Thermal Properties of SiOC Glasses and Glass Ceramics at Elevated Temperatures

In the present study, the effect of the chemical and phase composition on the thermal properties of silicon oxide carbides (SiOC) has been investigated. Dense monolithic SiOC materials with various carbon contents were prepared and characterized with respect to their thermal expansion, as well as thermal conductivity. SiOC glass has been shown to exhibit low thermal expansion (e.g., ca. 3.2 × 10⁻⁶ K⁻¹ for a SiOC sample free of segregated carbon) and thermal conductivity (ca. 1.5 W/(m∙K)). Furthermore, it has been observed that the phase separation, which typically occurs in SiOC exposed to temperatures beyond 1000–1200 °C, leads to a decrease of the thermal expansion (i.e., to 1.83 × 10⁻⁶ K⁻¹ for the sample above); whereas the thermal conductivity increases upon phase separation (i.e., to ca. 1.7 W/(m∙K) for the sample mentioned above). Upon adjusting the amount of segregated carbon content in SiOC, its thermal expansion can be tuned; thus, SiOC glass ceramics with carbon contents larger than 10–15 vol % exhibit similar coefficients of thermal expansion to that of the SiOC glass. Increasing the carbon and SiC content in the studied SiOC glass ceramics leads to an increase in their thermal conductivity: SiOC with relatively large carbon and silicon carbides (SiC) volume fractions (i.e., 12–15 and 20–30 vol %, respectively) were shown to possess thermal conductivities in the range from 1.8 to 2.7 W/(m∙K

Capturing the statewide incidence of neonatal abstinence syndrome in real time: the West Virginia experience

Background Neonatal abstinence syndrome (NAS) is one of the consequences at birth affecting the newborn after discontinuation of prenatal drug exposure to mainly opioids. The objective of this study was to determine the extent of the problem in the state of West Virginia (WV) using a real-time statewide surveillance system. Methods Project WATCH is a surveillance tool that since 1998 collects data on all infants born in the state of WV. NAS surveillance item was added to the tool in October 2016. This study examined all births (N = 23,667) in WV from October to December 2017. The data from six WV birthing facilities were audited for 1 month to evaluate how well this tool was capturing NAS data using κ-statistics. Results The 2017 annual incidence rate of NAS was 51.3 per 1000 live births per year for all births and 50.6 per 1000 live births per year for WV residents only. The κ-coefficient between the hospital medical records and Project WATCH data was 0.74 (95% confidence interval: 0.66–0.82) for NAS. Conclusion The study provides justification to develop effective systems of care for the mother–infant dyad affected by substance use, especially targeting pregnant women in rural communities

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Mechanical and Thermal Properties of SiOC-based Glasses and Glass Ceramics

Polymer-derived silicon oxycarbides (SiOC) exhibit improved mechanical properties in comparison to vitreous silica, a unique crystallization resistance and excellent stability in harsh environments. Consequently, silicon oxycarbides are potential candidates for high- temperature applications, for example in ceramic heaters, high-temperature reactors, combustion engines or as part of thermal protection systems. For these applications, the precise knowledge of the mechanical properties like hardness, elasticity and creep, but also of the thermal properties like thermal conductivity and thermal expansion is of paramount interest. In the present study the intrinsic mechanical and thermal properties of silicon oxycarbides were systematically assessed in order to obtain a fundamental understanding concerning the relationship between their phase composition, microstructure and properties. Therefore, a SiOC glass and a series of SiOC glass ceramics with varying compositions were synthesized and carefully characterized. It is demonstrated that the concept of phase separation (i.e. glass vs. glass ceramic) is important in SiOC materials. It has a large impact on thermal expansion, thermal transport and the activation volume carrying deformation at high temperatures (as expressed by the activation energy for creep). Furthermore, it is shown, that upon the proper choice of composition and microstructure, tailored mechanical and thermal properties can be realized within the SiOC system: (i) Increasing amounts of Si-C bonds in SiOC glasses or β-SiC nanoparticles in SiOC glass ceramics leads to an increase of Young’s modulus, indentation hardness, creep resistance and viscosity due to an increase of the glass network connectivity in SiOC glasses and the homogeneous distribution of β-SiC nanoparticles with good mechanical properties, respectively. On the other hand, the incorporation of Si-C bonds reduces the thermal transport in SiOC glasses as lower mass fractal networks and defects/oxygen vacancies are formed. However, amounts > 20 vol.% β-SiC nanoparticles lead to an increase of the thermal transport in SiOC glass ceramics. (ii) The high aspect ratio segregated carbon phase leads to a significant increase in thermal transport as well as in thermal expansion of SiOC materials already for small amounts. It has a moderate influence on Young’s modulus (decrease), creep resistance and viscosity (increase) in comparison to Si-C bonds/β-SiC nanoparticles, whereas hardness remains unbiased. The segregated carbon phase is responsible for the enhanced anelastic recovery of SiOC glass ceramics

Further Validation of the Child Routines Questionnaire: Child Self Report

There has been a lack of empirical studies on the impact of child routines on adjustment. A series of instruments, the Child Routines Questionnaires (CRQ) and the Adolescent Routines Questionnaires, were developed to assess routines in childhood. Recently, a self-report version of the CRQ was developed for children aged eight to 12. Initial validity estimates of the CRQ were weak, which may have been a result of cross-informant variance stemming from parent and child reports. The primary purpose of this study is to reevaluate the factorial and construct validity of the self-report CRQ with use of a single informant. The 39-item Child Routines Question-Child Self Report was completed by 374 children ages eight to 12. Children also completed measures on family stability and child behaviors, and caregivers completed a demographic form and a child behavior questionnaire. Although lower than expected fit statistics were obtained with the Confirmatory Factor Analysis, Exploratory Factor Analysis reaffirmed the three-factor structure of the CRQ-CSR in the current study, with several items changing factors. Nonetheless, internal consistency was excellent and consistent with the measure development study, while validity coefficients were much stronger than those obtained during the measure development study. Due to the larger, more heterogeneous sample, the current CRQ-CSR factor structure obtained in this study is recommended for continued development and use of the measure

Silicon oxycarbide glasses and glass‐ceramics: “All‐Rounder” materials for advanced structural and functional applications

Silicon oxycarbides can be considered as being carbon‐containing silicates consisting of glass networks in which oxygen and carbon share bonds with silicon. The carbon‐for‐oxygen substitution in silicate glass networks has been shown to induce significant changes in the network connectivity and consequently strong improvements in the properties of the silicate glass network. For instance, SiOC glasses exhibit Young's moduli, hardness values, glass transition, and crystallization temperatures which are superior to those of vitreous silica. Moreover, the silicon oxycarbide glass network exhibits unique structural features such as reduced mass fractal dimension and nano‐heterogeneity, which significantly affect and/or dictate its properties and behavior. In the present Review, a consideration of the current state of the art concerning the synthesis, processing, and various structural and functional properties of silicon‐oxycarbide‐based glasses and glass‐ceramics is done. Thus, the synthesis of silicon oxycarbides starting from macromolecular precursors such as polysiloxanes or alkoxysilanes‐based sol‐gel systems as well as current advances related to their processing will be critically reviewed. In addition, various structural and functional properties of silicon oxycarbides are presented. Specific emphasis will be put on the intimate correlation between the molecular architecture of the precursors and the structural features and properties of the resulting silicon oxycarbides

Thermal Properties of SiOC Glasses and Glass Ceramics at Elevated Temperatures

In the present study, the effect of the chemical and phase composition on the thermal properties of silicon oxide carbides (SiOC) has been investigated. Dense monolithic SiOC materials with various carbon contents were prepared and characterized with respect to their thermal expansion, as well as thermal conductivity. SiOC glass has been shown to exhibit low thermal expansion (e.g., ca. 3.2 × 10−6 K−1 for a SiOC sample free of segregated carbon) and thermal conductivity (ca. 1.5 W/(m∙K)). Furthermore, it has been observed that the phase separation, which typically occurs in SiOC exposed to temperatures beyond 1000–1200 °C, leads to a decrease of the thermal expansion (i.e., to 1.83 × 10−6 K−1 for the sample above); whereas the thermal conductivity increases upon phase separation (i.e., to ca. 1.7 W/(m∙K) for the sample mentioned above). Upon adjusting the amount of segregated carbon content in SiOC, its thermal expansion can be tuned; thus, SiOC glass ceramics with carbon contents larger than 10–15 vol % exhibit similar coefficients of thermal expansion to that of the SiOC glass. Increasing the carbon and SiC content in the studied SiOC glass ceramics leads to an increase in their thermal conductivity: SiOC with relatively large carbon and silicon carbides (SiC) volume fractions (i.e., 12–15 and 20–30 vol %, respectively) were shown to possess thermal conductivities in the range from 1.8 to 2.7 W/(m∙K)

Elastic properties and fracture toughness of SiOC‐based glass‐ceramic nanocomposites

Four different SiOC glass ceramics were synthesized and their fracture toughness (KIc) and fracture surface energy (γ) were assessed by means of the single‐edge precracked beam (SEPB) method. In addition, the elastic moduli were measured and the Vickers indentation behavior (hardness and microcracking) was characterized. In particular, the dependence of KIc on the free carbon content and on the fraction of crystallized nanoparticles (SiC, ZrO2, HfO2) was investigated. An increase in KIc, from about 0.73 to 0.99 MPa √m is observed as the free carbon content is increased from less than 1 to 12 vol%. The addition of Hf and Zr (resulting in 4.5 to 7.8 vol% HfO2 and ZrO2 nanoparticles) was found to increase KIc to an extent similar to the free carbon content. Moreover, predicted KIc values, assuming that the crack travels through all phases accounting for their respective volume fractions, disrupting the weakest links within the structural units, are in agreement with the experimental values

Synthesis and high-temperature creep behavior of a SiLuOC-based glass-ceramic

In this work, a lutetium-modified silicon oxycarbide (SiOC) glass ceramic was prepared from a single-source precursor via pyrolysis and subsequent hot pressing. It is shown that the main crystalline phase in the hot-pressed SiLuOC is Lu2Si2O7. The high-temperature (HT) creep behavior of SiLuOC was assessed by compression creep experiments performed between 1100 and 1300°C at constant true stresses between 25 and 75 MPa. The calculated viscosity values of SiLuOC were found to be significantly higher as compared to those of SiRE(Al,Mg)ON glasses (RE = rare earth elements). Thus, the presented SiLuOC-based glasses might be used as alternative sintering aids for the liquid-phase sintering of HT creep resistant Si3N4 monolithic samples

Perovskite Sr1−xBaxW1−yTay(O,N)3: synthesis by thermal ammonolysis and photocatalytic oxygen evolution under visible light

To study the effect of partial Ba2+-to-Sr2+ and/or Ta5+-to-W4–6+ substitution on various properties of SrW(O,N)3, cubic perovskite-type W- and/or Ta-based oxynitrides Sr1−x Ba x W1−y Ta y (O,N)3, where x,y = 0,0; 0.25,0; 0.125,0.125; 0,0.25; and 1.1, were synthesized by ammonolyzing their corresponding oxide precursors under an NH3 flow. The synthesized oxynitrides have highly porous structures and consist of small crystallites in the range of 53–630 nm and with specific surface areas in the range of 5.4–14.7 m2·g−1. Interestingly, the Ta5+-to-W4~6+ substitution in SrW(O,N)3 can suppress the formation of reduced tungsten species during thermal ammonolysis. The weaker absorptions beyond 560 and 580 nm in the UV–Vis diffuse reflectance spectra, which correspond to reduced tungsten species, are observed in SrW0.75Ta0.25(O,N)3 and Sr0.875Ba0.125W0.875Ta0.125(O,N)3 compared to SrW(O,N)3 and Sr0.75Ba0.25W(O,N)3. The XPS results reveal that low-valent transition metal oxides, nitrides, and oxynitrides and/or tungsten metal are present on the surfaces of the as-synthesized oxynitrides. After 5 h of the photocatalytic oxygen evolution reaction, CoO x -loaded SrW0.75Ta0.25(O,N)3 exhibited the highest amount of evolved O2 gas due to its higher specific surface area and lower concentration of intrinsic defects. During the photocatalytic reaction, the N2 gas is also evolved because of the self-oxidation of oxynitrides consuming photo-generated holes. The estimated TONs of the oxynitride samples exceeded one, evidencing that the observed O2 gas evolution reactions were catalytic. Accordingly, the photostability enhancement of oxynitrides reduces the loss of photo-generated charge carriers and increases their photocatalytic activity