Ceramic Materials Commons^™

Final-Stage Densification Kinetics Of Direct Current–Sintered Zrb2, Austin D. Stanfield, Steven M. Smith, Suzana Filipović, Nina Obradović, Vladimir Buljak, Gregory E. Hilmas, William Fahrenholtz

Materials Science and Engineering Faculty Research & Creative Works

Final-stage sintering was analyzed for nominally phase pure zirconium diboride synthesized by borothermal reduction of high-purity ZrO₂. Analysis was conducted on ZrB₂ ceramics with relative densities greater than 90% using the Nabarro–Herring stress–directed vacancy diffusion model. Temperatures of 1900°C or above and an applied uniaxial pressure of 50 MPa were required to fully densify ZrB₂ ceramics by direct current sintering. Ram travel data were collected and used to determine the relative density of the specimens during sintering. Specimens sintered between 1900 and 2100°C achieved relative densities greater than 97%, whereas specimens sintered below 1900°C failed to …

The Effect Of Crystal Anisotropy On Fracture Toughness And Strength Of Zrb2 Microcantilevers, Tamás Csanádi, Ahmad Azizpour, Marek Vojtko, William Fahrenholtz

Materials Science and Engineering Faculty Research & Creative Works

The influence of crystal anisotropy on the micromechanical properties of ceramic grains plays an important role in the design of the macromechanical performance of bulk polycrystalline samples. To this end, the effect of crystal orientation on fracture toughness and strength was investigated by microcantilever bending experiments combined with finite element method (FEM) simulations in grains of a polycrystalline ZrB2 sample. The sample was prepared by hot pressing and the crystal orientations were determined by electron backscatter diffraction after careful surface preparation. The bending tests were carried out on notched and unnotched microcantilevers cut from specific grains along the prismatic (⊥ …

Strength Retention Of Single-Phase High-Entropy Diboride Ceramics Up To 2000°C, Lun Feng, William Fahrenholtz, Gregory E. Hilmas, Yue Zhou, Jincheng Bai

Materials Science and Engineering Faculty Research & Creative Works

The mechanical properties of single-phase (Hf_0.2,Nb_0.2,Ta_0.2,Ti_0.2,Zr_0.2)B₂ ceramics with high purity were investigated. The resulting ceramics had relative density greater than 99%, and an average grain size of 4.3 ± 1.6 μm. At room temperature (RT), the Vickers hardness was 25.2 ± 0.6 GPa at a load of 0.49 N, Young's modulus was 551 ± 7 GPa, fracture toughness was 4.5 ± 0.4 MPa m1/2, and flexural strength was 507 ± 10 MPa. Flexural strength increased by more than 50% from 507 ± 10 MPa at RT to 776 ± …

Thermal And Electrical Properties Of Spark Plasma Sintered (Ti,Cr)B2 Ceramics, Steven M. Smith, Lun Feng, William Fahrenholtz, Gregory E. Hilmas, Laura Silvestroni

Mathematics and Statistics Faculty Research & Creative Works

Thermal and electrical properties were measured for TiB2 ceramics containing varying CrB2 contents up to 33 mol%. The room-temperature thermal diffusivity decreased with increasing Cr content from 0.330 ± 0.003 cm2/s for pure TiB2 to 0.060 ± 0.003 cm2/s for (Ti0.66Cr0.33)B2. The amount of anisotropy in the coefficients of thermal expansion increased with increasing Cr content and the c-axis had the greatest dependence on Cr addition, with an increase of more than 25% in the thermal expansion for 33 mol% CrB2 compared to TiB2, whereas the a-axis only increased by about 8%. The electrical conductivity was the lowest for (Ti0.66Cr0.33)B2 …

Oxidation Behavior Of Nb-Coated Zirconium Diboride, Jan E. Förster, William Fahrenholtz, Gregory E. Hilmas, Ravisankar Naraparaju

Materials Science and Engineering Faculty Research & Creative Works

Metallic Nb-Coatings Were Deposited on Top of ZrB₂ by Means of Magnetron Sputtering to Improve its Oxidation Resistance. High Temperature Oxidation Tests Have Revealed that the Metallic Nb-Coatings Lead to the Formation of a Dense Solid and Protective Reaction Zone in Addition to a More Stable B₂O₃ Liquid Solution at the Surface. Compared to Baseline ZrB₂, a Reduction in the Oxidation Kinetics, as Well as the Thickness of the Porous Zirconia Layer by 71%, Has Been Achieved with the Help of Nb-Coatings. a Liquid Phase Sintering by Molten Nb₂O₅ Mechanism Was …

Mechanical Properties Of Zrb2 Ceramics Determined By Two Laboratories, Jeffrey J. Swab, Jecee Jarman, William Fahrenholtz, Jeremy Lee Watts

Materials Science and Engineering Faculty Research & Creative Works

The mechanical properties for zirconium diboride (ZrB2) were measured at two laboratories and compared. Two billets of ZrB2 were prepared by hot-pressing commercial powder. The relative densities of the billets were >99% and with an average grain size of 5.9 ± 4.5 µm. Both laboratories prepared American Society for Testing and Materials (ASTM) C1161 B-bars for strength and ASTM C1421 bars with notch configuration A for fracture toughness. Specimens were machined by diamond grinding at the Army Research Laboratory (ARL) and electrical discharge machining (EDM) at Missouri S&T. Strength bars tested at Missouri S&T were polished to a.25 μm finish …

High Temperature Dielectric Properties Of Calcium Zirconate, Alan Devoe, Hung Trinh, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

The electrical properties of dense, high purity CaZrO3 discs, sintered at 1380°C with and without added ZrO2, were investigated up to 950°C. Dielectric constant, loss tangent, and electrical conductivity were measured from 25 to 725°C, and the real and imaginary impedances were measured between 800 and 950°C by impedance spectroscopy techniques. Dielectric constant increased by 8% above 300°C and loss tangent increased from.1% at 25°C to ∼2% above 300°C. Activation energy of electrical conductivity determined between 300°C and 950°C by alternative current (AC) and direct current (DC) measurements. These results indicate that CaZrO3 could be a useful dielectric material for …

Thermal And Electrical Properties Of Spark Plasma Sintered (Ti,Cr)B2 Ceramics, Steven M. Smith, Lun Feng, William Fahrenholtz, Gregory E. Hilmas, Laura Silvestroni

Materials Science and Engineering Faculty Research & Creative Works

Thermal and electrical properties were measured for TiB₂ ceramics containing varying CrB₂ contents up to 33 mol%. The room-temperature thermal diffusivity decreased with increasing Cr content from 0.330 ± 0.003 cm²/s for pure TiB₂ to 0.060 ± 0.003 cm²/s for (Ti_0.66Cr_0.33)B2. The amount of anisotropy in the coefficients of thermal expansion increased with increasing Cr content and the c-axis had the greatest dependence on Cr addition, with an increase of more than 25% in the thermal expansion for 33 mol% CrB₂ compared to TiB₂, whereas the …

Boro/Carbothermal Reduction Co-Synthesis Of Dual-Phase High-Entropy Boride-Carbide Ceramics, Lun Feng, William Fahrenholtz, Gregory E. Hilmas, Stefano Curtarolo

Materials Science and Engineering Faculty Research & Creative Works

Dense, dual-phase (Cr,Hf,Nb,Ta,Ti,Zr)B₂-(Cr,Hf,Nb,Ta,Ti,Zr)C ceramics were synthesized by boro/carbothermal reduction of oxides and densified by spark plasma sintering. The high-entropy carbide content was about 14.5 wt%. Grain growth was suppressed by the pinning effect of the two-phase ceramic, which resulted in average grain sizes of 2.7 ± 1.3 µm for the high-entropy boride phase and 1.6 ± 0.7 µm for the high-entropy carbide phase. Vickers hardness values increased from 25.2 ± 1.1 GPa for an indentation load of 9.81 N to 38.9 ± 2.5 GPa for an indentation load of 0.49 N due to the indentation size effect. Boro/carbothermal …

Thermal And Electrical Properties Of Spark Plasma Sintered (Ti,Cr)B2 Ceramics, Steven M. Smith, Lun Feng, William Fahrenholtz, Gregory E. Hilmas, Laura Silvestroni

Materials Science and Engineering Faculty Research & Creative Works

Thermal and electrical properties were measured for TiB2 ceramics containing varying CrB2 contents up to 33 mol%. The room-temperature thermal diffusivity decreased with increasing Cr content from 0.330 ± 0.003 cm2/s for pure TiB2 to 0.060 ± 0.003 cm2/s for (Ti0.66Cr0.33)B2. The amount of anisotropy in the coefficients of thermal expansion increased with increasing Cr content and the c-axis had the greatest dependence on Cr addition, with an increase of more than 25% in the thermal expansion for 33 mol% CrB2 compared to TiB2, whereas the a-axis only increased by about 8%. The electrical conductivity was the lowest for (Ti0.66Cr0.33)B2 …

System Analysis Of An Internal Combustion Engine (Ice) – Solid Oxide Fuel Cell (Sofc) Hybrid Cycle, Jose Javier Colon Rodriguez

Graduate Theses, Dissertations, and Problem Reports (ETD)

Due to the intermittent nature of renewable energy and the rigid operation of existing coal plants, the need for flexible power generation technology is eminent. Hybrid energy systems have shown potential for flexible, grid following dynamics while maintaining higher efficiencies. The work below focuses on the performance analysis of a proposed 100 kW pressurized Internal Combustion Engine (ICE) and Solid Oxide Fuel Cell (SOFC) hybrid system. The un-utilized fuel from the SOFC stack provided the chemical energy to operate the engine. A turbocharger was used to deliver the necessary air flow for both the stack and engine. An external reformer …

Manganese-Based A-Site High-Entropy Perovskite Oxides For Solar Thermochemical Hydrogen Production, Cijie Liu

Graduate Theses, Dissertations, and Problem Reports (ETD)

Non-stoichiometric perovskite oxides have been studied as a new family of redox oxides for solar thermochemical hydrogen (STCH) production owing to their favourable thermodynamic properties. However, conventional perovskite oxides suffer from limited phase stability and kinetic properties, and poor cyclability. Here, we report a strategy of introducing A-site multi-principal-component mixing to develop a high-entropy perovskite oxide, (La_1/6Pr_1/6Nd_1/6Gd_1/6Sr_1/6Ba_1/6)MnO₃ (LPNGSB_Mn), which shows desirable thermodynamic and kinetics properties as well as excellent phase stability and cycling durability. LPNGSB_Mn exhibits enhanced hydrogen production (~77.5 mmol moloxide^–1) compared to (La …

Assembly Of Ceramic Particles In Aqueous Suspensions Induced By High-Frequency Ac Electric Field, James E. John Iv

Mechanical & Aerospace Engineering Theses & Dissertations

Ceramic materials processed using colloidal methods have been the focus of a great deal of research aimed at tailoring the final structure and microstructure of the finished ceramic sample. To this end, various external field effects have been investigated to modify the suspension microstructure without manipulating the ceramic particles directly. In a previous work in the field of ice templating it has been shown that AC electric fields are able to produce microstructural changes in ice templated ceramics that have significantly improved the final mechanical properties. However, the mechanisms for this process are still not well understood in ceramics.

To …

Material Characterization And Comparison Of Sol-Gel Deposited And Rf Magnetron Deposited Lead Zirconate Titanate Thin Films, Katherine Lynne Miles

Mechanical Engineering ETDs

Lead zirconate titanate (PZT) has been a material of interest for sensor, actuator, and transducer applications in microelectromechanical systems (MEMS). This is due to their favorable piezoelectric, pyroelectric and ferroelectric properties. While various methods are available to deposit PZT thin films, radio frequency (RF) magnetron sputtering was selected to provide high quality PZT films with the added capability of batch processing. These sputter deposited PZT films were characterized to determine their internal film stress, Young’s modulus, composition, and structure. After characterization, the sputtered PZT samples were poled using corona poling and direct poling methods. As a means of comparison, commercially …

An Experimental Study Of Norton And Thule Cooking Pot Performance, Caelie Marshall Butler

Dissertations and Theses

Ceramic technology was adopted by hunter-gatherers of the Paleo-Inuit Norton tradition in the Western Arctic between 2800 and 2500 years B.P., corresponding with an increase in the use of aquatic resources. Pottery production and use continued until approximately 1,500 BP, and resumed during the Neo-Inuit Birnirk and Thule periods, approximately 1,350 years BP. The technical characteristics of Norton and Thule ceramics suggest they performed differently when used for cooking, with Norton ceramics best suited for cooking using direct or suspended heat, and Thule ceramics best suited for indirect heat. Prior experimental archaeological research has focused on Thule ceramics, with limited …

Study Of Asymptotic Velocity In The Bondi–Hoyle Accretion Flows In The Domain Of Kerr And 4-D Einstein–Gauss–Bonnet Gravities, Orhan Donmez, Fatih Dogan, Tuba Sahin

Materials Science and Engineering Faculty Research & Creative Works

Understanding the physical structures of the accreted matter very close to a black hole in quasars and active galactic nucleus (AGN) is an important milestone to constrain the activities occurring in their centers. In this paper, we numerically investigate the effects of the asymptotic velocities on the physical structures of the accretion disk around the Kerr and Einstein–Gauss–Bonnet (EGB) rapidly rotating black holes. The Bondi–Hoyle accretion is considered with a falling gas towards the black hole in an upstream region of the computational domain. Shock cones are naturally formed in the downstream part of the flow around both black holes. …

Developing Positive Thermal Coefficient (Ptc) Heaters For Solar Electric Cooking, Katarina Ivana Brekalo, Andrew Shepherd

Physics

Positive Thermal Coefficients, PTCs, are materials that abruptly change in resistance in response to changes in temperature. The purpose of this experiment is to explore the viability of using the switching type ceramic PTC thermistor as a replacement for current resistive heaters. These types of PTCs have a nonlinear change in resistance with increases in temperature. This device will be used as a temperature-controlling heating element intended to power an Insulated Solar Electric Cooker (ISEC). The ISEC is designed to cook meals throughout the day for impacted communities as an alternative cooking method that doesn’t require biofuel as an energy …

Machine Learning Mosa Monitoring System, Aditya G. Manjunath, Sabahudin Vrtagic, Fatih Dogan, Milan Dordevic, Mileta Zarkovic, Jasmin Kevric, Goran Dobric

Materials Science and Engineering Faculty Research & Creative Works

This research paper deals with the problem of Metal-Oxide Surge Arrester (MOSA) condition monitoring and a new methodology in surge arrester monitoring and diagnostics is presented. A machine learning algorithm (back propagation regression) is used to estimate the non-linearity coefficient of the surge arrester, based on operating voltage and leakage current of the arrester. Using a simulated system, this research investigates the possibility of application and efficiency of machine learning. It is shown that the applied learning algorithm results are competitive with the model results parameters calculated as R2 = 0.999 and mean absolute real error computed as 0.005 which …

Modeling Hierarchical Porous Electrodes With Tailored Anisotropic Structure, Debanjan Sarker

All Theses

Modern electric vehicles and consumer electronics applications demand high specific energy from Li-ion batteries, which can be charged and discharged faster. In the search for high specific energy, researchers have tried to make thicker battery electrodes which contain a greater proportion of active material. While chemical and structural modification of electrodes can help to increase the electronic conductivity of active material, the microstructure of porous electrodes can be engineered to enhance ion transport for fast charge and discharge. Previous research has shown that macropores introduced by directional freeze tape casting can enhance the performance of thick porous electrodes. For instance, …

Synthesis And Consolidation Of The Aluminosilicate Mineral Anorthite, Lauren E. Eccles

Pursuit - The Journal of Undergraduate Research at The University of Tennessee

Solid-state ceramic synthesis is a fabrication process involving high temperature reactions of solid component powders and is used to prepare materials with novel and advanced properties. Regarding synthetic mineral ceramics, the solid-state process makes it possible to design synthetic minerals with specific compositions and properties not commonly found in their natural, comparatively impure, counterparts. This study focuses on the synthesis of the feldspar anorthite, CaAl₂Si₂O₈, via solid-state procedures and the densification of the synthesized powders using the technique of uniaxial hot-pressing. Constituent powders of aluminum sesquioxide (Al₂O₃), silicon dioxide (SiO …