scholarly journals Structural-phase transformation kinetics during sintering of alumina ceramics using metastable nanopowders

2005 ◽  
Vol 37 (1) ◽  
pp. 35-43 ◽  
Author(s):  
A.S. Kaigorodov ◽  
V.R. Khrustov ◽  
V.V. Ivanov ◽  
A.I. Medvedev ◽  
A.K. Shtol’ts
Keyword(s):  
Diffusion Processes ◽  
Structural Phase ◽  
Alumina Ceramics ◽  
Transformation Kinetics ◽  
Structural Phase Transformation ◽  
Positive Role ◽  
Polymorphous Transition ◽  
Mg Addition ◽  
Kinetics Of

The processes taking place during pressureless sintering of nano- metastable Al2O3, compacted up to high densities (0.7 of the theoretical density) using the magnetic pulsed method were studied. The influence of MgO, TiO2 and ZrO2 additives on the kinetics of Al2O3 polymorphous transition, shrinkage and microstructure evolution during annealing at temperatures up to 1450?C has been studied. We have found that the process of annealing is two-staged starting with a polymorphous transition. Doping changes the starting temperature as well as the shrinkage depth at both stages. TiO2 and ZrO2 additives decrease the temperature of the onset of shrinkage, whereas MgO increases it. The best composition contained MgO in the series of examined types of ceramics with an ?-Al2O3 matrix. The positive role of Mg addition in the production of dense and hard Al2O3 ceramics is related to the nature of Mg influence on the activation of diffusion processes in Al2O3, as well as to the way of uniform distribution of MgO dopant in the material. All these factors provide effective damping of diffusion processes and limit ?-Al2O3 crystal growth. Highly dense MgO, ZrO2 and TiO2 doped Al2O3 ceramics with a grain size of 190, 220, and 250 nm and microhardness of 22, 17 and 17 GPa, correspondingly have been obtained.

Effect of cluster-gradient architecture of nanostructured topocomposites on features of tribointeraction with heterophased material

2020 ◽  
pp. 130-135
Author(s):  
D.N. Korotaev ◽  
K.N. Poleshchenko ◽  
E.N. Eremin ◽  
E.E. Tarasov
Keyword(s):  
Wear Resistance ◽  
Titanium Alloy ◽  
Energy Dissipation ◽  
Phase Structure ◽  
Diffusion Processes ◽  
Structural Phase ◽  
High Wear Resistance ◽  
Wear Characteristics ◽  
And Diffusion

The wear resistance and wear characteristics of cluster-gradient architecture (CGA) nanostructured topocomposites are studied. The specifics of tribocontact interaction under microcutting conditions is considered. The reasons for retention of high wear resistance of this class of nanostructured topocomposites are studied. The mechanisms of energy dissipation from the tribocontact zone, due to the nanogeometry and the structural-phase structure of CGA topocomposites are analyzed. The role of triboactivated deformation and diffusion processes in providing increased wear resistance of carbide-based topocomposites is shown. They are tested under the conditions of blade processing of heat-resistant titanium alloy.

On the Role of Diffusion in the Oxidation of Fe, Ni, Co and the Fe-Sn Alloy by Calcium and Sodium Sulfates

2006 ◽  
Vol 258-260 ◽  
pp. 63-67
Author(s):  
V.M. Chumarev ◽  
V.P. Maryevich ◽  
V.A. Shashmurin
Keyword(s):  
Co Oxidation ◽  
Chemical Reaction ◽  
Diffusion Processes ◽  
Transport Processes ◽  
Diffusion Transport ◽  
Sodium Sulfates ◽  
Product Forms ◽  
Kinetics Of ◽  
Dominant Part

Diffusion processes play a dominant part in the macro kinetics of Fe, Ni and Co oxidation by calcium and sodium sulfates. Here, the reaction product forms a compact covering which spatially divides the reagents on the surface in the same way as in the oxidation and sulfidization of metals by oxygen and sulfur. Therefore, it is possible to assume in advance that interaction of metals with calcium and sodium sulfates will be determined not by the actual chemical reaction properly but by the diffusion transport processes.

scholarly journals Transformation kinetics of vapor-deposited thin film organic glasses: the role of stability and molecular packing anisotropy

2015 ◽  
Vol 17 (46) ◽  
pp. 31195-31201 ◽  
Author(s):  
Cristian Rodríguez-Tinoco ◽  
Marta Gonzalez-Silveira ◽  
Joan Ràfols-Ribé ◽  
Aitor F. Lopeandía ◽  
Javier Rodríguez-Viejo
Keyword(s):  
Thin Film ◽  
Thermodynamic Stability ◽  
Growth Front ◽  
Molecular Packing ◽  
Front Velocity ◽  
Transformation Kinetics ◽  
Organic Glasses ◽  
Kinetics Of ◽  
Deposition Conditions

The growth front velocity of indomethacin glasses depends on deposition conditions but is not unambigously determined by its thermodynamic stability when the structure is not completely isotropic.

Thickness-induced structural phase transformation of layered gallium telluride

2016 ◽  
Vol 18 (28) ◽  
pp. 18719-18726 ◽  
Author(s):  
Q. Zhao ◽  
T. Wang ◽  
Y. Miao ◽  
F. Ma ◽  
Y. Xie ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Structural Stability ◽  
Crucial Role ◽  
Structural Phase ◽  
Structural Phase Transformation ◽  
Gallium Telluride ◽  
Spontaneous Phase

We report a spontaneous phase transformation of GaTe, occurring when the bulk is exfoliated to a few layers. The results demonstrate the crucial role of interlayer interactions in the structural stability.

Metamorphic reaction rate laws and development of isograds

1986 ◽  
Vol 50 (357) ◽  
pp. 359-373 ◽  
Author(s):  
Antonio C. Lasaga
Keyword(s):  
Diffusion Processes ◽  
Relative Role ◽  
Mineral Surfaces ◽  
Surface Kinetics ◽  
Rate Laws ◽  
Careful Treatment ◽  
Reaction Zones ◽  
Kinetics Of ◽  
And Diffusion

AbstractNew data on the kinetics of dehydration of muscovite + quartz suggest the necessity for a careful treatment of both surface kinetics and diffusion processes in metamorphic reactions. A new model is proposed that illustrates the relative role of diffusion and surface reactions in the overall metamorphic process. The rate law for the reaction at mineral surfaces derived from the experimental data is shown to be probably non-linear and similar to rate laws derived from Monte Carlo calculations. The experimental rate data is then used in a heat flow calculation to model the evolution of the muscovite isograd in the field. The position of the isograd, the temperature oversteps above equilibrium, and the width of ‘reaction zones’ are then analysed as a function of intrusion size and kinetic parameters.

scholarly journals Role of Hydrodynamics, Li+ Addition and Transformation Kinetics on the Formation of Plate-Like {001} Calcite Crystals

Crystals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 250
Author(s):  
Nives Matijaković Matijaković Mlinarić ◽  
Jasminka Kontrec ◽  
Branka Njegić Njegić Džakula ◽  
Giuseppe Falini ◽  
Damir Kralj
Keyword(s):  
Crystal Growth ◽  
Ultrasound Irradiation ◽  
Research Model ◽  
Transformation Kinetics ◽  
Lithium Ions ◽  
Mechanical Stirring ◽  
Wide Range ◽  
Experimental Parameters ◽  
Kinetics Of

Plate-like calcite crystals with expressed unstable {001} planes are interesting research model for investigations of interfacial interactions of different additive molecules, but also the crystal growth mechanisms. The aim of this study is to reproducibly prepare a significant amount of well-defined plate-like calcite crystals and to investigate the critical experimental parameters. Thus, in precipitation system c(NaHCO3) = c(CaCl2) = 0.1 mol dm−3, the influence of hydrodynamic parameters (mode of mixing of the reaction components) and a presence of lithium ions Li+ within a wide range of concentrations, 0.0 mol dm−3 < c(Li+) < 1.0 mol dm−3, have been studied. In addition, the kinetics of the solution mediated transformation of the initially formed metastable polymorph, vaterite, were followed in order to reproducibly describe the formation of stable calcite with expressed unstable morphology. The results indicate that the plate-like calcite is formed predominantly when the ultrasound irradiation is applied at c(Li+) ≥ 0.3 mol dm−3. On the other hand, when the magnetic and mechanical stirring are applied at higher Li+ concentrations, truncated rhombohedral crystals in a mixture with plate-like crystals are obtained. It was also found that the Li+ addition significantly prolonged the transformation, mainly by inhibiting the crystal growth of calcite.

Are Three Items Sufficient to Measure Sense of Coherence?

2018 ◽  
Vol 34 (4) ◽  
pp. 229-237 ◽  
Author(s):  
Francesca Chiesi ◽  
Andrea Bonacchi ◽  
Caterina Primi ◽  
Alessandro Toccafondi ◽  
Guido Miccinesi
Keyword(s):  
Sense Of Coherence ◽  
Convergent Validity ◽  
Clinical Sample ◽  
Clinical Samples ◽  
Depression Symptoms ◽  
Time Saving ◽  
Positive Role ◽  
Patients With Cancer ◽  
Measure Sense

Abstract. The present study aimed at evaluating if the three-item sense of coherence (SOC) scale developed by Lundberg and Nystrom Peck (1995) can be effectively used for research purpose in both nonclinical and clinical samples. To provide evidence that it represents adequately the measured construct we tested its validity in a nonclinical (N = 658) and clinical sample (N = 764 patients with cancer). Results obtained in the nonclinical sample attested a positive relation of SOC – as measured by the three-item SOC scale – with Antonovsky’s 13-item and 29-item SOC scales (convergent validity), and with dispositional optimism, sense of mastery, anxiety, and depression symptoms (concurrent validity). Results obtained in the clinical sample confirmed the criterion validity of the scale attesting the positive role of SOC – as measured by the three-item SOC scale – on the person’s capacity to respond to illness and treatment. The current study provides evidence that the three-item SOC scale is a valid, low-loading, and time-saving instrument for research purposes on large sample.

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