When going to small dimensions, material properties change depending on the size and shape. Direct write lithography is a versatile technique for modifying and shaping materials at the nano- and microscale to study and control a wealth of physical properties.
Direct laser lithography can be used to create microscale patterns, structures and textures as well as contacts for electronic devices and measurements. Thermal lithography can do the same on the nanoscale and also directly generate various material modifications by local heating. Moreover, states of matter that are not accessible macroscopically can be reached thanks to ultra-fast heating or cooling, and high local pressure that can be applied with the nanoscale heated tip of the NanoFrazor.
The use of liquid bath furnaces has shown to be an energy efficient and environmentally friendly way for both the primary and secondary production of non-ferrous metals such as lead, nickel and copper.
Typical for these kinds of furnaces is the injection or generation of reactive gasses which occurs below the surface of the liquefied feed material. The large amount of rising gases during processing can cause foaming of liquid slag, as illustrated in the schematic below.
This slag phase is in most cases present as the upper layer of the liquid bath. The formation of excessive amounts of slag foam can hinder the production and lower the available capacity of existing smelting and converting furnaces. It is thus important to control this phenomenon and keep foaming to a minimum.
It is generally accepted that the formation of slag foam is caused by a combination of a large amount of rising gases and the inherent foam stability of the slag, which in turn depends on the physical properties of the liquid slag. These causes are studied on a fundamental level. Foaming stability is modelled using novel computer simulations, supported by experiments.
The generation of gasses is studied by investigating the behaviour of liquid slags to absorb and release oxygen gasses. These gasses can be absorbed over a large period of time and suddenly be released afterwards which contributes to the large amount of rising gases and thus slag foaming during copper smelting.
Make the slag and the steel will make itself” is an old phrase in steelmaking. Slags are liquid oxide phases, which play an important role in many pyrometallurgical process. This is also the case in the convertor process.
The convertor process is a necessary step in the steel production. During this process carbon, phosphor and other impurities present in the ‘pig iron’ from the blast furnace are removed and steel is produced. This steel is tapped from the convertor and further refined, next cast, rolled and further finished.
In a convertor, the hot liquid pig iron from the blast furnace is charged together with scrap and oxygen is blown on it. During the process, two main phases are present in the convertor: the liquid metal phase and the slag phase. This slag phase plays an important role in refining the metal phase (removing C, P, Si, etc.) but a good slag will also protect the installation from damage that could be caused by the inherent interactions at high temperatures.
Even though there is general agreement on the importance of the slag and its functions in steelmaking, a profound and complete understanding of slags has not been reached yet. Gaining insight in the process, the working principle and the interaction between the slag and metal phase is rather difficult since a convertor is in reality a ‘black box’. Thermodynamic modelling of the process is a possibility to gain insight and gather more knowledge about the process.
The goal of this PhD is to apply thermodynamic models and calculations upon industrial convertor process, in order to gain fundamental knowledge and understanding of the slag phase
Metal losses in slags occur in pyrometallurgical production processes and limit the overall process efficiency. The metal losses are generally subdivided in two types: chemical losses referring to dissolved copper in the slag and mechanical losses referring to entrained copper droplets in the slag.
For the mechanical losses, several causes can be found, one of them being the attachment of metal droplets to spinel particles in the slag. The spinel particles hinder the sedimentation process of the metal droplets. However, no fundamental understanding of this phenomenon is available.
First, a suitable methodology was developed, consisting of two complementary approaches, as illustrated in the figure below:
- The different interactions (copper-spinel, slag-spinel and slag-copper-spinel) were studied in separately by a sessile drop methodology.
- The complete system (metal-slag-spinel) was also studied during smelting experiments: for this, two experimental set-ups were developed to study the attachment of copper droplets to spinels in the slag. One set-up allowed studying the influence of the sedimentation time, while the other one allowed an evaluation as a function of the slag height.
Many experiments are needed to investigate the influence of all parameters and, even though the microstructure and composition can be investigated. Moreover, it is very difficult to study the effect of each parameter individually because it is virtually impossible to keep the others constant. Hence, it is not straightforward to reveal the underlying chemical and physical phenomena with experiments.
The phase field method already proved to be a very powerful and versatile modelling tool for microstructural evolution, e.g. during solidification, solid-state phase transformations and solid-state sintering.
A binary phase-field model simulates the attachment of liquid metal droplets to solid particles in liquid slags with a non-reactive solid particle. The influence of several parameters on the attachment of the metal droplets to the solids was investigated: the interfacial energies, the particle morphology, initialization method, solid particle movement and the speed of the solid particle movement.
Depending on the interfacial energies, four regimes were observed: no wettability of the metal on the particle, low wettability, high wettability and full wetting, as illustrated in the upper part of the figure below.
Afterwards, it was investigated how rigid body motion of the solid particle influences the attachment, as shown in the lower part of the figure below. A major observation is the fact that the apparent contact angle of the metal is larger when rigid body motion is present, which corresponds to a lower apparent wettability.
The study on the influence of the speed of the rigid body motion also showed that there is a trade-off between the attraction of the metal towards the solid particle and the speed of the movement of the solid particle.