SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Ceramic engineering

170

Aluminum-doped zinc oxide ceramics with yttria doping (AZO:Y) ranging from 0 to 0.2 wt.% were fabricated by pressureless sintering yttria-modified nanoparticles in air at 1,300°C. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, a physical property measurement system, and a densimeter were employed to characterize the precursor nanoparticles and the sintered AZO ceramics. It was shown that a small amount of yttria doping can remarkably retard the growth of the as-received precursor nanoparticles, further improve the microstructure, refine the grain size, and enhance the density for the sintered ceramic. Increasing the yttria doping to 0.2 wt.%, the AZO:Y nanoparticles synthetized by a coprecipitation process have a nearly sphere-shaped morphology and a mean particle diameter of 15.1 nm. Using the same amount of yttria, a fully dense AZO ceramic (99.98% of theoretical density) with a grain size of 2.2 μm and a bulk resistivity of 4.6 × 10-3 Ω·cm can be achieved. This kind of AZO:Y ceramic has a potential to be used as a high-quality sputtering target to deposit ZnO-based transparent conductive films with better optical and electrical properties.

Concepts: Electron, X-ray, Scanning electron microscope, Ceramic engineering, Pottery, Ceramic, Sintering, Clay

39

Nanolasers hold promise for applications including integrated photonics, on-chip optical interconnects and optical sensing. Key to the realization of current cavity designs is the use of nanomaterials combining high gain with high radiative efficiency. Until now, efforts to enhance the performance of semiconductor nanomaterials have focused on reducing the rate of non-radiative recombination through improvements to material quality and complex passivation schemes. Here we employ controlled impurity doping to increase the rate of radiative recombination. This unique approach enables us to improve the radiative efficiency of unpassivated GaAs nanowires by a factor of several hundred times while also increasing differential gain and reducing the transparency carrier density. In this way, we demonstrate lasing from a nanomaterial that combines high radiative efficiency with a picosecond carrier lifetime ready for high speed applications.

Concepts: Laser, Carbon, Nanomaterials, Sol-gel, Semiconductor, Silicon, Materials science, Ceramic engineering

29

Sintering of nanoparticle inks over large area-substrates is a key enabler for scalable fabrication of patterned and continuous films, with multiple emerging applications. The high speed and ambient condition operation of photonic sintering has elicited significant interest for this purpose. In this work, we experimentally characterize the temperature evolution and densification in photonic sintering of silver nanoparticle inks, as a function of nanoparticle size. It is shown that smaller nanoparticles result in faster densification, with lower temperatures during sintering, as compared to larger nanoparticles. Further, high densification can be achieved even without nanoparticle melting. Electromagnetic Finite Element Analysis of photonic heating is coupled to an analytical sintering model, to examine the role of interparticle neck growth in photonic sintering. It is shown that photonic sintering is an inherently self-damping process, i.e., the progress of densification reduces the magnitude of subsequent photonic heating even before full density is reached. By accounting for this phenomenon, the developed coupled model better captures the experimentally observed sintering temperature and densification as compared to conventional photonic sintering models. Further, this model is used to uncover the reason behind the experimentally observed increase in densification with increasing weight ratio of smaller to larger nanoparticles.

Concepts: Nanoparticle, Temperature, Heat, Finite element method, Silicon, Gold, Liquid, Ceramic engineering

29

Bioactive glasses are reported to be able to stimulate more bone regeneration than other bioactive ceramics but they lag behind other bioactive ceramics in terms of commercial success. Bioactive glass has not yet reached its potential but research activity is growing. This paper reviews the current state of the art, starting with current products and moving onto recent developments. Larry Hench’s 45S5 Bioglass® was the first artificial material that was found to form a chemical bond with bone, launching the field of bioactive ceramics. In vivo studies have shown that bioactive glasses bond with bone more rapidly than other bioceramics, and in vitro studies indicate that their osteogenic properties are due to their dissolution products stimulating osteoprogenitor cells at the genetic level. However, calcium phosphates such as tricalcium phosphate and synthetic hydroxyapatite are more widely used in the clinic. Some of the reasons are commercial, but others are due to the scientific limitations of the original Bioglass 45S5. An example is that it is difficult to produce porous bioactive glass templates (scaffolds) for bone regeneration from Bioglass 45S5 because it crystallizes during sintering. Recently, this has been overcome by understanding how the glass composition can be tailored to prevent crystallization. The sintering problems can also be avoided by synthesizing sol-gel glass, where the silica network is assembled at room temperature. Process developments in foaming, solid freeform fabrication and nanofibre spinning have now allowed the production of porous bioactive glass scaffolds from both melt- and sol-gel-derived glasses. An ideal scaffold for bone regeneration would share load with bone. Bioceramics cannot do this when the bone defect is subjected to cyclic loads, as they are brittle. To overcome this, bioactive glass polymer hybrids are being synthesized that have the potential to be tough, with congruent degradation of the bioactive inorganic and the polymer components. Key to this is creating nanoscale interpenetrating networks, the organic and inorganic components of which have covalent coupling between them, which involves careful control of the chemistry of the sol-gel process. Bioactive nanoparticles can also now be synthesized and their fate tracked as they are internalized in cells. This paper reviews the main developments in the field of bioactive glass and its variants, covering the importance of control of hierarchical structure, synthesis, processing and cellular response in the quest for new regenerative synthetic bone grafts. The paper takes the reader from Hench’s Bioglass 45S5 to new hybrid materials that have tailorable mechanical properties and degradation rates.

Concepts: Crystal, In vivo, Sol-gel, Solid, In vitro, Glass, Ceramic engineering, Bioactive glass

28

Despite the continuing interest in the applications of functionalized nanomaterials, the controlled and reproducible synthesis of many important functionalized nanoparticles (NPs) above the milligram scale continues to be a significant challenge. The synthesis of functionalized NPs in automated reactors provides a viable approach to circumvent some of the shortcomings of traditional nanomaterial batch syntheses, providing superior control over reagent addition, improved reproducibility, the opportunity to interface real-time product monitoring, and viable high-throughput synthetic approach. Here, we demonstrate the construction and operation of a simple millifluidic reactor assembled entirely from commercially available components found in almost any chemical laboratory. This reactor facilitates the aqueous gram-scale synthesis of a variety of functionalized gold nanoparticles, including the synthesis of gold nanospheres with tightly controlled core diameters and gold nanorods with controlled aspect ratios between 1.5 and 4.0. The absolute dimensions (i.e. the transverse diameter) of gold nanorods synthesized within the reactor) can also be tailored to produce different gold nanorod shapes, including “small” gold nanorods and gold nanocubes. In addition, the high-throughput synthesis approach facilitated by the flow reactor easily extends the synthesis of monodisperse functionalized gold nanoparticles to the gram scale. Lastly, we show that the reactor can interface with existing purification and monitoring techniques in order to enable the high-throughput functionalization/purification of gold nanorods and real-time monitoring of gold nanoparticle products for quality control. We anticipate that this millifluidic reactor will provide the blueprint for a versatile and portable approach to the gram-scale synthesis of monodisperse, hydrophilically functionalized metal NPs that can be realized in almost any chemistry research laboratory.

Concepts: Nanoparticle, Chemistry, Nanotechnology, Nanomaterials, Chemical synthesis, Gold, Colloidal gold, Ceramic engineering

28

Efficient and safe drug delivery has always been a challenge in medicine. The use of nanotechnology, such as the development of nano drug delivery systems (DDS), has received great attention with high enthusiasm owing to the potential that nanocarriers can theoretically act as “magic bullets” and selectively target affected organs and cells while sparing normal tissues. The family of nano DDS includes conventional nano drug delivery materials such as lipids and polymers that have been scaled to the nanometer size range. With the rapid development of synthesis and characterization techniques for engineered nanomaterials, new DDS platforms have emerged, including inorganic based nanocarriers, such as mesoporous silica nanoparticles (MSNP). MSNP are able to act as a multifunctional delivery platform that is capable of delivering therapeutic elements to a variety of disease models (especially cancer) at cellular and in vivo levels. Furthermore, MSNP have shown to be exceptional delivery platforms capable of protectively packaging hydrophobic and hydrophilic drug molecules as well as other therapeutic elements for controlled on-demand delivery. In addition, MSNP have demonstrated the capability to image the delivery site for theranostic purposes. These functionalities have led to the development of MSNP as novel multifunctional nanocarriers, and therefore provide them with unique advantages compared to other nanocarriers.

Concepts: Medicine, Nanoparticle, Nanotechnology, Nanomaterials, Sol-gel, Materials science, Mesoporous silica, Ceramic engineering

28

Significant advances in colloidal synthesis made in the past two decades have enabled the preparation of high quality nanoparticles with well-controlled sizes, shapes, and compositions. It has recently been realized that such nanoparticles can be utilized as ‘artificial atoms’ for building new materials which not only combine the size- and shape-dependent properties of individual nanoparticles but also create new collective properties by taking advantage of their electromagnetic interactions. The controlled clustering of nanoparticle building blocks into defined geometric arrangements opens a new research area in materials science and as a result much interest has been paid to the creation of secondary structures of nanoparticles, either by direct solution growth or self-assembly methods. In this tutorial review, we introduce recently developed strategies for the creation and surface modification of colloidal nanoparticle clusters, demonstrate the new collective properties resulting from their secondary structures, and highlight several of their many important technological applications ranging from photonics, separation, and detection, to multimodal imaging, energy storage and transformation, and catalysis.

Concepts: Nanoparticle, Nanotechnology, Sol-gel, Colloid, Materials science, Ceramic engineering, Colloidal crystal, Colloid-facilitated transport

23

Nanotechnology manipulates therapeutic agents at the nanoscale for the development of nanomedicines. However, there are current concerns over nanomedicines, mainly related to the possible toxicity of nanomaterials used for health medications. Due to their small size, they can enter the human body more readily than larger sized particles. Green chemistry encompasses the green synthesis of drug-loaded nanoparticles by reducing the use of hazardous materials in the synthesis process, thus reducing the adverse health impacts of pharmaceutics. This would greatly expand their potential in biomedical treatments. This review highlights the potential risks of nanomedicine formulations to health, delivery routes of green nanomedicines, recent advances in the development of green nanoscale systems for biomedical applications and future perspectives for the green development of nanomedicines.

Concepts: Chemistry, Nanotechnology, Nanomaterials, Human body, Ceramic engineering, Nanomedicine, Nanobiotechnology

13

Dense ceramic materials can form in nature under mild temperatures in water. By contrast, man-made ceramics often require sintering temperatures in excess of 1,400 °C for densification. Chemical strategies inspired by biomineralization processes have been demonstrated but remain limited to the fabrication of thin films and particles. Besides biomineralization, the formation of dense ceramic-like materials such as limestone also occurs in nature through large-scale geological processes. Inspired by the geological compaction of mineral sediments in nature, we report a room-temperature method to produce dense and strong ceramics within timescales comparable to those of conventional manufacturing processes. Using nanoscale powders and high compaction pressures, we show that such cold sintering process can be realized with water at room temperature to result in centimetre-sized bulk parts with specific strength that is comparable to, and occasionally even higher than, that of traditional structural materials like concrete.

Concepts: Density, Sedimentary rock, Thermodynamics, Solid, Ceramic engineering, Ceramic, Sintering, Clay

12

Alumina toughened zirconia (ATZ) and zirconia toughened alumina (ZTA) are currently the materials of choice to meet the need for tough, strong, and bioinert ceramics for medical devices. However, the mechanical properties of ZrO2/Al2O3 dispersion ceramics could be considerably increased by reducing the corresponding grain sizes and by improving the homogeneity of the phase dispersion. Here, we prepare nanoparticles with an intraparticular phase distribution of Zr(1-x)AlxO(2-x/2) and (γ-, δ-)Al2O3 by the simultaneous gas phase condensation of laser co-vaporized zirconia and alumina raw powders. During subsequent spark plasma sintering the zirconia defect structures and transition alumina phases transform to a homogeneously distributed dispersion of tetragonal ZrO2 (52.4 vol%) and α-Al2O3 (47.6 vol%). Ceramics sintered by spark plasma sintering are completely dense with average grain sizes in the range around 250 nm. Outstanding mechanical properties (flexural strength σf = 1500 MPa, fracture toughness KIc = 6.8 MPa m(½)) together with a high resistance against low temperature degradation make these materials promising candidates for next generation bioceramics in total hip replacements and for dental implants.

Concepts: Oxygen, Dental implant, Plasma, Ceramic engineering, Ceramic materials, Sintering, Zirconium dioxide, Spark plasma sintering