PATENT DOCUMENT

Publication Number: US-10017872-B2
Application Number: US-201514878850-A
Country: US
Kind Code: B2

Title: Metal oxide films with reflective particles

Abstract:
The embodiments described herein relate to anodic films and methods for forming anodic films. The methods described can be used to form anodic films that have a white appearance. Methods involve positioning reflective particles on or within a substrate prior to or during an anodizing process. The reflective particles are positioned within the metal oxide of the resultant anodic film but substantially outside the pores of the anodic film. The reflective particles scatter incident light giving the resultant anodic film a white appearance.

Claims:
What is claimed is: 
     
       1. A part, comprising:
 a metal substrate; and 
 a metal oxide layer overlaying the metal substrate, the metal oxide layer including:
 an ordered region having substantially parallel pore structures that are arranged in an ordered manner and that extend from a top surface of the metal oxide layer to the metal substrate such that, of an amount of light incident onto an external surface of the metal oxide layer, a portion of the amount of light passes through the substantially parallel pore structures and is reflected from the metal substrate, and 
 reflective melted regions formed around perimeter of the top surface of the metal oxide layer that are separated from each other and from the substrate by the ordered region such that each of the reflective melted regions is equidistant from each other, the reflective melted regions characterized as having a microstructure that is different than the ordered region, wherein the reflective regions include (i) irregularly arranged pore structures, and (ii) reflective particles capable of reflecting light there-from, wherein the reflective regions are separated from each other such that at least a remaining portion of the amount of light incident onto the external surface is reflected from the reflective particles and combines with the amount of light reflected from the metal substrate, thereby imparting a white appearance to the metal oxide layer. 
 
 
     
     
       2. The part of  claim 1 , wherein the reflective particles include a metal oxide material. 
     
     
       3. The part of  claim 1 , wherein the reflective particles include at least one of titanium oxide, zirconium oxide, zinc oxide or aluminum oxide. 
     
     
       4. The part of  claim 1 , wherein the reflective particles comprise a metal material. 
     
     
       5. The part of  claim 1 , wherein the reflective particles comprise at least one of aluminum, steel or chromium. 
     
     
       6. The part of  claim 1 , wherein the reflective melted regions are without dyed particles. 
     
     
       7. The part of  claim 1 , wherein the reflective particles comprise at least one of titanium carbide, silicon carbide or zirconium carbide. 
     
     
       8. The part of  claim 1 , wherein the reflective melted regions are characterized as having a crystalline microstructure. 
     
     
       9. The part of  claim 1 , wherein the reflective particles have an average particle diameter ranging from about 100 nm to about 400 nm. 
     
     
       10. The part of  claim 1 , wherein the irregularly arranged pore structures are formed around the reflective particles. 
     
     
       11. The part of  claim 1 , wherein the metal oxide layer has a lightness L value ranging from about 85 to about 100. 
     
     
       12. An enclosure for an electronic device, the enclosure comprising:
 a part comprising: 
 a metal substrate; and 
 a metal oxide layer overlaying the metal substrate, the metal oxide layer including: an ordered region having substantially parallel pore structures that are arranged in an ordered manner and that extend from a top surface of the metal oxide layer to the metal substrate, such that, of an amount of light incident onto an external surface of the metal oxide layer, a portion of the amount of light passes through the substantially parallel pore structures and is reflected from the metal substrate, and 
 reflective melted regions that are formed around a perimeter of the top surface of the metal oxide layer and are separated from each other and from the metal substrate by the ordered region such that the reflective melted regions are equidistant from each other, the reflective melted regions characterized as having a microstructure that is different than the ordered region, wherein the reflective melted regions include (i) irregularly arranged pore structures, and (ii) reflective particles capable of reflecting light there-from, wherein the reflective melted regions are separated from each other such that at least a remaining portion of the amount of light incident onto the external surface is reflected from the reflective particles and combines with the amount of light reflected from the metal substrate, thereby imparting the metal oxide layer with a white appearance. 
 
     
     
       13. The enclosure of  claim 12 , wherein the reflective particles have an average particle diameter ranging from about 100 nm and about 400 nm. 
     
     
       14. The enclosure of  claim 12 , wherein the reflective particles include at least one of titanium oxide, zirconium oxide, zinc oxide, aluminum oxide, aluminum, steel, chromium, titanium carbide, silicon carbide or zirconium carbide. 
     
     
       15. The enclosure of  claim 12 , wherein the irregularly arranged pore structures are formed around the reflective particles. 
     
     
       16. The enclosure of  claim 12 , wherein the reflective particles are spherically shaped. 
     
     
       17. An enclosure for an electronic device, the enclosure comprising:
 a part comprising: 
 a metal substrate; and 
 a metal oxide layer overlaying the metal substrate, the metal oxide layer including: 
 an ordered region having substantially parallel pore structures that are arranged in an ordered manner and that extend from a top surface of the metal oxide layer to the metal substrate such that, of an amount of light incident onto an external surface of the metal oxide layer, a portion of the amount of light passes through the substantially parallel pore structures and is reflected from the metal substrate, and 
 reflective melted regions that are formed around a perimeter of the top surface of the metal oxide layer and are separated from each other and from the metal substrate by the ordered region such that the reflective melted regions are equidistant from each other, the reflective melted regions characterized as having a microstructure that is different than the ordered region, wherein the reflective melted regions include (i) irregularly arranged pore structures, and (ii) reflective particles capable of reflecting light there-from, wherein the reflective melted regions are separated from each other such that at least a remaining portion of the amount of light incident onto the external surface is reflected from the reflective particles and combines with the amount of light reflected from the metal substrate, thereby imparting a white appearance to the metal oxide layer. 
 
     
     
       18. The enclosure of  claim 17 , wherein the reflective particles include at least one of titanium oxide, zirconium oxide, zinc oxide, aluminum oxide, aluminum, steel, chromium, titanium carbide, silicon carbide, or zirconium carbide.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/462,412, filed Aug. 18, 2014 entitled METHODS FOR PRODUCING WHITE APPEARING METAL OXIDE FILMS BY POSITIONING REFLECTIVE PARTICLES PRIOR TO OR DURING ANODIZING PROCESSES,” which is a continuation of International PCT Application No. PCT/US2014/051527, filed Aug. 18, 2014, and claims priority to U.S. Provisional Application No. 61/897,786, filed Oct. 30, 2013 entitled “METHODS FOR PRODUCING WHITE APPEARING METAL OXIDE FILMS BY POSITIONING REFLECTIVE PARTICLES PRIOR TO OR DURING ANODIZING PROCESSES,” each of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DESCRIBED EMBODIMENTS 
     This disclosure relates generally to methods for producing anodic films. More specifically, disclosed are methods for producing anodic films having white appearances by using reflective particles. 
     BACKGROUND 
     Anodizing is an electrolytic passivation process used to increase the thickness of a natural oxide layer on a surface of metal part, where the part to be treated forms the anode electrode of an electrical circuit. The resultant metal oxide film, referred to as an anodic film, increases the corrosion resistance and wear resistance of the surface of a metal part. Anodic films can also be used for a number of cosmetic effects. For example, techniques for colorizing anodic films have been developed that can provide an anodic film with a perceived color. For example, blue dyes can be infused within pores of an anodic film that cause the anodic film to appear blue as viewed from a surface of the anodic film. 
     In some cases, it can be desirable to form an anodic film having a white color. However, conventional attempts to provide a white appearing anodic film have resulted in films that appear to be off-white or muted grey, and not a crisp appearing white that many people find appealing. 
     SUMMARY 
     This paper describes various embodiments that relate to white appearing anodic films and methods for forming the same. 
     According to one embodiment, a method for forming a metal oxide film on a metal substrate is described. The method includes positioning reflective particles within the metal substrate. The method also includes converting at least a portion of the metal substrate to the metal oxide film such that the metal oxide film includes at least part of the reflective particles embedded therein. The embedded reflective particles impart a white appearance to the metal oxide film. 
     According to another embodiment, a part is described. The part includes a metal substrate. The part also includes a metal oxide film formed on the metal substrate. The metal oxide film includes a pattern of first metal oxide portions surrounded by a second metal oxide portion. Each of the first metal oxide portions includes reflective particles embedded therein such that the metal oxide film takes on a white appearance. 
     According to a further embodiment, a method for forming a metal oxide film on a metal substrate is described. The method includes adding the reflective particles within an electrolytic bath. The method also includes forming the metal oxide film by anodizing the metal substrate in the electrolytic bath such that at least part of the reflective particles are embedded within the metal oxide film during the anodizing. The embedded reflective particles impart a white appearance to the metal oxide film. 
     These and other embodiments will be described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The described embodiments and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings in no way limit any changes in form and detail that may be made to the described embodiments by one skilled in the art without departing from the spirit and scope of the described embodiments. 
         FIGS. 1A-1C  illustrate various light scattering mechanisms for providing a perceived white appearance to a metal oxide film. 
         FIG. 2  shows a graph indicating relative light scattering as a function of average particle diameter. 
         FIG. 3  shows a cross-section view of a part after undergoing a traditional coloring method. 
         FIG. 4  shows a cross-section view of a part after undergoing a particle embedding procedure prior to or during an anodizing process. 
         FIG. 5  shows an electrolytic plating cell configured to co-deposit metal with reflective particles. 
         FIGS. 6A-6B  show cross-section views of a part undergoing a co-plating process involving co-deposition of metal and reflective particles. 
         FIG. 7  shows a flowchart indicating steps involved in forming a white metal oxide film using a co-plating process as described with reference to  FIGS. 5 and 6A-6B . 
         FIGS. 8A-8F  shows cross-sectional views of a part undergoing a thermal infusion procedure followed by an anodizing process. 
         FIGS. 9A-9E  shows cross-sectional views of another part undergoing a different thermal infusion procedure followed by an anodizing process. 
         FIG. 10  shows a flowchart indicating steps involved in forming a white metal oxide film on a substrate involving a thermal infusion process as described with reference to  FIGS. 8A-8F and 9A-9E . 
         FIGS. 11A-11C  show cross-section views of a part undergoing a blasting process. 
         FIG. 12  shows a flowchart indicating steps involved in forming a white metal oxide film using a substrate blasting process as described with reference to  FIGS. 11A-11C . 
         FIGS. 13A-13C  show cross-section views of a part undergoing formation of a composite metal layer involving a powder metallurgy process. 
         FIGS. 14A-14D  show cross-section views of a part undergoing formation of a composite metal layer involving formation of a porous preform of reflective particles. 
         FIGS. 15A-15D  show cross-section views of a part undergoing formation of a composite metal layer involving a casting process. 
         FIG. 16  shows a flowchart indicating steps for forming a white appearing metal oxide film involving the formation of a composite material described with reference to  FIGS. 13A-13C, 14A-14D, and 15A-15D . 
         FIG. 17A  shows an anodizing cell used to simultaneously form an oxide layer and deposit particles within the oxide layer during an anodizing process. 
         FIG. 17B  shows a cross-section view of a part after a simultaneous particle embedding and anodizing process. 
         FIG. 18  shows a flowchart indicating steps involved in forming a white metal oxide film using a simultaneous particle embedding and anodizing process. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Representative applications of methods according to the present application are described in this section. These examples are being provided solely to add context and aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the described embodiments may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the described embodiments. Other applications are possible, such that the following examples should not be taken as limiting. 
     This application relates to various embodiments of methods and apparatuses for improving the cosmetics and whiteness of metal oxide coatings. Methods include positioning reflective particles on or within a substrate prior to or during an anodizing process in such a way that the resultant metal oxide film appears white. The white appearing metal oxide films are well suited for providing protective and attractive surfaces to visible portions of consumer products. For example, methods described herein can be used for providing protective and cosmetically appealing exterior portions of metal enclosures and casings for electronic devices, such as those manufactured by Apple Inc., based in Cupertino, Calif. 
     The present application describes various methods of forming a metal layer on a substrate and then converting at least a portion of the metal layer to a metal oxide layer. As used herein, the terms “film”, “layer”, and “coating” are used interchangeably. In some embodiments, the metal layer is an aluminum layer. Unless otherwise described, as used herein, “aluminum” and “aluminum layer” can refer to any suitable aluminum-containing material, including pure aluminum, aluminum alloys or aluminum mixtures. As used herein, “pure” or “nearly pure” aluminum generally refers to aluminum having a higher percentage of aluminum metal compared to aluminum alloys or other aluminum mixtures. As used herein, the terms oxide film, oxide layer, metal oxide film, and metal oxide layer may be used interchangeably and can refer to any appropriate metal oxide film. In some embodiments, the metal oxide layer is converted to a metal oxide layer using an anodizing process. Thus, the metal oxide layer can be referred to as an anodic film. 
     In general, white is the color of objects that scatter nearly all incident visible wavelengths of light. Thus, a metal oxide film can be perceived as white when nearly all visible wavelengths of light incident a top surface of the metal oxide film are scattered. One way of imparting a white appearance to a metal film is by embedding reflective particles within the film. The particles can influence the scattering of light from the metal oxide film through reflection, refraction, and diffraction. Reflection involves a change in direction of the light when it bounces off a particle within the film. Refraction involves a change in the direction of light as it passes from one medium to another, such as from the oxide film medium and the particle medium. Diffraction involves a change in direction of light as it moves around a particle in its path. 
       FIGS. 1A-1C  illustrate how particles in a metal oxide film can scatter incident light by reflection, refraction and diffraction, respectively. At  FIG. 1A , light ray  106  enters metal oxide film  102  having particles  104  embedded therein. As shown, light ray  106  bounces off one of particles  104  and exits top surface  108  of oxide film  102 . In this way, light ray  106  is reflected off a particle  104 . At  FIG. 1B , light ray  110  enters metal oxide film  102  and changes direction when it encounters a first particle  104 . Light ray  110  then encounters a second, third, and fourth particle  104 , each time changing direction, until light ray  110  finally exits top surface  108  of oxide film  102 . In this way, light ray  110  is refracted by several particles  104  within oxide film  102 . At  FIG. 1C , incoming light is depicted as light wave  112 . Light wave  112  enters metal oxide film  102  and encounters a first particle  104 , which causes light wave  112  to diffract. In diffraction, light wave  112  spreads out and scatters in different directions. Light wave  112  can then encounter a second particle  104 , which causes further diffraction until the light wave  112  exits top surface  108  of oxide film. Thus, incident light can be scattered off of particles  104  by way of reflection, refraction, and diffraction, imparting a white appearance to oxide film  102  as viewed from top surface  108 . It should be noted that reference made herein to “reflective particles” can refer to particles that can reflect, refract, and/or diffract visible light when positioned within an oxide film. In some embodiments, the particles are required to highly reflect, refract, and/or diffract incoming visible light in order to provide a sufficiently white metal oxide film. 
     Generally, the higher the refractive index of the particles  104 , the greater amount of scattering will occur from oxide film  102 . The reflectivity of a particle is proportional to its refractive index. Thus, particles having a high refractive index are generally highly reflective. For embodiments described herein, any suitable type of particles capable of interacting with incoming light such that the metal oxide film appears white can be used. In some embodiments, the particles have a high refractive index. In some embodiments, particles include those made of metal oxides such as titanium oxide, zirconium oxide, zinc oxide, and aluminum oxide. In some embodiments, metal particles such as aluminum, steel, or chromium particles are used. In some embodiments, carbides such as titanium carbide, silicon carbide, or zirconium carbide is used. In some embodiments, a combination of one or more of metal oxide, metal, and carbide particles is used. It should be understood that the above examples are not meant to represent an exhaustive list of particles that can be used in accordance with the embodiments described herein. 
     In addition to the material of the particles, the size of the particles can affect the amount of light scattering that occurs. This is because the particle size can affect the amount of light refraction that occurs.  FIG. 2  shows graph  200  showing relative light scattering as a function of average particle diameter in nanometers (nm). As shown, particles having an average diameter ranging from about 200 and 300 nm exhibit the highest amount of light scattering. This range corresponds to about half the wavelength of visible light. Particles having an average diameter of less than 200 nm or greater than 300 nm can also produce an anodic film having a white appearance. However, more of the particles having diameters of less than 200 nm or greater than 300 nm will be needed in order to produce a film having the same amount of whiteness as films with particles having diameters between about 200 and 300 nm. 
     The shape of the particles can also affect the amount of white appearance of an anodic film. In some embodiments, particles having a roughly spherical shape scattered light most efficiently, and thereby impart the whitest appearance to a film. The quantity of particles within the oxide film can vary depending on desired cosmetic and structural properties of the oxide film. It is generally desirable to use enough particles to create a white appearing oxide film but not so many particles that the oxide film becomes highly stressed. Too many particles can cause the oxide film to lose its structural integrity and cause cracks within the film. 
     In embodiments described herein, reflective particles are situated on a substrate before an anodizing process or during an anodizing process. This results in a different placement of particles within the anodic film compared to anodic films colored using traditional methods. In traditional methods, dye is deposited into the pores of the anodic film after the anodic film is already formed. To illustrate,  FIG. 3  shows a close-up cross-section view of part  300  after undergoing a traditional coloring method. During an anodizing process, a portion of substrate  302  is converted to anodic film  304 . Anodic pores  306  grow in a perpendicular direction with respect to top surface  308  and are highly ordered in that they are parallel and evenly spaced with respect to each other. After a portion of substrate  302  is converted to anodic film  304 , dye particles  305  are deposited within pores  306 , imparting a color to substrate  302  in accordance with the color of dye particles  305 . 
     In the embodiments described herein, methods involve embedding particles within a substrate prior to anodizing or during anodizing.  FIG. 4  shows a close-up cross-section view of part  400  after undergoing a particle embedding procedure prior to or during an anodizing process. Particles  406  are embedded within substrate  402  before or during an anodizing process. During the anodizing process, at least a portion of substrate  402  is converted to anodic film  404 . Since particles  406  are already embedded within substrate  302  prior to the anodizing process or are embedded within anodic film  404  during an anodizing process, pores  408  grow around particles  406 . That is, pores  408  proximate to particles  406  curve around particles  406  during the anodizing process. In this way, particles  406  can be positioned within the oxide material of metal oxide layer  404  but outside of pores  408 . 
     As described above, the material, average size, shape, and amount of particles  406  can be chosen such that the resultant oxide layer  404  has a white appearance as viewed from top surface  410 . In some embodiments, the material, average size, and shape of particles  406  are chosen to maximize light scattering (e.g., through reflection, refraction, and diffraction). Particles  406  should be large enough such that visible light incident top surface  410  can scatter off particles  406 , but not so large as to substantially disrupt the pore structure of oxide layer  404  and negatively affect the structural integrity and/or cosmetic quality of oxide layer  404 . In some embodiments, the average diameter of particles  406  ranges from about 200 nm to about 300 nm. In other embodiments, the averaged diameter of particles  406  is less than about 200 nm and/or greater than about 300 nm. Anodizing generally occurs until a target thickness for the oxide layer  404  is achieved. In some embodiments, oxide layer  404  is grown to a thickness ranging from about 5 to 50 microns. 
     The amount of perceived whiteness of an oxide film can be measured using any of a number of color analysis techniques. For example, a color opponent process scheme, such as an L,a,b (Lab) color space based in CIE color perception schemes, can be used to determine the perceived whiteness of different oxide film samples. The Lab color scheme can predict which spectral power distributions (power per unit area per wavelength) will be perceived as the same color. In a Lab color space model, L indicates the amount of lightness, and a and b indicate color-opponent dimensions. In some embodiments described herein, the white metal oxide films have L values ranging from about 85 to about 100 and a,b values of nearly 0. Therefore, these metal oxide films are bright and color-neutral. 
     Different methods for positioning reflective particles within a metal oxide film in accordance with described embodiments will now be described. In some embodiments, methods involve positioning the particles on or within a substrate prior to an anodizing process; these methods will be described below with reference to  FIGS. 5-12 . In some embodiments, methods involve forming a composite material that includes particles dispersed within a metal material prior to an anodizing process; these methods will be described below with reference to  FIGS. 13-16 . In some embodiments, methods involve positioning particles within an anodic film during an anodizing process; these methods will be described below with reference to  FIGS. 17-18 . It should be noted that metal substrates in the embodiments described below can be made of any of a number of suitable metals. In some embodiments, the metal substrates include pure aluminum or aluminum alloy. 
     Co-Plating Metal with Reflective Particles 
     One method for positioning reflective particles within a substrate prior to anodizing involves a co-deposition plating process. During the plating process, reflective particles are co-deposited with metal onto a part resulting in a plated metal layer having reflective particles deposited therein.  FIG. 5  shows electrolytic plating cell  500  configured to co-deposit metal ions  508  with reflective particles  504  onto a part. Plating cell  500  includes container or tank  502 , power supply  514 , cathode (part)  510 , anode  512 , and plating bath  506 . Plating bath  506  includes a mixture of reflective particles  504  and dissolved metal ions  508 . Plating bath  506  can include any of a number of suitable chemicals to help the dissolution of metal ions  508 . During a plating process, power supply  514  applies a voltage across part  510  and anode  512 , which causes positively charged metal ions  508  to migrate toward part  510 . Particles  504  become entrained in the flow of metal ions  508  and also move toward part  510 . Particles  504  then become co-deposited onto part  510  along with metal ions  508 . 
       FIGS. 6A-6B  show cross-section views of part  600  undergoing a co-deposition process and an anodizing process in accordance with described embodiments. At  FIG. 6A , part  600  has undergone a deposition process whereby metal  604  is deposited along with particles  606  onto a surface of substrate  602 . The resultant aggregate metal layer  608  includes metal  604  with particles  606  embedded therein. Aggregate metal layer  608  can be formed using any suitable process, including the co-plating process described above with reference to  FIG. 5 . Aggregate metal layer  608  can be deposited to any suitable thickness. In some embodiments, aggregate metal layer  608  is plated to a thickness ranging from about 5 micrometers to about 50 micrometers. 
     After the plating process is complete, part  600  can then be exposed to an anodizing process. At  FIG. 6B , metal  604  of aggregate metal layer  608  is at least partially converted to metal oxide  610  using an anodizing process, forming aggregate metal oxide layer  614 . Anodizing involves exposing part  600  to an electrolytic process, whereby part  600  acts as the anode and at least a portion of metal  604  become oxidized. Any suitable anodizing process can be used. After the anodizing process, particles  606  remain positioned with metal oxide  610 . Since particles  606  are positioned within metal  604  prior to anodizing, the pores of metal oxide  610  grown around particles  606 , similar to as described above with reference to  FIG. 4 . As described above, particles  606  can be chosen such that they scatter incident light through reflection, refraction, and diffraction, thereby imparting a white appearance to aggregate metal oxide layer  614  as viewed from top surface  612 . 
       FIG. 7  shows flowchart  700  indicating steps involved in forming a white metal oxide film using co-deposition of metal with reflective particles and anodizing. At  702 , an aggregate metal layer having reflective metal particles embedded therein is formed. The aggregate metal layer can be formed using a co-plating process whereby the particles are plated onto a substrate along with metal ions. The concentration of particles in the electroplating solution can vary depending, in part, upon the desired concentration of particles in the plated metal. At  704 , at least a portion of the aggregate metal layer is converted to an aggregate metal oxide layer. In some embodiments, the conversion is accomplished using an anodizing process. The resultant aggregate metal oxide layer scatters incident light and has a white appearance. 
     Thermal Infusion of Reflective Particles 
     Another method for positioning reflective particles within a substrate prior to anodizing involves thermal infusion. In a thermal infusion procedure, localized portions of a metal substrate are melted into liquid or partial liquid form. Reflective particles are then allowed to mix in with the melted metal portions.  FIGS. 8A-8F and 9A-9E  illustrate cross-sectional views of parts  800  and  900  using two embodiments of thermal infusion procedures. At  FIG. 8A , a solution  804  is disposed on a surface of metal substrate  802 . Solution  804  has reflective particles  806  dispersed therein. Solution  804  is chosen such that particles  806  can be dispersed but not be substantially dissolved therein. Thus, the chemical nature of solution  804  (e.g. aqueous, non-aqueous, acidic, alkaline) will depend, on part, on the material of particles  806 . In some embodiments, solution  804  is heated, either by heating solution  804  prior to dispensing onto substrate  802  or by heating substrate  802  that will then heat solution  804 . 
     At  8 B, portions  808  of substrate  802  are thermally treated such that portions  808  are melted into liquid or partial liquid form. In some embodiments, portions  808  are melted using a thermal spray method in which a flame locally heats portions of substrate  802 . In some embodiments, portions  808  are melted using a laser beam. When the laser beam is directed to a surface of substrate  802 , laser energy is transferred in the form of heat to portions  808  proximate to the laser beam. These portions  808  then melt or partially melt. The wavelength of the laser beam and dwell time at each portion  808  can vary depending, in part, upon the material of substrate  802 . The wavelength and dwell time should be chosen such that energy from the laser beam can be absorbed in the form of heat by substrate  802 . In some embodiments, the laser beam and dwell time are appropriate to melt portions  808  but not melt or change the shape of reflective particles  806 . In some embodiments where substrate  802  includes aluminum, the laser beam wavelengths ranges from low ultraviolet to infrared are used. 
     In some embodiments, a laser can be used to melt portions of substrate  802  in a particular pattern. In some embodiments, the laser is scanned over the surface of substrate  802  such that an ordered array of melted portions  808  is formed. In some embodiments, the ordered array is such that each of the melted portions  808  is equidistant from each other. In some embodiments, a substantially random of melted portions  808  is formed. In some embodiments, melted portions  808  are formed around edges or a perimeter of a feature of substrate  802 . In some embodiments, the laser beam is scanned such that melted portions  808  form a logo or writing. In some embodiments, a pulsed laser is used wherein each melted portion  808  corresponds with a pulse of the laser. In some embodiments, each melted portion  808  is pulsed by a laser beam more than one time. In some embodiments, a continuous laser is used, wherein the laser beam or the part is moved quickly between each melted portion  808 . 
     At  FIG. 8C , particles  806  intermingle with the melted metal and become infused within melted portions  808 . At  FIG. 8D , melted portions  808  are allowed to solidify into re-solidified metal portions  810  and solution  804  is removed. As shown, particles  806  remain within re-solidified metal portions  810 . Since re-solidified metal portions  810  have been melted and re-solidified, these portions can have a different microstructure than surrounding substrate  802 . In some embodiments, re-solidified metal portions  810  have a crystalline microstructure. 
     At  FIG. 8E , top surface  818  is optionally planarized to remove any surface irregularities due to the melting and re-solidification of re-solidified metal portions  810 . In some embodiments, top surface  818  is planarized using a polishing or buffing method. At  FIG. 8F , at least a portion of metal substrate  802 , including re-solidified metal portions  810 , is converted to metal oxide layer  812 . In some embodiments, metal oxide layer  812  is formed using an anodizing process. Metal oxide layer  812  includes first metal oxide portion  814  and second metal oxide portion  816 . First metal oxide portion  814  corresponds to the converted metal substrate  802  unaffected by thermal treatment. Second metal oxide portion  816  corresponds to the converted re-solidified metal portions  810 . Since the microstructure of re-solidified metal portions  810  can be different from the microstructure of surrounding substrate  802 , the anodic pore structure of first  814  and second  816  metal oxide portions can be different. In some embodiments, anodic pores  820  of first oxide portion  814  are substantially parallel and highly ordered while the anodic pores (not illustrated) of second oxide portion  816  are curved around particles  806 , similar to as described above with reference to  FIG. 4 . In some embodiments, second oxide portion  816  is substantially free of anodic pores. As shown, second metal oxide portions  816  have reflective particles  806  embedded therein, giving second metal oxide portions  816  a white appearance. Reflective particles  806  can scatter visible light incident top surface  818  and impart a white appearance to oxide layer  812 . Note that the location of white second metal oxide portions  816  on substrate  802  can be accurately controlled by, e.g., the use of a laser, without the use of a mask. If white second metal oxide portions  816  are close together, the appearance of entire oxide layer  812  will appear white. If second metal oxide portions  816  are clustered together in a pattern such as a logo or writing, those clustered metal oxide portions  816  will appear white while surrounding first metal oxide portion  814  will appear a different color. In some embodiments, first metal oxide portion  814  will be substantially transparent or translucent such that the color of underlying substrate  802  is visible from top surface  818 . 
       FIGS. 9A-9E  illustrate another method for thermally infusing reflective particles within portions of a substrate. At  FIG. 9A , a laser beam is directed to a surface of substrate  902  melting or partially melting first portion  908   a . In addition, dispenser  904  dispenses reflective particles  906  onto melted first portion  908   a . Particles  906  can be dispensed before, at the same time, or shortly after first portion  908   a  is melted by the laser beam. Particles  906  then become mixed with the liquid or partial liquid metal of melted portion  908   a . At  FIG. 9B , the laser beam is moved to a second portion  908   b  of substrate  902  and dispenser  904  dispensed particles  906  onto melted second portion  908   b . Particles  906  are then mixed in melted second portion  908   b , similar to first portion  908   a . At  FIG. 9C , first and second portions  908   a  and  908   b  are allowed to re-solidify forming re-solidified metal portions  910  with particles  906  embedded therein. As with the re-solidified metal portions  810  described above with respect to  FIG. 8D , re-solidified metal portions  910  can have a different microstructure than surrounding substrate  902 . 
     At  FIG. 9D , top surface  918  is optionally planarized to remove any surface irregularities due to the melting and re-solidification of re-solidified metal portions  910 . At  FIG. 9E , at least a portion of metal substrate  902 , including re-solidified metal portions  910 , is converted to metal oxide layer  912 . Metal oxide layer  912  includes first metal oxide portion  914  and second metal oxide portion  916 . Since the microstructure of re-solidified metal portions  910  can be different from the microstructure of surrounding substrate  902 , the anodic pore structure of first  914  and second  916  metal oxide portions can be different. In some embodiments, anodic pores  920  of first oxide portion  914  are substantially parallel and highly ordered while the anodic pores (not illustrated) of second oxide portion  916  curve around particles  906 . In some embodiments, second oxide portion  916  is substantially free of anodic pores. Reflective particles  906  can scatter visible light incident top surface  918  and impart a white appearance to oxide layer  912 . 
       FIG. 10  shows flowchart  1000  indicating steps involved in forming a white metal oxide film on a substrate using a thermal infusion process prior to anodizing. At  1002 , portions of the metal substrate are melted. In some embodiments, the melted portions are arranged in a pattern or design on the substrate. In some embodiments, the melting is accomplished using a laser beam directed at a top surface of the substrate. In some embodiments, the melting is accomplished using a thermal spray method. At  1004 , reflective particles are infused within the melted portions of the substrate. In some embodiments, the particles are dispersed in a solution that is spread on the top surface and that mix in with the liquid metal of the melted portions. In some embodiments, the particles are dispensed from a dispenser on the melted portions and that get mixed in with the liquid metal of the melted portions. At  1006 , a top surface of the substrate is optionally planarized to remove surface irregularities caused by the melting and infusing processes. In some embodiments, planarizing is accomplished by polishing (mechanical or chemical) the top surface. At  1008 , at least a portion of the metal substrate is converted to metal oxide, forming a white appearing metal oxide. In some embodiments, the conversion is accomplished using an anodizing process. In some embodiments, the entire metal oxide layer appears white as viewed from the top surface. In other embodiments, portions of the metal oxide layer appear white while other portions of the metal oxide layer do not appear white, as view from the top surface. 
     Blasting of Reflective Particles 
     An additional method for positioning reflective particles within a substrate prior to anodizing involves blasting reflective particles onto a surface of a substrate prior to anodizing.  FIGS. 11A-11C  show cross-section views of part  1100  undergoing a blasting process and an anodizing process in accordance with described embodiments. At  11 A, particles  1104  are propelled toward top surface  1106  of substrate  1102  at high pressures. The high pressure causes at least a portion of particles  1104  to become embedded within top surface  1106 . In a typical blasting operation, a blasting media is used only to form a textured surface on a substrate. In the embodiments described herein, a blasting process is used to embed reflective particles onto the surface of the substrate. In some embodiments, the blasting nozzle that propels particles  1104  is positioned close to surface  1106  to increase the amount of particles  1104  that become embedded. In some embodiments, particles  1104  have irregular or jagged shapes to increase the likelihood for particles  1104  to become embedded onto surface  1106 . In some embodiments, portions of surface  1106  are masked prior to the blasting process in order to create patterns or designs on surface  1106 . 
     At  FIG. 11B , surface  1106  is optionally partially cleaned to remove a portion of particles  1104  from surface  1106 . In a typical blasting operation, the surface is fully cleaned and polished to remove all of the blasting media and smoothed the surface prior to further processing. The cleaning typically includes desmutting and degreasing process. The polishing process typically involves a chemical polishing process. In the embodiments presented herein, surface  1106  is partially cleaned or not cleaned at all prior to subsequent processing such that particles  1104  remain embedded within substrate  1102 . In one embodiment, reduced desmutting and degreasing processes are used, whereby the exposure of substrate  1102  to the desmutting and degreasing solutions are reduced. In some embodiments, no chemical polishing process is used. In some embodiments, the material of particles  1104  is chosen for their resistance to dissolving during desmutting, degreasing and/or chemical polishing processes in addition to being chosen for light scattering ability. In some embodiments, particles  1104  are made of metal. At  FIG. 11C , at least a portion of substrate  1102  is converted to metal oxide layer  1108 . In some embodiments, metal oxide layer  1108  is formed using an anodizing process. As shown, particles  1104  are situated primarily within the upper portion of oxide layer  1108  near top surface  1106 . During an anodizing process, the anodic pores within oxide layer  1108  can grow around particles  1104  such that particles  1104  are positioned outside of the pores, similar to the anodic pores described above with reference to  FIG. 4 . 
       FIG. 12  shows flowchart  1200  indicating steps involved in forming a white metal oxide film using a substrate blasting process prior to anodizing. At  1202 , reflective particles are embedded onto a surface of a substrate. In some embodiments, a blasting process whereby reflective particles are propelled toward the substrate surface is used. At  1204 , the substrate surface with embedded particles is optionally partially cleaned and/or smoothened. At  1206 , at least a portion of the embedded substrate is converted to metal oxide. In some embodiments, an anodizing process is used. The resultant metal oxide film has a white appearance due to the scattering of incident light by the reflective particles. 
     As described above, some methods described herein involve forming a composite metal material prior to an anodizing process. The composite metal material is bulk material that contains reflective particles within a metal base. Methods can include, but are not limited to, powder metallurgy, infiltration of a porous preform, and casting metal with particles dispersed therein. Some of these methods will be described in detail below with reference to  FIGS. 13-16 . 
     Powder Metallurgy 
     One method of forming a composite metal material involves blending and pressing of reflective particles and metal particles onto a surface of a substrate prior to anodizing. The blending of powdered materials and pressing them into a desired shape is sometimes referred to as powder metallurgy. In the embodiments described herein, reflective particles are mixed in with metal particles and pressed together under high pressure forming a composite metal layer.  FIGS. 13A-13C  show cross-section views of part  1310  undergoing formation of a composite metal layer using powder metallurgy followed by anodizing.  FIG. 13A  shows a mixing system  1300 , which includes mixing container  1302 . Composite material mixture  1308 , which includes reflective particles  1306  and metal particles  1304 , is placed in container  1302  and mixed. Mixing system  1300  can include a mixing apparatus (not shown) that can agitate composite material mixture  1308  to keep that reflective particles  1306  are substantially evenly distributed amongst metal particles  1304 . In some embodiments, container  1302  is rotated or vibrated to mix particles  1304  and  1306 . In some embodiments, a stirring apparatus is placed in container  1302  to mix particles  1304  and  1306 . After particles  1304  and  1306  are sufficiently blended, composite material mixture  1308  can be compressed into a layer onto a substrate. 
       FIG. 13B  shows part  1310 , which includes composite mixture  1308  after it has been compressed into composite metal layer  1318  onto substrate  1312 . During the compression process, metal particles  1304  are fused together forming a continuous matrix of metal  1314 . Reflective particles  1306  remain intact during the compression process and become lodge within metal matrix  1314 . The compression process can include any suitable process that causes substantially all of metal particles  1304  to compress and fuse together. In some embodiments, reflective particles  1306  are left substantially intact and substantially unchanged in shape during the compressing. In some embodiments, a hot isostatic pressing process is used. During a hot isostatic pressing process, composite material mixture  1308  can be placed on substrate  1312  and part  1310  is subjected to an elevated temperature and an elevated isostatic gas pressure. Under the elevated temperature and pressure, metal particles  1304  fuse together into a continuous metal matrix  1314  with reflective particles  1306  embedded therein. In some embodiments, a cold spraying process is used, whereby composite mixture  1308  is shot at the surface of substrate  1312  at a high enough pressure that metal particles  1304  deform upon impact and fuse together. As shown, reflective particles  1306  are distributed throughout composite metal layer  1318 , not just on the surface. Since composite metal layer  1318  is formed on substrate  1312  using a compression process, substrate  1312  is not limited to electrically conductive materials. Substrate  1312  can be made of plastic, ceramic, or non-conductive metals. In some embodiments, substrate  1312  is made of a conductive material or a combination of conductive material and non-conductive material. 
     At  FIG. 13C , metal matrix  1314  of composite metal layer  1318  is converted to metal oxide  1320 . Reflective particles  1306  remain substantially intact and in place during the conversion process. In some embodiments, an anodizing process is used to convert metal  1314  to metal oxide  1320 . Since reflective particles  1306  are in place during anodizing, the pores of the anodic film can grow around particles  1306 , such as described above with reference to  FIG. 4 . As described above, the material, average size, shape, and amount of reflective particles  1306  can be chosen such that the resultant oxide layer  1324  has a white appearance as viewed from top surface  1322 . 
     Infiltration of Porous Preform of Reflective Particles 
     Another method for forming a composite metal material involves infiltrating a porous preform of reflective particles with liquid metal (e.g., aluminum). In one embodiment, the porous preform of reflective particles is made by mixing reflective particles with a binder material to form a binder complex. The binder complex is then be compressed until the reflective particles bind together. The binder material is then removed, leaving the porous preform of reflective particles. In another embodiment, the porous preform of reflective particles is made by compacting the reflective particles together without binder material. 
       FIGS. 14A-14D  show cross-section views of part  1400  undergoing positioning of reflective particles within a metal oxide film that includes forming a porous preform of reflective particles. At  FIG. 14A , binder complex layer  1408  is formed using any suitable method. Binder complex layer  1408  includes binder material  1404  and reflective particles  1406 , which are dispersed within binder material  1404 . Reflective particles  1406  can be mixed within binder material  1404 , and then the mixture can be compressed together. In some embodiments, binder complex layer  1408  is compressed within a mold (not shown) that provides a general shape to binder complex layer  1408 . In some embodiments, binder complex layer  1408  is compressed onto a separate substrate (not shown). Binder material  1404  can be made of any of a number of suitable materials that can be removed during a subsequent binder material  1404  removal process. Suitable types of binder material  1404  can include wax (e.g. paraffin wax), various polymers, and organic compounds. In some embodiments, reflective particles  1406  remain substantially intact during the pressing process. The pressing process can compact binder complex layer  1408  with sufficient pressure to force adjacent reflective particles  1406  to adhere with one another. 
       FIG. 14B  shows part  1400  after a binder material  1404  removal process, leaving porous preform  1410 . Binder material  1404  can be removed using any suitable method, such as by sublimation, liquefaction followed by drainage, or liquefaction followed by vaporization. In some embodiments, removal of binder material  1404  involves heating part  1400  until binder complex layer  1408  “burns off” into gaseous form. In some embodiments, heating causes binder material  1404  to first liquefy and then vaporize, i.e., “burn off” In some embodiments, once in liquid form, binder material  1404  can be drained off of porous preform  1410 . In some embodiments, the binder material removal process leaves substantially no trace of binder material  1404  within porous preform  1410 . Heating can occur, for example, by placing part  1400  in a furnace. In some embodiments, binder material  1404  is heated to a temperature high enough for removal of binder material  1404  but lower than the melting temperature of reflective particles  1406 . Once binder material  1404  is removed, voids  1412  remain within porous preform  1410  where binder material  1404  once was. In this way, porous preform  1410  is a porous structure made of adhered together reflective particles  1406 . Note that in some embodiments, porous preform  1410  is made without the aid of binder material  1404 . That is, reflective particles  1406  can be compressed together with sufficient pressure to force adjacent reflective particles  1406  to adhere with one another without the aid of binder material  1404 . 
       FIG. 14C  shows part  1400  after a metal infiltration process. During the metal infiltration process, metal  1414  in molten form can be poured onto porous preform  1410  and within voids  1412 . Reflective particles  1406  can remain substantially in place within porous preform  1410  during the metal infiltration process such that reflective particles  1406  are dispersed within metal  1414 . In some cases, part  1400  is placed under vacuum conditions to decrease the pressure within voids  1412 , thereby forcing the molten metal  1414  to completely fill voids  1412 . In some embodiments, porous preform  1410  is placed within a mold (not shown) prior to the infusion of metal  1414  to give composite metal layer a particular shape. Metal  1414  is then allowed to cool and solidify, forming composite metal layer  1416 . At  FIG. 14D , a portion of metal  1414  of composite metal layer  1416  is converted to metal oxide layer  1418 , using, for example, an anodizing process. In some embodiments, substantially all of metal  1414  is converted to metal oxide layer  1418 . Reflective particles  1406  remain substantially intact and in place during the conversion process. Since reflective particles  1406  are in place during anodizing, the pores within metal oxide layer  1418  can grow around particles  1406 , such as described above with reference to  FIG. 4 . As described above, the material, average size, shape, and amount of reflective particles  1406  can be chosen such that oxide layer  1420  has a white appearance as viewed from top surface  1422 . 
     Casting of Metal with Dispersed Reflective Particles 
     A further method of forming a composite metal material involves casting of metal that has reflective particles dispersed therein.  FIGS. 15A-15D  show cross-section views of part  1500  undergoing a casting process in accordance with some embodiments.  FIG. 15A  shows crucible  1502  that is configured to hold melted metal  1504 . Reflective particles  1506  are added to and mixed with melted metal  1504  to form composite material mixture  1508 . Reflective particles  1506  can be mixed within melted metal  1504  using any suitable means, including slowly adding while folding in reflective particles  1506  or mixing melted metal  1504  using a tool such as a rod. In some embodiments, the mixing is continued until reflective particles  1506  are substantially evenly dispersed within melted metal  1504 . 
     At  FIG. 15B , composite metal mixture  1508 , while in liquid form, is poured into mold  1510 . Mold  1510  can be any suitable type of mold, including a sand casting mold or die-casting mold. Mold  1510  can have any suitable shape for providing a final shape to composite metal mixture  1508 . In some embodiments, mold  1510  has a shape that corresponds to giving composite metal mixture  1508  a shape of an enclosure for an electronic device. In some embodiments, pressure is applied to composite metal mixture  1508  while in mold  1510  to remove air bubbles within composite metal mixture  1508 . In some cases, composite metal mixture  1508  is placed under vacuum conditions to remove air bubbles within composite metal mixture  1508 . In some embodiments, some reflective particles  1506  are added to liquid metal  1504  during the molding process. That is, some or all of reflective particles  1506  are placed within mold  1510  prior to pouring in liquid metal  1504 . 
     At  FIG. 15C , composite metal mixture  1508  is allowed to cool and solidify and is removed from mold  1510 . Solidified composite metal mixture  1508  retains a shape in accordance with the shape of mold  1510 . At  FIG. 15D , a portion of metal  1504  of composite metal mixture  1508  is converted to metal oxide layer  1512 . In some embodiments, substantially all of metal  1504  is converted to metal oxide layer  1512 . Reflective particles  1506  can remain substantially intact and in place during the conversion process. In some embodiments, an anodizing process is used to convert metal  1504  to metal oxide layer  1512 . Since reflective particles  1506  are in place during anodizing, the pores of metal oxide layer  1512  can grow around particles  1506 , such as described above with reference to  FIG. 4 . As described above, the material, average size, shape, and amount of reflective particles  1506  can be chosen such that the resultant oxide layer  1512  has a white appearance as viewed from top surface  1514 . 
       FIG. 16  shows flowchart  1600  indicating steps for forming a white appearing metal oxide film involving the formation of a composite metal material in accordance with described embodiments. At  1602 , a composite metal mixture is formed by mixing reflective particles within a metal base. In some embodiments, the composite metal mixture is formed using a power metallurgic technique, whereby reflective particles are mixed with metal particles. In some embodiments, the composite metal mixture is formed by forming a porous preform of reflective particles and then infiltrating metal within voids of the porous preform. In some embodiments, the composite metal mixture is formed using a casting technique whereby reflective particles are mixed within a melted metal base. In some embodiments, the volume fraction of reflective particles should be up to about 60% by volume in order to achieve an optimum combination of white cosmetics, mechanical strength, and ductility in a resulting composite metal layer. 
     At  1604 , a composite metal layer is formed by shaping the composite metal mixture. For powder metallurgic methods, the shaping can involve compressing the mixture of reflective particles and metal particles with sufficient force to fuse the metal particles together. In some embodiments, a hot isostatic pressing process is used. In other embodiments, a cold spraying process is used. For porous preform methods, the shaping can be accomplished at the same time that the composite mixture is formed. That is, the shaping can occur while pressing the reflective particles together into a porous preform and infiltrating metal within voids of the porous preform. In some embodiments, the porous preform can be pressed within a mold to create a general shape for the porous preform. In some embodiments, the metal is infiltrated within the pores while the porous preform is positioned on a substrate and/or a mold to give a general shape to the composite metal layer. For casting methods, the shaping can involve pouring the melted metal, which have reflective particles mixed therein, into a mold where it is allowed to solidify and take on a general shape in accordance with a shape of the mold. At  1606 , at least a portion of the metal of the composite metal layer is converted to a metal oxide layer. In some embodiment, the conversion is accomplished using an anodizing process. The resultant metal oxide layer has a white appearance due to the scattering of incident light by the reflective particles. 
     Depositing Particles During Anodizing Process 
     In some embodiments, forming a white appearing metal oxide layer involves depositing reflective particles within the metal oxide during an anodizing process.  FIG. 17A  shows anodizing cell  1700  used to deposit particles  1706  within an oxide layer during an anodizing process. Anodizing cell  1700  includes container or tank  1702 , which is configured to hold electrolytic bath  1704 , anode  1708 , and cathode  1710 . During an anodizing process, anode  1708  is the part that is anodized. Power supply  1712  applies a voltage across anode part  1708  and cathode  1710 . When voltage is applied, electrons are withdrawn from anode part  1708 , allowing ions at the surface of part  1708  to react with water in electrolytic bath  1704  and to form an oxide film on part  1708 . Electrolytic bath  1704  includes reflective particles  1706 , which are negatively charged. In some embodiments, reflective particles  1706  are made of a substance that is negatively charged when placed in electrolytic bath  1704 , such as SiO 2 . In some embodiments, reflective particles  1706  are covered with a coating or sizing that give reflective particles  1706  a negative charge when placed in electrolytic bath  1704 . In one embodiment, TiO 2  particles are covered with a SiO 2  coating to make the TiO 2  particles negatively charged. In some embodiments, reflective particles  1706  are covered with a dispersing agent that help disperse and evenly distribute reflective particles  1706  within electrolytic bath  1704  and prevent reflective particles  1706  from agglomerating. 
     Since reflective particles  1706  are negatively charged, they are attracted to and travel toward anode part  1708  while the oxide film is being formed. Reflective particles  1706  that are at the surface of anode part  1708  during the anodizing process can become embedded within the anodic film. In some embodiments, electrolytic bath  1704  is agitated to keep reflective particles  1706  from settling to the bottom of tank  1702  due to gravity. In some embodiments, electrolytic bath agitated or mixed during the anodizing to keep particles  1706  from settling. In some embodiments, anode part  1708  is positioned near the bottom of tank  1702  such that particles  1706  settle onto anode part  1708  during the anodizing process. 
       FIG. 17B  shows a cross-section view of part  1708  after a simultaneous particle embedding and anodizing process. During the anodizing process, at least a portion of  1713  is converted to metal oxide layer  1714 . The reflective particles, which are negatively charged, become embedded within metal oxide layer  1714 . In some embodiments, particles  1706  are substantially evenly distributed within metal oxide layer  1714 . During anodizing, the pores of the anodic film grow around particles  1706 , similar to pores  408  described above with reference to  FIG. 4 . 
       FIG. 18  shows flowchart  1800  indicating steps involved in forming a white metal oxide film using a simultaneous particle embedding and anodizing process. At  1802 , a substrate is established as an anode of an anodizing cell. At  1804 , negatively charged particles are added to the electrolytic bath of the anodizing cell. The particles can be chosen for their light scattering ability, as described above. At  1806 , at least a portion of the substrate is converted to an oxide layer while negatively charged particles are simultaneously embedded within the oxide layer. The resultant aggregate metal oxide layer scatters incident light and has a white appearance. 
     It should be noted that relative amount of reflective particles used in composite material methods may differ from methods involving positioning particles within a substrate. For example, in composite metal material methods, higher amounts of reflective particles can generally correlate with stronger and whiter composite material. However, higher amounts of reflective particles can also reduce ductility of the resultant composite material. Therefore, the volume fraction of reflective particles can be optimized for desired strength, whiteness, and ductility. In some applications, a volume fraction of reflective particles up to about 60% is used in order to achieve an optimum combination of white cosmetics, mechanical strength, and ductility in the resulting composite metal layer. For the non-bulk composite metal material methods, which include co-plating metal with reflective particles, thermal infusion of reflective particles, blasting of reflective particles, and depositing of reflective particles during anodizing, a significant amount of the mechanical properties of the metal layer can come from the base metal of the substrate. Thus, it may be necessary in some cases to have as high a volume fraction as possible to increase whiteness. In some applications, a volume fraction of reflective particles around 60% or higher is used in order to achieve an optimum of whiteness of the resulting metal layer. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20151008
Publication Date: 20180710
Grant Date: 20180710
Priority Date: 20131030
Inventors: BROWNING, LUCY E.
MCDONALD, Daniel T.
LYNCH, STEPHEN B.
TRYON, BRIAN S.
Assignee: APPLE INC
CPC Classifications: [{"code": "C25D11/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/12111", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "C25D15/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/12111", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D15/00", "inventive": true, "first": true, "tree": "[]"}, {"code": "C25D11/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y10T428/12111", "inventive": false, "first": false, "tree": "[]"}, {"code": "C25D11/16", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "C25D11/02", "inventive": true, "first": true, "tree": "[]"}, {"code": "C25D15/00", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 52995793