What is the main cause of chemical corrosion?
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Direct chemical action of environmental or atmospheric gases with metal surfaces.
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What is the main cause of chemical corrosion?
Direct chemical action of environmental or atmospheric gases with metal surfaces.
Name some gases involved in chemical corrosion.
Oxygen, halogen, hydrogen sulfide, sulfur dioxide, nitrogen.
What is one type of chemical corrosion?
Dry or chemical corrosion.
How does chemical corrosion occur?
Through the interaction of gases with metal surfaces in immediate proximity.
What is corrosion?
A process of deterioration or destruction of a solid metallic material due to unwanted chemical or electro-chemical environments.
What reaction occurs at cathodic areas during electrochemical corrosion?
Reduction reaction (gain of electrons).
Where does corrosion typically start?
At the surface of the metallic material.
What are tool steels used for?
Making tools such as hammers, shears, drills, and dies for drawing wires.
How do cathodic reactions typically affect the cathode?
They usually do not affect the cathode, as most metals cannot be further reduced.
What is pitting corrosion?
A localized accelerated attack resulting in the formation of cavities in the metal.
What is the most familiar example of corrosion?
Rusting of iron.
How is corrosion related to the extraction of metals?
Corrosion is the reverse process of the extraction of metals.
What characteristics do tool steels generally possess?
Great strength, toughness, hardness, and resistance to wear and softening.
What occurs first in the mechanism of corrosion?
Oxidation at the surface of the metal.
What do dissolved constituents in the conducting medium do at the cathodic part?
They accept electrons to form ions (e.g., OH−, O2−).
What does pitting corrosion result in?
The formation of pinholes, pits, and cavities in the metal.
What impurities may be found in metals after initial extraction?
Silica, Phosphorous, Carbon, Oxides of certain metals, etc.
What forms on iron during rusting?
A layer of reddish scale and powder of oxide (Fe3O4).
What usually causes pitting corrosion?
The breakdown or cracking of the protective film on a metal.
What does metallurgy deal with?
The extraction of metal from ores and the preparation of alloys.
What elements are commonly found in tool steels?
Tungsten (4-21%), chromium (4-4.5%), vanadium (1-2%), and 0.5 to 0.75% carbon.
What type of attraction exists between positive ions and negative electrons in metals?
Strong electrostatic attraction.
What happens to metallic ions at the anodic part and ions formed at the cathodic part?
They diffuse towards each other through the conducting medium to form a corrosion product.
What are metals?
Elements that are typically shiny, good conductors of heat and electricity, and malleable.
What forms a barrier that restricts further oxidation during corrosion?
The resulting metal oxide scale.
What is a common cause of corrosion involving dissimilar metals?
Contact between two dissimilar metals, often near fasteners or weld joints.
What is the primary purpose of a steel making plant?
To produce steel from raw materials.
What are the benefits of adding Molybdenum to alloys?
Increases strength at elevated temperatures, corrosion resistance, and abrasion resistance while eliminating temper brittleness.
What refining method is used for volatile metals?
Distillation.
What happens to iron when it rusts?
It becomes weak.
What are the two areas formed during pitting corrosion?
Small anodic areas and large cathodic areas.
What is elasticity in materials?
The property that allows a material to regain its initial shape when the load causing deformation is removed.
What is dry corrosion?
Corrosion that occurs without the presence of moisture or water.
What causes oxidation corrosion?
The attack of oxygen on the metal surface, usually in the absence of moisture.
What is the complete process of metallurgy up to?
Purification of metals.
What are high-speed steels used for?
Making cutting tools that require resistance to wear and softening at high temperatures.
What does the strong attraction between particles in metals result in?
High melting and boiling points.
What is the role of electrons set free at the anode?
They flow through the metal and are consumed in the cathodic reaction.
What must happen for oxidation to continue in the corrosion process?
The metal must diffuse outwards or oxygen must diffuse inwards through the scale.
What are alloys?
Mixtures of two or more elements, where at least one is a metal, designed to enhance properties.
How does moisture contribute to corrosion between dissimilar metals?
Moisture acts as an electrolyte, forming a cell where the two metals serve as electrodes.
What role do metals and their alloys play in modern civilization?
They are the backbone of modern civilization.
What can produce corrosion current in pitting corrosion?
The correct environment with small anodic and large cathodic areas.
What is a perfectly elastic material?
A material that completely recovers its original state upon removal of the deforming force, such as steel and glass.
What is a consequence of corrosion that can lead to operational issues?
Plant shutdown due to failure.
What is a common example of corrosion on copper?
Formation of a green film of basic carbonate [CuCO3 + Cu(OH)2].
What are the main raw materials used in steel production?
Iron ore, coke, and limestone.
What properties are enhanced by Tungsten in alloys?
Red hardness, toughness, abrasion resistance, and shock resistance.
What are stainless steels primarily known for?
Their resistance to corrosion by atmosphere and chemicals.
Which refining method is suitable for easily fusible metals?
Liquation.
What is the first step in the preparation of ores?
Concentration or ore dressing.
Which metals are not attacked by oxygen?
Noble metals such as silver (Ag), gold (Au), and platinum (Pt).
What are the primary factors that contribute to dry corrosion?
High temperatures and the presence of corrosive gases.
What is a key property of mild steels regarding corrosion?
They undergo corrosion quickly.
What are impurities in metal ores called?
Gangue or Matrix.
What are metals primarily characterized by?
High electrical and thermal conductivity, malleability, ductility, and luster.
What external factors can accelerate corrosion in dissimilar metals?
Moisture and conductive salts provide an external conductive path, short-circuiting the cell.
What is an alloy?
A mixture of two or more metals, or a metal and another element.
What is the structure of a body-centered cubic (bcc) crystal?
Metal atoms occupy the eight corners of a cube and one atom in the center.
What are the two main components involved in electrochemical corrosion?
The formation of anodic and cathodic areas in contact with each other, and the presence of a conducting medium.
What is the purpose of creating alloys?
To improve strength, corrosion resistance, and other physical properties.
Which diffusion process contributes more to corrosion?
The outward diffusion of metal.
What is the mechanism of galvanic corrosion in acidic solutions?
Corrosion occurs by the hydrogen evolution process.
What happens when a positively charged metal ion combines with negative electrons?
Equilibrium is reached and further reaction stops.
What is a common misconception about metals?
That all metals are hard.
What are some causes of the breakdown of the protective film?
Surface roughness, scratches, local straining, alternating stresses, sliding under load, impingement attack, and chemical attack.
What happens when two dissimilar metals are electrically connected and exposed to an electrolyte?
The metal higher in the electro-chemical series undergoes corrosion.
What are some examples of hydroxide ores?
Talc (Mg3(Si4O10)(OH)2) and Brucite (Mg(OH)2).
What is plasticity?
The inability of a material to regain its initial shape when the load causing deformation is removed.
What is a common action taken to address corroded equipment?
Replacement of corroded equipment.
What is the general reaction for oxidation corrosion?
Metal + O2 → Metal oxide.
What conditions lead to the corrosion of copper?
Exposure to moist air containing carbon dioxide.
What happens if the corrosion product is an insoluble compound?
It acts as a protective coating on the metal surface, stopping further corrosion.
What process is commonly used in steel making?
The blast furnace process.
What is fatigue resistance?
It is the property of a material that enables it to overcome fatigue caused by repeated stresses.
What essential element do stainless steels contain?
Chromium.
What improvements does Vanadium provide in alloys?
Increases tensile strength, ductility, and shock resistance.
How can oxidizable impurities be removed from metals?
Through oxidation.
What is one method used for rough separation of ores?
Hand picking.
What is pitting corrosion?
A localized form of corrosion that leads to the creation of small holes or pits in a material.
What types of materials are most affected by dry corrosion?
Metals, particularly those that form oxides easily.
What is Electrochemical Corrosion also known as?
Wet Corrosion.
Why do cars rust quickly in areas where salt is used on roads?
Salt creates conditions that promote rapid corrosion due to moisture and conductive paths.
What is the strength of mild steels?
About 40 kg/mm².
What are the three principal steps in metal extraction?
Preparation of ores, production of the metal, and refining of the metal.
What are the primary characteristics of metals?
Metals are typically malleable, ductile, conductive, and have a shiny appearance.
What is the carbon content range in medium-carbon steels?
Between 0.30% to 0.8%.
What is the carbon content in heat-treatable stainless steels?
Up to 1.2 percent.
What happens in neutral or slightly alkaline solutions during galvanic corrosion?
Oxygen absorption occurs.
What is an example of a common alloy?
Steel, which is primarily made of iron and carbon.
What is the coordination number of the hexagonal close-packed (hcp) structure?
What is an alloy?
A mixture of two or more elements, where at least one is a metal.
What are metals in their combined state known as?
Minerals.
What gases can cause corrosion besides oxygen?
SO2, Cl2, and H2S.
What role does moisture or an aqueous medium play in corrosion?
It acts as an electrolyte.
Which metals are exceptions to the general hardness of metals?
Sodium (Na), Potassium (K), and Mercury (Hg).
What are alloy steels?
Steels that have small amounts of one or more metals added to impart special properties.
What is the term for corrosion that occurs between dissimilar metals?
Galvanic corrosion.
How is plasticity utilized in materials like wet clay?
It is used for making earthenware, bricks, tiles, etc.
What is metal extraction?
The process of obtaining metals from concentrated ores.
What is the chromate ore mentioned in the text?
Crocoites (PbCrO4).
How do alkali metals react to oxidation corrosion?
They are rapidly oxidized even at low temperatures.
What factors can influence which parts of a metal serve as anodes and cathodes?
Many factors, including irregular corrosion patterns.
What is the primary purpose of a steel making plant?
To produce steel from raw materials.
What is specific gravity in relation to metals?
It is the relative mass of a certain volume of a material compared to the mass of the same volume of water.
What is the role of coke in steel production?
To provide carbon and heat for the reduction of iron ore.
What causes fatigue failure in materials?
Repeated loading and unloading.
What is corrosion?
The process of eating away of metal surface by the action of the surrounding environment.
What causes pitting corrosion?
It is often caused by the presence of chlorides and other aggressive ions in the environment.
What is galvanic corrosion?
Corrosion that occurs when dissimilar metals are in contact, even if not initially touching.
What other elements may be found in stainless steel besides chromium?
Nickel, molybdenum, etc.
What preventive measure can be taken to combat corrosion?
Preventive maintenance such as painting.
What occurs if the corrosion product is a gas or dissolves in the solution?
The phenomenon of corrosion continues unaltered.
What is the composition of Nichrom alloy?
Contains 60% Nickel, 1.2% Chromium, and the rest Iron.
What are the main properties of metals?
Metals typically exhibit high electrical and thermal conductivity, malleability, ductility, and luster.
What method is employed for achieving high purity in metal refining?
Electrolytic refining.
In galvanic corrosion, where does the electron current flow?
From the anodic metal to the cathodic metal, which is copper.
How are mild steels affected by saline water?
They are not much affected by saline water.
What is a common example of dry corrosion?
Oxidation of metals at high temperatures.
What equipment is used to grind ores for better identification of particles?
Ball mill or roller mill.
Under what conditions does Electrochemical Corrosion occur?
When the metal is in contact with moist air or dipped in an aqueous medium.
What influences the technology used for metal extraction?
The chemical reactivity of the metal.
Why are alloys created?
To enhance certain properties such as strength, corrosion resistance, or ductility.
What is the chromium content range in heat-treatable stainless steels?
Generally 12 to 16 percent, less than 18 percent.
How do medium-carbon steels compare to mild steels in terms of toughness and hardness?
They are tougher and harder than mild steels.
How do alloys differ from pure metals?
Alloys have enhanced properties compared to their constituent metals.
What are ores?
Minerals from which metals can be conveniently and economically obtained.
What is the purpose of creating alloys?
To enhance properties such as strength, corrosion resistance, and hardness.
What shape do hcp crystals have?
Hexagonally shaped.
What are the most common depolarizers in corrosion?
Oxygen, acids, and cations of less active metals.
What is ductility?
The property of a material that allows it to be drawn into wires.
What are aluminum alloys commonly referred to as?
Light-weight alloys.
What does the extent of corrosion caused by other gases depend on?
The nature of the corrosion product.
In galvanic corrosion, which metal acts as the anode?
The metal higher in the electro-chemical series (e.g., zinc).
What is notable about Gallium's melting point?
Gallium has a very low melting point.
What is a key characteristic of high-carbon steels regarding hardening?
They can be hardened and tempered easily.
What is porosity?
The ratio of volume occupied by pores to the volume of a material.
What effect does nickel have when added to alloy steels?
It improves tensile strength, ductility, toughness, elasticity, heat, and corrosion resistance.
What is the primary use of spring steel?
Used in situations where sudden shock absorption is required.
At what temperatures are metals generally slightly attacked by oxygen?
At ordinary temperatures.
What are manganese nodules primarily composed of?
Manganese, along with iron, nickel, copper, and cobalt.
What factors determine the method of metal extraction?
The chemical and physical properties of the metals concerned.
What happens to atoms in regions that have undergone stress?
They tend to have higher free energies and become anodic.
What are common examples of corrosion?
Rusting of iron, tarnishing of silver jewelry, and formation of green film on copper.
What are the main raw materials used in steel production?
Iron ore, coke, and limestone.
How is specific gravity calculated?
It is the ratio of the densities (mass per unit volume) of the material to that of water.
How can fatigue resistance be enhanced in metals?
By annealing.
What is the significance of limestone in steel making?
It acts as a flux to remove impurities.
Which materials are most susceptible to pitting corrosion?
Stainless steels and aluminum alloys are particularly susceptible.
How can copper tubing in plumbing lead to corrosion in steel piping?
Dissolved Cu2+ in water can plate out on steel, creating a corrosion cell.
What percentage of chromium is especially effective in stainless steel?
16 percent or more.
What design consideration is often necessary due to corrosion?
Overdesign to allow for corrosion.
What is the oxidation reaction for zinc in galvanic corrosion?
Zn → Zn²⁺ + 2e.
What is the anodic process in corrosion?
Fe(s) → Fe²⁺(aq) + 2e⁻.
Name a method used for further concentration of ores after initial grinding.
Gravity separation.
At what temperatures can Nichrom be used?
1,000 to 1,100 °C.
What are metals?
Elements that are typically shiny, good conductors of heat and electricity, and malleable.
What is the definition of an alloy?
An alloy is a mixture of two or more elements, where at least one is a metal, designed to enhance certain properties.
What is the science and technology of separating metals from ores called?
Metallurgy.
How does dry corrosion differ from wet corrosion?
Dry corrosion occurs in the absence of moisture, while wet corrosion requires moisture or liquid electrolytes.
What is the structure and color of mild steels?
Fibrous structure with a dark-bluish color.
What causes Electrochemical Corrosion?
The existence of separate anodic and cathodic areas between which current flows through a conducting solution.
What are the typical characteristics of heat-treatable stainless steels?
They are magnetic, tough, and can be worked in a cold state.
What is the difference between a metal and an alloy?
A metal is a pure element, while an alloy is a combination of metals or a metal with other elements.
What is the carbon content range in steel?
0.15 to 1.5%.
What are some common types of alloys?
Steel, bronze, and brass.
What property makes medium-carbon steels shock-resistant?
Their composition and structure.
What is the significance of the composition in alloys?
The specific proportions of elements determine the alloy's properties.
Are all minerals considered ores?
No, all ores are minerals but not all minerals are ores.
What are covalent crystals formed from?
Atoms that form strong covalent bonds.
How does impure metal behave in contact with an aqueous medium?
It behaves like an electrolytic or galvanic cell and is oxidized.
Which metal is the most ductile?
Gold.
What are the two important components of aluminum alloys?
Aluminum and magnesium.
What is corrosion?
The gradual eating away of metals and alloys.
What happens to the anode in galvanic corrosion?
It is attacked and gets dissolved.
How does low porosity affect a material?
It makes the material light in mass.
In what types of projects are metals commonly employed?
Engineering projects and products such as agriculture implements, aircraft, automobiles, buildings, bridges, railways, and machinery.
How can high-carbon steels be further hardened?
By heating to a high temperature followed by quenching in water or oil.
What is the carbon content range in high-carbon steels?
0.8 to 1.5%.
What is the maximum percentage of chromium that can be added to alloy steels?
Up to 18%.
What happens to metals at high temperatures regarding oxidation?
Almost all metals (except Ag, Au, and Pt) are oxidized.
What characteristic do spring steels possess?
High elastic limits.
What is Pyro Metallurgy?
A method of extracting metal through chemical reactions of metallic ores at high temperatures.
What is the nature of the corrosion process?
Corrosion is slow and occurs only at the surfaces of metals.
How many elements are known, and how many of those are confirmed?
109 elements known, with 106 confirmed.
What are the two main types of corrosion?
Chemical (or Dry) Corrosion and Electrochemical (or Wet) Corrosion.
What processes can produce stress in metals?
Forming or machining.
What is the chemical formula for Kupfernickel?
NiAs.
What process is commonly used in steel making?
The blast furnace process.
How can pitting corrosion be detected?
It can be detected through visual inspection or non-destructive testing methods.
What does specific heat measure?
The quantity of heat in calories required to raise the temperature of 1 g of a material by one degree Centigrade.
What is creep in materials?
Continual deformation under load at high temperatures.
What happens when copper encounters chrome-plated fittings?
Copper can lead to the formation of Cr3+ salts, resulting in greenish stains.
Where does corrosion occur in galvanic corrosion?
At the anodic metal.
How does chromium protect stainless steel from corrosion?
By forming a dense, tough film of chromium oxide at the surface.
What may the cathodic steps in corrosion involve?
The reduction of oxygen gas, protons, or metal ions.
How does corrosion affect operational efficiency?
It leads to a loss of efficiency.
What is the chromium content range in magnetic alloys?
12 to 22 percent.
What are some applications of Nichrom alloy?
Used in making parts of boilers, steam lines, stills, gas turbines, aero-engine valves, retorts, and annealing boxes.
Can you name a common alloy and its components?
Steel, which is primarily made of iron and carbon.
