Applied MineralogistThe bulletin of the pplied ineralogy roupA M G

June 2017Volume 2, Number 2

Edited by: George Guice Andrew Dobrzanski

Web: http://www.minersoc.org/amg.htmlTwitter: @amg_minEmail: amgminsoc@gmail.com

From the AMG committee

Hello and welcome to this 4-page edition of Applied Mineralogist - the bulletin of the Applied Mineralogy Group.

This edition contains a huge variety of fascinating features, from the complications associated with studying radioactive materials, to characterising aggregates using QEMSCAN®. As always, this edition contains fun facts and a fantastic photomicrograph. If you, like Bernardo, want to be included in our #AppliedMineralogy f ea ture, ment ion @amg_min in your photomicrograph tweets to increase your chance of being noticed.

Postgraduates, remember to apply for our travel bursary before the end of August. Up to £400 is a v a i l a b l e ! Fo r f u l l d e t a i l s , g o t o : http://www.minersoc.org/amg.html.

#AppliedMineralogy @MicROCKscopica

The photomicrograph shows an intr icate ("symplectic") intergrowth of pyroxene and plagioclase in a granulite from N. Manitoba, Canada.

The coherent distribution of colours, indicating optical continuity, shows that this pattern is actually provided by one crystal of pyroxene and one of plagioclase intimately compenetrated. These minerals formed by replacement of a pre-existing crystal of garnet.

Width of view: 1.7 mm. (Sample courtesy of Martha Growdon). Photo by Bernardo Cesare, Geosciences Department, University of Padova, Italy.

More fantastic photomicrographs, visit Bernardo’s website: www.microckscopica.org

Characterisation of aggregates using automated scanning electron microscopy (QEMSCAN®) Peter Scott & Gavyn Rollinson (Camborne School of Mines)

The UK annually consumes ~100 million tonnes of crushed rock aggregates. Dominant uses include: road-building and repairing, rail ballast and various concrete products. Aggregate properties and their suitability for use vary widely within and between different rock types. Hence, in a sales contract, a description of the petrography is required, alongside identification of rock type. Additionally, a description of physical properties, such as strength, susceptibility to abrasion and skid resistance is important. Thin section optical microscopy, which traditionally involves point counting, is typically used to establish rock identity and mineral percentages. However, the technique can suffer from operator bias and subjectivity, particularly when recognising and identifying smaller phases, many of which may bind the rock together or are alteration products of larger crystals. Both of these can have a marked effect on the aggregate properties.

An automated scanning electron microscope, such as a ®QEMSCAN , provides an objective way to assess the

petrography and mineralogy of an aggregate. It scans the surface of a polished sample, rapidly collecting backscattered electron and X-ray spectra data. These data can provide quantitative mineralogy of the major, minor and trace phases. Grain and/or crystal sizes and their contact relationships, can also be established.

Ordovician granodiorite from Mountsorrel Quarry in Leicestershire is illustrated in Figure 1a. This is an important source of strong, general purpose, roadstone and rail ballast with a moderate skid resistance (Polished Stone Value (PSV) = 51-53). The rock can be described generally as equigranular, with plagioclase, K-feldspar and quartz as the major minerals, but with significant chloritisation and minor epidotisation. An example of determined statistics from Moutsorrel Quarry are: - plagioclase feldspar (35-49%, average size 106- 245 µm) - K-feldspar (22-26%, 67-129 µm)

In this issue:

Ÿ From the AMG committee

Ÿ #AppliedMineralogy @MicROCKscopica

Ÿ Aggregate characterisation using QEMSCAN®

Ÿ Special feature: Radioactive materials and EMPA

Ÿ Coffee room small-talk: mineral application factsŸ Calendar Ÿ About us

AMGAMG

Electron Probe Micro-Analysis (EPMA) has been one of the key analytical tools for the nuclear industry since its birth. Having ‘grown up’ in the 50's and 60's, E P M A i s o n e o f t h e f ew techniques available which can provide micron-scale analysis of these unique materials with little sample preparation.

The aim of this short article is to give you some idea as to the complications associated with samples from the nuclear industry, relative to more common EMPA samples . It's based on a lecture presented as part of a NERC Advanced Training short course on the Fundamentals of EPMA, held at the University of Bristol in September 2016.

ShieldingThe first and most obvious problem is that these materials are radioactive (RA) – that is, they

emit ionising radiation. Since the different types of radiation have different properties, they require different levels and types of shielding.

Biological ShieldingOur main concern is to protect the analysis systems from the damaging effects of the radiation. How much shielding is required, and of what type, will depend on what type of radiation our samples emit, and how much. The analytical systems include not just the instruments, but also the fragile biological bits we'll call ‘the operators'. The first line of protection for the operators is physical separation. For a- and b-emitters we can use glove boxes, possibly with leaded gloves (typically of the 'one-size-fits-nobody' variety) and leaded glass windows (Fig. 1). The leaded gloves in particular are very tiring to use for prolonged periods, and make manipulating

small tools and samples difficult. Glove boxes also have the benefit that the environment the samples are handled and stored in can be tightly controlled, for example low O and H O levels for 2 2

sensitive materials. For the more penetrating g- and n-emitters, heavier metal shielding and remote manipulation is needed. In these 'hot cells' the windows may be as much as 1m thick. To transfer samples between a box-line and an out-of-line instrument we need a transfer system. This consists of a transfer arm docked to a boxline, and an EPMA with a m a t c h i n g d o c k i n g p o r t

- quartz (23-30%, 288-434 µm) - chlorite (0.5-6.1%, 26-78µm) - biotite (0.5-2.7%, 30-131µm) - muscovite (0.2-0.7%, 19-21µm) - hornblende (1.2-1.9%, 29-104µm) - calcite (0.01-1.0%, 19-43µm) - epidote (0.03-0.3%, 20-35µm) - Fe oxides (0.4-0.7%, 55-70 µm) - ilmenite (0.06-0.21%, 40-50 µm) - seven minerals in amounts greater than 0.01%.

A single sample of a Silurian sandstone, known in the aggregate industry as a gritstone, from Roan Edge Quarry, near Kendal, Cumbria is illustrated in Figure 1b. This is a high quality roadstone that is suitable for use on motorway surfaces (PSV = 63-65). It is fine grained, made up of quartz (37%), plagioclase (16%), K-feldspar (14%), chlorite (13%), biotite (10%), muscovite (6%) and calcite (2%), plus eight other minerals in amounts greater than 0.01%. Percentages of the major minerals vary considerably between different samples from the same quarry. The quartz is present as grains (median size 41 µm), as are some of the plagioclase and K-feldspar, although the feldspars and the other minerals mostly appear to be interstitial and/or diagenetic and act to bind the rock together.

2mm 0.5mm

Special Feature: Electron Probe Microanalysis of Radioactive MaterialsMike Matthews (AWE) © British Crown Owned Copyright 2017/AWE

Figure 1: Typical box-line for handling and preparing a-emitting materials.

Reference: Scott P.W. & Rollinson, G.K. 2015. Pp 49-68 in Hunger, E. and Brown, T. J. (Eds.) Proceedings of the 18th Extractive Industry Geology Conference 2014 and technical meeting 2015, EIG Conferences Ltd, 250pp. For further details, see: http://www.eigconferences.com/2016-proceedings/

Figure 1: (a) Mountsorrel granodiorite, Leicestershire. (b) Roan Edge gritstone, Cumbria. Colours: Pale blue – plagioclase. Green – K-feldspar. Pale pink – quartz. Purple – biotite. Pale purple – muscovite. Grey-green – Ca amphibole. Black – Fe oxides. Red – ilmenite. Bright green – chlorite. Bright blue – calcite.

a) b)

respectively. A double-door system

maintains containment of both the

transfer vessel and the box-

line/instrument throughout the

sample transfer. Once in the

instrument, the analysis chamber

walls are usually sufficient to protect

the operator from a- and b-sources.

For the more penetrating radiations,

this isn't sufficient and the instrument

itself is installed in a lead lined

chamber and operated remotely.

Instrument ShieldingWe also need to consider what effects

the radiation has on the instrument.

This can range from adverse effects

on our analysis, such as spurious

peaks or elevated backgrounds, to

physical damage. Fig. 2 shows the

very noticeable degradation of

resolution of an unshielded Silicon

Drift Detector (SDD) used for

analysing Pu samples. Tribet et al.

(2016)  reported RA damage to an

SDD, noting that there was a sharp

loss of resolution after each use. This

partially recovered between uses,

but resolution still degraded steadily

with time. Since such detectors

require line-of-sight of the sample

this type of damage is very difficult to

completely prevent. However, a

heavy metal collimator in front of the

sensor reduces the area and

therefore the rate of damage

accumulation (although with a

commensurate loss in intensity).

Retracting the detector behind a

heavy metal flap when not in use can

also significantly increase the

useable lifetime of the detector. Fig. 3

shows two ED spectra for a 15keV

analysis of a compound sample

containing areas of Pu-alloy. The

upper plot shows the spectrum with

the beam on and the lower shows the

spectrum recorded with the beam off.

Whilst the lower energy peaks

disappear in the 'beam-off' spectrum,

the higher energy peaks remain.

These are generated by RA-induced

self-fluorescence in Pu-alloy areas of

the sample. The wide field of

acquisition of the ED detector mean

tha t these peaks would no t

necessarily only appear for the

sample containing the RA elements,

but also for any adjacent samples not

containing any RA material. Note also

that although the analysis was carried

Figure 2: Time sequence of EDS spectra acquired on the same sample using an unshielded SDD. The loss of resolution is due to RA damage in the detector. (Brierley, pers. comm., with permission).

Figure 3: EDS spectra acquired at 15kV on a U-alloy sample with the beam on (upper) and beam off (lower). The high energy characteristic x-ray lines are produced by RA induced self-fluorescence in the sample. (Brierley, pers. comm. With permission).

out at 15keV, the background and

characteristic peaks are evident

above 20keV. The main defence

against this type of effect is to limit as

far as possible the mass of RA, for

example by minimising sample size

and loading fewer samples. The gas

counter in a Wavelength Dispersive

Spectrometer (WDS) is also not

immune to RA effects. Although it

doesn't have direct line-of-sight of the

sample, the more penetrating

radiations can pass through the

analysis chamber and spectrometer

housing walls to cause unwanted

ionisations in the counter gas. This

can dramatically increase the

background signal. Walker (1999)  3reported a background level of 2x10

cps for an unshielded spectrometer.

The addition of heavy metal shielding

in the spectrometer housing and

around the sample block reduced this 2to 1x10 cps. He was able to further

1reduce the level to 1x10 cps by using

the energy filtering capability of the

counter electronics to suppress the

higher energy ionisations. Whilst this

d i d r e d u c e t h e m e a s u r e d

background signal it doesn't prevent

the ionisations still reaching the

counter through the shielding and

these effectively reduce the useable

c o u n t ra t e o f t h e d e t e c t o r.

Interested in joining the Mineralogical Society and Applied Mineralogy Group? Go to: for membership details.http://www.minersoc.org/

Coffee break small-talk: mineral application facts

Did you know?

Ÿ That the magnetising force of a Dy-Nd-Fe-B magnet is over 10-12 times that of a ferrite magnet?

Ÿ That the UK produced 65,000 tonnes of high

quality acid-grade fluorspar in 2016?

3Ÿ That Tritium ( H) has the same half life as a

honey-badger? (12.32 years)?

Ÿ The 440 m high Sears Tower (Illinois)

contains enough aggregates (concrete, sand,

gravel) to pave 13 km of road.

Calendar

REDOX, Special interest groups of the Min. Soc., Manchester. http://www.minersoc.org/Redox.html

Goldschmidt 2017, Paris, France. https://goldschmidt.info/2017/

14th Biennial SGA meeting, Québec City, Canada. http://sga2017.ca/

AMG bursary deadline. See: http://www.minersoc.org/amg.html

Fermor Meeting, London, UK.

https://www.geolsoc.org.uk/fermor17

Platinum Symposium, Mokopane, South Africa

Granulites & granulites, Ullapool, UK

JUN‘17 21 - 22

AUG ‘17 7 - 11

AMGAMG

So why bother?After the not inconsiderable

effort and cost of manufacturing,

installing, and operating a

s h i e l d e d i n s t r u m e n t a n d

preparation facilities, EPMA is

capable of producing very high

quality analyses.   Fig. 4 shows an

RGB composite qualitative x-ray

map of sub-micron UC and Pu Fe 6

inclusions in a Pu-Ga alloy.

Bremier et al. (2003)  published a

study of the effects of fabrication

additives to the microstructure of

nuclear fuel pellets. The pellet

m i c ro s t r u c t u re c a n h a ve

significant potential impacts for

the utilisation and ageing profile

of the fuel. With the high full-life

cost of a nuclear reactor any

improvements in efficiency are

highly desirable.

ConclusionsTo briefly conclude, EPMA of

radioactive material is not cheap

or trivial and can be extremely

time consuming. The overhead of

having to prepare the samples in

a box-line, then transfer them to

t h e i n s t r u m e n t i s n o t

insignificant. Also, the highly

shielded instruments may be

limited to loading only one

sample at a time. Even something

as simple as changing a W-

filament can take several days

and require several people to

achieve, and servicing the

instrument is also obviously not

trivial. However, it is achievable,

and is capable of producing high

fidelity results (with effort).

E P M A o f f e r s s i g n i f i c a n t

advantages in the type of data

that can be obtained. It is also

very satisfying to be able to tease

out good results from these tricky

and unique materials.

References

[1] Tribet et al. (2016) Electron

Probe Microanalysis of

Transuranium Elements in Nuclear

Fuels and Waste Matrixes, Electron

Probe Microanalysis of Materials

Today Practical Aspects

[2] Walker (1999) Electron probe

microanalysis of irradiated nuclear

fuel: an overview, J. Anal. At.

Spectrom.

[3] Brémier et al. (2003) Large area

quantitative X-ray mapping of

(U,Pu)O nuclear fuel pellets using 2

wavelength dispersive electron

probe microanalysis, Spectrochim.

Acta - Part B At. Spectrosc.

Figure 4: Red (U), green (Fe), blue (Ga) composite image showing the association of UC and Pu Fe sub-micron inclusions in a 6

Pu-Ga alloy. Pu Fe is a low melting point 6

eutectic phase which forms at the grain boundaries and triple points.

AUG ‘17 20 - 23

SEP ‘171

JUL ‘1830 - 6

About UsFounded in 1963 by Norman F.M. Henry, the AMG is a special interest group of the Mineralogical Society of Great Britain and Ireland. We encourage and promote the study and research of mineralogy applied to ores and related industrial mineral materials. This encompasses: ore microscopy, fluid inclusions, nuclear minerals, coals, refractories, slags, ceramics, building materials, nuclear waste disposal, carbon capture and storage, down-hole borehole alteration, and mineral-related health hazards.

SEP ‘1725 - 27

20 µm

JUL ‘18 10 - 13