US20080173548A1

US20080173548A1 - Chrome plated articles of variable surface appearance

Info

Publication number: US20080173548A1
Application number: US12/009,905
Authority: US
Inventors: Richard Lee Macary
Original assignee: Arlington Plating Co
Current assignee: Arlington Plating Co
Priority date: 2007-01-23
Filing date: 2008-01-23
Publication date: 2008-07-24

Abstract

A process for applying patterning across the surface of a chrome plated article. The process uses electroplated layers of nickel and chromium in combination with controlled and selectively applied dimpling treatment of coated layers to impart patterns of predefined differential reflectivity across the final surface while nonetheless retaining corrosion resistance.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims priority from U.S. Provisional Patent Application 60/886,170, filed Jan. 23, 2007, in the name of Richard Lee Macary, the contents of which are hereby incorporated by reference in their entirety as if fully set forth herein.

TECHNICAL FIELD

The present invention relates generally to chrome plating and, more particularly, to the production of articles using selective combinations of surface texturizing and electroplating to produce variable surface appearances of predefined character while nonetheless maintaining substantial corrosion resistance.

BACKGROUND OF THE INVENTION

Electroplating is used to apply one or more layers of metal across a surface of a pre-formed part. The applied layers may provide aesthetic enhancement and/or corrosion resistance to the underlying substrate. The ability of an electroplated coating to protect an underlying metal substrate is dependent upon a number of factors. These factors include the position of the metal coating material in the galvanic series, the adhesion between the coating and the underlying layer and the porosity of the coating layer. In the chrome plating of aluminum parts, the aluminum is typically coated with an initial layer of copper with one or more overlying layers of nickel followed by a relatively thin surface layer of chromium. The layered arrangement of nickel and chromium provides substantial adherence to the underlying part in combination with desired low permeability. In such structures, the outer layer of chromium provides a highly reflective appearance which maintains its reflectivity even upon prolonged exposure to atmospheric conditions.
When an aluminum part which has been coated with nickel and chromium is exposed to an environment where salt or other corrosive agents are present, the over-plated layers provide a substantial barrier against permeation of the corrosive agents to the aluminum based metal. However, in the performance of this function, the over-coated layers are exposed to the corrosive agent. As a result of this exposure, the metal forming the protective layers undergoes a gradual oxidation process in which the metal is converted to its ionic form while simultaneously liberating electrons. Under typical atmospheric conditions the generated electrons combine with available oxygen to maintain charge equilibrium. Under normal conditions, these reactions occur uniformly across the surface such that any degradation due to metal oxidation is substantially imperceptible. Thus, in spite of exposure to corrosive environments, an aluminum part properly coated with nickel and chromium may provide corrosion protection over a significant duration while maintaining substantial surface reflectivity.
In order to protect and maintain the long term corrosion resistance and reflectivity of chrome-plated parts, it is generally desirable to promote uniformity of the over-coated layers across the plated part. Such uniformity permits the naturally occurring oxidation and reduction reactions to take place across the entire surface thereby avoiding the possibility of localized corrosive attack. It is well known that in the event of surface irregularities such a pits or the like, there may be a tendency for coated parts to experience concentrated and accelerated corrosion at the location of such irregularities. Such accelerated corrosion may be particularly aggressive in environments where salt or other sources of chlorine are present. Such corrosion begins with the naturally occurring oxidation reaction of metal (M) to metal ions and free electrons as described generally by the following formula:
M→M⁺ +e
In order to maintain charge neutrality, this reaction is initially balanced by the reduction reaction of oxygen to hydroxide ions according to the following formula:
O₂+2H₂O+4e→4OH⁻
These initial reactions are relatively benign. However, as they proceed, the oxygen available to carry out the second reaction may become depleted within the pit after a relatively short period of time such that the oxygen reduction reaction can no longer take place at that location. Without the continuous production of negatively charged hydroxide ions (OH⁻), the metal cations (M⁺) tend to build up at the location of the pit. In order to balance the charge, negatively charged chloride ions as will be present in any salt solution naturally migrate to the location of the pit to combine with the metal ions and form a metal chloride. This results in a localized increased concentration of metal chloride at the location of the pit. If water is present, the metal chloride thereafter dissociates into an insoluble hydroxide and a free acid according to the following reaction:
M⁺Cl⁻+H₂O=MOH↓+H⁺Cl⁻
The presence of the free acid thereafter facilitates substantially aggressive localized corrosion within the pit.
As will be appreciated, these reactions are self-promoting and accelerate as metal dissolution within the pit progresses. The development of such pitting corrosion within a chrome-plated article may lead to the rapid and substantially irreversible degradation of appearance. Thus, in the manufacture of chrome-plated parts it is generally considered desirable to avoid the presence of localized depressions or zones of depressions which may serve as starting points for localized pitting corrosion.
As previously noted, it is generally considered desirable for naturally occurring oxidation and reduction reactions to take place substantially uniformly across the surface of a plated part so as to promote the longevity of the plating. Surface zones of different character may have slightly different resistance levels to corrosion when exposed to a common environment. Under those circumstances, surface zones with a higher propensity for corrosion may be slightly anodic with respect to zones with a lower propensity for corrosion. This may give rise to the undesirable situation in which the metal oxidation for the entire system is preferentially concentrated at zones where there is already some diminished corrosion resistance. In order to avoid this situation, surface treatments across chrome-plated articles have generally tended to be applied substantially across the entire surface so as to provide a substantially uniform character.

SUMMARY OF THE INVENTION

The present invention provides advantages and alternatives over the prior art by providing a process using electroplated layers of nickel and chromium in combination with controlled and selectively applied shot-peening or other dimpling treatment of coated layers to impart predefined differential reflectivity across the final surface while nonetheless retaining corrosion resistance.
In accordance with one contemplated aspect, a method is provided for patterning a surface of a chrome plated article having substantial corrosion resistance. One exemplary method includes providing a base substrate and depositing a semi-bright nickel layer at a position above the substrate. A bright nickel layer may thereafter be deposited at a position above the semi-bright nickel with a surface layer of chromium at a position above the bright nickel. The bright nickel layer and/or the chromium layer is bombarded with an impact media at discrete, predefined impact zones to produce a pattern of dimpled surface zones. The dimpled surface zones provide a distinctive reflective character relative to adjacent smooth surface zones to yield visually perceptible patterning. Despite the presence of the dimpled surface zones, the chrome plated article is characterized by substantial corrosion resistance in salt-rich environments such that the chrome plated article remains free from blisters and corrosion spots when subjected to acid-salt spray testing.
It is to be understood that other aspects, advantages, and features will become apparent through reading of the following detailed description of preferred embodiments and practices and/or through practice of the invention by those of skill in the art. Accordingly, the detailed description is to be understood as being exemplary and explanatory only and in no event is the invention to be limited to any illustrated and described embodiments. On the contrary, it is intended that the present invention shall extend to all alternatives and modifications as may embrace the principles of this invention within the true spirit and scope thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only, with reference to the accompanying drawings which are incorporated in and which constitute a part of the specification herein, and together with the general description given above, and the detailed description set forth below, serve to explain the principles of the invention wherein:

FIG. 1 is a flow chart setting forth steps for an exemplary plating and treatment process for patterning a chrome plated article;

FIG. 2 illustrates a patterned surface of an article formed by the process set forth in FIG. 1;

FIG. 3 is a schematic view taken generally along line 3-3 in FIG. 2 illustrating an exemplary arrangement of coating layers with localized dimpling;

FIG. 4 is a view similar to FIG. 3 illustrating another potential arrangement of coated layers with localized dimpling; and,

FIG. 5 is a flow chart setting forth steps for another exemplary plating and treatment process for patterning a chrome plated article.

DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein, to the extent possible, like reference numerals are utilized to designate corresponding components throughout the various views. FIG. 1 is a flow diagram setting forth exemplary steps in a process for introducing aesthetic or communicative designs of variable reflectivity across the surface of a chrome-plated article while maintaining substantial corrosion resistance. By way of example only, and not limitation, FIG. 2 illustrates an exemplary chrome plated article 10 produced by the process of FIG. 1. As shown, the exemplary chrome plated article 10 includes an exterior show surface 12, wherein visible designs 14 in the form of alphanumeric characters have been developed across the surface 12. Of course, the process may also be utilized to impart aesthetic designs if desired. The designs 14 are visually perceptible across the exterior show surface 12 of a finished article due to variable light reflectance characteristics of the designs 14 relative to the remainder of the exterior show surface 12. It has been found that through use of controlled material layering and physical treatment, the designs 14 may be imparted while maintaining substantial corrosion resistance characteristics.
Referring simultaneously to FIGS. 1 and 3, an exemplary process for the introduction of designs across a chrome plated surface is shown in conjunction with the resultant layered structure. In this regard, it is to be understood that FIG. 3 and other figures illustrating exemplary layered arrangements are not to scale. Rather such figures are presented merely as an aid to understanding the relative positional relationship of various layers in exemplary constructions. As shown, the exemplary process is initiated by providing a base structure 20 (FIG. 3) such as a cast or extruded aluminum part which has been electroplated with a layer of polished and buffed copper 22 so as to provide a surface suitable for subsequent reception of electrodeposited nickel. As shown, the copper plated base structure is thereafter electroplated with a layer of semi-bright nickel 24 with an over layer of bright nickel 26. By way of example only, and not limitation, in accordance with one contemplated practice the layer of semi-bright nickel 24 may have a thickness of about 0.0006 inches with the bright nickel 26 having a thickness of about 0.0004 inches. However, it is contemplated that these levels may be readily adjusted as desired. The nickel plating operations may be carried out in a traditional Watts nickel plating bath incorporating nickel sulfate NiSO₄in combination with nickel chloride NiCl₂and boric acid at a pH of about 3.85 and a current density of about 20 asf using bagged nickel anodes. However, other suitable plating techniques may likewise be utilized if desired.
As will be appreciated, the semi-bright nickel 24 is preferably substantially sulfur-free and is characterized by a substantially columnar structure while the bright nickel 26 is preferably substantially lamellar in structure. The semi-bright nickel 24 will preferably be slightly cathodic (i.e. more noble) than the bright nickel 26. The potential difference between the semi-bright nickel 24 and the bright nickel 26 is preferably in the range of about 110 millivolts to about 200 millivolts.
As shown in FIG. 1, following the application of the bright nickel 26, a stencil or mask is applied across the bright nickel surface. By way of example only, and not limitation, one suitable material for forming such a stencil is believed to be a high tack adhesive prespacing tape sold under the trade designation SCPS-53X marketed by the 3M Company having a place of business in St. Paul, Minn. However, other suitable stenciling materials capable of maintaining a fixed position on the bright nickel surface may likewise be utilized if desired. In accordance with the potentially preferred practice, the stenciling material provides openings corresponding to the desired final designs 14 (FIG. 2) while substantially covering the remainder of the surface. By way of example, for a finished part having designs 14 corresponding to alphanumeric characters as shown in FIG. 2, the stenciling material would include cutouts corresponding to those alphanumeric characters.
Following the application of the stencil material across the surface of the bright nickel 26, the structure is subjected to a so called “shot-peening” process in which the stenciled surface is bombarded with a surface disrupting impact media so as to apply a fine dimpling at zones across the surface of the bright nickel 26 which are not covered by the stencil. One suitable impact medium is believed to be smooth surface glass impact beads characterized by a diameter of about 150 to 250 microns. However, other suitable impact materials such as polished garnet and the like may also be used if desired. By way of example only, it has been found that suitable glass impact beads are marketed under the trade designation Ballotini Impact Beads manufactured by Potters Industries, Inc., having a place of business in Valley Forge, Pa. During the shot-peening process, the beads are typically delivered through a blast nozzle at an air pressure of about 50 to 90 pounds per square inch for about 10 to 15 seconds. This impact level provides a relatively fine dimpling across the uncovered zones of the bright nickel 26 while leaving the covered zones substantially intact.
Once the shot-peening process is completed and the stencil is removed, the nickel may thereafter be reactivated to permit further plating. By way of example only, such reactivation may be carried out using a periodic reverse cyanide activator or other technique as will be well known to those of skill in the art. Following the reactivation, a relatively thin layer of micro-porous high activity nickel 30 may be applied across the entire surface. The micro-porous nickel 30 is preferably anodic relative to the underlying layer of bright nickel 26. By way of example only, the potential difference between the micro-porous nickel 30 and the bright nickel 26 will preferably be not less than about 15 millivolts. Also, the layer of micro-porous nickel 30 may have a thickness of about 0.00005 inches, although this level may be adjusted as desired. The micro-porous structure and anodic character of the micro-porous nickel relative to the underlying bright nickel 26 serve to distribute oxidation substantially across the entire surface of the structure thereby aiding in the avoidance of concentrated localized degradation. Finally, a relatively thin layer of chromium 32 may be electroplated across the entire structure. By way of example only, and not limitation, the layer of chromium 32 may have a thickness of about 0.00004 inches, although this level may be adjusted as desired.
As best illustrated through simultaneous reference to FIGS. 2 and 3, the shot-peening process imparts a pattern of roughened or dimpled zones 40 incorporating a multiplicity of depressed craters 42 formed by impact of the peening media. It is to be understood that the illustrated size of the depressed craters is not to scale and has been substantially enlarged in the figures to facilitate ease of understanding. The dimpled zones 40 are disposed in adjacent relation to smooth zones 44 across the surface of the article 10. The variable surface character of the final part gives rise to visually perceptible patterning due to different light reflectance characteristics in the dimpled zones 40 and the smooth zones 44. Specifically, due to the presence of the craters 42, the dimpled zones 40 tend to reflect light in a more disbursed pattern than light reflected from the smooth zones 44. Thus, by applying predefined patterns of dimpled zones 40 in combination with smooth zones 44, a patterning effect is obtained across the show surface.
It is also contemplated that the process may be adapted to reverse the relative positions of the dimpled zones 40 and the smooth zones 44 such that the visually perceptible pattern is defined by the smooth zones with a contrasting background defined by the dimple zones. Such a procedure may be carried out by shot-peening the surface of the bright nickel 26 with a masking material in place covering only portions corresponding to elements of the desired final design 14. This procedure produces dimpled zones across substantially the entire surface with the exception of the discrete portions corresponding to the final design which are covered during the shot-peening process.
Regardless of whether the applied design is formed by dimpled or smooth zones, it is contemplated that the nickel layers may be adjusted so as to provide levels of corrosion resistance consistent with an environment of final intended use. In this regard, while the layered arrangement illustrated and described in relation to FIG. 3 may be used to provide substantial corrosion resistance under extreme conditions, such a level of resistance may not be required for all applications. For articles requiring slightly lower corrosion resistance, it is contemplated that the micro-porous nickel may be eliminated if desired. FIG. 4 illustrates an exemplary layered arrangement for a plated article 110 having such a structure, wherein elements corresponding to those previously described are designated by like reference numerals within a 100 series. In the construction illustrated in FIG. 4, the chromium 132 is disposed in direct overlying relation to bright nickel 126 with all other layers being arranged as previously described in relation to FIG. 3. Although this structure may provide a slightly reduced level of corrosion resistance, it is nonetheless believed to be suitable for most end use applications such as automotive trim components and the like.
It is also contemplated that the process may be adjusted to permit shot-peening of the article subsequent to final plating rather than at an intermediate stage. By way of example only, FIG. 5 sets forth an exemplary process for introduction of a desired design wherein the design is applied by a shot-peening process carried out subsequent to final chrome plating. As shown, according to the exemplary process set forth in FIG. 5, the initial copper-plated part is subjected to layered plating of semi-bright nickel, bright nickel, microporous nickel and chromium. Following the plating of the chromium layer, a stencil defining a desired surface pattern is applied across the chromium layer and the plated part is thereafter subjected to a shot-peening process as previously described to impart a desired pattern of dimpled zones. The final resultant structure resembles that which is shown in FIG. 3. In the event that slightly reduced corrosion resistance levels are suitable, it is contemplated that the step of applying micro-porous nickel may be eliminated thereby yielding a structure substantially as illustrated in FIG. 4. As with the previously described embodiments, a visually perceptible design is created by the difference in reflectivity between the dimpled zones subject to impingement during the shot peening process and the smooth surface zones which remain intact.
It is also contemplated that the desired variable reflectivity character may be achieved by use of zones having different degrees of texturing. In this regard, at least a portion of the smooth zones 44, 144 may be replaced with zones having at least some texturing, provided that such textured zones have different reflectively from the dimpled zones 40, 140. By way of example only, it is contemplated that such differential reflectivity may be achieved by applying different texturing techniques or different degrees of texturing at adjacent zones. In one such arrangement, smooth zones 44, 144 may be replaced with textured zones having relatively low levels of dimpling or other surface texturing such that differential reflectivity relative to dimpled zones 40, 140 is retained.
Regardless of whether or not the shot-peening is carried out before or after the final chrome plating step, the surface of the final article nonetheless includes dimpled zones having high concentrations of depressions or craters which would normally be expected to promote the initiation and development of corrosion. Such craters provide a classic environment for the development of deep pitting corrosion wherein chlorine ions are attracted to the craters to balance positive charges produced by the oxidation of metal at those locations. However, it has been found that chrome plated articles utilizing dimpled surface patterning in conjunction with underlying nickel layers surprisingly maintain substantial corrosion resistance when subjected to accelerated corrosion testing in a salt-rich environment. Specifically, it has been found that parts incorporating surface patterns imparted by surface dimpling as described herein have final corrosion resistance levels sufficient to resist perceptible corrosion when subjected to a standard copper-accelerated acetic acid-salt spray (fog) test as set forth in ASTM designation B 368 as will be well known to those of skill in the art. According to this test method, metallic specimens are treated in a fog chamber at a temperature of 49±1 degree Celsius using a solution of 5 parts by weight of reagent grade sodium chloride (NaCl) in 95 parts of water with the addition of 0.25 grams of reagent grade copper chloride to each liter of the salt solution. The pH of the salt-copper solution is adjusted to the range of 3.1 to 3.3 as measured on a sample of the collected spray by the addition of glacial acetic acid. The pH measurement is made electrometrically at 25 degrees Celsius. In testing, it has been found that after being subjected to this test for three 22 hour cycles, the parts were free from any blisters or corrosion spots. Such corrosion resistance indicates suitability for use in environments in which parts may be contacted by salt including automotive, motorcycle, and watercraft applications.
As will be appreciated, the present invention provides a patterning technique which utilizes the intentional introduction of surface irregularities in the form of craters which would be expected to promote pitting corrosion and render the part unsuitable for service in corrosive environments. However, the parts nonetheless retained substantial corrosion resistance so as to be suitable for use in a salt-rich atmosphere.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventor intends for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A method for patterning a surface of a chrome plated article having substantial corrosion resistance, the method comprising the steps of:

(a) providing a base substrate;

(b) depositing a semi-bright nickel layer at a position above the substrate;

(c) depositing a bright nickel layer at a position above the semi-bright nickel;

(d) depositing a chromium layer at a position above the bright nickel, said chromium layer defining an outer show surface of the chrome plated article; and

(e) bombarding a surface of at least one of the bright nickel layer and the chromium layer with an impact media at discrete, predefined impact zones across said surface to produce a pattern of dimpled surface zones having a first reflective character in combination with other adjacent surface zones having a second different reflective character across said outer show surface, said dimpled surface zones corresponding to said predefined impact zones wherein the chrome plated article is characterized by substantial corrosion resistance in salt-rich environments such that the chrome plated article remains free from blisters and corrosion spots when subjected to acid-salt spray testing as set forth in ASTM designation B 368 for a testing period up to 66 hours.

2. The method as recited in claim 1, wherein said impact media comprises glass beads.

3. The method as recited in claim 1, wherein said predefined pattern comprises at least one alphanumeric character.

4. The method as recited in claim 1, wherein during the bombarding step, the surface of said at least one of the bright nickel layer and the chromium layer is covered with a stencil material with openings corresponding to said predefined impact zones.

5. The method as recited in claim 1, wherein said impact media comprises glass beads delivered through a nozzle at an air pressure of about 50 to 90 pounds per square inch.

6. The method as recited in claim 1, comprising the additional step of depositing a micro-porous nickel layer at a position between the bright nickel layer and the chromium layer.

7. The method as recited in claim 1, wherein said base substrate comprises copper plated aluminum.

8. A chrome plated article formed by the method of claim 1.

9. A method for patterning a surface of a chrome plated article having substantial corrosion resistance, the method comprising the steps of:

(a) providing a copper plated aluminum substrate;

(b) electroplating a semi-bright nickel layer across the substrate;

(c) electroplating a bright nickel layer across the semi-bright nickel;

(d) bombarding an upper surface of the bright nickel layer with an impact media to produce an array of craters arranged at discrete, predefined impact zones across said upper surface; and

(e) electroplating a chromium layer at a position above the bright nickel, said chromium layer defining an outer show surface of the chrome plated article, said outer show surface having a predefined pattern of dimpled surface zones having a first reflective character in combination with other adjacent surface zones having a second different reflective character, said dimpled surface zones corresponding to said predefined impact zones across the underlying bright nickel layer, wherein the chrome plated article is characterized by substantial corrosion resistance in salt-rich environments such that the chrome plated article remains free from blisters and corrosion spots when subjected to acid-salt spray testing as set forth in ASTM designation B 368 for a testing period up to 66 hours.

10. The method as recited in claim 9, wherein said impact media comprises glass beads.

11. The method as recited in claim 9, wherein said predefined pattern comprises at least one alphanumeric character.

12. The method as recited in claim 9, wherein during the bombarding step, the upper surface of the bright nickel layer is covered with a stencil material with openings corresponding to said predefined impact zones.

13. The method as recited in claim 9, wherein said impact media comprises glass beads delivered through a nozzle at an air pressure of about 50 to 90 pounds per square inch.

14. The method as recited in claim 9, comprising the additional step of electroplating a micro-porous nickel layer at a position between the bright nickel layer and the chromium layer.

15. A chrome plated article formed by the method of claim 9.

16. A method for patterning a surface of a chrome plated article having substantial corrosion resistance, the method comprising the steps of:

(a) providing a copper plated aluminum substrate;

(b) electroplating a semi-bright nickel layer across the substrate;

(c) electroplating a bright nickel layer across the semi-bright nickel;

(d) electroplating a chromium layer at a position above the bright nickel, said chromium layer defining an outer show surface of the chrome plated article, and

(e) bombarding the outer show surface with an impact media to produce an array of craters collectively forming a predefined pattern of dimpled surface zones having a first reflective character in combination with other adjacent surface zones having a second different reflective character, wherein the chrome plated article is characterized by substantial corrosion resistance in salt-rich environments such that the chrome plated article remains free from blisters and corrosion spots when subjected to acid-salt spray testing as set forth in ASTM designation B 368 for a testing period up to 66 hours.

17. The method as recited in claim 16, wherein during the bombarding step, the upper surface of the bright nickel layer is covered with a stencil material with openings corresponding to said predefined impact zones.

18. The method as recited in claim 16, comprising the additional step of electroplating a micro-porous nickel layer at a position between the bright nickel layer and the chromium layer.