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Kaptay / Day 1 / 1. Structure of the course High-temperature interfacial forces, energies and phenomena by G.Kaptay. Day 1. Basics. Day 2. Forces. Day 3. Energies. Day 4. Phenomena. Kaptay / Day 1 / 2. Day 1. Basics of interfacial science. George Kaptay kaptay@hotmail.com.

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## Day 1. Basics

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**Kaptay / Day 1 / 1**Structure of the course High-temperature interfacial forces, energies and phenomena by G.Kaptay Day 1. Basics Day 2. Forces Day 3. Energies Day 4. Phenomena**Kaptay / Day 1 / 2**Day 1. Basics of interfacial science George Kaptay kaptay@hotmail.com A 4-day short course**Kaptay / Day 1 /3**Basics of thermodynamics (G = H - TS) The behaviour and properties of materials are dictated by their desire to minimize their energy, G (Gibbs energy). There are two desires: i. as strong as possible bonds (love) and ii. as high as possible freedom (at the same time). Strong bonds = negative enthalpy (H) (G ~ H) High freedom = positive entropy (S) (G ~ -S) Freedom has no sense without ability to move, what is proportional to T (K). Thus, (G ~ -T*S) G = H -T*S**Kaptay / Day 1 / 4**Back to thermodynamics (G = H - TS) G = H -T*S = f(T, p, xi, r, fields) At low T (low ability to move, i.e. winter, old age): negative H (strong love, strong bonds) is preferred At high T (high ability to move, i.e. summer, young age): positive S (high freedom) is preferred fcc bcc liquid vapour Total mixing is preferred (no compounds, no segregation) Heat capacity (Cp): HT = HTo + Cp*(T-To) (with increased T the bonds become weaker: H → +)**Kaptay / Day 1 / 5**Interfacial energy**Kaptay / Day 1 / 6**The average molar Gibbs energy (J/mol) of phases (with interfaces) and consequences There are 8 consequences of the existence of the interfaces and of the above equation. They are grouped according to the driving force: A/V min, min, G min.**Kaptay / Day 1 / 7**Consequence #1. The equilibrium shape of phases Case i. Liquid in microgravity and free space A/V min**Kaptay / Day 1 / 8**Consequence #1. The equilibrium shape of phases Case ii. Solids (Wulff’s theorem).**Kaptay / Day 1 / 9**Consequence #1. The equilibrium shape of phases Case iii. Liquid in contact with a flat solid surface.**Kaptay / Day 1 / 10**Possibility 1. If W > 2l/g = 0o “the liquid perfectly wets the solid”**Kaptay / Day 1 / 11**Possibility 2. If 2l/g > W > l/g 0o < < 90o “the liquid wets the solid”**Kaptay / Day 1 / 12**Possibility 3. If l/g > W > 0 90o < < 180o “the liquid does not wet the solid”**Kaptay / Day 1 / 13**Possibility 4. If W = 0 = 180o “the liquid does not wet the solid at all” but this situation exists only if gas = liquid2**Kaptay / Day 1 / 14**Consequence #1. The equilibrium shape of phases Case iv. Liquid in contact with solid, in gravity**Kaptay / Day 1 / 15**#1. The equilibrium shape/position of phases Case v. Liquid in contact with a capillary Non-wetting No penetration wetting penetration**Kaptay / Day 1 / 16**Not stable Stable Many small phases One big phase V = V A > A Consequence #2. The equilibrium size of phases A/V min Ostwald ripening. Smaller phases join together**Kaptay / Day 1 / 17**The Kelvin equations (nano-equilibrium) b a (small liquid in gas) (small solid in liquid) (small solid in liquid)**Kaptay / Day 1 / 18**Gas phase Structured first layer Structured second layer Diffuse bulk liquid Consequence #3. Interface re-structuring min**Kaptay / Day 1 / 19**min Consequence #4. Adsorption of gases on the surface of solids and liquids Driving force: is reduced due to adsorption Reduces in row: metals – ionics – covalents with H-bond – covalents with van der Waals bond. In the same row the tendency of adsorption decreases. Covered surface area by adsorption increases with partial pressure of adsorbant, and decreases with temperature (entropy effect).**Kaptay / Day 1 / 20**min See P86 Consequence #5. Inner adsorption of components from the solid or liquid solution**Kaptay / Day 1 / 21**min Consequence #6. Marangoni convection**Kaptay / Day 1 / 22**min Consequence #6. Marangoni convection**Kaptay / Day 1 / 23**Gmin See J99, J105 Consequence #7. Surface phase transition**Kaptay / Day 1 / 24**High adsorption, invers T-dependence Low adsorption, normal T-dependence**Kaptay / Day 1 / 26**Gmin Consequence #8. Supersaturation at nucleation**Kaptay / Day 1 / 27**Gmin See J106, J108 Consequence #8/2. Supersaturation at nucleation (with the Gibbs energy change of the parent phase) Stabilization of nano-nuclei**Kaptay / Day 1 / 28**8/2. Minimum on the nucleation curve The stabilization of nano-nuclei seems to be possible from oversaturated solutions Time is against it – Ostwald ripening. Very high cooling rates are requested to stabilze nano-nuclei**Kaptay / Day 1 / 29**General modeling algorithm Interfacial energies Interfacial forces Interfacial phenomena Complex phenomena**Kaptay / Day 1 / 30**3 tasks: • Classification and modeling of interfacial forces, acting on phases (Day 2), ii. As the interfacial forces will turn out to be functions of different interfacial energies, we should also model the interfacial energies in different systems (Day 3), iii. Finally, we can deal with modeling of different interfacial phenomena, and basedon that, even some complex phenomena (Day 4).**Kaptay / Day 1 / 32**Thanks for your atention so far And see you tomorrow….

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