Saudi Cultural Missions Theses & Dissertations
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Item Restricted CAD CAM Ceramics. A Review of the Scientific Literatures(Saudi Digital Library, 2025-04-04) Alsurayyie, Fatimah; Claydon, NicholasAbstract This study aims to provide a review of the literature on CAD/CAM ceramic restorations, focusing on their clinical properties compared to conventional restorations. In addition to manual searching, three scientific databases were searched for study designs that address at least one of the outcomes of interest regarding CAD/CAM ceramic restorations, including in vitro, in vivo, systematic, and narrative reviews. Up-to-date evidence supports an equivalent outcome of CAD/CAM to the conventional, including superior wear characteristics compared to the standard metal-ceramic restorations, with polished monolithic zirconia showing particularly promising wear characteristics compared to other ceramics. However, there are conflicting results regarding the abrasiveness of lithium disilicates compared to monolithic zirconia, though all were found to cause more wear than natural teeth, and the importance of surface treatment (polishing, glazing) was emphasized. Translucent monolithic zirconia improved aesthetics. However, it requires adequate thickness to compensate for the reduced strength (≥1.0 mm). There were deficiencies in long-term clinical trials regarding longevity; the available short- to medium-term studies showed high survival of CAD/CAM ceramic restorations (>90% at 5 years), expecting better performance with continuous technological development. Moreover, CAD/CAM workflow helped reduce laboratory time spent on restoration fabrication, which is necessary for increasing productivity. Based on laboratory and short-term clinical studies, the potential for CAD/CAM to surpass traditional methods is promising. However, the clinical evidence supporting CAD/CAM ceramic restorations is still not extensive. Therefore, well-conducted large clinical studies are needed to confirm the promising long-term performance of CAD/CAM ceramic restorations. Moreover, to help in the continuous enhancement of the material.7 0Item Restricted Mechanical and Tribological Properties of Cold Sprayed Ni/CrC-NiCr Metal Matrix Composites(Northeastern University, 2025) Batwa, Sohayb; Muftu, Sinan; Nourian, AhmadCold spray (CS) is a solid-state deposition method involving severe plastic deformation of micron-sized powder particles accelerated to supersonic speeds. These particles are propelled through a compressed gas stream, such as air, nitrogen, or helium, using a de Laval nozzle. Since CS operates at low temperatures, no melting takes place during deposition. This offers a distinct advantage over other thermal spraying techniques resulting in unique and significant advantages. Metal-matrix composites (MMC) combine the high hardness, wear resistance, and thermal stability of ceramics with the ductility, toughness, and thermal conductivity of metals. In the development of coatings through CS technology, the feedstock powder is crucial for achieving the desired engineering properties, and it becomes more significant when cermet MMC powders are used. This dissertation aims to experimentally investigate the mechanical and tribological properties of a cold-sprayed cermet based MMC. Chromium carbide-nickel chromium (CrC-NiCr) was used as the cermet particle where CrC is a ceramic and NiCr is a ductile binder. This cermet particle was used in the MMC by using Ni as the overall binder. Therefore, the MMC is designated as (CrC-NiCr)/Ni. The first part of the study focuses on: (i) investigating the influence of increasing the metallic (NiCr) binder percentage in the cermet particle, and (ii) exploring the effects of varying the matrix-to-cermet ratio, i.e. Ni to (CrC-NiCr) ratio, in the feedstock blend on the microstructure and mechanical properties of the CS deposits. Results indicate that increasing the binder phase percentage in the cermet particles enhances deposition efficiency, cermet area fractions, and interparticle adhesion. This also results in coatings with porosity less than 1%, as well as improved ductility and shear strength. To address inter-splat defects and brittleness of the MMCs, the second part of this study examines the effects of post-spray annealing on the mechanical properties and microstructure. Scanning transmission electron microscopy (STEM) demonstrated improved interparticle bonding between matrix splats, with fractographic analyses indicating a shift from brittle to ductile fracture mechanisms. Mechanical tests reveal that post-process annealing significantly enhances the ultimate tensile strength (UTS), elongation, and adhesion shear strength of the coatings, however, it adversely affects coating hardness. The third part of this study investigates the effects of various post-spray heat treatments on the microstructure and tribological behavior of cold-sprayed Ni/CrC-NiCr metal matrix composite (MMC) coatings. Post spray (PS) laser heat treatment (LHT) and plasma arc heat treatments (PAHT), along with two furnace annealing temperatures were employed. Results shows the wear rate of the MMCs is significantly influenced by the type of heat treatment. PS-LHT and PAHT facilitated the formation of thin oxide tribo-film (mainly Cr22O33) that acted as solid lubricants, reducing metal-to-metal contact and abrasive wear.3 0Item Restricted MECHANICAL PROPERTIES OF SINGLE ELECTROSPUN NANOFIBERS FOR BIOMEDICAL APPLICATIONS(Saudi Digital Library, 2023) Alharbi, Nouf Ayed; Guthold, MartinElectrospun fibers have garnered considerable attention for biomedical applications due to their unique properties, including high surface area-to-volume ratio, tunable mechanical properties, biocompatibility, and controlled drug release. Electrospinning is a versatile technique for producing fibers at the nanoscale. It can produce fibers from a wide range of materials, including synthetic polymers, natural polymers, and blends of both materials. Measuring the mechanical properties of electrospun fibers is crucial for understanding their suitability for various biomedical applications. We used a combination of an atomic force microscope and an inverted optical microscope to investigate the mechanical properties of a single electrospun nanofiber made of polycaprolactone (PCL) with three different molecular weights, a blend of PCL and fibrinogen, as well as hydrated PCL fibers and human fibrinogen. In addition, we determined the mechanical properties of a fibrous mesh made of human fibrinogen. The findings showed that the molecular weight of PCL has no significant impact on the mechanical properties of the fiber, as fibers produced from different molecular weights showed similar mechanical properties. The mechanical properties of blended fibers were observed to be influenced by the ratio of fibrinogen to PCL, with extensibility, elastic limit, and relaxation times increasing as the PCL ratio increased from 25% to 75%. Hydrated PCL fibers were found to have mechanical properties similar to those of dry single fibers. Interestingly, the extensibility of both dry and hydrated single human fibrinogen fibers was greater than that of other electrospun fibers. However, the hydrated fibers were more extensible and softer than the dry fibers and the fibrous fibrinogen meshes. The study found that stiffness-related mechanical properties, including the Young's modulus, stress at rupture, and elastic and total moduli, of electrospun fibers made from different polymers were dependent on fiber diameter. Specifically, when the fiber diameter decreased below a threshold between 100-200 nm, the Young's modulus increased several-fold compared to that of larger diameter fibers. However, when the diameter was larger than 100-200 nm, the modulus remained almost constant.38 0