Last month I focused on preparing an article (“Microstructure and mechanical properties of AA7475/AlN compacts with varied reinforcing particles size”) and an abstract (“Effect of reinforcement particle size on microstructure and mechanical behavior of AlZnMgCu/AlN nano-composites produced using mechanical alloying”) for two oncoming conferences – “Composites 2012 – theory and practice” which will be held in Poraj on 18-20 April and “International Symposium on Metastable, Amorphous and Nanostructured Materials (ISMANAM)” which will be held on 18-22 June in Moscow.

Among the researches of acidic texture performed on multicrystalline silicon texture some selected wafers were subjected to the production of solar cells. Then optoelectronic parameters (reflectance in the range of 400-1100 nm and the current-voltage characteristics) were examined. I am pleased to announce that the reflectivity of the best solar cell was reduced to 10% and the effectiveness of the obtained solar cells was founded to be 13.6%.

In the last month I decided to focus my attention on polyelectrolyte layers internal structure and its influence on physico-chemical properties of the multilayer coating. Therefore I made a literature review and I prepared a series of samples for FTIR (Fourier Transform Infrared Spectroscopy) evaluation. Fourier Transform Infrared Spectroscopy is a very sensitive technique to investigate the internal structure of thin films. This is due to the fact that polypeptides, proteins and polysaccharides have specific vibration modes that can be clearly identified by infrared spectroscopy. The amide I and amide II bands of polypeptides and proteins are investigated and their decomposition allows to obtain access to the respective percentages of the different types of secondary structures (α-helix, β-sheet, random structures) [1]. For polysaccharides, the saccharide rings as well as the negatively charged carboxylic and sulfate groups present well defined chemical signatures that can be used to determine the composition of complex mixtures. It is possible to quantify ion pairing in thin films, i.e; to give a quantitative estimate of the amounts of positive and negative charges interacting between each other [2].

1. Roach P., D. Farrar, and C. C. Perry. 2005. Interpretation of protein adsorption: surface-induced conformational changes. J. Am. Chem. Soc. 127:8168-73.
2. Crouzier T., and C. Picart. 2009. Ion pairing and hydration in polyelectrolyte multilayer films containing polysaccharides. Biomacromolecules 10:433-442.

In February I also continued issue concerning polyelectrolyte coatings optimal stiffness determination. Herein I have performed observations of growth and cell morphology of commercially available HUVEC line and fibroblast line on the prepared during the previous month functionalized polyelectrolyte surfaces with varying degrees of chemical cross-linking.

Recently I have spent a lot of time preparing my first paper related to PhD project. I hope it will be published in the 3D Materials Science conference proceedings. Its title is “A Toolbox for Geometric Grain Boundary Characterization” which means I have focused on short description of package of software tools developed by myself during last months. Writing this paper was a great opportunity to sum up my results and put them in the right order. We are now able to fully characterize a given boundary, recognize whether it belongs to any group of geometrically characteristic boundaries, provide boundary plane indices in coordinate systems of the first and the second grain. We can deal with both cubic and hexagonal close-packed polycrystals. We can also find all characteristic boundaries assuming certain misorientaion. For a given misorientations, such catalogues of characteristic boundaries are presented in the form of stereographic projections of boundary plane normals. We have used three different methods including analytical calculations, as well as purely numerical searches. Fortes decomposition and distance minimizations make it possible to directly introduce some uncertainties. Having several methods enables to perform various cross-checks which might be important for further investigations. Finally, obtained images can be linked to similar figures obtained experimentally.

In February, I passed exams of 'Fundamentals of solidification', 'Advanced scanning electron microscopy in materials science' and 'Transmission electron microscopy in materials science'.
I attended in PAS Seminars:
- MSc Eng. Jakub Kawalko: 'The use of methods and optical systems for measuring the stability of photo degradable materials',
- Prof. Antonio G. Checa: 'Multi-level approach to the study of microstructures fabricated by invertebrate molluscs',
- MSc Eng. Adam Debski: 'The enthalpy of formation of inter-metallic phases of lithium-silicon system'.
In that month, I also prepared a draft article under the title: ‘Early stages of recrystallization in ultra fine-grained AA1050 aluminium alloy’:
Abstract
Early stages of recrystallization in aluminium alloys are of considerable practical interest. They were observed for the AA1050 alloy. The samples were processed by equal channel angular pressing along route A up to six passes and then annealed for 1h at different temperatures to obtain different states of recrystallization. Microstructures have been analyzed in sections perpendicular to the extrusion direction, using scanning electron microscopy equipped with high-resolution electron backscattered diffraction facility.
The ECAP-deformed alloy contained a structure of flat grains with the spacing between high angle boundaries ranged from 100nm to 1µm. On annealing, structure coarsened and gets transformed into nearly equiaxed grains. Particular role in the rise of nuclei (at early stages of recrystallization) was attributed to migration of low-angle boundaries and cells coalescence. Later recrystallization stages were attributed to high-angle grain boundaries migration. These processes led to nearly equiaxed grains of similar size. It was documented that length of traces of low- and high- angle boundaries decrease with increasing time of annealing.
The average values of misorientation across both types of grain boundaries systematically grow. Orientation mappings showed that although orientations of new grains were widely scattered, they were not completely random.
Keywords : aluminium alloy, equal channel angular pressing, recovery and recrystallization, microstructure, EBSD