Green Body Samples Research Articles

Sample selection for models to represent ceramic cores fabricated by stereolithography three-dimensional printing

In this study, ceramic cores were fabricated by stereolithography three-dimensional printing (SLA-3DP) with excellent synthetic mechanical properties. To this end, green body samples were first three-dimensionally printed in three models, after which the samples were sintered at different temperatures. High-temperature flexural strengths of the ceramic core samples printed in model 2 reached a maximum value of 24.2 MPa at a sintering temperature of 1250 °C during casting heat test at 1550°C. Meanwhile, the high- and room-temperature flexural strengths of ceramic core samples printed in model 2 were much stronger than those printed in models 1 and 3. Moreover, shrinkage, porosities, bulk densities and phase compositions of ceramic core samples printed in three models at different sintering temperatures did not show obvious differences. The ceramic core samples showed distinct mechanical properties as they had different fracture modes. We call this the “surface effect”. The anisotropy flexural strength was induced by weak binding between layers. The recommended choice of sample for different models to represent ceramic cores fabricated by stereolithography three-dimensional printing is model 2. Herein, based on the results of systematic characterization of high-throughput samples, we report the basic research, evaluation and prediction system of composition design, process optimization, microstructure and property defect analysis of ceramic cores made of SLA-3DP.

Defect control in digital light processing of high-solid-loading ceramic core

In order to investigate the defect control mechanism and the optimal cure parameter window, high-solid-loading ceramic-core green-body samples were fabricated by digital light processing (DLP) with different cure parameters. The defects appearing on the sample surface were observed. The causes of the wrong-cured zone and the propagation mechanism of UV light in the ceramic suspension were explained. The effect of different cure parameters on the printed structure of single- and multi-layer samples was investigated. The results showed that the single-layer sample had excellent cure accuracy, and the step effect was significantly reduced in the multi-layer samples at the exposure energy density of 6–8 mW/cm2 and the exposure time of 2.5–3.5s. Based on the systematic observation of the sample structure, a system for prediction, evaluation, and process optimization of defects in ceramic-core green-body samples was proposed.

Progress towards wafer-scale fabrication based on gel casting technique for 1–3 randomised piezocomposite μUS linear array

Microultrasound (μUS) linear arrays operating at frequencies over 25 MHz have applications in high resolution biomedical imaging. 1–3 connectively piezoceramic – polymer composite (“piezocomposite”) material is attractive for fabrication of these devices due to its high effective electromechanical coupling coefficient and low acoustic impedance for better acoustic matching between transducer and tissue. However, a major concern with this type of material comes from interference between the fundamental thickness-mode resonance and spurious modes, which is usually generated by wave propagation and reflection within the repetitive and symmetrical structure of classical piezocomposite. In general, a fine spatial scale is required of the material structure to suppress the spurious modes; however, the fabrication process is challenging using standard dice-and-fill methods at the fine scales required for high frequencies. A promising way to overcome this challenge is to manipulate the lateral geometry and spacing of the piezoceramic pillars with a random distribution. In this work, gel casting in association with a micromoulding technique has been developed for manufacturing 1–3 randomised piezocomposite active material for μUS linear arrays. 48 vol% solid loading of piezoceramic powder with 30 wt% Hydantoin resin content was employed to prepare a low viscosity aqueous suspension. Through varying powder size, it was found that the suspension with 1.22 µm powder had the highest viscosity, ~ 0.47 Pa.s, and a short gelation time, ~ 10 mins. However, all suspensions had viscosities less than 1 Pa.s at a shear rate of 100 s−1, indicating that they had good flowability. The green body samples showed mean flexural strength 49.7 ± 2.49 MPa. After piezocomposite fabrication with randomised pillars, surface planarisation was used to obtain reliable edge definition of photolithographically-defined electrodes. 20-element arrays with 50-μm element pitch were configured using a bilayer lift-off process. The 1–3 randomised piezocomposite demonstrated its capability to minimise the effects of spurious modes in the thickness mode frequency range, while the thickness resonances provided k33 = 0.67. Without a matching layer, the array produced a − 6 dB bandwidth of 38.4%- and − 20-dB pulse length of 0.26 μs. These results show that 1–3 randomised piezocomposite fabricated from gel-casting associated with a micromoulding technique is feasible for fabrication of μUS linear arrays and may offer a route to small wafer-scale production.

Fabrication of Zirconia/ 304 Stainless Steel Functionally Graded Materials Using Centrifugal Slurry Methods and Spark Plasma Sintering

Functionally graded materials (FGMs) are multi-phase composites to be engineered with gradual spatial variations of constituents. Centrifugal techniques enable to have a continuous gradient manner in FGMs. In this study, zirconia (ZrO2)/ 304 stainless steel (SUS304) FGMs were fabricated using centrifugal slurry methods with powders of ZrO2 and SUS304 mixed with a dispersant, ammonium polycarboxylic acid (PCA). The green body samples produced by centrifugal techniques were consolidated using spark plasma sintering (SPS). The fabricated samples were investigated on their microstructures and contents using scanning electron microscope (SEM) with EDX and micro Vickers and nanoindentation hardness. The results demonstrated that controlling of the continuous gradient were possibly achieved using the combination of the current techniques.

Nanoscale physico-mechanical properties of an aging resistant ZTA composite

ObjectiveTo characterize the effects of aging on the nanomechanical properties and 3D surface topographical parameters of an experimental Zirconia Toughened Alumina (ZTA) composite compared to its respective individual counterpart materials. MethodsDisk-shaped specimens comprised of three material groups were processed: 1) ZTA 70/30 (70% alumina reinforced with 30% second-generation 3Y-TZP); 2) Zpex (Second-generation 3Y-TZP), and; 3) Al2O3 (High purity Alumina) (n = 10/material, 12 × 1 mm). After synthesis, ceramic powders were pressed, the green-body samples were sintered and polished. Nanoindentation testing was performed to record elastic modulus (E) and hardness (H). Interferometry was utilized to assess 3D surface roughness parameters (Sa, Sq), while X-ray diffraction (XRD) and scanning electron microscope (SEM) assessed the crystalline content and microstructure. All tests were performed before and after simulated aging (134°C, 2.2 bar, 20 h). Statistical analyses were performed using linear mixed-model and least square difference pos-hoc tests (α = 5%). ResultsXRD spectra indicated increase of monoclinic peaks for Zpex (~18%) relative to ZTA 70/30 (~2.5%) after aging. Additionally, aging did not affect the surface roughness parameters of ZTA 70/30 and Al2O3, although a significant increase in Sa was recorded for Zpex following aging (~90 nm) (p < 0.001). Al2O3 yielded the highest H and E values (H:21 GPa, E: 254 GPa), followed by ZTA 70/30 (H: 13 GPa, E: 214 GPa) and Zpex (H:11 GPa, E: 167 GPa), all significantly different (p < 0.03). ConclusionZTA 70/30 and Al2O3 presented high hydrothermal stability with respect to all evaluated variables, where artificial aging significantly increased the monoclinic content and surface roughness of Zpex.

Copper additive manufacturing using MIM feedstock: adjustment of printing, debinding, and sintering parameters for processing dense and defectless parts

In the present study, an additive manufacturing process of copper using extrusion 3D printing, solvent and thermal debinding, and sintering was explored. Extrusion 3D printing of metal injection moulding (MIM) feedstock was used to fabricate green body samples. The printing process was performed with optimized parameters to achieve high green density and low surface roughness. To remove water-soluble polymer, the green body was immersed in water for solvent debinding. The interconnected voids formed during solvent debinding were favorable for removing the backbone polymer from the brown body during thermal debinding. Thermal debinding was performed up to 500 °C, and ~ 6.5% total weight loss of the green sample was estimated. Finally, sintering of the thermally debinded samples was performed at 950, 1000, 1030, and 1050°C. The highest sintering temperature provided the highest relative density (94.5%) and isotropic shrinkage. Micro-computed tomography (μCT) examination was performed on green samples and sintered samples, and qualitative and quantitative analysis of the porosity confirmed the benefits of optimized printing conditions for the final microstructure. This work opens up the opportunity for 3D printing and sintering to produce pure copper components with complicated shapes and high density, utilizing raw MIM feedstock as the starting material.

The Relationship between the Flow Properties of Clay Slurry Samples and the Properties of Ceramic Green/Sintered Products

This study investigated the effects of various dispersants (Dolapix PC-67, Dolapix SPC 7, Darvan CN, Darvan A821 and Na2SiO3) on the flow properties of slurry prepared using ESC-3 clay to find the optimum dispersant type and dispersant dosage to produce the required properties in green and sintered products produced by slip casting. By considering the flow curves of slurry, it was determined that the most suitable dispersant was Dolapix PC-67 and the dosage was ~0.1%. Afterwards, slurry was prepared in bar-shaped samples keeping the same experimental conditions and using Dolapix PC-67 dosages of 0, 0.03, 0.1 and 1.0 wt. %. The resulting green body samples were dried and sintered at 1200°C. Some physico-mechanical tests were applied to both the green and sintered samples, as well as investigating their microstructure, crystallinity and secondary phase formations using SEM and XRD. Some of the results obtained were as follows: (i) adding dispersant to the slurry had a positive effect on the physical and mechanical properties of the green and sintered products obtained by slip casting. (ii) Determination of the optimum dispersant dosage used in the ceramic slurry by slip casting is an important factor. When the properties of the green/final products and their flow curves measured by Ford cup were considered, it can be said that the dispersant dosage at which the shortest flow duration was obtained did not always correspond to the best results for the physico-mechanical properties of green/final products. (iii) The relationship between the green and sintered samples prepared from slip casting using different dispersant dosages, and the flow curves of these slips, could not be observed from their SEM images.

Evolution of SLA-Based Al2O3 Microstructure During Additive Manufacturing Process.

Evolution of additively manufactured (AM) ceramics’ microstructure between manufacturing stages is a hardly explored topic. These data are of high demand for advanced numerical modeling. In this work, 3D microstructural models of Al2O3 greenbody, brownbody and sintered material are presented and analyzed, for ceramic samples manufactured with SLA-based AM workflow, using a commercially available ceramic paste and 3D printer. The novel data, acquired at the micro- and mesoscale, using Computed Tomography (CT), Scanning Electron Microscopy (SEM) and Focused Ion-Beam SEM (FIB/SEM) techniques, allowed a deep insight into additive ceramics characteristics. We demonstrated the spatial 3D distribution of ceramic particles, an organic binder and pores at every stage of AM workflow. The porosity of greenbody samples (1.6%), brownbody samples (37.3%) and sintered material (4.9%) are analyzed. Pore distribution and possible originating mechanisms are discussed. The location and shape of pores and ceramic particles are indicative of specific physical processes driving the ceramics manufacturing. We will use the presented microstructural 3D models as input and verification data for advanced numerical simulations developed in the project.

Optical method for evaluation of shrinkage in two dimensions during drying of ceramic green bodies

The evolution of shrinkage and mass during drying of kaolin and alumina green bodies was characterized. Standard practise uses a position sensor with simultaneous mass measurement. In this work an optical method was developed to follow shrinkage in two orthogonal directions. Green body samples were made by pressing of ceramic pastes. Results have been compared through the well known Bigot curves which show two distinct stages. First a linear shrinkage with the evaporated water loss is observed. Then in the second stage with further water loss, negligible dimension changes occur. For each material, the overall shrinkage values are identical in the two directions parallel to the pressing axis, but higher in the pressing direction. This difference is related to the shaping method yielding a preferential orientation of grains. Anisotropy in shrinkage is more significant for kaolin with tabular shaped grains compared to the more isometric grains of alumina.

Aging resistant ZTA composite for dental applications: Microstructural, optical and mechanical characterization

ObjectiveTo synthesize a zirconia toughened alumina (ZTA) composite with 70% alumina reinforced by 30% zirconia for dental applications and to characterize its microstructure and optical properties for comparison with the isolated counterpart materials and a first-generation 3Y-TZP. MethodsDisc-shaped specimens were divided in four groups (n = 70/material): (1) 3YSB-E (first generation 3Y-TZP), (2) Zpex (second generation 3Y-TZP), (3) alumina, and (4) ZTA-Zpex 70/30. After synthesis, ceramic powders were pressed, and green-body samples sintered following a predetermined protocol. Specimens were polished to obtain a mirror surface finish. Apparent density was measured by Archimedes principle. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the crystalline content and microstructure. Reflectance tests were performed to determine the contrast-ratio (CR) and translucency-parameter (TP). Mechanical properties were assessed by biaxial flexural strength (BFS) test. All analyses were conducted before and after artificial aging (20 h, 134 °C, 2.2 bar). Optical parameters were evaluated through repeated-measures analysis of variance and Tukey tests (p < 0.05). BFS data were analyzed using Weibull statistics (95% CI). ResultsHigh density values (95–99%) were found for all ceramic materials and SEM images exhibited a dense microstructure. While XRD patterns revealed the preservation of crystalline content in the ZTA composite, an increase in the monoclinic peak was observed for pure zirconias after aging. Significantly higher CR and lower TP values were observed for the ZTA composite, followed by alumina, 3YSB-E, and Zpex. The highest characteristic stress was recorded for 3YSB-E, followed by intermediate values between ZTA and Zpex, and the lowest for alumina. Aging affected the optical and mechanical properties of both zirconias, while remained stable for ZTA composite and alumina. SignificanceThe synthesis of experimental 70−30% ZTA composite was successful and its relevance for dental applications relies on its higher masking ability, aging resistance, and strength similar to zirconia.

Wideband frequency tunability of CaCu3Ti4O12‐based dielectric resonator antennas via the addition of glass

AbstractIn this study, DRAs produced using CaCu3Ti4O12 (CCTO) as a high dielectric material (εr) was added with BaO–SrO–Nb2O5–B2O3–SiO2 (BSNBS) glass for possible tunability in a wideband frequency range. BSNBS glass (0.01‐1 wt%) was mixed with CCTO powders (calcined) and compacted at 250 MPa into mixed‐powder pellets. All the green body samples were then sintered at 1040°C for 10 hours. The wideband frequency tunability, measured using a network analyzer, showed that the addition of ≤0.05 wt% BSNBS glass decreased the resonance frequency from 9.51 to 9.33 GHz; later, the values increased to 9.89 GHz when BSNBS content was &gt; 0.05 wt%. The εr of each sample was around 11‐36 when measured at 9.5‐11.8 GHz. The radiation pattern of CCTO for each sample that had been set up as a DRA radiated the signal equally or nearly identical to each other. Furthermore, the addition of BSNBS glass produced micrographs with finer grains, improved the density and reduced the porosity of the composite. Therefore, the addition of the BSNBS glass is a successful aid in the wideband frequency tunability of pure CCTO‐based ceramics when used as DRAs.

Aligning α‐alumina platelets via uniaxial pressing of ceramic‐filled polymer blends for improved sintered transparency

AbstractUniaxial warm pressing was used to align alumina platelet‐filled polyethylene‐based copolymer blends. The solids loading (30‐40 vol.%) and platelet diameter (1.2 and 11 μm) were varied to compare effects on viscosity, percent reduction, and final alignment. All ceramic‐filled thermoplastic polymer blends exhibited pseudoplastic behavior. Crystallographic alignment of green body samples was quantified by the orientation parameter (r) and grain misalignment angle (full width at half maximum, FWHM) obtained from rocking curve analysis. Blends with 11 μm diameter platelets displayed a higher temperature sensitivity constant, better flow properties, and higher alignment compared to blends with 1.2 μm diameter platelets. Optimal samples produced with blends containing 30 vol.% of 11 μm diameter platelets demonstrated an alignment of r = .251 ± .017; FWHM = 11.16° ± 1.16°. A sample with optimal alignment was hot‐pressed to transparency and obtained an in‐line transmission of 70.0% at 645 nm. The final alignment of this pre‐aligned hot‐pressed sample (r = .254 ± .008; FWHM = 11.38° ± 0.54°) improved when compared to a non‐pre‐aligned sample (r = .283 ± .005; FWHM = 13.40° ± 0.38°).

Aging resistance of an experimental zirconia-toughened alumina composite for large span dental prostheses: Optical and mechanical characterization

PurposeTo synthesize a zirconia-toughened alumina (ZTA) composite with 85% alumina matrix reinforced by 15% zirconia and to characterize its optical and mechanical properties before and after artificial aging, to be compared with a conventional dental zirconia (3Y-TZP). Material and methodsAfter syntheses, ZTA and 3Y-TZP powders were uniaxially and isostatically pressed. Green-body samples were sintered and polished to obtain 80 disc-shaped specimens per group (12 × 1 mm, ISO 6872:2015). The crystalline content and microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Optical properties were determined by the calculation of contrast ratio (CR) and translucency parameter (TP) using reflectance data. Mechanical properties were assessed by Vickers hardness, fracture toughness and biaxial flexural strength test (BFS). All analyses were conducted before and after artificial aging (20h, 134 °C, 0.22 MPa). Optical parameters and microhardness differences were evaluated through repeated-measures analysis of variance (p < 0.05). BFS data were analyzed using Weibull statistics (95% CI). ResultsThe synthesis of the experimental ZTA composite was successful, with 98% of theoretical density, as shown in the SEM images. XRD patterns revealed typical zirconia and alumina crystalline phases. ZTA optical properties parameters showed no effect of aging, with a high CR and low TP values denoting a high masking-ability. 3Y-TZP presented lower masking-ability and aging significantly affected its optical properties. ZTA Vickers hardness, fracture toughness and Weibull parameters, including characteristic stress and Weibull modulus were not influenced by aging, while 3Y-TZP presented a significant decrease in characteristic stress and increase in fracture toughness after aging. The ZTA probability of survival for missions of 300 and 500 MPa was estimated at ~99% validating its use for 3-unit posterior fixed dental prostheses (FDP), and no different from conventional 3Y-TZP. At high-stress mission (800 MPa) a significant decrease in probability of survival was observed for aged 3Y-TZP (84%) and for immediate and aged ZTA (73 and 82% respectively). ConclusionThe ZTA composite presented a dense microstructure, with preservation of the crystalline content, optical and mechanical properties after artificial aging, which encourages future research to validate its potential use for large span FDP.

The effect of high-energy methods of forming on the sintering behaviour and properties of Si3N4-based materials

In the study, Si3N4-Al2O3-Y2O3 samples were obtained in two stages. In the first stage, the materials were compacted using different methods: Isostatic Pressing, UHP (Ultra High Pressure), and SC (Shock Compaction). In the second stage, the green body samples obtained were sintered using the free sintering method.Powder mixtures, in wt%, 88 Si3N4 - 6 Al2O3 - 6Y2O3, were based on commercial nano - and micropowders. The parameters of green bodies compaction and sintering processes were optimised using the criteria of highest density, hardness, and Young's modulus. When compared to theoretical density values, the density of green body samples was 58% for the Isostatic Pressing and 82% for UHP and Shock Compaction. The Vickers hardness was measured only for Shock Compacted green body samples and was ~10.8–14 GPa depending on the applied load during the measurement. The largest changes in lattice constant parameters were measured for the Y2O3 phase for the dynamic compaction method (a = 0.02% - 2.26%).The highest relative density was measured for materials which were compacted by UHP method and subsequently free sintered (95%). Young's modulus for UHP and Isostatic green body free sintered samples was 284 GPa and 241 GPa, respectively. The hardness values of samples after free sintering were as follows: 11.7GPa for Isostatic, 14.8 GPa for UHP, and 17.6 GPa for Shock Compaction samples.

Characterization of Zirconia- Hydroxyapatite Nanocomposites for Orthopedic and Dental Applications

Zirconium oxide ceramic was proposed for different biomedical applications. It is used in orthopedic as hip and knee prostheses and in dentistry due to the good mechanical, biological high corrosion and wear resistance properties, addition to the aesthetic property owing to tooth like color. Zirconia stabilized with Y2O3 has the best properties for these applications. The present work aims to study the effect of (5 and 10)Wt.% hydroxyapatite (HA) as additives to 3 mol% yttria stabilized zirconia (3YSZ) nano powder matrix. The green body samples were shaped by powder technology using cold pressing then sintering at (1300 and 1400)ᵒC. The 3YSZ/ HA nanocomposites samples were characterized by XRD to investigate phase stability with varying percent's of HA and different sintering temperatures, the mechanical properties (maximum bending strength and hardness) were investigated as a function of the HA content, the changes of the thermal expansion coefficient for composite samples were investigated using Dilatometer. The experimental results proved that additions of (5 and 10)Wt.% HA to 3YSZ matrix reduce both hardness and max. bending strength, while increasing sintering temperature from 1300ᵒC to 1400ᵒC leading to an increase in the hardness and bending strength for all composite samples. The results of thermal expansion test showed a reduction in the thermal expansion coefficient with presence of HA%, however the coefficient of 3YSZ/ 10%HA is closer to 3YSZ from 3YSZ/ 5%HA. EDS analysis shows improvement in the bioactivity of inert 3YSZ with HA% additions represented by increasing Ca and P ions on the composite samples after immersing in SBF for 6 days.

Sintering behavior and thermal expansion of zirconia\u2013titanium composites

The dilatometric and thermogravimetric methods were used to investigate the sintering conditions of 3Y–ZrO2 and 3Y–ZrO2–Ti composites. For the materials preparation, the nanometric zirconia stabilized by 3 mol% Y2O3 powder and micrometric titanium powder (3 and 10 vol%) were used. The green body samples were formed by slip casting method. The morphology of samples microstructures was determined by SEM observations. The stereological analysis of zirconia and zirconia–titanium composites was carried out using computer program. The density was measured using the Archimedes method. The hardness of sinters was also investigated. Addition of Ti into ZrO2 influenced the sintering behavior and thermal expansion of obtained composites. The analysis of the sintering process and characteristic temperatures confirmed the increase of onset and final temperature of shrinkage with the increase in Ti content. The changes of the thermal expansion curves for the pure zirconia and 3Y–ZrO2–Ti composites were the result of the αTi → βTi transformation and the transition temperature of the zirconia m → t transformation. The zirconia and composite samples were characterized by relative density about 98%, close to theoretical density. The slight growth of zirconia grains was observed.

Fabrication of ZrO2-Ti Composites by Slip Casting Method

AbstractSlip casting is one of the most popular shaping method in ceramic technology which allows producing a large number of elements in small period of time. This shaping technique gives a possibility to fabricate ceramic or composite materials such as ZrO2-Ti. Ti with its properties (low density, high melting point, high-temperature strength, good corrosion resistance and others) combine with ZrO2(high flexure strength, high compression resistance and very high KIC) can be considered for different applications as constructional and functional materials. For the preparation of such composite nanometric zirconium oxide powder stabilized by 3 mol% Y2O3and micrometric titanium powder were used. Water-based slurries with 35, 40, 45 and 50 vol.% solid phase content were prepared with 3, 10 and 15 vol.% addition of titanium powder. Zeta potential and pH of prepared slurries were considered. The pH changes were tested as a function of Ti content. The viscosity of the prepared slurries was measured. The sedimentation tests for selected slurries were performed. The casting rate for slurry of 35% solid phase with 10 vol.% Ti was examined. These measurements showed good stability of slurries. With the increasing of the solid phase concentration the density of the green bodies increased. However, the increase of the content of Ti powder reduced the density of green body samples. For selected samples the SEM observations was carried out. Composites produced by slip casting were characterized by a homogenous distribution of Ti particles in the ZrO2matrix.

Experimental investigation of the elastoplastic response of aluminum silicate spray dried powder during cold compaction

Mechanical experiments have been designed and performed to investigate the elasto-plastic behaviour of green bodies formed from an aluminum silicate spray dried powder used for tiles production. Experiments have been executed on samples obtained from cold compaction into a cylindrical mould and include: uniaxial strain, equi-biaxial flexure and high-pressure triaxial compression/extension tests. Two types of powders have been used to realize the green body samples, differing in the values of water content, which have been taken equal to those usually employed in the industrial forming of traditional ceramics. Yielding of the green body during compaction has been characterized in terms of yield surface shape, failure envelope, and evolution of cohesion and void ratio with the forming pressure, confirming the validity of previously proposed constitutive models for dense materials obtained through cold compaction of granulates.

51722 Detection sensitivity of x-ray CT imaging fof NDE of green-state ceramics : Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 28 Jul.–28 Aug. 1991), Vol. 11B, pp. 1861–1868. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992)

Improved ceramic-processing methods that use pressure slip-casting and injection molding are being developed at Norton Advanced Ceramics, with a goal of producing reliable structural ceramics for advanced heat engines. Nondestructive evaluation (NDE) of ceramic parts at different stages of processing can provide useful diagnostic information to help improve processing techniques. For example, an evaluation of density gradients in as-cast green-body samples can be used to judge mold performance and make changes in mold design. Also, the ability to detect minute flaws (20 to 50 {mu}m), such as agglomerates, inclusions, and voids, in green-body, presintered, and densified parts is important in ensuring structural reliability of the final parts, because these flaws, above certain critical sizes, can lead to catastrophic failure. Three-dimensional microfocus X-ray computed tomography (CT) and nuclear magnetic resonance imaging (MRI) systems have been developed at Argonne National Laboratory (ANL) for application to quantitative NDE evaluation of ceramics. This paper evaluates the detection sensitivity of the ANL X-ray CT system when used to determine density gradients, inclusions, and voids in green-state Si{sub 3}N{sub 4} ceramics. A theoretical account of key system- and sample-related parameters affecting X-ray CT detection sensitivity is given, and results of experimental evaluation are presented. Density calibrationmore » phantoms and net-shape-formed tensile rods with seeded defects were used in the experimental evaluation of detection limits. 6 refs., 6 figs., 1 tab.« less