Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
  • C01B21/072—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with aluminium
  • C01B21/0722—Preparation by direct nitridation of aluminium
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/30—Particle morphology extending in three dimensions
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/30—Particle morphology extending in three dimensions
  • C01P2004/45—Aggregated particles or particles with an intergrown morphology
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/80—Compositional purity
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]

Definitions

• the invention relates to a process for producing aluminum nitride in the form of powders or platelets.
• Aluminum nitride is a ceramic with exceptionally high thermal conductivity, which is only outpaced by beryllium oxide. This property, associated with high volume resistivity and dielectric constant, makes aluminum nitride a substrate of choice for the assembly of microelectronic components, whose power and density increases steadily.
• No. 5,710,382 (Dow Chemical) thus describes a combustion process in which an aluminum powder mixed with a diluent, a ceramic, carbon or other products is converted into aluminum nitride in various forms.
• the ignition temperature is typically 1050 ° C and the maximum temperature can reach more than 2000 ° C.
• Patent Applications JP 9 012 308 and EP 0 887 308 describe a process in which a mixture of aluminum powder and aluminum scrap with a diameter of between 0.1 and 5 mm is nitrided at a temperature of between 500 and
• the problem that the present invention seeks to solve is the production of aluminum nitride, especially in the form of a powder of high purity, by an economical process that does not require the use of aluminum powder as raw material. nor the use of very high temperatures.
• a first object of the invention is a process for producing aluminum nitride in which
• a multilayer structure comprising N layers consisting of aluminum-based rolled products, separated by N1 interstitial spaces, N being at least equal to 10, the average density of the multilayer structure being controlled by stacking or winding. to be between 0.4 and 2 g / cm 3, the interstitial spaces being open to allow the circulation of a gas in said interstitial spaces, (ii) heating said multilayer structure under a nitrogen atmosphere, the cycle thermal heating comprising at least one phase in which the temperature of the nitrogen atmosphere is maintained between 400 ° C and 660 ° C and during which the majority of the nitriding occurs.
• Another object of the invention is an aluminum nitride wafer obtainable by the process according to the invention, characterized in that its microscopic structure is laminated.
• Yet another object of the invention is an aluminum nitride powder obtainable by the method according to the invention comprising particles whose microscopic structure is stratified.
• Yet another subject of the invention is a micronized aluminum nitride powder whose median particle size D50 is less than 1 ⁇ m, and preferably less than 0.7 ⁇ m and the ratio D90 / D10 is less than 8 ⁇ m. and preferably less than 6.
• Figure 1 stack of rolled products used in the context of the invention.
• Figure 2 coil used in the context of the invention.
• FIG. 3 relationship obtained between the average density of the multilayer structures and the nitriding yield.
• Figure 4 X-ray diffraction spectrum of the powder obtained.
• Figure 5 5a. Microscopic observation of the aluminum nitride powder obtained.
• 5b schematic representation of Figure 5a showing a stratified structure.
• FIG. 6 Granulometry of a micronized powder of nitride obtained.
• the chemical composition of standardized aluminum alloys is defined for example in the standard EN 573-3.
• the method according to the invention comprises at least two steps.
• a multilayer structure of controlled average density comprising N layers consisting of aluminum-based rolled products, separated by N1 interstitial spaces, N being at least equal to 10, is prepared by stacking or winding.
• aluminum are of rectangular cross section.
• N is at least 50.
• the interstitial spaces are open to allow the circulation of a gas in said interstitial spaces.
• the average density of the multilayer structure is equal to the ratio between its mass and its volume, it is generally less than or equal to the average density of the rolled products used.
• a first example of a multilayer structure produced in the context of the invention is a stack of rolled products as shown in FIG. 1.
• N layers of rolled products (1) of substantially identical dimensions are stacked on each other. the others, each layer being separated from the next by an interstitial space of average thickness ei (2).
• the geometrical parameters of a stack as defined in the context of the invention are the length L E , the width IE, less than or equal to the length, and the thickness es in the direction perpendicular to the substantially parallel planes defined by the rolled products.
• a stack of rolled products thus comprises N products laminates of substantially identical dimensions separated by NI interstitial spaces.
• the average density of the stack is the ratio between its mass and its volume V E :
• a second example of multilayer structure according to the invention is a coil obtained by cylindrical winding of a rolled product of substantially constant width such as that shown in FIG. 2.
• the geometrical parameters of the coil are the width IB the diameter D B and the winding height hs.
• Each turn of the winding constitutes a layer or turn (1).
• the turns are separated from an interstitial space of average thickness ei (2).
• a roll of rolled products thus comprises
• the coil may be wound on a winding cylinder (3), for example steel, but in a preferred manner the coil is wound on a retractable cylinder which is removed prior to nitriding.
• the density of the rolled products can vary significantly when said rolled products are etched.
• electrochemically etched rolled products such as those made in the aluminum capacitor industry can have a density up to 30% less than that of similar sized aluminum products.
• the interstitial space has a complex shape: the successive layers can be in some places in contact and in other places separated by a space of given thickness.
• the average thickness of an interstitial space, e 15 is a parameter for describing this interstitial space.
• a more complete description of the interstitial space could also include information on the shape of the interstitial space such as in particular the density of the contact points, the standard deviation of the average thickness, the maximum thickness of the interstitial space. interstitial space, this information is however not essential in the context of the invention.
• the average thickness of each interstitial space is controlled.
• the control of the average thickness of the interstitial space can be carried out in different ways: it is possible, for example, to control the roughness of the rolled products or, preferably, to place in at least one interstitial space ceramic and / or metallic particles the role of spacing the rolled products.
• the particles that can be used to space the rolled products to control the average thickness of the interstitial space of the multilayer structures are metallic and / or ceramic particles that comprise aluminum.
• these particles are ceramic particles comprising aluminum nitride.
• the morphology and size of the particles that can be used to control the average thickness of the interstitial space can influence the nitriding efficiency.
• the dimensions of the particles used are of the order of one millimeter.
• the particles used are flakes, that is to say that their length and / or their width is about ten times greater than their thickness.
• pressure can be exerted on the stack, for example by means of metal plates to control the average thickness of the interstitial space.
• the average thickness of the interstitial space during winding can be controlled by acting on the winding parameters, which in the example of a new coil is obtained by winding an initial coil (" trans-winding ") the pulling force exerted on the winding side of the new coil and the retaining force exerted on the unwinding side of the initial coil.
• the average density of the multilayer structure In order for the yield obtained during the nitriding reaction to be of industrial interest, the average density of the multilayer structure must be between 0.4 g / cm 3 and 2 g / cm 3 . In a preferred manner, the average density of the multilayer structure is greater than 0.6 g / cm 3 and preferably greater than 0.8 g / cm and less than 1.8 g / cm and preferably less than 1, 4 g / cm.
• the homogeneity of the density within the multilayer structures can influence the nitriding efficiency obtained and it is preferable that the density be as homogeneous as possible within the multilayer structures. This result can be obtained in particular by controlling the variations in the thickness of the interstitial spaces ei.
• the average controlled thickness of the interstitial spaces is substantially identical for the NI interstitial spaces of the multilayer structure.
• the variations of ⁇ are less than 20% and preferably less than 10%.
• these particles are preferentially introduced into each interstitial space.
• the present inventors have found that it is preferable for the smallest distance to cross the multilayer structure parallel to the layers, ie for example the width I E in the case of stacks or the width I B in the case of the coils, at least equal to a certain threshold value so that the nitriding efficiency is industrially interesting.
• the threshold value is in general 40 mm and preferably 50 mm. In some cases, and particularly if the smallest distance to cross the multilayer structure is less than 40 mm, it may be advantageous to wrap the multilayer structures in aluminum foil.
• the present inventors believe that during the nitriding reaction, an important technical parameter is the diffusion of the nitrogenous atmosphere in the multilayer structure.
• One of the effects of this diffusion could be the reaction of oxygen molecules present in the nitrogenous atmosphere on the ends of the multilayer structure and their removal, which is favorable because oxygen is a poison of the nitriding reaction. If the path traveled by the oxygen molecules by diffusion between the layers is less than said threshold value, the oxygen removal phenomenon probably does not occur sufficiently which limits and can even prevent the nitriding reaction.
• the average density of the multilayer structure is too low, the diffusion phenomena described above are probably insufficient. Moreover, the multilayer structures of low average density are difficult to handle. If the average density of the multilayer structure is too high, the present inventors have found that local melting phenomena of aluminum due to the heat generated by the nitriding reaction take place and adversely affect the nitriding reaction.
• wrought scrap it is possible to use wrought scrap within the scope of the invention if it allows for a multilayer structure according to the invention.
• the use of wrought scrap is of economic interest because the transformation into aluminum nitride is more profitable than recycling by the usual channels.
• the aluminum rolled products used in the context of the invention comprise high purity aluminum whose aluminum content is greater than 99.9% by weight.
• the use of high purity aluminum thus makes it possible to improve the purity of the aluminum nitride obtained.
• the aluminum rolled products comprise aluminum-based rolled products which have been etched before the manufacture of the multilayer structure, that is to say having undergone a chemical and / or electrochemical treatment intended to increase their surface and / or their roughness. This type of etching treatment is commonly used in the aluminum electrolytic capacitor industry, particularly with high purity aluminum. Etch processing is also commonly used in the aluminum rolled products industry for lithography process applications.
• the aluminum rolled products used in the context of the invention advantageously have a thickness of between 5 and 500 ⁇ m and preferably a thickness of between 6 and 200 ⁇ m so as to transform the layers of substantially integrally laminated product into nitride. aluminum.
• the multilayer structure from the first step is heated under a nitrogen atmosphere, the heating thermal cycle comprising at least one phase in which the temperature of the nitrogen atmosphere is maintained between 400 ° C. and 660 ° C. and during which the majority of nitriding occurs.
• the heating may in particular be carried out in a closed oven (treatment with batches) or in a pass-through oven (continuous treatment).
• the thermal cycle of this heating step can comprise several phases.
• a first phase makes it possible to reach a temperature of the nitrogen atmosphere of 400 ° C.
• the duration of this phase has little effect on the nitriding yield.
• the temperature of the nitrogenous atmosphere is maintained between 400 ° C. and 660 ° C.
• the majority of the nitriding reaction occurs during this second phase.
• Most of the reaction is meant that more than 50% of the aluminum present has reacted.
• the present invention thus makes it possible in certain cases to obtain a nitriding yield greater than 90% or even greater than 99% at the end of this second phase.
• a high temperature for example greater than 700 ° C to obtain a total nitriding of aluminum products in metallic form.
• the maximum temperature of 660 ° C used in the second phase greatly limits the risks of aluminum melting, which affect the quality of the aluminum nitride obtained.
• a minimum temperature of 400 ° C and preferably 500 ° C is required to initiate the nitriding reaction. Since the nitriding reaction is highly exothermic, the temperature reached by the aluminum can in certain cases exceed the temperature of the nitrogenous atmosphere during this second phase.
• the duration of this second phase is generally at least 2 hours and preferably at least 5 hours. The optimal duration of this second phase depends on the size of the multilayer structures treated. The present inventors have found that in certain cases it is advantageous to oscillate the temperature of the nitrogenous atmosphere during at least a part of this second phase between low points whose temperature is between 400 ° C. and 550 ° C. and high points whose temperature is between 550 ° C and 660 ° C.
• An oscillation is defined by two low points and a high point or by two high points and a low point.
• the number of said oscillations during the second phase is at least equal to 3. These oscillations seem to prevent the nitriding reaction from accelerating uncontrollably.
• the frequency and duration of the oscillations must be adapted according to the size of the samples.
• a third phase generally consists in cooling the nitrogen atmosphere to a temperature sufficiently low that the nitrided samples can be handled.
• one or more additional phases may be introduced between the first and third phases. It may be useful in particular to introduce an additional phase between the second and third phases at a temperature above 660 ° C., for example up to about 1000 ° C., so as to further improve the nitriding efficiency in the case where this one is insufficient. This economically unfavorable phase because of the high temperature and the increase in the duration of the operation is however not necessary in general and is therefore preferably avoided.
• the temperature of the nitrogenous atmosphere does not exceed 660 ° C. for the duration of the heating step.
• the temperature of the atmosphere is controlled by a control loop using the temperature measured in the multilayer structure.
• the nitrogenous atmosphere comprises nitrogen in the form of N 2 di-nitrogen.
• the nitrogenous atmosphere may also comprise other nitrogen-containing gases such as ammonia NH 3 , as well as reducing gases such as dihydrogen H 2 , methane CH 4 , and more generally hydrocarbon gases of general formula
• the nitrogenous atmosphere contains a minimum of oxygen because this element is a poison of the nitriding reaction.
• Oxygen can in particular be present in the form of di-oxygen or water vapor. Controlled diffusion conditions in the context of the invention, however, allow to tolerate an oxygen content in the nitrogen atmosphere of 50 ppm or 100 ppm in some cases.
• the aluminum rolled products are placed under a vacuum of at least 0.1 bar before being placed under a nitrogen atmosphere.
• a sweeping of said nitrogenous atmosphere is carried out at a furnace-dependent rate used.
• the sweep rate is advantageously between 1 and 10 times the volume of the oven per hour.
• the present invention makes it possible to directly obtain aluminum nitride platelets whose microscopic structure is stratified.
• the thickness of these plates of at least 1 mm and the thickness of the layers is between 5 and 250 microns.
• the minimum width of the plates is 40 mm. This method is economically very advantageous because it avoids platelet shaping steps that are obtained in traditional processes from aluminum nitride powder.
• the aluminum nitrides obtained are milled and optionally sieved, advantageously under a dry, inert or reducing atmosphere, so as to obtain an aluminum nitride powder formed of particles having a size of between 0.5 ⁇ m or less and 500 ⁇ m.
• the aluminum nitride powder according to the invention comprises particles in which it can be observed that the microscopic structure of the powder is laminated, the thickness of the layers being between 5 and 250 microns. This stratified structure can in certain cases bring technical advantages to the powder obtained, such as a variation of certain thermal and / or mechanical properties between the direction parallel to the strata and the direction perpendicular to the strata.
• Powders comprising particles whose microscopic structure is laminated obtained by the process according to the invention have the advantage of being easily milled in the form of micronized powder.
• micronized aluminum nitride powders having a median particle size (D 50) of less than 1 ⁇ m and preferably less than 0.7 ⁇ m are obtained from the coarse nitrides.
• the micronized powders according to the invention also have a homogeneous particle size, whose ratio D90 / D10 is less than 8 and preferably less than 6.
• the nitrides are milled in three stages. In a first step, the stacks or nitride coils are crushed coarsely so as to obtain pieces of a dimension less than 1 cm.
• these pieces are milled in a ball mill to obtain a powder of median diameter (D50) less than 500 microns and preferably less than 100 microns.
• D50 median diameter
• a powder with a D50 of between 50 and 500 ⁇ m is typically obtained, comprising particles in which it can be observed that the microscopic structure of the powder is laminated.
• a ball mill whose jar and balls are ceramic, especially zirconia, alumina or preferably aluminum nitride.
• the powders from the ball mill are micronised in an air jet and fluidized bed mill.
• the parts in contact with the powder in the air jet and fluidized bed mill are ceramic.
• the grinding operations are carried out under a dry atmosphere, whose dew point is less than 10 ° C. and preferably less than 0 ° C.
• a dry atmosphere whose dew point is less than 10 ° C. and preferably less than 0 ° C.
• the aluminum rolled products used are of high purity aluminum
• the oxygen content is at most 2% by weight and preferably at most 1.5% by weight
• the carbon content is less than 0.03% by weight and preferably less than 0.02% by weight
• the content of the other impurities is less than 0.01% by weight and preferably lower to 0.005% by weight.
• a coil of width I B 39 mm and a density equal to 2.6 g / cm 3 was heat-treated at 590 ° C. for 5 hours under nitrogen. No nitriding was observed.
• the nitriding tests were carried out either on stacks of sheets or on coils.
• the geometrical parameters of the stack are the length L E , the width IE and the thickness es ( Figure 1).
• the thickness variations e ⁇ were obtained in particular by placing the pressure stacks under stainless steel plates of different masses.
• the geometrical parameters of the coils are the width I B the diameter D B and the winding height h ⁇ ( Figure 2).
• the average density of the stack of sheets or coil is a useful parameter allowing to compare the two types of geometry. In the case of the coil, the volume VB considered for the calculation of the average density is
• V B (3.14 (DB 2 - (D B - 2h B ) 2 ) / 4). I 8 .
• particles of aluminum nitride with a length and a width of the order of 1 to 3 mm and a thickness of about 100 microns were introduced between the sheets.
• the samples were placed in a furnace with a volume of approximately 1 m 3 in which a vacuum of the order 10 -2 bar was achieved, followed by the introduction of a di-nitrogen flow rate of the order of 5 Nm / h throughout the duration of the test.
• Phase 1 rise to 400 ° C in 0.5h to 5h
• Phase 2 temperature increase until reaching a value between 590 and 650 ° C.
• the duration of phase 2 is greater than or equal to 2h.
• Phase 3 Cooling at 60 ° C / h C2: Phase 1 Climb to 400 ° C in 4 to 5 hours,
• Phase 2 maintenance at a temperature above 400 ° C and below 660 0 C for 6h.
• the temperature of the atmosphere oscillates between low points whose temperature is between 450 0 C and 500 0 C and high points whose temperature is between 550 ° C and 650 ° C, the number with oscillation being equal to 3.
• Phase 3 Cooling at 60 ° C / h
• the nitriding rate is determined by weighing the samples after the test. A correction is made to the raw result obtained by weighing to take into account, on the one hand, the external surfaces of the stacks and coils which are not subjected to nitriding and, on the other hand, the weight of the AIN particles introduced between the sheets and which do not participate. not to the reaction.
• Table 2 nitriding yield obtained
• Figure 3 illustrates the relationship between the average density of the samples and the nitriding yield obtained.
• FIG. 5a an AlN particle is observed from sample bob22.
• the particle has a thickness of about 400 microns and there are 5 layers of aluminum nitride with a thickness of about 80 microns.
• This structure has been schematized in FIG. 5b.
• composition determined for the nitrides obtained with the bob 13 and bob 9 samples are given in Table 3.
• the characteristics of this powder were a D50 value of 0.56 ⁇ m, a D10 value of 0.26 ⁇ m and a D90 value of 3.47 ⁇ m, a D90 ratio of D10 of 4.6.
• the micronized powder therefore has a D50 value of less than 0.7 ⁇ m and a ratio
• composition of the micronized powder obtained is given in Table 4.

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• 2006
  • 2006-10-16 FR FR0609040A patent/FR2907110A1/fr active Pending
• 2007
  • 2007-08-03 WO PCT/FR2007/001342 patent/WO2008046974A1/fr active Application Filing
  • 2007-08-03 CN CN200780038331.2A patent/CN101522563A/zh active Pending
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  • 2007-08-03 EP EP07823395A patent/EP2081868A1/de not_active Withdrawn
  • 2007-08-03 CA CA002666410A patent/CA2666410A1/fr not_active Abandoned
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