Effect Of Hydrothermal Aging Research Articles

Effect of hydrothermal aging on color stability and translucency of two zirconia generations compared to lithium disilicate ceramics.

An esthetically acceptable ceramic restoration should have optical properties like the teeth and reflect, transmit, and absorb light. The present investigation compared how hydrothermal aging affected the properties of two types of zirconia and lithium disilicate. Thirty rectangular samples (12×14×1 mm) were prepared and sectioned from three different ceramic blocks/blanks (n=10), then assigned into three groups according to the ceramic type: group Z: IPS e.max ZirCAD prime, gradient zirconia (3Y/5Y-TZP); group K: Katana UTML (5Y-TZP); and group E: IPS e.max CAD (lithium disilicate). Color analysis of samples was performed before and after hydrothermal aging (1, 3, and 5 hours) using a spectrophotometer. Color difference (∆E00), translucency parameter (TP00), and contrast ratio (CR) were evaluated. The microstructural analysis was performed using x-ray diffraction (XRD). Data were statistically analyzed at a significance level of P<0.05. A statistically significant variation was observed across means of ∆E00, TP00, and CR at different times. Group Z displayed the highest statistically significant mean ∆E00. Group E demonstrated the greatest statistically significant mean TP00. Group K exhibited the most statistically significant mean CR. Hydrothermal aging significantly affected the optical characteristics of lithium disilicate and zirconia ceramics. The translucency of samples increased with aging.

Effect of benzoyl chloride treatment on morphological, thermal, mechanical, and hydrothermal aging properties of date palm/polyvinyl chloride (PVC) composites

The use of natural fibers has seen a significant rise in the composites sector, resulting in the creation of polymer composites with exceptional strength. These environmentally-friendly alternatives offer a compelling substitute for synthetic composites. This study explores the use of date palm waste as reinforcement for the fabrication of polyvinyl chloride (PVC) composites. A surface modification method was essential for improving the binding interaction between palm fibers and PVC composites. The two-hour benzoyl chloride treatment at 140 °C played a crucial role. The study examined the effects of hydrothermal aging on mechanical properties of composites, using various techniques such as surface morphology analysis, Fourier Transform Infrared spectroscopy, and Thermogravimetric Analysis, on composites made of untreated fibers and those treated with benzoyl chloride. Although the treatment of palm fiber-reinforced composites with benzoyl chloride improved their mechanical properties, it is crucial to note that hydrothermal aging reduced their tensile strength by 10%. Despite this, these composites prove to be well-suited for applications requiring moderate strength and stiffness in mild environmental conditions. These composites, while utilizing benzoyl chloride for surface treatment, still represent a more sustainable alternative to traditional synthetic composites by incorporating renewable date palm waste and enhancing mechanical properties, which potentially reduces overall environmental impact.

Nanocomposites based on MWCNT and nanoclay: Effect of acrylated epoxidized soybean oil on curing and composite properties

UV and thermal-curing hybrid epoxy adhesives are generally developed with a combination of epoxy acrylates and thermal-curing epoxy resin. This study modified bisphenol-A type epoxy resin (ER) with acrylated epoxidized industrial crop soybean oil (AESO) to obtain a dual-curable epoxy system. Hydroxylated multi-walled carbon nanotube (MWCNTOH) and montmorillonite-type nanoclay (NC) first was used as nano reinforcement in this system. Both thermal and UV-curing were applied to composites. Tensile and hardness tests, thermogravimetric analysis (TGA), and four-point probe electrical conductivity measurements were used for the nanocomposite characterization. Although (UV+thermal) curing increased the thermal strength of the nanocomposites, it caused a decrease in their electrical conductivity and moisture absorption. The highest tensile strength values were obtained as 107 MPa and 97 MPa for thermally cured 1.5 wt% MWCNTOH and 2 wt% NC composites, respectively. The effect of the AESO ratio on UV curing of nanocomposites was investigated and 10 % was found to be the most suitable. MWCNTOH composites also exhibited the highest electrical conductivity with a percolation threshold of 1.5 wt%. The effect of hydrothermal aging on thermal and electrical conductivity properties showed that only T5 and T10 values of thermally or (UV+thermally) cured MWCNTOH and NC composites decreased, T50 values did not change significantly.

Interface Induced by Hydrothermal Aging Boosts the Low-Temperature Activity of Cu-SSZ-13 for Selective Catalytic Reduction of NOx.

Hitherto, sulfur poisoning and hydrothermal aging have still been the challenges faced in practical applications of the Cu-SSZ-13 catalyst for the selective catalytic reduction (SCR) of NOx from diesel engine exhaust. Here, we elaborately design and conduct an in-depth investigation of the synthetic effects of hydrothermal aging and SO2 poisoning on pristine Cu-SSZ-13 and Cu-SSZ-13@Ce0.75Zr0.25O2 core@shell structure catalysts (Cu@CZ). It has been discovered that Cu@CZ susceptible to 750 °C with 5 vol % H2O followed by 200 ppm SO2 with 5 vol % H2O (Cu@CZ-A-S) could still maintain nearly 100% NOx conversion across the significantly wider temperature region of 200-425 °C, which is remarkably broader than that of the Cu-SSZ-13-A-S (300-400 °C) counterpart. The experimental results show that the hydrothermal aging process results in the migration of highly active Cu species within the cage of Cu-SSZ-13 to the CZ surface, forming CuO/CZ with abundant interfaces, which significantly enhances the adsorption and subsequent activation of NO, leading to the generation of reactive N2O3 and HONO intermediates. Moreover, density functional theory (DFT) calculations reveal that the H of the HONO* species can function as Brønsted acid sites, effectively adsorbing NH3 to generate the active NH4NO2* intermediate, which readily decomposes into N2 and H2O. Furthermore, this pathway is the rate-determining step with an energy barrier of 0.93 eV, notably lower than that of the "standard SCR" pathway (1.42 eV). Therefore, the formation of the new CuO/CZ interface profoundly boosts the low-temperature NH3-SCR activity and improves the coresistance of the Cu@CZ catalyst to sulfur poisoning and hydrothermal aging.

Transient kinetic analysis of the standard SCR reduction half cycle on Cu-SSZ-13 catalysts: Roles of temperature, hydrothermal aging and H2O feed content

Transient Response Methods (TRM) are applied to investigate the reduction half-cycle (RHC) of the Standard SCR reaction over a state-of-the-art Cu-SSZ-13 catalyst at temperatures ranging from 135 to 350°C. We assess the effects of hydrothermal aging (HTA), water feed content and temperature on the reaction redox chemistry. By testing three samples with different aging levels, we reveal the CuII reduction rate to be unaffected by HTA in the whole T-range under investigation. Kinetic analysis assesses the inhibiting role of water on the RHC, consistent with literature. As long as enough NH3 is stored on the catalyst surface, reduction transients are accurately predicted assuming a second-order dependence of the reduction rate on the copper(II) fraction, also at temperatures exceeding 200°C. Remarkably, under wet conditions the low-T CuII reduction mechanism remains the same at least up to 300°C.

The effect of speed sintering and hydrothermal aging on the biaxial flexural strength and microstructure of recent cubic zirconia material

The effect of speed sintering and hydrothermal aging on the biaxial flexural strength and microstructure of recent cubic zirconia material

Experimental characterization and numerical prediction for mechanical aging of epoxy and its carbon fiber‐reinforced composite under hydrothermal conditions

AbstractThe Aqueous environment impairs the mechanical performance of carbon fiber‐reinforced polymers (CFRPs) and decreases the durability of engineering structures made of CFRPs primarily by degrading the resin matrix. Hence, the objective of this study is to investigate and accurately predict the influence of hydrothermal aging on the epoxy and its carbon fiber reinforced polymer (CFRP). Particularly, this work developed a modeling method that combined Fick's model, empirical aging model and elastoplastic constitutive model to predict the mechanical behavior of hydrothermally aged epoxy matrix. After the experimental characterization, this epoxy modeling method demonstrated its predictive capability on the mechanical response of the deteriorated epoxy under different hydro‐thermal‐salt conditions, with the mean absolute percent error (MAPE) of approximately 4.61%. Furthermore, the transverse compressive behavior of unidirectional (UD) CFRPs could be predicted by using the representative volume element (RVE) model with the degraded matrix behavior predicted via this epoxy modeling method. Integrated with this CFRP modeling, results from mechanical tests and fracture analysis further demonstrated that the hydrothermal aging effect on the transverse compressive performance of the UD CFRPs was dominated by the deterioration of their resin matrix. Therefore, this study demonstrates the feasibility of the finite element analysis (FEA) for mechanical aging of the epoxy matrix and its CFRP under hydrothermal conditions via employing the proposed integrated modeling method.Highlights Degradation of epoxy polymer under hydro‐thermal‐salt aging conditions. Integrated model to predict mechanical response of hydrothermally aged epoxy. RVE model to predict the mechanical behavior of hydrothermally aged CFRP. Hydrothermal aging on the transverse compressive behavior of UD CFRP.

The distinctions of the interfacial nanostructures and properties between carbon fiber reinforced fast and conventional curing epoxy composites subjected to hydrothermal treatments

The vital role of the interphase in loading transfer in carbon fiber reinforced resin composites has received considerable critical attention. In this study, to quantitatively distinguish between the effects of hydrothermal aging on the interfacial nanostructures and properties of carbon fiber reinforced fast and conventional curing epoxy composites, peak force quantitative nano-mechanics (PF-QNM) technique by atomic force microscopy (AFM) was utilized to determine the interfacial modulus, adhesion and thickness. In addition, the shear behavior was studied by short-beam strength test, and the water uptake was investigated by water adsorption test. Based on the modulus contrast of the interphase in PF-QNM modulus image, the average interfacial thickness of the fast curing epoxy composites after 18 h of hydrothermal aging was 67 nm, increased 236 % when compared with the unaged composites. It was much higher than the rise of 70 % of the conventional curing epoxy composites after 18 h of hydrothermal aging while the interfacial thickness was 69 nm. Consistently, the average interfacial thickness of the fast and conventional curing epoxy composites determined by the adhesion were 68 nm (widened 247 %) and 68 nm (widened 67 %). In a word, the interfacial thickness of the fast curing epoxy composites was about 4 times than that of the conventional curing epoxy composites after 18 h of hydrothermal aging, because of the fast curing caused microcracks and flaws. Then, after 192 h of hydrothermal aging, the decreasing of short-beam strength of the fast curing epoxy composites were almost 1.6 times than that of the conventional curing epoxy composites, due to the faster growing of microcracks and delamination on the side surface of the fast curing epoxy composites short-beam samples during testing. Lastly, the maximum water absorption and diffusion coefficient of the fast curing epoxy composites were 1.2 % and 5.5 × 10−7 cm2/s respectively, which were both 1.3 times that of the conventional curing epoxy composites. Significantly, all the results proved that, attributing to the fast curing caused microcracks and flaws in the fast curing epoxy composites, through which water preferred to enter a composite along the fibers and interphase, the interphase in the fast curing epoxy composites were more sensitive to the hydrothermal aging than the conventional curing epoxy composites. Therefore, the water uptake, interfacial thickness and short-beam strength of the fast curing epoxy composites changed faster.

The Effect of Hydrothermal Aging on The Color Stability of Gradient Zirconia. In Vitro Study

The Effect of Hydrothermal Aging on The Color Stability of Gradient Zirconia. In Vitro Study

Effect of Hydrothermal Aging on the Flexural Strength and Microhardness of Materials Used for Additive or Subtractive Manufacturing of Definitive Restorations.

To evaluate the flexural strength (FS) and microhardness of various CAD/CAM restorative materials intended for definitive use. The effect of hydrothermal aging on the mechanical properties of these materials was also investigated. A total of 210 bar-shaped specimens (17 × 4 × 1.5 mm ± 0.02 mm) were fabricated via either subtractive manufacturing (SM) methods-reinforced composite resin (SM-CR), polymer-infiltrated ceramic network (SM-PICN), fine-structured feldspathic ceramic (SMFC), nanographene-reinforced polymethyl methacrylate (PMMA; SM-GPMMA), PMMAbased resin (SM-PMMA)-or additive manufacturing (AM) methods with urethane acrylate-based resins (AM-UA1 and AM-UA2). Specimens were then divided into two subgroups (nonaged or hydrothermal aging; n = 15). A three-point flexural strength test was performed, and five specimens from the nonaged group were submitted to microhardness testing. Specimens were subjected to 10,000 thermal cycles, and the measurements were repeated. Regardless of aging, SM-CR had the highest FS (P < .001), followed by SM-GPMMA (P ≤ .042). In nonaged groups, AM-UA2 had a lower FS than all other materials except SM-FC (P = 1.000). In hydrothermal aging groups, AM specimens had lower FS values than other materials, except SM-PMMA. With regard to microhardness, there was no significant difference found between any of the tested materials (P ≥ .945) in the nonaged and hydrothermal aging groups. The effect of hydrothermal aging on FS varied depending on the type of restorative material. Regardless of aging condition, SM-CR showed the highest FS values, whereas SM-FC had the highest microhardness. Hydrothermal aging had no significant influence on the microhardness of the tested materials.

The effect of hydrothermal aging on Mn2O3/Cu-SSZ-39 composite catalysts for selective catalytic reduction of NOx by NH3

The latest generation of fuel-efficient engines produces exhaust at cooler temperatures, highlighting a need for enhancement in the low-temperature effectiveness of Cu-zeolite catalysts. The metal oxide/Cu-zeolite composite catalysts have demonstrated superior deNOx performance at lower temperatures compared to Cu-zeolite alone. However, the hydrothermal stability of these composite catalysts remains unexplored. In this study, we focus on the Mn2O3/Cu-SSZ-39 catalyst, chosen for its exceptional activity at low temperatures. The synergy between the nitrate groups on Mn2O3 and NH4+ ions on the Brønsted acid sites of Cu-SSZ-39 enhances NOx conversion efficiency. Nonetheless, the efficiency of Mn2O3/Cu-SSZ-39 diminishes following exposure to hydrothermal conditions at various temperatures (700 °C, 750 °C, and 800 °C), with the degradation degree intensifying at higher temperatures. Characterization studies revealed that hydrothermal treatment leads to the recrystallization of Mn2O3 particles, which reduces the content of active adsorbed oxygen. This reduction impedes the formation of active bridged nitrates in the aged catalysts and disrupts the SCR pathway through the interaction between bridged nitrates and NH4+ on the composite catalysts. Despite these challenges, some adsorbed oxygen remains on the Mn2O3/Cu-SSZ-39 after aging, ensuring that the aged composite catalyst still exhibits higher activity than the fresh Cu-SSZ-39 catalyst. This observation suggests that there is potential for the application of Mn2O3/Cu-SSZ-39 in practical scenarios.

Effect of Hydrothermal Aging on Damping Properties in Sisal Mat-Reinforced Polyester Composites.

Hydrothermal aging is a matter of considerable concern for natural fiber-reinforced polymers; it can alter dimensional stability and induce microcracks and macro strain on the composite structure. This study applied a sorption kinetic model and examined the effects of water on the damping factor of sisal mat-reinforced polyester composites. The experimental data were fitted well using a Boltzmann sigmoid function, suggesting a promising first step toward kinetic water sorption modeling. Additionally, a damping test was carried out using the impulse excitation technique, highlighting the composite material's dynamic response under varying water absorption conditions. The result showed that damping exhibited sensitivity to water absorption, increasing significantly during the first 24 h of immersion in water, then remained steady over time, inferring a critical time interval. An empirical model proved satisfactory with the correlation coefficient for sorption rates and damping of sisal mat polymeric composites.

A review of the effect of hydrothermal aging on the mechanical properties of 2D fiber‐reinforced resin matrix composites

Abstract2D fiber reinforced resin matrix composites (2D FRRMC) are widely applied for aerospace, generator blades, and other high‐end equipment manufacturing fields due to their excellent mechanical properties. However, 2D FRRMC will face a variety of complex environments in the service process, and the long‐term complex environment will significantly impact the physical and mechanical properties of 2D FRRMC. It is necessary to understand and analyze the changes of materials during service. A comprehensive review of the research on the effect of hydrothermal aging on the mechanical properties and re‐ drying of 2D FRRMC in recent years was presented in this article, which contains interlaminar shear properties, compression properties, tensile properties, and aging mechanism, etc. Finally, the current challenges and prospects of 2D FRRMC were discussed. These discussions and proposed strategies will enlighten thoughts and offer ways to apply 2D FRRMC in complex environments better, study 2D FRRMC in complex environments, and study the effects of hydrothermal aging on materials in the future.

Effect of Hydrothermal Aging on the Tribological Performance of Nitrile Butadiene Rubber Seals.

High temperature and humidity affect the tribological performance of nitrile butadiene rubber (NBR) seals, which affects the precise positioning of cylinder systems. Therefore, it is crucial to study the effect of hydrothermal aging on the tribological performance of the NBR seals. In this study, the changes in the tribological performance of the NBR seals under hydrothermal aging conditions were investigated. The results show that the volatilization of additives and the increase in crosslink density of the NBR seals occurs in the hydrothermal aging environment, leading to the deterioration of their surface quality, elastic deformability, and tribological performance. The formation of surface micropores due to additive volatilization is the main factor in the degradation of tribological performance.

Hydrothermal aging effect on crushing characteristics of intraply hybrid composite pipes

In this study, the crushing properties of hybrid glass, basalt, and carbon fiber-reinforced composite pipes under a hydrothermal aging environment were investigated. Hybrid and non-hybrid composite pipes manufactured by filament winding technique were immersed in distilled water and seawater at 30 °C for four months. The water sorption parameters of the samples were calculated theoretically and weighed experimentally. Dry and aged pipes were subjected to quasi-static axial compression to examine aging effects on the crushing properties. The experimental weighing results showed that all composites exhibited a Fickian-like water absorption line. The non-hybrid basalt pipes were the most water-absorbing among all groups. In addition, the results proved that the hybridization effect in pipes is highly effective on water absorption parameters. In line with the results of non-hybrid pipes, hybrid pipes containing basalt fiber absorbed more water than other hybrid ones. Additionally, pipes aged in different environments showed that composite pipes absorbed more distilled water compared to seawater. Also, it was found that hydrothermal aging having adverse effects on the crushing characteristics of the pipes led to significant decreases. This can be explained by the degradation of the fiber–matrix interphase due to aging. However, maximum specific energy absorptions were achieved from non-hybrid carbon pipes regardless of environmental conditions. Also, the hybridization enhanced the crushing properties of the non-hybrid pipes that have lower characteristics. Additionally, it can be said that hybrid samples providing better stability in crushing showed better mean crushing load values since they mostly had a progressive crushing mode. The maximum mean crushing loads were obtained from the unconditioned hybrid GC samples as 36.2 kN which was 9.5 % and 34 % higher than unconditioned hybrid CB and BG samples. In conclusion, the study proved that the samples with low crushing properties can be improved by hybridization even if they are subjected to harsh environmental conditions.

Hydrothermal aging behavior and effects on carbon fabric/polyphenylene sulfide composite

AbstractCarbon fabric/polyphenylene sulfide (CF/PPS) composite has been used in the aircraft industry, which might suffer moisture and high temperature in service, leading to degradation and even failure. Therefore, knowledge of hydrothermal aging behavior and effects is needed to ensure service life. This work explores the water diffusion behavior, crystallization, and interfacial properties of CF/PPS composite under hydrothermal aging in continuous 3 months and periodical cycles. Diffusion coefficients were calculated through the Fickian model, crystallization behaviors were measured through differential scanning calorimetry and polarized optical microscope, and interfacial properties were characterized by interfacial shear strength, and interlaminar shear strength. The results demonstrate the crystal morphology transforms from transverse crystals to spherulites at the CF/PPS interface after recrystallization through hydrothermal aging, revealing water has a significant impact on the nucleation performance of T300 carbon fiber in the PPS matrix. Hydrothermal aging affects the crystallinity and crystal morphology of CF/PPS composite after recrystallization, and impacts the micro and macro interfacial properties.Highlights Transverse crystals transform to spherulites at CF/PPS interface after water uptake. Water impacts on nucleation performance of T300 carbon fiber in PPS matrix. Hydrothermal aging effect can be accumulated and promotes water uptake. ILSS drop is related to water uptake content, crystallization and IFSS changes.

Multi-objective optimization study of hydrothermal aging on NOx-assisted soot catalytic combustion and secondary pollution emission in regeneration of CeO2 catalytic diesel particulate filter

The present study aimed to explore the effect of hydrothermal aging on the heterogeneous catalytic combustion process of soot in CeO2 catalytic diesel particular filter and the formation of secondary pollutants (N2O and CO).The present study was based on a fixed-bed experimental bench for NOx-assisted soot catalytic oxidation in CeO2-CDPF with different soot loading and catalyst coating amounts. A non-linear regression surrogate model and a multi-objective optimization decision approach were used to analyze the trade-off relationship between the design variables and the optimization objectives. The results showed that lower levels of soot loading (2.5 g/L), CeO2 catalyst coating amount (2.5 g/L) and higher NOx concentration (1000 ppm) in fresh catalysts were favorable for improving the performance of soot-assisted catalytic combustion and minimizing the formation of N2O and CO. However, it was observed that higher levels of catalyst coating amount (10 g/L) resulted in better soot catalytic combustion performance with lower N2O and CO emissions. Global sensitivity analysis showed a positive correlation between N2O and CO peak concentrations and peak temperatures with soot loading, but a negative correlation with catalyst loading. Over time, hydrothermal aging of CDPF caused the inhibitory effect of CeO2 catalyst on N2O to shift from negative to positive correlation, while also decreasing the synergistic performance of NOx in soot catalytic combustion.

Accelerated Zero-Stress Hydrothermal Aging of Dry E-Glass Fibers and Service Life Prediction Using Arrhenius Model

Comprehending the degradation of glass fibers is crucial for service applications involving dry and wet conditions, especially when prolonged contact with water above room temperature is present. Depending on the polymer material, both thermosetting and thermoplastic matrices can permit the ingress of moisture. Therefore, fiber reinforcements embedded in the polymer matrix may experience moisture exposure. Additionally, some structural applications use fiber devoid of any matrix (dry fibers), in which water exposure must be avoided. In all of these cases, moisture may, therefore, have a significant impact on the reinforcing elements and the rate of degradation. The present work focuses on the effects of hydrothermal aging on the mechanical durability of long E-glass fibers by immersion in water at 60 °C, 71 °C, and 82 °C. A service life forecast model was created utilizing the Arrhenius technique, and a master curve of strength variation with exposure time was created for E-glass fibers at 60 °C. Using this modeling approach, it is possible to approximate the amount of time it will take to attain a given degradation level over a specified range of temperatures. Scanning electron microscopy was used to evaluate morphological changes in fiber surfaces due to hydrothermal exposure, while Fourier transform infrared spectroscopy and mass dissolution studies were used to elucidate the mechanism of the strength loss.

An experimental study on the hydrothermal aging effect on the free vibration properties of hybrid aramid/glass/epoxy composites: Comparison of sea water and distilled water

AbstractThe purpose of this experimental work is to investigate the impact of hydrothermal aging on the viscoelastic characteristics of hybrid aramid/glass/epoxy composites. In addition to the hybrid composites prepared by vacuum infusion method in two different hybrid configurations ([G3A3]S, [A3G3]S) and two non‐hybrid composite groups ([G6]S, [A6]S) were included for comparison purposes. Composite samples were kept in 4 different aging environments (distilled water 25°C, distilled water 70°C, seawater 25°C, and seawater 70°C) for 6 weeks. To assess the dynamic properties (natural frequency and damping ratio) of composites, a free vibration test was conducted. The vibration test results of the samples were calculated by the half‐power bandwidth method. The results revealed that hydrothermal aging did not have serious effects on first‐mode natural frequency. It was observed that the damping ratios of hybrid composites increased after hydrothermal aging when compared with unaged samples. The results from dynamic aspects like the storage modulus and loss modulus were consistent among themselves. The parameters of the storage modulus and loss modulus have both decreased as a result of hydrothermal aging. In addition, the results proved that the rise in temperature accelerated the degradation in mechanically deteriorated composite materials. It was also found that aging in seawater was induced to more deterioration of hybrid and non‐hybrid composite materials.Highlights The order of the fabrics play an important role in free vibration properties of hybrid composites. Aging hybrid composites at different temperatures affects their free vibration properties. and values decreased more as the temperature increased. Hydrothermal aging has increased the dumping ratio values of composite materials.

Influence of shading on zirconia's phase transformation and flexural strength after artificial aging.

The aim of this study was to determine the phase transformation and the influence of aging on the flexural strength of different colored zirconia. The effect of hydrothermal aging in an autoclave was compared with the effect of mechanical stress by simulating chewing. High-strength zirconia (3Y-TZP) was investigated in three different colors: uncolored, A3, and D3. Disc-shaped specimens (N=3) were analyzed by X-ray diffraction (XRD), and flexural strength was determined on bar-shaped specimens (N=15) in a 4-point bending test before and after performing two different aging protocols: aging in an autoclave (134°C, 70h) and aging in a chewing simulator (5kg load, 1.2 million cycles). During autoclave aging, the fraction of monoclinic phase on the surface was determined every 5h. Once this exceeded 25vol%, aging of the bar specimens was stopped. While in the unstained group the mean value of the proportion of monoclinic phase already exceeded 25vol% after 30h in the autoclave, this was the case in both stained groups only after 70h. No measurable phase transformation could be detected after chewing simulation. Only color A3 showed a statistically significant (p≤0.05) decrease in flexural strength after aging in the chewing simulator. The colored zirconia showed a higher resistance to phase transformation through hydrothermal aging. The metal oxides in the staining solutions are assumed to hinder the phase transformation in the zirconia. Therefore, the significant reduction in the stained zirconia after chewing simulation is particularly interesting.