Materials science, also commonly known as materials
science and engineering, is an interdisciplinary field which deals with the
discovery and design of new materials. This relatively new scientific field
involves studying materials through the materials paradigm (synthesis,
structure, properties and performance). It incorporates elements of physics and chemistry,
and is at the forefront of nanoscience and nanotechnology
research. In recent years, materials science has become more widely known as a
specific field of science and engineering.
It is an important part of forensic engineering (the investigation of
materials, products, structures or components that fail or do not operate or
function as intended, causing personal injury or damage to property) and failure
analysis, the latter being the key to understanding, for example, the cause
of various aviation accidents. Many of the most pressing scientific problems
that are faced today are due to the limitations of the materials that are
available and, as a result, breakthroughs in this field are likely to have a
significant impact on the future of technology.
History
The material of choice of a given era is often a defining
point. Phrases such as Stone Age, Bronze Age,
Iron Age,
and Steel Age are great examples. Originally
deriving from the manufacture of ceramics and its putative derivative metallurgy, materials
science is one of the oldest forms of engineering and applied science. Modern
materials science evolved directly from metallurgy,
which itself evolved from mining and (likely) ceramics and the use of fire. A
major breakthrough in the understanding of materials occurred in the late 19th
century, when the American scientist Josiah Willard Gibbs demonstrated that the thermodynamic
properties related to atomic
structure in various phases
are related to the physical properties of a material. Important elements of
modern materials science are a product of the space race:
the understanding and engineering of the metallic alloys, and silica and carbon materials,
used in the construction of space vehicles enabling the exploration of space.
Materials science has driven, and been driven by, the development of
revolutionary technologies such as plastics, semiconductors,
and biomaterials.
Before the 1960s (and in some cases decades after), many materials
science departments were named metallurgy departments, reflecting
the 19th and early 20th century emphasis on metals. The field has since
broadened to include every class of materials, including ceramics, polymers, semiconductors,
magnetic
materials, medical implant materials, biological materials and
nanomaterials (materiomics).
Fundamentals
The materials paradigm represented in the form of a
tetrahedron.
A material is defined as a substance (most often a solid,
but other condensed phases can be included) that is intended to be used for
certain applications.There are a myriad of materials around us—they can be
found in anything from buildings to spacecrafts. Materials can generally be
divided into two classes: crystalline and non-crystalline.
The traditional examples of materials are metals, ceramics and polymers. New
and advanced materials that are being developed include semiconductors,
nanomaterials,
biomaterials,[3]
etc.
The basis of materials science involves studying the
structure of materials, and relating them to their properties.
Once, a materials scientists knows about this structure-property correlation,
he/she can then go on to study the relative performance of a material in a
certain application. The major determinants of the structure of a material and
thus of its properties are its constituent chemical elements and the way in
which it has been processed into its final form. These characteristics, taken
together and related through the laws of thermodynamics
and kinetics, govern a material’s microstructure,
and thus its properties.
Structure
As mentioned above, structure is one of the most important
components of the field of materials science. Materials science examines the
structure of materials from the atomic scale, all the way up to the macro
scale. Characterization is the way
materials scientists examine the structure of a material. This involves
techniques such as diffraction with x-rays, electrons, or
neutrons,
and various forms of spectroscopy and chemical
analysis such as Raman spectroscopy, energy-dispersive spectroscopy
(EDS), chromatography, thermal
analysis, electron microscope analysis, etc. Structure is
studied at various levels, as detailed below.
Atomistic structure
This deals with the atoms of the materials, and how they are
arranged to give molecules, crystals, etc. Much of the electrical, magnetic and
chemical properties of materials arise from this level of structure. The length
scales involved are in angstroms (0.1 nm). The way in which the atoms and
molecules are bonded and arranged is fundamental to studying the properties and
behavior of any material.
Nanostructure
Nanostructure deals with objects and structures that are in
the 1—100 nm range. In many materials, atoms or molecules agglomerate
together to form objects at the nanoscale. This leads to many interesting
electrical, magnetic, optical and mechanical properties.
In describing nanostructures it is necessary to
differentiate between the number of dimensions on the nanoscale. Nanotextured surfaces have one dimension
on the nanoscale, i.e., only the thickness of the surface of an object is
between 0.1 and 100 nm. Nanotubes have two dimensions on the
nanoscale, i.e., the diameter of the tube is between 0.1 and 100 nm; its
length could be much greater. Finally, spherical nanoparticles
have three dimensions on the nanoscale, i.e., the particle is between
0.1 and 100 nm in each spatial dimension. The terms nanoparticles and ultrafine particles (UFP) often are used
synonymously although UFP can reach into the micrometre range. The term
'nanostructure' is often used when referring to magnetic technology. Nanoscale
structure in biology is often called ultrastructure.
Materials whose atoms/molecules form constituents in the
nanoscale (i.e., they form nanostructure) are called nanomaterials.
Nanomaterials are subject of intense research in the materials science community
due to the unique properties that they exhibit.
Microstructure
Microstructure is defined as the structure of a prepared
surface or thin foil of material as revealed by a microscope above 25×
magnification. It deals with objects in from 100 nm to few cm. The
microstructure of a material (which can be broadly classified into metallic,
polymeric, ceramic and composite) can strongly influence physical properties
such as strength, toughness, ductility, hardness, corrosion resistance,
high/low temperature behavior, wear resistance, and so on. Most of the
traditional materials (such as metals and ceramics) are microstructured.
The manufacture of a perfect crystal of a
material is physically impossible. For example, a crystalline material will
contain defects such as precipitates, grain boundaries (Hall–Petch
relationship), interstitial atoms, vacancies or substitutional atoms. The
microstructure of materials reveals these defects, so that they can be studied.
Macrostructure
Macrostructure is the appearance of a material in the scale
millimeters to meters—it is the structure of the material as seen with the
naked eye.
Crystallography
Crystallography is the science that examines the arrangement
of atoms in crystalline solids. Crystallography is a useful tool for materials
scientists. In single crystals, the effects of the crystalline arrangement of
atoms is often easy to see macroscopically, because the natural shapes of
crystals reflect the atomic structure. In addition, physical properties are
often controlled by crystalline defects. The understanding of crystal
structures is an important prerequisite for understanding crystallographic defects.
Mostly, materials do not occur as a single crystal, but in poly-crystalline
form (i.e., as an aggregate of small crystals with different orientations).
Because of this, the powder diffraction method, which uses diffraction patterns
of polycrystalline samples with a large number of crystals, plays an important
role in structural determination. Most materials have a crystalline structure.
But, there are some important materials that do not exhibit regular crystal
structure. Polymers
display varying degrees of crystallinity, and many are completely
non-crystalline. Glass
as, some ceramics, and many natural materials are amorphous,
not possessing any long-range order in their atomic arrangements. The study of
polymers combines elements of chemical and statistical thermodynamics to give
thermodynamic, as well as mechanical, descriptions of physical properties.
Bonding
To obtain a full understanding of the material structure and
how it relates to its properties, the materials scientist must study how the
different atoms, ions and molecules are arranged and bonded to each other. This
involves the study and use of quantum
chemistry or quantum physics. Solid-state physics, solid state chemistry and physical chemistry are also involved in the
study of bonding and structure.
Properties
Materials exhibit a myriad of properties. The important
properties of materials are as follows:
- Mechanical properties
- Chemical Properties
- Electrical Properties
- Thermal Properties
- Optical Properties
- Magnetic Properties
The properties of a materials determine its usability and
hence its engineering application.
Synthesis and processing
Synthesis and processing involves the creation of a material
with the desired micro/nanostructure. From an engineering standpoint, a
material cannot be used in industry if no economical manufacturing method for
it has been developed. Thus, the processing of materials is very important to
the field of materials science.
Different materials require different processing/synthesis
techniques. For example, the processing of metals has historically been very
important and is studied under the branch of materials science known as physical
metallurgy. Also, chemical and physical techniques are also used to
synthesis other materials such as polymers, ceramics, thin films, etc.
Currently, new techniques are being developed to synthesize nanomaterials such
as graphene.
Thermodynamics
Thermodynamics is concerned with heat and temperature
and their relation to energy and work. It defines macroscopic
variables, such as internal energy, entropy, and pressure, that
partly describe a body of matter or radiation. It states that the behavior of
those variables is subject to general constraints, that are common to all
materials, not the peculiar properties of particular materials. These general
constraints are expressed in the four laws of thermodynamics. Thermodynamics describes
the bulk behavior of the body, not the microscopic behaviors of the very large
numbers of its microscopic constituents, such as molecules. The behavior of
these microscopic particles is described by, and the laws of thermodynamics are
derived from, statistical mechanics.
The study of thermodynamics is fundamental to materials
science. It forms the foundation to treat general phenomena in materials
science and engineering, including chemical reactions, magnetism,
polarizability, and elasticity. It also helps in the understanding of phase
diagrams and phase equilibrium.
Kinetics
Kinetics is the study of the rates at which
systems that are out of equilibrium change under the influence of various
forces. When applied to materials science, it deals with how a material changes
with time (moves from non-equilibrium to equilibrium state) due to application
of a certain field—it details the rate of various processes evolving in
materials including shape, size, composition and structure. Diffusion is
important in the study of kinetics as this is the most common mechanism by
which materials undergo change.
Kinetics is essential in processing of materials because,
among other things, it details how the microstructure changes with application
of heat.
Materials in research
Materials science has received much attention from
researchers. In most universities, many departments ranging from physics to chemistry to chemical engineering—in addition to materials
science departments—are involved in materials research. Research in materials
science is vibrant and consists of many avenues. The following list is in no
way exhaustive, it just serves to highlight certain important research areas.
Nanomaterials
Nanomaterials describe, in principle, materials of which a
single unit is sized (in at least one dimension) between 1 and 1000 nanometers
(10−9 meter) but is usually 1—100 nm.
Nanomaterials research takes a materials science-based
approach to nanotechnology, leveraging advances in materials metrology and
synthesis which have been developed in support of microfabrication
research. Materials with structure at the nanoscale often have unique optical,
electronic, or mechanical properties.
The field of nanomaterials is loosely organized, like the
traditional field of chemistry, into organic (carbon-based) nanomaterials such
as fullerenes, and inorganic nanomaterials based on other elements, such as
silicon. Examples of nanomaterials include fullerenes,
carbon
nanotubes, nanocrystals, etc.
Biomaterials
A biomaterial is any matter, surface, The study of
biomaterials is called biomaterials science. It has experienced steady
and strong growth over its history, with many companies investing large amounts
of money into the development of new products. Biomaterials science encompasses
elements of medicine,
biology, chemistry, tissue engineering and materials science.
Biomaterials can be derived either from nature or
synthesized in the laboratory using a variety of chemical approaches utilizing
metallic components, polymers, ceramics or composite materials. They are often used and/or
adapted for a medical application, and thus comprises whole or part of a living
structure or biomedical device which performs, augments, or replaces a natural
function. Such functions may be benign, like being used for a heart valve,
or may be bioactive
with a more interactive functionality such as hydroxy-apatite
coated hip
implants. Biomaterials are also used everyday in dental applications,
surgery, and drug delivery. For example, a construct with impregnated
pharmaceutical products can be placed into the body, which permits the
prolonged release of a drug over an extended period of time. A biomaterial may
also be an autograft,
allograft
or xenograft
used as a transplant material.
Electronic, optical and magnetic materials
Semiconductors, metals, and ceramics are used today to form
highly complex systems, such as integrated electronic circuits, optoelectronic
devices, and magnetic and optical mass storage media. These materials form the
basis of our modern computing world, and hence research into these materials
are of vital importance.
Semiconductors are a traditional example of these type
of materials. They are materials that have properties that are intermediate
between conductors and insulators. Their electrical conductivities
are very sensitive to impurity concentrations, and this allows for the use of doping to achieve desirable electronic
properties. Hence, semiconductors form the basis of the traditional computer.
This field also includes new areas of research such as superconducting
materials, spintronics, metamaterials,
etc. The study of these materials involves knowledge of materials science and solid state physics or condensed matter physics.
Computational materials science and materials theory
With the increase in computing power, simulating the
behavior of materials has become possible. This enables materials scientists to
discovery properties of materials previously unknown, as well as to design new
materials. Up until now, new materials were found by a time consuming trial and
error process. But, now it is hoped that computational techniques could
drastically reduce that time, and allow us to tailor materials properties. This
involves simulating materials at all length scales, using methods such as density functional theory, molecular dynamics, etc.
Materials in industry
Radical materials advances can drive the
creation of new products or even new industries, but stable industries also
employ materials scientists to make incremental improvements and troubleshoot
issues with currently used materials. Industrial applications of materials
science include materials design, cost-benefit tradeoffs in industrial
production of materials, processing techniques (casting, rolling, welding, ion
implantation, crystal growth, thin-film deposition, sintering, glassblowing,
etc.), and analytical techniques (characterization techniques such as electron microscopy, x-ray
diffraction, calorimetry, nuclear microscopy (HEFIB), Rutherford backscattering, neutron diffraction, small-angle X-ray
scattering (SAXS), etc.).
Besides material characterization, the material
scientist/engineer also deals with the extraction of materials and their
conversion into useful forms. Thus ingot casting, foundry techniques, blast
furnace extraction, and electrolytic extraction are all part of the required
knowledge of a materials engineer. Often the presence, absence or variation of
minute quantities of secondary elements and compounds in a bulk material will
have a great impact on the final properties of the materials produced, for
instance, steels are classified based on 1/10 and 1/100 weight percentages of
the carbon and other alloying elements they contain. Thus, the extraction and
purification techniques employed in the extraction of iron in the blast furnace
will have an impact of the quality of steel that may be produced.
Ceramics and glasses
Another application of material science is the structures of
glass and ceramics,
typically associated with the most brittle materials. Bonding in ceramics and
glasses use covalent and ionic-covalent types with SiO2 (silica or
sand) as a fundamental building block. Ceramics are as soft as clay and as hard
as stone and concrete. Usually, they are crystalline in form. Most glasses
contain a metal oxide fused with silica. At high temperatures used to prepare
glass, the material is a viscous liquid. The structure of glass forms into an
amorphous state upon cooling. Windowpanes and eyeglasses are important
examples. Fibers of glass are also available. Scratch resistant Corning Gorilla
Glass is a well-known example of the application of materials science to
drastically improve the properties of common components. Diamond and carbon in
its graphite form are considered to be ceramics.
Engineering ceramics are known for their stiffness and
stability under high temperatures, compression and electrical stress. Alumina, silicon
carbide, and tungsten carbide are made from a fine powder of
their constituents in a process of sintering with a binder. Hot pressing
provides higher density material. Chemical vapor deposition can place a film of
a ceramic on another material. Cermets are ceramic particles containing some
metals. The wear resistance of tools is derived from cemented carbides with the
metal phase of cobalt and nickel typically added to modify properties.
Composite materials
A 6 μm diameter carbon filament (running from bottom left to
top right) siting atop the much larger human hair.
Filaments
are commonly used for reinforcement in composite materials.
Another application of materials science in industry is the
making of composite materials. Composite materials are
structured materials composed of two or more macroscopic phases. Applications
range from structural elements such as steel-reinforced concrete, to the
thermally insulative tiles which play a key and integral role in NASA's Space Shuttle thermal
protection system which is used to protect the surface of the shuttle from
the heat of re-entry into the Earth's atmosphere. One example is reinforced Carbon-Carbon (RCC), the light
gray material which withstands re-entry temperatures up to 1510 °C
(2750 °F) and protects the Space Shuttle's wing leading edges and nose
cap. RCC is a laminated composite material made from graphite rayon cloth and
impregnated with a phenolic resin. After curing at high temperature in
an autoclave, the laminate is pyrolized to convert the resin to carbon,
impregnated with furfural alcohol in a vacuum chamber, and cured/pyrolized to
convert the furfural
alcohol to carbon. In order to provide oxidation resistance for reuse
capability, the outer layers of the RCC are converted to silicon
carbide.
Other examples can be seen in the "plastic"
casings of television sets, cell-phones and so on. These plastic casings are
usually a composite material made up of a thermoplastic
matrix such as acrylonitrile-butadiene-styrene
(ABS) in which calcium carbonate chalk, talc, glass
fibers or carbon fibers have been added for added strength,
bulk, or electrostatic dispersion. These additions may be referred to as
reinforcing fibers, or dispersants, depending on their purpose.
Polymers
Polymers are also an important part of materials science.
Polymers are the raw materials (the resins) used to make what we commonly call
plastics. Plastics are really the final product, created after one or more
polymers or additives have been added to a resin during processing, which is
then shaped into a final form. Polymers which have been around, and which are
in current widespread use, include polyethylene,
polypropylene,
PVC, polystyrene,
nylons, polyesters, acrylics,
polyurethanes,
and polycarbonates.
Plastics are generally classified as "commodity",
"specialty" and "engineering" plastics.
PVC (polyvinyl-chloride) is widely used, inexpensive, and
annual production quantities are large. It lends itself to an incredible array
of applications, from artificial leather to electrical insulation and cabling, packaging and
containers.
Its fabrication and processing are simple and well-established. The versatility
of PVC is due to the wide range of plasticisers
and other additives that it accepts. The term "additives" in polymer
science refers to the chemicals and compounds added to the polymer base to
modify its material properties.
Polycarbonate would be normally considered an engineering
plastic (other examples include PEEK, ABS). Engineering plastics are valued for
their superior strengths and other special material properties. They are
usually not used for disposable applications, unlike commodity plastics.
Specialty plastics are materials with unique
characteristics, such as ultra-high strength, electrical conductivity,
electro-fluorescence, high thermal stability, etc.
The dividing lines between the various types of plastics is
not based on material but rather on their properties and applications. For
instance, polyethylene (PE) is a cheap, low friction polymer
commonly used to make disposable shopping bags and trash bags, and is
considered a commodity plastic, whereas medium-density polyethylene (MDPE) is
used for underground gas and water pipes, and another variety called Ultra-high
Molecular Weight Polyethylene UHMWPE is an engineering plastic which is used extensively as
the glide rails for industrial equipment and the low-friction socket in
implanted hip
joints.
Metal alloys
The study of metal alloys is a significant part of materials
science. Of all the metallic alloys in use today, the alloys of iron (steel, stainless
steel, cast
iron, tool
steel, alloy steels) make up the largest proportion both by
quantity and commercial value. Iron alloyed with various proportions of carbon
gives low, mid and high carbon steels. An iron carbon alloy is only
considered steel if the carbon level is between 0.01% and 2.00%. For the
steels, the hardness
and tensile strength of the steel is related to the amount of carbon present,
with increasing carbon levels also leading to lower ductility and toughness.
Heat treatment processes such as quenching and tempering can significantly
change these properties however. Cast Iron is defined as an iron–carbon alloy
with more than 2.00% but less than 6.67% carbon. Stainless steel is defined as
a regular steel alloy with greater than 10% by weight alloying content of
Chromium. Nickel and Molybdenum are typically also found in stainless steels.
Other significant metallic alloys are those of aluminium, titanium, copper and magnesium. Copper
alloys have been known for a long time (since the Bronze Age),
while the alloys of the other three metals have been relatively recently
developed. Due to the chemical reactivity of these metals, the electrolytic
extraction processes required were only developed relatively recently. The
alloys of aluminium, titanium and magnesium are also known and valued for their
high strength-to-weight ratios and, in the case of magnesium, their ability to
provide electromagnetic shielding. These materials are ideal for situations
where high strength-to-weight ratios are more important than bulk cost, such as
in the aerospace industry and certain automotive engineering applications.
Relation to other fields
Materials science evolved—starting from the 1960s—because it
was recognized that to create, discover and design new materials, one had to
approach it from a unified manner. Thus, materials science and engineering
emerged at the intersection of various fields such as metallurgy,
solid state physics, chemistry, chemical engineering, mechanical engineering and electrical engineering.
The field is inherently interdisciplinary,
and the materials scientists/engineer must be aware and make use of the methods
of the physicist, chemist and engineer. The field thus, maintains close
relationships with these field. Also, many physicists, chemists and engineers
also find themselves working in materials science.
The overlap between physics and materials science has led to
the offshoot field of materials physics, which is concerned with the
physical properties of materials. The approach is generally more macroscopic
and applied than in condensed matter physics. See important publications in materials
physics for more details on this field of study.
The field of materials science and engineering is important
both from a scientific perspective, as well as from an engineering one. When
discovering new materials, one encounters new phenomena that may not have been
observe before. Hence, there is lot of science to be discovered when working
with materials. Materials science also provides test for theories in condensed
matter physics.
Materials for an engineer is of utmost importance. The usage
of the appropriate materials is crucial when designing systems, and hence,
engineers are always involved in materials. Thus, materials science is becoming
increasingly important in an engineer's education.
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