Thursday, March 20, 2014

Zinc phosphate “arrowheads” in the SEM

Imaging some zinc that had been soaked in a phosphate buffered saline-based solution last week, I ran across lots of little zinc phosphate crystals.  Two really stood out, and are shaped almost exactly like arrowheads.  Far out!

Zinc phosphate arrowhead (1)

Zinc phosphate arrowhead (2)

The instrument used was Michigan Tech’s Hitachi S-4700 FE-SEM.  Both of these images were captured in “low magnification” mode because the salt crystals are so darn big.  They measure a little less than 0.1 mm, and so they are a little smaller than you can see with the naked eye.

Thursday, March 13, 2014

ResearchGate introduces new “open review” feature

ResearchGate, a peer networking site for research professionals, is introducing an "open review" feature that allows users to comment on published studies and characterize them as "reproducible" or "non-reproducible," among other things. This could evolve into a very important tool for disseminating post-publication validation studies, and would be a welcome alternative to the current expensive, centralized validation efforts.

image

The statement that “peer review isn’t working” might be a little harsh, but there is at least anecdotal evidence to back it up. 

They seem to zero in on the current controversy surrounding the article “Stiumuls-triggered fate conversion of somatic cells into pluripotency,” using that as an example publication.  It is marked “non-reproducible” on the announcement page:

image

There are still some questions to be answered here. 

Could there be opportunity for abuse of this systems?  

Will it be an issue for novice ResearchGate users, who might tend to clutter the "reviews" area with unrelated questions and criticisms? 

The latter seems more likely, as ResearchGate does not easily allow for anonymity, and the “questions” feature is already cluttered with easily answered questions from undergraduate and graduate students.  Hopefully the helpful “open reviews” on ResearchGate will not be in the minority, as is currently the case with the questions feature.

Monday, June 17, 2013

Degradable zinc stent research featured in the June 2013 MRS Bulletin

Exciting news!  Our research on bioabsorbable zinc stents has been featured in the June 2013 edition of the Materials Research Society (MRS) Bulletin.  The article discusses our recent article in Advanced Materials titled “Zinc Exhibits Ideal Physiological Corrosion Behavior for Bioabsorbable Stents” (read it on Scribd).  They interview my advisor, Prof. Drelich, about our research program and discovery.

Bio Focus: Is zinc the perfect material for bioabsorbable stents?

I believe this article is free-to-read, but I could be wrong about that.  Feel free to contact me if you would like a copy!

Monday, April 29, 2013

New results in the Journal of the American Ceramic Society on rehydroxylation ceramic dating (2/2)

This post, second in a series of two (click for part one), discusses our communication to the Journal of the American Ceramic Society, entitled “Effect of humidity instability on rehydroxylation in fired clay ceramics” by J. Drelich, P. K. Bowen, and T. J. Scarlett, which appeared in vol. 96, issue 4, pages 1047-1050.  The abstract is as follows:

Several samples of the XIX-century Davenport pottery and XX-century structural masonry were reheated at 500°C and then exposed to a humid gas of controlled relative humidity. Changes in the sample masses were recorded in response to both systematic and transient step changes in humidity. In addition, a reheated masonry sample underwent a sequence of soaking and drying and hundreds of hours of interactions with humid air in between these treatments to examine long-term effects of extreme humidity fluctuations. All experimental results indicate that instantaneous humidity and the sample's hygral history have a negligible effect on the long-term kinetics of mass gain. This important finding provides strong experimental support for the newly developed rehydroxylation (RHX) ceramic dating technique by proving that humidity affects physically bonded water in the ceramics, but has a negligible effect on chemically bonded water.

doi: 10.1111/jace.12262
Preprints archived at ResearchGate and Scribd

In plain English: we messed with the humidity during rehydroxylation of fired clay ceramics, and it had no effect on the kinetics of mass gain.  Therefore, there is no long-term effect on the rehydroxylation (RHX) behavior that would skew projected dates.

It was stated in earlier work on RHX dating that humidity did not seem to have any serious effect on the performance of rehydroxylation ceramic dating, but definitive evidence was not provided.  This communication works to fill this void, and provides some definitive results for a certain sample type that shows that the original assertions were correct.  To prove this, the humidity was modulated both transiently (a brief burst of high humidity) and systematically (a change from low to high humidity partway through the test). 

In the first (transient) case, the slope of the time1/4 trendline was shown to be the same before and after the humidity was increased and again decreased, indicating that the rehydroxylation kinetics did not change.  Even when the sample was severely abused by soaking in water (i.e. raining) and being dried near the boiling point (i.e. baked in the sunshine), there were no indications that the long-term behavior experienced any changes (see image below).  This is good news!

Figure 3, 300dpi

The second (systematic) case showed the same thing: no changes in the trend were observed with a single jump in the humidity level.  This shows that a systematic change in humidity, like would be experienced season-to-season (such as winter-to-spring or monsoon-to-dry season), does not have an impact on the rate of water uptake.  (The same cannot be said for temperature, of course!)

Scribd preprint

Effect of Humidity Instability on Rehydroxylation in Fired Clay Ceramics by Patrick Bowen

Saturday, March 30, 2013

New results in the Journal of the American Ceramic Society on rehydroxylation ceramic dating (1/2)

We were busy at the end of last year.  We submitted one paper to the Journal of the American Ceramic Society (JACerS) on October 1st of last year, a communication to Advanced Materials on October 24th, and then a separate communication to JACerS in December.  Both of the JACerS papers have now made an appearance online, their preprints archived on Scribd and ResearchGate

This entry, part one in a series of two, discusses “Modeling Rehydration/Rehydroxylation Mass-Gain Curves from Davenport Ceramics” by P. K. Bowen, J. Drelich, and T. J. Scarlett, which appears in the Journal of the American Ceramic Society, vol. 96, issue 3, pages 885-891.  The abstract is as follows:

Rehydroxylation ceramic dating, a new technique that has shown promise as an archaeometric breakthrough, was applied to XIX-century samples of Davenport ceramics from Parowan, Utah in the United States. The samples were dried at 500°C to remove both physically and chemically bonded water and then exposed to a 20% relative humidity air to record the progression of rehydration/rehydroxylation over a period of 40 days. Both time1/4 and time1/n analyses were applied to the experimental mass gain vs. time results in an attempt to find the most appropriate treatment for the data. The time1/4 analysis yielded poor reproducibility and non-ideal fitting results to the Stage II mass gain, in which water reacts with meta-clays. Application of the time1/n model, where ‘n’ is the rehydroxylation exponent, improved the apparent linearity of Stage II mass gain in small samples. However, the time1/n treatment still provided a poor fit to data from larger specimens, indicating that some secondary effects related to sample size and water transport may exist. To examine the effects of porosity and macrostructure on rehydration/rehydroxylation processes, a pulverized sample of the same material was analyzed, resulting in improved sample-to-sample agreement in time1/n irrespective of mass variations. These findings have implications on the application of rehydroxylation ceramic dating.

doi: 10.1111/jace.12175
Preprints archived at ResearchGate and Scribd

In plain English: we compared and contrasted two empirical models in modeling post-heating mass gain curves.

A time1/4 treatment, the conventional approach, did not represent the sample behavior well; the results were quite obviously nonlinear with respect to the power law.  An expanded, time1/n (where the exponent is not fixed to n = 4) approach did a little bit better, but not all that much.  This is bad news.  While the time1/n approach is not proven for dating samples, it was, at first, a good way to better describe the rehydroxylation kinetics (see our 2011 contribution).  Now, it seems, it is only a bit better than the specific, time1/4, power law.

These samples, in theory, should provide wonderful rehydroxylation dating results!  What is going on?

To attempt to answer that question, we crushed some ceramic samples.  Instead of a ceramic sherd, now we were dealing with a fairly uniform ceramic powder.  Doing the same experiments yielded results that agreed much better with a power law (according to the generalized time1/n analysis), possibly indicating some contribution by the macro- and mesopore structure of the samples.  Of course, the kinetics of rehydroxylation were accelerated by this treatment because of the larger number of active surface sites.  Nevertheless, it is an interesting outcome.

It is quite early to speculate about why, exactly, the samples exhibit nonideal mass-gain, but it is evident to us that we are not alone in this observation.  With some luck, we, as a community, can tackle this issue and get rehydroxylation ceramic dating back on the track to archaeometric implementation.

Scribd preprint

Modeling Rehydration/Rehydroxylation Mass Gain Curves from Davenport Ceramics by Patrick Bowen