Abstract MAX phases, ternary transition metal carbides and nitrides, represent one of the largest families of layered materials. They also serve as precursors to MXenes, two‐dimensional (2D) carbides and nitrides. The possibility of oxygen substitution in the carbon sublattice, forming oxycarbide MAX phases and MXenes, was recently reported using secondary ion mass spectrometry. However, while the effect of oxygen substitution on the properties of MXenes was investigated, little is known about its effect on the properties of MAX phases. Here, we explore the influence of process parameters (e.g., particle size, synthesis temperature, annealing time, etc.) and oxygen presence in the lattice on the oxidation resistance of Ti3AlC2MAX phase powders. We show that X‐ray diffraction measurements can identify oxygen substitution and assist in selecting MAX precursors to synthesize stable and highly conductive MXenes. Eliminating the substitutional oxygen from the MAX phase lattice increases the onset of oxidation by 400°C, from approximately 490 to 890°C. Finally, we discuss the impact of oxygen substitution in the MAX phases on the synthesis of MXenes and their resulting properties.
more »
« less
Influence of porosity on elastic properties of Ti 2 AlC and Ti 3 SiC 2 MAX phase foams
MAX phase foams could have various applications where tailored functional and mechanical properties are required. In this study, Ti2AlC and Ti3SiC2 MAX phase foams with controlled porosity and pore size were produced and characterized. The foams were produced from MAX phase powders by powder metallurgy method using crystalline carbohydrate as a space holder. Foams with overall porosity up to approximately 71 vol% and pore size from 250 μm to 1000 μm were successfully produced; micro-porosity and macro-porosity was characterized. Poisson's ratio and elastic moduli of the foams were measured by resonant ultrasound spectroscopy (RUS) and analyzed as a function of porosity and pore size. Different models were used to fit the experimental data and interpret the effect of pore size and amount of porosity and on elastic properties. It was found that the amount and type of porosity has a larger influence on the elastic properties than the pore size.
more »
« less
- Award ID(s):
- 1729350
- PAR ID:
- 10073598
- Date Published:
- Journal Name:
- Journal of alloys and compounds
- Volume:
- 764
- Issue:
- 5
- ISSN:
- 1873-4669
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Recently, the manufacturing of porous polydimethylsiloxane (PDMS) with engineered porosity has gained considerable interest due to its tunable material properties and diverse applications. An innovative approach to control the porosity of PDMS is to use transient liquid phase water to improve its mechanical properties, which has been explored in this work. Adjusting the ratios of deionized water to the PDMS precursor during blending and subsequent curing processes allows for controlled porosity, yielding water emulsion foam with tailored properties. The PDMS-to-water weight ratios were engineered ranging from 100:0 to 10:90, with the 65:35 specimen exhibiting the best mechanical properties with a Young’s Modulus of 1.17 MPa, energy absorption of 0.33 MPa, and compressive strength of 3.50 MPa. This led to a porous sample exhibiting a 31.46% increase in the modulus of elasticity over a bulk PDMS sample. Dowsil SE 1700 was then added, improving the storage capabilities of the precursor. The optimal storage temperature was probed, with −60 °C resulting in great pore stability throughout a three-week duration. The possibility of using these water emulsion foams for paste extrusion additive manufacturing (AM) was also analyzed by implementing a rheological modifier, fumed silica. Fumed silica’s impact on viscosity was examined, revealing that 9 wt% of silica demonstrates optimal rheological behaviors for AM, bearing a viscosity of 10,290 Pa·s while demonstrating shear-thinning and thixotropic behavior. This study suggests that water can be used as pore-formers for PDMS in conjunction with AM to produce engineered materials and structures for aerospace, medical, and defense industries as sensors, microfluidic devices, and lightweight structures.more » « less
-
Boundary conditions between a porous solid and a fluid has been a long-standing problem in modeling porous media. For deformable poroelastic materials such as hydrogels, the question is further complicated by the elastic stress from the solid network. Recently, an interfacial permeability condition has been developed from the principle of positive energy dissipation on the hydrogel–fluid interface. Although this boundary condition has been used in flow computations and yielded reasonable predictions, it contains an interfacial permeability g as a phenomenological parameter. In this work, we use porescale models of flow into a periodic array of solid cylinders or parallel holes to determine g as a function of the pore size and porosity. This provides a means to evaluate the interfacial permeability for a wide range of poroelastic materials, including hydrogels, foams and biological tissues, to enable realistic flow simulations.more » « less
-
Abstract The properties of foams, an important class of cellular solids, are most sensitive to the volume fraction and openness of its elementary compartments; size, shape, orientation, and the interconnectedness of the cells are other important design attributes. Control of these morphological traits would allow the tailored fabrication of useful materials. While approaches like ice templating have produced foams with elongated cells, there is a need for rapid, versatile, and energy‐efficient methods that also control the local order and macroscopic alignment of cellular elements. Here, a fast and convenient method is described to obtain anisotropic structural foams using frontal polymerization. Foams are fabricated by curing mixtures of dicyclopentadiene and a blowing agent via frontal ring‐opening metathesis polymerization (FROMP). The materials are characterized using microcomputed tomography (micro‐CT) and an image analysis protocol to quantify the morphological characteristics. The cellular structure, porosity, and hardness of the foams change with blowing agent, concentration, and resin viscosity. Moreover, a full factorial combination of variables is used to correlate each parameter with the structure of the obtained foams. The results demonstrate the controlled production of foams with specific morphologies using the simple and efficient method of frontal polymerization.more » « less
-
Abstract Beta-tricalcium phosphate (β-TCP)-based bioinks were developed to support direct-ink 3D printing-based manufacturing of macroporous scaffolds. Binding of the gelatin:β-TCP ink compositions was optimized by adding carboxymethylcellulose (CMC) to maximize the β-TCP content while maintaining printability. Post-sintering, the gelatin:β-TCP:CMC inks resulted in uniform grain size, uniform shrinkage of the printed structure, and included microporosity within the ceramic. The mechanical properties of the inks improved with increasing β-TCP content. The gelatin:β-TCP:CMC ink (25:75 gelatin:β-TCP and 3% CMC) optimized for mechanical strength was used to 3D print several architectures of macroporous scaffolds by varying the print nozzle tip diameter and pore spacing during the 3D printing process (compressive strength of 13.1 ± 2.51 MPa and elastic modulus of 696 ± 108 MPa was achieved). The sintered, macroporous β-TCP scaffolds demonstrated both high porosity and pore size but retained mechanical strength and stiffness compared to macroporous, calcium phosphate ceramic scaffolds manufactured using alternative methods. The high interconnected porosity (45–60%) and fluid conductance (between 1.04 ×10 −9 and 2.27 × 10 −9 m 4 s/kg) of the β-TCP scaffolds tested, and the ability to finely tune the architecture using 3D printing, resulted in the development of novel bioink formulations and made available a versatile manufacturing process with broad applicability in producing substrates suitable for biomedical applications.more » « less
An official website of the United States government

