JP3612943B2 - Manufacturing method of exhaust gas filter - Google Patents

Description

【００７１】
ここで、試料Ｎｏ２〜４は本発明によるもので、ＴｉＯ_２の添加によって、格子壁の化学組成がＡｌ_２Ｏ_３とＴｉＯ_２が略等モルで構成されている。なお、添加するＴｉＯ_２の種類は、表１に示すデータ採取においてはアナターゼ型を使用したが、ルチル型やアナターゼ型とルチル型の混合粉末でも同様な傾向を示した。
【００７２】
試料Ｎｏ１は、第１のセラミックス原料のみの使用で、ＴｉＯ_２を添加していない。この試料については、熱処理による熱膨張係数の変化はなくチタン酸アルミニウムの高温安定性はあるが、圧縮強度が低い。そして、試料Ｎｏ１の格子壁は、振動が激しい条件下においてクラックを生じやすい。一方、試料Ｎｏ２〜４の格子壁は機械的強度が高く振動に対してクラックを生じにくい。
【００７３】
試料Ｎｏ５は、第１のセラミックス原料にＴｉＯ_２を多めに添加したものである。この試料については、機械的強度は高くクラックを生じにくいが、高温安定性に劣る。これは、チタン酸アルミニウムがコランダムとルチルに分解した結果で、高熱膨張のコランダムとルチルが格子壁の熱膨張係数の値を引き上げているからである。
【００７７】
【発明の効果】
以上のように、本発明によれば、Ａｌ₂Ｏ₃がＴｉＯ₂に対して等モルより３〜６ｗｔ％多く配分されたチタン酸アルミニウムからなる主成分と、少なくともＳｉＯ₂を３〜１０ｗｔ％、Ｆｅ₂Ｏ₃を１〜３ｗｔ％有する副成分とからなる第１のセラミックス原料を用意する工程と、ＴｉＯ₂からなる第２のセラミックス原料を第１のセラミックス原料に添加して、第１のセラミックス原料と第２のセラミックス原料の総量としてＡｌ₂Ｏ₃とＴｉＯ₂が略等モルになるように調整する工程と、調整された第１のセラミックス原料と第２のセラミックス原料を造孔剤、結合剤、可塑剤、水とともに混合してセラミックス坏土を作製する工程と、セラミックス坏土をハニカム形状に押出成形する工程と、得られた押出成形体を加熱、焼結して多孔質セラミックスを形成する工程とにより排ガスフィルタを製造することとしているので、チタン酸アルミニウムの分解が抑制されて機械的強度が向上し、寸法精度が安定した排ガスフィルタを製造することができるという有効な効果が得られる。
【００７８】
第１のセラミックス原料の平均粒子径を８〜３０μｍとすることにより、排ガスフィルタの焼成収縮率を低減することができるという有効な効果が得られる。
【００７９】
第２のセラミックス原料の平均粒子径を１０μｍ以下とすることにより、第１のセラミックスと焼結反応し易く、排ガスフィルタの機械的強度が向上するという有効な効果が得られる。
【図面の簡単な説明】
【図１】本発明の一実施の形態による排ガスフィルタを示す斜視図
【図２】図１の排ガスフィルタの端面部の拡大図
【図３】図１の排ガスフィルタの断面における排ガスの流路を示す概略図
【図４】図１の排ガスフィルタにおける格子壁のＸ線回折図
【図５】比較例である従来の排ガスフィルタの格子壁のＸ線回折図
【符号の説明】
１ 排ガスフィルタ
２ 貫通孔
３ 格子壁
４ 封止材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas filter for filtering black smoke and the like contained in exhaust gas discharged from a diesel engine or the like, and a method for manufacturing the same.
[0002]
[Prior art]
In recent years, as environmental problems have become serious, the treatment of black smoke dispersed in the atmosphere together with exhaust gas discharged from combustion engines such as diesel engines has become a problem. In order to solve this problem, an exhaust gas filter is provided in the middle of the exhaust pipe of a combustion engine such as a diesel engine, and black smoke is filtered and collected by this exhaust gas filter to discharge only the exhaust gas.
[0003]
By the way, if a large amount of black smoke is trapped in the exhaust gas filter, the exhaust gas filter becomes clogged and obstructs the exhaust gas flow path, resulting in an adverse effect on the combustion efficiency of the engine. Will be affected. For this reason, when reaching a predetermined collection amount provided in advance, it is necessary to burn black smoke together with air to gasify it, remove clogging, return the exhaust gas filter to the initial state, and regenerate it.
[0004]
The regeneration of the exhaust gas filter mainly uses an electric heater system, and a control unit that detects that a predetermined amount of black smoke is collected controls to stably burn the black smoke. Here, the electric heater method is that an electric heater is provided on the inflow side or outflow side of the exhaust gas, and the exhaust gas filter is heated by energizing the electric heater and is blackened by the air supplied from the inflow side or outflow side of the exhaust gas. It burns smoke. During regeneration, the diesel engine is continuously operated using a spare exhaust gas filter.
[0005]
By the way, the collected black smoke is distributed over the entire surface of the exhaust gas filter, but the black smoke on the entire surface does not burn at the same time, but gradually proceeds from the end of the exhaust gas filter on the electric heater side. Therefore, a temperature gradient occurs depending on the portion of the exhaust gas filter, and a thermal stress is generated due to a difference in thermal expansion. In normal use, the amount of black smoke collected is predicted and burned at a relatively early stage to regenerate the exhaust gas filter. In this case, the black smoke gradually burns at 600 to 900 ° C., and the exhaust gas filter is not heated suddenly and is not subject to a large thermal stress.
[0006]
On the other hand, when the control by the control unit is not sufficient, or when black smoke is collected over a predetermined amount, the black smoke burns rapidly due to heating, and suddenly rises to a high temperature of 1000 ° C or higher, which is abnormal Burn. At this time, the exhaust gas filter is partially subjected to a large thermal shock, and cracks are generated due to fatigue failure.
[0007]
Therefore, the exhaust gas filter needs to be made of a material that can withstand the sudden thermal shock caused by the abnormal combustion, and low thermal expansion and high thermal shock resistance are strongly required. Furthermore, it is necessary that the black smoke collection efficiency is high, and at the same time, the flow path resistance of the exhaust gas generated by the black smoke collection is small.
[0008]
Therefore, in order to satisfy these requirements, various developments have been made on the materials, structures, manufacturing methods, and the like of exhaust gas filters.
[0009]
Here, the porous ceramic material constituting the lattice wall of the exhaust gas filter will be described.
[0010]
For example, one of the materials commonly used for exhaust gas filters is a cordierite sintered body (2MgO · 2Al) with a small thermal expansion coefficient and excellent thermal shock resistance.₂O₃・ 5SiO₂) The thermal expansion coefficient of this cordierite shows anisotropy depending on the crystal direction, and the crystal a-axis is 2.0 × 10^-6K^-1, C-axis is -0.9x10^-6K^-1Is different.
[0011]
However, the one formed into a honeycomb shape by the extrusion molding method has a c-axis because plate crystals such as kaolin and talc contained in the raw material in the process are dispersed in a direction parallel to the lattice wall due to shearing force. Is slightly oriented in the extrusion direction (exhaust gas passage direction). As a result, the thermal expansion coefficient in the extrusion molding direction of cordierite is about 0.5 × 10^-6K^-1The coefficient of thermal expansion in the direction perpendicular to the extrusion direction is about 0.9 × 10^-6K^-1As a result, the thermal expansion coefficient is small and the anisotropy is reduced throughout, and an exhaust gas filter having high thermal shock resistance is manufactured.
[0012]
On the other hand, as a porous ceramic material, in addition to conventional cordierite, aluminum titanate (Al₂O₃・ TiO₂) Has begun to be considered. Aluminum titanate has a high melting temperature of 1600 ° C. or higher, and can sufficiently withstand the high temperature during regeneration.
[0013]
However, the thermal expansion coefficient of this aluminum titanate also shows anisotropy depending on the crystal direction, and the crystal a-axis is 11.8 × 10 6.^-6K^-1, B-axis is 19.4 × 10^-6K^-1, C-axis is -2.6 × 10^-6K^-1In addition, the anisotropy is large compared to cordierite crystals. And when such anisotropy is large, there is a problem that microcracks are easily generated between crystal grains. Another problem is that aluminum titanate crystals are easily decomposed into titanium oxide (rutile) and aluminum oxide (corundum) at a high temperature (750 to 1200 ° C.).
[0014]
In this way, aluminum titanate is a material with low expansion and excellent heat resistance. However, compared to other ceramic materials, the mechanical strength is low due to microcracks between crystal grains generated during production, and the production conditions In some cases, there is a problem that the coefficient of thermal expansion tends to change and become large due to a change in material due to decomposition of crystal grains.
[0015]
Accordingly, improvements have been made in improving the mechanical strength and control of the thermal expansion coefficient of aluminum titanate, and some have already been put into practical use.
[0016]
For example, Japanese Patent Publication No. Sho 62-40061 discloses a structure of a ceramic honeycomb whose main component is aluminum titanate. In addition to aluminum titanate, this is SiO₂Is contained in an amount of 4 to 10 wt% to improve the strength and high temperature stability of the ceramic honeycomb. Japanese Laid-Open Patent Publication No. 4-26544 discloses a structure of high fracture strain ceramics whose main component is aluminum titanate. This is because SiO₂, Fe₂O₃Is added as a crystal other than aluminum titanate, corundum, mullite, rutile, etc., to increase the breaking strain and make it difficult to damage the ceramic.
[0017]
[Problems to be solved by the invention]
However, the technique for improving the strength and high-temperature stability of the ceramic honeycomb described in Japanese Examined Patent Publication No. 62-40061 is useful as a catalyst carrier, but is insufficient as an exhaust gas filter. That is, the catalyst carrier and the exhaust gas filter both have a lattice wall porosity of 30 to 50%, which is the same level, but the lattice wall has a large difference in pore diameter. The average pore size of the exhaust gas filter is generally 10 to 20 μm, and black smoke can be collected with high efficiency at this average pore size, whereas the average pore size of the catalyst carrier is generally submicron to several μm. This is because the mechanical strength of the ceramic honeycomb is lower as the pore diameter is larger, and the lattice walls of the exhaust gas filter are extremely easily broken because they form continuous air holes.
[0018]
Further, the technique described in JP-A-4-26544, which increases the breaking strain and makes it difficult to damage ceramics, is useful in a relatively low temperature range, but when used at 750 to 1200 ° C., aluminum titanate Since it is easily decomposed into titanium oxide (rutile) and aluminum oxide (corundum), it is still insufficient as an exhaust gas filter. In other words, this ceramic is composed of SiO as a subsidiary component.₂2.0-5.5%, Fe₂O₃However, since aluminum titanate contains other crystal components such as corundum, mullite, rutile, etc., it decomposes extremely in the temperature range of 750-1200 ° C. This is because it becomes easier.
[0019]
Therefore, the present invention provides an exhaust gas filter capable of suppressing cracking due to vibration while suppressing decomposition of aluminum titanate when the exhaust gas filter is heated to 600 ° C. or higher, which is the combustion temperature of black smoke, and regenerated. It aims at providing the manufacturing method.
[0023]
[Means for Solving the Problems]
To solve this challenge,The manufacturing method of the exhaust gas filter of the present invention is made of Al.₂O_ThreeIs TiO₂A main component composed of aluminum titanate distributed in an amount of 3 to 6 wt% more than equimolar, and at least SiO₂3 to 10 wt%, Fe₂O_ThreePreparing a first ceramic raw material comprising a subcomponent having 1 to 3 wt% of TiO,₂The second ceramic raw material made of is added to the first ceramic raw material, and the total amount of the first ceramic raw material and the second ceramic raw material is Al.₂O_ThreeAnd TiO₂And adjusting the first ceramic raw material and the second ceramic raw material together with a pore-forming agent, a binder, a plasticizer, and water to prepare a ceramic clay. And a step of extruding the ceramic clay into a honeycomb shape and a step of heating and sintering the obtained extrudate to form a porous ceramic.
[0024]
Thereby, since the aluminum titanate is synthesized in advance using the first ceramic material, it is possible to manufacture an exhaust gas filter in which the decomposition of the aluminum titanate is suppressed, the mechanical strength is improved, and the dimensional accuracy is stable.
[0025]
In this method for producing an exhaust gas filter, it is desirable that the first ceramic raw material has an average particle size of 8 to 30 μm, and the second ceramic raw material has an average particle size of 10 μm or less.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Of the present inventionClaim1The invention described in Al₂O_ThreeIs TiO₂A main component composed of aluminum titanate distributed in an amount of 3 to 6 wt% more than equimolar, and at least SiO₂3 to 10 wt%, Fe₂O_ThreePreparing a first ceramic raw material comprising a subcomponent having 1 to 3 wt% of TiO,₂The second ceramic raw material made of is added to the first ceramic raw material, and the total amount of the first ceramic raw material and the second ceramic raw material is Al.₂O_ThreeAnd TiO₂And adjusting the first ceramic raw material and the second ceramic raw material together with a pore-forming agent, a binder, a plasticizer, and water to prepare a ceramic clay. A process for extruding the ceramic clay into a honeycomb shape, and heating and sintering the obtained extrudate to form porous ceramics. Decomposition is suppressed, mechanical strength is improved, and an exhaust gas filter having stable dimensional accuracy can be produced.
[0030]
Claim2The invention described in claim 11In the described invention, the first ceramic raw material has an average particle size of 8 to 30 μm and a method for producing an exhaust gas filter, which has an effect of reducing a firing shrinkage rate of the exhaust gas filter.
[0031]
And claims3The invention described in claim 11Or2In the described invention, the second ceramic raw material has an average particle diameter of 10 μm or less and a method for producing an exhaust gas filter, which has an effect of being easily sintered with the first ceramic and improving mechanical strength.
[0032]
Hereinafter, embodiments of the present invention will be described with reference to FIGS. Note that the same members are denoted by the same reference symbols throughout the drawings for describing the embodiments, and redundant description is omitted.
[0033]
1 is a perspective view showing an exhaust gas filter according to an embodiment of the present invention, FIG. 2 is an enlarged view of an end surface portion of the exhaust gas filter of FIG. 1, and FIG. 3 shows a flow path of exhaust gas in the cross section of the exhaust gas filter of FIG. FIG. 4 is a schematic diagram, FIG. 4 is an X-ray diffraction diagram of a grating wall in the exhaust gas filter of FIG. 1, and FIG.
[0034]
As shown in FIG. 1, a cylindrical exhaust gas filter 1 has a large number of through-holes 2 in the exhaust gas flow channel direction which is the length direction thereof. The through hole 2 is partitioned by a lattice wall 3 made of porous ceramics and having a large number of continuous air holes. One end surface portion 1 a that is the exhaust gas inlet of the through hole 4 and the other end surface portion 1 b that is the exhaust gas outlet are alternately closed by the sealing material 4.
[0035]
Such an exhaust gas filter 1 is manufactured as follows.
First, Al₂O₃Is TiO₂A main component composed of aluminum titanate distributed in an amount of 3 to 6 wt% more than equimolar, and at least SiO₂3 to 10 wt%, Fe₂O₃A first ceramic raw material comprising 1 to 3 wt% of an auxiliary component is prepared. In addition, added SiO₂, Fe₂O₃Such subcomponents are effective in sintering and suppressing decomposition of aluminum titanate, which is the main component.
[0036]
Next, TiO₂A second ceramic raw material made of is added to the first ceramic raw material, and the total amount of the first ceramic raw material and the second ceramic raw material is Al.₂O₃And TiO₂Is approximately equimolar (Al₂O₃: TiO₂= 56.1 wt%: 43.9 wt%).
[0037]
Then, the adjusted first ceramic raw material and second ceramic raw material are mixed with a pore forming agent, a binder, a plasticizer, water and the like for forming continuous air holes in the lattice wall to form a clay. This is extruded through a honeycomb-shaped mold.
[0038]
Thereafter, the obtained extrusion-molded body is dried and heat-treated at 1500 ° C., and the through-hole 2 is filled with the preliminarily prepared sealing material 4 (main component is aluminum titanate), and then heat-treated at 1400 ° C. Thereby, the above-mentioned exhaust gas filter 1 is obtained.
[0039]
Here, SiO contained in the lattice wall 3₂The amount of is suitably in the range of 3 to 10 wt%. That is, when less than 3 wt%, aluminum titanate is Al.₂O₃And TiO₂And the thermal expansion coefficient increases rapidly. Moreover, when more than 10 wt%, SiO₂This is because crystallization (such as cristobalite) causes a rapid increase in the coefficient of thermal expansion. That is, SiO₂This is because cracks are likely to occur in the lattice wall 3 due to an increase in thermal expansion.
[0040]
In addition, Al contained in the lattice wall 3₂O_ThreeAnd TiO₂Is approximately equimolarso,Al₂O_ThreeAnd TiO₂When the content of Si is deviated from an equimolar amount (theoretical composition ratio), other crystal phases are likely to exist in addition to aluminum titanate, even if SiO₂Or Fe₂O_ThreeThis is because aluminum titanate is likely to be decomposed even if it contains. And when aluminum titanate decomposes | disassembles, it will become easy to produce a crack in the lattice wall 3 by the increase in thermal expansion.
[0041]
Here, in the present embodiment, a mercury porosimeter manufactured by Shimadzu Corporation (micromeritics poreizer 9320 type) was used in evaluating the lattice wall 3.
[0042]
This apparatus is based on the mercury intrusion method and determines how many cc of mercury per 1 g of mercury penetrates the exhaust gas filter. More specifically, the lattice wall 3 of the exhaust gas filter 1 is housed in a predetermined container, and mercury is injected into the container by changing the pressure stepwise. When the pressure in the container is low, mercury enters only relatively large pores, and when the pressure is high, mercury enters even small pores. Therefore, by measuring how many cc of mercury per gram enters the lattice wall 3 of the exhaust gas filter at a predetermined pressure, it is possible to determine how many continuous air holes with a predetermined pore diameter exist. .
[0043]
The average pore diameter of the continuous air holes formed in the lattice wall 3 is 7 to 20 μm, and the porosity is suitably 30 to 40%. That is, if the average pore diameter is smaller than 7 μm, the pressure loss becomes too high, and if it is larger than 20 μm, the black smoke collecting efficiency is lowered. Further, if the porosity is less than 30%, the pressure loss becomes too high, and if it is more than 40%, the mechanical strength becomes extremely low.
[0044]
Furthermore, the average particle diameter of the first ceramic raw material is suitably in the range of 8 to 30 μm. This is because if the average particle size is less than 8 μm, the firing shrinkage rate of the exhaust gas filter is large, resulting in poor dimensional accuracy, and if it is greater than 30 μm, the sinterability is poor and the mechanical strength is low.
[0045]
When an auxiliary component effective for sintering aluminum titanate is contained in the lattice wall 3, the sintering property of the aluminum titanate particles is promoted, and a strong exhaust gas filter 1 is obtained at a relatively low heat treatment temperature. be able to. In addition, when the lattice wall 3 contains an auxiliary component effective for suppressing decomposition of aluminum titanate, the lattice wall 3 is exposed to a temperature of 600 ° C. or more for a long time when the exhaust gas filter 1 is regenerated (burning black smoke). However, decomposition of the aluminum titanate can be prevented.Added SiO ₂ , Fe ₂ O _Three This subcomponent is effective for sintering and suppressing decomposition of aluminum titanate as a main component. other,Subcomponents effective for suppressing sintering and decomposition of aluminum titanate, ZrO₂MgO and rare earth oxides. In the present embodiment, an example is shown as a subcomponent, but any component may be contained as long as it is effective for sintering and suppressing decomposition of aluminum titanate.
[0046]
The columnar exhaust gas filter 1 thus obtained is configured so that the diameters of the end surface portions 1a and 1b are about 130 to 160 mm and the length along the exhaust gas flow channel direction is about 140 mm to 170 mm. Moreover, the size of the exhaust gas filter 1 is often used when the engine displacement is 2000 to 3000 cc. The reason is that the exhaust gas filter 1 having such a capacity can efficiently collect black smoke and the like in the exhaust gas. In addition, since the exhaust gas filter 1 is cylindrical, stress can be distributed isotropically, processing distortion generated in the manufacturing process is reduced, and the strength is increased.
[0047]
Here, since the exhaust gas filter 1 is made of porous ceramics, many continuous air holes are formed on the outer peripheral surface 1c. However, since heat insulating material or the like is in close contact with the outer peripheral surface 1c during use, Will not leak. When the exhaust gas filter 1 is attached to a diesel engine or the like, the exhaust gas filter 1 is wrapped with an inorganic fibrous heat insulating material or the like, and further stored and fixed in a storage container such as SUS.
[0048]
In the present embodiment, the diameters of the end surface portions 1a and 1b are substantially the same, but the diameter on the end surface portion 1a side is formed larger than the diameter on the end surface portion 1b side, or the opposite is formed. May be.
[0049]
Here, the detailed structure of the end surface portions 1a and 1b will be described. Since the end surface portions 1a and 1b have basically the same structure, the end surface portion 1a will be described here for explanation.
[0050]
FIG. 2 is an enlarged view of an end surface portion of the exhaust gas filter of FIG.
The end surface portion 1a is provided with a plurality of through holes 2 having a rectangular cross section along the direction of the exhaust gas flow path of the exhaust gas filter. The through holes 2 are separated by a lattice wall 3 provided with a number of continuous air holes. . The lattice wall 3 is continuously formed from the end surface portion 1a to the end surface portion 1b. The thicknesses t1 and t2 of the lattice wall 3 are 0.2 to 0.3 mm (the number of through holes 2 is 200 cells / square inch) and 0.4 to 0.5 mm (the number of the through holes 2 is 100 cells / square). It is preferable to configure within a range of (inch). If it is smaller than this, the mechanical strength becomes too low, or the collection efficiency is lowered. Further, if it is larger than this, inconveniences such as an increase in pressure loss may occur.
[0051]
In this embodiment, t1 = t2 because the extrusion molding method is adopted in consideration of mass productivity. However, in other molding methods (for example, a method of laminating processed sheets), t1 <t2 or t1>. You may make it become t2. For example, in FIG. 2, the thickness of the lattice wall 3 parallel to the arrow direction L is increased, and the thickness of the lattice wall 3 parallel to the arrow direction M orthogonal to the arrow direction L is decreased, thereby being parallel to the arrow direction M. Since the exhaust gas easily passes through the lattice wall 3 and the flow rate can be adjusted, the outflow amount of the exhaust gas can be controlled. In addition, by increasing the thickness of the lattice wall 3 on the inner side of the outer peripheral portion (inside the outer peripheral surface 1c), the exhaust gas on the outer peripheral portion side can be easily passed through from the inner peripheral portion, and It is also possible to make the passage amount uniform. And by this, the collection amount of black smoke etc. can be equalize | homogenized in each part of the end surface part 1a of the exhaust gas filter 1, The local stress produced when attaching the exhaust gas filter 1 to a diesel engine etc., use Prevention of damage to the exhaust gas filter 1 due to vibration at the time can be mitigated.
[0052]
Moreover, it is preferable that the pitch A1 along the arrow direction L of the lattice wall 3 and the pitch A2 along the arrow direction M are in the range of 2 mm to 4 mm, respectively. If the pressure is smaller than this, the pressure loss of the exhaust gas becomes high, and if it is larger than this, the amount of trapped black smoke or the like is reduced. In the present embodiment, since A1 = A2, the mechanical strength is isotropically improved and the collection ability is made uniform in each part, so that stable filter characteristics can be obtained. In addition, the cross-sectional shape of the through-hole 2 is made rectangular by making the lengths of the pitch A1 and the pitch A2 different from each other, and a difference is provided in the flow rate of the exhaust gas passing through the long side portion and the short side portion of the formed rectangle. Then, since the bias of the collection ability can be adjusted arbitrarily, the degree of freedom in the design of the storage container of the exhaust gas filter 1 and the configuration of piping connected thereto can be increased.
[0053]
As described above, the sealing material 4 is provided alternately in either of the through holes 2 on the end surface portion 1b side that are the same as the through holes 2 on the end surface portion 1a side. In general, the sealing material 4 is made of the same material composition as that of the lattice wall 3, or a different type of material having a relatively close thermal expansion coefficient is selected, thereby causing cracks or the like generated around the through-hole 2. It is prevented.
[0054]
Moreover, the thermal expansion coefficient of the lattice wall 3 and the sealing material 4 is adjusted by making the main components of the lattice wall 3 and the sealing material 4 the same, and changing the types of the subcomponents and the addition amount thereof. In addition, the hardness and the like of the paste-like sealing material 4 can be adjusted at the time of manufacture, so that workability can be improved and productivity can be improved.
[0055]
Here, the flow path of the exhaust gas when the sealing material 4 is provided in each of the through holes 2 of the end surface portions 1a and 1b will be described with reference to FIG.
[0056]
As shown in FIG. 3, the through hole 2 is partitioned by the lattice wall 3 into an inflow hole 2 a and an outflow hole 2 b. When exhaust gas flows from the end surface portion 1a side, the exhaust gas first flows into the inflow hole 2a in the open state, but the through hole 2 of the opposite end surface portion 1b is sealed by the sealing material 4, so that the lattice It passes through the wall 3, flows out into the outflow hole 2 b, passes through the open through-hole 2, and is discharged out of the system from the end surface portion 1 b. Then, when the exhaust gas passes through the lattice wall 3 made of porous ceramic in this way, black smoke or the like in the exhaust gas is collected inside the exhaust gas filter.
[0057]
Next, the chemical composition and crystal state of the material of the lattice wall 3 will be described in detail. The chemical composition of the lattice wall 3 is Al constituting aluminum titanate.₂O_ThreeAnd TiO₂In addition to the main component consisting ofSiO effective for suppressing sintering and decomposition of at least main component aluminum titanate ₂ , Fe ₂ O _Three A minor component of is added.Subcomponents effective for suppressing sintering and decompositionAsSiO₂, Fe₂O_Three, ZrO₂, MgO, rare earth oxides, etc.ThereThe The reason for this is Al₂O_ThreeAnd TiO₂This is because if aluminum titanate is synthesized only from the above, problems such as insufficient strength due to insufficient sintering and decomposition of aluminum titanate occur.
[0058]
Further, the crystal state of the lattice wall 3 requires that the aluminum titanate crystal particles and the subcomponents exist as a solid solution or a liquid phase and hardly contain other crystal particles. When crystal grains other than aluminum titanate are contained, the high-temperature stability of aluminum titanate tends to be inferior, and decomposition proceeds rapidly in the temperature range of 750 to 1200 ° C. In order to improve the mechanical strength of aluminum titanate products, attempts have been made to make other crystal particles other than aluminum titanate, such as mullite, corundum, rutile, cordierite, etc. There is a problem with stability and it cannot be used. Therefore, in order to improve mechanical strength while maintaining high temperature stability as an exhaust gas filter, crystal particles other than aluminum titanate must not be present.
[0059]
The lattice wall 3 in the present embodiment has a substantially theoretical composition of aluminum titanate (Al₂O₃And TiO₂Is substantially equimolar). As a result, Al₂O₃And TiO₂Does not become surplus, and corundum and rutile are hardly generated.
[0060]
Here, it was shown that crystal grains other than aluminum titanate should not be present, but the high-temperature stability of aluminum titanate varies depending on the type and abundance of other crystal grains. Of course, the smaller the amount of other crystal particles present, the better the high temperature stability. For example, when a small amount of corundum or rutile is present, the decomposition of aluminum titanate progresses considerably slowly and is in a practical range.
[0061]
FIG. 4 is an X-ray diffraction diagram of a grating wall in the exhaust gas filter of FIG. The lattice wall from which data was collected has aluminum titanate and a small amount of rutile. FIG. 5 is an X-ray diffraction pattern of a conventional grating wall as a comparative example. This conventional lattice wall is made of aluminum titanate and rutile and is shown for reference. The measurement used an X-ray diffractometer manufactured by Rigaku.
[0062]
The data shown in FIGS. 4 and 5 were obtained by the X-ray diffraction method. In the X-ray diffraction method, X-rays generated from a tube are irradiated onto a fixed sample, and reflected and scattered X-rays are counted by a detector. At this time, when the sample contains a crystalline substance, a sharp peak appears. This peak is peculiar to the arrangement of the crystal lattice, and the X-ray diffraction pattern (pattern) is almost constant in the X-ray diffraction method.
[0063]
4 and 5, the vertical axis represents the X-ray intensity diffracted by the grating wall 3, and the horizontal axis represents the scanning angle 2θ.
[0064]
In these drawings, 5a is an aluminum titanate crystal peak, and 5b is a rutile crystal peak. When the measurement is performed with the conditions of the X-ray diffractometer and the sample state kept constant, the intensities of the crystal peaks 5a and 5b are almost the same. In this case, the intensity of the crystal peaks 5a and 5b is large when the amount of crystal particles present in the sample is large, and is small when the amount of crystal particles present in the sample is small. Comparing FIG. 4 with FIG. 5, it can be seen that the rutile crystal peak 5b in FIG. 4 is extremely smaller than the aluminum titanate crystal peak 5a, and the amount of rutile present is small. Moreover, although the rutile crystal peak 5b in FIG. 5 is smaller than the aluminum titanate crystal peak 5a, it is not small as shown in FIG. 4, and it can be seen that rutile exists to some extent.
[0065]
As described above, the lattice wall of the present embodiment from which the data of FIG. 4 is obtained has a small amount of rutile, so that the decomposition rate is slow even at 750 to 1200 ° C. (Low thermal expansion) can be maintained. At the same time, the mechanical strength can be increased.
[0066]
【Example】
Next, examples of the present invention will be described.
[0067]
The first ceramic raw material having the following chemical composition is added to the second ceramic raw material TiO.₂Powder is weighed by changing the addition amount, and 100 parts by weight of ceramic raw material (total amount of first ceramic raw material and second ceramic raw material) is 15 parts by weight of synthetic resin as a binder and 15% by weight of methyl cellulose as a pore-forming agent. Part was added and mixed dry. To this, 2 parts by weight of glycerin and 26 parts by weight of water were added as plasticizers, mixed and kneaded to form a clay. This was extruded through a honeycomb-shaped mold, and the extruded product was dried and heat-treated at 1500 ° C. To this, a sealing material whose main component is aluminum titanate was alternately filled in both end surfaces so as to form a checkered pattern in the through holes, and heat treatment was performed again at 1400 ° C. to produce an exhaust gas filter.
[0068]
Al₂O₃... 53.2 wt%
TiO₂  ... 38.1 wt%
SiO₂  ... 6.2 wt%
Fe₂O₃... 2.5 wt%
As a characteristic of the lattice wall obtained here, the thermal expansion coefficient is about −2 × 10 × in the direction of the exhaust gas flow path.^-6K^-1The average pore diameter was 11 μm and the porosity was 35%.
[0069]
For the exhaust gas filter thus obtained, the theoretical composition of aluminum titanate (Al₂O₃1 mole, TiO₂(Table 1) shows the deviation from 1 mol), the thermal expansion coefficient of the lattice wall in the direction of the exhaust gas flow path (room temperature to 800 ° C .: before and after heat treatment), and compressive strength. The heat treatment here was performed in order to check the high temperature stability of aluminum titanate. The heat treatment temperature was set to 1000 ° C. considered to be most easily decomposed in the chemical composition of the lattice wall, and the heat treatment time was set to 500 hours.
[0070]
[Table 1]

[0071]
Here, sample Nos. 2 to 4 are according to the present invention, and TiO₂The chemical composition of the lattice wall becomes Al₂O₃And TiO₂Is composed of approximately equimolar amounts. TiO to be added₂In the data collection shown in Table 1, the anatase type was used, but the same tendency was observed with the rutile type and the mixed powder of the anatase type and the rutile type.
[0072]
Sample No. 1 is the use of only the first ceramic raw material, TiO₂Is not added. For this sample, there is no change in the coefficient of thermal expansion due to heat treatment, and the aluminum titanate has high temperature stability, but the compressive strength is low. And the lattice wall of sample No1 is easy to produce a crack under conditions with intense vibration. On the other hand, the lattice walls of Samples Nos. 2 to 4 have high mechanical strength and are less likely to crack against vibration.
[0073]
Sample No5 is the first ceramic raw material with TiO₂Is added in a large amount. About this sample, although mechanical strength is high and it is hard to produce a crack, it is inferior to high temperature stability. This is because aluminum titanate is decomposed into corundum and rutile, and high thermal expansion corundum and rutile increase the value of the coefficient of thermal expansion of the lattice wall.
[0077]
【The invention's effect】
As aboveAccording to the present invention, Al₂O_ThreeIs TiO₂A main component composed of aluminum titanate distributed in an amount of 3 to 6 wt% more than equimolar, and at least SiO₂3 to 10 wt%, Fe₂O_ThreePreparing a first ceramic raw material comprising a subcomponent having 1 to 3 wt% of TiO,₂The second ceramic raw material made of is added to the first ceramic raw material, and the total amount of the first ceramic raw material and the second ceramic raw material is Al.₂O_ThreeAnd TiO₂And adjusting the first ceramic raw material and the second ceramic raw material together with a pore-forming agent, a binder, a plasticizer, and water to prepare a ceramic clay. And the step of extruding the ceramic clay into a honeycomb shape and the step of heating and sintering the obtained extrudate to form porous ceramics. As a result, it is possible to produce an exhaust gas filter with improved mechanical strength and stable dimensional accuracy.
[0078]
By setting the average particle diameter of the first ceramic raw material to 8 to 30 μm, an effective effect that the firing shrinkage rate of the exhaust gas filter can be reduced is obtained.
[0079]
By setting the average particle diameter of the second ceramic raw material to 10 μm or less, an effective effect that the sintering reaction with the first ceramic is facilitated and the mechanical strength of the exhaust gas filter is improved can be obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an exhaust gas filter according to an embodiment of the present invention.
FIG. 2 is an enlarged view of an end surface portion of the exhaust gas filter of FIG.
3 is a schematic diagram showing a flow path of exhaust gas in the cross section of the exhaust gas filter of FIG.
4 is an X-ray diffraction pattern of a grating wall in the exhaust gas filter of FIG.
FIG. 5 is an X-ray diffraction pattern of a grating wall of a conventional exhaust gas filter as a comparative example.
[Explanation of symbols]
1 Exhaust gas filter
2 Through hole
3 lattice walls
4 Sealing material

Claims (3)

A main component Al ₂ O ₃ consists 3～6Wt% number allocated aluminum titanate from equimolar to TiO _2, the sub having at least SiO ₂ and 3~10wt%, 1~3wt% of Fe ₂ O ₃ A step of preparing a first ceramic raw material composed of components, a second ceramic raw material composed of TiO ₂ being added to the first ceramic raw material, and a total amount of the first ceramic raw material and the second ceramic raw material a step of Al ₂ O ₃ and TiO ₂ is adjusted to be approximately equimolar as said and adjusted the first ceramic raw material second ceramic raw material pore forming agent, binder, plasticizer, with water A process for producing a ceramic clay by mixing, a process for extruding the ceramic clay into a honeycomb shape, and heating and sintering the obtained extruded body to obtain a porous ceramic Manufacturing method of the exhaust gas filter, characterized in that a step of forming a. Manufacturing method of the exhaust gas filter of claim 1, wherein the average particle size of the first ceramic raw material is 8 to 30 m. The method for producing an exhaust gas filter according to claim 1 or 2, wherein an average particle diameter of the second ceramic raw material is 10 µm or less.

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