micro Mondays: cone 8 SEM view

micro Mondays: cone 8 SEM view

Today’s featured image shows a low-magnification SEM view of the cone 8 reduction cooled sample we introduced two weeks ago.  If you compare today’s image with the camera image from that post, you should be able to see that the brighter red patches in the camera image correspond to the more highly textured parts of today’s SEM image.  In upcoming posts we’ll show higher magnification SEM images to examine their detailed structure!

Acknowledgments:  Part of this work was performed at the Stanford Nano Shared Facilities (SNSF) of Stanford University.

micro Mondays: bejeweled

micro Mondays: bejeweled

In last week’s post we introduced a new surface sample of a high-iron stoneware piece by Dan Murphy that was wood fired to cone 8 and reduction cooled.  Today’s featured post shows a close-up image of this sample taken with a high power optical microscope under bright, direct illumination.  At the end of this post you can find a high resolution graphic that shows the location of this microscope image in relation to the camera photo from last week.

An extended study of images like this one (with bright direct illumination) gives the impression that the ceramic surface consists of a black-gunmetal glossy substrate with red-orange crystals growing on top.  We are of course led to wonder about the chemical composition and morphological details of these crystals and the substrate – next week we’ll begin looking at some SEM and EDS images that provide some clues.

Acknowledgments:  Part of this work was performed at the Stanford Nano Shared Facilities (SNSF) of Stanford University.

21nov16full

micro Mondays: cone 8 reduction cool

micro Mondays: cone 8 reduction cool

This week we shift our focus to a new surface sample, taken from a piece by Dan Murphy (Utah State University).  The clay is a high-iron stoneware body and the piece was wood-fired to cone 8 and reduction cooled.  Today’s featured image shows a close-up of a typical surface feature on this piece — a “splotch” of brighter red-orange color sitting on a darker purple-black background.  Looking at the piece by eye, areas with a high density of this sort of splotch have a bright red tone whereas areas without them appear darker, tending towards black.  Today’s featured image was taken with a DSLR camera with a macro zoom lens; starting next week we’ll look at optical and electron microscope images to reveal the fine structure of this feature.  Dan and I began studying this and other similar samples last July; we are planning a continuing research program that will utilize both the surface analysis facilities at Stanford and the ceramics facilities at USU.

The high-iron reduction cooled surface is quite different from the high-fired porcelaneous “hexagons” surface that we have discussed over the past couple of months.  There is no glassy matrix and we did not need to use acid etching to reveal the micro/nano-crystalline structures that we will show in upcoming posts.  The images raise some intriguing questions about how iron crystals form in cone 8 reduction-cool firings, and whether there could be drastically different physical mechanisms of color formation in firings that stop at cone 8 versus firings that continue to cone 10 and above…

micro Mondays: the corundum conundrum

micro Mondays: the corundum conundrum

I had the pleasure to chat yesterday with Dr. Bill Carty from Alfred University about the story of the alumina/hematite hexagons that I learned from the Kusano et al. paper, which we’ve been exploring here in the microMondays blog posts.  Bill was most surprised by the part about the alumina hexagons crystallizing out of the melt, as the formation of only mullite crystals would be expected in the cooling of a simple aluminosilicate melt.  Bill and Dan Murphy (of Utah State University) and I came around to thinking that it must be something about the fluxes present and perhaps atmospheric reduction that promotes alumina crystallization, and therefore flashing, but the details are mysterious and will require further technical investigation.  To me it’s quite gratifying to experience the story coming full circle back to craft practice with the identification of compelling new questions for scientific research!

Next week we’ll move on to looking at a different sort of sample with quite different crystal properties that determine its surface qualities.

Acknowledgments:  Part of this work was performed at the Stanford Nano Shared Facilities (SNSF) of Stanford University.

micro Mondays: A tool called nanoSIMS

micro Mondays: A tool called nanoSIMS

Today’s featured image is a “small” image in that it is only 256×256 pixels, but it conveys a lot of information!  Last week we discussed how the EDS (Energy-Dispersive Spectroscopy) tool on an electron microscope can provide information on not only the topography but the elemental composition of microscopic features on a ceramic surface, but we noted that the spatial resolution of this technique is insufficient to provide strong evidence in support of the idea that red iron oxide (hematite) crystals decorate the edges of larger alumina hexagonal platelets.  Today’s featured image was acquired using a very sophisticated instrument called a nanoSIMS (nano Secondary Ion Mass Spectrometer).  The featured image is a false-color image of one of our familiar hexagons, in which green indicates the presence of silicon, blue indicates the presence of alumina, and red indicates the presence of iron.  Here we more clearly see that iron is localized to the exposed edges of the hexagonal platelet, which itself is clearly an alumina crystal.  In the original work by Y. Kusano and co-workers on alumina, hematite and flashing colors, a rather different technical approach was utilized that required removal of the hexagonal platelets from the ceramic surface so that they could be studied in isolation using a TEM (Transmission Electron Microscope) instrument.  That body of research provides quite detailed and conclusive identification of the hematite and alumina crystals.  Here in this series of NCECA blog posts however we will stick to analysis techniques that allow us to study microstructures on fired ceramic surfaces in situ.

K-12 STEAM Connections:  Some of your students may not be familiar with, or fully understand, the concept of a false-color image.  More common examples of false-color images include weather maps, thermal images, and red/blue/purple election maps of the USA.  As noted in the brief Wikipedia article on false color, “false color” representations can be used to artistic effect as in the work of Andy Warhol…

Acknowledgments:  Part of this work was performed at the Stanford Nano Shared Facilities (SNSF) of Stanford University.