Materials

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14 pages, 21651 KiB

Open AccessFeature PaperArticle

Optimization and Characterization of Preceramic Inks for Direct Ink Writing of Ceramic Matrix Composite Structures

by Giorgia Franchin, Halide Selin Maden, Larissa Wahl, Andrea Baliello, Marco Pasetto and Paolo Colombo

Materials 2018, 11(4), 515; https://doi.org/10.3390/ma11040515 - 28 Mar 2018

Cited by 44 | Viewed by 6757

Abstract

In a previous work, an ink based on a preceramic polymer, SiC fillers, and chopped carbon fibers was proposed for the production of Ceramic Matrix Composite (CMC) structures by Direct Ink Writing (DIW) and subsequent pyrolysis. Thanks to the shear stresses generated at [...] Read more.

In a previous work, an ink based on a preceramic polymer, SiC fillers, and chopped carbon fibers was proposed for the production of Ceramic Matrix Composite (CMC) structures by Direct Ink Writing (DIW) and subsequent pyrolysis. Thanks to the shear stresses generated at the nozzle tip during extrusion, carbon fibers can be aligned along the printing direction. Fumed silica was added to the ink in order to enhance its rheological properties; however, the printed structures still showed some deformation in the Z direction. In this work, a second ink was successfully developed to limit deformation and at the same time avoid the addition of fumed silica, which limited the potential temperature of application of the composites. Instead, the positive role of the preceramic polymer on the ink rheology was exploited by increasing its concentration in the ink. Rheological characterization carried out on both inks confirmed that they possessed Bingham shear thinning behavior and fast viscosity recovery. Single filaments with different diameters (~310 µm and ~460 µm) were produced with the latter ink by DIW and subsequent pyrolysis. Tested under a four-point flexural test, the filaments showed a mean flexural strength above 30 MPa, graceful failure, and fiber pull-out. The results of this work suggest that CMC components can effectively be fabricated via DIW of a preceramic ink with embedded short fibers; the preceramic polymer is able to provide the desired rheology for the process and to develop a dense matrix capable of incorporating both fibers and ceramic particles, whereas the fibers addition contributes to an increase of the fracture toughness of the material and to the development of a graceful failure mode. Full article

(This article belongs to the Special Issue Polymer Derived Ceramics and Applications)

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16 pages, 26633 KiB

Open AccessArticle

FEM Modeling of In-Plane Stress Distribution in Thick Brittle Coatings/Films on Ductile Substrates Subjected to Tensile Stress to Determine Interfacial Strength

by Kaishi Wang, Fangzhou Zhang and Rajendra K. Bordia

Materials 2018, 11(4), 497; https://doi.org/10.3390/ma11040497 - 27 Mar 2018

Cited by 8 | Viewed by 4481

Abstract

The ceramic-metal interface is present in various material structures and devices that are vulnerable to failures, like cracking, which are typically due to their incompatible properties, e.g., thermal expansion mismatch. In failure of these multilayer systems, interfacial shear strength is a good measure [...] Read more.

The ceramic-metal interface is present in various material structures and devices that are vulnerable to failures, like cracking, which are typically due to their incompatible properties, e.g., thermal expansion mismatch. In failure of these multilayer systems, interfacial shear strength is a good measure of the robustness of interfaces, especially for planar films. There is a widely-used shear lag model and method by Agrawal and Raj to analyse and measure the interfacial shear strength of thin brittle film on ductile substrates. The use of this classical model for a type of polymer derived ceramic coatings (thickness ~18 μm) on steel substrate leads to high values of interfacial shear strength. Here, we present finite element simulations for such a coating system when it is subjected to in-plane tension. Results show that the in-plane stresses in the coating are non-uniform, i.e., varying across the thickness of the film. Therefore, they do not meet one of the basic assumptions of the classical model: uniform in-plane stress. Furthermore, effects of three significant parameters, film thickness, crack spacing, and Young’s modulus, on the in-plane stress distribution have also been investigated. ‘Thickness-averaged In-plane Stress’ (TIS), a new failure criterion, is proposed for estimating the interfacial shear strength, which leads to a more realistic estimation of the tensile strength and interfacial shear strength of thick brittle films/coatings on ductile substrates. Full article

(This article belongs to the Special Issue Polymer Derived Ceramics and Applications)

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17 pages, 13079 KiB

Open AccessFeature PaperArticle

Microporosity and CO₂ Capture Properties of Amorphous Silicon Oxynitride Derived from Novel Polyalkoxysilsesquiazanes

by Yoshiaki Iwase, Yoji Horie, Sawao Honda, Yusuke Daiko and Yuji Iwamoto

Materials 2018, 11(3), 422; https://doi.org/10.3390/ma11030422 - 13 Mar 2018

Cited by 5 | Viewed by 3271

Abstract

Polyalkoxysilsesquiazanes ([ROSi(NH)_1.5]_n, ROSZ, R = Et, nPr, iPr, nBu, sBu, nHex, sHex, cHex, decahydronaphthyl (DHNp)) were synthesized by ammonolysis at −78 °C of alkoxytrichlorosilane (ROSiCl₃), which was isolated by distillation as a reaction product of SiCl₄ [...] Read more.

Polyalkoxysilsesquiazanes ([ROSi(NH)_1.5]_n, ROSZ, R = Et, nPr, iPr, nBu, sBu, nHex, sHex, cHex, decahydronaphthyl (DHNp)) were synthesized by ammonolysis at −78 °C of alkoxytrichlorosilane (ROSiCl₃), which was isolated by distillation as a reaction product of SiCl₄ and ROH. The simultaneous thermogravimetric and mass spectrometry analyses of the ROSZs under helium revealed a common decomposition reaction, the cleavage of the oxygen–carbon bond of the RO group to evolve alkene as a main gaseous species formed in-situ, leading to the formation of microporous amorphous Si–O–N at 550 °C to 800 °C. The microporosity in terms of the peak of the pore size distribution curve located within the micropore size range (<2 nm) and the total micropore volume, as well as the specific surface area (SSA) of the Si–O–N, increased consistently with the molecular size estimated for the alkene formed in-situ during the pyrolysis. The CO₂ capture capacity at 0 °C of the Si–O–N material increased consistently with its SSA, and an excellent CO₂ capture capacity of 3.9 mmol·g⁻¹ at 0 °C and CO₂ 1 atm was achieved for the Si–O–N derived from DHNpOSZ having an SSA of 750 m²·g⁻¹. The CO₂ capture properties were further discussed based on their temperature dependency, and a surface functional group of the Si–O–N formed in-situ during the polymer/ceramics thermal conversion. Full article

(This article belongs to the Special Issue Polymer Derived Ceramics and Applications)

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23 pages, 9289 KiB

Open AccessArticle

Novel Precursor-Derived Meso-/Macroporous TiO₂/SiOC Nanocomposites with Highly Stable Anatase Nanophase Providing Visible Light Photocatalytic Activity and Superior Adsorption of Organic Dyes

by Eranezhuth Wasan Awin, Abhijeet Lale, Kollamala Chellappan Nair Hari Kumar, Umit Bilge Demirci, Samuel Bernard and Ravi Kumar

Materials 2018, 11(3), 362; https://doi.org/10.3390/ma11030362 - 1 Mar 2018

Cited by 25 | Viewed by 5480

Abstract

Titania (TiO₂) is considered to have immense potential as a photocatalyst, the anatase phase in particular. There have been numerous attempts to push the limits of its catalytic activity to higher wavelengths to harness the visible electromagnetic radiation. Most of the [...] Read more.

Titania (TiO₂) is considered to have immense potential as a photocatalyst, the anatase phase in particular. There have been numerous attempts to push the limits of its catalytic activity to higher wavelengths to harness the visible electromagnetic radiation. Most of the investigations till date have been restricted to fine-tuning the bandgap by doping, control of defect chemistry at the surface and several to first principle simulations either with limited success or success at the cost of complexities in processing. Here, we report a simple and elegant way of preparing ceramics through precursor chemistry which involves synthesis of macroporous and mesoporous nanocomposites with in situ formation of TiO₂ nanocrystals into a robust and protecting SiOC matrix. The in situ nanoscaled TiO₂ is anatase of size 9–10 nm, which is uniformly distributed in an amorphous SiOC matrix forming a new generation of nanocomposites that combine the robustness, structural stability and durability of the SiOC matrix while achieving nanoscaled TiO₂ functionalities. The stabilization of the anatase phase even at temperature as high as 1200 °C was evident. With an average pore size of 6.8 nm, surface area of 129 m²/g (BET) and pore volume of 0.22 cm³/g (BET), mesoporosity was achieved in the nanocomposites. The composites exhibited visible light photocatalytic activity, which is attributed to the Ti–O–C/TiC bonds resulting in the reduction of band gap by 0.2 to 0.9 eV. Furthermore, the heterojunction formed between the amorphous SiOC and crystalline TiO₂ is also expected to minimize the recombination rate of electron-hole pair, making these novel nanocomposites based on TiO₂ extremely active in visible wavelength regime. Full article

(This article belongs to the Special Issue Polymer Derived Ceramics and Applications)

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18 pages, 2160 KiB

Open AccessArticle

Thermal Properties of SiOC Glasses and Glass Ceramics at Elevated Temperatures

by Christina Stabler, Andreas Reitz, Peter Stein, Barbara Albert, Ralf Riedel and Emanuel Ionescu

Materials 2018, 11(2), 279; https://doi.org/10.3390/ma11020279 - 10 Feb 2018

Cited by 73 | Viewed by 9032

Abstract

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 [...] Read more.

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). Full article

(This article belongs to the Special Issue Polymer Derived Ceramics and Applications)

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9 pages, 2603 KiB

Open AccessFeature PaperArticle

High-Temperature Raman Spectroscopy of Nano-Crystalline Carbon in Silicon Oxycarbide

by Felix Rosenburg, Emanuel Ionescu, Norbert Nicoloso and Ralf Riedel

Materials 2018, 11(1), 93; https://doi.org/10.3390/ma11010093 - 9 Jan 2018

Cited by 72 | Viewed by 12734

Abstract

The microstructure of segregated carbon in silicon oxycarbide (SiOC), hot-pressed at T = 1600 °C and p = 50 MPa, has been investigated by VIS Raman spectroscopy (λ = 514 nm) within the temperature range 25–1000 °C in air. The occurrence of the [...] Read more.

The microstructure of segregated carbon in silicon oxycarbide (SiOC), hot-pressed at T = 1600 °C and p = 50 MPa, has been investigated by VIS Raman spectroscopy (λ = 514 nm) within the temperature range 25–1000 °C in air. The occurrence of the G, D’ and D bands at 1590, 1620 and 1350 cm⁻¹, together with a lateral crystal size L_a < 10 nm and an average distance between lattice defects L_D ≈ 8 nm, provides evidence that carbon exists as nano-crystalline phase in SiOC containing 11 and 17 vol % carbon. Both samples show a linear red shift of the G band up to the highest temperature applied, which is in agreement with the description of the anharmonic contribution to the lattice potential by the modified Tersoff potential. The temperature coefficient χ_G = −0.024 ± 0.001 cm⁻¹/°C is close to that of disordered carbon, e.g., carbon nanowalls or commercial activated graphite. The line width of the G band is independent of temperature with FWHM-values of 35 cm⁻¹ (C-11) and 45 cm⁻¹ (C-17), suggesting that scattering with defects and impurities outweighs the phonon-phonon and phonon-electron interactions. Analysis of the Raman line intensities indicates vacancies as dominating defects. Full article

(This article belongs to the Special Issue Polymer Derived Ceramics and Applications)

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4720 KiB

Open AccessFeature PaperArticle

Synthesis of a Novel Polyethoxysilsesquiazane and Thermal Conversion into Ternary Silicon Oxynitride Ceramics with Enhanced Thermal Stability

by Yoshiaki Iwase, Yoji Horie, Yusuke Daiko, Sawao Honda and Yuji Iwamoto

Materials 2017, 10(12), 1391; https://doi.org/10.3390/ma10121391 - 5 Dec 2017

Cited by 10 | Viewed by 3801

Abstract

A novel polyethoxysilsesquiazane ([EtOSi(NH)_1.5]_n, EtOSZ) was synthesized by ammonolysis at −78 °C of ethoxytrichlorosilane (EtOSiCl₃), which was isolated by distillation as a reaction product of SiCl₄ and EtOH. Attenuated total reflection-infra red (ATR-IR), ¹³C-, and [...] Read more.

A novel polyethoxysilsesquiazane ([EtOSi(NH)_1.5]_n, EtOSZ) was synthesized by ammonolysis at −78 °C of ethoxytrichlorosilane (EtOSiCl₃), which was isolated by distillation as a reaction product of SiCl₄ and EtOH. Attenuated total reflection-infra red (ATR-IR), ¹³C-, and ²⁹Si-nuclear magnetic resonance (NMR) spectroscopic analyses of the ammonolysis product resulted in the detection of Si–NH–Si linkage and EtO group. The simultaneous thermogravimetric and mass spectrometry analyses of the EtOSZ under helium revealed cleavage of oxygen-carbon bond of the EtO group to evolve ethylene as a main gaseous species formed in-situ, which lead to the formation at 800 °C of quaternary amorphous Si–C–N with an extremely low carbon content (1.1 wt %) when compared to the theoretical EtOSZ (25.1 wt %). Subsequent heat treatment up to 1400 °C in N₂ lead to the formation of X-ray amorphous ternary Si–O–N. Further heating to 1600 °C in N₂ promoted crystallization and phase partitioning to afford Si₂N₂O nanocrystallites identified by the XRD and TEM analyses. The thermal stability up to 1400 °C of the amorphous state achieved for the ternary Si-O-N was further studied by chemical composition analysis, as well as X-ray photoelectron spectroscopy (XPS) and ²⁹Si-NMR spectroscopic analyses, and the results were discussed aiming to develop a novel polymeric precursor for ternary amorphous Si–O–N ceramics with an enhanced thermal stability. Full article

(This article belongs to the Special Issue Polymer Derived Ceramics and Applications)

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6250 KiB

Open AccessArticle

Properties and Applications of High Emissivity Composite Films Based on Far-Infrared Ceramic Powder

by Yabo Xiong, Shaoyun Huang, Wenqi Wang, Xinghai Liu and Houbin Li

Materials 2017, 10(12), 1370; https://doi.org/10.3390/ma10121370 - 29 Nov 2017

Cited by 8 | Viewed by 5065

Abstract

Polymer matrix composite materials that can emit radiation in the far-infrared region of the spectrum are receiving increasing attention due to their ability to significantly influence biological processes. This study reports on the far-infrared emissivity property of composite films based on far-infrared ceramic [...] Read more.

Polymer matrix composite materials that can emit radiation in the far-infrared region of the spectrum are receiving increasing attention due to their ability to significantly influence biological processes. This study reports on the far-infrared emissivity property of composite films based on far-infrared ceramic powder. X-ray fluorescence spectrometry, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray powder diffractometry were used to evaluate the physical properties of the ceramic powder. The ceramic powder was found to be rich in aluminum oxide, titanium oxide, and silicon oxide, which demonstrate high far-infrared emissivity. In addition, the micromorphology, mechanical performance, dynamic mechanical properties, and far-infrared emissivity of the composite were analyzed to evaluate their suitability for strawberry storage. The mechanical properties of the far-infrared radiation ceramic (cFIR) composite films were not significantly influenced (p ≥ 0.05) by the addition of the ceramic powder. However, the dynamic mechanical analysis (DMA) properties of the cFIR composite films, including a reduction in damping and shock absorption performance, were significant influenced by the addition of the ceramic powder. Moreover, the cFIR composite films showed high far-infrared emissivity, which has the capability of prolonging the storage life of strawberries. This research demonstrates that cFIR composite films are promising for future applications. Full article

(This article belongs to the Special Issue Polymer Derived Ceramics and Applications)

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