JP4426384B2 - Coating material and fireproof insulation - Google Patents

Description

  The present invention relates to a heating element that generates heat when irradiated with microwaves. For example, a heating element for baking a ceramic material by irradiating microwaves in a furnace, particularly when baking an alumina material. And a heating element suitable for firing at a high temperature of 1600 ° C. or higher.

  Conventionally, an electric furnace, a gas furnace, or the like is generally used for firing ceramic materials or the like. However, from the standpoints of energy saving and environmental load reduction, the microwave baking method has been attracting attention as an effective baking method.

  For example, Patent Document 1 and Patent Document 2 disclose a heating element (refractory heat insulating material) having a microwave absorption characteristic substantially equivalent to a material to be baked when the material to be baked is self-heated by microwave irradiation. ) Discloses a microwave firing method in which the temperature difference between the fired product and the heating element (fireproof heat insulating material) is eliminated by surrounding the fired product so that the fired product can be uniformly fired. Has been.

Further, Patent Document 3 discloses a heating element and a refractory heat insulating material that are suitable for firing an alumina material that is fired at a high temperature of 1600 ° C. or higher, by further developing the above technique.
JP 2002-130960 A Japanese Patent Laid-Open No. 2003-240451 Japanese Patent Application No. 2004-070464

  A typical example of the fine ceramic material is alumina ceramics. This alumina ceramic is generally fired at a high temperature of 1600 ° C. or higher.

  When such an alumina ceramic material is self-heated by microwave irradiation and fired, there are the following problems.

  Since alumina has a small dielectric loss in a low temperature region, even when it is irradiated with microwaves, heat generation due to its own microwave absorption is poor. Therefore, by applying the technology disclosed in Patent Document 1 and Patent Document 2, a heating element (for example, the same alumina material as the material to be fired) having a microwave absorption characteristic equivalent to alumina as the material to be fired. It is difficult to raise the temperature to the target firing temperature even if microwaves are irradiated around alumina to be fired.

  Further, when alumina itself rises to a high temperature range of 1000 ° C. or higher by some external means, the microwave absorption (dielectric loss) of alumina itself increases. Once the alumina is heated to a high temperature, self-heating due to absorption of microwaves becomes remarkable. Thereafter, the temperature is raised by self-heating and finally reaches the firing temperature.

  Therefore, in the case where microwave firing is performed by a method in which an alumina ceramic material that is a material to be fired is surrounded by a heating element having an equivalent microwave absorption characteristic (for example, the same alumina material as the material to be fired), If the unit consisting of the alumina ceramic material that is the object to be fired and the heating element surrounding it is not heated to 1000 ° C. or more by another heating means, the unit is self-heated by microwave absorption. I could not.

  However, in order to raise the temperature of the unit composed of the alumina ceramic material to be fired and the heating element surrounding it to the temperature at which it self-heats by microwave absorption, it is necessary to provide another heating means. As well as making the temperature control in the furnace complicated.

  Therefore, even if it is a material with low microwave absorption at a low temperature such as alumina, only one type of heating element that generates heat substantially equivalently to the object to be fired in the firing temperature range without providing another heating means. Therefore, a technique for uniformly firing an alumina ceramic material as a material to be fired has been required.

  In order to fire the alumina material by self-heating by microwave absorption by using only one type of heating element that generates heat substantially equivalently to the alumina ceramic material that is the object to be fired, without providing another heating means Has both the characteristics that the heating element self-heats from room temperature to 1000 ° C. by microwave irradiation, and generates heat substantially equivalent to alumina as a fired object at 1000 ° C. or more. Was requested.

As a result of repeated studies, the inventor of the present application forms the heating element from an aggregate and an inorganic binder, the aggregate is made of alumina particles, and the inorganic binder is an inorganic binder containing a Na ₂ O component. The inventors have found that a heating element having both characteristics can be obtained, and filed a patent document 3. The heating element disclosed in Patent Document 3 mentions sodium silicate as a suitable inorganic binder containing a Na ₂ O component. The presence of the Na ₂ O component in the inorganic binder causes the heating element to exhibit the above characteristics, that is, the self-heating characteristics from room temperature to 1000 ° C.

However, the Na ₂ O component in sodium silicate may react with the refractory insulation adjacent to the heating element when exposed to high temperatures, which may degrade the refractory insulation. 2) When used repeatedly It has been found that Na ₂ O in sodium silicate evaporates, and as a result, the heating function of the heating element is lowered. 3) Since the heat shrinkage of the heating element is larger than that of the refractory insulation integrated with the heating element, the heating element peels off near the boundary surface between the heating element and the refractory insulation when used repeatedly. Turned out to be.

  In addition to the above characteristics, the object of the present invention is that there is little deterioration of the adjacent refractory insulation, maintains a good heat generation function even after repeated use, and generates heat near the boundary surface between the heating element and the refractory insulation. It is providing the heat generating body which has the characteristic that a body does not peel.

As a result of studies conducted in view of the above problems, the present inventor has first reached the conclusion that the Na ₂ O component is indispensable in order for the heating element to exhibit self-heating characteristics from room temperature to 1000 ° C. did. If the Na ₂ O component of the heating element is contained as β-alumina, the adjacent refractory heat insulating material does not react with the heating element, and even if it is repeatedly used at a high temperature, the heating element has a good heating function. It has been found that it is possible to maintain. Furthermore, among the many types of alumina, in particular, if fused alumina is the main component constituting the heating element, peeling of the heating element near the boundary surface between the heating element and the refractory heat insulating material is eliminated. I found that I can do it. The present invention has been made based on such knowledge.

Examples of the solving means of the present invention are the coating material according to claims 1 to 5 and the fireproof heat insulating material according to claims 6 and 7 .

  According to the present invention, even if the object to be baked is made of a material that has low microwave absorption at low temperatures and is difficult to be baked by self-heating, only one type of heating element is provided without providing another heating means It becomes possible to fire the object to be fired uniformly.

  Therefore, the configuration of the microwave baking furnace is not complicated, and temperature control during the operation can be easily performed.

Furthermore, there is no deterioration of the refractory insulation due to the Na ₂ O component in the heating element, and it becomes possible to maintain a good heating function of the heating element even when used repeatedly at high temperatures. Since peeling near the boundary with the heat insulating material is eliminated, the durability of the furnace can be greatly improved.

The heating element of the present invention comprises electrofused alumina and β-alumina. The heating element of the present invention comprises alumina and β-alumina, which are the same materials as the material to be fired, and the important point is that among the many types of alumina, especially fused alumina is selected. In addition, the Na ₂ O component of the heating element is contained as β-alumina.

  Considering that the heating element needs to generate heat at a high temperature equivalent to the alumina that is the object to be fired, it is preferable that the heating element comprises alumina particles that are the same material as the material to be fired. However, since the heat shrinkage of the heating element is larger than the heat shrinkage of the refractory insulation integrated with the heating element, the heating element peels off near the boundary surface between the heating element and the refractory insulation when used repeatedly. Investigated that there is. As a result of intensive studies in view of this problem, it has been found that the above-described peeling largely depends on the type of alumina used. There are various types of alumina particles, such as calcined alumina and fused alumina, depending on the production method, and it has been found that it is particularly preferable to select fused alumina. When fused alumina is used as the alumina particles constituting the heating element, it is possible to suppress the heat shrinkage of the heating element, and peeling near the boundary between the heating element and the refractory insulation that may occur due to repeated use. Can be resolved.

  The alumina particles used have an average particle size (average particle size measured by JIS R 1692 (1997) “particle size distribution measurement method of fine ceramic raw material by laser diffraction / scattering method”. It is more preferable to include fused alumina in the range of 100 μm.

  When the average particle size of the fused alumina constituting the heating element is 15 μm or more, the heating function of the heating element by microwave absorption can be kept more stable.

  Further, if the average particle diameter of the fused alumina constituting the heating element is 100 μm or less, as described later, when the heating element is formed as a coating material, the coatability and workability of the coating material are improved. Can keep.

  As described above, the heating element includes alumina particles. When alumina reaches a high temperature of 1000 ° C. or higher, the dielectric loss rapidly increases (the microwave absorption increases) and self-heats. However, at a temperature lower than this, since the microwave absorption of alumina itself is small, it is difficult to raise the temperature by self-heating of alumina itself.

  Therefore, since the alumina particles constituting the heating element do not generate heat by self-heating at a low temperature range of 1000 ° C. or lower, it is necessary to cause the heating element to generate heat by self-heating even in a low temperature range where the microwave absorption of the alumina constituting the heating element is small. There is. Therefore, the inventor of the present application first uses sodium silicate as the inorganic binder that binds the alumina particles constituting the heating element, so that the resulting heating element can be used in the low temperature range where the alumina does not self-heat. The inventors have found that excellent self-heating characteristics are exhibited by microwave absorption (Patent Document 3).

However, if a heating element containing sodium silicate as an inorganic binder is repeatedly used at a high temperature, it reacts with the refractory insulation adjacent to the heating element due to the Na ₂ O component in the sodium silicate at a high temperature. It has been found that heat insulation may be deteriorated. Further, it has been found that when repeatedly used at a high temperature, the Na ₂ O component evaporates, and as a result, the heat generation function of the heating element may deteriorate.

In view of such a problem, a result of intensive studies, the self-heating characteristics in a low temperature region, although Na 2 _O component is essential, be contained the Na 2 _O component of the heating element as a β- alumina It has been found that the deterioration of the refractory heat insulating material due to the reaction between the Na ₂ O component and the refractory heat insulating material can be eliminated. Furthermore, it has been found that when the Na ₂ O component of the heating element is added as β-alumina, the heating element exhibits a stable heating function even if the heating element is repeatedly used at high temperatures.

β-alumina is represented by a general formula R ₂ O · 11Al ₂ O ₃ (R is an alkali metal) in a broad sense, and in a narrow sense, it indicates sodium-β-alumina where the alkali metal R is Na. . The ideal chemical composition is Na ₂ O · 11Al ₂ O ₃ but generally contains an excess of Na ₂ O. Furthermore, beta beta .'- alumina chemical composition is represented by _{Na 2 O · 7Al 2 O 3} , is a chemical composition represented by _{Na 2 O · 5~6Al 2 O 3} "- knowledge that alumina is present It has been.

  In the present specification, in addition to β-alumina, the above β′-alumina and β ″ -alumina are also collectively referred to as “β-alumina”.

  In the present invention, it is possible to use not only β-alumina deviating from the ideal chemical composition but also β′-alumina and β ″ -alumina, and β-alumina in the present invention is β-alumina in a narrow sense. It is not limited to.

β-alumina is an ionic conductor having a two-dimensional or layered conduction path, and its crystal structure is a layered structure composed of a surface on which Na ⁺ ions are present and an oxygen layer having a structure similar to a spinel structure. Since Na ⁺ ions can easily migrate along this layer, they exhibit very high Na ⁺ ion conductivity. Substances with ions that contribute to electrical conduction generate heat not only due to dielectric loss but also due to power loss due to conduction current. For these reasons, it can be considered that β-alumina is effective for exhibiting an excellent heat generation function in a heat generating element with a slight Na ₂ O content in a low temperature range of 1000 ° C. or lower.

  The average particle diameter of the β-alumina particles used (JIS R 1692 (1997) “Average particle diameter measured by laser diffraction / scattering method of fine ceramic raw material”. The same applies hereinafter). A range of 100 μm is more preferable. When the average particle diameter of β-alumina is within the above range, as will be described later, when the heating element is formed as an irregular coating material, the coating property and workability of the coating material can be kept better. it can.

The density of the heating element of the present invention is preferably 1000 to 1500 kg / m ³ .

Furthermore, it is preferable to add an inorganic binder made of SiO ₂ component to the heating element. Addition of the inorganic binder increases the strength of the heating element. Further, at a high temperature, the SiO ₂ component of the inorganic binder reacts with a part of the fused alumina to produce a small amount of mullite, which is a reaction accompanied by volume expansion. Heating shrinkage of the heating element is offset. Therefore, peeling near the boundary between the heating element and the refractory heat insulating material due to heat shrinkage can be more effectively eliminated. However, if mullite is generated more than necessary, the heating function of the heating element at high temperatures may be reduced.

  Furthermore, when the heating element of the present invention contains inorganic fibers as a reinforcing material, the thermal shock resistance of the resulting heating element is improved, which is more preferable. As the inorganic fiber serving as a reinforcing material, alumina silica fiber, alumina fiber, and mullite fiber are preferable. Since the firing temperature of alumina is as high as 1600 ° C. or higher, among these, alumina fibers and mullite fibers excellent in heat resistance at higher temperatures can be used more preferably.

  The heating element of the present invention is more preferably formed of an irregular coating material in the form of slurry or cement. When the heating element is formed by a coating material, a thickener and water can be appropriately used in addition to fused alumina, β-alumina, and, if necessary, an inorganic binder and inorganic fibers.

  A structure in which an inorganic fibrous material is used as a base material and the heating element is provided on one surface of the base material is suitable as a refractory heat insulating material for a microwave firing furnace.

  The base material on which the heating element is provided is preferably a material that can transmit microwaves and has excellent heat insulating properties. When the microwave is absorbed by the base material and the consumption of the microwave by the base material is increased, the amount of energy required for firing the object to be fired increases as a result. Moreover, in order to suppress the temperature drop of the heating element due to radiative cooling, the base material preferably has high heat insulating properties. In particular, the firing temperature of alumina is as high as 1600 ° C. or higher, and the heat insulating property of the base material is important in order to suppress the radiative cooling of the exothermic heating element. Furthermore, in the microwave firing, since the high-speed temperature rise and the high-speed cooling are performed, the substrate is preferably excellent in thermal shock resistance.

  Examples of the base material satisfying such characteristics include inorganic fiber materials such as ceramic fiber blankets, blocks and boards mainly composed of alumina fibers, mullite fibers, and alumina sill force fibers. A ceramic fiber fireproof heat insulating material can transmit microwaves and has excellent thermal shock resistance in addition to excellent heat insulation and heat resistance, and can be preferably used. In particular, since the blanket and the block are excellent in elasticity, the blanket and the block can be more preferably used in a portion where the heating element is bonded and bonded. If the blanket or block with excellent elasticity is used at the part where the heating element is bonded and bonded, the heating shrinkage of the heating element can be alleviated with the blanket and block. It is more effective in eliminating peeling near the boundary.

  The schematic diagram of the embodiment of the fireproof heat insulating material which concerns on this invention is shown in FIGS. 1-3.

  FIG. 1 shows a refractory heat insulating material obtained by bonding (coating) a heating element (coating material) 1 to a ceramic fiber board 2.

  FIG. 2 shows a refractory heat insulating material obtained by bonding (coating) a heating element (coating material) 1 to a ceramic fiber blanket 3. FIG. 2 shows an example in which the ceramic fiber blanket 3 is bonded to the ceramic fiber board 2.

  FIG. 3 shows a refractory heat insulating material obtained by bonding (coating) a heating element (coating material) 1 to a ceramic fiber block 4. FIG. 3 shows an example in which the block 4 is coupled to the board 2.

Next, the present invention will be specifically described with reference to examples.

  Based on the composition shown in Table 1, a predetermined amount of raw materials were blended, and this was stirred and kneaded with a mixer to obtain an irregular coating material for forming a heating element.

  The average particle size of the powder shown in Table 1 was measured by JIS R 1692 (1997) “Method for measuring particle size distribution of fine ceramic raw material by laser diffraction / scattering method”. The amount is shown in parts by weight.

  Using a heating element obtained by the composition shown in Table 1, an experiment was performed in which an alumina ceramic was fired in a microwave firing furnace.

  As shown in FIG. 3, a plurality of ceramic fiber blocks 4 (16D block made by Saint-Gobain TM, thickness 25 mm) are bonded to one side of the ceramic fiber board 2 (FMX-17RB made by Saint-Gobain TM, thickness 25 mm). Then, the coating material 1 produced by the above blending was applied to the surface of the block 4 on the ceramic fiber board 2 with a thickness of 2 mm (in the embodiment shown in the schematic diagram of FIG. 3). Then, it was dried at 100 ° C. for 3 hours and calcined at 1000 ° C. for 1 hour to obtain a refractory heat insulating material A provided with the heating element of the present invention.

  Moreover, as shown in FIG. 1, the coating material 1 produced by the said mixing | blending was apply | coated by the thickness of 2 mm to the single side | surface of the ceramic fiber board 2 (FMX-17RB made from Saint-Gobain TM, thickness 25mm). (This is the embodiment shown in the schematic diagram of FIG. 1). Then, it was dried at 100 ° C. for 3 hours and calcined at 1000 ° C. for 1 hour to obtain a refractory heat insulating material B provided with the heating element of the present invention.

  Next, using the refractory heat insulating materials A and B, a furnace internal space of 200 × 200 × 200 mm was created with the surface provided with the heating element inside. At this time, the above-mentioned refractory heat insulating material A was installed on the furnace ceiling and side walls, and the above refractory heat insulating material B was installed on the bottom surface of the furnace. In order to further insulate the manufactured closed space in the furnace, a layer of a ceramic fiber board 2 (FMX-16CV and 14R manufactured by Saint-Gobain TM) having a thickness of 25 mm was disposed on the outside thereof to provide a heat insulating layer.

  Next, a base material for an alumina molded product having a size of 100 × 50 × 35 mm, which was molded by adding an appropriate amount of force ruboxymethylcellulose and water to an alumina powder, was prepared as an object to be fired. Two substrates of the alumina molded product were irradiated with microwaves having a frequency of 2.45 GHz in the above-described closed space, and the furnace temperature was measured with a radiation thermometer.

  In Table 1, four types of fused alumina 1-4, two types of baked alumina 1-2, and one type of β-alumina were used.

  Example 1 is 80 parts by weight of fused alumina powder 2 (average particle size 15 μm), 10 parts by weight of fused alumina 3 (average particle size 7 μm), 10 parts by weight of β-alumina (average particle size 15 μm), mullite fiber It is a heating element produced from a coating material composed of 9 parts by weight.

  In Example 2, 60 parts by weight of fused alumina powder 2 (average particle size 15 μm), 30 parts by weight of fused alumina 3 (average particle size 7 μm), 10 parts by weight of β-alumina (average particle size 15 μm), mullite fiber It is a heating element produced from a coating material composed of 9 parts by weight.

  In Example 3, 85 parts by weight of fused alumina powder 1 (average particle size 67 μm), 5 parts by weight of fused alumina 4 (average particle size 2 μm), 10 parts by weight of β-alumina (average particle size 15 μm), mullite fiber It is a heating element produced from a coating material composed of 9 parts by weight.

  In Example 4, 80 parts by weight of fused alumina powder 1 (average particle size 67 μm), 10 parts by weight of fused alumina 4 (average particle size 2 μm), 10 parts by weight of β-alumina (average particle size 15 μm), mullite fiber It is a heating element produced from a coating material composed of 9 parts by weight.

  In Example 5, 70 parts by weight of fused alumina powder 1 (average particle size 67 μm), 20 parts by weight of fused alumina 4 (average particle size 2 μm), 10 parts by weight of β-alumina (average particle size 15 μm), mullite fiber It is a heating element produced from a coating material composed of 9 parts by weight.

Example 6 is 80 parts by weight of fused alumina powder 2 (average particle size 15 μm), 10 parts by weight of fused alumina 3 (average particle size 7 μm), 10 parts by weight of β-alumina (average particle size 15 μm), mullite fiber It is a heating element produced from a coating material composed of 9 parts by weight and 5 parts by weight of silica sol (solid content: 40% by weight).

  In Example 7, 80 parts by weight of fused alumina powder 2 (average particle size 15 μm), 10 parts by weight of fused alumina 3 (average particle size 7 μm), 10 parts by weight of β-alumina (average particle size 15 μm), mullite fiber It is a heating element produced from a coating material composed of 9 parts by weight and 12 parts by weight of silica sol (solid content: 40% by weight).

  In Example 8, 80 parts by weight of fused alumina powder 2 (average particle size 15 μm), 10 parts by weight of fused alumina 3 (average particle size 7 μm), 10 parts by weight of β-alumina (average particle size 15 μm), mullite fiber This is a heating element made of a coating material composed of 9 parts by weight and 25 parts by weight of silica sol (solid content: 40% by weight).

  In Example 9, 85 parts by weight of fused alumina powder 2 (average particle size 15 μm), 15 parts by weight of fused alumina 3 (average particle size 7 μm), 5 parts by weight of β-alumina (average particle size 15 μm), mullite fiber This is a heating element made of a coating material composed of 9 parts by weight and 25 parts by weight of silica sol (solid content: 40% by weight).

  In Example 10, 85 parts by weight of fused alumina powder 2 (average particle size 15 μm), 15 parts by weight of fused alumina 3 (average particle size 7 μm), 5 parts by weight of β-alumina (average particle size 15 μm), mullite fiber It is a heating element produced from a coating material composed of 9 parts by weight and 37 parts by weight of silica sol (solid content: 40% by weight).

  In Example 11, 85 parts by weight of fused alumina powder 2 (average particle size 15 μm), 15 parts by weight of fused alumina 3 (average particle size 7 μm), 5 parts by weight of β-alumina (average particle size 15 μm), mullite fiber It is a heating element produced from a coating material composed of 9 parts by weight and 50 parts by weight of silica sol (solid content: 40% by weight).

  As a representative example of Examples 1 to 11, in particular, the heat generation characteristics of the heating element of Example 10 are shown in FIG. The time required for raising the temperature in the furnace to 1600 ° C. is 140 minutes for the first temperature rise, and slightly longer than the first temperature rise for the second and subsequent temperature rises. However, the temperature rise time is in the range of 180 ± 20 minutes, and it can be found that the heat generation characteristics are stabilized. The other examples were the same.

  In addition, in the temperature rise curve in the furnace of FIG. 4, a portion having a step-like shape is seen at around 800 ° C., which is the radiation temperature used when measuring the furnace temperature of the microwave baking furnace. This occurs because the meter switches from low temperature to high temperature, and there is no problem with the furnace.

  Moreover, in Examples 1-11, even if it heated up inside the furnace repeatedly to 1600 degreeC, peeling in the vicinity of the boundary of a heat generating body and a refractory heat insulating material did not arise. Furthermore, the heating element and the refractory insulation did not react and the refractory insulation did not deteriorate.

  Comparative Example 1 is calcined alumina powder 1 (average particle size 5 μm) 100 parts by weight, β-alumina (average particle size 15 μm) 5 parts by weight, mullite fiber 9 parts by weight, silica sol (solid content 40% by weight) 50 parts by weight. It is a heat generating body produced from the coating material comprised by this.

  Comparative Example 2 is calcined alumina powder 2 (average particle size 13 μm) 100 parts by weight, β-alumina (average particle size 15 μm) 5 parts by weight, mullite fiber 9 parts by weight, silica sol (solid content 40% by weight) 50 parts by weight. It is a heat generating body produced from the coating material comprised by this.

  In the heating elements of Comparative Examples 1 and 2, the heat generation characteristics were good as in Examples 1-11. However, when the temperature inside the furnace is repeatedly raised, particularly in the ceiling part of the furnace, peeling near the boundary between the heating element and the refractory heat insulating material becomes remarkable, and the durability is inferior.

An end face of a refractory heat insulating material obtained by bonding (coating) a heating element (coating material) to a ceramic fiber board is shown. An end face of a refractory heat insulating material obtained by bonding (coating) a heating element (coating material) to a ceramic fiber blanket is shown. An end face of a refractory heat insulating material obtained by bonding (coating) a heating element (coating material) to a ceramic fiber block is shown. It is a graph which shows the temperature rising characteristic in the furnace measured using the radiation thermometer based on Example 10 of this invention.

Explanation of symbols

1 Heating element (coating material)
2 Ceramic fiber board 3 Ceramic fiber blanket 4 Ceramic fiber block

Claims (7)

Heating element which generates heat by irradiation with microwaves, see contains the fused alumina and beta-alumina as a material for forming the heating element, alumina, beta-alumina, a binder, in addition to the inorganic fibers, water and A coating material comprising a thickener . The coating material according to claim 1, wherein the fused alumina includes fused alumina having an average particle size of 15 μm or more and 100 μm or less. The coating material according to claim 1 or 2, wherein the heating element contains an inorganic binder containing a SiO ₂ component. The coating material according to any one of claims 1 to 3, wherein the heating element further contains inorganic fibers as reinforcing fibers. The coating material according to claim 4, wherein the inorganic fiber is at least one selected from alumina fiber and mullite fiber. It is a refractory heat insulating material for a microwave firing furnace, and a heating layer is provided on one side of the substrate, the substrate is mainly composed of an inorganic fibrous material, and the heating layer is any one of claims 1 to 5. A fireproof heat insulating material comprising the coating material according to the item . The fireproof heat insulating material according to claim 6 , wherein the inorganic fibrous material comprises an inorganic fibrous blanket or an inorganic fibrous block.

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