Crystallization kinetics of La2O3–Al2O3–B2O3 glass–ceramic composites

One glass formulation (L2 glass) with the composition of La₂O₃, Al₂O₃ and B₂O₃ in a molar ratio of 10:10:80 was selected to cofire with Al₂O₃ filler. The composites underwent a two-stage crystalline evolution in the temperature range of 800 to 975 °C. The crystallization kinetics of LaBO₃ grains and the transformation to LaAl₂B₃O₉ phase were investigated by DTA, XRD, SEM/EDS, and TEM. The results showed that the Al₂O₃ filler plays an important role as the heterogeneous sites of LaBO₃ nuclei, and as reactant for the formation of flaky LaAl₂B₃O₉ crystals. The apparent activation energy of LaBO₃-phase formation in L2 glass was 534 kJ/mol and reduced to 466 kJ/mol by the addition of Al₂O₃. The detail transformation reactions, kinetics, and the crystalline orientation relationship between those phases are reported.     

微波加热法制备Al2O3-SiO2-ZrO2-TiO2复合陶瓷膜

采用微波加热的方法,以硝酸铝、正硅酸乙酯、氧氯化锆、钛酸丁酯为原料,制备复合溶胶;并在氧化铝基陶瓷管上成功制备了Al2O3-SiO2-ZrO2-TiO2复合膜.应用扫描电子显微镜（SEM）、X射线衍射（XRD）、差热分析（DTA）等手段对复合膜的物相组成、表面形貌和孔径进行了分析.结果表明：采用微波加热法更易获得粒径小、分布集中的复合溶胶;微波干燥可以大大缩短干燥时间;制备的复合陶瓷膜完整,内部无明显宏观缺陷.     

Phase diagram of the Al2O3–ZrO2–La2O3 system

The phase diagram of the Al₂O₃–ZrO₂–La₂O₃ system was constructed in the temperature range 1250–2800 °C. The liquidus surface of the phase diagram reflects the preferentially eutectic interaction in the system. Three new ternary and two new binary eutectics were found. The minimum melting temperature is 1665 °C and it corresponds to the ternary eutectic LaAlO₃ + T-ZrO₂ +  La₂O₃·11Al₂O₃. The solidus surface projection and the schematic of the alloy crystallization path confirm the preferentially congruent character of phase interaction in the ternary system. The polythermal sections present the complete phase diagram of the Al₂O₃–ZrO₂–La₂O₃ system. No ternary compounds or regions of remarkable solid solution were found in the components or binaries in this ternary system. The latter fact is the theoretical basis for creating new composite ceramics with favorable properties in the Al₂O₃–ZrO₂–La₂O₃ system.     

Modified Al2O3-based ceramic

Translated from Steklo i Keramika, No. 1, pp. 27–29, January, 1990.     

Preparation and characterisation of mixed matrix Al2O3- and TiO2-based ceramic membranes prepared using polymeric synthesis route

Al₂O₃- and TiO₂-based ceramic membranes prepared using polymeric synthesis route were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and gas permeability tests. The influence of the final calcination temperature and the systematic investigation of the properties of the membranes are provided. The calcination temperature affected morphological, structural and chemical properties, as well as the gas permeability of the ceramic membranes. XRD analysis revealed rhombohedral and tetragonal structures of Al₂O₃ and TiO₂-based ceramic, respectively, prepared at calcination temperatures of 1100 and 1200 °C. The TiO₂-based ceramic matrix calcined at temperatures of 1100 and 1200 °C exhibited a well-defined crystalline microstructure with the grains increasing in size as a function of temperature. FTIR analysis revealed that phosphorus additives in orthoclase clay tend to form phosphonate groups during the calcination process. The decomposition of organic source was not fulfilled as tested at calcination temperatures of 1000, 1100 and 1200 °C.     

Air plasma-sprayed Y2O3 coatings for Al2O3/Al2O3 ceramic matrix composites

Al₂O₃/Al₂O₃ ceramic matrix composites (CMC) are candidate materials for hot-gas leading components of gas turbines. Since Al₂O₃/Al₂O₃ CMC are prone to hot-corrosion in combustion environments, the development of environmental barrier coatings (EBC) is mandatory. Owing to its favorable chemical stability and thermal properties, Y₂O₃ is considered a candidate EBC material for Al₂O₃/Al₂O₃ CMC. Up to 1 mm thick Y₂O₃ coatings were deposited by means of air plasma spraying (APS) on Al₂O₃/Al₂O₃ CMC with a reaction-bonded Al₂O₃ bond-coat (RBAO). APS Y₂O₃ coatings exhibit a good adherence in the as-deposited state as well as upon isothermal annealing up to 1400 °C. Moreover, furnace cyclic testing performed at 1200 °C revealed an excellent durability. This is explained by the formation of a continuous, approximately 1 μm thick reaction zone at the APS Y₂O₃/RBAO interface. The reaction zone between Y₂O₃ and Al₂O₃ comprises three layers of thermodynamically stable yttrium-aluminates exhibiting strong bonding, respectively.     

TiO2与SiO2掺杂对Al2O3相转变的研究

通过球磨混合法,制备TiO2、SiO2和TiO2+SiO2掺杂的Al2 O3粉体,经不同温度煅烧后进行X射线衍射(XRD)测试,比较研究这三种掺杂对Al2 O3粉体相转变温度的影响.研究结果表明,TiO2、SiO2掺杂对γ-Al2 O3向α-Al2 O3的相转变均有促进作用.在掺杂质量分数为0.5％的情况下,二者可分别...     

A strong ceramic in the Al2O3-ZrO2-Y2O3 system

Conclusions A highly dense ceramic based on the eutectic composition of the Al₂O₃-ZrO₂ system was obtained using 3 mole % Y₂O₃ addition. The ceramic has a fine-grained structure and high hardness and strength.Translated from Ogneupory, No. 2, pp. 8–10, February, 1987.     

液相法制备棒状Al2O3及Al2O3-ZrO2陶瓷复合粉体

采用二乙三胺五乙酸（DTPA）为配合剂,以简易的液相法合成出微纳米纤维状Al和Al-Zr前体,煅烧处理制备了棒状α-Al₂O₃和Al₂O₃-ZrO₂复合陶瓷粉体。同时研究了DPTA∶Al³⁺质量比、反应温度与时间对陶瓷粉体形态的影响。利用X射线衍射（XRD）、热分析（TG/DSC）以及扫描电子显微镜（SEM）对粉体进行了表征。结果表明：较高的DTPA∶Al³⁺质量比以及较长的反应时间有利于制备高长径比的纤维棒状Al和Al-Zr配合物前体。合成纳米纤维状α-Al₂O₃和Al₂O₃-ZrO₂前体的最优条件是反应温度60℃,反应时间5.5h,DTPA∶Al³⁺比例为1.2∶1。相应地,该前体煅烧后可以制备出棒状α-Al₂O₃和Al₂O₃-ZrO₂复合陶瓷粉体。     

Failure mechanism of the Y2O3 doped BaZrO3/Al2O3 composite ceramic mould during directional solidification of TiAl-Based alloys

Directional solidification of Ti–46Al–8Nb (at.%) intermetallic in the Y₂O₃ doped BaZrO₃/Al₂O₃ composite ceramic mould was carried out using Bridgman apparatus. To increase the success rate of Ti–46Al–8Nb single crystals preparation and improve the quality of the ingots, the failure mechanism of the mould in directional solidification experiments was evaluated. Nucleation and propagation of cracks in the moulds were investigated by tracing each key process of the experiment, the effect of pores in the mould on the target alloy was revealed by studying the mould/metal interface. The results show that the macrocracks in the facecoat of the mould would lead to the leakage of the alloy melt. Furthermore, the alloy melt would infiltrate into the mould through large-size pores, which would increase the oxygen content of the target alloy, and also form inclusions containing O, Zr, Si and Y elements in the alloy ingot.     

Cathodic plasma electrolytic deposition of ZrO2/YSZ doped Al2O3 ceramic coating on TiAl alloy

ZrO₂/yttria-stabilized zirconia (YSZ) doping Al₂O₃ ceramic coating was fabricated via cathodic plasma electrolytic deposition (CPED) technique. The microstructures and the chemical and phase compositions of the doped coating were characterized, the mechanical properties and the high temperature oxidation resistance were evaluated, and the doping mechanism was also discussed in detail. The results showed that, doped Zr⁴⁺ and Y³⁺ ions could effectively reduce the working voltage during CPED process and increase the content of metastable γ-Al₂O₃ in the coating. Accordingly, the doped ZrO₂/YSZ significantly refined the grain size of Al₂O₃, as well as remarkably improved the high temperature oxidation resistance, the micro-structural compactness and hardness of the Al₂O₃ CPED coating. This study displayed here constructed an efficiently method for the fabrication of multifunctional coating on the surface of TiAl alloy.     

La3+掺杂TiO2光催化性能研究

采用溶胶-凝胶法制备了La^3＋／TiO2光催化剂,研究了该催化剂对亚甲基蓝的光催化降解效果。结果表明,La^3＋掺杂量（摩尔分数）2．8％、催化剂用量1．2g／L、体系pH值为11时,12mg／L亚甲基蓝溶液经2h光催化降解,其降解率可达99．1％。与纯TiO2相比,La^3＋/TiO2光催化剂显示出良好的光催化活性。     

Al2O3纤维增强钛酸铝陶瓷

介绍了一种Al2O3纤维增强钛酸铝陶恣复合材料，在一定范围内随着Al2O3纤维含量的增加，复合材料的抗弯强度和断裂韧性均提高，当Al2O3纤维含量达到4.5%(体积分数）时抗弯强度和断裂韧性达到最大值，使钛酸铝基体材料分别提高近120％和75％。     

Phases in La2O3 and NiO doped (Zr,Sn)TiO4 microwave dielectric ceramics

Dielectric ceramics with composition in the ZrO₂–SnO₂–TiO₂ system containing La₂O₃ and NiO as sintering aids were prepared and investigated by XRD, XPS, SEM, EDS, and microwave dielectric measurements. Ceramics prepared with defloculed slurry using a Dyno-Mill^®, and sintered at 1370°C exhibit very good microwave dielectric characteristics: ε=37 and QF up to 62 000 at 4 GHz. We have observed a matrix phase with at least two or three different secondary phases in function of the employed grinding media (balls of zircon or magnesium stabilised zirconia). So, we have synthesised and characterised these phases.     

Phase formation in Al2O3-C refractories with Al addition

Depending on the recipe and the firing conditions, several non-oxides can be formed in Al₂O₃-C refractories. In this paper, the effect of the purity of the recipe components on the phase formation in Al₂O₃-C refractories with Al addition was investigated. Two test series were sintered from 800 °C to 1600 °C under air embedded in coke breeze. One test series was with brown fused alumina, and the other was with tabular alumina. At temperatures of up to 1200 °C the phase formation was the same for both recipes. For temperatures greater than 1400 °C, the impurities of brown fused alumina enhanced the formation of a polytype, while Al₄O₄C and Al₂₈O₂₁C₆N₆ were formed in the other series. The findings explain the occurrence of several non-oxides in disequilibrium at the chosen temperatures. The occurrence of Al₄C₃ was of particular interest due to its low hydration resistance. It was formed at 1200 °C.     

Phase development of phosphate-bonded Al2O3-MgAl2O4 high-temperature ceramics: XRD and solid-state NMR investigations

This article describes investigations on the phase development (T ≤ 1500℃) of phosphate-bonded Al₂O₃-MgAl₂O₄ high-temperature ceramics by a combination of solid-state MAS NMR and X-ray diffraction analyses. The ceramic body was bonded with inorganic hydrogen orthophosphates (Al, Mg, Ca, Zr) with a total binder content of 3 wt.% P₂O₅. The binding mechanisms of these phosphate-bonded ceramics could be extensively deduced by analyses of phase developments during hardening, strength development, and high-temperature phase formation at T ≤ 1500℃: The formation of a network of aluminum phosphate compounds by acid and condensation reactions of the phosphate with the ceramic body is proven to be the active binding process. The binding process is initiated by the formation of active phosphoric acid phosphate phases, which in principle prerequisites water solubility of the binder. Thermal treatment, especially at T ≤ 600℃, promotes the degree of P-cross-linking of the phosphate structures. In addition to these phosphate-ceramic reactions, it was also possible to identify parallel pure phosphate–phosphate conversions of the initial phosphates (via condensation and polymerization) without reactions with ceramic components. The contribution of these structures to the binding effect can be estimated to be minor. Only at temperatures of T ≥ 600℃, these Ca, Mg and Zr phosphates begin to react with the ceramic material to form aluminum phosphates. The phosphate bond has a permanent effect until the formation of the ceramic bond (T > 1000℃). High-temperature phases are usually crystalline PO₄-sintered structures which are formed by reaction with MgAl₂O₄.     

Solubility and microstructural development of TiO2-containing 3Al2O3·2SiO2 and 2Al2O3·SiO2 mullites obtained from single-phase gels

The interdependence of the titanium oxide amount and the anisotropic growth of mullites prepared from single-phase gels were investigated. Gels with stoichiometries 3(Al_2−xTi_xO₃)·2(SiO₂) and 2(Al_2−xTi_xO₃)·(SiO₂), with 0 ≤ x ≤ 0.15 were prepared by the semialkoxide method. Gels and specimens heated at temperatures between 1200 and 1600 °C were characterized by using infrared spectroscopy (IR), X-ray diffraction (XRD) and transmission and field emission scanning electron microscopies (TEM and FESEM). Al₂TiO₅ as minor impurity was detected in both series of mullites for gel precursor compositions x = 0.10 and x = 0.15, obtained at temperatures between 1200 and 1600 °C. Variations of lattice parameters of mullite, processed at temperatures from the range between 1400 and 1600 °C, with the starting nominal amount of titanium oxide indicated that the solubility limit of titanium oxide was in ranges 3.8–4.1 and 4.1–4.4 wt% TiO₂ for 3:2 and 2:1 mullites series, respectively. The anisotropic growth of titanium-doped mullite crystalline grains was significant only when the nominal amount of titanium oxide exceeded the limit of solubility into the mullite structure (for both mullite series). Stronger anisotropy occurred for the 3:2 series specimens, i.e. for the SiO₂-richer mullites. In both series of mullites, the anisotropic grain growth was observed for the process temperatures higher than 1400 °C; the crystalline grains of mullites processed at lower temperatures were equiaxials and of almost the same size.     

Nanoindentation of Al2O3/Al2TiO5 composites: Small-scale mechanical properties of Al2TiO5 as reinforcement phase

The mechanical properties of alumina/aluminum titanate composites (Al₂O₃/Al₂TiO₅) were evaluated and analyzed by nanoindentation. Indentations with different penetration depths were performed, and residual imprints on specimens were located and observed by combining complementary characterization techniques. The mechanical response of composites was found to be determined by grain size of alumina and aluminum titanate, as evaluated from indentations performed at 1500 nm of penetration depth. On the other hand, small indents in individual grains permitted to assess the hardness as well as the elastic modulus of non-cracked particles of Al₂TiO₅ through implementation of different analytical indentation models. The attained values for the local mechanical properties were validated through critical comparison of them with those predicted by the rule of mixtures. Results showed no evidence of microcracking on grains of the reinforcing phase for all the tested composites, before and after low penetration depth indentations. Elastic modulus of Al₂TiO₅ was found to be higher than the values reported on bulk aluminum titanate, presumably because of the absence of microcracking for small grain sizes. The bulk composite mechanical response is finally discussed on the basis of contributions from those of the individual phases.     

等离子喷涂Al2O3陶瓷涂层的研究

研究等离子喷涂Al2O3陶瓷涂层的抗热震性能,分析并计算等离子喷涂Al2O3陶瓷涂层和AlAl2O3涂层中的残余应力,得出了两种涂层的应力分布,测试了TiO2含量对Al2O3陶瓷涂层性能的影响,检验了影响涂层质量的工艺参数.     

Blood compatibility of La2O3 doped diamond-like carbon films

La₂O₃ doped diamond-like carbon films (DLC) with different concentration were deposited by using Radio-Frequency magnetron sputtering. The microstructure and surface properties of DLC films were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle test. The blood compatibility of the samples was evaluated by tests of platelet adhesion. Results show the sp²-bonded C content increases with increasing of La₂O₃ concentration doped. A remarkable decrease of platelet adhered on the surface of the La₂O₃ doped DLC films was observed comparing to the Chrono flex used in clinical application, suggesting that La₂O₃ doped DLC is able to enhance its blood compatibility. The mechanism of hemocompatibility of doped films was discussed. Our results demonstrate that La₂O₃ doped DLC films are potentially useful biomaterials with good blood compatibility.