Final Report: A Cost-Competitive Functional Trivalent Chromium Plating Process To Replace Hexavalent Chromium Plating

EPA Contract Number: 68D99048
Title: A Cost-Competitive Functional Trivalent Chromium Plating Process To Replace Hexavalent Chromium Plating
Investigators: Renz, Robert P.
Small Business: Faraday Technology, Inc.
EPA Contact: Manager, SBIR Program
Phase: I
Project Period: September 1, 1999 through March 1, 2000
Project Amount: $69,873
RFA: Small Business Innovation Research (SBIR) - Phase I (1999) RFA Text |  Recipients Lists
Research Category: SBIR - Pollution Prevention , Pollution Prevention/Sustainable Development , Small Business Innovation Research (SBIR)

Description:

The research objectives of this program were to demonstrate the reduced-cost, performance-based technical and economic feasibility of the proposed cost-competitive functional trivalent chromium plating process to replace hexavalent chromium plating. Specifically, the Phase I program addressed the following questions:
  1. Can an appropriate CM-ECD waveform be "fine-tuned" to the proposed reduced-cost trivalent chromium plating chemistry?

  2. Can our cost-competitive functional trivalent chromium plating process achieve the technical parameters of 1) plating thickness, 2) plating rate, 3) hardness, and current efficiency equivalent to or greater than commercially available hexavalent chromium plating processes?

  3. Is our cost-competitive functional trivalent chromium plating process economically viable, as compared to currently available hexavalent chromium plating processes?

    Summary/Accomplishments (Outputs/Outcomes):

    Overall Plating Results Table 1 summarizes the appearance, chromium thickness, plating rate, and plating efficiency results for each set of tests. For comparison, data from standard hexavalent chromium plating processes is included in the table. The optimum result from the Taguchi #3 set of experiments gives a plating efficiency and rate (29.7% and 135 µm/hour, respectively) better than typically seen for a hexavalent chromium plating process (24% and 80 µm/hour, respectively), and produces a shiny deposit.

    Table 1: Overall Results from the 3 Taguchi Arrays of Plating Experiments

      CM-ECD Trivalent Chromium Plating Process Hexalavent Chromium Plating Process
     
    Taguchi #1
    Taguchi #2
    Taguchi #3
    Rod
    Conditions
    Copper/Dull
    Copper/Polished
    Steel/Hardened & Ground
    Steel/Hardened & Ground
     
    Range
    Best
    Range
    Best
    Range
    Best
    Appearance
    Black to Shiny
    Shiny
    Black to Shiny
    Shiny
    Dull to Shiny
    Shiny
    Shiny
    Chromium
    Thickness
    (µm)
    3.1 - 28
    19.9
    0 - 19.8
    15.5
    2.5 - 35.0
    20.3
    -
    Plating
    Efficiency
    (%)
    4.6 - 41
    29.1
    0 - 28.9
    22.7
    3.7 - 51.3
    29.7
    ~24
    Plating
    Rate
    (µm/hr)
    20.8 - 121.7
    53
    0 - 123.3
    41.3
    10 - 466.7
    135
    ~80

    Hardness Tests

    Three rods were selected for hardness tests; the results are given in Table 2. They were Rod #34, Rod #35, and a rod plated in a hexavalent chromium plating solution labeled D1. The data shows that hardness values were comparable for all of the rods, indicating that the CM-ECD trivalent chromium plating process gave equivalent coating hardness to both a hexavalent chromium plating process and a DC trivalent chromium plating process.

    Table 2: Hardness Tests

     
    Rod #34
    Rod #35
    Rod D1
    HV/100
    792
    766
    783
    HV/100
    750
    783
    766
    HV/100
    775
    783
    766
    Average
    772
    777
    772

    Based on the above results, further rods were plated for hardness tests, but the CM-ECD frequency was reduced. Table 3 gives the hardness results for Rod #42 and Rod #43 which were plated at a higher frequency than Rod #35. Rod #44 was plated under DC conditions.

    Table 3: Hardness Tests

     
    Rod #42
    Rod #43
    Rod 44
    HV/100 870 830 830
    HV/100 900 805 830
    HV/100 850 780 816
    Average 873 805 825

    The data for the second group of rods (42, 43, and 44) show increased hardness values of the first group (Table 2), but again, comparable hardness values across the group. It is difficult draw any definite conclusions as to why the all of the hardnesses were higher in the second group since they were performed by the same person under the same conditions on the same equipment. One possible explanation would be that the second group were plated with a new trichromium sulfate bath.

    Trivalent Chromium Chemistry Cost Comparison

    The figures below reflect the replacement chemistry costs associated with replenishing the plating bath after plating the desired chromium amount. Our selected Cr2(SO4)3*7.5H2O (commercially available Cr+3 bath) at $5.33 per pound of chromium is on the order of the comparable CrO3 (commercially available Cr+6 bath) at $4.81 per pound of chromium. Therefore, chemistry cost is very similar to that associated with hexavalent chromium plating.

    Conclusions:

    The research objectives of this program were to demonstrate the reduced-cost, performance-based technical and economic feasibility of the proposed cost-competitive functional trivalent chromium plating process to replace hexavalent chromium plating. The technical data (summarized in Table 4) indicate equivalent or superior: 1) plating rate, 2) hardness, and 3) current efficiency compared to current functional hexavalent chromium plating processes. In addition, the costs associated with our CM-ECD Cr+3 functional trivalent chromium plating process and conventional hexavalent chromium plating processes for functional applications are comparable. Table 4 provides our datat comparison.

    Table 4: Data Comparison of a Current Cr+6 Process and Faraday's CM-ECD Cr+3 Process

    Current
    Cr+6
    Process
    Faraday
    Cr+3
    Process
    Plating
    Rate µm/hr
    80 135
    Hardness
    (Vickers)
    777 772
    Current
    Efficiency
    24% 30%

    Therefore, the results have demonstrated the feasibility of depositing chromium from a low-cost chromium sulfate bath, and addressed the program research objectives:

    1. Can an appropriate CM-ECD waveform be "fine-tuned" to the proposed reduced-cost trivalent chromium plating chemistry?

    The CM-ECD parameters of average current density and frequency were investigated as to their effect on plating from a low-cost trivalent chromium sulfate plating chemistry. In addition, the rotation rate of the rods and the temperature of the bath was also optimized. In general, a higher rotation rate was preferred to achieve a higher plating rate and efficiency. The chromium thickness increased with increasing current density and temperature. Better results were obtained at lower frequencies.

    Therefore, the objective of tuning a CM-ECD waveform to the low-cost trivalent chromium plating chemistry was successfully achieved.

    2. Can the proposed cost-competitive functional trivalent chromium plating process achieve the technical parameters of 1) plating thickness, 2) plating rate, 3) hardness, and current efficiency equivalent to or greater than commercially available hexavalent chromium plating processes?

    Although a wide range of values were obtained for 1) plating thickness, 2) plating rate, 3) hardness, and current efficiency by plating from a chromium sulfate (Cr+3) bath. In many cases, these values exceeded those obtained using commercially available hexavalent chromium plating processes.

    In particular, the optimum result for chromium plating onto hardened and ground steel rods showed a plating efficiency and rate (29.7% and 135 µm/hour, respectively) for the trivalent chromium plating process, better than typically seen for a hexavalent chromium plating process (24% and 80 µm/hour, respectively), as well as producing a shiny deposit.

    Additionally, Vickers hardness measurements showed comparable hardness values for trivalent and hexavalent chromium plating processes.

    Therefore, the proposed cost-competitive functional trivalent chromium plating process succeeded in achieving the technical parameters of 1) plating thickness, 2) plating rate, 3) hardness, and current efficiency equivalent to or greater than commercially available hexavalent chromium plating processes.

    3. Is the proposed cost-competitive functional trivalent chromium plating process economically viable, as compared to currently available hexavalent chromium plating processes?

    As reflected above, the chemistry cost for our selected Cr2(SO4)3*7.5H2O (commercially available Cr+3 bath) at $5.33 per pound of chromium is on the order of the CrO3 (commercially available Cr+6 bath) at $4.81 per pound of chromium. Therefore, chemistry cost is very similar to that associated with hexavalent chromium plating.

    Also as reflected in our Phase I Final Report, costs associated with 1) waste treatment, 2) ventilation, and 3) power consumption are substantially lower for our CM-ECD Cr+3 functional chromium plating process as compared to conventional hexavalent Cr+6 commercial processes. NOTE: The data to support these cost comparisons were obtained from one of our proposed Phase II partner's actual plant calculations and are deemed to be confidential and proprietary.

    Therefore, the CM-ECD Cr+3 process for functional applications is cost-competitive when compared to currently available hexavalent chromium plating processes.

    Journal Articles:

    No journal articles submitted with this report: View all 2 publications for this project

    Supplemental Keywords:

    Economic, Social, & Behavioral Science Research Program, Scientific Discipline, Toxics, Waste, Water, Sustainable Industry/Business, hexavalent chromium, National Recommended Water Quality, Chemistry, Technology for Sustainable Environment, New/Innovative technologies, Engineering, 33/50, Engineering, Chemistry, & Physics, Economics & Decision Making, cost reduction, chromium & chromium compounds, pollution standards, Chromium, electroplating, pollution prevention, cost effectiveness, chromium electroplating baths

    SBIR Phase II:

    A Cost-Competitive Functional Trivalent Chromium Plating Process To Replace Hexavalent Chromium Plating  | Final Report