Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
  • C03B5/16—Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
  • C03B5/167—Means for preventing damage to equipment, e.g. by molten glass, hot gases, batches
  • C03B5/1672—Use of materials therefor
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/50—Piezoelectric or electrostrictive devices having a stacked or multilayer structure
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B17/00—Forming molten glass by flowing-out, pushing-out, extruding or drawing downwardly or laterally from forming slits or by overflowing over lips
  • C03B17/06—Forming glass sheets
  • C03B17/064—Forming glass sheets by the overflow downdraw fusion process; Isopipes therefor
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
  • C03B5/16—Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
  • C03B5/167—Means for preventing damage to equipment, e.g. by molten glass, hot gases, batches
  • C03B5/1672—Use of materials therefor
  • C03B5/1675—Platinum group metals
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
  • C23C28/321—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer with at least one metal alloy layer
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
  • C23C28/322—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
  • C23C28/345—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
  • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
  • C23C28/36—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including layers graded in composition or physical properties

Definitions

• the present disclosure relates to protective coating and method for metals, hi particular, the present invention relates to oxide protective coating for noble metals and method for forming such coatings.
• the present invention is useful, e.g., in the passivation and protection of platinum components of glass delivery systems at elevated operation temperatures in oxidative atmosphere.
• An exemplary process carried out in a hostile thermal environment is a glass production process, such as, for example, an overflow downdraw fusion process as described in U.S. Pat. No. 3,338,696 (Dockerty) and U.S. Pat. No. 3,682,609 (Dockerty). While many glass processing apparatuses are made of durable, inert materials, such as noble metals, high process operating temperatures can nevertheless create a hostile environment wherein components are subjected to oxidation and thermal stress. Glass for electronic displays, for example, can be processed using noble metal delivery, holding, and forming apparatuses.
• Temperatures used in such glass processing techniques can be sufficiently high to oxidize bare surfaces of noble metal parts, creating volatile noble metal oxides that in turn are reduced and can form metal particles.
• the reduced metal particles can form inclusion contaminants in glass produced by such a process.
• the tolerance for such contaminants can be low, especially in semiconductor applications, wherein a very high glass quality (smoothness, homogeneity, etc.) is required.
• a first aspect of the present invention relates to a device comprising: (i) a first layer having a first surface comprising a first metal; and
• the interface between the first layer and the second layer is substantially dense and has an irregular topography
• the second metal is capable of forming an alloy with the first metal when the second metal is deposited on the first surface of the first metal at an elevated temperature.
• (C) when one major surface of a metal film consisting of a mixture of the second metal and the first metal having a thickness substantially equal to the second layer supported by an inert substrate is exposed to air at a temperature in the range from 1000 0 C to the melting temperature of the first metal for a sufficient period of time, the metal film can be completely oxidized to form a dense oxide film on the inert substrate.
• the first metal comprises a noble metal
• the second metal comprises at least one of Al, Zr and Si.
• the first layer comprises Pt; and the second layer consists essentially Of Al 2 O 3 .
• the interface between the first layer and the second layer has a convolution index of at least 1.50, in certain embodiments at least 1.55, in certain embodiments at least 1.60, in certain embodiments at least 1.65, in certain embodiments at least 1.70, in certain embodiments at least 1.75.
• the second layer has a thickness from about 5 ⁇ m to about 80 ⁇ m, in certain embodiments from about 10 ⁇ m to about 70 ⁇ m, in certain other embodiments from about 20 ⁇ m to about 60 ⁇ m, in certain embodiments from about 20 ⁇ m to about 50 ⁇ m, in certain other embodiments from about 25 ⁇ m to about 45 ⁇ m, in certain other embodiments from about 30 ⁇ m to about 40 ⁇ m.
• the device is a component of a molten glass delivery system.
• the device is a finer tube of a glass melting system.
• the device is a stir chamber where a molten glass is subject to shear stress.
• the device is a cover of a stir chamber.
• the device is a flange, such as an electric flange for transmitting electrical power.
• the second layer covers essentially all area of the exposed surface of the device which is otherwise exposed to 02-containining atmosphere. In certain more specific embodiments, the external surface of the device is covered by the second layer.
• the second layer is substantially impermeable to an oxide of the first metal, such as PtO 2 .
• the second layer is substantially impermeable to O 2 .
• the second layer is substantially free of the second metal in metallic state.
• a second aspect of the present invention relates to a method for protecting a first surface of a first layer comprising a first metal in a device from oxidation at an elevated temperature when exposed to an oxidative atmosphere, comprising the following steps: (a) providing a precursor layer comprising a second metal on at least part of the first surface of the first metal, said second metal capable of forming an alloy with the first metal under the condition the precursor layer is provided; and
• the first metal comprises Pt.
• the first metal comprises Pt
• the second metal comprises at least one of Al, Si and Zr.
• the precursor layer in step (a), has a thickness of from about 7 ⁇ m to about 120 ⁇ m, in certain embodiments from about 10 ⁇ m to about 100 ⁇ m, in certain other embodiments from about 15 ⁇ m to about 80 ⁇ m, in certain other embodiments from about 20 ⁇ m to about 60 ⁇ m, in certain embodiments from about 20 ⁇ m to about 50 ⁇ m, in certain other embodiments from about 25 ⁇ m to about 45 ⁇ m, in certain other embodiments from about 30 ⁇ m to about 40 ⁇ m.
• the interface between the first layer and the second layer is substantially dense and has an irregular topography.
• the second layer in step (b), is formed such that the interface between the first layer and the second layer has a convolution index of at least 1.50, in certain embodiments at least
• step (a) comprises at least one of CVD, pack cementation, slurry coating, sputtering, electroplating, and the like.
• step (b) is carried out in a pre-heating step.
• step (b) is carried out in-situ when the device is installed in an operation system.
• the operation system is a glass melting and/or delivery system.
• the second layer has a thickness from about 5 ⁇ m to about 80 ⁇ m, in certain embodiments from about 1O -Um to about 70 ⁇ m, in certain other embodiments from about 20 ⁇ m to about 60 ⁇ m, in certain embodiments from about 20 ⁇ m to about 50 ⁇ m, in certain other embodiments from about 25 ⁇ m to about 45 ⁇ m, in certain other embodiments from about 30 ⁇ m to about 40 ⁇ m.
• the precursor layer provided consists essentially of a mixture of the first metal and the second metal.
• step (b) the elevated temperature is in the range from 1000°C to the melting temperature of the first metal.
• step (b) at the end of step (b), wherein the elevated temperature is in the range from 1000°C to the melting temperature of the precursor layer.
• step (b) the second metal in the precursor layer is completely converted into an oxide thereof.
• step (b) the precursor layer is heated to the elevated temperature at a temperature elevation rate such that oxidation of the second metal occurs without significant flowing of a molten second metal over the first metal.
• a third aspect of the present invention relates to a process for making a glass sheet by using a device according to the present invention described summarily supra and in greater detail infra.
• the device comprises a stir chamber, a finer, a flange, or a connecting tube.
• a dense, refractory protective coating can be formed on the external surface of a metal structure to protect it from detrimental oxidation.
• the coating can be formed on surfaces having a complex shape.
• the coating can be formed with a relatively low cost.
• the coating can have a high inter-facial bonding strength between the first metal layer and the second oxide protecting layer.
• FIG. 1 shows a scanning electron microscope image of the cross-section 100 of a Pt-Rh coupon bearing a precursor layer comprising metallic Al.
• FIG. 2 shows a scanning electron microscope image of the cross-section of one Pt-Rh coupon bearing a fully oxidized Al 2 O 3 layer.
• FIG. 3 is a scanning electron microscope image of a surface of a Pt-Rh substrate, after a layer OfAl 2 O 3 previously formed thereon was removed.
• FIGS. 4 and 5 show the process of image collection and analysis for obtaining the information on Pt-Rh substrates processed according to the certain embodiments of the present invention.
• any subset or combination of these is also disclosed.
• the sub-group of A-E, B-F, and C-E would be considered disclosed.
• This concept applies to all aspects of this application including, but not limited to, steps in methods of making and using the disclosed compositions.
• steps in methods of making and using the disclosed compositions are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific embodiment or combination of embodiments of the disclosed methods.
• wt% or “weight percent” or “percent by weight” of a component, unless specifically stated to the contrary, refers to the ratio of the weight of the component to the total weight of the composition in which the component is included, expressed as a percentage.
• convolution index describes the topography of an interface between a first layer of material and a second layer of a material.
• the convolution index (CI) is defined as follows:
• CI Lc/Ls, where Lc is the length of the curved line segment connecting two points on the interface, obtained by intercepting the interface with a plane substantially perpendicular to the central plane of the first layer of material, measured on the resolution scale of about 1 ⁇ m; and Ls is the length of a straight line segment connecting the same two points.
• a protocol for measuring convolution index is described in detail infra.
• a substantially dense interface means an interface substantially free of voids when viewed on the resolution scale of 1 ⁇ m.
• the device of the present invention comprises (i) a first layer comprising a first metal having a first surface; and (ii) a second layer comprising an oxide of a second metal bonding directly to the first surface of the first layer and covering at least a part of the first surface of the first layer, wherein: (A) the interface between the first layer and the second layer is substantially dense and has an irregular topography; and (B) the second metal is capable of forming an alloy with the first metal when the second metal is deposited on the first surface of the first metal at an elevated temperature.
• the first metal and second metal further meet the following conditions: (C) when one major surface of a metal film comprising the second metal and the first metal having a thickness substantially equal to the second layer supported by an inert substrate is exposed to air at an elevated temperature between 1000 0 C and the melting point of the first metal, the second metal in the metal film can be substantially completely oxidized to form a dense oxide film over the inert substrate.
• the device of the present invention can be a stand-alone apparatus or a part of a large system.
• the device can be a vessel for containing a fluid or a reaction media.
• the device may further comprise additional layers abutting the first or second layer.
• the device may comprise, above and abutting the second layer, a third layer covering at least part of the second layer.
• the device may further comprise, above and abutting a second surface of the first layer, a fourth layer covering at least the second surface of the first layer.
• the device may further comprise other functional components separate from the first and second layers.
• the device of the present invention comprises a conduit for carrying a high temperature fluid, such as a glass melt, which comprises a wall made of the first metal covered with the second layer of oxide of the second metal.
• a conduit for carrying a high temperature fluid such as a glass melt
• Such conduit can be, e.g., a finer, a connecting tube between different stations of a glass melting and delivery system and the like.
• the device of the present invention comprises a vessel in which a high temperature fluid, such as a glass melt, is stirred and homogenized.
• the first metal advantageously comprises a noble metal.
• the first layer of the device of the present invention may be allowed to contact the high-temperature fluid the device is designed to handle.
• the finer wall may be constructed by Pt or a Pt-Rh alloy, the internal surface of which is allowed to contain glass melt during normal operation thereof, and the external surface of which is covered by an Al 2 O 3 coating.
• the first layer may consist of a single metal, or multiple metals in combination.
• noble metals are typically very expensive and therefore the first layer is desired to be as thin as possible.
• the oxidation causes the loss of the metal, thinning of metal wall, and Pt inclusions in glass melt due to subsequent dissociation of PtO 2 gas and condensation of particulate Pt on colder surfaces, which are all highly undesirable.
• the second layer of oxide of the second metal in the device of the present invention can function to inhibit the diffusion of O 2 from the atmosphere to which the device is exposed, thereby inhibiting the above reaction (1), even at an elevated temperature such as the normal operating temperature of a glass finer, which may be as high as over 1500 0 C.
• the second metal when in metallic state, can form an alloy with the first metal in metallic state when both metals are allowed to contact at an elevated temperature, such as at above 500 0 C.
• the alloying capability enables the formation of the intricate and convoluted interface between the first layer and the second layer of the device of the present invention.
• the alloy as described supra, can be a mixture or combination of the two metals at various mole percentages.
• the first metal and the second metal may form multiple types of alloys under a given alloying condition.
• Pt which may be a first metal
• Al which may be a second metal
• various compositions represented by Pt x AI y at an elevated temperature such as 800°C when the two metals are allowed to contact each other.
• the first layer may comprise multiple metals in combination (such as a Pt-Rh alloy).
• the other metal included in the first layer may be capable of forming an alloy with the second metal at an elevated temperature as well, though it is not so required for the present invention to work.
• the second layer comprising an oxide of the second metal, covers at least part of the first surface of the first layer and at least partially separates the covered part of the first surface of the first layer from an environment that it would otherwise be exposed to, e.g., an atmosphere with which the first surface of the first layer is reactive under the normal operating condition of the first layer such as when being subjected to an elevated temperature, a fluid corrosive to the first surface of the first layer, or an additional layer with which the first surface of the first layer does not meet a compatibility requirement.
• the oxide of the second layer is a refractory material.
• the finer of a glass melting and delivery system can operate at a temperature as high as 1500°C.
• Pt and Pt-Rh alloys are suitable candidate materials for the finer wall.
• Suitable oxides for the second layer covering the external surface of the finer wall can be, e.g., Al 2 O 3 , ZrO 2 , MgO, TiO 2 , SiO 2 , and the like, and mixtures and combinations thereof. In certain embodiments, Al 2 O 3 and ZrO 2 are particularly desirable.
• Si is included in the group of a possible second metal for the convenience of description in the present application.
• metal or metals of the first layer and the oxide of the second layer have coefficient of thermal expansions (CTEs) that are substantially similar.
• CTEs coefficient of thermal expansions
• Pt, Pt-Rh and Al 2 O 3 have similar CTEs under the normal glass making conditions.
• the second layer is substantially dense, i.e., essentially free of voids and cracks larger than 1 ⁇ m.
• the second layer is essentially free of voids and cracks larger than 500 run.
• the second layer is essentially free of voids and cracks larger than 300 nm.
• the second layer is essentially free of voids and cracks larger than 100 nm. The denser the second layer, the slower the diffusion rate of a fluid (such as O 2 or other gas) through the layer, and the more effective the separation and protection it provides to the first surface of the first layer.
• a fluid such as O 2 or other gas
• PtO 2 has a significantly larger molecular size than O 2 , and thus diffuses through the second layer with more spatial volumetric resistance.
• the reaction (1) would reach equilibrium quickly, thus preventing further oxidation and loss of Pt. Therefore, in certain embodiments of the present invention, it is highly desired that the second layer is so dense that it substantially inhibits the diffusion of an oxide of the first metal in gaseous phase through it under the operating condition.
• the second layer (such as an Al 2 O 3 layer) is essentially free of voids and cracks that would allow the free diffusion of PtO 2 under the normal operating condition of the device. It is even more desired in certain embodiments that the second layer is essentially free of voids and cracks such that O 2 diffusion under the normal operating condition is inhibited. [0068] It is desired in certain embodiments that the second layer is essentially free of the second metal in metallic state, i.e., the second metal in the second layer is substantially completely oxidized. Such fully oxidized second layer is stable under the normal operating condition of the device.
• part of the second metal in the second layer is in metallic state, which may be desirable in certain embodiments. It is also not ruled out that a part of the second metal in metallic state forms a mixture such as an intermetallic under the second layer at the end of the step (b).
• the remaining second metal in metallic state especially in the area adjacent to the first layer, may replenish part of the spent second layer during operation, hence is desirable in certain embodiments.
• due to the capability of the second metal in metallic state to alloy with the first metal it may diffuse deeper into the bulk of the first layer during operation of the device, causing weakening of the first layer, and hence is undesirable.
• the interface between the first layer and the second layer in the device of the present invention is substantially convoluted.
• a rugged, curved line on the resolution scale of 1 ⁇ m can be observed, via, e.g., an electron microscope.
• the high convolution index of the interface between the first layer and the second layer is a significant feature distinguishing the present invention from that of the coated metals in the prior art.
• the interface between the first and second layers in the device of the present invention has a convolution index of at least 1.48, in certain embodiments at least 1.50, in certain embodiments at least 1.60, in certain other embodiments at least 1.70, in certain embodiments at least 1.80.
• a thicker second layer can provide higher resistance against diffusion of fluid through it.
• a thicker coating can be more costly to form, and may be unnecessary in certain embodiments.
• the thickness of the second layer is defined as the average shortest distance from the surface of the second layer farther from the first layer to the first surface of the first layer.
• the second layer has a thickness of at most 80 ⁇ m, in certain other embodiments at most 60 ⁇ m, in certain other embodiments at most 50 ⁇ m, in certain other embodiments at most 40 ⁇ m, in certain embodiments at most 30 ⁇ m.
• the thickness of the second layer is at least 5 ⁇ m in certain embodiments, in certain embodiments at least 10 ⁇ m, in certain embodiments at least 20 ⁇ m, in certain embodiments at least 30 ⁇ m.
• the convoluted interface between the first layer and the second layer may comprise certain interlocking features, i.e., certain part of the first layer protrudes into the second layer, and/or certain part of the second layer protrudes into the first layer.
• Such interlocking feature is especially desirable for a robust adhesion between the two layers.
• Interlocking features on the scale of 1 ⁇ m are not easy to form by using conventional coating methods such as chemical vapor deposition of the oxide of the second layer directly.
• Interlocking features essentially free of voids, which are especially difficult to form using conventional coating methods but can be obtained by the present invention, are highly desirable due to the high interfacial adhesion strength and low fluid (such as O 2 ) diffusivity it can provide in tandem.
• the protruding part of the first metal is directly connected with the bulk with the first layer, and/or that the protruding part of the oxide of the second layer is directly connected with the bulk of the oxide of the second layer.
• Such continuous structures of the first layer and second layer are conducive to the bonding strength between the first layer and the second layer. Nonetheless, it is not ruled out that in certain embodiments in the bulk of the oxide of the second metal in the second layer, certain discreet particles of the first metal is present without direct bonding with the bulk of the first metal. It is also not ruled out that in certain embodiments below the second layer, certain discreet islands of the oxide of the second metal are formed and trapped within the bulk of the fist metal.
• the high convolution index of the interface between the first and second layers provides a large contact area between the two layers, thus significantly enhances the adhesion between the two layers.
• the interlocking features, if present, further improve the bonding.
• the presence of the protective coating of the second layer in a device of the present invention can reduce the oxidation and loss of the first layer.
• the first metal comprises precious metal such as Pt
• such protection can translate into significant extension of device life and capital savings.
• FIG. 1 shows a scanning electron microscope image of the cross-section 100 of one Pt-Rh coupon bearing a precursor layer comprising metallic Al. The structure and composition of this cross-section in FIG. 1 is described in greater detail infra.
• FIG. 2 shows a scanning electron microscope image of the cross-section of one Pt-Rh coupon bearing a fully oxidized Al 2 O 3 layer prepared by using the metallization process of the present invention described infra.
• FIG. 3 is a scanning electron microscope image of a surface of a Pt-Rh substrate, after a layer OfAl 2 O 3 previously formed thereon was removed. This image reveals the convoluted nature of the first surface of the Pt-Rh layer.
• II Process for making the device
• a second aspect of the present invention is directed to a method for protecting a first surface of a first layer comprising a first metal in a device from oxidation at an elevated temperature when exposed to an oxidative atmosphere, comprising the following steps: (a) providing a precursor layer comprising a second metal in metallic state on at least part of the first surface of the first metal, said second metal capable of forming an alloy with the first metal under the condition the precursor layer is provided; and (b) forming a second layer comprising an oxide of the second metal by exposing the precursor layer to an oxidative atmosphere at an elevated temperature.
• Step (a) may comprise a step of sputtering, chemical vapor deposition, slurry deposition, and the like, to form the precursor layer of the second metal in metallic state.
• the second metal may enter into the first layer and the first metal may enter into the precursor layer, forming a gradient of the first metal and a gradient of the second metal in the interface at the same time.
• the precursor layer comprises at least a top portion essentially free of the second metal, and it is desired that the second metal does not penetrate the full thickness of the first layer.
• the precursor layer comprises mixtures of the first metal and the second metal throughout the thickness thereof.
• a precursor layer consisting essentially of Pt x AIy can be formed if Al is deposited on the surface of a Pt substrate.
• the Al layer can be deposited by sputtering, traditional chemical vapor deposition, slurry deposition, and the like. Since Pt and Al are known to form alloys represented by Pt x AI y , the interface is thus a mixture of Pt-Al with various Pt/ Al molar ratios.
• the first metal, the first layer, and the second metal can be as described supra in connection with the device of the present invention.
• the first metal can be a noble metal such as Pt or Pt-Rh alloy, and the like
• the second metal can be Al, Zr, Ti, Si, Mg, and mixtures and combinations thereof, and the like.
• the thickness of the precursor layer is defined as the average shortest distance from the surface of the precursor layer farther from the first layer to the first surface of the first layer where the concentration of the second metal is negligible.
• the thickness of the precursor layer is determined, in part, by the desired thickness of the final second layer of the oxide of the second layer. It is desired that the thickness of the precursor layer, especially where the first metal comprises Pt and the second metal comprises Al, is no more than 120 ⁇ m in certain embodiments, no more than 100 ⁇ m in certain embodiments, no more than 80 ⁇ m in other embodiments, no more than 60 ⁇ m in other embodiments, no more than 50 ⁇ m in other embodiments, still no more than 40 ⁇ m in other embodiments.
• the thickness of the precursor layer is at least 20 ⁇ m in certain embodiments, in order to form a first layer of oxide of the second metal of sufficient thickness.
• the precursor layer has a thickness of from about 20 ⁇ m to about 60 ⁇ m in certain embodiments, from 20 ⁇ m to about 50 ⁇ m in certain other embodiments, from about 25 ⁇ m to about 45 ⁇ m in certain other embodiments, from about 30 ⁇ m to about 40 ⁇ m in certain other embodiments.
• the precursor layer can be formed by using various techniques, such as conventional chemical vapor deposition, plasma enhanced chemical vapor deposition, slurry deposition, sputtering, electroplating, and the like.
• the initial metal layer of the second layer is too thick to be completely oxidized into the second layer of the second metal, it may be desirable to subject the as-deposited precursor layer of the second metal to a thinning step, e.g., a chemical-mechanical polishing step, to reduce the thickness of the second metal layer to a desired range.
• a thinning step e.g., a chemical-mechanical polishing step
• An especially desirable technique for directly forming an Al-containing metal layer over a first metal, such as one comprising Pt is by slurry deposition. Such process can result in a substantially dense Al-Pt alloy layer with a substantially uniform thickness in the range of 20-60 ⁇ m without the need of a thinning step.
• step (a) may include a step of post-deposition heat treatment before step (b). Formation of a mixture comprising the first metal and the second metal prior to step (b) is highly desirable for the formation of an interface with high convolution index in the device of the present invention. Certain thin deposition processes are carried out a temperature where a mixture or intermetallic between the firs metal and the second metal forms at too low a speed. A post-deposition heat treatment in which the interface is heated to a temperature higher than the deposition temperature can facilitate the formation of the metal mixture in the precursor layer prior to step (b).
• the interface between the first layer and the precursor layer comprises a gradient of the first metal and the second metal, ranging from an area on one end containing negligible level of the second metal to a middle area where an alloy or mixture is present, to an area on the opposite end containing the lowest level of the first metal.
• the interface ranges from the first layer consisting essentially of Pt, to a middle area which can be represented by Pt-Al, and to an area consisting essentially of Al.
• the interface ranges from the surface of the first layer consisting essentially of Pt, to a middle area which can be represented by Pt- Al, and to an area on the opposite end consisting essentially OfAl 2 Pt.
• the precursor layer comprises a mixture of Pt and Al throughout the thickness thereof can be particularly advantageous due to the significantly higher melting temperature OfAl 2 Pt than Al.
• the precursor layer is exposed to an O 2 -containing atmosphere at an elevated temperature.
• oxidation in step (b) can be carried out in air at above 500°C, such as at above 800 0 C, e.g., at above 1500 0 C.
• the precursor layer is oxidized into the second layer under such conditions.
• the first metal consists of Pt
• the second metal consists of Al as an example.
• the aluminum in the surface region of the Al- containing precursor layer is first oxidized to Al 2 O 3 . O 2 then diffuses through the Al 2 O 3 layer to oxidize the metallic Al below.
• the second metal when in metallic state, is desired to have a higher reactivity than the first metal with O 2 at an elevated temperature, as in the case of an embodiment where the first metal is Pt and the second metal is Al.
• the first metal when O 2 diffuses through the layer of oxide formed over the second metal in step (b), and reaches atoms of the first metal in the intermediate zone of the interface, the first metal will remain in a reduced metallic state due to the reducing effect of the second metal.
• the second metal is preferentially oxidized.
• the oxide of the second metal tends to aggregate in the precursor layer with the top oxide layer, and the first metal in metallic state tends to aggregate with the bulk of the first layer, thus eventually form a dense, substantially void-free second layer abutting and over a substantially continuous first surface of the first layer. It is also believed that the aggregations of the first metal and the oxide of the second metal in the precursor layer in step (b) take place in a substantially random manner, resulting in a rugged, irregular topography of the interface between the first layer and the second layer at the end of step (b). In certain embodiments, interlocking features on the ⁇ m scale are formed as a result.
• the second layer comprises, in addition to an oxide of the second metal, a non-negligible amount of the second metal in metallic state, hi applications where structural strength of the first layer is important, and the second metal entering and remaining in the first metal layer can unduly compromise the strength of the first layer, it is highly desired that all second metal in the precursor layer is oxidized in step (b).
• step (b) it may be desirable to allow certain amount of the second metal to remain alloyed with the first metal at the end of step (b), as the remaining second metal can be further oxidized during the operation of the device at a later stage, which could presumably repair or maintain the integrity of the second layer, which could have been compromised by process conditions, such as normal wear and tear.
• the second layer is formed such that the interface between the first layer and the second layer has a convolution index of at least 1.50, in certain embodiments at least 1.55, in certain embodiments at least 1.60, in certain embodiments at least 1.65, in certain embodiments at least 1.70, in certain embodiments at least 1.75.
• the thus formed second layer comprising the oxide of the second metal can effectively inhibit the diffusion of O 2 through it to further oxidize the first metal, due to the dense nature of the second layer.
• the thus formed second layer may be permeable to O 2 , but is nonetheless substantially impermeable to the gaseous oxide of the first metal.
• the second metal is Al
• the first metal is Pt
• the Al 2 O 3 layer can act as a much more significant inhibiting layer against PtO 2 diffusion than for O 2 , effectively inhibiting the continuous oxidation and removal of metallic Pt. Therefore, the oxide of the second metal such as Al 2 O 3 serves as a protecting layer against the oxidation of the first metal.
• the elevated temperature is in the range from 1000 0 C to the melting temperature of the first metal. It has been found that where the second metal contained in the precursor layer is oxidized into a dense coating over the first layer, a high temperature is desired in order to expedite the diffusion of O 2 through the oxide layer, which is desired for the complete oxidation of the second metal. Nonetheless, it is desired that the oxidation step does not cause the first layer to melt, hi certain other embodiments where the precursor layer consists essentially of a mixture such as an intermetallic of the first metal and the second metal, it is desired that in step (b), the elevated temperature is in the range from 1000 0 C to the melting temperature of the mixture in the precursor layer.
• step (b) the precursor layer is heated to the elevated temperature at a temperature elevation rate such that oxidation of the second metal occurs without significant flowing of a molten metal over the first metal.
• the first metal is Pt and the second metal is Al, it was found that Al tends to penetrate Pt at about 1000 0 C by forming an alloy.
• step (b) is carried out in a pre-heating step before a device of the present invention is formed and installed in an operation system.
• the finer tube may be completely made before installation in a glass making system by subjecting a Pt tube covered by a layer of Al-Pt alloy in an oxidation step at an elevated temperature.
• the device may be formed in-situ in the installation of the operation system.
• the device in an embodiment where the device is a Pt finer tube covered by Al 2 O 3 made by the present invention process, it may be made in-situ by following the following steps: (1) depositing a layer containing Al on the external surface of a Pt tube; (2) install the tube resulting from step (1) into a glass melting system; and (3) pre-heating the glass melting system such that the tube is heated to an elevated temperature in air, whereby the precursor Al-containing layer is oxidized to form the second layer. [0098] IIL Process for making glass
• a third aspect of the present invention is a glass-making process using a device of the present invention.
• the glass-making process can include (1) melting a batch material in a melting tank to obtain a glass melt; (2) delivering the glass melt to down-stream process via conduits; (3) conditioning the glass melt; and (4) forming the glass melt into a desired form.
• one or more device of the present invention can be employed.
• certain components of the glass melting tank may be a noble metal covered with Al 2 O 3 and/or ZrO 2 layer made according to the present invention
• the delivery system in step (2), may be a Pt-Rh tube having an external surface covered by Al 2 O 3 and/or ZrO 2
• a finer or a stir chamber may be a device of the present invention
• the device in step (4), which may include a fusion draw, a float, or a slot draw, or other forming process, the device, such as the isopipe in a fusion down-draw process, can be a device of the present invention comprising Pt, partly or wholly, covered by Al 2 O 3 and/or ZrO 2 .
• All the Pt-Rh coupons tested comprised Rh at about 20% by weight.
• a series of clean Pt-Rh coupons comprising 20% by weight of Rh were prepared and then coated with Al-Pt intermetallic according to the process of the present invention by using a slurry deposition process or CVD process.
• a resultant Al-Pt aluminide coated Pt-Rh coupon was subsequently observed and/or tested.
• the aluminized Pt-Rh coupons were then oxidized in air at about 1450°C for about 72 hours.
• the resultant Al 2 O 3 -coated Pt-Rh coupon were subsequently observed and/or tested.
• FIG. 1 shows a scanning electron microscope image of the cross-section 100 of one Pt-Rh coupon bearing a precursor layer comprising metallic Al.
• the composition of the precursor layer, the first layer and the interface can be determined through any appropriate characterization method.
• Scanning electron microscopy (SEM) coupled with an electron probe micro-analyzer (EPMA) can, for example, be used to ascertain the composition at a given location within the precursor layer and/or the bulk metal component.
• 1, 103 is a layer of plated Ni added to aid the preparation of the cross-section of the sample, and is not part of the device; 105, 107, 109, I l ia and 111b are the various major phases of the precursor layer, each having a varying concentration of components and a varying physical structure, 113 is bulk Pt-Rh metal. Compositions determined from the EPMA at the various locations are reported in TABLE I, below.
• FIG. 2 is a scanning electron microscope image of a cross-section of a Pt-Rh substrate comprising a fully oxidized AI 2 O 3 layer 201 prepared by the aluminization- oxidation method of the present invention.
• 203 is the bulk Pt-Rh metal, and
• 205 is a layer of mounting material formed to aid in the preparation of the cross-section for imaging.
• FIG. 3 is a scanning electron microscope image of a surface of a Pt-Rh substrate, after a layer of Al 2 O 3 previously formed thereon was removed. This image reveals the convoluted nature of the first surface of the Pt-Rh layer.
• a cross-section, protected by a resin, of each coated coupon was prepared for imaging. SEC photographs were obtained of the prepared cross-sections. Around 20 such images were collected and analyzed for each coupon. To quantify the degree of convolution, a "convolution index" was measured and calculated as follows. [00107] Backscattered images were collected on the JEOL 6610 SEM running at 2OkV. [00108] Low magnification images ( ⁇ 10x — 25x) were first collected so that the entire coupon was visible. Around ten images were collected from both, the upper and lower boundaries of the coupon. After selecting a location, the SEM image was focused and adjusted to ensure that the coupon was oriented horizontal to the field of view. A backscattered electron image was then collected at 150x at the highest possible pixel resolution. [00109] Images were analyzed using the NIH Image J program
• the brightness and contrast were adjusted to ensure a sharp difference in the brightness of the Pt-Rh region and the Al 2 O 3 or ZrO 2 coating. There was no other manipulation performed on the image.
• the image was then binarized so that the Pt-Rh region showed up as pure black (pixel value 0) while the rest of the image was pure white (pixel value 255).
• the Pt-Rh area was then selected and its perimeter measured. The length of the convoluted interface was obtained after subtracting the horizontal and vertical lengths from the perimeter.
• FIG. 4 shows the process flow of image processing to obtain the convolution index of the sample.
• step 4.1 a SEM image of a cross-section of the sample is obtained, including a Pt-Rh region and an oxide region 401.
• step 4.2 the Pt-Rh region of the image is separated from the overall image and binarized.
• step 4.3 the length of the perimeter Lp of the Pt-Rh region ABCDA and the three straight sides Ll, L2 and L3 are measured. The length of the convoluted interface Lc is then calculated as follows:
• Lc Lp - Ll - L2 - L3.
• FIG. 5 shows the interface images of one exemplary sample (El, corresponding to images 5.1A and 5.1B) according to the present invention and the four comparative examples (CEl, corresponding to images 5.2A and 5.2B; CE2, corresponding to images 5.3A and 5.3B; CE3, corresponding to images 5.4A and 5.4B; and CE4, corresponding to images 5.5A and 5.5B).
• the larger images are included in the left column (i.e., images 5.1A, 5.2A, 5.3 A, 5.4A and 5.5A), and the enlarged images of the areas enclosed in rectangles shown in the image in the left column are included in the right column (i.e., images 5.1B, 5.2B, 5.3B, 5.4B and 5.5B, corresponding to 5.1A, 5.2A, 5.3A, 5.4A and 5.5A, respectively).
• the alumina coated Pt-Rh coupons do have a more intricate interface as compared to the plasma-spray zirconia coated coupons.

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