Patent Application
20150209826
1. Field of the Disclosure
The present disclosure relates generally to ceramic materials and methods for making and using them. More particularly, the present disclosure relates to silicon oxynitride materials having a variety of surface energies, articles comprising such materials, and methods for making and using them.
2. Technical Background
Ceramic films are widely used in the components of electronic devices, solar cells, light-emitting diodes, and wear-resistant parts. SiOx, as an example, is a good dielectric material that can be further modified into low-K dielectrics, for use with Cu wiring, to replace the conventional Al/SiO2 technology in microelectronics industry. SiOx can also be used as an environmental barrier or a protective coating in various applications due to its impermeability to gas species, such as moisture, O2, N2, Ar, Kr and Xe. Desired properties for such coatings include low weight, low atomic diffusion or permeability, and sometimes, high transparency. Moreover, in certain applications, e.g., self-cleaning coatings and multilayer-structured MEMS, a certain level of hydrophobicity or hydrophilicity is desirable to maximize functionality.
The wetting property of solid surfaces is mainly governed by microstructure and chemical composition. Recent research in the field has mostly focused on patterned surfaces and composite materials with one phase that carries the hydrophobic/hydrophilic property. Typical methods of making such films are self-assembled monolayer (SAM), lithography/imprinting techniques, plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), reactive sputtering and sol-gel processing. The vapor phase and sputtering processes have a variety of limitations, including high capital cost, environmental concerns, potentially high defect density and the need for line-of-sight geometries. And sol-gel derived coatings suffer from the high shrinkage associated with the ceramic conversion or low temperature tolerance.
Accordingly, there remains a need for ceramic materials having selectable levels of hydrophobicity/hydrophilicity, and for improved methods for making such materials.
In one aspect, the present disclosure provides a method for forming a ceramic/substrate interface comprising a ceramic material disposed on a substrate. The method includes:
In another aspect, the disclosure provides a method for forming a ceramic/substrate interface comprising a ceramic material disposed on a substrate. The method includes:
In another aspect, the disclosure provides an article having a patterned surface. The article includes at least
In another aspect, the disclosure provides a method for making an article having a patterned surface as described above. The method includes
A method for forming an article having a silicon oxynitride material at the surface thereof, the silicon oxynitride material having a surface energy of no more than 30 mN/m. The method includes:
Another aspect of the disclosure is an article having a silicon oxynitride material at the surface thereof, the silicon oxynitride material having a surface energy of no more than 30 mN/m.
Additional aspects and embodiments will be evident to the person of ordinary skill in the art in view of the present disclosure.
Before the disclosed processes and materials are described, it is to be understood that the aspects described herein are not limited to specific embodiments, apparati, or configurations, and as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and, unless specifically defined herein, is not intended to be limiting.
Throughout this specification, unless the context requires otherwise, the word “comprise” and “include” and variations (e.g., “comprises,” “comprising,” “includes,” “including”) will be understood to imply the inclusion of a stated component, feature, element, or step or group of components, features, elements or steps but not the exclusion of any other integer or step or group of integers or steps.
As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise.
Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.
Polymeric precursors such as polysiloxanes and polysilazanes can be converted to ceramics in various forms, including foams, fibers, and tapes. When using them to form coatings, shrinkage during pyrolysis can be a concern as it can lead to cracking if the coating thickness exceeds a critical thickness. However, the shrinkage of polymer-derived coatings made from high-yield preceramic polymers such as polysiloxanes and polysilazanes is significantly lower than that for sol-gel derived coatings. The shrinkage can be further reduced by adding inert and reactive particles. Such approaches have demonstrated the ability to make crack free coatings of practical thicknesses.
Perhydropolysilazane (PHPS) is a versatile polymer. It is a precursor to both SiO2 and Si3N4, depending on annealing atmosphere and conditions. To make the process suitable for roll-to-roll mass production, research has been conducted on converting PHPS into amorphous ceramics at or near room temperatures by exposing the as-deposited film to either reactive environments, like ammonia gas or hydrogen peroxide solution; or ultraviolet (UV) light sources, resulting in predominantly SiOx in oxygen and predominantly SiNx in nitrogen. Often the materials formed by such methods can be a mixed oxide/nitride of silicon, as some nitrogen will often remain from the silazane polymer, and some oxygen is often present in the film even when reacted in an inert environment. Additionally, heat treatment of PHPS has also been extensively investigated, revealing that the polymer can be fully converted to an inorganic at intermediate with a high ceramic yield. Here, too, silicon oxynitrides are often formed, with the relative amount of oxygen and nitrogen in the film being controllable by the reaction conditions. Examples of heat treatment of PHPS are described, for example, in Bauer, F.; Decker, U.; Dierdorf, A.; Ernst, H.; Heller, R.; Liebe, H.; Mehnert, R., Preparation of moisture curable polysilazane coatings Part I. Elucidation of low temperature curing kinetics by FT-IR spectroscopy. Prog. Org. Coat. 2005, 53, (3), 183-190; Günthner, M.; Wang, K.; Bordia, R. K.; Motz, G., Conversion behaviour and resulting mechanical properties of polysilazane-based coatings. J. Eur. Ceram. Soc. 2012, 32, (9), 1883-1892; AND Schwab, S. T.; Graef, R. C.; Blanchard, C. R.; Dec, S. F.; Maciel, G. G., The pyrolytic conversion of perhydropolysilazane into silicon nitride. Ceram. Int. 1998, 24, (6), 411-414, each of which is hereby incorporated by reference herein in its entirety for all purposes.
The inventors have surprisingly discovered that silicon oxynitride materials can be provided with radically different surface energies depending on the extent of conversion and oxidation of a substantially perhydrogenated polysilazane to silicon oxynitride. The inventors have determined that the extent of conversion of oxidation of polysilazane can be controlled using process parameters such as the amount of energy used in the processing of the polysilazane, Critically, the inventors have discovered that the silicon oxynitride formed by exposing to energy (e.g., heat energy) a substantially perhydrogenated polysilazane experiences an abrupt surface energy transition from low surface energy to high surface energy (e.g., from hydrophobic to hydrophilic) within a relatively narrow window of applied energy. For example, the relatively narrow window can be a relatively small temperature window when the energy is supplied by heat treatment for a particular amount of time, or a relatively small time window when the energy is supplied by heat treatment at a particular temperature. In other embodiments, the relatively small window can be a relatively small intensity window when the energy is supplied by radiation (e.g., UV radiation) for a particular amount of time, or a relatively small time window when the energy is supplied by radiation (e.g., UV radiation) at a particular intensity. This surprising property allows the person of ordinary skill in the art to form a number of new articles and to practice a number of new methods as described herein.
One aspect of the disclosure is a method for forming a ceramic/substrate including a ceramic material disposed on a substrate. One embodiment of such a method is shown in cross-sectional schematic cross-sectional flowchart view in
In view of the disclosure provided herein, the person of ordinary skill in the art can perform the heat treatment at a variety of temperatures and for a variety of times in order to form a silicon oxynitride having a desirably high surface energy and thus a desirably high level of hydrophilicity. For example, in certain embodiments, the layer of substantially perhydrogenated polysilazane is heat treated at a temperature in the range of about 325° C. to about 700° C. In other embodiments, the layer of substantially perhydrogenated polysilazane is heat treated at a temperature in the range of about 400° C. to about 600° C. For example, in certain embodiments, the layer of substantially perhydrogenated polysilazane is heat treated at a temperature in the range of about 325° C. to about 650° C., about 325° C. to about 550° C., about 350° C. to about 750° C., about 350° C. to about 700° C., about 350° C. to about 650° C., about 350° C. to about 600° C., about 350° C. to about 550° C., about 400° C. to about 750° C., about 400° C. to about 700° C., about 400° C. to about 650° C., about 400° C. to about 600° C., about 400° C. to about 550° C., about 500° C. to about 750° C., about 500° C. to about 700° C., or about 500° C. to about 650° C. The heat treatment can be performed (i.e., at a temperature described above), for example, for a time within the range of about 1 minute to about 10 hours. In certain embodiments, the heat treatment is performed for a time in the range of about 1 minute to about 7 hours, about 1 minute to about 6 hours, about 1 minute to about 5 hours, about 1 minute to about 4 hours, about 1 minute to about 3 hours, about 1 minute to about 2 hours, about 5 minutes to about 7 hours, about 5 minutes to about 6 hours, about 5 minutes to about 5 hours, about 5 minutes to about 4 hours, about 5 minutes to about 3 hours, about 5 minutes to about 2 hours, about 15 minutes to about 7 hours, about 15 minutes to about 6 hours, about 15 minutes to about 5 hours, about 15 minutes to about 4 hours, about 15 minutes to about 3 hours, about 15 minutes to about 2 hours, about 30 minutes to about 7 hours, about 30 minutes to about 6 hours, about 30 minutes to about 5 hours, about 30 minutes to about 4 hours, about 30 minutes to about 3 hours, about 30 minutes to about 2 hours, about 30 minutes to about 7 hours, about 1 hour to about 6 hours, about 1 hour to about 5 hours, about 1 hour to about 4 hours, about 1 hour to about 3 hours, or about 1 hour to about 2 hours.
As described above, the heat treatment can be performed to provide a silicon oxynitride film with a desirably high surface energy. For example, in certain embodiments, the heat treatment is performed to provide the exposed surface of the silicon oxynitride film with a surface energy of at least about 50 mN/m. In other embodiments, the heat treatment is performed to provide the exposed surface of the silicon oxynitride film with a surface energy of at least about 52 mN/m, at least about 55 mN/m, or at least about 57 mN/m. In certain embodiments, the heat treatment is performed to provide the exposed surface of the silicon oxynitride film with a surface energy in the range of about 50 mN/m to about 80 mN/m, or about 52 mN/m to about 80 mN/m, or about 55 mN/m to about 80 mN/m, or about 57 mN/m to about 80 mN/m, or about 50 mN/m to about 75 mN/m, or about 52 mN/m to about 75 mN/m, or about 55 mN/m to about 75 mN/m, or about 57 mN/m to about 75 mN/m, or about 50 mN/m to about 70 mN/m, or about 52 mN/m to about 70 mN/m, or about 55 mN/m to about 70 mN/m, or about 57 mN/m to about 70 mN/m, or about 50 mN/m to about 65 mN/m, or about 52 mN/m to about 65 mN/m, or about 55 mN/m to about 65 mN/m, or about 57 mN/m to about 65 mN/m, or about 50 mN/m to about 60 mN/m, or about 52 mN/m to about 60 mN/m, or about 55 mN/m to about 60 mN/m, or about 57 mN/m to about 60 mN/m.
As described in more detail below, high surface energy silicon oxynitride films can advantageously provide increased wetting and bonding of an overlying ceramic material. Accordingly, another aspect of the disclosure relates to the use of high surface energy silicon oxynitride films to make a ceramic/substrate interface. One embodiment of such a method is shown in cross-sectional schematic flowchart view in
In certain embodiments, the exposure of the layer of the substantially perhydrogenated polysilazane to energy is performed to provide the exposed surface of the silicon oxynitride film with a surface energy of at least about 52 mN/m, at least about 55 mN/m, or at least about 57 mN/m. In certain embodiments, the exposure to energy is performed to provide the exposed surface of the silicon oxynitride film with a surface energy in the range of about 50 mN/m to about 80 mN/m, or about 52 mN/m to about 80 mN/m, or about 55 mN/m to about 80 mN/m, or about 57 mN/m to about 80 mN/m, or about 50 mN/m to about 75 mN/m, or about 52 mN/m to about 75 mN/m, or about 55 mN/m to about 75 mN/m, or about 57 mN/m to about 75 mN/m, or about 50 mN/m to about 70 mN/m, or about 52 mN/m to about 70 mN/m, or about 55 mN/m to about 70 mN/m, or about 57 mN/m to about 70 mN/m, or about 50 mN/m to about 65 mN/m, or about 52 mN/m to about 65 mN/m, or about 55 mN/m to about 65 mN/m, or about 57 mN/m to about 65 mN/m, or about 50 mN/m to about 60 mN/m, or about 52 mN/m to about 60 mN/m, or about 55 mN/m to about 60 mN/m, or about 57 mN/m to about 60 mN/m.
The energy used to form the high surface energy silicon oxynitride layer can take a variety of forms. For example, in certain embodiments, the energy used to form the high surface energy silicon oxynitride layer is heat energy. The heat energy can be, for example, provided by heat treatment using any of the temperature and/or time ranges described above with respect to heat treatment of substantially perhydrogenated polysilazane. Of course, in view of the disclosure provided herein, the person of ordinary skill in the art can determine other suitable heat treatment regimens to provide a silicon oxynitride layer having a desired surface energy; e.g., hotter temperatures for shorter amounts of time; or cooler temperatures for longer amounts of time. In other embodiments, the energy used to form the high surface energy silicon oxynitride layer is radiation (e.g., ultraviolet radiation such as VUV radiation), provided, for example, by irradiation with a laser or with a lamp, or electron beam radiation. The person of ordinary skill in the art will appreciate that exposure with radiation will exhibit behavior similar to that described above and detailed below with respect to
The methods described above use a substantially perhydrogenated polysilazane. In certain embodiments, the substantially perhydrogenated polysilazane is perhydropolysilazane, having the idealized formula H(SiH2NH)nH. As the person of ordinary skill in the art will appreciate, the perhydropolysilazane can be provided in a partially-crosslinked and/or cyclized state, meaning the true chemical formula of the perhydropolysilazane can differ somewhat from the idealized formula. Moreover, in certain embodiments, the substantially perhydrogenated polysilazane is not completely substituted with hydrogen, but rather includes a relatively small amount (e.g., less than 10%, less than 5%, less than 2%, less than 1%, less than 0.5%) of organic substitutions in place of the hydrogen substituents of perhydropolysilazane. The use of the term “perhydrogenated” herein is meant to describe only the chemical substitution of the polysilazane; perhydrogenated materials need not be synthesized using a hydrogenation process.
In the methods described above, the layer of substantially perhydrogenated polysilazane can be provided with a variety of thicknesses. For example, in certain embodiments, the layer of substantially perhydrogenated polysilazane is in the range of about 10 nm to about 10 μm (e.g., about 100 nm to about 5 μm) in thickness. In certain embodiments, relatively thicker coatings of silicon oxynitride of a desired surface energy can be built up by forming multiple layers (e.g., depositing a substantially perhydrogenated polysilazane, exposing to energy to provide a desired surface energy, then repeating the deposition/exposure steps to build up to a desired thickness).
The person of ordinary skill in the art will appreciate that the heat treatment of the substantially perhydrogenated polysilazane layer or the exposure of the substantially perhydrogenated polysilazane layer to energy can be performed in a variety of fashions. For example, in certain embodiments, the heat treatment of the substantially perhydrogenated polysilazane layer or the exposure of the substantially perhydrogenated polysilazane layer to energy is performed in an oxygen-containing atmosphere, e.g., air. The person of ordinary skill in the art can adjust exposure conditions (e.g., time, temperature, type of energy source, atmosphere) to provide materials having a desired surface energy based on the disclosure herein.
The methods described above can be used in conjunction with a number of different types of substrates. For example, in certain embodiments, the substrate is a metal substrate, optionally with a surface layer of metal oxide. The optional metal oxide layer can be grown in a separate step via thermal oxidative techniques, or can be a thin layer of metal oxide resulting from atmospheric oxidation, as the person of ordinary skill in the art would appreciate. Of course, in other embodiments, the substrate is a semiconductor material (e.g., silicon), optionally with a semiconductor oxide surface layer or a glass material (e.g., a silica glass). In certain embodiments, the substrate can be a polymeric material, e.g., a polymer matrix composite.
Similarly, the methods described above can be used in conjunction with a variety of different ceramic materials. The ceramic material can be, for example, amorphous, partially crystalline or substantially crystalline, and can be homogeneous or inhomogeneous. Moreover, the ceramic material can be filled, for example, with particles of one or more different materials. In one particular embodiment, the ceramic material is a silicon oxycarbide material. The silicon oxycarbide material can have particles dispersed therein, for example, ZrSi2 particles. In other embodiments, the ceramic material is a glass material, e.g., a silica glass or a silicate glass, silicon carbide or silicon carbonitride.
In the methods described above, either the final ceramic material or a precursor thereof can be provided onto the exposed surface of the silicon oxynitride layer. In certain embodiments, it is a precursor of the ultimately-desired ceramic material that is provided on the exposed surface of the silicon oxynitride layer. For example, in certain embodiments, a siloxane polymer (e.g., polyhydromethylsiloxane) is provided on the exposed surface of the silicon oxynitride layer; the siloxane polymer can be converted to silicon oxide or silicon oxycarbide by heat or application of other energy. In other embodiments, an organically modified silicate or a silica sol is provided on the exposed surface of the silicon oxynitride layer; these materials can be converted to amorphous siliceous materials by heat or application of other energy. In other embodiments, a carbon-containing polysilazane can be provided on the exposed surface of the silicon oxynitride layer; this material can be converted to silicon carbonitride by heat or application of other energy.
The ceramic materials in the methods described above can be formed with a variety of thicknesses. For example, in certain embodiments, the ceramic material is in the range of about 1 μm to about 5000 μm (e.g., about 100 to 1000 μm) in thickness. Of course, in other embodiments the ceramic material is thicker than about 1000 μm; in such embodiments, the silicon oxynitride can help to bond a ceramic body to a substrate.
In recent years, there has been an increasing interest in developing polymer derived ceramic (PDC) composite coatings on different metallic substrates as thermal or environmental barrier coatings (EBC). Such coatings are described, for example, in Günthner, M.; Schutz, A.; Glatzel, U.; Wang, K.; Bordia, R. K.; Greiβl, O.; Krenkel, W.; Motz, G., High performance environmental barrier coatings, Part I: Passive filler loaded SiCN system for steel. J. Eur. Ceram. Soc. 2011, 31, (15), 3003-3010; and Wang, K.; Günthner, M.; Motz, G.; Bordia, R. K., High performance environmental barrier coatings, Part II: Active filler loaded SiOC system for superalloys. J. Eur. Ceram. Soc. 2011, 31, (15), 3011-3020, each of which is hereby incorporated herein by reference in its entirety for all purposes. However, one common problem with all these coatings is the presence of residual porosity, which leads to catastrophic failures of the metal-ceramic interface due to the formation and growth of a thermally grown oxide (TGO) layer. As described in more detail below, the present inventors have determined that the methods described above can be used to provide thermal/environmental barrier coatings that are resistant to failure at the metal/ceramic interface. As the person of ordinary skill in the art will appreciate the silicon oxynitride bond coats described herein can be used with top coat materials described in the above-referenced publications.
Another aspect of the disclosure is an article having a patterned surface in which different regions of the surface of the article have different surface energies. Such articles can be formed, for example, by exposing the regions to different amounts of energy (e.g., heat, radiation), thereby providing different surface energies to the regions, in the manner otherwise described herein. One embodiment is shown in schematic perspective view in
It can be especially desirable for there to be a substantial amount of surface energy contrast between the first region and the second region. For example, in certain embodiments, the surface energy of the second silicon oxynitride material is at least about 30 mN/m less than the surface energy of the first silicon oxynitride material. In various embodiments, the surface energy of the second silicon oxynitride material is at least about 32 mN/m less, at least about 35 mN/m less, or about 38 mN/m less than the surface energy of the first silicon oxynitride material. In certain embodiments, the surface energy of the second silicon oxynitride material is in the range of about 30 mN/m to about 40 mN/m less, about 32 mN/m to about 40 mN/m, or at least about 35 mN/m to about 40 mN/m less than the surface energy of the first silicon oxynitride material.
In certain embodiments, the second region is substantially contiguous with the first region on the patterned surface. For example, the second region is desirably within about 500 μm, within about 200 μm, or within about 100 μm of the first region. Such sharp transitions between regions of substantially different surface energy can be especially desirable when using the different regions to pattern liquids, e.g., liquid solutions of polymers to be applied onto the first regions. In certain embodiments, a first region is substantially surrounded by a second region, as shown in
As described in more detail otherwise herein, exposure of substantially perhydrogenated polysilazanes to different amounts of energy can result in substantially different surface energies. In certain embodiments, the first silicon oxynitride material has a substantially lower concentration of Si—H bonds at the patterned surface than does the second silicon oxynitride material. As described in more detail below with respect to the experimental data, exposing a perhydrogenated silazane to relatively more energy provides a relatively higher surface energy due to removal of Si—H bonds from the surface thereof.
The first silicon oxynitride material can have, for example, a surface energy in the range of about 30 mN/m to about 65 mN/m. In certain embodiments, the first silicon oxynitride material has a surface energy in the range of about 30 mN/m to about 80 mN/m, or about 40 mN/m to about 80 mN/m, or about 50 mN/m to about 80 mN/m, or about 52 mN/m to about 80 mN/m, or about 55 mN/m to about 80 mN/m, or about 57 mN/m to about 80 mN/m, or about 30 mN/m to about 75 mN/m, or about 40 mN/m to about 75 mN/m, or about 50 mN/m to about 75 mN/m, or about 52 mN/m to about 75 mN/m, or about 55 mN/m to about 75 mN/m, or about 57 mN/m to about 75 mN/m, or about 30 mN/m to about 70 mN/m, or about 40 mN/m to about 70 mN/m, or about 50 mN/m to about 70 mN/m, or about 52 mN/m to about 70 mN/m, or about 55 mN/m to about 70 mN/m, or about 57 mN/m to about 70 mN/m, or about 40 mN/m to about 65 mN/m, or about 50 mN/m to about 65 mN/m, or about 52 mN/m to about 65 mN/m, or about 55 mN/m to about 65 mN/m, or about 57 mN/m to about 65 mN/m, or about 30 mN/m to about 60 mN/m, or about 40 mN/m to about 60 mN/m, or about 50 mN/m to about 60 mN/m, or about 52 mN/m to about 60 mN/m, or about 55 mN/m to about 60 mN/m, or about 57 mN/m to about 60 mN/m. The first silicon oxynitride material can be, for example, substantially hydrophilic at the patterned surface.
Whatever the surface energy of the first silicon oxynitride material, the second silicon oxynitride material has a substantially lower surface energy. For example, in one embodiment, the second silicon oxynitride material has a surface energy of no more than about 25 mN/m. In certain embodiments, the second silicon oxynitride material has a surface energy in the range of about 10 mN/m to about 25 mN/m, or about 10 mN/m to about 20 mN/m, or about 10 mN/m to about 15 mN/m, or about 15 mN/m to about 25 mN/m, or about 15 mN/m to about 20 mN/m, or about 20 mN/m to about 25 mN/m. The second silicon oxynitride material can be, for example, substantially hydrophobic at the patterned surface.
Another aspect of the disclosure is a method for making the article having the patterned surface as described above. In one embodiment, the method includes disposing a substantially perhydrogenated polysilazane on a surface of the article. The substantially perhydrogenated polysilazane is exposed to two different energies to form the two regions. In the first region, the substantially perhydrogenated polysilazane is exposed to energy sufficient to form the first silicon oxynitride film. In the second region, the substantially perhydrogenated polysilazane is exposed to energy sufficient to form the second silicon oxynitride film. As the surface energy is lower in the second region than in the first, the second region is exposed to substantially less energy than the first region. For example, in certain embodiments, in the first region, the substantially perhydrogenated polysilazane is heat-treated at a temperature of at least about 325° C. to form the first silicon oxynitride material; and in the second region, the substantially perhydrogenated polysilazane is heat treated at a temperature of no greater than about 300° C. to form the second silicon oxynitride material. In certain such embodiments, the substantially perhydrogenated polysilazane in the first region is heat-treated at a temperature of at least about 400° C., or at least about 500° C., or in the range of about 325° C. to about 1200° C., or in the range of about 400° C. to about 1200° C., or in the range of about 500° C. to about 1200° C., or in the range of about 325° C. to about 1000° C., or in the range of about 400° C. to about 1000° C., or in the range of about 500° C. to about 1000° C., or in the range of about 325° C. to about 800° C., or in the range of about 400° C. to about 800° C., or in the range of about 500° C. to about 800° C. In certain such embodiments, the substantially perhydrogenated polysilazane in the second region is heat treated at a temperature in the range of about 100° C. to about 300° C., or in the range of about 150° C. to about 300° C., or about 200° C. to about 300° C. The heating regiments may be performed for the times and under the conditions as described above. Of course, in other embodiments, different heating regimens can be used. In any event, the person of ordinary skill in the art can determine the necessary heating conditions to provide the desired surface energies to the first and second silicon oxynitride materials.
In other embodiments, types of energy other than heat (such as those described above) can be used to convert the substantially perhydrogenated polysilazane to the first silicon oxynitride material and the second silicon oxynitride material. The person of ordinary skill in the art will determine the necessary exposure conditions to provide the desired surface energies to the first and second silicon oxynitride materials.
The person of ordinary skill in the art can use conventional methodologies to provide the pattern of the first and second regions on the surface. For example, laser heating can be used to provide finely controlled heating at two different energy levels in the two regions. Electron beam lithography and photolithography can also be used to provide different energy exposures in the different regions.
The article can take many forms, for example, the form of a substrate bearing the silicon oxynitride materials of the first and second regions. The article can be formed from a variety of materials, e.g., metals (optionally with a metal oxide at the surface as otherwise described herein), ceramic materials such as glasses, silicon oxides, semiconductors such as silicon, among many others.
As the person of ordinary skill in the art will appreciate, the exposure of the various regions to energy (heat or otherwise) can be performed sequentially. It can particularly be useful to expose the first region to energy in two separate steps, one performed at the conditions under which the second region is exposed to energy, and another to provide the desired surface energy to the silicon oxynitride material of the first region. For example, the substantially perhydrogenated polysilazane can be disposed on the surface of the article, then the entire surface of the article (or, at least, both the first and second regions) can be exposed to energy sufficient to convert the substantially perhydrogenated polysilazane to the second silicon oxynitride material (i.e., having a relatively low surface energy) throughout both the first and second regions. The first region can then be exposed to additional energy (through masking or targeted radiation or otherwise targeted application of energy) in order to convert the second silicon oxynitride material to the first silicon oxynitride material (i.e., having a relatively high surface energy) in the first region, leaving the second region with a low surface energy. As the person of ordinary skill in the art will appreciate, conventional microelectronic processing techniques can be adapted for use into making patterned surfaces as described herein. For example, one particular approach to make pattered surfaces is to mask different regions and expose unmasked regions to either heat or UV radiation.
Another aspect of the disclosure is a method for forming an article having a silicon oxynitride material at the surface thereof, the silicon oxynitride material having a surface energy of no more than 30 mN/m. The method includes forming a layer of substantially perhydrogenated polysilazane on the article; exposing the layer of substantially perhydrogenated polysilazane to energy sufficient to form a silicon oxynitride layer having an exposed surface having a surface energy no more than about 30 mN/m; and refraining from exposing the silicon oxynitride layer having the exposed surface having the surface energy no more than about 30 mN/m to energy sufficient to increase the surface energy of the exposed surface to a value above about 30 mN/m. An example of such a method is shown in schematic view in
In certain embodiments, layer of substantially perhydrogenated polysilazane is exposed to energy sufficient to form a silicon oxynitride layer having a surface energy of no more than about 25 mN/m. In certain embodiments, the second silicon oxynitride material has a surface energy in the range of about 10 mN/m to about 30 mN/m, or about 10 mN/m to about 25 mN/m, or about 10 mN/m to about 20 mN/m, or about 10 mN/m to about 15 mN/m, or about 15 mN/m to about 30 mN/m, or about 15 mN/m to about 25 mN/m, or about 15 mN/m to about 20 mN/m, or about 20 mN/m to about 30 mN/m, or about 20 mN/m to about 25 mN/m.
In certain embodiments, the method includes refraining from exposing the silicon oxynitride layer to energy sufficient to increase the surface energy of the exposed surface to a value above about 25 mN/m, about 20 mN/m, or about 15 mN/m. That is, the method includes preventing the silicon oxide layer from being exposed to energy sufficient to increase the surface energy of the exposed surface to a value above about 25 mN/m, about 20 mN/m, or about 15 mN/m. As the person of ordinary skill in the art would appreciate from the disclosure herein, exposure of a low-surface energy silicon oxynitride material to more energy would tend to push it through the surface energy transition and convert it to a higher surface energy material. By refraining from exposing the silicon oxynitride layer to such high energy, the person of ordinary skill in the art can retain a desirable low surface energy, and, for example, a substantially hydrophobic surface. Accordingly, the person of ordinary skill in the art will avoid higher-energy processes (e.g., involving strong UV radiation or high temperatures) in further processing of the article.
The exposure to energy can be performed in a variety of manners, for example, as described above with respect to the second silicon oxynitride material of the patterned article embodiments. In certain embodiments, the exposure of the layer of substantially perhydrogenated polysilazane to energy comprises heating at a temperature of no greater than about 300° C. In certain such embodiments, the substantially perhydrogenated polysilazane in the second region is heat treated at a temperature in the range of about 100° C. to about 300° C., or in the range of about 150° C. to about 300° C., or about 200° C. to about 300° C. The heating regiments may be performed for the times and under the conditions as described above. Of course, in other embodiments, different heating regimens can be used. In other embodiments, the exposure of the layer of substantially perhydrogenated silazane to energy comprises exposure to radiation, such as ultraviolet radiation. As described above, in certain embodiments, the exposure to energy of the layer of substantially perhydrogenated polysilazane is performed in an oxygen-containing atmosphere. In all cases, the person of ordinary skill in the art can determine the necessary conditions to provide the desired surface energy to the silicon oxynitride layer.
The substantially perhydrogenated silazanes described above can be used in practicing this aspect of the disclosure. For example, in one embodiment, the substantially perhydrogenated polysilazane is perhydrosilazane. The substantially perhydrogenated silazane can be formed as described above, for example, at a thickness in the range of about 10 nm to about 10 μm.
Another aspect of the disclosure is an article having a silicon oxynitride material at the surface thereof, the silicon oxynitride material having a surface energy of no more than 30 mN/m. The article can be made, for example, as described above, and can have surface energy values as described above. Notably, the article is not merely in the process of being fabricated, with the silicon oxynitride material being exposed to further energy to convert it to a substantially higher surface energy. The silicon oxynitride material can thus be substantially hydrophobic, which can be desirable in a variety of applications as described above.
Various aspects of the disclosure are further presented with respect to the description of the experiments, the data presented and the analysis thereof below.
Film Preparation:
Metal sheet (nickel-based superalloy Inconel 617) was cut into coupons of 30 mm×10 mm×1.2 mm (L×W×H) in size, polished to 1200 grit finish and cleaned using an ultrasonication bath prior to processing. For the silicon oxynitride (SiON) ceramic films, perhydropolysilazane PHPS NN 120-20 (a solution of 20 wt. % PHPS in dibutyl ether, Clariant Advanced Materials GmbH, Sulzbach, Germany) was used as the polymer precursor. For the double-layer environmental barrier coating systems, a SiON film served as the bond coat, while the top coat layer was a composite of filler particles and a polymer-derived SiOC ceramic matrix. The top coat was made from a precursor slurry of submicron ZrSi2 particles (Accumet Materials Co., Ossining, N.Y., USA) and polyhydromethylsiloxane (PHMS) polymer (HMS-992, Gelest Inc., Morrisville, Pa., USA). To prepare the top coat slurry, 30 vol. % of ZrSi2 powder was mixed with 70 vol. % of PHMS and half of the required n-octane (98+%, Alfa Aesar, Ward Hill, Mass., USA) solvent. The slurry was ball-milled (zirconia media) for 4 hours in order to mix all the reactants well and remove agglomerates. 0.05 wt % of Ru3(CO)12 (Alfa Aesar) catalyst (with respect to PHMS) was dissolved in the other half of the required n-octane, and the resulting solution was added to the slurry, which was ball-milled for another 30 minutes prior to dip coating. The volume ratio of (filler+PHMS) to n-octane was 3:5.
Coating layers (of both the PHPS and the top coat precursor slurry) were prepared by dip-coating, using a mechanical testing frame, Instron 4505 (Illinois Tool Works Inc., Norwood, Mass., USA), in sequence. Moderate withdrawal speed was used: 500 mm Reproducible processing of these coatings requires control over the viscosity of the slurry and the withdrawal speed.
Heat treatments (i.e., for both the conversion of PHPS to SiON and the conversion of the precursor to the top coat) were performed in a tube furnace with flowing air (flux rate: ˜3 L h−1) environment. Heat treatment of the PHPS was performed at a variety of temperatures between room temperature (RT) and 800° C. (RT, 200° C., 400° C., 600° C. and 800° C.; heating rate: 2° C./min, holding time: 2 h). For the systems including a top coat, the PHPS was heated at 800° C. as described above, and conversion of the precursor layer to the top coat was performed in two steps. First the PHMS was cross-linked at 150° C. (heating rate: 2° C./min, holding time: 2 h) in the presence of humid air (˜40 mL of water placed in the tube). After cross-linking, the precursor was heated at 800° C. (heating rate: 2° C./min, holding time: 2 h) to form the top coat.
Surface Energy Characterization: Contact angle measurements were carried out on an optical goniometer instrument (VCA Optima, AST Products, Inc., Billerica, Mass., USA). Shape of drops with a pre-determined volume (0.5-1 μL) was recorded by a CCD camera and then contact angles were measured using the analysis software (VCA Optima Series). Surface energy was composed of additive polar and dispersive portions,
γi=γiP+γiD
where i denotes a specific phase (solid S or liquid L) and the superscripts P and D denote the polar and dispersive components. These two components are responsible for the non-London interactions (polar forces, such as hydrogen bonding) and the London dispersion interactions (induced dipole-dipole forces, such as Van der Waals force) between the two phases, respectively. A Kaelble plot was used to derive these two components and the master equation took a linear regression form, shown as follows,
in which θ is the contact angle. Mapping this to the typical linear equation y=ax+b, with
the slope ‘a’ and intercept ‘b’ correspond respectively to the square roots of dispersive and polar surface energy components of the solid phase. To determine the ‘a’ and ‘b’ values, the contact angle θ with different known liquids (having known surface energies) was measured. Three different liquids were used, having the listed surface energies (both polar and dispersive components) in units of mN/m: deionized water (γP: 50.3, γD: 21.5), ethylene glycol (γP: 15.2, γD: 32.8) and formamide (γP: 23.5, γD: 34.4). Using the contact angle data and the γP and γD values for the three liquids, the γP and γD values for a particular surface can be determined. Contact angle data were collected on PHPS films annealed at RT, 200, 250, 300, 350, 400, 600 and 800° C. A larger number of films were investigated between 200° C. and 400° C. because this was the temperature range of significant changes in film's surface chemistry. Further details regarding surface energy calculations can be found in Fowkes, F. M., Determination of interfacial tensions, contact angles, and dispersion forces in surfaces by assuming additivity of intermolecular interactions in surfaces. J. Phys. Chem-US. 1962, 66, (2), 382; Kaelble, D. H., Dispersion-polar surface tension properties of organic solids. J. Adhesion 1970, 2, 66-81; and Matsunaga, T.; Ikeda, Y., Dispersive component of surface free energy of hydrophilic polymers. J. Colloid Interf. Sci. 1981, 84, (1), 8-13, each of which is hereby incorporated herein by reference in its entirety.
Chemical and Microscopic Analysis:
Chemical analysis on the PHPS films was performed using Fourier transform infrared spectroscopy (FTIR) (powder) and Raman spectroscopy (785 nm laser, Renishaw inVia Raman Microscope, Renishaw Inc., Hoffman Estates, Ill., USA). Pellet samples for FTIR were made from powders (particle size: <35 μm) derived from PHPS annealed in air for 2 hours at temperatures between RT and 800° C. at 200° C. interval. A Perkin Elmer 1720 (wavenumber 4000-400 cm−1 and step size 0.5 cm−1) series FTIR spectrophotometer was used in transmission mode. Finally, microstructures of the films and coating systems were examined using scanning electron microscopy (SEM) (JSM-7000F, JEOL-USA, Inc., Peabody, Mass., USA).
While not intending to be bound by theory, the inventors provide the following discussion of the data generated as described above:
Surface Energy of SiON Films from Contact Angle Measurements
In an oxidizing environment, the heat treatment of PHPS films is essentially an oxygen-enriching process of crosslinked (SiH2NH)n network that involves both compositional and microstructural evolutions. This leads to a continuous change in the bonding states of the atoms on the outermost layer of the film. This change in surface chemistry leads to a change in surface energy, which can be quantitatively characterized by contact angle measurement as described above.
Surprisingly, the plot of
FTIR and Raman spectroscopy was used to investigate the changes in the chemical state of the film during annealing in order to understand the mechanism of the surface energy transition. The FTIR and Raman spectra are presented in
The FTIR spectra yield insight into the conversion process of the PHPS polymer. For low temperature annealing, the film showed characteristics of ligands including elements like hydrogen. As annealing temperature increases, both N—H and Si—H bands decreased in intensity due to crosslinking and conversion to ceramic phase. N—H band completely disappeared after 400° C., while intensity of the Si—H band strongly decreased after 600° C., i.e., the hydrogen atoms bonded to nitrogen were most reactive and were released in small molecule forms during the early stage of annealing, followed by the Si—H group. After annealing at 800° C., there was no evidence of hydrogen in the final product, so it became a SiON ceramic. Similar trends are observed for the Si2N—H group. Its absorption band at 1180 cm−1 disappeared after 400° C. Up to 800° C., Si—O—Si and Si—N—Si bands were observed and prominent. Particularly, Si—N—Si was embedded in the broad Si—O—Si band, and a similar situation could also be found in the Raman spectra too. The Si—N—Si bonding is in PHPS' molecular structure, while Si—O—Si is due to the substitution of nitrogen atoms with oxygen due to annealing in air. In addition, the intensity of these absorption bands grew substantially with increasing temperature, showing the progress of pyrolysis. Similar results have been reported on other types of polysilazane polymers.
The Raman spectra agree well with the results from the FTIR spectra, except that Raman scattering seems to be more sensitive to different vibrational modes of Si—H bonds. ν (Si—H), δ (Si—H) and ω (N—H) peaks have strong intensities for the PHPS film deposited at room temperature, they diminish significantly when crosslinking takes place at 200° C., and eventually vanish at 400° C. when the film converts to a ceramic-like inorganic material. At about 505 cm−1, the Si—N bond is the backbone of PHPS molecules and has a strong signal for samples annealed at low temperatures. This band is significantly reduced as temperature increases, but is still present up to 800° C. The reason for its decrease in intensity is that nitrogen was gradually replaced by oxygen, therefore, as the annealing temperature increases, there are fewer Si—N bonds. As shown in
Combined FTIR and Raman spectroscopic analysis demonstrated that a PHPS film could be fully converted to an inorganic ceramic material at temperature as low as 400° C., as evidenced by the almost complete disappearance of hydrogen. Oxygen is found in the FTIR spectra of PHPS films heat-treated at low temperatures, e.g., 200° C. This may be attributed to three possible oxygen sources: the native oxygen impurity in the PHPS molecules, the incorporated oxygen due to partial crosslinking at room temperature, and the —OH group due to exposure in air. For heat treatment at 800° C. in air, the final product exhibits a mixture of Si—O (majority) and Si—N bonds, but the four bonded atoms of the Si tetrahedron can be any combination of O and N. Therefore, it is a silicon oxynitride amorphous film.
A detailed XPS investigation on these films revealed that there was only negligible intensity of Si—N bonds at or near the top surface (within about 2 nm) of the SiON films annealed at 600° C. and above. Particularly, the empirical formula of annealed SiON films (disregarding H content) at the surface evolves from SiO0.616N0.284Hx (at RT) to SiO1.881N0.003 (at 800° C.)—a significant decrease in the N content. A previously-reported glow discharge optical emission microscopy (GDOES) measurement on a similar PHPS film pyrolyzed at 800° C. demonstrated that this top SiO2 layer can be roughly 15% of the total film thickness. In contrast, both the FTIR and Raman studies described above confirmed the presence of significant Si—N bond content in PHPS films heat treated at temperatures as high as 800° C. Without intending to be bound by theory, the inventors believe this is due to the much higher probe depth of these spectroscopic techniques, and that the Si—N signal in the Raman spectra is from the interior of the film. Thus, the inventors believe that the silicon oxynitride films heat treated at high temperature exhibit an oxygen gradient, or equivalently a nitrogen gradient, in the thickness direction, which is schematically depicted in
The observed changes in the chemical state of the PHPS suggest a likely explanation for the significant surface energy transition described above with respect to
However, the polar component noticeably drops from the maximum 48.66 mN/m at 400° C. to 27.51 mN/m at 800° C.—a decrease of ˜43%. This could be correlated with different stages in the PHPS pyrolysis. Thermogravimetric (TG) analysis on PHPS reveals that the weight gain associated with its pyrolysis in air mainly lies between 150° C. and 400° C., during which significant chemical reactions, as discussed above, take place both in the body and on the surface of the evolving film. (This TG experiment is described in Günthner, M.; Wang, K.; Bordia, R. K.; Motz, G., Conversion behaviour and resulting mechanical properties of polysilazane-based coatings. J. Eur. Ceram. Soc. 2012, 32, (9), 1883-1892, which is hereby incorporated herein by reference in its entirety for all purposes.) The TG result explains the substantial increase in surface energy due to the formation of highly polar Si—OH bonds up to this point. Subsequently, beyond 400° C., the film gets into the densification stage so that Si—OH bonds are gradually removed and replaced by Si—O—Si bonds, resulting in a less and less polar surface. Upon further heating above 800° C., it can be speculated that the polar and dispersive components will continue to decrease and increase, respectively.
PHPS can be heat treated to form films with a dense microstructure. For example, a layer of PHPS was heat treated at 800° C. to form a silicon oxynitride film.
Multilayer coatings were fabricated as described above. A schematic cross-sectional view of an example of a multilayer coating system is provided as
The delamination of top coat layer is likely to happen after PHMS crosslinking (150° C.) but before ceramic conversion (600-800° C.). Experimentally, it was observed that PHMS top coats that spalled off from RT- and 200° C.-treated PHPS bond coats remained in a single thin piece having a wavy contour. This implies that when the PHMS top coat is applied on the low-temperature annealed PHPS bond coat surface, the very poor wetting between the PHMS and the PHPS limits bonding due to the weak London dispersive contribution. Therefore, the top coat is more or less “free standing” during the final heat treatment. It crosslinks and shrinks at 150° C., and then spalls off completely before there is enough activation energy to form primary chemical bonds between the two layers. Accordingly, in such a multilayer system, a hydrophilic bond coat is desired to bond the top coat in the polymeric state.
The effectiveness of the SiON/PHPS bond coat as an oxygen barrier was examined by long-term static oxidation tests (at 800° C. for 200 hours).
However, after 200 hour exposure, there is a distinct difference between the two coating systems as shown in
In contrast, the double-layer coating system (
Thus, an amorphous silicon oxynitride ceramic film was fabricated by the heat treatment of an inorganic polymer, perhydropolysilazane (PHPS). Notably, its surface energy showed a significant transition from low surface energy (more hydrophobic) to higher surface energy (more hydrophilic) within a narrow annealing temperature window of ˜100° C. The total surface energy increased about 5 times, which was primarily due to an increase in the polar component of 20-40 times. Without intending to be bound by theory, the phenomenon was explained by studying the chemical evolution on the surface of the film as a function of heat treatment temperature. It was demonstrated that heat treatment in air could lead to films with compositional gradients in oxygen and nitrogen along the thickness direction. The dense and hydrophilic SiON ceramic was then used as the bond coat in a double-layer EBC system, which showed outstanding performance in long-term static oxidation tests at 800° C.
This application claims the benefit of priority of U.S. Provisional Patent Application No. 61/933,140, filed Jan. 29, 2014, which is hereby incorporated herein by reference in its entirety.
This invention was made with government support under contract no. FA95550-09-1-0633 awarded by the United States Air Force Office of Scientific Research. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61933140 | Jan 2014 | US |
