Eco friendly functional materials – status summary of work of Dr. Caterina E. Tommaseo

re:look Aufriss


Dr. Caterina E. Tommaseo

Dezember 2021



Primary source paper: Research work and publications by author


Introduction


The author’s studies of various research topics in the field of material- and environmental sciences show that the common goal is to understand the processes taking place in materials, thereby influencing their properties. Today this understanding is necessary to explore for example environmentally friendly substitute additives in concrete etc. including eco-friendly and sustainable materials. The main parameters are the material components with their structural order-disorder states and their interplay with each other mainly through grain boundaries and intra-/intergranular exchanges. Last but not least the texture of a material as a whole has to be taken into account, as it contains the complexity of driving processes in connection with its environment and finally its unique use in the fields of technique and environment. The research of such complex processes was carried out applying unique techniques for the study of macro- and microstructural development under ex-situ but also in-situ heating and pressure conditions using different radiation sources (X-ray, infrared, synchrotron radiation, etc.) depending on the analyses methods needed to get a deeper insight of the material. Possible applications of two representative materials are presented in the paragraphs below followed by current research applications and a short outlook.


Application as backfill materials in the disposal of radioactive waste


The author`s study [1, 2] on pure polycrystalline salt and doped with SiO_2 gel showed a general decrease in yield strength in the pure samples compared to those doped with silica gel. All samples, irrespective of grain size, showed higher yield strength with silica gel additives. These observations demonstrated that Silica gel additives in the bulk halite cause a lower strain accumulation, expressed through a larger Young’s modulus, and lower plasticity. Important basic parameters for strengthening and deformation accommodation in polycrystalline materials are grain boundaries. As nanoparticles are added to a common material, the intragranular or intergranular structure is formed, thereby improving the mechanical properties of materials [3]. The amorphous phase likely protects the single grains in the crystalline phase from deformation, alleviating strain accumulation by the introduction of defects and therefore the preservation of the grain shape. The density of a material goes along not only with (compressive) strength but also with pore minimization and chemical/physical resistance of a material. The mentioned results have therefore important implications for radioactive waste disposal. Indeed in the case of salt concrete used as backfill material for radioactive waste disposal, sulphate-resistant blast furnace cement and hard coal fly ash, which have latent hydraulic or pozzolanic properties, serve as binders. Compression, compaction, and densification processes, increasing with depth and pressure, play a primary role.


Application as environmentally friendly materials


The influence of Fe-additive and structural defects on the mechanical behavior of synthetic oxide ceramics (MgO) is shown with in situ pressure experiments using the diamond anvil cell [4]. (Mg,Fe)O, with higher Fe content shows a weaker texture and a lower elastic stress anisotropy than the Fe-periclase with lower Fe content. This correlates with the fact that with increasing Fe content, bonding becomes less ionic, and the strength decreases, which could result in a lower stacking fault energy, which means that less stress is needed to nucleate partial dislocations from grain boundaries. In fact, in these calculations, a dissociation of the full dislocation {110}<1-10> in partials is observed. The increasing number of dislocations could block each other’s motions leading to the resulting lower texture in (Mg,Fe)O. Another aspect that has to be considered in order to understand the deformation behavior of Fe-periclase is the complex defect structure associated with very high Fe contents. The less ionic bonding strength in (Mg,Fe)O and the probably existing vacancies in the (Mg,Fe)O crystal structure [5] might increase the density of dislocations [6].


AlMn alloys used as a functional material for e.g. beverage cans, packaging material, and wires have the advantage to be less corrosive. Ex situ and in situ analyses using unique techniques were performed [7, 8] to get information about the grain size distribution and grain shape in the AlMn alloys with increasing Mn additives. The observed unhindered and equal growth of different grain orientations independence of the second phase particles precipitations could be explained by an energetically favorable process as a preferred rotation of grains into a convenient position in relation to the neighboring grains promoting independently from grain orientation grain growth.



Current research application


In building materials, in backfill materials for the radioactive waste disposal, and in restoration work, the process of choosing the right material is an essential step ensuring for example high compressive strength, water-repellent properties, high tightness to prevent leakage, chemical and physical resistance. The research fields are numerous starting with the choice of the right additives like carbon, amorphous silica, silica fume, fly ash, nanomaterials, and ecological material up to the manufacturing processes and the processes taking place during the hydration and hardening phase. The last mentioned processes are still a point of debate and play a crucial role in the understanding of the complex mechanisms taking place in the material and the related damage mechanisms to be reduced. Especially the use of certain additives promotes crack and pores minimizations in building materials. The compositional ratio and the grain size impact the mechanical properties of a material and are still a relevant topic for different research fields in material science and environmental sciences [9]. In fact, in the specific case of concrete the admixture of silica fume, nano silica effectively increases not only the compressive strength but also the durability of the concrete [10]. The action of the additives as cementing, pozzolanic, or filler materials [11] is decisive for the aimed improvement of the mechanical performance and durability of concrete. Recent studies [12] demonstrated that MgO-based concrete has not only higher durability but also a reduced environmental impact and higher sustainability. Another new challenge is an eco-friendly concrete: a bio receptive concrete facades allow biofilms to grow on it without affecting the concrete itself. Additionally, the green facades contribute in the city to air purification and cooling in the summertime [13].



Outlook for future work


The use of sustainable, environmentally friendly, and ideally zero energy materials play in our time more than ever an important role. Additionally, the grand challenge is to find innovative solutions to minimize changes in shape that over time can lead to failure in materials and to maximize the life of the material.





[1] Tommaseo, C.E. (2015) Microstructural development of in situ heated and deformed pure and silica gel doped polycrystalline halite using high energy synchrotron radiation. Journal of Earth and Engineering Science, 5, 27-43. DOI: 10.17265/2159-581X/2015. 01. 002


[2] Tommaseo, C.E. (2015) Structural changes during microstructural development in natural salt samples. Journal of Structural Geology, 72, 111-123. DOI: 10.1016/j.jsg 2014.12.004


[3] Wang J.L., Meng L.J., Influence of Carbon Nano-Fiber on Mechanical Property of PALC, Applied Mech. Mater., 2014, 535, 785-787.


[4] Texture development and elastic stresses in magnesiow}ustite at high pressure, Caterina E. Tommaseo, Jim Devine, Sebastien Merkel, Sergio Speziale, Hans-Rudolf Wenk Phys Chem Minerals (2006) 33: 84–97


[5] Jacobsen SD, Reichmann HJ, Spetzler HA, Mackwell SJ, Smyth JR, Angel RJ, McCammon C (2002) Structure and elasticity of single-crystal (Mg,Fe)O and a new method of generating shear waves for gigahertz ultrasonic interferometry. J Geophys Res 107(B2):1–14


[6] Heidelbach F, Stretton I, Langenhorst F, Mackwell S (2003) Fabric evolution during high shear–strain deformation of magnesiow}ustite. J Geophys Res B 108:2154


[7] Tommaseo, C.E. und Klein, H. (2010). Oriented grain growth analyses with in situ annealing experiments using high energy synchrotron radiation. Advanced engineering materials volume 12, issue 3, pp. 222-227


[8] Tommaseo, C.E. und Klein H. (2009). H. Grain growth analyses of AlMn alloys using texture and microstructure imaging techniques with high-energy synchrotron radiation (Praktische Metallographie, Practical metallography 02/2009, Seite 77-96)


[9] Porwal H.,Tatarko P.,Saggar R.,Grasso S.,Mani M.K.,Dlouhý I., et. al., Tribological properties of silica-graphene nano-platelet composites, Ceram.Int.,2014,40,12067-12074.


[10] Justin Montgomery, Taher M. Abu-Lebdeh, Sameer A. Hamoush and Miguel Picornell (2016). "Effect of nano silica on the compressive strength of hardened cement paste at different stages of hydration." American journal of engineering and applied sciences. DOI: 10.3844/ajeassp.2016.166.177


[11] Juenger, M. C. G. G. & Siddique, R. Recent advances in understanding the role of supplementary cementitious materials in concrete. Cem. Concr. Res. 78, 71–80 (2015).


[12] Influence of quartz powder and silica fume on the performance of Portland cement Scientific Reports 10:21461 (2020).


[13] M. Veeger, A. Prieto, M. Ottelé Exploring the Possibility of Using Bioreceptive Concrete in Building FaçadesJOURNAL OF FACADE DESIGN & ENGINEERING VOLUME 9, NUMBER 1 (2021)


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