Partial Reduction of NiAl2O4 - Mechanism and the Influence of Doping

1995 ◽  
Vol 398 ◽  
Author(s):  
Z. Zhang ◽  
E. Üstündag ◽  
S.L. Sass
Keyword(s):  
Reaction Mechanism ◽  
Intermediate Stage ◽  
Reduction Reaction ◽  
Reduction Mechanism ◽  
Partial Reduction ◽  
Metal Ceramic ◽  
Mechanism And Kinetics ◽  
Equilibrium Phases ◽  
Metastable Defect

ABSTRACTMetal-ceramic microstructures were formed in situ by partial reduction of the spinel compound NiAl2O4. At 1300°C the reduction reaction passed through an intermediate stage involving the formation of Ni and metastable “defect spinel” phases, before the appearance of the equilibrium phases, Ni + α-Al2O3. At 1100°C, depending on the reduction time, the products of the reduction reaction were Ni and the metastable “defect spinel” for less than 24 hours; Ni + θ-Αl2Ο3 for 24-48 hours; and Ni + GI-AI2O3 for 144-168 hours. The effects of dopants, such as Cr2O3, MgO, TiO2 and Y2O3, on the reduction mechanism and kinetics were examined and shown, in the case of TiO2, to have a controlling influence. A reduction reaction mechanism is proposed.

Displacement Reactions in the Ni-Al-O System Resulting in Periodic Layer Structures

1994 ◽  
Vol 365 ◽  
Author(s):  
Daniel W. Song ◽  
Ramesh Subramanian ◽  
RÜdiger Dieckmann
Keyword(s):  
Reaction Mechanism ◽  
Periodic Structures ◽  
Ceramic Composites ◽  
Processing Technologies ◽  
Layer Structures ◽  
Metal Ceramic ◽  
Displacement Reactions ◽  
Periodic Layer ◽  
In Situ Processing

ABSTRACTDisplacement reactions may play an important role in in situ processing technologies for the production of metal-ceramic composites. To better understand such reactions displacement reactions between NiO and Al were studied at high temperatures. Different reaction layers with periodic structures were observed involving Al2O3, Al3Ni, Al3Ni2, Ni and Al. The experimental observations are presented and discussed with regard to the reaction mechanism.

In-situ formation of metal-ceramic microstructures by partial reduction reactions

1995 ◽  
Vol 75 ◽  
pp. 241-255 ◽  
Author(s):  
R. Subramanian ◽  
E. Üstündagˇ ◽  
S.L. Sass ◽  
R. Dieckmann
Keyword(s):  
Partial Reduction ◽  
Reduction Reactions ◽  
Metal Ceramic ◽  
In Situ Formation

Ductile Phase Toughened Ceramics by Partial Reduction Reactions in the Ni-AI-O System: Mechanical Properties and Effect of Dopants

1994 ◽  
Vol 365 ◽  
Author(s):  
E. Üstündağ ◽  
P. Ret ◽  
Y. Shapiro ◽  
R. Subramanian ◽  
R. Dieckmann ◽  
...  
Keyword(s):  
Spinel Phase ◽  
Microstructural Characterization ◽  
Processing Parameters ◽  
Nucleation Site ◽  
Reduction Reaction ◽  
Phase Identification ◽  
Partial Reduction ◽  
Ductile Phase ◽  
Reduction Reactions

ABSTRACTPartial reduction reactions in the Ni-Al-O system, starting with the spinel compound NiAl2O4, are used to form metal-ceramic microstructures in situ. Two different morphologies of nearly pure Ni particles, equiaxed and rod-like, form within a ceramic matrix depending on the choice of processing parameters. Electron microscopy studies were performed for microstructural characterization, phase identification and chemical analysis. The fracture toughness of the Ni-Al2O3 mixture was significantly improved with respect to that of the original spinel phase. It is shown that cracking at the original spinel grain boundaries, likely due to the large volume changes associated with the reduction reaction, can be avoided by the addition of small amounts of ZrO2. It is seen that ZrO2 also acts as a nucleation site for the precipitating metal and hence allows morphology control in microstructures obtained by partial reduction reactions.

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