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106117 results in Materials Science

Page 441 of 5306

  • 22 - Chemical Aspects of Biotechnology

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    11 May 2018
    Print publication:
    16 May 2015, pp 1121-1137

  • Summary

    Introduction

    Biotechnology is technology based on biology in which living organisms like bacteria, viruses, fungi, yeast, plants and animal cells are used to modify various processes and produce useful products. The UN Convention on Biological Diversity, Part 2, defines biotechnology as ‘any technological application that uses biological systems, living organisms or derivatives thereof to make or modify products or processes for specific use’. The word ‘biotechnology’ owes its origin to two Greek words bios meaning ‘pertaining to life’ and technikos meaning ‘involving human knowledge and skills’.

    The science of biotechnology is not new although its systematic study and scientific applications started only a few decades ago. There are evidences in history to prove that biotechnology was used even thousands of years ago in ancient times to produce foods like bread by adding yeast, for the preparation of beverages like beer and wine by the fermentation of various grains and fruit juices, to convert milk into curd, cheese and yogurt, in the field of medicine, in ayurveda, for strengthening the immune system, selective breeding to improve the quality of crops and livestock by mating organisms of desired characteristics to produce offsprings with specific features.

    The modern aspect of biotechnology includes genetic engineering where genes are modified to develop special traits within individuals, to make them disease resistant, increase productivity, produce high yielding variety of crops, develop food products, fruits and vegetables that are more nutritious, disease resistant and taste better than the conventional food items. Other tools of modern biotechnology are tissue culture, molecular breeding which help to improve the quality and productivity of plants and animals, increase their commercial value and make them more useful for man and society.

    Applications of Biotechnology

    Biotechnology is an applied science with multiple applications in various fields like agriculture, medicines, textiles, paper and pulp, mining and metal refining, waste management, energy sector, food processing, livestock management in marine and aquatic life, forestry, industrial sector, etc.

    The main applications of biotechnology are discussed here.

    (i) Biotechnology in agriculture The application of biotechnology to agriculture is called green biotechnology. The use of biotechnological tools can increase the production of crops, develop high yielding and more nutritious crops, improve their resistance to diseases and adverse conditions like drought, develop insect protected biotech crops and thereby reduce the use of chemical pesticides and fertilizers.

  • 14 - Electrochemistry

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    11 May 2018
    Print publication:
    16 May 2015, pp 743-814

  • Summary

    Introduction

    Electrochemistry is the branch of science which deals with the relationship between electrical energy and chemical energy and the inter-conversion of one form into other. If electrical energy causes chemical reactions to occur, then the process is called electrolysis; for example, water can be made to split into hydrogen and oxygen by the passage of electric current. On the other hand, electrical energy can be produced as a result of chemical change. Such changes are called electrochemical changes and find use in the manufacture of cells and batteries which generate electricity due to chemical changes. Both electrolytic and electrochemical changes have widespread applications in chemistry. This chapter however deals only with various electrochemical changes and their applications in chemistry.

    Types of Conductors

    Conductors are substances which allow electricity to pass through them; for example, copper, silver, gold, etc. Those substances which do not allow the passage of electric current through them are called non–conductors or insulators; for example, wood, rubber, etc.

    Conductors can be of two types:

  • (i) Metallic conductors Metallic conductors allow electricity to pass through them without undergoing any chemical change. The flow of electric current through metallic conductors is due to the flow of electrons in the metal. Common examples of metallic conductors are metals like copper, silver, etc.

  • (ii) Electrolytic conductors These are substances which allow electricity to pass through them in their molten states or in their aqueous solutions. Electric current brings about decomposition in them. The charge is carried by the ions and conduction occurs due to the movement of ions. Thus, these substances do not conduct electricity in solid state but in molten state or in aqueous solutions as the ions can move about freely in molten state or in aqueous state. Substances like these are termed as electrolytes. Example: Molten solution of NaCl. The differences between metallic and electrolytic conductors are summarized in Table 14.1.

  • (iii) Non-electrolytes These are substances which do not conduct electricity at all, neither in their molten state nor in their aqueous solution. Example sugar, glucose, urea, etc.

  • 23 - Analytical Techniques in Chemistry

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    11 May 2018
    Print publication:
    16 May 2015, pp 1138-1148

  • Summary

    Introduction

    Analytical chemistry is an important branch that helps in qualitative and quantitative analyses. Qualitative analysis gives information regarding the presence or absence of a component, whereas quantitative analysis addresses the question of how much? Analytical chemistry is an interdisciplinary science that plays a vital role in all streams of chemistry such as organic, inorganic, physical, industrial and biochemistry. It is not only confined to qualitative and quantitative analyses but the advancement of science and development in the field of instrumentation has further quantified its scope. It finds extensive use in environmental science, agricultural science, pollution studies, oceanography, clinical chemistry, medical science, manufacturing industries, biological science, forensic science, and so on.

    Type of Analysis

    Three types of analyses can be carried out

  • (a) Physical analysis

  • (b) Chemical analysis

  • (c) Instrumental analysis

    • Physical Analysis

    The study of physical parameters such as color, smell, physical state, solubility, specific gravity, melting point and boiling point helps in the preliminary investigation of the compound.

    The physical properties can be measured by various chemical and instrumental methods, for instance, mass can be estimated by gravimetry, volume by volumetry, electric potential and electric current by conductometry, potentiometry, absorption or emission of radiation by spectroscopy, scattering of radiation by turbidimetry, nephelometry, refraction by refractometry, rotation by polarimetry and optical rotatory dispersion and diffraction by X-ray electron diffraction methods. These physical and physicochemical methods enable the qualitative and quantitative estimations of the compound.

    Chemical Analysis

    The qualitative and quantitative estimations of organic and inorganic compounds can be carried out chemically.

    Qualitative Estimation of Inorganic Compounds

    The qualitative analysis of inorganic compounds is carried out by determining the acid and basic radicals in the compound. For organic compounds, the aromatic and functional groups are determined by the use of specific reagents and compounds.

    The quantitative estimation of chemical reactions can be carried out by the following methods of analysis.

    (i) Gravimetric analysis In gravimetric analysis, the substance to be estimated is converted into an insoluble precipitate, which is collected, dried and weighed. The process involves several steps in which the sample is prepared, precipitated, filtered, washed, dried and weighed. If the sample is electrolyzed and the material deposited at one of the electrodes is weighed, then the process is called electrogravimetry.

    The weight of the sample obtained helps in quantitative estimation of the desired substance.

  • 10 - Liquid Crystals

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    11 May 2018
    Print publication:
    16 May 2015, pp 518-527

  • Summary

    Introduction

    A crystal is a solid substance in which the atoms occupy definite positions called lattice points. When these solids are heated, the atoms leave their lattice positions and the solid changes into a liquid. In a liquid, atoms are randomly oriented. In some molecules in between these two stages there is an intermediate state in which although the solid acquires a tendency to flow like a liquid, the atoms are still arranged parallel to one another like that in a solid, i.e., the degree of order is intermediate between that of a solid and a liquid. They are less ordered than a solid and more ordered than a liquid. This intermediate state is termed as the liquid crystal state or the mesophase. Liquid crystal is regarded as the fourth phase of matter (the other three phases being solid, liquid and gas).

    The study of liquid crystals dates back to the year 1888, when it was observed by an Austrian botanist named Friedrich Reinitzer that cholesteryl benzoate has two distinct melting points. He observed that when cholesteryl benzoate is heated, it changes into a very viscous cloudy liquid at a more or less sharp characteristic temperature called the transition temperature. On further increasing the temperature, the cloudiness disappears again sharply at a new temperature called the melting point of the solid. Beyond the melting point, it behaves like an ordinary liquid. However, between the transition point and the melting point, the substance exhibits the fluidity of a liquid and the optical properties of a solid crystal.

  • 19 - Green Chemistry

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    11 May 2018
    Print publication:
    16 May 2015, pp 1015-1031

  • Summary

    Introduction

    From the onset of human civilization, man has worked continuously to make his life comfortable. Chemistry has played a vital role in improving the quality of human life. Gone are the days when man wandered for food, travelled on bullock cart, used pigeons to send messages and depended on conventional treatment methods for his well being. Sophisticated cultivation techniques, advanced means of transport, postal services, telegraph and now mobile and internet have replaced the older methods, and medical science has grown tremendously. However, all this has endangered our environment, our health and our non-renewable natural resources.

    Let us consider a small example. When man learnt to cultivate, he depended on nature for growing crops. Sometimes, he lost his crops to diseases and at other times, to the invasion of insects and pests. His yield was less. As he gradually acquired knowledge, he developed pesticides to fight against pests and diseases; he developed inorganic fertilizers which increased the yield of crops drastically. High yielding varieties were discovered, but the use of pesticides, herbicides, nitrogenous fertilizers have led to ground water pollution by the leaching of these chemicals into the ground. Occurrence of pesticide residues in food products, fertilizer run off from fields leading to eutrophication are the adverse effects of using pesticides and fertilizers. Hence, the discovery and use of these products have increased the potential risk to human health and environment.

    Similarly, the use of refrigerators and air conditioners for a comfortable living has adversely affected the environment due to the emission of chlorofluorocarbons. These CFCs have lead to the depletion of the ozone layer which filtered the ultraviolet radiations of the sun causing cancers. All the above can be attributed to the growth and contribution of chemistry. Now, while environmental chemistry seeks to study the role and effect of pesticides, herbicides and chlorofluorocarbons in the environment and also seeks measures to mitigate their effects, green chemistry addresses environmental concerns at the molecular level. It aims to design procedures that can reduce the production of waste, promote the efficient use of the raw material, design pesticides and herbicides that will not contaminate food products and will not cause ground and water pollution.

    Let us consider another example. The use of polythene bags is increasing tremendously. Its adverse effects are many and have caused concern among the international community.

  • 5 - Engineering Materials

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    11 May 2018
    Print publication:
    16 May 2015, pp 276-320

  • Summary

    Cement

    Introduction

    Cement is a binder, a substance that sets and hardens independently, and can bind other materials together. It is used in construction for binding materials like bricks, stones, and tiles and is also used for flooring and plastering purposes.

    Cements used in construction can be either hydraulic or non-hydraulic. Hydraulic cements (for example, Portland cement) set and harden because of hydration and hydrolysis reactions between the anhydrous cement powder and water.

    Non-hydraulic cement such as slaked limes (calcium hydroxide mixed with water), harden due to the carbonation reaction by carbon dioxide present naturally in the air.

    Cement alone cannot be used for construction work. It is used as a mixture with sand and crushed stones. It may be used as mortar or concrete.

    Mortar It is a mixture of cement, sand and water which is used for binding bricks together and for plastering.

    Concrete It is a mixture of cement, gravel (crushed stones), sand and water. It is used in flooring works, columns, beams, foundations, etc. If instead of cement, lime is used, then the concrete is known as lime concrete.

    Reinforced concrete construction (RCC) It is concrete reinforced with steel rods or heavy wire mesh. Reinforced concrete is used in floors, beams, girders, columns, slabs, bridges, etc. It imparts high tensile strength to structures.

    Portland cement was discovered by Joseph Aspdin in 1824. The name Portland cement comes from the fact that the colour and quality of the resulting concrete are similar to Portland stone, a kind of limestone found in England.

    Types of cements

    The different types of cements based on Indian Standards are as follows:

  • Ordinary Portland cement It is the most important type of cement and is commonly called OPC. It is made by grinding and mixing clay and lime bearing minerals in proper proportions and then heating the mixture to nearly 1400°C. It is not in much use these days, having been replaced by PPC (Portland pozzolana cement).

  • Portland pozzolana cement It can be fly ash based or calcined clay based. PPC is obtained by mixing OPC with suitable pozzolans at a certain temperature. Pozzolans are deposits of volcanic ash produced by rapid cooling. When mixed with slaked lime, pozzolans show properties similar to cement when it comes in contact with water. PPC is commonly used for various construction activities.

  • 16 - Photochemistry

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    11 May 2018
    Print publication:
    16 May 2015, pp 883-912

  • Summary

    Introduction

    Generally speaking, all chemical reactions require energy over and above the average kinetic energy of the molecules. The reactant molecules convert into products only after acquiring this extra energy called the activation energy. Sometimes, this activation energy is very low and the molecules can undergo spontaneous transformations even at room temperatures. However, in most cases, additional energy has to be supplied to the molecules to bring about the chemical change. If this extra energy is provided by absorption of heat from outside, then the reactions are called thermal or thermochemical reactions. In thermal reactions, the provided heat is distributed among the molecules such that all the molecules in the system have almost the same energy. When they acquire sufficient energy, they react to form products. Another way of providing activation energy to the molecules is by the absorption of electromagnetic radiation in the visible and ultraviolet region. Such reactions are termed as photochemical reactions. Unlike thermal conditions, in photochemical reactions, the absorption of light excites an individual molecule to an excited electronic state without affecting the surrounding molecules (Table 16.1). This selective excitation of individual molecules is a unique character of photochemical reactions. The chemistry of the excited state is different from that of the ground state. The reaction occurs and the molecule gradually returns to its ground state.

    The radiations can range from radiowaves to γ–rays, but for all practical purposes, the light radiations of visible and ultraviolet regions lying between 2000–8000 Å are considered, because these radiations possess sufficient energy to excite molecules from the ground state to higher electronic states.

    Common examples of photochemical reactions are given below.

    Photochemistry is defined as the study of chemical effects produced by light radiations ranging from 2000 to 8000 Å wavelength.

    Significance of Photochemistry

    Photochemistry finds applications in varied fields. It helps to save energy and enables the sustainable use of resources. Since solar energy is abundantly available and photochemical reactions are selective, they can help to carry out reactions under mild conditions, thus saving energy. Photochemistry finds use in the production of solar cells (photovoltaic cells), in catalysis and in pollution control. Photosynthesis and vision are some common examples of photochemical reactions involving supramolecules (explained later in this chapter). Supramolecular photochemistry finds use in micelles, production of optical sensors and devices like molecular machines, switches, molecular wires, light harvesting antennas, etc.

  • 15 - Spectroscopy

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    11 May 2018
    Print publication:
    16 May 2015, pp 815-882

  • Summary

    Introduction

    Spectroscopy is that branch of science which deals with the study of the interaction of electromagnetic radiation with matter. It is the most powerful tool available for the study of structures of atoms and molecules.

    Before discussing how electromagnetic radiations interact with matter, it is important to learn about electromagnetic radiations.

    Electromagnetic radiations

    Electromagnetic radiation is a form of radiant energy which has both particle as well as wave nature. In vacuum, it normally travels in a straight line with the speed of light (3 ×108 m/s). It has both electric and magnetic field components which are coplanar and oscillate perpendicular to each other and perpendicular to the direction of wave propagation (Fig. 15.1).

    Properties of electromagnetic radiations

    The properties of electromagnetic radiation can be described easily by ascribing wave nature to these radiations.

    (a) Wavelength It is denoted by λ (lambda) and is defined as the distance between two adjacent crests (C−C) or troughs (T−T) in a particular wave (Fig. 15.2). It can be expressed in cm. The other units for expressing wavelength are given below.

    Angstrom (Å) 1 Å = 10-8 cm = 10-10 m

    Nanometer (nm) or millimicron (mμ)

    1 nm = 1 mμ= 10−7 cm = 10−9 m

    (iii) Micron (μ) 1μ=10−4 cm = 10−6 m

    The wavelength of visible light ranges from 3800 Å (violet end) to 7600 Å (red end).

    (b) Frequency It is denoted by ν(nu) and is defined as the number of waves which can pass through a point in one second. Frequency is expressed in cycles per second or Hertz (Hz) where 1 Hz = 1 cycle/s.

    where c = velocity of electromagnetic radiation in cm/s = 2.998 × 1010 cm/s.

    λ= wavelength.

    We know that the wavelength of visible light is 3800−7600 Å. The corresponding frequency can be calculated as follows.

  • When λ= 3800 Å = 3800 × 10−8 cm,

  • When λ= 7600 Å = 7600 × 10−8 cm.

    • Thus, the frequency range of visible light is 7.88 × 108 MHz to 3.94 × 108 MHz.

    (c) Velocity Velocity of a wave is denoted by c and is defined as the distance travelled by a wave in one second. Electromagnetic radiations travel with the speed of light, hence the value of c is 2.998 × 108 cm/s or 18600 miles per second.

  • Preface

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    11 May 2018
    Print publication:
    16 May 2015, pp xvii-xx

  • Summary

    Engineering chemistry is taught as a compulsory subject to first year undergraduate students of all the branches of engineering. The scope of the subject is very wide and writing a book for a heterogeneous variety of students across the country was a challenging assignment. The needs of the students are diversified and incorporate a combination of the both traditional topics and the latest trends in the subject including emerging areas like liquid crystals, green chemistry and nanochemistry.

    This book has been organized to meet syllabi requirements of almost all Indian universities. The aim of this text is to enable the student to develop capabilities in self learning and understanding. It is a student oriented book and my teaching experience, stretching more than two decades, gave me insight into the mental status of the students at this level and the problems they confront while studying the subject. Two important facts have been kept in mind one, students reading this text are taking their first steps into the world of technical education and two, that English is a second language for most of these students.

    Keeping these objectives in mind the book has been written in very simple language. The book has nearly 350 figures and illustrations, over 500 solved, unsolved problems along with review questions and it also includes more than 450 multiple choice questions.

    All chapters are provided with highly descriptive and well labeled figures. A simple look at a figure will enable the student to grasp the underlying description. Theoretical explanations have been supplemented with solved and unsolved problems wherever required to enhance the process of understanding, learning and reproducing the principles involved. The problems have been blended with the text so that the student need not turn pages. The book aims to familiarize the student with the university pattern of examination: to meet this objective, numerical problems that have appeared in various university and board exams have been included at appropriate places.

    Organization of the book

    The book has been organized into twenty four chapters. It begins with topics of common interest like fuels, water, corrosion and phase rule followed by engineering materials, polymers and lubricants.

  • 12 - Surface Chemistry

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    11 May 2018
    Print publication:
    16 May 2015, pp 608-643

  • Summary

    Introduction

    Various physical and chemical reactions occur at the interfaces or boundaries of two different phases like solid–liquid interface, solid–solid interface, solid–gas interface, liquid–gas interface, liquid–solid interface and liquid–liquid interface. These reactions have been of great interest to the chemists worldwide as they have important applications in industrial and domestic field.

    All these changes occurring at the boundaries of different phases are studied under a branch of chemistry called surface chemistry. Surface chemistry not only deals with the reactions occurring at the interfaces but also studies the nature of surfaces and the reactions taking place at the surfaces. Adsorption and colloidal properties are some of the important effects that occur at the solid and liquid interfaces.

    Adsorption

    The surface of solid or liquid has a tendency to attract and retain molecules of other species (gas or liquids). This phenomenon of attracting and retaining molecules on the surface is termed as adsorption (latin word surbere; to suck up). The material on the surface of which adsorption occurs is termed as adsorbent and the substance adsorbed on the surface is called adsorbate. Now, the question arises why does adsorption occur? Adsorption occurs because of the presence of unbalanced forces at the surface of liquids and solids. In a solid or liquid, the molecules present in the bulk are attracted equally from all sides and the net force experienced by the molecule in the bulk is zero. However, the molecule that lies near the surface (known as surface molecule) is being attracted only by the molecules below it because there are no molecules above it. Hence, a net downward force is experienced by the surface molecule. Because of this downward force the surface molecule tends to attract and retain other species (a gas or a dissolved substance). These species do not penetrate inside the molecule but remain on the surface. Hence, their concentration is higher on the surface than in the bulk.

  • 21 - Basics of Environment Science

  • Shikha Agarwal
  • Book:
    Engineering Chemistry
    Published online:
    11 May 2018
    Print publication:
    16 May 2015, pp 1056-1120

  • Summary

    Introduction

    The word ‘environment’ is derived from the French word environner which means ‘encircle’ or ‘surround’. Everything surrounding an individual, both living and non-living, the plants, animals, the air, the water, the soil, rivers, mountains, deserts, light, heat is his or her environment. In fact, some scientists define environment as ‘everything that is not me’, hence the outside world in which we live, being a part of it, is our environment.

    Formally, environment can be defined as ‘all components of the earth including air, water and land, all layers of the atmosphere, all organic and inorganic matter, all living organisms and interacting natural systems’.

    Multidisciplinary Nature of Environment Science

    Environment science is multidisciplinary involving components from various branches of science (Fig. 21.1).

  • Chemistry Most pollutants are chemicals. Methods of their removal, their analysis, effects on living and non-living systems, all require a knowledge of chemistry.

  • Botany Without the knowledge of botany, it is impossible to know about the vegetation on earth.

  • Zoology All animals including man are an important component of the environment

  • Physics Knowledge of physics is essential to understand various environmental factors like heat, light, radiation, etc.

  • Geography It studies climate, vegetation, nature of soil, natural resources, their management and maintenance, all of which are a part of the environment

  • Meteorology Climatic conditions like wind flow, rainfall, snowfall, temperature change affect living beings, and hence are closely related to environmental science.

  • Sociology Society is responsible for the deterioration of the environment. Increasing pollution, social habits all affect the environment.

  • Other subjects like engineering, microbiology, biochemistry, seismology, oceanography, etc are also directly or indirectly related to environmental science.

Page 441 of 5306