Showing papers on "Ceramic published in 2014"

Strong, lightweight, and recoverable three-dimensional ceramic nanolattices

Abstract: Ceramics have some of the highest strength- and stiffness-to-weight ratios of any material but are suboptimal for use as structural materials because of their brittleness and sensitivity to flaws. We demonstrate the creation of structural metamaterials composed of nanoscale ceramics that are simultaneously ultralight, strong, and energy-absorbing and can recover their original shape after compressions in excess of 50% strain. Hollow-tube alumina nanolattices were fabricated using two-photon lithography, atomic layer deposition, and oxygen plasma etching. Structures were made with wall thicknesses of 5 to 60 nanometers and densities of 6.3 to 258 kilograms per cubic meter. Compression experiments revealed that optimizing the wall thickness-to-radius ratio of the tubes can suppress brittle fracture in the constituent solid in favor of elastic shell buckling, resulting in ductile-like deformation and recoverability.

Strong, tough and stiff bioinspired ceramics from brittle constituents

Abstract: High strength and high toughness are usually mutually exclusive in engineering materials. In ceramics, improving toughness usually relies on the introduction of a metallic or polymeric ductile phase, but this decreases the material’s strength and stiffness as well as its high-temperature stability. Although natural materials that are both strong and tough rely on a combination of mechanisms operating at different length scales, the relevant structures have been extremely difficult to replicate. Here, we report a bioinspired approach based on widespread ceramic processing techniques for the fabrication of bulk ceramics without a ductile phase and with a unique combination of high strength (470 MPa), high toughness (17.3 MPa m1/2), and high stiffness (290 GPa). Because only mineral constituents are needed, these ceramics retain their mechanical properties at high temperatures (600 °C). Our bioinspired, material-independent approach should find uses in the design and processing of materials for structural, transportation and energy-related applications. The toughness of ceramic materials can be improved by introducing a polymeric or metallic ductile phase, yet most often this is at the expense of strength, stiffness and high-temperature stability. Now, a simple processing route based on widespread ceramic processing techniques is shown to produce bulk ceramics that mimic the structure of natural nacre and have a unique combination of high strength, toughness and stiffness, even at high temperatures.

Additive Manufacturing of Ceramic‐Based Materials

Abstract: This paper offers a review of present achievements in the field of processing of ceramic-based materials with complex geometry using the main additive manufacturing (AM) technologies In AM, the geometrical design of a desired ceramic-based component is combined with the materials design In this way, the fabrication times and the product costs of ceramic-based parts with required properties can be substantially reduced However, dimensional accuracy and surface finish still remain crucial features in today's AM due to the layer-by-layer formation of the parts In spite of the fact that significant progress has been made in the development of feedstock materials, the most difficult limitations for AM technologies are the restrictions set by material selection for each AM method and aspects considering the inner architectural design of the manufactured parts Hence, any future progress in the field of AM should be based on the improvement of the existing technologies or, alternatively, the development of new approaches with an emphasis on parts allowing the near-net formation of ceramic structures, while optimizing the design of new materials and of the part architecture

Study on mechanical and wear properties of Al 7075/Al2O3/graphite hybrid composites

Abstract: This work investigated the influence of graphite on the wear behavior of Al 7075/Al 2 O 3 /5 wt.% graphite hybrid composite. The investigation reveals the effectiveness of incorporation of graphite in the composite for gaining wear reduction. The Al 7075 (aluminium alloy 7075) reinforced with Al 2 O 3 –graphite were investigated. The composites were fabricated using liquid metallurgy route. Ceramic particles along with solid lubricating materials were incorporated into aluminium alloy matrix to accomplish reduction in both wear resistance and coefficient of friction. The Al 7075/Al 2 O 3 /graphite hybrid composite was prepared with 5 wt.% graphite particles addition and 2, 4, 6 and 8 wt.% of Al 2 O 3 . The hardness, tensile strength, flexural strength and compression strength of the Al 7075–Al 2 O 3 –graphite hybrid composites are found to be increased by increased weight percentage of ceramic phase. The wear properties of the hybrid composites containing graphite exhibited the superior wear-resistance properties.

Electromagnetic properties of Si–C–N based ceramics and composites

Abstract: Besides the excellent high-temperature mechanical properties, Si3N4 and SiC based ceramics containing insulating or electrically conductive phase are attractive for their tunable dielectric propert...

High-strength cellular ceramic composites with 3D microarchitecture

Abstract: To enhance the strength-to-weight ratio of a material, one may try to either improve the strength or lower the density, or both. The lightest solid materials have a density in the range of 1,000 kg/m3; only cellular materials, such as technical foams, can reach considerably lower values. However, compared with corresponding bulk materials, their specific strength generally is significantly lower. Cellular topologies may be divided into bending- and stretching-dominated ones. Technical foams are structured randomly and behave in a bending-dominated way, which is less weight efficient, with respect to strength, than stretching-dominated behavior, such as in regular braced frameworks. Cancellous bone and other natural cellular solids have an optimized architecture. Their basic material is structured hierarchically and consists of nanometer-size elements, providing a benefit from size effects in the material strength. Designing cellular materials with a specific microarchitecture would allow one to exploit the structural advantages of stretching-dominated constructions as well as size-dependent strengthening effects. In this paper, we demonstrate that such materials may be fabricated. Applying 3D laser lithography, we produced and characterized micro-truss and -shell structures made from alumina–polymer composite. Size-dependent strengthening of alumina shells has been observed, particularly when applied with a characteristic thickness below 100 nm. The presented artificial cellular materials reach compressive strengths up to 280 MPa with densities well below 1,000 kg/m3.

Topological‐Structure Modulated Polymer Nanocomposites Exhibiting Highly Enhanced Dielectric Strength and Energy Density

Abstract: Dielectric materials with high electric energy densities and low dielectric losses are of critical importance in a number of applications in modern electronic and electrical power systems. An organic–inorganic 0–3 nanocomposite, in which nanoparticles (0-dimensional) are embedded in a 3-dimensionally connected polymer matrix, has the potential to combine the high breakdown strength and low dielectric loss of the polymer with the high dielectric constant of the ceramic fillers, representing a promising approach to realize high energy densities. However, one significant drawback of the composites explored up to now is that the increased dielectric constant of the composites is at the expense of the breakdown strength, limiting the energy density and dielectric reliability. In this study, by expanding the traditional 0–3 nanocomposite approach to a multilayered structure which combines the complementary properties of the constituent layers, one can realize both greater dielectric displacement and a higher breakdown field than that of the polymer matrix. In a typical 3-layer structure, for example, a central nanocomposite layer of higher breakdown strength is introduced to substantially improve the overall breakdown strength of the multilayer-structured composite film, and the outer composite layers filled with large amount of high dielectric constant nanofillers can then be polarized up to higher electric fields, hence enhancing the electric displacement. As a result, the topological-structure modulated nanocomposites, with an optimally tailored nanomorphology and composite structure, yield a discharged energy density of 10 J/cm3 with a dielectric breakdown strength of 450 kV mm–1, much higher than those reported from all earlier studies of nanocomposites.

Fabrication, characterization, properties and theoretical analysis of ceramic/PVDF composite flexible films with high dielectric constant and low dielectric loss

Abstract: Calcium barium zirconate titanate (Ba0.95Ca0.05Zr0.15Ti0.85O3, BCZT) ceramic particles were prepared by a conventional solid-state method. BCZT powders were modified by dopamine through a chemical coating method. The composite flexible films based on dopamine@BCZT and polyvinylidene fluoride were fabricated via a solution casting method. The microstructure and morphology were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, and field emission scanning electron microscopy. A precision impedance analyzer and a dielectric withstand voltage test were used to test the dielectric constant, loss tangent, and breakdown strength. TEM results showed that dopamine was uniformly coated on the surface of BCZT particles with an average thickness of 20 nm. SEM results showed that the ceramic particles were dispersed homogeneously in the matrix. The dielectric constant increased with the increase of BCZT contents, while the loss tangent remained constant in the frequency range of 103 to 105 Hz. Different theoretical models were employed to predict the effective dielectric constants of the composite films, and the estimated results were compared with the experimental data. Weibull distribution was used to analyze the dielectric breakdown strength, and the results showed that the breakdown strength decreased then stayed over 60 kV mm−1.

Additive manufacturing of ceramics: A review

Abstract: Additive manufacturing (AM) of ceramics is coming to an aera where the first industrial applications are becoming economically profitable. This review paper provides a survey of AMmethods reported in literature to shape ceramic components. It demonstrates that AM has produced ceramic parts that have no cracks or large pores and have mechanical properties close to those of conventionally produced ceramics. Crackand pore-free ceramics can be manufacturedbyoptimizing theAMprocess parameters orperforming extradensification steps after theAMprocess. It is also advisable to incorporate colloidal processing techniques in the AM process. Finally, the paper demonstrates that, especially forAMof ceramics, themulti-step indirectAMprocesses aremore appropriate to shape different types of ceramics, while the single-step direct AM processes can produce ceramic parts more rapidly.

A review of the electrodeposition of metal matrix composite coatings by inclusion of particles in a metal layer: an established and diversifying technology

Abstract: Following a brief overview of their history, which dates back to the 1920s with marked developments during the 1960s and 1970s, the principles of composite coatings, achieved by including particles dispersed in a bath into a growing electrodeposited metal layer, are considered. The principles and role of electroplating compared to other techniques for realising such coatings, are considered. A good quality particle dispersion (often aided by a suitable type and concentration of surfactants) appropriate choice of work-piece shape/geometry and controlled agitation in the bath are seen to be prerequisites for achieving uniform coatings having a well-dispersed particle content by electroplating. Examples are provided to illustrate the influence of bath composition and plating conditions on deposit properties. Engineering applications of included particle composite layers are illustrated by examples of hard ceramic, soft ceramic and polymer inclusion composite coatings from the recent literature. Current trends in the development of composite plated coatings are summarised and their diverse applications are seen to include the use of finely structured (especially nanostructured) and functionally active particles together with hybrid and more complex, e.g. hierarchical, structures for applications ranging from tribology to speciality electronics, magnetic and electrochemical energy conversion materials.

Optical temperature sensor based on upconversion emission in Er-doped ferroelectric 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 ceramic

Abstract: Optical temperature sensing properties based on upconversion emission of Er-doped 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 ferroelectric ceramics are reported. The fluorescence intensity ratio of green upconversion emissions at 525 and 550 nm in the temperature range of 200–443 K was investigated. The maximum sensing sensitivity and temperature resolution were found to be 0.0044 K−1 and 0.4 K, respectively, suggesting that the Er-doped 0.5Ba(Zr0.2Ti0.8)O3- 0.5(Ba0.7Ca0.3)TiO3 ferroelectric ceramic possesses potential application in optical temperature sensing. Ferroelectric and piezoelectric properties were also investigated. These results reveal that the Er-doped 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 ferroelectric ceramic is a promising multifunctional sensing material.

Light curing strategies for lithography-based additive manufacturing of customized ceramics

Abstract: Lithography-based additive manufacturing (AM) is increasingly becoming the technology of choice for the small series or single unit production. At the TU Vienna a digital light processing (DLP) system was developed for the fabrication of complex technical ceramics, requiring high levels of detail and accuracy. The DLP-system used in this study creates a ceramic green part by stacking up layers of a photo-curable resin with a solid loading of around 45 vol.% zirconia. After a thermal debinding and sintering step the part turns into a dense ceramic and gains its final properties. The native resolution of the DLP process depends on the light engine's DMD (digital mirror device) chip and the optics employed. Currently it is possible to print 3D-structures with a spatial resolution down to 40 μm. A modification of the light source allows for the customization of the light curing strategy for each pixel of the exposed layers. This work presents methods to improve the geometrical accuracy as well as the structural properties of the final 3D-printed ceramic part by using the full capabilities of the light source. On the one hand, the feasibility to control the dimensional overgrowth to gain resolution below the native resolution of the light engine—a sub-pixel resolution—was evaluated. Overgrowth occurs due to light scattering and was found to be sensitive to both exposure time and exposed area. On the other hand, different light curing strategies (LCSs) and depths of cure (Cd) were used for the 3D-printing of ceramic green parts and their influence on cracks in the final ceramic was evaluated. It was concluded that softstart LCSs, as well as higher values for Cd, reduce cracks in the final ceramic. Applying these findings within the 3D-printing process may be another step toward flawless and highly accurate ceramic parts.

Toward hard yet tough ceramic coatings

Abstract: Over the past decades, hard and super hard ceramic coatings have been developed and widely used in various industrial applications Meanwhile, an increasing number of studies have realized that the toughness is just as crucial, if not more, than hardness especially for ceramic coatings However, hardness and toughness do not go naturally hand in hand In other words, hard coatings usually are brittle and less durable while toughened coatings are of lower strength For practical engineering applications, it is more desirable to have coatings with high hardness without sacrificing toughness too much In this article, a review is presented on continuous progress to realize hard-yet-tough ceramic coatings from an angle of hardening as well as toughening

Significantly enhanced dielectric property in PVDF nanocomposites flexible films through a small loading of surface-hydroxylated Ba0.6Sr0.4TiO3 nanotubes

Abstract: Polymer composite flexible films with high dielectric constant are highly desirable in electronic and electrical industry. Higher loading of the ceramic fillers is usually needed in order to realize high dielectric constant. However, such composites exhibit low breakdown strength and poor mechanical and processing properties. In this work, by incorporating high aspect ratio surface-hydroxylated Ba0.6Sr0.4TiO3 nanotubes (BST NT) prepared via electrospinning into a polyvinylidene-fluoride (PVDF) matrix, PVDF nanocomposite flexible films with high dielectric constant have been successfully obtained. The nanocomposite containing 10 vol% BST NT-OH has a dielectric constant of 48.2 at 1 kHz, which is 6.1 times higher than that of the pure PVDF (7.9). The dielectric properties of the composites are closely related to the combined effects of the surface modification, large aspect ratio, high surface area and paraelectric polarization behavior of the BST NT.

Annealing-free fabrication of highly oxidation-resistive copper nanowire composite conductors for photovoltaics

Abstract: Copper nanowire (CuNW)-network film is a promising alternative to the conventional indium tin oxide (ITO) as a transparent conductor. However, thermal instability and the ease of oxidation hinder the practical applications of CuNW films. We present oxidation-resistive CuNW-based composite electrodes that are highly transparent, conductive and flexible. Lactic acid treatment effectively removes both the organic capping molecule and the surface oxide/hydroxide from the CuNWs, allowing direct contact between the nanowires. This chemical approach enables the fabrication of transparent electrodes with excellent properties (19.8 Ω sq−1 and 88.7% at 550 nm) at room temperature without any atmospheric control. Furthermore, the embedded structure of CuNWs with Al-doped ZnO (AZO) dramatically improves the thermal stability and oxidation resistance of CuNWs. These AZO/CuNW/AZO composite electrodes exhibit high transparency (83.9% at 550 nm) and low sheet resistance (35.9 Ω sq−1), maintaining these properties even with a bending number of 1280 under a bending radius of 2.5 mm. When implemented in a Cu(In1−x,Gax)(S,Se)2 thin-film solar cell, this composite electrode demonstrated substantial potential as a low-cost (Ag-, In-free), high performance transparent electrode, comparable to a conventional sputtered ITO-based solar cell. A highly thermal and oxidation-resistive AZO/Cu nanowire/AZO composite electrode for thin-film solar cells was fabricated at room temperature without any atmospheric control. Our novel transparent composite electrode showed good thermal oxidation stability as well as high conductivity (∼35.9 Ω/sq), transparency (83.9% at 550 nm) and flexibility. Metal nanowire-based materials are promising alternatives to the conventional transparent electrodes found in solar cells and touchscreen displays because they are naturally flexible and stretchable — attributes that can dramatically improve device lifetimes. Current efforts, however, have been hampered by the need for expensive silver nanowires; lower-cost materials, such as copper nanowires, possess an insulating surface oxide film that deteriorates device conductivity. Jooho Moon and co-workers from Yonsei University, South Korea, have now uncovered a surprising way to remove oxides and organic capping molecules from copper nanowires using lactic acid, a biomolecule commonly found in milk. Room temperature lactic acid treatments, followed by washes with organic solvents, yielded transparent copper nanowire networks that feature direct, metal-to-metal contact. Photovoltaic testing revealed these bendable electrodes had excellent conductivity for high-performance solar applications.

Resin bond to indirect composite and new ceramic/polymer materials: a review of the literature.

Abstract: tatement of the Problem Resin bonding is essential for clinical longevity of indirect restorations. Especially in light of the increasing popularity of computer-aided design/computer-aided manufacturing-fabricated indirect restorations, there is a need to assess optimal bonding protocols for new ceramic/polymer materials and indirect composites. Purpose of the Study The aim of this article was to review and assess the current scientific evidence on the resin bond to indirect composite and new ceramic/polymer materials. Materials and Methods An electronic PubMed database search was conducted from 1966 to September 2013 for in vitro studies pertaining the resin bond to indirect composite and new ceramic/polymer materials. Results The search revealed 198 titles. Full-text screening was carried out for 43 studies, yielding 18 relevant articles that complied with inclusion criteria. No relevant studies could be identified regarding new ceramic/polymer materials. Most common surface treatments are aluminum-oxide air-abrasion, silane treatment, and hydrofluoric acid-etching for indirect composite restoration. Self-adhesive cements achieve lower bond strengths in comparison with etch-and-rinse systems. Thermocycling has a greater impact on bonding behavior than water storage. Conclusions Air-particle abrasion and additional silane treatment should be applied to enhance the resin bond to laboratory-processed composites. However, there is an urgent need for in vitro studies that evaluate the bond strength to new ceramic/polymer materials. Clinical Significance This article reviews the available dental literature on resin bond of laboratory composites and gives scientifically based guidance for their successful placement. Furthermore, this review demonstrated that future research for new ceramic/polymer materials is required.

Advanced Ceramics from Preceramic Polymers Modified at the Nano-Scale: A Review

Abstract: Preceramic polymers, i.e., polymers that are converted into ceramics upon heat treatment, have been successfully used for almost 40 years to give advanced ceramics, especially belonging to the ternary SiCO and SiCN systems or to the quaternary SiBCN system. One of their main advantages is the possibility of combining the shaping and synthesis of ceramics: components can be shaped at the precursor stage by conventional plastic-forming techniques, such as spinning, blowing, injection molding, warm pressing and resin transfer molding, and then converted into ceramics by treatments typically above 800 °C. The extension of the approach to a wider range of ceramic compositions and applications, both structural and thermo-structural (refractory components, thermal barrier coatings) or functional (bioactive ceramics, luminescent materials), mainly relies on modifications of the polymers at the nano-scale, i.e., on the introduction of nano-sized fillers and/or chemical additives, leading to nano-structured ceramic components upon thermal conversion. Fillers and additives may react with the main ceramic residue of the polymer, leading to ceramics of significant engineering interest (such as silicates and SiAlONs), or cause the formation of secondary phases, significantly affecting the functionalities of the polymer-derived matrix.

Size-dependence of the dielectric breakdown strength from nano- to millimeter scale

Abstract: Dielectric breakdown decisively determines the reliability of nano- to centimeter sized electronic devices and components. Nevertheless, a systematic investigation of this phenomenon over the relevant lengths scales and materials classes is still missing. Here, the thickness and permittivity-dependence of the dielectric breakdown strength of insulating crystalline and polymer materials from the millimeter down to the nanometer scale is investigated. While the dependence of breakdown strength on permittivity was found to be thickness-independent for materials in the nm–mm range, the magnitude of the breakdown strength was found to change from a thickness-independent, intrinsic regime, to a thickness-dependent, extrinsic regime. The transition-thickness is interpreted as the characteristic length of a breakdown-initiating conducting filament. The results are in agreement with a model, where the dielectric breakdown strength is defined in terms of breakdown toughness and length of a conducting filament.

Fracture Toughness of Plasma‐Sprayed Thermal Barrier Ceramics: Influence of Processing, Microstructure, and Thermal Aging

Abstract: Fracture toughness has become one of the dominant design parameters that dictates the selection of materials and their microstructure to obtain durable thermal barrier coatings (TBCs). Much progress has been made in characterizing the fracture toughness of relevant TBC compositions in bulk form, and it has become apparent that this property is significantly affected by process-induced microstructural defects. In this investigation, a systematic study of the influence of coating microstructure on the fracture toughness of atmospheric plasma sprayed (APS) TBCs has been carried out. Yttria partially stabilized zirconia (YSZ) coatings were fabricated under different spray process conditions inducing different levels of porosity and interfacial defects. Fracture toughness was measured on free standing coatings in as-processed and thermally aged conditions using the double torsion technique. Results indicate significant variance in fracture toughness among coatings with different microstructures including changes induced by thermal aging. Comparative studies were also conducted on an alternative TBC composition, Gd2Zr2O7 (GDZ), which as anticipated shows significantly lower fracture toughness compared to YSZ. Furthermore, the results from these studies not only point towards a need for process and microstructure optimization for enhanced TBC performance but also a framework for establishing performance metrics for promising new TBC compositions.