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Questions and Answers
What is the main factor that determines the properties of materials?
What happens to the strength, hardness, and toughness of carbon steel as the carbon content increases?
What is added to carbon steel to make it stainless?
What is the term for the thick structure of materials above millimeter that can be identified with magnifying glass or naked eyes?
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What are minerals in materials?
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Why do different clinkers in cement result in different characteristics?
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What are the three levels of structure in materials?
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What is the importance of chemical composition in materials?
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What is the term for the chemical constituents of materials?
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What is an example of a material that has different properties due to different mineral compositions?
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What is the charge of the nucleus in an atom?
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What is the driving force behind the bonding of atoms?
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What type of bond involves the transfer of an electron?
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What is a characteristic of ionic bonds?
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What type of bond is common in organic molecules?
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What is a characteristic of metallic bonds?
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What is the 'sea of electrons' model used to describe?
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Which of the following is NOT a characteristic of ionic bonds?
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What is the result of the electrostatic attraction between the nucleus and electrons in an atom?
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Which type of bond can only occur between atoms of different elements?
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What is the minimum scale that must be considered at the engineering level?
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What is the shape of the representative cell if the material is isotropic?
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What is the main focus of study at the meso-structure level?
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What is the term used to describe the material structural level?
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What is the size of the wall thickness of a wood cell?
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What is the term used to describe the atomic and molecular structures of materials?
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What is the size of the representative cell for concrete?
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What is the term used to describe a material whose properties can only be described with reference to orientation?
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What is the size of the length of a brick?
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At which level is the material considered as a composite of different phases?
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Study Notes
Materials Composition and Structure
- The composition of materials can be classified into two types: chemical composition and mineral composition.
- Chemical composition refers to the chemical constituents of a material, which affect its properties.
- Increasing carbon content in carbon steel changes its strength, hardness, and toughness.
- Adding chromium, nickel, and other chemical components to steel creates stainless steel.
Mineral Composition
- Many inorganic materials consist of a variety of mineral compositions.
- Minerals are monomers and compounds with specific chemical components and structures.
- Mineral compositions affect the properties of building materials such as natural stone, inorganic gel, and cement.
- Different clinkers in cement result in different characteristics.
Structure of Materials
- The structure of materials can be divided into three levels: macro-structure, meso-structure, and micro-structure.
- Macro-structure refers to the thick structure above millimeter that can be identified with the naked eye or magnifying glass.
- At the engineering level, the total material is considered as continuous and homogeneous, and average properties are assumed throughout the whole volume of the material body.
- The minimum scale that must be considered is governed by the size of the representative cell, which varies from 10-3 m for metals to 0.1 m for concrete and 1 m for masonry.
Meso-structure
- Meso-structure refers to the micro-level structure that can be observed by optical microscope.
- This level is a step up in size from the molecular level, and the material is considered as a composite of different phases that interact to realize the behavior of the total material.
- The size, shape, and interface of grains and particles, as well as the size, shape, and distribution of pores and micro-cracks, are studied at this level.
Microstructure
- Microstructure refers to the atomic and molecular structures of materials that can be studied by electron microscopy, X-ray diffractometer, and other means.
- Atoms, the building block of elements, consist of a nucleus surrounded by a cloud of orbiting electrons.
- The nucleus consists of positively charged protons and neutral neutrons, and has a net positive charge that holds the negatively charged electrons in position by an electrostatic attraction.
Bonding of Atoms
- Atoms tend to arrange themselves in the most stable patterns possible, which means they have a tendency to complete or fill their outermost electron orbits.
- Atoms join with other atoms to do just that, resulting in three types of bonds: ionic, covalent, and metallic.
Ionic Bond
- Ionic bonding involves a transfer of an electron, so one atom gains an electron while one atom loses an electron.
- The strength, hardness, and melting point are high, but volatile; some are soluble and density is medium.
- Examples of ionic bonds include calcium chloride, gypsum, limestone, and others.
Covalent Bond
- Covalent bonding involves the sharing of electrons between two atoms.
- The bonding force is strong, and the strength, hardness, melting point, and density of atomic crystal are high.
- Examples of covalent bonds include diamond, quartz, and silicon carbide.
Metallic Bond
- Metallic bonding is similar to covalent bonding, because it involves sharing electrons.
- The simplest model of metallic bonding is the "sea of electrons" model, which imagines that the atoms sit in a sea of valence electrons that are delocalized over all the atoms.
- The strength and hardness are volatile, and the density is high.
- Metal materials such as iron, steel, aluminum, copper, and their alloys have good thermal conductivity and electrical conductivity due to the presence of free ions.
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Description
Learn about the composition of materials, including chemical composition and mineral composition, and how they affect material properties.
