Agent passivating

Fig. 1.41 Schematic anodic polarisation curves for a passivatable metal showing the effect of a passivating agent that has no specific cathodic action, but forms a sparingly soluble salt with the metal cation, a without the passivating agent, b with the passivating agent. The passive current density, the active/passive transition and the critical current density are all lowered in b. The effect of the cathodic reaction c, is to render the metal active in case a, and passive...

As an anodic passivating agent, nitrite enhances the formation of magnetite film and produces reducing conditions. It is simple to detect and test, but the high feed level and reserve requirement limit this product to small LPHW and LP steam boiler heating systems. 

Tannin chemistry is complex and tannin blends (composed of singletree species tannins mixed together) offer a number of useful water treatment functions. Apart from oxygen-scavenging abilities, they act as passivating agents, film-formers, sequestrants, and polymeric sludge dispersants (for more details, see Section 10.3). 

Passivating agents are chemicals that promote the formation of a passivating film on the surface of a metal or alloy, such that the electrochemical behavior of the metal or alloy then approaches that of an appreciably more noble metal. 

A Facile One-Pot Synthesis of MSe (M = Cd orZn) Nanoparticles Using Biopolymer as Passivating Agent... 

We have reported a simple, green, bench top, economical and environmentally benign room temperature synthesis of MSe (M=Cd or Zn) nanoparticles using starch, PVA and PVP as passivating agents. The whole process is a redox reaction with selenium acting as the oxidant and MSe as the reduction product. An entire "green" chemistry was explored in this synthetic procedure and it is reproducible. The optical spectroscopy showed that all the particles are blue shifted from the bulk band gap clearly due to quantum confinement. Starch capped CdSe nanoparticles showed the presence of monodispersed spherical... 

Surface Modifying Agents 4.1 Capping and Passivating Agents... 

A transient optical absorption study of charge recombination dynamics was recently reported on CD CdS with a crystal size of 5 nm (no details of the deposition were provided) [35]. Three different time constants for the decay of the transient absorption bleaching were measured (0.8 psec, 17 psec, and 800 psec) and were attributed to three groups of nanocrystals with specific defects. Tri-octylphosphine oxide (TOPO), a well-known passivating agent for CdSe nanocrystals that acts by binding to Cd, was found to increase the relative contribution of the 800-psec recombination, which was therefore attributed to volume recombination, since the TOPO is expected to reduce the relative contribution of surface recombination (represented by the two shorter time constants). 

Metallic Pigments, The leading metallic pigment is zinc dnst, which is used mostly in zinc-rich primers, where it acts as a passivating agent. Aluminum flake is used for the silvery metallic appearance that it imparts. 

This is fundamental, as the application of microbiocides, biodispersants, passivating agents, and cleaners are normally based on the total volume of water in the cooling system. 

Zinc polyphosphate has also been used successfully as a passivating agent, often in combination with chromate. The zinc is a cathodic... 

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