Effect of various post materials and resin luting cements on microleakage in endodontically treated root canals

The effect of various post materials luted with different resin luting cements on microleakage in root canals was studied in the present study. Sixty carious and crack-free premolars were prepared using a step-back technique and obturated with gutta-percha. The roots were randomly divided into six groups (n = 10). Two different post types, glass fiber reinforced posts and zirconium posts (ZP), were cemented three different resin adhesive cements (Panavia F 2.0, Smartcem 2, and Variolink II) in the root canals. All specimens were thermal cycled and stored in the methylene blue solution for one week. The roots were sectioned horizontally into three sections: apical, middle, and coronal. The occlusal direction of each section was digitally photographed under a stereomicroscope. Dye penetration area was calculated as the methylene blue-infiltrated surface divided by total dentin area. After the two-way Anova test results, Tukey HSD and Bonferroni tests were used for multiple comparisons. According to the test results, ZP luted with Panavia F showed the best microleakage results and glass fiber posts luted with smartcem 2 showed the most unsuccessful microleakage results (p = 0.146).     

Influence of pH cycling and mechanical loading on the resin-dentin microtensile bond strength

The durability of adhesive interfaces is still a problem in adhesive restorations in dentistry. Laboratorial ageing methods have been proposed to predict the performance of materials, but they still require standardization. The objective of this study was to evaluate the resin-dentin microtensile bond strength of composite restorations subjected to pH cycling and different levels of mechanical loading. Resin blocks were built over a flat superficial dentin of bovine incisors (n = 40), using a three-step adhesive system. Half of the specimens were submitted to 10 cycles of pH cycling, followed by mechanical loading (0, 500,000; 1,000,000; 2,000,000 cycles – 98 N, 4 Hz). The other half was directly subjected to mechanical loading. After ageing, all groups were subjected to a microtensile bond test. Data were analyzed using two-way ANOVA and Tukey’s test (α = 0.05). The frequency of the early de-bonding was compared using the Chi-square test (α = 0.05). The statistical analysis revealed that the cross-product interaction ‘pH cycling’ vs. ‘number of mechanical loading cycles’ (p = 0.72) as well as the main factor ‘pH cycling’ (p = 0.49) was not statistically significant, and they were not able to reduce the resin–dentin bond strength values. Regarding the number of mechanical loading cycles, the groups subjected to 2,000,000 cycles showed lower bond strength values than the others (p = 0.003). The frequency of debonded specimens increased with mechanical loading. Therefore, it can be concluded that in this restorative model, at least 2,000,000 mechanical cycles are need to decrease the microtensile strength and simulate the ageing of the interface.     

Heat treatment of silanized feldspathic ceramic: Effect on the bond strength to resin after thermocycling

PurposeThis study aimed to evaluate the effect of heat treatment (at 77 °C) of a silanized feldspathic ceramic on microtensile bond strength (μTBS) with a resin cement before and after being aged by thermocycling.Material and methodsTwenty-four blocks (12×10×4 mm³) of a CAD/CAM feldspathic ceramic (Vitablocks Mark II, Vita) were obtained and randomly divided into three groups, according to the surface treatment prior to the cementation: Group AS – hydrofluoric acid 10%+silane; Group S77 – silane+heating at 77 °C for 60 s; and Group AS77 – hydrofluoric acid 10%+silane+heating at 77 °C for 60 s. Ceramic blocks were cemented to composite resin blocks with a resin cement. The sets were subsequently cross-sectioned into 1 mm² beams for μTBS testing. The beams of each group were randomly divided into two subgroups: aging (thermocycling, 12,000 cycles between 5 °C and 55 °C) and non-aging (tested immediately). One-way ANOVA and Tukey's test (α=0.05) and Weibull analysis (95% CI) were used to analyze the data.ResultsGroup AS77 had the lowest pre-test failure number during the cutting among the groups. There was no significant difference (p=0.255) between the μTBS mean values of the non-aged groups. After aging, the mean value of S77 was significantly lower than those of AS77 and AS (p=0.005). There was no difference in the Weibull modulus (m) and characteristic strength (σ₀) of the aged and non-aged groups for all comparisons. Before aging, heat treatment of silanized feldspathic ceramic (non acid-etched surface) demonstrated bond strength similar to that achieved with hydrofluoric-acid-etching treatment however, it had lower bond strength after aging.ConclusionThe combination of hydrofluoric-acid-etching treatment with heat treatment silanized feldspathic ceramic did not improve the bond strength of the interface.     

Evaluation of different desensitizing agents effect on shear bond strength of adhesive resin cement to dentin

Desensitizing agents can inhibit the bonding strength between dentin and adhesive resin cement. This study evaluated the effects of different desensitizing agents on the shear bond strength of adhesive resin cement to dentin. Sixty freshly extracted and caries free teeth were classified into five experimental groups, randomly (n?=?12). Each group was treated with a different desensitizing agent (Teethmate, Shield Force Plus, Admira Protect and Ultra-Ez) respectively, except for an untreated control group. After desensitizing agents and adhesive resin cement were applied to each dentin surface, all specimens were stored in incubator at 37?°C for 24?h. The shear bond strength was tested with a Universal testing machine at a 0.5?mm/min crosshead speed. Data were analysed by using a statistical software (SPSS 22). The results of the measurements were analysed by Kruskal Wallis test with Bonferroni correction and multiple comparisons were made by Wilcoxon test (p???.01). Specimens were examined by a scanning electron microscope, additionally. The Shield Force Plus showed significantly the highest shear bond strength compared with other groups (p?<?.01). Ultra-Ez showed the lowest shear bond strength (p?>?.01). There was no significant difference among Teethmate and Admira Protect groups (p?>?.01). Desensitizing agents containing resin monomers increased the bonding strength, however desensitizers containing calcium phosphate, potassium nitrate and fluoride did not effect the bonding strength of resin cement to dentin.     

Evaluation of the shear bond strength of two resin cements on different CAD/CAM materials

Objective: This study investigated the bond strength of two resin cements (Panavia F 2.0 and Multilink N) to different CAD/CAM materials: resin nanoceramic (RNC; Lava Ultimate), hybrid ceramic (HC; Vita Enamic), zirconia-reinforced lithium silicate ceramic (ZLDC; Vita Suprinity), and lithium disilicate glass-ceramic (LDG; IPS e.max CAD HT).

Material and methods: CAD/CAM blocks of 2-mm thickness were sectioned with a slow-speed diamond-saw sectioning machine. The slabs were then embedded in autopolymerizing acrylic resin (n = 12), and resin cements were applied to the surface of the specimens. All specimens were stored in water for 24 h and subjected to 5000 thermal cycles. Bond strength was measured by means of the shear bond strength test. The data were statistically analyzed by two-way ANOVA and Tukey LSD post hoc tests.

Results: The results of the two-way ANOVA test indicated that the bond strength values varied significantly depending on the CAD/CAM restorative materials, resin cements, and interaction of these variables (p < 0.05). The RNC group showed the highest bond strength for Panavia F 2.0 (p < 0.05); there were no significant differences among other CAD/CAM materials for Panavia F 2.0 (p > 0.05). The LDG group showed the highest bond strength for Multilink N, it was followed by the ZLDC group (p < 0.05); there were no significant differences between RNC and HC groups (p > 0.05).

Conclusions: Choosing resin cements for restorations should be done carefully because bond strength values vary significantly depending on the resin cement and CAD/CAM restorative material.     

Efficacy of multi-mode adhesive systems on dentin wettability and microtensile bond strength of resin composite

Purpose: To evaluate the wetting ability and the microtensile bond strength of adhesive systems in various depths of dentin. Materials and Method: 48 extracted human molars cut in half in buccolingual direction. Buccal and lingual surfaces were used to obtain deep (n = 48) and superficial (n = 48) dentin. Groups were divided into 4 subgroups: Self-etch (CSE), etch&rinse (SB), multi-mode self-etch (SAU) and multimode etch&rinse (EAU) adhesive systems. 3 consecutive contact-angle measurements were obtained: T0- 3 μl drop of distilled water on dentin; T1-Droplet of the adhesive; T2- Distilled water after polymerization of the adhesive. After composite build-ups, microtensile measurements were performed. Contact angle data were analysed with analysis of variance for repeated measures. Bond strength data were analyzed by repeated measures analysis of variance, comparisons were made according to the logarithmic values (p < 0.05). Results: The difference between groups was not significant regardless of dentin depth for all measurements (p < 0.05). All groups except CSE enhanced the wetting ability of the adhesive but reduced the wetting ability of distilled water after application of the adhesive (p < 0.05). Regarding adhesive systems, the groups showed no significant difference between bond strengths to various depths of dentin except SAU (p > 0.05); in SAU, bond strength to deep dentine were significantly higher than superficial dentin (p < 0.05). Regarding adhesives’ bond strength, CSE showed significantly greater values than the other groups (p < 0.05). Conclusion: The cavity depth does not affect the bonding ability for all adhesive systems; self-etch adhesive systems might be a better choice since different adhesives may influence the wetting ability and microtensile bond strength of the dentin substrates.     

Effects of surface treatments on the shear bond strength of luting cements to zirconia

Objective: The aim of this in vitro study was to evaluate the effect of surface treatments on the shear bond strength of resin cements to zirconia. Material and methods: Sintered zirconia specimens (n = 192) were divided into four different surface treatment groups: control (no treatment); airborne-particle abrasion; glaze layer and hydrofluoric acid (HF) application, and hot etching solution application. Then, each group was divided into four subgroups (n = 12), and three different resin cements were applied to the zirconia surfaces. The shear bond strength value of each specimen was measured after 5000 thermo cycles. The failure types were examined with a stereomicroscope and the effects of the surface treatments were evaluated with a scanning electron microscope. Results were analyzed using analysis of variance and Tukey’s post hoc tests (α = 0.05). Results: The surface treatment and resin cement type significantly affected the bond strength results (p < 0.05). For all resin cements, the airborne-particle abrasion treatment increased the shear bond strength values (p < 0.05). The glaze layer & HF application increased shear bond strength values for all groups, except the Single Bond Universal-RelyX Unicem Aplicap group (p < 0.05). The surface roughness values of airborne-particle abraded specimens were similar to comparable values for specimens from the control group and the hot etching solution group (p > 0.05). The glaze layer & HF application group produced the highest surface roughness values (p < 0.05). Conclusion: The results of this study recommend using the appropriate combination of surface treatment and adhesive/silane coupling agent to achieve durable zirconia-resin bonding.     

Assessment of the initial and aged dentin bond strength of universal adhesives

This study evaluated the effect of mechanical loading on microtensile bond strengths (μTBS) of universal adhesives to dentin and quantified adhesive dentin penetration using micro-Raman spectroscopy. Human molars had occlusal dentin exposed and were allocated into eight groups: All-Bond Universal and Scotchbond Universal using etch-and-rinse and self-etch approaches, Adper Prompt L-Pop, Adper Single Bond Plus, Clearfil SE Bond, and Optibond FL. Following bonding procedures and build-ups, specimens were either stored in water at 37 °C for 24 h or mechanically loaded (50,000 cycles, 50 N) prior to μTBS test. Additional teeth were prepared for micro-Raman analysis of adhesive penetration and FE-SEM. Data were analyzed by two-way ANOVA and Tukey׳s post hoc test (P<0.05). Mechanical loading had no deleterious effect on μTBS with the exception of Adper Prompt L-Pop. Incomplete infiltration of the demineralized dentin was noticed for adhesives using the etch-and-rinse approach and for Scotchbond Universal in the self-etch approach.     

The influence of delayed light curing on the degree of conversion and polymerization contraction stress in dual-cured resin luting agents

The aim of the study was to assess the effect of delayed photo-initiation on the polymerization contraction stress (PCS) and degree of conversion (DC) of a dual-cure resin-luting agent. Thirty-five disk (6 mm × 1 mm) samples (n = 10 each group) of dual cure resin luting agent for PCS assessment were fabricated and polymerized using two illuminated quartz rods. Based on the delay in photo-initiation, 30 disks were divided among six groups [group A-0 min (min) delay, group B-2 min, group C-4 min, group D-6 min, group E-8 min and group F-10 min]. A non-photoinitiated group (group G – chemical cure – n = 5) was included as control. The PCS for all specimens was assessed using a Tensometer. For DC evaluation thirty-five specimens were divided into seven groups with delays in photo-initiation (group H-0 min, group I-2 min, group J-4 min, group K-6 min, group L-8 min and group M-10 min, group N-chemical cure). DC was assessed using attenuated total reflectance spectroscopic technique. Statistical comparison among groups was performed using analysis of variance (α = 0.05). The maximum and minimum PCS and DC values with delayed photo-initiation was observed in group-C (3.34 MPa) & group-F (2.44 MPa); and group-M (0.78 MPa) and group-H (0.55 MPa) respectively. Chemically cured samples showed the least PCS (group-G, 1.94) and DC (group-N, 0.53) values in their respective categories. PCS significantly decreased with delayed photo-initiation. A significant increase in DC was noticed when photo-initiation was delayed in the dual cure resin luting agent.     

Effect of aging type and aged unit on the repair strength of resin composite to feldspathic porcelain in testing microtensile bond strength

The aim of the present study is to investigate the effect of aging type (thermocycling vs. water storage) and aged unit (block vs. stick) on the repair strength of resin composite to feldspathic porcelain in testing microtensile bond strength (μTBS). Ceramic specimens (N = 30) (10 × 5.7 × 4.5 mm³, Vita Mark II, Vita) were obtained from CAD–CAM blocks. One surface was etched with 10% HF and silanized. An adhesive was applied and resin composite blocks were constructed incrementally on the conditioned surface. The specimens were randomly divided into five groups (n = 6): Control (C): Non-aged; BTC: Blocks were thermocycled (5–55 °C, 6000 cycles); STC: Sticks were thermocycled; BS: Blocks aged in water storage (6 months) after themocycling; SS: Blocks aged in water storage (6 months) after thermocycling. After μTBS test, failure types were classified. Data (MPa) were statistically analyzed (1-way and Dunett and 2-way ANOVA, Tukey`s) (α = 0.05). Two-parameter Weibull distribution values including the Weibull modulus, scale (m), and shape (0) values were calculated. Aging type (p = 0.009) and aged unit (p = 0.000) significantly affected the results. Interaction terms were also significant (p = 0.000). Considering the stick level, there was no significant difference between thermocycling (STC: 25.7 ± 2.3) and water storage (SS: 25.3 ± 3.8) (p > 0.05) but the results were significantly higher when blocks were thermocycled (BTC: 31.6 ± 2.9) (p < 0.05). Weibull modulus and characteristic strength was the highest in BTC (m = 4.2; σ_o: 34.4) among all other groups (m = 3–3.9; σ_o: 14.6–28.5). Adhesive failures were common and cohesive failures occurred in less than 5% in all groups. Aging protocol was detrimental on durability of repair strength of resin composite to feldspathic porcelain. Exposing the sticks to either thermocycling or water storage aging should be considered in in vitro studies.     

Effect of cigarette smoking on the bond strength between resin cement and dental CAD/CAM ceramics

Although the effects of cigarette smoking on several dental problems have been widely studied, the association between tobacco exposure and resin-ceramic bonding is rarely reported. This study investigated the resin-ceramic adhesion (shear bond strength, SBS) and associated risk factors on three selected dental CAD/CAM ceramics using a novel model to simulate the exposure to cigarette smoking. Specimens from IPS e.max® CAD, Vitabloc® Mark II for Cerec and Zirconia Cercon were prepared and treated using silicacoating and silane. A layer of resin cement was applied on the treated ceramic surfaces and light activated. Specimens were placed in a chamber and challenged with various numbers of cigarettes (0, 1, 5, 10, and 15). Then, the specimens were subjected to SBS test and fractured surfaces were examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX) to determine the failure mode and surface composition. Overall, the mean SBS of IPS e.max^® CAD (9.6 ± 3.4 MPa), Vitabloc^® Mark II for Cerec (9.3 ± 2.5 MPa) and Zirconia Cercon (8.7 ± 3.0 MPa) did not show any statistical significant difference (p = 0.192 > 0.05), such that the adhesion of resin bonded to glass-based ceramics (IPS e.max® CAD and Vitabloc® Mark II for Cerec) decreased with cigarette smoke exposure, but increased for the resin bonded to zirconia ceramic (Zirconia Cercon). Furthermore, the number of cigarettes has a statistically significant effect on the SBS (p = 0.001), such that in general 5 cigarettes yielded the lowest mean SBS (7.6 ± 2.1 MPa). SEM-EDX analyses showed mostly adhesive failures in all experimental groups with changes in surface morphology and chemical composition after smoking challenge. Cigarette smoking produces a different effect on resin-ceramic bonding depending on ceramic type that may be due to chemical reactions in the bonding interface and changes in temperature and moisture. Further work should explore the mechanism to which cigarette smoke affects the resin-ceramic bonding and its clinical relevance.     

高压喷涂偶联剂对氧化锆表面微观形貌及粘接效果的影响

探讨使用不同压力气体喷涂偶联剂对氧化锆表面形貌及氧化锆-树脂粘合剂粘接强度的影响。烧结、喷砂后的氧化锆瓷片,按偶联剂种类(CP;ZP)和喷涂气体压力的高低(L 0.1 MPa;H 0.3 MPa)随机分为CPL、CPH、ZPL、ZPH 4个实验组及无偶联剂处理的对照组NP(n=15)。各组处理后的氧化锆瓷片利用激光共聚焦显微镜观察5组氧化锆表面形貌并测量粗糙度,并与树脂粘合剂(SA luting)粘接并测试微剪切强度。激光共聚焦显微镜观察显示,CPL和ZPL组中氧化锆表面光滑平坦,CPH、ZPH组的氧化锆表面则保留了高低不平的微观形貌,平均粗糙度明显高于低压气体喷涂组。CPH组的微剪切粘接强度最高(24.82±7.34)MPa,其次为CPL组(17.93±1.53)MPa、ZPL组(15.67±3.39)MPa和ZPH组(9.59±5.97)MPa,对照组最低(8.77±3.12)MPa。偶联剂喷涂压力显著影响氧化锆-树脂粘合剂的粘接强度。,,     

Effect of thermal cycling and low pressure sandblasting on the bond strength of a self-adhesive cement to Y-TZP zirconia

The aim of this investigation was to assess the influence of several surface treatments on the shear bond strength (SBS) of a self-adhesive resin cement containing 10-methacryloxydecyl-dihydrogenphosphate monomer to densely sintered zirconia ceramic, before and after thermal cycles. Hundred densely sintered zirconia cylinders were divided into five groups (n = 20). Each of them received a different surface treatment: (1) control [No_T], with the zirconia surface unconditioned, (2) low pressure air abrasion [Sand_S], (50 μm, 1 bar), (3) standardized air abrasion [Sand_H], (50 μm, 2.8 bar), (4) standardized Rocatec? Plus (silica-coated alumina oxide) air abrasion (2.8 bar) and silanization [Roc_H], (5) low pressure Rocatec? Plus (silica-coated alumina oxide) air abrasion (1 bar) and silanization [Roc_S]. Five more surface-treated specimens were addressed to scanning electron microscope for qualitative observations. After specimen fabrication, subgroups of 10 bonded samples were stored in water either for 24 h (T1) or subjected to 5000 thermal cycles (T2); SBSs were determined with a universal testing machine at a crosshead speed of 1 mm/min. At T1, mean SBSs (MPa) obtained for the examined groups were: [Sand_H] 16.24 ± 2.95; [Sand_S] 16.01 ± 2.68; [Roc_H] 17.17 ± 1.64; [Roc_S] 15.92 ± 1.99. All surface treatments positively affected (p < 0.05) the initial self-adhesive cement adhesion to zirconia with respect to No_T (13.29 MPa). Artificial aging decreased the bond strength in all test groups significantly, but no spontaneous debonding was observed in [No_T]: at T2, SBS values ranged from 7.76 ± 2.37 (No_T) to 8.89 ± 1.74 (Sand_S), with no statistically significant difference between groups (p = 0.5293). Both air abrasion with alumina oxide and Rocatec? universal bonding system, used with hard or low air pressure, produced comparable effects on cement–zirconia interface before and after thermal cycles. After artificial aging, minimal differences in bond strength values between sandblasted and control groups were not of statistical significance.     

Effects of coating pressure on the thermal and mechanical properties of glow discharge polymer films

The glow discharge polymer (GDP) films for laser fusion targets were successfully fabricated by plasma polymerization technology at different coating pressures. The chemical structure of GDP films was characterized by the Fourier transform infrared (FT-IR) spectrum. The thermal stability was evaluated by thermal-gravimetric analysis (TGA). The mechanical properties were measured by nano-indentation technology. The thickness of GDP films was measured by profile meter. The results show that the deposition rate of GDP films increases with increasing coating pressure. The olefinic structure, the ratio of carbon/hydrogen, and the content of CC in GDP films increase as the pressure increases. At the lower coating pressure, the thermal stability, hardness and Young's modulus of GDP films were well. By calculation, the buckle strength of the GDP films can meet the ICF experiments.     

Effects of two silane surface modifications with different functional groups on the thermal conductivity and mechanical properties of UV-cured composites with high ceramic filler loading

With rapid technological advancements, efficient thermal management is becoming increasingly important to sustain the stable operation of electronic devices. In this study, aluminum nitride (AlN) fillers with various acrylate monomers were subjected to two types of silane surface treatments to prepare composites with a high loading of AlN filler (65 wt%). The acrylates—isobornyl acrylate (IBOA), 1,4-butanediol diacrylate (BDDA), and trimethylolpropane triacrylate (TMPTA)—were mixed with bisphenol A ethoxylate dimethacrylate (Bis-EMA) as an oligomer, and phenylbis (2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) as a photo-initiator in different proportions to obtain resin matrices. Pristine AlN and AlN functionalized with APTES and MPS were used as fillers. The effect of the acrylate functional group in silanes on the thermal and mechanical properties of the acrylate resin was explored. The thermal conductivities of the IBOA/AlN/APTES and IBOA/AlN/TMPTA composites with a high loading of the filler functionalized with APTES and MPS were 1.34 and 1.57 W/(m?K), respectively, 4.15 and 5.28 times higher than that of the composite with neat resin. The enhanced filler–matrix compatibility increased the tensile strength of the composites. The findings highlighted that silane functionalization of AlN can enhance the thermal conductivity and mechanical properties of the composite.     

Effects of pressure on densification behaviour,microstructures and mechanical properties of boron carbide ceramics fabricated by hot pressing

Effects of pressure, from ordinary (30 MPa) to high pressure (110 MPa), on densification behaviour, microstructures and mechanical properties of boron carbide ceramics sintered by hot pressing are investigated. With increasing pressure, the relative density sharply increases within 30–75 MPa, slowly increases within 75–100 MPa and finally stagnates. For samples within 75–100 MPa, densification begins at approximately 1000 °C, and the dominant densification process ends before the soaking stage. High relative densities of 98.49% and 99.76% are achieved. For samples within 30–50 MPa, densification begins at approximately 1500 °C, and the soaking stage (initial 20 min) is still important for the dominant densification process. The final relative densities are only 87.90% and 92.32%. The above-mentioned differences are derived from contributions of pressure, and the dominant densification mechanism under high pressure is plastic deformation. The average grain size of the samples slightly increases with increasing soaking time. The grain size under higher pressure is larger than that under lower pressure at corresponding periods because grains grow easily with reduced pores. Vickers hardness and fracture toughness increase as grain size decreases in fully dense samples. However, when the samples do not achieve full density, relative density becomes more influential than grain size in hardness and toughness. A soaking time of 30 min is enough for samples under 100 MPa. Prolonging the soaking time has deleterious effects on mechanical properties. The relative density, grain size, hardness and fracture toughness of the samples under 100 MPa for 30 min are 99.73%, 1.96 µm, 37.85 GPa and 3.94 MPa m^1/2, respectively.     

Effects of pyrochlore content on the phase,structure, and properties of uranium-rich glass ceramics

In this study, the effects of the pyrochlore content on the phase, structure, and properties of uranium-rich glass ceramics were studied by modifying the mass ratio of the uranium pyrochlore in the glass ceramics. The results indicate that U has a high occupancy rate of approximately 0.7 f.u. at the A position of pyrochlore, and the crystal pyrochlore phase in the glass matrix can increase or decrease according to the U amount in the waste. Specifically, at a high occupancy rate and crystallization amount, the U loads reach 20 wt% in the sample, which exceeds the reported 16 wt% maximal U loads of pyrochlore-based glass ceramics. Furthermore, all the samples have excellent mechanical properties and chemical stabilities. The bulk density of each sample is more than 90% the theoretical density, which is 10–20% higher than those of the glass ceramics prepared by pressure sintering. Moreover, the Vickers hardness values of all samples exceed 6 GPa, and the U leaching rate after 21 days is only 6.7 × 10⁻⁵ g m⁻² d⁻¹, which is an order of magnitude lower than those of brannerite glass ceramics under equal leaching conditions.     

Effects of carbonyl nickel powder addition on the mechanical properties,microstructure, and yttrium segregation of sintered 3YSZ composites

In this study, the effects of the addition of carbonyl nickel powder on the density, microstructure, and mechanical properties of sintered yttria-stabilized zirconia (3YSZ) were investigated. Sintering at 1300 °C resulted in the optimum comprehensive mechanical properties. The addition of 5 vol% carbonyl Ni increased the fracture toughness and flexural strength from 9.51 MPa m^1/2 to 14.5 MPa m^1/2 and from 747 MPa to 873 MPa, respectively. The addition of carbonyl nickel showed greater improvement than did the addition of spherical Ni powder. The dendritic morphology improved the interface bonding between the ceramic and the metal, enabling a bridging mechanism of the ductile phase. However, further Ni addition decreased the mechanical properties. X-ray diffraction results showed that the amounts of the monoclinic phase (M) and cubic phase (C) of 3YSZ increased, whereas the amount of the tetragonal phase (T) decreased. The Y segregation near the Ni particles, which was confirmed by an energy dispersive spectrometer (EDS), caused the phase changes. The segregation of Y occurred during the cooling stage, rather than the holding stage, of sintering. During the cooling stage, the heat mismatch between Ni and ZrO₂ resulted in strong elastic strain energy, which promoted Y segregation.     

Effects of applied pressure and temperature during curing operation on the strength of tubular single-lap adhesive joints

Adhesive joints have been widely used for fastening thin adherends because they can distribute the load over a larger area than the mechanical joint, require no holes, add very little weight to the structure and have superior fatigue resistance. However, the load capabilities of adhesive joints are affected by both applied pressure and temperature during cure, as well as by service environments because the adhesion characteristics of adhesives are very sensitive to manufacturing and environmental conditions. In this study, the tensile load capabilities of tubular single-lap adhesive joints with an epoxy adhesive were experimentally investigated with respect to service temperature and the applied pressure and temperature during curing operation. The effects of the applied pressure on the tensile load capabilities of tubular single-lap adhesive joints were studied by measuring the actual cure finish temperature using thermocouples and dielectrometry. From the experiments, it was found that the actual cure finish temperature of tubular single-lap adhesive joints increased as applied pressure increased, which increased residual thermal stress in the adhesive layer to decrease the load capabilities of adhesive joints. From finite element analysis and experimental results of tubular singlelap adhesive joints, the optimal geometry condition for adhesive joints was also investigated.     

Effects of nanosilica filler surface modification and compatibilization on the mechanical,thermal and microstructure of PP/EPR blends

Polypropylene/ethylene-propylene rubber/nanosilica (PP/EPR/nano-SiO₂) composites were prepared by a melt blending masterbatch process using a Brabender mixer. In order to improve the interfacial adhesion and achieve diverse desired properties of the composites, nanosilica surface silylation by means of two silane coupling agents: N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (AEAPTMS) and 3-methacryloxypropyltrimethoxysilane (MPTMS) was explored. The composites were also compatibilized using three compatibilizers: methyl methacrylate grafted PP (MMA-g-PP), glycidylmethacrylate grafted PP (GMA-g-PP) and maleic anhydride grafted PP (MAH-g-PP). The properties of the blends and the composites were examined using tensile and Izod impact tests, differential scanning calorimetry (DSC), thermogravimetric analysis (ATG) and scanning electron microscopy (SEM). According to the mechanical property evaluations, the incorporation of nano-SiO₂ particles into PP/EPR blend improved the tensile strength and Young’s modulus of the composites. The elongation and Izod impact strength were adversely affected. A significant improvement in the mechanical properties was obtained for the composites with AEAPTMS-SiO₂ and MAH-g-PP. The DSC results indicated that the incorporation of the modified silica and MAH-g-PP increased the crystallinity of the composites. However, no significant variation in the crystallinity was observed as a result of the addition of MMA-g-PP and GMA-g-PP. The TGA results revealed that the composites exhibit a higher thermal stability than that of the neat matrix. SEM micrographs of the fractured surfaces revealed a two-phase morphology with EPR nodules being dispersed in the PP matrix. SEM also indicated that the incorporation of MAH-g-PP into PP/EPR composites contributes to a better dispersion of the EPR phase and nano-SiO₂ particles in the polymer matrix.