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1.
The application of an external dc electric field E = 5 kV/cm during the solution heat treatment (SHT) of AA6022 at 475–552°C increased the as-quenched resistivity. An increase continued throughout subsequent natural aging, and there occurred an increase in the tensile properties for the T4 temper. The increase in yield and tensile strength produced by the electric field applied during the SHT is equivalent to a reduction of 10–25°C in the SHT temperature. A thermodynamic analysis of the results indicated that the field reduced both the enthalpy H
s and entropy S
s of solution, giving a reduction in Gibbs free energy G
s, and in turn an increase in solubility of the alloying constituents. 相似文献
2.
The solid-state thermal behaviour of -Al2O3 doped with 10 mol% Cr (oxide) was studied with respect to phase-transition behaviour and the co-ordination of the dopant Cr cations. A series of transformations: -Al2O3 -Al2O3 -Al2O3 -Al2O3 was observed for Cr2O3-doped alumina samples between 500 °C and 1100 °C. Rapid grain growth occurred at temperatures close to 1100 °C. The electron spin resonance (ESR) spectra for the sample heat-treated at 500 °C corresponded to the resonance of -Cr3+ in an amorphous Cr oxide impregnated onto the - and -alumina support. The change of ESR spectrum indicated the existence of Cr3+, suggesting the formation of a solid solution with the same structures as -Al2O3 and/or -Al2O3 at 800–1000 °C. The evaluation of catalytic activities for model exhaust was performed under lean-burn (an excess of oxygen) condition of air/fuel ratio A/F = 18 and space velocity SV = 100 000 h–1 . The modified Al2O3 catalyst heat-treated at 1000 °C in air showed removal conversion of 100% for hydrocarbon (C3H6), 92% for CO and 5% for NO at 550 °C. Present results suggest that Cr-modification to Al2O3 leads to catalytic improvement with good thermal durability. 相似文献
3.
An Al-6061 metal matrix composite, reinforced with 10 vol % Al2O3 particulates, was subjected to equal-channel angular (ECA) pressing at room temperature to a total strain of 5. It is shown that the intense plastic straining introduced by ECA pressing reduces the grain size from 35 m to 1 m and this leads to an increase in the microhardness measured at room temperature. Inspection revealed some limit cracking of the larger Al2O3 particulates as a consequence of the ECA pressing. Tensile testing after ECA pressing gave a maximum ductility of 235% at a temperature of 853 K when testing at strain rates from 10–4 to 10–3 s–1. It is suggested that high strain rate superplasticity is not achieved in this material after ECA pressing due to the presence of relatively large Al2O3 particulates. 相似文献
4.
The a.c. and d.c. electrical conductivities of some hot-pressed polycrystalline nitrogen ceramics have been measured between 400 and 1000° C. The materials examined were Si3N4, 5.0% MgO/Si3N4 and two sialons, Si(6–z) · Al
z
· O
z
· N(8–z) having z 3.2 and z 4.0 respectively. The electrical behaviour of all the materials showed similar general features. The d.c. conductivities were about 10–10 –1 cm–1 at 400° C and rose to between 10–6 and 10–5 –1 cm–1 at 1000° C. The a.c. Data, taken over the frequency range 15 Hz to 5 kHz showed that below about 500° C the a.c. conductivity (
a.c.) varied with frequency as
a.c.
s
where 0.7
d.c.) agreed well with the relation
d.c. = A exp(–B/T
1/4). Above 700° C both the a.c. and d.c. conductivities followed log T
–1. Hall effect and thermoelectric power measurements enabled the Hall mobility to be estimated as less than 10–4 cm2 V–1 sec–1 at 400° C and showed that the materials were all p-type below 900° C and n-type above 900° C. The electrical properties of all four materials are consistent with the presence of a glassy phase. 相似文献
5.
V. Buscaglia M. Alvazzi Delfrate M. Leoni C. Bottino P. Nanni 《Journal of Materials Science》1996,31(7):1715-1724
The formation of Al2(1–x)Mg
x
Ti(1+x)O5 solid solutions from Al2O3-TiO2-MgAl2O4 powder mixtures of 1 m particle size and moderate purity has been studied at 1300°C for different final composition values: x=0 (pure Al2TiO5), 10–3, 10–2 and 10–1. Analysis of the kinetic data and microstructural observation indicates that MgAl2O4 affects the mechanism of Al2TiO5 formation by providing active nuclei for the growth of the new phase. These nuclei are probably constituted by Mg0.5AlTi1.5O5, i.e. the equimolar Al2TiO5-MgTi2O5 solid solution, and are formed by reaction between MgAl2O4 and TiO2 at temperatures above 1150 °C. As the value of x increases, the number of titanate particles per unit volume accordingly increases and the conversion of the original oxides is faster. At values of x10–2, the prevailing mechanism is the nucleation and growth of Al2TiO5 nodules for fractional conversion up to 0.8. Further conversion of the residual Al2O3 and TiO2 particles dispersed into the titanate nodules is slower and controlled by solid-state diffusion through Al2TiO5. At x=0.1, a large number of nucleation sites is present, and solid-state diffusion through Al2TiO5 becomes important even in the initial stage of reaction, as the diffusion distances are strongly reduced. The study of Al2TiO5 formation under non-isothermal conditions in the temperature range 1250–1550°C shows that reaction proceeds between 1300 and 1350 °C for x=0.01 and between 1250 and 1300 °C for x=0.1. Densification of the titanate becomes important at temperatures above 1300°C for x=0.1, but only above 1450 °C for x=0.01. 相似文献
6.
Haematite (-Fe2O3) was reduced to magnetite (Fe3O4) under hydrothermal conditions, by the use of an autoclave into which hydrogen gas was able to be admitted. The stable reduced conditions for magnetite precipitation were produced even at 100 °C. In acid and neutral mineralizers, the rate of haematite reduction was small below 300 °C and increased with an increase in reaction temperature above 300 °C. Magnetite crystals obtained in these solutions were large and faceted octahedrons in shape. Alkaline mineralizers except NaOH solution accelerated the reduction at low temperatures below 300 °C and gave small magnetite crystals. The reduction of haematite to magnetite was completed even at 150 °C in concentrated CsOH solution (1.0 mol l–1). 相似文献
7.
Microsphere-filled lightweight calcium phosphate cements 总被引:1,自引:0,他引:1
The incorporation of inorganic and organic microsphere fillers into calcium phosphate cement (CPC) to produce lightweight cementitious materials that could be used under hydrothermal conditions at high temperatures between 200 and 1000 °C was investigated. An aluminosilicate based hollow microsphere, with a density of 0.67 gcm–3 and a particle size of 75–200 m, was the most suitable having a low slurry density of 1.3 gcm–3, and a compressive strength greater than 6.89 M Pa. This microsphere-filled lightweight CPC exhibited the following characteristics: 1. after autoclaving at 200 °C, amorphous ammonium calcium orthophosphate (AmCOP) salt and Al2O3·xH20 gel phases, formed by the reaction between calcium aluminate cement and an NH4H2P04 based fertilizer, were primarily responsible for the development of strength; 2. at a hydrothermal temperature of 300 °C, the microsphere shell moderately reacted with the CPC to form an intermediate reaction product, epistilbite (EP), while crystalline hydroxyapatite (HOAp) and boehmite (BO) were yielded by the phase transformations of AmCOP and Al2O3·xH2O, respectively; 3. at an annealing temperature of 600 °C, the HOAp phase remained in the cement body, even though an EP anorthite (AN) phase transition occurred; 4. at 1000 °C, the phase conversion of HOAp into whitlockite was completed, while the AN phase was eliminated; and 5. the microsphere demonstrated excellent thermal stability up to temperatures of 1000 °C.This work was performed under the auspices of the US Department of Energy, Washington, DC, under Contract No. DE-AC02-76CH00016. 相似文献
8.
V. K. Srivastava 《Journal of Materials Science》1986,21(10):3638-3642
Glass fibre-reinforced plastic (GRP) cylinders are increasingly used for highly stressed structural elements. The higher the demands on the materials, the higher are the fault detection requirements to be met by non-destructive materials testing methods. Acousto-ultrasonics is a valuable aid for the non-destructive evaluation of GRP composite materials, because it may be the answer to evaluating effects of subtle defects in composites. The aim of the research is to evaluate the burst pressure of GRP cylinders by acousto-ultrasonics techniques. The theoretical results have been found to be in good agreement with the experimental values. Hence the results strongly suggest that stress wave factor measurements can be exploited successfully to predict burst pressure of GRP cylinders.Nomenclature
P
Internal pressure, kgf cm–2
-
d
Internal diameter, cm
-
t
Thickness of cylinder, cm
- (N
,N
,N
)
Resultant forces, kgf
- (M
,M
,M
)
Moments, kg cm
- [A]
Extensional stiffness matrix
- [B]
Bending stretching coupling matrix
- [D]
Flexural stiffness matrix
- (
0
,
0
,
0
)
Midplane strains
- (k
,k
,k
)
Curvatures
-
n
Number of laminae
-
Z
Distance from midplane, cm
-
u
Ultimate tensile strength of GRP composite, kg cm–2
-
S
W
Stress wave factor
-
m
Material parameter
-
Filament winding angle 相似文献
9.
The thermal expansion behavior of three epoxy-fiberglass composite specimens was measured from 20 to 120°C (70 to 250°F) using a fused quartz push-rod dilatometer. Billets produced by vacuum-impregnating layers of two types of fiberglass cloth with an epoxy were core-drilled to produce cylindrical specimens. These were used to study expansion perpendicular and parallel to the fiberglass layers. This type of composite is used to separate the copper conductors that form a helical field coil in the Advanced Toroidal Facility, a plasma physics experiment operated by the Fusion Energy Division at Oak Ridge National Laboratory. The coil is operated in a pulsed mode and expansion data were needed to assess cracking and joint stresses due to expansion of the copper-composite system. The dilatometer is held at a preselected temperature until steady state is indicated by stable length and temperature data. Before testing the composite specimens, a reliability check of the dilatometer was performed using a copper secondary standard. This indicated thermal expansion coefficient () values within ±2% of expected values from 20 to 200°C. The percentage expansion of the composite specimen perpendicular to the fiberglass layers exceeded 0.8% at 120°C, whereas that parallel to the fiberglass layers was about 0.16%. The expansion in the perpendicular direction was linear to about 70°C, with an value of over 55×10–6 °C–1. Anomalous expansion behavior was noted above 70°C. The expansion in the direction parallel to the fiberglass layers corresponds to an value of about 15×10–6 °C–1. The lower values in the parallel direction are consistent with the restraining action of the fiberglass layers. The values decreased with the specimen density and this is consistent with literature data on composite contraction from 20 to –195°C.Nomenclature
Thermal expansion coefficient, °C–1
-
L
L(T
2)–L(T
1), cm
-
T
T
2–T
1, °C
-
L
0
Length at room temperature, cm
-
L(T
i
)
Length at temperature T
i
, cm
-
T
i
Temperature, °C
-
T
0
Room temperature, °C
Paper presented at the Ninth International Thermal Expansion Symposium, December 8–10, 1986, Pittsburgh, Pennsylvania, U.S.A. 相似文献
10.
B. Gillot M. El Guendouzi A. Rousset P. Tailhades 《Journal of Materials Science》1986,21(8):2926-2932
During oxidation in air of finely-grained manganese-substituted magnetites (Mn
0.8x
2+
Fe
1–0.8x
3+
)A– (Fe
1+0.6x
3+
Fe
1–0.8x
2+
Mn
0.2x
3+
)BO
4
2–
(A=tetrahedral, B=octahedral) the temperature dependence of the electrical conductivity over a temperature range of 100 to 700° C was investigated. Below 500° C the evolution of electrical conductivity might be closely associated with the position and nature of cations in the spinel lattice. The profile of the =f(t) curves show that the mechanism of electrical conduction in the temperature range 150 to 300° C can be explained in terms of the oxidation of Fe2+ to Fe3+ ions at octahedral sites. For the temperature range 300 to 400° C the conductivity involves the hopping of electrons from tetrahedral-site Mn2+ ions to tetrahedral-site Mn3+ ions. Above 500° C the oxidation of Mn2+ ions leads to an increase in conductivity with the generation of new phases of -Fe2O3, Mn2O3 and -(MnFe)2O3. 相似文献
11.
The oxidation of dispersed aluminium oxynitride particles in an alumina matrix has been studied. The kinetics law of this reaction is linear and the activation energy is 420±40 kJ mol–1 (100±10 kcal mo–1). A-alumina layer is formed and leads to-alumina above 1200° C. The-alumina formation produces surface compressive stresses, and thus the mechanical properties (
f, HV) are improved. We have proved that the formation of-alumina in the Al2O3-AION composite can lead to the best properties for this ceramic. A-alumina layer has a very interesting effect on the wear resistance of this material. 相似文献
12.
Accurate lattice parameters of strontium tungstate, an isotype of scheelite, have been determined as a function of temperature by the X-ray powder method in the temperature range 28 to 355° C. Both the lattice parameters are found to increase with temperature. Using these data, the two coefficients of thermal expansion,
a
along the a-axis and
a
along the c-axis, have been calculated. The temperature dependence of the coefficients could be expressed by the following equations:
a
=5.88×10–6–25.63×10–10
T + 59.49×10–12
T
2
c
=13.20×10–6–18.18×10–10T+71.45×10–12
T
2. Here T is the temperature in °C. 相似文献
13.
The ageing (1300 °C for 1–300 h) dependence of the microstructure of the metastable tetragonal (t-) ZrO2 (plasma-sprayed Y-PSZ with 5 mol% Y2O3) in the sintered (1300 °C, 5 h) t-ZrO2/NiO (10 mol%) composite was studied by transmission electron microscopy. Short-term (10 h) ageing caused incomplete decomposition of t-ZrO2 into tweed assemblages containing t-ZrO2 relics and tetragonal (t-) ZrO2 precipitates in the cubic (c-) ZrO2 matrix. The t-ZrO2 relics retained anti-phase domain boundary (APB) and primary deformation twins, but no secondary deformation twins. Further ageing (e.g. up to 100 or 300 h) caused growth of the twin variants of t-ZrO2 with {101} habit plane. The large t-ZrO2 variants transformed directly into m-ZrO2 twins, but not into t-ZrO2 colonies. In addition to the relics in the aged samples, t-ZrO2 with APB may also form locally from a solute-redistributed c-ZrO2 by slow cooling. 相似文献
14.
M. S. Setty 《Journal of Materials Science》1989,24(11):4120-4127
The sheet resistance of Cd2SnO4 thick films was reduced from 15580 to 0.09 k with respect to dopant concentration and peak firing temperature (600 to 900° C). Distinct colour changes were observed in these films. The inorganic binder introduced an impurity which greatly induce changes in its electrical properties. The Arrhenius relation (logR–103/T) generally indicated slopes of 2 to 3 for all the compositions of Cd2–x
Pb
x
SnO4 (x=0.002, 0.01, 0.02, 0.04 and 0.1). The donor ionization energies (E
d) varied from 0.01 to 0.76 eV. Resistance measurements during heating-cooling cycles indicated the possible presence of structural defects such as oxygen vacancies and cadmium interstitials. The oxidation of dopant (Pb2+Pb4++2e) contributed in a major way to the overall conductivity. Scanning electron micrographs showed a progressive network formation due to sintering, thus contributing to the carrier mobility. 相似文献
15.
Internal modes of vibrations are studied here at different temperatures (27–800°C) and in the frequency range 200–4000 cm–1 through heat treatment. The baseline method was used. The strong bands of SiO4 tetrahedra in this glass show an increase in absorbance at high temperature (600–800°C). The deformation of SiO4 tetrahedra is investigated. This is found to depend on the ionic radius of the divalent metal oxide introduced, and the coordination number of the cation. Also from a study of the temperature dependence of the relative integrated intensity of the modes 600–800 and 850–1450 cm–1, the relaxation time and rotational energy barrier of the glasses selected indicate that the glassy phases are transformed to crystalline phases at 500°C. 相似文献
16.
Measurement of the Surface Tension of Undercooled Liquid Ti90Al6V4 by the Oscillating Drop Technique
The surface tension of liquid Ti90Al6V4 was measured. The samples have been processed containerlessly by electromagnetic levitation, which allows the handling of highly reactive materials and measurements in the undercooled temperature region. The use of digital image processing allows the identification of oscillation modes and calculation of the surface tension from the l = 2 and m = 0, m = 2 oscillation modes. A linear least squares fit to the data showed the following temperature dependence:
= 1.389 ± 0.09 – 9.017 × 10–4 ± 5.64 × 10–5(T – 1660°C) [Nm–1] 相似文献
17.
A new compound of aluminium boron carbide, Al8B4C7, has been successfully synthesized. Single-crystal and powder X-ray crystallographic data on Al8B4C7 are given, and the possible space group is identified as P63 cm, P¯6c2, or P63/mcm. Powder X-ray diffraction lines are indexed in the 2-range from 10° to 110°. The unit cell dimensions obtained from a least-square fit computer program are: a=5.906±0.002 Å, c=15.901±0.001 Å, V=480.43±0.03 Å3. In addition, the possibility of a wide range variance of boron content in this compound is denied. 相似文献
18.
O. V. Al’myasheva E. N. Korytkova A. V. Maslov V. V. Gusarov 《Inorganic Materials》2005,41(5):460-467
Thermodynamic analysis of phase equilibria in the Al2O3-H2O system at temperatures from 120 to 380°C and pressures from 1 to 70 MPa is carried out, and the dehydration of aluminum hydroxide under hydrothermal conditions is studied experimentally. The results indicate that -AlOOH (boehmite), which commonly appears in experimental phase diagrams, is a nonequilibrium phase in these temperature and pressure ranges. The dehydration rate and mechanism are shown to strongly depend on the crystallinity of the parent aluminum hydroxide and the pressure in the hydrothermal system.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 5, 2005, pp. 540–547.Original Russian Text Copyright © 2005 by Almyasheva, Korytkova, Maslov, Gusarov. 相似文献
19.
The irradiation hardening of polyethylene (PE) crystals is explained in terms of the intersection and interaction between cross-links and dislocations. The elastic energies and forces of interaction between cross-links and the dislocations responsible for the various plastic deformation modes are calculated using a force dipole model of a cross-link and the strain field of the dislocation. The elastic energies of interaction are in all cases less than 0.7 eV (1.12×10–19 J) and they are greater for edge than for screw dislocations. The hardening which arises from the direct intersections is calculated using a Morse potential model for the cross-link strength, and it is found that these interactions involve energies of the order of 3.6 eV (5.76×10–19 J). From these results it is concluded that at 0 K both types of interaction produce similar hardening. However, since the elastic interaction energies are small, the hardness of cross-linked PE crystals at moderate temperatures is due solely to direct intersections of cross-links and dislocations. The strongest interactions take place between cross-links and those dislocations which produce chain-axis slip and this explains why this mode of deformation is readily suppressed by irradiation. The forces of interaction between cross-links and twin dislocations are not negligible, but since their interaction energies are of the order of 0.1 eV (0.16×10–19 J), twinning deformation, at moderate temperatures, should not be affected by irradiation. By combining all the possible deformation modes, the relationship
c=41/2, is derived for the increase in yield stress,
c (GPa), in terms of the atomic concentration of cross-links,, provided that these are uniformly distributed in the crystal. 相似文献
20.
We studied the structural and optical properties of (Ba, Sr)TiO3 (BST) films deposited on the transparent substrates at various temperatures of 350–650°C and annealed at 450–650°C. Improved crystallization can be observed on 650°C annealed film whose substrate temperature is 350°C. The refractive index increased from 2.17 to 2.59 at =410 nm for the BST films deposited at 350–650°C and it varied from 2.17 to 2.25 after annealing up to 650°C. In addition, the refractive-index dispersion data related to the short-range-order structure of BST films obeyed the single-oscillation energy model. The indirect energy gap of the films deposited on Al2O3 and quartz substrates was found to be about 3.5 eV. According to the analysis of reflectance data, the optical inhomogeneity of films can be reduced by depositing the films at intermediate temperatures 450–550°C. 相似文献