Structure evolution,thermal properties and sintering resistance of promising thermal barrier coating material La2(Zr0.75Ce0.25)2O7

Rare-earth doped zirconates are promising candidate materials for high-performance thermal barrier coatings (TBCs). The phase and microstructure stability is an important issue for the materials that must be clarified, which is related to the long-term stable work of TBCs at high temperatures. In this work, La₂(Zr_0.75Ce_0.25)₂O₇ (LCZ) ceramic coatings prepared by atmospheric plasma spraying present a metastable fluorite phase, which can transform into stable pyrochlore under high-temperature annealing. The detailed structure evolution of the ceramic coatings is characterized systematically by SEM, XRD and Raman. The associated thermal properties of LCZ ceramics were also reported. Results show that LCZ ceramic has an ultralow thermal conductivity (0.65 W/m·K, 1200 °C), which is only 1/3 of that of yttria-stabilized zirconia (YSZ). The thermal expansion coefficients of LCZ ceramic increase from 9.68 × 10^-6 K^-1 to 10.7 × 10^-6 K^-1 (300 - 1500 °C), which are relatively larger than those of La₂Zr₂O₇. Besides, Long-term sintering demonstrates that LCZ ceramic coating has preferable sintering resistance at 1500 °C, which is desirable for TBC applications.     

提高测井仪器耐高温性能的方法研究

为实现大深度井、高温井的地层参数测量,提高测井仪器的耐高温性能,研究了隔热、吸热技术在提高石油测井仪器的耐高温性能方面的作用.在实验室条件下通过模拟石油测井正常的工作时序,对采用热障涂层和相变储能设计的自然伽玛能谱的探测器管腔内的温升状况进行了实验测试.结果表明,采用隔热、吸热技术能够提高石油测井仪器的耐高温性能,可以实现井下仪器在200℃高温环境下按照正常测井时序工作3～4 h,且仪器探测器管腔内的温度控制在150℃内.伽玛能谱仪器的实验室高温循环测试以及高温实井试验测试表明,器件高温失效概率有显著的降低.     

激光制备陶瓷热障涂层的研究和发展

论述了激光制备陶瓷热障涂层的研究和发展状况 .激光制备陶瓷热障涂层包括激光重熔和激光熔覆两种方法 .激光重熔等离子喷涂热障涂层可获得等离子喷涂涂层所不具备的外延生长致密的柱状晶组织 ,提高涂层应变容限及热震性能 .激光熔覆可获得自动分层的梯度热障涂层成分及柱状晶组织 ,改善涂层的高温氧化及热震性能 .通过激光工艺参数的优化及涂层体系成分及性能的合理设计 ,可获得优于等离子喷涂 ,接近电子束物理气相沉积的热障涂层性能     

Synthesis of non-porous and nanocrystalline lanthana-doped zirconia layers by MOCVD method at low temperatures and pressure

Amorphous and nanocrystalline lathana-doped zirconia layers were synthesized by the MOCVD method using La(tmhd)₃ and Zr(tmhd)₄ as reactants on planar and tubular quartz glass substrates. The synthesis temperature was in the range of 500–700 °C. The gas pressure in the CVD reactor was modified between 3 × 10³ and 6 × 10³ Pa. Argon and air were used as carrier gases. Air was also necessary for oxidation of carbon, which is a solid by-product of reactant pyrolysis. Other synthesis parameters were selected in order to obtain a value of the extended criterion Gr_x/Re_x² below 0.01. Then, laminar gas flow in the CVD reactor will be maintained. The surface, as well as the cross-section of deposited layers were observed using a scanning electron microscope (SEM). Their chemical composition was investigated by means of EDS analysis. XRD investigations on obtained layers were also performed. There was correlation between the chemical composition of reactants and obtained layers when the synthesis process was controlled by reactant diffusion to the substrate. The phenomenon of La³⁺ ion segregation in obtained layers was also observed. The layers exhibited good adhesion to the substrate.     

QT500表面等离子喷涂8YSZ热障涂层TGO的残余应力状态及数值分析

分别采用超音速火焰喷涂(HOVF)和等离子喷涂(APS)在QT500球墨铸铁基体上制备Co Ni Cr Al Y粘结层(BC)和8YSZ陶瓷隔热层(TC),研究了试样在1050℃高温环境中经过2.5、8、15、50、100 h恒温氧化后体系的应力情况。利用扫描电子显微镜(SEM)对热生长氧化物(TGO)的微观形貌进行观察与分析,并用拉曼荧光光谱仪(RFS)分析了其应力的分布及变化规律,并通过力学模型进行了残余应力的数值计算。结果表明:由陶瓷层与粘结层之间的热失配而导致TGO中产生残余压应力,其最大值范围为1.9557~1.9603 GPa;残余压应力在高温氧化初始阶段逐渐减小,至15 h达到最小值,随之逐渐增大后趋于稳定;在恒温阶段,θ-Al2O3转变为α-Al2O3所引起的体积收缩是TGO中残余应力减小并趋于稳定的直接原因。     

Oxide growth and damage evolution in thermal barrier coatings

Cracking in thermal barrier coatings (TBC) is triggered by the development of a thermally-grown oxide (TGO) layer that develops during thermal cycling from the oxidation of aluminum present in the bond coat (BC). In the present communication a numerical model is presented that describes the interactive development of the TGO morphology and the fracture processes in TBC systems in a mesh-independent way. The evolution of the TGO–BC mixture zone is described by an oxygen diffusion–reaction model. The partition-of-unity method is employed for the simulation of discrete cracking, where cracks can nucleate and propagate across finite elements at arbitrary locations and orientations. The validity of the model is demonstrated through the analysis of a representative TBC system subjected to a specific thermal cycling process. A parametric analysis demonstrates the sensitivity of the response of the TBC system to the fracture strength of the top coat. The simulation results indicate that cracks appear primarily at the current location of the BC–TGO interface and may nucleate at early stages of thermal cycling. These results are in good agreement with recent experimental observations reported in the literature.     

The mei3 region of the Schizosaccharomyces pombe genome

Expression of the mei3 gene is sufficient to induce meiosis in the fission yeast Schizosaccharomyces pombe. The mei3 gene is located 0.64 Mb from the telomere of the left arm of Sz. pombe chromosome II. We have sequenced and analysed 107 kb of DNA from the mei3 genomic region. The sequence includes 14 known genes (bag1-B, csh3, dps1, gpt1, mei3, mfm3, pac1, prp31, rpl38-1, rpn3, rti1, spa1, spm1 and ubc4) and 26 other open reading frames (ORFs) longer than 100 codons: a density of one protein-coding gene per 2.7 kb. Twenty-one of the 40 ORFs (53%) have introns. In addition there is one lone Tf1 transposon long terminal repeat (LTR), tRNA(Trp) and tRNA(Ser) genes and a 5S rRNA gene. 14 of the novel ORFs show sequence similarities which suggest functions of their products, including a coatomer alpha-subunit, a catechol O-methyltransferase, protein kinase, asparagine synthetase, zinc metalloprotease, acetyltransferase, phosphatidylinositol 4-kinase, inositol polyphosphate phosphatase, GTPase-activating protein, permease, pre-mRNA splicing factor, 20S proteasome component and a thioredoxin-like protein. One predicted protein has similarity to the human Cockayne syndrome protein CSA and one with human GTPase XPA binding protein XAB1. Three ORFs are likely to code for proteins because they have sequence similarity with hypothetical proteins, three encode predicted coiled-coil proteins and four are sequence orphans.     

Strain analysis of plasma sprayed thermal barrier coatings under mechanical stress

The stiffness of air plasma sprayed (APS) thermal barrier coatings (TBCs) was determined from bending experiments combining strain analysis on a microstructural level with macroscopic mechanical parameters. Tests were performed with freestanding and attached TBCs, the latter either loaded in tension or in compression. Relationships are derived, which describe the TBC stiffness in a multilayer composite (attached TBC) and for a bimodular material that possess a lower stiffness in tension than in compression (stand-alone TBC). The increase of in-plane stiffness with increasing compressive stress emphasizes the importance of the spraying defects for the elastic response of the coating.     

两种捕收剂对金红石的捕收性能研究

通过单矿物和人工混合矿浮选试验,研究了SHA （水杨羟肟酸）和TBC两种药剂对金红石的捕收性能。试验结果表明,新型有机药剂TBC对金红石有较强的捕收能力和选择性,可以有效分离金红石和方解石以及金红石和石英,作为一种潜在的钛矿物捕收剂,值得进一步研究和推广。