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1.
《Materials Science & Technology》2013,29(7-8):732-738
AbstractThere is a growing need in both aerospace and commercial markets for lighter weight, higher stiffness, higher thermal stability materials to solve the design engineers’ problems of reduced mass, higher access speeds, improved mechanical and thermal stability for today's advanced technology. To address those needs, Brush Wellman Inc. has developed, characterised, and put into high volume production a family of beryllium metal matrix composites. There are two classes of materials that have been developed to provide these engineering benefits to the designer in both the commercial and aerospace markets. The first family of materials is aluminium beryllium (AlBeMet, which is a registered tradename of Brush Wellman). This material is a metal matrix composite consisting of pure beryllium and aluminium, with 20–62 vol.-%Be and the remainder aluminium. The material is produced by both powder metallurgy and net shape technologies such as investment casting and semi-solid forming. The materials properties that make it attractive for the design engineer are a density that is 25% less than that of aluminium, a specific stiffness four times those of aluminium, titanium, steel, and magnesium, a higher dampening capacity than aluminium, and a coefficient of thermal expansion almost 50%lower than aluminium. The second family of materials is a beryllium–beryllium oxide metal matrix composite, which are called E materials. This material was developed to address the thermal management needs of the electronic packaging design engineer. The material properties that make this material attractive to the electronic packaging engineer are: a density 20–25% that of Kovar, Invar, and CuMoCu, and 30% less than Al–SiC; a thermal conductivity ranging from 210 to 240 W m-1 K-1and a tailorable coefficient of thermal expansion, ranging from 6×10-6 to 8.7×10-6 K-1. 相似文献
2.
In this paper, the metal to ceramic transition of the Al-N2 system was investigated using classical reactive pulsed-DC magnetron sputtering and HIgh Power Impulse Magnetron Sputtering (HIPIMS) at a constant average current of 3 A. Optical emission spectroscopy measurements revealed more ionised aluminium species in the HIPIMS discharge compared to pulsed-DC sputtering. It also showed excited N0 and ionised N+ species in reactive Ar/N2 HIPIMS discharges. The corresponding evolution of the consumed nitrogen flow as a function of the N2 partial pressure revealed that a higher amount of reactive gas is needed to achieve stoichiometric AlN with HIPIMS. Electron probe micro-analysis and X-ray diffraction measurements confirmed that a partially poisoned aluminium target is enough to allow the deposition of stoichiometric hcp-AlN thin films via HIPIMS. To go further in the comparison of both processes, two stoichiometric hexagonal aluminium nitride thin films have been deposited. High power impulse magnetron sputtered hcp-AlN exhibits a higher nano-hardness (18 GPa) than that of the coating realised with conventional pulsed-DC sputtering (8 GPa). 相似文献
3.
The electrical conductivity of SrSn1−xFexO3−δ increases with the Fe content and reaches a value of ∼10−1 S/cm at 25°C at x=1. Compounds with low Fe content exhibit both ionic and electronic conductivity, while the higher Fe content perovskites are mainly electronic conductors with a conductivity independent of the oxygen partial pressure over a wide range from 0.21 to 10−22 atm. 相似文献
4.
The electrical conductivity of high purity tin dioxide doped with antimony was studied at temperatures of 900 to 1200° C and partial pressures of oxygen between 10–8 and 1 atm. For specimens having a dopant concentration over 1 × 1019Sb cm–3, the electrical conductivity decreased slightly with temperature and independent of oxygen partial pressure. The electrical conductivity of specimens having a dopant concentration under 1 × 10–8Sb cm–3 increased with temperature and with decreasing partial pressure of oxygen. The significance of the dopant and the thermally created defects is discussed. 相似文献
5.
Silicon nitride films were prepared by reactive plasma sputtering in nitrogen at a pressure of 2×10-4 Torr. The residual gas in the reactor during film sputtering was analysed. The chemical composition of the films was determined from infrared absorption spectra in the wavelength region 2.0–15.0 μm and by the elastic scattering of 3He particles.The best quality silicon nitride films were obtained in pure nitrogen at the minimum residual gas pressures. An absorption minimum at 11.0 μm in the infrared spectra, corresponding to the Si-N chemical bond in the Si3N4 molecule, was observed in our films, indicating that their composition was close to stoichiometric.With a residual hydrogen pressure above 10% or a residual oxygen pressure above 2% the generation of new chemical bonds Si-H, N-H and Si-O respectively was observed in the silicon nitride films. 相似文献
6.
《Materials Chemistry and Physics》1987,18(3):287-294
Highly densified bodies (~ 98 % theoretical density) of the Bi2O3-Y2O3(Er2O3) systems containing 30 moles % Y2O3 and 20 moles % Er2O3 respectively were prepared from both mixed oxides and coprecipitated oxalates. DC ionic conductivity and impedance complex plane analysis on sintered samples were performed. Under oxygen partial pressure ranging from 1 to 10 Pa was found that, samples containing 30 moles % yttria showed a pure ionic conductivity up to an oxygen partial pressure of 10−20 Pa. Samples containing 20 moles % erbia, extended its ionic conductivity up to an oxygen partial pressure of 10−22 Pa. The impedance analysis shows the presence of only one semicircle at low tempertures and it is attributed to bulk conductivity contribution. The conductivity was higher for the Bi2O3-Er2O3 sintered solid electrolytes, in such a case, a conductivity as high as 1.38 ohm cm at 700ºC was obtained. The activation enthalpy for the conduction process was calculated in the temperature range from 200º to 700ºC in all the cases. Microstructural development in the sintered sample was also studied. 相似文献
7.
《Thin solid films》1986,138(1):79-86
IR transmission spectroscopy in conjunction with X-ray diffraction was used to characterize the phase composition of aluminium films after nitrogen ion implantation. Aluminium films deposited onto single-crystal silicon and implanted with 30 keV nitrogen ions (14N2+) to a dose of 1017-1018 ions cm-2 were subsequently characterized for aluminium nitride (AIN) formation by IR spectroscopy. The formation of a stoichiometric AIN layer was evident from the IR absorption band observed at 648 cm-1. Furthermore, X-ray diffraction of an aluminium foil after nitrogen implantation at 110 keV to a dose of 5.0 × 1017 ions cm-2 on each side revealed the presence of a polycrystalline AIN phase. A thermal treatment at 700°C did not yield any new crystalline phases. 相似文献
8.
Norton NBD 200 silicon nitride ceramics were implanted with sodium to a dose of 7.0×1015cm-2 at 72 keV (1 at% peak sodium content at 100 nm). The sodium-implanted samples were further implanted with aluminium to 7.3×1015cm-2 at 87 keV (1 at% peak aluminium content at 100 nm). The implanted and unimplanted samples were oxidized in 1 atm dry oxygen
at 1100 and 1300°C for 2–6 h. Profilometry and scanning electron microscopy measurements indicated that sodium implantation
led to up to a two-fold increase in the oxidation rate of silicon nitride. The sodium effect was effectively neutralized when
aluminium was co-implanted. The opposite effects of sodium and aluminium on the oxidation resistance of silicon nitride can
be attributed to their different roles in modifying the structure and properties of the oxide formed.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
9.
Electrical conductivity and defect structure of polycrystalline tin dioxide doped with antimony oxide 总被引:3,自引:0,他引:3
Electrical conductivity () of tin dioxide doped with antimony has been measured as functions of temperature and oxygen partial pressure (p02>
). Variation of electrical conductivity is explained by assuming that the antimony oxide forms a substitutional solid solution and doubly ionized oxygen vacancies are predominant defects. Above –10–5 atm oxygen partial pressure antimony ions are present predominantly in the pentavalent state in tin dioxide lattice. However, it is converted to the trivalent state below this oxygen partial pressure accompanied by a sudden rise in conductivity. 相似文献
10.
The defect structure of undoped polycrystalline Ta2O5 was investigated by determining the temperature [850–1050°C] and oxygen partial pressure [100–10?19 atm.] dependence of the electrical conductivity. The data were found to be proportional to the power of the oxygen partial pressure for the oxygen pressure range <10?8 atm. and independent of the oxygen partial pressure for PO2 > 10?6 atm. The enthalpy of formation of doubly ionized oxygen vacancies plus two electrons is estimated to be 118.31 Kcal/mole [5.13 eV]. The observed conductivity data are explained on the basis of the presence of unknown acceptor impurities in the undoped samples. 相似文献
11.
Suman Nandy Biswajit Saha Manoj K. Mitra K. K. Chattopadhyay 《Journal of Materials Science》2007,42(14):5766-5772
Thin films of NiO (bunsenite) with (200) preferential orientation were synthesized on glass substrates by direct current sputtering
technique in Ar+O2 atmosphere. Nanostructural properties of the NiO films were investigated by X-ray diffraction and also by atomic force microscopic
(AFM) studies. Electrical and optical properties of the deposited films were investigated as a function of different partial
pressure of oxygen in the sputtering gas mixture during deposition. The films showed p-type electrical conduction and the
conductivity depends on the partial pressure of oxygen. The electrical conductivity (σRT) was found to be .0615 S cm−1 for films deposited with 100% O2 and its value sharply decreased with the decrease the partial pressure of O2; for example σRT for 50% O2 was 6.139 × 10−5 S cm-1. The mechanism of the origin of p-type electrical conductivity in the NiO film is discussed from the viewpoint of nickel
or oxygen vacancies, which generate holes and electrons respectively. X-ray photoelectron spectroscopic studies supported
the above argument. Corresponding optical properties showed that the transparency decreases with increasing oxygen partial
pressure and the bandgap also decreases. 相似文献
12.
Thermal conductivity of calcium-doped aluminium nitride ceramics 总被引:1,自引:0,他引:1
Aluminium nitride ceramics were prepared with the addition of up to 12wt% of calcium oxide as a sintering aid. Both the oxygen and the calcium content of the samples decreased during sintering with increasing sintering temperature and soaking time. Higher amounts of calcium oxide resulted in higher thermal conductivities, with values up to 142 W m–1 K–1. Moderate sintering temperatures, short temperature soaking times and the use of inexpensive Ca-based sintering additives should enable the production of aluminium nitride ceramics with sufficiently high thermal conductivity at relatively low cost. 相似文献
13.
I. M. Pohrelyuk V. M. Fedirko O. I. Yas’kiv Dong-Bok Lee O. V. Tkachuk Chen Li 《Materials Science》2009,45(4):562-570
We investigate the influence of the nonstoichiometry (the degree of completeness) of titanium nitride TiN on the degree of
its modification with oxygen. The completeness of titanium nitride was controlled by changing the nitriding temperature, nitriding
time, and partial nitrogen pressure. It is shown that as the completeness of titanium nitride decreases, which leads to an
increase in the intensity of oxynitriding, and as the nitrogen content in the ternary compound TiN
x
O1 – x
decreases, the level of surface hardening of titanium alloys after oxynitriding diminishes. 相似文献
14.
An ion beam source was used to deposit silicon nitride films by reactive sputtering a silicon target with an Ar+N2 beam. The nitrogen fraction in the sputtering gas was 0.05 to 0.80 at a total pressure of 6 to 20×10?5 torr. The ion beam current was 50 mA at 500 V. A rate of deposition of about 2 nm min?1 (0.12 μm h?1) was found, and the spectra indicated that Si3N4 was obtained for a fraction of nitrogen higher than 0.50. However, the AES spectra also indicated that the sputtered silicon nitride films were contaminated with oxygen and carbon and contained significant amounts of iron, nickel, and chromium, most probably sputtered from the holder of the substrate and target. 相似文献
15.
As-fired aluminium nitride (AIN) substrates with smooth and uniform surface have been developed by green sheet and firing technology. The effect of setting for firing on surface roughness was investigated. AIN substrates were fabricated by pressureless sintering of green sheets piled up and sandwiched between AIN plates in an AIN crucible. The thermal conductivity, surface roughness and bending strength of the substrate sintered at 1770 °C for 2 h under a pressure of 1 MPa nitrogen were 194 Wm–1 K–1, 0.15 (m and 353 MPa, respectively. 相似文献
16.
The defect structure of acceptor (Al or Cr)-doped polycrystalline calcium titanate was investigated by measuring the oxygen partial pressure dependence (at 10° to 10–18 atm) of the electrical conductivity at 1000 and 1050° C. The observed electrical conductivity data were proportional to
for the oxygen pressure range < 10–10 atm and proportional to
for the oxygen pressure range ( 10–7 atm. The conductivity values were observed to increase with the acceptor concentration in the p-type region with the shift in the conductivity minima towards lower oxygen partial pressure. The absolute value of the electrical conductivity in the acceptor-doped samples were lower in the n-type region compared to the values in the undoped CaTiO3. Aluminium and chromium were found to be equally effective in acting as acceptor impurities in CaTiO3. The defect chemistry of CaTiO3 is dominated by the added acceptor impurities for the entire oxygen partial pressure range used in this investigation. 相似文献
17.
A number of zirconia-based materials show promise as electrode materials in magnetohydrodynamic (MHD) generators. As a part of an exploratory programme to find suitable materials for graded electrode applications in MHD generators, partially stabilized and fully stabilized sintered ceramic materials are prepared and characterized. The oxygen ion transference number t
ion(O2–) and electrical conductivity of this material are measured up to 1670 K in the oxygen partial pressure range 1 to 10–6 atm. The activation energies for conduction are determined. The electrical properties of this material are characterized by mixed conduction, ionic and electronic. The observed conductivity data are explained in terms of the defect equilibrium reactions between tetravelent Ce4+ and trivalent Ce3+ ions. 相似文献
18.
Jijian Xu Feng Xu Meng Qian Fangfang Xu Zhanglian Hong Fuqiang Huang 《Advanced materials (Deerfield Beach, Fla.)》2017,29(31)
Conductive carbon nitride, as a hypothetical carbon material demonstrating high nitrogen doping, high electrical conductivity, and high surface area, has not been fabricated. A major challenge towards its fabrication is that high conductivity requires high temperature synthesis, but the high temperature eliminates nitrogen from carbon. Different from conventional methods, a facile preparation of conductive carbon nitride from novel thermal decomposition of nickel hydrogencyanamide in a confined space is reported. New developed nickel hydrogencyanamide is a unique precursor which provides self‐grown fragments of ?N?C?N? or N?C? C?N and conductive carbon (C‐sp2) catalyst of Ni metal during the decomposition. The final product is a tubular structure of rich mesoporous and microporous few‐layer carbon with extraordinarily high N doping level (≈15 at%) and high extent of sp2 carbon (≈65%) favoring a high conductivity (>2 S cm?1); the ultrahigh contents of nongraphitic nitrogen, redox active pyridinic N (9 at%), and pyrrolic N (5 at%), are stabilized by forming Ni? N bonds. The conductive carbon nitride harvests a large capacitance of 372 F g?1 with >90% initial capacitance after 10 000 cycles as a supercapacitor electrode, far exceeding the activated carbon electrodes that have <250 F g?1. 相似文献
19.
Ionic and electronic conductivity and compressive creep of hot-pressed polycrystalline acceptor-dominated Al2O3 were measured as a function of oxygen partial pressure and grain size varying from 3 to 200 m. Hole conduction shows a slight preference for grainboundaries; ionic conduction is slightly hindered by grain boundaries, indicating that fast oxygen grain-boundary diffusion involving charged species does not occur. Conductivity and creep are accounted for on the basis of a model in which there is fast grain-boundary migration by a neutral oxygen species. 相似文献
20.
J.-H. Lee S. M. Yoon B.-K. Kim H.-W. Lee H. S. Song 《Journal of Materials Science》2002,37(6):1165-1171
The electrical conductivity of CeO2-ZrO2 system was measured as functions of the temperature and oxygen partial pressure and of the composition. The ionic conduction was prevailing in the ZrO2 rich phase due to the increase of ionic defect concentration via homovalent doping effect. The enhancement of n-type electronic conductivity was observed in intermediate and CeO2 rich phase compared with pure CeO2, which originated either from homovalent doping effect or increase of electronic mobility due to the change of transport mechanism. 相似文献