Computation of sintering stress and bulk viscosity from microtomographic images in viscous sintering of glass particles

Sintering stress and bulk viscosity were derived as functions of relative density from microtomographic images in viscous sintering of glass particles. Three methods were proposed to estimate the sintering stress from relative density, specific surface area, and average of curvature on pore surface, which were directly measured by X‐ray microtomography. The surface energy method gave valid value in the final stage of sintering, while the mixed method gave better estimation in the intermediate stage. For the initial stage of sintering, the sintering stress was calculated from the average contact radius and the average coordination number observed by X‐ray microtomography. The sintering stress at the final stage increased in free sintering, but it decreased in constrained sintering due to pore coarsening. The bulk viscosity was calculated from the shrinkage rate and the sintering stress.     

3D printing of polycaprolactone/bioactive glass composite scaffolds for in situ bone repair

3D printing technology can fabricate customized scaffolds based on patient-derived medical images, so it has attracted much attention in the field of developing bone repair scaffolds. Polycaprolactone (PCL) is a suitable polymer for preparing bone repair scaffolds because of its good biocompatibility, thermal stability, excellent mechanical properties and degradable properties. However, PCL is a bioinert material and cannot induce new bone formation at the defect site. In this study, the bioactive material 58s bioactive glass was mixed into PCL to form PCL/bioactive glass composite material. The results of contact angle showed that the hydrophilicity of the scaffold was significantly enhanced with the increase of bioactive glass content. In vitro experiment results showed that, with the increase of bioactive glass content, cell adhesion and proliferation were enhanced, the expression levels of Runx2 and Collagen I(COL-I) were upregulated. The experimental results of in vivo radial defect repair in rats also showed that the effect of bone repair was improved with the increase of bioactive glass content. In conclusion, PCL customized bone repair scaffold containing 20% bioactive glass has widely potential used in the field of clinical bone repair.     

3D mesoporous bioactive glass/silk/chitosan scaffolds and their compatibility with human adipose-derived stromal cells

Human adipose-derived stem/stromal cells (hASCs) have been popularly studied as cell-based therapy in the field of regenerative medicine due to their ability to differentiate into several cell types. In this study, in order to improve the mechanical strength and bioactivity of scaffolds for bone tissue engineering, three types of mesoporous bioactive glasses with different shapes and compositions were dispersed in the silk fibroin/chitosan (SF/CS)-based scaffolds, which were fabricated with a combination of freezing and lyophilization. The characteristic and physical properties of these composite scaffolds were evaluated. The biocompatibility was also assessed through hASCs in vitro tests. Both Alamar Blue® and Live/Dead assay® revealed that the spherical mesoporous bioactive glass doped scaffolds enhanced cell viability and proliferation. Furthermore, the addition of spherical mesoporous bioactive glass into SF/CS scaffolds encouraged hASC osteogenic differentiation as well. These results suggested that this composite scaffold can be applicable material for bone regeneration.     

3D analysis of ceramic powder sintering by synchrotron X-ray nano-tomography

In-depth investigation of the sintering phenomena in ceramic powders remains challenging, with the typical size of the individual particles being around 1 µm or less, i.e., at the resolution limit of X-ray micro-tomography (μCT). This has been dealt with, thanks to the state-of-the-art hard X-ray nano-analysis beamline at the upgraded European Synchrotron Radiation Facility (ESRF). Complete 3D images were obtained for representative ceramic powder systems with a voxel size as low as 25 nm, so as to depict particles and pores with adequate details and follow the entire sintering process. Subsequent quantitative image analyses were used to explore microstructural changes, including the evolution of relevant sintering parameters with respect to the grains and the pores. Notably, a study adopted in this research on the advancement of pore curvatures can be linked to tracking the stages of sintering.     

Deepening our understanding of bioactive glass crystallization using TEM and 3D nano-CT

One key issue influencing a broader application of Bioglass 45S5 in tissue engineering is its inherent crystallization tendency, severely limiting the mechanical strength of 3D porous scaffolds. Despite numerous studies, Bioglass 45S5 crystallization is not yet fully understood with regard to the mechanisms involved or morphology of the crystal phases forming. Here we show how two cutting-edge imaging techniques, state-of-the-art transmission electron microscopy (TEM) with image correction including energy dispersive X-ray spectroscopy and X-ray nano-computed tomography (nano-CT), allowed us to visualize changes in microstructure from near-nucleation to almost full crystallization in bulk Bioglass 45S5. At early times of heat treatment at 660 °C the formation of phase-separated nano-droplets within the glassy matrix was observed. Later, besides surface crystallization, bulk crystallization of combeite spheres was predominant. The formation of the first combeite spheres, their coarsening with time and finally their merging at near full crystallization were recorded by in situ high-temperature optical microscopy videos. The 3D nature of these spheres was confirmed by nano-CT, while TEM showed that their internal structure was composed of sub-micron grains. X-ray diffraction analysis at early time points showed a much higher crystalline fraction in bulk samples compared to powder samples, highlighting the influence of processing and sample morphology. These results show the importance of using complementary techniques for gaining insight into the crystallization process in the volume. In addition, we show that TEM and nano-CT are suitable characterization techniques to visualize the crystallization even in fast crystallizing systems, such as bioactive glasses.     

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.     

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.     

In situ characterization of floc morphology by image analysis in a turbulent Taylor–Couette reactor

Flocculation of bentonite was performed in a turbulent Taylor–Couette reactor under various shear rates. Image processing enabled to determine various morphological characteristics of individual flocs. Not only their mean values but also their distributions were studied under various hydrodynamic conditions. Relevant properties were selected. The temporal evolution of radius of gyration and circularity distributions was monitored during the flocculation process. Although size and shape are obviously correlated, this article points out that their dependency to hydrodynamics is different, showing that flocs of similar sizes produced under different hydrodynamic conditions exhibit different shapes. The sizes are calibrated by the turbulence as the double radius of gyration is close to Kolmogorov microscale, whereas the circularity seems correlated to the rotation speed. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2389–2403, 2014     

基于三维XCT对碳化引起水泥砂浆内部缺陷改变的测试和分析

为了揭示碳化反应对水泥砂浆内部缺陷分布的影响规律,采用三维XCT(X-ray computed tomography)对碳化前后的水泥砂浆的三维内部缺陷体积分数和缺陷尺度分布进行了定量分析.通过XCT的配套软件VG Studio MAX 2.0对水泥砂浆内部缺陷的投影进行三维重构.并通过配套的三维缺陷分析模块软件从三维...     

Three-dimensional mathematical analysis of particle shape using X-ray tomography and spherical harmonics: Application to aggregates used in concrete

The properties of composites made by placing inclusions in a matrix are often controlled by the shape and size of the particles used. Mathematically, characterizing the shape of particles in three dimensions is not a particularly easy task, especially when the particle, for whatever reason, cannot be readily visualized. But, even when particles can be visualized, as in the case of aggregates used in concrete, three-dimensional (3-D) randomness of the particles can make mathematical characterization difficult. This paper describes a mathematical procedure using spherical harmonic functions that can completely characterize concrete aggregate particles and other particles of the same nature. The original 3-D particle images are acquired via X-ray tomography. Three main consequences of the availability of this procedure are mathematical classification of the shape of aggregates from different sources, comparison of composite performance properties to precise morphological aspects of particles, and incorporation of random particles into many-particle computational models.     

3D structure of oil droplets in hardened geopolymer emulsions

Geopolymer (GP) cements have the ability to integrate huge amounts of organic oils by direct emulsion in the fresh paste. Moreover, the oil emulsion remains stable during GP hardening. This allows to design tailored GP/oil (GEOIL) composites for an array of industrial applications. Using 3D X-ray micro-Computed Tomography (micro-CT), this research determines the spatial distribution of an industrial oil emulsion inside a GP cement (emulsification in the fresh state, imaging in the hardened state), depending on the oil volume fraction (from 5% to 60% total volume). The oil droplet size distribution, mean distance between droplets, and connectivity of the oil system are determined quantitatively.     

In situ X-ray analysis under controlled potential conditions: An innovative setup and its application to the investigation of ultrathin films electrodeposited on Ag(1 1 1)

An innovative setup to combine electrochemical and in situ surface X-ray diffraction (SXRD) measurements is described. This electrochemical cell has a different design from the other ones commonly used for X-ray diffraction studies. It allows the sample surface to stay always completely immersed into the solution under controlled potential conditions even during the SXRD measurements. The X-ray beam crosses the liquid (about 1 cm) and the cell walls. Because of the high X-ray energy, the beam attenuation is negligible and by an appropriate positioning of the detector arm slits it is possible to minimize the diffuse scattering induced by the liquid and cell walls in order to still detect the minima of the crystal truncation rods (CTRs). The liquid solution in the cell is managed by a special device, which allows the controlled exchange of the electrolyte solutions necessary in the electrochemical atomic layer epitaxy (ECALE) growth. The whole setup can be remotely controlled from outside the experimental hutch by a dedicated computer. As an example we report measurements on S layers deposited at underpotential on the Ag(1 1 1) surface, and on CdS films of increasing thickness.