Introduction
1) Scope & Outcome
- System: Room-temperature trication zinc phosphate (Zn–Mn–Ni) for ferrous substrates (CR/HR steel; compatible with GI/GA with fluoride).
- Target film: Fine-grained grey phosphate, 1.5–3.0 g/m².
- Typical line: Clean → Rinse → Activate → Phosphate (25–40 °C) → Rinse → Non-chrome passivate → Dry → Paint.
2) Concentrate — Manufacturing Formula
Lab Batch Ticket ID 190863 for Trication Phosphate chemical concentrate – click here
Manufacturing notes
- Charge ~50% water → add H₃PO₄ slowly with cooling.
- Slurry ZnO, MnCO₃, Ni salt separately; add under agitation to clear solution.
- Dissolve NaNO₃, then fluoride; add surfactant + dispersant; QS with water; 10 µm filtration.
- Sodium nitrite can be supplied as a separate pack.
3) Working Bath Make-Up (per 1,000 L)
| Target working bath | Range |
|---|---|
| Temperature | 25–40 °C |
| Total Acid (TA) | 22–28 points |
| Free Acid (FA) | 1.0–1.5 points |
| FA/TA | 1:15 to 1:25 |
| Zinc (as Zn²⁺) | 0.6–1.0 g/L |
| Manganese (as Mn²⁺) | 0.25–0.45 g/L |
| Nickel (as Ni²⁺) | 0.12–0.25 g/L |
| Nitrate (as NO₃⁻) | 1.5–3.0 g/L |
| Fluoride (free F⁻) | 50–150 mg/L |
| Immersion time | 3–10 min (spray: 60–180 s) |
Charge recipe (example to mid-spec):
- Deionized water: 800 L
- Concentrate: 120 kg (yields ~TA 24–26 points in most systems)
- Replenisher: hold (see §6)
- Top up DI water to 1,000 L, mix, heat only if <25 °C, then qualify by titration and adjust.
4) Process Sequence & Set-Points
- Alkaline Cleaner: 2–5% @ 55–65 °C, 3–5 min → Rinse.
- Acid Pickle (HR/rust only): 8–12% HCl @ RT, 1–3 min → Rinse.
- Activation: Ti-based, 0.5–1.0 g/L, pH 8.5–9.5, 25–35 °C, 30–60 s, gentle agitation.
- Cold Trication Phosphating: as §3.
- Water Rinse: overflow, conductivity <200 µS/cm.
- Non-chrome Passivation: Zr/Ti-fluoro complex, 50–200 mg/L metal, pH 3.8–4.6, 20–40 s.
- Drying: 90–120 °C metal temperature, 5–10 min; avoid flash rust.
5) Analytical Control (Daily)
5.1 Free Acid (FA) — points
- Pipette 10 mL bath + 50 mL DI → titrate with 0.1 N NaOH to pH 3.6 (or bromophenol blue end).
- FA (points) = mL NaOH × N × 10 / 1.0 (for 10 mL aliquot with 0.1 N, FA = mL × 1.0).
5.2 Total Acid (TA) — points
- Continue same flask to pH 8.2 (phenolphthalein).
- TA (points) = total mL NaOH to pH 8.2 × N × 10.
- FA/TA must be in band; adjust with concentrate (↑TA & metals) or NaOH (↓FA & TA).
5.3 Metals (spot or EDTA)
- Zn²⁺: Zincon spectro/complexometric; target 0.6–1.0 g/L.
- Mn²⁺: Periodate or formaldoxime spectro; target 0.25–0.45 g/L.
- Ni²⁺: Dimethylglyoxime/spectro; target 0.12–0.25 g/L.
5.4 Nitrate (accelerator)
- Ion-selective or spectro (UV): 1.5–3.0 g/L. If low → add Accelerator A.
5.5 Fluoride
- ISE or SPADNS: 50–150 mg/L free F⁻. Add Fluoride Additive if <50 mg/L (especially for GI/GA).
5.6 Coating Weight
- Degrease a treated coupon → strip phosphate in 10% CrO₃ + 1% H₃PO₄ (or 10% diammonium persulfate) 2 min → dry and weigh.
- Target 1.5–3.0 g/m² (immersion). Spray: 1.2–2.0 g/m².
6) Replenishment Rules
Define:
- C = concentrate addition (kg/1000 L)
- R = replenisher (metals-rich, low acid) addition (kg/1000 L)
Typical actions:
- FA low (<1.0) & TA low: Add C: ~3–5 kg/1000 L, recheck FA/TA.
- FA high (>1.5) & TA ok: Add R 2–4 kg/1000 L plus small NaOH to pull ratio into band.
- Nitrate low (<1.5 g/L): Add Accelerator A: 0.1 kg/1000 L increments.
- Fluoride low (<50 mg/L): Add Fluoride Additive: 0.05 kg/1000 L increments.
- Metals low (Zn/Mn/Ni): Add R 2–6 kg/1000 L; verify after 20 min circulation.
Rule-of-thumb starter:
- 1 kg C in 1000 L raises TA ~0.2–0.3 points (plant-specific; calibrate during first week).
- 1 kg R in 1000 L raises Zn by ~0.02–0.04 g/L (vendor-specific).
7) Activation & Passivation — Ready-Refs
7.1 Activator (Ti-based), 1,000 L
- DI water 800 L → Add Activator powder 0.75 kg → Stir 15 min → pH 8.8–9.2 (NH₄OH) → QS to 1000 L.
- Conductivity: 1.2–2.5 mS/cm. Refresh 1–2×/shift bleed-feed.
7.2 Non-chrome Sealer (Zr), 1,000 L
- DI water 900 L → Add Zr concentrate to 100 mg/L Zr → Adjust pH 4.2 (HNO₃) → QS.
- Rinse-free if drag-out low; otherwise quick DI spray.
8) Troubleshooting
| Symptom | Likely Cause | Corrective Action |
|---|---|---|
| Low coating weight | Low TA/metals; weak activation; low nitrate | Add C/R; refresh activator; add Accelerator A; increase time to spec |
| Coarse, powdery film | High FA/TA; low accelerator; oily surface | Reduce FA/TA (add R, small NaOH); boost accelerator; improve cleaning |
| Bare spots | Poor wetting; low F⁻; high carry-over | Add surfactant; correct F⁻; improve rinses; maintain overflow |
| Black smut | Over-pickling HR; high iron in bath | Shorten pickle; decant/bleed 5–10%; increase filtration |
| Paint adhesion poor | Skipped passivation; high sludge | Normalize passivation; desludge; verify coating weight |
9) Sludge & Bath Housekeeping
- Continuous side-stream filtration (50–100 µm) + weekly cartridge 10 µm.
- Desludge cone-bottom sumps every 2–4 weeks.
- Maintain Fe²⁺ in bath by periodic bleed-feed (1–3%/week) on heavy HR loads.
10) QA Benchmarks
- Salt spray (ASTM B117) over epoxy-polyester powder: ≥480 h to 3 mm creep (with Zr passivation).
- Cross-hatch adhesion (ISO 2409): Class 0–1 after 24 h cure.
- Humidity (ASTM D2247): ≥500 h no blistering (F to M, size ≤8).
11) Safety, Handling, CAS (reference)
| Material | CAS |
|---|---|
| Phosphoric acid | 7664-38-2 |
| Zinc oxide | 1314-13-2 |
| Zinc carbonate (basic) | 5263-02-5 |
| Manganese carbonate | 598-62-9 |
| Nickel sulfate hexahydrate | 10101-97-0 |
| Sodium nitrate | 7631-99-4 |
| Sodium nitrite | 7632-00-0 |
| Sodium fluoride | 7681-49-4 |
| Polyacrylate dispersant (generic) | 9003-01-4 |
PPE: Acid-resistant gloves/apron, goggles/face shield, local exhaust. Nickel is sensitizing—implement exposure monitoring. Neutralize effluent; separate fluoride-bearing streams if required by local norms.
12) Example Daily Control Sheet (snapshot)
- FA: 1.2 pt | TA: 24.5 pt | FA/TA: 1:20
- Zn: 0.78 g/L | Mn: 0.32 g/L | Ni: 0.16 g/L
- NO₃⁻: 2.1 g/L | F⁻: 90 mg/L
- Coat wt: 2.2 g/m² (immersion 6 min) → OK
13) Consumables Summary (per 10,000 m² steel/month, typical)
- Concentrate: 85–110 kg
- Replenisher: 60–90 kg
- Accelerator A: 5–10 kg
- Fluoride Additive: 1–3 kg
- Activator: 2–4 kg
- Zr Sealer: 3–6 kg (as 100% basis)
Decision Matrix — Cold vs Hot Phosphating
| Criteria | Cold Phosphating (Room Temp) | Hot Phosphating (Conventional) |
|---|---|---|
| Plant Size / Investment | ✔ Best for small/medium workshops with limited infrastructure | ✖ Requires large-scale automated lines with heating & sludge handling |
| Energy Consumption | ✔ No heating → low operating cost | ✖ High energy usage → higher opex |
| Corrosion Resistance | ✖ Low–moderate (needs paint topcoat, short-term storage protection only) | ✔ High corrosion protection (with paint/oil, suitable for long-life products) |
| Film Thickness & Strength | Thin film; adequate as paint base | Thicker crystalline film; stronger, more durable |
| Sludge Generation | Low → simpler maintenance | High → needs regular desludging & filtration |
| Line Speed / Productivity | ✔ Faster adaptation, suitable for manual / semi-auto lines | ✔ Ideal for continuous production, high-volume automotive |
| Applications (Best Fit) | – Touch-up kits, aerosol sprays |
- Motorbike spares, bolts, nuts
- Workshops with low throughput
- Maintenance jobs | – Automotive OEM (cars, trucks)
- Appliances (refrigerators, washing machines)
- Defense equipment, aerospace ground hardware
- Heavy machinery & construction equipment |
| Surface Compatibility | Steel; requires fluoride additive for galvanized/aluminum | Works on steel, galvanized steel, aluminum, cast iron (with activators/fluorides) |
| Paint Adhesion | ✔ Sufficient for light-duty coatings | ✔ Excellent adhesion for powder coating, e-coat, liquid paints |
| Lifecycle Cost | ✔ Lower initial + running cost; good for job coaters | Higher cost but justified in OEM production & warranty parts |
Guidance:
- Choose Cold Phosphating if:
- You are running a low-to-medium production scale,
- Energy saving is critical,
- Coating is only a paint base and not expected to provide standalone corrosion resistance.
- Choose Hot Phosphating if:
- You need OEM-level durability and long warranty corrosion performance,
- Your line is high-volume with continuous production,
- Customers demand compliance with automotive / appliance standards (e.g., 480–1000 h salt spray).
