Multilayered Zirconia Research Articles

New multi-layered zirconias: Composition, microstructure and translucency

ObjectivesTo fully realize the range of indication and clinical advantages of the new multi-layered zirconias, a comprehensive understanding of their chemical composition, microstructure, low temperature degradation (LTD) resistance, and translucency properties is paramount. MethodsA zirconia system (Katana, Kuraray Noritake), including 3 distinct grades of multi-layered zirconias, was selected for study: Ultra Translucent Multi-layered zirconia (UTML), Super Translucent Multi-layered zirconia (STML), and Multi-layered zirconia (ML). For different materials and their individual layers, the chemical composition, zirconia phase fractions, and microstructure were determined by X-ray fluorescence (XRF), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). Also, their resistance to LTD and translucency properties were characterized. ResultsOur findings revealed no major differences amongst layers, but the 3 materials were very distinct―UTML: 5Y-PSZ (5 mol% yttria-partially-stabilized zirconia) with ˜75 wt% cubic content and a 4.05 (±0.85) μm average grain size, STML: 4Y-PSZ with ˜65 wt% cubic content and a 2.81 (±0.17) μm average grain size, and ML: 3Y-PSZ with <50 wt% cubic content and a 0.63 (±0.03) μm average grain size. After water aging at 120 °C for 12 h, greater monoclinic content was found in ML. UTML and STML did not show detectable monoclinic phase. The translucency was similar among layers, and also between UTML and STML, which were superior to ML. SignificanceFor each multi-layered zirconia grades, the layers are only differed in pigment types and contents, which yield remarkably natural shade gradients. Also, despite the significant compositional difference between STML and UTML, both materials showed similar translucencies.

Effect of different coloring liquids on the flexural strength of multilayered zirconia.

PURPOSEThe purpose of this study was to evaluate the effect of two coloring liquids (aqueous and acid-based coloring liquids) and the position of multilayered zirconia on the flexural strength of multilayered zirconia.MATERIALS AND METHODSThe multilayered zirconia specimens were divided into upper and lower positions. The specimens were divided into three subgroups (n=10): non-shaded, acid-based coloring liquid, and aqueous coloring liquid. The specimens were cut using a milling machine and were immersed in either a acid-based coloring liquid or aqueous coloring liquid 2 times for 5 seconds. The specimens were sintered in a sintering furnace according to the manufacturer's introduction. The flexural strength of the specimen was measured using a universal testing machine and the surface of the specimen was observed using a field emission scanning electron microscope.RESULTSThe flexural strength of multilayered zirconia was 400 – 500 MPa. There was no statistically significant difference among all groups (P>.05).The flexural strength of the multilayered zirconia was not influenced by the kind of coloring liquid used (P>.05). The flexural strength of the multilayered zirconia colored with the coloring liquids was not influenced by its position (P>.05).CONCLUSIONThe different coloring liquid application did not affect the flexural strength of multilayered zirconia of all positions.

İki Farklı Hızlı Sinterleme Protokolünün ve İki Farklı Yüzey İşleminin Çok-Katmanlı Monolitik Zirkonyanın Işık Geçirgenliği Üzerine Etkisi

İki Farklı Hızlı Sinterleme Protokolünün ve İki Farklı Yüzey İşleminin Çok-Katmanlı Monolitik Zirkonyanın Işık Geçirgenliği Üzerine Etkisi

Color agreement between try-in paste and resin cement: Effect of thickness and regions of ultra-translucent multilayered zirconia veneers.

Background. The current study aimed at identifying the color agreement between try-in pastes and the respective resin cements and investigated the effect of thickness and regions of Ultra-Translucent Multilayered Zirconia Veneers. Methods. A total of 90 cubic zirconia discs were prepared at two different thicknesses (0.5 mm and 0.7 mm) (n=45) in five groups in terms of the shade of the try-in paste and resin cement as follows: Universal, Clear, Brown, White and Opaque. Try-in paste and the respective resin cement were applied between the specimens and composite substrate, respectively, and colorimetric evaluation was carried out using CIE-Lab system. For each specimen, ΔE between the try-in paste and cement was calculated. Data were analyzed with SPSS 17 using Multifactor ANOVA (P<0.05). Results. Multifactor ANOVA results showed that ΔE values were significantly affected by the resin cement shade and the thickness of ceramic veneer (P<0.05). The results showed better shade agreement between the try-in paste and the respective resin cement with thicker ceramic veneers. The results of Tukey HSD revealed that ΔE values for the Clear, Universal and Brown shades were less than those of the White and Opaque shades. Lighter shades exhibited better agreement between the try-in paste and the respective resin cement. Conclusion. Perceptible color difference was found between the try-in pastes and the respective resin cement in most colors investigated. Although, the agreement of the try-in pastes and the respective resin cement was affected by the thickness of zirconia veneers, the different regions of multilayered ultra-translucent zirconia ceramic showed no significant effect.

Computable translucency as a function of thickness in a multi-layered zirconia

Statement of problemDetermining the relationship between variable thicknesses and the translucency of dental ceramics is essential for optimizing esthetics in different clinical situations. PurposeThe purpose of this in vitro study was to analyze the relationship between layer thickness and translucency of 2 multi-layered monolithic zirconia materials and to develop an equation by which the grade of translucency can be calculated dependent on the materials' layer thicknesses in advance. Material and methodsTwo semisintered multi-layered zirconia blanks, namely KATANA Zirconia Super Translucent Multi-Layered Disk (Noritake Dental Supply Co, Ltd) and Zirconia Ultra Translucent Multi-Layered Disk (UTML) (Noritake Dental Supply Co, Ltd), were sectioned (N=96) to separate the 4 layers (n=12 per layer): enamel layer, transition layer 1, transition layer 2, body layer. All specimens were sintered in a furnace (M2 Plus; Thermo-Star) at 1500°C for 2 hours and automatically polished under water cooling up to P2400 for the thicknesses of 1.6, 1.3, 1.0, 0.7, and 0.4 mm. Transmittance of visible light was measured using a spectrophotometer (Lambda 35; Perkin Elmer). Data were analyzed using the Kolmogorov-Smirnov, 2-way ANOVA, and Scheffé post hoc tests (α=.01) and curve fitting. ResultsAnalyzing the fitting of the values of the 8 material groups to the linear, exponential, and logarithmic curves, 7 of the 8 groups (not UTML body layer) fitted the most (R-square value closer to 1.0) to the logarithmic curve. Constants were obtained from the distance to the x-axis and the curvature. ConclusionsThe methodology of this study provided the materials' specific constants a and b by analyzing the translucency behavior of KATANA Super Translucent Multi-Layered Disk and Ultra Translucent Multi-Layered Disk in different thicknesses, allowing further translucency calculation by applying the developed formula and the constants.

EVALUATION OF BIAXIAL FLEXURAL STRENGTH AND TRANSLUCENCY OF MULTICHROMATIC TRANSLUCENT ZIRCONIA AND LITHIUM DISILICATE CERAMICS

INTRODUCTION: Full-contour (monolithic) zirconia restorations are gaining in popularity. High translucent zirconia materials and multilayered zirconia blocks might help to overcome the aesthetic drawbacks of traditional zirconia for fabrication of monolithic restorations OBJECTIVES: Were to evaluate the biaxial flexural strength and translucency of CAD/CAM: multichromatic ultra-translucent zirconia and comparing it with multichromatic high translucency Lithium Disilicate glass-ceramic. MATERIALS AND METHODS40 ceramic specimens were divided into two main groups; Group I: CAD/CAM multichromatic ultratranslucent Zirconia( UTML KATANA Zirconia) & Group II: Pressable multichromatic high translucent Lithium Disilicate glass-ceramic (e.max press multi). Each group was subdivided into two sub groups; sub group A: disc specimens (12mm diameter×1.5mm thickness) were fabricated (n=10) & thermocycled (500 cycles, 5°/55°C, 15 sec dwell time).Then, biaxial flexural strength was measured in MPa. Sub group B: rectangular specimens (12mm length × 10mm width × 1.5mm thickness) were fabricated (n=10). Spectrophotometric analysis was conducted to evaluate and compare the degree of translucency by translucency parameter (TP). Data were analyzed using student t-test & ANOVA with repeated measures test. RESULTS Statistical analysis of Biaxial flexural strength using student t-test revealed that group I (607.24 ± 71.79) showed higher statistically significant biaxial flexural strength values than group II (290.69 ± 41.19) ( p <0.001*). Results of translucency revealed that there were significant statistical differences between the two subgroups where IPS e.max Press Multi provided better translucency than UTML KATANA zirconia. CONCLUSIONS: Multi layered zirconia showed higher mechanical, but lower optical properties than lithium disilicate. The multi layered zirconia showed four layers with different light transmittance capabilities. It might therefore be useful for enhancing the aesthetic appearance of full-contour zirconia restorations made from this material in stress bearing areas.

Translucency of IPS e.max and cubic zirconia monolithic crowns

Statement of problemAlthough several monolithic zirconia ceramics have recently been introduced, the need for improved optical properties remains. The newest cubic-zirconia has been claimed to have optimal translucency characteristics for esthetic restorations. PurposeThis in vitro study evaluated the optical properties of novel cubic ultratranslucent (UT) and supertranslucent (ST) zirconia by comparing them with lithium disilicate (L-DIS) glass-ceramic for the manufacture of monolithic computer-aided design and computer-aided manufacturing (CAD-CAM) molar crowns. Material and methodsThe UT and ST multilayered zirconia and the low-translucency grade L-DIS were milled. Eighty monolithic crowns were made from 2 CAD files, corresponding to thicknesses of 1.0 and 1.5 mm, and subdivided (n=20) into 4 groups: UT1.0, UT1.5, ST1.0, and L-DIS1.5. All groups were shaded using A2 color standard. Translucency of the crowns was measured by total transmission, using a photoradiometer in a dark chamber; furthermore, the contrast ratio was analyzed using a dental spectrophotometer applied to the buccal surface of the crowns. Data were analyzed using the Kruskal-Wallis and post hoc multiple Mann-Whitney U tests with Bonferroni correction (α=.05 divided by the number of tests performed in each set). ResultsWhen the ceramic types were analyzed, using total transmission and contrast methods, they showed significantly different translucency levels: UT1.0>ST1.0>UT1.5>L-DIS1.5 (total transmission P<.001). Contrast ratio evaluation yielded similar results (P≤.006); however, the differences between ST1.0 and UT1.5 were not significant. ConclusionsBoth the ST1.0 and UT1.0 crowns, even at the maximum thickness tested (UT1.5), showed significantly higher translucency than L-DIS. Zirconia translucency was improved by eliminating the tetragonal phase, which is responsible for the toughening effect; thus, further studies are advocated to investigate the mechanical resistance of cubic zirconia.

Optical and Mechanical Properties of Newly Developed Monolithic Multilayer Zirconia.

To evaluate the optical and mechanical properties of newly introduced monolithic multilayer zirconia with two types of monolithic zirconia. Three brands of monolithic zirconia were used in this study: Ceramill Zolid FX Multilayer (CZF), Prettau Anterior (PA), and Zenostar T (ZT). Translucency parameter (TP), contrast ratio (CR), flexural strength, fracture toughness, hardness, brittleness index, and microstructures were assessed. Data were analyzed using one-way ANOVA and Tukey's test. The statistical significance was set at p < 0.05. A Weibull analysis was conducted on the flexural strength data. CZF revealed significantly higher TP and lower CR compared with PA and ZT monolithic zirconia (p < 0.05). ZT showed higher flexural strength and fracture toughness compared with CZF and PA (p < 0.001). On the other hand, CZF revealed significantly higher hardness values compared with PA and ZT (p < 0.001). CZF and PA revealed higher brittleness index than ZT monolithic zirconia (p < 0.001). ZT showed small grain microstructure while CZF and PA showed larger grains. ZT had a higher characteristic strength (σ0 ), Weibull modulus (m), and a lower probability of failure compared with CZF and PA. The optical and mechanical properties of the tested monolithic zirconia are material dependent. Fully stabilized monolithic zirconia materials (CZF and PA) are relatively more translucent than partially stabilized zirconia (ZT).

Low temperature degradation of single layers of multilayered zirconia in comparison to conventional unshaded zirconia: Phase transformation and flexural strength.

The aim of this study was to evaluate the transformation of yttrium stabilized tetragonal zirconia (Y-TZP) to monoclinic phase and its change in flexural strength of the various layers of multilayered zirconia (enamel layer, transition layer 1, transition layer 2 and body layer) in comparison to two conventional zirconia ceramics. Additionally, the ball-on-three-balls test was compared with a conventional biaxial flexural strength test. The crystallographic structure of the four layers of Katana Zirconia ML (Kuraray), e.max ZirCAD (Ivoclar Vivadent) and Lava Plus (3M ESPE) was investigated by x-ray-diffraction before and after hydrothermal aging in an autoclave for 5, 10, 15 and 20h. The biaxial flexural strength was examined with a piston-on-three-ball test and a ball-on-three-balls test. There was a significant difference of the ratio of transformation with respect to the tested materials, also between the four different layers of multilayered zirconia. After 20h of hydrothermal aging the mean ratio of monoclinic phase ranged from 9.9vol% (LAVA Plus) to 44.2vol% (Katana Zirconia ML, enamel layer). However, hydrothermal aging had no significant influence on the flexural strength of any material. Furthermore, the flexural strength measured by the ball-on-three-balls test was higher than that measured by the piston-on-three-ball test. A ratio of 40% monoclinic phase at the surface did not significantly influence the biaxial flexural strength. Both test methods provide reliable results. However, as the ball-on-three balls test is less dependent on surface roughness, it might be preferred for investigations adapted to clinical reality.

Relative Translucency of a Multilayered Ultratranslucent Zirconia Material.

The aim of this study was to compare the translucency parameter (TP) of ultratranslucent multilayered (UTML) zirconia according to thickness and layer level. Rectangles of UTML zirconia with four layers [dentin layer (DEL), first transitional layer (FTL), second transitional layer (STL), and enamel layer (ENL)] and four different thicknesses (0.4, 0.6, 0.8, and 1 mm) were milled from blanks. Digital images were taken in a dark studio against white and black backgrounds under simulated daylight illumination and international commission on illumination (CIE) Lab* color values recorded using Photoshop Creative Cloud software. The TP was computed and compared according to thickness and layer level using analysis of variance (ANOVA) followed by Bonferroni post hoc analysis for multiple comparisons. Significance was set at p < 0.05. In each thickness, TP values were similar between any two layers. The significant effect of thickness on the TP was observed only in the first two layers. In the DEL, translucency was significantly greater at 0.4 mm than all other thicknesses. In the FTL, differences were significant between 0.4 and 0.8 mm and between 0.4 and 1 mm. The investigated zirconia does not seem to show gradational changes in relative translucency from dentin to enamel levels regardless of the thickness used. Thickness affected the TP only in the first two layers with better translu-cency at 0.4 mm. Since relative translucency does not seem to be significantly different between layers, clinicians can modify the apicocoronal positioning of the UTML layers within the restoration according to the desired Chroma without any implications on the clinically perceived translucency. While the thickness of 0.4 mm may be suggested for anterior esthetic veneers because of its higher translucency, the other thicknesses of 0.6 to 1 mm can be used to mask colored abutments in full contour restorations.

Yüzey İşlemi Yapılan Zirkonya Kaideli Çok Tabakalı CAD/CAM Seramik Kronların Kırılma Dayanıklılığı

Objective: The purpose of this study was to evaluate the effect of different surface treatments on the fracture strength of veneered zirconia crowns designed by multilayer technique. Material and Methods: Thirty zirconia cores (Sirona inCoris ZI) were constructed (inLab 4.4) on metal dies. Zirconia cores were divided into three groups: sandblasting with 30 ìm silica-coated aluminum oxide particles (Group C), sandblasting with 50 ìm aluminum oxide particles (Group K) and sandblasting with 50 ìm aluminum oxide particles then silica coating with Silano-Pen (Group KS). Thirty feldsphatic ceramic (VITABLOCS Mark II) veneers were fabricated (inLab 4.4). Veneers were cemented to the cores. Crowns were cemented to the metal dies. A universal test machine was used for the fracture strength test at a crosshead speed of 1 mm/min. The data were analyzed with one-way ANOVA (á=0.05). Results: Surface pre-treatment methods affected the fracture strength (p<0.05). Higher fracture strengths were obtained in Group KS (p<0.05). No significant differences were found between Group K and Group C (p>0.05). Conclusion: Although Group K and C showed lower flexural strength, it was higher than the maximum loads which may occur clinically (Fmax=600N on one tooth). Also, Silano-Pen application is advisable for increasing the fracture strength. Clinical Relevance: The multilayer zirconia crowns can be applied successfully, especially in single-crown restorations.

Electrophoretic deposition of multilayered (cubic and tetragonal stabilized) zirconia ceramics for adapted crack deflection

The electrophoretic deposition process was used to produce multi-layered ceramics consisting of alternating layers of fully stabilized cubic zirconia and partially stabilized tetragonal zirconia to make use of their different mechanical behaviour, investigating the possibility to deflect advancing cracks at the interfaces of the different layers. This crack deflection is apparently impacted by a toughening mechanism only found in the tetragonal stabilized zirconia polymorph and is characterized by the stress induced transformation of the metastable tetragonal phase into the monoclinic one, which is accompanied by a volume increase resulting in a closing mechanism for advancing cracks.While improving the electrophoretic deposition process, we investigated the transformation toughening mechanism at the layer interfaces and their effect on crack propagation. Investigations involved a combination of different imaging methods, including light microscopy, white light interferometry, atomic force microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and Raman spectroscopy.

A Passive Pressure Sensor Fabricated by Post-Fire Metallization on Zirconia Ceramic for High-Temperature Applications

A high-temperature pressure sensor realized by the post-fire metallization on zirconia ceramic is presented. The pressure signal can be read out wirelessly through the magnetic coupling between the reader antenna and the sensor due to that the sensor is equivalent to an inductive-capacitive (LC) resonance circuit which has a pressure-sensitive resonance frequency. Considering the excellent mechanical properties in high-temperature environment, multilayered zirconia ceramic tapes were used to fabricate the pressure-sensitive structure. Owing to its low resistivity, sliver paste was chosen to form the electrical circuit via post-fire metallization, thereby enhancing the quality factor compared to sensors fabricated by cofiring with a high-melting-point metal such as platinum, tungsten or manganese. The design, fabrication, and experiments are demonstrated and discussed in detail. Experimental results showed that the sensor can operate at 600 °C with quite good coupling. Furthermore, the average sensitivity is as high as 790 kHz/bar within the measurement range between 0 and 1 Bar.

Study of spin coated multilayer zirconia and silica films for non-quarterwavelength optical design based antireflection effect at 1,054 nm

A non-quarterwavelength optical design (design wavelength, λo = 1,054 nm) based antireflection (AR) coating was prepared by sol–gel spin coating technique. Two materials, zirconia and silica were chosen for the deposition of AR layers on borosilicate crown glass, refractive index (R. I. = 1.51). For this design, the bottom and middle layers were of zirconia with the R. I. range 1.941–1.958 while the top layer was of silica with R. I. 1.455. To understand the surface feature after each deposition, refractive index and physical thickness of the layers were measured ellipsometrically (λ = 632.8 nm) at different points over the area, 10 mm × 10 mm with an interval of 0.5 mm along the centre based perpendicular projection made on an imaginary chord. The surface feature was examined by plotting the measured values of the optical parameters against the displacement. The surface roughness decreased with increasing layers. This was verified by the study of AFM images of the layers. Specular reflection of the antireflection coated product at λ0 was comparable to that of the theoretically simulated curve.

Preparation and Humidity Sensitivity of Multi-Layered Zirconia Thin Films by Sol–Gel Method

Multi-layered zirconia (ZrO2 thin film on the Pt/Ti/SiO2/Si substrate has been prepared as humidity sensing material by sol–gel method. Annealing temperature was 450 C. A TiO2 thin film was added in between ZrO2 film and the substrate for improving the adhesion. The films were characterized by using X-ray diffraction (XRD), atomic force microscope (AFM) and Fourier-transform infrared (FT-IR) spectra. The impedance of the humidity sensor changes about four orders of magnitude within the relative humidity (RH) range of 11–98%, indicating a good sensitivity. The response time of the sensor was about 5 s. The humidity sensing mechanism was discussed by means of the complex impedance curves and an equivalent circuit of the sensor.

Characterization of zirconia modified porous stainless steel supports for Pd membranes

A thin well-bonded zirconia film was formed on a porous stainless steel support by a sol-gel dip-coating method followed by firing in hydrogen atmosphere. The zirconia layer has a cubic phase structure. The surface composition of the film was analyzed by X-ray photoelectron spectroscopy. A comparison between H2-fired and air-fired samples indicated that the surface/interface composition of the sample fired in air was rich in Fe2O3, whereas that of the fired in H2 contained more metastable cubic zirconia phase and spinel type iron chromate. Binding energy shifts of Zr and Fe in the mixed oxides, together with the presence of iron and chromium oxides suggests that interfacial reaction between the coating and the substrate occurred, which is favorable for a good adhesion of the layers. The average pore size of the support modified by multilayer zirconia coatings declined drastically from original 2 μm to the coated top-layer 0.4 μm. The ZrO2 film showed a hydrogen selectivity of 2.7 for H2/N2, and a hydrogen flux of 1.159 × 10−3 mol/m2.s at room temperature and with a pressure difference of 101 kPa across the film.

Multi-layered adsorption of 3Y–ZrO 2 nanoparticles on polystyrene microsphere

Multi-layered adsorption of 3Y–ZrO 2 nanoparticles on polystyrene (PS) microsphere using layer-by-layer (LBL) assembly technique was investigated. By employing sodium poly (acrylic acid) (PAANa) and polyethylenimine (PEI) to modify the zeta potential of the powders, the heterocoagulation takes place between the coating powders and microspheres substrate and the zirconia coating on the surface of polystyrene spheres was successfully formed. Dense, uniform multi-layered zirconia can be obtained on the surface of polystyrene spheres and the thickness of zirconia coating increased by repeating the coating process. The diameter of the spheres expands to 1.5 μm after the first coating and 1.65 μm after the third coating comparing with the original polystyrene spheres with diameter of 1.4 μm.

Layer-by-layer self-assembly of multilayer zirconia nanoparticles on silica spheres for HPLC packings.

A novel zirconia-based HPLC packing material, ZrO2/SiO2, which consists of micrometer-sized silica spheres as core and nanometer-sized zirconia particles as surface coating, was prepared by a layer-by-layer self-assembly technique. The material exhibits favorable characteristics for HPLC applications, including high surface area and pore volume, good pore structure, narrow particle size, and pore size distribution. Not only the support ZrO2/SiO2 but also the stationary-phase C18 bonded ZrO2/SiO2 exhibits excellent chemical stability. In addition, good permeability was observed for both of them. High specific area surface and good permeability of ZrO2/SiO2 permit a high loading amount of chiral polymer on it and greatly improved the enantioselectivity and resolution for some chiral separations.

Thermal conductivity and phase evolution of plasma-sprayed multilayer coatings

Multilayer coatings were prepared using small-particle plasma spray to investigate the effect of interfaces on thermal conductivity and phase stability. Monolithic and multilayer alumina and yttria partially-stabilized zirconia coatings, with 0, 3, 20, and 40 interfaces in 200–380 μm thick coatings were studied. Thermal conductivity was determined for the temperature range 25 °C to 1200 °C using the laser flash method and differential scanning calorimetry. Thermal conductivity of the multilayer coatings was accurately modeled by a series heat transfer equation, indicating that interfacial resistance plays a negligible role in heat transfer in the direction perpendicular to the coating plane. Powder X-ray diffraction results indicate that identical phase transitions occur in all the coatings. Independent of coating microstructure (i.e. layer thickness), as-sprayed γ-Al_2O_3 transforms to α-Al_2O_3 after 100 hours at 1200°C; as-sprayed metastable t′–ZrO_2 converts to a mixture of t–ZrO_2 and c–ZrO_2 after 100 hours at 1300 °C. Thus, the results indicate that the interfaces do not aid in stabilizing the as-sprayed phases after prolonged severe heat treatments.

Temperature Distribution in a Composite of Opaque and Semitransparent Spectral Layers

The analysis of radiative transfer becomes computationally complex for a composite when there are multiple layers and multiple spectral bands. A convenient analytical method is developed for combined radiation and conduction in a composite of alternating semitransparent and opaque layers. The semi- transparent layers absorb, scatter, and emit radiation, and spectral properties with large scattering are included. The two-flux method is used, and its applicability is verified by comparison with a basic solution in the literature. The differential equation in the two-flux method Is solved by deriving a Green's function. The solution technique is applied to analyze radiation effects in a multilayer zirconia thermal barrier coating with internal radiation shields for conditions in an aircraft engine combustor. The zirconia radiative properties are modeled by two spectral bands. Thin opaque layers within the coating are used to decrease radiant transmission that can degrade the zirconia insulating ability. With radiation shields, the temperature distributions more closely approach the opaque limit that provides the lowest metal wall temperatures.