Archives for the Month of March 2008 on Geol 390
Research Proposal Outline: Check
My proposal outline is due tomorrow and I've just finished writing it. I have a bit more information on my project now. Tests will all be run at 1 atm because diffusion in olivine is a slow process and pressure just makes it slower. At temperatures below 1400 degrees, it can take 6+ months to get just the minimum diffusion length to enable electron microprobe analysis. Obviously, we wouldn't want to make this take that much longer. I don't even have a year to finish this, so that is clearly unacceptable. Temperatures will range from 1400 C to 2000 C and 3 different lengths of time will be tested in order to check the accuracy of the experiments, as the diffusion coefficient should not change as a function of time. In addition, diffusion will be measured in all 3 crystal axes in half of the experiments and just the fastest axis in the rest. This is in order to get a feel for how it works in all directions, but still get the project completed on time.
Chakraborty and Friends
The due date for my proposal outline is fast approaching. It's approaching about as fast as Monday is approaching. This is because they are, in fact, the same day.
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?
Annotated Bibliographies and Questions
Questions I have while I'm reading articles...
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.
Review Articles and Car Stereos
I've picked up a few more articles regarding my project. Prof. Hauck has noted more than once how useful review articles can be. I happened to find two this week, one entitled "Diffusion in solid-Earth systems" (Watson, Baxter) and another "Diffusion in minerals at high pressure: a review" (Bejina et al.) I've been looking at them and found them extremely useful. The latter attempts to create a database of diffusion rates above 1 GPa. In this database, there are values for diffusion in olivine. However, the only elements represented are Mg, Fe, and Ni. There doesn't seem to be much research done into trivalent cation diffusion yet unless I'm just unable to find information on the topic, which wouldn't surprise me. I'm having trouble finding articles on combustion synthesis but I know they have to be out there somewhere. I have a few other articles printed as well, and a few I have to find in hard copy at the library.
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.