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Optical Materialography Part 2: Image Analysis

JoVE 10433

Source: Faisal Alamgir, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA

The imaging of microscopic structures of solid materials, and the analysis of the structural components imaged, is known as materialography. Often, we would like to quantify the internal three-dimensional microstructure of a material using only the structural features evidenced by an exposed two-dimensional surface. While X-ray based tomographical methods can reveal buried microstructure (for example the CT scans we are familiar with in a medical context), access to these techniques is quite limited due to the cost of the associated instrumentation. Optical microscope based materialography provides a much more accessible and routine alternative to X-ray tomography. In Part 1 of the Materialography series, we covered the basic principals behind sample preparation. In Part 2, we will go over the principals behind image analysis, including the statistical methods that allow us to quantitatively measure microstructural features and translate information from a two-dimensional cross section to the three-dimensional structure of a material sample.


 Materials Engineering

X-ray Diffraction

JoVE 10446

Source: Faisal Alamgir, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA

X-ray diffraction (XRD) is a technique used in materials science for determining the atomic and molecular structure of a material. This is done by irradiating a sample of the material with incident X-rays and then measuring the intensities and scattering angles of the X-rays that are scattered by the material. The intensity of the scattered X-rays are plotted as a function of the scattering angle, and the structure of the material is determined from the analysis of the location, in angle, and the intensities of scattered intensity peaks. Beyond being able to measure the average positions of the atoms in the crystal, information on how the actual structure deviates from the ideal one, resulting for example from internal stress or from defects, can be determined. The diffraction of the X-rays, that is central to the XRD method, is a subset of the general X-ray scattering phenomena. XRD, which is generally used to mean can wide-angle X-ray diffraction (WAXD), falls under several methods that use the elastically scattered X-ray waves. Other elastic scattering based X-ray techniques include small angle X-ray scattering (SAXS), where the X-rays are incident on the sample over the small


 Materials Engineering

Ceramic-matrix Composite Materials and Their Bending Properties

JoVE 10481

Source: Sina Shahbazmohamadi and Peiman Shahbeigi-Roodposhti, School of Engineering, University of Connecticut, Storrs, CT

Bones are composites, made of a ceramic matrix and polymer fiber reinforcements. The ceramic contributes compressive strength, and the polymer provides tensile and flexural strength. By combining ceramic and polymer materials in different amounts, the body can create unique materials tailored for a specific application. As biomedical engineers, having the ability to replace and replicate bone due to disease or traumatic injury is a vital facet of medical science. In this experiment we will create three different ceramic-matrix composites with plaster of Paris (which is a calcium sulfate compound), and allow them to undergo three-point bending test in order to determine which preparation is the strongest. The three composites are as follows: one comprised only of plaster of Paris, one with chopped glass shards mixed in a plaster matrix and lastly a plaster matrix with a fiberglass network embedded within it.


 Materials Engineering

Focused Ion Beams

JoVE 10482

Source: Sina Shahbazmohamadi and Peiman Shahbeigi-Roodposhti, School of Engineering, University of Connecticut, Storrs, CT

As electron microscopes become more complex and widely used in research labs, it becomes more of a necessity to introduce their capabilities. Focused ion beam (FIB) is an instrument that can be employed in order to fabricate, trim, analyze and characterize materials on mico- and nano-scales in a wide variety of fields from nano-electronics to medicine. FIB systems can be thought of as a beam of ions that can be used to mill (sputter), deposit, and image materials on micro- and nano-scales. The ion columns of FIBs are commonly integrated with the electron columns of scanning electron microscopes (SEMs). The goal of this experiment is to introduce the state of the art in focused ion beam technologies and to show how these instruments can be used in order to fabricate structures that are as small as the smallest membranes that are found in the human body.


 Materials Engineering

Nanocrystalline Alloys and Nano-grain Size Stability

JoVE 10484

Source: Sina Shahbazmohamadi and Peiman Shahbeigi-Roodposhti, School of Engineering, University of Connecticut, Storrs, CT

Alloys with grain size less than 100 nm are known as nanocrystaline alloys. Due to their enhanced physical and mechanical properties, there is an ever-increasing demand to employ them in various industries such as semiconductor, biosensors and aerospace.  To improve the processing and application of nanocrystalline alloys, it is necessary to develop close to 100% dense bulk materials which requires a synergistic effect of elevated temperature and pressure. By increasing the applied temperature and pressure, small grains start to grow and lose their distinguished properties. Thus, it is technologically important to reach a compromise between inter-particle bonding with minimum porosity and loss of nano-scale grain size during consolidating at elevated temperatures. In this study we aim to eliminate oxygen from solid solution to improve the nano-grain size stability at elevated temperatures. Nano-crystalline Fe-14Cr-4Hf alloy will be synthesized in a protected environment to avoid oxide particles formation.


 Materials Engineering

Directional Solidification and Phase Stabilization

JoVE 10485

Source: Sina Shahbazmohamadi and Peiman Shahbeigi-Roodposhti, School of Engineering, University of Connecticut, Storrs, CT

Directional solidification zone melting is a metallurgical process in which a narrow region of a crystal (usually in the form of bar) is melted. The furnace moves along the rod shape sample, meaning that the molten zone is moved along the crystal and the molten zone is moved from one end of the bar to the other. This mechanism is widely used in alloys, however solute atoms tend to segregate to the melt. In this type of alloy, the impurities also concentrate in the melt, and move to one end of the sample along with the moving molten zone. Therefore, zone melting is used most extensively for commercial material refining. Fig. 1. shows how the high-impurity molten-zone moves from one side of the bar to the other. The vertical axis is the impurity concentration and the horizontal axis is the sample length. Due to the tendency for impurities to segregate to the molten region, its concentration in the melt is higher than in the solid. Therefore, as the molten materials travel to the end of bar, the impurity will be transported to the end of bar and leave the high purity solid material behind it. Figure


 Materials Engineering

Hydrogel Synthesis

JoVE 10486

Source: Amber N. Barron, Ashlea Patterson, and Taylor D. Sparks, Department of Materials Science and Engineering, The University of Utah, Salt Lake City, UT

Hydrogels are a versatile class of cross-linked polymers produced through relatively simple procedures and with generally inexpensive materials. They can be formed from solution and involve a polymer backbone formed from monomer reagents, an initiator which makes the polymer reactive and a crosslinking species which binds the polymer chains together. An important aspect of these materials is that they swell in the presence of water, but this response can be tuned further to enhance swelling as a function of salinity, pH, or other signals. As a final product, hydrogels can be used in aqueous or dry environments, with a range of useful properties such as flexibility, high absorbance, transparency and thermal insulation. They are commonly used for liquid absorbance, sensors, consumer products, and drug delivery.


 Materials Engineering

Differential Scanning Calorimetry

JoVE 10487

Source: Danielle N. Beatty and Taylor D. Sparks, Department of Materials Science and Engineering, The University of Utah, Salt Lake City, UT

Differential scanning calorimetry (DSC) is an important measurement to characterize thermal properties of materials. DSC is used primarily to calculate the amount of heat stored in a material as it heats up (heat capacity) as well as the heat absorbed or released during chemical reactions or phase changes. However, measurement of this heat can also lead to the calculation of other important properties such as glassy transition temperature, polymer crystallinity, and more. Due to the long, chain-like nature of polymers it is not uncommon for polymer strands to be entangled and disordered. As a result, most polymers are only partially crystalline with the remainder of the polymer being amorphous. In this experiment we will utilize DSC to determine polymer crystallinity.


 Materials Engineering

Thermal Diffusivity and the Laser Flash Method

JoVE 10488

Source: Elise S.D. Buki, Danielle N. Beatty, and Taylor D. Sparks, Department of Materials Science and Engineering, The University of Utah, Salt Lake City, UT

The laser flash method (LFA) is a technique used to measure thermal diffusivity, a material specific property. Thermal diffusivity (α) is the ratio of how much heat is conducted relative to how much heat is stored in a material. It is related to thermal conductivity (), how much heat is transferred through a material due to a temperature gradient, by the following relationship: (Equation 1) where ⍴ is the density of the material and Cp is the specific heat capacity of the material at the given temperature of interest. Both thermal diffusivity and thermal conductivity are important material properties used to assess how materials transfer heat (thermal energy) and react to changes in temperature. Thermal diffusivity measurements are obtained most commonly by the thermal or laser flash method. In this technique a sample is heated by pulsing it with a laser or xenon flash on one side but not the other, thus inducing a temperature gradient. This temperatu


 Materials Engineering

Electroplating of Thin Films

JoVE 10489

Source: Logan G. Kiefer, Andrew R. Falkowski, and Taylor D. Sparks, Department of Materials Science and Engineering, The University of Utah, Salt Lake City, UT

Electroplating is a process that uses electric current to reduce dissolved metal cations so that they form a thin coating on an electrode. Other thin film deposition techniques include chemical vapor deposition (CVD), spin coating, dip coating, and sputter deposition among others. CVD uses a gas-phase precursor of the element to be deposited. Spin coating spreads the liquid precursor centrifugally. Dip coating is similar to spin coating, but rather than spinning the liquid precursor, the substrate is completely submerged in it. Sputtering uses plasma to remove the desired material from a target, which then plates the substrate. Techniques such as CVD or sputtering produce very high quality films but do so very slowly and at high cost since these techniques typically require a vacuum atmosphere and small sample size. Electrodeposition doesn't rely on a vacuum atmosphere which greatly reduces the cost and increases scalability. In addition, relatively high rates of deposition can be achieved with electrodeposition.


 Materials Engineering

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