Selective External Oxidation of the Intermetallic Compound, BaAg_5

The selective oxidation of BaAg_5 has been examined at 650–680°C in flowing 3%H2/Ar (po2 ≤ 1.1×x×10^–19atm). Under these conditions, a continuous external barium oxide scale formed. Depletion of Ba from the underlying BaAg_5 led to the formation of a continuous Ag layer between the oxide scale and the BaAg_5. Ba was only detected along grain boundaries in the continuous Ag layer, which was consistent with the negligible solubility reported for Ba in bulk Ag. The local thickness of the continuous Ag layer was inversely correlated to the local Ag grain size. Subsequent experiments with Ag-clad BaAg_5 revealed that surface oxide formation commenced at exposed Ag grain boundaries. BaAg_5 specimens clad with fine grained Ag foil exhibited more extensive oxide formation in a given time than specimens clad with coarse grained Ag foil. These observations confirmed that outward Ba migration through the continuous Ag layer occurred preferentially along Ag grain boundaries. This work demonstrates that an intermetallic compound may undergo external oxidation even when a continuous metallic (or intermetallic) layer, that possesses a low solubility for the oxidizable element, forms under the oxide scale

Mass uptake during oxidation of metallic alloys: literature data collection, analysis, and FAIR sharing

The area-normalized change of mass ($\Delta$m/A) with time during the oxidation of metallic alloys is commonly used to assess oxidation resistance. Analyses of such data can also aid in evaluating underlying oxidation mechanisms. We performed an exhaustive literature search and digitized normalized mass change vs. time data for 407 alloys. To maximize the impact of these and future mass uptake data, we developed and published an open, online, computational workflow that fits the data to various models of oxidation kinetics, uses Bayesian statistics for model selection, and makes the raw data and model parameters available via a queryable database. The tool, Refractory Oxidation Database (https://nanohub.org/tools/refoxdb/), uses nanoHUB's Sim2Ls to make the workflow and data (including metadata) findable, accessible, interoperable, and reusable (FAIR). We find that the models selected by the original authors do not match the most likely one according to the Bayesian information criterion (BIC) in 71% of the cases. Further, in 56% of the cases, the published model was not even in the top 3 models according to the BIC. These numbers were obtained assuming an experimental noise of 2.5% of the mass gain range, a smaller noise leads to more discrepancies. The RefOxDB tool is open access and researchers can add their own raw data (those to be included in future publications, as well as negative results) for analysis and to share their work with the community. Such consistent and systematic analysis of open, community generated data can significantly accelerate the development of machine-learning models for oxidation behavior and assist in the understanding and improvement of oxidation resistance

The effects of combined micron-/submicron-scale surface roughness and nanoscale features on cell proliferation and differentiation

Titanium (Ti) osseointegration is critical for the success of dental and orthopedic implants. Previous studies have shown that surface roughness at the micro- and submicro-scales promotes osseointegration by enhancing osteoblast differentiation and local factor production. Only relatively recently have the effects of nanoscale roughness on cell response been considered. The aim of the present study was to develop a simple and scalable surface modification treatment that introduces nanoscale features to the surfaces of Ti substrates without greatly affecting other surface features, and to determine the effects of such superimposed nano-features on the differentiation and local factor production of osteoblasts. A simple oxidation treatment was developed for generating controlled nanoscale topographies on Ti surfaces, while retaining the starting micro-/submicro-scale roughness. Such nano-modified surfaces also possessed similar elemental compositions, and exhibited similar contact angles, as the original surfaces, but possessed a different surface crystal structure. MG63 cells were seeded on machined (PT), nano-modified PT (NMPT), sandblasted/acid-etched (SLA), and nano-modified SLA (NMSLA) Ti disks. The results suggested that the introduction of such nanoscale structures in combination with micro-/submicro-scale roughness improves osteoblast differentiation and local factor production, which, in turn, indicates the potential for improved implant osseointegration in vivoTitanium (Ti) osseointegration is critical for the success of dental and orthopedic implants. Previous studies have shown that surface roughness at the micro- and submicro-scales promotes osseointegration by enhancing osteoblast differentiation and local factor production. Only relatively recently have the effects of nanoscale roughness on cell response been considered. The aim of the present study was to develop a simple and scalable surface modification treatment that introduces nanoscale features to the surfaces of Ti substrates without greatly affecting other surface features, and to determine the effects of such superimposed nano-features on the differentiation and local factor production of osteoblasts. A simple oxidation treatment was developed for generating controlled nanoscale topographies on Ti surfaces, while retaining the starting micro-/submicro-scale roughness. Such nano-modified surfaces also possessed similar elemental compositions, and exhibited similar contact angles, as the original surfaces, but possessed a different surface crystal structure. MG63 cells were seeded on machined (PT), nano-modified PT (NMPT), sandblasted/acid-etched (SLA), and nano-modified SLA (NMSLA) Ti disks. The results suggested that the introduction of such nanoscale structures in combination with micro-/submicro-scale roughness improves osteoblast differentiation and local factor production, which, in turn, indicates the potential for improved implant osseointegration in viv

Differential responses of osteoblast lineage cells to nanotopographically-modified, microroughened titaniumealuminumevanadium alloy surfaces

Surface structural modifications at the micrometer and nanometer scales have driven improved success rates of dental and orthopaedic implants by mimicking the hierarchical structure of bone. However, how initial osteoblast-lineage cells populating an implant surface respond to different hierarchical surface topographical cues remains to be elucidated, with bone marrow mesenchymal stem cells (MSCs) or immature osteoblasts as possible initial colonizers. Here we show that in the absence of any exogenous soluble factors, osteoblastic maturation of primary human osteoblasts (HOBs) but not osteoblastic differentiation of MSCs is strongly influenced by nanostructures superimposed onto a microrough Ti6Al4V (TiAlV) alloy. The sensitivity of osteoblasts to both surface microroughness and nanostructures led to a synergistic effect on maturation and local factor production. Osteoblastic differentiation of MSCs was sensitive to TiAlV surface microroughness with respect to production of differentiation markers, but no further enhancement was found when cultured on micro/nanostructured surfaces. Superposition of nanostructures to microroughened surfaces affected final MSC numbers and enhanced production of vascular endothelial growth factor (VEGF) but the magnitude of the response was lower than for HOB cultures. Our results suggest that the differentiation state of osteoblast-lineage cells determines the recognition of surface nanostructures and subsequent cell response, which has implications for clinical evaluation of new implant surface nanomodifications.Surface structural modifications at the micrometer and nanometer scales have driven improved success rates of dental and orthopaedic implants by mimicking the hierarchical structure of bone. However, how initial osteoblast-lineage cells populating an implant surface respond to different hierarchical surface topographical cues remains to be elucidated, with bone marrow mesenchymal stem cells (MSCs) or immature osteoblasts as possible initial colonizers. Here we show that in the absence of any exogenous soluble factors, osteoblastic maturation of primary human osteoblasts (HOBs) but not osteoblastic differentiation of MSCs is strongly influenced by nanostructures superimposed onto a microrough Ti6Al4V (TiAlV) alloy. The sensitivity of osteoblasts to both surface microroughness and nanostructures led to a synergistic effect on maturation and local factor production. Osteoblastic differentiation of MSCs was sensitive to TiAlV surface microroughness with respect to production of differentiation markers, but no further enhancement was found when cultured on micro/nanostructured surfaces. Superposition of nanostructures to microroughened surfaces affected final MSC numbers and enhanced production of vascular endothelial growth factor (VEGF) but the magnitude of the response was lower than for HOB cultures. Our results suggest that the differentiation state of osteoblast-lineage cells determines the recognition of surface nanostructures and subsequent cell response, which has implications for clinical evaluation of new implant surface nanomodifications

Role of a2b1 integrins in mediating cell shape on microtextured titanium surfaces

Surface microroughness plays an important role in determining osteoblast behavior on titanium. Previous studies have shown that osteoblast differentiation on microtextured titanium substrates is dependent on alpha-2 beta-1 (a2b1) integrin signaling. This study used focused ion beam milling and scanning electron microscopy, combined with three-dimensional image reconstruction, to investigate early interactions of individual cells with their substrate and the role of integrin a2b1 in determining cell shape. MG63 osteoblast-like cells on sand blasted/acid etched (SLA) Ti surfaces after 3 days of culturing indicated decreased cell number, increased cell differentiation, and increased expression of mRNA levels for a1, a2, aV, and b1 integrin subunits compared to cells on smooth Ti (PT) surfaces. a2 or b1 silenced cells exhibited increased cell number and decreased differentiation on SLA compared to wild-type cells. Wild-type cells on SLA possessed an elongated morphology with reduced cell area, increased cell thickness, and more apparent contact points. Cells on PT exhibited greater spreading and were relatively flat. Silenced cells possessed a morphology and phenotype similar to wild-type cells grown on PT. These observations indicate that surface microroughness affects cell response via a2b1 integrin signaling, resulting in a cell shape that promotes osteoblastic differentiation. VC 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 564–573, 2015.Surface microroughness plays an important role in determining osteoblast behavior on titanium. Previous studies have shown that osteoblast differentiation on microtextured titanium substrates is dependent on alpha-2 beta-1 (a2b1) integrin signaling. This study used focused ion beam milling and scanning electron microscopy, combined with three-dimensional image reconstruction, to investigate early interactions of individual cells with their substrate and the role of integrin a2b1 in determining cell shape. MG63 osteoblast-like cells on sand blasted/acid etched (SLA) Ti surfaces after 3 days of culturing indicated decreased cell number, increased cell differentiation, and increased expression of mRNA levels for a1, a2, aV, and b1 integrin subunits compared to cells on smooth Ti (PT) surfaces. a2 or b1 silenced cells exhibited increased cell number and decreased differentiation on SLA compared to wild-type cells. Wild-type cells on SLA possessed an elongated morphology with reduced cell area, increased cell thickness, and more apparent contact points. Cells on PT exhibited greater spreading and were relatively flat. Silenced cells possessed a morphology and phenotype similar to wild-type cells grown on PT. These observations indicate that surface microroughness affects cell response via a2b1 integrin signaling, resulting in a cell shape that promotes osteoblastic differentiation. VC 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 564–573, 2015

Reactive conversion of bioclastic nanostructures

Issued as final reportUnited States. Air Force. Office of Scientific Researc

Near net-shape, ultra high melting, erosion resistant carbide/metal composites with tailored fibrillar microstructures via the displacive compensation of porosity process

Issued as final reportAir Force Office of Scientific Research (U.S.

Materials “Alchemy”: Chemical Transformation of 3-D Macro-to-Microscale Structures into Replicas Tailored for Catalytic, Optical, Energy, and Aerospace Applications

Dr. Kenneth H. Sandhage presented a lecture at the Nano@Tech Meeting on February 26, 2013 at 12 noon in room 1116 of the Marcus Nanotechnology Building.Dr. Ken H. Sandhage is the B. Mifflin Hood Professor in the School of Materials Science and Engineering, and an Adjunct Professor in the School of Chemistry and Biochemistry at the Georgia Institute of Technology. He is the Director of the Center for Biologically Enabled Advanced Manufacturing (BEAM). Dr. Sandhage received a B.S. (1981) in Metallurgical Engineering with highest distinction from Purdue University, and a Ph.D. (1986) in Ceramics from the Massachusetts Institute of Technology. After working as a Senior Scientist at Corning, Inc. and American Super-conductor Corp., he was on the faculty in the Dept. of Materials Science and Engineering at Ohio State University for 12 years before joining Georgia Tech in 2003. Dr. Sandhage’s research focuses on novel reaction processing of advanced materials for electromagnetic, chemical, optical, sensor, refractory, and structural applications. This research has resulted in several patented processes for fabricating near net-shaped ceramics and composites at modest temperatures: the Bioclastic and Shape -preserving Inorganic Conversion or BaSIC method, U.S. Patent 7,067,104; the Displacive Compensation of Porosity or DCP method, U.S. Patent 6,407,022; the Volume Identical Metal Oxidation or VIMOX method, U.S. Patent 5,447,291. Sandhage and his students hold 23 patents. A major current initiative is biologically-enabled materials processing, including Genetically Engineered Materials and Micro/nanodevices (GEMs). Dr. Sandhage has received several distinctive honors throughout his career, including: 5 best paper awards, such as the Purdy Award from the American Ceramic Society (1996); the Outstanding Materials Engineer Award from Purdue (1997); and the Lumley Research Award from Ohio State (1997, 2002). In 1999-2000, he was a Humboldt Fellow in the Advanced Ceramics Group at the Technical University of Hamburg-Harburg. He was the advisor to students Matt Dickerson and Ray Unocic, who were recipients of the 2002 National Collegiate Inventors Award. Dr. Sandhage is a Fellow of the American Ceramic Society, a member of the National Materials Advisory Board of the National Academies, and a member of the Materials Research Society and TMS. He has also been a technical consultant for a number of companies and law firms.Runtime: 47:18 minutesNature provides remarkable examples of microscale structures with complex three-dimensional (3-D) morphologies and finely-patterned features formed by living organisms. For example, intricate 3-D microscale silica or chitinous structures with organized nanoscale features are formed by diatoms (single celled algae) or Morpho butterflies, respectively. Synthetic rapid-prototyping or self-assembly approaches have also yielded 3-D structures with microscale and/or nanoscale particles/pores in certain desired arrangements. While such 3-D patterned structures can be attractive for particular applications, the materials readily formed by these processes may not possess preferred chemistries for a broader range of uses. The scalable fabrication of structures with complex 3-D morphologies and with a range of tailorable chemistries may be accomplished by separating the processes for structure formation and for chemical tailoring; that is, structures with a desired 3-D morphology may first be assembled in a readily-formed chemistry and then converted into a new functional chemistry via a morphology-preserving transformation process. In this presentation, several shape-preserving chemical conversion (conformal coating-based and fluid/solid reaction-based) approaches will be discussed for generating 3-D replicas of biogenic and synthetic structures comprised of ceramic, metal, or composite materials for catalytic, optical, energy harvesting/storage, and aerospace applications

Intragranular Nanocomposites via Internal Reduction of Carbide Solid Solutions

A reaction-based processing technique to synthesize intragranularmetal-metal/carbide-matrix micro/nanocomposite particles via internal reduction of carbide solid solutions is introduced. The presented method is the first-demonstrated analogue of internal reduction in oxide solid solutions for non-oxide-based ceramic systems. Selected thermodynamic, kinetic, and crystallographic analyses are discussed