The Latin American steel making company Ternium S.A. aims to develop and produce a new type of advanced high strength steel (AHSS) in which the main alloying elements are carbon, aluminium, manganese, and silicon. The present work is the first phase of the development project and it involves casting and characterization of four steel compositions with varying amounts of the aforementioned elements. The results revealed that the Mn-content had a large impact on the development of hard phases during solidification. A steel with a Mn-content of 2 %wt. had almost completely transformed to pearlite during cooling, while a steel with a 4 %wt. Mn-content consisted of primarily martensite and retained austenite. Only the impact of the Mn-content is evaluated. The columnar grain size for two of the four steel compositions were in the range of 20-30 mm, which is similar to those observed from continuous casting. This indicate that the heat transfer rate was slow enough to allow these grains to grow. Measurements during casting showed an initial cooling rate of 10-20°C/min at a distance of 10 mm inside the ingot, which is much slower than the surface cooling rate during continuous casting (100-150°C/min). It was assumed that the cooling rate was similar for all castings since the methodology was identical. However, the steel used for cooling rate measurements was not characterized, why a correlation between cooling rate and composition could not be obtained. A heat transfer model was developed to gain further knowledge of the solidification process. As a reference to the heat transfer model, a eutectic Bi-42Sn alloy was cast with temperaturemonitoring using a casting setup identical to that of the steel castings. A similar cooling rate tothe Bi-42Sn reference casting was obtained where the cooling was faster from above of the ingot than below. Thus, the last part of the metal to solidify during the simulation was situated in the lower half of the ingot. This provides a model for testing future steel compositions.

Using Fe57 Mossbauer spectroscopy, two alternative sites occupied by cobalt (10-4 at. % ) impurity atoms in aluminum have been isolated. The substitutional site A is the stable position after annealing the sample above 840 K, followed by a rapid quench. The impurity atoms in site A are characterized by a single line Mossbauer spectrum (indicative of a cubic environment), a room-temperature f = 0.502 (r. m. s. displ. 0.071 A) and an I. S. (reI. to Fe) = -0.421 mm/sec. For anneals below 770 K the cobalt atoms migrate to site B, which is characterized by a well resolved quadrupole doublet (indicative of a non-cubic environment), a large change in the value of the room-temperature f = - 0.766 (r. m. s. displ. 0.071 A), I. S. = -0.150 mm/sec (increased s-electron density at the nucleus). All linewidths· are approximately 0.21 mm/sec, indicating high uniformity of impurity sites. The site distribution [A] / [B} varies from about 5 % to 95 % for anneals between 770 K and 830 K.

Indiana University-Purdue University Indianapolis (IUPUI) / The luting agent is a crucial factor in the outcome of cemented fixed restorations. A new water-based cement, Ceramir C&B (CM), approved to be marketed in the US, is composed of calcium aluminate and glass ionomer. CM is a luting agent indicated for permanent cementation of cast restorations, all-zirconia or all-alumina crowns, and prefabricated metal and cast dowel and cores. The manufacturer claims that the cement has demonstrated favorable biocompatibility properties when tested in vitro and in vivo and has proven to be bioactive. The objective of this study was to evaluate volumetric dimensional changes and the amount of Ca2+ released by the new luting agent. Twenty specimens of each material, namely calcium aluminate glass ionomer, resin-modified glass ionomer, and two resin luting agents, were fabricated and weighed. The 20 specimens for all materials were divided into four groups (five samples in each group) based on storage conditions: silicone oil at 22°C and 37°C and distilled water at 22°C and 37°C. Using the manufacturers’ instructions for each material, cylindrical specimens were prepared with dimensions of 7 +0.1 mm in diameter and 2 +0.1 mm in height. A 0.01-mg resolution balance was used to determine volumetric dimensional change using an Archimedean equation. Measurements were made 30 minutes after mixing, and at the time intervals of 7 days, 14 days, 21 days, and 30 days, and after total dehydration of the specimen. Chemical analyses of the solutions were performed using atomic absorption spectroscopy to determine the Ca+2 ion concentration. Moreover, the pH values were measured to determine the OH–concentration in the solutions. The results showed that CM had the most expansion among the tested luting agents in distilled water at 22°C and 37°C, and significantly increased at higher temperature. In silicone oil, resin-modified glass ionomer shrank the most and also shrank more with the high temperature. The result of the ion concentration analysis indicated that Ca+2 and OHion release increased with increasing time and also significantly with temperature rise. In conclusion, calcium aluminate-glass ionomer exhibited the most significant dimensional change when stored in water storage. The solubility of the tested luting agents should be evaluated in the future because they were not evaluated in this study. Furthermore, to evaluate the clinical effect of the dimensional changes, the impact on the gap formation at tooth-crown margins should be determined in future work.

Indiana University-Purdue University Indianapolis (IUPUI) / BACKGROUND: Dental erosion is a multifactorial condition that causes irreversible loss of dental hard tissues. Its development is highly influenced by saliva, with higher prevalence in hyposalivatory patients. There is no scientific consensus regarding the restorative treatment of choice for eroded teeth in such highly erosive conditions and to date, this has not been studied under in-vitro conditions. OBJECTIVES: To investigate the effect of erosion on direct tooth-colored restorations and adjacent enamel/dentin under different simulated salivary flow rates. METHODS: Bovine enamel and dentin specimens were prepared (n =16) and restored with the testing restorative materials, resin-composite (Filtek Z250), resin-modified glass ionomer (Fuji II LC), high viscosity glass ionomer cement (Fuji IX), and low viscosity glass ionomer cement (Fuji II).Then, submitted to an in-vitro erosion cycling model simulating different salivary flow rates (normal 0.5 ml/min and low 0.05 ml/min) and dental erosion protocols for 5 days. Surface loss of the restorative material and surrounding enamel/dentin surfaces were analyzed. A mixed-model ANOVAs and Sidak adjustment were used for statistical comparisons (p < 0.05). RESULTS: The surface loss was lower at 0.5 than at 0.05 ml/min, for all tested restorative materials except resin composite. Surface loss was higher in enamel and dentin adjacent to Filtek Z250 compared to Fuji II LC and Fuji IX, with no significant difference in enamel and dentin surface loss adjacent to Filtek Z250 and Fuji II. The restorations surface degradation was significantly lower for Filtek Z250 than for Fuji II, Fuji II LC, and Fuji IX, at both 0.5 and 0.05 ml/min; moreover, the surface loss was significantly lower for Fuji II LC than for Fuji II and Fuji IX, which did not differ from each other. CONCLUSION: Within the limitations of this study, it can be concluded that low salivary flow promoted higher erosive conditions. The use of Fuji II LC and Fuji IX may reduce erosive effects on enamel and dentin adjacent to restoration. Of the materials evaluated, resin-modified glass ionomer restoration may be the most suitable for restoration for patients at higher risk of erosion with low exposure to fluoride.

Indiana University-Purdue University Indianapolis (IUPUI) / Polymerization shrinkage is one of the most significant problems associated with resin-matrix composite. Shrinkage results in contraction stress in the resin, leading to possible debonding in certain areas of the adhesive joint and potentially adversely affecting the bond strength. The reduction in the stress may improve the adaptation of the resin restoration, and decrease the problems that are associated with contraction stress, such as postoperative pain and recurrent caries. Recently, it has been found that varying the inhibitor concentration would reduce the polymerization shrinkage without affecting mechanical properties. In this study, we investigated the effects of varying the initiator and initiator levels on polymerization shrinkage stress, strength, and degree of conversion. An experimental composite was prepared by using a blend of BisGMA: UDMA: TEGMA (1:1:1 weight ratio) with 70 wt% silanated glass fillers. Four levels of inhibitors (BHT 0.0 %, 2%, 6%, 20%) and initiators (CQ 2%, 6%, 20%, 60%) were used (total of 16 combinations). A tensiometer was used to measure the polymerization contraction stress, contraction stress rate and gel time for each resin. FTIR was used to measure the degree of conversion. The flexural strength and flexural modulus were determined using the three-point bending test. Resin-matrix composite with 0.0-percent BHT and 2.0-percent CQ showed the highest contraction stress and stress rate and the shortest gel time, while resin-matrix composite with the 6.0-percent BHT and 6-percent CQ showed the lowest contraction stress and stress rate and the longest gel time. At an extremely high concentrations of CQ (20 percent and 60 percent) and high BHT concentration (20 percent) low degree of conversion values were observed. Overall, from the collected data, group F (2-percent BHT and 6-percent CQ) and G (6-percent BHT and 6-percent CQ) provide the most desirable combination of strength (above 80 MPa) and stress (below 3 MPa) are present as a potential dose combination range of CQ and BHT. In conclusion, the effect of inhibitors and initiators appears to change in different resin formulation. Increasing the levels of both the inhibitor and the initiator decrease the polymerization contraction stress and stress rate, and the impact on the conversion is unpredictable. In this study, we found a decrease in both the conversion value and depth of cure.

Perovskite solar cells exhibit outstanding device performance and photovoltaic potential in recent ten years. However, the photoactive layer of the majority of perovskite solar cells with outstanding efficiency currently contains toxic lead. Although perovskite solar cells will be encapsulated prior to application to enhance the device's stability and prevent lead leakage, it is still possible for the devices to be broken or exposed to the environment during actual use. Correspondingly, Pb may enter water or soil through rainfall, posing health risks to humans and other creatures. To prepare perovskite solar cell devices with both high performance and low toxicity, current research concentrates primarily on Pb-Sn hybrid perovskite solar cells as Sn is less toxic than Pb from an environmental standpoint. To intuitively compare the lead leakage of Pb-based perovskite solar cells and Pb-Sn hybrid perovskite solar cells, this study simulated the lead leakage scenario under heavy rainfall conditions using self-prepared, good-performance solar cell devices. Our results indicate that Pb-Sn hybrid perovskite solar cells have less lead leakage than Pb-based perovskite solar cells. The lead leakage concentration of Pb-Sn hybrid perovskite solar cells was 36.8% (in the dripping test) and 41.2% (in the soaking test) lower than that of Pb-based perovskite solar cells.

Industries’ interest in nanomaterials is tremendous and catalysis is one of their applications. Catalysts allow reactions to occur under milder conditions, avoiding committing excessive heat or pressure to foster reactions. The discovery of Frustrated Lewis Pairs (FLP) in 2006 led to a new concept of homogeneous catalysis: metal-free acids and bases preventing from forming an Lewis adduct because their bulkiness create an active clamp that is able to cleave dihydrogen and other small molecules at room temperature. Transferring the FLP concept to the “nano”-world which is more relevant for industrial applications, requires well-designed nanoparticles and rationalization of their interaction with ligands aiming at forming a FLP between nanoparticles and ligands. The following project conducted at LCMCP (Laboratoire de Chimie de la Matière Condensée de Paris) under the supervision of Sophie Carenco aimed at studying the insertion of phosphorus in metallic nanoparticles in order to tune their catalytic activity and demonstrate Frustrated-Lewis Pair catalytic behaviours. To that end, copper nanoparticles and bimetallic core-shell nickel-cobalt nanoparticles were synthesized in colloidal solution. The phosphidation of both nanoparticles was investigated with trioctylphosphine (TOP) as the phosphorous source. Nanoparticles were characterized by X-Ray Diffraction, Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy. Starting from the failure to reproduce a published procedure of copper phosphide nanoparticles synthesis, conditions of the reaction and the washing procedure were successively improved aiming the obtention of copper phosphide nanoparticles. The one-pot synthesis with hot-injection of TOP at the second step (320°C, 1h), allowed to isolate copper phosphide nanoparticles but a longer reaction time did not result in enhanced phosphorus doping. Further work would need to examine the reproducibility problems faced and investigate harsher reaction conditions (eg. higher temperature). Cu3P nanoparticles would be interesting to test as catalysts for hydrosilylation of benzaldehyde or CO2, a model reaction for CO2 hydrogenation. The synthesis of core-shell nickel-cobalt nanoparticles has been previously rationalized by Sophie Carenco’s team. Phosphidation was attempted from this optimized procedure. We started with harsh conditions (&gt; 250°C, &gt; 1h30) which caused reconstruction of the nanoparticles after leaching of the cobalt shell. In such conditions, the core-shell structure is not retained and a NiCoP alloy is obtained. Milder conditions allowed to retain the structure but further studies are required to characterize and locate the phosphorus insertion in the core-shell nanoparticles. NiCoP alloy and phosphidized core-shell Ni@Co will be of great interest to apply in catalysis for water splitting and hydrogenation of nitriles, respectively.

Indiana University-Purdue University Indianapolis (IUPUI) / Resilon is a resin-based obturation material that claims to create a monoblock through bonding of RealSeal sealer to the dentin walls and to the core material. Resilon is comprised of a biodegradable polymer, polycaprolactone, and inorganic fillers. Resilon has been shown to undergo enzymatic hydrolysis by bacterial enzymes such as lipase. This study aims to demonstrate if bacteria found within the infected root canal system are capable of degrading Resilon utilizing an agar disc hydrolysis method. A 0.1-percent Resilon emulsion and a gutta-percha emulsion were prepared with Tryptic Soy Agar in plates. Several bacterial species were inoculated in eight spots each on the Resilon and gutta-percha agar plates and the plates were observed for the formation of hydrolytic halos surrounding bacteria signifying their ability to degrade the material. The bacterial enzyme Lipase PS served as a positive control. P. intermedia, P. aeruginosa, P. assacharoylitica, S. epidermidis and S. aureus all demonstrated hydrolytic halos, clear zones, at each of the eight inoculation locations (100%, 95%CI 63%-100%) on the Resilon plates. The halos were similar to those seen in the positive lipase control. No halos were seen with E. faecalis, F. nucleatum, S. mutans, S. sanguis, or P. gingivalis at any of the eight inoculation spots (0%, 95%CI 0%-37%) on the Resilon plates. No hydrolytic halos were seen around any bacterial colonies or the Lipase PS on the gutta-percha plates. The results of this study indicate that bacteria found in endodontic infections can hydrolize Resilon dispersed into an emulsion. The potential exists for Resilon degradation after its use as an obturation material in infected root canal systems. Given that root canal therapy does not render a canal void of microorganisms, it is prudent to obturate the root canal system with a material that cannot be degraded by bacteria and their enzymes.

Tuberculosis (TB) is an airborne disease caused by Mycobacterium tuberculosis, with an incidence in a quarter of the world population. Despite the scientific and technological advances, an effective diagnostic method has not yet been found that allows an early diagnosis and, also, to detect the strain present in the patient. The combination of nanotechnology with molecular diagnostics has shown promising advances offering new possibilities, such as the development of nanoflares.  Nanoflares represent a new class of molecular probes, composed of gold nanoparticles functionalized with a recognition sequence that can be amplified by rolling circle amplification (RCA) technique, producing a fluorescence signal.  This thesis focuses in the synthesis of gold nanoparticles, with different coatings and sizes, as well as their subsequent application in the preparation and optimization of nanoflares for the genotyping of synthetic M. tuberculosis targets using RCA technique. The different preparations of nanoflares have an impact in the assay sensitivity, showing two times increase in sensitivity for citrate-coated nanoparticles with respect to those coated with PEG. Furthermore, it was observed that the sensitivity is directly related to the synthesized particle size.  Sensitivity is also affected by the application of a purification post-treatment of the synthesis product. This post-treatment reduces the sensitivity of nanoflares by up to 37% but, by contrast, extends its useful life.  The results obtained are shown as a proof of concept for a future cost-effective, rapid and robust in situ diagnostic method that identifies the strain of tuberculosis present in the patient.

The objective of this work was the development of an efficient adsorbent for irreversible immobilization of heavy metals in contaminated soils. The adsorbent was prepared by pillaring montmorillonite with silica followed by the grafting of a chelate ligand onto its surface. Its structure was studied by the Brunauer, Emmett, and Teller Method adsorption of N2, Dynamic Light Scattering, and Scanning Electron Microscopy. The adsorption capacity of the organoclay was measured by its mixing with contaminated kaolin soil samples and by analysis of heavy metal contents in leachate. The adsorbent was efficient in immobilization of heavy metals in both neutral aqueous and acidic media. In addition, the adsorbent was efficient in environmental samples reducing the concentration of iron in all samples in aqueous and acidic media. As a result, the adsorbent can be used for reduction of heavy metal leaching from contaminated sites.