Vickers Microhardness Values Research Articles

The Effect of Sintering Temperature on Vickers Microhardness and Flexural Strength of Translucent Multi-Layered Zirconia Dental Materials

This study evaluated the effects of the sintering temperature on Vickers microhardness and three-point flexural strength values of two multi-layered zirconia materials. Multi-layered zirconia systems with four distinct layers were selected: DD cube ONE ML (4Y-TZP) and DD cubeX2 ML (5Y-TZP). In total, 96 plate-shaped A2-shade specimens were obtained using individual layers of these two zirconia materials. The individual layers were then divided equally into batches with three different sintering temperatures (1300, 1450, and 1600 °C), and the Vickers microhardness was assessed. Another group of 72 bar-shaped specimens was prepared from the same materials. These were similarly divided into three different sintering temperatures, and the flexural strength was assessed. SEM was used to conduct fractographic analyses. The data were analyzed using SPSS 24.0 software with a p-value < 0.05. The microhardness and flexural strength of 4Y-TZP were higher than those of the 5Y-TZP at all the sintering temperatures. A significant difference was found in the microhardness and flexural strength values between groups sintered at different sintering temperatures (p < 0.05). The highest microhardness and flexural strength values were found at 1450 °C (p < 0.05). The microhardness values of different layers were not significantly different (p > 0.05). The sintering temperature and type of ceramic material significantly affected the microhardness and flexural strength. However, the layers did not significantly affect the microhardness.

Yttrium aluminum garnet-based filler resin composites used as clear aligner attachments.

The objective of this study was to develop a novel resin composite containing yttrium aluminum garnet (Y3Al5O12, YAG) nanoparticles for clear aligner attachments. After the silanization of YAG, their Fourier-transform infrared (FT-IR) and thermogravimetric (TGA) analyses were performed. By conducting flexural and compressive strength measurements, the optimal YAG concentration was selected for the subsequent experiments. Next, Vickers microhardness values, fluidities, attachment volumes, conversion degrees, and volumetric shrinkages of the resin were determined. The obtained FT-IR and TG results revealed that γ-methacryloxypropy ltrimethoxysilane coupling agent was successfully grafted onto the surface of YAG, which enabled their use as inorganic fillers. Furthermore, adding 9 wt% YAG in the resin can increase Vickers hardness and fluidity, reduce polymerization shrinkage, and enhance the restoration of the clear aligner attachment shape on the premise of guarantee proper flexural and compressive strength of the resin, which can help control tooth movement and increase orthodontic efficiency.

Microstructures and properties of as-cast AlCrFeMnV, AlCrFeTiV, and AlCrMnTiV multi-principal element alloys

This study reports on the as-cast microstructures of AlCrFeMnV, AlCrFeTiV, and AlCrMnTiV equimolar multi-principal element alloys. Thermodynamic modeling predicts that these alloys solidify as BCC solid solutions, with additional phases forming at lower temperatures. We present the measured densities, the elastic modulus values measured by nanoindentation, and the Vickers microhardness of the alloys. These properties are correlated to the underlying microstructures, as measured by x-ray diffraction, scanning electron microscopy, and atom-probe tomography. The densities of the alloys range from 5.53 to 6.42 ×103 kgm−3. The elastic modulus of AlCrFeMnV, AlCrFeTiV, and AlCrMnTiV are 211, 194, and 175 GPa, respectively, and their Vickers microhardness values are 3.9, 6.1, and 5.7 GPa, respectively. After arc-melting, AlCrFeMnV and AlCrFeTiV are BCC solid solutions while AlCrMnTiV has two phases: a BCC phase and a minor hexagonal C14 Laves phase that is enriched in V and Cr.

Effect of bioactive glass particles on mechanical and adhesion properties of resin cements.

The aim of this study is to evaluate the mechanical and adhesive properties of three different resin cements with bioactive glass (BAG) incorporated in two different ratios. BAG was added to different resin cements (3M Rely-X Ultimate, GC Link Ace, and GC Link Force) in different ratios (5% and 10% by weight). The three-point flexural strength, microhardness, and bond strength properties were evaluated. The fracture types of the groups were then analyzed using a stereo microscope. The data were analyzed using a multifactorial analysis of variance and Tukey's post-hoc tests (α < 0.05). The addition of BAG reduced the flexural strength of the resin cements (P < 0.05).The effect of BAG addition on the Vickers microhardness value was significantly different for each cement group (P < 0.05). In addition, with the exception of the GC link force group (10% BAG addition), the BAG addition decreased the bond strength of cements to dentin in all the groups (P = 0.171). The results of this study confirmed that different resin cements comprising different ratios of BAG exhibited different flexural strength, hardness, and bond-strength properties. Since the bond strength values increased with the addition of 10% BAG in the GC Link Force cement group, the effects of different BAG compositions could be worth investigating in future studies.

Beyazlatıcı Diş Macunlarının Kompozit Rezinlerin Mikrosertliğine ve Yüzey Pürüzlülüğüne Etkisi: Bir İn Vitro Çalışma

Objective: This study aimed to assess the effect of different types of whitening toothpastes on the microhardness and surface roughness of composite resins. Material and Methods: 120 discshaped samples each of Clearfil Majesty Esthetic and Gradia Direct Anterior composite resins were randomly assigned to 4 groups, based on the toothpaste used [three whitening toothpastes: Signal White Now (SWN), Colgate Optic White (COW), Ipana 3D White Luxe (IWL), and one non-whitening toothpaste: Sensodyne Promine (SP)]. The samples were brushed using an electrical toothbrush for 4 minutes. Before and after toothbrushing surface roughness (n=15) and Vickers microhardness (n=15) values were measured and the topography of the composite resins was observed using scanning electron microscopy. Data were analyzed using repeated measures analysis of variance and Bonferroni correction (p˂0.05). Results: The surface roughness was significantly affected by the toothpastes (p=0.013) and there was a significant interaction between toothpastes and composite resins (p˂0.001). The surface roughness of composite resins significantly increased after toothbrushing with all toothpastes. SWN and IWL showed significantly higher surface roughness values than SP (p=0.024 and p=0.028, respectively). There was a significant increase in the microhardness values for Gradia Direct Anterior after toothbrushing with SWN, IWL and SP (p=0.003, p˂0.001 and p=0.029, respectively). Conclusion: In this study, it was determined that all toothpastes increased the surface roughness values of Clearfil Majesty Esthetic and Gradia Direct Anterior, and all toothpastes (except COW) increased the microhardness values of Gradia Direct Anterior. Clinicians should notify patients of the abrasive capacity of all toothpastes, especially those that are whitening.

How the Duration and Mode of Photopolymerization Affect the Mechanical Properties of a Dental Composite Resin.

Composite materials are the most common materials in use in modern dentistry. Over the years, the methods of photopolymerization of composite materials have been improved with the use of various devices, such as quartz tungsten halogen lamps (QTHs), light-emitting diode units (LEDs), plasma-arc lamps and argon-ion lasers. This study aimed to compare the mechanical properties of a composite material, depending on the time and mode of photopolymerization. One hundred and forty rectangular specimens (25 × 2 × 2 mm) and forty-two disc-shaped samples (5 mm diameter and 2 mm thickness) were prepared from shade A2 Boston composite resin. Samples were cured using the following seven photopolymerization protocols: four fast-cure modes (full power for 3, 5, 10, and 20 s), two pulse-cure modes (5 and 10 shots of 1 s exposures at full power), and one step-cure mode (soft start with a progressive cycle lasting 9 s). Specimens were subjected to a flexural strength test, Vickers microhardness test, and FTIR spectroscopy test. A 2-factor ANOVA and post-hoc tests were carried out to assess the differences in the flexural strength parameter between the tested groups of samples before and after aging. A mixed-model ANOVA was carried out to assess the differences in the Vickers microhardness parameter between the tested groups of samples before and after aging. The lowest values of flexural strength (p < 0.001) and Vickers microhardness (p < 0.001) were obtained for the 3 s mode for the pre- and post-aging groups. The FTIR mapping tests showed a much more homogeneous chemical structure of the composite after 20 s of continuous irradiation, compared to the sample irradiated for 5 s in the continuous mode. The mode and cure time affects the mechanical properties of the composite resin. Appropriate selection of the cure mode and time ensures better mechanical properties of composite resin. This suggests that the survival of dental restorations within the oral cavity could be extended by using longer photopolymerization durations.

Shear strain induced recrystallization/recovery phenomena within rotary swaged Al/Cu composite conductors

The presented study aims to assess the effects of room temperature rotary swaging on structure, dynamic restoration processes in particular, within newly designed Al/Cu composite conductors. Swaging was processed from the original diameter of 50 mm (assembled billets) to the diameters of 20 mm, 15 mm, and 10 mm (final conductors). Cross-sectional samples of the swaged conductors were subjected to thorough structure analyses via electron microscopy, analyses of HV0.2 Vickers microhardness and specific electric resistivity were performed to supplement the study. Swaging to 15 mm primarily imparted structure recovery, while the final swaging to 10 mm introduced dynamic recrystallization within both the composite components (the fractions of high angle grain boundaries within Al and Cu were 78.7%, and 74.2%, respectively). The 10 mm composite Cu also featured increased fraction of Cube (Euler angles of φ 1 = 0°, ϕ = 0°, and φ 2 = 0°) ideal recrystallization texture orientation. As regards the specific electric resistivity, this parameter was influenced primarily by accumulated dislocations, grain size and arrangement (e.g. bimodal distribution), as well as possible presence of texture. The lowest specific electric resistivity of 20.589 Ωm·10 −9 was measured for the 15 mm conductor exhibiting dynamic restoration. The Cu component of this composite also featured the highest HV0.2 Vickers microhardness value. • Rotary swaging at room temperature successfully used to produce Al-Cu conductors. • Swaging to 15 mm diameter imparted dynamic recovery. • Swaging to 10 mm diameter introduced dynamic recrystallization. • Electric resistivity decreased within dynamically recovered structure.

Assessment of Micro-Hardness, Degree of Conversion, and Flexural Strength for Single-Shade Universal Resin Composites.

Single-shade universal resin composites (SsURC) are preferred in clinical practice to reduce time for shade selection and obtain good esthetic results. In this study, the static mechanical properties of seven new SsURCs were investigated, their spectral analyzes were performed and scanning electron microscopy (SEM) evaluations were presented. Charisma Diamond One/DO, Admira Fusion x-tra/AFX, Omnichroma/OC, OptiShade/OS, Essentia Universal/EU, Zenchroma/ZC, Vittra APS Unique/VU were used in a three-point bending test to determine flexural strength (FS) and elastic modulus (EM); Vickers micro-hardness (VHN) and hardness-ratio (HR) were performed with a micro-hardness tester from top/bottom after 24-h/15-days of storage in distilled water at 37 °C (±1 °C). The degree of conversion (DC) was assessed by using Fourier transform infrared spectroscopy (FTIR). The structure of the resin matrix and filler content were assessed by SEM. Data were analyzed using IBM SPSS V23 and the R program and the significance level was taken as p &lt; 0.05. The main effect of the tested SsURCs was found to be statistically significant on FS, EM, VHN, and DC values (p &lt; 0.001). Bis-GMA free SsURCs (AFX, DO, VU) showed better DC and HR except for OC. All seven tested SsURCs conform to the requirements of ISO standards for dental resin composites for all tested categories.

Effect of Thermal Cycling on the Flexural Strength and Hardness of New-Generation Denture Base Materials.

To evaluate the flexural strength and Vickers microhardness of different CAD-CAM denture base materials. Sixty rectangular specimens (64 × 10 × 3.3 ± 0.2mm) were fabricated from 3 different denture base materials (G-CAM, Graphene-reinforced polymethylmethacrylate, GC), Ivotion Base (Prepolymerized polymethylmethacrylate, IV), and Denturetec (3D-printed resin, DT) either by using additive (DT) or subtractive manufacturing (IV and GC). Specimens of each group were divided into 2 subgroups (thermal cycled or nonthermal cycled, n = 10/group). Nonthermal cycled specimens were stored in distilled water at 37°C for 24 hours and subjected to 3-point flexural strength test with a universal testing machine. Thermal cycled specimens were initially evaluated for Vickers microhardness and subjected to thermal cycling (10,000 cycles at 5-55°C). Vickers microhardness values were remeasured, and the specimens were subjected to 3-point flexural strength test. Data were analyzed by using 2-way analysis of variance and Bonferroni-corrected Tukey honestly significant difference tests (α = 0.05). Material type and condition significantly affected flexural strength (p ≤ 0.004), whereas their interaction was nonsignificant (p = 0.778). Overall flexural strength of the materials in decreasing order was GC, IV, and DT (p < 0.001), regardless of the condition. Material had a higher effect on flexural strength (ηp2 = 0.731) than thermal cycling (ηp2 = 0.142). The effect of the interaction between the material type and thermal cycling on Vickers microhardness was significant (p < 0.001). GC had the highest microhardness before and after thermal cycling (p < 0.001). IV had higher microhardness than DT before thermal cycling (p < 0.001). However, DT and IV showed similar microhardness after thermal cycling (p = 0.665). Thermal cycling decreased the microhardness of GC and IV (p ≤ 0.022), whereas its effect on DT's microhardness was nonsignificant (p = 0.538). Material type had the highest effect on microhardness (ηp2 = 0.864) followed by the interaction between the main factors (ηp2 = 0.258). Graphene-reinforced polymethylmethacrylate had the highest flexural strength and Vickers microhardness values, regardless of thermal cycling. Thermal cycling reduced the flexural strength of all resins. Thermal cycling reduced the microhardness of milled polymethylmethacrylate, but not that of 3D-printed resin.

Evolution of the Microstructure and Phase Composition of the Products Formed in the Reaction between Iridium and W2B.

In the present study, we perform a systematic examination of the products formed by mixing and heating of tungsten boride and iridium powders at different ratios in a broad temperature range using qualitative and quantitative X-ray analysis and time-of-flight neutron diffraction (TOF-ND), in combination with scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) performed at different accelerating voltages. The well-known and unknown ternary W-Ir-B phases were detected. The Vickers microhardness value for the new ternary W2Ir5B2 boride was measured. Based on these findings, the ternary W2Ir5B2 boride can be considered hard.

Microstructure and biocorrosion studies of spark plasma sintered yttria stabilized zirconia reinforced Ti6Al7Nb alloy in Hanks' solution

A study of spark plasma sintered Ti6Al7Nb alloy reinforced with yttria stabilized zirconia (YSZ) has been carried out to assess the biocorrosion response in Hank's solution. The results indicate that the microstructural changes resulting from YSZ addition to Ti6Al7Nb were considerably different from pure Ti6Al7Nb. All the Ti6Al7Nb + YSZ composites showed a higher Vickers microhardness value with Ti6Al7Nb + 10%YSZ exhibiting the most enhanced hardness value of 955.3 HV0.1. Furthermore, all Ti6Al7Nb + YSZ present higher corrosion resistance in Hank's solution than Ti6Al7Nb alloy except Ti6Al7Nb + 1YSZ which shows a significant drop in Ecorr and Icorr values. This could be due to grain refinement with less stable oxide film growth kinetics. The combination of mechanical property and corrosion resistance of the fabricated Ti6Al7Nb + YSZ alloy could make it a suitable material for dental implant in the nearest future.

Mechanical properties and corrosion resistance of two new titanium alloys for orthopaedics applications

Due to the compatibility problems of biomaterials currently used in biomedicine, the effect of Silicon addition to the innovative TiMoZr alloy has been investigated. The mechanical properties of these two alloys and their corrosion resistance in simulated body fluid were analyzed in order to recommend them for the manufacture of medical instruments. After the application of the corresponding techniques, the metallographic study shows only the two-phase structure of the sample with silicon, which has lower modulus of elasticity values and higher Vickers microhardness values. The sample without silicon offers a higher resistance to corrosion, although these values between the two samples are very close.

Microstructural Evolution of Inconel 718 during Aging and Its Correlation with Electric Conductivity Measurements

Abstract The microstructural evolution of the nickel-base superalloy Inconel 718 after exposition at 750°C for different holding times (10 min–1,000 h) was characterized and correlated with the Eddy current (EC) technique. The results showed that electrical conductivity increases with aging time. This behavior was associated with the precipitation and coarsening of the metastable γ″ phase and its transformation into the detrimental δ phase after 100 h. EC nondestructive evaluation was correlated with X-ray diffraction patterns in terms of the precipitation and growth of secondary carbides that were observed in the scanning electron microscope. Vickers microhardness values were also in agreement with microstructural changes and EC measurements, as the maximum hardened condition can be associated with the precipitation of secondary phases before the transformation of the γ″ phase into the δ phase.

Continuous cooling transformation (CCT) diagrams of β Ti-40Nb and TMZF alloys and influence of cooling rate on microstructure and elastic modulus

Considering an increase in the interaction time between a patient and a metallic implant, new problems can emerge, such as stress shielding and fracture due to mechanical failure. Thus, metallic biomaterials that are used as implants need to be improved decreasing their elastic modulus as the mechanical biocompatibility between a bone and an implant can be improved and prevent the stress shielding phenomena. Therefore, β Ti alloys have gained ground over the last decades as both the β phase and the martensitic α″ phase can lead to a decrease in the elastic modulus. This research aimed to obtain experimental continuous cooling transformation (CCT) diagrams for metastable β Ti-12Mo-6Zr-2Fe (TMZF) and stable β Ti-40Nb (wt. %) alloys through dilatometry tests and differential scanning calorimetry (DSC) analysis. The microstructure characterization by optical (OM) and scanning electron microscopy (SEM), the elastic modulus, E (GPa) and the Vickers microhardness (HV) were analyzed under varied cooling rates from the β field, as well as rapidly solidified by copper mold casting. The results showed that the higher the cooling rate imposed, the lower the Vickers microhardness and elastic modulus values for both alloys, which were 56 GPa and 144 HV for Ti-40Nb and 74 GPa and 333 HV for the best condition (rapid solidified).

Remineralization activities of toothpastes with and without aloe vera with different ratios of fluoride on demineralized enamel: An In-vitro study.

The aim of this in-vitro study was to evaluate and compare the efficacy of both pure aloe vera and commercially available toothpastes with different fluoride compounds and different fluoride amounts on artificial initial enamel lesions by Vicker's microhardness values. In the study, 72 extracted human molar teeth were divided into mesiodistal and 144 specimens were prepared using the vestibule and palatal/lingual surfaces of the teeth. After the surface treatments and initial microhardness measurements, all the specimens were placed in a demineralizing solution (pH: 4.5) for 7 days, resulting in artificial initial enamel lesion, and were randomly assigned to eight groups (n = 18). After the teeth were subjected to pH cycle for 14 days, microhardness measurements were repeated and the data were recorded. Statistical analyzes were performed using MedCalc Statistical Software version 12.7.7. The significance level was determined to be 0.05. In the statistical results, when the microhardness values after demineralization and post-cycle were compared, Groups B1 and A2 showed the lowest values, while Groups A3 and B3 did not show a significant difference in terms of microhardness values after demineralization and post-cycle, and only Group B4 showed statistically significantly higher values. This study emphasized the remineralization effects of fluoride on initial enamel lesions. It can be said that toothpaste containing 1450 ppm fluoride and aloe vera provides an effective remineralization and sodium monofluorophosphate formulation may have a synergistic effect with aloe vera.

Influence of a budget single-peak light-curing unit on the microhardness and bond strength of bulk-fill resin composites to the gingival floor of proximal class II cavity preparations

ObjectiveTo evaluate the Vickers microhardness (VH) and long-term microtensile bond strength (μTBS) of bulk-fill resin-based composites (RBCs) at the bottom of the proximal boxes of Class II restorations when photo-cured using two different light-curing units (LCUs). MethodsMesio-occlusal-distal (MOD) cavities were prepared in 99 third molars (n = 7 per group) and restored with Tetric N-Ceram Bulk-Fill (TNC, Ivoclar), Filtek Bulk-Fill Flow (FBF, 3 M ESPE), or SDR flow+ (SDR, Dentsply Sirona). The RBCs were photo-cured with a dual-peak (Bluephase 20i, Ivoclar) or a single-peak budget LCU (Rainbow Curing Light, SML). The energy delivered by the lights were similar. The amount of light transmitted (% of maximum transmission) through the RBCs and the light beam profile through the restored teeth were recorded (n = 5). VH values were measured at the periphery of the RBC in the proximal box. After 24-h storage in water or after additional thermocycling, the teeth were sectioned to make 1 mm2 sticks. The μTBS of bulk-fill RBCs to the dentin on the gingival floor of the proximal boxes was then measured. Two-way repeated-measures ANOVA and 2-way ANOVA were used to analyze the VH and μTBS data, respectively, and Bonferroni's post-hoc test (α = 5%). No comparisons were made among RBCs. ResultsWhen the bonding agent was photo-cured with the budget light, all the specimens failed. Therefore, the Bluephase 20i photo-cured all the bonding resins and the budget light was only used to photo-cure the RBCs. The Bluephase 20i delivered a more homogeneous and wider light distribution through the restored teeth, higher VH values for TNC and SDR groups (p < 0.05), and higher μTBS in the TNC group (p < 0.05) than those produced by the single-peak budget LCU. The μTBS values to the dentin at the gingival floor of the proximal boxes decreased after thermocycling in the SDR group (p < 0.05). ConclusionWhen the bonding agent was photo-cured with the budget light, all the specimens failed. Photo-curing the RBC with a single-peak, budget LCU compared to the Bluephase 20i reduced the VH and μTBS values of bulk-fill RBCs to the gingival floor.

Mechanical Characterization of Dental Prostheses Manufactured with PMMA-Graphene Composites.

The use of a PMMA composite with graphene is being commercialized for application as dental prostheses. The different proportions of fibers provide a wide range of colors that favors dental esthetics in prostheses. However, there are no studies that have explained the influence that graphene has on the mechanical properties. In this contribution, we studied the PMMA and PMMA material with graphene fibers (PMMA-G) in the form of discs as supplied for machining. The presence of graphene fibers has been studied by Raman spectroscopy and the Shore hardness and Vickers micro hardness were determined. Mechanical compression tests were carried out to obtain the values of maximum strength and Young’s modulus (E) and by means of pin-on-disc wear tests, the specific wear rate and the friction coefficients were determined following the established international standards. Finally, the samples were characterized by field emission scanning electron microscopy (FESEM) to characterize the graphene’s morphology inside the PMMA. The results showed the presence of graphene in PMMA and was estimated in an amount of 0.1027% by weight in G-PMMA. The Shore hardness and Vickers microhardness values did not show statistically significant differences. Differences were observed in the compression maximum strength (129.43 MPa for PMMA and 140.23 for PMMA-G) and E values (2.01 for PMMA and 2.89 GPa for PMMA-G) as well as in the lower wear rate for the G-PMMA samples (1.93 × 10−7 for PMMA and 1.33 × 10−7 mm3/N·m) with a p < 0.005. The coefficients of friction for PMMA-G decreased from 0.4032 for PMMA to 0.4001 for PMMA-G. From the results obtained, a slight content in graphene produced a significant improvement in the mechanical properties that could be observed in the prosthesis material. Therefore, we can state that the main attraction of this material for dental prosthesis is its esthetics.

Preparation, microstructure, and mechanical behaviour of Ni3Al-based superalloy reinforced with carbide particles

The preparation, microstructure, and mechanical behaviour of Ni3Al-based superalloy have been studied. The superalloy reinforced with carbide particles forming in-situ in the melt was prepared by vacuum induction melting (VIM) followed by centrifugal casting. The as-cast alloy was subjected to heat treatment consisting of solid solution annealing, quenching, and ageing. The microstructure of the heat-treated superalloy consists of blocky MC carbides (6.9 vol%), which are uniformly distributed within the columnar grains containing cuboidal γ′(Ni3Al) precipitates (57.3 vol%) embedded in the γ (Ni-based solid solution) matrix and along γ′ grain boundaries. The equivalent plastic strain distribution in the plastic zone underneath Vickers macroindentation and within the compression specimens deformed to engineering strains ranging from 0.05 to 0.27 is calculated using finite element analysis (FEA). The correlation curve between experimentally measured Vickers microhardness values and calculated equivalent plastic strains has been proposed to quantify the level of local strain hardening state of the studied Ni3Al-based superalloy. The room temperature compressive strain hardening behaviour is evaluated and measured strain hardening exponent and strain hardening rate are discussed.

Isovalent Bi substitution induced low thermal conductivity and high thermoelectric performance in n-type InSb

In this paper, thermoelectric (TE) properties of n-type InSb1-xBix (x = 0.00, 0.02, 0.05 and 0.10) polycrystalline samples, synthesized by single-step vacuum melting reaction, have been studied in the temperature range of 300–623 K. P-XRD confirms the phase purity and preferred orientation of (220) plane. FE-SEM back-scattered electron (BSE) micrographs reveal surface morphology and phase homogeneity, and elemental mapping with EDS is used to identify the chemical composition. The elemental existence and oxidation state of In3+, Sb3+, and Bi3+ in InSb1-xBix are rechecked through XPS analysis. With Bi substitution, the electrical conductivity of InSb increases, whereas Seebeck coefficient starts decreasing. However, the maximum Seebeck coefficient, S of −241 μV/K at 423 K, was achieved for the composition of InSb0.98Bi0.02. Interestingly, a huge reduction in lattice thermal conductivity, κlattice from ∼17.5 W/mK (InSb) to 13.1 W/mK (InSb0.9Bi0.10) at 300 K is observed due to increased phonon scattering from mass-fluctuation and created point defects. Further, the maximum thermoelectric figure of merit, zT was achieved as ∼0.56 at 623 K with higher Vickers micro-hardness values of ∼140 HV for the composition of InSb0.98Bi0.02 which is notably higher than the recently reported InSb based materials.

Effect of erosive media on microhardness and fracture toughness of CAD-CAM dental materials

BackgroundErosive acids might create surface flaws and deteriorate the mechanical properties of CAD-CAM materials. This invitro study aimed to investigate the effect of simulated gastric HCl and extrinsic erosive acids on surface microhardness and fracture toughness of CAD-CAM materials.Methods400 bar-shaped specimens (17×4×2 mm3) were prepared from 4 different CAD-CAM dental materials (n = 100/group); monolithic zirconia (Ceramill Zolid HT+, Amanngirbach, Austria), lithium disilicate ceramic (IPS e.max CAD, Ivoclar Vivadent, Liechtenstein), nanohybrid resin composite (Grandio Blocs, VOCO) and polymer-infiltrated glass network (Vita Enamic, VITA Zahnfabrik). Specimens from each material type were further subdivided into 5 groups (n = 20) according to the erosive media applied (simulated gastric HCl, white wine, Coca-Cola®, orange juice, and artificial saliva that served as a control). Specimens were immersed for 24 h in an incubator at 37 ℃, then ultrasonically cleaned in distilled water and air-dried. Half of the specimens were tested for Vickers microhardness (VHN) at parameters of 500 gf for 10 s, while the rest of the specimens underwent 3-point flexure till fracture. Fractured surfaces were examined under a scanning electron microscope (SEM) for fracture toughness (KIC) calculation using the quantitative fractographic analysis method. Data collected were statistically analyzed using two-way analysis of variance (α = 0.05) after verification of data normality and homogeneity of variances.ResultsErosive media created surface flaws that lowered the surface microhardness of the material and initiated the fracture pattern under different loads according to material type. The material type was a more predominant factor than erosive media that affected either the microhardness or the fracture toughness of CAD-CAM dental materials. The highest VHN and KIC values were found among Ceramill Zolid HT+ groups followed by IPS e.max CAD and Grandio Blocs regardless of the erosive media employed. Erosive media significantly reduced the VHN and KIC in Vita Enamic specimens compared to the rest of the material types.ConclusionAll CAD-CAM materials used, except Vita Enamic, showed high resistance against the erosive acids indicating higher longevity of the material in patients frequently exposed to either extrinsic or intrinsic acid.