Al Depletion Research Articles

Long‐Term High‐Temperature Oxidation of Al10CoCrFeNi30 High‐Entropy Alloy

The combined effects of high‐temperature and long‐term exposure to oxidation environment on an AlCoCrFeNi‐based high entropy alloy (HEA) are investigated. The alloy has a composition of Al10Co20Cr20Fe20Ni30 (at%) and is oxidized in lab air at 1000 °C for 1000 h to emulate working conditions and long operation cycles of gas turbines. The microstructure and oxide formation of the HEA are characterized using scanning electron microscopy, energy‐dispersive spectroscopy, and X‐ray diffraction. The performance of the HEA is compared to that of Inconel 625 and Hastelloy X and shows slower oxidation kinetics than Inconel 625 until 750 h. The HEA has the thinnest oxide layer of the three alloys and exhibits a triplex structure with a continuous Cr2O3 outer scale, a semi‐continuous Al2O3 subscale, and deep AlN precipitates. The matrix shows signs of Cr and Al depletion after 1000 h, leading to its inability to replace the degraded oxide scales that evaporated or spalled, and decreases its long‐term oxidation resistance. Overall, the HEA shows good oxidation resistance until 750 h, but may benefit from a higher Al content on the surface to form a longer‐lasting Al2O3 subscale that would remain protective beyond 750 h.

Unveiling the diffusion pathways under high-temperature oxidation of Cr2AlC MAX phase via nanoscale analysis

The MAX phase chromium aluminium carbide (Cr2AlC) is a potential candidate for high-temperature structural and energy applications due to the unique combination of properties, including excellent oxidation and corrosion resistance in harsh environmental conditions. In this work, the oxidation behaviour of bulk Cr2AlC was studied at temperatures of 1000 °C and 1200 °C in humid synthetic air, mimicking a realistic application environment. An α-Al2O3 scale forms at both temperatures, consisting of both inward and outward-growing layers, with a continuous Cr7C3 layer beneath the oxide. A special focus was put on employing atom probe tomography (APT) to analyse the oxide and carbide layers at the nanoscale. Decomposition of Cr2AlC to Cr7C3 is the main source (>70%) of aluminium needed for the oxide scale formation, while Al depletion in the underlying MAX phase remains marginal (<1 at%), exhibiting a pattern different from the common high-temperature oxidation of alloys. Al diffusion to the oxide scale proceeds predominantly through grain boundaries (GBs) in Cr2AlC and through the bulk in Cr7C3. Ionic diffusion through GBs of the large-grained inner alumina layer seems to be the rate-limiting step for the oxide scale growth, resulting in the apparent parabolic oxidation kinetics. No segregation of Cr, C or any impurities, which could affect ionic transport, was found at these alumina GBs by APT, rendering the results of this study as characteristic of a pure Cr2AlC oxidation.

On the oxidation and interdiffusion behavior of an AlCoCrFeNiY high-entropy alloy bond coat on a directionally solidified Ni-based superalloy

The oxidation and interdiffusion behavior of a novel AlCoCrFeNiY bond coat deposited on a directionally solidified Ni-based superalloy were systematically studied at 1050, 1100 and 1150 °C, and compared with a conventional NiCoCrAlY coating deposited on the same substrate. The AlCoCrFeNiY bond coat exhibits lower oxide growth rates due to its large columnar grains and low Al activity at the oxide scale/bond coat interface. Meanwhile, AlCoCrFeNiY has higher resistance to oxide spallation than NiCoCrAlY, which is attributed to the formation of a clean and defect-free metal/oxide interface. Significant interdiffusion occurs across the AlCoCrFeNiY/superalloy substrate interface. Our experimental evidence and thermodynamic modelling suggest that Fe accelerates interdiffusion and destabilizes the γ’ phase, thereby causing the formation of a thick and γ’-depleted interdiffusion zone. In addition, the AlCoCrFeNiY bond coat undergoes more Al depletion and subsequent β to γ transformation compared with NiCoCrAlY. Based on the findings in this work, a novel AlCoCrFeNiY/NiCoCrAlY double-layer bond coat was designed, tested and validated to achieve optimal balance between oxidation and interdiffusion.

Influence of pre-aluminizing on elemental diffusion behavior and fracture mechanism of thermal barrier coatings

The development of high-performance aero-engines raises the urgent requirement of coatings deposited on blades, containing both thermal barrier coatings (TBCs) on the external surface and aluminide coatings in the internal winding cooling channels. A TBC system with a low activity aluminizing process before deposition of conventional TBC was developed here to evaluate the feasibility of co-deposition technology. The thermal cyclic oxidation behavior of co-deposited “Al-modified TBC” was examined at 1100 °C and compared to that of conventional TBC. The cross-sectional microstructure evolution and elemental diffusion behavior of the modified TBC were also investigated. Even though the underlying aluminizing layer can serve abundant Al for the upper NiCoCrAlYHf layer to eliminate “Al depletion” in conventional TBC, which is a main reason for spallation, the Al-modified TBC system exhibited shorter thermal cycling life than conventional TBC. The spallation mechanism was discussed. Cracks caused by the fast growth rate of thermally grown oxide (TGO), Cr-rich precipitates resulted from the decreased γ/γ′-phase in the coating, and Re-rich precipitates originated from outward diffusion through the aluminide layer were mainly responsible for the failure.

Hot salt corrosion behavior of the Ti-44Al-4Nb-1.5Mo-(B,Y) alloy in the temperature range of 750–950 °C

Hot salt corrosion behavior of TNM alloy (Ti-44Al-4Nb-1.5Mo-(B, Y) (at.%)) was investigated in cyclic conditions at 750 °C, 850 °C and 950 °C for 100 h in the 75 wt% Na2SO4 + 25 wt% NaCl salt mixture. The hot salt corrosion resistance of γ、α2 and β phase in the alloy was studied by short-term quasi-in-situ hot corrosion experiments. Results show that the hot salt corrosion resistance of the three phases decreases in the following order: γ、α2、β. The weight changes of TNM alloy after hot salt corrosion at 750 °C, 850 °C and 950 °C for 100 h are 13.8 mg/cm2, -19.6 mg/cm2 and -26.7 mg/cm2. Under the condition of hot salt corrosion at 750 °C, the corrosion scales are mainly composed of a mixed corrosion scale of TiO2 and Al2O3, Al2O3 scale, and Al depletion zone, similar to the morphology of a high-temperature oxidation scale. The corrosion scales are seriously peeled off and destructive transverse cracks are generated inside the corrosion scales under the conditions of hot salt corrosion at 850 °C and 950 °C. The acid-base corrosion dissolution of oxides in the corrosive medium and the formation of volatile chlorides are the main causes of cracks in the TiO2 and Al2O3 scales. In addition, the Nb element in the TNM alloy is mainly enriched beneath the corrosion scales to form a NaNbO3 layer, which can inhibit the decomposition and penetration of the corrosive medium. Mo element reacts with the S element to form MoS2, which anchors the S element to a certain extent.

Integrated effect of aging and heavy ion radiation on FeNiCrAl duplex alloy for accident-tolerant fuel cladding

Alumina-forming duplex FeNiCrAl alloy with superior mechanical properties and high-temperature oxidation resistance has been regarded as an accident-tolerant fuel cladding material. This work investigated the effect of aging and the radiation resistance of FeNiCrAl duplex alloy after up to 2000 hours thermal aging and 3.5 MeV Fe13+ ion radiation. The ferrite phase containing B2 phase shows much fewer radiation defects and lower radiation hardening rate than conventional FeCrAl alloy. The coherent B2 phase precipitate is critical in hindering dislocation and inhibiting the formation of radiation induced defects which is proved via experiment and molecular dynamics simulation. Besides, the Al depletion of B2 phase and nano-sized precipitation are characterized by using Time-of-Flight Secondary Ion Mass Spectrometry and Atom Probe Tomography. These findings effectively illuminate microstructure evolution of FeNiCrAl duplex alloy after long-term aging and radiation and lead to new insight for designing advanced accident-tolerant fuel material.

A 200-year snapshot of soil development in pyroclastic deposits derived from the 1815 super explosive eruption of Mount Tambora in Indonesia

Early-stage pedogenic processes and formation rates on completely obliterated volcanic landscapes, such as the super explosive 1815 Mount Tambora eruption, have not previously been robustly explored. The objectives of this study were to determine (i) the mineralogical composition of the sand fraction, selected physical and chemical soil properties and potential nutrient reserves after 200 years of pedogenesis, and (ii) chemical weathering indices, rate of soil formation, and rates of C and N accretion. Soil formation was examined for five soil profiles on stable plain/foot slope positions representing the diversity of soils in these landscape positions, which are important for agricultural production. Results showed that the soil mineralogical composition of the sand fraction was dominated by easily weatherable minerals (e.g., labradorite and augite volcanic glass) indicating high potential nutrient reserves (e.g., Ca2+, Mg2+, K+, P) as confirmed by X-ray fluorescence (XRF) analyses. Allophanic material formation was minimal (<2.3%) owing to the preferential accumulation of Al3+ into Al-humic complexes. The low contents of allophanic materials and metal-humus complexes resulted in low P-retention (17.5–43.4%) within the soil solum, with the highest value in surface horizons (33–43%). Morphological features showed rapid solum (A + B horizons) development of 22 to 107 cm. Shallow soils occurred on shallow eruption deposits (consisting of pyroclastic flow underlain by pumice), whereas the deepest soils were found on thick deposit consisting of either trachyandesite pyroclastic or basaltic andesite materials. The chemical index of alteration (CIA) followed the order of A horizons (48.4 ± 4.6) > B horizons (45.4 ± 2.4) > C horizons (43.8 ± 4.2) ≈ tephra/lava (43.1), indicating accumulation of Al oxides and depletion of base cations in the upper horizons. Similarly, the base depletion index (BDI) showed a trend of A horizons (1.13 ± 0.18) < B horizons (1.25 ± 0.09) < C horizons (1.34 ± 0.20) ≈ tephra/lava (1.35), indicating depletion of base cations (Ca2+, Mg2+, K+, Na+) from the soil surface to C horizons. Based on solum depths (A + B horizons) and 200 years of post-eruption soil development, the solum formation rate ranged from 1.2 to 5.3 mm yr−1. Appreciable stocks of SOC (2.3–12.8 kg C m−2) and SON (0.21–0.77 kg m−2) accumulated over the 200 year period. Eruption materials from the Mt. Tambora eruption with a precisely known timescale contributed new pedological insights documenting rapid soil formation rates from pyroclastic materials leading to a rapid recovery of soil functions to support agricultural production.

Systematic study of radiation-induced segregation in neutron-irradiated FeCrAl alloys

This work systematically reports grain boundary radiation-induced segregation (RIS), and insights into RIS mechanisms, in FeCrAl alloys. Recently, FeCrAl alloys have received significant attention as direct replacement accident tolerant fuel (ATF) claddings for light water cooled nuclear reactors, because of their corrosion and high-temperature oxidation resistance characteristics. One degradation method not studied in detail is RIS, which could sufficiently alter grain boundary chemistry, potentially compromising the superior aqueous corrosion resistance. This study focuses on candidate ATF FeCrAl alloys C06M, C35M, C36M, and C37M that are neutron irradiated to 1.8 displacements per atom (dpa) at 357°C. Grain boundary Cr enrichment and Al depletion are observed in all irradiated alloys that span the 10-13 wt.% Cr and 5-6 wt.% Al composition space. Fe will either enrich or deplete at grain boundaries to balance the grain boundary composition. The Cr enrichment is attributed to interstitial diffusion, consistent with that in body centric cubic 9-12 wt.% Cr steels. The depletion of Al occurs through the same mechanisms as α−α′ phase partitioning previously observed in FeCrAl alloys. This study underscores the need for FeCrAl alloy design to consider RIS implications on corrosion and oxidation susceptibility.

The influence of V addition on the structure, mechanical properties, and oxidation behaviour of TiAlSiN coatings deposited by DC magnetron sputtering

The influence of V content on the morphology, structure, hardness (H) and reduced Young's modulus (E), adhesion, and oxidation resistance of TiAlSiN coatings is investigated. The coatings were produced by DC reactive magnetron sputtering, with increasing V contents from 0, 4.8 and 11.0 at.%. All coatings exhibit a fcc type structure. The coating with 4.8 at.% of V shows the highest values of H and E, whereas the values are similar for the reference coating and the coating with 11.0 at.% of V. The coatings adhere well to the substrates and show a dense and compact columnar growth extending from the adhesive interlayer to the top surface of the coatings. The dynamic thermal gravimetric oxidation curves reveal that V additions decreases the onset point of oxidation significantly and degrades the oxidation resistance of the coatings. A dual oxide layer is formed on the top surface of the reference coating: an outer porous Ti–Al–O rich layer with plate-like features on the top, which classified to TiO2 (rutile and anatase) and Al2O3 phases, and an inner Ti–Si–O rich layer with Al depletion that identified as mixture of amorphous Si–O and Ti–Si–O protective oxides. The diffusion of V to the top surface governs the oxidation process of the V-containing coatings, i.e. increasing V concentration leads to disrupt the formation of the protective continuous oxide layers easily.

Compatibility of Fe-Cr-Al and Fe-Cr-Al-Mo oxide dispersion strengthened steels with static liquid sodium at 700 [formula omitted

The corrosion behavior and tensile properties of oxide dispersion strengthened (ODS) FeCr, FeCrAl, FeCrAlMo steels and 316H stainless steel were evaluated after 1000 h at 700 ∘C in static sodium with and without an oxygen getter (Zr foil). Without Zr foil to getter the dissolved oxygen in the liquid sodium, combined oxidation (formation of Cr, Fe-rich or Al-rich oxides) and dissolution of the studied materials was observed. For the ODS FeCr, Cr- and Fe-rich oxide formation and dissolution induced Cr depletion in the underlying alloy and led to the formation of laves phases that were observed to be detrimental to the room temperature tensile properties. For ODS FeCrAlMo and FeCrAl Al-rich oxide formation and dissolution resulted in Al depletion in the underlying alloys but did not impact tensile properties at room temperature. For 316H temperature induced sensitization combined with oxidation decreased room temperature tensile properties. With Zr foil added as oxygen getter, roughened surfaces and Al depletion profiles suggested the dissolution of ODS FeCr and FeCrAl into the liquid sodium while limited dissolution was observed for ODS FeCrAlMo and 316H. For the 316H and ODS FeCrAlMo steels, precipitates were formed at the grain boundaries after exposure. Tensile properties of ODS FeCr, FeCrAl and FeCrAlMo were not affected by the 1000 h corrosion exposure with Zr foil added to the sodium but for 316H temperature-induced grain boundary sensitization negatively affected the tensile properties.

Impact of sintering temperature on phase composition, microstructure, and porosification behavior of LTCC substrates

Phase development and changes in crystalline composition of LTCC material during the sintering process were investigated using in-situ X-ray diffraction (XRD) measurements. CeramTape GC was chosen as the chemically simplest model system composed of alumina particles and glass for the investigations. The chemical characterization and microstructural analyses of the tapes sintered with some representative firing profiles were performed by techniques such as (scanning) transmission electron microscope, energy-dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and XRD. Moreover, the porosification behavior of LTCC substrates fired at different peak temperatures was studied. These investigations are important for the subsequent wet chemical etching, representing an approach which allows to reduce locally the permittivity of LTCC tapes. Treatment with a KOH solution shows non-selective etching behavior for all substrates. In addition, highly porous silica structures corresponding to Ca and Al depletion from the anorthite phase were observed in all samples after etching treatment.

Understanding the growth mechanisms of TiO2/Al2O3 mixed scales formed on Al-depleted Ti2AlC at 1000–1200 °C

We present a detailed study of thermally grown oxide scales on a bulk Ti2AlC material and explore its oxide growth mechanisms at 1000 °C, 1100 °C and 1200 °C, respectively. The oxide scale predominantly consists of an outer TiO2-rich layer and an inner TiO2/Al2O3 mixed layer. The formation of such a duplex microstructure is caused by the phase transformation from Ti2AlC to TiC at the scale/substrate interface and the Al depletion due to the formation of impurities. The insufficient supply of Al to scale/substrate interface, together with the competition from growth of TiO2, prevents formation of a continuous Al2O3 scale.

Oxidation mechanism and kinetics of nuclear-grade FeCrAl alloys in the temperature range of 500–1500 °C in steam

The oxidation mechanism and kinetics of two nuclear-grade FeCrAl alloys were investigated in steam up to 1500 °C by transient and isothermal oxidation tests. The slow α-alumina formation kinetics well matched only for the temperature range from 1000 °C to 1300 °C. Below 1000 °C, formation of transient alumina caused faster kinetics. In addition, an excessive Fe-rich oxide formation was observed on the inner surface due to rough surface at 600 °C. Above 1300 °C, convoluted α-alumina was easily spalled and caused faster kinetics. Moreover, the oxide spallation caused Cr and Al depletion and catastrophic oxidation above 1400 °C by the formation of Fe-rich oxide. The catastrophic oxidation caused a liquid phase in Fe-rich oxides, which significantly changed the tube segment geometry.

Oxidation and cracking behaviors of triple-layered Cr2AlC coating

Cr 2 AlC coating has potential applications as high temperature protective coating . However, inevitable interdiffusion at coating/substrate interface promotes Al depletion and deteriorates its oxidation resistance . In the present work, the oxidation behavior of a triple-layered Cr 2 AlC coating, with (Cr,Al) 2 O 3 inner layer, amorphous intermediate layer and crystalline Cr 2 AlC outer layer, was investigated at 900 and 1000 °C in air. The effect of the (Cr,Al) 2 O 3 inner layer as diffusion barrier was evaluated during the oxidation process . It is showed that the triple-layered Cr 2 AlC coating could effectively improve the oxidation resistance of the M38G alloy substrate, due to the Cr 2 AlC outer layer. The (Cr,Al) 2 O 3 inner layer could prohibit internal nitridation and retard interdiffusion at the coating/substrate interface, improving oxidation resistance of the triple-layered Cr 2 AlC coating. Furthermore, cracking of the triple-layered Cr 2 AlC coating was found after oxidation at 900 and 1000 °C, due to the thermal stress and internal stress introduced by intermediate amorphous layer crystallization during oxidation. • The triple-layered coating improves the oxidation resistance of the M38G alloy effectively. • The (Cr,Al) 2 O 3 inner layer prohibits inter diffusion and internal nitridation during oxidation. • Thermal stress and stress due to amorphous layer crystallization lead to cracking of the coating.

Increasing the oxidation resistance of γ-TiAl by applying a magnetron sputtered aluminum and silicon based coating

In this study, the suitability of a magnetron sputtered Al–18Si (at.%) coating as oxidation protection for a γ-TiAl based TNB-V2 alloy was investigated. The coating microstructure and its changes as well as the evolution of the different phases during the different steps, deposition process, post heat treatment and isothermal oxidation test, was studied using x-ray diffraction as well as scanning and transmission electron microscopy.The well adherent coating provides a homogenous, dense and crack free crystalline microstructure of Si grains in an Al matrix. The phase evolution analysis during a 20 h post-heat treatment at 550 °C with in situ x-ray diffraction reveals the complete formation of the TiAl3 phase due to the reaction of Ti from the TNB-V2 substrate and Al from the coating. During oxidation at 850 °C for 300 h, a thermally grown α-Al2O3 layer was formed providing excellent oxidation resistance. The formation of α-Al2O3 relies on the presence of TiAl3 whereas the silicon acted as a getter for Ti and thus could prevent the formation of TiO2. Furthermore, the finally formed Ti5Si3 phase reduces the inwards diffusion of Al into the substrate and prevents fast Al depletion in the coating. Moreover, the hierarchical coating microstructure, consisting of a TiAl3 matrix with a network-like structure of the Ti5Si3 phase, could be beneficial in terms of mechanical properties.

A diffusion-coupled cohesive element model for cracking analysis of thermal barrier coatings

The diffusion of Al from the bond-coat (BC) causes a continuous thickening of thermal-growth-oxide (TGO) layer, resulting in increased interface stresses at the interface of top-coat (TC) and BC. Moreover, the formation of TGO results in Al depletion in the BC layer. The presence of Ni, Co, Cr, and Al porous oxide combination may degrade the thermal barrier coating system (TBCs) interface. In this paper, a diffusion-coupled cohesive zone model (DCZM) is proposed to analyze the stress distributions and cracking behaviors in TBCs. The simulation methodology considers the thermal mismatch stress, oxidation growth stress, and diffusion-induced strength degradation. The results indicate that the Al diffusion increased the tensile stress on the interface by 4.2% in each cycle, and the failure time for TBCs was observed approximately 10% lesser than that of non-diffusion models. Furthermore, the interface with higher degradation sensibility has a shorter crack initiation life.

Precipitation behavior near shrinkage porosity in a large sand casting of Haynes 282 alloy

The precipitation behavior of L12 structure Ni3(Al,Ti)-type γ' precipitates near shrinkage porosity in a large sand casting of Haynes 282 alloy has been investigated by scanning/transmission electron microscopy in conjunction with energy dispersive x-ray spectroscopy. The experimental results revealed that in the carbonitride-rich region close to the shrinkage porosity, γ' precipitates could still form with comparable sizes though at lower volume density than those in the general cast Ni matrix. The resulting γ' precipitates had a very high Al/Ti ratio. Close to oxide-rich pore surfaces, an absence of γ' precipitates was observed due to Al and Ti depletion by forming Al oxides and Ti carbonitrides, respectively. This work suggests that Al rather than Ti plays a dominant role in the formation of γ' precipitates in porous regions in cast Haynes 282 alloys.

Processing, characterisation and oxidation resistance of βNiAl bond coat: Al and Zr effects

Platinum-modified-?NiAl is a bond coat (BC) material for thermal barrier coatings (TBCs) applications applied on aeroengine hardware to reduce their surface temperatures. However, it is desirable to minimize its production and material costs by the low-cost alternatives of similar performance. It has been acknowledged that the small concentration of the reactive elements (REs), such as Zr, Hf, and Y, could tremendously enhance the oxide adhesion even in some cases better than Pt modified counterparts. The aim of this study was to design and fabricate the Zr-modified-?NiAl bond coat on CMSX-4 superalloy using an aluminizing method. Moreover, the study focused on the development of a systematic understanding of underlying mechanisms behind the beneficial effects of REs. Initially, three sets of BCs were prepared: Zr-free ?NiAl (undoped), Al and Zr co-deposited in a single-step process (1SP), and Zr and Al, which were individually deposited in two processing steps (2SP): zirconizing and aluminizing. Such three sets of BCs helped to understand the processing, as well as Zr and Al effects on scale adhesion. In particular, 1SP/2SP BCs showed uniformity of Zr in the form of precipitates and networks that caused hardness enhancement. All BCs were isothermally oxidized at 1150?C for 100 hours wherein 2SP revealed the best spallation resistance, microstructural stability, and its Zr-oxide pegs were extended to substrates. In addition to the Zr effect, BC Al content was found to affect the oxide adhesion equally. Under identical Zr contents (of 1SP and 2SP = 1at %), the higher Al showed the better spallation resistance while lower Al caused the inverse effect of Zr owing to its reactive nature that was termed as over doping. Moreover, it was established that over-doping either local or into entire BC, accelerated the Al depletion that destabilized the ?NiAl into ??-Ni3Al phase. An extensive discussion is presented in the light of the observed results.

High-temperature mechanical properties of γ/γ′ Co–Ni–W–Al superalloy microlattices

Cobalt-based superalloy microlattices were created via (i) three-dimensional-extrusion printing of inks containing a suspension of Co-, Ni- and W-oxide particles, (ii) H2-reduction of the oxides and sintering to a homogenous Co-Ni-W alloy, (iii) Al pack-cementation to deposit Al on the microlattice struts, followed by Al-homogenization. The resulting Co-(18–20)Ni-(5–6)W-(10–13)Al (at.%) microlattices, with 27–30% relative density and 350 μm diameter struts, display a peak in yield strength at 750 °C, consistent with their γ/γ′ aged microstructure. Oxidation resistance is strongly improved compared to Al-free printed Co-Ni-W lattices, via the formation of an Al2O3 surface layer. However, the resulting Al depletion within the struts reduces creep resistance at 850 °C, which nevertheless remains similar to Ni-based superalloy foam, with 35% relative density.

Chemical gradients at the surface of TiO2-doped cordierite glass-ceramics

After crystallizing monolithic cordierite glass samples nucleated by TiO2, ToF-SIMS, GI-XRD and Raman spectroscopic measurements were performed on their surface. Compositional gradients (Mg and Al depletion, Si and Ti enrichment) and a different crystalline assemblage from the one in the interior were identified. The Al-Si ordering process during the indialite-cordierite phase transition appeared moreover to proceed slower on the surface. These differences were absent in the TiO2-free reference sample; they were therefore related to the role of TiO2 as a nucleating agent and to the resulting crystallization sequence. In addition, similar effects were observed in powders of the same composition as the monoliths.