Monel

Monel or Monel Metal is an alloy made of nickel (roughly 70%), copper (25 to 29%), and a small percentage of manganese, silicone, carbon, and iron. This mixture was popular from the early to mid 1900s and was used in several architectural applications. Monel is stronger than steel, resistant to corrosion, and readily fabricated.

History
Monel was first recognized in the mid nineteenth century nickel industry that had formed around large ore deposits in Canada. Investors became interested in the iron that was found in the ore. Several attempts to extract the ore proved unsuccessful. As the metal was more clearly understood, the Orford Nickel and Copper Company began shipping ore to Pennsylvania to be refined into metallic nickel. In an attempt to expand the company, the president, Robert Thompson, looked for investors. Ambrose Monell soon became part of the company, followed soon by Robert Crooks Stanley. Stanley believed that the metal they were extracting could be taken directly out of the ore, rather than refining the copper and nickel. After several attempts, Stanley found an alloy that was tough but malleable. The new metal received the name Monel after the company’s name. One L had been dropped from Ambrose Monell’s name because owners could not use their name as the company’s.

Soon, manufacturing of sheet, plate and mill goods using this Monel metal were being created. The first piece of Monel sheet metal was installed in 1908 on New York City’s Pennsylvania Station. After years of trying to promote their product, INCO doubled their sales in less than two years because they started promoting their corrosion resistant, low-weight-to-strength ratio, and the cost saving product.

In 1929, INCO and their largest competitor, Mond Nickel company, merged in an attempt to keep up with consumer demand. Soon, the Monel was being marketed under the Mond name. Roughly 30 years later, Monel began to be displaced by stainless steel, which is cheaper to make and cheaper to form into the desired shapes. Monel was further pushed from the market by the US Government's close control of nickel supplies, which were considered of strategic importance during the Cold War.

Metallurgy
Monel, unlike most other metals, cannot be extruded. Sheets of Monel can be welded, brazed, or soldered. Monel was available in full-finished, and cold-rolled sheets. Also, the cold-rolled sheets could come in dead soft, soft, skin hard, quarter hard, and half hard tempered. Cold rolled half sheets were commonly used in commercial cabinetry. Often a silver satin finished known as No.8, was applied to cold rolled sheets. In casting, the alloys differ slightly from the sheet and bar goods. The Monel must first be filed to remove all imperfections then smoothed on a grinder and then have a finish polish applied. During heating of Monel (regardless of what form it was in) when heated, a thin black oxide film appeared. Polishing this oxide carefully often would lead to a two tone finish. Chemical etching, engraving, and sandblasting were other popular finishes for Monel.

Uses and Installation
Monel offered a variety of uses in any of its forms. Sheet and plate goods were ideal for air ducts, gutters, mailboxes, lighting fixtures, and even sinks. INCO also sold Monel roofing sheets that came with explicit instructions on installing the roofing properly. Monel as a roofing membrane meant fewer joints meant a tighter roof. When INCO introduced a crimped version of the Monel sheet metal, the need for expansion joints for long runs was eliminated.

Monel castings were used as both ornamental to everyday use. Monel castings were popular for handrail fittings, rosettes, plaques, pilasters, and grilles. Another use for Monel forgings was hardware in bank vaults and safes. Monel is suitable for harsh climates and inaccessible locations because of its resistance to corrosion. When someone could not afford a solid piece of Monel, they could have a thin sheet of metal laminated onto cheap backing and modeled to fit almost anything.

Identification
When no manufacturer's mark (e.g. INCO) can be found, Monel can be difficult to differentiate from other metals. Because the material contains a small percentage of ferrous metal, a magnet held to its surface will exhibit a slight magnetic pull. However, its ferrous content is insufficient for significant oxidation (i.e. Monel is highly resistant to rust). Monel will sometimes exhibit a greenish or brownish buildup around welded seams or joints or where it is in contact with another metal.

A slightly more advanced method of identification involves exposing the metal to be identified to a small amount of nitric acid. Nitric acid will react with the copper and nickel contained in Monel and cause it to turn a blue-green color. Nitric acid produces toxic fumes and should only be used in a well ventilated area. In addition, proper safety gear including rubber gloves and a face mask should be worn. To avoid disfigurement of the object under examination, tests should be performed in an inconspicuous location.

Conservation
While Monel is resistant to corrosion and deterioration caused by most other elements, it is still suggested that the alloy is treated. Corrective measures are necessary to prevent extreme surface discoloration as well as to prevent more severe deterioration of the metal. Like most metals and alloys, it is imperative to match the deterioration with the proper treatment.

Deterioration
It is normal for Monel to develop a patina (colored skin) once is has been installed for a period of time. The thickness and color of the patina is determined by several factors, the most prevalent being its location. Frequently, an interior Monel will develop a light tarnish at some point; this can usually be remedied by an occasional wipe with a dry cloth. When Monel is installed outdoors, the metal will usually develop a light gray or a medium brown patina. When Monel is protected from rain, a coating of hydroscopic corrosion product will form. Monel is most damaged by stagnant water, nitric oxides, and sulfur dioxide. Stagnant saltwater causes pitting where marine organisms are likely to accumulate but the damage will eventually slow. Acids are not usually seen as a problem for Monel and the resistance to alkalis is high as well. Acid salts like zinc chloride, ammonium sulfate, aluminum sulfate, and ammonium chloride are mildly corrosive. Acid and alkaline oxidizing salts are highly corrosive however. Monel can be combined with brasses, bronzes, and copper in either indoor or outdoor with little galvanizing. In severe weather, these metals will corrode and are not recommended in use with Monel. Chemical testing to identify Monel is the easiest way, as magnetic testing is unreliable (Monel’s magnetism changes with temperature).

Conservation Techniques-architecture
While several methods are effective for cleaning but stubborn stain removal is more of a challenge, as is preserving existing patinas. For most part, washing or degreasing the metal or removing and replacing protective coatings generally are the most care that a Monel will require. Most small scratches or corrosion can be covered or removed by polishing and adding a protective coat. Monel is usually protected by some type of lacquer or oil. It is suggested that hot wax and other methods for treating bronze may also be applied to Monel. It is always recommended that Monel be washed and degreased first using a neutral PH soap and warm water, as well as a lint-free cloth. The water used for the final wash should be distilled. Removing the lacquer or paint, a lacquer solvent should remove the lacquer without damaging the metal (given the solvent is a methylene chloride-based gel). For stains, it is recommended that a 5% oxalic acid (toxic - use rubber gloves !) and powdered pumice be applied. All of these methods should be washed with a mild soap and have a finishing wash of distilled water. If the Monel had a finish on it, such as lacquer, it should be reapplied.

Cleaning

 * Mechanical removal of corrosion products


 * Chemical removal of corrosion products

Organic acids mixture

47,5 gms citric acid

47,5 gms sodium gluconate

4,9 gms tartaric acid

1-10 lit water

Immerse objects in cold or hot(80 C) solution,after treatment  rinse well.

According to:

USPT 4,264,418


 * Electrochemical removal of corrosion products

20-50 gms sodium hydroxide

1 lit water

stainless steel anode,up to 12 v ,current density at least 0,5/Adm2

According to:

W.Machu:Metallische Ueberzuge,Leipzig 1948


 * Ultrasonic removal of corrosion products

4-6 gms sodium carbonate

6-8 gms trisodium phosphate

10-12 gms sodium silicate

1 lit distilled water

2-5 minutes,then rinse well and repeat if needs

According to:

Dasoyan,M.A.;Palmskaya,I.J.;Saharova,E.V. Tehnologiya elktrohimicheskih pokritiy

Leningrad 1989.


 * Laser removal of corrosion products

Protective coatings

 * Clearcoats / Paraloid B 72 / Paraloid B 67 / Paraloid B 44 / ORMOCER


 * Waxes / Renaissance Wax / Cosmolloid 80 H / DIY mixtures


 * Combinations / basecoat Paraloid B 72 + topcoat Renaissance wax etc.

Replacement
Though Monel is still manufactured by Inco Alloys International, only sheet goods are readily available. It may still be possible to get rolled and cast forms from this business but it is likely to be much more expensive.