Chrome

MAR TRIVALENT CHROME

MAR TRIVALENT CHROME is a new technology chromium plating process.

MAR TRIVALENT CHROME can replace conventional or proprietary hexavalent chromium based electrolytes with minor changes in processing sequence.

MAR TRIVALENT CHROME provides a lighter colour deposit than the first generation trivalent chromium processes.

MAR TRIVALENT CHROME is characterized by:

BATH COMPOSTION

OPERATING CONDITIONS

PROCESS CONTROL AND SOLUTION REPLENISHMENT

General

All constituents should be maintained within the ranges specified. Additions of all constituents should be made every 5 amp-hours/litre or each 6 hours of accumulated operation. If additions are not made on these regular bases, it will result in imbalance of the solution and the necessity to make large additions which will require additional electrolyzing to restore the bath to operating condition. Addition schedules should be established for each installation to adjust for varying amounts of drag-out. All additions should be made during, or just preceding electrolysis. The MAR TRIVALENT CHROME solution is maintained by addition of Compound A, Compound AR, Compound C, Compound WA, and control of pH, as described below. The information given should allow for near optimum performance for most installations. Occasionally, the solution should be analyzed and adjustments made to optimize the solution. Large additions of Compound A 20 g/litre or greater, Compound AR 7.5 g/litre or greater, or smaller quantities if both are added together, may unbalance the chromium complex which will requiring re-electrolysis for 30-60 minutes to avoid plating defects. To avoid re-electrolysis, these additions should be broken up and spread over twenty-four operating hours, along with the regular maintenance additions.

MAR TRIVALENT CHROME Compound A

MAR TRIVALENT CHROME Compound A is used for replenishment. It is used to maintain the conductivity which can be lost through drag-out. It also prevents the formation of hexavalent chromium. Compound A may dissolve with difficulty unless special precautions are used. Fast addition rates may result in the formation of wet lumps of additive which may not dissolve. The Compound A is preferably distributed slowly in small quantities and evenly over the surface of the solution, giving most of the material time to dissolve before further additions are made.

The concentration of Compound A should be maintained by keeping the specific gravity of the solution at a minimum value of 1.27. An addition 15 g/litre of Compound A will raise the specific gravity approximately 0.01 units. It is preferred to make this addition subsequent to any additions of Compound AR

High concentrations of Compound A may result in the formation of some crystals, especially if the solution temperature is low. The presence of crystals may result in plugged air agitation lines or coated anodes. The latter may result in reduced current. If the crystals pose a problem, the affected equipment and anodes should be removed and cleaned (scrubbed).

Low concentrations of Compound A will reduce conductivity of the bath resulting in reduced current or the need of increased voltage to maintain cathode current density.

Concentration of the Compound A can be determined by analysis provided.

MAR TRIVALENT CHROME Compound AR

MAR TRIVALENT CHROME Compound AR is used to replenish the chromium plated from the solution and is added on the basis of ampere-hours. Compound AR must be distributed slowly and evenly over the surface of the solution in the same manner as Compound A discussed above. Compound AR should be added at the rate of 340 g/1,000 ampere hours, and after at least every 6 hours of accumulated actual plating time. This additive may be controlled by a conventional analytical procedure.

MAR TRIVALENT CHROME Compound C

MAR TRIVALENT CHROME Compound C forms a stable compound with the chromium allowing it to plate out from the trivalent state. The optimum concentration should be held at 8% BV. High concentrations of Compound C may result in some precipitation of chromium salts, especially if the solution is unbalanced in other respects, such as high pH, and high temperature. Low Compound C reduces plating rate. It is important that Compound C be maintained within the range specified. Compound S is consumed by drag-out and electrolysis. It should be added at the rate of 3 litres/1,000 ampere hours until a specific consumption rate for the individual installation has been established based on solution analysis.

MAR TRIVALENT CHROME Compound S

MAR TRIVALENT CHROME Compound S functions to clear the deposit of dark smudges and provides satisfactory metal distribution. Low Compound S may result in dark smudges in the deposit and decreased chromium thickness in mid-current density areas. High concentrations are not especially harmful; however, amounts greater than 10 ml/litre may result in reduced coverage and/or hazy, white patches in the deposit. Compound S is consumed mainly by electrolysis and should be added based on an average consumption of 25-50 ml/1,000 ampere hours.

MAR TRIVALENT CHROME Compound WA

MAR TRIVALENT CHROME Compound WA is used at the time of solution make-up to provide a satisfactory metal distribution and promote a clear deposit. This additive is depleted through normal dragout. Additions of Compound WA can be controlled by surface tension analysis provided.

Low concentrations of Compound WA will decrease the thickness of the deposit on the LCD areas.

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