Corrosion in Steels – Its Types and Testing...

Corrosion in Steels – Its Types and Testing Corrosion is a universal natural process. The effect of corrosion is seen in every-day life in the form of rusted steel parts. Corrosion has a huge economic impact. About a fifth of the global annual steel production goes towards simply replacing steel parts damaged by corrosion. Even though it involves higher up-front cost, correct and efficient corrosion protection at the source helps save money and resources in the long run. Failure due to corrosion can result into dramatic consequences. Corrosion is the gradual degradation of a metal by chemical, often electrochemical reaction with the surrounding environment. Corrosion results into loss of material properties such as mechanical strength, appearance, and impermeability to liquids and gases. Whether steel is corrosion resistant in a specific environment depends on the combination of the chemical composition of steel and the aggressiveness of the environment. As per ISO 8044:2010, corrosion is the physicochemical interaction between a metal and its environment, which results in changes in the metal’s properties and which may lead to significant functional impairment of the metal, the environment, or the technical system of which they form a part. Corrosion takes place when there is a change in the steel’s or system’s properties which may lead to an undesirable outcome. This can range simply from visual impairment to complete failure of technical systems which cause great economic damage and even present a hazard to the people. The typical corrosion process can be regarded as the thermodynamically favoured reverse reaction of the metal-winning (extraction) process (Fig 1). Like all chemical reactions, corrosion processes take place when conditions favour the related chemical reactions (thermodynamics). Then, potential other factors drive the speed of the reaction (kinetics). Fig 1  Chemical reactions of iron during...

Preference of Steel as a Material of Construction...

Preference of Steel as a Material of Construction Steel is one of the most widely used materials, particularly in construction, engineering, white goods, and automobile industries. Steel is also used widely in the manufacture of electrical motors, power generation (nuclear, conventional fuels and wind), power transmission, and railway network. It is also used for gears and engines where it has to be very tough and withstand high temperatures. There is a group of steels known as ‘Advanced High Strength Steels’ (AHSS), which are specially treated steels that can be rolled very thin without losing the element of strength needed for the specific purpose.  These steels are particularly useful for the manufacture of automobiles, helping to reduce the overall mass and thus decrease the consumption of the fuel. Steels with a thin coating of tin are used to make cans for beverages and food. Steels coated in various ways with zinc are used in roofing, for example, and in automobiles as the zinc gives protection to steel against corrosion. It is estimated that there are more than 20,000 million tons of steel in use, which means that there is more than 2 tons of steel is in use for every person living on the Earth. The construction industry is the main user of steel. It uses steel from small buildings to huge bridges and uses it in multiple ways even within a single construction.  A bridge, as an example, may use steel in the huge suspension ropes, the steel plate flooring for the road, the beams for the columns, and for the safety barriers and lighting columns. A large amount of steel is also used in the reinforce concrete. In fact, steel is either used or used to produce all the items needed in our daily life....

Alumina and its Role in Iron and Steelmaking...

Alumina and its Role in Iron and Steelmaking Alumina is a chemical compound of aluminum (Al) and oxygen (O2) with the chemical formula aluminum oxide (Al2O3). It is the most commonly occurring of several aluminum oxides. It is significant in its use to produce aluminum metal. It is being used as an abrasive material because of its hardness. It is also being used as a refractory material owing to its high melting point. Aluminum oxide is an amphoteric substance. It can react with both acids and bases, acting as an acid with a base and a base with an acid, neutralizing the other and producing a salt.  It is insoluble in water. Aluminum oxide has a white solid appearance and is odorless. The molar mass of aluminum oxide is 101.96 grams per mole. Specific gravity of alumina is 3.986. It is insoluble in water. Melting point of aluminum oxide is 2072 deg C while the boiling point is 2977 deg C. Alumina affects the processes of producing iron and steel during the production of iron and steel. Besides alumina is a very important refractory material for the lining of furnaces and vessels in iron and steel plants. Role of alumina in ironmaking Alumina during ironmaking enters the process through impurities in the input materials mainly iron ore. Alumina affects the sintering of iron ore. The most harmful effect of alumina is to worsen the RDI (reduction degradation index) value of sinter. RDI value increases as the alumina content rises. It is seen that within a 10 % to 10.5 % CaO content range, an increase of 0.1 % in the alumina content raises the RDI by 2 points. The strength and quality of sinter deteriorate as the alumina content rises. Alumina promotes the formation of SFCA (silico ferrite of calcium and aluminum), which is beneficial for sinter strength, but the strength of the ore components is lower, since a...

Limestone and Lime

Limestone and Lime Limestone is an odorless white, grayish-white or tan material that ranges from sized stone to a granular powder. It is often described as the most versatile mineral. Limestone is the name given to any rock formed which consists mostly of calcium carbonate (CaCO3), but to geologists, limestone is only one of several types of carbonate rocks. These rocks are composed of more than 50 % carbonate minerals, generally containing the mineral calcite (pure CaCO3). Limestone is a sedimentary rock composed mainly of CaCO3. It is formed by the deposition either of the skeletons of small creatures and/or plants (organic limestones), or by chemical precipitation, or by deposition of fragments of limestone rock, on the beds of seas and lakes. Limestones are contaminated to a greater or lesser extent by the deposition of sand or clay which is the source of the impurities usually found in the limestone. Generally there is a difference in quality in a deposit from one layer to the next. The purest carbonates and the most suitable from the production point of view tend to be the thick bedded type. Carbonate deposits may be found in horizontal layers as deposited, or at an angle from the horizontal due to earth movements. They will vary in density, hardness and chemical purity. Limestone rocks are extremely common and make up a significant portion of the crust of the Earth. They serve as one of the largest carbon repositories on our planet. The properties of limestone make it one of the most widely used minerals. Some limestones may contain small percentage of magnesium carbonate (MgCO3). These limestones are known as dolomitic limestones. Impurities (such as clay, sand, organic remains, iron oxide, and other materials) cause limestones to show different colours, especially with weathered surfaces. Limestone may be crystalline, clastic, granular,...

Dolomite – A Useful Mineral...

Dolomite – A Useful Mineral Dolomite is also known as dolostone and dolomite rock.  It is a sedimentary rock which primarily consists of the mineral dolomite. It is found in sedimentary basins worldwide. Dolomite rock is similar to limestone rock. Both dolomite and limestone rocks share the same colour ranges of white-to-gray and white-to-light brown (although other colours such as red, green, and black are also possible). Both the rocks have approximately the same hardness, and they are both soluble in dilute hydrochloric (HCl) acid. The original mineral name ‘dolomie’ was given by NT Saussare, in 1792, in honor of the French geologist Deodat Guy de Dolomieu (1750–1801). Dolomite, the rock, contains a large proportion of dolomite the mineral. Ideal dolomite has a crystal lattice consisting of alternating layers of Ca and Mg, separated by layers of CO3 and is typically represented by a stoichiometric chemical composition of CaMg(CO3)2, where calcium and magnesium are present in equal proportions. Dolomite originates in the same sedimentary environments as limestone i.e. in warm, shallow, marine environments where calcium carbonate (CaCO3) mud accumulates in the form of shell debris, fecal material, coral fragments, and carbonate precipitates. Dolomite is thought to form when the calcite in carbonate mud or limestone is modified by magnesium-rich groundwater. The available magnesium facilitates the conversion of calcite into dolomite. This chemical change is known as dolomitization. Dolomitization can completely alter a limestone into a dolomite, or it can partially alter the rock to form a dolomitic limestone. Dolomite is a complex mineral. It is relatively a soft mineral which can be easily crushed to a soft powder. The mineral is an anhydrous carbonate mineral consisting of a double carbonate of calcium (Ca) and magnesium (Mg). It is chemically represented by CaMg(CO3)2 or CaCO3.MgCO3. It theoretically contains...

Waste Heat Recovery Devices...

Waste Heat Recovery Devices  Industrial furnaces are used for carrying out certain processes which requires heat. Heat in the furnace is provided by (i) fuel energy, (ii) chemical energy, (iii) electrical energy or (iv) a combination of these energies. Gases which are generated during the process leaves the furnace at a temperature which is the inside temperature of the furnace and hence have a high sensible heat content. Sometimes the exhaust gases carries some chemical energy, which raises the temperature of exhaust gases further due to post combustion because of this chemical energy. The heat energy contained in the exhaust gases is the waste energy since it gets dumped in the environment. However, it is possible to recover some part of this energy if investments are made in waste heat recovery devices (WHRDs). Methods for waste heat recovery include (i) transferring heat between exhaust gases and combustion air for its preheating, (ii) transferring heat to the load entering furnaces, (iii) generation of steam and electrical power, or (iv) using waste heat with a heat pump for heating or cooling facilities. WHRDs work on the principle of heat exchange. During heat exchange the heat energy of the exhaust gases gets transferred to some other fluid medium. This exchange of heat reduces the temperature of the exhaust gases and simultaneously increases the temperature of the fluid medium. The heated fluid medium is either recycled back to the process or utilized in the production of some utilities such as steam or power etc. The benefits of WHRDs devices are multiple namely (i) economic, (ii) resource (fuel) saving, and (iii) environmental. The benefits of these devices include (i) saving of fuel, (ii) generation of electricity and mechanical work, (iii) reducing cooling needs, (iv) reducing capital investment costs in...