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Special Issue "Advanced Glasses, Composites and Ceramics for High Growth Industries"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (31 December 2018)

Special Issue Editors

Guest Editor
Prof. Milena Salvo

Department of Applied Science and Technology, Politecnico di Torino, Italy
Website | E-Mail
Phone: +390110904706
Interests: joining; coatings; ceramics; glasses and glass-ceramics; composites
Guest Editor
Prof. Mike Reece

School of Engineering and Materials Science, Queen Mary University of London, UK
Website | E-Mail
Interests: field assisted processing; thermoelectrics; functional ceramics
Guest Editor
Prof. Aldo R. Boccaccini

Institute of Biomaterials, University of Erlangen-Nuremberg, Germany
Website | E-Mail
Phone: 4991318528601
Fax: +49 9131 85 28602
Interests: biomaterials; bioactive glasses; composites; tissue engineering

Special Issue Information

Dear Colleagues,

“Advanced glasses, Composites And Ceramics for High growth Industries” (CoACH) is a European Training Network (ETN) (http://www.coach-etn.eu/) funded by the Horizon 2020 program. The project is studying the next generation of materials that could bring innovation in the healthcare, construction, energy and other sectors. From new bioactive glasses for bone implants to eco-friendly cements and new environmentally friendly thermoelectrics for energy conversion, the novel materials developed in CoACH pave the way for innovative products, improved cost competitiveness and positive environmental impact. The broad range of research activities conducted within the framework of CoACH includes (i) new antibacterial glasses and hybrid coatings; (ii) energy efficient, low-cost and eco-friendly cement and insulation materials produced from industrial wastes; (ii) innovative materials for energy production and harvesting and (iv) sensors and polymer composites used in harsh environments. The present Special Issue will contain papers resulting from the CoACH project, showcasing the breadth of materials and processes developed during the project.

Prof. Milena Salvo
Prof. Mike Reece
Prof. Aldo R. Boccaccini
Guest Editors

Manuscript Submission Information

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Keywords

  • Glasses
  • Composites
  • Bioactive glasses
  • Antibacterial materials
  • Coatings
  • Geopolymers
  • Glass-ceramics
  • Cements
  • Thermoelectrics
  • Field assisted processing
  • Sensors

Published Papers (14 papers)

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Open AccessArticle Exposure of Glass Fiber Reinforced Polymer Composites in Seawater and the Effect on Their Physical Performance
Materials 2019, 12(5), 807; https://doi.org/10.3390/ma12050807
Received: 25 December 2018 / Revised: 20 February 2019 / Accepted: 1 March 2019 / Published: 8 March 2019
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Abstract
An innovative testing methodology to evaluate the effect of long-term exposure to a marine environment on Glass Fiber Reinforced Polymers (GFRPs) has been investigated and is presented in this paper. Up to one-year ageing was performed in seawater, to simulate the environment for [...] Read more.
An innovative testing methodology to evaluate the effect of long-term exposure to a marine environment on Glass Fiber Reinforced Polymers (GFRPs) has been investigated and is presented in this paper. Up to one-year ageing was performed in seawater, to simulate the environment for offshore oil and gas applications. The performance of an epoxy and epoxy-based GFRP exposed at different temperatures from 25 to 80 °C was quantified. The materials were also aged in dry air, to de-couple the thermal effect from the seawater chemical action. Gravimetric testing and Dynamic Mechanical Analysis (DMA) were conducted in parallel on progressively aged specimens. The effect of specimen geometry and the anisotropic nature of diffusion are comprehensively discussed in this paper. For the quasi-infinite specimens, the results show an exponential increase in the seawater absorption rate with temperature. The methodology allowed for the prediction of the diffusivity at a temperature of 4 °C as 0.23 and 0.05 × 10−13 m2/s for the epoxy and the epoxy-based composite, respectively. The glass transition temperature reduces as sea water is absorbed, yet the sea water effects appear to be reversible upon drying. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Glass-Ceramic Foams from ‘Weak Alkali Activation’ and Gel-Casting of Waste Glass/Fly Ash Mixtures
Materials 2019, 12(4), 588; https://doi.org/10.3390/ma12040588
Received: 10 December 2018 / Revised: 25 January 2019 / Accepted: 12 February 2019 / Published: 15 February 2019
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Abstract
A ‘weak alkali activation’ was applied to aqueous suspensions based on soda lime glass and coal fly ash. Unlike in actual geopolymers, an extensive formation of zeolite-like gels was not expected, due to the low molarity of the alkali activator (NaOH) used. In [...] Read more.
A ‘weak alkali activation’ was applied to aqueous suspensions based on soda lime glass and coal fly ash. Unlike in actual geopolymers, an extensive formation of zeolite-like gels was not expected, due to the low molarity of the alkali activator (NaOH) used. In any case, the suspension underwent gelation and presented a marked pseudoplastic behavior. A significant foaming could be achieved by air incorporation, in turn resulting from intensive mechanical stirring (with the help of a surfactant), before complete hardening. Dried foams were later subjected to heat treatment at 700–900 °C. The interactions between glass and fly ash, upon firing, determined the formation of new crystal phases, particularly nepheline (sodium alumino–silicate), with remarkable crushing strength (~6 MPa, with a porosity of about 70%). The fired materials, finally, demonstrated a successful stabilization of pollutants from fly ash and a low thermal conductivity that could be exploited for building applications. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Oxidation Protective Hybrid Coating for Thermoelectric Materials
Materials 2019, 12(4), 573; https://doi.org/10.3390/ma12040573
Received: 14 December 2018 / Revised: 28 January 2019 / Accepted: 6 February 2019 / Published: 14 February 2019
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Abstract
Two commercial hybrid coatings, cured at temperatures lower than 300 °C, were successfully used to protect magnesium silicide stannide and zinc-doped tetrahedrite thermoelectrics. The oxidation rate of magnesium silicide at 500 °C in air was substantially reduced after 120 h with the application [...] Read more.
Two commercial hybrid coatings, cured at temperatures lower than 300 °C, were successfully used to protect magnesium silicide stannide and zinc-doped tetrahedrite thermoelectrics. The oxidation rate of magnesium silicide at 500 °C in air was substantially reduced after 120 h with the application of the solvent-based coating and a slight increase in power factor was observed. The water-based coating was effective in preventing an increase in electrical resistivity for a coated tethtraedrite, preserving its power factor after 48 h at 350 °C. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Studies on Cell Compatibility, Antibacterial Behavior, and Zeta Potential of Ag-Containing Polydopamine-Coated Bioactive Glass-Ceramic
Materials 2019, 12(3), 500; https://doi.org/10.3390/ma12030500
Received: 23 December 2018 / Revised: 18 January 2019 / Accepted: 29 January 2019 / Published: 6 February 2019
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Abstract
Dopamine is a small molecule that mimics the adhesive component (L-DOPA) of marine mussels with a catecholamine structure. Dopamine can spontaneously polymerize to form polydopamine (PDA) in a mild basic environment. PDA binds, in principle, to all types of surfaces and offers a [...] Read more.
Dopamine is a small molecule that mimics the adhesive component (L-DOPA) of marine mussels with a catecholamine structure. Dopamine can spontaneously polymerize to form polydopamine (PDA) in a mild basic environment. PDA binds, in principle, to all types of surfaces and offers a platform for post-modification of surfaces. In this work, a novel Ag-containing polydopamine coating has been developed for the functionalization of bioactive glass-ceramics. In order to study the interactions between the surface of uncoated and coated samples and the environment, we have measured the surface zeta potential. Results confirmed that PDA can interact with the substrate through different chemical groups. A strongly negative surface zeta potential was measured, which is desirable for biocompatibility. The dual function of the material, namely the capability to exhibit bioactive behavior while being antibacterial and not harmful to mammalian cells, was assessed. The biocompatibility of the samples with MG-63 (osteoblast-like) cells was determined, as well as the antibacterial behavior against Gram-positive Staphylococcus carnosus and Gram-negative Escherichia coli bacteria. During cell biology tests, uncoated and PDA-coated samples showed biocompatibility, while cell viability on Ag-containing PDA-coated samples was reduced. On the other hand, antibacterial tests confirmed the strong antimicrobial properties of Ag-containing PDA-coated samples, although tailoring of the silver release will be necessary to modulate the dual effect of PDA and silver. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Development and Characterization of Bioactive Glass Containing Composite Coatings with Ion Releasing Function for Antibiotic-Free Antibacterial Surgical Sutures
Materials 2019, 12(3), 423; https://doi.org/10.3390/ma12030423
Received: 11 January 2019 / Revised: 24 January 2019 / Accepted: 26 January 2019 / Published: 30 January 2019
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Abstract
Resorbable (Vicryl® Plus) sutures were coated with zinc-doped glass (Zn-BG) and silver-doped ordered mesoporous bioactive glass (Ag-MBG) particles by a dip coating technique. A multilayer approach was used to achieve robust coatings. The first coating was a polymeric layer (e.g., PCL or [...] Read more.
Resorbable (Vicryl® Plus) sutures were coated with zinc-doped glass (Zn-BG) and silver-doped ordered mesoporous bioactive glass (Ag-MBG) particles by a dip coating technique. A multilayer approach was used to achieve robust coatings. The first coating was a polymeric layer (e.g., PCL or chitosan) and the second one was a composite made of BG particles in a polymer matrix. The coatings were characterized in terms of morphology by scanning electron microscopy (SEM), in vitro bioactivity, and antibacterial properties. Chitosan/Ag-MBG coatings showed the ability to form hydroxyl-carbonate-apatite on their surfaces after immersion in SBF. An antibacterial effect against Gram (+) and Gram (-) bacteria was confirmed, highlighting the potential application of the coated sutures for antibiotic-free approaches. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Optical Fiber Sensors for the Detection of Hydrochloric Acid and Sea Water in Epoxy and Glass Fiber-Reinforced Polymer Composites
Materials 2019, 12(3), 379; https://doi.org/10.3390/ma12030379
Received: 13 December 2018 / Revised: 15 January 2019 / Accepted: 23 January 2019 / Published: 25 January 2019
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Abstract
Optical fiber sensors (OFSs), which rely on evanescent wave sensing for the early detection of the diffusion of water and hydrochloric acid through glass fiber-reinforced polymers (GFRPs), have been developed and tested. Epoxy and GFRP specimens, in which these sensors were embedded, were [...] Read more.
Optical fiber sensors (OFSs), which rely on evanescent wave sensing for the early detection of the diffusion of water and hydrochloric acid through glass fiber-reinforced polymers (GFRPs), have been developed and tested. Epoxy and GFRP specimens, in which these sensors were embedded, were subjected to tests in artificial sea water and hydrochloric acid. The sensors were able to detect the diffusion of chemicals through the epoxy and GFRP samples on the basis of a drop in the reflected signal from the tip of the optical sensor probe. Water and hydrochloric acid diffusion coefficients were calculated from gravimetric measurements and compared with the experimental response of the OFSs. Furthermore, mechanical tests were carried out to assess the influence of the sensors on the structural integrity of the GFRP specimens. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Electrolyte-Supported Fuel Cell: Co-Sintering Effects of Layer Deposition on Biaxial Strength
Materials 2019, 12(2), 306; https://doi.org/10.3390/ma12020306
Received: 13 December 2018 / Revised: 11 January 2019 / Accepted: 15 January 2019 / Published: 18 January 2019
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Abstract
The mechanical reliability of reversible solid oxide cell (SOC) components is critical for the development of highly efficient, durable, and commercially competitive devices. In particular, the mechanical integrity of the ceramic cell, also known as membrane electrolyte assembly (MEA), is fundamental as its [...] Read more.
The mechanical reliability of reversible solid oxide cell (SOC) components is critical for the development of highly efficient, durable, and commercially competitive devices. In particular, the mechanical integrity of the ceramic cell, also known as membrane electrolyte assembly (MEA), is fundamental as its failure would be detrimental to the performance of the whole SOC stack. In the present work, the mechanical robustness of an electrolyte-supported cell was determined via ball-on-3-balls flexural strength measurements. The main focus was to investigate the effect of the manufacturing process (i.e., layer by layer deposition and their co-sintering) on the final strength. To allow this investigation, the electrode layers were screen-printed one by one on the electrolyte support and thus sintered. Strength tests were performed after every layer deposition and the non-symmetrical layout was taken into account during mechanical testing. Obtained experimental data were evaluated with the help of Weibull statistical analysis. A loss of mechanical strength after every layer deposition was usually detected, with the final strength of the cell being significantly smaller than the initial strength of the uncoated electrolyte (σ0 ≈ 800 MPa and σ0 ≈ 1800 MPa, respectively). Fractographic analyses helped to reveal the fracture behavior changes when individual layers were deposited. It was found that the reasons behind the weakening effect can be ascribed to the presence and redistribution of residual stresses, changes in the crack initiation site, porosity of layers, and pre-crack formation in the electrode layers. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Shear Performance at Room and High Temperatures of Glass–Ceramic Sealants for Solid Oxide Electrolysis Cell Technology
Materials 2019, 12(2), 298; https://doi.org/10.3390/ma12020298
Received: 21 December 2018 / Revised: 11 January 2019 / Accepted: 15 January 2019 / Published: 18 January 2019
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Abstract
To provide a reliable integration of components within a solid oxide electrolysis cell stack, it is fundamental to evaluate the mechanical properties of the glass–ceramic sealing materials, as well as the stability of the metal–glass–ceramic interface. In this work, the mechanical behavior of [...] Read more.
To provide a reliable integration of components within a solid oxide electrolysis cell stack, it is fundamental to evaluate the mechanical properties of the glass–ceramic sealing materials, as well as the stability of the metal–glass–ceramic interface. In this work, the mechanical behavior of two previously developed glass–ceramic sealants joined to Crofer22APU steel is investigated at room temperature, 650 °C, and 850 °C under shear load. The mechanical properties of both the glass–ceramics showed temperature dependence. The shear strength of Crofer22APU/glass–ceramic/Crofer22APU joints ranged from 14.1 MPa (20 °C) to 1.8 MPa (850 °C). The elastic modulus of both glass–ceramics also reduced with temperature. The volume fraction of the crystalline phases in the glass–ceramics was the key factor for controlling the mechanical properties and fracture, especially above the glass-transition temperature. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Spectroscopic Properties of Er3+-Doped Particles-Containing Phosphate Glasses Fabricated Using the Direct Doping Method
Materials 2019, 12(1), 129; https://doi.org/10.3390/ma12010129
Received: 4 December 2018 / Revised: 17 December 2018 / Accepted: 21 December 2018 / Published: 3 January 2019
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Abstract
The effect of the incorporation of Er2O3-doped particles on the structural and luminescence properties of phosphate glasses was investigated. A series of different Er2O3-doped TiO2, ZnO, and ZrO2 microparticles was synthesized using [...] Read more.
The effect of the incorporation of Er2O3-doped particles on the structural and luminescence properties of phosphate glasses was investigated. A series of different Er2O3-doped TiO2, ZnO, and ZrO2 microparticles was synthesized using soft chemistry and then added into various phosphate glasses after the melting at a lower temperature than the melting temperature. The compositional, morphological, and structural analyses of the particles-containing glasses were performed using elemental mapping by field emission-scanning electron microscopy (FE-SEM) with energy dispersive x-ray spectrometry (EDS) and x-ray diffraction (XRD). Additionally, the luminescence spectra and the lifetime values were measured to study the influence of the particles incorporation on the spectroscopic properties of the glasses. From the spectroscopic properties of the glasses with the composition 50P2O5-40SrO-10Na2O, a large amount of the Er2O3-doped particles is thought to dissolve during the glass melting. Conversely, the particles were found to survive in glasses with a composition 90NaPO3-(10 − x)Na2O-xNaF (with x = 0 and 10 mol %) due to their lower processing temperature, thus clearly showing that the direct doping method is a promising technique for the development of new active glasses. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Extension of the ‘Inorganic Gel Casting’ Process to the Manufacturing of Boro-Alumino-Silicate Glass Foams
Materials 2018, 11(12), 2545; https://doi.org/10.3390/ma11122545
Received: 26 November 2018 / Revised: 10 December 2018 / Accepted: 11 December 2018 / Published: 14 December 2018
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Abstract
A new technique for the production of glass foams, based on alkali activation and gel casting, previously applied to soda-lime glass, was successfully extended to boro-alumino-silicate glass, recovered from the recycling of pharmaceutical vials. A weak alkali activation (2.5 M NaOH or NaOH/KOH [...] Read more.
A new technique for the production of glass foams, based on alkali activation and gel casting, previously applied to soda-lime glass, was successfully extended to boro-alumino-silicate glass, recovered from the recycling of pharmaceutical vials. A weak alkali activation (2.5 M NaOH or NaOH/KOH aqueous solutions) of fine glass powders (below 70 µm) allowed for the obtainment of well-dispersed concentrated aqueous suspensions, undergoing gelation by treatment at low temperature (75 °C). Unlike soda-lime glass, the progressive hardening could not be attributed to the formation of calcium-rich silicate hydrates. The gelation was provided considering the chemical formulation of pharmaceutical glass (CaO-free) to the formation of hydrated sodium alumino-silicate (N-A-S-H) gel. An extensive direct foaming was achieved by vigorous mechanical stirring of partially gelified suspensions, comprising also a surfactant. A sintering treatment at 700 °C, was finally applied to stabilize the cellular structures. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Solid-Liquid Interdiffusion (SLID) Bonding of p-Type Skutterudite Thermoelectric Material Using Al-Ni Interlayers
Materials 2018, 11(12), 2483; https://doi.org/10.3390/ma11122483
Received: 30 October 2018 / Revised: 22 November 2018 / Accepted: 4 December 2018 / Published: 6 December 2018
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Abstract
Over the past few years, significant progress towards implementation of environmentally sustainable and cost-effective thermoelectric power generation has been made. However, the reliability and high-temperature stability challenges of incorporating thermoelectric materials into modules still represent a key bottleneck. Here, we demonstrate an implementation [...] Read more.
Over the past few years, significant progress towards implementation of environmentally sustainable and cost-effective thermoelectric power generation has been made. However, the reliability and high-temperature stability challenges of incorporating thermoelectric materials into modules still represent a key bottleneck. Here, we demonstrate an implementation of the Solid-Liquid Interdiffusion technique used for bonding Mmy(Fe,Co)4Sb12 p-type thermoelectric material to metallic interconnect using a novel aluminium–nickel multi-layered system. It was found that the diffusion reaction-controlled process leads to the formation of two distinct intermetallic compounds (IMCs), Al3Ni and Al3Ni2, with a theoretical melting point higher than the initial bonding temperature. Different manufacturing parameters have also been investigated and their influence on electrical, mechanical and microstructural features of bonded components are reported here. The resulting electrical contact resistances and apparent shear strengths for components with residual aluminium were measured to be (2.8 ± 0.4) × 10−5 Ω∙cm2 and 5.1 ± 0.5 MPa and with aluminium completely transformed into Al3Ni and Al3Ni2 IMCs were (4.8 ± 0.3) × 10−5 Ω∙cm2 and 4.5 ± 0.5 MPa respectively. The behaviour and microstructural changes in the joining material have been evaluated through isothermal annealing at hot-leg working temperature to investigate the stability and evolution of the contact. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Mechanical Performance of Glass-Based Geopolymer Matrix Composites Reinforced with Cellulose Fibers
Materials 2018, 11(12), 2395; https://doi.org/10.3390/ma11122395
Received: 1 November 2018 / Revised: 22 November 2018 / Accepted: 26 November 2018 / Published: 28 November 2018
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Abstract
Glass-based geopolymers, incorporating fly ash and borosilicate glass, were processed in conditions of high alkalinity (NaOH 10–13 M). Different formulations (fly ash and borosilicate in mixtures of 70–30 wt% and 30–70 wt%, respectively) and physical conditions (soaking time and relative humidity) were adopted. [...] Read more.
Glass-based geopolymers, incorporating fly ash and borosilicate glass, were processed in conditions of high alkalinity (NaOH 10–13 M). Different formulations (fly ash and borosilicate in mixtures of 70–30 wt% and 30–70 wt%, respectively) and physical conditions (soaking time and relative humidity) were adopted. Flexural strength and fracture toughness were assessed for samples processed in optimized conditions by three-point bending and chevron notch testing, respectively. SEM was used to evaluate the fracture micromechanisms. Results showed that the geopolymerization efficiency is strongly influenced by the SiO2/Al2O3 ratio and the curing conditions, especially the air humidity. The mechanical performances of the geopolymer samples were compared with those of cellulose fiber–geopolymer matrix composites with different fiber contents (1 wt%, 2 wt%, and 3 wt%). The composites exhibited higher strength and fracture resilience, with the maximum effect observed for the fiber content of 2 wt%. A chemical modification of the cellulose fiber surface was also observed. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessArticle Effect of Heat Treatment on the Properties of Wood-Derived Biocarbon Structures
Materials 2018, 11(9), 1588; https://doi.org/10.3390/ma11091588
Received: 3 August 2018 / Revised: 17 August 2018 / Accepted: 21 August 2018 / Published: 2 September 2018
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Abstract
Wood-derived porous graphitic biocarbons with hierarchical structures were obtained by high-temperature (2200–2400 °C) non-catalytic graphitization, and their mechanical, electrical and thermal properties are reported for the first time. Compared to amorphous biocarbon produced at 1000 °C, the graphitized biocarbon-2200 °C and biocarbon-2400 °C [...] Read more.
Wood-derived porous graphitic biocarbons with hierarchical structures were obtained by high-temperature (2200–2400 °C) non-catalytic graphitization, and their mechanical, electrical and thermal properties are reported for the first time. Compared to amorphous biocarbon produced at 1000 °C, the graphitized biocarbon-2200 °C and biocarbon-2400 °C exhibited increased compressive strength by ~38% (~36 MPa), increased electrical conductivity by ~8 fold (~29 S/cm), and increased thermal conductivity by ~5 fold (~9.5 W/(m·K) at 25 °C). The increase of duration time at 2200 °C contributed to increased thermal conductivity by ~12%, while the increase of temperature from 2200 to 2400 °C did not change their thermal conductivity, indicating that 2200 °C is sufficient for non-catalytic graphitization of wood-derived biocarbon. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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Open AccessLetter Detrimental Effects of Doping Al and Ba on the Thermoelectric Performance of GeTe
Materials 2018, 11(11), 2237; https://doi.org/10.3390/ma11112237
Received: 15 October 2018 / Revised: 6 November 2018 / Accepted: 9 November 2018 / Published: 11 November 2018
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Abstract
GeTe-based materials are emerging as viable alternatives to toxic PbTe-based thermoelectric materials. In order to evaluate the suitability of Al as dopant in thermoelectric GeTe, a systematic study of thermoelectric properties of Ge1−xAlxTe (x = 0–0.08) alloys processed [...] Read more.
GeTe-based materials are emerging as viable alternatives to toxic PbTe-based thermoelectric materials. In order to evaluate the suitability of Al as dopant in thermoelectric GeTe, a systematic study of thermoelectric properties of Ge1−xAlxTe (x = 0–0.08) alloys processed by Spark Plasma Sintering are presented here. Being isoelectronic to Ge1−xInxTe and Ge1−xGaxTe, which were reported with improved thermoelectric performances in the past, the Ge1−xAlxTe system is particularly focused (studied both experimentally and theoretically). Our results indicate that doping of Al to GeTe causes multiple effects: (i) increase in p-type charge carrier concentration; (ii) decrease in carrier mobility; (iii) reduction in thermopower and power factor; and (iv) suppression of thermal conductivity only at room temperature and not much significant change at higher temperature. First principles calculations reveal that Al-doping increases the energy separation between the two valence bands (loss of band convergence) in GeTe. These factors contribute for Ge1−xAlxTe to exhibit a reduced thermoelectric figure of merit, unlike its In and Ga congeners. Additionally, divalent Ba-doping [Ge1−xBaxTe (x = 0–0.06)] is also studied. Full article
(This article belongs to the Special Issue Advanced Glasses, Composites and Ceramics for High Growth Industries)
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