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Microstructure and thermal properties of aluminum nitride ceramics are strongly affected by sintering conditions. Reducing sintering environments, which are typically encountered during liquid-phase sintering of aluminum nitride in graphite furnaces, have a particular impact on the distribution of secondary phase and properties in the final ceramic part. In order to gain a deeper understanding of the effect of the sintering atmosphere, a systematic study of sintering conditions during consolidation of aluminum nitride ceramics at 1700 °C containing calcium oxide and yttrium oxide as sintering additives was carried out, varying carbon content in the sintering environment as well as nitrogen partial pressure. Compositional and microstructural changes were clarified employing electron microscopy techniques as well as phase and mass loss analysis. An increased migration of the secondary phase in the presence of reducing species was observed, resulting in a significant change in microstructural evolution, which was shown to affect mechanical as well as thermal properties of the resulting materials. Based on these findings, suitable sintering parameters for aluminum nitride ceramics leading toward consistent reducing conditions are proposed, resulting in materials with a flexural strength of 390 MPa and thermal conductivity of up to 175 W m-1 K−1. Thus, a robust framework for generating materials with well-controllable properties, an essential prerequisite for current and future applications of aluminum nitride in the field of thermal management, is provided. [ABSTRACT FROM AUTHOR]

Abstract: Purpose: To determine the association between hormonal contraceptive (HC) use, and behavior-related and biological cardiovascular risk factors among teenage girls in Germany. Methods: HC use was assessed among 2,285 girls aged 13–17 years who participated in the health survey for children and adolescents (German Health Interview and Examination Survey for Children and Adolescents, KiGGS), between years 2003 and 2006. Prevalence of HC use was determined according to sociodemographic variables, behavior-related health risks, and overweight status. We compared HC users and nonusers with respect to biological cardiovascular risk factors, including systolic and diastolic blood pressure, and serum concentrations of lipids, lipoproteins, high sensitivity C-reactive protein (hs-CRP), and homocysteine. Results: HC users were more likely than nonusers to combine several behavior-related health risks, independent of sociodemographic factors. In particular, HC use was strongly associated with current smoking (odds ratio: 3.4, 95% confidence interval: 2.7–4.3). HC use and behavioral factors showed an additive effect on biological cardiovascular risk factors, explaining between 6% and 30% of the population variance. Relative contributions of HC use ranged from <1% for systolic and diastolic blood pressure to 12% for hs-CRP. Conclusions: HC use among 13–17-year-old girls in Germany is significantly correlated with a more unfavorable cardiovascular risk profile, which is partly explained by a clustering of behavioral risk factors among HC users. When prescribing HC to teenagers, physicians should systematically assess avoidable behavioral cardiovascular risk factors and provide counseling tailored to the risk profile of the individual patient. [Copyright &y& Elsevier]

Abstract: Objectives: Left ventricular hypertrophy (LVH) is a precursor of morbidity and mortality in women. Use of menopausal hormone therapy (MHT) might be associated with decreased left ventricular mass (LVM) and lower risk of LVH, although results of previous observational and clinical studies are inconclusive. Therefore, we analyzed the association between MHT use and either LVM indexed to height2.7 (LVMI) or LVH determined echocardiographically. Methods: Data from women aged ≥45 years recruited for the population-based Study of Health in Pomerania were used for cross-sectional (n =975) and longitudinal (n =675; 361 women without LVH at baseline) analyses. Information on ever (past and current) and never use of MHT were obtained. Linear (LVMI) or logistic (LVH) regression analyses were performed while controlling for potential confounders. Results: Crude and age-adjusted analyses suggested an association between ever use of MHT and lower odds for LVH. This association was no longer significant in fully adjusted models. Compared to women who never used MHT, the odds ratios of LVH for ever MHT users were 0.97 [95%-confidence interval (95%-CI) 0.71–1.30] in cross-sectional and 0.70 (95%-CI 0.44–1.11) in longitudinal fully adjusted analyses. Similarly, results with an alternative classification of MHT use (never, past, and current) indicated no significant associations with LVH after full adjustment. Conclusions: This study provides little evidence of an association between MHT use and LVH. Differences in lifestyle or health-related factors between never and MHT users could provide an explanation, in part, for the presumptive protective benefit of MHT on LVH. [Copyright &y& Elsevier]

MXenes have gained notable attention in tribology due to their excellent wear resistance based on the formation of beneficial tribofilms. However, studies using MXenes as solid lubricants have mainly focused on multi-layer Ti 3 C 2 T x coatings, while little is known about the tribological performance of MXene composites. Therefore, our study aims at scrutinizing and understanding the tribological behavior of MXenes and MXene composites as solid lubricants under reciprocating sliding conditions. Theoretical predictions regarding the resulting interlayer adhesion and coating-substrate adhesion helped to design the hybrid coatings. Multi-layer Ti 3 C 2 T x , molybdenum disulfide (MoS 2) and two hybrid coatings using Ti 3 C 2 T x and MoS 2 (random mixture and sandwich-like) were spray-coated onto steel substrates with a coating thickness of about 800 nm. Dry sliding tests using a steel ball as counter-body were carried out at room temperature. The coatings' morphology and formed tribofilms were holistically characterized by scanning and transmission electron microscopy (SEM, TEM) as well as X-ray photoelectron spectroscopy (XPS). Our results demonstrate that both hybrid coatings notably reduce friction and wear, outperforming their respective pure coatings (Ti 3 C 2 T x and MoS 2). This is attributed to synergistic effects between Ti 3 C 2 T x and MoS 2 , with adhesion forces appearing to be the governing mechanism in enhancing the formation of stable tribofilms. Numerical calculations validate our experimental results, verifying that hybrid coatings exhibit low interlayer friction and high adhesion to ferrous substrates. Consequently, our work reveals the potential of Ti 3 C 2 T x /MoS 2 hybrid coatings to further optimize friction and wear. [Display omitted] [ABSTRACT FROM AUTHOR]

The effect of heating rate on the decomposition kinetics of α″ martensite is continuously studied for a β-quenched Ti-6Al-6V-2Sn α + β alloy using fast in situ high energy synchrotron X-ray diffraction. The investigations are complemented with ex situ as well as dynamic metallographic analysis to reveal the mechanisms of phase transformation during critical stages of heating. The initial microstructure consists in a homogeneous distribution of fine acicular αʺ plates subdivided into domains associated with spinodal decomposition of αʺ, formed during β → αʺ transformation upon quenching. Quantitative phase analysis based on the Rietveld method provides the continuous evolution of lattice parameters, revealing the progression of diffusion-driven processes controlling the decomposition of αʺ into stable α and β phases (αʺ → α + β). The onset of this transformation shifts to higher temperatures with increasing heating rate. During the first stage of stabilization, precipitation of fine β particles occurs along the boundaries of twin related αʺ plates, while formation of β and α phases in the interior of α″ plates is identified at higher temperatures. Early formation of α takes place along boundaries of internal {111} α″ nano-twins, propagates up the borders of α″ plates, and can eventually further extend towards internal twins of neighbour martensite plates. Internal nano-twinning of αʺ plates takes place during αʺ decomposition owing to stress concentrations associated with structural heterogeneities within αʺ plates, i.e. spinodal decomposition of αʺ. The results obtained point to a relevant role of twin interfaces during phase precipitation. [ABSTRACT FROM AUTHOR]

The wet chemical porosification of low temperature co-fired ceramics (LTCC) applying ortho-phosphoric acid enables the implementation of areas with low permittivity directly into the as-fired substrate surface. Currently, the corresponding chemical reaction is only investigated for the widely used anorthite forming tape DuPont 951. In this paper the research is extended to cover celsian forming tapes with different ceramic particles. As the investigations show, the residual glass after porosification together with the grains should provide stable phases or components and ensure a bearing surface for further metallization. In the LTCC investigated here, the necessary selective etching to the containing celsian phase is given. However, the locality of the pores suffers from the presence of willemite, which is a second predominantly dissolved phase. The high amount of modifier oxides and the agglomeration of the dispersed corundum grains further weaken the stability of the LTCC substantially with respect to this treatment. [ABSTRACT FROM AUTHOR]

With the porosification of sintered Low Temperature Co-fired Ceramic (LTCC) surfaces areas with alternating dielectric properties can be created by embedding air. The method, including a wet-chemical treatment with phosphoric acid, is also investigated in detail for several commercial celsian forming tapes. Since the results of these materials cannot provide the required selectivity, in this work the analysis is extended to anorthite forming tapes. Furthermore, the investigations include a LTCC based on lanthanum borate. The results show that the porosification with phosphoric acid is not applicable to the latter material. In contrast, the silicate based, corundum containing tapes feature the most satisfying porosification results. Thereby, the stability of the glass, the size of the grains, the exclusivity of the crystallized phase and its degree of crystallization are identified as the tape features which directly influence the porosification results. [ABSTRACT FROM AUTHOR]

Phase development and changes in crystalline composition of LTCC material during the sintering process were investigated using in-situ X-ray diffraction (XRD) measurements. CeramTape GC was chosen as the chemically simplest model system composed of alumina particles and glass for the investigations. The chemical characterization and microstructural analyses of the tapes sintered with some representative firing profiles were performed by techniques such as (scanning) transmission electron microscope, energy-dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and XRD. Moreover, the porosification behavior of LTCC substrates fired at different peak temperatures was studied. These investigations are important for the subsequent wet chemical etching, representing an approach which allows to reduce locally the permittivity of LTCC tapes. Treatment with a KOH solution shows non-selective etching behavior for all substrates. In addition, highly porous silica structures corresponding to Ca and Al depletion from the anorthite phase were observed in all samples after etching treatment. [ABSTRACT FROM AUTHOR]

The effect of phase transformation kinetics on the formation of α in the β-quenched Ti–5Al–5Mo–5V–3Cr–1Zr metastable β titanium alloy is investigated as a function of heating rate by means of in situ high energy synchrotron X-ray diffraction complemented by metallographic analysis. Quantitative phase analysis based on the Rietveld method provides the continuous evolution of phase volume fractions and lattice parameters, revealing variations in the phase transformation sequence with increasing heating rate. The initial microstructure consists in a matrix of equiaxed metastable β grains with ω ath particles located along dislocation lines as well as within domains associated with spinodal decomposition of β. During the first stage of slow heating diffusion-driven formation of the metastable phases ω and α iso ″ takes place with further decomposition of β. This effect contributes to the formation of ω and is observed as a symmetric pattern of parallel domains that reflect compositional modulations in the matrix. Evidences of the role of dislocations during phase transformation are presented. Furthermore, the results show that the stable α phase forms via two different paths: (a) slow heating rates provide homogeneous distribution of fine α plates formed through the evolution of ω, while (b) fast heating rates suppress this mechanism and promote the formation of α only from β grain boundaries. [ABSTRACT FROM AUTHOR]

Measuring the dimensions and number density of nanoparticles dispersed in a solid matrix is usually accomplished via transmission electron microscopy (TEM) which suffers from high cost, low throughput, and small analytical volume. In comparison, scanning backscattered electron microscopy is inexpensive, requires little sample preparation, and allows for the analysis of large sample areas. However, the information depth is usually not known precisely and depends on several factors such as the composition of the nanoparticles and the matrix as well as the size of the nanoparticles, hindering the reconstruction of the actual size distribution and three-dimensional number density. Here we present a method to estimate the information depth for spherical nanoparticles of different sizes in order to accurately determine size distribution and number density. The approach is based on Monte Carlo simulation of electron trajectories in the material and analysis of the obtained backscattered electron signal-to-noise-ratio. Our experimental results are compared to those obtained via TEM and good agreement is demonstrated; this shows that TEM can be replaced by scanning electron microscopy for studying nanocomposites in many cases. [ABSTRACT FROM AUTHOR]

In the automotive industry Al-Mg-Si alloys are often chosen for high strength extruded profiles. However, the production of such profiles can be challenging for high alloy contents. Among several processing steps, the homogenization heat treatment before extrusion is readily accessible to modifications to improve high temperature formability. In this work, the influence of five different homogenization variants on the flow stress of AA6082 at elevated temperatures was assessed by compression testing in a deformation dilatometer at 450 °C, 480 °C, and 510 °C. The observed differences in flow stress were interpreted with regards to the microstructure. Samples from billets homogenized at higher soak temperatures exhibited lower hot flow stresses in subsequent dilatometer testing, indicating better processability. Since the decrease in flow stress is approximately constant at all test temperatures, it is suggested that it is due to a lower number density of relatively temperature-stable α-Al(Mn,Fe)Si dispersoids formed during homogenization at higher temperatures; these dispersoids are stable at all three test temperatures. In contrast, the influence of a cooling rate variation was relatively minor and diminishes at higher test temperatures since Mg-Si precipitates – whose size and number density is affected by changes of the cooling rate – are less stable at the higher test temperatures. [ABSTRACT FROM AUTHOR]

Characterization of Mg-Si precipitates is crucial for optimizing the homogenization heat treatment of Al-Mg-Si alloys. Although sample preparation is key for high quality scanning electron microscopy imaging, most common methods lead to dealloying of Mg-Si precipitates. In this article we systematically evaluate different sample preparation methods: mechanical polishing, etching with various reagents, and electropolishing using different electrolytes. We demonstrate that the use of a nitric acid and methanol electrolyte for electropolishing a homogenized Al-Mg-Si alloy prevents the dissolution of Mg-Si precipitates, resulting in micrographs of higher quality. This preparation method is investigated in depth and the obtained scanning electron microscopy images are compared with transmission electron micrographs: the shape and size of Mg-Si precipitates appear very similar in either method. The scanning electron micrographs allow proper identification and measurement of the Mg-Si phases including needles with lengths of roughly 200 nm. These needles are β″ precipitates as confirmed by high resolution transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Abstract: Within a prospective protocol, the incidence and impact of achievement of molecular remission (mCR) and high-risk cytogenetics was investigated in 73 patients with multiple myeloma (MM) after autologous (auto)–allogeneic (allo) tandem stem cell transplantation (SCT). After induction chemotherapy, patients received melphalan 200 mg/m2 before undergoing auto-SCT, followed 3 months later by melphalan 140 mg/m2 and fludarabine 180 mg/m2 before allo-SCT. Sixteen patients had high-risk cytogenetic features, defined by positive FISH for del(17p13) and/or t(4;14). Overall, 66% of the patients achieved CR or near-CR, and 41% achieved mCR, which was sustained negative (at least 4 consecutive samples negative) in 15 patients (21%), with no significant difference in incidence between the patients with high-risk cytogenetics and others (P = .70). After a median follow-up of 6 years, overall 5-year progression-free survival was 29%, with no significant difference between del 17p13/t(4;14)-harboring patients and others (24% versus 30%; P = .70). The 5-year progression-free survival differed substantially according to the achieved remission: 17% for partial remission, 41% for CR, 57% for mCR, and 85% for sustained mCR. These results suggest that auto–allo tandem SCT may overcome the negative prognostic effect of del(17p13) and/or t(4;14) and that achievement of molecular remission resulted in long-term freedom from disease. [Copyright &y& Elsevier]

Objective: To investigate post-transplant immunotherapy with escalating donor-lymphocyte infusions (DLI) and novel agents (thalidomide, bortezomib, and lenalidomide) to target complete remission (CR). Materials and Methods: Thirty-two patients with multiple myeloma who achieved only partial remission after allogeneic stem cell transplantation were treated with DLI. If no CR was achieved, one of the novel agents was added to target CR. Results: CR defined either by European Group for Blood and Marrow Transplantation criteria, flow cytometry, or molecular methods as assessed by patient-specific immunoglobulin H–polymerase chain reaction or plasma cell chimerism polymerase chain reaction was accomplished in 59%, 63%, and 50% of patients, respectively. Achievement of CR resulted in improved 5-year progressive-free and overall survival, according to European Group for Blood and Marrow Transplantation criteria (53% vs 35%; p =0.03 and 90% vs 62%; p =0.06), flow cytometry (74% vs 15%; p =0.001 and 100% vs 52%; p =0.1), or molecular methods (84% vs 38%; p =0.001 and 100% vs 71%; p =0.03). Conclusions: Our finding demonstrates the clinical relevance of posttransplantation therapies to upgrade remission, and of remission''s depth for long-term survival in myeloma patients. [Copyright &y& Elsevier]

[Display omitted] We present a combined experimental and computational investigation of phase stability and mechanical properties in the Al-Cu-Mg-Zn quaternary system. Samples containing different relative compositions were prepared using magnetron sputtering and investigated by electron microscopic and X-ray based methods. To classify the technical relevance of the samples, the indentation hardness was measured. The phase stability was studied computationally using a cluster expansion approach based on density functional theory (DFT) methods in a comprehensive screening of the structural and stoichiometric configuration space. Upon decreasing Cu concentration, a transition from an FCC to a mixed FCC/BCC crystal system and significant changes in the mechanical properties depending on Valence Electron Concentration (VEC) and atomic size differences (δ r) was observed experimentally. The corresponding crystallographic phases were assigned by XRD and the experimentally observed phase transition was confirmed by the computational screening of formation energies. Since to date, quaternary complex light metal alloy systems cannot be reliably predicted, this is an important step towards a priori modelling of this class of materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • The adhesion strength of AlN/Si as the weakest interface in an optoelectronic GaN based system is successfully determined for the first time. • The interfacial fracture energy of the AlN/Si interface is strongly dependent on the layer design and microstructure yielding energy release rates between 2.8 J/m2 and 13.6 J/m2. • Cross-sectional nanoindentation and four-point bending delamination tests revealed comparable local and large area interfacial fracture energy values. • The probability of interfacial delamination or cohesive fracture in multilayers can be predicted by the proposed analytical model, allowing optimized thin film design. Wide bandgap semiconductors such as group III-nitrides and SiC are considered as key materials for the fabrication of smaller, more reliable and efficient power electronics. Fabrication of robust and durable power devices requires an optimized design based on the understanding of the interfacial adhesion properties of the constituent thin-film heterostructures. In this study, the adhesion properties of GaN/AlN layers grown on Si substrates were investigated. Particularly, the influence of the AlN buffer layers, necessary for GaN growth on Si, on the delamination response was determined. The interfacial adhesion strength was obtained using cross-sectional nanoindentation (CSN) and four-point bending (4PB) tests. Analytical models based on beam- and elastic plate theory which were applied respectively to calculate the interfacial fracture energy (G ic) for both methods are found to be in good agreement provided the loading conditions are similar. Detailed transmission and scanning electron microscopy investigations prior and subsequent to delamination reveal the microstructural details of the relevant interfaces and provide insights into the encountered mechanisms of interfacial failure. Finally, the probability of delamination along the weakest interface is discussed based on a fracture mechanics model. [ABSTRACT FROM AUTHOR]

Abstract: Electron-microscopy suitable In2O3 thin films prepared by thermal deposition of In2O3 powder in 10−2 Pa O2 at 600K and, for comparison, a commercial polycrystalline In2O3 powder catalyst were tested in methanol steam reforming and in both routes of the water–gas shift reaction as a function of reaction temperature. The effect of oxidative (1bar O2, 373–673K, 1h) and reductive (1bar H2, 373–673K, 1h) catalyst pre-treatments was assessed. The resulting structural and morphological changes occurring during catalyst activation and catalytic reaction were monitored by (high-resolution) transmission electron microscopy, scanning electron microscopy and surface area measurements by N2 adsorption according to BET. Both the In2O3 thin film and the powder sample were observed to be structurally stable under typical catalyst pre-treatments in oxygen and hydrogen at temperatures T ≤673K and T <673K, respectively, as well as under typical methanol steam reforming conditions at temperatures T ≤680K. No pronounced catalyst sintering was observed below 673K. Both In2O3 samples were found to be highly active and selective toward CO2 in methanol steam reforming over a broad temperature range (450< T <673K). Selectivities of >95% toward CO2 were usually observed, with at maximum 5% or less CO formed. No dependence of selectivity on either reaction temperature or oxidative/reductive pre-treatment was observed. No catalytic activity in both routes of the water–gas shift reaction as tested in the same temperature region where the catalysts exhibit high reforming activity and selectivity, could be observed. Therefore In2O3 based catalysts offer a broad range of temperature not influenced by unwanted CO formation via the inverse water–gas shift process. [Copyright &y& Elsevier]

[Display omitted] • Strong influence of the Cu-ZrO 2 interface dimensions on the CO 2 selectivity in MSR. • Variation of Cu loading shows intrinsic contributions of ZrO 2 and Cu surface fraction. • ZrO 2 is an active support in methanol steam reforming. • ZrO 2 influences all reaction channels of the overall reaction mechanism. • Cu-ZrO 2 interfacial dimensions are independent of structural effects. On Cu/ZrO 2 catalysts, variation of the Cu loading from 0.2 wt% to 80 wt% allows assessing the influence of the Cu-ZrO 2 interface on the methanol steam reforming (MSR) performance by steering Cu particle size and morphology, revealing the contribution of potential active sites at the interface and the intrinsic relative contributions of the support and Cu surface fraction. As ZrO 2 influences both CO 2 -selective and selectivity-spoiling MSR reaction channels, disentangling support-specific effects from the special phase-boundary reactivity and the intrinsic Cu° reactivity is possible by our approach. By choosing a broad range of Cu loadings, a comparison of the most extreme cases of strong predominance of bulk-like Cu sites (80 wt% Cu) vs. highly dispersed Cu (0.2 wt%), dominated by interfacial and support reactivity, becomes accessible. Cu (80 wt%)/ZrO 2 evolves as the best MSR catalyst by avoiding adverse support effects and providing a high number of support-wetting bulk-like Cu sites. [ABSTRACT FROM AUTHOR]

• La 2 NiO 4 exhibits remarkable kinetic metastability in the DRM mixture up to 800 °C. • Decomposition of La 2 NiO 4 yields mainly a Ni/La 2 O 3 composite. • Reaction-formed hydrogen aids the decomposition of La 2 NiO 4 at lower temperatures. • Considerable coking and encapsulation of exsolved Ni revealed by in situ XRD. We focus on the stability and bulk/surface structural properties of the Ruddlesden-Popper phase La 2 NiO 4 and their consequences for dry reforming of methane (DRM) activity. Fuelled by the appearance as a crucial intermediate during in situ decomposition of highly DRM-active LaNiO 3 perovskite structures, we show that La 2 NiO 4 can be equally in situ decomposed into a Ni/La 2 O 3 phase offering CO 2 capture and release necessary for DRM activity, albeit at much higher temperatures compared to LaNiO 3. Decomposition in hydrogen also leads to an active Ni/La 2 O 3 phase. In situ X-ray diffraction during DRM operation reveals considerable coking and encapsulation of exsolved Ni, yielding much smaller Ni crystallites compared to on LaNiO 3 , where coking is virtually absent. Generalizing the importance of intermediate Ruddlesden-Popper phases, the in situ decomposition of La-based perovskite structures yields several obstacles due to the high stability of both the parent perovskite and the Ruddlesden-Popper structures and the occurrence of parasitic structures. [ABSTRACT FROM AUTHOR]

Low temperature co-fired ceramics (LTCC) technology has been successfully used in microelectronics, automotive, and telecommunication applications. However, their generally high permittivity is unfavorable for micromachined devices operated at high frequencies. To overcome this drawback, we have established a wet-chemical etching process as an effective approach which can be applied to LTCC substrates in their as-fired state and allows for a local permittivity reduction in regions of interest. Understanding the etching mechanism is essential for the selection of appropriate etching conditions to control the degree of porosification. Therefore, in the present work, we report on an effective approach to achieve a tailored porosification of LTCC substrates. Different characterization techniques such as scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and Raman Spectroscopy were used for investigation of the morphology and chemical composition of the substrates and thereby studying the etching mechanism. Furthermore, using dynamic-mechanical analysis at temperatures up to 550 °C, the stiffness behavior of the LTCC substrates after wet-chemical etching was investigated, and promising results for the applicability of such modified modules were obtained, even when operated at elevated temperatures up to 550 °C. Finally, a practical correlation between the mechanical properties and the relative porosification depth is presented, which is independent of etching conditions and the substrate thickness, and is valuable for optimization of the suitable depth of porosification for securing the desired mechanical properties. Image 1 • Employing wet chemical etching for porosification of LTCC substrates for local reduction of permittivity. • Detail study on kinetics and mechanism of the etching process. • Tailoring porosification degree and the corresponding depth of porosification by a careful selection of etching parameters. • Achieving high surface quality which allows for a high-quality metal deposition for further applications. • Investigating the stiffness behavior of the substrates over a large temperature range up to 550 °C. [ABSTRACT FROM AUTHOR]