2026-09-23T04:28:17Z https://www.ideals.illinois.edu/oai-pmh

oai:www.ideals.illinois.edu:2142/72171 2023-07-11 col_2142_5131 col_2142_13836 com_2142_5130 com_2142_13835 com_2142_234

Embargo set by: Seth Robbins for item 72339 Lift date: Forever Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs U of I Only 188 p. Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1993. http://hdl.handle.net/2142/72171 (UMI)AAI9411570 Engineering, Materials Science Buchanan, Relva C. Borglum, Brian Philip 2014-12-17T20:48:42Z 2014-12-17T20:48:42Z 10000-01-01 1993 1993 The cementitious reaction has been used to successfully develop a calcium aluminate ceramic material that has a low dielectric constant, low dielectric loss, and high resistivity and maintains these properties at high relative humidities. The electrical resistivity of typical cements change from 10$\sp $ ohm$\cdot$cm for strongly dried materials to 10$\sp6$ ohm$\cdot$cm upon exposure to high relative humidity environments. This is attributed to the development of parallel conduction pathways in the connected porosity of the materials as they fill with water. The developed material maintains its insulating ability upon exposure to 93% relative humidity, with resistivity changing only to 10$\sp $ ohm$\cdot$cm. This material was formed at moderate temperatures (200$\sp\circ$C) utilizing particle packing strategies that densified the system. Submicron silica fume not only reduced water demand during processing, but reacted chemically to form a silica-substituted hydrogarnet matrix. This produces dense microstructures and increases thermal stability to temperatures greater than 300$\sp\circ$C. Processing steps were developed that aided in the densification of these materials. A dispersant system was developed for calcium aluminates that reduced water content and provided a high degree of fluidity, without accelerating the hydration reaction. Additionally, uniaxial pressing the cement pastes was used to remove water from the paste and force particle rearrangement into densely packed structures. The dielectric constant of the developed material is approximately 11.5 at 1 MHz. Hollow silica microspheres were introduced into the chemically bonded matrix and reduced the dielectric constant to 5.1 at 1 MHz, which is in the range of values desired for microelectronic packaging applications. The low temperature nature of chemically bonded ceramics makes possible the formation of composite structures that would be difficult using high temperature processes. Electrical properties are dominated by the degree of connected porosity, and not by the reaction product phase. The ability to minimize porosity ultimately determines the electrical resistivity, dielectric constant, and dissipation factor of the chemically bonded matrix when water vapor is present. Anhydrous hexagonal anorthite $\rm(CaAl\sb2Si\sb2O\sb8)$ was synthesized at moderate temperatures ($>$200$\sp\circ$C) under hydrothermal conditions and has very desirable strength and thermal stability properties. However, because it is porous in nature it is not suited for use as an electrical insulator in humid environments. Made available in DSpace on 2014-12-17T20:48:42Z (GMT). No. of bitstreams: 1 9411570.pdf: 5629025 bytes, checksum: 19195842a723eff2ff1350ed8d710eac (MD5) Previous issue date: 1993 Effect of Processing on Electrical Properties of Calcium Aluminate-Based Chemically Bonded Ceramics text Materials Science and Engineering Ceramics Engineering University of Illinois at Urbana-Champaign Dissertation Ph.D.