Dr E. Ramanathan PhD
Improvement made in this version
One of our clients complained about white powder formation after surface conditioning with the previous version.
Causes for the formation of white powder
Based on the formulation version-1 provided, there is a possibility of white powder formation, especially under certain processing or aging conditions. Here’s a breakdown of potential formulation-level causes from your ingredients:
Critical Review of Each Ingredient:
- Phosphoric Acid (30 kg)
- Role: pH adjustment, mild etching.
- Risk: High concentration (30%) may lower pH too much, causing precipitation of titanium/zirconium compounds if not properly buffered.
- Sodium Fluoride (6 kg)
- Role: Grain refinement.
- Risk: High fluoride can react with Ti/Zr compounds forming insoluble fluorotitanates/fluorozirconates, leading to white precipitate, especially at low pH.
- Titanium Fluoride or ZrOCl₂·8H₂O (1 kg)
- Role: Surface activator.
- Risk: Ti or Zr compounds are prone to hydrolysis and precipitation as white powder (e.g., TiO₂, ZrO₂), especially in acidic or hard water conditions.
- Sodium Molybdate (1.5 kg)
- Role: Corrosion inhibitor.
- Risk: Generally stable, but can salt out at high concentrations or low temperatures.
- Marlowet 5165 (1.2 kg)
- Role: Anionic wetting agent.
- Risk: May not be sufficient to fully disperse Ti/Zr colloids at this dosage; try increasing to improve dispersion.
- Deionized Water (60.3 kg)
- Positive: Use of DI water is good; rules out hard water issues.
Likely Causes of White Powder Formation:
- Fluoride–Titanium/Zirconium Interaction
TiF₄ + NaF ⇌ TiF₆²⁻ or TiO₂↓ (white) if hydrolyzed at low pH. - Low Surfactant Dosage
1.2% Marlowet may be inadequate to stabilize fine Ti/Zr particles—could lead to agglomeration and settling. - No Chelating or Buffer System
Absence of stabilizing agents like citric acid, EDTA, or organophosphonates may allow premature Ti/Zr precipitation. - No Crystal Growth Modifiers
Without modifiers, surface precipitation is less controlled, leading to uneven or visible powdery residues.
Suggestions for Formulation Improvement:
- Reduce Phosphoric Acid to ~15–20 kg
– Prevents excessive acidification and precipitation. - Optimize Sodium Fluoride Dose (~3–4 kg)
– Excess fluoride can destabilize Ti/Zr species. - Add Citric Acid (~0.5–1.0 kg)
– Acts as a buffer and chelating agent to stabilize Ti/Zr ions. - Increase Marlowet 5165 to 2.0–2.5 kg
– Improves dispersion of inorganic solids, reducing visible residues. - Consider Adding Organophosphonates (~0.2–0.5 kg)
– These control scale formation and inhibit unwanted precipitation.
Summary:
The formulation v1 may lead to white powder formation due to:
- High acidity,
- Excess fluoride,
- Insufficient surfactant or stabilizers.
Surface Conditioner Formula V2
Reformulating with proper buffering, optimized fluoride, and stabilizers (citric acid, phosphonates) can resolve the issue.
Here is the revised surface conditioner formulation with adjusted concentrations and stabilizers to minimize white powder formation:
| No | Raw Materials | Function | Revised kg |
|---|---|---|---|
| 1 | Phosphoric Acid (85%) | Acidifier, mild etching, pH control | 18.000 |
| 2 | Sodium Fluoride | Grain refiner, promotes phosphate seed | 3.000 |
| 3 | Zirconium Oxychloride (ZrOCl₂·8H₂O) or Ti Fluoride | Surface activator | 1.000 |
| 4 | Citric Acid (Mono or Anhydrous) | Chelating agent, pH buffer | 0.800 |
| 5 | Sodium Molybdate | Corrosion inhibitor | 1.500 |
| 6 | Marlowet 5165 (or equivalent) | Anionic wetting/dispersing agent | 2.000 |
| 7 | Dequest 2010 or ATMP (Organophosphonate) | Crystal growth modifier, scale inhibitor | 0.300 |
| 8 | Deionized Water | Carrier | 73.400 |
| Total | 100.000 |
Key Changes:
- Phosphoric Acid reduced from 30 kg → 18 kg to prevent over-acidification.
- Sodium Fluoride reduced from 6 kg → 3 kg to avoid excessive fluoride interaction with Ti/Zr.
- Citric Acid added for buffering and Ti/Zr stabilization.
- Surfactant (Marlowet) increased to ensure better dispersion.
- Dequest 2010/ATMP added to control unwanted precipitation of zirconium/titanium salts.
This revised formula offers better colloidal stability, minimizes white powder formation, and enhances overall surface activation for zinc phosphating.
Comparison of formula V1 and V2
The comparison of the original and revised surface conditioner formulations is shown in the table. It highlights the changes in key ingredients to reduce white powder formation and improve formulation stability.
Here is the comparison table of Version 1 vs. Version 2 of the surface conditioner formulation:
| No | Raw Materials | Function | Version 1 (kg) | Version 2 (kg) |
|---|---|---|---|---|
| 1 | Phosphoric Acid (85%) | Acidifier, etching, pH control | 30.000 | 18.000 |
| 2 | Sodium Fluoride | Grain refiner, promotes phosphate seed | 6.000 | 3.000 |
| 3 | Titanium Fluoride or Zirconium Oxychloride | Surface activator | 1.000 | 1.000 |
| 4 | Sodium Molybdate | Corrosion inhibitor | 1.500 | 1.500 |
| 5 | Marlowet 5165 | Anionic wetting/dispersing agent | 1.200 | 2.000 |
| 6 | Citric Acid | Chelating agent, pH buffer | – | 0.800 |
| 7 | Dequest 2010 or ATMP (Organophosphonate) | Crystal growth modifier, scale inhibitor | – | 0.300 |
| 8 | Deionized Water | Carrier | 60.300 | 73.400 |
| Total | 100.000 | 100.000 |
Key Enhancements in Version 2:
- Lower acid and fluoride to reduce precipitate formation.
- Added citric acid and Dequest for stability and scale control.
- Increased surfactant for better dispersion.
