JP3897631B2 - Composite structure and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a composite structure in which a transparent polycrystalline structure made of a brittle material is formed on the surface of a base material, and specifically to a light-transmitting member such as an optical element.
[0002]
[Prior art]
A brittle material such as an oxide has a characteristic of transmitting light in the wavelength region of visible light (defined here as 380 to 760 nm) due to its unique energy band structure.
[0003]
However, in the case of a single crystal or amorphous, the characteristics often appear, but in the case of a polycrystal, incident light is absorbed, scattered, and reflected due to the existence of crystal interfaces, bubbles, impurities, and other reasons. It is difficult to ensure transparency.
[0004]
Further, in order to form a polycrystalline film on a substrate, a CVD or sol-gel method is used for a polycrystalline thin film of several tens to several hundreds nm, and when a thick film of several μm or more is used, a thermal spraying method is generally used. In addition to thermal spraying, recently the gas deposition method (Keishu Seiichiro: Metals, January 1989 issue) and electrostatic fine particle coating method (Igawa et al .: Preprint of the academic conference of the Japan Society for Precision Mechanics Autumn Showa 52) It has been proposed as a film forming method.
[0005]
In the gas deposition method, ultrafine particles such as metals and ceramics are aerosolized by gas stirring and accelerated through a minute nozzle to form a compact layer of ultrafine particles on the surface of the substrate, which is heated and fired. To form a coating. In the electrostatic fine particle coating method, fine particles are charged and accelerated using an electric field gradient, and thereafter a film is formed on the same basic principle as in the gas deposition method.
[0006]
Further, as prior arts improved from the above-described gas deposition method or electrostatic fine particle coating method, JP-A-8-81774, JP-A-10-202171, JP-A-11-21676, or JP-A-2000-212766. What is disclosed in the Gazette is known.
[0007]
In the technique disclosed in Japanese Patent Laid-Open No. 8-81774, two types of metals or organic substances having different melting points are heated and evaporated by resistance wire heating, electron beam heating, high frequency induction heating, sputtering, arc plasma, etc. By using a nozzle for each metal having a different melting point, the ultrafine particles are sprayed onto the substrate based on the cross-sectional CAD data of a three-dimensional shape. By repeating, a three-dimensional solid object composed of two types of metals having different melting points is formed, and then the low-melting point metal part is melted by heating the three-dimensional solid object at an intermediate temperature between the melting points of the two types of metals. It is removed to leave only the refractory metal part.
[0008]
The technique disclosed in Japanese Patent Application Laid-Open No. 10-202171 is for spraying ultrafine particles obtained by heating and evaporation using the resistance wire heating, electron beam heating, high frequency induction heating, sputtering, arc plasma, or the like toward the substrate. In this case, a three-dimensional object having no shoulder is obtained by performing through the opening of the mask.
[0009]
The technique disclosed in Japanese Patent Application Laid-Open No. 11-21677 prevents the ultrafine particles from aggregating into large particles when transporting the aerosol containing the ultrafine particles or when the metal or ceramic is heated and evaporated. In order to do so, a classifier is arranged in an intermediate path.
[0010]
Japanese Laid-Open Patent Publication No. 2000-212766 has been proposed by the present inventors, and this publication discloses a method of forming a film of ultrafine particles without heating by a heating means. Specifically, by irradiating an ultrafine particle having a particle diameter of 10 nm to 5 μm (not obtained by heating and evaporation unlike the prior art) with an ion beam, an atomic beam, a molecular beam, or a low temperature plasma, The ultrafine particles are activated without melting and sprayed onto the substrate in this state at a speed of 3 m / sec to 300 m / sec to promote the bonding between the ultrafine particles to form a sliding contact layer. is there.
[0011]
[Problems to be solved by the invention]
Forming a thick structure by CVD or a sol-gel method takes a long time for film formation and causes cracks in the film. Furthermore, in the case of the thermal spraying method, relatively large bubbles of about several μm or more remain in the film, and an electrode material such as copper or tungsten from the electrode of the thermal spray gun is added to the film in a trace amount, and impurities and Therefore, it is difficult to form a film with high translucency.
[0012]
Further, by a gas deposition method or electrostatic fine particle coating method, a technique disclosed in Japanese Patent Laid-Open No. 8-81774, Japanese Patent Laid-Open No. 10-202171, Japanese Patent Laid-Open No. 11-21676, or Japanese Patent Laid-Open No. 2000-212766. However, a highly transparent polycrystalline structure cannot be obtained, and the translucency of the polycrystalline structure cannot be freely controlled.
[0013]
[Means for Solving the Problems]
The present invention has been made based on the following findings.
That is, when a mechanical impact force is applied to a brittle material (ceramics) that does not have spreadability, the crystal lattice shifts or breaks along the wall open surface such as the interface between crystallites. When these phenomena occur, a new surface is formed on the slipping surface or fracture surface, in which atoms originally present inside and bonded to other atoms are exposed. The part of the atomic layer on the new surface is exposed to an unstable surface state by an external force from a stable atomic bond state, and the surface energy is high. The active surface joins the adjacent brittle material surface, the newly formed brittle material surface, or the substrate surface, and shifts to a stable state. The addition of continuous mechanical impact force from the outside causes this phenomenon to occur continuously, and the joining progress and densification are performed by repeated deformation and crushing of fine particles, and a transparent layer of brittle material is formed. .
Further, an embodiment of the present invention in which the above-described mechanical impact is caused to cause the brittle material to collide with the substrate with the carrier gas is hereinafter referred to as a fine particle beam deposition method. This method is also called an aerosol deposition method. By using the fine particle beam deposition method, it is possible to make the structure dense and hence transparent by combining various conditions such as appropriate gas species and gas flow rate conditions, and the particle diameter of the brittle material fine particles used. They found out.
[0014]
In addition, when a structure is formed using a gas that easily causes discharge, such as helium, a discharge phenomenon may be observed during the formation. In such a case, the transparency of the structure may deteriorate significantly. It was observed. Therefore, it can be said that it is a preferable method to form a structure using a gas that does not easily cause discharge. The pressure at the time of structure formation in the fine particle beam deposition method is in the range of several to several hundred kPa, but in this range, the magnitude relationship of the spark voltage due to the gas species is almost equal, and air discharge is likely to occur at high and low voltage values. Whether or not is discussed. It can be said that oxygen, nitrogen, dry air, carbon dioxide gas and the like hardly generate air discharge, and rare gases such as helium, neon, and argon easily generate air discharge.
The gas in which air discharge hardly occurs in this case refers to a gas having a composition in which no discharge phenomenon is observed in the vicinity of the formation of a polycrystalline brittle material structure. Refers to the gas as the main component.
[0015]
Here, the interpretation of the words that are important for understanding the present invention will be described below.
(Polycrystalline)
In this case, it refers to a structure in which crystallites are joined and integrated. The crystallite is essentially one crystal, and its diameter is usually 5 nm or more. However, the case where the fine particles are taken into a transparent structure without being crushed rarely occurs, but is substantially polycrystalline.
(Crystal orientation)
In this case, it refers to the degree of orientation of crystal axes in a transparent structure that is polycrystalline. Whether or not there is orientation is generally determined by standard X-ray diffraction, etc. JCPDS (ASTM) data is judged as an index.
The peak intensity of the three major diffraction peaks in this index, which is the material constituting the brittle material crystal in the transparent structure, is defined as 100%. In this case, it is assumed that there is substantially no orientation in a state where the deviation of the peak intensity of the other two peaks is within 30% of the index value.
(interface)
In this case, it refers to the region that forms the boundary between crystallites.
(Grain boundary layer)
It is a layer with a certain thickness (usually several nm to several μm) located at the grain boundary in the interface or sintered body. It usually has an amorphous structure different from the crystal structure in the crystal grain, and in some cases, segregates impurities. Accompany.
(Anchor part)
In this case, it refers to the unevenness formed at the interface between the base material and the transparent structure, and in particular, the surface of the original base material is not formed when the transparent structure is formed, instead of forming the unevenness on the base material in advance. It refers to irregularities formed with varying accuracy.
(Internal distortion)
The lattice strain contained in the raw material fine particles is a value calculated by using the Hall method in the X-ray diffraction measurement, and the deviation is expressed as a percentage on the basis of a standard substance obtained by sufficiently annealing the fine particles.
[0016]
In the composite structure according to the present invention, a transparent structure is formed on the surface of the substrate, the transparent structure is made of a brittle material, is polycrystalline, and the crystal has substantially no crystal orientation. There is substantially no grain boundary layer composed of a glass layer at the interface between the crystals, and a part thereof is an anchor portion that bites into the substrate surface.
[0017]
The composite structure is characterized in that there is substantially no void having a size of 20 nm or more in the film thickness direction in the polycrystalline structure.
[0018]
The voids correspond to bubbles and pores in the structure, but even when the particle beam deposition method is used, depending on the structure formation conditions, the particles may be sufficiently crushed or deformed when colliding with the particles or forming the structure. It does not occur, and the fine particles are taken into the structure while maintaining the shape of the primary particles. In such a case, a void is formed between the incorporated primary particles and the surrounding structures. When submicron-sized fine particles are used, if the voids are large, they are formed with a size of several tens of nm. The interface between the air gap (gas phase) and the structure is considered to cause reflection and scattering of light, and the presence of a large number of them deteriorates the transparency of the structure. On the other hand, in the particle beam deposition method, a huge amount of particles are accelerated and repeatedly collided with the base material to form a structure, so that such voids are stochastically formed regardless of the structure formation conditions. There are cases where it is formed. Therefore, an appropriate formation condition is selected, and a measure is taken to keep the transparency as much as possible. The fact that there is substantially no void, for example, is determined from a transmission electron microscope image by a method such that the average amount of voids with a size of 20 nm or more in the film thickness direction is 1 or less in 1 μm square. The method of doing etc. can be considered.
[0019]
As the composite structure, the base material is also transparent, and the transparent structure has a thickness of 1 μm or more and a visible light transmittance of 80% or more. Moreover, as a constituent material of the transparent structure, a material mainly composed of aluminum oxide can be given. The purity of the transparent structure is preferably 99% or more.
[0020]
The visible light in this case refers to an electromagnetic wave having a wavelength of 380 to 760 nm. When the reflection loss at the surface or interface of the structure is not taken into consideration, I / I ₀ is referred to as internal transmittance in the incident light I ₀ and the transmitted light I. For this, Beer's law,
I / I ₀ = exp (−ax)
Here, there is a relationship of a: extinction coefficient, x: distance through which light passes through the structure, and greatly depends on x.
When the structure is formed with a thick film, the light transmittance in the film thickness direction is often a problem, and the transmittance measurement is also performed in this direction.
In the present invention, the transmittance when the film thickness is 1 μm or more which is a practical film thickness formed by the particle beam deposition method is taken up. However, it is possible to form a thick film of about several hundred μm by the particle beam deposition method. It is.
[0021]
Moreover, as a base material, although quartz glass etc. which transmit most visible light are preferable, the thing in which a base material is not transparent is also contained in this invention. That is, examples of the base material include glass, metals, ceramics, metalloids, and organic compounds, and brittle materials include aluminum oxide, titanium oxide, zinc oxide, tin oxide, iron oxide, zirconium oxide, and yttrium oxide. , Oxides such as chromium oxide, hafnium oxide, beryllium oxide, magnesium oxide, silicon oxide, diamond, boron carbide, silicon carbide, titanium carbide, zirconium carbide, vanadium carbide, niobium carbide, chromium carbide, tungsten carbide, molybdenum carbide, carbonized Carbides such as tantalum, boron nitride, titanium nitride, aluminum nitride, silicon nitride, niobium nitride, nitrides such as tantalum nitride, boron, aluminum boride, silicon boride, titanium boride, zirconium boride, vanadium boride, boron Niobium tantalum, tantalum boride, chromium boride, molybdenum boride Borides such as titanium and tungsten boride, or mixtures and multi-component solid solutions, piezoelectric / pyroelectrics such as barium titanate, lead titanate, lithium titanate, strontium titanate, aluminum titanate, PZT, and PLZT Ceramics, high toughness ceramics such as sialon and cermet, biocompatible ceramics such as hydroxyapatite and calcium phosphate, silicon, germanium, or metalloid materials with various doping materials such as phosphorus added thereto, gallium arsenide, indium arsenide And semiconductor compounds such as cadmium sulfide.
[0022]
As a method for producing the above composite structure, for example, in a gas atmosphere in which air discharge is unlikely to occur, brittle material fine particles to which internal strain has been applied in advance are collided with a substrate at high speed, and the brittleness is caused by the impact of this collision. The material fine particles are deformed or crushed, and the fine particles are recombined through an active new surface generated by the deformation or crushing to form a transparent structure on the surface of the substrate.
[0023]
For example, a film having a desired transmittance is formed by mixing a gas species that is likely to generate discharge, such as helium, neon, and argon, and a gas species that is difficult to generate, and performing structure formation while controlling the gas partial pressure. It is possible. If the transmittance can be controlled, application to an optical member having wavelength selectivity such as a spectral filter is expected.
It is also suggested that a considerably transparent film can be produced by controlling the gas type and gas pressure so as to suppress the discharge phenomenon as much as possible. In other words, a brittle material polycrystal that is transparent in the visible light region is formed by colliding fine particles of a brittle material with a substrate at high speed in a gas atmosphere in which rare gases such as helium, argon, and neon are eliminated as much as possible to form a polycrystalline structure. A membrane can be obtained.
[0024]
In the method of the present invention, since a structure is formed without firing, the crystal growth can be suppressed and fine crystals can be stopped, and a polycrystalline body composed of nanometer-level crystal grains can be obtained. Can be formed.
[0025]
The transparent film can be used by replacing parts that had previously been used with high-hardness bulk such as aluminum oxide in parts that are subject to sliding, such as the protective transparent plate of an optical sensor, with inexpensive glass, and using this method only on the surface. It may be possible to improve the wear resistance by forming a transparent brittle material film.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
Example 1
FIG. 1 is a view showing an example of a composite structure manufacturing apparatus according to the present invention, in which various gas cylinders 11 of nitrogen, dry air, and helium are connected to an aerosol generator 13 via a transport pipe 12 and further transported. A nozzle 15 having a rectangular opening of 10 mm × 0.4 mm is disposed in the structure forming apparatus 14 through the tube 12. At the tip of the nozzle 15, a quartz glass substrate 16 installed on the XY stage 17 is arranged facing the nozzle 15 with an interval of 10 mm. The structure forming chamber 14 is connected to an exhaust pump 18.
[0027]
The operation of the brittle material structure manufacturing apparatus having the above configuration will be described below. After filling fine particles of aluminum oxide with a submicron particle size and purity of 99.8% into the aerosol generator 13, the gas cylinder 11 is opened, and dry air is introduced into the aerosol generator 13 through the transport pipe 12 at a flow rate of 3 liters / minute. Then, an aerosol in which aluminum oxide fine particles are dispersed in a gas is generated. The aerosol is further conveyed in the direction of the structure forming chamber 14 through the conveying tube 12 and aluminum oxide fine particles are jetted from the nozzle 15 toward the substrate 16 while being accelerated at a high speed.
[0028]
At this time, the speed of the aluminum oxide fine particles is accelerated from the subsonic speed to the sound speed. The pressure in the structure forming chamber 14 was several kPa. However, the pressure in the vicinity of the structure formation seems to be larger due to the effect of gas injection. The aluminum oxide fine particles in the aerosol that have been sufficiently accelerated to obtain kinetic energy collide with the substrate 16, are finely crushed by the energy of the impact, and the generated fine fragment particles are bonded to the substrate 16, and further the fine fragment particles. They are joined together to form a dense aluminum oxide structure. The substrate 16 was swung by the XY stage 17 to form a 10 μm thick aluminum oxide film (structure) having a predetermined area. The structure forming chamber is in a low vacuum state at 1 kPa or less when formed by the operation of the exhaust pump. Such an operation was performed by switching the gas to not only dry air but also nitrogen or helium gas, and a structure was formed under various gas atmospheres to obtain an aluminum oxide film having an equivalent film thickness.
[0029]
FIG. 2 shows the spectrophotometer of the transmittance of the aluminum oxide film thus obtained in the ultraviolet to visible wavelength region. Compared with the same film thickness of 7 μm, the aluminum oxide film formed with dry air has a high transmittance, and transmission of 80% or more is seen in the visible light region, whereas when helium gas is used, the transmittance is low. It can be seen that it is very low. When a 10 μm film is formed using nitrogen gas, the transmittance characteristics are almost the same as those of the dry gas.
[0030]
FIG. 3 is a photograph of an aluminum oxide film formed using dry air and helium gas. A film using dry air is obtained as shown in FIG. As shown in (b), an opaque material having a black color is obtained.
[0031]
By the way, when helium gas was used, a light emission phenomenon (discharge phenomenon) was observed in the vicinity of a region where the aluminum oxide fine particles collided with the base material 16 and the structure was formed. FIG. 4 shows the measurement of the wavelength of this light. FIG. 4 shows the emission line spectrum when the aluminum oxide film shown in FIG. 3 is formed. As shown in (a), no light emission is observed in dry air, while as shown in (b), a number of emission lines unique to helium are observed when helium gas is used.
[0032]
Furthermore, the present inventors have concluded that even when brittle materials having the same particle size are used, there is a difference in the formation speed and the achieved film thickness of the structure to be formed, which is caused by the internal strain of the particles. .
Therefore, FIG. 5 shows the result of an experiment conducted on the relationship between the thickness of the structure achieved in the same formation time as the internal strain. In the experiment, aluminum oxide fine particles having a purity of 99.6% were pulverized using a planetary mill to change the characterization of the fine particles, and then a structure was formed on the aluminum substrate by an ultrafine particle beam deposition method. The internal strain of the fine particles was measured by X-ray diffraction, and the amount of strain was determined based on 0% obtained by subjecting the fine particles to thermal aging to remove the internal strain.
In addition, SEM photographs (Hitachi in-lens SEM S-5000) of fine particles at points A, B, and C in FIG. 5 are shown in FIGS.
[0033]
FIG. 5 shows that an internal strain of 0.01 to 2.50% is sufficient to obtain a film thickness of 1 μm, but 0.1 to 2.0% is necessary to obtain a stable film thickness. Is preferable. As shown in FIG. 6, when there is no internal strain, the crack does not occur when there is no internal strain, but when the internal strain exceeds a certain value, in this case, 2.0% or more, the crack is completely cracked. 8 is formed, and the fragments that fall off adhere to the surface, resulting in a re-aggregation state as shown in FIG.
[0034]
Thus, it is preferable to use a pulverizing means capable of giving a large impact for the pulverization applied to the fine particles in the pulverization treatment for distorting the fine particles. This is because a large strain can be imparted to the fine particles relatively uniformly. As such a pulverizing means, it is preferable to use a vibration mill, an attritor, or a planetary mill that can give a large acceleration of gravity compared to a ball mill often used for pulverizing ceramics. Most preferably, a planetary mill that can provide acceleration is used. Focusing on the state of the fine particles, since the crack cancels the internal strain, the most preferable is the fine particle whose internal strain is increased until just before the crack is generated. In the state shown in FIG. 7, some cracks are generated, but sufficient internal strain remains.
[0035]
(Example 2)
In Example 2, as another example, the result of fine observation of a transparent aluminum oxide structure and a cloudy opaque aluminum oxide structure will be described. Using an aluminum oxide fine particle A having a purity of 99.8% and a particle size of about 0.6 μm and an aluminum oxide fine particle B having a purity of 99.9% or more and a particle size of about 0.2 μm, an apparatus equivalent to that shown in FIG. When a film-like aluminum oxide structure having a film thickness of about 4 μm was formed on each substrate by a fine particle beam deposition method using a nitrogen gas as a carrier gas at a flow rate of 7 L / min, a transparent structure was obtained with fine particles A. As a result, an opaque structure was obtained with the fine particles B. The size of the nozzle opening used at this time was 17 mm × 0.4 mm. The pressure in the structure forming chamber at this time was 100 to 200 Pa. These structures were observed with a transmission electron microscope (TEM) H-9000UHR manufactured by Hitachi, Ltd. for microscopic cross-section observation. FIG. 9 shows a TEM image of the structure made of the fine particles A, and FIG. 10 shows a TEM image of the structure made of the fine particles B. The vertical direction in the figure corresponds to the film thickness direction. It can be seen that the structure of the fine particles A is dense and consists of fine crystallites of several tens of nm. On the other hand, in the structure of fine particles B, it can be seen that spherical particles of about 100 nm, which are regarded as primary particles of fine particles B, are mixed in the structure, and there are many voids around these spherical particles. You can see that From this TEM image, it is observed that the size of the gap in the film thickness direction is often 20 nm or more. If there are many such gaps, light scattering / reflection occurs at the interface between the particles and the gap, and the structure is opaque. It seems to be.
In addition, in the aluminum oxide fine particle B having a small particle diameter, spherical particles of about 100 nm are mixed and become cloudy. This is probably because the kinetic energy is small and the crystal lattice displacement and crushing in the fine particle beam deposition method are insufficient. .
[0036]
(Example 3)
Next, the anchor part formed with the structure formation is shown in FIG. In addition, in FIG. 11, the upper part shows the result of measuring the unevenness of the substrate surface before film formation, and the lower part shows the result of measuring the unevenness of the surface of the substrate after peeling the brittle material film after film formation, that is, the unevenness of the anchor part. Show.
In an apparatus equivalent to that shown in FIG. 1, aluminum oxide fine particles having a purity of 99.8% or more and submicron particle diameter are mixed with nitrogen gas to generate an aerosol, and directed toward a brass substrate having a mirror-finished surface. After injecting under the condition of a gas flow rate of 7 L / min and forming an aluminum oxide film with a film thickness of about 10 μm, a tensile stress is applied to the film and the film is peeled off from the substrate to expose the anchor portion. The Sato anchor portion was measured using a stylus type surface shape measuring instrument Dektak 3030 manufactured by Nippon Vacuum Technology Co., Ltd. The upper profile in FIG. 11 is the surface profile of the brass substrate before the structure is formed, and the lower profile is the profile of the anchor portion. From the figure, it can be seen that the anchor is formed by the collision of the fine particles. The surface roughness Ra of the surface profile measuring device was 7.7 nm for the substrate surface and 73.8 nm for the anchor layer at a sweep distance of 200 μm. Even when glass, which is a transparent material, was used as the substrate, a similar anchor portion was confirmed between the substrate and the structure.
[0037]
【The invention's effect】
As described above, according to the present invention, a base material and a transparent structure can be obtained by providing a polycrystalline structure with a brittle material, high visible light transmittance, and high hardness on a substrate surface such as glass. Can be obtained. Therefore, it can be widely used for optical parts, machine parts, ornaments and the like.
[0038]
Further, according to the present invention, it is possible to easily and accurately control the visible light transmittance of a transparent structure, and the application range is further widened.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an apparatus for producing a composite structure according to the present invention. FIG. 2 is a graph showing transmittance of an aluminum oxide film in the ultraviolet to visible wavelength region. FIG. 3 (a) is dry air. A photograph showing the transparency of the polycrystalline structure when in use, (b) is a photograph showing the transparency of the polycrystalline structure when using helium gas. FIG. 4 (a) is when forming an aluminum oxide film when using dry air. The emission line spectrum (b) is the emission line spectrum when the aluminum oxide film is formed when helium gas is used. FIG. 5 is a graph showing the relationship between the internal strain and the film thickness of the brittle material fine particles. SEM photograph of fine particles [FIG. 7] SEM photograph of fine particles at point B in FIG. 5 [FIG. 8] SEM photograph of fine particles at point C in FIG. I Surface profile showing the over-di photograph 10 shows the unevenness of the cross-sectional TEM image photograph 11 substrate and the anchor portion of the structure which is formed by using aluminum oxide fine particles B

Claims (5)

  A composite structure in which a transparent structure is formed on the surface of a base material, the transparent structure being made of a brittle material, being polycrystalline, and having substantially no crystal orientation, There is substantially no grain boundary layer composed of a glass layer at the interface, and a part thereof is an anchor portion that bites into the substrate surface.  2. The transparent composite structure according to claim 1, wherein a void having a size of 20 nm or more in the film thickness direction is substantially not present in the polycrystalline structure.  The composite structure according to claim 1 or 2, wherein the substrate is also transparent, the transparent structure has a thickness of 1 µm or more and a visible light transmittance of 80% or more. Transparent composite structure. In the composite structure according to any one of claims 1 to 3, a composite structure, wherein the transparent structure is a main component of aluminum oxide. The composite structure according to any one of claims 1 to 4, wherein the purity of the transparent structure is 99% or more.

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