Predictive approach to thermodynamic properties of the metastable Cr3C carbide

In thermodynamic modeling of phase diagrams it is often necessary to deal with the properties of metastable compounds, which are not known from experiments. As an illustrative example, we choose the Cr₃C(oP16) carbide, which is involved in the modeling of the Me₃C(oP16) (cementite) structure of the Fe-Cr-C system but is metastable in the Cr-C system. We discuss in detail the estimation of its thermodynamic properties, relying on regularities in bonding properties of 3d-transition metal carbides, and an account of the vibrational entropy through the so-called entropy Debye temperature. Our predictions are compared with values derived in thermodynamic modeling of the Fe-Cr-C phase diagram. Relying on the present results, we perform calculations of metastable phase equilibria in the Cr-C system and use them in analyzing information about Cr₃C from splat-quenching experiments.     

Synthesis and alteration of α-LiFeO2 by mechanochemical processes

The effects of grinding on a stoichiometric mixture of LiOH · H₂O and -FeOOH were studied. It was found that, in the course of grinding, losses of structural water occurred and a phase structurally related to disordered -LiFeO₂ was formed. X-ray diffraction data suggest the occurrence of an ordered phase as intermediate and both -Fe₂O₃ and -Fe₂O₃ were undetected during the comminution process. A prolonged mechanical treatment of this mixture originated an elimination of Li⁺ from the -LiFeO₂ structure and the appearance of the spinel phase, -LiFe₅O₈. Additionally, the mechanical activation of a sample of -LiFeO₂ prepared at high temperatures also leads to a similar rearrangement of cations. The structural transformation is explained with the help of a model in which the vacancies of Li⁺ created during grinding promote the migration of the Fe³⁺ ions from octahedral to tetrahedral sites.     

New Interfacial Rheology Characteristics Measured using a Spinning‐Drop Rheometer at the Optimum Formulation of a Simple Surfactant–Oil–Water System

A new spinning‐drop tensiometer with an oscillating rotation velocity was used to measure the interfacial rheological properties of systems with very low interfacial tensions in the zone close to the so‐called optimum formulation of surfactant–oil–water systems. 2 simple formulation scans were selected: One with an extended anionic surfactant using a salinity variation in the water phase, and another with a mixture of 2 nonionic surfactants in a scan produced by changing their proportion. With both systems it was corroborated that at optimum formulation (i.e., at hydrophilic–lipophilic deviation (HLD) = 0), both the interfacial tension and the emulsion stability exhibit a deep minimum. A clear relationship was also found between the phase behavior and the interfacial rheological properties (dilational elasticity and viscosity). For the very first time and in both kinds of scans (salinity or average ethylene oxide number), it was found that the interfacial elastic modulus E and the interfacial viscosity, as well as the phase angle also exhibit a minimum at optimum formulation. These groundbreaking findings could be applied to emulsion instability at optimum formulation and to its applications in emulsion breaking.     

Effect on wear resistance of nanoparticles addition to a powder polyester coating through ball milling

The wear properties of a textured polyester powder coating with pyrogenic silica nanoparticles addition were evaluated. Raw powders of a commercial, textured polyester organic coating were mixed with low amounts of SiO₂ nanoparticles (0.5–3 wt%) using ball milling, a simple and economical method. Nanoparticles were mixed into the powder of thermoset organic coating for 10 min in a two-body planetary ball mill. Particle size distribution of the powder was measured to evaluate the milling effect. The coatings were applied and cured in an industrial installation on aluminum substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of the coatings were taken to analyze the homogeneity of the organic coating. Roughness, gloss and color were measured in order to evaluate their appearance. The effect of nanoparticles on abrasive and erosion wear performances was measured. Pin-on-disk wear tests were carried out. Erosion measurements were performed with free fall of sand on the samples, a test based on ASTM D968 standard. The results showed that the milling process provides a good distribution of nanoparticles as no agglomerates were found. The addition of 0.5 wt% silica nanoparticles allows for improvement of the wear resistance of the coatings.     

3D Electrophoresis‐Assisted Lithography (3DEAL): 3D Molecular Printing to Create Functional Patterns and Anisotropic Hydrogels

The ability to easily generate anisotropic hydrogel environments made from functional molecules with microscale resolution is an exciting possibility for the biomaterials community. This study reports a novel 3D electrophoresis‐assisted lithography (3DEAL) platform that combines elements from proteomics, biotechnology, and microfabrication to print well‐defined 3D molecular patterns within hydrogels. The potential of the 3DEAL platform is assessed by patterning immunoglobulin G, fibronectin, and elastin within nine widely used hydrogels and characterizing pattern depth, resolution, and aspect ratio. Furthermore, the technique's versatility is demonstrated by fabricating complex patterns including parallel and perpendicular columns, curved lines, gradients of molecular composition, and patterns of multiple proteins ranging from tens of micrometers to centimeters in size and depth. The functionality of the printed molecules is assessed by culturing NIH‐3T3 cells on a fibronectin‐patterned polyacrylamide‐collagen hydrogel and selectively supporting cell growth. 3DEAL is a simple, accessible, and versatile hydrogel‐patterning platform based on controlled molecular printing that may enable the development of tunable, chemically anisotropic, and hierarchical 3D environments.