Testing Self Healing Properties in Polymers

Mussels and barnacles have the ability to stick to underwater surfaces with the help of a cross-linked protein structure. Reduction in the plastic consumption can be achieved by using toughened polymers. Synthesized cross-linking polymers can be used for underwater adhesion by mimicking the protein structure used by mussels and barnacles. One such polymer is poly(3,4-dihydroxystyrene-co-styrene) having enhanced toughness. Traditionally, blister tests measure the adhesion between a substrate to a surface but this was modified to serve as the driving force to drive crack propagation in controlled flaws. The modified blister tests were carried out on polystyrene (PS) samples. Once the method of controlled crack propagation was perfected, the testing was extended to samples of the copolymer of styrene and 3,4-dihydroxystyrene. Samples were made in aluminium pans by solution casting PS in toluene and drying them in an inert oven. Melting PS pellets in the pans directly on a hot plate at 350°F is another way of making samples. The samples were indented with a Vickers micro-hardness tester. Samples were pressurized and changes in crack size and geometry were monitored via optical microscope. The parameters for successful control of crack growth such as sample thickness, air pressure and exposure time were optimized. These parameters will be used to consistently test and study samples for controlled crack growth. This is a part of the ongoing research about toughened polymers

Characterization of Lead-Free Piezo-Ceramics

Lead zirconate titanate (PZT) has been the most commonly used piezoelectric material due to its high piezoelectric performance under varied operating conditions. However, it has been noticed that the lead component is toxic, causing some environmental issues and a lead free substitute material was introduced. The substituted environmental friendly piezoelectric material, Ba(Zr0.2Ti0.8)O3–x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) system that can fulfill the need of high piezoelectricity has been developed. The research was conducted to characterize the BZT-xBCT system with five different compositions (x=0.06, 0.08, 0.1, 0.12 and 0.14).. XRD was applied to examine the crystal structure of the samples before and after poling and polarization measurement was conducted. The results from the experiments allow us to find out the piezoelectricity performance of BZT-xBCT system of different compositions that have distinct crystal structures on microscopic scale. It is found that after poling, the intensity peaks do not shift, compared with that before poling, but the ratio between two peaks at the same 2theta degree increases, which means the domain structure changes. Polarization curves for 0.08, 0.1, 0.12 and 0.14 are as expected but the 0.06 one is not. This research will contribute to ongoing research on BZT-XBCT system, and better understanding of piezoelectric materials

Intermetalic Growth Rate in Transient Liquid Phase Sintering of Pb-Free Solder Interconnects

Following the electron devices are widely used in daily life, Pb-free solder alloy, as the replacement of Pb solder joint material, needs extensive researches to observe the properties for using and simulation purpose. Solder are used as the joint to connect two work pieces in printed wiring board of electronics. Most lead-free solders comprise tin (Sn) as the majority component, and nominally pure b-Sn is the majority phase in the microstructure of these solders. The most important thing for solder joint that researchers care about is its life cycle. Due to the incomplete of the mechanical profile of Pb-free solder joint for now, this research worked on obtain data of life cycles. At the boundary of the Sn phase and Ag phase, the intermetallic would grow during the heating process, which affects the life cycle of the solder. This study incorporates mechanical testing and measurement of the intermetallic in scanning electron microscope (SEM) images in image J, to get enough data of life cycle to form a profile and the effects of the intermetallic. The measurement on images shows that the intermetalic layer grows in scallop-shape and the thickness increases with the temperature and sintering time. The growth rate can be modeled as a linear equation of the power of one half of the sintering time. This measurement will contribute to the ongoing research about the transit liquid phase sintering and the ball-grid array (BGA) reliability

Tool for Correlating EBSD and AFM Data Arrays

Ceramic and semiconductor research is limited in its ability to create holistic representations of data in concise, easily-accessible file formats or visual data representations. These materials are used in everyday electronics, and optimizing their electrical and physical properties is important for developing more advanced computational technologies. There is a desire to understand how changing the composition of the ceramic alters the shape and structure of the grown crystals. However, few accessible tools exist to generate a dataset with the proper organization to understand correlations between grain orientation and crystallographic orientation. This paper outlines an approach to analyzing the crystal structure using data collected from atomic force microscopy (AFM) and electron backscattered diffraction (EBSD) scans to build an accurate image of the crystal structure and orientation in the ceramic. The following tool takes data from AFM and EBSD scans of the same surface to create an accessible and easily-manipulatable data organization that stores several parameters relating to the crystallographic information of the surface. While this code was tested using on barium strontium titanate, but can of other materials with crystalline surfaces can take advantage of this analysis tool

Grain Boundary Migration of NiO-MgO Alloys

Grain boundary engineering offers enhanced control of microstructure development during processing, leading to improved final material properties. However, using the effects of the interfacial energy anisotropy on grain boundary mobility to control microstructure development is not well understood. The NiO-MgO system is studied as it has complete solid solubility and a transition in the faceting behavior with composition due to changes in the interfacial energy anisotropy. NiO-MgO powders were produced through the amorphous citrate process and modifications to the process were made to reduce particle and agglomerate size. The powders were pressed and sintered in various conditions to produce fine grained high purity dense samples. Wet milling demonstrated a reduction in the overall particle and agglomerate size of the powders. Pressureless sintering showed an increase in the densification of the NiO-MgO compacts with increased heating rate. Wet milling and high heating rates produced near fully dense samples with relative apparent densities of \u3e95% and open porositie

Note: Thermal analog to atomic force microscopy force-displacement measurements for nanoscale interfacial contact resistance

Thermal diffusion measurements on polymethylmethacrylate-coated Si substrates using heated atomic force microscopy tips were performed to determine the contact resistance between an organic thin film and Si. The measurement methodology presented demonstrates how the thermal contrast signal obtained during a force-displacement ramp is used to quantify the resistance to heat transfer through an internal interface. The results also delineate the interrogation thickness beyond which thermal diffusion in the organic thin film is not affected appreciably by the underlying substrate

The origins of internal stresses in polycrystalline AL2O3 and their effects on mechanical properties

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1979.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.Vita.Bibliography: leaves 120-126.by John Edward Blendell.Sc.D

Grain growth in Nio–MgO and its dependence on faceting and the equilibrium crystal shape

The impact of faceting on grain growth was approached by model experiments in NiO–MgO. Grain growth rates were found to be 10 times higher in NiO compared to MgO. As the self-diffusion acoefficients differ by a factor of 250, grain growth in NiO is unexpectedly slow compared to MgO. Recently, the movement of steps was identified as the atomic mechanism of grain boundary migration. According to the equilibrium crystal shape, grain boundaries in NiO are more faceted. The faceted grain boundaries of NiO have fewer steps at the grain boundaries resulting in a relatively lower mobility

Equilibrium and kinetic shapes of grains in polycrystals

The equilibrium crystal shape is a convex shape bound by the lowest energy interfaces. In many polycrystalline microstructures created by grain growth, the observed distribution of grain boundary planes appears to be dominated at low driving forces (after long grain growth times) by the planes present in the equilibrium crystal shape. However, at earlier stages of grain growth, it is expected that kinetic effects will play an important role in grain boundary motion and morphology. Analogous to the equilibrium crystal shape, the kinetic crystal shape of seed crystals growing from a liquid at higher supersaturations is bound by the slowest growing orientations. This study presents an equivalent construction for grain boundaries in polycrystals and uses it to determine the kinetic crystal shape for strontium titanate as a function of temperature. Relative grain boundary mobilities for strontium titanate for the low energy crystallographic orientations from seeded polycrystal experiments are used to calculate the kinetic crystal shapes as a function of temperature and annealing atmosphere. The kinetic crystal shapes are then compared to the morphologies and orientations of the interfaces of the growing seed crystals, and to the equilibrium crystal shapes, as we