Crystalline Ceramics Research Articles

Design of polymer-derived SiC for nuclear applications from the perspective of heterogeneous interfaces

Polymer-derived SiC ceramics have been increasingly used in the field of nuclear energy. Herein, we synthetized polymer-derived SiCs with varying SiC/C heterogeneous interfacial properties by pyrolyzing the ceramics at different temperatures. Subsequently, we studied the effect of these interfacial properties on the irradiation behavior (i.e., volume swelling, amorphization, and mechanical properties) of the SiC ceramics. In the case of crystalline ceramics (pyrolyzed at 1150–1500°C), the presence of a nano-crystalline graphite (NC-G) phase with sp3/sp2 hybridization ratios of 0.40–1.27 further enhanced the swelling resistance of nano-SiC by increasing the defect trapping capability of the interfaces. In contrast, amorphous ceramics (pyrolyzed at 900–1100°C) showed low penetration depths and superior stabilities upon irradiation. These strong ion cascade blocking characteristics may result from the atomic short-range order of these materials. This approach allows optimum design of polymer-derived SiC with superior swelling resistance and stability under room-temperature irradiation.

Formulation of a Statistical Mechanical Theory To Understand the Li Ion Conduction in Crystalline Electrolytes: A Case Study on Li-Stuffed Garnets

Ionic conductivity in solids is being computed using a wide range of computational methods such as molecular dynamics simulations and is measured using experimental methods, including electrochemical impedance spectroscopy and dc methods, and solid-state nuclear magnetic resonance spectroscopy. We report for the first time a statistical mechanical approach to estimate Li ion conductivity in the crystalline Li-stuffed garnet-type structure Li5La3Ta2O12, Li5.5La2.5Ba0.5Ta2O12, and Li6La2BaTa2O12. The estimated conductivity and activation energy for ionic conduction were found to be very consistent with experimental values for all three investigated garnets. The ionic conductivity was computed from the electrostatic friction coefficient of the Li ion using a combination of nonequilibrium statistical mechanics and electrostatics. The developed theory is derived from the fundamental transport equations that can be adapted to a wide range of crystalline ceramics electrolytes where crystallographic information i...

Preliminary studies of PVA/PVP blends incorporated with HAp and β-TCP bone ceramic as template for hard tissue engineering.

Polyvinylalcohol (PVA) and Polyvinylpyrrolidone (PVP) blend incorporated with hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) is electrospun as nanofibrous composite scaffolds to act as suitable template for bone tissue engineering. Microscopic and spectroscopic characterizations confirm uniform integration of the crystalline calcium phosphate ceramics in the scaffolds. PVA-PVP blends are usually amorphous in nature and addition of phosphate ceramic particles specifically HAp elevates its crystalline behavior which is substantiated by XRD details. Further incorporation of ceramics is confirmed using FT-IR as characteristic PO43- groups for HAp and β-TCP were observed in the distinguished composites. Single glass transition temperature is observed for pure and composite blends indicating the formation of highly miscible blends. Also, addition of these ceramics augments the thermal stability of the blend scaffolds. Biocompatibility of the prepared (PVA: PVP)-HAp and (PVA: PVP)-TCP scaffolds is assessed using MG-63 Osteoblast cell lines in the time interval of 1st, 4th and 7th day. The cell viability percentage for (PVA: PVP)-HAp is high compared to β-TCP added blend composites, reinforcing the fact that scaffolds with good mechanical strength and enhanced porosity supports better cell adhesion.

Effects of Helium Ion Irradiation on Properties of Crystalline and Amorphous Multiphase Ceramic Coatings

The Al2O3-TiO2 crystalline and amorphous multiphase ceramic coatings were prepared on a martensitic steel by laser in situ reaction technique and impose irradiation with 200 keV He ions at different doses. The helium ion irradiation goes 1.55 μm deep from the surface of coating, and the displacement per atom (dpa) for the Al2O3-TiO2 coating is 20.0. When the irradiation fluency is 5 × 1017 ions/cm2, defects are identified in crystalline areas and there form interfacial areas in the coating. These crystal defects tend to migrate and converge at the interfaces. Moreover, helium ion irradiation is found to exert no effect on surface chemical composition and phase constitution of the coatings, while surface mechanical properties for the coatings after irradiation differ from those before irradiation. Further nano-indentation experiments reveal that surface nano-hardness of the Al2O3-TiO2 multiphase coatings decreases as the helium ions irradiation flux increases. Such Al2O3-TiO2 crystalline and amorphous multiphase ceramic coatings exhibit the strongest resistance against helium ion irradiation which shall be applied as candidate structural materials for accelerator-driven sub-critical system to handle the nuclear waste under extreme conditions.

Tratamento de superfície para a cimentação adesiva de cerâmicas à base de zircônia: revisão de literatura

Objetivo: analisar, por meio de uma revisão da literatura, os diferentes métodos de tratamento de superfície de peças protéticas à base de zircônia e os seus efeitos sobre a cimentação adesiva. Material e Métodos: a seleção dos artigos foi realizada por meio de uma busca na base de dados PubMed/MEDLINE. A amostra final foi composta por 31 estudos publicados entre 2011-2016. Resultados: as cerâmicas à base de zircônia (ZrO2) têm propriedades importantes, como durabilidade química, alta tenacidade à fratura, módulo de elasticidade e dureza. Apesar da dificuldade de ligação da superfície da ZrO2 aos cimentos resinosos, estes são uma boa opção para unir as restaurações indiretas aos tecidos dentários. Entretanto, o condicionamento com ácido hidrofluorídrico e a silanização não melhoram a força de união entre o cimento resinoso convencional e cerâmica de alto conteúdo cristalino. Por esta razão, é necessário um modo de tratamento de superfície diferente para proporcionar uma força de ligação adequada. Conclusão: os estudos disponíveis sugerem que o jateamento com partículas de óxido de alumínio e a silicatização proporcionam rugosidade superficial e uma adequada resistência adesiva, no entanto, induzem à transformação de fase tetragonal em monoclínica. Por outro lado, a infiltração seletiva por vidro demonstra não gerar danos à superfície da ZrO2, porém, há a necessidade de mais pesquisas sobre esse recente método.

Silica Coating of Nonsilicate Nanoparticles for Resin-Based Composite Materials

This study was designed to develop and characterize a silica-coating method for crystalline nonsilicate ceramic nanoparticles (Al2O3, TiO2, and ZrO2). The hypothesis was that the coated nonsilicate nanoparticles would stably reinforce a polymeric matrix due to effective silanation. Silica coating was applied via a sol-gel method, with tetraethyl orthosilicate as a silica precursor, followed by heat treatment. The chemical and microstructural characteristics of the nanopowders were evaluated before and after silica coating through x-ray diffraction, BET (Brunauer-Emmett-Teller), energy-dispersive x-ray spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy analyses. Coated and noncoated nanoparticles were silanated before preparation of hybrid composites, which contained glass microparticles in addition to the nanoparticles. The composites were mechanically tested in 4-point bending mode after aging (10,000 thermal cycles). Results of all chemical and microstructural analyses confirmed the successful obtaining of silica-coated nanoparticles. Two distinct aspects were observed depending on the type of nanoparticle tested: 1) formation of a silica shell on the surface of the particles and 2) nanoparticle clusters embedded into a silica matrix. The aged hybrid composites formulated with the coated nanoparticles showed improved flexural strength (10% to 30% higher) and work of fracture (35% to 40% higher) as compared with composites formulated with noncoated nanoparticles. The tested hypothesis was confirmed: silanated silica-coated nonsilicate nanoparticles yielded stable reinforcement of dimethacrylate polymeric matrix due to effective silanation. The silica-coating method presented here is a versatile and promising novel strategy for the use of crystalline nonsilicate ceramics as a reinforcing phase of polymeric composite biomaterials.

Properties of phosphate glass waste forms containing fluorides from a molten salt reactor

Radioactive fluoride wastes are generated during the operation of molten salt reactors (MSRs) and reprocessing of their spent fuel. Immobilization of these wastes in borosilicate glass is not feasible because of the very low solubility of fluorides in this host. Alternative candidates are thus an active topic of research including phosphate-based glasses, crystalline ceramics, and hybrid glass–ceramic systems. In this study, mixed fluorides were employed as simulated MSRs waste and incorporated into sodium aluminophosphate glass to obtain phosphate-based waste form. These waste forms were characterized by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Leaching tests were performed in deionized water using the product consistency test A method. This study demonstrates that up to 20 mol% of simulated radioactive waste can be introduced into the NaAlP glass matrix, and the chemical durability is much better than that of borosilicate. The addition of Fe2O3 in the NaAlP glass matrix results in increases of the chemical durability at the expense of fluoride loading (to 6.4 mol%). Phosphate glass vitrification of radioactive waste containing fluorides is a potential method to treat and dispose of MSR wastes.

An Experimental Study on Mechanical Modeling of Ceramics Based on Microstructure

The actual grinding result of ceramics has not been well predicted by the present mechanical models. No allowance is made for direct effects of materials microstructure and almost all the mechanical models were obtained based on crystalline ceramics. In order to improve the mechanical models of ceramics, surface grinding experiments on crystalline ceramics and non-crystalline ceramics were conducted in this research. The normal and tangential grinding forces were measured to calculate single grit force and specific grinding energy. Grinding surfaces were observed. For crystalline alumina ceramics, the predictive modeling of normal force per grit fits well with the experimental result, when the maximum undeformed chip thickness is less than a critical depth, which turns out to be close to the grain size of alumina. Meanwhile, there is a negative correlation between the specific grinding energy and the maximum undeformed chip thickness. With the decreasing maximum undeformed chip thickness, the proportions of ductile removal and transgranular fracture increase. However, the grinding force models are not applicable for non-crystalline ceramic fused silica and the specific grinding energy fluctuates irregularly as a function of maximum undeformed chip thickness seen from the experiment.

Plastic deformation in nanocrystalline TiN at ultra-low stress: An in situ nanoindentation study

It is well adopted that a majority of ceramic materials have low ductility and the plastic yielding in crystalline ceramics occurs succeeding elastic deformation. Here by using in situ nanoindentation we show, however, that in nanocrystalline TiN, massive non-elastic events, such as grain rotation and grain boundary (GB) sliding, occur at ultra-low stresses (<1GPa), well below the yielding strength of the material (6–8GPa). Furthermore, by performing in situ nanoindentations on TiN with different average grain sizes of 110nm, 35nm and 20nm, we observed a prominent grain size effect: that is specimens with smaller average grain sizes possess greater plastic deformation than the ones with larger grains. This in situ nanoindentation study thus provides new perspectives on understanding plasticity of hard nanocrystalline ceramics at room temperature.

A state-of-the-art review of micron-scale spatially resolved residual stress analysis by FIB-DIC ring-core milling and other techniques

Quantification of residual stress gradients can provide great improvements in understanding the complex interactions between microstructure, mechanical state, mode(s) of failure and structural integrity. Highly focused local probe non-destructive techniques such as X-ray diffraction, electron diffraction or Raman spectroscopy have an established track record in determining spatial variations in the relative changes in residual stress with respect to a reference state for many structural materials. However, the interpretation of these measurements in terms of absolute stress values requires a strain-free sample often difficult to obtain due to the influence of chemistry, microstructure or processing route. With the increasing availability of focused ion beam instruments, a new approach has been developed which is known as the micro-scale ring-core focused ion beam-digital image correlation technique. This technique is becoming the principal tool for quantifying absolute in-plane residual stresses. It can be applied to a broad range of materials: crystalline and amorphous metallic alloys and ceramics, polymers, composites and biomaterials. The precise nano-scale positioning and well-defined gauge volume of this experimental technique make it eminently suitable for spatially resolved analysis, that is, residual stress profiling and mapping. Following a summary of micro-stress evaluation approaches, we focus our attention on focused ion beam-digital image correlation methods and assess the application of micro-scale ring-core methods for spatially resolved residual stress profiling. The sequential ring-core milling focused ion beam-digital image correlation method allows micro- to macro-scale mapping at the step of 10–1000 μm, while the parallel focused ion beam-digital image correlation approach exploits simultaneous milling operation to quantify stress profiles at the micron scale (1–10 μm). Cross-validation against X-ray diffraction results confirms that these approaches represent accurate, reliable and effective residual stress mapping methods.

Ion-beam irradiation and 244Cm-doping investigations of the radiation response of actinide-bearing crystalline waste forms

Abstract

A continuous method to prepare poorly crystalline silver-doped calcium phosphate ceramics with antibacterial properties

Silver-doped calcium phosphate ceramics were prepared in discontinuous and continuous processes with different amounts of incorporated silver (up to 1.8 wt% silver).

Fatigue behavior of partially crystalline ceramics

Fatigue behavior of partially crystalline ceramics

Similar healthy osteoclast and osteoblast activity on nanocrystalline hydroxyapatite and nanoparticles of tri-calcium phosphate compared to natural bone.

While there have been numerous studies to determine osteoblast (bone forming cell) functions on nanocrystalline compared to micron crystalline ceramics, there have been few studies which have examined osteoclast activity (including tartrate-resistant acid phosphatase, formation of resorption pits, size of resorption pits, and receptor activator of nuclear factor κB [RANK]). This is despite the fact that osteoclasts are an important part of maintaining healthy bone since they resorb bone during the bone remodeling process. Moreover, while it is now well documented that bone formation is enhanced on nanoceramics compared to micron ceramics, some have pondered whether osteoblast functions (such as osteoprotegerin and RANK ligand [RANKL]) are normal (ie, non-diseased) on such materials compared to natural bone. For these reasons, the objective of the present in vitro study was to determine various functions of osteoclasts and osteoblasts on nanocrystalline and micron crystalline hydroxyapatite as well as tri-calcium phosphate materials and compare such results to cortical and cancellous bone. Results showed for the first time similar osteoclast activity (including tartrate-resistant acid phosphatase, formation of resorption pits, size of resorption pits, and RANK) and osteoblast activity (osteoprotegerin and RANKL) on nanocrystalline hydroxyapatite compared to natural bone, whereas osteoclast and osteoblast functions on micron crystalline versions of these ceramics were much different than natural bone. In this manner, this study provides additional evidence that nanocrystalline calcium phosphates can serve as suitable synthetic analogs to natural bone to improve numerous orthopedic applications. It also provides the first data of healthy osteoclast and osteoblast functions on nanocrystalline calcium phosphates compared to natural bone.

Adhesion to Dental Ceramics

All-ceramic restorations are attractive because of their long lasting esthetics and the ability to with- stand the oral conditions. However, bonding to ceramics has challenged the dental community for the last few decades. The clinical success of a ceramic restoration is strongly dependent on the quality and durability of the bond between the resin cement and the restoration. This study presents the bonding mechanisms and the me- chanical tests to evaluate the adhesive interfaces of resin-bonded ceramic restorations, mainly the zirconia- based restorations, which are the most popular. An adequate bond involves ceramic surface changes for mechanical retention, which can be achieved using primers, such as acids and airborne particle abrasion. Selective etching of high crystalline content ceramics mostly occurs within grain boundaries that offer little micromechanical retention and an insufficient bond to resin. The most popular surface treatment to improve adhesion to high crystalline content ceramics involves the treatment of surfaces with airborne particle abrasion and chemical bonding. Yet, there are reports on new methods to enhance the resin bond to zirconia that need further investigation. This study provides scientific evi- dences to guide the clinical procedures on bonding ceramic restorations.

Effect of spark plasma sintering process on the microstructure and mechanical properties of Nano crystalline hydroxyapatite ceramics prepared by hydrolysis in polyol medium

The aim of the study was to investigate the role of microstructure and porosity on the mechanical behaviour of sintered hydroxyapatite synthesized by polyol process. This process describes a new approach for the synthesis of hydroxyapatite nanoparticles, which involves precipitation and hydrolysis reactions conducted in polyol medium. In the present work a non-conventional technique, spark plasma sintering, was used to consolidate such nanocrystalline apatites at non-conventional, very low temperatures (T &lt; 300°C) so as to preserve the surface hydrated layer present on the nanocrystals. The hydroxyapatite nanoparticles have been successfully conducted by spark plasma sintering process, resulting in a dense HA compacts. Besides, the sintering behaviour of hydroxyapatite powders at different temperatures ranging was studied. The microstructure, Vickers microhardness, nanoindentation and density are described. Finally, the resulting mechanical properties determined on the microwave sintered samples (E = 136 ±4 GPa, HV = 8.2 GPa, and KIC= 1.6 ±0.03 MPa m1/2) are significantly higher than those usually reported in the literature, whatever the sintering process, and could allow the use of hydroxyapatite for structural applications. Keywords: Hydroxyapatite; Polyol; Spark Plasma Sintering; Mechanical Properties.

Formation and Surface Structural Features of Crystalline Ceramic Nanocomposite Coatings on Aluminium Using Lithium Sulphate with Silicate Additive

We have synthesized a series of the ceramic coatings by anodization of aluminium using lithium sulphate and sodium silicate additive. Our experiments show that the present coatings are nanocomposites in nature, consisting of a mixture of nanocrystalline alumina, silica, aluminium silicate and mullite; the formation of alumina was similar to conventional anodizing technology, while the formation of mullite was attributed to an addition of sodium silicate. The microhardness of the coatings progressively increased with the increasing current density up to 0.2 A/cm2, which could mainly be attributed to the decrease of porosity in the interfacial region of the oxides up to the range. From the performance of the coatings against corrosion (Tafel/Nyquist plots), it was inferred that the coatings fabricated by lithium sulphate–sodium silicate bath have enhanced corrosion resistance (R p = 3.12 kΩ), as well as better microhardness value than that of the lithium sulphate bath alone (R p = 660.96 Ω) which confirm the perception that the silica particles included in the anodized alumina matrices randomly. Presence of Al, Si and O indicated that the electrolyte components had been intensively incorporated into the coatings.

Radiation stability test on multiphase glass ceramic and crystalline ceramic waste forms

A radiation stability study was performed on glass ceramic and crystalline ceramic waste forms. These materials are candidate host materials for immobilizing alkali/alkaline earth (Cs/Sr-CS)+lanthanide (LN)+transition metal (TM) fission product waste streams from nuclear fuel reprocessing. In this study, glass ceramics were fabricated using a borosilicate glass as a matrix in which to incorporate CS/LN/TM combined waste streams. The major phases in these multiphase materials are powellite, oxyaptite, pollucite, celsian, and durable residual glass phases. Al2O3 and TiO2 were combined with these waste components to produce multiphase crystalline ceramics containing hollandite-type phases, perovskites, pyrochlores and other minor metal titanate phases.For the radiation stability test, selected glass ceramic and crystalline ceramic samples were exposed to different irradiation environments including low fluxes of high-energy (∼1–5MeV) protons and alpha particles generated by an ion accelerator, high fluxes of low-energy (hundreds of keV) krypton particles generated by an ion implanter, and in-situ electron irradiations in a transmission electron microscope. These irradiation experiments were performed to simulate self-radiation effects in a waste form. Ion irradiation-induced microstructural modifications were examined using X-ray diffraction and transmission electron microscopy. Our preliminary results reveal different radiation tolerance in different crystalline phases under various radiation damage environments. However, their stability may be rate dependent which may limit the waste loading that can be achieved.

Porous Ceramic Materials From Polysiloxane-Clay Composites

This study describes the structural, porosity and morphological changes of porous polymer-derived ceramics obtained by pyrolysis of polysiloxane-clay composites, containing a pore former based on poly(dimethylsiloxane) and nickel acetate as nanostructure inductor. The composites were blended in a steel mold, thermally treated at 950 °C and 1500 °C (inert atmosphere). The increase of the temperature together with the presence of Ni resulted in more crystalline and porous ceramics and a higher ordering process of Cfree phase in the Ni-containing sample. The ceramics revealed a wide pore size distribution, from micro to macropores. At 950 °C the ceramic revealed the presence of pores and Ni- and C-rich islands dispersed on the fracture surface. However, at 1500 °C, nanowires with large aspect ratio, constituted by Si, C and O elements were generated. Thus, the presence of Ni associated to higher pores amount gave rise to an appropriate environment for the nucleation and growth of SiCO nanowires.

Indentation size effect in metallic glasses: Mean pressure at the initiation of plastic flow

Nanoindentation tests using a spherical indenter of tip radius 10µm have been performed on Zr- and Pd-based metallic glasses, focusing on the cumulative distribution of the first yield load. When normalized using the macroscopic yield stress, the distribution of mean pressure at yield is nearly independent of the glass composition. Collecting literature data, there is a clear indentation size effect in metallic glasses: the smaller the indenter tip radius, the larger the indentation pressure at yield. The magnitude of the size effect in metallic glasses is compared with, and found to lie between, the cases of crystalline metals and ceramics.