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The Lanthanide Metals – Another Museum display for the Home Office

Last Updated: 4th Sep 2019

By Gareth Evans

Adventures with the 4f-block elements – PART 1


INTRODUCTION

This article highlights my preliminary work with Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium and Ytterbium. These members of the Lanthanide metals are very stable, and can be handled in air and at room temperature without any elaborate procedures, such as the use of argon glove boxes or high vacuum encapsulation techniques.

In Part 2 of the series, I will focus on the following Lanthanide metals; Lanthanum, Cerium, Praseodymium, Neodymium, Samarium and Europium. Though these elements are considered to be very reactive, my experience shows that they retain a metallic luster for several days to a few weeks provided the relative humidity is below about 30%. Europium is about as reactive as Lithium.

I will also include the construction details for a home-made Argon glove box in Part 2 of the series.

BACKGROUND

The Lanthanide metals are also known as the rare earth elements (rare earth metals or rare earth elements, abbreviated to REE) comprise a group of elements which are, remarkably similar in both their physical and chemical properties. This feature is attributable to their unique electronic configuration.

The term rare earth element is misleading as some of the Lanthanide metals are very common. Cerium, the most common rare earth, is more abundant than Cobalt. Yttrium is more abundant than Lead. Thulium is as abundant as Antimony, Mercury, Bismuth or Silver.

Promethium is truly the only real rare earth element. In minerals containing the rare earth metals it is present only in ultra-small amounts (<10−19%) resulting from either nuclear reactions with cosmic rays or the spontaneous fission of Uranium-238.

The tri-positive oxidation state dominates the chemistry of the Lanthanide metals. In the rare earth group, the increasing nuclear charge with a nearly uniform outer electronic structure results in a slight decrease in atomic radius as the atomic number increases. This shrinkage is largely responsible for the slight differences in the properties of these elements.

A more detailed discussion of the Lanthanide metals, their chemistry and their physical properties can be found online, see Wikipedia.

EVERY BEAUTIFUL PICTURE DESERVES AN EQUALLY BEAUTIFUL FRAME

It was my intention to create a significant display of the Lanthanide metals for my Home Office. I wanted the display to look very Victorian, so I chose to display the Lanthanide metals in apothecary style bottles.

Shown are some photos of the Lanthanide elements used to create the new display.

Terbium
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Thulium
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Ytterbium
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Shown below are the style of bottle that will be used for the Lanthanide metals; Lanthanum, Cerium, Praseodymium, Neodymium, Samarium and Europium. These bottles will become the focus of the second part of the series.

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Shown in the photo below are my first two Lanthanide metal display bottles for Thulium and Ytterbium. The wood I used is called Tasmanian Oak, but it is actually a species of Eucalyptus. It is a hard wood that stains well, and the stain I used was walnut. It was my intent to give the bottles a 19th century antique look – something you might have seen in the British Museum in the late 1800’s.

The holes in the wood serve two functions. Firstly, I needed the holes so I could secure and turn the wood in my metal lathe, and secondly the holes will be used to secure an internal display so the metals will appear as if they are floating in air. The last job is making the ‘antique’ labels.

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Below are the photos of my first two complete bottles – one contains a 900 gram ingot of Ytterbium and the other 500 gram of Thulium. The Ytterbium ingot was cleaned prior to display.

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Thulium in the bottle


The bottle labels are only temporary, and will be replaced with a more antique looking label after all the Lanthanides metals have been prepared for display.

The bottle contains an outer tube of borosilicate glass. The dimensions of this tube are 150 mm in height with an outer diameter of 85 mm. The lanthanide metal is contained in an inner tube of ‘scratch resistant’ polycarbonate. The dimensions of the polycarbonate tube are 130 mm in height with an outer diameter of 50 mm. This two bottle approach was chosen for several reasons, to protect the glass, to protect the wood, but also aesthetics. I have seen a few 18th century vintage bottles of this design and I liked the look. The end caps are secured by bolts that I machined on my metal turning lathe. On the top of the top caps is a decorative brass nut that I also machined on the lathe. It was knurled to give a decorative look. Below is a photo of the inner bottle.

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PROCEDURE

The manufacture of these display bottles required some simple woodwork, wood turning on the lathe and some minor metal turning also on the metal turning lathe. After the wood had been turned and sanded it was stained and varnished in maple. I have included some photos showing the hands-on work required to make the display.

Every project begins with something and this adventure began with Tasmanian oak. It is in fact a species of Eucalyptus, and it is available in many lengths and widths from the local hardware store.

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First the stock was cut into octagons before being turned on the metal turning lathe.

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The circular head caps were also cut from the main stock. Both top and bottom caps were then turned on the lathe to make the recess for the borosilicate glass tube. The octagon bases were then milled to size so that the distance between the outer recess diameter and the side of the octagon was the same in all cases. All wooden components were sanded using 240 grit paper, followed by three coats of stain and two coats of clear varnish.

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The end caps for the internal polycarbonate tube were also made from Tasmanian Oak. They were turned to size on the lathe, such that each had an outer lip the same diameter as the outer diameter of the polycarbonate tube. The hole was recessed so the mechanical hardware would fit snuggly. The plugs were also sanded with 240 grit paper, followed by three coats of stain and two coats of clear varnish. Tube and caps were held together with three very small brass screws.

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To hold everything in place, I turned a length of free-matching steel on the metal lathe (12L14) so the diameter of the turned piece could be given a M5 fine pitch thread. The diameter of the steel bar was 12 mm and the length of the machined section was 45 mm.

I also turned a small section of 12 mm diameter brass bar and gave it a decorative knurl. The knurled piece was then drill and tapped to take a M5 screw.

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WHY DO THIS?

The connection between minerals and the chemical elements is both a profound and an obvious one, but too few mineral collectors also collect the chemical elements. There are many reasons for this lack of interest, and finding suitable material that would display well is certainly high on the list. It became clear to me in the early days of my adventures with the chemical elements that a significant display would require a significant amount of work on my part. I am making things that cannot be bought or at the very least would cost too much to buy.




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