So I've started writing my researh proposal and progress is slow. We got out proposal outlines back a few days ago. Steve had a few questions on it, such as...

(In Steve notation)
1. Why olivine? Relevance to Earth
Olivine makes up a large portion of the upper mantle and is commonly found as xenoliths in volcanic rocks.

2. Why are trivalents geochemically interesting? (WRT mantle & olivine)
In olivine, there's a possibility that interactions between trivalent cations and vacancies formed by their presence can increase the rate of diffusion. More information is necessary here, I'll get back to you on this one.

3. Why use spinels and not doped olivine powders [as a source of Ga and Cr]?
Ga and Cr spinels can be more easily synthesized in the lab. Other elements in spinel (Mg, Si, O) are also present in forsterite, so their presence will not alter our results.

4. Why single crystal [of forsterite]?
Diffusion in polycrystalline materials can be largely controlled by space in between crystals, as crystal contacts facilitate diffusion. In addition, it is necessary to understand single crystal diffusion in order to understand polycrystalline diffusion.

I could use more information on all of these questions, but these are the answers, to the best of my knowledge. I'll be talking to Dr. Van Orman about some of these in the near future.

Here are some fun facts and questions I have from reading more articles today.

Fun Facts (& Opinions):
"If we assume that the vacancies mix within the
octahedral site without significant deviation from ideality, that is Xv(Fe)VI ~= av(Fe)VI, then the data in Fig. 1B indicate that Xv(Fe)VI
10–20 times XCrVI within the diffusion zone. This would seem to contradict the suggestion of extrinsic mechanism and favor an interstitial mechanism for the diffusion
of Cr3+ in olivine. However, since the concentrations
of both Cr3+ and octahedral vacancies are very dilute, the
probability of finding V(Fe)VI and Cr3+ ions adjacent to
one another could be too small for these vacancies to be
effective for diffusion of Cr3+. In that case the extrinsic
mechanism would be a viable mechanism for the diffusion
of Cr3+ despite the fact that Xv(Fe)VI > XCrVI. Clearly, further
work is needed to understand the reason for the lack
of effect of fO2 change between WI and WI + 2 on the D(Cr)." (Ito et al.)

If I understand this correctly, Ito et al. seem to suggest that the number of Cr3+ and vacancies are few enough that the odds of there being enough adjacent Cr3+ ions and vacanies to expediate diffusion is low. This specifically references Fe vacancies. Is this pertinent to Mg vacancies, as our experiments will be conducted on forsterite?

Another comment on this article. These experiments were conducted in near-vacuum conditions because the research was aiming at using this data for solar system objects. Then why test oxygen fugacity? Seems silly to me.

Questions:

1. Why does oxygen fugacity affect diffusion?

2. It's interesting to see how D(Ni) in olivine can change based on several parameters tested by Petry et al. What factors will I be changing and factors will be kept constant (with regards to T, P, oxygen fugacity, crystallographic orientation,and composition)? Partial answer: I do believe composition and crystallographic orientation will be constant. Composition of the olivine and spinel should be about constant, while crystallographic orientation could be random, depending on whether we're using single crystals or polycrystals.

3. How do scientific publications condense 50 page articles into 10 pages? Magic? Is there literature on the topic? Can I use a reverse process to increase the length of my essays five fold?

1. To determine whether or not olivine crystals rising from the upper mantle, I suspect these experiments will be run at higher pressures. I don't know this for sure though, I should check which press we may be using.

2. How pertinent is information on say, ZnGa2O4 combustion synthesis to MgGa2O4 combustion synthesis?

3. What happened to Dimebag Darrell's guitar solos after "Vulgar Display of Power"?

4. How long does it take for olivine temperatures to equilibrate with their surroundings? I'm sure there's data on this somewhere, but I don't have time to look it up right now. I'll get back to you on that.

A forthcoming entry will have answers to these questions. I know you're on the edge of your seat, but you'll just have to wait. Patience is a virtue.

If GeoRef and ISI Web of Science were boxers, ISI would win by TKO in the first round. GeoRef has yet to satisfactorily find enough articles, where ISI gives me too many results, all of which are pertinent to my searches, if not always my research.

I also spliced the wires to my car stereo back together while waiting to pick up my sister from work. It's working again. It's been a productive day.

Dr. Van Orman also addressed my earlier question about why a trivalent cation would not just hop right back in to the vacancy formed when it moved. The vacancy is 'mobile', as Mg is also able to hop into the site, stopping another ion from just popping back into place.

In class we've been meeting with the geology faculty, who have been describing possible research opportunities with them. We have only two professors left I believe, Dr. Ralph Harvey and Dr. Peter Whiting.

Background:
Scientists are debating whether or not olivine (Mg,Fe)2(SiO4) is open to transfer of rare earth elements with the Earth's mantle. Research has been done to find diffusion constants, however some papers disagree. Two researchers have found diffusion coefficients differing by two orders of magnitude.

Katherine Crispin, a graduate student in the geology dept., has been doing similar research on trivalent cation diffusion in MgO.

I remember a presentation Katherine gave last semester regarding progress in her research. She mentioned the following: When trivalent cations are used as substitutions for Magnesium, a divalent cation, a Magnesium vacancy must exist per 2 trivalent ions in order to charge balance the mineral. The vacancy can be considered to have a negative charge due to the lonely electrons in the atoms surrounding it in the crystal structure which have nothing to bond to. Similarly, the trivalent ion can be considered to have a positive charge, as there are no extra electrons surrounding it in the lattice to balance it. She suggested an attraction between adjacent vacancies and trivalent cations may pull the cation into the vacancy, increasing it's rate of diffusion.

My Project:
I will investigate diffusion of Scandium in olivine. Scandium is a trivalent rare earth element with an atomic radius similar to that of Magnesium. It is possible that the same effect mentioned above may increase the rate of diffusion of Scandium in olivine, specifically Forsterite, the Magnesium end member.

Why:
Olivine makes up a large portion of the Earth's mantle. In addition, the use of Forsterite, as opposed to the iron end member or a solid solution of the two, makes the process easier as Iron can be trivalent.

Questions I Have:
Should a vacancy pull a scandium in, I imagine an adjacent vacancy is created. What would stop that new vacancy from pulling the Scandium back, creating a sort of see-saw effect, resulting in a no net change in diffusion rate?

Links:
Olivine (Wikipedia)
Magnesium (Wikipedia)
Scandium (Wikipedia)
Rare Earth Elements (Wikipedia)

I had the following questions:
1. In what way does Mercury's orbit oscillate in 88 day cycles?

2. "Further, Fe-S alloys are better
characterized at the relevant pressures and temperatures [Fei
et al., 1997; Hillgren et al., 2000] for Mercury’s interior
than other candidate compounds (e.g., Fe-C, Fe-Si)."

Why isn't Fe-Ni a possibility? If I remember correctly, Ni is the second
most abundant element in the Earth's core and Sulfur is significantly
less so.

3. It seems to me that this paper assumes that the core must account for atleast the lion's share of the high bulk density, as opposed to the
crust. Why can't the crust be of an abnormally dense composition? What
do we know about the crust of Mercury?

I looked into orbital libration a little bit and I found this, which I thought was interesting. It's an animation of the moon's librations.
http://www.youtube.com/watch?v=_3ryt9fBOBE