Binder jetting is an additive manufacturing process in which a part is fabricated layer-by-layer using inkjet technology to selectively dispense binder into powder layers in a designated area. The approach gives this process significant advantages over other additive manufacturing processes such as lower cost, capability to print in a wide range of materials, and little to no heat applied. Although binder jetting has many advantages and has been successful implemented in various industries its overall rate of adoption is slow compared to other processes. This is largely due to poor mechanical properties and consistency in printing which stems from a poor understanding of the interaction between the binder droplets and the powder bed. This is evident as print parameters for new machines and new materials are primarily determined by trial and error. The purpose of this thesis is to report the impact of various inkjet print parameters and humidity on the printing process in binder jetting. The binder/powder interaction is complex and highly dynamic where picoliter-sized droplets impact the powder bed at velocities of 1-10 m/s. Current methods of predicting this interaction assume that it is based only on binder and powder properties. This work studies the impact of inkjet printing parameters that are often overlooked with these assumptions. The impact of droplet velocity, droplet spacing, and droplet inter-arrival time was evaluated based on single line formation and effective saturation levels when printed into various powder material and sizes. Higher droplet velocities were found to decrease effective saturation with larger droplets (92-212 pl). However, droplet velocity had a negligible impact on saturation when printing with smaller droplets from 30 m orifice (29-65 pl). Line formation was dependent on both droplet inter-arrival time and droplet spacing. Max droplet spacing correlated to the square root of inter-arrival time. These results can guide selection of printing parameters that maximize build rates and reduce defects in printed parts. As the binder/powder interaction is difficult to observe and often line formation has been used as a method of observation. However, no report relating line formation to full layer parts exists. Optimal parameters determined in line printing are used for full feature parts. In addition, the impact of ambient humidity on the printing process is studied. The direct use of parameters optimized for line printing in printing a part was shown to be ineffective. When droplet spacing, line spacing, and layer thicknesses are comparable, single and multiple layers can be formed. Over short exposure periods of powder to ambient humidity produces negligible difference however, extended exposure periods significantly reduce the saturation and increase part size. Surface roughness is identified as a possible source of printing defects. Surface roughness increases significantly when printing the first layer but decreases with successive layers. This demonstrates a strong interaction between layers. The surface roughness and effective saturation was insensitive to line and droplet spacing below 60 m. Steam powder conditioning reduces sensitivity of both surface roughness and saturation to printing parameters but causes bleeding beyond the part boundaries. Further research should include improved methods of predicting ideal printing parameters and connecting it based on geometry and parts size. Further research is needed to confirm impact of surface roughness on defects in binder jetting parts. Development of methods to control spread of binder in premoistened powder to take advantage of its potential.

<p>  </p> <p>This dissertation investigated the influence of formulation and process design on the internal density structure and nutrient release of urea fertilizer as an alternate route to overcome nutrient leaching problems. The first part of the work focused on producing urea composites with different binders to optimize the formulation and composite microstructure. The second part of the study compared the microstructure and release kinetics of dry compacted and bilayer urea granules. Finally, the third part determined nitrate and ammonium leaching using disturbed soil column experiments. The optimization of granule microstructure and formulation design developed in this work yielded a 97.5 % reduction in the initial dissolution rate of modified urea granules compared to conventional urea fertilizer. Thus, the development of processing platforms focused on granule internal density distributions demonstrated a fundamental contribution to optimizing nutrient release properties.</p>

The objective of this study was to develop a research platform using a John Deere 425 Hay Cuber and to evaluate inield densification of grass-based biomass for energy fuel sources. The hay cuber was repaired, modernized, and instrumented to provide a stable test platform on which to quantify and evaluate operating parameters. Bermudagrass was chosen as a model for cubing energy grasses such as Giant miscanthus and switchgrass. Lignin sulfonate binder was added to windrowed bermudagrass at 27.6 kg/tonne (50 lbs/ton) to increase the lignin content to that of energy grasses. The material output from the cuber was collected and separated into cubes and fines to evaluate the effectiveness of densification operations. Bermudagrass treated with binder produced significant regressions that accounted for 83% of variation in production parameters.

This dissertation describes a new vinyl-acrylic copolymer that displays great potential for applications in lithium ion batteries by enabling processes that are novel, faster, safer, and less costly than existing manufacturing methods. Overall, the works presented are based on tailored chemical synthesis directly applied to lithium ion battery manufacturing. Current manufacturing methods still have many flaws such as toxic processes and other time consuming if not costly steps. Understanding the chemistry of materials and processes related to battery manufacturing allows the design of techniques and methods that can ultimately improve the performance of existing batteries while reducing the cost. Chapter 1 provides an introduction to lithium batteries in terms of energy output, standard electrode and electrolyte materials, and processes for fabricating battery components. In this chapter, slightly more emphasis is placed on the electrolyte aspects of lithium battery technology, namely the plasticization of gel polymer hosts by liquid electrolyte and the standalone solid polymer electrolytes. Chapter 2 focuses on the free radical polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA), methyl methacrylate (MMA), and isobutyl vinyl ether (IBVE) monomers to afford a vinyl-acrylic poly(PEGMA-co-MMA-co-IBVE) random copolymer and its detailed properties as a soluble, amorphous, and adhesive electrolyte that is able to permanently hold 800 times its own weight. Such material properties envision a printable battery manufacturing procedure, since existing electrolytes lack adhesion at a single macromolecular level. Without adhesion, the cathode and anode layers easily delaminate from the cell assembly, not to mention weak interfacial contact and poor mass transfer with the electrolyte. Many soft matter type electrolytes have been reported, but they lack either adhesive strength or ease of solubility. Obtaining both properties in iv a single material is a rarity. Chapter 3 aims at improving the ionic conductivity of the poly(PEGMA-co-MMA-co-IBVE) copolymer electrolyte by studying the effect of internal and external plasticizers, molecular weight of PEGMA monomer, and addition of inorganic solid state electrolytes. The inorganic electrolyte additives include Li(1+x+y)AlxTi(2-x)SiyP(3-y)O12, LiILi2WO4 mixture, Li7La3Zr2O12, and Li2S-P2S5 as part of an organic-inorganic hybrid approach. Electrolytes can also be used as an electrode binder so long as it has structural integrity and allows ion transfer to and from the active electrode material during insertion/extraction processes. In Chapter 4, the use of this electrolyte as a water-soluble binder for the aqueous fabrication of LiCoO2 cathodes is presented. Results of this study demonstrated the first aqueous process fabrication of thick, flexible, and fully compressed lithium ion battery electrodes by using commercial nickel foam as a supporting current collector. This feat is rather impressive because these properties are far superior to other aqueous binders in terms of material loading per electrode, specific area capacity, durability, and cell resistance. Finally, Chapter 5 expands on this concept by using the poly(PEGMA-co-MMA-co-IBVE) copolymer for the aqueous fabrication of a low voltage Li4Ti5O12 anode type electrode. Each component of a lithium ion battery serves a distinct role and undergoes unique electrochemical processes during cycling. The fact that this poly(PEGMA-co-MMA-co-IBVE) copolymer can be used in all three components, albeit for only about 50 cycles in a liquid half cell setup, demonstrates as a proof of concept that switching the current toxic manufacturing of lithium-ion batteries to an aqueous process is highly feasible. Furthermore, new electrode manufacturing techniques are also deemed possible. A conclusive summary along with directions for future work concerning the v novelties of this unique multifunctional vinyl-acrylic copolymer as an electrolyte, a cathode binder, and an anode binder are discussed in Chapter 6.

Processing of ceramics has always been difficult due to how hard and brittle the material is. Fused Deposition of Ceramics (FDC) is a method of additive manufacturing which allows ceramic parts to be built layer by layer, abetting more complex geometries and avoiding the potential to fracture seen with processes such as grinding and milling. In the process of FDC, a polymeric binder system is mixed with ceramic powder for the printing of the part and then burned out to leave a fully ceramic part. This experiment investigates a new combination of materials, zirconia and acrylic binder, optimizing the process of making the material into a filament conducive to the printer system and then performing trials with the filament in the printer to assess its feasibility. Statistical analysis was used to determine optimal parameter levels using response surface methodology to pinpoint the material composition and temperature yielding the highest quality filament. It was discovered that although the mixture had adequate melting characteristics to be liquefied and printed into a part, the binder system did not provide the stiffness required to act as a piston to be fed through the printer head. Further studies should be completed continuing the investigation of zirconia and acrylic binder, but with added components to increase strength and rigidity of the filament.

Binder jetting is an additive manufacturing process that layer by layer builds a 3D model by selectively binding regions of powder using binder deposited though an inkjet printhead. The process offers several advantages over other additive manufacturing processes including fast build rates, vast material selection, decreased cost, and part resolution. The main disadvantage of binder jetting is poor mechanical properties, stemming from a poor understanding of the process physics. Porosity in final parts is not uncommon, but there is little understanding of where the porosity originates. The purpose of this thesis is to report the investigation of increased powder bed cohesion and its effects on part formation, part properties, and printing parameters in binder jetting. The interaction between binder and powder is complex. Binder exiting the printhead impacts the powder bed at speeds up to 10 m/s. The kinetic energy carried by the droplet disperses into the powder bed on impact, causing some powder particles to eject from the bed and other particles to rearrange within the bed. The particle ejection and rearrangement is theorized to be the physical cause of porous regions in binder jetted parts. This work uses a method called pre-wetting to introduce small amounts of moisture into the powder bed to effectively increase the cohesive forces between powder particles. Increased cohesion makes particle ejection and rearrangement during the powder/binder interaction more difficult. A method of accomplishing pre-wetting was developed and achieved successful moisture delivery using water and a water/tri-ethylene glycol mixture. Printed lines were used to characterize moisture content and study its effects on line formation and saturation levels. Low levels of moisture were shown to perform the best. Particle ejection and rearrangement was shown to decrease with moisture addition. Pre-wetting was shown to eliminate the defect known as balling, increasing the parameters known to successfully print lines. Water was identified as a poor substance for pre-wetting due to rapid evaporation, but tri-ethylene glycol/water solutions succeeded in proper moisture delivery. Saturation levels in lines decrease with added moisture and part dimensions increase. high-speed x-ray imaging verified pre-wetting reduction in particle ejection and rearrangement as well as supply some preliminary understanding of void formation during the printing process. The first few layers of the binder jetting process have been shown to increase in surface roughness values when compared to the undisturbed powder bed. This is likely due to a balling-like effect seen in layers. The effects of pre-wetting on layer and multi-layer formation were studied. Pre-wetting reduced the surface roughness levels in printed layers to the levels near the levels seen in undisturbed powder beds. In contrast, saturation levels in layers and multi-layers increased in value above those found in parts printed into dry powder, giving indication that porous regions within bound parts are being eliminated. Layer and multi-layer parts showed increased part dimensions with the addition of moisture. Overall, pre-wetting was shown to greatly reduce the effects of the binder/powder interaction and results strongly suggest that pre-wetting mitigates defect creation during the printing process. Further research should include testing of thicker multi-layer parts to study how saturation trends continue with increased layer numbers. In-process drying should be used in conjunction with pre-wetting in multi-layer parts to determine its effects on saturation levels and part dimensions. Post processing should be done to partially sinter, or infiltrate multi-layer parts created with and without pre-wetting to analyze porosity.

No description available.

Binder jet additive manufacturing (BJ) offers unique advantages, including the ability to produce complex geometries and utilize a wide range of materials, but faces challenges related to part quality and defect formation. This thesis investigates the effects of process parameters on droplet-powder interaction, powder relocation, and line formation in BJ printing. A custom BJ test platform was developed to enable precise control over key process parameters and in-situ monitoring. High-speed synchrotron X-ray imaging revealed modes of powder relocation above and below the powder bed surface. Testing revealed that parameters that increase moisture in the powder bed, such as lower droplet spacings, printing adjacent to previously printed geometry, and pre-wetting, reduce powder disturbance. Powder ejection above the powder bed surface was found to be affected by powder material, density, pre-wetting, previously printed geometry, and droplet spacing. Powder relocation below the powder bed surface was found to be largely independent of binder infiltration behavior, suggesting that powder relocation below the powder bed surface is driven by the kinetic impact of the droplet. A novel approach for analyzing printed lines demonstrated the sensitivity of line formation to various parameters, including droplet spacing, inter-arrival time, volume, and velocity. Lines were found to ball more readily at lower droplet spacings when printing at lower droplet velocities, although other coupled droplet parameters such as droplet volume and formation of satellite droplets also play a role. In printing conditions susceptible to balling, the droplets at the beginning of printed lines were observed to agglomerate, relocating powder and introducing error to the starting position of the line. Pre-wetting the powder bed with a water/TEG mixture significantly reduced balling and increased the range of droplet spacings and inter-arrival times resulting in successful line formation. Printing with low droplet velocities on moisture treated powder beds further increased the range of inter-arrival times that successfully formed lines. Reducing the kinetic energy of droplet impact by reducing droplet velocity and reducing the impact of balling by pre-wetting presents a set of process print process parameters that show promise to reduce powder relocation during the printing process. These findings provide valuable insights into the fundamental mechanisms of droplet-powder interaction, modes of powder relocation during printing that may contribute to porosity defects seen in final parts, and print process parameters that mitigate powder relocation due to droplet-powder interaction.

There is a link between the thermal and electrical properties of metal. The equation which links these two properties is called the Wiedemann-Franz Law. Also there is an emerging technology within Additive Manufacturing called Binder Jet Printing which can print high purity copper without heat stress within the material. Due to the Binder Jet Printings ability to print high resolution prints without any print through, this makes future use of this technology a necessity for future electrical and thermal components within computers . However a thermal and electrical conductivity analysis of binder jetted copper has never been performed, and needs to be for simulation with this material. Therefore within this thesis the relationship of the thermal and electrical properties of printed binder jetted copper part will be researched. To find the electrical resistivity of binder jetted copper, three sets of 2mm diameter rods where printed and then placed within a modified four wire resistance method test. For the thermal conductivity measurements a laser flash diffusivity machine was used, and three sets of 11 copper disks of approximately 1cm diameter by 1mm where printed. The data shows a strong linear trend linking electrical resistivity to the density ratio of the copper. Within the thermal conductance measurement, a lot more variability was seen within the three different prints. The 70% density ratio prints saw a large 13% spread in density ratios throughout the prints, which is believed to be caused by improper sintering due to temperature gradients near the door of the kiln. The 82% density prints saw better grouping of density ratios by placing the specimens in the back of the kiln. Lastly, the 92% prints saw the best density ratio grouping but the largest thermal conductivity variance. Even though the scatter plot for the thermal conductivity measurements are not as precise as the electrical resistivity measurements, it still shows a linear trend which matches the NASA data from 1971. Overall, these linear trends can be modeled and compiled into a new form of the Wiedemann-Franz law, which accounts for the density ratio of the binder jetted print. / Master of Science

The mechanical performance evaluation of asphalt binder has always been a challenging issue for pavement engineers. Recently, the Phase Field Method (PFM) has emerged as a powerful computational tool to simulate the microstructure evolution of asphalt binder. PFM analyzes the structure from the free energy aspect and can provide a view of the whole microstructure evolution process. In this dissertation, asphalt binder performance is analyzed by PFM in three aspects: first, the relationship between asphalt chemistry and performance is investigated. The components of asphalt are simplified to three: asphaltene, resin and oil. Simulation results show that phase separation will occur under certain thermal conditions and result in an uneven distribution of residual thermal stress. Second, asphalt cracking is analyzed by PFM. The traditional approach to analyze crack propagation is Classic Fracture Mechanics first proposed by Griffith, which needs to clearly depict the crack front conditions and may cause complex cracking topologies. PFM describes the microstructure using a phase-field variable which assumes positive one in the intact solid and negative one in the crack void. The fracture toughness is modeled as the surface energy stored in the diffuse interface between the intact solid and crack void. To account for the growth of cracks, a non-conserved Allen-Cahn equation is adopted to evolve the phase-field variable. The energy based formulation of the phase-field method handles the competition between the growth of surface energy and release of elastic energy in a natural way: the crack propagation is a result of the energy minimization in the direction of the steepest descent. Both the linear elasticity and phase-field equation are solved in a unified finite element frame work, which is implemented in the commercial software COMSOL. Different crack mode simulations are performed for validation. It was discovered that the onset of crack propagation agrees very well with the Griffith criterion and experimental results. Third, asphalt self-healing phenomenon is studied based on the Atomic Force Microscopy (AFM) technology. The self-healing mechanism is simulated in two ways: thermodynamic approach and mechanical approach. Cahn-Hilliard dynamics and Allen-Cahn dynamics are adopted, respectively. / Ph. D.