Ceramics sintering and shaping using the electrical field assisted sintering method

Ceramic powders are often produced by sol-gel method or by pyrolysis of some form of precursors. This presentation will emphasize the consolidation of such powders using the Electrical Field Assisted Sintering (EFAS) method. The role played by the external electrical field and/or the heating rate will be specifically investigated. This observation will be supported by in-situ sintering studies inside a TEM in the presence of a biased electrical voltage. One can take advantage of the EFAS process to produce functionally graded material by using asymmetric die design. Similarly, one can consolidate, as well as form to shape, ceramic components in-situ in the EFAS chamber by designing the die appropriately. Since EFAS is a fast process, grain growth can be minimized during consolidation, leading to excellent optical transmission properties in nanoceramics. Superplasticity in ceramics can be achieved at significantly lower temperatures. This investigation was supported in part by ONR grant with Lawrence Kabacoff as the Program Manager

Association between serum ca-125 levels and severity of pre-eclampsia: a case-control study conducted in a tertiary care centre, West Bengal

Background: Screening test for pre-eclampsia has been a topic of extensive research in last few decades, and to identify a cost effective and accurate one is of immense importance. This study was conducted to determine an association between serum CA-125 levels and severity of pre-eclampsia, and thus to specify clinical utility of this biochemical marker in prediction, diagnosis and follow-up of pre-eclampsia.Methods: A case-control study involving 40 women with non-severe pre-eclampsia, 40 women with severe pre-eclampsia and 40 healthy pregnant women matched for age, parity and gestational age at enrolment were taken in a tertiary care centre in West Bengal.Results: The CA-125 levels in three categories of participants were: normotensive (15.76±2.95), non-severe pre-eclampsia (26.98±2.28), severe pre-eclampsia (44.99±11.23), p<0.001. CA-125 levels correlated positively with systolic blood pressure (r=0.78, p<0.001), diastolic blood pressure (r=0.79, p<0.001), negatively with platelet levels (r=-0.67, p<0.001) and with birth weight of baby (r=-0.54, p<0.001). When cut-off for serum CA-125 levels was accepted as 35 IU/ml, the sensitivity and specificity of the marker was found to be 92.1% and 97.1% respectively. Positive predictive value 95.5%, Negative predictive value 94.4%.Conclusions: We can infer from this study that maternal serum CA-125 levels are associated with pre-eclampsia and its severity. As it is much more available and less expensive, it seems to be a promising as a screening test

Formation of Aluminum Particles with Shell Morphology during Pressureless Spark Plasma Sintering of Fe-Al Mixtures: Current-Related or Kirkendall Effect?

A need to deeper understand the influence of electric current on the structure and properties of metallic materials consolidated by Spark Plasma Sintering (SPS) stimulates research on inter-particle interactions, bonding and necking processes in low-pressure or pressureless conditions as favoring technique-specific local effects when electric current passes through the underdeveloped inter-particle contacts. Until now, inter-particle interactions during pressureless SPS have been studied mainly for particles of the same material. In this work, we focused on the interactions between particles of dissimilar materials in mixtures of micrometer-sized Fe and Al powders forming porous compacts during pressureless SPS at 500-650 °C. Due to the chemical interaction between Al and Fe, necks of conventional shape did not form between the dissimilar particles. At the early interaction stages, the Al particles acquired shell morphology. It was shown that this morphology change was not related to the influence of electric current but was due to the Kirkendall effect in the Fe-Al system and particle rearrangement in a porous compact. No experimental evidence of melting or melt ejection during pressureless SPS of the Fe-Al mixtures or Fe and Al powders sintered separately was observed. Porous FeAl-based compacts could be obtained from Fe-40at.%Al mixtures by pressureless SPS at 650 °C

Apert's syndrome

Apert's syndrome (acrocephalosyndactyly) is a rare congenital disorder characterized by craniosynostosis, mid-facial malformations and symmetrical syndactyly. We present a 2-month-old girl having features of Apert's syndrome, with cerebral cortical atrophy and bifurcation of the right first metatarsal base, a hitherto undescribed finding

Field-induced mass transport phenomena in flash sintered high temperature ceramics explored by in situ SEM and TEM

Flash sintering has attracted significant attention lately as its remarkable rapid densification process at low sintering temperature leads to the retention of fine grains and enhanced dielectric properties. However, the underlying mechanism of flash sintering and mechanical behaviors of flash-sintered ceramics remain poorly understood. Here, we report the microstructure of flash-sintered yttria-stabilized zirconia (YSZ) and TiO2 by transmission electron microscope (TEM) and their high temperature in-situ micropillar compression studies inside a scanning electron microscope (SEM). Our studies on flash-sintered YSZ show that YSZ exhibits high inelastic strain (~ 8%) primarily due to phase transformation toughening below 400°C. At higher temperatures, crack nucleation and propagation are significantly retarded and prominent plasticity arises mainly from dislocation activities. The holding time and current density limit after the onset of flash for flash-sintered TiO2 significantly affect the microstructure and mechanical behavior. High dislocation density and stacking faults have been observed in the flash-sintered TiO2 under TEM. The presence of high-density defects generated during flash sintering plays a major role in the overall microstructure and mechanical behavior of ceramics

Direct observation of Lomer-Cottrell Locks during strain hardening in nanocrystalline nickel by in situ TEM

Strain hardening capability is critical for metallic materials to achieve high ductility during plastic deformation. A majority of nanocrystalline metals, however, have inherently low work hardening capability with few exceptions. Interpretations on work hardening mechanisms in nanocrystalline metals are still controversial due to the lack of in situ experimental evidence. Here we report, by using an in situ transmission electron microscope nanoindentation tool, the direct observation of dynamic work hardening event in nanocrystalline nickel. During strain hardening stage, abundant Lomer-Cottrell (L-C) locks formed both within nanograins and against twin boundaries. Two major mechanisms were identified during interactions between L-C locks and twin boundaries. Quantitative nanoindentation experiments recorded show an increase of yield strength from 1.64 to 2.29 GPa during multiple loading-unloading cycles. This study provides both the evidence to explain the roots of work hardening at small length scales and the insight for future design of ductile nanocrystalline metals

Nanoscale stacking fault-assisted room temperature plasticity in flash-sintered TiO2.

Ceramic materials have been widely used for structural applications. However, most ceramics have rather limited plasticity at low temperatures and fracture well before the onset of plastic yielding. The brittle nature of ceramics arises from the lack of dislocation activity and the need for high stress to nucleate dislocations. Here, we have investigated the deformability of TiO2 prepared by a flash-sintering technique. Our in situ studies show that the flash-sintered TiO2 can be compressed to ~10% strain under room temperature without noticeable crack formation. The room temperature plasticity in flash-sintered TiO2 is attributed to the formation of nanoscale stacking faults and nanotwins, which may be assisted by the high-density preexisting defects and oxygen vacancies introduced by the flash-sintering process. Distinct deformation behaviors have been observed in flash-sintered TiO2 deformed at different testing temperatures, ranging from room temperature to 600°C. Potential mechanisms that may render ductile ceramic materials are discussed

Deformation mechanisms of flash sintered yttria-stabilized zirconia via in situ micromechanical testing

Flash sintering has been applied to sintering a variety of ceramic materials. However, the mechanical behavior of flash-sintered ceramics is less well understood. In this study, the deformation mechanisms of flash-sintered yttria stabilized zirconia (YSZ) were investigated via in-situ microcompression test at temperatures of 25 to 650oC. The flash sintered YSZ exhibits high fracture strain due to transformation induced toughening below the test temperatures of 400oC. At higher temperatures, crack nucleation and propagation are significantly retarded, and no more catastrophic failures are observed. Strain rate jump tests were also performed at elevated temperature (450 ~ 650oC) to investigate the temperature dependent deformation mechanisms. The activation energy for deformation and its implication are discussed

The absence of plasma in “spark plasma sintering”

Spark plasma sintering (SPS) is a remarkable method for synthesizing and consolidating a large variety of both novel and traditional materials. The process typically uses moderate uni-axial pressures (&lt;100 MPa) in conjunction with a pulsing on-off DC current during operation. There are a number of mechanisms proposed to account for the enhanced sintering abilities of the SPS process. Of these mechanisms, the one most commonly put forth and the one that draws the most controversy involves the presence of momentary plasma generated between particles. This study employees three separate experimental methods in an attempt to determine the presence or absence of plasma during SPS. The methods employed include: in-situ atomic emission spectroscopy, direct visual observation and ultra-fast in-situ voltage measurements. It was found using these experimental techniques that no plasma is present during the SPS process. This result was confirmed using several different powders across a wide spectrum of SPS conditions

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency–Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research