Reactive intermediate phase cold sintering in strontium titanate.

Dense (>96% theoretical) strontium titanate ceramics were fabricated at 950 °C (conventional sintering temperature > 1400 °C) using a reactive intermediate phase cold sintering process. An aqueous solution of SrCl2 mixed with TiO2 nanoparticles was added to SrTiO3 powders and pressed at 180 °C to obtain a highly compacted green body. During the post-press heating step at 950 °C, the TiO2 and SrCl2 create in-filling micro-reactions around each grain resulting in dense (>96%) SrTiO3 ceramics. Nano- and micron-sized starting powders were used, demonstrating that this reactive intermediate phase cold sintering route can densify a wide range of starting powder sizes, as it not reliant on an amorphous-to-crystalline precipitation through the terrace ledge kink mechanism, as has been identified repeatedly in previous cold sintering mechanisms. Moreover, this process has the potential to densify a wide variety of functional oxides, as a range of different low-temperature chemical synthesis routes could be used.

Drivers of U.S. toxicological footprints trajectory 1998-2013.

By exploiting data from the Toxic Release Inventory of the United States, we have established that the toxicological footprint (TF) increased by 3.3% (88.4 Mt) between 1998 and 1999 and decreased by 39% (1088.5 Mt) between 1999 and 2013. From 1999 to 2006, the decreasing TF was driven by improvements in emissions intensity (i.e. gains in production efficiency) through toxic chemical management options: cleaner production; end of pipe treatment; transfer for further waste management; and production scale. In particular, the mining sector reduced its TF through outsourcing processes. Between 2006 and 2009, decreasing TF was due to decrease in consumption volume triggered by economic recession. Since 2009, the economic recovery increased TF, overwhelming the influence of improved emissions intensity through population growth, consumption and production structures. Accordingly, attaining a less-toxic economy and environment will be influenced by a combination of gains in production efficiency through improvement in emissions mitigation technologies and changes in consumption patterns. Overall, the current analysis highlights the structural dynamics of toxic chemical release and would inform future formulation of effective mitigation standards and management protocols towards the detoxification of the environment.

Collective dynamics underpins Rayleigh behavior in disordered polycrystalline ferroelectrics.

Nanoscale and mesoscopic disorder and associated local hysteretic responses underpin the unique properties of spin and cluster glasses, phase-separated oxides, polycrystalline ferroelectrics, and ferromagnets alike. Despite the rich history of the field, the relationship between the statistical descriptors of hysteresis behavior such as Preisach density, and micro and nanostructure has remained elusive. By using polycrystalline ferroelectric capacitors as a model system, we now report quantitative nonlinearity measurements in 0.025-1 microm(3) volumes, approximately 10(6) times smaller than previously possible. We discover that the onset of nonlinear behavior with thickness proceeds through formation and increase of areal density of micron-scale regions with large nonlinear response embedded in a more weakly nonlinear matrix. This observation indicates that large-scale collective domain wall dynamics, as opposed to motion of noninteracting walls, underpins Rayleigh behavior in disordered ferroelectrics. The measurements provide evidence for the existence and extent of the domain avalanches in ferroelectric materials, forcing us to rethink 100-year old paradigms.

Osteoconductivity of modified fluorcanasite glass-ceramics for bone tissue augmentation and repair.

Modified fluorcanasite glasses were fabricated by either altering the molar ratios of Na(2)O and CaO or by adding P(2)O(5) to the parent stoichiometric glass compositions. Glasses were converted to glass-ceramics by a controlled two-stage heat treatment process. Rods (2 mm x 4 mm) were produced using the conventional lost-wax casting technique. Osteoconductive 45S5 bioglass was used as a reference material. Biocompatibility and osteoconductivity were investigated by implantation into healing defects (2 mm) in the midshaft of rabbit femora. Tissue response was investigated using conventional histology and scanning electron microscopy. Histological and histomorphometric evaluation of specimens after 12 weeks implantation showed significantly more bone contact with the surface of 45S5 bioglass implants when compared with other test materials. When the bone contact for each material was compared between experimental time points, the Glass-Ceramic 2 (CaO rich) group showed significant difference (p = 0.027) at 4 weeks, but no direct contact at 12 weeks. Histology and backscattered electron photomicrographs showed that modified fluorcanasite glass-ceramic implants had greater osteoconductivity than the parent stoichiometric composition. Of the new materials, fluorcanasite glass-ceramic implants modified by the addition of P(2)O(5) showed the greatest stimulation of new mineralized bone tissue formation adjacent to the implants after 4 and 12 weeks implantation.

(111)(p) microtwinning in SrRuO(3) thin films on (001)(p) LaAlO(3).

SrRuO(3) (SRO) thin films grown on (001)(p) (p = pseudocubic) oriented LaAlO(3) (LAO) by pulsed laser deposition have been characterized using transmission electron microscopy. Observations along the 100(p) directions suggests that although the SRO layer maintains a pseudocube-to-pseudocube orientation relationship with the underlying LAO substrate, it has a ferroelastic domain structure associated with a transformation on cooling to room temperature to an orthorhombic Pbnm phase (a(-)a(-)c(+) Glazer tilt system). In addition, extra diffraction spots located at +/-1/6(ooo)(p) and +/-1/3(ooo)(p) (where ;o' indicates an index with an odd number) positions were obtained in 110(p) zone-axis diffraction patterns. These were attributed to the existence of high-density twins on {111}(p) pseudocubic planes within the SrRuO(3) films rather than to more conventional mechanisms for the generation of superstructure reflections.

Magnetic color symmetry of lattice rotations in a diamagnetic material.

Oxygen octahedral rotations are the most common phase transitions in perovskite crystal structures. Here we show that the color symmetry of such pure elastic distortions is isomorphic to magnetic point groups, which allows their probing through distinguishing polar versus magnetic symmetry. We demonstrate this isomorphism using nonlinear optical probing of the octahedral rotational transition in a compressively strained SrTiO3 thin film that exhibits ferroelectric (4mm) and antiferrodistortive (4{'}mm{'}) phases evolving through independent phase transitions. The approach has broader applicability for probing materials with lattice rotations that can be mapped to color groups.

In vitro biocompatibility of fluorcanasite glass-ceramics for bone tissue repair.

Fluorcanasite glass-ceramics were produced by controlled two stage heat-treatment of as-cast glasses. These glasses were modified from stoichiometric fluorcanasite composition by either adding P(2)O(5) or altering the molar ratios of Na(2)O and CaO. Commercial bioactive 45S5 Bioglass(R) was also prepared in-house to evaluate the relative in vitro biocompatibility of fluorcanasite glass-ceramics. The scanning electron microscopy (SEM) images showed that cells had colonized the surfaces of fluorcanasite glass-ceramics to form a confluent sheet. Quantitative MTT assay results were in good agreement with the qualitative SEM observations. It was concluded that incorporation of excess calcium oxide or P(2)O(5) in stoichiometric glass composition improved in vitro biocompatibility. Controlled heat-treatment further improved the biological response of cultured bone cells to modified fluorcanasite glass-ceramics when compared with their parent glasses. Ion release and pH data suggested a strong correlation between solubility (in particular, Na ion release) and biocompatibility. Reduced solubility, Na ion release, and related pH effects appeared to be the principal mechanisms responsible for improvement in in vitro biocompatibility.

In vitro biocompatibility of a novel Fe2O3 based glass ionomer cement.

INTRODUCTION: Since their invention in the late 1960s, glass ionomer cements (GICs) have been used extensively in dentistry but recently they have also been utilised in ear nose and throat (ENT) surgery. Unfortunately, Al3+, a component of conventional ionomer glasses, has been linked to poor bone mineralisation and neurotoxicity. OBJECTIVE: The aim of the research was to modify a commercial ionomer glass composition by substituting Al2O3 with Fe2O3. METHODS: Glasses with the following molar compositions were fabricated: 4.5SiO2*3M2O3*XP2O5*3CaO*2CaF2 (M = Al or Fe, X = 0-1.5). The glasses were characterised using X-ray fluorescence (XRF) and X-ray powder diffraction (XRD). Cements were prepared using a standard ratio of; 1 g of glass powder: 0.2 g of dried polyacrylic acid: 0.3 g of 10% tartaric acid solution. Cement formation was assessed using a Gilmore needle and in vitro biocompatibility was investigated for novel cement formulations. RESULTS: XRF revealed that the Fe2O3-based glasses had Al2O3 contamination from the crucibles and also had undergone substantial F- losses. XRD gave peaks that corresponded to magnetite Fe3O4 (JCPDS # 19-629) in all compositions. Apatite Ca5(PO4)3(OH,F) (JCPDS # 15-876) was identified in P2O5 containing glasses. It was possible to fabricate cements from all of the Fe2O3-based ionomer glasses. Good in vitro biocompatibility was observed for the Fe2O3-based cements. CONCLUSION: Ionomer glasses may be prepared by entirely replacing Al2O3 with Fe2O3. Cement setting times appeared to be related to P2O5 content. Fe2O3-based cements showed good in vitro biocompatibility.

Devitrification of ionomer glass and its effect on the in vitro biocompatibility of glass-ionomer cements.

The effects of devitrification of an ionomer glass with a molar composition 4.5SiO(2).3Al(2)O(3).1.5P(2)O(5).3CaO.2CaF(2) on cement formation and in vitro biocompatibility were investigated. Differential thermal analysis was used to study the phase evolution in the glass, and to determine the heat treatments for production of glass-ceramics. X-ray diffraction patterns from glass frit heat-treated at 750 degrees C for 2h contained peaks corresponding to apatite (JCPDS 15-876), whereas for samples heat-treated at 950 degrees C for 2h apatite and mullite (JCPDS 15-776) were the major phases detected. Transmission electron microscopy (TEM) confirmed that apatite and apatite-mullite phases were present after heat treatments at 750 degrees C and 950 degrees C respectively. Glass and glass-ceramics were ground to prepare <45microm powders and glass ionomer cements were produced using a ratio of 1g powder: 0.2g PAA: 0.3g 10% m/v tartaric acid solution in water. In vitro biocompatibility was evaluated using cultured rat osteosarcoma (ROS) cells. Scanning electron microscopy (SEM) showed that cells colonised the surfaces of cements prepared using untreated ionomer glass and glass crystallised to form apatite (750 degrees C/2h). However, quantitative evaluation using MTT and total protein assays indicated that more cell growth occurred in the presence of cements prepared using ionomer glasses crystallised to apatite than cements prepared using untreated glass. The least cell growth and respiratory activity was observed on cements made with crystallised glass containing both apatite and mullite. It was concluded that the controlled devitrification of ionomer glasses could be used to produce GIC bone cements with improved biocompatibility.

Formation of apatite layers on modified canasite glass-ceramics in simulated body fluid.

Canasite glass-ceramics were modified by either increasing the concentration of calcium in the glass, or by the addition of P2O5. Samples of these novel materials were placed in simulated body fluid (SBF), along with a control material (commercial canasite), for periods ranging from 12 h to 28 days. After immersion, surface analysis was performed using thin film X-ray diffraction, Fourier transform infrared reflection spectroscopy, and scanning electron microscopy equipped with energy dispersive X-ray detectors. The concentrations of sodium, potassium, calcium, silicon, and phosphorus in the SBF solution were measured using inductively coupled plasma emission spectroscopy. No apatite was detected on the surface of commercial canasite, even after 28 days of immersion in SBF. A crystalline apatite layer was formed on the surface of a P2O5-containing canasite after 5 days, and after 3 days for calcium-enriched canasite. Ion release data suggested that the mechanism for apatite deposition was different for P2O5 and non-P2O5-containing glass-ceramics.