For this to work there must be an electron pathway between the anode and the metal to be protected (e.g., a wire or direct contact) and an ion pathway between both the oxidizing agent (e.g., water or moist soil) and the anode, and the oxidizing agent and the metal to be protected, thus forming a closed circuit; therefore simply bolting a piece of active metal such as zinc to a less active metal, such as mild steel, in air (a poor conductor and therefore no closed circuit) will not furnish any protection.

On Thursday, December 1, 2016 at 9:43:07 AM UTC-5, wrote:
For this to work there must be an electron pathway between the anode and the metal to be protected (e.g., a wire or direct contact) and an ion pathway between both the oxidizing agent (e.g., water or moist soil) and the anode, and the oxidizing agent and the metal to be protected, thus forming a closed circuit; therefore simply bolting a piece of active metal such as zinc to a less active metal, such as mild steel, in air (a poor conductor and therefore no closed circuit) will not furnish any protection.

First, the issue is protection in a wet environment, so there is an "ion pathway" (electrolyte). Plain, pure water is not much of an electrolyte -- but neither is it a severe corrosion problem. Salt in the water, or even many contaminants, produce more of a corrosion problem AND a better ion pathway..

The direct contact with the metal surface being protected usually is enough of a conducting path. Many protective electrodes used in marine environments are just screwed onto the metal being protected, and they work quite well.

--
Ed Huntress

wrote in message
...
On Thursday, December 1, 2016 at 9:43:07 AM UTC-5,
wrote:
For this to work there must be an electron pathway between the anode
and the metal to be protected (e.g., a wire or direct contact) and
an ion pathway between both the oxidizing agent (e.g., water or
moist soil) and the anode, and the oxidizing agent and the metal to
be protected, thus forming a closed circuit; therefore simply
bolting a piece of active metal such as zinc to a less active metal,
such as mild steel, in air (a poor conductor and therefore no closed
circuit) will not furnish any protection.

First, the issue is protection in a wet environment, so there is an
"ion pathway" (electrolyte). Plain, pure water is not much of an
electrolyte -- but neither is it a severe corrosion problem. Salt in
the water, or even many contaminants, produce more of a corrosion
problem AND a better ion pathway.

The direct contact with the metal surface being protected usually is
enough of a conducting path. Many protective electrodes used in marine
environments are just screwed onto the metal being protected, and they
work quite well.

--
Ed Huntress

===============

There is a sacrificial anode in your electric water heater. Home Depot
now carries replacements.

Wonder if the anti-static strips that are drug behind cars that work in
the gas fields and other explosive places would work as the cathode to
'earth' connection ?

Martin

On 12/1/2016 8:43 AM, wrote:
For this to work there must be an electron pathway between the anode and the metal to be protected (e.g., a wire or direct contact) and an ion pathway between both the oxidizing agent (e.g., water or moist soil) and the anode, and the oxidizing agent and the metal to be protected, thus forming a closed circuit; therefore simply bolting a piece of active metal such as zinc to a less active metal, such as mild steel, in air (a poor conductor and therefore no closed circuit) will not furnish any protection.

Conductive drag strap.
Martin

On 12/1/2016 9:19 AM, Jim Wilkins wrote:
wrote in message
...
On Thursday, December 1, 2016 at 9:43:07 AM UTC-5,
wrote:
For this to work there must be an electron pathway between the anode
and the metal to be protected (e.g., a wire or direct contact) and
an ion pathway between both the oxidizing agent (e.g., water or
moist soil) and the anode, and the oxidizing agent and the metal to
be protected, thus forming a closed circuit; therefore simply
bolting a piece of active metal such as zinc to a less active metal,
such as mild steel, in air (a poor conductor and therefore no closed
circuit) will not furnish any protection.

First, the issue is protection in a wet environment, so there is an
"ion pathway" (electrolyte). Plain, pure water is not much of an
electrolyte -- but neither is it a severe corrosion problem. Salt in
the water, or even many contaminants, produce more of a corrosion
problem AND a better ion pathway.

The direct contact with the metal surface being protected usually is
enough of a conducting path. Many protective electrodes used in marine
environments are just screwed onto the metal being protected, and they
work quite well.

On Thu, 1 Dec 2016 06:43:03 -0800 (PST), wrote:

For this to work there must be an electron pathway between the anode and the metal to be protected (e.g., a wire or direct contact) and an ion pathway between both the oxidizing agent (e.g., water or moist soil) and the anode, and the oxidizing agent and the metal to be protected, thus forming a closed circuit; therefore simply bolting a piece of active metal such as zinc to a less active metal, such as mild steel, in air (a poor conductor and therefore no closed circuit) will not furnish any protection.
There are ALL KINDS OF ELECTRONIC RUST BUSTERS ON THE MARKET - SOME
USING SACRIFICIAL ANODES, SOME NOT - AND none OF THEM TERRIBLY
EFFECTIVE AT REDUCING OR PREVENTING RUST.