Vickers Hardness Research Articles

Analysis for Fabrication Conditions of Scalpel with Ti<sub>47</sub>Cu<sub>38</sub>Zr<sub>7.5</sub>Fe<sub>2.5</sub>Sn<sub>2</sub>Si<sub>1</sub>Ag<sub>2</sub> Bulk Metallic Glass Alloys

This study investigated the manufacturing conditions and properties of Ti<sub>47</sub>Cu<sub>38</sub>Zr<sub>7.5</sub>Fe<sub>2.5</sub>Sn<sub>2</sub>Si<sub>1</sub>Ag<sub>2</sub> amorphous bulk metallic glass (BMG) to examine its applicability for scalpels for medical use. Ti-base BMG alloys have excellent mechanical properties and biocompatibility, making them a suitable scalpel material. In this study, a vacuum suction casting method was used to manufacture a BMG alloy scalpel. After examining various manufacturing conditions, to successfully suppress the occurrence of pores and manufacture a BMG with excellent shape the optimal conditions were determined to be 236 A of arc current, 20 s of melting time, 2 s of suction time, 10°C of coolant temperature, and -0.1 MPa of suction pressure. XRD analysis confirmed that the Ti-base BMG had a completely amorphous structure. Vickers hardness measurements showed that the Ti<sub>47</sub>Cu<sub>38</sub>Zr<sub>7.5</sub>Fe<sub>2.5</sub>Sn<sub>2</sub>Si<sub>1</sub>Ag<sub>2</sub> amorphous bulk metal material (BMG) scalpel had a hardness of 781 Hv, and was superior to a commercial stainless steel (SUS) scalpel in terms of durability. In the pork skin cutting tests, the Ti-base BMG scalpel maintained its edge without chipping, while the SUS scalpel showed chipping and an uneven cutting surface. These research results suggest that Ti-based BMG can provide better high-strength performance and durability than commercial SUS scalpels, and demonstrate its potential for application as a medical tool. However, bulk amorphous alloys with excellent glass formability (GFA) still require a detailed study of the optimal fabrication conditions to avoid pores and defects.

Investigating the Tribological Performance and Wear Mechanisms of Stainless Steel 316L in Cold Metal Transfer-Based Wire Arc Additive Manufacturing Under Varied Loads and Thermal Inputs

Abstract In recent years, cold metal transfer (CMT)-based wire arc additive manufacturing (WAAM) has gained significant attention in the manufacturing sector, particularly for its ability to produce components with low thermal input and high deposition rates. This study investigated the tribological behaviour of SS316L walls fabricated using CMT-based WAAM, employing a ball-on-plate linear reciprocating test with tungsten carbide (WC) counter body under varying thermal inputs and applied loads (15 N, 20 N, and 25 N). The tests were conducted for 10 minutes at a frequency of 15 Hz and a stroke length of 2 mm. Results indicate that the coefficient of friction (COF) increased slightly with applied loads, yielding an average COF of 0.22 across all loads. Wear rate analysis revealed that both increased applied load and heat input led to a higher wear rate, with the maximum wear rate (3.39 × 10−3 mm3/m) occurring at high heat input and 25 N, while the minimum wear rate (1.2 × 10−3 mm3/m) was observed at low heat input and 15 N. Vickers microhardness results demonstrated an inverse relationship between hardness and heat input, with hardness increasing by 11% as heat input decreased from high to low. FESEM analysis of wear tracks showed significant craters, abrasive grooves, delamination, surface cracks, and particle adhesion, identifying an abrasive-dominant wear mechanism with surface fatigue, partial adhesion, and oxidative wear. Wear debris analysis showed sharper angular particles and larger irregularly shaped flakes. X-ray diffraction (XRD) spectra confirmed δ-ferrite and γ-austenite phases pre- and post-wear, with post-wear analysis showing an α′-martensite peak, indicating phase transformation during wear.

Effects of mixing of europium oxide in resin composites on the fluorescence characteristics and mechanical properties

ObjectiveThe objective of this study is to disperse europium oxide (Eu2O3) in a resin composite (RC) using a planetary centrifugal mixer and assess its effects on photoluminescence and mechanical properties.Materials and methodsA commercially available RC was mixed with Eu2O3 at various concentrations using a planetary centrifugal mixer. The fabricated samples were evaluated using scanning electron microscopy and a spectrofluorometer to assess their crystal structures, particle sizes, and photoluminescence properties. Vickers microhardness measurements were performed, along with a three-point bending test. Statistical analyses were performed to assess the mechanical properties.ResultsThe intensity of red fluorescence increased with the increase of europium oxide concentration. The fluorescence spectra at 613 and 620 nm exhibited higher intensities under excitation at 254 nm. Eu2O3 was dispersed in RC regardless of the Eu2O3 concentration, and no aggregation was observed. Regarding the mechanical properties, there were no significant differences in the flexural strength or modulus, and the Vickers hardness gradually increased with increasing Eu2O3 concentration.ConclusionTo mix Eu2O3 with RC, visible fluorescence emission was observed even with increasing the Eu2O3 concentration, and the mechanical properties of RC were unaffected. Based on our study, a 15 wt% concentration of Eu₂O₃ is the appropriate concentration, as it achieves strong fluorescence emission without compromising the mechanical properties or color tone of the RC.

Technological dental sealants: in vitro evaluation of material properties and antibiofilm potential

BackgroundDue to the launch of new self-etching and self-adhesive sealing materials combined with the release of bioactive ions in the dental market, this in vitro study aimed to compare physical values of surface roughness (RS), vickers microhardness (VM), compositional energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), microbiological tests (inhibition halo-HI and surface microbial adhesion-MAS) and mechanical microshear bond strength (MBS).MethodsThe following groups were analyzed: Beautisealant® self-etching sealant (Shofu)(G1), FluroShield® conventional sealant (Dentsply)(G2- Control Group), Flow Constic® self-adhesive/self-etching resin (DMG)(G3) and Beautifil Flow Plus F03® conventional resin (Shofu)(G4). For the physical and compositional tests, specimens were molded and submitted to finishing/polishing in a metallographic polisher. RS and VM were measured through 5 readings. For the HI test, specimens were exposed to S. mutans for 24 h in brain–heart infusion (BHI) agar under microaerophilic conditions, with the diameter of the HI (mm) measured by digital caliper. For the MAS test, a bacterial biofilm of S. mutans was induced for five days in BHI broth + 5% sucrose and measurement of CFU/ml (log10 from serial dilutions). For the MBS test, specimens were made in bovine enamel with the addition of the experimental group FluroShield® (Dentsply) + Single Bond Universal® adhesive (3 M)(G5) and measured in a universal testing machine. Data were submitted to ANOVA and Tukey's post hoc tests (p < 0.05) using the SPSS software.ResultsDifferent compositions proven in the EDS test were not determinants of the promotion of different RS: G1 = 0,19 (± 0,07), G2 = 0,15 (± 0,053), G3 = 0,13 (± 0,046), G4 = 0,14 (± 0,056); HI: G1 = 17,7 (± 1,36), G2 = 18,7 (± 3,47), G3 = 18,9 (± 4,87), G4 = 17,9 (± 3,61) and MAS: G1 = 5,22 (± 0,12), G2 = 5,15 (± 0,15), G3 = 5,12 (± 0,20), G4 = 5,06 (± 0,24). However, statistically influenced the values of VM: G1 = 16,71 (± 1,93), G2 = 16,28 (± 4,91), G3 = 26,11 (± 3,46), G4 = 37.9 (± 4.87), promoted lesser bacterial adhesion (G4 = 5.06 ± 0.24), and demonstrated fluoride ion only in the G4. Higher MBS was found in the conventional materials G5 = 8.38 (± 2.05) and G2 = 6.28 (± 1.35).ConclusionsBioactive materials and self-adhesive/self-etching for sealing pits and fissures did not demonstrate superior mechanical and antimicrobial properties performance compared to conventional techniques.

The Effect of Final Cooling Temperature on Nano Cu Precipitation in a Cu-Bearing High-Strength Low-Alloy Steel

Nano Cu precipitation plays a crucial role in significantly improving the performance of the Cu-bearing high-strength low-alloy steel. The final cooling temperature effects the transformation products of austenite during the continuous cooling process, as well as the nano precipitations of steel. This study investigated the microstructure and hardness at different final cooling temperatures (750, 700, 650, 600, 550, and 500 °C) using the MMS-300 thermal simulation experimental machine (Northeastern University, Shenyang, China) and Vickers hardness tester. The changes in microstructure and the phase transformation law of austenite were determined during continuous cooling and then analyzed. The precipitation reaction of nano Cu precipitation during continuous cooling was studied using transmission electron microscopy (TEM), revealing the precipitation state under different final cooling temperature conditions. The results showed that the precipitations led to an increase and then a decrease in the microhardness, and the microhardness reaches its peak at 550 °C. The precipitations changed from spherical to elliptical, and the size gradually increased when the final cooling temperature increased.

Tantalum-lanthanum mixing effect on structural and mechanical properties of aluminate glasses

Aluminate glasses are known for their superior mechanical and optical properties. Here, we investigated the tantalum (Ta)-lanthanum (La) mixing effect on structural and mechanical properties of these glasses. Using the aerodynamic levitation and laser melting technique, we prepared a series of aluminate glasses with the molar composition 54Al2O3·(46-x)La2O3·xTa2O5, where x = 0.0, 9.2, 18.4, 23.0, 32.2, 36.8, and 46.0. The structural, thermal, and mechanical analyses revealed that substituting Ta for La strongly impacted the local Al environment in the glasses, thereby affecting their glass transition temperature and mechanical properties. The Vickers microhardness (HV) varied non-monotonically with the molar ratio R (defined as Ta/(Ta+La) = x/46), reaching a maximum HV value of 8.59 GPa at R = 0.8. This trend was explained in terms of both the average bond energy and the bond number density. Moreover, the crack initiation resistance of the studied glasses increased as R rose. This work aids in the design of oxide glasses with high crack resistance and hardness.

Dual-layered carbonated hydroxyapatite/polypyrrole: A novel strategy for bone fracture repair implants

This study presents the fabrication of a carbonate-doped hydroxyapatite/polypyrrole thin film on 304 stainless steel (CHA/PPY/304 SS) using a cyclic voltammetry electrochemical method to enhance bone fracture repair. The in-situ substitution mechanism was evaluated through estimated reaction energy, and the impact of surface modification on structural properties was examined using the Rietveld refinement method. Following the electrodeposition of CHA on PPY-coated 304 SS, a distinctive flower-like structure emerged, with average cluster and pore sizes of 3 ± 1 μm and 130 ± 10 nm, respectively. Rietveld refinement analysis revealed A-type carbonate substitution, indicated by an increase in the a parameter and a reduction in the c parameter compared to the standard. Subsequent deposition of the bilayer coating on 304 SS significantly improved adhesion strength to 10.7 ± 0.2 MPa, along with increased hydrophilicity and Vickers hardness. Notably, enhanced bioactivity was observed, evidenced by thickened nanoflake-like structures and the formation of island-like apatite deposits after immersion in simulated body fluid (SBF) for 7 days. This bilayer coating shows promise for surface modification of metallic implants and tissue engineering scaffolds.

Effects of Al addition on Vickers hardness increase by thermal aging of Fe–Cr–Al alloys — Evaluation by systematic experiments, machine learning modeling, and first-principles calculations

Effects of Al addition on Vickers hardness increase by thermal aging of Fe–Cr–Al alloys — Evaluation by systematic experiments, machine learning modeling, and first-principles calculations

THE DIFFERENCES IN THE EFFECTS OF PROPOLIS, SODIUM HYPOCHLORITE, AND EDTA AS AN IRRIGANT SOLUTIONS ON THE MICROHARDNESS OF ROOT CANAL DENTIN: IN-VITRO STUDY

Sodium hypochlorite (NaOCl) and EDTA are commonly used irrigants due to their antimicrobial properties and ability to dissolve both organic and inorganic components. However, the use of these chemicals at varying concentrations and durations can affect the physical and chemical properties of root canal dentin. Recently, propolis has gained attention as an alternative irrigant because it shows similar potential to conventional irrigants. The aim of this study is to examine whether there are differences in the effects of propolis extract, NaOCl, and EDTA on the microhardness of root canal dentin. This study utilized 24 single-rooted premolar teeth. The crowns were removed, and the roots were longitudinally split into two halves. Samples were randomly divided into six groups (n=8), each immersed in 8% propolis, 20% propolis, 30% propolis, 2.5% NaOCl, 5% NaOCl, and 17% EDTA. The microhardness of root canal dentin was measured using a Vickers Hardness Tester before and after immersion. Data were analyzed using One Way ANOVA. The results showed that 8% propolis had the smallest decrease in microhardness among all treatment groups, with an average difference in initial and final microhardness of 3.68, followed by 20% propolis, 2.5% NaOCl, 5% NaOCl, 30% propolis, and 17% EDTA. The conclusion of this study is that there are significant differences (p&lt;0.05) among the treatment groups regarding the microhardness of root canal dentin. Extracts of 8% and 20% propolis can be used as alternative irrigants.

Investigation of the antibacterial activity, cytotoxicity, and effects on enamel and composite resin of mouthwash formulations prepared with three different Boron compounds.

This study investigated the use of oral rinse solutions formulated with boron-containing compounds, known for their antibacterial activity, as an alternative to chlorhexidine (CHX). Boron nitride (BN), boric acid (BA) and sodium borate (SB) were used in the study. BN was used in nanosuspension (BN-NS) due to its low solubility in water. BA and SB were also prepared and used in solution form (BA-S, SB-S). Antibacterial activity against cariogenic bacteria was evaluated using agar well diffusion and microdilution techniques, and antibiofilm activity was evaluated using the crystal violet method. Cytotoxicity in human gingival cell lines (HGF-1) was evaluated using MTT and LDH assays. Surface hardness was measured with Vicker's Microhardness tester and surface roughness was measured with a profilometer. CHX was used as the control group. BN-NS, BA-S, and SB-S showed antibacterial and antibiofilm activity against all cariogenic bacteria. BN-NS and SB-S demonstrated much lower cytotoxicity compared to CHX, while BA-S exhibited similar cytotoxicity. SB-S caused an increase in enamel surface hardness (p = 0.017), whereas no significant changes were observed in surface roughness or hardness in the other groups (p > 0.05). BN-NS and SB-S showed antibacterial effects and antibiofilm activity on all tested cariogenic bacteria. BN-NS and SB-S showed lower cytotoxicity than CHX, and their effects on enamel and composite resin surfaces were similar to the control group. Further studies are needed to support the use of BN-NS and SB-S as alternatives to CHX. BN-NS and SB-S are promising alternatives to the antibacterial agent CHX, which is known to be cytotoxic.

In vitro evaluation of dye penetration and dentin microhardness after laser irradiation using photon-induced photoacoustic streaming and shock wave enhanced emission photoacoustic streaming tips compared to ultrasonic activation

The purpose of this study was to compare the penetration of methylene blue (MB) dye after laser irradiation using PIPS (photon-induced photoacoustic streaming) and SWEEPS (shockwave enhanced emission photoacoustic streaming) methods compared to Passive ultrasonic irrigation (PUI) and to study their effect on dentin microhardness. A total of 44 single-rooted human teeth which were extracted for orthodontic or periodontal reasons were used. The teeth were decapitated to standardize roots to 12 mm in length. Canals were prepared up to size #30.6% and divided randomly into four groups (n = 11/group) according to the method of NaOCl activation: Group I: Er: YAG laser activation with PIPS tip; Group II: Er: YAG laser activation with SWEEPS tip; Group III: passive ultrasonic irrigation (PUI) and Group IV: conventional needle irrigation (CI). MB dye was injected then teeth were sectioned horizontally into coronal, middle and apical sections. Penetration depth/area percentages were measured using stereomicroscopy. Coronal specimens were further subjected to Vickers microhardness testing. Data were statistically analyzed. SWEEPS and PIPS activation methods provided higher dye penetration depth and area percentages compared to PUI with no statistically significant differences between all test groups. However, all test groups showed statistically significant differences with the CI (control) group. SWEEPS activation provided higher microhardness values with statistically significant differences with the other groups. Laser irrigant activation using PIPS and SWEEPS is comparable to PUI concerning MB dye penetration. However, SWEEPS preserved dentin microhardness significantly which can be beneficial for the long-term prognosis of root canal treated teeth.

The Microstructure, Hardness and Density Investigation of Mg Composites Reinforced with Nanoclay

Magnesium (Mg) stands out as a prevalent material in engineering, finding essential utility as a biomaterial due to its unique combination of low density, stiffness, high damping capacity, superior bending resistance, and impressive specific strength. Despite its high reactivity and somewhat inadequate mechanical properties for rigorous engineering applications, the incorporation of reinforcing nanoparticles has shown significant potential in enhancing the performance of magnesium-based composites. This study investigates the microstructure evaluation, hardness, and density of magnesium composites reinforced with nanoclay using a powder metallurgy approach. Nanoclay was preferred as a reinforcement element at weight percentages of 1%, 3%, 5%, and 7%. The densities of the composites were measured using the Archimedean principle, revealing that the addition of nanoclay generally increases the density of the composites due to the higher density of nanoclay compared to pure magnesium. However, the composite with 5% nanoclay exhibited a lower density than the one with 3% nanoclay, likely due to agglomerations leading to increased internal voids. Surface preparation for Vickers hardness testing involved sanding with 600, 1000, and 2000 mesh sanders, followed by polishing with 6μ and 3μ diamond suspensions. Hardness measurements, conducted using an AOB Vickers microhardness tester, indicated that the highest hardness value was observed in the composite with a 7% weight percentage of nanoclay, demonstrating that nanoclay addition enhances hardness. However, the composite with 3% nanoclay showed lower hardness compared to other reinforced composites. Optical images of the structures revealed metallographic spots indicative of contamination. These findings contribute to the understanding of the structural and mechanical behavior of nanoclay-reinforced magnesium composites, highlighting the potential for optimizing such materials for various applications in automotive, aerospace, and medical fields.

The antibiofilm effect and mechanism of silver nanowire-modified glass ionomer cement against multi-species oral biofilm

BackgroundTo investigate the antibiofilm effect and mechanism of the silver nanowire (AgNW)-modified glass ionomer cement (GIC) against multi-species oral biofilm, and to examine the mechanical and biochemical properties of this novel GIC material.MethodsConventional GIC was incorporated with different concentrations of AgNW and silver nanoparticles (AgNP). Multi-species biofilms of Streptococcus mutans, Streptococcus sobrinus, Lactobacillus fermentum, and Lactobacillus rhamnosus were cultured for 72 h on GIC specimens. Scanning electron microscopy (SEM) was adopted to examine the accumulation of biofilm on GIC surfaces. A live/dead assay was performed to assess the viability of bacteria. Extracellular polysaccharides (EPS) were labelled with Alexa Fluor 647-labelled dextran conjugate and then observed by a confocal laser scanning microscope (CLSM). The D/L-Lactic Acid Assay Kit was used to evaluate the lactic acid production of the multi-species biofilms. Compressive strength, surface roughness, hardness, and wettability were measured by a universal testing machine, an atomic force microscope (AFM), a Vickers microhardness tester, and a contact angle meter, respectively. Colour stability and fluoride release of GIC specimens were assessed by VITA Easyshade® V and ion chromatography. Cell counting kit-8 (CCK-8) was used to study cytotoxicity.ResultsSEM images showed that fewer biofilms were accumulated on the AgNW-GIC surfaces. The live/dead assay showed that the ratio of live bacteria was significantly lower in AgNW-GIC groups than in conventional GIC (5.8% vs. 100%, p < 0.0001). The EPS production was significantly less in AgNW-GIC groups compared to conventional GIC (p < 0.0001). There is no difference between groups regarding lactic acid production and fluoride release. The mechanical strength including compressive strength, surface roughness, hardness, and wettability were comparable between groups. The colour change between AgNW-GIC and conventional GIC was much milder than that between AgNP-GIC and conventional GIC. The results of cytotoxicity showed no significant differences in cell viability between groups.ConclusionsThis study demonstrated that AgNW-GIC had an excellent antibiofilm effect against multi-species oral biofilm, comparable mechanical and biochemical properties, and did not significantly affect the colour stability of GIC. The antibiofilm mechanism of AgNW-GIC may be related to inhibiting the viability and EPS production of bacteria.

In Situ Synthesis of MoSi2-SiC Composites by Two-Step Spark Plasma Sintering

The effect of different SiC doping content on the properties of MoSi2-based composites was analyzed in this study. The MoSi2-SiC composites were fabricated in situ by the SPS technique, utilizing self-synthesized carbon-containing Mo powder and Si powder as raw materials. A two-step sintering process was employed to ensure the formation of a uniform and dense composite structure. The microstructures and mechanical properties of these composites with various compositions were characterized. The results show that the composites were primarily composed of MoSi2, SiC, and a minor proportion of MoSiC phase. The introduction of SiC as a second phase was found to considerably enhance the mechanical properties of the MoSi2 matrix material. In particular, the MoSi2-26mol.%SiC sample exhibited Vickers hardness, fracture toughness, and flexural strength values of 16.1 GPa, 6.7 MPa·m1/2, and 496 MPa, respectively, corresponding to increases of 33%, 24%, and 28% compared to the pure MoSi2 material.

Mechanical and degradation behavior of Mg-1%Sn-x%HAp composite for biomedical application

Metal implants are preferred for orthopedics due to their strength and durability. A biodegradable metal with a density similar to bone, magnesium (Mg) is being considered for medical implants. This study examines the mechanical and corrosive properties of Mg-1%Sn-x%HAp composites with weight percentages of 0, 2, 5, and 7. Mechanical alloying is used to fabricate the composites. Adding hydroxyapatite (HAp) improves corrosion resistance and biocompatibility characteristics. SEM, XRD, and electrochemical tests were used for characterization. The results showed that adding HAp improved composite mechanical properties and corrosion resistance. SEM and EDS confirmed that Sn and HAp were uniformly distributed in Mg. Additionally, the XRD found α-Mg, Mg2Sn, and CaSn3 phases are present in the composite. Density, hardness, compressive and polarization test were performed to analyze the mechanical and chemical properties of the composite pallets. The Mg-1%Sn-2%HAp composites have a density of 1.744 g/cm³, close to human cortical bone. Hydroxyapatite (HAp) increased Vickers hardness by 26% in the Mg-1%Sn-7%HAp composite compared to the alloy. The Mg-1%Sn-7%HAp composite has 121.14 MPa ultimate compressive strength due to greater HAp content. This enhancement increased brittleness and decreased compressive strain. Electrochemical corrosion studies showed that the Mg-1%Sn-2%HAp composite had the lowest corrosion rate (0.28568 mm/year) and current density (12.502 µA/cm²). Due to a protective apatite layer and Sn-based oxides, the composite exhibits good corrosion resistance. The Mg-1%Sn-2%HAp composite showed good mechanical properties and corrosion resistance as a biodegradable orthopedic implant material.

Role of dysprosium substitution on microscopy architecture, structural stability, and crack propagation mechanism in Bi-2212 engineering ceramics

Abstract This study achieves a strong link between microscopy architecture and fundamental characteristics including electrical conductivity, superconducting, and key mechanical design properties of Bi2.1-xDyxSr2.0Ca1.1Cu2.0Oy (Bi-2212) ceramic structures with different dysprosium molar ratio ranges of 0.00 ≤ x ≤ 0.10. The Dy/Bi substituted Bi-2212 ceramics are characterized by scanning electron microscopy (SEM), electrical resistivity (ρ-T), Electron Dispersive x-ray (EDX) investigations, and microindentation Vickers hardness (Hv) tests. Powder x-ray diffraction (XRD) experimental inspection is also studied to support SEM and Hv results. All experimental findings show significant improvement with an increase in the Dy impurity molar ratio to x = 0.01. On this basis, the Bi2.09Dy0.01Sr2.0Ca1.1Cu2.0Oy ceramic structure exhibits the lowest resistivity of 8.95 mΩ.cm at 300 K and transition width of 4.75 K, and the highest T c o n s e t of 85.00 K and T c o f f s e t of 80.25 K. Additionally, XRD examinations show that optimum Dy ion substitution in the Bi-2212 system stabilizes the high superconducting phase by improving crystallinity, crystallite size, grain orientation distributions, texturing, and interlayer interactions. In contrast, excessive substitution severely deteriorates crystallographic properties. Further, SEM images reveal that the presence of optimum Dy impurity enhances the crystallinity, couplings between the adjacent layers, homogeneous surface appearance, and microstructure. Moreover, the key mechanical design features and stability of the durable tetragonal phase improve significantly for x = 0.01. As a result, the material exhibits superior mechanical properties, including a microhardness of 0.5556 GPa, fracture toughness of 0.5390 MPa.m1/2, elastic modulus of 45.5389 GPa, shear modulus of 18.2156 GPa, yield strength of 0.1852 GPa, and resilience of 0.3766 MPa under a 0.295 N load.

The impact of bleaching using 15% carbamide peroxide on surface properties of CAD-CAM composite structures

This study aims to evaluate the effects of the home bleaching method on the surface microhardness and surface roughness of both polished and unpolished CAD-CAM resin composite materials. A polymer-infiltrated ceramic network (PICN) block, Enamic (VE), along with four resin composite blocks (RCB) (Grandio [GN], Lava™ Ultimate [LV], BRILLIANT Crios [B], and Cerasmart [CS]), were prepared to dimensions of 14 mm × 12 mm × 2 mm and were categorized into unpolished and polished groups (n = 4). Microhardness measurements were conducted using a Vickers microhardness tester (300 gf load for 20 s) at various time points: before home bleaching, after home bleaching with 15% Opalescence for 8 h and for 56 h, 24 h after bleaching, and one month after bleaching. Surface topography was examined using a stylus contact profilometer (n = 4) and a scanning electron microscope (n = 3) at ×40 k magnification. Control specimens from each group were also measured. Data were analyzed using one-way ANOVA, Tukey’s post hoc test, two-way ANOVA and an independent t-test. The polished samples demonstrated a decrease in hardness after 8 h of bleaching, with the most significant reduction observed in VE, followed by GN, LV, CS, and BR. Significant differences were noted between all materials except for CS and LV. After 56 h, VE exhibited the greatest decrease in hardness, followed by GN, LV, BR, and CS, with significant differences between all materials except BR and CS. In the unpolished group, VE showed the highest reduction in hardness after 8 h of bleaching, followed by LV, GN, BR, and CS. After 56 h, the order was VE, LV, GN, CS, and BR, with significant differences observed between all materials except BR and CS. Similar trends in hardness reduction were observed at 24 h and 1 month post-bleaching. Additionally, hardness was significantly reduced after polishing for all materials. Overall, the reduction in hardness was significantly influenced by the type of material, the time, and the interaction between these factors (p < 0.05). Home bleaching using 15% carbamide peroxide significantly decreased microhardness. This effect was more pronounced in unpolished groups and with prolonged exposure. Further studies are recommended to determine the suitable concentration and duration of 15% carbamide peroxide application to ensure its use is safe for CAD-CAM materials.

Advancing Thermoelectrics in Lead‐Free Rhombohedral GeTe via Interfacial Engineering With MXene

AbstractLead‐containing GeTe‐based thermoelectric (TE) materials exhibit outstanding performance, but the toxicity of lead (Pb) limits their practical applications. Lead‐free GeTe‐based TE materials present a promising alternative for environmentally sustainable and scalable applications. Here, Bi doping is used to reduce the majority carrier concentration in GeTe, combined with uniform incorporation of nanoscale layered MXene via high‐energy ball milling. This approach significantly enhances the structural symmetry of GeTe, while MXene further reduces carrier concentration and improves carrier mobility. Consequently, the Ge0.93Bi0.07Te‐0.6 mass% MXene sample achieves an impressive average power factor of ≈28.40 µW m−1 K−2 across 303–603 K. Moreover, point defects, multilayer nanostructures, and grain boundaries reduce thermal conductivity to ≈1.04 W m−1 K−1 at 603 K. A maximum ZTmax of ≈2.1 at 603 K, an average ZTavg of ≈1.1, and a Vickers microhardness of ≈ 236.75 Hv are obtained. In particular, a high power density of ≈1.54 W cm−2 and a maximum conversion efficiency of ≈7.5% at a temperature difference of 300 K are achieved in a 7‐pair TE module. These outcomes represent the highest performance levels for lead‐free GeTe‐based materials. This work uncovers a straightforward method to enhance the structural symmetry of GeTe‐based compounds, providing insights for advancing lead‐free TE technologies.

Evaluation of the impact of acidic medications and fluoride-containing mouthwash on the enamel surface using quantitative light-induced fluorescence, microhardness, and scanning electron microscopy: an in vitro study

BackgroundDue to their acidic nature, certain medications can have deleterious effects on tooth enamel. Fluoride is a popular method for reversing these effects. Therefore, this study aimed to assess the impact of acidic medications, specifically anti-asthmatic drugs and vitamin C tablets, on enamel surfaces and to investigate the effects of fluoride following drug exposure.MethodsAn in vitro experimental study was conducted on ninety-six healthy human posterior teeth. Forty-eight samples were tested for surface demineralization via quantitative laser fluorescence (QLF), and the other forty-eight samples were tested for enamel microhardness via a Vickers hardness tester. The samples were divided into six groups: (i) Group DW_NF- samples immersed in distilled water with no fluoride exposure; (ii) Group DW_F- samples immersed in distilled water with intermittent fluoride exposure; (iii) Group VC_NF- samples treated with vitamin C only; (iv) Group VC_F- samples treated with vitamin C and fluoride mouthwash; (v) Group SB_NF- samples exposed to salbutamol inhaler with no fluoride exposure; (vi) Group SB_NF- samples exposed to salbutamol inhaler followed by fluoride exposure. For the evaluation of surface morphology by scanning electron microscopy (SEM), two random samples used for QLF from each group were taken. The Wilcoxon signed-rank test, Kruskal‒Wallis test, and post hoc test were applied as appropriate. The p value was set at 0.05.ResultsFollowing exposure to medication, significantly higher QLF values were observed in Group VC_F and Group SB_F than in Group DW-NF (control group) (p = 0.15 and 0.004, respectively). The difference in the QLF values was significantly greater in Group VC_NF than in the control group DW-NF, indicating greater demineralization with acidic medications (p = 0.034). Significant changes in surface microhardness were detected in Group VC_F compared with the control group (p = 0.024). Qualitative analysis of SEM images revealed erosion at the enamel surface in all groups except the control group, with the most prominent erosion in the vitamin C- and fluoride-treated groups (VC_F group).ConclusionThis study demonstrated the erosive potential of vitamin C tablets on enamel surfaces. Furthermore, the use of acidic fluoride mouthwash immediately after exposure to acidic medication exacerbates enamel demineralization.

Prediction of coating layer thickness and surface hardness in electric discharge coating process using RSM, ANN, and ANFIS with ANOVA optimization

Electric discharge coating (EDC) process is one of the unique and notable surface modification processes that enhance the surface properties of substrates. The coating layer thickness and surface hardness developed by the coating process are the predominant reason for substrate protection and performance enhancement. To enhance the coating efficiency and develop the desired output, optimization of input parameters and forecasting of output parameters was required. In this work, Mg alloy substrates are coated with Cu–Ni green compact electrodes by an EDC process. During the EDC process peak current ( I), pulse duration ( Ton), and compaction load for the electrode ( L) are major influencing parameters of coating layer thickness which are considered as input parameters. The coating layer thickness and surface hardness of the coating substrate were estimated by an optical microscope and Vickers hardness tester, respectively, and also considered as a response. The observed data were analyzed and optimized through analysis of variance (ANOVA) and response surface morphology (RSM) which provides a static relationship between the input parameter and response. Additionally, a prediction model was developed with a machine-learning approach. Two different tools namely artificial neural network (ANN) and, adaptive neuro-fuzzy inference system (ANFIS), were employed for accurate prediction of the model. From the ANN and ANFIS analysis regression coefficient (R) values were 0.97991 and 0.9912, respectively. The present study provides machine-learning capabilities and supports optimizing the input parameter to the target output in the EDC process.