Junior labs are the first chance you really get to "get your hands dirty" and explore beyond theory. The techniques, practices, data analysis, and communications skills you learn in your Junior Labs will provide invaluable experience for grad school, industry, or wherever life takes you.
Thermal stresses and strains – When materials are heated, there is usually an accompanying change in dimension as the atoms vibrate more. Students measure the expansion of four materials (two glasses and two metals) when they are heated to about 600C, and compare their experimental thermal expansion coefficients to published values. They also determine the elastic modulus of several materials by recording and analyzing the sound generated when a suspended bar is struck with a mallet.
Phase equilibria via optical microscopy – Phase diagrams are used in Materials Science and Engineering to determine what the stable (equilibrium) phases are at a given pressure, temperature, and composition. In this lab, the students are given several mixtures of two organic crystalline polymers with a known phase diagram. They heat and cool the samples under the optical microscope, and analyze the microstructures in the resulting images. The rate of cooling is also varied to show how non-equilibrium conditions can change the results.
Differential scanning calorimetry (DSC) – DSC is a popular research technique used to study phase changes in materials. The amount of energy necessary to raise or lower the temperature of a sample by one degree is measured, and compared to an empty reference pan. Phase changes such as melting and crystallization can be seen as peaks (either exothermic or endothermic) in the DSC curve. The shape of the DSC curve varies greatly with material; in general, metals have a very sharp, narrow peak, while polymers are much broader. DSC is used to study a variety of materials, and can even be used to generate portions of a phase diagram.
Pyrometry – In the pyrometry lab, students are introduced to the principles of non-contact temperature measurement. A rod of material is placed in a tube furnace and heated to a set temperature. The infrared radiation that is given off by the sample is collected by the pyroelectric detector, and a corresponding voltage is measured. By comparing the results from experimental samples to a simulated “black body”, the students can calculate emissivity values and then compare them to reference values from the literature.
Absorption and humidity – Humidity sensors (like the one in your dryer!) are often made of polymer thin films that can absorb water. In this lab, we use what’s called a quartz crystal microbalance to determine how much water a particular polymer can absorb at a given film thickness and relative humidity level. As water adsorbs and absorbs into the polymer film, the mass of the polymer on the quartz crystal changes. This in turn changes the resonance frequency that quartz crystal vibrates at. By measuring the change in frequency, the students are able to calculate just how much water has been added. They also get to practice spin coating polymer films on to the quartz crystals.
Thermoelectric energy conversion – In some materials, electric current can be directly converted into heat (Peltier effect). The reverse is also true – applying heat can be used to generate electricity (Seebeck effect). The students are given a commercial thermoelectric module (composed of P and N type semiconductors), and are able to investigate firsthand how both processes work. They are also able to calculate how efficient the module is.
Polymer crystallization – The properties of a material depend strongly on the microstructure, which is in turn influenced by the processing the material has undergone. In this lab, students investigate how the crystallization temperature affects the growth rate of polymer crystals, and also the size of the resulting microstructural features. Using the heating stage and an optical microscope, students can watch and record in real time how polyethylene oxide crystals form from the melt as the liquid polymer is quickly cooled down. DSC is also used to measure the latent heat of fusion and melting temperature, in order to compare the experimental growth rate to the theoretical model.
Heat diffusion – Diffusion is one of the most important concepts in Materials Science and Engineering. Both mass and heat diffusion are a function of time and position inside the material, and can be described by similar kinetic equations. Here, we are investigating the flow of heat through the material, or how the temperature changes. Two methods are used to do this: the so-called “flash” method using the pyroelectric detector, and the Angstrom method. In both cases, a thermal diffusivity can be calculated and compared to literature values.
Mechanical properties – Who doesn’t love to break stuff?! In the first week of this lab, students get hands-on experience with one of the most familiar topics in MatSE: stress-strain curves. Metal samples are pulled in tension until failure, and the resulting curves analyzed. Rockwell hardness tests are also performed on all the samples prior to tensile testing. In the second week of the lab, students watch a demo on fracture toughness, and perform impact tests on both metal and polymer samples. During the impact tests, weights are dropped onto the sample from a height in order to observe the fracture behavior. By varying the temperature between 0 and 100C, the students can observe firsthand how the behavior changes, especially for samples that undergo a brittle to ductile transition. This is one of our students’ most popular labs, and it uses the Mechanical Testing Instructional Laboratory (MTIL) facilities in Talbot Laboratory. Oh, and students (and instructors…) are allowed to take home their broken specimens as souvenirs!
Photoelectric energy conversion – Solar energy holds great potential as a source of alternative (renewable) energy. In this lab, we look at how solar cells and P-N junctions work, including how light is converted into electricity. Current-voltage plots are made under a variety of conditions (in both the dark and in the light, and forward and reverse biased). We also calculate some device parameters for our commercial solar cells, including fill factor and efficiency. Students also determine how device performance is affected by the wavelength of light hitting the solar cell.
Viscosity – Viscosity is a measure of the resistance of a liquid to flow. Liquids like acetone and water have a low viscosity, since there is little resistance for the molecules to overcome. Substances like molten glass and pitch, on the other hand, have very high viscosities and flow very sluggishly. Some liquids have viscosities that vary with shear rate – the classic example is cornstarch and water (oobleck), which acts more like a liquid when it’s strained slowly, and like a solid when you strain it quickly (which is why you can run across a pool of it). In this lab, we do a calibration with liquids of known viscosity, and then use that calibration to calculate the viscosity for unknown mixtures of various concentrations (water and alcohol, and of two alcohols).
Creep – Besides being the topic of lab instructor Jessica Terbush’s PhD thesis, creep is time-dependent and important to understand when materials are used at temperatures over 50% of their melting point. You don’t want your car engine deforming as you drive down the highway, or your jet engine falling apart mid-flight. In this lab, samples of aluminum are placed inside a furnace and weights are suspended from the bottom of the sample. Tests are done under two conditions, constant load/stress and constant temperature. Using the calculated creep rates, students are able to determine the stress exponent and activation energy, which also allows them to comment on what the active mechanism is.