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Friday, 11 March 2011

Surface chemistry: A close look at hydrophobicity_Wetting_non-Wetting_Bulk Steelmaking Macro to Nanotechnology and Biomimicry

This post was motivated by a recent publication (14 Feb. 2011 in Nature Asia Materials) entitled

 Surface chemistry: A close look at hydrophobicity : research highlight : NPG Asia Materials (ref. 1)

Much progress has been made in understanding the phenomena involved in the wetting of solid surfaces by liquids, in the characterisation of wetting phenomena since Charles Macintosh (FRS) chemist and engineer famous for the impermeable named after him (1766 – 1843) for that that matter since my very first study as young,high temperature physical chemistry,research scientific officer involved in "wetting- non-wetting of refractory surfaces by liquid steel (mpt.1500°C) so fundamental to steelmaking and it's manufacturing process improvement.(1969-71)  It appeared to provide a surprising historical insight into the study of wetting, hydrophobia-hydrophilic as well as an occasion to revisit themes treated pragmatically in my very first study project involving the formation of gas bubbles on refractory surfaces in steel, perhaps re-situate it in what has today become a flourishing inspirational approach to many biomimetic material innovations.  Our focus at the time (1970) was the then new vacuum degassing DH and RH processes whereby liquid steel is recycled through a vacuum chamber. Deoxidation is by carbon forming CO/CO2 gas bubbles formed under the prevailing vacuum conditions. Often the liquid steel circulation was hindered in the narrow recirculation legs by unwanted CO/CO2 gas bubbles. We confirmed the role of liquid wetting, active or unwetted pore size, the influence of choice of refractory materials, and the combined influence of the overhead atmospheric pressure and the pressure of the head weight of liquid steel. The total pressure was varied by reducing the atmospheric pressure. Data is shown below:


Ref. 2 The growth of carbon monoxide bubbles on refractory surfaces during vacuum degassing of iron melts.  J. Alexander, G.S.F Hazeldean, M.W. Davies Sheffield Conf. 1971  and BISRA -Corp Labs of British Steel Corp. Report CH/28/71.

If I personally did not follow-up this applied research in bulk liquid metal degassing, it did stand me in good stead for rapidly coming to terms with gas bubble phenomena in liquid steel and special alloys. For example Fe-Ni and Fe-Ni-Co alloys, Invars and Covars highly sensitive to CO gas solubility and rimming or degassing during solidification. The larger the ingot the more difficult it is to solidify and subsequently remove remaining traces of gas blow-holes. Nevertheless ingot sizes were increased from 4T to 10T and even to 18T. Similarly improvements were made in VIM-vacuum induction melting and refining and VAR-vacuum arc remelting etc. all stemming from intimate knowledge of C deoxidation reaction its theoretical and practical limitations and of the physics and chemistry of wetting.

If I and worse the reader feels that this is old-hat stuff, I and hopefully the reader like me will be most encouraged by the historical background referenced in the title paper:
Surface chemistry: A close look at hydrophobicity : research highlight : NPG Asia Materials  (14 Feb. 2011) Ref. 3.

Wenzel's referenced work is "Wenzel RN (1936) Resistance of solid surfaces to wetting by water. Ind Eng Chem" and Cassies referenced work is Cassie ABD, Baxter S (1944) Wettability of porous surfaces. Trans Faraday Soc 40:546–551.28:988–994. [ WENZEL STATE _ WENZEL-CASSIE-TRANSITION_free from PNAS.ORG [Pdf format] (Ref. 3)

Of course lower temperature (RT) phenomena and modern computing techniques and computer technological advance readily allow molecular dynamic (MD) simulations to be carried out. If accent in the 1960-1980's focused on macro-phenomena and increasing productivity and economies of size. Recent approaches focus more and more on the infinitely small-nanoscience and technology first driven by micro-electronics (Moore's Law ) and much more recently inspired by biomimicry cf for example The Biomimicry Institute

The types of  applications, inventions, innovations arising from nanotechnology and the biomimetic approach are given in ref. 4 below.

NB. Recent great mind who moved from solid state physics to explore  
"Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves"
 and on to soft materials is the late and much regreted Pierre-Gilles de Gennes, who associated with Francoise Brochard-Wyart and David Quere authored the book in the above title. cf also amazon's offer in Books below.

1. Surface chemistry: A close look at hydrophobicity : research highlight : NPG Asia Materials

2. Ref. 2 The growth of carbon monoxide bubbles on refractory surfaces during vacuum degassing of iron melts. J. Alexander, G.S.F Hazeldean, M.W. Davies Sheffield Conf. 1971 and BISRA -Corp Labs of British Steel Corp. Report CH/28/71.


4. Hydrophobicity - Superhydrophobicity

5. Good overall introduction to physics of Wetting, Adhesion, Biomimicry, Friction:
Nick Fang's Lecture_Wetting_Adhesion_Biomimicry_Friction_Macro to Nano [pdf]


1. Whisky - Chemical up-date from the RCS-Chemistry World

2. Water repellent properties, Biomimicry, Self Assembling Molecules, Network of micro- nanowires, excellent imagery in "Nanomaterials: Cu Water Strider .

3. Metaklett-steel grips, Biomimicry and Shape Memory Alloy meanders

4. Nanotechnology - to many to list - use blog search tool - top left.  


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