starts, the heater 201a and the heater 201b are energized to heat the rotary furnace 202. The temperature rising rate is, for example, 150 ° C. per hour (150 ° C./h). Along with the heating, an inert gas is introduced from the introduction pipe 205 at a flow rate of 1 L / min. This is for making the reducing atmosphere in the furnace constant and forcing the gas generated by the hydrolysis reaction of urea water to flow downstream. When the temperature in the furnace reaches 1400 ° C., urea water is introduced from the nitriding agent introduction pipe 204 at a flow rate of 10 mL / min. After the flow is stabilized, the sample 206 is introduced from the upstream side. Here, the sample 206 is an aluminum oxide powder mixed with europium oxide having a molar fraction of 2%. The supply amount into the furnace is, for example, 1 g per minute. The sample 206 slowly descends the inside of the slightly inclined rotary furnace. It takes about 2 hours for the sample 206 to pass through the rotary furnace 202, and this passing time is adjusted by the rotation speed and the tilt angle. While descending, the sample 206 is deprived of oxygen by the reducing atmosphere, and sequentially becomes a product 208a, a product 208b, and a product 208c. This is because the deoxidizing structure material 203 installed in the furnace provides a very strong reducing atmosphere. And it is nitrided by reacting with ammonia generated from urea water. As a result of the sequential nitridation, when it finally reaches the lower end (right end in FIG. 2) of the rotary furnace, it is pushed out as a reaction fired product 207 to the outside. Here, the reaction baked product 207 is made of aluminum oxynitride using europium exhibiting green fluorescence as an activator.

  In the case of this furnace structure, it is advantageous to obtain a fired product continuously. It is also an advantage that the structure of the furnace is simple.

  In addition, although urea water was mentioned here as an example, the same effect is acquired even if it is hydrazine water. Moreover, although there is a concern about oxidation due to excess oxygen gas, this is not a problem because it is effectively removed by the deoxidized structure material 203. In order to actively remove oxygen, it is also effective to mix a small amount of an organic compound such as methanol with the raw material. In this case, excess oxygen is removed by combustion of methanol. If the amount of methanol is increased too much, carbon will be mixed into the fired product, so it is necessary to prepare a mixed amount of methanol or the like according to the raw material.

  Although the furnace is supposed to rotate here, it is not necessary to rotate when the raw material falls spontaneously. In addition, since the purpose is to lower the raw material while slowly stirring, the effect can be obtained even if the furnace is vibrated instead of rotating.

  According to the present invention, it is possible to realize a nitride firing furnace that does not require high temperature and pressure and that does not require gas equipment. As a result, the fired product can be supplied at low cost.

100, 200 Baking apparatus 101a, 101b, 201a, 201b Heater 102 Heat-resistant container 102a Gas introduction hole 102b, 103b Exhaust hole 103 Deoxygenation container 104, 204 Nitrating agent introduction pipe 105 Heat-resistant crucible 106, 206 Sample 202 Rotary furnace 202a Wall 202b Hollow Part 203 Deoxygenated structure material 205 Introduction pipe 207 Reaction fired product

Claims (6)

A firing apparatus for firing a raw material to form a fired product,
A furnace, a heater for heating the furnace, a pipe for introducing a nitriding agent containing water into the furnace, and a deoxidation member disposed in the furnace,
The deoxygenation member, Ri Na than likely member to oxidation than the starting material,
The firing apparatus according to claim 1, wherein the nitriding agent is urea, a carbamide compound, a hydrazine compound, or an azide compound . The firing apparatus according to claim 1, wherein the member is made of at least one of carbon, aluminum, and titanium. The firing apparatus according to claim 1, wherein the furnace is cylindrical and rotatable . The firing apparatus according to claim 3 , wherein the furnace rotates when heated by the heater to form the fired product . A mechanism for supplying a nitriding agent on the furnace, and wherein the nitriding agent is dropped by gravity, baking apparatus according to claim 1. The firing apparatus according to claim 1, wherein the nitriding agent is introduced into the furnace as a liquid containing water .

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