Examination of CaO-Dy2O3 for potential use as a high-temperature transformation toughening System

1988 ◽  
Vol 46 ◽  
pp. 790-791
Author(s):  
M. M. Fleming ◽  
W. M. Kriven
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
Transformation Toughening ◽  
Stabilized Zirconia ◽  
Two Phase ◽  
Volume Increase ◽  
Partially Stabilized Zirconia ◽  
Temperature Transformation ◽  
Fast Quenching ◽  
Potential Use

Similarities exist between the tetragonal to monoclinic transformation of ZrO2 and the monoclinic (B) to cubic (C) transformation of Dy2O3. On cooling the transformation occurs at 1950°C and is accompanied by an 8 % volume increase which causes shattering of bulk specimens. The transformation can be suppressed, however, by minor additions of CaO. An attempt was made to fabricate a “PSD” analogue to partially stabilized zirconia (PSZ).As-received and chemically precipitated powders of pure Dy2O3 were mixed with CaO (0 to 25 mol%), uniaxially and cold isostatically pressed, sealed in small Mo crucibles and sintered at various temperatures (1900° or 1650°C) and times before cooling or subsequent annealing treatments. Some pellets were annealed in the two phase (B + C) region at 1700°C for 2 hours before quenching. Specimens were examined by XRD, TEM, EDS, HVEM, and STEM.A fast quenching in combination with the =8 mol% CaO additions were found to be essential for retention of the high temperature B phase down to room temperature.

TEM Studies of modulated structures in the monoclinic (B) phase Of CaO-stabilized Dy2O3

1988 ◽  
Vol 46 ◽  
pp. 580-581
Author(s):  
Y. J. Kim ◽  
W. M. Kriven
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
Rapid Quenching ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Modulated Structure ◽  
Volume Increase ◽  
Modulated Structures ◽  
Temperature Transformation ◽  
Intermediate Rate

Dysprosia (Dy2O3) undergoes a monoclinic (B) to cubic (C) transformation on cooling through 1950°C, which is accompanied by an 8% volume increase and shattering. Minor additions of CaO combined with rapid quenching, however, are able to stabilize the high temperature phase down to room temperature. The similarities with the tetragonal to monoclinic transformation of ZrO2 suggest that it may be a possible high temperature transformation toughener. A sample of 8 mol% CaO was sintered at 1900°C and cooled at an intermediate rate. About 90% of B phase, which invariably had a modulated structure, was retained.From TEM studies of this B phase, it was shown that most of the selected area diffraction (SAD) patterns in different orientations consisted mainly of three types of reflections: (i) major reflections from the monoclinic lattice; (ii) satellites associated with each major reflection; and (iii) split reflections at the middle of the framework of major reflections. Depending on the orientation, (ii) and (iii) were accompanied by twinned reflections. Fig. 1 displays (i) and (iii) type reflections.

Deformation of calcia-stabilized zirconia single crystals

1984 ◽  
Vol 42 ◽  
pp. 400-401
Author(s):  
C.E. Voegele-Kliewer ◽  
T.E. Mitchell ◽  
A.H. Heuer
Keyword(s):  
High Temperature ◽  
Single Crystals ◽  
Room Temperature ◽  
Fluorite Structure ◽  
Phase Region ◽  
Stabilized Zirconia ◽  
Two Phase

This study is an investigation of slip in calcia-stabilized zirconia (CSZ) single crystals and the resulting dislocation substructures. CSZ has the high temperature cubic fluorite structure when cooled rapidly to room temperature, but it can be aged in the two phase region to produce either tetragonal precipitates (hypoeutectoid) or ϕ1 precipitates (hypereutectoid). In the present study, the effect of ageing to produce tetragonal precipitates prior to deformation was also examined.

Low Temperature Co-fired Ceramics Processing Parameters Governing the Performance of Miniaturized Force Sensors

2012 ◽  
Vol 2012 (CICMT) ◽  
pp. 000411-000416
Author(s):  
Michael Weilguni ◽  
Walter Smetana ◽  
Goran Radosavljevic ◽  
Johann Nicolics ◽  
Werner Goebl ◽  
...  
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Room Temperature ◽  
Processing Parameters ◽  
Gauge Factor ◽  
Force Sensors ◽  
Stabilized Zirconia ◽  
Temperature Coefficient Of Resistance ◽  
Microscope Images ◽  
Resistive Thick Film

For the development of miniaturized force sensors, built up in ceramics technology with piezo-resistive principle, the compatibility of the piezo-resistive thick-film paste with the substrate and termination paste has to be verified. This paper deals with the compatibility of the ESL 3414-A piezo-resistive paste on HTCC (high temperature co-fired ceramics) substrates (alumina as reference and the partially stabilized zirconia tape ESL 42013-A) as well as on LTCC (low temperature co-fired ceramics) substrates (Heraeus AHT01-005, AHT08-047, CT707; and CeramTec GC) under different manufacturing conditions. The sheet resistance at room temperature, the longitudinal gauge factor at room temperature and the temperature coefficient of resistance have been measured. The results are compared with microscope images showing cracks in distinct cases. Finally, the compatibility and thus applicability of the ESL 3414-A on the investigated substrates is evaluated.

scholarly journals The High-Temperature Transformation from 1T- to 3R-LixTiS2 (x = 0.7, 0.9) as Observed in situ with Neutron Powder Diffraction

2015 ◽  
Vol 229 (9) ◽  
Author(s):  
Dennis Wiedemann ◽  
Suliman Nakhal ◽  
Anatoliy Senyshyn ◽  
Thomas Bredow ◽  
Martin Lerch
Keyword(s):  
High Temperature ◽  
Powder Diffraction ◽  
Electrode Material ◽  
Room Temperature ◽  
Lithium Ion ◽  
Neutron Powder Diffraction ◽  
Titanium Disulfide ◽  
Temperature Transformation

AbstractLayered titanium disulfide is used as lithium-ion intercalating electrode material in batteries. The room-temperature stable trigonal 1T polymorphs of the intercalates Li

The Potential of Electronic High Temperature Devices Based Upon Polymer Derived Ceramics

2005 ◽  
Author(s):  
Weixing Xu ◽  
Jayanta Kapat ◽  
Louis C. Chow ◽  
Linan An ◽  
Wenge Zhang
Keyword(s):  
Electrical Conductivity ◽  
High Temperature ◽  
Room Temperature ◽  
Polymer Derived Ceramics ◽  
Micro Parts ◽  
Varied Composition ◽  
Potential Use ◽  
Lithography Technique ◽  
High Temperature Gas ◽  
Good Agreement

In this paper, we describe the potential use of polymer-derived ceramics (PDCs) for micro-sensors for high-temperature gas turbine applications. PDCs have several unique properties such as ease of microfabrication, excellent mechanical, materials and thermal properties, and tunable electrical conductivity. The electrical conductivity of PDCs with varied composition is measured as a function of temperature from room temperature upon to 700°C. Our results reveal that with suitable doping, the electrical conductivity could be controlled from insulating to semiconducting. Next, we measure the cure depth of the precursors as a function of UV intensity and exposure time. A model is developed to predict the cure depth as a function of photoinitiator concentration and light intensity. Good agreement between theory and experimental data is obtained. Finally, a few typical micro parts are fabricated by lithography technique.

Effect of Iron Substitution on the High-temperature Properties of Sm(Co,Cu,Ti)z Permanent Magnets

2001 ◽  
Vol 674 ◽  
Author(s):  
Jian Zhou ◽  
Ralph Skomski ◽  
David J. Sellmyer ◽  
Wei Tang ◽  
George C. Hadjipanayis
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
Permanent Magnets ◽  
Site Occupancy ◽  
Positive Temperature Coefficient ◽  
Positive Temperature ◽  
X Ray Diffraction ◽  
Two Phase ◽  
X Ray ◽  
Iron Substitution

ABSTRACTRecently, Ti-substituted Sm-Co permanent magnets have attracted renewed attention due to their interesting high-temperature coercivity. Our presentation deals with the effect of iron substitutions on the magnetic properties of the materials. X-ray diffraction shows that the investigated Sm(Co,Fe,Cu,Ti)z materials (z = 7.0 - 7.6) are two-phase magnets, consisting of 1:5 and 2:17 regions. The iron content affects both the coercivity and the magnetization. Depending on composition and heat treatment, some samples show a positive temperature coefficient of the coercivity in the temperature range from 22 °C to 550 °C. Moderate amounts of iron enhance the room-temperature coercivity. For example, the room-temperature coercivity of Sm(Co6.0Fe0.4Cu0.6Ti0.3) is 9.6 kOe, as compared to 7.6 kOe for Sm(Co6.4Cu0.6Ti0.3). At high temperatures, the addition of Fe has a deteriorating effect on the coercivity, which is as high as 10.0 kOe at 500 °C for Sm(Co6.4Cu0.6Ti0.3). The room-temperature magnetization increases on iron substitution, from 73 emu/g for Sm(Co6.4Cu0.6Ti0.3) to 78 emu/g for Sm(Co6.0Fe0.4Cu0.6Ti0.3). The observed temperature dependence is ascribed to the preferential dumbbell-site occupancy of the Fe atoms.

Neue Arsenide mit ThCr2Si2- oder einer damit verwandten Struktur: Die Verbindungen ARh2As2 (A: Eu, Sr, Ba) und BaZn2As2 / New Arsenides with ThCr2Si2-type or Related Structures: The Compounds ARh2As2 (A: Eu, Sr, Ba) and BaZn2As2

2007 ◽  
Vol 62 (2) ◽  
pp. 155-161 ◽  
Author(s):  
Andrea Hellmann ◽  
Anke Löhken ◽  
Andreas Wurth ◽  
Albrecht Mewis
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
Two Phase ◽  
Atomic Size ◽  
X Ray ◽  
Β Phase ◽  
Vertex Sharing ◽  
3D Network ◽  
Ray Methods ◽  
High Temperature Modification

Four new arsenides of rhodium and zinc were prepared by heating mixtures of the elements at high temperatures (1000 - 1200 °C) and investigated by single crystal X-ray methods. EuRh2As2 (a = 4.067(1), c = 11.319(2) Å ) and BaRh2As2 (a = 4.053(1), c = 12.770(3) Å ) crystallize with the well-known ThCr2Si2-type (I4/mmm; Z = 2). Due to the rigid layers of RhAs4 tetrahedra, and to the atomic size of europium and barium, the As-As distances between the layers with values of 2.97 and 3.66 Å, respectively, are very long. SrRh2As2 is polymorphic and undergoes two phase transitions at about 190 and 282 °C. Main features of the three crystal structures are also layers of RhAs4 tetrahedra. At room temperature α-SrRh2As2 (a = 5.676(1), b = 6.178(2), c = 11.052(2) Å ) probably crystallizes with the BaNi2Si2-type (Cmcm; Z = 4), whereas β -SrRh2As2 (a = 5.760(3), b = 6.067(4), c = 11.264(5) A° , Fmmm, Z = 4) forms a new orthorhombically distorted variant of the ThCr2Si2-type. Single crystals grown in a flux of lead and quenched at high temperature show that the γ -phase (a = 4.112(1), c = 11.431(6) Å ) crystallizes with the ThCr2Si2-type. The same is true for the high temperature modification of BaZn2As2 (β -phase; a = 4.120(1), c = 13.578(1) Å ), whereas the already known α-BaZn2As2 forms the α-BaCu2S2-type (Pnma; Z = 4) consisting of a 3D-network of edge- and vertex-sharing ZnAs4 tetrahedra with Ba atoms in the voids of this network.

Precipitation in Partially-Stabilized Zirconia

1976 ◽  
Vol 34 ◽  
pp. 628-629
Author(s):  
D. L. Porter ◽  
A. H. Heuer
Keyword(s):  
Phase Region ◽  
Precipitate Size ◽  
Tetragonal Symmetry ◽  
Stabilized Zirconia ◽  
Two Phase ◽  
Slow Cooling ◽  
Partially Stabilized Zirconia ◽  
Large Particles ◽  
Solid Solution Matrix ◽  
Solution Matrix

Precipitation in commercial partially-stabilized zirconia (PSZ) has been studied in order to facilitate "alloy design" in these materials. The commercial material used in this study is a 2.8 wt. % MgO alloy and has the cubic flourite structure at its sintering temperature. Upon cooling, a nearly MgO-free ZrO2 phase with tetragonal symmetry precipitates, which on further cooling inverts martensitically to a phase with monoclinic symmetry. At room temperature, commercial PSZ's therefore consist of a cubic solid solution matrix containing monoclinic precipitate; size, morphology, and distribution of the precipitate phase strongly influence mechanical properties.Figures I and II show typical microstructures of the material as it is commercially produced. Both large and small precipitates are present (Figure I), indicative of precipitation over a range of temperatures during slow cooling through the two-phase region. Figure II shows heavily-twinned monoclinic particle; such large particles produced during commercial fabrication are believed to be deleterious to the mechanical behavior.

HREM studies of modulated structures of the monoclinic (B) phase in CaO-Dy2O3 solid solutions

1990 ◽  
Vol 48 (4) ◽  
pp. 218-219
Author(s):  
Y. J. Kim ◽  
W. M. Kriven
Keyword(s):  
High Temperature ◽  
Solid Solutions ◽  
Room Temperature ◽  
Rapid Quenching ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Volume Increase ◽  
Normal Lattice ◽  
Modulated Structures ◽  
Moderate Resolution

Dysprosia (Dy203) undergoes a monoclinic (B) to cubic (C) transformation on cooling through 1860°C, which is accompanied by an 8% volume increase and shattering. Minor additions of CaO combined with rapid quenching, however, are able to stabilize the high temperature phase at room temperature, which is incommensurately modulated. TEM studies revealed the existence of three different modulations: q1 (001-type; λ ≈ 9.0 Å), q2 (200-type; λ ≈ 7.5 Å), and q3 (λ ≈ 40 Å). HREM studies on modulated specimens have been conducted to search for the origin of these modulated microstructures.Fig. 1 shows characteristic modulations in the [010]B orientation. Whereas both q1 and q2 look like normal lattice fringes in moderate resolution TEM images, HREM images indicate that they are actually not strictly linear but somewhat displaced. This discontinuity is more obvious in the HREM images displaying separate q1 and q2 modulations such as q1 in the [110] orientation (Fig. 2) and q2 in the [011] orientation (Fig. 3).

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