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The Center for Advanced Mineral, Metallurgical and Materials Processing



Materials Analysis
Thermogravimetric Analysis

Thermogravimetric analysis is the quantitative measurement of any change in weight of a substance under investigation or examination with a change in temperature.

For example, thermogravimetry (TG) can identify the loss in weight with time or temperature due to dehydration or decomposition on heating a sample. Thermograms are characteristic for a given compound or system because of the unique sequence of physiochemical reactions which occur over definite temperature ranges and at rates that are a function of the molecular structure.

Simultaneous Thermal Analysis

A popular and useful device is a combined DTA/TG (simultaneous thermal analysis: STA) system in which both thermal and mass change effects are measured concurrently on the same sample. STA can be used to follow the course of chemical reactions, thermal decompositions or phase changes as a function of temperature. The sensitive balance associated with the TG capability of the system allows the mass change of a specimen to be measured as a function of temperature. Simultaneous DTA, TG and mass spectrometer measurements provide information about the cause of the mass changes.

Dynamic Mechanical Analysis

DMA supplies an oscillatory force, causing a sinusoidal stress to be applied to the sample, which generates a sinusoidal strain. By measuring both the amplitude of the deformation at the peak of the sine wave and the lag between the stress and strain sine waves, quantities like the modulus, the viscosity, and the damping can be calculated. One can calculate properties like the tendency to flow from the phase lag and the stiffness from the sample recovery. These properties are often described as the ability to lose energy as heat and the ability to recover from deformation.

Dilatometric Analysis

The dilatometric method utilizes either transformation strains or thermal strains; the basic data generated are in the form of curves of dimension against time and temperature. This information is used in the fabrication of metallic alloys, compressed and sintered refractory compounds, glasses, ceramic products, composite materials, and plastics.

Scanning Electron Microscopy

The scanning electron microscope (SEM) permits the observation and characterization of heterogeneous organic and inorganic materials on a nanometer to micrometer scale. The popularity of the SEM stems from its capability of obtaining three-dimensional-like images of the surfaces of a very wide range of materials.

In the SEM, the area to be examined or the microvolume to be analyzed is irradiated with a finely focused electron beam, which may be swept in a raster across the surface of the specimen to form images or may be static to obtain an analysis at one position. The types of signals produced from the interaction of the electron beam with the sample include secondary electrons, backscattered electrons, characteristic x-rays, and other photons of various energies. These signals are obtained from specific emission volumes within the sample and can be used to examine many characteristics of the sample.

The imaging signals of greatest interest are the secondary and backscattered electrons because these vary primarily as a result of differences in surface topography. The secondary electron emission, confined to a very small volume near the beam impact area for certain choices of the beam energy, permits images to be obtained at a resolution approximately the size of the focused electron beam. The three-dimensional appearance of the images is due to the large depth of the field of the scanning electron microscope as well as to the shadow relief effect of the secondary and backscattered electron contrast.

Characteristic x-rays are also emitted as a result of electron bombardment. The analysis of the characteristic x-radiation emitted from samples can yield both qualitative identification and quantitative elemental information from regions of a specimen nominally 1 micron in diameter and 1 micron in depth under normal operating conditions. The evolution of the SEM and the specific capabilities of modern commercial instruments are discussed below.

Metallographic Analysis

Metallography may be defined as the study of the internal structure of metals and alloys, and of its relation to their composition, and to their physical and mechanical properties. The needs of practical metallurgy, especially in the iron and steel industries, have been the motive of the earliest, and of many of the most important metallographic investigations. The study of structure has proved itself an indispensable auxiliary to chemical analysis in the scientific control of the metallurgical industries, an auxiliary of which the applications become more extensive and more important every year. The characterization of materials by metallographic techniques has been paralleled by a remarkable improvement in material capabilities. The ability to measure and characterize those material parameters that provide improved mechanical and physical properties has led directly the development of new and better materials. The successful correlation of the structure and properties of materials, whether on a theoretical or empirical level, has been one of the primary forces in the current materials revolution.

Fourier Transform Infrared Spectroscopy (FT-IR)

In infrared (IR) spectroscopy, IR radiation is passed through a sample. Some of the infrared radiation is absorbed by the sample and some of it is passed through (transmitted). The resulting spectrum represents the molecular absorption and transmission, creating a molecular fingerprint of the sample. Like a fingerprint no two unique molecular structures produce the same infrared spectrum.

What information can FT-IR provide?

  • Identify unknown materials
  • Determine the quality or consistency of a sample
  • Determine the amount of components in a mixture

An infrared spectrum represents a fingerprint of a sample with absorption peaks which correspond to the frequencies of vibrations between the bonds of the atoms making up the material. Because each different material is a unique combination of atoms, no two compounds produce the exact same infrared spectrum. Therefore, infrared spectroscopy can result in a positive identification (qualitative analysis) of every different kind of material. In addition, the size of the peaks in the spectrum is a direct indication of the amount of material present. With modern software algorithms, infrared is an excellent tool for quantitative analysis of materials.

Raman Spectroscopy

Infrared (IR) absorption and Raman scattering are both commonly used to study and identify substances using the compound's characteristic internal vibrations.

Infrared spectroscopy is an absorption process, measuring the fraction of the light absorbed as the wavelength of the light is varied. The incident light is absorbed when the energy of the light closely matches the energy of a vibrational transition in the sample.

A tiny proportion (approximately 1 in 109) of the photons incident on a sample interacts with vibrations in the sample and is scattered at higher or lower energy (Raman scattered).

  • Raman spectroscopy involves the measurement of the difference in energy between the incident light and the Raman scattered photons, which corresponds to the energy of the vibrational transitions.
  • Forensics
  • Pharmaceuticals
  • Art restoration and archaeology
  • Catalysts
  • Polymers
Sintering Analysis

Sintering is the reduction of porosity and the agglomeration of particles.

Sintering is studied by plotting density or shrinkage data as a function of time and by actual examination of the microstructure at various stages of sintering using scanning electron microscopy, transmission microscopy, and lattice imaging.

Fatigue Analysis

Fatigue analysis tests are used to select the right materials to design and manufacture a particular component or structure.  This includes evaluating how a material behaves under various loads and in various environments, as well as evaluating the expected working life and cost of production of a component or structure.    

Nano-Indentation Analysis

It is not only hardness that is of interest to materials scientists. Indentation techniques can also be used to calculate elastic modulus, strain-hardening exponent, fracture toughness, and viscoelastic properties. The goal of nanoindentation tests is to extract elastic modulus and hardness of the specimen from load-displacement measurements. Conventional indentation hardness tests involve the measurement of the size of a residual plastic impression in the specimen as a function of the indenter load. This provides a measure of the area of contact for a given indenter load. In a nanoindentation test, the size of the residual impression is often only a few microns and this makes it very difficult to obtain a direct measure using optical techniques. In nano-indentation testing, the depth of penetration beneath the specimen surface is measured as the load is applied to the indenter. The known geometry of the indenter then allows the size of the area of contact to be determined. The procedure also allows for the modulus of the specimen material to be obtained from a measurement of the stiffness of the contact, that is, the rate of change of load and depth. The principal goal is to extract the elastic modulus and hardness of the specimen material from these experimental readings.

Tension Analysis

A tensile test, also known as a tension test, is probably the most fundamental type of mechanical test you can perform on material. Tensile tests are simple, relatively inexpensive, and fully standardized. By pulling on something, you will very quickly determine how the material will react to forces being applied in tension. As the material is being pulled, you will find its strength along with how much it will elongate.

You can learn a lot about a substance from tensile testing. As you continue to pull on the material until it breaks, you will obtain a good, complete tensile profile. A curve will result showing how it reacted to the forces being applied. The point of failure is of much interest and is typically called its "ultimate tensile strength" or UTS.

Compression Analysis

A compression test determines behavior of materials under crushing loads. The specimen is compressed and deformation at various loads is recorded. Compressive stress and strain are calculated and plotted as a stress-strain diagram which is used to determine elastic limit, proportional limit, yield point, yield strength and, for some materials, compressive strength.

Hardness Analysis

Hardness may be defined as the resistance of a material to permanent penetration by another material. A hardness test is generally conducted to determine the suitability of a material to fulfill a certain purpose or application. Conventional types of static indentation hardness tests, such as the Brinell, Vickers, Rockwell, and Knoop hardness, provide a single hardness number as the result, which is the most useful as it correlates to other properties of the material, such as strength, wear resistance, and ductility. The correlation of hardness to other physical properties has made it a common tool for industrial quality control, acceptance testing, and selection of materials.

With the rising interest in the testing of thin coatings and in order to obtain more information from an indentation test, instrumented indentation tests have been developed and standardized. In addition to obtaining conventional hardness values, instrumented indentation tests can also determine other material parameters such as Martens hardness, indentation hardness, indentation modulus, indentation creep and indentation relaxation.

Hardness testing is one of the longest used and well known test methods for metallic and other types of materials, and has special importance in the field of mechanical test methods, because it is a relative inexpensive, easy to use and hardly nondestructive method for the characterization of materials and products.

Hardness data are test-system dependent and not fundamental metrological values. For this reason, hardness testing uses a combination of certified reference materials and verified calibration machines to establish and maintain national and world-wide uniform hardness scales.

Impact Analysis

Impact testing is performed to evaluate the toughness of materials. There are several loading methods, including tension, compression, bending, and torsion. The typical test is the Charpy impact test in which three-point bending is employed. A hammer is dropped to hit a rectangular specimen. A V- or U-type notch is introduced to allow easy fracture due to stress concentration for ductile materials. In the case of brittle materials such as ceramics, or cast iron, a notch is not introduced. Parts of the hammer before and after hitting (breaking) a specimen are compared. The balance is considered to show the resistance to fracture, and the energy needed to bend and fracture the specimen.