Monocrystalline Aluminum Research Articles

Degradation of Monocrystalline Silicon Photovoltaic Modules From a 10-Year-Old Rooftop System in Florida

A system of 180 monocrystalline aluminum back-surface field modules were installed in Cocoa, Florida, for 10 years. In total, 156 modules are characterized and compared to 3 controls. Power degradation rates vary between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 0.14% to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 3.22% per year, with median and average rates of −0.92% and −1.05% per year, respectively. The losses are primarily resistive with minor optical and recombination loss contributions. Electroluminescence imaging shows a characteristic pattern, which is shown to be resistive in nature when compared to photoluminescence. Resistive losses are due to corrosion of the rear contact Ag/solder interface and, to a much lesser degree, gridline Ag oxidation. Moisture ingress through the backsheet is likely responsible for mediating corrosion. Optical losses are due mostly to a combination of antireflection coating degradation, minor encapsulant browning, and delamination. Minor front contact corrosion may contribute to recombination. This study expands upon previous work on this vintage of the module by examining a large sample set, comprehensive characterization including techniques not previously used on these modules, and a comparison between two other systems of different climates.

Variation in adhesion of Streptococcus mutans and Porphyromonas gingivalis in saliva-derived biofilms on raw materials of orthodontic brackets.

ObjectiveTo evaluate differences in the adhesion levels of the most common oral pathogens, Streptococcus mutans and Porphyromonas gingivalis, in human saliva-derived microcosm biofilms with respect to time and raw materials of orthodontic brackets.MethodsThe samples were classified into three groups of bracket materials 1) monocrystalline alumina ceramic (CR), 2) stainless steel metal (SS), and 3) polycarbonate plastic (PL), and a hydroxyapatite (HA) group was used to mimic the enamel surface. Saliva was collected from a healthy donor, and saliva-derived biofilms were grown on each sample. A real-time polymerase chain reaction was performed to quantitatively evaluate differences in the attachment levels of total bacteria, S. mutans and P. gingivalis at days 1 and 4.ResultsAdhesion of S. mutans and P. gingivalis to CR and HA was higher than the other bracket materials (SS = PL < CR = HA). Total bacteria demonstrated higher adhesion to HA than to bracket materials, but no significant differences in adhesion were observed among the bracket materials (CR = SS = PL < HA). From days 1 to 4, the adhesion of P. gingivalis decreased, while that of S. mutans and total bacteria increased, regardless of material type.ConclusionsThe higher adhesion of oral pathogens, such as S. mutans and P. gingivalis to CR suggests that the use of CR brackets possibly facilitates gingival inflammation and enamel decalcification during orthodontic treatment.

Normal incidence birefringence in nanoporous alumina

There are many works and interests focused on the development of optical sensors based on porous anodic aluminum oxide membranes (AAO). Normal incidence birefringence (BR) is present in AAO when is obtained from a monocrystalline aluminum substrate but his effect has been largely ignored since it is canceled out in a poly-crystalline substrate. Nevertheless, this averaging of BR limits the optical performance of AAO membranes in optical devices. In this work, we study normal incidence BR in AAO for different crystal orientations of the aluminium substrate using a polycrystalline substrate and a simple thermo-mechanical treatment to obtain millimeter size crystalline regions. We found that normal incidence BR is minimum at [100] and [111] orientations and reaches a maximum of ∼ 1.8 ⋅ 10−3 at intermediate orientations. In this case, the BR can be associated with a slight deformation of the structure perpendicular to the direction of the pores, confirmed through scanning electron microscope images. Furthermore, we propose a simple model of elliptical section pores that quantitatively explain the origin of normal incidence BR in AAO. Considering the effect of BR, the design of sensors could be improved to obtain higher quality factors or to incorporate new optical functionalities to these already versatile membranes.

In Vitro Determination of Genotoxicity Induced by Brackets Alloys in Cultures of Human Gingival Fibroblasts.

Orthodontic brackets release ions that can be reabsorbed in the oral mucosa, potentially causing complications, including cytotoxic effects and mutagenic alterations. The aim was to evaluate the genotoxicity induced by orthodontic appliance alloys in cultures of human gingival fibroblasts by comet assay. Eluates were obtained from the following brackets alloys: EconoLine (SS: stainless steel), MiniMirage (Ni-Ti: nickel-titanium), Nu-Edge (Co-Cr: cobalt-chromium), In-Vu (PC-polycrystals (PC) aluminum oxide), and Monocrystal IZE (monocrystalline (MC) aluminum oxide). Each bracket was sterilized and exposed to a corrosive process for 35 days. The obtained eluates were tested for genotoxicity of human gingival fibroblasts (HGFA) by the alkaline comet assay. All study groups showed genotoxic effects; there was a significant difference (p < 0.0001) among groups. The eluates obtained from Ni-Ti showed a 16-times greater genotoxic effect. There were differences in genotoxicity after comparing the Ni-Ti with SS (p < 0.01) and Co-Cr brackets (p < 0.001). The ceramic was more genotoxic than metallic brackets (SS and Co-Cr), but less than the Ni-Ti. This in vitro model will be useful for further study of early DNA damage caused by brackets and other biomaterials used in the oral cavity before their introduction into the clinical setting.

Variation of Static Frictional Forces in the Fixed Orthodontic System

Currently, the aesthetic appearance of fixed orthodontic appliances is an important factor for patients seeking orthodontic treatment. The aim of this study was to evaluate static frictional forces generated by different types of round 0.016 NiTi archwires, with and without aesthetic coating, when coupled with monocrystalline alumina brackets. The static frictional force was determined using a testing machine for measuring compression and tension forces. The results showed a variation of static frictional forces depending on the type of archwire used. Uncoated archwires have produced the lowest static frictional forces. Partially aesthetic coated archwires have generated lower static frictional forces than fully aesthetic coated ones. Fully aesthetic coated archwires have produced the highest static frictional forces, but no significant differences were noted between archwires with polymer and epoxy resin coating.

Variation of Static Frictional Forces in the Fixed Orthodontic System

Currently, the aesthetic appearance of fixed orthodontic appliances is an important factor for patients seeking orthodontic treatment. The aim of this study was to evaluate static frictional forces generated by different types of round 0.016` NiTi archwires, with and without aesthetic coating, when coupled with monocrystalline alumina brackets. The static frictional force was determined using a testing machine for measuring compression and tension forces. The results showed a variation of static frictional forces depending on the type of archwire used. Uncoated archwires have produced the lowest static frictional forces. Partially aesthetic coated archwires have generated lower static frictional forces than fully aesthetic coated ones. Fully aesthetic coated archwires have produced the highest static frictional forces, but no significant differences were noted between archwires with polymer and epoxy resin coating.

Atomistic simulation of the nanoindentation behavior of graphene/Al multilayered nanocomposites

In this paper, the mechanical behaviour of graphene/aluminum multilayered nanocomposites (GAMC) was studied by conducting the nanoindentation simulations using molecular dynamics (MD) method. The reinforcement effect of graphene on aluminum was investigated by two different cases: the graphene layers are considered as the reinforcement and the coating materials respectively. The microscopic deformation mechanism is investigated through the study of a hemispherical diamond indenter indenting against the monocrystalline Al and GAMC. For the graphene-coated Al composite (GCA), it is found that graphene coating layers have an effect on the characteristics of dislocation slip in Al matrix and improve the load carrying capacity of the GCA significantly. In addition, graphene-reinforced Al composite (GRA) with different spacing-distance of the graphene layers was investigated. It is concluded that the GRA shows an increasing nanoindentation properties with reducing the thickness of Al layers. Although the present research is based on monocrystalline aluminum, the deformation mechanism here can be applied to other face-centered-cubic (FCC) monocrystalline metals structures.

Low-temperature wetting of sapphire using Sn–Ti active solder alloys

Monocrystalline alumina, known as sapphire, is one of the most commonly used ceramics in electronic devices. Understanding its wettability is thus of great importance for its engineering applications. In this work, the low-temperature wetting mechanisms of Sn–Ti active solder alloy on C-plane sapphire was comprehensively studied using the sessile drop method. The addition of 0.1 wt % Ti was found to effectively improve the wettability of Sn–Ti alloys, and the lowest contact angle on the sapphire substrate was achieved at 950 °C when Ti content was increased to 3 wt%. Thermal dynamics analysis and experimental results indicated that the isothermal spreading of Sn–3Ti alloy is controlled by the Ti adsorption in the vicinity of wetting triple line. Moreover, sapphire was successfully brazed using Sn–3Ti alloy at 500, 550, and 600 °C, and the maximum shear strength was measured as 30.3 MPa. Our understanding of the wettability of sapphire provides the fundamental theory for developing new bonding technique for this important crystal.

In vitro Evaluation of Static Frictional Forces at the Bracket-archwire Interface

The aim of this research is to compare the static frictional forces generated by different bracket-archwire couples. The study group consisted of three types of ceramic brackets (polycrystalline alumina with stainless steel slot, polycrystalline alumina and monocrystalline alumina), one stainless steel bracket and two types of archwires (0.016` NiTi and 0.019x0.025` SS). Brackets corresponding to the upper right quadrant (form upper right central incisor to the upper right second premolar) were bonded on standardized maxillary models and elastomeric ligatures were used to secure the archwire to the bracket system. An in-vitro experiment was conducted using a testing machine designed to measure the compression and traction force, both in dry and wet testing conditions. The results indicated statistically significant differences between most bracket-archwire groups. According to the data obtained, stainless steel brackets produced the lowest static frictional forces, regardless of test conditions and orthodontic archwire type. Polycrystalline ceramic brackets with stainless steel slot generated higher static frictional forces than stainless steel brackets, but lower than ceramic brackets when combined with the 0.019`�0.025` SS archwire. No significant differences were found between polycrystalline and monocrystalline ceramic brackets. Experiments performed with 0.019�0.025` SS archwire produced greater static frictional forces than those with 0.016` NiTi wire. Static frictional forces were not significantly influenced by the test conditions.

Molecular Dynamics Simulation on the Non-thermal Equilibrium State of Plasma Induced by Hypervelocity Impact

The plasma phase transition in monocrystalline aluminum under hypervelocity impact is simulated using the effective core pseudo-potential method in the molecular dynamics. Firstly, plasma character...

Preparation Method of Spherical and Monocrystalline Aluminum Powder

This paper presents a new production method for a spherical and monocrystalline aluminum powder. Aluminum powder of irregular particle shapes was mixed with silica nanoparticles and heated to a temperature above the melting point of aluminum. Due to its molten state, high surface tension, and poor wettability, the aluminum particles were transformed into liquid and spherical droplets separated by silica nanoparticles. The spherical shape was then retained when the aluminum particles solidified. The influence of the processing temperature on the particle shape, phase composition, and microstructure was investigated. Moreover, calorimetric, X-ray diffraction, grain size, and scanning electron microscopy with electron backscatter diffraction (SEM-EBSD) measurements of the particles’ microstructure are presented. It is proven that, by this means, a spherical and monocrystalline aluminum powder can be efficiently created directly from an air-atomized irregular powder. The observed phenomenon of particles becoming round is of great importance, especially when considering powder preparation for powder-based additive manufacturing processes.

Study on diamond wire wear, surface quality, and subsurface damage during multi-wire slicing of c-plane sapphire wafer

This paper aims on slicing of c-plane mono-crystalline aluminum oxide using reciprocating electroplated diamond wire in rocking mode sawing process. Effect of process parameters and wire characteristics on the surface morphology, surface roughness, and subsurface damage had been investigated. The machined wafer topography, wire wear, and subsurface damage are observed using scanning confocal microscopy (CCI), electron microscopy (SEM), and focused ion beam machining (FIB) respectively. Raman spectroscopy is used to observe the distribution of amorphous regions as a measure of dominant material removal mode. Results show that with reduced diamond size, higher wire speed, and uniform grit distribution, the wafer exhibits lower surface roughness and subsurface damage. The effect of wire speed is more pronounced than abrasive size and distribution density on surface quality. The wafers have shown lower roughness and greater evidence of ductile removal with increased wire wear. However, subsurface cracks are more and slightly deeper for wafers with increased wire wear. The wire characteristics in the form of abrasive size and distribution have dominant effect on subsurface damage. Wire wear analysis has shown that the pulled out diamond abrasive from the nickel bonding layer is the main reason for wire wear. Higher wire speed, lower ingot feed rate, and lower diamond grits size are suggested for lower subsurface damage.

Molecular dynamics simulation for orientation dependence of deformations in monocrystalline AlN during nanoindentation

Molecular dynamics simulations were performed for the nanoindentations using a virtual cylindrical indenter on monocrystalline aluminum nitride (AlN) with the indentation surface orientations of [0001], [101¯0], [1¯21¯0] and [1¯012¯], respectively, to investigate the orientation dependence of the material. Vashishta potential was used to model the interactions between Al-Al, N-N, and Al-N atoms in the specimens. Simulation results indicated that the deformation mechanism varies with surface orientations at the initial inelastic stage. In the specimens with the surface orientations of [0001] and [101¯0] phase transformation plays a predominant part, in the case of [1¯21¯0] dislocation slip dominates the inelastic deformation, whereas in the case of [1¯012¯] both phase transformation and dislocation slip act a leading role. However, the phase transformation and dislocation slip occur in all the samples during the further indentation. We found two paths of B4 to B1 phase transitions. Path I includes two steps: Al and N atoms move along the [0001] axis by an anti-parallel vertical motion, followed by horizontal relative movement of the two types of atoms. Path II is similar to Path I, but the sequence of relative movement of Al and N atoms is different. Path I occurs in the cases of [0001] and [1¯012¯] orientations, while Path II in the cases of the other two orientations.

Modeling and analysis of wire motion during rocking mode diamond wire sawing of mono-crystalline alumina oxide wafer

Wire sawing has been a primary method for slicing of silicon, silicon carbide, and sapphire for over two decades. Diamond wire sawing has offered faster and cleaner means as compared to slurry wire sawing. Diamond wire contact with workpiece along with other factors such as feed rate and wire diameter has resulted in the increase of normal cutting force. Contact length strongly affects abrasive numbers in the slicing area which further influences slicing performance in terms of material removal, surface topography, and sub-surface damage. This study developed a mathematical model to develop wire web and to evaluate contact length during rocking mode diamond wire sawing process. Effect of rocking mode along with rocking angle on wire web and further on contact length between wire and workpiece is studied with matlab simulations and results are compared with experiments. Results demonstrated that rocking mode reduces the contact length to almost half and decreases the equivalent chip thickness to improve the surface roughness. However, there is minimal effect of rocking angle on contact length. Saw marks model has been verified with experiments on sapphire or mono-crystalline alumina oxide wafer. It is observed that saw marks obtained from simulation is in agreement with experimental results. The results can extend the further investigation on rocking mode diamond wire sawing for slicing of brittle materials for better sub-surface damage.

Intrinsic spin-Hall effect in aluminum

With the help of an artificially created spin imbalance that induces a charge imbalance unrelated to the Lorentz force, the relativistic spin-Hall effect (SHE) in 3D superpure monocrystalline aluminum was first studied. The nonlinear behavior of SHE in a magnetic field is revealed as a direct proof of the manifestation of the intrinsic (band) mechanism of the spin polarization of electrons in a nonmagnetic metal under spin-orbit interaction conditions with a minimized external impurity spin-polarization factor. Based on the data obtained, the spin-orbit coupling coefficient in aluminum is estimated.

Understanding the bonding mechanisms of directly sputtered copper thin film on an alumina substrate

The evaluation of bonding mechanisms between magnetron sputtered copper (Cu) thin films and a ceramic substrate was carried out using polycrystalline and monocrystalline alumina (Al2O3) substrates with different surface roughness. Three different bonding mechanisms, viz., surface adsorption, mechanical interlocking, and diffusion bonding have been assessed. A tensile test was applied to measure the interfacial adhesion strength between the Cu films and the Al2O3 substrate. The contribution to the interfacial adhesion from each of the bonding mechanisms was elucidated based on the adhesion strength. Without special surface pre-treatment, physical adsorption is the main factor for the film adhesion, contributing ~5.9MPa adhesion strength between this directly sputtered Cu film and a flat Al2O3 substrate. For substrates with surface roughness around 350–500nm, mechanical interlocking enhances the film adhesion up to 18.6% compared to the flat surface. Post-deposition annealing at 300°C has increased adhesion strength by 18%, and diffusion bonding may be operative.

Surface charge measurements on different dielectrics in diffuse and filamentary barrier discharges

Previously, we reported on the measurement of surface charges during the operation of barrier discharges (BDs) using the electro-optic Pockels effect of a bismuth silicon oxide (BSO) crystal. With the present work, the next milestone is achieved by making this powerful method accessible to various dielectrics which are typically used in BD configurations. The dynamics and spatial distribution of positive and negative surface charges were determined on optically transparent borosilicate glass, mono-crystalline alumina and magnesia, respectively, covering the BSO crystal. By variation of the nitrogen admixture to helium and the pressure between and , both the diffuse glow-like BD and the self-stabilized discharge filaments were operated inside of a gas gap of . The characteristics of the discharge and, especially, the influence of the different dielectrics on its development were studied by surface charge diagnostics, electrical measurements and ICCD camera imaging. Regarding the glow-like BD, the breakdown voltage changes significantly by variation of the cathodic dielectric, due to the different effective secondary electron emission (SEE) coefficients. These material-specific SEE yields were estimated using Townsend’s criterion in combination with analytical calculations of the effective ionization coefficient in helium with air impurities. Moreover, the importance of the surface charge memory effect for the self-stabilization of discharge filaments was quantified by the recalculated spatio-temporal behavior of the gap voltage.

Comparison of the static frictional resistance and surface topography of ceramic orthodontic brackets: an in vitro study

Abstract Objectives The aim of this study was to investigate the frictional resistance (FR) and surface topography of newly available polycrystalline alumina (PCA) ceramic brackets characterised by a yttria-stabilised zirconia (YSZ) coating of the slots, compared with monocrystalline alumina (MCA) ceramic brackets and stainless steel (SS) brackets. Methods The FR was investigated using a universal testing machine. The test groups included PCA (Clarity Advanced, 3M Unitek, CA, USA) and MCA (Inspire Ice, Ormco, CA, USA). The control group included SS brackets. A sliding test was performed for each bracket type with three bracket-wire angulations (0°, 5°, 10°). A total of 225 sliding tests were performed in a dry environment, and 225 tests were performed in a wet environment of artificial saliva. A scanning electron microscope was used for qualitative assessments. The surface topography of the bracket slots was quantitatively assessed using an optical profilometer. Results In the dry environment, the overall FR values were significantly lower for PCA and SS brackets compared with MCA brackets (p &lt; 0.001), but no significant difference was found between PCA and SS brackets. In the wet environment, there were no significant differences between the bracket groups and their overall FR values. There was a significant correlation between the overall FR and the bracket-wire angulation values (p &lt; 0.001). The bracket slot surface topography revealed that the PCA bracket slots had the highest roughness values, followed by SS and MCA brackets (p &lt; 0.001). There was no significant correlation between the roughness values of the bracket slots and the FR in a passive configuration for all bracket types. Conclusion A yttria-stabilised zirconium coating of the PCA ceramic bracket slots might be a positive approach to apply for the reduction of FR.

Mono or polycrystalline alumina-modified hybrid ceramics

ObjectivesThis study evaluated the effect of addition of alumina particles (polycrystalline or monocrystalline), with or without silica coating, on the optical and mechanical properties of a porcelain. MethodsGroups tested were: control (C), polycrystalline alumina (PA), polycrystalline alumina-silica (PAS), monocrystalline alumina (MA), monocrystalline alumina-silica (MAS). Polycrystalline alumina powder was synthesized using a polymeric precursor method; a commercially available monocrystalline alumina powder (sapphire) was acquired. Silica coating was obtained by immersing alumina powders in a tetraethylorthosilicate solution, followed by heat-treatment. Electrostatic stable suspension method was used to ensure homogenous dispersion of the alumina particles within the porcelain powder. The ceramic specimens were obtained by heat-pressing. Microstructure, translucency parameter, contrast ratio, opalescence index, porosity, biaxial flexural strength, roughness, and elastic constants were characterized. ResultsA better interaction between glass matrix and silica coated crystalline particles is suggested in some analyses, yet further investigation is needed to confirm it. The materials did not present significant differences in biaxial flexural strength, due to the presence of higher porosity in the groups with alumina addition. Elastic modulus was higher for MA and MAS groups. Also, these were the groups with optical qualities and roughness closer to control. The PA and PAS groups were considerably more opaque as well as rougher. SignificancePorcelains with addition of monocrystalline particles presented superior esthetic qualities compared to those with polycrystalline particles. In order to eliminate the porosity in the ceramic materials investigated herein, processing parameters need to be optimized as well as different glass frites should be tested.

In vitro evaluation of frictional forces of two ceramic orthodontic brackets versus a stainless steel bracket in combination with two types of archwires.

Purpose:The aim of this study was to compare frictional forces between monocrystalline alumina (MA), polycrystalline alumina (PA), and stainless steel (SS) brackets with two SS wires: Rectangular and round.Materials and Methods:In this in vitro study, 60 0.022 brackets [20 PA (0° torque, Forestadent, Germany) and 20 MA (0° torque, Ormco, California, USA)] brackets plus 20 SS brackets (0° torque, Foretadent, Germany) and 60 SS archwires (30 rectangular 0.019 ×0.025 archwires and 30 round 0.018 archwires, Ortho Technology, USA) were used in subgroups of 10 from the combination of all brackets and all archwires. A universal testing machine (Instron, Model STM 250, Germany) was used to investigate the static frictional resistance. The angulation between the bracket and wire was 0°, and the wires were pulled through the slots at a crosshead speed of 10 mm/min. Two-way and one-way analyses of variance (ANOVA) and Tukey tests were used to analyze the data.Results:Mean (SD) static frictional force for each group was as follows: MA + round: 3.47 (0.38); MA + rectangular: 4.05 (0.47); PA + round: 4.14 (0.37); PA + rectangular: 4.45 (0.65); SS + round: 3.28 (0.22); and SS + rectangular: 4.22 (0.61). Significant effects of bracket types (P = 0.001) and archwire types (P = 0.000) on the friction force were detected using ANOVA. Tukey test indicated significant differences between PA brackets with both SS and MA brackets (P < 0.05), but not between SS and MA brackets. The two archwires as well had significantly different effects (Tukey P = 0.000).Conclusions:Based on the present in-vitro study, the PA brackets might create higher frictional forces compared to both SS and MA brackets. The rectangular 0.019 ×0.025 archwire might create greater forces than round 0.018 archwire.