Welcome to this lecture on the design of materials for recycling.
My name is Erik Offerman.
I work at the Department of Materials Science and Engineering at
the Delft University of Technology in Netherlands.
This is the second part of the lecture,
and the first part of the lecture was about the complexity of
the materials world and how that affects the recycling rates.
The second part of this lecture is about moving forward.
What are the opportunities?
The goal of this lecture is to provide you with
insight on how we can design materials for recycling.
Now that is an importance and new field to me because as a material scientist,
I've always developed new materials
and designed new materials to improve the performance of these materials.
But now that we have to move to a circular economy,
I'm being challenged to think ahead at
the moments that materials need to be recycled again.
So, therefore, the challenge that we face is how to
design materials in such a way that when these materials are recycled,
they have the same or better properties whereas at the same time minimize costs,
minimize environmental footprint and minimize material losses.
I propose four pathways forward for the design of materials for recycling.
First path is to design materials with minimal sensitivity for impurities.
The second path is to design
materials with the desirable mixing of elements during recycling.
The third path is to design materials with a reduced number of alloying elements,
and a fourth path is to design materials with fewer elements from the periodic table.
The first path is to design alloys with minimal sensitivity for impurities.
For example, if we take a metallic alloy as you can see here in the figure,
it's, for example, an aluminium alloy with
a matrix of aluminium which means you have mainly aluminium atoms,
and added to that are eight alloying elements, eight chemical elements.
So those are indicated by the little spheres with numbers in them from 1 to 8.
That is very schematically a metallic alloy.
Now if you want to recycle this metallic alloy at
a certain moment once you have separated from other waste,
you want to smelt the alloy.
And in that smelting process,
some impurities from the waste that you could not
get rid of will be incorporated in this alloy.
Now if we can design alloys in such a way that there are
less sensitive or at least minimally sensitive to impurities,
we can still create high-performance alloys during
the smelting process and even
increase the recovery rate of these high-performance alloys,
because you do not degrade the alloy by the addition of impurities,
if you have already taken into account beforehand that
some impurities will be added during the smelting process into recycling.
The second path forward that I propose is to design
material combinations that result in desirable mixtures of elements during recycling.
So what do I mean by that?
I'll take the example shown in the figure.
Suppose we have a metallic alloy again consisting
of something like eight alloying elements,
and now this alloy is coated with a coating and this coating also has
an alloying element or an element of which it is made of.
Now these coatings are often added to prevent the metal
from corroding or to make
a hard outer coating so that you can use it for drilling purposes.
Now if you think beforehand about
the effects that in end this material has to be recycled,
you can think of combinations of
elements that are used in the coating and that are used in the metallic alloy that
actually, match that you can get a desirable combination of alloying elements once you
smelt the combination of the metallic alloy plus the coating.
And on the other part of the picture where you see
the molten material that has solidified in it
nicely has all the alloying elements of the original alloy
plus an additional alloying element number nine from the coating.
And they fit nicely together.
The third path forward is to design alloys with
a reduced amount of alloying elements while maintaining or improving performance.
What do I mean by that?
I suppose you have an alloy with a large number of alloying elements,
let's say eight alloying elements,
and you want to recycle and smelt it together with another alloy also
consisting of eight alloying elements but different alloying elements.
Now in this case,
you will end up with a new alloy consisting of 16 alloying elements.
And there is a higher chance of
unfavorable combinations of alloying elements
which reduce the properties of your material.
Then, when you do it differently, and differently.
I mean reducing the complexity of the alloy
by reducing the number of alloying elements in it.
So suppose you have alloy one consisting of
three alloying elements numbered one to three in this case,
and you have a second alloy with
three different alloying elements numbered four to six in this case.
And when you smelt them together,
you get a new alloy consisting of six alloying elements.
For this alloy, the chance is reduced that you
get unfavorable combinations of alloying elements.
However, this trick will only work once because now you have an alloy
a new alloy with six alloying elements whereas you started with three alloying elements.
And the fourth path provides a solution for this.
The fourth path forward is to design alloys that
use fewer elements from the periodic table to create a wide range of properties.
Suppose we have alloy one consisting of
just three alloying elements numbered here one to three,
and you have a second alloy which also
contains the same alloying elements number one to three,
but in different concentrations and maybe
with a different microstructure and alloy number one.
In other words, alloy number one and alloy number two
have different properties but they have the same chemical elements.
Now if you smelt these two alloys together,
you end up with a new alloy also consisting of just three alloying elements.
And this is a cycle that can be repeated many times,
because if you now want to recycle,
re-recycle the alloy again you still have
an alloy with only just three chemical elements.
And you can combine that again with a second alloy with
the same three elements as smelted and to form a new alloy,
and this cycle can be repeated over and over.
Ester van der VoetDr.
