Upconversion luminescence properties of Li+-doped ZnWO4:Yb,Er

2008 ◽  
Vol 23 (8) ◽  
pp. 2078-2083 ◽  
Author(s):  
Xi-xian Luo ◽  
Wang-he Cao
Keyword(s):  
Liquid Phase ◽  
Calcination Temperature ◽  
Crystal Field ◽  
Lower Energy ◽  
Upconversion Luminescence ◽  
Peak Position ◽  
Liquid Phase Sintering ◽  
Red Shift ◽  
Luminescence Properties ◽  
Sintering Process

Upconversion luminescence (UPL) characteristics and effects of Li+ ion on the UPL of ZnWO4:Yb,Er polycrystalline phosphors were investigated. It was shown that introduction of Li+ ions could reduce the calcination temperature by about 200 °C and increase the crystallinity of ZnWO4:Yb,Er by a liquid-phase sintering process via formation of Li2WO4 and other intermediates. UPL efficiency is remarkably promoted by Li+ ions. Moreover, the UPL spectrum of Li+-doped ZnWO4:Yb,Er presents a red shift, and the strongest peak position shifts from 553 to 559 nm. These can be attributed to a shift in the 4f level barycenter to lower energy, which results from lowering of the symmetry of the crystal field around Er3+.

Rheology of Al-Cu-Mg pre-alloyed powder in supersolidus liquid phase sintering process

2017 ◽  
Vol 56 (4) ◽  
pp. 442-449 ◽  
Author(s):  
H. Momeni ◽  
S. G. Shabestari ◽  
H. Razavi
Keyword(s):  
Liquid Phase ◽  
Liquid Phase Sintering ◽  
Alloyed Powder ◽  
Sintering Process

Effect of WC Addition on Phase Formation and Microstructure of TiC-Ni Composites

2008 ◽  
Vol 55-57 ◽  
pp. 353-356
Author(s):  
Nawarat Wora-uaychai ◽  
Nuchthana Poolthong ◽  
Ruangdaj Tongsri
Keyword(s):  
Liquid Phase ◽  
Tungsten Carbide ◽  
Phase Formation ◽  
Liquid Phase Sintering ◽  
Precipitation Process ◽  
Solid Solution Phase ◽  
Binder Phase ◽  
Sintering Process ◽  
X Ray Diffraction ◽  
X Ray

In this research, titanium carbide-nickel (TiC-Ni) composites, with tungsten carbide addition, were fabricated by using a powder metallurgy technique. The TiC-Ni mixtures containing between 0-15 wt. % tungsten carbide (WC), were compacted and then sintered at 1300°C and 1400°C, respectively. The phase formation and microstructure of the WC-added TiC-Ni composites have been investigated by X-ray diffraction and scanning electron microscopy techniques. Mechanical properties of these composites were assessed by an indentation technique. The X-ray diffraction patterns showed no evidence of tungsten rich phases in the sintered WC-added cermets. This indicates that during the sintering process, tungsten carbide particles were dissolved in metallic binder phase (Ni phase) via dissolution/re-precipitation process during liquid phase sintering. The liquid phase formed during sintering process could improve sinterability of TiC-based cermets i.e., it could lower sintering temperatures. The TiC-Ni composites typically exhibited a core-rim structure. The cores consisted of undissolved TiC particles enveloped by rims of (Ti, W)C solid solution phase. Hardness of TiC-Ni composites increased with WC content. Sintering temperature also had a slight effect on hardness values.

True Sedimentation and Particle Packing Rearrangement during Liquid Phase Sintering

2007 ◽  
Vol 534-536 ◽  
pp. 609-612
Author(s):  
Jong K. Lee ◽  
Lei Xu ◽  
Shu Zu Lu
Keyword(s):  
Liquid Phase ◽  
Concentration Gradient ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Liquid Phase Sintering ◽  
Particle Packing ◽  
Sintering Process ◽  
Second Stage ◽  
Packing Efficiency ◽  
Two Stages

When an alloy such as Ni-W is liquid phase sintered, heavy solid W particles sedimentate to the bottom of the container, provided that their volume fraction is less than a critical value. The sintering process evolves typically in two stages, diffusion-driven macrosegregation sedimentation followed by true sedimentation. During sedimentation, the overall solid volume fraction decreases concurrently with elimination of liquid concentration gradient. However, in the second stage of true sedimentation, the average solid volume fraction in the mushy zone increases with time, and oddly, no concentration gradient is necessary in the liquid zone. In this work, we propose that the true sedimentation results from particle rearrangement for higher packing efficiency.

Physical, Mechanical and Electrical Properties of W-20 wt.% Cu Composite Produced by Liquid Phase Sintering Process

2014 ◽  
Vol 879 ◽  
pp. 21-26
Author(s):  
Fauzi Ismail ◽  
Mohd Asri Selamat ◽  
Norhamidi Muhamad ◽  
Abu Bakar Sulong ◽  
Nurzirah Abdul Majid
Keyword(s):  
Particle Size ◽  
Liquid Phase ◽  
Electrical Properties ◽  
Microstructure Evolution ◽  
Sintering Temperature ◽  
Cold Isostatic Pressing ◽  
Liquid Phase Sintering ◽  
Sintering Process ◽  
Composite Powders ◽  
Mechanical And Electrical Properties

In this study, the effect of sintering temperature on the properties of tungsten-copper (W-Cu) composite produced by liquid phase sintering (LPS) process has been investigated. W-20 wt.% Cu composite powders with particle size less than 1 μm was prepared by cold compaction and followed by cold isostatic pressing. The green specimens were then sintered under nitrogen based atmosphere in the temperature range of 1100°C to 1300°C. The sintering studies were conducted to determine the extent of densification and corresponding to microstructure changes. In addition, the properties of the sintered specimens such as physical appearance, microstructure evolution, mechanical and electrical properties were presented and discussed.

The Influence of Production Process Parameters on the Properties W-Ag, Mo-Ag Composites

2007 ◽  
Vol 534-536 ◽  
pp. 1513-1516
Author(s):  
Jan Leżański ◽  
Marcin Madej
Keyword(s):  
Liquid Phase ◽  
Production Process ◽  
Process Parameters ◽  
Liquid Phase Sintering ◽  
Sintering Process ◽  
Powder Mixtures ◽  
Microstructure And Properties ◽  
Silver Additions

Attempts have been made to describe the influence of production process parameters on the microstructure and properties of W - Ag and Mo - Ag composites. The compositions of powder mixtures are W + 30% Ag and Mo + 30%Ag. Silver additions assists densification during sintering by a liquid phase sintering process. The main goal of this work is to compare properties and microstructure of as-sintered and as-infiltrated composites.

scholarly journals Interpretation of Frenkel’s theory of sintering considering evolution of activated pores: I. Confirmation of the time constant

2014 ◽  
Vol 46 (2) ◽  
pp. 141-147 ◽  
Author(s):  
C.L. Yu ◽  
D.P. Gao ◽  
C.B. Xu ◽  
N.B. Tang ◽  
T. Zhao
Keyword(s):  
Particle Size ◽  
Liquid Phase ◽  
Theoretical Calculation ◽  
Time Constant ◽  
Liquid Phase Sintering ◽  
Sintering Process ◽  
Time Constants ◽  
Constant Determination ◽  
Cordierite Glass ◽  
Sintering Shrinkage

Frenkel?s theory of liquid-phase sintering was interpreted regarding pores as the activated component. The data of isothermal sintering shrinkage vs. time of the cordierite glass by Giess et al. are trained using the model by Nikolic et al. to obtain the relative density at varied temperatures and time. Then, the time constants are obtained as 1998.86mins, 388.21mins, 89.79mins and 26.11mins at 800?C, 820?C, 840?C and 860?C, respectively. The calculated time constants are close to that by the theoretical calculation, deviation of which arises from the fact that particle size is variable during the sintering process. The time constant determination is crucial to the research of the whole sintering process.

Low Angle Grain Boundary Dewetting in Sapphire

2001 ◽  
Vol 7 (S2) ◽  
pp. 384-385
Author(s):  
B.J. Hockey ◽  
M-K. Kang ◽  
S.M. Wiederhorn ◽  
J.E. Blendell
Keyword(s):  
Liquid Phase ◽  
Grain Boundary ◽  
Liquid Phase Sintering ◽  
Sintering Process ◽  
Transmission Electron ◽  
Wide Range ◽  
Grain Boundary Wetting ◽  
Tape Cast ◽  
Single Boundary ◽  
Current Emphasis

The structure and composition of low angle grain boundaries produced in sapphire by a liquid phase sintering process were investigated by conventional and high resolution transmission electron microscopy (CTEM and HRTEM, respectively). Considering the current emphasis on producing ceramics with textured microstructures for various applications, the question of grain boundary wetting vs. dewetting has become a relevant issue to determining the microstructure development and the properties of these liquid phase sintered materials. Accordingly, the present study was designed to cover a wide range of tilt misorientations, twist misorientations, and boundary orientations.The boundaries were formed by the directed growth of two sapphire plates, both having nominal <0001>, , or surface orientations through an alumina tape-cast containing an anorthite composition glass phase. After an initial hot-pressing stage, followed by an anneal at 1600° C for 200 hours, the samples typically contained a single boundary delineated by isolated pockets of entrapped glass, Fig. 1.

Faceting behavior of Al2O3 in the presence of glassy phase

1987 ◽  
Vol 45 ◽  
pp. 152-153
Author(s):  
Y. Kouh Simpson
Keyword(s):  
Liquid Phase ◽  
Glass Phase ◽  
Glassy Phase ◽  
Liquid Phase Sintering ◽  
Sintering Process ◽  
Final Microstructure ◽  
Amorphous Glass ◽  
Glass Interface ◽  
Energy Consideration

It is well known that A1203 can reach near-theoretical density by a liquid-phase sintering process in which an amorphous glass phase containing SiO2, CaO and Al2O3 helps density Al2O3. Understanding the faceting behavior of Al2O3 in the presence of such a glass phase is important since the movement of the facets and the type of facets that form during the liquid-phase sintering process determine the final microstructure of the grain boundaries that ultimately control the properties of Al2O3 compacts. As a part of a larger study on the role of impurities in the sintering process of Al2O3 compacts, a new investigation has been carried out to examine the nature and the type (e.g. facet planes) of the crystalline Al2O3, / amorphous glass interface in systematic experiments in which densification aids such as SiO2, CaO and MgO are reacted with single crystal Al2O3. Substantial anisotropy, both from an energy consideration and a kinetics consideration, in the Al2O3/ glass interface is to be expected, and has been observed in this investigation.

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