Why does bath alkalinity fall after a grade change?
Hydration changes the active material per unit of commercial mass. Equal addition weights need not give equal total alkalinity.
Compare rinse residue at a common alkalinity basis
Normalize to the specified Na₂O basis and run parallel trials on the same substrate with matched process conditions and rinse water. If cleaning is effective but white marks remain, measure rinse residue separately.
What causes white marks on the surface?
Check water quality, rinsing and concentration. Compare residue on the same substrate. Metal degreasing: Use the actual oil soil and steel coupons to compare degreasing efficiency and residue after rinsing. Builders for powder detergents: Compare dissolution rate, alkalinity and formulation moisture uptake.
Checking Hydration state and Total alkalinity
Hydration state (Chemical composition): Check whether the commercial product is anhydrous or hydrated, and verify its label. Total alkalinity (% by mass): Express as Na₂O on an as-received basis. Insoluble matter (% by mass): Keep water temperature, solution concentration and filtration method constant.
What to record
- Hydration state
- Na₂O basis
- Bath alkalinity
- Rinse water
- Surface residue
Technical references
Products and processes
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