Materials Engineering

Optical microscopy of solid materials starts with careful sample preparation. Materialography is the study of microscopic structures in solids and the features seen in those images. It helps reveal details such as porosity, grain size and shape, and whether the microstructure shows anisotropy, or direction-dependent structure.

This lesson focuses on the preparation steps used before optical microscopy. It covers the techniques and procedures needed to ready a solid material sample for imaging.

Optical materialography can be used to measure the microstructure of solid materials. It focuses on the microscopic structures seen in an exposed surface and uses them to study the material more deeply.

A common goal is to estimate the three-dimensional microstructure of a sample from a two-dimensional cross section. This approach relies on the structural features visible in the image. It helps turn surface observations into quantitative data about the material.

X-ray tomography can also...

X-ray photoelectron spectroscopy, or XPS, is a surface analysis method for studying materials. It measures elemental composition, empirical formula, chemical state, and electronic state of the elements in a sample. Because the signal comes from the top few nanometers, XPS is especially useful for examining surfaces.

To collect an XPS spectrum, a material is irradiated with an X-ray beam. At the same time, the instrument measures the kinetic energy and number of electrons that escape from the...

X-ray diffraction is a materials science method for finding crystal structure. It uses incident X-rays that strike a sample and scatter from its atoms and molecules. The scattered X-rays are measured by their intensity and scattering angle.

The results are plotted as intensity versus angle. Scientists then analyze the position of the peaks and their strength to determine the structure of the material. This method can also show how a real crystal differs from an ideal one. It can reveal effects...

Focused ion beams are used in microfabrication and nano-fabrication. A focused ion beam, or FIB, is an instrument that can fabricate, trim, analyze, and characterize materials on micro- and nano-scales. These tools are used in many fields, from nano-electronics to medicine.

FIB systems work with a beam of ions. That beam can mill, or sputter, material away. It can also deposit material and image surfaces at small scales. In many research labs, the ion column of a FIB is integrated with the...

Zone melting directional solidification is a metallurgical process used to move a narrow molten region through a crystal, usually a bar-shaped sample. A furnace travels along the rod, so the molten zone moves from one end of the bar to the other. This controlled motion changes how material forms as it solidifies.

In alloys, solute atoms tend to separate into the melt. Impurities also concentrate in the molten zone instead of staying in the solid. As the molten region moves forward, it carries...

Differential scanning calorimetry, or DSC, is a method used to measure the thermal properties of materials. It helps scientists see how much heat a material stores as it warms up. This heat storage is called heat capacity.

DSC also measures the heat absorbed or released during chemical reactions and phase changes. From these measurements, it can help determine other properties such as glass transition temperature and polymer crystallinity. Polymers often have long, chain-like structures that...

Laser flash analysis measures thermal diffusivity, which describes how fast heat moves through a material compared with how much heat it stores. This material-specific property helps show how a sample transfers thermal energy and how it responds to temperature changes.

Thermal diffusivity is related to thermal conductivity, the measure of how heat moves through a material because of a temperature difference. That relationship also depends on the material’s density, shown as ρ, and its specific...

Electroplating is a way to add a thin metal coating to a surface using electric current. In this process, dissolved metal cations are reduced and form a film on an electrode. The method is also called electrodeposition.

This page also compares electroplating with other thin film deposition methods. Chemical vapor deposition, or CVD, uses a gas-phase precursor. Spin coating spreads a liquid precursor by spinning it outward. Dip coating is similar, but the substrate is fully submerged instead of...

Dilatometry measures how a material changes in size as temperature changes. It can track changes in length, area, shape, or volume. The method is used to calculate thermal expansion, which is the expansion of a substance when it is heated.

Thermal expansion matters when choosing materials for systems that face changing temperatures. Some materials need high thermal expansion, such as the liquid in a thermometer, because the change helps detect temperature shifts. Other uses need materials with...

Electrical impedance describes how a circuit element resists the flow of electricity. It is a more general measure than electrical resistance, especially when a circuit is not simple enough to be described by resistance alone.

Resistance is the ability of a circuit element to resist current. It is defined by Ohm's law, which relates voltage and current. That relationship works well for ideal resistors, but many real circuit elements are more complex.

When an alternating current, or AC, is...

Bone helps show how ceramic-matrix composites work. In this material system, the ceramic part gives compressive strength, while the polymer fiber reinforcement adds tensile and flexural strength. By changing the amounts of ceramic and polymer, engineers can make materials for specific uses.

This idea matters in biomedical engineering, where replacing or copying bone after disease or traumatic injury is an important goal. For this study, plaster of Paris, a calcium sulfate compound, is used to...

Nanocrystalline alloys are metals with grain sizes smaller than 100 nm. These tiny grains can give the material enhanced physical and mechanical properties. That is why nanocrystalline alloys are used or studied for semiconductor devices, biosensors, and aerospace parts.

A major challenge is making dense bulk materials from these alloys. To reach close to 100% density, the material must be processed with elevated temperature and pressure. But as temperature and pressure rise, the small grains...

Hydrogels are cross-linked polymers that can absorb water and swell. They are made with relatively simple procedures and inexpensive materials, which makes them useful for many school-level chemistry and materials science topics.

A hydrogel starts with a polymer backbone built from monomer reagents. An initiator makes the polymer reactive, and a crosslinking species connects the chains together. This network gives the material its final structure.

Water absorption is one of the key features...