TaB
2
-SiC coating modified by different content of MoSi
2
was fabricated on graphite substrate with SiC inner coating by liquid phase sintering to elevate the anti-oxidation capability of the TaB
2
...-SiC coatings. As compared to the sample with the TaB
2
—40wt%SiC coating, the coating sample modified with MoSi
2
exhibited a weight gain trend at lower temperatures, the fastest weight loss rate went down by 76%, and the relative oxygen permeability value reduced from about 1% to near 0. More importantly, the large amount of SiO
2
glass phase produced over the coating during oxidation was in contact with the modification of MoSi
2
, which was proved to be beneficial to the dispersion of Ta-oxides. A concomitantly formed continuous Ta-Si-O-B compound glass layer showed excellent capacity to prevent oxygen penetration. However, when the TaB
2
content was sacrificed to increase the MoSi
2
content, the relative oxygen permeability of the coating increased instead of decreased. Thus, on the basis of ample TaB
2
content, increasing the MoSi
2
content of the coating is conducive to reducing the relative oxygen permeability of the coatings in a broad temperature region.
To achieve high oxygen blocking structure of the ZrB
2
-MoSi
2
coating applied on carbon structural material, ZrB
2
-MoSi
2
coating was prepared by spark plasma sintering (SPS) method utilizing ZrB
2
...-MoSi
2
composite powders synthesized by self-propagating high-temperature synthesis (SHS) technique as raw materials. The oxygen blocking mechanism of the ZrB
2
-MoSi
2
coatings at 1973 K was investigated. Compared with commercial powders, the coatings prepared by SHS powders exhibited superior density and inferior oxidation activity, which significantly heightened the structural oxygen blocking ability of the coatings in the active oxidation stage, thus characterizing higher oxidation protection efficiency. The rise of MoSi
2
content facilitated the dispersion of transition metal oxide nanocrystals (5–20 nm) in the SiO
2
glass layer and conduced to the increasing viscosity, thus strengthening the inerting impact of the compound glass layer in the inert oxidation stage. Nevertheless, the ZrB
2
-40 vol%MoSi
2
coating sample prepared by SHS powders presented the lowest oxygen permeability of 0.3% and carbon loss rate of 0.29×10
−6
g·cm
−2
·s
−1
. Owing to the gradient oxygen partial pressure inside the coatings, the Si-depleted layer was developed under the compound glass layer, which brought about acute oxygen erosion.
•TaxHf1−xB2–SiC coating was prepared on SiC coated C/C by in-situ reaction method.•TaB2 and HfB2 were introduced in the form of solid solution TaxHf1−xB2.•The coating could protect C/C for 1480h with ...only 0.57% mass loss at 1773K in air.•Oxidation layer consists of out Ta–Si–O compound layer and inner SiO2 glass layer.•Ta–Si–O compound silicate layer presents a better stability than SiO2 glass layer.
A TaxHf1−xB2–SiC coating was prepared by in-situ reaction method on SiC coated C/C composites. TaxHf1−xB2 phase is the form of solid solution between TaB2 and HfB2. Isothermal oxidation behavior at 1773K and ablation behavior of the coated C/C were tested. TaxHf1−xB2–SiC/SiC coating could protect the C/C from oxidation at 1773K for 1480h and ablation above 2200K for 40s. During oxidation, oxides of Ta and Hf atoms exist as “pinning phases” in the compound glass layer consisted of outer Ta–Si–O compound silicate layer and inner SiO2 glass layer, which was responsible for the excellent oxidation resistance.
In order to reduce production cost and effectively improve the oxidation protection ability of the ultra-high temperature ceramics (UHTCs) ZrB2–SiC coating for the SiC-coated carbon/carbon (C/C) ...composites, a ZrB2–SiC outer coating was prepared by in-situ reaction method on SiC-coated C/C. Instead of costly ZrB2 powder, inexpensive B2O3, ZrO2, Si and C powders were used as raw materials to prepare the outer ZrB2–SiC coating with well-developed microstructures. The ZrB2 and SiC phases in the outer coating were synchronously obtained during the preparation of the coating. The isothermal oxidation behavior of the coated C/C composites at 1773K was investigated. The double-layer ZrB2–SiC/SiC coating could prevent C/C composites from oxidation at 1773K for 550h. During oxidation, a kind of ‘embedding structure’ containing ZrO2 and ZrSiO4 will be formed on the surface of the compound silicate glass layer, which is responsible for the excellent oxidation resistance of the ZrB2–SiC outer coating.
•ZrB2–SiC coating was prepared by in-situ reaction method on SiC-coated C/C.•ZrB2 was synthesized through in situ reaction by reducing ZrO2 using B2O3 and C.•The coating could protect C/C for 550h with only 0.22% mass loss at 1773K in air.•The “embedding structure” causes the occurrence of crack deflecting and termination.•Dual protection of SiO2 glass layer and “pinning phases” causes excellent resistance.
In order to improve the oxidation resistance of the TaB2–SiC based coating applied on carbon/carbon (C/C) composites, TaC phase was in-situ introduced and a TaB2–TaC–SiC ultra-high temperature ...ceramics (UHTCs) coating was prepared on the surface of SiC coated C/C composites by in-situ synthesis method. The results showed that the outer coating consists of smooth non-angular TaB2 phase, regular hexagonal prism shape TaC phase and SiC phase, which are synchronously obtained during the preparation of the coating. The multilayer coating could protect the C/C composites against oxidation for 400h at 1773K in air with only 1.43% weight loss. A double self-healing oxidation layers (inner SiO2 glass layer and outer compound Ta–Si–O silicate glass layer) formed on the surface of the coating provides a dual oxidation protection for the coating, which was responsible for the excellent oxidation resistance.
Mo(Si,Al)2-MoB composite coatings were deposited on TZM alloy by a single-step pack cementation process. The microstructure development of the coatings and the influence of deposition temperature on ...the coating structure are investigated. The coatings form via a sequence manner of first Al depositing and then Al-Si-B or Si-B co-depositing, while increasing the deposition temperature will move Al-Si-B or Si-B co-depositing ahead during the process. The coatings prepared at 1250 °C for more than 4 h consist of thick Mo(Si,Al)2 outer layer with dispersed MoB particles and thin MoB inner layer. The oxidation-resistant performance and degradation mechanism for the coatings during oxidation at 1400 °C are discussed.
•Mo(Si,Al)2-MoB composite coatings were prepared on TZM alloy.•Elements deposition sequence for the coating preparation was elucidated.•Effect of deposition temperature on the coating structure was studied.•The coatings exhibited excellent oxidation resistance at 1400 °C.
In this study, we synthesized Bi
2
Mo
3
O
12
and Bi
2
Mo
3
O
12
/MoO
3
composites through a simple solution combustion synthesis (SCS) route. The structure, morphology, and photocatalytic property ...for the degradation of Congo Red (CR) were characterized by x-ray diffraction, scanning electron microscopy (SEM), x-ray photoelectron spectroscopy and ultraviolet–visible spectrophotometer absorption spectroscopy. The phases of the samples were characterized to be Bi
2
Mo
3
O
1
and Bi
2
Mo
3
O
12
/MoO
3
. The SEM results showed Bi
2
Mo
3
O
12
particles were uniformly distributed on the MoO
3
sheets. Bi
2
Mo
3
O
12
and MoO
3
in the Bi
2
Mo
3
O
12
/MoO
3
composites were clearly demonstrated by the lattice spacing from high-resolution transmission electron microscopy results. The maximum degradation rate of Bi
2
Mo
3
O
12
/MoO
3
composite was 83% at 60 min, showing excellent photocatalytic performance. A possible mechanism is proposed for the degradation of CR over Bi
2
Mo
3
O
12
/MoO
3
composites, in which
h
+
and ·O
2−
are the main active species and play an important role in the degradation of pollutants.
Porous TiAl3 intermetallics were synthesized from Ti-75 at.% Al elemental powder mixtures using an energy-saving and rapid reactive method of thermal explosion (TE). The results demonstrated that the ...actual temperature of the compact climbed rapidly from 673 °C to 1036 °C within 24 s, indicating that an obvious TE reaction occurred during sintering process. The video graphs suggested that the TE in Ti–Al system behaved instant occurrence and overall heating whether from axial or radial direction. The silver wires and NaCl particles that pressed on the surface of the sample disappeared due to the heavy heat released during TE reaction. Only pure TiAl3 phases were synthesized in TE products and the open porosity of 55.4% was easy to obtain. After high-temperature treatment at 1000 °C, large amounts of sintering-neck formed and then improved the compressive strength of porous TiAl3 materials. Moreover, the mass gain curve of porous TiAl3 intermetallics oxidized at 650 °C for 120 h exhibited the parabolic oxidation rate law. XPS analysis confirmed that the strong O 1s peak was 531.4 eV which was the typical binding energy of Al2O3. Therefore, the excellent oxidation resistance of porous TiAl3 foams would be considered as good candidate materials for prolonging the service life at high temperatures.
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•The thermal explosion occurred in Ti–75Al at.% compacts with 55.4% open porosity.•TE products were evenly distributed and formed interconnected pore channels.•Porous TiAl3 materials exhibit excellent oxidation resistance with parabolic law.
Bioglass coatings derived from electrophoretic deposition method were fused on Ti surface by laser cladding process using a continuous CO2 laser. The specimens were studied by field-emission scanning ...electron microscopy, X-ray diffraction and bonding tests. Titanium oxide layer with hierarchical structures consisting of submicron rows of leaf-like embossments and nano-pores was obtained by combining acid etching and anodization processes, which increased the surface roughness of Ti. When heat-treatment temperature was 700 °C and high, CaSiO3 phase began to crystallize from the bioglass matrix and the crystallinity reached its maximum at 700 °C. During the electrophoretic deposition process, porous bioglass coatings composed of bioglass particles and fibers were deposited on Ti surface. Bioglass coatings with similar hierarchical structure containing submillimeter bioglass beads and microfibers were synthesized on Ti surface by laser fusion. There are no obvious microcracks at the interface of the Ti-coating, which revealed the good bonding between Ti-porcelain. With the laser scanning distance decreased, the bond strength increased accordingly. After only one day immersion in SBF, calcium phosphate began to precipitate on the bioglass coatings' surfaces. The thickness of the calcium phosphate precipitation and the amount of microparticles increased with immersion time.
•Bioglass coatings were fused on Ti surface by laser cladding process.•Surface roughness of Ti was increased by surface modification of Ti.•Apatite precipitated on the bioglass coatings after 1 day immersion.•The thickness of the apatite precipitation increased with immersion time.
A double layer TaB2-TaSi2-SiC-Si/TaC-SiC coating was prepared on the surface of C/C composites to improve the oxidation resistance of the composites, which was prepared by in situ reaction method ...through pack cementation technique. The phase composition and microstructures of the multiphase coating were characterized by XRD and SEM-EDS. The inner coating is composed of TaC and SiC, while the outer multiphase coating is composed of TaB2, TaSi2, SiC and Si. The multilayer coating is about 200μm in thickness and does not display penetrating crack or big cavities. The coating could protect C/C from oxidation at 1773K in air for 330h with only 0.9% weight loss, thanks to the formed silicate glass layer containing SiO2 and tantalum oxides.
•TaB2-TaSi2-SiC-Si/TaC-SiC coating was prepared on C/C by a two-step pack cementation.•TaC was synthesized through in situ reaction by reducing Ta2O5 with C.•TaB2 was synthesized through in situ reaction by reducing Ta2O5 using B2O3 and C.•The coating could protect C/C for 330h with only 0.9% mass loss at 1773K in air.
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