Potassium pyrophosphate, CAS 7320-34-5, is a white inorganic salt supplied as blocks, powder or granules, with a molecular weight of 330.05. It dissolves readily in water to give a strongly alkaline solution — 1% in water reads pH 10.51 ± 1 — and it is insoluble in alcohol. In a metal plating process those two properties do most of the work: the pyrophosphate ion holds metal ions in solution as a complex while keeping the bath pH inside a narrow band, so the deposit stays even and the bath does not swing every time a brightener or a pH correction goes in.
Two grades come out of the same production stream. Export grade carries 96% K4P2O7 with published limits on chloride and lead; plating grade is refined to 98% and is the specification most often written into a new bath make-up. Both are strongly hygroscopic, so a part-used bag is closed again and the store kept dry.
The salt also works well outside plating: as a builder in industrial detergents, a cleaning agent, a dispersant in pigment and coating systems, and as a buffer wherever a stable alkaline pH is needed. This offer covers the industrial grades for plating work — including decorative gold plating — as well as cleaning and coating.
| Index name | Export grade | Plating grade |
| Tetrapotassium pyrophosphate (K4P2O7), % | 96 | 98 |
| Appearance | White block, powder or granular solid | White block, powder or granular solid |
| Iron (Fe), % | 0.005 | 0.005 |
| Water insolubles, % | 0.08 | 0.08 |
| pH value (1% water solution) | 10.51 ± 1 | 10.51 ± 1 |
| Orthophosphate (PO4) | No distinct yellow colour when reacted with 0.1 N AgNO3 | No distinct yellow colour when reacted with 0.1 N AgNO3 |
| Chloride (Cl), % | 0.45 | – |
| Heavy metal content (Pb), % | 0.01 | – |
| Total phosphorus content (P2O5), % | 41 | – |
Where a bath depends on a complexant, this one is doing two jobs at once. It keeps metal ions available for deposition instead of letting them drop out as hydroxide, and it holds the pH steady enough that the deposition rate stays consistent through a shift. The visible result is a coating that builds uniformly across the part — including the recesses and low-current areas that go patchy when a bath drifts — and that adheres without the blistering that follows a pH swing mid-plate.
In an electroless nickel plating process the same behaviour matters for a different reason. There is no current to push the metal into shape, so everything depends on the bath chemistry staying in balance; a complexant that also buffers cuts the number of corrections an operator has to make and keeps the plating rate from wandering between batches.
Shops running automotive hardware and electronic components care about both ends of that. A softer, duller deposit on a fastener shows up later in a salt-spray report; a patchy deposit on a contact shows up as contact resistance. Keeping the complexant and the buffer in a single addition simplifies make-up and daily top-up, and removes one variable when a defect has to be traced back to the tank.
The reason this salt turns up in conversion projects such as zinc plating, nickel plating and decorative gilding is straightforward: it complexes metal ions in alkaline solution without any cyanide in the tank. That single change touches three things at once — the rinse water, the effluent treatment and the operator's exposure. There is no cyanide to oxidise before discharge, no cyanide-bearing drag-out carried down the line on the work, and none of the special handling a cyanide bath demands at every step.
Potassium pyrophosphate adds a second practical advantage: it is a solid with low volatility, so nothing evaporates out of the tank into the workshop air. What goes in stays in the bath until it leaves on the parts or is removed at bath change, and because the salt dissolves completely there is no undissolved heel to dig out at the end of a campaign.
High solubility reduces waste in a quieter way too. Material that dissolves quickly can be made up in the tank instead of in a separate mixing vessel, which means fewer transfers, less handling, and less left clinging to drums and scoops. For a shop measuring consumption per square metre of work, that gap is real money over a year.
None of this makes a non-cyanide bath maintenance-free. pH, metal concentration and the build-up of breakdown products still have to be watched, and the complexant ratio still has to stay in range. What changes is the number of hazards the line has to manage while it does that.
Fasteners and hardware are the classic case: high volume, barrel or rack, and a corrosion result the customer checks. A non-cyanide zinc line has to deliver a bright, uniform, adherent coating over threads and recesses where current density falls away, and it has to do that shift after shift without the additive package drifting out of balance.
That is where the split of duties matters. The acid zinc plating chemicals on the line — carriers, brighteners and softeners — set the grain, the levelling and the brightness. The complexant keeps the metal available and the bath stable enough for those additives to work at a consistent current density. When the balance slips, zinc hydroxides form and the result is a dull or streaked part that no amount of brightener will recover.
Moving a zinc line off cyanide also removes a whole class of effluent work: no cyanide destruction step, no chlorination stage, and no separate cyanide stream to segregate from the acid and alkaline rinses. For a shop running both barrel and rack work, the practical benefit is a make-up that dissolves cleanly at tank volume and a bath that answers predictably to titration. The operator measures, adds, and carries on.
Decorative gilding is judged on appearance before anything else, which is why the bath chemistry has to be repeatable rather than merely correct. A gilded layer on a jewellery item or a luxury fitting is thin, so any drift in pH or in complexant balance shows up immediately as a colour shift — one batch slightly redder, the next slightly paler — and no amount of polishing hides it.
A pyrophosphate system gives the plater a bath that holds its working point. The complexant keeps the gold available at a steady rate and the buffer absorbs the small acid additions that come with drag-in and brightener top-up, so the colour stays where it was set. On barrel work, where hundreds of small items tumble through the same tank, that stability is the difference between a batch that matches the previous order and one that has to be sorted.
The environmental side is the other reason shops move this way. Cyanide-based gold plating carries handling and effluent obligations at every step; a non-cyanide bath removes them, which is easier on the operators and easier to explain to a customer asking how the finish was produced.
What the salt does not do is set the colour for you. Gold concentration, current density and the additive package still decide the shade — the complexant's job is to keep those three constant while the work goes through.
Two things drive the real cost of a raw material like this: what you pay per kilogram of pyrophosphate content, and how often the line stops because a delivery slipped. On the first, the 96% and 98% grades have to be compared on active content rather than on bag price — a 98% grade at a slightly higher bag price can still be the cheaper make-up when the bath is dosed by assay. On the second, the material comes from a plant with an annual capacity of 3,000–5,000 tons, so a scheduled campaign is not competing for a spot allocation.
Buying both grades from one supplier removes a quieter cost as well. The acid zinc plating chemicals, the buffering salts and the cleaning products on a line are often bought from different vendors, each with its own drum size, paperwork and delivery rhythm. Consolidating the salt into the existing chemical order reduces the number of incoming inspections, the number of certificates to file, and the number of purchase orders raised each month.
Logistics is organised rather than improvised: consignments are classified and routed according to the material's classification, which is what keeps a hygroscopic solid dry between the plant and your store.
Fengfan has worked in surface finishing for more than 40 years. The company's Tech Park in Wuhan's Dongxihu district brings research, production and quality control onto a single site of about 67 acres, with a floor space of roughly 7,000 m² dedicated to surface-treatment additives.
Customers are spread across more than 20 Chinese provinces and more than 30 countries. The company holds a vice-chairman seat on the electroplating commission of the China Surface Engineering Association, and its engineers have published more than 100 technical papers and hold more than 20 patents in the field.
That background is worth having when a metal plating process is being changed rather than simply resupplied. A conversion away from cyanide, a change of complexant, a bath that will not hold its pH — those are the moments when the supplier's own technical depth, and not only the price per bag, decides how quickly the line is running again.
Developed in Fengfan's Tech Park, this product reflects decades of research and development in surface treatment additives. Rigorous testing supports batch-to-batch consistency and confirms that the material meets ISO and industry benchmarks for purity (≥98%) and performance.
Application requirements vary with the process line, substrate and performance target. Share your specific use case with our technical team and we will confirm the grade, dosage and compatibility that suit your application.
Choosing the right match is where most sourcing decisions stall. As a trading supplier, we keep one point of contact from first enquiry to after-sales: tell us what you are making and the conditions you work under, and we shortlist the closest matches from our supplier network, compare specifications and arrange samples before you commit to a bulk order. If something does not behave as expected, we work with the supplying partner on the cause and a practical fix, and stay with the case until it is settled. Email, WeChat or WhatsApp enquiries get a reply within 24 hours.
Plating grade, at 98%, is the one to specify when the salt is going into a new non-cyanide bath or a conversion, because the make-up calculation runs on the pyrophosphate content. Export grade, at 96%, carries the full published limit set — chloride at 0.45% and lead at 0.01% — and suits cleaning, dispersing and buffering duties. Both grades share the same iron limit of 0.005% and water-insolubles limit of 0.08%, so the choice comes down to assay and to which limit set your own purchase specification needs on the certificate.
The complexant is not a substitute for the brightener package. On a non-cyanide zinc line the acid zinc plating chemicals — carriers, brighteners and softeners — set the grain, the levelling and the brightness, while the pyrophosphate keeps the metal ions in solution and the bath stable enough for those additives to work at a consistent current density. What is worth checking before a switch is the make-up ratio in your own bath: send the current formulation and a bath analysis to the sales contact and the addition rate can be reviewed against the grade you intend to use.
There is no single figure that fits every bath — the make-up concentration comes from your formulation and from the titration you already run. What the specification gives you is a fixed reference: the assay, the iron and insolubles limits and the pH of a 1% solution, so a new batch can be checked against the previous one before it goes into the tank. If your formulation was written around a different grade, recalculate the make-up weight from the assay instead of keeping the same bag count.
Pyrophosphate is one of the complexants used in decorative gilding where a cyanide bath is being replaced, and the driver is usually operator safety and effluent treatment rather than cost. Whether a particular bath converts cleanly depends on the formulation, the substrate and the colour target, so the practical route is to bench-test the replacement against your current bath before committing a production line. Compare colour and brightness first, because a gilded layer is judged on appearance before anything else.
Iron that enters a bath co-deposits with the metal being plated. In a nickel plating bath it competes with nickel, dulls the deposit and can make the layer brittle; in a zinc bath it tends to show as a dark, uneven finish. Holding iron at 0.005% keeps the salt from being a source of it, which leaves the anodes, the work and the water as the only routes in — and those are the ones you can control and test.
The solid is hygroscopic, so a bag that has stood open will draw moisture and may cake. Caked material is still usable, but it dissolves more slowly: break it up, allow longer under agitation, and close the bag properly between uses. Storing under cover in a dry room prevents most of it, and weighing against the assay on the certificate keeps the dose right even if the material has picked up a little moisture.
