Sodium Hydroxide

Product Overview

Sodium Hydroxide (NaOH) - caustic soda - is the strongest everyday alkali in the finishing shop and the electrolyte backbone of alkaline zincate zinc plating. As white flakes or pearls it dissolves with strong heat release into the 100-140 g/L caustic solutions that hold zincate zinc in solution, and at lower levels it is the working alkali of soak cleaners, electrocleaners and aluminum etching tanks. In QLQ's finishing plants caustic soda runs the alkaline zinc lines on steel hardware, builds the cleaner stages ahead of the nickel-chrome decoration lines, and neutralizes the acid waste streams. Two commercial forms dominate: flake ≥ 99% and pearl; for plating the relevant impurities are iron, chloride and carbonate, because iron films and stains work while chloride and carbonate drift into the process tanks that follow. Grades sold for soap or oil refining are not held to metal limits that matter to a plating line. Caustic is the chemical that demands the most respect in the store - concentrated solutions are among the most corrosive materials routinely handled, and every handling step in this article assumes full PPE.

Product Identity (Encyclopaedia Card)

What it is and what it does. Sodium hydroxide (caustic soda) is the principal alkaline of soak cleaners, electro-cleaners, zincate baths and the alkaline tin and zinc plating systems.

• Supplied as flakes or pearls, typically 99%; strongly hygroscopic, and it absorbs carbon dioxide from the air, so bags must be resealed.
• In the electro-cleaner it provides the saponification that turns oily soil into a rinseable soap.
• Dissolving it in water is strongly exothermic - a 50% solution can boil.

Typical Use in a Plating / Finishing Line

Safety, Handling & Storage

Quality Documents Shipped With Every Batch

Buyer Questions We Answer Every Week

How It Works in Each Station of the Line

Caustic does four jobs. In alkaline zincate plating it is not an accessory but the solvent system itself: 100-140 g/L NaOH dissolves zinc oxide into sodium zincate and carries the current, and the Zn-to-NaOH ratio is the master control of the bath - too little caustic and zinc precipitates, too much and efficiency collapses. In cleaning, 25-60 g/L caustic saponifies oils and lifts soils at 60-90°C, usually buffered with carbonate and silicate. In electrocleaning it carries the current that scrubs the part surface with gas evolution. And in aluminum preparation, hot caustic is the etchant that strips old oxide and gives the matte etch some anodizers and adhesive-bonding lines need. At the effluent station it is the primary neutralizer of acid waste - dosed with care, because overshooting into strong alkali redissolves the metal hydroxide sludge the plant just settled.

How to Check Quality Before Loading a Batch

How QLQ controls it: caustic deliveries are quarantined until COA assay and impurity figures match the specification, and each lot's make-up is confirmed in a small dissolution test before it is used on the production lines. Lot numbers follow the chemical into the zinc and cleaner make-up sheets, so a cloudy bath or a stained barrel can be traced to the exact delivery.

Common Problems & Fixes (Workshop Table)

Handling & Safety for the Plating Line

• Corrosivity: caustic burns are deep and slow to appear. Wear face shield or goggles, rubber or PVC gloves with rolled cuffs, rubber apron and boots whenever handling flake, solution or wet work.
• Dissolving: always add caustic slowly to water with stirring - never water to caustic. The heat of solution can boil water instantly and spatter concentrated caustic.
• Eye protection is mandatory: a single droplet in the eye is sight-threatening. Eyewash stations must be adjacent to every caustic make-up and dosing point, tested weekly.
• Storage: caustic is hygroscopic and absorbs CO2, forming carbonate and caking. Keep bags sealed on dry pallets and use oldest stock first.
• First aid: eye contact - flush with water for at least 15 minutes and go to hospital; skin - remove contaminated clothing, brush off dry flakes, flush copiously, then seek medical advice for anything beyond a trivial spot.
• Spills: contain and dilute with large volumes of water, or neutralize small spills with dilute acid after sweeping; never use hot water on a caustic spill (it accelerates the burn and the reaction).

What It Does on Iron, Zinc Alloy, Copper and Stainless Steel Parts

FAQ

Alkaline zinc bath cloudy or cleaning stages weak? QLQ supplies high-purity caustic soda with COA and engineers who help customers in 10+ countries run zincate and cleaning lines safely. Contact us with your bath analysis.