I made sintering to ZrO2 Y2O3 (Y 3 mol %) using efferent temperatures (1400 - 1500 - 1600 - 1700), different holding time (3h - 6h -12h) and different sintering techniques (in atmosphere furnace and PAS). Samples that were sintered in atmosphere furnace were white, except two samples were yellow. The yellow samples were sintered in 1400o C and 1500o C for 12 hours. Samples that were sintered in PAS were black. I want to know the purposes of these different colors.
Hi Khalid, the ones sintered in non-oxidizing atmosphere turn black as you have oxygen substoichiometry (e.g. in hydrogen, hotpress / SPS in graphite mold) even in post-HIP ing (of samples sintered in oxidizing atmosphere in argon) you may get some greyish colour which can be removed by annealing in air. Oxygen vacancies are populated by electrons which cause the black colour like free electrons in metals.
This oxygen vacancies cause an additional stabilization.
see: Chen, M., Hallstedt, B., Gauckler, L.: “Thermodynamic modeling of the ZrO2–YO1.5 system”, Solid State Ionics 170 , 255–274, 2004.
Whether the zirconia sintered in air turns white or has a more or less yellowish colour is not easy to predict, it seems to depend on the impurities, the density and the grain sizes. So far I cannot give you a clear statement on this.
One potential cause for yellow in sintered zirconia is the presence of Mo vapor when fired in a MoSi2 electric furnace. This is typically caused by damage to the silicate glass layer that forms on the heating elements and protects the elements from oxidation. If the glaze (glass) layer blisters, Mo vapor (MoO3) can be generated during firing that will interact with the zirconia causing it to turn yellow.
Khalid, Colors in ceramics are due tto color centers. Black appearence is due to access of electrons (lack of oxygen). For soultions to that see Frank's answer. Yellowish color is common in M+4 oxides. e.g. CeO2, UO2 etc., Since ZrO2 comprizes of Zr+4 ions you might get yellowish color.
Khalid. Typically Mo from the heating elements lead to a more greenish color. And the effect should be more distinct the higher the temperature is. Are you sure, that no accidental contamination happened during sample preparation?
Dear Khalid i want ask about your forming methed to prepare your sample, are you used polymer binder? I think almost zirconia sinered samples in the light yellow color between 1400 and 1600 C.....thanks
I ,very humbly, request your good self that it will be my pleasure to have a fruitful academic discussion further if you find any point not coming up to your expections.
Yes; I agree with respected Frank Kern wrt his explanation of blackening of the color in PAS.
In order to explain yellow color of YSZ, first a few lines about its structure given as{Pls see an attached file}:
Doping Zirconia with Yttria (Y2O3) replaces Zr4+ with Y3+ and adds Oxygen Vacancies.The substitution of Zr4+ with Y3+ causes the negative net charge in the lattice; for every mole of yttria incorporated into the zirconia lattice, the charge neutrality condition is kept by forming an oxygen vacancy. In a Kroger-Vink notation, it is written as follows:
Y2O3------2Y′Zr+3OxO+V¨O
Where Y′Zr means Y in the Zr site with the apparent negative charge, and V¨O is the vacancy in the oxygen site with double positive charge. Oxo is the lattice oxygen, i.e., oxygen in the oxygen site with net charge of zero(0). The electron get trapped in the vacancies created by the deficient oxygen. THE ELECTRONS THUS ENTRAPPED IN THE ANION VALANCIES ARE CALLED { F- CENTERS}* WHICH ARE RESPONSIBLE FOR IMPARTING COLORS TO ANION DEFICIENT . It may further be noted that intensity of F- COLOR is dependent on the concentration of the ANION VACANCIES. THE more the number of vacancies**, the more will be intensity of the color. Since you have sintered with3% Y[7.8% Y2O3] and so YSZ has attained the maximum stability** *, the YSZ should should have absorbed around 560-590 nm( may have different yellow intensities at rwo temperatures) to emit yellow color.
* F- FARBE- a German word- means color.
** Have already discussed in my answer to your another related question
*** The concentration of Oxygen vacancy is determined by the concentration of the dopant.
For Khalid Tayeb
Although, I could never have a chance to pursue the “RESEARCH” aggressively, yet having been a learner thorough out my life, I quote three references( can give 1-2 more if asked) to support my humble idea regarding the color in such cases. I may, further, add that the references mentioned at [A] and [B] are already reported in Research Gate as their authors happen to be our worthy RG Colleagues; one having over 70 publications and quite a few are on the COLOR. Yes; I will be sorry if I have misunderstood their basic idea. I hope yourself/ every body agree with the well established Kroger-Vink notation . I await your/ our RG friends’ exalted comments; no matter even if proved wrong in this academic discussion as learning is continuous process.
[A]Luminescence of F+‐type centers in undoped Lu3Al5O12 single crystals
V. Babin, V.V. Laguta, A. Maaroos, A. Makhov, M. Nikl, S. Zazubovich
[V.V. Laguta is our RG colleague]
[B]Luminescence of F+ and F centers in AI2O3-Y2O3 oxide compounds
Y Zorenko, T Zorenko, T Voznyak, A Mandowski, Qi Xia, M Batentschuk, J Friedrich
[Yu. Zorenko is our RG colleague]
[C}Journal of Physics: Condensed Matter Volume 16 Number 23
Jean-Marc Costantini et al 2004 J. Phys.: Condens. Matter 16 3957 doi:10.1088/0953-8984/16/23/014
Colour centre production in yttria-stabilized zirconia by swift charged particle irradiations
Jean-Marc Costantini1, François Beuneu2, Didier Gourier3, Christina Trautmann4, Georges Calas5 and Marcel Toulemonde6
Hi, the black color means that the metal oxide was reduced to its metallic form
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