Production of Ni3Ti-TiC x intermetallic-ceramic composites employing combustion synthesis reactions

Combustion synthesis (CS) of nickel, titanium, and carbon (graphite) reactant particles can result in NiTi-TiC (stoichiometric) or Ni₃Ti-TiC _x (nonstoichiometric) composites. Since NiTi exhibits both superelasticity and shape memory properties while Ni₃Ti does not, it is important to understand the SHS reaction conditions under which each of these composite systems may be synthesized. The stoichiometry of TiC _x , for which 0.3 ≤ x ≤ 0.5, has an important controlling effect on the formation of either Ni₃Ti or NiTi; i.e., formation of TiC_0.7 results in a depletion of titanium and formation of Ni₃Ti. This deficiency should be considered when developing the SHS reaction. This article examines the SHS conditions under which Ni₃Ti-TiC _x composites are produced. Ignition, combustion, and microstructure characteristics of nickel, titanium, and carbon (graphite) particles were investigated as a function of initial relative density and thermophysical properties of the reactant mixture. Combination of the thermophysical properties and burning velocities controlled TiC _x particle size, yielding a dependence of particle size on cooling rate. Theoretical calculations were performed and are in good agreement with the experimental data presented.     

Production of Ni3Ti?TiC x intermetallic-ceramic composites employing combustion synthesis reactions

Combustion synthesis (CS) of nickel, titanium, and carbon (graphite) reactant particles can result in NiTi−TiC (stoichiometric) or Ni₃Ti−TiC _x (nonstoichiometric) composites. Since NiTi exhibits both superelasticity and shape memory properties while Ni₃Ti does not, it is important to understand the SHS reaction conditions under which each of these composite systems may be synthesized. The stoichiometry of TiC _x , for which 0.3≤x≤0.5, has an important controlling effect on the formation of either Ni₃Ti or NiTi;i.e., formation of TiC_0.7 results in a depletion of titanium and formation of Ni₃Ti. This deficiency should be considered when developing the SHS reaction. This article examines the SHS conditions under which Ni₃Ti−TiC _x composites are produced. Ignition, combustion and microstructure characteristics of nickel, titanium, and carbon (graphite) particles were investigated as a function of initial relative density and thermophysical properties of the reactant mixture. Combination of the thermophysical properties and burning velocities controlled TiC _x particle size, yielding a dependence of particle size on cooling rate. Theoretical calculations were performed and are in good agreement with the experimental data presented. Guglielmo Gottoli, formerly Graduate Research Assistant, Metallurgical and Materials Engineering Department, Institute for Space Resources, Colorado School of Mines     

The Interplay between Fe3O4 Superparamagnetic Nanoparticles,Sodium Butyrate,and Folic Acid for Intracellular Transport

Combined treatments which use nanoparticles and drugs could be a synergistic strategy for the treatment of a variety of cancers to overcome drug resistance, low efficacy, and high-dose-induced systemic toxicity. In this study, the effects on human colon adenocarcinoma cells of surface modified Fe₃O₄ magnetic nanoparticles (MNPs) in combination with sodium butyrate (NaBu), added as a free formulation, were examined demonstrating that the co-delivery produced a cytotoxic effect on malignant cells. Two different MNP coatings were investigated: a simple polyethylene glycol (PEG) layer and a mixed folic acid (FA) and PEG layer. Our results demonstrated that MNPs with FA (FA-PEG@MNPs) have a better cellular uptake than the ones without FA (PEG@MNPs), probably due to the presence of folate that acts as an activator of folate receptors (FRs) expression. However, in the presence of NaBu, the difference between the two types of MNPs was reduced. These similar behaviors for both MNPs likely occurred because of the differentiation induced by butyrate that increases the uptake of ferromagnetic nanoparticles. Moreover, we observed a strong decrease of cell viability in a NaBu dose-dependent manner. Taking into account these results, the cooperation of multifunctional MNPs with NaBu, taking into consideration the particular cancer-cell properties, can be a valuable tool for future cancer treatment.     

Out-Of-Plane Metal Coordination for a True Solvent-Free Building with Molecular Bricks: Dodging the Surface Ligand Effect for On-Surface Vacuum Self-Assembly

The desirable self-assembly (SA) of repeated 2D stacked layers requires a “holistic analysis” of three interconnected components: the electrode, the interface, and the molecular component; among them, the contact interface bears the largest burden responsibilities. Epitaxial growth (EG) of coherent 2D+n stacked heterojunction by solvent-free deposition holds great promise, although the feasibility has never been demonstrated given multiple drawbacks (e.g., surface-ligand effect, SLE). Here, it is demonstrated how a coherent 2D+n (n = 3) layered heterorganic film is grown on an archetypal Fe metal electrode. The groundbreaking achievement is the result of the in-vacuum integration of: i) chemical decoupling of the basal organic layer (a Zn^II-tetraphenylporphyrine, ZnTPP) from the metal electrode, ii) 2D-ordering of the ZnTPP commensurate to the substrate, iii) rigid, stoichiometric, and orthogonally arranged, the molecule-to-molecule coupling between ZnTPP and a ditopic linear bridging ligand (i.e., DPNDI) guided by SA coordination chemistry, and iv) sharp (chemical) termination of the layered film.     

Long-lived charged states in single-walled carbon nanotubes

We present continuous wave photoinduced absorption spectroscopy of single-walled carbon nanotubes dispersed in a polymer matrix. The spectrum is dominated by a modulation of the absorption line shape, predominantly of large diameter tubes, that we assigned to electroabsorption caused by local electric fields arising from trapped photoinduced charges. The lack of selectivity in the excitation points to an efficient migration of the photoexcited states, either the singlet excitons or the charges resulting from their dissociation.     

Numerical modeling of 3D halo current path in ITER structures

Disruptions represent one of the main concerns for Tokamak operation, especially in view of fusion reactors, or experimental test reactors, due to the electro-mechanical loads induced by halo and eddy currents. The development of a predictive tool which allows to estimate the magnitude and spatial distribution of the halo current forces is of paramount importance in order to ensure robust vessel and in-vessel component design. With this aim, two numerical codes (CARIDDI, CAFE) have been developed, which allow to calculate the halo current path (resistive distribution) in the passive structures surrounding the plasma. The former is based on an integral formulation for the eddy currents problem particularized to the static case; the latter implements a pair of 3D FEM complementary formulations for the solution of the steady-state current conduction problem. A simplified plasma model is adopted to provide the inputs (halo current injected into the first wall). Two representative test cases (ITER symmetric and asymmetric VDEs) have been selected to cross check the results of the proposed approaches.     

Bioprinting Complex Cartilaginous Structures with Clinically Compliant Biomaterials

Bioprinting is an emerging technology for the fabrication of patient‐specific, anatomically complex tissues and organs. A novel bioink for printing cartilage grafts is developed based on two unmodified FDA‐compliant polysaccharides, gellan and alginate, combined with the clinical product BioCartilage (cartilage extracellular matrix particles). Cell‐friendly physical gelation of the bioink occurs in the presence of cations, which are delivered by co‐extrusion of a cation‐loaded transient support polymer to stabilize overhanging structures. Rheological properties of the bioink reveal optimal shear thinning and shear recovery properties for high‐fidelity bioprinting. Tensile testing of the bioprinted grafts reveals a strong, ductile material. As proof of concept, 3D auricular, nasal, meniscal, and vertebral disk grafts are printed based on computer tomography data or generic 3D models. Grafts after 8 weeks in vitro are scanned using magnetic resonance imaging and histological evaluation is performed. The bioink containing BioCartilage supports proliferation of chondrocytes and, in the presence of transforming growth factor beta‐3, supports strong deposition of cartilage matrix proteins. A clinically compliant bioprinting method is presented which yields patient‐specific cartilage grafts with good mechanical and biological properties. The versatile method can be used with any type of tissue particles to create tissue‐specific and bioactive scaffolds.     

Effects of calcium nitride and calcium carbonate gasifying agents on the combustion synthesis of Ni3Ti-TiC composites

The synthesis of nickel-titanium (NiTi) intermetallic composites is of considerable interest due to the ability to create a porous material with high strength and improved wear resistance. The effects of adding a carbon reactant to modify the reaction products and exothermicity have been studied using two reaction stoichiometries involving elemental nickel, titanium and carbon (graphite). The present study examines the synthesis of porous Ni₃Ti intermetallic composites in the presence of calcium nitride or calcium carbonate gasifying agent. Both gasifying agents show significant effects on the ignition characteristics of the reaction, burning velocities and TiC particle sizes present in the final product, but do not affect the combustion temperatures.     

Gain and ultrafast optical switching in PMMA optical fibers and films doped with luminescent conjugated polymers and oligomers

Conjugated luminescent polymers and oligomers, exhibiting stimulated emission (SE), are dispersed in polymethylmethacrylate (PMMA), films and optical fibers, either by blending or upon copolymerisation. With this PMMA doping, we aim to achieve gain and ultrafast optical switching. The modification of the dopant's chemical structure allows the tuning of the SE spectral region. Furthermore, we aim to achieve dopant chain isolation while maximising their concentration. In this paper, we present an overview of the research done in this area in the context of the European Union (EU)-funded research project "plastic optical fibers with embedded active polymers for data communications - POLYCOM".