Abstract:
A method for depositing a metal onto a substrate including the steps of providing a plating bath including ions of the metal, positioning the substrate in the plating bath, positioning at least one counter electrode in the plating bath, performing a first electrolytic process for a predetermined first period of time, performing a second electrolytic process for a predetermined second period of time and looping between the first and second electrolytic processes to form a coating of the metal on the substrate.

Description:
BACKGROUND 
       [0001]    The present disclosure relates to forming layering of a coating and, more particularly, to forming layering of trivalent chromium for equivalent performance characteristics normally associated with a hexavalent chromium coating. 
         [0002]    The present disclosure also relates to forming layering in the deposit with disassociated cracks and, more particularly, to forming layering in the deposit using a looping first electrolytic process followed by a second electrolytic process and, still more particularly, to forming layering in the deposit using a looping first electrolytic process followed by a second electrolytic process whereby said first electrolytic process and said second electrolytic process are separated by an off-time. 
         [0003]    As hexavalent chromium [Cr(VI)] plating continues to be scrutinized for its known human carcinogenicity, a reliable and cost-effective alternative coating is desirable. One such alternative is trivalent chromium [Cr(III)]. While one skilled in the art believes the use of trivalent chromium to be limited only to decorative use, the subject matter of this disclosure is also applicable for functional use. 
         [0004]    Chromium coatings are widely used in a variety of industries. Plating operations are used to fabricate two types of chromium coatings, functional and decorative. Functional chromium coatings consist of a thick layer of chromium, typically 1.3 to 760 μm (F. Altmayer,  Plating  &amp;  Surface Finishing,  82 (2), 26 (1995), to provide a surface with functional properties such as hardness, corrosion resistance, wear resistance and low coefficient of friction. Applications of functional chromium coatings include strut and shock absorber rods, hydraulic cylinders, crankshafts and industrial rolls. Carbon steel, cast iron, stainless steel, copper, aluminum and zinc are substrates commonly used with functional chromium. Decorative chromium coatings consist of a thin layer of chromium, typically 0.003 to 2.5 μm (F. Altmayer,  Plating  &amp;  Surface Finishing,  82 (2), 26 (1995), to provide a bright surface with wear and tarnish resistance when plated over a nickel layer. It is used for plating automotive trim/bumpers, bath fixtures and small appliances. 
         [0005]    Cr(VI) plating has been commercialized for many years. However, a Cr(VI) plating bath operates at an elevated temperature and produces a problematic mist of chromic acid. Since worker exposure to Cr(VI) plating baths is regulated by OSHA, exhaust/scrubber systems must be installed for Cr(VI) plating operations and the exposure limit is 0.01 mg/m (L. R. Ember,  Chemical and Engineering News , Feb. 18, 1991) (L. Banker, “Chromium Air Emissions Standards for Hard, Decorative Chromium and Chromium Anodizing,”  Proc.  16 th AESF/EPA Conference , Orlando, Fla., AESF, Washington, D.C., 1995). The Clean Air Act, as well as local constraints, regulates the emission of chromium to the air and water. Since Cr(VI) plating produces hazardous air emissions, all Cr(VI) platers must control and monitor the bath surface tension and report the results to the EPA. By contrast, Cr(III) platers are not required to monitor bath surface tension (L. Banker, “Chromium Air Emissions Standards for Hard, Decorative Chromium and Chromium Anodizing,”  Proc.  16 th AESF/EPA Conference , Orlando, Fla., AESF, Washington, D.C., 1995). 
         [0006]    The USEPA has identified chromium as one of  17  “high-priority” toxic chemicals. The USEPA selected the high-priority chemicals based on their known health and environmental effects, production volume and potential for exposure (L. R. Ember,  Chemical and Engineering News , Feb. 18, 1991). Under former USEPA administrator William K. Reilly&#39;s Industrial Toxic Program, the high-priority toxic chemicals were targeted for 50% reduction by 1995 (D. J. Hanson,  Chemical and Engineering News , Jun. 3, 1991). 
         [0007]    The chemistry of chromium provides a basis for understanding the toxicology. Chromium can exist in oxidation states ranging from II to VI. However, only Cr(III) and Cr(VI) are stable enough to actually be used as a basis for electrodeposition. Cr(VI) is readily reduced to the more stable Cr(III) and, in this process, substances in contact with Cr(VI) are oxidized. Cr(VI) compounds are very soluble as compared to Cr(III) compounds. Therefore, in the environment, Cr(VI), on release into a stream or aquifer, is much more likely to dissolve and move with the flow. In fact, one method that has been used to stabilize Cr(VI) (i.e., make it less mobile) in the environment is to reduce it to Cr(III). The use of Cr(III) in industrial and commercial processes is preferred over Cr(VI) on the basis of the comparison of their toxicities. 
         [0008]    From an environmental perspective, plating from additive-free Cr(III) solution has several advantages relative to Cr(VI):
       1. Cr(III) is non-toxic, non-hazardous and is not an oxidizer. Therefore, meeting air quality regulations is easier and working conditions are greatly improved. The exposure limit for Cr(III) is an order of magnitude higher than that for Cr(VI).   2. Disposal costs are significantly reduced for Cr(III) plating. Hydroxide sludge generation is reduced ten to twenty times because Cr(III) generally operates at a Cr(III) content of about 4 to 20 g/L vs. 150 to 300 g/L for a Cr(VI) bath.   3. Since there are no proprietary additives in the Cr(III) bath, the rinse water may be recycled       
 
         [0012]    In addition, Cr(III) has the following technical advantages:
       1. The Cr(III) plating bath is not sensitive to current interruptions (G. E. Shahin,  Plating  &amp;  Surface Finishing,  79 (8), 19 (1992).   2. Drag-in of chloride and sulfate from any previous nickel plating operations into the Cr(III) process is tolerated (D. L. Snyder,  Products Finishing,  61 (8), (1989). By contrast, chloride and sulfate drag-in upset the catalyst balance in a Cr(VI) process.   3. Throwing power for Cr(III) plating, which is poor in a Cr(VI) bath, is good and similar to other metals such as copper (D. L. Snyder,  Products Finishing,  61 (8), (1989).       
 
         [0016]    As described above, Cr(III) plating has numerous environmental, health and technical advantages relative to Cr(VI) plating. Considerable research has been done to study Cr(III) plating, including the effects of the plating bath chemistry on plating thickness, brightness, hardness and corrosion resistance (G. Scott, U.S. Pat. No. 5,196,109 (1991) (M. Constantin, et al.,  Galvanotechnik,  82 (11), 3819 (1991) (J.-Y. Hwang,  Plating  &amp;  Surface Finishing,  78 (5), 118 (1991) and the effect of current waveforms on chromium deposit structure, distribution, brightness and hardness (Z.-M. Tu, et al.,  Plating  &amp;  Surface Finishing,  77 (10), 55 (1990) (J. Dash, et al.,  Proc. AESF SUR/FIN  1991, AESF, Washington, D.C., 1991; p. 947). 
         [0017]    By including proprietary organic additives, Cr(III) plating baths are commercially available for decorative chromium coating applications. However, the additives are difficult to control because of their low concentration. Furthermore, the additives react and breakdown with time to form contaminants. Due to these contaminants, the used Cr(III) bath and rinse water cannot be replenished and recycled due to the “drag-in” and buildup of these contaminants. Finally, decorative Cr(III) plating still suffers from low current efficiency. 
         [0018]    Currently, functional chromium plating from a Cr(III) bath is not commercially available because of the difficulty of plating thick chromium coatings with the appropriate properties. In addition, the low current efficiency and low plating rate of Cr(III) baths lead to unfavorable economics. Due to the rapid drop in current efficiency, the practical limit for existing conventional DC Cr(III) plating is 2.5 μm (Z.-M. Tu, et al.,  Plating  &amp;  Surface Finishing,  80 (11), 79 (1993). The plating thickness increases quickly at the beginning of the electroplating process. As plating continues, the deposition rate diminishes and becomes negligible. 
         [0019]    During Cr(III) plating, chromium is deposited and hydrogen is evolved at the cathode, as described by the following reactions: 
         [0000]      Cr +3 +3 e   − →Cr(φ 0 =−0.74 V SHE )  (1) 
         [0000]      2H + +2 e   − →H 2 (φ 0 =0.0 V SHE )  (2) 
         [0020]    The current efficiency for chromium plating from a Cr(III) bath is usually below 20%. Therefore, about 80% of the current is used for the hydrogen evolution reaction. As a result, the pH near the cathode surface increases dramatically and chromic hydroxide (K sp =5.4×10 −31 ) precipitates in the high pH layer at the cathode. The sedimentation of chromic hydroxide covers the cathode surface and its thickness increases as the plating time and pH increase. This promotes an increase of cathode polarization, a further decrease of chromium plating efficiency (i.e., an increase in the hydrogen evolution reaction), and an increase of impurities in the plating film. All of these factors retard the normal growth of crystals in the plating film and lead to the prevention of further plating of chromium. The evolution of hydrogen continues as the only reaction. The precipitation of chromic hydroxide at the cathode also results in surface cracks and reduces the hardness and brightness of the chromium coating. An approach to overcoming the hydrogen evolution problem by utilizing pulsed reverse current plating has been previously described by Tamhaukar et. al. (U.S. Pat. No. 5,242,535 filed 29 Sep. 1992) and Taylor (U.S. patent application Ser. No. 08/871,599 filed 9 Jun. 1997, now abandoned). 
         [0021]    Accordingly, there is a need for a method for producing functional Cr(III) coatings which do not form continuous cracks from the coating surface through to the substrate. 
       SUMMARY 
       [0022]    In one aspect, the disclosed method for depositing a metal onto a substrate includes the steps of providing a plating bath including ions of the metal, positioning the substrate in the plating bath, positioning at least one counter electrode in the plating bath, performing a first electrolytic process for a predetermined first period of time, performing a second electrolytic process for a predetermined second period of time and looping between the first and second electrolytic processes to form a coating of the metal on the substrate. 
         [0023]    Other aspects of the disclosed method will become apparent from the following description, the accompanying drawings and the appended claims. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  illustrates a commercially available Cr(VI) deposit without continuous cracks as described in the prior art; 
           [0025]      FIG. 2  illustrates a Cr(III) deposit with continuous cracks as described in the prior art; 
           [0026]      FIG. 3A  illustrates the beginning stage of a deposit of Cr(III) according to one aspect of the disclosed method; 
           [0027]      FIG. 3B  illustrates further progression of the deposit of  FIG. 3A ; 
           [0028]      FIG. 3C  illustrates further progression of the deposit of  FIG. 3B ; 
           [0029]      FIG. 3D  illustrates further progression of the deposit of  FIG. 3C ; and 
           [0030]      FIG. 3E  illustrates the final stage of the deposit of  FIG. 3D , wherein the final Cr(III) coating deposit is formed without continuous cracks from the coating surface through to the substrate. 
       
    
    
       [0031]    The descriptions and identification of the items in the figures are tabulated in the following table: 
         [0000]    
       
         
               
               
             
           
               
                   
               
               
                 Numeral 
                 Item Description 
               
               
                   
               
             
             
               
                 100 
                 Substrate 
               
               
                 200 
                 Coating 
               
               
                 200a 
                 Initial Coating Layer 
               
               
                 200b 
                 Additional Coating Layer 
               
               
                 200c 
                 Additional Coating Layer 
               
               
                 200d 
                 Final Coating Layer 
               
               
                 302 
                 Cracks Formed to the Coating Layer Surface 
               
               
                 304 
                 Cracks Formed Within the Coating Layer 
               
               
                 306 
                 Cracks Formed to the Coating Layer Base 
               
               
                 308 
                 Cracks Formed Continuously From the Substrate through 
               
               
                   
                 the Coating Surface 
               
               
                 308a 
                 Cracks Formed Continuously From the Substrate through 
               
               
                   
                 the Coating Layer Surface 
               
               
                 308b 
                 Cracks Formed Continuously From the Prior Layer 
               
               
                   
                 through the Coating Layer Surface 
               
               
                 308c 
                 Cracks Formed Continuously From the Prior Layer 
               
               
                   
                 through the Coating Layer Surface 
               
               
                 308d 
                 Cracks Formed Continuously From the Prior Layer 
               
               
                   
                 through the Coating Layer Surface 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION 
       [0032]    The present disclosure provides a method for achieving a functional Cr(III) coating with minimal or reduced disassociated cracks. The Cr(III) coating is produced by forming layering in the deposit using a looping first electrolytic process followed by a second electrolytic process whereby said first electrolytic process and said second electrolytic process may be separated by an off-time to form disassociated cracks in the coating. The first electrolytic process may be either a direct current process, a pulse current process or a pulse reverse current process. The second electrolytic process may be either a direct current process, a pulse current process or a pulse reverse current process. The pulse current process and pulse reverse current processes are described in U.S. Pat. No. 6,203,684 to Taylor, the entire contents of which are incorporated herein by reference. 
         [0033]    The resulting coating is built up from a series of layers. This layering structure enables interruption to crack propagation to reduce the likelihood of crack propagation from the substrate through the outer coating layer surface. The greater the number of layering used to form the coating the less likely the number of cracks propagating from the substrate to the outer surface of the coating. One skilled in the art may adjust the timing of the first electrolytic process and the second electrolytic process to obtain an acceptable level of cracks propagating from the substrate to the surface of the coating without undo experimentation. 
         [0034]      FIG. 1  illustrates a commercially available Cr(VI) deposit without continuous cracks as described in the prior art. The coating ( 200 ) built up from the substrate ( 100 ) has desirable crack formation including those residing from the coating through the coating surface ( 302 ), those residing within the coating ( 304 ), and those residing from the substrate ( 100 ) into the coating ( 306 ). 
         [0035]      FIG. 2  illustrates a Cr(III) deposit with continuous cracks as described in the prior art. The coating ( 200 ) built up from the substrate ( 100 ) has desirable crack formation including those residing from the coating through the coating surface ( 302 ), those residing within the coating ( 304 ), and those residing from the substrate into the coating ( 306 ). Additionally, undesirable cracks ( 308 ) residing from the substrate ( 100 ) through the coating surface are also present. 
         [0036]      FIG. 3A  illustrates the beginning stage of the deposition method according to an aspect of the present disclosure, wherein a layer of Cr(III) is deposited. The initial layer ( 200   a ) of the coating ( 200 ) built up from the substrate ( 100 ) may have desirable crack formation including those cracks ( 302 ) residing from the layer ( 200   a ) through the layer ( 200   a ) surface, those cracks ( 304 ) residing within the layer ( 200   a ), and those cracks ( 306 ) residing from the substrate ( 100 ) into the layer ( 200   a ). Additionally, cracks ( 308   a ) residing from the substrate ( 100 ) through the layer surface ( 200   a ) may be present. 
         [0037]      FIG. 3B  illustrates further progression of the deposition of Cr(III), wherein a second layer of Cr(III) is deposited. An additional layer ( 200   b ) of the coating ( 200 ) built up from the initial layer ( 200   a ) may have desirable crack formation including those cracks ( 302 ) residing from the layer ( 200   b ) through the layer ( 200   b ) surface, those cracks ( 304 ) residing within the layer ( 200   b ), and those cracks ( 306 ) residing from the layer ( 200   a ) into the layer ( 200   b ). Additionally, cracks ( 308   b ) residing from the layer ( 200   a ) through the layer surface ( 200   b ) may be present. 
         [0038]      FIG. 3C  illustrates further progression of the deposition of Cr(III), wherein a layer of Cr(III) is deposited. An additional layer ( 200   c ) of the coating ( 200 ) built up from the prior layer ( 200   b ) built up from the initial layer ( 200   a ) has desirable crack formation including those cracks ( 302 ) residing from the layer ( 200   c ) through the layer ( 200   c ) surface, those cracks ( 304 ) residing within the layer ( 200   c ), and those cracks ( 306 ) residing from the layer ( 200   b ) into the layer ( 200   c ). Additionally, cracks ( 308   c ) residing from the layer ( 200   b ) through the layer surface ( 200   c ) may be present. 
         [0039]      FIG. 3D  illustrates further progression of the deposition of Cr(III), wherein a layer of Cr(III) is deposited. An additional layer ( 200   d ) of the coating ( 200 ) built up from the prior layer ( 200   c ) built up from the prior layer ( 200   b ) built up from the initial layer ( 200   a ) has desirable crack ( 302 ) formation including those residing from the layer ( 200   d ) through the layer ( 200   d ) surface, those cracks ( 304 ) residing within the layer ( 200   d ), and those cracks ( 306 ) residing from the layer ( 200   c ) into the layer ( 200   d ). Additionally, cracks ( 308   d ) residing from the layer ( 200   c ) through the layer surface ( 200   d ) may be present. 
         [0040]      FIG. 3E  illustrates the final stage of the deposition of Cr(III), wherein the final Cr(III) coating ( 200 ) deposit is formed without continuous cracks ( 308 ) from the substrate ( 100 ) through the coating ( 200 ) surface. Desirable crack formation including those cracks ( 302 ) residing from the coating ( 200 ) through the coating ( 200 ) surface, those cracks ( 304 ) residing within the coating ( 200 ), and those cracks ( 306 ) residing from the substrate ( 100 ) into the coating ( 200 ) are present. 
         [0041]    The disclosed method will be illustrated by the following examples, which are intended to be illustrative only and not limiting. 
       EXAMPLE 1 
     Comparative 
       [0042]    This example illustrates the use of the electric field consisting only of a first electrolytic process with Average current (I ave ) of 6.08 amps, forward time of 9.00 ms, Cathodic on-time (T c ) of 9.00 ms, Reverse time of 1.00 ms, Anodic on-time (T a ) of 0.30 ms, Anodic off-time (T off ) of 0.70 ms, Peak cathodic current (I c ) of 6.99 amps, and Peak anodic current (I a ) of 6.99 amps. Total plating time was 180 min. 
         [0043]    This example was plated using a 30 L plating bath prepared as follows:
       1. Heat 15 liters of DI water to about 71° C. (160° F.).   2. Add 490 g of Cr 2 (SO 4 )3·8.5H 2 O from Elementis Chromium in small increments.   3. Continue stirring and heating and add 300 g of (NH 4 ) 2 SO4 to the bath in small increments.   4. Continue stirring and heating and add 63 g of H 3 BO 3  to the bath in small increments.   5. Continue stirring and heating and add 180 mL of HCOOH to the bath. PH 1.6.   6. Cool below 50° C. and adjust the pH to 2.5 with KOH. 95 g of KOH used.   7. Continue stirring and add DI water to a volume of 3 liters.   8. Add 1.2 g of dodecyl sodium sulfate as a surfactant.   9. To electrolyze the solution (produce Cr 2+ ), add 0.7 g CrCl 2 .       
 
         [0053]    The coating was plated onto a rod having a diameter of about ⅜ inch and, under magnification, the coating exhibited about 280 cracks formed continuously from the substrate through the coating surface. Therefore, calculating a coating circumference of about 2.99 cm based upon the rod diameter, the coating was observed to have about 94 continuous cracks per centimeter. 
       EXAMPLE 2 
       [0054]    This example illustrates the use of the looping electric field consisting of a first electrolytic process for 7 min with Average current (I ave ) of 4.64 amps, forward time of 9.00 ms, Cathodic on-time (T c ) of 9.00 ms, Reverse time of 1.00 ms, Anodic on-time (T a ) of 0.30 ms, Anodic off-time (T off ) of 0.70 ms, Peak cathodic current (I c ) of 5.33 amps, and Peak anodic current (I a ) of 5.33 amps. The first electrolytic process followed by a second electrolytic process was followed by a direct current of 5.00 amps for 3.00 min. Total plating time was 120 min. 
         [0055]    This example was plated using a 30 L plating bath prepared as follows:
       1. Heat 15 liters of DI water to about 71° C. (160° F.).   2. Add 4900 g of Cr 2 (SO 4 )3·8.5H 2 O from Elementis Chromium in small increments.   3. Continue stirring and heating and add 3000 g of (NH 4 ) 2 SO4 to the bath in small increments.   4. Continue stirring and heating and add 630 g of H 3 BO 3  to the bath in small increments.   5. Continue stirring and heating and add 1800 mL of HCOOH to the bath. PH 1.68.   6. Cool below 50° C. and adjust the pH to  2 . 5  with KOH. 870 g of KOH used.   7. Continue stirring and add DI water to a volume of 30 liters.   8. Add 12.0 g of dodecyl sodium sulfate as a surfactant.   9. To electrolyze the solution (produce Cr 2+ ), add 7.0 g CrCl 2 .       
 
         [0065]    The coating was plated onto a rod having a diameter of about ⅜ inch and, under magnification similar to EXAMPLE 1, the coating exhibited about 50 cracks formed continuously from the substrate through the coating surface. Therefore, calculating a coating circumference of about 2.99 cm based upon the rod diameter, the coating was observed to have about 17 continuous cracks per centimeter. 
       EXAMPLE 3 
       [0066]    This example illustrates use of the looping electric field consisting of a first electrolytic process for use of the looping electric field consisting of a first electrolytic process 9 min with Average current (I ave ) of 4.64 amps, forward time of 9.00 ms, Cathodic on-time (T c ) of 9.00 ms, Reverse time of 1.00 ms, Anodic on-time (T a ) of 0.30 ms, Anodic off-time (T off ) of 0.70 ms, Peak cathodic current (I c ) of 5.33 amps, and Peak anodic current (I a ) of 5.33 amps. The first electrolytic process followed by a second electrolytic process was followed by a direct current of 5.00 amps for 3.00 min. Total plating time was 120 min. 
         [0067]    This example was plated using the same plating bath described in EXAMPLE 2. The coating was plated onto a rod having a diameter of about ⅜ inch and, under magnification similar to EXAMPLE 1, the coating exhibited about 84 cracks formed continuously from the substrate through the coating surface. Therefore, calculating a coating circumference of about 2.99 cm based upon the rod diameter, the coating was observed to have about 28 continuous cracks per centimeter. 
       EXAMPLE 4 
       [0068]    This example illustrates the use of the looping electric field consisting of a first electrolytic process for 9 min with Average current (I ave ) of 4.64 amps, forward time of 9.00 ms, Cathodic on-time (T c ) of 9.00 ms, Reverse time of 1.00 ms, Anodic on-time (T a ) of 0.30 ms, Anodic off-time (T off ) of 0.70 ms, Peak cathodic current (I c ) of 5.33 amps, and Peak anodic current (I a ) of 5.33 amps. The first electrolytic process followed by a second electrolytic process was followed by a direct current of 5.00 amps for 1.00 min. Total plating time was 120 min. 
         [0069]    This example was plated using the same plating bath described in EXAMPLE 2. The coating was plated onto a rod having a diameter of about 3/8  inch and, under magnification similar to EXAMPLE 1, the coating exhibited about 89 cracks formed continuously from the substrate through the coating surface. Therefore, calculating a coating circumference of about 2.99 cm based upon the rod diameter, the coating was observed to have about 30 continuous cracks per centimeter. 
       EXAMPLE 5 
       [0070]    This example illustrates the use of the looping electric field consisting of a first electrolytic process for 3 min with Average current (I ave ) of 4.64 amps, forward time of 9.00 ms, Cathodic on-time (T c ) of 9.00 ms, Reverse time of 1.00 ms, Anodic on-time (T a ) of 0.30 ms, Anodic off-time (T off ) of 0.70 ms, Peak cathodic current (I c ) of 5.33 amps, and Peak anodic current (I a ) of 5.33 amps. The first electrolytic process followed by a second electrolytic process was followed by a direct current of 5.00 amps for 1.00 min. Total plating time was 120 min. 
         [0071]    This example was plated using the same plating bath described in EXAMPLE 2. The coating was plated onto a rod having a diameter of about ⅜ inch and, under magnification similar to EXAMPLE 1, the coating exhibited about 74 cracks formed continuously from the substrate through the coating surface. Therefore, calculating a coating circumference of about 2.99 cm based upon the rod diameter, the coating was observed to have about 25 continuous cracks per centimeter. 
       EXAMPLE 6 
       [0072]    This example illustrates the use of the looping electric field consisting of a first electrolytic process for 2.5 min with Average current (I ave ) of 4.64 amps, forward time of 9.00 ms, Cathodic on-time (T c ) of 9.00 ms, Reverse time of 1.00 ms, Anodic on-time (T a ) of 0.30 ms, Anodic off-time (T off ) of 0.70 ms, Peak cathodic current (I c ) of 5.33 amps, and Peak anodic current (I a ) of 5.33 amps. The first electrolytic process followed by a second electrolytic process was followed by a direct current of 5.00 amps for 0.5 min. Total plating time was 120 min. 
         [0073]    This example was plated using the same plating bath described in EXAMPLE 2. The coating was plated onto a rod having a diameter of about ⅜ inch and, under magnification similar to EXAMPLE 1, the coating exhibited about 68 cracks formed continuously from the substrate through the coating surface. Therefore, calculating a coating circumference of about 2.99 cm based upon the rod diameter, the coating was observed to have about 23 continuous cracks per centimeter. 
         [0074]    All documents cited herein are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. 
         [0075]    Although various aspects of the disclosed method have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.