Alonizing is a

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

metallizing Metallizing is the general name for the technique of coating metal on the surface of objects. Metallic coatings may be decorative, protective or functional. Techniques for metallization started as early as mirror making. In 1835, Justus von Lie ...

process in that it is a

thermochemical Thermochemistry is the study of the heat energy which is associated with chemical reactions and/or phase changes such as melting and boiling. A reaction may release or absorb energy, and a phase change may do the same. Thermochemistry focuses on ...

treatment that involves enriching the surface layer of an object with one or more

metallic elements A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

.Postfach, R. C. (1987). Diffusion Metallizing Processes. Journal of Metals, 39(10), A72-A72. Specifically, alonizing is the diffusion of

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...

into the surface of a base metal through high temperature vapors.Weinbaum, M. J., & McGill, W. A. (1982). Alonizing--Combining the Metallurgical Properties of Aluminum with the Mechanical Strength of Steel. Journal of the Electrochemical Society, 129(8), C322-C322. The types of metals that can be alonized include all types of wrought and cast

steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...

s (i.e. plain carbon and low alloy grades,

ferritic A ferrite is a ceramic material made by mixing and firing large proportions of iron(III) oxide (Fe2O3, rust) blended with small proportions of one or more additional metallic elements, such as strontium, barium, manganese, nickel, and zinc. Th ...

and

austenitic Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 ...

steels, highly alloyed nickel-chromium steels, etc.).Wyatt, J. (n.d.). Alonizing Process. Alonizing. Retrieved November 15, 2011, from cfile235.uf.daum.net/attach/171E6E514DF0EAB11C23B5 This process results in an

alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...

with the surface properties of aluminum while retaining the base metal's inherent

strength Strength may refer to: Physical strength *Physical strength, as in people or animals * Hysterical strength, extreme strength occurring when people are in life-and-death situations *Superhuman strength, great physical strength far above human c ...

and rigidity.Wyatt, J. (n.d.). Alonizing. Alonizing. Retrieved November 15, 2011, from cfile239.uf.daum.net/attach/18194C514DF0EA9A1C4919 Therefore, alonizing does not change the high-temperature mechanical properties of the base metal, which is the advantage of alonizing over simply creating an

aluminum alloy An aluminium alloy (or aluminum alloy; see spelling differences) is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two principal ...

(aluminizing the surface versus aluminum throughout the alloy).Materials of Construction - Alonizing/Calorizing. (n.d.). Sulphuric Acid on the Web. Retrieved November 15, 2011, from http://www.sulphuric-acid.com/techmanual/Materials/materials_alonizing.htm

Process

The process consists of first placing the metal in an airtight vessel, called a

retort In a chemistry laboratory, a retort is a device used for distillation or dry distillation of substances. It consists of a spherical vessel with a long downward-pointing neck. The liquid to be distilled is placed in the vessel and heated. The n ...

. The metal is then encircled by a blend of aluminum powders. The retort is then closed and placed in a pressure-controlled

kiln A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Kilns have been used for millennia to turn objects made from clay int ...

. At the elevated temperatures (typically greater than 300 °C, usually between 700 and 1100 °C) of the kiln, the aluminum is in its liquid phase and diffuses into the surface of the metal and forms an alloy with the substrate. This alloy usually contains a minimum of 20 percent aluminum. Conventional case depth for carbon and alloy steel is 0.0127-0.0508 centimeters, and for stainless and nickel base alloys is 0.00508-0.0254 centimeters.Aluminizing Corrosion Protection - Alonizing. (n.d.). Wire Cloth Aluminizing. Retrieved November 15, 2011, from http://www.marcospecialtysteel.com/aluminizing.html After cooling, the metal is removed from the retort and from the excess powder. At this point, additional secondary operations are performed as needed. This process ensures uniform alloy protection over the entire surface of the base metal.

Purpose

The purpose of the alonizing process is to improve the base metal's

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...

and

corrosion resistance Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

by providing a protective diffusion layer of aluminum alloyed with the base metal at the surface. This layer remains effective at all temperatures up to the

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...

of the base metal. Since the layer created is an alloy with the base metal, the layer cannot be removed without a

machining Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...

process. The protective diffusion layer provides the following

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

protection properties: *

Sulfidation Sulfidation (British spelling also sulphidation) is a process of installing sulfide ions in a material or molecule. The process is widely used to convert oxides to sulfides but is also related to corrosion and surface modification. Inorganic, mate ...

Resistance – protection from hydrogen sulfide, hyposulfurous, and sulfurous acid attack *

Oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

Resistance – aluminum oxide forms stable coating *

Carburization Carburising, carburizing (chiefly American English), or carburisation is a heat treatment process in which iron or steel absorbs carbon while the metal is heated in the presence of a carbon-bearing material, such as charcoal or carbon monoxide. ...

Resistance – resists carbon diffusion * Hydrogen Permeation – reduces rate of hydrogen diffusion The reason

is used to form the alloy is because it is very corrosion resistant itself. When

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

is present, aluminum reacts to form an aluminum oxide layer, which is chemically bound to the surface and seals the core aluminum from any further reaction.Perryman, J. (n.d.). Corrosion Resistance of Aluminum. Waterfront Solutions. Retrieved November 30, 2011, from www.floodbreak.com/default/Maintenance%20Ops/Aluminum%20corrosion%20paper.pdf Therefore, diffusing aluminum into a base metal increases its corrosion resistance. However, the alloys formed are extremely variable because they vary not only in the types of metals being alonized, but also in the amount of time spent alonizing and hence the time allotted for aluminum to diffuse into the surface (resulting in varying percentages of aluminum in the resulting alloys). The type of metal that should be chosen for the alonized process depends on the desired application, since the resulting alloy retains similar properties of the base metal, including

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

it can withstand,

ductility Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...

, its own corrosion properties, etc. Though corrosion protection properties are gained, the chemicals and gases that typically corrode aluminum are not resisted. The amount of time spent alonizing also depends on the desired application considering the amount of corrosion resistance desired to gain versus some of the negative effects that can come with aluminum including softness,

brittleness A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Bre ...

, and

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

.Holtzer, M., & Dzioba, Z. (1992). Improved corrosion resistance of cast carbon steel in sulphur oxides by alonizing. Werkstoffe und Korrosion. Materials and corrosion., 43(2), 69-72.

Applications

Alonized materials are used most commonly in tubing and piping utilized in corrosive environments. These types of tubing and piping include

furnace A furnace is a structure in which heat is produced with the help of combustion. Furnace may also refer to: Appliances Buildings * Furnace (central heating): a furnace , or a heater or boiler , used to generate heat for buildings * Boiler, used t ...

tubes, reformer tubes,

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...

tubes, waste gas heater tubes, line pipe and downhole tubes for wells and production vessels, sulphur condensers and piping used in oil and chemical production and power generation and wrought metal products, bars, rods, plates and sheets, panels, water well panels, and wire screens and metal castings by adding aluminum or aluminum and silicon corrosion and erosion preventive diffusion coatings.ALONIZING. (n.d.). Findownersearch. Retrieved November 17, 2011, from http://www.findownersearch.com/alonizing-8207219-brand.html

References

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