ESCORT ACID ZINC PROCESS - 2000  
AMMONIUM CHLORIDE BASE

This  is  a  low cost bright acid zinc plating  bath  offering  good brightness,  leveling  and ductile deposit with  good  tolerance  to impurities  with  two components of brightner and carrier.  It  also offer  good  acceptance  to chromate film, only  difference  to  the potassium  chloride  bath  is the temperature  as  it  require  good cooling  /  refrigeration system to avoid large consumption  of  the brightner and carrier.  

Bath make up  :                   (for barrel plating)  

Acid zinc liquid 241 a             :     120 ml./ltr.

Ammonium chloride               :     120 gms./ltr.

Acid zinc carrier 2080-m         :     50 ml/ltr.

Acid zinc brightner 2080-r        :     1 ml./ltr.

Operating conditions  :-  

Ph                                        :     5.0 - 5.8

Operating temperature            :     25* c

Cathode efficiency                  :     95%

Voltage                                  :     2 - 8 volts

Working current density           :     0.5 - 5 amp/dm.sq.

Anodes                                   :     pure 99.99% zinc slab with titanium hooks.

Anode area                             :     1 : 1 anode to cathode

Anode bags                            :     p.p. bags required

Tank                                      :     p.p. lined m.s.tank

Filtration                                 :     continuous

Cooling                                   :     refrigeration must

Cooling coils                           :     titanium preferably.

Agitation                                 :     required  for  rack  only.

                                       cathode  rod 3m/min.

Ventilation                              :     optional but advised.

Bath maintenance  :-       for barrel     optimum    

Zinc metal gm./ltr.             25 - 40         30

Total chloride gm./ltr.         100 - 115      110  

Control of bath    :-

Zinc  metal         :   

Zinc content is normally maintained from  the anodes  which should be increase or  decrease as   required  by the  result  of   period analysis  large  additions  can  be  made  by addition of acid zinc liquid 241-a,100 ml. Of 241-a will give 25 gms. Zinc metal.  

Chloride Ion       :  

The chloride ion is maintained by the addition  of  ammonium  chloride which  contain   66.7%  chloride. Extra pure grade ammonium  chloride should    be    use    otherwise     metallic contamination may generate.   

Preparation of bath   :-  

This  electrolyte used highly soluble salts which  are  readily dissolved to make up the plating bath as follows :  

1)   fill the tank apprx. 2/3 full of hot tap water, a  new  plating

     tank  should  be clean and leached with  2%  hydrochloric  acid

     preferably overnight prior to use.  

2)   add recommended amount of acid zinc liquid 241-a stir well.  

3)   add recommended amount of extra pure ammonium chloride and  stir

     until  dissolved.  Ammonium  chloride  cools  the  baths  as  itdissolves.

4)   add the correct amount of carrier 2080-m and brightner 2080-r.  

5)   add the anodes to the bath, bring to final operating volume  and

     check and adjust bath temperature.  

6)   check the ph of  bath  with a ph meter and adjust if  necessary

     with  ammonium hydroxide. Since the ph of a freshly  made  bath

     will generally be on the low side. 

7)   filter if necessary to remove any suspended material.  

8)   start plating.  

Function  of  components in ammonium chloride  bright  acid  zinc

Plating bath  :

Zinc  metal   :   the effect of zinc metal concentration  in  the bright ammonium chloride bath are as follows:  

Raising the zinc metal content will  :-  

1)  increase the maximum allowable current density.  

2)  decrease burning and or granular deposits.  

3)  improve covering power.  

4)  decrease throwing power ( uniformity of deposit thickness).  

5)  increase drag-out costs.  

6)  increase waste treatment costs.  

Lowering  the  zinc metal content will of course have  the  opposite effect.  Based on the above conditions, a higher zinc metal  content is  normally  employed  in rack plating to meet  be  higher  current density  requirement  and a lower concentration is  used  in  barrel baths,  where  drag-out and uniform plate  thickness  are  important factors.  

The  zinc  metal  content of an acid bath should  be  maintained  by keeping  and  adequate anode area in the bath.   Zinc  anodes  don't dissolve in bright acid ammonium chloride zinc bath during  standing and there is no problem in leaving the anodes in the bath  overnight and during week ends. If titanium anode basket are used they  should always  be  kept  as full as possible or the bath  will  attack  the titanium  anodicaly  and destroy the baskets in a period  of  weeks. Baskets should be kept at least half full at all times. With  proper maintenance of the bath anode area no additions of acid zinc  liquid 241-a should be required for an operating bath unless a catastrophic accidental solution loss occurs.

Chloride Ion  :-

The  chloride  ion provides the conductivity for the acid  bath.  It should  be maintain as close as possible to the optimum  recommended value for the particular process uses. 

A low chloride content  :-  

1)  reduces bath conductivity.  

2)  causes hazy or dull deposits at low current densities.  

3)  reduces coverage at low current densities.  

4)  reduces anode corrosion.  

5)  reduces plating rate.

A high chloride content  :-  

1)  increase bath conductivity.

2)  increase high current density burning.  

3)  lowers  cloud point of the bath causing it to be  cloudy  at

    high temperature.

4)  increases drag-out and operating costs.

5)  may cause oiling out of brightness.  

The  main  source of chloride ion in these baths  is  from  ammonium chloride maintenance additions. Initially some chloride is introduce from the acid zinc liquid 241-a. To raise the zinc metal content 1.0 gm/ltr.  Addition of acid zinc liquid 241-a required  4.0   ml./ltr.this also raises the chloride ion content by 1.08 gm./ltr.  

For  practical  purposes it is sufficient to remember to  raise  the chloride  contents  1.0 gm./ltr. Require 1.5  gm./ltr.  Of  ammonium chloride and each ml./ltr. Of acid zinc liquid 241-a added generates 0.27 gm./ltr. Of chloride in the bath. 

Operating temperature  :-

* Raising the operating temperature  :-  

1)  increases hazy or dull deposits at low current densities.  

2)  increase brightner consumption.  

3)  increase the tendency of the brightner to cloud out of solution.  

4)  reduces drag-out and promotes better rinsing.  

* Lowering the operating temperature  :-

1)  increase the tendency for high current density burning.  

2)  causes oiling out of the brightners usually  at  temperature

    below 13*c.  

3)  reduces the plating rate and covering power.  

Ph  :

There is very little variation in the recommended operating ph value of  ammonium  chloride  bright acid zinc  process-2000.  Bath  would function  quite  well in range of 5.0 - 5.8 within this  optimum  ph range.  The  effects of ph variation are relatively minor  but  will vary the bath operating characteristics as follows  :  

*  low ph within recommended range  :-

1)  increases levelling  

2)  increases brightness in low current densities.  

3)  increases ductility of deposits.  

4)  increases throwing power.  

* Higher ph values within recommended range  :-  

1)  improves covering power.  

2)  improves cathode efficiency  

* Low ph value below approximately 5.0  :-  

1)  increase tendency to burn at high current densities.  

2)  can precipitate brightner from bath.  

3)  can cause white patchy deposits.  

4)  cause streaking and or pitting at high current densities.  

5)  lower plating speed.  

* High ph value above approximately 5.9  :-  

1)  will precipitate brightners out of bath.  

2)  cause rough deposits.  

3)  give poor low current density coverage.  

4)  cause dull or hazy low current densities.  

5)  cause a drop in zinc metal content.  

During  plating in an acid zinc bath the anode efficiency is  almost always greater than the cathode efficiency which means that hydrogen ions are neutralized during plating causing a drop in acidity and  a slow  but  steady rise in the ph. Ph measurement should  made  on  a daily or twice daily basis and hydrochloric acid added to reduce the ph to the operating range. Additions of ammonium hydroxide to  raise the  ph are almost never necessary except incase where overdoses  of hydrochloric acid have been made in error.

The amount of hydrochloric acid required to adjust a given operating acid  zinc  line  should stay relatively the same from  day  to  day unless  there is some abnormally variation in production. If the  ph fluctuates abnormally  under  usual  production  conditions  it  is usually and indication that the anode area is low and this should be corrected.  

Addition agents  : function  of  acid  zinc  brightner - 2080 r  and Acid zinc carrier 2080 - m.   

* Low maintenance brightner - 2080 r produces  :-  

1)  dull deposits at low current densities.  

2)  reduced coverage at low current densities.  

3)  an overall haze on work.  

*  High maintenance brightner - 2080 r produces :-  

1)  streaking or pitting especially at high current densities.  

2)  whitish spots or oiling out of brightner.  

3)  missed plating or no plate at very low current densities.  

* How carrier 2080-m causes  :-  

1)  increased high current density burning.  

2)  dull or hazy low current densities.  

3)  dull over-all haze.  

4)  oiling out of brightner. 

5)  reduction of cloud point of bath. 

6)  pitting or streaking at high current densities.  

* High carrier  2080-m causes  :-  

1)  dull deposits or over-all hazes

2)  excessive foaming.  

Ammonia base acid zinc chloride bath operate with 3 to 5% acid  zinc carrier 2080-m. Addition agents for ammonium chloride acid zinc bath normally check by daily or weekly hull cell test.  

Effluent treatment  :-  

Detoxification  of excort acid zinc process - 2000 solution is  very simply, as compare to cyanide zinc process. Collect the waste  water in  a  container, neutralised it to a ph 7.5 to 8.5  by  adding  25% solution of caustic soda with enough stirring. This will precipitate the  zinc as hydroxide sludge which can be removed by  filtering  the solution  or  by  allowing the sludge to settle  and  decanting  the solution.  Local  regulations regarding sludge  disposal  should  be followed  or it should be sold to zinc recovery plant. Clear  liquid can be discharged into a sewage system, assuring there are no  other pollutants present.  

Note    : 

Our recommendations are made in goods faith and based  on our  skill and experience. However, since the  conditions of  use  of these products are beyond  our  control  this information  is  given  on  the  express  condition   and agreement that "mahavir expochem ltd." will not be liable to  any person by reason thereof. Nothing here  in  shall deemed  to  be a recommendation to use  any  products  in violation of any existing patent rights.