Exploring thermal and mechanical properties of selected transition elements under extreme conditions: Experiments at high pressures and high temperatures

Transition metals (Ti, Zr, Hf, Mo, W, V, Nb, Ta, Pd, Pt, Cu, Ag, and Au) are essential building units of many materials and have important industrial applications. Therefore, it is important to understand their thermal and physical behavior when they are subjected to extreme conditions of pressure and temperature. This dissertation presents: • An improved experimental technique to use lasers for the measurement of thermal conductivity of materials under conditions of very high pressure (P, up to 50 GPa) and temperature (T up to 2500 K). • An experimental study of the phase relationship and physical properties of selected transition metals, which revealed new and unexpected physical effects of thermal conductivity in Zr, and Hf under high P-T. • New phase diagrams created for Hf, Ti and Zr from experimental data. • P-T dependence of the lattice parameters in α-hafnium. Contrary to prior reports, the α-ω phase transition in hafnium has a negative dT/dP slope. • New data on thermodynamic and physical properties of several transition metals and their respective high P-T phase diagrams. • First complete thermodynamic database for solid phases of 13 common transition metals was created. This database has: All the thermochemical data on these elements in their standard state (mostly available and compiled); All the equations of state (EoS) formulated from pressure-volume-temperature data (measured as a part of this study and from literature); Complete thermodynamic data for selected elements from standard to extreme conditions. The thermodynamic database provided by this study can be used with available thermodynamic software to calculate all thermophysical properties and phase diagrams at high P-T conditions. For readers who do not have access to this software, tabulated values of all thermodynamic and volume data for the 13 metals at high P-T are included in the APPENDIX. In the APPENDIX, a description of several other high-pressure studies of selected oxide systems is also included. Thermophysical properties (Cp, H, S, G) of the high P-T ω-phase of Ti, Zr and Hf were determined during the optimization of the EoS parameters and are presented in this study for the first time. These results should have important implications in understanding hexagonal-close-packed to simple-hexagonal phase transitions in transition metals and other materials.

Outdoor experiential team -building and the college adjustment and persistence of freshmen in learning communities

Student retention is a primary goal in all higher education institutions. Students who are more adjusted to college life are more likely to persist. The purpose of this research was to determine the effects of an outdoor experiential team-building program on the college adjustment of first-semester freshmen in learning communities at a diverse, urban university. The participants in this quasi-experimental study were first-semester freshmen enrolled in learning communities. A total of 123 students participated, with 61 students in the experimental group and 62 students in the comparison group. There were no significant differences between the two groups in relation to age, gender, or ethnicity. The students in the experimental group participated in the team-building program, which consisted of three events spaced three and four weeks apart. At the end of the semester, students in both the experimental and comparison groups completed the Student Adaptation to College Questionnaire (SACQ), a 67-item self-report survey. ^ Independent samples t-test of the SACQ scores (for attachment to the institution, social adjustment, and overall adaptation to college) between groups was done, and the analyses revealed no statistically significant differences. Chi-square analyses revealed no significant difference in the enrollment pattern between the two groups over a four-year period. Repeated measures ANOVAs revealed that from the first semester of enrollment to the second semester there was a significant drop in GPA for students from the comparison group and no such drop in GPA for students from the experimental group who had participated in at least two of the team building activities. A repeated measures ANOVA was conducted for the first year by semester and ethnicity. No ethnic differences were found, and no interaction was found by ethnicity and semester. ^ Should colleges and universities continue to utilize outdoor experiential team-building programs as a creative way to influence students' connection to the institution they should further investigate its value on students' adjustment to college. Future studies should also consider other variables influenced by team-building programs that affect students' college adjustment, such as collaborative learning. Faculty should be included in the planning process to increase their participation. ^