铌硅化物基超高温合金Si-Y2O3共渗涂层的组织及其高温抗氧化性能

采用Si-Y₂O₃包埋共渗工艺在铌硅化物基超高温合金表面制备Y改性的硅化物涂层, 研究其在1250℃的恒温氧化性能. 采用扫描电镜(SEM)、能谱(EDS)与X射线衍射(XRD)分析Si-Y₂O₃共渗涂层氧化前后的物相组成和组织变化. 结果表明：涂层具有明显分层的结构, 由外至内依次为(Nb,X)Si₂(X表示Ti, Hf和Cr)外层和(Nb,X)₅Si₃过渡层, 在过渡层与基体之间有不连续分布的细小(Cr,Al)₂(Nb,Ti)块状沉淀. EDS分析表明, 涂层中的Y分布是不均匀的, (Cr,Al)₂(Nb,Ti)相的Y含量为0.94at%左右, 而(Nb,X)Si₂和(Nb,X)₅Si₃相的Y含量为0.46at%～0.57at%. 经1250℃分别氧化5, 10, 20, 50和100h后, Si-Y₂O₃共渗涂层保持其原始的相组成, 并在其表面形成以TiO₂、 SiO₂和Cr₂O₃组成的致密混合氧化膜, 且与基体结合良好.     

ZrO2对NiO/CeO2/γ-Al2O3复合催化剂结构的影响

以Ni(NO₃)_2·6H₂O、Al(NO₃)₃·9H₂O、ZrOCl_2·8H₂O和Ce(NO₃)_3·6H₂O为原料,采用共沉淀法分别制备了NiO/CeO₂/γ-Al₂O₃和NiO/CeO₂-ZrO₂/Al₂O₃催化剂.通过X射线衍射（XRD）、透射电子显微镜（TEM）和近边X射线吸收精细结构（XANES）等方法对催化剂的组成结构进行表征.结果表明,煅烧温度高于600℃时,NiO/CeO₂/γ-Al₂O₃催化剂中的NiO与γ-Al₂O₃载体发生作用,形成NiAl₂O₄尖晶石;而NiO/CeO₂-ZrO₂/Al₂O₃催化剂中,NiO能够稳定存在,没有NiAl₂O₄尖晶石生成,且Al₂O₃与CeO₂和ZrO₂作用形成一种新的Zr_0.30Ce_0.45Al_0.25O_1.87固溶体.     

超疏水-亲水CaBi4Ti4O15涂层制备及其表面浸润性研究

采用简单的涂抹方法, 在衬底上制备了CaBi₄Ti₄O₁₅涂层; 经不同温度退火和120℃放置处理, 得到了浸润性从超疏水到亲水, 其表面接触角从152.5°到43.6°变化的CaBi₄Ti₄O₁₅涂层表面; 通过扫描电镜分析,研究了不同退火温度下涂层表面微观结构变化对表面 浸润性的影响. 结果表明: CaBi₄Ti₄O₁₅涂层表面晶粒和孔洞尺寸变化是导致其表面浸润性从超疏水到亲水变化的主要原因, 而包含纳米颗粒的阶层结构导致亲水CaBi₄Ti₄O₁₅涂层表面呈现出超疏水性.     

硫化物晶体的生长习性

在自然界中硫化物晶体的种类较多,其结构较复杂,其中硫离子以S^2-和对硫S^2-₂形式存在．一部分晶体的生长习性得不到满意的解释．本文采用配位多面体生长习性法则合理地解释了MoS₂、ZnS、CuFeS₂和PbS晶体的生长习性．发现MOS₂晶体的生长习性为六方平板状｛0001｝,其各晶面的生长速度为：V_＜0001＞＜V_＜1010＞;CuFeS₂和ZnS晶体的生长习性为四面体,其各晶面的生长速度为：V_＜111＞＞V_＜001＞＞V_＜111＞;PbS晶体的生长习性为八面体｛111｝,立方体只是它的一种习性变化.     

高能球磨Al-Y2O3粉体固相反应制备YAG陶瓷的研究

用高纯Al粉体和Y₂O₃粉体(Al-Y₂O₃粉体)为原料采用固相反应法制备了YAG陶瓷. Al-Y₂O₃粉体高能经过球磨, 煅烧生成YAG粉体, 再真空烧结制备高致密YAG陶瓷. 采用DTA-TG对球磨Al-Y₂O₃粉体进行分析, 采用XRD、SEM对球磨的Al-Y₂O₃粉体、YAG粉体及YAG陶瓷进行了表征. 实验表明: Al-Y₂O₃粉体在～569℃时, Al粉强烈氧化, 并与Y₂O₃粉反应, 600℃煅烧出现YAM相, 随煅烧温度升高出现YAP相, 1200℃煅烧生成YAG粉体. 成型YAG素坯在1750℃保温2h真空烧结出YAG相陶瓷, YAG陶瓷相对密度可达98.6%, 晶粒生长均匀, 晶粒尺寸为810μm.     

Eu2+在多铝酸钠体系中的发光

应用高温固相法合成了Na的多铝酸盐,并研究了Eu^2＋在体系中的发光性能．结果表明,Na_1＋xMgAl_11－xO₁₇体系在整个组成范围内保持Na的β－Al₂O₃结构不变,而对于Na_1．67－2xBa_xAl1_0．33O₁₇体系,在x＝0．30附近体系结构发生转变,x＜0．30,体系形成Na的外β－Al2O3结构的固溶体,x＞0．30,体系形成Ba的β－Al₂O₃结构的有序体;与体系组成和结构的变化相对应,Eu^2＋的发射能量和发光强度产生相应的变化,在Na的β－Al₂O₃中Eu^2＋存在高、低能两种发射中心;通过系列化研究,获得了新的组成的、具有β－Al₂O₃结构的荧光体Na_0．67Ba_0．50Mg_0．67Al_10．33O₁₇：Eu^2＋,在较低的掺杂浓度（0．05mol）下可以产生较强的发光．     

燃烧合成Ti3AlC2粉体的机理研究

利用淬火实验并结合XRD、SEM研究了燃烧合成Ti₃AlC₂粉体的机理.实验结果表明,燃烧合成Ti₃AlC₂粉体的机理是溶解再析出机制.即先生成的TiC晶核重新溶解到Ti-Al熔体中,同时三元碳化物开始析出并发育成层状结构.反应可以分为三个阶段:A.预热阶段;B.初始反应阶段;C.溶解析出阶段.     

Nb2O5掺杂高温无铅(Ba,Bi,Na)TiO3基PTCR陶瓷结构与电性能研究

采用固相反应法制备了施主掺杂浓度不同的Nb₂O₅（分别为0.1mol%、 0.3mol%、 0.5mol%、 0.7mol%）掺杂(Ba, Bi,Na)TiO₃基PTCR陶瓷. 对其微观结构及电性能进行研究发现：随着Nb₂O₅掺杂浓度的增加,陶瓷晶粒尺寸先变大后变小,室温电阻率也随之先减小后增大,说明Nb₂O₅的掺杂量存在一个临界施主掺杂浓度. 当Nb₂O₅施主掺杂量为临界施主掺杂浓度0.5mol%时,获得了居里温度T_c为 183℃、室温电阻率ρ为1.06×10³Ω·cm、升阻比ρ_max/ρ_min为1.0×10⁴的高温无铅PTCR陶瓷. 通过交流复阻抗谱分析,探讨了Nb₂O₅施主掺杂在该PTCR陶瓷中的作用机理.     

CrO3对Fe2O3+Al铝热反应系统反应过程的影响

用铝热-重力分离法制备了不含铁铝尖晶石（FeAl₂O₄）的陶瓷内衬复合钢管,并通过热力学计算分析了有关反应的优先顺序,结果表明,在Fe₂O₃+Al系统中强氧化剂CrO₃与Al的反应并不是一步完成而是分步反应,FeAl₂O₄优先于Cr₂O₃与Al反应,因而加入CrO₃添加剂可有效地去除陶瓷层中的尖晶石相,从而提高复合钢管的耐蚀性能.     

Yb3+掺杂SiO2-Bi2O3-B2O3玻璃的物理性质及光谱性质

选取玻璃组分60SiO₂-xBi₂O₃-(30-x)B₂O₃-2K₂O-7Na₂O-1Yb₂O₃(以mol％记,x=0,5,10,15,20,25,30)为研究对象。通过测试试样的物理性质和光谱性质,应用倒易法(reciprocity method)计算Yb³⁺离子的受激发射截面(σ_emi),并且计算了Yb³⁺的自发辐射几率(A_rad),²F_5/2能级的辐射寿命(T_rad)。讨论了玻璃中Bi₂O₃和B₂O₃的组成变化对其物理性质、Yb³⁺离子的吸收特性、发光特性以及OH^-离子对实测Yb³⁺荧光寿命(T_f)的影响。结果表明:Yb³⁺掺杂的Si₂-Bi₂O₃-B₂O₃具有较好的光谱性能,是一种新型的Yb³⁺掺杂双包层光纤候选基质材料。     

X-ray diffraction study of calcium nitrate tetrahydrate melt at 328 K

The hydration structure of calcium nitrate tetrahydrate, Ca(NO₃)₂ · 4.1 H₂O, melt at 328 K has been investigated by X-ray scattering and correlation method. Analysis of the radial distribution function and model fitting revealed that in the hydrate melt, a Ca²⁺ ion is surrounded by about six oxygen atoms, 4.1 of which come from water molecules at the average distance of 0.241 nm, 2.0 coming from the nitrate ions at the average distance of 0.254 nm. In the first coordination shell of the melt, the formation of a direct Ca²⁺-NO ₃ ^– correlation, such as contact ion pairs, was suggested. The hydration structure of the melt analysed was compared with that of Ca(NO₃)₂ · 3.5H₂O melt previously reported, and the decrease from nine of the reported melt to six in this melt was observed in the number of the nearest neighbour oxygen atoms around a Ca²⁺ ion. This implies that in the highly concentrated aqueous solution, the structure of the first coordination shell around the cation changes markedly with a small difference in the water molecule content.     

铝及其合金熔体的增黏及泡沫化特性

研究了纯铝、普通铝硅合金和新型多组元铝合金的增黏和泡沫化特性．这三者加入Ca增黏后的物相组成和发泡后的气泡壁微观组织以及三者熔体的表面张力．结果表明：Ca加入后，经过搅拌形成的大量弥散分布的细小Al-Ca中间化合物颗粒快速增加了纯铝以及新型多组元铝合金熔体的黏度，而Ca加入普通铝硅合金中与Si等元素形成较大的颗粒，因而增黏效果不如前两者；Ca的加入也显著降低新型多组元铝合金和纯铝熔体的表面张力，普通铝硅合金降低不多；在相同的表观黏度下，表面张力的差异是引起纯铝．普通铝硅合金、新型多组元铝合金等三种熔体泡沫化特性差异的主要原因．     

基于高温熔凝法Al_2O_3/ZrO_2/YAG共晶陶瓷显微组织演变规律

作为超高温结构材料,共晶氧化物陶瓷的力学性能和显微组织密切相关。采用高温熔凝法制备Al_2O_3/ZrO_2/YAG共晶陶瓷体,研究熔体温度和结晶种子对凝固组织影响规律,运用经典形核机制和Jackson-Hunt共晶生长模型探讨了凝固组织的演变机理。研究表明,随着熔体温度升高(1750~2000℃),凝固体物相组成从α-Al_2O_3,c-ZrO_2和YAG转变为α-Al_2O_3,c-ZrO_2和亚稳相YAP。凝固组织依次经历:非共晶Al_2O_3/ZrO_2/YAG、不规则共晶Al_2O_3/ZrO_2/YAG、纳米纤维状共晶Al_2O_3/ZrO_2/YAG和复杂粗大的亚稳复合陶瓷Al_2O_3/ZrO_2/YAP。分析表明,凝固组织的演变源于异质晶核点不断钝化导致形核过冷度和凝固路径改变,所以合理选择熔体温度和结晶种子是共晶组织调控的关键。     

Microstructure and properties of SiC-whisker-reinforced Si<Subscript>3</Subscript>N<Subscript>4</Subscript> ceramics with calcium aluminate additions

Silicon-nitride-based ceramics containing Al₂O₃-CaO sintering aids and reinforced with silicon carbide whiskers have been prepared by hot pressing at 1650°C in a nitrogen atmosphere, and their microstructure, phase composition, and mechanical properties have been studied. The results indicate that the Si₃N₄ ceramic containing 15 wt % calcium aluminate additions and 10 wt % SiC fibers has a dense microstructure with a uniform distribution of skeletal and dendritic silicon carbide crystals. The observed variations in the morphology of the crystals are tentatively attributed to the secondary crystallization of silicon carbide from the eutectic calcium aluminate melt during cooling.     

Microstructural evolution during combustion reaction between CuO and Al induced by high energy ball milling

The product of the combustion reaction between CuO and Al induced by high energy ball milling has been characterised by using X-ray diffractometry and scanning electron microscopy. It has been observed that the combustion reaction can be ignited very easily by the ball milling. The reaction product consists of polycrystalline Cu in bulk and particle forms and a large number of nanometer sized spherical Al2O3 particles attached to the surface of the Cu. It has been demonstrated that this microstructure is evolved through rapid solidification of Cu and Al2O3 melts and rapid condensation of Cu vapour. Cu and Al2O3 phases are separated in the reaction product. The reason for this is mainly attributed to the large difference in their density and the shaking force of the ball mill.     

Crystallization behaviour of calcium aluminate glass fibres

Crystallization behaviour of as-spun and fully-nucleated calcium aluminate (CA) glass fibres produced via inviscid melt spinning (IMS), was studied. Differential thermal analysis (DTA) scans on the as-spun and fully-nucleated CA fibres were performed at different heating rates. By applying the Kissinger method to the DTA scan data the activation energy values for crystallization were determined to be 569 and 546 kJ mol–1, respectively for the as-spun and fully-nucleated CA fibres. The Ozawa analysis on the DTA scan data gave the Avrami parameters at 2.7 and 2.4, respectively, for the as-spun and fully-nucleated CA fibres, which indicates high tendency of bulk crystallization mode. The formation of equilibrium phases of Ca12Al14O33 and CaAl2O4 in the crystallized CA fibres was identified by using X-ray diffraction (XRD).     

Solid state compatibilities in CaO–CaO.Al2O3–CaSO4–CaF2 system

The determination of the phases assemblages in equilibrium in the CaO–CaO.Al2O3–CaSO4–CaF2 system at 1100°C has been performed. Four assemblages are found and one more is deduced. 3CA.CaSO4 appears in all compatibility tetrahedra in solid state or in melt presence. It is compatible with C3A, C12A7ss, CA, C11A7.CaF2 and the aluminate formed depends on Al2O3 and CaF2 proportion, (cement chemistry abbreviations: C=CaO, A=Al2O3). © 1998 Kluwer Academic Publishers     

添加剂对离心自蔓延高温合成陶瓷层组织结构与性能的影响

为了改善钢管内衬陶瓷层的韧性,在铝热剂中分别添加ZrO2,Al2O3,SiO2进行改性,采用离心自蔓延高温合成工艺制备了钢管内衬陶瓷层,研究了添加剂对陶瓷层形貌、结构和性能的影响.结果表明:加入ZrO2或Al2O3可以改变陶瓷层的组织结构,使Al2O3由树枝状晶变为等轴晶;加入SiO2可在Al2O3枝晶间隙形成网状Ca...     

Preparation of large-size Al2O3/GdAlO3/ZrO2 ternary eutectic ceramic rod by laser directed energy deposition and its microstructure homogenization mechanism

Laser 3D printing based on melt growth has great potential in rapid preparation of Al2O3-based eutectic ceramics.In this work,large-scale Al2O3/GdAlO3/ZrO2 ternary eutectic ceramic rod with diameter of 4-5 mm and height higher than 250 mm was additively manufactured by laser directed energy deposition.Especially,heat treatment was applied to eliminate the microstructure heterogeneity in the as-deposited eutectic ceramic,and the microstructure homogenization mechanism was studied in depth.The results indicate that colonies and banded structures completely disappear after the heat treatment,producing a homogeneous network eutectic structure.The microstructure homogenization is revealed to experience three stages of discontinuous coarsening,continuous coarsening and microstructure coalescence.Addi-tionally,it is found that the eutectic spacing linearly increases with the heat treatment time,meaning that the coarsening behavior of the laser 3D-printed Al2O3/GdAlO3/ZrO2 eutectic ceramic satisfies well with the Graham-Kraft model.     

Oxygen coordination of magnesium and calcium in binary magnesia and calcia metaphosphate glasses

An X-ray diffraction study has been carried out on binary phosphate and silicate glasses with MgO or CaO in equimolar composition. The structure of a 60 mol% CaO–40 mol% Al₂O₃ glass was also investigated for comparison. The electron radial distribution function was calculated by the usual Fourier transformation and interpretation of it was made in terms of pair functions. The number of oxygens around magnesium is evaluated to be four in both phosphate and silicate glasses. On the other hand, the number of oxygens which surround calcium appears to depend upon the component of network formers: namely, the oxygen coordination numbers around calcium are five in phosphate, six in silicate and four in aluminate glasses, respectively.