O′-Sialon-ZrO_2复合材料抗氧化性研究

用气／固相反应动力学、分形理论，探讨了Ｏ′－Ｓｉａｌｏｎ－ＺｒＯ２复合材料的抗氧化动力学。Ｏ′－Ｓｉａｌｏｎ－ＺｒＯ２复合材料抗氧化性能较好。氧化过程分为三个阶段，即前期为界面化学反应控速；中期为化学反应与扩散混合控速；后期为扩散控速。     

Thermodynamics of the Na2O−P2O5 system

The activity of Na₂O in the melts of the Na₂O?P₂O₅ system has been determined using a high temperature electrochemical cell with a Na₂O?WO₃ melt at the reference electrode and fused silica as the solid electrolyte as shown below. $$_{Na_2 O - WO_3 melt}^{Pt(s),O_2 (g)} \left| {_{fused silica}^{ Na^ + } } \right|_{Na_2 O - P_2 O_5 melt}^{O_2 (g), Pt(s)} $$ The thermodynamics of the Na₂O?P₂O₅ binary system in the composition range of 50 to 75 mole pet Na₂O has been studied. The activities of Na₂O and P₂O₅ in the melt have been carefully analyzed. The free energy of four sodium phosphates has been evaluated with the help of the phase diagram of this system. Based on this study, a solid-state phase transformation for the 3Na₂O·P₂O₅ compound has been suggested at a temperature below 1217 K. The entropy of the transformation is near zero. The enthalpy of transformation is estimated to be 101.51 kJ/mole 3Na₂O·P₂O₅.     

Effects of Y2O3 on Thermal Shock of Al2O3／TiCN Composites

Advancedstructuralceramics ,suchasoxides ,nitridesandcarbides ,havebecomepreferredrefracto rymaterialsforaviation ,spaceflight ,energyandmet allurgybecauseoftheirchemicalstability ,creepresis tanceandhightemperaturestrength .Buttheyareaf fectedgreatlybyte…     

Effect of Fe2O3 Loading Amount on Catalytic Properties of Monolithic Fe2O3/Ce0.67Zr0.33O2 -Al2O3 Catalyst for Methane Combustion

Ce0.67Zr0.33O2-Al2O3 solid solution was prepared by the co-precipitation method. Fe2O3-based catalysts supported on the solid solution were obtained by the impregnation method. The article revealed that the optimal loading amount of Fe2O3 on Ce0.67Zr0.33 O2-Al2O3 in our experimental condition for catalytic combustion of methane was 8% （ mass fraction）. The prepared catalysts were characterized by BET, TPR, XRD analyses, and their catalytic activity was investigated after being calcined at 873 K and after being aged in water gas at 1273 K. When the loading amount of Fe203 was 8% （ mass fraction）, the catalyst held the highest activity, and the best temperature speciality and thermal stability. The complete-conversion temperature of methane for fresh and aged sample was 788 and 838 K, respectively. The range between the light-off temperature and the complete-conversion temperature was only 15 K. The characterization results of XRD indicated that Fe2O3 was well dispersed on the Ce0.67Zr0.33O2-Al2O3 matrix. The results of BET and TPR were in good harmony with the catalytic activity results.     

Effects of La2O3/Li2O/TiO2- Coating on Electrochemical Performance of LiCoO2 Cathode

Conventional cathode material （LiCoO2） was modified by coating with a thin layer of La2O3/Li2O/TiO2 for improving its performance for lithium ion battery. The morphology and structure of the modified cathode material was characterized by SEM, XRD, and Auger electron spectroscopy. The performance of the cells with the modified cathode material was examined, including the cycling stability, the diffusion coefficient under different voltages, and the C-rate discharge. The results showed that the cell composed of the coated cathode material discharged at a large current density, and possesses a stable cycle performance in the range from 3.0 to 4.4 V. It was explained that the rate of Li ion diffusion increased in the cell while using La2O3/Li2O/TiO2-coated LiCoO2 as the cathode and the coating layer may act as a faster ion conductor （La2O3/Li2O/TiO2）.     

Effect of Strong Basic Oxide (Li_2O, Na_2O, K_2O and BaO) on Property of CaO-Based Flux

Intraditionalconvertersteelmakingprocess ,therephosphorizationofliquidsteelcausedbyladleslagstakesplacebecausetheoxidabilityandbasicityofslagsaredecreasedwhenthedeoxidizingandal loyingoperationsofsteelarecarriedoutinladle .Atpresent ,mainmeasuresofcontrollingrephosphori zationincludeincreasingoriginalbasicityandoxid abilityofslags ,whichcanincreasethemeltingpoint ,viscidityofslagsandtheamountofworkfordeoxidizationandalloyforalloying .Atthesametime ,theslagswithhighoxidabilityincreasetheox ygen…     

Effects of MgO on Properties of La2O3-TiO2 Ceramics

The influence of MgO on sintering and dielectric properties of La2O3-TiO2 ceramics was investigated, and the mechanism also discussed. The results show that La2O3-TiO2 ceramics with MgO can be sintered between 1200 and 1280 ℃. With the increasing of the MgO, the dielectric constant of the material decreases, but the temperature coefficient of dielectric constant increases. Between 1 and 40 MHz,     

Solidus surface of the equilibrium diagram of the HfO2—Y2O3—La2O3 system

The phase equilibria on the solidus surface of the phase diagram of the HfO ₂−Y₂O₃−La₂O₃ system have been investigated using DTA in helium up to 2500°C, TA with solar energy in air up to 3000°C, X-ray phase analysis, petrography, and electron microscopy. Five solid solution fields based on hexagonal (H) and cubic (C) crystal modifications of Y₂O₃, cubic modifications of HfO₂ with fluorite structure (F), high-temperature cubic modifications of La₂O₃ (X), and crystallization field of the ordered phase La₂Hf₂O₇ with the pyrochlorine (Py) type structure have been found on the solidus surface. The ternary system has three quaternary novariant equilibria of the eutectic (1) and peritectic (2) type. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(407), pp. 56–65, May–June, 1999.     

Synthesis of ZrO2-HfO2-Y2O3-Sc2O3 Nano-Particles by Sol-Gel Technique in Aqueous Solution of Alcohol

Zirconium dioxide is a significant material withgood physicochemical characteristics . It is used inmanyfields such as energysources ,material and envi-ronment . Cubic phase zirconium dioxide doped withyttria (YSZ) is alreadyin wide use in solid oxygenfu-…     

Oxidation of Al2O3-30%TiCN-0.2%Y2O3 Composite

Thecuttingtoolmaterialshavegoodoxidationre sistance ,buttheyareoxidizedathightemperature(about 10 0 0℃ )duringoperation .Themechanicalpropertyofthecuttingtoolmaterialswillbechange d[1,2 ] .Therefore ,researchonoxidationbehaviorofcuttingtoolsmaterialsathi…     

Low-temperature synthesis of α-Al2O3

The paper considers the production of nanocrystalline α-Al₂O₃ powder at a temperature below 900 °C. It is shown that α-Al₂O₃ forms after high-temperature treatment of aluminum nitrate mixed with a mineralizer at 650 °C (holding time of 6 h). The primary particles of α-Al₂O₃ are 25 to 30 nm in size and the specific surface area is 15.2 m²/g. The powder is used to produce self-reinforced composites in the ZrO₂-Y₂O₃-CeO₂-Al₂O₃ system.     

Effect of La2O3-Dopant on Microstructure and Microwave Dielectric Properties of CaO-MgO-Nb2O5-TiO2 System Ceramics

With the development of microwave integratedsystem for wireless communication, requirements ofthe microwave device are combined with high dielec tric constants (εr), low dielectric losses (Q = 1/tanδ) and near zero temperature coefficient for stabili ty and frequency selectivity[1,2]. But it is hard to findmaterials that satisfy all above mentioned requiredcharacteristics. In general, a ceramic with a high di electric constant has a larger positive temperature coef fi…     

Kinetics of Na2O evaporation from CaO–Al2O3–SiO2–MgO–TiO2–Na2O slags

The present work is carried out to study the evaporation of Na₂O from CaO–Al₂O₃–SiO₂–TiO₂–MgO–Na₂O slags with high basicity and high alumina in the temperature range of 1500–1560°C. The ratio of evaporation was determined by monitoring the Na₂O content change of the slag melt under isothermal reduction conditions. The results show that the evaporation ratio increases with increasing the temperature. Higher basicity and increasing concentrations of Na₂O, Al₂O₃ are also found to increase the evaporation ratio of Na₂O, while MgO addition only slightly enhances the evaporation ratio. With TiO₂ content increasing, the evaporation ratio first increases and then decreases. The evaporation rate of Na₂O appears to be controlled by chemical reaction at the slag/gas interface in the beginning, followed by a mixed reaction-mass transfer regime, and finally a liquid-phase mass transport step. The apparent activation energy is 134.74?kJ?mol^?1 for the chemical reaction regime and 268.53?kJ?mol^?1 for the liquid-phase mass diffusion step.     

Mechanical Behaviors of ZrO2-Al2O3 Ceramic Composites with Y2O3 as Stabilizer

Forlongthebrittlenessofceramicmaterialshasstoodinthewayofindustrialapplicationanddevelop ment.However ,inrecentyears ,suchprogressasthephasetransformationtougheningofzirconia ,thedis persionofparticletougheningandthefiberorwhiskertougheninghavewellimprove…     

Enrichment Mechanism of Phosphate in CaO-SiO2-FeO-Fe2O3-P2O5 Steelmaking Slags

The phosphate-enrichment behavior has experimentally been investigated in CaO-SiO₂-FeO-Fe₂O₃-P₂O₅ steelmaking slags. The reaction ability of structural units in the slags has been represented the mass action concentration \( N_{i} \) from the developed ion and molecule coexistence theory (IMCT)- \( N_{i} \) model based on the IMCT. The defined enrichment possibility \( N_{{{\text{c}}i{\text{ {-}c}}j}} \) and enrichment degree \( R_{{{\text{c}}i{\text{{-}c}}j}} \) of solid solutions containing P₂O₅ from the developed IMCT- \( N_{i} \) model have been verified from the experimental results. The effects of binary basicity, the mass percentage ratio \( {{ ( {\text{pct Fe}}_{t} {\text{O)}}} \mathord{\left/ {\vphantom {{ ( {\text{pct Fe}}_{t} {\text{O)}}} { ( {\text{pct CaO)}}}}} \right. \kern-0pt} { ( {\text{pct CaO)}}}} \) , and mass percentage of P₂O₅ in the initial slags on phosphate-enrichment behavior in the slags has also been discussed. The results show that the P₂O₅ component can easily be bonded by CaO to form tricalcium phosphate 3 CaO·P₂O₅, and the formed 3CaO·P₂O₅ can react with the produced dicalcium silicate 2CaO·SiO₂ to generate solid-solution 2CaO·SiO₂-3CaO·P₂O₅ under fixed cooling conditions. The maximum value of the defined enrichment degree \( R_{{{\text{C}}_{ 2} {\text{S{-}}} {\text{C}}_{ 3} {\text{P}}}} \) of solid-solution 2CaO·SiO₂-3CaO·P₂O₅ is obtained as 0.844 under conditions of binary basicity as 2.5 and the mass percentage ratio \( {{ ( {\text{pct Fe}}_{t} {\text{O)}}} \mathord{\left/ {\vphantom {{ ( {\text{pct Fe}}_{t} {\text{O)}}} { ( {\text{pct CaO)}}}}} \right. \kern-0pt} { ( {\text{pct CaO)}}}} \) as 0.955 at fixed cooling conditions.     

Long-Lasting Properties of Rare Earth-Doped Y2O2S Phosphors

The aim of this presentation is to report a new result of afterglow materials. The Y2O2S:Ln^3 (Ln = Sm, Tm)phosphors show bright reddish orange and orange-yellow colors when excited by UV or visible light. The main spectroscopic characterizations of Sm^3 and Tm^3 in yttrium oxysulfide and their long-lasting phosphorescence were measured and discussed in this presentation. Their long-lasting phosphorescence can be seen by the naked eyes clearly for about one hour in the dark room after the irradiation light sources were removed. XRD and photoluminescence (PL) spectra as well as the luminance decay were used to characterize these long-lasting phosphorescence phosphors. The results of XRD indicate that the products synthesized through the flux fusion method under 1050℃ for 6 h have a good crystallization without any detectable amount of impurity phase. Both the PL spectra and luminance decay results reveal that these phosphors have efficient luminescent and good long-lasting properties. We believe that the experimental data gathered in our present work will be useful in finding some new long-lasting phosphors with different colors.     

Thermodynamic properties of the MgAl2O4−MnAl2O4 spinel solid solution

The thermodynamic properties of the MgAl₂O₄−MnAl₂O₄ system are required for calculating the deoxidation equilibrium of molten iron and nickel containing magnesium, manganese, and aluminum. The thermodynamic properties of the MgAl₂O₄−MnAl₂O₄ spinel solid solution have been determined by equilibrating it with silver at known oxygen partial pressures. The free energy of formation of MnAl₂O₄ from its oxide components at 1673 and 1823 K was found to be −30.6 and −28.2 kJ/mol, respectively. It was observed that the MgAl₂O₄−MnAl₂O₄ spinel solid solution exhibited small negative deviations from ideal behavior at 1673 and 1823 K. The excess partial free energies of MgAl₂O₄, , and MnAl₂O₄, , at 1673 and 1823 K are expressed asG

Transformation of α-Fe2O3 to Fe3O4 Realized by Mechanochemical Reaction of α-Fe2O3 and SrCO3

A transformation from ??-Fe₂O₃ with rhombohedral structure to Fe₃O₄ with spinel face-centered cubic (fcc) structure was realized by ball milling the mixture of SrCO₃ and ??-Fe₂O₃ powders with molar ratio of 1:3 under ambient air in the current work, but it was not observed by ball milling the ??-Fe₂O₃ powders. The transformation is due to a mechanochemical reaction between SrCO₃ and ??-Fe₂O₃ in the milling process, and the ??-Fe₂O₃ catalyzes the decomposition of SrCO₃, while the decomposition promotes the transformation of ??-Fe₂O₃ to Fe₃O₄. X-ray diffraction, X-ray photoelectron spectrometry, and magnetic measurements indicate that the transformation finishes completely upon milling of 120?hours, and the mixture milled for 120?hours consists of Fe₃O₄ and a Sr element. However, Sr does not incorporate into the Fe₃O₄ but exists in grain boundary of the Fe₃O₄ in a form of a Sr-O bond. It is found that the product obtained by ball milling the mixture is different from that prepared by sintering the mixture at atmospheric pressure, which product is SrFeO_2.97 with cubic structure. The mechanism of the transformation and origin of difference in products obtained in the ball milling and sintering processes are also discussed in the current work.     

Phase diagram assessment of CaO–Al2O3–La2O3 system

Considering the significance of CaO–Al₂O₃–RE₂O₃ (RE?=?rare earth) phase diagrams, the Redlich–Kister expression was employed to evaluate the binary phase diagrams of CaO–Al₂O₃, La₂O₃–Al₂O₃ and CaO–La₂O₃ systems in the present work. Also, the activities of CaO and Al₂O₃ in the CaO–Al₂O₃ binary system were calculated. The phase diagram of the CaO–Al₂O₃–La₂O₃ ternary system was first assessed by Kohler extrapolation method. The accuracy of calculated phase diagrams was validated by comparing with existing experimental points and the calculation results from the literature. The obtained diagrams will lay a foundation for Al-killed steelmaking process, metallurgical flux and other fields’ industrial application.