Surface Degradation of Bulk AlN+Al Nano-composites

Bulk AlN + Al nanocomposite materials were Synthesized by sintering the compacts of AlN and Al nanoparticles, which were produced by an active plasma-metal reaction method. The sudeces of as-prepared nanocomposite was investigated by X-ray photoelectron spectroscopy (XPS).Results show the surfaces are much degraded and the degradation products are alumina(Al2O3),boehmite(AIOOH), bayerite(AI(OH)3) layer. The mechanism of degradation behaviour in moist environment was also discussed     

Microstructure and ionic conductivity of alternating-multilayer structured Gd-doped ceria and zirconia thin films

Multilayer thin film of Gd-doped ceria and zirconia have been grown by sputter-deposition on α-Al₂O₃ (0001) substrates. The films were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The Gd-doped ceria and zirconia layers had the fluorite structure and are highly textured such that the (111) plane of the films parallel to the (0001) plane of the α-Al₂O₃. The epitaxial relationship can be written as and , respectively. The absence of Ce³⁺ features in the XPS spectra indicates that the Gd-doped ceria films are completely oxidized. The ionic conductivity of this structure shows great improvement as compared with that of the bulk crystalline material. This research provides insight on designing of material for low temperature electrolyte applications.     

Al2O3/Al复合材料的界面结构特征

利用高分辩透射电子显微镜研究挤压铸造法制备的亚微米 Al 2O 3颗粒增强 Al 基复合材料的界面微观结构。结果表明 : Al基体的 (200) 和 (111) 面优先沿 Al 2O 3颗粒表面生长 , 在复合材料界面处 Al 基体与 Al 2O 3颗粒具有 Al (200) ∥Al 2O 3 (101 2) 、Al [011 ] ∥Al 2O 3 [0221 ] 的晶体学位向关系并形成半共格界面 , 且界面存在 Al (111) / / Al 2O 3 ( 1120) 的共格关系。界面干净无任何反应物。接近界面的 Al 基体中出现了柏氏矢量为 b= 1/ 3 [ 111 ] 弗兰克不全刃位错 , 该刃位错引起界面附近基体中明显的晶格应变场 , 位错周围晶格变形场的范围约为 20～30 层原子面宽度 , 而在 Al 2O 3颗粒靠近界面的区域中未观察到位错等缺陷。并从晶体学角度对界面的形成机制进行了分析。     

Nitrogen monoxide adsorption on Pt4 clusters coated on gamma-Al2O3 (111) surface

The nitrogen monoxide (NO) adsorption on platinum tetramer (Pt4) clusters supported on gamma alumina (gamma-Al2O3) with surface index (111) was investigated by using ab-initio calculation based on density functional theory. The Pt4 geometries used in this study are tetrahedron and planar rhombus. The adsorption of Pt4 on gamma-Al2O3 (111) surface in tetrahedron configuration is energetically more favorable as compared to that of the planar rhombus. However, it was found that NO molecule adheres strongly to Pt4 with planar configuration on gamma-Al2O3(111) surface. In addition, the NO adsorption calculation on the isolated Pt4 clusters also shows similar preference to planar configuration. The local density of states (LDOS) reveals that the difference in reactivity comes from the different hybridization strengths between the electronic states of nitrogen atom and those of platinum tetramers. The results are in good agreement with the experiments which show similar tendency for CO and N2O reactivity to gas-phase platinum clusters.     

The crystallographic orientation relationship between Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> in the composite material Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al–Mg–Si alloy

The formation mechanism of spinels on Al₂O₃ particles in the Al₂O₃/Al–1.0 mass% Mg₂Si alloy composite material has been investigated by transmission electron microscopy (TEM) in order to determine the crystallographic orientation relationship. A thin sample of the Al₂O₃/Al–Mg–Si alloy composite material was obtained by the FIB method, and the orientation relationship between Al₂O₃ and MgAl₂O₄, which was formed on the surface of Al₂O₃ particles, was discovered by the TEM technique as follows:

Insights into the structural,electronic, and magnetic properties of Fe2−x Ti x O3/Fe2O3 thin films with x = 0.44 grown on Al2O3 (0001)

The interface between hematite (α-Fe ₂ ^III O₃) and ilmenite (Fe^IITiO₃), a weak ferrimagnet and an antiferromagnet, respectively, has been suggested to be strongly ferrimagnetic due to the formation of a mixed valence layer of Fe²⁺/Fe³⁺ (1:1 ratio) caused by compensation of charge mismatch at the chemically abrupt boundary. Here, we report for the first time direct experimental evidence for a chemically distinct layer emerging at heterointerfaces in the hematite—Ti-doped-hematite system. Using molecular beam epitaxy, we have grown thin films (~25 nm thickness) of α-Fe₂O₃ on α-Al₂O₃ (0001) substrates, which were capped with a ~25 nm thick Fe_2?x Ti _x O₃ layer (x = 0.44). An additional 3 nm cap of α-Fe₂O₃ was deposited on top. The films were structurally characterized in situ with surface X-ray diffraction, which showed a partial low index orientation relationship between film and substrate in terms of the [0001] axis and revealed two predominant domains with \( (0001) _{{{\text{Fe}}_{2} {\text{O}}_{3} }} \;||\;(0001) _{{{\text{Al}}_{2} {\text{O}}_{3} }}, \) one with \( [10\bar{1}0]_{{{\text{Fe}}_{2} {\text{O}}_{3} }} \;||\;[10\bar{1}0]_{{{\text{Al}}_{2} {\text{O}}_{3} }}, \) and a twin domain with \( [01\bar{1}0]_{{{\text{Fe}}_{2} {\text{O}}_{3} }} \;||\;\;[10\bar{1}0]_{{{\text{Al}}_{2} {\text{O}}_{3} }}. \) Electron energy loss spectroscopy profiles across the Fe_2?x Ti _x O₃/Fe₂O₃ interface show that Fe²⁺/Fe³⁺ ratios peak right at the interface. This strongly suggests the formation of a chemically distinct interface layer, which might also be magnetically distinct as indicated by the observed magnetic enhancement in the Fe_2?x Ti _x O₃/α-Fe₂O₃/Al₂O₃ system compared to the pure α-Fe₂O₃/Al₂O₃ system.     

Al2O3/Al2O3 Joint Brazed with Al2O3-particulate-contained Composite Ag-Cu-Ti Filler Material

1.IntroductionTo improve the mechanical properties and relieve mis-matches between the filler metals and base materials,the particulates of superalloys,ceramic or carbon fiberswere added into the conventional brazing filler metal toform composite filler material.The method has beenused in aero-engine component repairing[1,2],fine castcomponent joining[3],wide clearance butt jointing[4],ce-ramic brazing[5,6]and electronic package[7].However,the method was used mostly in metal brazing.The mi-cro…     

Mechanism of the reduction of carbon/alumina powder mixture in a flowing nitrogen stream

The mechanism of the reduction of carbon/alumina powder mixture in a flowing nitrogen stream was studied. Five steps were found to be involved in the overall reaction. $$\begin{gathered} Al_2 O_{3f} (s) + 2C_f (s)\mathop \to \limits^{k_1 } Al_2 O(g) + 2CO(g) \hfill \\ Al_2 O(g) + solid surface\mathop \rightleftharpoons \limits_{k_2^\prime }^{k_2 } [Al_2 O]_s \hfill \\ [Al_2 O]_s + CO(g) + N_2 (g)\mathop \to \limits^{k_3 } 2AlN(s) + CO_2 (g) \hfill \\ CO_2 (g) + C_f (s)\mathop \rightleftharpoons \limits_{k_4^\prime }^{k_4 } CO(g) + [O]_c \hfill \\ [O]_c \mathop \to \limits^{k_5 } CO(g) \hfill \\ \end{gathered}$$ The consumption rates of Al₂O₃ and carbon, and the production rate of AIN, were determined to be $$\begin{gathered} \frac{{d[Al_2 O_3 ]}}{{dt}} = - 143.88(1 + m)exp( - 290 580/RT) [Al_2 O_3 ][C]^2 / \hfill \\ \left\{ {1 + 5.83 x 10^{14} exp( - 427 497/RT)\frac{{[CO_2 ]}}{{[CO]}}} \right\}^2 kg mol s^{ - 1} m^{ - 3} \hfill \\ \frac{{d[C]}}{{dt}} = - 409.504 exp ( - 254 500/RT) [Al_2 O_3 ][C]^2 / \hfill \\ \left\{ {1 + 5.83 x 10^{14} \exp ( - 427 497/RT)\frac{{[CO_2 ]}}{{[CO]}}} \right\}^2 kg mol s^{ - 1} m^{ - 3} \hfill \\ \frac{{d[AlN]}}{{dt}} = 53.24(1 + m) exp( - 290 580/RT) [Al_2 O_3 ][C]^2 / \hfill \\ \left\{ {1 + 5.83 x 10^{14} exp( - 427 497/RT)\frac{{[CO_2 ]}}{{[CO]}}} \right\}^2 kg mol s^{ - 1} m^{ - 3} \hfill \\ \end{gathered}$$ in the temperature range 1648–1825 K.     

Surface,grain-boundary and interfacial energies in Al2O3 and Al2O3-Sn,Al2O3-Co systems

Using the multiphase equilibrium method for the measurement of contact angles, the surface and grain-boundary energies of polycrystalline Al₂O₃ in the temperature range of 1473 to 1923 K were determined. Linear temperature functions were obtained by extrapolation for both quantities between absolute zero and the melting point of Al₂O₃. The temperature dependence of the surface and grain boundary energies can be expressed as $$\gamma _{{\rm A}l_2 O_3 } = 2.559 - 0.784 \times 10^{ - 3} T(J m^{ - 2} )$$ and $$\gamma _{{\rm A}l_2 O_3 - Al_2 O_3 = } 1.913 - 0.611 \times 10^{ - 3} T(J m^{ - 2} )$$ respectively. The interfacial energies of Al₂O₃ in contact with the molten metals tin and cobalt revealed a linear dependence on temperature.     

A method for the calculation of interfacial energies in Al2O3 and ZrO2/liquid-metal and liquid-alloy systems

A method is proposed by which the interfacial energy, γ_SL, of polycrystalline solid oxides (Al₂O₃, ZrO₂) in contact with liquid metals and certain binary liquid alloys can be calculated from the values of the surface energy of the oxides, γ_SV, and the liquid metals or liquid alloys, γ_LV, respectively. According to this method, the interfacial energy depends on the geometric mean of surface interactions, (γ_SV γ_LV)^1/2, the molar volumes, V, of the solid and liquid phases, and a parameter, K, which depends on the geometric details of the oxide surface defined by the ion sites in the oxide as well as the stoichiometry of the elements in the oxide and is given by the equation, $$\gamma _{SL} = \left( {K\frac{{V_{metal} }}{{V_{oxide} }} + 1} \right)^{2/3} (\gamma _{SV} \gamma _{LV} )^{1/2}$$ The method was verified using interfacial energy data obtained by measurements of the contact angle, θ, formed between the oxides and the liquid metals and liquid alloys with the sessile drop technique. A good agreement was observed between the calculated and the experimentally estimated values of γ_SL at the melting point of the metals and alloys.     

TEM observation of liquid-phase bonded aluminum–silicon/aluminum nitride hetero interface

Liquid-phase bonded aluminum–silicon/aluminum nitride interface structure was investigated using high-resolution transmission electron microscopy. A textured layer of aluminum formed a stable orientation relationship with aluminum nitride, which showed Al(111) to be tilted by about 4° with respect to the AlN(0001) interface plane. The unique orientation relationship between Al and AlN was predicted as one of the stable orientation relationships using coincidence of reciprocal lattice point method, which surveys the degree of geometrical coherency between two crystals in three-dimensional space. A stable orientation relationship was found to be (001)[1_boxclose \bar{1} 0]Al//(2[`2] \bar{2} 03)[11[`2] \bar{2} 0]AlN.     

Solid-phase low temperature steam-assisted synthesis of thermal stable alumina nanowires

A simple steam-assisted solid phase synthesis method was developed for synthesis of boehmite nanowires in the presence of TEAOH surfactant. The boehmite nanowires had uniform diameters (12-16 nm) and length up to 1-2 microm. The morphology of the nanostructured wires was well preserved after being converted to pure gamma-Al2O3 by thermal treatment at 600 degrees C for 5 h. The nanowires of Al2O3 exhibited excellent thermal stability by retarding the phase transformation and maintaining the wires-like nanostructure after being aged up to 1300 degrees C by preventing sintering between particles at high temperatures. The surface areas of Al2O3 nanowires could be maintained as high as 68 m2/g at 1300 degrees C while the surface areas of Al2O3 micropowder shrank to 0.89 m2/g after same thermal treatment. Both in-situ XRD and 27Al NMR results indicated that the crystal structure of gamma-Al2O3 nanowires was not transformed to alpha-Al2O3 at 1300 degrees C whereas micropowder Al2O3 was fully converted to alpha-Al2O3 at 1100 degrees C.     

Sputter deposited nanocrystalline Ni-25Al alloy thin films and Ni/Ni3Al multilayers

Thin films of nominal composition Ni-25at%Al have been sputter deposited from a target of the intermetallic compound Ni₃Al at different substrate deposition temperatures. The film deposited on an unheated substrate exhibited a strongly textured columnar growth morphology and consisted of a mixture of metastable phases. Nanoindentation studies carried out on this film exhibited a strong strain hardening tendency. In contrast, the film deposited at 200 °C exhibited a recrystallized non-textured microstructure consisting of grains of a partially ordered Ni₃Al phase. At higher deposition temperatures (∼400 °C), larger grains of the bulk equilibrium, long-range ordered, Ll₂ Ni₃Al phase were observed in the film. Unlike the film deposited on an unheated substrate, the films deposited at elevated temperatures did not exhibit any dependence of the hardness on the indentation depth and, consequently no strain hardening. The average hardness of the film deposited at 200 °C was higher than the one deposited at 400 °C. In addition to monolithic Ni-25Al thin films, multilayered Ni/Ni3Al thin films were also deposited. Multilayers deposited non-epitaxially on unheated substrates exhibited a strong {111} fiber texture while those deposited epitaxially on (001) NaCl exhibited a {001} texture. Free-standing multilayers of both types of preferred orientations as well as of different layer thicknesses were deformed in tension untill fracture. Interestingly, the {111} oriented multilayers failed primarily by a brittle fracture while the {001} multilayers exhibited features of ductile fracture.     

Interface structure and strain development during compression tests of Al2O3/Nb/Al2O3 sandwiches

The interface structure of an Al₂O₃/Nb/Al₂O₃ sandwich produced by solid-state diffusion bonding was investigated in detail by various transmission electron microscopy (TEM) methods. The joint possessed at one interface a , , and on the other interface a and orientation relationship. At both interfaces, misfit dislocations formed to compensate the lattice mismatch as found by high-resolution transmission electron microscopy (HRTEM). Electron energy-loss near edge structure (ELNES) studies revealed that the interface is terminating with an Al layer resulting in Al–Nb bonds. Identical sandwiches were investigated on the meso- and macroscopic scale by performing compression tests and simultaneously monitoring the strain development at (001)_Nb and crystal faces. The full-field optical strain measurements (FFOM) revealed that the strain is localized at the interfaces when observed at the (001)_Nb face while it is along the maximum shear directions of 36–54° inclined to the interface when observed at the face. The strain localization along a specific maximum shear direction results in the cleavage of Al₂O₃, always initiating from the interface possessing the and orientation relationship.     

Charge-trapping characteristics of Al2O3/Cu/Al2O3 nanolaminate structures prepared through atomic layer deposition

The nanolaminate Al2O3/Cu/Al2O3 structures were constructed on p-type Si (001) substrates using atomic layer deposition (ALD) process with the aim to fabricating nonvolatile charge-trap memories. Low temperature Cu thin layers were deposited through plasma-enhanced atomic layre depositon of Cu aminoalkoxide (Cu(dmamb)2) combined with hydrogen plasma and Al2O3 layers were prepared by thermal atomic layer deposition of trimethylaluminum (TMA) combined with H2O. Nonvolatile features were confirmed using capacitance-voltage (C-V) measurements. The copper film functions as a charge-trapping layer and the Al2O3 thin layers were employed as tunneling and control oxide layers. Line shapes and binding energies of Cu metal and the thin layer of 6 nm Cu in nanolaminate structures were observed in the X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (TEM) image. The V(FB) shift width of the Al2O3 (28 nm)/Cu (6 nm)/Al2O3 (4.2 nm)/Si laminate structure is found to be 4.75 V in voltage sweeping between -10 and +10 V, leading to the trap density of 1.68 x 10(18) cm(-3).     

TiO2和O-Al2O3晶体的生长习性

通过水热法制备粉体的实验观察到金红石、锐钛矿和α-Al2O3晶体的生长习性．采用配位多面体生长习性法则合理地解释了Ti O2和α-Al2O3的生长习性．其主要结果为α-Al2O3晶体的生长习性为平板{0001}，其各晶面的生长速度为：V｛0001 }＜V｛1123}；锐钛矿的生长习性为四面体，其各晶面的生长速度为V<010>=V<001>>V<010>>V<111>．而PBC理论很难合理地解释α-Al2 O3晶体的生长习性．     

Effects of temperature and ferromagnetism on the γ-Ni/γ′-Ni3Al interfacial free energy from first principles calculations

The temperature dependencies of the γ(f.c.c.)-Ni/γ′-Ni₃Al(L1₂) interfacial free energy for the {100}, {110}, and {111} interfaces are calculated using first-principles calculations, including both coherency strain energy and phonon vibrational entropy. Calculations performed including ferromagnetic effects predict that the {100}-type interface has the smallest free energy at different elevated temperatures, while alternatively the {111}-type interface has the smallest free energy when ferromagnetism is absent; the latter result is inconsistent with experimental observations of γ′-Ni₃Al-precipitates in Ni–Al alloys faceted strongly on {100}-type planes. The γ(f.c.c.)-Ni/γ′-Ni₃Al interfacial free energies for the {100}, {110}, and {111} interfaces decrease with increasing temperature due to vibrational entropy. The predicted morphology of γ′-Ni₃Al(L1₂) precipitates, based on a Wulff construction, is a Great Rhombicuboctahedron (or Truncated Cuboctahedron), which is one of the 13 Archimedean solids, with 6-{100}, 12-{110}, and 8-{111} facets. The first-principles calculated morphology of a γ′-Ni₃Al(L1₂) precipitate is in agreement with experimental three-dimensional atom-probe tomographic observations of cuboidal L1₂ precipitates with large {100}-type facets in a Ni-13.0 at.% Al alloy aged at 823 K for 4096 h. At 823 K this alloy has a lattice parameter mismatch of 0.004 ± 0.001 between the γ(f.c.c.)-Ni-matrix and the γ′-Ni₃Al-precipitates.     

Rolling and annealing textures of a SiCw/Al composite

A SiC whisker reinforced pure aluminum composite (SiC_w/Al) was fabricated using a squeeze casting route and cold-rolled to 50% reduction in thickness. Some cold-rolled composites were then annealed at 500 °C for 1 h. The pure aluminum was also cold-rolled and annealed in the above way for comparison purpose. The textures of the cold-rolled and annealed materials were examined using XRD technique. It was found that the dominant texture components in the cold-rolled composites consisted of {112}〈111〉, {100}〈011〉 and {123}〈634〉. They were much weaker than those in the cold-rolled aluminum. When the cold-rolled composites were annealed, the new texture components {211}〈213〉, {013}〈131〉 and {011}〈211〉 occurred and had the similar intensity as the texture components remained from the deformation state. This indicated that the recovery reaction and recrystallization occurred simultaneously when the cold-rolled composite was annealed 1 h at 500 °C. Like the situation of the deformed materials, the annealing texture was also much weaker in the composite than in the aluminum. The weaker deformation and annealing textures in the composites can be attributed to the introduction of the whiskers.     

Comparison of the energy-response factor of LiF and Al2O3 in radiotherapy beams

A Monte Carlo study of the energy-response factor of aluminium oxide (Al2O3) and lithium fluoride (LiF) TLDs in kilovoltage and megavoltage photon beams relative to 60Co gamma rays has been performed using EGSnrc Monte Carlo simulations. The sensitive volume of the detector was simulated as a disc of diameter 2.85 mm and thickness 1 mm. The phantom material was water and the irradiation depth was 2.0 cm in kilovoltage photon beams and 5.0 cm for megavoltage photon beams. The results show that the energy-response of the Al2O3 and LiF-TLDs is constant within 3% for photon beam energies in the energy range of 60Co gamma rays to 25 MV X rays. However, both detectors show an enhanced response for kilovoltage photon beams, which in the case of 50 kV X rays is 3.2 times higher than that for 60Co gamma rays. The energy-response factor was 1.46 for LiF irradiated in 50 kV X rays. The Al2O3 detector has an energy-response that is 2.2 times higher than that of LiF in 50 kV X rays decreasing to 1.19 for 250 kV X rays. The results show that the addition of 0.1 or 1% of carbon by weight (as dopant) into the Al2O3 does not change the Monte Carlo determined energy-response factor by more than 1%.     

Composition Influence on the Thermo-optical Properties and Luminescence Efficiency of Europium-Doped Calcium Aluminosilicate Glasses

In this work, the influence of the composition on the thermal and thermo-optical properties and luminescence of europium-doped calcium aluminosilicate glasses is investigated. High purity reagents were used to prepare samples with nominal compositions: $2.5\hbox {Eu}_{2}\hbox {O}_{3},\,4.1\hbox {MgO},\,(7 + x)\hbox {SiO}_{2},\,(47.4 - x/2)\hbox {CaO},\,\hbox {and} (39 - x/2)\hbox {Al}_{2}\hbox {O}_{3},\,x = (0, 22, 27, 32, 37, 42,\,\hbox {and}\,47)\,(\hbox {in mass}\%)$ . The ratio CaO/ Al $_{2}$ O $_{3}$ was kept at 1.2. At room temperature, measurements of the specific heat, mass density, temperature coefficient of the optical path length, and refractive index were performed. Two-beam thermal lens spectroscopy in the mismatch mode was used to determine the absolute values of the thermal diffusivity at room temperature. Using the thermal lens signal, the rate of heat generated by the nonradiative process was estimated, which showed a large decrease with increasing silica content. The decrease of this parameter can be related to the increase of the luminescence efficiency, which agrees with the results of luminescence spectroscopy. These results suggest an increase in the luminescence efficiency of europium-doped calcium aluminosilicate glasses at increments of increasing silica content.