Tuesday, 12 May 2015

Low cost laser cut optical mounts

I have been thinking about low cost ways of mounting optics in the lab and as long as you don't need a very rigid mount (i.e. for interferometer) you can get away with these plastic optical mounts.

The advantages of these laser cut mounts over 3d printed mounts are the speed at which you can make a mounts which is an order of magnitude faster and the cost (if you wanted to outsource making of them) is much lower with many different companies now providing low cost laser cutting. We have a CO2 laser cutter in the lab so we can make around ten of these in about 10-20 minutes. They are designed for 1 inch 25.4 mm optics such as lenses and mirrors and with the springs allow for adjustment and alignment of the optics.

A screw in the side holds the optic in place while the three bolts offset from the mounting plate allow for adjustment of the angle of the optic.

The back mounting plate has a slot for a 4 mm bolt to connect it to an optical post.

One big improvement would be to cut the same design out aluminium which would allow for a more rigid design so that more precise instruments could be constructed. Comparing the physical properties of different materials.

Material Coefficient of linear expansion (μm/(m K)) Young's Modulus (MPa)
Acrylic 75 3200
Aluminium 22.2 69000
PET 59.4 2700
PLA 80-90 1750
ABS 80 2200
Sources 1,2,3,4,5

Aluminum is optimal with a very high rigidity and low thermal coefficient of linear expansion. PET has a low coefficient but isn't as rigid as Acrylic. PLA and ABS both 3d printed materials lack rigidity and have high thermal coefficients. So for some applications acrylic optical mounts may provide high enough rigidity with low enough thermal expansion for some applications. However I can imagine some crosslinked epoxies could improve the properties of optical mounts made by 3d printers (quick search found a resin with Young's modulus of 2700)

I am currently working on using these in a spectrometer design. I will upload the designs soon for the optical mount and fixtures needed once I have refined the design a bit more.

Tuesday, 21 April 2015

Kawau Island copper mines

Visited Kawau Island off the east coast of New Zealand in the Hauraki gulf last weekend. In 1844 copper was discovered on the Island and a mine was set up next to the coast. The chimney you see below is the engine house that housed a big steam engine to pump water out of the mine.

Here is the description of the history of the site.

I loved to see the amazing copper carbonate deposits around the copper mine and on the rocks around the area.

The rocks around the site were clearly a greenish-blue copper carbonate colour.

 However the rocks around the cave entrance were more of blue colour.

This indicates the fresh water around the cave, probably flows over the rocks when it rains, is hydrating the copper and giving rise to the classic Cu2+ colour.

The basic copper carbonate is green-blue colour and is called Malachite (Cu2CO3(OH)2).
 The hydrated copper carbonate is a blue colour and is called Azurite (Cu3(CO3)2(OH)2).
Azurite is broken down into Malachite over time. Here is an excellent picture of a rock caught during the transition.

Sarah Thompson in the Photon Factory works on pigments and their photo degradation. So I was interested to see if this breakdown is important for Azurite pigments.
Raphael, Madonna and Child Enthroned with Saints, The Metropolitan Museum of Art
Sure enough in Raphael's Madonna and Child Enthroned with Saints the Virgin's mantle is darkened and a green colour due to Malachite where orginally it would have been a dark blue Azurite.

A painting with it particulary well preserved is Hans Holbein's Lady with a Squirrel and a Starling.

Hans Holbein the Younger, Lady with a Squirrel and a Starling, National Gallery, London
 It was a great day and the views from the boat were well worth the trip.

Thursday, 9 April 2015



Keen to do a science and technology fair project but don't know where to start. Check out a website a group of students and teachers (including I) put together in 2012 to give students resources to do science and technology fair projects and teachers the resources to integrate science and technology fair projects with NCEA. I have just added a Facebook page and added in a new forum to the wiki. Also if you a teacher or student and want to contribute that would be great.

There are five main sections of the website including

Steps - What are the steps to complete a science or technology project? What are some tips and tricks to making award winning projects.
Pathways - A teachers resource for NCEA integration with science and technology projects.
Forum - Need help with your science and technology fair project or need help with ideas check out the forum.
Other projects - Get inspired with other students projects and where they have taken them.
Mentoring - Want to get connected with groups and researchers that can help you with your topic. Fill in the form and we can get back to you with people that can help.

Monday, 6 April 2015

Lunar Eclipse

This Saturday stayed up with some leaders from Easter camp out at Bucklands beach to watch the lunar eclipse. Thanks to Jack Fowler we captured the whole event on his iphone pushed up against the eyepiece of my small 76 mm Newtonian telescope with a moon filter. Here are the shots.

Thanks also to the group that stayed up till 1pm with me to capture the eclipse that started at around 11pm.

Tuesday, 27 January 2015

We have only just worked out how sodium explodes in water

This classic experiment is one of the many explosions that encouraged me to pursue a career in chemistry. But ever wonder why it explodes I thought that the generation of hydrogen on the surface had a part to play this does explain the burning but for an explosion you need to have a large enough surface area to have a reaction fast enough to really get a boom. If you know anything about the thermite reaction or flour bombs a huge surface area allows the reaction to proceed fast enough to build up pressure and explode. Also unlike gun powder which already has the fuel and oxidant mixed together only at the sodium water interface can you get the reaction so surface area is crucial. Using a high speed camera and some neat simulations researchers have just work out how sodium increases it's surface area enough to cause an explosion.

Put most simply sodium quite easily gives up its outer most electron and becomes the positive sodium ion. What they found was that when sodium is put into water the water sucks the electrons from the surface of the sodium metal. Without the electron you just have positive ions which repel each other this causes small needle like fingers of sodium to extend into the water. This greatly increases the surface area causing hydrogen gas build up and allows for the big explosion.

The high speed images show the needle like filaments. The crucial frame is 0.4ps 5th image from the top middle column where you can see the needles of sodium and potassium (potassium is added to make a liquid metal for easier dropping). The next frame shows the explosion at the surface.

Now comes the awesome simulations. So using quantum calculations they modeled nano drops and show the electrons (blue in the image below) moving into the water and then the sodium ions breaking apart as there are no longer any electron glue to hold them together.
Scaling up the simulations using some assumptions that reduce the amount of computer processing time they showed a larger drop exploding at the surface.

Check out the movie they put together and the paper. I wonder what other elementary reactions are still not fully understood.