Materials Science Forum Vol. 1093

Abstract: Extrinsic light excitation has much lower absorption coefficient compared to intrinsic light excitation, which can better utilize the “bulk” of semiconductor rather than a thin surface as the depth of light absorption is much larger, making it suitable for higher power applications. However, commercial technology computer aided design (TCAD) software has not developed a model for extrinsic light excitation. Therefore, we construct a model of Vanadium-compensated semi-insulating (VCSI) 6H-SiC photoconductive semiconductor switch (PCSS) illuminated with sub-bandgap light, and realize the process of light absorption at V deep acceptor level in Silvaco TCAD simulation by modifying the electron emission rate. Then, we simulate the transient response of 6H-SiC triggered by a nanosecond light pulse and discuss the feasibility of this method.

Abstract: Interface properties of 4H-SiC N-MOS and P-MOS capacitors with two different NO annealing conditions are characterized by the conductance method. With the enhancement of nitrogen passivation, the density of interface states is reduced as expected. Fast interface states (response frequencies >1 MHz) are observed for both N-MOS and P-MOS capacitors with weak NO passivation. After strong NO passivation, the fast states are passivated to the interface states with lower response frequency in N-MOS and significantly suppressed in P-MOS. It indicates that the nitridation may passivate the defects by shifting them from shallow level to deep level.

Abstract: The rare earth element is a critical element in many industrial sectors. Due to unbalanced supply and demand, it is necessary to look for an alternative source. Coal ash is a waste product of power plant combustion. Previous research revealed that coal ash contained levels of rare earth elements. This research uses coal fly ash from the Paiton power plant. The objectives of this study were to determine the effect of the Na₂SO₄ concentration, stirring rate, and temperature on the recovery of REE concentrate. The experiment was conducted in four steps: (1) alkaline leaching, the process was carried out for 2 hours at 90°C with fly ash solid to 8 M NaOH solution ratio of 1:4 to break the aluminosilicate bonds. (2) Acid leaching of residue for 4 hours at 90°C in 3 M HCl. (3) Precipitation of residue to remove the impurities such as Fe using 1 M NaOH at pH 5. (4) Precipitation of filtrate from process (3) using Na₂SO₄ to produce REE concentrate precipitates. The best condition to obtain the highest REE residue is conducting recovery at the concentration of 20% Na2SO4, stirring rate of 500 rpm, and temperature of 50°C, with a yield of 88.72%.

Abstract: Sorption behavior of neodymium (Nd) from cerium (Ce) and samarium (Sm) on anion-exchange resins was investigated by column techniques. The anion exchange studies involved the sorption of Nd, Ce and Sm ions onto Dowex 1-X4 (100–200 mesh) in nitric acid – methanol medium. Separation of neodymium from cerium and samarium was carried out by column method to find out the best separation parameter condition with variating HNO₃ concentration and weight of resin. The best elution profile was found using 0.3M HNO₃ : methanol (1 : 9) as eluent through 1.25 grams of Dowex 1-X4 resin with 97.16 % Sm recovery and 95.59 % Nd recovery, while Ce was retained in the column.

Abstract: Rare Earth Elements (REE) concentrate from the processing of xenotime minerals still contains a mixture of REE and its impurities, so it requires a further separation process to purify the content of each element. The first step to separating each element of REE is to dissolve the REE concentrate in strong acid as a feed for the liquid-liquid extraction or ion exchange column process. The REE concentrate was dissolved in 3 variations of strong acids, namely hydrochloric acid, nitric acid, and sulfuric acid. XRF and FTIR analyses were done before and after the dissolution process. The results showed that sulfuric acid is the best dissolution reagent for the total rare earth elements (71.75%) but is less selective for separating light REE, heavy REE, and their impurities. Better selectivity for separating light REE and heavy REE is shown by dissolution with nitric acid with dissolution levels of 37.32% and 81.91%, respectively. Meanwhile, hydrochloric acid showed the lowest dissolution results for the total element of REE (63.14%) but had the best selectivity to prevent the dissolving of radioactive elements. The results of the FTIR analysis showed that REE-chloride, REE-nitrate, and REE-sulfate bonds had been formed in each dissolving filtrate.

Abstract: The addition of CsNO₃ against Nd and Cs recovery in nuclear fuel using the precipitation method has been carried out. Precipitation methods have been carried out by previous researchers to separate cesium in U₃Si₂/Al and UMo/Al nuclear fuels. The recovery of cesium in the nuclear fuel obtained was more than 95%. After got optimal recovery for Cs separation, in this research would use the method for Nd separation. Beside the Cs isotope, the Nd isotope was the result of fission product after the radiation process of nuclear fuel in nuclear reactor. Both isotopes were used as burn-up indicators. To obtain optimal Nd recovery, in the separation process using the precipitation method, weight various CsNO₃ are added. CsNO₃ as a carrier in this method. The nuclear fuel solution containing Nd was added 100, 200, 400, 600 and 1000 mg of CsNO₃. Then the mixed solution was added 4 mL of HClO₄ and cooled at 0oC using an ice bath for 1 hour. A precipitate would form after cooling process for 1 hour. The liquid phase was separated from the solid phase. Then Nd and Cs in the liquid phase were analyzed using XRF. The analysis results of the Nd content in the liquid phase showed that the optimal recovery was 94.21% with the addition of 200 mg of CsNO₃. While most of the Cs is in the solid phase with recovery greater than 99% on the addition of CsNO₃ between 100-1000 mg.

Abstract: The separation process of Dysprosium (Dy) from other Rare Earth Elements (REE) in monazite was carried out considering various applications of Dy in high purity. The Dy elements can be used as a dopant in Thermoluminescence Detector (TLD) crystals to monitor the personnel dose of radiation workers. The separation process of Dy is hard to do due to the similarity of the physical and chemical properties of all REE. This research was conducted to separate Dy by a precipitation process at a certain pH. The feed used is Rare Earth Hydroxide (REOH) concentrate from a monazite processing. The variation of the precipitation used was pH 4.5 to pH 8.5 with 0.5 intervals. The highest precipitation of Dy with an efficiency of 24.47% was obtained at pH 8. Other REEs precipitated at pH 8.5, while the Dy was found the most in the filtrate.

Abstract: Soil as a building material is gaining renewed interest from academia, and the construction sector, mainly for fabricating low-environmental impact homes. The fabrication of houses with soil using traditional methods such as adobe, cob, and rammed earth dates back to ancient times. However, emerging construction technologies, such as 3D printing, can be compatible with this material for building purposes. The article presents the validation of a 3D printing system for construction applications and the evaluation of soil-cement matrices' printability. First, the paper defines the printing parameters through experimental testing on soil matrices. Then, the article evaluates the printability of soil-cement matrices through filament printing and stacking tests. The results show that the 3D printing system prototype can fabricate small and medium-sized elements with soil matrices after correctly defining the pumping speed, printing speed, and layer height. Furthermore, experimental printing test results demonstrate that soil-cement matrices can be easily extruded and stacked; however, their printability capacity is strongly affected by the total water content and printing speed. This research highlights the suitability of soil-cement mixtures for additive manufacturing, a promising outcome that can facilitate the construction of homes in remote areas using 3D printing systems.

Abstract: Due to economic, sustainable, and aesthetic benefits, academia and the construction industry are exploring the use of earth in modern construction is being widely studied. Unfortunately, earth as a construction material has low mechanical, poor water durability resistance, and the potential to swell and crack. Therefore, this paper evaluates chitosan and potato starch, natural biodegradable polymers, as stabilizers to improve mechanical strength and water durability resistance of printable earth-based matrix reinforced with sisal fibers. Although the test results indicated that the chitosan had a better performance as an earth stabilizer than potato starch, adding both stabilizers resulted in earthen composites with higher compressive strength and lower water permeability. These results demonstrate the feasibility of using natural stabilizers to improve the performance of earth-based materials for 3D printing without affecting their printability capacities.

Abstract: 3D concrete printing is an innovative construction process based on fully autonomous material deposition. One of the challenges of implementing this technology is the development of printable concrete formulations, as this material must exhibit particular fresh-state properties. Among these, buildability is one of the most important. This property describes the material's ability to support weight at very early ages, allowing a layer-by-layer construction. Therefore, this paper aims to evaluate two approaches for improving concrete buildability: the optimization of the superplasticizer dosage and the external application of quick-setting admixture. The results showed that reducing superplasticizer content improved buildability by increasing the static yield strength. However, this approach has a collateral disadvantage as concretes presented problems during extrusion. On the other hand, the results of cylinder stability and Vicat tests indicate that the external application of quick-setting admixture leads to concretes with improved buildability without affecting the initial workability and a faster hardening process. According to these results, the latter approach can potentially be applied in small and large-scale 3D printing.