Relationship between FDM 3D Printing Parameters Study: Parameter Optimization for Lower Defects

Technology evolution and wide research attention on 3D printing efficiency and processes have given the prompt need to reach an understanding about each technique’s prowess to deliver superior quality levels whilst showing an economical and process viability to become mainstream. Studies in the field have struggled to predict the singularities that arise during most Fused Deposition Modeling (FDM) practices; therefore, diverse individual description of the parameters have been performed, but a relationship study between them has not yet assessed. The proposed study lays the main defects caused by a selection of printing parameters which might vary layer slicing, then influencing the defect rate. Subsequently, the chosen technique for optimization is presented, with evidence of its application viability that suggests that a quality advance would be gathered with such. The results would help in making the FDM process become a reliable process that could also be used for industry manufacturing besides prototyping purposes.

Laser Annealing of P and Al Implanted 4H-SiC Epitaxial Layers

This work describes the development of a new method for ion implantation induced crystal damage recovery using multiple XeCl (308 nm) laser pulses with a duration of 30 ns. Experimental activity was carried on single phosphorus (P) as well as double phosphorus and aluminum (Al) implanted 4H-SiC epitaxial layers. Samples were then characterized through micro-Raman spectroscopy, Photoluminescence (PL) and Transmission Electron Microscopy (TEM) and results were compared with those coming from P implanted thermally annealed samples at 1650–1700–1750 °C for 1 h as well as P and Al implanted samples annealed at 1650 °C for 30 min. The activity outcome shows that laser annealing allows to achieve full crystal recovery in the energy density range between 0.50 and 0.60 J/cm2. Moreover, laser treated crystal shows an almost stress-free lattice with respect to thermally annealed samples that are characterized by high point and extended defects concentration. Laser annealing process, instead, allows to strongly reduce carbon vacancy (VC) concentration in the implanted area and to avoid intra-bandgap carrier recombination centres. Implanted area was almost preserved, except for some surface oxidation processes due to oxygen leakage inside the testing chamber. However, the results of this experimental activity gives way to laser annealing process viability for damage recovery and dopant activation inside the implanted area.

Pseudo-Dynamic Modeling to Evaluate a Remote Gas-to-Liquids Process

A project team was given the task of evaluating various technology options for design of a small-scale gas-to-liquids (GTL) process operated remotely at or near an individual gas source. For this study, small-scale plants were considered those producing between 100 and 500 barrels per day of liquid fuels. In addition, being remote enforced limitations on utility sources available to the plant site such as water and grid power. A secondary goal was development of a dynamic model of the plant to use in operator training. To accomplish these objectives, the authors investigated the suitability of a process-simulation application. The conceptual design of the GTL unit included many different possibilities, such as front-end design, back-end design, heat integration, and recycling of materials. Complications associated with plant start-up and shutdown, utilities, process reliability, and economics were included in the decision-making process. The authors present selective results from a steady-state model and sensitivity studies. Considerations for the development of the dynamic model included both a fully rigorous dynamic model and a pseudo-dynamic steady-state-based model; results of the latter model are provided. The study concluded that an industrial steady-state simulation tool provided sufficient flexibility to complete the material and energy-balance calculations, sensitivity analyses, and pseudo-dynamic modeling. This study yielded significant insights into the importance of model assumptions and their impact on the overall process viability. The pseudo-dynamic model also provided insight for improving the process control design. During the work completed the authors determined that the object-oriented structure adopted for the model enabled an efficient, rapid model development.

3C-SiC on Si Substrates Using Pendeo-Epitaxial Growth

Cubic silicon carbide (3C-SiC) growth using Pendeo-epitaxy technique was successfully achieved on Si(001) substrates. 3C-SiC was grown by chemical vapor deposition (CVD) with silane and propane as precursors. Effects of underlying stripes and seed 3C-SiC layers thickness on PE 3C-SiC films were investigated. Root mean square (RMS) measurements using atomic force microscope (AFM) showed that surface morphology of PE 3C-SiC films remarkably improves with an increase of the seed 3C-SiC layer thickness, and the values were from 9.8 nm for 3 µm thick seed layer to 0.5 nm for 10 µm thick seed layer thickness. Additionally, domain boundary densities were counted, and the values also strongly depend on the seed layer thickness: from >1500/mm2 for 3 µm seed layer thickness to <100/mm2 for 10 µm seed layer thickness. Pendeo-epiaxial growth profiles with various width/separation dimensions of stripes were also investigated, and stripes with width of 10 µm and separation of 5 µm provide the best profile and process viability.

Restoration of Uranium In-Situ Leaching Sites

In recent years in-situ leach mining has emerged as a new technology for the recovery of uranium from strata that cannot be mined economically by other means. Because the ore bodies lie within groundwater aquifers, a significant determinant in the process' viability is the requirement that such aquifers be protected from contamination. Since ammonia is one of the constituents of the leach solutions now being field tested, one environmental problem to be resolved is the removal of ammonia at the end of mining. A second related question is the fate of the ammonia that is not removed by the restoration procedure. This paper considers the displacement and migration of ammonium cations in a flowing electrolyte with concomitant ion exchange. The ion exchange is an important feature since, during the solution mining phase, ammonium cations adsorb onto the mineral exchange sites and must be removed from these sites. A mathematical model is used to simulate this process, and the model is tested against the results of laboratory experiments. It is found that the simulations are adequate if an appropriate selection of parameters is made. The model then is used to simulate restoration procedures and to determine the rate of migration of unrecovered ammonium in the groundwater. It is concluded that ammonium removal can be accomplished best using high concentrations of a cation that is exchanged selectively relative to ammonium cation. Introduction In-situ solution mining is a process rapidly being developed for the recovery of uranium from sandstone ore bodies. This mining technique is applicable when the uranium ore is too deep, too small in extent, or of too low a grade to justify using conventional mining techniques. Such ore bodies are numerous in south Texas, occurring along a broad band of the U.S. gulf coastal plain. The solution mining process being used in Texas is primarily an alkaline leach. The sandstone ores that may be solution-mined occur in aquifers, and the uranium is in the insoluble +4 state of oxidation. To be mobilized, the uranium must be oxidized to the +6 state and then complexed with carbonate ions to form the highly soluble uranyl dicarbonate or uranyl tricarbonate ions. Thus, alkaline leach solutions contain an oxidant (usually hydrogen peroxide) and a mixture of carbonates and bicarbonates. To minimize formation damage, most solution mining now employs ammonium carbonate/bicarbonate as the carbonate source. These solutions have been found effective in dissolving the uranium minerals found in south Texas sandstone ores.1 However, the restoration of the mining site is also a primary consideration. Since the ore bodies that can be solution-mined occur in aquifers, government regulations require that water quality at the mining site not be degraded below the quality that existed at the inception of mining. Furthermore, the permitting procedures require that groundwater restoration be completed at one site before the next site on a particular lease may be mined.2 Obviously, environmental aspects will be an important consideration governing the success of in-situ solution mining.