Inhibition of mild steel by polyphosphates

The Unexpected Role of Carbonate Impurities in Polyphosphate Corrosion Inhibition

“…Thus, these results confirm that cathodic film formation is the primary inhibition mechanism during the early stages of exposure to SAPP. This can be attributed to the clear films known to ultimately develop on cathodic regions in the presence of polyphosphate species 6 , 10 , 15 , however little is understood about the formation of such cathodic films. In the present work, fluctuations in charge transfer resistance values at the cathode are indicative of an evolving structure, where the formed film is broken down and replaced by an initially less resistive structure, which in turn grows increasingly protective.…”

“…This reversion to orthophosphate species at the cathode has been proposed 11 , but not confirmed, before, since local pH values are known to exceed 10 when corrosion at the cut edge is uninhibited 22 , 23 . Previously however, films attributed to polyphosphate species (morphologically distinct from the precipitates formed by orthophosphate inhibitors) have been detected in ex-situ tests after lengthy exposure times 15 , 19 , 24 . In accordance with those studies, polyphosphate absorbance peaks at 1244 cm −1 and 1352 cm −1 (corresponding to symmetric and asymmetric PO 2 vibrations respectively) were in fact detected after 24 hours exposure 25 .…”

“…One explanation lies in improved cathodic inhibition, provided by the formation of a tightly bound protective film. Whilst the presence of such a film was first described by Uhlig in 1955 13 , and has been confirmed by numerous authors since 10 , 14 , 15 , its formation is not well understood, since polyphosphates are expected to revert to orthophosphates by hydrolysis under the alkaline conditions at cathodic sites. Nonetheless, it is widely accepted that film quality determines inhibitor efficiency at the cathode.…”

Inhibition de la corrosion d'un acier au carbone par des produits dérivés de phosphonates en association avec des sels de zinc

“…En effet, on observe une valeur minimale de i ^ (11 \iA-cm -2 ) pour une concentration de 6x10-5 M. Pour des concentrations supérieures de ZnP0 3 F, i^ croît. Un tel phénomène a déjà été mis en évidence par LAHODNY-SARC et KARTELAN (1976) -notamment dans le cas des polyphosphates -et peut trouver son origine dans le fait qu'aux fortes concentrations, il se formerait un complexe métallique soluble qui entraînerait une accélération de la corrosion. Dans toute la gamme de concentration étudiée le monofluorophosphate de zinc est moins efficace que les produits dérivés de phosphonates en association avec les sels de zinc.…”

A New Route for the Synthesis of Alkali Polyphosphate from Economical Starting Materials: Preparation and Characterization of Sodium Cyclotriphosphate

“…12,13 Steel corrosion in similar conditions of sea water was reduced by addition of small amounts of alkali polyphosphates in the presence of divalent cations, such as Ca, Mg, Zn, and dissolved oxygen thanks to the formation of thin film between polyphosphates and metal cations and thereby inhibits the electrochemical processes that lead to corrosion. [10][11][12][13][14] Sodium cyclotriphosphate (SCTP) is an important polyphosphate since it is used in different applications as mentioned above. In addition, SCTP is used as starting material for the preparation of all other metal cyclotriphosphates, such as K 3 P 3 O 9 , Ag 3 P 3 O 9 •H 2 O, Na 2 LiP 3 O 9 , Mn 3 (P 3 O 9 )2 • 10 H 2 O, Ca 3 (P 3 O 9 )2 • 10H 2 O, Ba 3 (P 3 O 9 )2 • 4H 2 O, Ln(Bi)Na P 3 O 9 • 9H 2 O, Tl 3 P 3 O 9 , etc.…”