MAX Phase Research Articles

Manufacturing of High Purity Cr2AlC MAX Phase Material and Its Characterization

AbstractPresent study discusses about a technique for producing high-purity Cr2AlC MAX phase materials and gaining insight into their thermal behavior for high-temperature applications. The research conducted involved synthesizing a pure layered ternary carbide Cr2AlC MAX phase material by mixing powders of Chromium, Aluminum, and Carbon and then subjecting them to two-step pressureless sintering process in argon atmosphere. First step involves the annealing of ball-milled mixture at 750 °C for 2 h followed by the second step in which the annealed mixture is subjected to heat-treatment at 1350 °C for 2 h. Analysis using XRD and Raman techniques revealed that the synthesized product consists of Cr2AlC phase, without any impurities. SEM studies confirmed that the Cr2AlC had a layered topography, while EPMA analysis indicated that the atomic percentage of Cr, Al, and C was consistent with the XRD phase analysis. XPS investigations confirmed the presence of Cr-C bonds representing Mn+1Xn of the MAX phase material. TG-DSC results showed an approximately 2% increase in weight. The Cr2AlC phase exhibited an endothermic pattern below 725 °C, an exothermic pattern above it, and did not decompose up to 1400 °C in vacuum environment. High-temperature XRD analysis at various temperatures also confirmed no formation of Al2O3 or CrO impurity compounds.

Large control of friction and wear enabled by Ti3AlC2 MAX- multilayer graphene-polydopamine composites

Friction and wear pose significant challenges in moving mechanical systems. Despite efforts to address these challenges with MAX phase materials, many of these materials lack effective lubrication and wear protection under ambient conditions. Here, we developed a composite coating that addresses these challenges through a combination of materials chemistry and engineering. This coating, composed of polydopamine-functionalized Ti3AlC2 MAX (F-MAX) and multilayer graphene (MGr), known as F-MAX + MGr, demonstrated exceptional tribological performance. At its best composition, the F-MAX + MGr composite coating reduced the friction at sliding interfaces by 82 % and decreased the wear on the counterpart ball by 99.76 % compared to bare surfaces. Importantly, its tribological performance surpassed that of pristine MAX, F-MAX, and MGr coatings. This improvement is attributed to the synergistic lubricating effect of the inherently low shear strengths of Ti3AlC2 MAX and MGr, the chemical properties of PDA, and the occurrence of incommensurate contacts at the interfaces. This work pioneers slippery and wear-resistant surfaces via a combination of chemical modification and materials engineering, with implications for both fundamental science and technological advancement.

Ti3AlC2 MAX Phase Modified Screen-Printed Electrode for the Fabrication of Hydrazine Sensor.

Hydrazine is considered a powerful reducing agent and catalyst, showing diverse applications in agricultural industries, toxic degradation research, and wastewater management. Additionally, hydrazine can trigger some specific reactions when combined with suitable oxidants. Due to its highly polar nature, hydrazine can easily dissolve in alcohol, water, and various other polar solvents. Therefore, it can be extensively utilized in different areas of application and industries such as rocketry and various chemical applications. Despite its beneficial properties, hydrazine is unstable, posing significant risk due to its highly toxic nature. It is extremely hazardous to both human health and the environment. It can cause various illnesses and symptoms such as dizziness, temporary blindness, damage to the central nervous system, and even death when inhaled in sufficient quantities. Therefore, it is highly important to monitor the level of hydrazine to prevent its toxic and hazardous effects on human beings and the environment. In the present study, we discuss the simple fabrication of a disposable cost-effective and eco-friendly hydrazine sensor. We used a screen-printed carbon electrode, i.e., SPCE, as a base for the construction of a hydrazine sensor. The Ti3AlC2 MAX has been used as a suitable and efficient electrode material for the fabrication of disposable hydrazine sensors. We modified the active surface of the SPCE using a drop-casting approach. The resulting Ti3AlC2 MAX modified SPCE (Ti3AlC2@SPCE) has been utilized as an efficient and low-cost hydrazine sensor. Cyclic voltammetry, i.e., CV, and linear sweep voltammetry, viz., LSV, was employed as a sensing technique in this study. The optimization of pH and electrode material loading was conducted. The Ti3AlC2@SPCE exhibited excellent sensing performance toward hydrazine oxidation. A reasonable detection limit (0.01 µM) was achieved for hydrazine sensing. The fabricated sensor also demonstrated a reasonable linear range of 1-50 µM. This work provides the design and fabrication of simple disposable Ti3AlC2@SPCE as a suitable electrode for the determination of hydrazine using LSV technology.

Low-cost synthesis of Ti3C2Tx MXene-based sponge for solar steam generation and clean water production

MXenes are layered 2D materials with fascinating properties such as large surface area, good electrical conductivity, good chemical, and electrochemical stabilities, etc. However, the high cost of MAX phases remains a major bottleneck for the large-scale synthesis of Ti3C2Tx MXene for industrial applications. This motivated us to strategically design a method for the large-scale synthesis of Ti3C2Tx MXene using low-cost waste-derived precursors. Initially, we used carbon soot obtained from car exhaust as a low-cost carbon precursor for the synthesis of the Ti3AlC2 MAX phase. Further, the Ti3C2Tx MXene is synthesized from this MAX phase with better purity. Furthermore, the Ti3C2Tx MXene-activated carbon (AC) composite is prepared and coated over a natural biodegradable sponge (NBS) in order to use it as an efficient photothermal/solar absorber to produce steam using solar energy. The NBS layer exhibits a microporous structure that provides adequate water transportation and concentrated heat for interfacial water evaporation whereas the Ti3C2Tx MXene and AC provide large surface area and stability to the absorber. The Ti3C2Tx MXene-AC@NBS composite successfully produced solar evaporation rates of up to 1.8 kg m2/h with a solar steam conversion efficiency of 89.82 % with one sun solar irradiation.

Long-term oxidation of Ti3Al0.8Sn0.2C2 in air at 1200 °C

The addition of Sn into the raw materials is currently one of the most widely used methods to improve the purity and mechanical properties of Ti3AlC2. It follows in this work to investigate the oxidation behavior of the resulting Ti3Al0.8Sn0.2C2 at 1200 °C with the oxidation time up to 500 h. The oxidation kinetics shows that its oxidation resistance is much worse than that of common MAX phases including Ti3AlC2, Ti2AlC, and Cr2AlC. The oxide layer mainly consists of TiO2 and Al2O3, with only a small amount of SnO2 at the beginning of the oxidation stage. Cracks induced by the internal thermal stress penetrate through the entire oxide layer after only 1 h, which is an important reason for the rapid oxidation of the internal substrate layer. This work is expected to provide some inspiration and reference for Ti3Al0.8Sn0.2C2 used as the potential high-temperature structural material.

In situ growth of TiO2 on Ti3C2Tx MXene for improved gas-sensing performances

In this study, in situ prepared multiple semiconducting TiO2 in a metallic Ti3C2Tx channel were investigated, which were derived from the Ti3AlC2 MAX phase by oxidation treatments. Several tiny TiO2 particles were in situ formed on the Ti3C2Tx MXene surface when it was heated to 150 °C at ambient conditions. The phase transformation of pristine Ti3C2Tx MXene to oxidized TiO2 was accelerated when the gas-sensing channel was heated to higher temperatures up to 200 °C, yielding a TiO2/Ti3C2Tx composite. The experimental results revealed that the heat-treatment temperature played an important role in the gradual development of the morphology and gas-sensing activity of the TiO2/Ti3C2Tx sensing channel. In particular, the optimal heating temperature of the composite resulted in a good response and recovery time for NO2 molecules. Furthermore, first-principles calculations indicated the good sensing ability of the TiO2/Ti3C2Tx composite for NO2 than for other gases. These results suggest a new strategy for developing gas-sensing ability by forming a Schottky barrier through a simple process.

Freeze-sonication delamination method of high crystalline-quality MXene with high yield

MXene has attracted broad attention for its unique physicochemical properties and has flourished in many research areas. Since MXene obtained by high crystalline-quality MAX phase has excellent stability and properties, the etching of high crystalline-quality MAX phase and delamination into monolayer will become an inevitable trend. However, the delamination of the high crystalline-quality MXene is significantly more challenging than conventional MXene because of the more vital van der Waals forces of the more regular interlayer structure. Here, we propose a freeze-sonication delamination (FSD) strategy that can solve the difficult problem of efficiently exfoliation of high crystalline-quality MXene. The principle is to utilize the synergistic effect of ultrasound and ionic intercalation to allow a large number of water molecules to penetrate into the interlayer, which results in volume expansion, and then ultrasound to obtain monolayer MXene in a frozen state. This method not only increases the yield of high crystalline-quality monolayer MXene but also prevents the size reduction and the nanosheet destruction. The yield of monolayer MXene reached 74.2 % with a concentration of 19.8 mg/mL after six FSD cycles (the time of ultrasound treatment is 5 min after per freeze). Meanwhile, under the protection of ice, the obtained monolayer MXene has a larger size with more complete nanosheets than ultrasound-delaminated MXene. Supercapacitors made of high crystalline-quality MXene exhibits excellent gravimetric capacitance of 261.1 F/g and satisfactory cycling stability.

Effect of oxygen substitution and oxycarbide formation on oxidation of Ti3AlC2 MAX phase

AbstractMAX 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 Ti3AlC2 MAX 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.

Microstructure and mechanical properties of (CrxTi1-x)2AlC 211 MAX phases as composites through spark plasma sintering

MAX phases are intriguing materials due to their unique properties. However, each of these materials possesses its own weaknesses when subjected to service conditions. For example, while one MAX phase exhibits self-lubricating feature, it may not perform well under high load conditions. This study investigates the impact of adding chromium to Ti2AlC on microstructure and mechanical properties. Samples are prepared through ball-milling and spark plasma sintering (SPS), then analyzed using various techniques. The presence of different phases, including MAX phases (Ti2AlC and Cr2AlC), carbides (TiC and Cr7C3), and low amounts of oxides, is identified. Hardness, fractography, and wear characteristics are assessed through indentation and sliding tests. The study correlates the wear rate of each sample with experimental (H/E) and theoretical indicators (B/G), showing the production of composites with improved properties suitable for diverse applications.

Thermal self-crosslink after etching for regulated preparation of Ti3C2 type MXene membrane and its preliminary gas separation

We present an innovative methodology for the synthesis of MXene membranes through a dual-stage process involving etching and subsequent thermal self-crosslinking. A molar ratio of 1 (Al3+):9 (F−) using HCl/LiF was employed to convert raw Ti3AlC2 (MAX phase) into MXene within 48 h at 40 °C. This procedure predominantly yielded monolayers distinguished by diameters exceeding 500 nm, elevated crystallinity and a high overall yield. Advanced characterization techniques, including FESEM, TEM, HRTEM, AFM, XPS, and FTIR, were utilized. Instrumental analysis confirmed the formation of MXene exhibiting a single-flake morphology with diameters exceeding 500 nm. These monolayers were intact and continuous, with smooth peripheries and a uniform thickness of 2.1 nm. The surfaces were predominantly composed of carbon (C), oxygen (O), and titanium (Ti) atoms, interconnected by chemical bonds such as C–Ti–O, C–Ti–OH, C–C, C–O, and Ti–O. In the subsequent phase, vacuum filtration facilitated the assembly of a self-supporting MXene membrane. Thermal treatment at 170 °C for 30 h resulted in the reinforcement of C–Ti–O bonds within the nanosheets, increasing their prevalence to 43.14 % and 19.47 %, respectively. This thermal regulation reduced the interlayer d-spacing from 4.33 to 3.54 Å, which significantly improved the gas separation efficiency beyond the Knudsen diffusion limit, as demonstrated by the αH2/CF4 value exceeding 23.0.

The arising of ferromagnetism in Al-doped Mn2(Ga1−xAlx)C MAX phases

The magnetic properties of ordered MAX phases Mn2(AlxGa1−x)C (x = 0.125, 0.25, 0.5, 0.75 and 0.875) have been studied within the DFT-GGA. We have found that increase of Al atom at A-site leads to the formation of the ferromagnetic phase with large magnetization of about 3.6 μB/f.u. The investigation of the phase stability is performed by comparing the total energy of the MAX phases with that of a set of competitive phases for calculation of the phase formation enthalpy. Up to a concentration of Al atoms x = 0.7 the compound remains thermodynamically stable. The exchange constants analysis shows the crucial role of exchange interactions between manganese atoms along the c-axis in forming of ferromagnetism. The magnetic transition temperature of Mn2(AlxGa1−x)C alloys increases with increase of the aluminum concentration.

Laser cladded Co08–xTi3AlC2 coatings: Microstructure, corrosive–wear and electrochemical corrosion

MAX phase played the positive role during the corrosive–wear process of metal coatings, and Ti3AlC2 was added into Co08 coating by laser cladding to improve its corrosive–wear and electrochemical properties. The effects of Ti3AlC2 mass fraction on the corrosive–wear and electrochemical properties of obtained coatings in 3.5 % NaCl solution were investigated using a reciprocating wear tester and electrochemical workstation, respectively. The results show that the Co08–xTi3AlC2 coatings are composed of Co (Ni, Cr, W, Mo), AlFe and Ti3AlC2 phases, and their hardness is increased with the Ti3AlC2 mass fraction. The average coefficients of friction of Co08–5 %Ti3AlC2, –10 %Ti3AlC2 and –15 %Ti3AlC2 coatings are 0.56, 0.47, and 0.41, respectively, and the corresponding wear rates are 418.99, 389.67, and 339.33 μm3 N−1 s−1, respectively, showing that the Co08–15 %Ti3AlC2 coating has the best friction reduction and wear resistance among the three kinds of coatings. The wear mechanism of Co08–5 %Ti3AlC2, –10 %Ti3AlC2 and –15 %Ti3AlC2 coatings are abrasive wear, adhesive wear, and abrasive wear/adhesive wear, respectively. Moreover, the corrosion resistance of Co08–xTi3AlC2 coatings is increased by the Ti3AlC2 mass fraction, which is attributed to the protection role of corrosion products by the addition of Ti3AlC2.

Study of Synthesis Processes of Superconducting (?) MAX Phase Ti2InN

Study of Synthesis Processes of Superconducting (?) MAX Phase Ti₂InN

Comparative analysis of the solid lubrication performance - Ti3AlC2 versus Ti3C2Tx coatings

Due to the long-standing use of MAX phase materials since the 1960s and the emergence of MXenes in 2011, both are celebrated for their extraordinary mechano-tribological properties, including layered structures, high mechanical strength, and thermal conductivity. Nevertheless, there remains a crucial research gap in comprehensively comparing their tribological performance under solid lubrication, underscoring the need for an in-depth investigation. To close this research gap, we deposited MAX phase and MXene coatings by spray-coating on stainless-steel substrates. Subsequently, we evaluated their tribological properties, deciphered the underlying mechanisms using linear-reciprocating tribometry and high-resolution material characterizations. Our results demonstrated that the MXene coatings surpass the MAX phase coating in friction reduction by 81.82 %. In terms of wear depth, MXene coating has shown a notably reduced depth compared to both the reference steel sample and the MAX phase coating. Advanced tribochemical analysis indicates that MXenes' superior tribological performance is endorsed by their ability to form a thick, patchy-like transferlayer on the counterbody, which results from their ability to shear and delaminate under acting contact stress. Our study offers a framework for future investigations into utilizing MXene-based materials in tribological applications.

Q-switched giant pulsed erbium-doped all-fiber laser with V2ZnC MAX phase saturable absorber

Q-switched giant pulsed erbium-doped all-fiber laser with V2ZnC MAX phase saturable absorber

Microstructure and mechanical properties of in-situ nano TiC reinforced Ni-based alloy composites prepared by spark plasma sintering

Carbide dispersion reinforcing has been demonstrated to be an effective way of strengthening metal matrix composites. However, plagued by the nerve-wracking fact that the carbide particles tend to aggregate at the grain boundary of the metal matrix, grow up, and form an incoherent interface with it, their improvement in mechanical strength tends to be limited. In this study, spark plasma sintering (SPS) was used to prepare the bulk alloy Ni20Cr and its composites with different carbides including TiC, SiC, and Ti3SiC2. Plasma leads to discharge and elevates temperature at the interface to melt the Ni20Cr alloy particles locally. When cooled down, the alloy is heterogeneously solidified on the surface of the carbide and builds up a coherent interface with it. Owing to the decomposition of Ti3SiC2 during sintering, it completely transformed into nanosized TiC particles, which are engulfed by the outer melted layer of Ni20Cr and well dispersed within the alloy grains. In comparison to the Ni20Cr alloy, the composite with merely 4 wt% Ti3SiC2 gains over three times enhancement in yield strength to 879 MPa, while keeping a moderate high elongation of 17.8 %. Finite element analysis demonstrated that the combination of SPS and precursor MAX phase of Ti3SiC2, which results in the in-situ precipitation of coherent ultrafine TiC particles in alloy grains, plays the key role in getting a good balance between mechanical strength and ductility for the Ni20Cr matrix composites.

Al2O3 fiber-reinforced MAX phase ceramic matrix composite

In the aerospace industry, lightweight can reduce the weight of the engine and improve the thrust-weight ratio of the engine. Ceramic matrix composites have attracted widespread attention in the industry due to their much lower density compared to high-temperature alloys and excellent high-temperature performance. SiC fiber-reinforced SiC ceramic matrix composites are the most outstanding representatives, but their long manufacturing cycle and high manufacturing costs limit their widespread use. Ti2AlC is a new type of ceramic material with the characteristics of low density, high melting point, high-temperature resistance, oxidation resistance, and corrosion resistance of ceramic materials, as well as the conductivity and machinability of metals. However, its mechanical properties are slightly inadequate. The use of chopped fibers for toughening can compensate for these deficiencies to a certain extent and improve mechanical properties. This article first explored the influence of various process parameters on the mechanical properties of pure-phase Ti2AlC ceramic materials in SPS preparation technology and then prepared Ti2AlC composites reinforced with 10 vol%, 20 vol%, and 30 vol% Al2O3 chopped fibers. The results showed that the samples prepared at 1300 °C, 40 MPa, and 10 min had a flexural strength of 697 MPa and a fracture toughness of 9.83 MPa m1/2 when the volume ratio of the reinforcement phase was only 10 vol%, which was the same as that of the continuously fiber-reinforced SiCf/SiC composites. This study showed that the MAX phase matrix composites reinforced with chopped fibers have the potential to become high-temperature structural materials by adjusting the composite composition and optimizing the preparation process.

Phase formation mechanism of Cr2AlC MAX phase coating: In-situ TEM characterization and atomic-scale calculations

Cr2AlC, a representative MAX phase, gains increasing attention for the excellent oxidation tolerance and corrosion resistance used in harsh high temperature and strong radiation environments. However, the lack of the phase formation mechanism has become the key bottleneck to the practical applications for Cr2AlC synthesis with high purity at low temperatures. In this work, we fabricated the amorphous Cr–Al–C coating by a hybrid magnetron sputtering/cathodic arc deposition technique, in which the in-situ heating transmission electron microscopy (TEM) was conducted in a temperature range of 25–650 °C to address the real-time phase transformation for Cr2AlC coating. The results demonstrated that increasing the temperature from 25 to 370 °C led to the structural transformation from amorphous Cr–Al–C to the crystalline Cr2Al interphases. However, the high-purity Cr2AlC MAX phase was distinctly formed at 500 °C, accompanied by the diminished amorphous feature. With the further increase of temperature to 650 °C, the decomposition of Cr2AlC to Cr7C3 impurities was observed. Similar phase evolution was also evidenced by the Ab-initio molecular dynamics calculations, where the bond energy of Cr–Cr, Cr–Al, and Cr–C played the key role in the formed crystalline stability during the heating process. The observations not only provide fundamental insight into the phase formation mechanism for high-purity Cr2AlC coatings but also offer a promising strategy to manipulate the advanced MAX phase materials with high tolerance to high-temperature oxidation and heavy ion radiations.

Theoretical Study of Carbon K‐Edge Energy‐Loss Near‐Edge Structure Spectra in the Ordered Mo2TiAlC2 MAX and Mo2TiC2 MXene

By means of density functional theory, the energy‐loss near‐edge structure (ELNES) of carbon K‐edge of Mo2TiAlC2 and corresponding MoTiC2 Mxene at orientational‐independent condition is dealt with. Compared to the MAX (M is transition metal, A is an elment from group 13–16, X is C or N) phase, the energy separations increase between the main spectral features at the C K edge of Mo2TiC2 MXene owing to the structural change and decreased bond length. The dispersions of the C K edge in both systems are similar to p‐symmetry densities of states. It is indicated that the source of the first fine structure at the C 1s edge in both phases mainly comes from the electron transfer to px + py‐like character. The other fine structures result from the transition to hybridization of pz and px + py states with the prominent contribution of px + py‐like character. Moreover, the comparison of C K‐edge ELNES spectra in three Mo‐based compounds reveals that, ongoing from Mo2TiAlC2 to Mo2TiC2 and then to Mo2C, the energy position of the fine structures is shifted to higher energies (blueshifted), due to the quantum confinement effects and the change of the chemical environment around the excited carbon.

Synergism of Al and Si occurs on corrosion of Ti3Al1−xSixC2 MAX in the static Pb-Bi eutectic at 550 ºC

MAX phase ceramics attract increased attention for lead-cooled fast reactors due to their promising compatibility with lead-bismuth eutectic (LBE). This work systematically investigates the corrosion behaviors of five Ti3Al1−xSixC2 MAXs with Al/Si complex A component in static LBE at 550 ºC up to 3000 h. Based on the lattice structure, mechanical properties, surface morphologies, and elemental composition during corrosion, a synergism of Al and Si during oxidation and diffusion is found, which contributes to a continuous and well-attached Al2O3 layer with improved LBE corrosion resistance. Therefore, the multi-element design will bring a broad space for the applications of MAX ceramics.