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Highlights • Revealing alterations in chemistry, elemental distribution and morphology in sound molar human tooth in its natural form. • Correlative electron microscopy techniques for nanostructuring and nanoanalysis of hard biomaterials. • Nanoscale characterization of dental tissues, e.g. dentin, enamel and their transition zone. Abstract In this study, natural molar human tooth specimens were investigated for determining their micro- and nanoscale structural morphology, chemistry and crystallinity. The differences were tracked comparatively for both enamel and dentin layers and at their interfaces. Although dental material structures are hard and tough and the cross-sectioning of these materials using mechanical methods is challenging, FIB-SEM dual-beam instruments serve for preparing ultra-thin homogenous lamella sections. In this work, both FIB-SEM and TEM based advanced characterization methods were applied to reveal different morphological characteristics of dental tissue via complementary imaging and diffraction analysis. In addition, SEM-EDS and Raman spectroscopy techniques provided additional information about the elemental distribution and the chemical composition differences of the dental tissues. According to electron microscopy examinations at the intersection between the enamel and the dentin layers, it was shown that the enamel was denser and polycrystalline, while the dentin layer was porous, fibrillar and of negligible long-range order, due to its tubular structure and organic components. In particular, EDS mapping and linescan analyses showed almost no differences in the elemental distribution. Raman results confirmed that both tissues had similar chemical composition except dentin showed spectral background effects in the spectrum due to its tubular structure and organic components. [ABSTRACT FROM AUTHOR]

Polymeric solutions as a subcategory of non-Newtonian fluids are prepared by the dissolution of polymeric additives into a solvent and find applications in many areas. Their advantage over new generation fluids such as nanofluids is that they have no side effects such as agglomeration and sedimentation of particles, which is common for nanofluids. This study presents an experimental study on nucleate pool boiling of aqueous Xanthan gum solutions of different concentrations. The results revealed that heat transfer coefficients of prepared polymeric solutions were lower than those of pure water. Heat transfer coefficients decreased with concentration until the concentration reached a certain amount (500 mg/L). Beyond this value, there was no change in heat transfer performance with concentration. Nevertheless, a monotonically decreasing trend was observed for high concentrations (⩾4000 mg/L), which is associated with sharp changes in surface tension and boiling patterns beyond a certain concentration. In visualization studies, different pool boiling patterns were recorded particularly for high concentrations, which bolster the heat transfer results. RAMAN tests were also conducted to check for the stability of the solutions. [ABSTRACT FROM AUTHOR]

The present study describes sintering behaviour of hydroxyapatite (HAp) upon addition of lithium iron phosphate (LFP) (1–10 wt.%) system in inert (Ar) atmosphere. The interaction between materials and melting of LFP influenced early and intermediate stages of HAp sintering, shifting the densification curves towards low-temperature side. Analysis of densification process indicated significant differences upon LFP addition. The reaction mechanism that assumes the initial interaction between phosphates from LFP and calcium from HAp was proposed, generating calcium vacancies and contributing to HAp densification. Cross-sections of sintered samples showed changes in microstructural properties, with uniform atomic distribution and presence of Li 2 Fe 3 O 4 spherical inclusions (200 nm) located at grain boundaries of calcium phosphate matrix. The Rietveld refinement analysis indicated changes in structural and microstructural parameters like crystallite size, anisotropy and microstructural strain of HAp upon LFP addition. Mechanical characterisation indicated improvements in fracture behaviour upon LFP addition. [ABSTRACT FROM AUTHOR]

• B 2 O 3 in Pechini-processed strontium aluminate tunes rare earth dopant partitioning. • SPS freezes in Eu2+, Dy3+ and B concentrations above solubility limits of Sr 4 Al 14 O 25. • When diffusion is limited, Eu Dy concentration exceed solubility limits and segregate to the intergranular phase. • Crystal structure of grains identified by Eu2+ peaks in SEM cathodoluminescence spectra. • 4-fold coordinated B appears in Sr 4 Al 14 O 25 grains exhibiting persistent afterglow. B has been proposed to extend persistent luminescence from minutes to > 10 h in Eu, Dy, and B co-doped Sr 4 Al 14 O 25 (S4A7EDB) by facilitating the incorporation of Eu2+ and Dy3+ into adjacent Sr sub-lattice sites and enabling energy transfer between them. To evaluate additional influences of B on the kinetics of microstructural evolution and dopant distribution that support afterglow in S4A7EDB, the effect of heating rates to 1300 °C is compared for spark-plasma sintering and conventional sintering, with and without the addition of B 2 O 3. Analysis of the microstructure and elemental distribution, by a combination of imaging, WDS, and CL in the SEM, XRD, dilatometry, and STEM-EELS, reveals that when the diffusivity of Eu and Dy is increased, Eu and Dy segregate to the intergranular phase. The partitioning of Eu and Dy concentrations to below their solubility limit in the grains appears to be essential to material structure enabling longer afterglow. [ABSTRACT FROM AUTHOR]

Ceramic pigments emitting long afterglow have enormous potential for emerging lighting applications that consume zero energy from the power grid. One of the most efficient compounds is strontium aluminate, when co-doped with 2 rare-earth elements — an optically active emitter, such as Eu2+, and an auxiliary ion, such as Dy3+— and B. To date, spectrophotometric methods are commonly used to determine the material structure supporting long afterglow, yielding indirect evidence of energy transfer between the rare-earth co-dopants. Here, atomic resolution HAADF-STEM imaging is used to resolve columns of Sr sub-lattice sites in the (012)-projection of a Sr 4 Al 14 O 25 :Eu,Dy single crystal. Through quantitative STEM image simulations, heavy rare earth dopants are shown to incorporate substitutionally into Sr sites, causing an enhancement in image contrast over that of neighboring atomic columns by 125%. DFT structural simulations demonstrate that Eu2+ and Dy3+ would incorporate into adjacent Sr lattice sites along the [012], enabling energy transfer between them that we see as afterglow. With the help of atomic resolution HAADF-STEM imaging, we also provide direct experimental evidence of clustering of ionic point defects induced by B doping, leading to extremely long (>14 h) afterglow in strontium aluminate phosphors. [ABSTRACT FROM AUTHOR]

In this study, enhanced subcooled boiling heat transfer was achieved at high mass fluxes by applying a new surface enhancement method. In this method, polyperfluorodecylacrylate (pPFDA) was applied on the inner walls of the 4 cm long stainless steel hypodermic microtubes with inner diameters of 889 and 600 μm. Initiated chemical vapor deposition (iCVD) was employed for coating inner walls of the microtubes with different coating thicknesses of ∼50 and ∼160 nm. iCVD could serve for a surface deposition method for closed geometries like microtubes and offered a uniform coating. The experiments were performed at high mass fluxes of 6000, 7000, and 8000 kg/m 2 s with de-ionized (DI) water (as the coolant). The Joule heating method was used for applying heat to the test section, which was located at the end (the last 2 cm) of the microtube. Temperature measurements were done at the very end of the microtubes. The experimental results indicated that pPFDA coated microtubes could significantly enhance flow boiling heat transfer. The largest heat transfer enhancement was achieved as ∼61% pertinent to the coated microtube of an inner diameter of 889 μm with the coating thickness of 160 nm, at G = 8000 kg/m 2 s, relative to its bare surface counterpart (at the same heat flux). The coatings were proven to be reliable and reproducible by analyzing the coated microtubes after performing boiling experiments with the Raman spectroscopy method. [ABSTRACT FROM AUTHOR]