Sapphire:
The black
sheep of the
watch industry
Richard Foster and Daniele Fregonese of Advanced Energy
Minerals, alongside Frederic Falise of Scientific Visual SA, discuss
the sustainability of sapphire – an important material in the watch
industry
EVERY time you look at your watch, you are taking
advantage of the properties of sapphire without
noticing them. Sapphire is important in our everyday
life because of its transparency and imperviousness
to scratches. In addition to watch covers, it is used in
large volumes for applications from LED substrates
to scratchproof windows for military vehicles.
A sizeable quantity of sapphire is used to make
jewellery and watches, where high-end consumers
are growing conscious of the sustainability of the
products they buy. They would rather buy well-made
products that last and maintain their value than
cheaper goods they would have to throw away after
a short time.
Industrially produced synthetic sapphire is as
hard as natural sapphire but more transparent
because it lacks the trace elements that give gems
their various hues. Sapphire is often marketed as
‘scratch resistant’ or ‘virtually scratchproof’. This
is because it measures nine on the Mohs scale of hardness, meaning that it can only be scratched by
a harder substance such as diamond, which is rated
at ten. (1)
The industrial process to manufacture and customise
sapphire takes place in three major steps. The
first step is to manufacture the high-purity alumina
(aluminium oxide, called HPA). The second step is
to crystallise this HPA at very high temperatures, of
around 2,050°C, to form a raw crystal of synthetic
sapphire. In the third step, this crystal mass is
shaped and sliced into pieces with diamond-coated
saws. The resulting wafers are then ground and
polished for the desired application.
These processes cause a substantial carbon
footprint that we may not think about until we
are made aware of it. For instance the total
crystallisation step (second step) generates
43Kg CO2 per kg of sapphire produced.
However, it can be reduced substantially by
careful attention to each step.
Producing HPA
Manufacturing HPA starts with a mineral feedstock. If
this feedstock is manufactured only with hydropower,
its only carbon footprint at the gate of the factory
where HPA is manufactured is from the transportation.
If the source is close to the factory, this can be
minimal or even brought to zero by compensation.
This is the case for Advanced Energy Minerals (AEM)
which manufactures HPA in Québec, Canada. It uses
feedstock from Québec that is produced predominantly
with hydropower.
The AEM factory was designed to minimise power
consumption by using a patented chlorine leach
crystallisation process. Local renewable sources,
hydro and wind from Hydro Quebec, provide AEM’s
power. The factory at Cap-Chat is the neighbour of
Le Nordais wind park with 133 turbines. Currently,
renewables are at 96%, with specific plans to reach
100% by the end of the year. This will reduce CO2
emissions from the current value of less than two
tonnes of CO2 per tonne of HPA to practically zero.
This is in strong contrast to those using the
traditional alkoxide process, typically non-renewably
powered, which emits 12.3 tonnes of CO2 per tonne
of HPA. Other producers have a goal of reducing this
by a factor of five, which is still very high.
Customisation to meet customer requirements
makes the following process steps more efficient.
AEM has a product line to deliver customised 4N and
5N compacted alumina to its customers. This ranges
in size from pucks of a few grams to giant pucks of
up to 21kg.
HPA to sapphire
The processes to convert HPA to sapphire all melt
the alumina at a temperature above 2,050°C. This is
followed by a slow cooling process that takes one to
two weeks to create a crystal of sapphire. Because
this is a low-tech process, the crystal is not perfect.
It can, however, be influenced by the quality of the
HPA used and the dexterity of the furnace operator.
Lower-purity HPA is used for LEDs. The next level
of purity finds application in watch covers. The
highest quality HPA is transparent to deep UV due
to its low titanium content. This makes it suitable
for medical applications. Crystallisation issues may
also impact the final product quality and determine
the final application. For instance, an LED device
containing an imperfect and inhomogenous sapphire
component may experience decreased efficiency, a
shorter lifespan, or a variation in emission colour. (3)
In addition to HPA quality, the different sapphire growing processes yield crystals that are suitable for different applications. For these reasons, the processes divide here. We have chosen a case study from the Swiss watch industry that shows the environmental benefits of attention to detail. The worldwide watch market of $71bn in 2022 has an expected CAGR of 5%. (4) In particular, it is an important economic driver in Switzerland, where watch exports total almost $25bn. (5) To fulfil this demand, 21 million watch covers are manufactured each year to high-quality standards in Switzerland. (There is also a huge market for smart watches manufactured in Asia that have crystal sapphire covers.) As we shall see, the remaining processing multiplies the environmental costs of the previous steps.
In addition to HPA quality, the different sapphire growing processes yield crystals that are suitable for different applications. For these reasons, the processes divide here. We have chosen a case study from the Swiss watch industry that shows the environmental benefits of attention to detail. The worldwide watch market of $71bn in 2022 has an expected CAGR of 5%. (4) In particular, it is an important economic driver in Switzerland, where watch exports total almost $25bn. (5) To fulfil this demand, 21 million watch covers are manufactured each year to high-quality standards in Switzerland. (There is also a huge market for smart watches manufactured in Asia that have crystal sapphire covers.) As we shall see, the remaining processing multiplies the environmental costs of the previous steps.
Sapphire crystals for watch covers are traditionally
grown with the Verneuil process. The result that
awaits further processing is called a ‘carrot’ in the
trade. It is close to a cylinder in form, approximately
15cm high and 3-4cm in diameter.
Of course, this step has a typical energy requirement
if not performed with green energy. The relevant
CO2 emission would be an average of 89g/kWh for
Switzerland or 475g/kWh worldwide.
Sapphire to watch cover
Because the crystal sapphire carrot has an imperfect
form and contains defects, there will be substantial
yield loss during the further processing steps.
This loss can be minimised by generating a digital
model of the carrot that is based on a 3D scan with
specialised confocal tomography equipment.
It is worth noting that cutting and polishing sapphire
is highly energy-consuming, as the material’s
exceptional hardness presents a significant
challenge
The first step with yield loss is the scrapping of
carrots after inspection and before further processing
due to an unacceptable rate of defects. This has
typically averaged 10% for carrots from the Verneuil
process. Grinding the remaining carrots to the
correct core size and shape produces a form factor yield of 42%. The yield
of cores is then 87%,
meaning that 13% of
cores that reach this
point are thrown away
because of small defects
in the crystal sapphire.
The yield from slicing
the core into wafers and
polishing them is 85%.
The result is an average
combined yield of 28%
in the watch industry
for a flat watch cover.6
This will have a diameter
ranging from 25-45mm
and a thickness from
1.6-6mm. The typical
weight is 4.6g.
The yield means dividing the incoming environmental cost by 0.28, which almost quadruples it. For a domed watch cover, this yield is much lower at 4%, multiplying the incoming cost by 25.
The yield means dividing the incoming environmental cost by 0.28, which almost quadruples it. For a domed watch cover, this yield is much lower at 4%, multiplying the incoming cost by 25.
These steps can all be optimised with digital quality
control from the Swiss company Scientific Visual.
The company manufactures scanners for quality
inspection of industrial crystals (Fig. 3). Using these
automated tools, individual steps can be optimised
to avoid defects. For example, it prevents defective
crystal parts from entering costly processing. In
addition, by providing feedback to crystal growers, fewer crystals will have to be scrapped. The
simulated form for the cylinder can be moved so that
a minimum of defects remain in the physical carrot.
Slicing can also be offset to bring defects between
adjacent wafers. These steps all work to bring the
yield for a flat cover to 34%. For a domed watch
cover, the improvement is from 4% to 5%, which is a
25% improvement.
These steps can all be
optimised using digital
quality control from the
Swiss company Scientific
Visual
Let’s see what the numbers show. In the worst-case
scenario, HPA emits 12.3 grams of CO2 per gram of
HPA. Manufacturing our flat watch cover emits:
12.3 x 4.6g /0.28 yield = 202g
And the domed watch cover emits:
12.3 x 4.6g /0.04 yield = 1.4kg
These numbers show why crystal sapphire has been
called the “black sheep of watchmaking”. (7)
The use of current low-emission HPA and digital
quality control reduces these values to 20g and
138g, respectively. This is even before zero-emission HPA eliminates the cost completely, if not
the wastage. The table above shows that the CO2
emissions can be reduced by 22%.
Conclusion
We have seen that the environmental cost of a watch
cover can be very high if one does not think about it.
Through attention to detail at all process steps, it can
be reduced to that from melting the HPA and running
the machines if their power sources are not green.
This can be applied to other markets and use cases
for sapphire, such as LEDs and other applications.
We will discuss these cases in a future article.
References
1. https://momentumwatch.com/blogs/momentum-blog/whats-the-benefit-of-sapphire-crystal-sapphire-vs-mineral-crystal
2. https://www.innovationnewsnetwork.com/high-purity-alumina-sustainably-produced/29593/
3. “Scientific_Visual_Eco-audit-watch-sapphire_article” at https:// scientificvisual.ch/
4. https://www.imarcgroup.com/watch-market
5. https://www.sueddeutsche.de/wirtschaft/rolex-luxusuhren-1.5777888
6. “Scientific_Visual_Eco-audit-watch-sapphire_slides_SSC_29_ Sept_20222” at https://scientificvisual.ch/
7. “LeTemps_ScientificVisual_22_Oct_2022” at https://scientificvisual. ch/
