Composition-induced microstructures in rhombohedral carbonates

1987 ◽  
Vol 51 (359) ◽  
pp. 71-86 ◽  
Author(s):  
D. J. Barber ◽  
M. Riaz Khan
Keyword(s):  
Electron Diffraction ◽  
Crystallographic Orientation ◽  
Solid Solubility ◽  
Single Phase ◽  
Crystal Defects ◽  
Second Phase ◽  
Two Phase ◽  
Diffraction Contrast ◽  
Second Phases ◽  
Metallic Impurities

AbstractRecent TEM observations of two-phase microstructures and associated crystal defects in selected, rare dolomites have been extended to calcite-structured (R3̄c) carbonates and to other natural and synthetic carbonates that crystallize with the dolomite (R3̄) structure. The samples included siderites (FeCO3), smithsonites (ZnCO3), ankerites (Ca[Mg,Fe](CO3)2), and kutnahorites (Ca[Mn,Fe](CO3)2).TEM methods show that the forms of second phases which result from the presence of common, divalent, metallic impurities are morphologically similar in R3̄c and R3̄ carbonates and occur more widely than hitherto realized. The most common form consists of thin ribbons of second phase which are coherent with and have the same crystallographic orientation as the host carbonate. Another form of microstructure, manifest as modulations in diffraction contrast, appears to be associated with incipient breakdown of single-phase carbonate. The results of extensive TEM/EDS microanalyses show that in siderite and ankerite the formation of ribbons is promoted by Ca impurity or Ca excess (with respect to R3̄c stoichiometry). In smithsonite, Cu and Ca impurities can play similar roles in relation to modulated microstructures. In kutnahorites, the perfection of grains and the absence of second-phase effects is strongly dependent on the ratio of Fe to Mn but is also affected by Ca in excess of the stoichiometric requirement. Electron diffraction results from several of the minerals show c-type spots, which can be interpreted as indicating ordering within basal layers of cations.The results show that, by correlating analytical TEM data with the study of second phases and incipient two-phase microstructures, it should be possible to determine the limits of solid solubility in carbonate systems.

scholarly journals Assessment of the Compositional Influences on the Toughness of TiCr2-Base Laves Phase Alloys

1996 ◽  
Vol 460 ◽  
Author(s):  
Katherine C. Chen ◽  
Samuel M. Allen ◽  
James D. Livingston
Keyword(s):  
Crystal Structure ◽  
Single Phase ◽  
Laves Phase ◽  
Second Phase ◽  
Vickers Indentation ◽  
Toughening Mechanisms ◽  
Two Phase ◽  
Laves Phases ◽  
Effective Factors ◽  
Alloying Effects

ABSTRACTSystematic studies of alloys based on TiCr2 have been performed in order to improve the toughness of Laves phase intermetallics. The extent to which alloy compositions and annealing treatments influence the toughness was quantified by Vickers indentation. The single-phase Laves behavior was first established by studying stoichiometric and nonstoichiometric TiCr2. Next, alloying effects were investigated with ternary Laves phases based on TiCr2. Different microstructures of two-phase alloys consisting of (Ti,Cr)-bcc+TiCr2 were also examined. Various toughening theories based on vacancies, site-substitutions, crystal structure (C14, C36, or C15) stabilization, and the presence of a second phase were evaluated. The most effective factors improving the toughness of TiCr2 were determined, and toughening mechanisms are suggested.

Investigation of a New Type of Al3Ti-Based Ll2 Alloy With Second Phase Precipitation

1994 ◽  
Vol 364 ◽  
Author(s):  
Gengxiang Hu ◽  
Jian Sun ◽  
Xiaojun Weng ◽  
Tong Li ◽  
Shipu Chen
Keyword(s):  
Single Phase ◽  
Solution Treatment ◽  
Second Phase ◽  
Quaternary Alloys ◽  
Two Phase ◽  
Ti Alloys ◽  
Second Phase Particles ◽  
New Type ◽  
Temperature Aging ◽  
Nb Additions

AbstractSince the L12 structured Al3Ti alloy exists only in a narrow compositional range, further alloying of the single phase Ll2 alloy to improve its property seems hardly successful. Developing two-phase or multiphase Al3Ti alloys may be an effective approach for strengthening and toughening. In this article, a new type of Al3Ti-based alloy which has a Ll2 matrix with precipitates of a second phase is reported. The quaternary alloys based on Al67Mn8Ti25, and modified with Nb additions, consist of an Ll2 matrix and DO22 second phase particles in the annealed state, but the second phase can be dissolved by solution treatment and precipitated during high temperature aging. Remarkable strenghtening and promising compressive ductility were exhibited by the experimental alloy. The influence of composition on the microstructure and properties of the alloys are reported also.

Release of corticosterone from the rat adrenal cortex in response to administration of (1–24)adrenocorticotrophin

1983 ◽  
Vol 98 (2) ◽  
pp. 173-NP ◽  
Author(s):  
G. R. Cam ◽  
J. R. Bassett
Keyword(s):  
Single Phase ◽  
De Novo ◽  
Plasma Corticosterone ◽  
Significant Rise ◽  
Second Phase ◽  
De Novo Synthesis ◽  
Microtubule Inhibitor ◽  
Corticosterone Concentration ◽  
Second Phases ◽  
Dose Dependent

The intraperitoneal injection of (1–24)ACTH (34–170 nmol/kg) in rats pretreated with betamethasone resulted in a biphasic rise in plasma corticosterone; only a single phase-response was observed after lower doses (3·4–17·0 nmol/kg). There was an initial rapid rise to a level of approximately 0·72 μmol corticosterone/l plasma over the first 10 min after injection, followed by a plateau phase in which there was no further significant rise in steroid levels up to 25 min. Between 25 and 30 min after injection there was a second significant rise in plasma corticosterone concentration. The amplitude of the first phase of steroid increase was essentially the same for all doses of (1–24)ACTH administered whereas the amplitude of the second phase was dose-dependent. The administration of the microtubule inhibitor, colchicine, greatly reduced the amplitude of the second phase of the response to (1–24)ACTH while not affecting the first phase. However, a second stimulus with (1–24)ACTH in colchicine-treated animals was without effect on plasma corticosterone concentrations; both the first and second phases of corticosteroid increase being abolished. It is proposed that the first phase of plasma corticosterone increase resulted from the release of corticosteroid from a storage form close to the cell membrane and not requiring microtubular transport, whereas the second phase was the result of transport from more distant storage sites or de-novo synthesis.

scholarly journals The Determination of Crystallographic Textures From Selected Areas of a Specimen by Electron Diffraction

1983 ◽  
Vol 6 (1) ◽  
pp. 45-61 ◽  
Author(s):  
F. J. Humphreys
Keyword(s):  
Electron Microscope ◽  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Pole Figure ◽  
Single Phase ◽  
Angular Resolution ◽  
Thin Foil ◽  
Two Phase ◽  
Pole Figures

A technique for the determination of partial pole figures with an angular resolution of <3°, from selected areas of a thin foil, is described. A microcomputer, interfaced to an unmodified JEOL 100 CX TEMSCAN electron microscope is used to scan a diffraction pattern over a detector, tilt the specimen in steps of 1.5° over a range of ±50°, and plot the resulting data as a semiquantitative pole figure. The application of the technique to the study of materials which deform inhomogeneously is discussed, and examples are given of pole figures obtained from deformed single phase and two phase aluminium specimens.

Modelling Interface Diffusion Creep: Single Phase Insights and Two Phase Challenges

2012 ◽  
Vol 715-716 ◽  
pp. 983-987
Author(s):  
John Wheeler ◽  
J.M. Ford
Keyword(s):  
Single Phase ◽  
Numerical Models ◽  
Shape Change ◽  
Grain Boundary Sliding ◽  
Diffusion Creep ◽  
Second Phase ◽  
Mathematical Framework ◽  
Two Phase ◽  
Interface Diffusion ◽  
Angular Velocities

Numerical and analytic models for diffusion creep have commercial and geological uses. For single phase polycrystals, numerical models of interface diffusion creep illustrate how grains rotate and what the relative contributions of grain shape change and grain boundary sliding are to the overall strain. In particular they shows that an equi-axed starting material will initially show large grain angular velocities but that these slow down as grain become slightly elongate. A steady state microstructure with some grain elongation and little or no grain rotation is reached. Consequently the equi-axed grain shapes seen in superplastic deformation require additional processes for a full explanation. For two phase aggregates, the mathematical framework cannot be simply extended it breaks down as the system becomes mathematically overdetermined. Further work is required to solve this problem. If the second phase is insoluble, the mathematics can, though, be extended successfully, paving the way for models of diffusion creep with insoluble second phase particles.

Improving the Low Temperature Ductility of NiAl

1988 ◽  
Vol 133 ◽  
Author(s):  
Sumit Guha ◽  
Paul R. Munroe ◽  
Ian Baker
Keyword(s):  
Intergranular Fracture ◽  
Room Temperature ◽  
Single Phase ◽  
Al Alloys ◽  
Second Phase ◽  
Two Phase ◽  
Slip Vector ◽  
Transgranular Cleavage ◽  
Ductile Tearing ◽  
Rapidly Solidified

ABSTRACTAs part of a study aimed at developing a ductile NiAl-based alloy, ingots of Ni-Fe-Al alloys were cast and hot extruded to rods. The purpose of the iron additions was two-fold viz; to produce a change in the slip vector from <001> to <111> and, in one alloy, to add a L12-structured ductile second phase. Extruded Ni-20A1–3OFe was two-phase, containing a pro-eutectic B2 phase in a fine lamellar structure (< 0.5 μm spacing) of B2+L12 phases. Room temperature tensile testing of both single extruded and double extruded alloys resulted in 8% and 22% plastic elongation and yield stresses of 850 and 760 MPa respectively. Fracture in both cases occurred by ductile tearing of the eutectic and transgranular cleavage of the proeutectic phase at 1350 MPa. The ductility in double extruded condition is higher than that reported earlier in rapidly solidified wires by Inoue et al., J. Mat. Sci., 19, (1984), 3097. By comparison, extruded single-phase B2-structured Ni- 30AI-2OFe exhibited a fracture strength of 780 MPa, no plasticity and a mixture of intergranular fracture and transgranular cleavage. This is in contrast to earlier work by Inoue et al. (ibid) where a yield stress of 400 MPa, 5% plastic strain and a mixture of dimple and intergranular fracture was reported.

Recent Advances on the Deformation Behavior of Two-Phase α+β Titanium Alloys

2019 ◽  
Vol 950 ◽  
pp. 55-59 ◽  
Author(s):  
Sreeramamurthy Ankem ◽  
William J. Joost ◽  
Samuel C. Schwarm
Keyword(s):  
Deformation Behavior ◽  
Single Phase ◽  
Elastic Interaction ◽  
Deformation Mechanisms ◽  
Second Phase ◽  
General Will ◽  
Two Phase ◽  
Ti Alloys ◽  
The Difference ◽  
The Individual

Two-phase materials, such as α+β Titanium (Ti) alloys, are technologically important. A number of factors can affect deformation behavior, including the interaction stresses between phases, the crystallographic relationships between phases, and the morphology. As a result, the deformation mechanisms of two-phase alloys may be different from the individual single-phase materials. For example, twinning may not occur in a single phase material if the grain size is very small but twinning can occur in a very fine grained alloy if the second phase contributes to the interfacial stresses due to elastic interactions. Interaction stresses can result from the difference in the elastic properties of the two phases. In particular, these elastic interaction stresses can be quantified by the finite element method (FEM). In this paper recent developments regarding two-phase deformation mechanisms will be reviewed and the ramifications on mechanical behavior in regard to two-phase Ti alloys in particular and on two-phase metallic materials in general will be outlined.

Assessment of bovine oocytes quality and their resistance to age-related changes after maturation in single-phase and two-phase culture systems

2021 ◽  
pp. 3-8
Author(s):  
G. Singina ◽  
I. Lebedeva ◽  
E. Shedova ◽  
E. Tsyndrina
Keyword(s):  
Single Phase ◽  
Phase System ◽  
Second Phase ◽  
Two Phase ◽  
Nuclear Maturation ◽  
Age Related ◽  
Prolonged Culture ◽  
Phase Culture ◽  
Phase Systems ◽  
Bovine Oocytes

Existing approaches to in vitro maturation (IVM) of bovine oocytes do not take into account their specific demands during terminal phase of IVM including the need for increasing of their resistance to age-re-lated changes. In this work, we performed for the first time a comparative investigation of nuclear maturation and abnormal changes of MII chromosomes in bovine oocytes after their maturation in single-phase system and different two-phase systems and after the subsequent prolonged culture of the ova. When using the single-phase system, cumulus-oocyte complexes (COCs) were cultured for 24 h in the medium TCM 199 containing 10% fetal bovine serum (FBS), 10 μg/ml FSH, and 10 μg/ml luteinizing hormone (LH). In the two-phase system, oocytes matured in the same conditions for first 16 h and then in a new medium (TCM 199 containing 10% FBS (Control) or the same medium supplemented with 50 ng/ml progesterone) for the remaining 8 h of IVM. After maturation in the single-phase and the two-phase systems, a part of COCs were transferred to an aging medium (TCM 199 containing 10% FBS) and further cultured for 24 h. The state of the nuclear material (stage of meiosis and abnormal changes of MII chromosomes) in the matured and aged oocytes was assessed using cytogenetic analysis. The rate of oocytes being at the MII stage of meiosis after IVM in the single-phase and the two-phase systems was similar and amounted 82.7-86.3%. In addition, no effect of the culture system on the rate of MII oocytes with abnormal morphology of chromosomes was revealed. For the single-phase culture, this rate after the end of the IVM period was 32.2±0.5% and for the two-phase systems culture 38.5±4.0%. The prolonged culture of matured oocytes led to an increase the frequency of destructive changes in MII chromosomes to 56.9±2.9 and 68.4±3.0%, respectively. Progesterone in the IVM medium (during the last 8 hours) also did not effect on the rate of nuclear maturation, but reduced the rate of oocytes with abnormal changes in chromosomes: after IVM, as compared with the Control and the two-phase system; after 24-hours prolonged culture as compared to control (P <0.05). The results of the study suggest that the two-phase maturation of bovine oocytes may be used as an alternative to the conventional IVM protocol and that progesterone during the second phase of IVM causes an increase in the quality of ova and their resistance to subsequent age-related transformations.

Microstructural Studies of the Deformation of TiAl Alloys

1988 ◽  
Vol 133 ◽  
Author(s):  
Ernest L. Hall ◽  
Shyh-Chin Huang
Keyword(s):  
Room Temperature ◽  
Single Phase ◽  
Elevated Temperatures ◽  
Alloy Composition ◽  
Two Phase ◽  
Tial Alloys ◽  
Second Phases ◽  
Bend Tests ◽  
Microstructural Studies ◽  
Strength And Ductility

ABSTRACTThe mechanical behavior and microstructures of TiAl alloys after tensile and bend tests at room temperature and elevated temperatures were studied. The results for two-phase Ti52Al48 alloys are compared with those of single phase Ti48Al52, and the effect of adding 3 at. pct. vanadium as a substitute for Ti in these two alloys is considered. It is shown that Ti52Al48 has greater strength and ductility than Ti48Al52 at room temperature and elevated temperatures up to 871°C (1600°F). Adding vanadium increases the ductility of both binary alloys. The microstructure of the Ti52Al48 alloy deformed at room temperature contains primarily twins and 1/2<110> easy slip dislocations, whereas the similar Ti48Al52 sample exhibits superdislocations and associated pinned faulted dipoles. If these samples are deformed at 540°C (1000°F) or above, the Ti52Al48 exhibits extensive twinning, and the pinned faulted dipoles in the Ti48Al52 sample disappear. The vanadium additions do not noticeably change the deformation microstructure at room temperature. It is suggested that the strength and ductility of these alloys may be controlled by tetragonality, bonding, interstitial element, and grain size effects, which in turn are affected by the presence of second phases and by the alloy composition.

SUBSTANTIATION OF TECHNOLOGICAL PARAMETERS OF SPIRAL ROLL OF MACHINE ROLLER- BEDFORMER FOR HARVESTING ONIONS

2019 ◽  
Keyword(s):  
Single Phase ◽  
Second Phase ◽  
General View ◽  
Technological Parameters ◽  
Two Phase ◽  
Quality Work ◽  
Solid Soil ◽  
Harvesting Process ◽  
Working Bodies ◽  
Param Eters

When harvesting onions, it is very important to maintain the soil in a loosened state, since the slotted working bodies used in the separation are not able to separate the soil impurities from the bulbs, since it is small and when separating from the soil impurities it is difficult to separate. Qualitative indicators of cleaning are deter-mined by how well the previous technological operations are performed. A specific feature of onion harvesting is the need for such an agrotechnical technique as ripening and drying the bulbs after removing them from the soil. The high-quality work of the harvesting machines, both in two-phase and single-phase methods of harvesting, is ensured by satisfactory preparation of the field before harvesting. Consideration is given to improving the quali-ty indicators of mechanized harvesting of onion-seedlings, due to the unsatisfactory process of separating the bulbs from solid soil lumps, due to the fact that the slotted working bodies used in the separation are not able to isolate solid lumps comparable in size to the pile of onions. In order to intensify the harvesting process, onion sets when selecting from rolls, in order to exclude or reduce the take-up and pick-up part, together with the bulbs of soil lumps and feed the onion pile to the separating working parts, a roller-bedformer is used as part of the machine for the first phase of onion harvesting. The article presents a constructive-technological scheme and a general view of a roller-bedformer that intensifies the process of separation of onions in the second phase of harvesting. The article reflects the results of theoretical studies on the substantiation of the technological param-eters of spiral roll of machine roller-bedformer for harvesting onions.

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