The coloring of geopolymers by the addition of copper compounds

The development of a new coloring technique is desirable to increase the commercial value of geopolymers. Selected copper compounds, i.e. Cu(OH)₂, CuO, Cu₂O, CuCO₃?Cu(OH)₂?H₂O, CuCl₂?2H₂O and CuSO₄?5H₂O, were added to the initial reactants in order to color the geopolymers in the same manner as naturally occurring minerals. When Cu(OH)₂, CuO and Cu₂O were used, these compounds remained in the geopolymer matrix following hardening of the material. On the contrary, CuCO₃?Cu(OH)₂?H₂O, CuCl₂?2H₂O and CuSO₄?5H₂O were not detected in the final products. XAFS analyses were performed to investigate the local structure of copper in the geopolymers produced. The results showed that the copper spectra of geopolymers incorporating Cu(OH)₂, CuO and Cu₂O correspond to those of pure Cu(OH)₂, CuO and Cu₂O, respectively. However, when CuCO₃?Cu(OH)₂?H₂O, CuCl₂?2H₂O and CuSO₄?5H₂O were added, the copper generated spectra similar to that of the mineral chrysocolla ((Cu, Al)₂H₂Si₂O₅(OH)₄?nH₂O) than the respective copper compounds.     

Preparation of Photodegradable Oligomers Containing Metal–Metal Bonds Using ADMET

ADMET was evaluated as a method for preparing organometallic polymers with metal–metal bonds in the main chain. The Cp₂Mo₂CO₄(Ph₂P(CH₂)₆CH=CH₂)₂ complex was synthesized, and the X-ray crystal structure is reported. The molecule did not undergo ADMET polymerization with Grubbs’ or Schrock’s catalysts. In a control experiment to test if the Ph₂P(CH₂)₆CH=CH₂ ligand was interfering with the ADMET reaction, the phosphine was reacted with Grubbs’ 2nd generation catalyst. The dimerized metathesis product Ph₂P(CH₂)₆CH=CH(CH₂)₆PPh₂ was obtained with no observed degradation or deactivation of the catalyst. To test the inherent ADMET reactivity of the Ph₂P(CH₂)₆CH=CH₂ ligand when it is bonded to a metal center, the mononuclear cis-Mo(CO)₄(Ph₂P(CH₂)₆CH=CH₂)₂ complex was synthesized and polymerized using Grubbs’ 2nd generation catalyst. These control experiments suggest that the inability of Cp₂Mo₂CO₄(Ph₂P(CH₂)₆CH=CH₂)₂ to polymerize is not due to electronic effects pertaining to the C=C unit of the Ph₂P(CH₂)₆CH=CH₂ ligand. Accordingly, steric effects are implicated in the inability of the Cp₂Mo₂CO₄(Ph₂P(CH₂)₆CH=CH₂)₂ to polymerize by ADMET.     

Comparison of the catalysed decomposition of hydrogen peroxide over superconducting and insulating barium cuprates—kinetics of decomposition over Y2BaCuO5

Catalytic activities of two non-conducting cuprates (Ba₂Cu₃O₅, Y₂BaCuO₅) and a superconducting cuprate YBa₂Cu₃O_7–δ, prepared by two different methods, were compared using H₂O₂ solution. The two non-conducting barium cuprates were found to be about two orders of magnitude more active than the superconducting perovskite-like YBa₂Cu₃O_7–δ. The near coincidence of the kinetic curves for the catalysed decomposition of H₂O₂ over YBa₂Cu₃O_7–δ, prepared either from the perovskite-like Ba₂Cu₃O₅ and Y₂O₃ or from its components, proves that Ba₂Cu₃O₅ is essential in the formation of YBa₂Cu₃O_7–δ. First-order kinetics were observed for the catalysed decomposition of H₂O₂ solution over the non-perovskite Y₂BaCuO₅ at the initial stages of the reaction, similar to that of the superconducting perovskite catalyst. A tentative scheme of the possible catalytic reactions for the decomposition of H₂O₂ solution over the insulator Y₂BaCuO₅ is given.     

Coordination of the carboxylate of the functionalized Strandberg anion in a three dimensional covalence framework

[H₃O]₂[{Cu₆(bipy)₁₀(H₂O)₄}{Cu₂(bipy)₂(H₂O)₄}{(HO₂CC₂H₄PO₃)Mo₅O₁₅(O₂CC₂H₄PO₃)}₂{(HO₂CC₂H₄PO₃)₂Mo₅O₁₅}₂]·30H₂O (1) was obtained from aqua solution. In 1 the linkage between bipy and Cu^2 + ions creates a layer with rhombus channel and an isolated chain. [(HOOCC₂H₄PO₃)₂Mo₅O₁₅]^4 – anions act as tridentate and tetradentate ligands, connecting the layers and the chains into a three dimensional covalent framework through the oxygen atoms of carboxylate groups and of MoO₆ octahedra.     

Thermal decomposition of ammonium sulphate

The thermal decomposition and vaporisation of ammonium sulphate, (NH₄)₂SO₄, is shown to take place via two distinct sets of reactions. In the first, ammonium pyrosulphate, (NH₄)₂S₂O₇, is the primary condensed phase product: 2(NH₄)₂SO₄ ← (NH₄)₂S₂O₇+2NH₃+H₂O The second stage concerns the decomposition of the pyrosulphate. Ammonia, sulphur dioxide, nitrogen and water are the major products, the dominant reaction being 3(NH₄)₂S₂O₇ ← 2NH₃+6SO₂+2N₂+9H₂O     

One-step purification of ethylene from acetylene and carbon dioxide by ultramicroporous carbons

The one-step adsorptive separation of high-purity ethylene (C₂H₄) from a ternary gas mixture (C₂H₂/C₂H₄/CO₂) is challenging and has not been reported on porous carbons. Herein, we report camphor seeds husk-derived ultramicroporous carbons (CSHs) show high affinities toward acetylene (C₂H₂) and carbon dioxide (CO₂) over C₂H₄. The optimized CSH-2-700 with high heteroatom contents and centered pore size distributions shows high C₂H₂ adsorption capacity (2.24 mmol g⁻¹) and record ideal adsorbed solution theory (IAST) C₂H₂/C₂H₄ selectivity (10.2) among one-step C₂H₄ purification adsorbents. Meanwhile, CSH carbons are the only carbon adsorbents that preferentially adsorb CO₂ over C₂H₄, with a CO₂/C₂H₄ selectivity of 1.9 under ambient conditions. Furthermore, dynamic breakthrough experiments verified its feasibility for one-step C₂H₄ purification from a three-component C₂H₂/C₂H₄/CO₂ gas-mixture.     

Adjacent relations of primary phase fields and invariant reactions of the system CaO-SiO2-Nb2O5-La2O3

The adjacent relation of primary phase fields and corresponding invariant reactions of the system CaO-SiO₂-Nb₂O₅-La₂O₃ are of great importance for the study on its phase diagram. In the present work, the phase equilibrium in the high w(La₂O₃) region of CaO-SiO₂-Nb₂O₅-La₂O₃ system was studied by thermodynamic equilibrium experiment. The adjacent relation of primary phase fields was determined and represented in the form of adjacent tetrahedrons. The Alkemade Rule applicable to quaternary phase diagram was deduced, which can be used to infer the liquidus temperature trend on univariant curves. The rule was then used to determine the possible temperature range of invariant reactions corresponding to the adjacent tetrahedron in CaO-SiO₂-Nb₂O₅-La₂O₃ system, and the result was shown in the form of Schairer diagram. Finally, the reaction types of five invariant points were determined according to the Lever Rule for quaternary phase diagram, including: ① L₁+CaO·3SiO₂·2La₂O₃→CaO·SiO₂+SiO₂+La₂O₃·Nb₂O₅, ② L₂→CaO·SiO₂+La₂O₃·Nb₂O₅+SiO₂+CaO·Nb₂O₅, ③ L₃+CaO·3SiO₂·2La₂O₃+2CaO·Nb₂O₅→10CaO·6SiO₂·Nb₂O₅+La₂O₃·Nb₂O₅, ④ L₄+10CaO·6SiO₂·Nb₂O₅→CaO·SiO₂+2CaO·Nb₂O₅+La₂O₃·Nb₂O₅, ⑤ L₅+2CaO·Nb₂O₅→CaO·Nb₂O₅+La₂O₃·Nb₂O₅+CaO·SiO₂.     

Metal Induced Decarboxylation of Aliphatic Free Radicals. I. Kinetics of the Reactions of Copper(I) and Copper(II) Ions with the 2-Methyl-2-Carboxylicacid-Propyl Free Radical in Aqueous Solutions. A Pulse Radiolysis Study

CH₂C(CH₃)₂CO₂H free radicals react with Cu²⁺_aq to form Cu^III-CH₂C(CH₃)₂CO₂H²⁺_aq, which probably is rapidly transformed into intermediate I. This intermediate decomposes into Cu⁺_aq + CO₂ + CH₂=C(CH₃)₂. This is the first system in which a metal ion induced β-carboxyl elimination reaction was observed. ·CH₂C(CH₃)₂CO₂H free radicals react with Cu^III-CH₂C(CH₃)₂CO₂H²⁺_aq to form Cu²⁺_aq and a mixture of (-CH₂C(CH₃)₂CO₂H)₂, (CH₃)₃CCO₂H, and HOCH₂C(CH₃)₂CO₂H. CH₂C(CH₃)₂CO₂H reacts with Cu⁺_aq to form Cu^II-CH₂C(CH₃)₂CO₂H⁺_aq. The latter intermediate decomposes both via homolysis and by a reaction with Cu²⁺_aq to form 2Cu²⁺_aq + (CH₃)₃CCO₂H. The spectra of the intermediates and the kinetics of reaction are reported.     

Activation of Supported Pd Metal Catalysts for Selective Oxidation of Hydrogen to Hydrogen Peroxide

Catalytic activity of supported Pd metal catalysts (Pd metal deposited on carbon, alumina, gallia, ceria or thoria) showing almost no activity in the liquid-phase direct oxidation of H₂ to H₂O₂ (at 295 K) in acidic medium (0.02 M H₂SO₄) can be increased drastically by oxidizing them using different oxidizing agents, such as perchloric acid, H₂O₂, N₂O and air. In the case of the Pd/carbon (or alumina) catalyst, perchloric acid was found to be the most effective oxidizing agent. The order of the H₂-to-H₂O₂ conversion activity for the perchloric-acid-oxidized Pd/carbon (or alumina) and air-oxidized other metal oxide supported Pd catalysts is as follows: Pd/alumina < Pd/carbon < Pd/CeO₂ < Pd/ThO₂ < Pd/Ga₂O₃. The H₂ oxidation involves lattice oxygen from the oxidized catalysts. The catalyst activation results mostly from the oxidation of Pd metal from the catalyst producing bulk or sub-surface PdO. It also caused a drastic reduction in the H₂O₂ decomposition activity of the catalysts. There exists a close relationship between the H₂-to-H₂O₂ conversion activity and/or H₂O₂ selectivity in the oxidation process and the H₂O₂ decomposition activity of the catalysts; the higher the H₂O₂ decomposition activity, the lower the H₂-to-H₂O₂ conversion activity and/or H₂O₂ selectivity.     

Comparison of hot corrosion resistance of Sm2Zr2O7 and (Sm0.5Sc0.5)2Zr2O7 ceramics in Na2SO4+V2O5 molten salt

Sm₂Zr₂O₇ and (Sm_0.5Sc_0.5)₂Zr₂O₇ ceramics were fabricated by a chemical co-precipitation and calcination method, and their hot corrosion behaviors in Na₂SO₄+V₂O₅ molten salt were investigated. Hot corrosion tests were carried at 700 °C, 800 °C and 900 °C for 4 h, and corroded surfaces were investigated using X-ray diffractometer and scanning electron microscopy. The corrosion products of Sm₂Zr₂O₇ ceramics were composed of SmVO₄ and monoclinic-ZrO₂, while those of (Sm_0.5Sc_0.5)₂Zr₂O₇ ceramic consisted of SmVO₄ and Zr₅Sc₂O₁₃. Considering the fact that Zr₅Sc₂O₁₃ is more desirable than monoclinic-ZrO₂ for thermal barrier coating applications, (Sm_0.5Sc_0.5)₂Zr₂O₇ showed better corrosion resistance to Na₂SO₄+V₂O₅ salt than Sm₂Zr₂O₇. The hot corrosion mechanisms of Sm₂Zr₂O₇ and (Sm_0.5Sc_0.5)₂Zr₂O₇ in Na₂SO₄+ V₂O₅ salt were discussed in detail.     

Convenient Modular Syntheses of Fluorous Secondary Phosphines and Selected Derivatives

Reactions of the fluorous primary phosphines R_fn(CH₂)₂PH₂ [R_fn=(CF₂)_n−1CF₃; n=6, 8, 10] and R_fn′CHCH₂ [(n′=6, 8, 10) (1 : 1; THF, reflux) in the presence of AIBN give the title compounds [R_fn(CH₂)₂][R_fn′(CH₂)₂]PH [n/n′=6/6 ( 4 , 55%), 8/8 ( 5 , 58%), 10/10 ( 6 , 53%), 8/6 ( 7 , 52%), 10/8 ( 8 , 51%)] as low-melting white solids on up to 10-g scales. The chiral tertiary phosphine [R_f6(CH₂)₂][R_f8(CH₂)₂][R_f10(CH₂)₂]P ( 9 ) is similarly prepared from 7 and R_f10CHCH₂ in the presence of VAZO (neat, 100 °C; 67%). The reaction of 5 and THF⋅BH₃ yields the phosphine borane 5 ⋅BH₃ (95%). Additions of triphosgene [(CCl₃O)₂CO] to 5 or R_f8(CH₂)₂PH₂ give [R_f8(CH₂)₂]₂PCl or R_f8(CH₂)₂PCl₂, which are characterized in situ. The CF₃C₆F₁₁/toluene partition coefficients of 4 – 9 increase with the number and lengths of the R_fn segments.     

Synthesis of polyphosphazene random copolymers bearing alkoxyethoxy and trifluoroethoxy functional groups

The anionically initiated copolymerization of (CH₃OCH₂CH₂O)(CF₃CH₂O)₂ P=N-Si(CH₃)₃, (CH₃OCH₂CH₂OCH₂CH₂O)(CF₃CH₂O)₂ P=N-Si(CH₃)₃, (CH₃OCH₂CH₂O)₂ (CF₃CH₂O) P=N-Si(CH₃)₃, and (CH₃OCH₂CH₂OCH₂CH₂O)₂ (CF₃CH₂O) P=N-Si(CH₃)₃ with (CF₃CH₂O)₃ P=N-Si(CH₃)₃ is reported. These materials were characterized by³¹P and¹H NMR, SEC, and DSC.In situ ³¹P NMR studies indicate that monomers are simultaneously consumed, SEC traces show that these random copolymers exhibit monomodal distributions, and there is a gradient in solubilities as well as thermal and mechanical properties which is dependent upon the repeating unit ratios.     

An investigation of angle-dependent optical properties of multi-layer structure pigments formed by metal-oxide-coated mica

The angle-dependent pigments with mica/TiO₂/Fe₂O₃, mica/TiO₂/Cr₂O₃ and mica/TiO₂/Co₂O₃ three-layer structure and with mica/TiO₂/Cr₂O₃/Fe₂O₃, mica/TiO₂/SiO₂/Fe₂O₃ and mica/TiO₂/SiO₂/Co₂O₃ four-layer structure were both prepared by the conventional wet chemical method. The obtained pigments were formed by precipitating different ions, such as Cr³⁺, Fe³⁺, Co²⁺ and SiO₃²⁻ on the pretreated substrates, mica titanium. The comparative optical effects of three-layer and four-layer structure pigments are investigated in detail by using the five angles' spectrophotometer. The results show that the angle-dependent effect and reflection rate of the pigment were improved by the increasing coated layers from three to four-layer structure. The possible mechanism was also discussed in this paper.     

Reaction products of triammonium pyrophosphate in different Indian soils

Studies were undertaken on the isolation and identification of reaction products of triammonium pyrophosphate (TPP), the major non-orthophosphate constituent of ammonium polyphosphate newly introduced in India, in representative soils of the alfisol, oxisol, entisol, mollisol and vertisol groups of India. Saturated solution of TPP were reacted with soils for periods of 30 minutes and one day with corresponding precipitation times of 15 days, three months and one year to isolate reaction products which were identified by X-ray diffraction technique, infra-red spectroscopy and chemical analyses. Six reaction products, namely, Ca(NH₄)₂P₂O₇ · H₂O, Mg(NH₄)₂P₂O₇ · 4H₂O, Ca(NH₄)₄H₂(P₂O₇)₂, Ca₃(NH₄)₄H₆(P₂O₇)₄·3H₂O, FeNH₄P₂O₇ and NH₄Al_0·33 Fe_0·67P₂O₇ were identified in different soils; Ca(NH₄)₂P₂O₇·H₂O and Mg(NH₄)₂P₂O₇ · 4H₂O occurring in abundance in most soils. Significant hydrolytic degradation of pyrophosphate reaction products to orthophosphate was not observed.Complementary studies where TPP in solid form was applied to soil, and reaction formed at and around the site of TPP placement were identified after six weeks incubation also showed the formation of Ca(NH₄)₂P₂O₇ · H₂O and Mg(NH₄)₂P₂O₇ · 4H₂O in the soils examined.     

Effect of support material on the catalytic performance of V2O5/P2O5 catalysts for the selective oxidation of but-1-ene and furan to maleic anhydride and its consecutive nonselective oxidation : I. Results of Catalytic Testing

The performance of Al₂O₃- and TiO₂-supported V₂O₅/P2O5 catalysts was studied with respect to activity and selectivity for the oxidation of but-1-ene and furan to maleic anhydride (MA) and its consecutive nonselective oxidation. TiO₂-supported catalysts result in better selectivities for MA both for but-1-ene and furan oxidation. For both the supports MA selectivity was affected by the amount of V₂O₅ and P₂O₅ loading: An increase of the V₂O₅/P₂O₅ loading resulted in improved MA selectivity for the Al₂O₃ support while the effect was opposite in the case of the TiO₂ support. For the oxidation of but-1-ene and furan the activity of the TiO₂-supported catalyst (V₂O₅/P₂O₅/TiO₂, = 5/ 5/90 mass-%) was higher than the Al₂O₃-supported catalyst (V₂O₅/P₂O₅/Al₂O₃ = 5/ 5/90 mass-%) while for the non-selective oxidation of MA to carbon dioxide the Al₂O₃,-supported catalyst was more active than the TiO₂-supported catalyst.     

Effect of Electronic Charge on Oxygen Atom of Oxygen-Containing Oxidizers on Characteristics of Reactive Rocket Fuels

Abstract

The calculations of typical oxygen-containing oxidizers of rocket fuels OF₂, O₂, ClO₃F, H₂O₂, N_{2O 4}, HNO₃, were carried out by quantum chemical semi-empirical MNDO method in Dewar and Teel parameterization with minimization of total energy of molecular system by Davidon-Fletcher-Powell method. The optimized electronic and geometric structure of these oxidizers was obtained. We established correlative dependencies between some parameters of the following reactive fuels (H₂, N₂H₄, N₂ H₂(cH₃)₂ ～CH₂～, Al H₃, B₅H₉, Be H₂): and minimum electronic charge on oxygen atom qo_min of oxygencontaining oxidizers. The latter being calculated by the MNDO method.     

Synthesis and characterization of calcium aluminate compounds from gehlenite by high-temperature solid-state reaction

The mineral transition mechanism and self-pulverization property of the sintered products in the Ca₂Al₂SiO₇-CaO system were systematically studied using pre-synthesized gehlenite determined by XRD, SEM, FTIR and particle size analyses. The minerals of Ca₁₂Al₁₄O₃₃, CaAl₂O₄, Ca₃SiO₅ and Ca₂SiO₄ are formed by the direct reactions of Ca₂Al₂SiO₇ with CaO. CaAl₂O₄ reacts with CaO to form Ca₁₂Al₁₄O₃₃ or Ca₃Al₂O₆, while Ca₃SiO₅ reacts with Ca₂Al₂SiO₇ to form Ca₂SiO₄ and calcium aluminate compounds. The sintered products mainly contain CaAl₂O₄, Ca₁₂Al₁₄O₃₃ and Ca₂SiO₄ at 1350?°C or above 1500?°C when the molar ratio of CaO to Al₂O₃ is 1.0. Increasing the sintering duration or the CaO consumption promotes the transition of Ca₂Al₂SiO₇ to Ca₂SiO₄ and calcium aluminate compounds when sintered at 1350?°C, which accordingly improves the self-pulverization property of the sintered products. The formed minerals of Ca₁₂Al₁₄O₃₃, CaAl₂O₄ and Ca₂SiO₄ transform into Ca₂Al₂SiO₇ again when the sintering temperature is between 1400?°C and 1450?°C, and the corresponding self-pulverization property of the sintered products deteriorates sharply.     

The effect of relative humidity on CO<Subscript>2</Subscript> capture capacity of potassium-based sorbents

Potassium-based sorbent was prepared by impregnation with potassium carbonate on activated carbon. The role of water and its effects on pretreatment and CO₂ absorption was investigated in a fixed bed reactor. K₂CO₃ could be easily converted into K₂CO₃·1.5H₂O working as an active species by the absorption of water vapor as the following reaction: K₂CO₃+3/2 H₂O→K₂CO₃·1.5H₂O. One mole of K₂CO₃·1.5H₂O absorbed one mole of CO₂ as the following reaction: K₂CO₃·1.5H₂O+CO₂ai2KHCO₃+0.5 H₂O. The K₂CO₃·1.5H₂O phase, however, was easily transformed to the K₂CO₃ phase by thermal desorption even at low temperature under low relative humidity. To enhance CO₂ capture capacity and CO₂ absorption rate, it is very important to maintain the K₂CO₃·1.5H₂O phase worked as an active species, as well as to convert the entire K₂CO₃ to the K₂CO₃·1.5H₂O phase during CO₂ absorption at a temperature range between 50 °C and 70 °C. As a result, the relative humidity plays a very important role in preventing the transformation from K₂CO₃·1.5H₂O to the original phase (K₂CO₃) as well as in producing the K₂CO₃·1.5H₂O from K₂CO₃, during CO₂ absorption between 50 °C and 70 °C.     

Synthesis of stimuli-responsive ionic cyclopolymers in search of phosphorous-free antiscalants

Ammonium persulfate-initiated cyclopolymerization of maleic acid (HO₂CC=CCO₂H) (MA) with diallylamine (–NR₂, R = CH₂ = CH-CH₂) derivatives (DADs): R₂NH⁺CH₂CO₂⁻ ( I ), R₂NCH₂CO₂⁻Na⁺ ( II ), R₂NCH₂CO₂Et ( III ), R₂NH⁺(CH₂)₃CO₂⁻ ( IV ), R₂N(CH₂)₃CO₂Et ( V ), R₂NH⁺(CH₂)₃SO₃⁻ ( VI ) and R₂N(CH₂)₃SO₃⁻Na⁺ ( VII ) gave a series of new pH-responsive alternate copolymers: –[(DAD-alt-MA)]_n– VIII - XIV , respectively. Homopolymers XV and XVI of the corresponding monomers IV and V ·HCl were also synthesized. The evaluation of the synthesized polymers as potential antiscalants in reverse osmosis (RO) plants was examined. An effective scale inhibitor must arrest the formation of scale for a residence time (≈15 min) of feed water in the RO chamber. R₂NH⁺(CH₂)₃CO₂⁻ ( IV )-alt-MA copolymer XI at a concentration of 5 ppm imparted 99% scale inhibition for 360 min, while at 2.5 and 1 ppm concentrations, the CaSO₄ scale inhibitions were found to be 99% and ≈ 100% during 120 and 20 min, respectively, at 40°C. Homopolymers XV and XVI , at a 20-ppm concentration, demonstrated ≈ 95% efficiency in inhibiting mild steel corrosion in 1 M HCl. In some important oilfield applications, requirement of simultaneous scale and corrosion inhibition make these polymers potential candidates for desalination and oilfield applications.     

Effects of rare-earth oxide doping on the thermal radiation performance of HfO2 coating

In this study, the REO-HfO₂ (REO = Tb₄O₇, Gd₂O₃ and Sm₂O₃) coatings and pure HfO₂ coatings were prepared by atmospheric plasma spraying. The chemical compositions, morphologies, infrared radiation performance and thermal resistances of the coatings were systematically investigated. The experimental results showed that the Tb₄O₇-HfO₂, Gd₂O₃-HfO₂, Sm₂O₃-HfO₂ and pure HfO₂ coatings had infrared emissivity values of 0.863, 0.852, 0.854 and 0.621, respectively, at room temperature. Based on the phase analysis, the higher infrared emissivity of the REO-HfO₂ coatings could be attributed to the fact that the newly formed RE₂Hf₂O₇ (RE = Tb, Gd and Sm) phase, which had a defective fluorite-type structure, and the RE³⁺ ions enhanced the lattice absorption and electron absorption. Additionally, the Tb₄O₇-HfO₂ coating exhibited a relatively higher infrared emissivity than those of the Gd₂O₃-HfO₂ and Sm₂O₃-HfO₂ coating over the wavelength range of 1–15 μm, which was due to the relatively higher vibrational frequency of the TbO bond in RE₂Hf₂O₇ (RE = Tb, Gd and Sm) and the transformation of Tb³⁺ into Tb⁴⁺ in the Tb₄O₇-HfO₂ system. In addition, the REO-HfO₂ ceramic coatings exhibited excellent thermal resistance, which could withstand high-temperature treatment at 1600 °C for at least 50 h without undergoing a phase change and exfoliation, and the infrared emissivity at different temperatures hardly changed after thermal treatment.