Dr E. Ramanathan PhD | Nanocoating Consultant
3-in-1 Concentrate Formulation (100 kg batch)
| Ingredient | Function | Qty (kg) |
|---|---|---|
| Phosphoric acid 75–80% | Acid source, phosphate coating | 14.0 |
| Sodium nitrate | Accelerator | 2.0 |
| Sodium hexametaphosphate | Chelant / hardness control | 1.0 |
| Sodium gluconate | Chelant / rust removal aid | 1.5 |
| C9–11 Alcohol Ethoxylate (7 EO) | Nonionic surfactant, wetting/emulsification | 3.0 |
| Low-foam EO/PO capped nonionic | Foam control surfactant | 0.8 |
| Coco-betaine (30%) | Amphoteric surfactant, wetting/soil lift | 1.5 |
| Phosphate-ester inhibitor (amine neutralized) | Flash-rust prevention | 0.5 |
| DPnB (Dipropylene glycol n-butyl ether) | Solvent for oily soils | 5.0 |
| Defoamer (silicone/mineral oil) | Foam control | 0.08 |
| Biocide (CMIT/MIT or BIT) | Bath preservation | 0.08 |
| Deionized/RO water | Balance | make up to 100 |
Appearance: Clear to slightly hazy liquid
Shelf life: 6–12 months sealed in HDPE drums
Working dilution: 3–5% v/v in industrial water
Step-by-Step Lab QC Testing SOP
For Three-in-One Cleaning & Phosphating Concentrate (100 kg batch)
This SOP ensures batch consistency, performance, and suitability before release.
1. Sample Collection
- Collect 250 mL representative sample in a clean, dry, HDPE bottle.
- Allow solution to cool to room temperature before testing.
2. Tests on Concentrate
(a) Appearance
- Visual check: clear to slight haze, no phase separation, no heavy sediment.
(b) Specific Gravity
- Use hydrometer or density cup at 30 °C.
- Expected: 1.10 – 1.15
(c) pH of 5% Solution
- Dilute 5 mL sample into 95 mL DI water.
- Measure with calibrated pH meter.
- Expected: 1.5 – 3.0
3. Tests on Working Bath (3–5% v/v)
(a) Free Acid (FA) Points
- Pipette 10 mL bath sample into a beaker.
- Add 50 mL DI water.
- Add 3–4 drops bromophenol blue indicator.
- Titrate with 0.1 N NaOH until color changes from yellow → blue-green.
- Calculation: FA (points)=mL NaOH used×1\text{FA (points)} = \text{mL NaOH used} \times 1
- Control Range: 10 – 15 points
(b) Total Acid (TA) Points
- Continue same titration with phenolphthalein indicator.
- End point = colorless → pink.
- Record total mL NaOH used.
- Calculation: TA (points)=mL NaOH total×1\text{TA (points)} = \text{mL NaOH total} \times 1
- Control Range: 30 – 50 points
- TA/FA ratio: 3–5 (optimum coating).
(c) Nitrate Accelerator
- Use spot test (dip KMnO₄-starch test paper in diluted sample).
- Purple/violet color confirms nitrate presence.
- For quantitative check: use ion-selective electrode or ion chromatography (optional).
(d) Coating Weight (on Test Panels)
- Prepare mild steel panels (50 × 100 mm), polish with emery, degrease with acetone.
- Treat panels in 3–5% bath at 25–40 °C for 3 minutes.
- Dry, weigh panel accurately (W1).
- Strip phosphate in boiling chromic acid solution (20 g/L CrO₃ + 50 mL/L H₃PO₄) for 5 min.
- Rinse, dry, reweigh (W2).
- Coating Weight: (W1–W2)×104/area in cm² (g/m2)(W1 – W2) \times 10^4 / \text{area in cm²} \; (g/m²)
- Expected: 0.2 – 1.0 g/m² (light phosphate suitable for painting).
(e) Water-Break Test
- After treatment and drying, flood panel with DI water.
- Pass: continuous water film, no break spots.
- Fail: beading → bath contamination or low acidity.
4. Acceptance Criteria
- Concentrate specific gravity: 1.10–1.15
- pH (5% dilution): 1.5–3.0
- FA: 10–15 points
- TA/FA: 3–5
- Coating weight: 0.2–1.0 g/m²
- Water-break free surface
5. Bath Maintenance
- Check FA & TA once per shift.
- If FA < 10 points → add concentrate.
- If oil/grease > 2 g/L → dump & recharge.
- Maintain bath temp 25–40 °C.
Three-in-One Cleaner & Phosphating Solution – QC Test Report
Batch No.: ___________ Date: ___________ Tested By: ___________
1. Concentrate Tests
| Parameter | Method | Spec. Range | Observed | Pass/Fail | Remarks |
|---|---|---|---|---|---|
| Appearance | Visual | Clear to slight haze, no separation | |||
| Specific Gravity @30 °C | Hydrometer / Density cup | 1.10 – 1.15 | |||
| pH (5% solution) | pH meter | 1.5 – 3.0 |
2. Working Bath Tests (3–5% v/v)
| Parameter | Method | Spec. Range | Observed | Pass/Fail | Remarks |
|---|---|---|---|---|---|
| Free Acid (FA, points) | Titration with 0.1 N NaOH, BPB indicator | 10 – 15 | |||
| Total Acid (TA, points) | Titration with 0.1 N NaOH, phenolphthalein | 30 – 50 | |||
| TA/FA Ratio | Calculation | 3 – 5 | |||
| Nitrate Presence | KMnO₄–starch test paper (spot test) | Positive (violet) | |||
| Coating Weight (g/m²) | Gravimetric, CrO₃/H₃PO₄ strip | 0.2 – 1.0 | |||
| Water-Break Test | DI water film | Continuous film |
3. Acceptance Summary
- Batch Status: ☐ Approved ☐ Rejected
- Remarks: _______________________________________________________
QC Analyst: ____________________ Signature: ______________
