X-ray computed tomography based microstructure reconstruction and numerical estimation of thermal conductivity of 2.5D ceramic matrix composite

In this study, the X-ray computed tomography was adopted to build 3D finite element models of the 2.5D ceramic matrix composite. The threshold segmentation method was used to identify the SiC matrix. An approach was developed to identify and number the matrix regions. The geometrical features of the 2.5D microstructure such as symmetry and periodicity were utilized to identify the boundaries of warp and weft. The warp, weft and porous matrix were denoted by different colors. The finite element model of 2.5D microstructure was built based on the color of each pixel. The finite element models combined with homogenization method were then used to predict the thermal conductivity of material. An element compression method was developed to reduce the total number of elements. The in plane and out-of-plane thermal conductivities were estimated by both numerical and experimental methods. The comparisons show that the numerical results fit experiments well.     

Effects of solid loading on stereolithographic additive manufactured ZrO2 ceramic: A quantitative defect study by X-ray computed tomography

In this study, the effects of solid loading on the defects and mechanical performance of stereolithographic additive manufactured ZrO₂ ceramic were studied by X-ray computed tomography (X-CT). ZrO₂ ceramics were fabricated by stereolithographic additive manufacturing from suspensions with different solid loading. The geometrical features and distribution of the defects within the ceramic were quantitatively characterized, classified, and analyzed, the formation mechanism were discussed. The correlations between the defects and mechanical properties were also investigated, and the effects of solid loading on the performance of ZrO₂ ceramic were revealed. The authors want to give a method, X-CT, for the defect characterization among stereolithographic additive manufactured ceramic.     

In situ tensile damage characterization of C/C composites through X-ray computed tomography and digital volume correlation

Carbon fiber reinforced carbon matrix (C/C) composites have been used in aerospace applications due to their excellent performance. Exploring their failure mechanisms is a subject of extensive research. Nowadays, to obtain information about changes in the failure processes, a technology known as in situ X-ray computed tomography is used. In this paper, tensile loads were applied to 3D fine-woven punctured and needle-punched C/C composites perpendicular to the punctured and needle-punched directions. In situ X-ray computed tomography was employed to observe damage development, and digital volume correlation was used to assess the laboratory X-ray computed tomographs to measure local strains. Assimilation of pores is observed in C/C composites, with cracks evolving from original micro-pores. While fine-woven punctured C/C composites present an elegant linear failure, needle-punched C/C composites present a traditional non-linear failure. This difference is due to the different structures of the preforms. Furthermore, the C/C composites are weak at the sites where they are punctured or needle-punched.     

A novel X-ray computed tomography method for fast measurement of multiphase flow

A new approach based on an improved genetic algorithm (GA) was proposed to implement the image reconstruction when using X-ray computed tomography (XCT) for the application of fast measurement of multiphase flow dynamics. Instead of directly using a traditional XCT, we pursued to develop a different discrete tomography (DT) method, aiming to achieve a high resolution in time during the measurements with only limited projection data. The proposed method assumed that the interested multiphase flow can be simplified as having distinct dense and dilute phases so that the local phase concentration can be binary-coded, e.g., 0 or 1 in a gas bubbling system. The mathematical problem under these circumstances is strongly ill-posed, and thus tackled with an optimization approach, i.e., a GA incorporated with the underlying physics as some constraints. The numerical simulations mimicking the physical measurements demonstrated the feasibility of the new approach, namely GA-XCT, especially with high robustness to the noise. Experiments were performed to simulate a transient measurement on the gas bubbles in water, with a portable X-ray tube and a 2D plane detector as the hardware and a static object rotating in between. The results further provided the validation of the GA-XCT being superior to the conventional algorithm, e.g., filtered back-projection (FBP) technique, in dealing with the tomography of multiphase system with binary local density field.     

Volumetric assessment of fatigue damage in a SiCf/SiC ceramic matrix composite via in situ X-ray computed tomography

To enhance the understanding of matrix cracking and damage progression on the macroscopic scale, within a 0/90° fibre reinforced SiC_f/SiC ceramic matrix composite (CMC), X-ray computed tomography (XCT) imaging and analysis have been performed in conjunction with a commercially available in-situ mechanical loading device. CMC test coupons were subjected to tensile cyclic loads and inspected using XCT without removal from the tensile loading device. Attempts to measure and quantify the resulting damage using volumetric image analysis techniques are presented, by characterising the crack network from XCT images acquired at both the maximum and minimum load condition during selected fatigue cycles. The XCT detection of significant crack development within the first loading half-cycle shows good agreement with cumulative acoustic emission energy data recorded under similar test conditions. The results are seen as an important step towards correlating the damage behaviour detected via different NDE and health monitoring techniques.     

Nondestructive and fined characterization of injection molded ceramic parts by industrial computed tomography

Nondestructive testing technology of industrial computed tomography(ICT) is introduced to investigate the injection molded bodies (green body, debinded body and, sintered part) in this study. The results show that ICT can characterize the defects qualitatively and quantitatively by comparing and analyzing the gray distribution of ICT images. The size, numbers and location of pores can be characterized precisely and the density distribution of the green body is quantitatively evaluated. The structure difference and evolution related with processing parameters is also analyzed by this technique. In addition, an image processing method is introduced to three-dimensional reconstruct the two dimensional images after threshold segmentation, and observe the internal structure and spatial morphology of the green body.     

X-ray Tomography Study on Green State Joining of Silicon Carbide Using Polymer Precursors

X-ray tomography has been used to investigate the density variations in SiC joints formed using polymer pastes. It has been demonstrated that X-ray tomography provides accurate bulk density measurements and volumetric density gradients. The results suggest that the magnitude of the applied pressure after green state joining and the amount of polymer (polycarbosilane, PCS) in the joining pastes influence the green density of the joints. All joints are prepared and applied in air atmosphere and at room temperature. The green densities of the joints increase from 54% to 66% of theoretical with the increase of the applied pressure from ambient to 138 MPa. Highest joint density without applied pressure is achieved using paste containing 50 vol% PCS. Furthermore, allylhydridopopolycarbosilane- (AHPCS-) containing pastes resulted in higher densities at the joint–matrix interface, indicating infiltration of polymer into the matrix.     

Quantitative measurement of gas hold-up distribution in a stirred chemical reactor using X-ray cone-beam computed tomography

Cone-beam type X-ray computed tomography (CBCT) is a potential method to measure three-dimensional phase distributions in vessels. An example for that is the measurement of gas profiles in stirred chemical reactors. Such data are highly valuable for the assessment and evaluation of chemical processes, for optimisation of the reactor and stirrer design, and for evaluation of computational fluid dynamics codes used to model the fluid flow and heat transfer in reactive systems. However, there are considerable difficulties for accurate quantitative measurements due to beam hardening and radiation scattering effects. In a theoretical and experimental work we have investigated the non-linear effects of both physical phenomena and developed a suitable measurement setup as well as calibration and software correction methods to achieve a highly accurate measurement of void fraction profiles with CBCT.     

Using X-ray tomography,PALS and Raman spectroscopy for characterization of inhibitors in epoxy coatings

Model paint materials were generated by adding a range of inorganic materials into an epoxy. The inorganic materials included inhibitors (Zn₃(PO₄)₂ and SrCrO₄) and a filler (rutile TiO₂).The SrCrO₄ system was characterized using SEM, TEM, PALS and Raman spectroscopy and found to have an even distribution of inhibitor in the polymer matrix. X-ray tomography was performed on the mixed SrCrO₄/TiO₂ and Zn₃(PO₄)₂/TiO₂ systems. A new technique called data constrained modelling was combined with the tomographic technique to produce a 3D distribution of the inorganic phases within the polymer matrix.     

Use of X-ray tomography to study the porosity and morphology of granules

X-ray computed tomography (XRCT) is a technique that uses X-ray images to reconstruct the internal microstructure of objects. Known as a CAT scan in medicine, it has found wide application for whole-body and partial-body imaging of hard tissues (e.g., bone). A modern tabletop XRCT system with a resolution of about 4 μm was used to characterize some pharmaceutical granules. Total porosity, pore size distribution, and geometric structure of pores in granules produced using different conditions and materials were studied. The results were compared to data obtained from mercury porosimetry. It was found that while XRCT is less precise in the determination of total porosity in comparison to mercury porosimetry, it provides detailed morphological information such as pore shape, spatial distribution, and connectivity. The method is nondestructive and accurate down to the resolution of the instrument.Tomographic images show that the pore network of individual granules comprises relatively large cavities connected by narrow pore necks. The major structural difference between granules produced at different conditions of compaction and shear is a reduction in the pore neck diameter; the cavity size is relatively insensitive to these conditions. Comparison of pore size distributions determined from tomographic images and mercury porosimetry indicates that mercury intrusion measures the pore neck size distribution, while tomography measures the true size distribution of pores ca. 4 μm or larger (the instrument resolution).     

Phase-inversion tape casting and synchrotron-radiation computed tomography analysis of porous alumina

A variant of tape casting based on the phase inversion phenomenon was adopted for fabrication of porous ceramic wafer. A slurry was prepared by dispersing alumina powder in an N-methyl-2-pyrrolidone (NMP) solution of the polymers polyethersulfone (PES) and polyvinylpyrrolidone (PVP). The slurry was cast using a doctor blade, and immersed in water to solidify the polymer solution via phase inversion. The green tape was dried and sintered at 1500 °C. The as-prepared ceramic wafer was characterized using synchrotron-radiation computed tomography (SR-CT). It was revealed that the ceramic wafer contained typical finger-like macrovoids, and the porosity resulting from these macrovoids was ~30%. The overall porosity of the wafer was 59%, as derived from the density data measured by Archimedes method in mercury. It is concluded that the phase inversion tape casting is a simple and effective method for preparation of porous ceramics.     

Experimental and numerical study on creep behaviors of 2D twill woven quartz fiber/silica matrix composites

This study investigates the creep deformation, damage, and rupture behaviors of 2D woven SiO₂/SiO₂ composites via experimental and numerical methods. In situ monotonic tensile tests and creep tests were conducted at 900 °C using a self-designed experimental system and digital image correlation. The tested specimens were characterized by X-ray computed tomography and scanning electron microscopy to conduct quantitative analyses and fracture observations. The obtained creep strain–time curves consist of primary and secondary stages, similar to the creep strain–time curves of most ceramic matrix composites. The matrix at the intersection of fiber bundles cracked under tensile loading. During subsequent creep loading, the propagation of matrix cracks, interfacial debonding, and fiber breakage in longitudinal fiber bundles were observed. At the mesoscale, the creep rupture entails a mechanism analogous to that observed in the monotonic tensile tests. Overall, the SiO₂/SiO₂ composites employed in this study exhibit excellent potential for long-term operation under mechanical loads at high temperatures. Next, a micromechanics-based creep model was proposed to simulate the creep behavior of the composites. In this model, the primary creep law and rule of mixtures were combined to describe the stress redistribution of various constituents and predict the deformation of the composites. In addition, the rupture life was predicted based on the global load-sharing model, two-parameter Weibull model, and shear lag model. The degradation of the matrix modulus and fiber strength was also considered to improve the accuracy of the simulation. The predicted results were in good agreement with the experimental data.     

Evaluation of the morphology and pore characteristics of silica refractory using X-ray computed tomography

Silica refractory has excellent high-temperature performance, but its apparent porosity is relatively high. In this work, samples obtained before and after creep testing of silica brick (1550 °C, 50 h), from used silica checker brick (existing only tridymite and amorphous) and from used dome brick (existing only cristobalite and amorphous) were investigated using a three-dimensional structure model based on X-ray computed tomography (CT). The results show that the porosity of silica brick was high but consisted mainly of interconnected pores, with a very small proportion of closed pores (smaller after long-term use). During the use of silica brick, the morphology and phase transformation caused large particles to rupture, and the mineralizer became liquid at high temperature. The broken particles and interconnected pores provided channels for the migration of the liquid in the brick at high temperature. The silica brick presented a homogeneous ceramic structure during long-term operation. Tridymite or cristobalite presented a solid frame leading to an excellent creep performance of the silica brick (the creep rate of the checker brick was ?0.16% at 1550 °C for 50 h). Results were discussed, compared with literature and a model for the transformation of the silica brick from a refractory structure to a homogeneous ceramic structure was established in this paper.     

Measurement of particle concentration in powder coating process using capacitance computed tomography and wavelet analysis

Capacitance computed tomography techniques were used to visualize particles movement in the draft tube of a spouted fluidized bed for the coating process of drug production. A total of 512 frames images of the particle concentration distribution were obtained at 10-millisecond intervals over a coating time of 5 min using a capacitance computed tomography system. The three-dimensional capacitance CT images (time and two-dimensional space images) were decomposed to wavelet time and space levels to extract the dominant particle distribution feature using three-dimensional discrete wavelet multiresolution at different coating times. As a result, the time and space dominant particle distribution with a specific frequency level can be visualized.     

Characterization of complex die-pressed Al2O3 green compact using liquid immersion,X-ray tomography,and numerical simulations

This study examined the compaction behavior of a green ceramic component with a complex shape formed by die pressing at 50 MPa using spray-dried alumina. Compared to a simple cylindrical sample, the sample with a complex shape revealed a higher degree of microstructural inhomogeneity and crack formation. Granule deformation and pore distribution at different sample locations were observed by optical microscopy after infiltrating liquid into the voids of a green compact. The refractive index of the immersion liquid should be different slightly from that of alumina for better observations. X-ray micro-computed tomography was also used to visualize the pore distribution and crack shape. Numerical simulations based on the Drucker-Prager/Cap model were performed to distinguish the stress and displacement distribution within the compact. The significant stress gradient at the crack initiation point could explain crack formation, whereas the application of a higher pressure resulted in a further increase in stress gradient.     

Granule rearrangement and pore structure of a spray-dried alumina compact observed by X-ray tomography

This study examined the compaction behavior of spray-dried Al₂O₃ granules with special emphasis on granule rearrangement and the resulting pore structure under different loads. A numerical simulation based on the finite element method was performed to estimate the density gradient in cylindrical compacts with different aspect ratios. The simulation results were compared with the experimental observations in terms of the density gradient, microstructural change, and pore distribution. A non-uniform pressure distribution in the compact resulted in a density gradient, where the top circumference showed the highest density, decreasing toward the center and bottom. The three-dimensional pore structures at different positions of the compact were visualized by X-ray micro-computed tomography, while two-dimensional images were also obtained using a liquid immersion technique for comparison. Good agreement between the simulation and experimental results was found, showing a density difference of ≤ 2 %.     

Performance modulation and 3D printing parameters optimization of implantable medical tricalcium-silicate/polyetherimide composite

Tricalcium silicate (C3S)/polyetherimide (PEI) stents are manufactured through an additive manufacturing process using binder jetting. The key issues of C3S/PEI composite ceramic slurry and additive manufacturing process parameters are discussed in detail. Firstly, the low-temperature auxiliary sintering temperature of the sample was determined, and the influence of PEI content on the compressive strength and bending strength before and after sintering was studied. The sintering temperature and optimal PEI content are 340 °C and 10 wt%. Under this PEI content, the flow rate change during the printing process of the slurry was measured, and a C3S/PEI composite slurry suitable for binder jetting additive manufacturing was obtained, and it had excellent mechanical properties. The effect of the parameters of the binder jetting additive manufacturing process on the molding quality of the C3S/10PEI composite ceramic slurry was studied. The effect of the printed layer height on the deposition line width and height was explored, resulting in a selection rule for the printing layer height using nozzle diameters. The influence of the number of layers of the printed sample on the height and line width of the sample is studied. Under the condition that the height of the printing layer is 80% of the nozzle diameter and the hot air assisted drying, the maximum error of the forming size is only 3.13%. Finally, the biocompatibility and cell adsorption effect of the scaffold were studied, and it was found that the C3S/PEI scaffold, which was additively manufactured by binder jetting and sintered at low temperature, had good biological properties.     

The application of multiscale quasi 4D CT to the study of SrCrO4 distributions and the development of porous networks in epoxy-based primer coatings

Transport paths for inhibitor release within a model strontium chromate (SrCrO₄) inhibited/epoxy primer have been studied using a combination of tomography techniques. It has been found that the SrCrO₄ particles form independent clusters within the model primer. The clusters have a range of fractal dimensions with the largest clusters (a few hundred microns in size) having a fractal dimension of 2.36. Leaching of the SrCrO₄ from the primer appears to be initially through direct dissolution of particles in contact with the electrolyte but changes to diffusion through void pathways created by dissolution of the SrCrO₄ phase. No evidence was found for the diffusion of chromate ions through the epoxy. Transport through such clusters does not follow Fickian diffusion, which has traditionally been employed to describe inhibitor release dynamics. Release kinetics typically follow a t^m behaviour where t is time and m is an index which would be 0.5 for Fickian diffusion. Thus the overall release with time will evolve, being initially the result of direct dissolution, then at intermediate times, be dominated by transport through the fractal network and at the final stage go to zero since all the strontium chromate will be dissolved from the cluster connected to the surface. Clusters not connected to the surface remain undissolved and form additional reservoirs for further release in when local damage occurs in their vicinity. This new model of inhibitor transport creates new strategies for the development of self-healing properties for coatings.     

蠕虫形管状镧铝复合介孔材料的合成及表征

The lanthanum aluminum mesoporous materials were synthesized using sodium dodecyl sulfate as a template agent by ultrasonic hydrothermal method.The resulting samples were characterized by low angle X-ray diffraction(XRD),N2 adsorption-desorption studies,transmission electron microscopy(TEM)and surface morphology analysis(SEM),surface acid(NH3-TPD),reducibility properties(TPR),X-ray energy dispersive spectrometer(EDS)and thermogravimetric analysis(TG/DTG).A l/La composite mesoporous material were synthesized with n(Al)︰n(La)=70︰1.0,80°C of reaction temperature,20 h of reaction time,12 h of crystallization time,650°C of calcination temperature.The specific surface area of the sample is 273.90 m 2 ·g ?1 ,with the average diameter 5.642 nm and pore volume 0.2354 cm 3 ·g ?1 .The samples have mesoporous structure and its particles are similar to a worm-shaped tubular structure.The influence of calcination temperature on the surface physical and chemical properties of Al/La composited mesoporous materials was examined,and the results showed that the acid strength was increased but the amount of acidic sites is decreased as the calcination temperature increased.It was found that the sample calcined at 650°C had appropriate acid content,acid strength and better reducibility.     

Microstructural evolution and texture analysis of magnesium phosphate cement

Three-dimensional quantitative image analysis from synchrotron X-ray microcomputed tomography indicated a coarsening of the microstructure of magnesium potassium phosphate cements driven by crystallization of K-struvite from the first amorphous product. Porosity and pore surface area increased because of the progressive build-up of a network of elongated/tabular crystal domains, with density higher than the amorphous. The known increase in strength with time is thought to occur thanks to the overwhelming contribution of a developing interlocked lath-shaped microstructure. Combined X-ray and neutron diffraction texture analysis indicated that at least a fraction of K-struvite nucleates at the surface of MgO grains, suggesting the intervention of more than one crystallization mechanism. The detected weak texture, compatible with a nearly random orientation of crystallites, and the isotropic pore fabric, are beneficial with respect to crack propagation.