Sonochemical Reactions Chemical changes/reactions induced by ultrasound No direct interaction of ultrasound field with molecules (in contrast to photochemistry,...) •Liquid phase reactions - chemical reactions driven by cavitation effects • Solid state reactions - introduction of defects = speeding up diffusion Sound Sound = pressure waves = periodic compression/expansion cycles traveling through a medium possessing elastic properties (gas, liqud, solid) Liquids and gases - longitudinal pressure waves - compression/rarefaction Solids - longitudinal and transverse waves The energy is propagated as deformations (tensile/compressive stress) in the media The molecules oscillate about their original positions and are not propagated The propagation of a sound wave = the transfer of vibrations from one molecule to another Longitudinal Pressure Waves 8^87 Sound In a typical liquid, the speed of sound decreases as the temperature increases, at all temperatures. The speed of sound in water is almost five times greater than that in air (340 m s1) Substance Speed of sound, u [m s-1] Air 343 Helium 965 Water 1482 Lead 1960 Steel 5960 Granite 6000 Speed of Sound The speed of sound (u) u2 = 1/Ksp = [dP/öp]s ~ 1/(<(V)2>) ks = adiabatic compressibility p = density P = pressure 1600 E 1500 1200*- 50 100 150 Temperature, °C 200 Sound Intensity Sound Intensity = Power / area = Watts/m2 Source of Sound Intensity (W/m2) Sound level (dB) Jet Airplane 30 m away 102 140 Air-raid Siren, nearby 1 120 Threshold of Pain 101 120 Concert -101 115 Riveter 103 100 Busy Traffic 105 70 Normal Conversations 106 60 Whisper 1010 20 Threshold of Hearing 1012 0 0 dB (10 12 W/m2) 10 dB = 10 as intense 20 dB = 102 as intense 30 dB = 103 as intense 120 dB = 1012 as intense Acoustic Pressure Pa = PA sin 271 ft Pa acoustic pressure PA pressure amplitude f sound frequency c = Xf (for 20 kHz, X = 7.5 cm) p = p + p 'total ra ^ rh Ph hydrostatic pressure compression compression displacement (x) graph r\ r\ r\ raref action M Pressure (P) graph \J f A Pa K f Acoustic Pressure I compression compression I displacement (x) graph ; rarefaction a J \J \J Pressure (P) graph M ■ ) i j 1 p. Compression and rarefaction (expansion) regions PA = driving pressure amplitude [Pa] I = irradiation intensity fW m~2] (500 W system - 1.3 105 W nr2) p = liquid density fkg m~3] c = sound velocity in liquid fm s_1] -l (Water 1482 m s"1) PA = 620 700 Pa = 6.2 bar Ultrasound Utrasound frequencies from 20 kHz to 50 MHz 0 10 _l_ 10 _L 10 _L 10 10 7 10 Human hearing ► Conventional power ultrasound frequency, Hz 16Hz-18kHz 20kHz - 100kHz Extended range for sonocherristry J_| 20kHz - 2MHz Diagnostic ultrasound 5MHz - 10MHz Generation of Ultrasound Transducer - a device converting one type of energy into another gas driven whistle (F. Galton), liquid atomizer siren liquid driven liquid whistle homogeniser, a jet of liquid passed through an orifice on a thin metal blade, vibrations, cavitation, mixing of immiscible liquids, ketchup, mayonnaise electromechanical magnetostrictive, Ni, Co/Fe, Al/Fe, Tb/Dy/Fe alloys shrink when placed in mg. field, solenoid, pulses, upper limit 100 kHz, cooling piezoelectric, oposite charges applied on crystal sides, contraction/expansion, quartz, Pb(Zr/Ti)Os ceramics (PZT), up to MHz Generation of Ultrasound casing containing transducer element generator upper fixed horn (booster) detachable horn screw fitting at null point Sonochemical Reactor Sonochemical Reactor Ultrasound Processor VCX 500 W Frequency 20 kHz 0 to 40 °C Argon (flow rate 62 cm3 mhr1) TIME of ultrasound treatment PULSE irradiation and a dwell time 2:2 TEMP maximum temperature 50 °C AMPL amplitude 50 % Sonochemical Reactor Ti alloy horn, minimum lenght is a half-wavelength of sound in a material, 26 cm for 20 kHz in Ti, multiples of 13 cm vibration amplitude 5-50 |j,m Sonochemical Reactor Sandwich transducer operating at 1-200 kHz Hydrodynamic Cavitation the passage of liquid through an orifice plate the kinetic energy/velocity of the liquid increases at the expense of the pressure throttling causes the pressure to fall (Bernoulli) below the threshold pressure for cavitation (vapor pressure) cavities are generated the liquid jet expands, the pressure recovers energetic collapse of the cavities Hydrodynamic Cavitation Lord Rayleigh for the British Admiralty 1895 cavitation erosion of propeller blades The University of Texas at Austin RR+-R =-[p -P-P(0]-4v —- — 2 p Fs 0 R pR SHEET CAVITATION LEADING EDGE DETACHMENT TIP VORTEX CAVITATION (developed) CLOUD CAVITATION BUBBLE CAVITATION HUB VORTEX CAVITATIO N TIP VORTEX CAVITATION (inception, desinence) I© 1996 S.A. Kinn» FACE SHEET CAVITATION Snapping Shrimp snaps a claw shut to create a water jet -speed of 30 m/s, or 100 km/h a drop of the pressure to below the vapor pressure of water - cavitation bubbles acoustic pressures of up to 80 kPa at a distance of 4 cm The pressure wave is strong enough to kill small fish M. Versluis, B. Schmitz, A. von der Heydt, D. Lohse, How Snapping Shrimp Snap: Through Cavitating Bubbles. Science 289, 2114-2117 (2000) Snapping Shrimp TINfE (ms) D. Lohse, B. Schmitz, M.Versluis, Nature 413, 477-478 (2001) -1.29 ms D. Lohse, B. Schmitz, M. Versi u is, Nature 413, 477-478 (2001) Relative atouslit pr$$Suf3 R/RO (bubble radius / initial radius) Acoustic Cavitation Cavitation effects = creation, growth, and implosive collapse of bubbles (1-2 jus) in a liquid = implosion HOT SPOT (1 ns) TRANSIENT CAVITATION: THE ORIGIN OF SONOCHEMISTRY Compression Expansion E 4 ■ % n JQ m IMPLOSION SHOCKWAVE FORMATION RAPID QUENCHING —I- 500 stable cavitation - bubbles oscillate for many cycles transient cavitation - transient cavities expand rapidly collapse violently Time (usee) Acoustic Cavitation Cavitation effects = creation, growth, and implosive collapse of bubbles in a liquid Bubble formation = breakage of liquid during expansion, overcoming tensile strength (pure water 1500 bar, only 6.2 bar available) Weak spots needed = dissolved gas molecules, solid particles, trapped gases Bubble growth (300 jus), energy absorption, size oscillations critical size (170-300 jum) = most efficient energy absorption, rapid growth, inefficient energy absorption, collapse campressicn compression campnsssicn compressor) Acoustic Cavitation Standing wave Low pressure .-—^--1 Bubble expansion ft Mil iillllill 911 Iii I Iii 111 1Bubbie collapse c Light I—p—J High pressure ^6243235 Acoustic Cavitation Bubbles collapse = spherically symmetrical implosion, shear forces, adiabatic compression, life time 1-2 jus Hot spot = end of the collapse temperature of the gas inside bubble 5 000 - 20 000 °C (for 1 ns) surrounding liquid layer 2000 °C pressure 500 - 1500 bar Extreme cooling rates 1010 K s-1 red hot steel poured into water 2500 K s-1 Homogeneous Sonochemistry Two-Site Mechanism Cavity interior Filled with gases and vapors temperatures 5 000 - 20 000 °C pressure 500 - 1500 bar Surrounding liquid layer temperatures 2000 °C Bulk liquid Shock waves, shear forces Homogeneous Sonochemistry Mechanism •••• SurrdVinding interface layer ■ A-B diffusion of volatile reagents Bulk liquid CD** nonvolatile reagents Shock waves, shear forces • ■ ■ How to Measure the Temperature inside a Bubble ? Sonoluminescence - Light generated during the implosive collapse of bubbles in liquids irradiated with ultrasound Kenneth S. Suslick University of Illinois 95% H2S04(aq.) under Ar 20 kHz (14 W/cm2) Ti horn directly immersed T = 298 K Apparent blackbody temperature Ar emission SO and CK+ emission 8 000 - 15 000 K A l4WfcmJ 22 w/cm2 I 1 3* i in c £ 6B0 14Wattsfcm2 22 Wattsfcm1 30 Wattstem2 30 W/cm2 BS0 Wavelength (nm) Temperature/Pressure inside a Bubble Neppiras Equation T =T max 0 Pa (r -1) Q P =Q max *~ V fi(r-i) Q r r-i J Pa = acoustic pressure T0 = solution temperature Y = Cp/Cv Q = gas pressure inside a bubble upon initiation of the collapse, at its maximum size Gas Y = Cp/Cv Kr 1.66 Ar 1.66 He 1.63 o2 1.41 Fate of Bubbles under Ultrasonic Irradiation Ultrasound qft Bubble / °öO nuclei V I Jisstilulinn \ Fragmentation Coy Ic scent c Reclined diffusion Buoyancy I "Inactive' buh hies Resonance size Collapse VV SL Rectified diffusion - during expansion phase the bubble has larger surface area - more gas diffuses inside than during compression gets out Single Bubble Sonoluminescence SBSL D. F. Gaitan, L. A. Crum, 1990 a method to trap a single sonoluminescing bubble within an acoustic standing wave field Standing acoustic wave field One bubble trapped The bubble oscillates for many cycles Bubble sonoluminescence Single Bubble Sonoluminescence SBSL D. F. Gaitan, L. A. Crum, 1990 Standing acoustic wave field 1 bar One bubble levitates in the acustic field The bubble oscillates for many cycles Bubble sonoluminescence Bjerknes force sound pressure p(x,t) I 1=0 location bubble force at the time t=0: volun}e V(t) A"" force at the time t=T/2: time- aver age d f or ce: C. A. and V. Bjerknes The force on an object in a liquid depends on its volume and the pressure gradient, the time averaged force drives the bubble towards the antinode of sound pressure and keeps it there. Single Bubble Sonoluminescence SBSL Proper conditions for a single sonoluminescing bubble within an acoustic standing wave field Single Bubble Sonoluminescence SBSL Single Bubble Sonoluminescence SBSL Red - MBSL in dodecane Blue - MBSL in water, 16 kHz Green - SBSL in water, 43 kHz Black - blackbody curve for 16200 K 40 200 300 400 500 600 700 WAVELENGTH (nanometers) Single Bubble Sonoluminescence SBSL Red - bubble radius Green - bubble temperature Blue - acoustic pressure 1.3 bar/25 kHz Multi Bubble Sonoluminescence MBSL Multi-bubble sonoluminescence Spatial and temporal average 250 bar Sonoluminescence Light generated during the implosive collapse of bubbles in liquids irradiated with ultrasound E c 1 CL CD 1 "3 £- ■4-1 o aj CL CO 10-12, 200 300 —----—^__85% H2S04 under Xe i ~ — ~ - - — 85% H2S04 under Ar " * ~ - ,- .___H20 under Xe H20 under Ar 400 500 600 Wavelength (nm) 700 Apparent blackbody temperature (all 4 spectra) 12500 ±1500 K Sonoluminescence 95% H2S04(aq.) blackbody temperature Ar emission an optically opaque plasma core 200 300 400 500 600 700 300 Sonoluminescence 95% H2S04(aq.) SO and 02+ emission with vibronic progression 160- 120 ,15 a 80 I to 40- 2=v' V nit a r1=v' i'i 12 i'a iU=^- v'-°\ I I I I I I I I I I V"=4 5 6 7 8 9 1011 121314 SO 0.0 250 300 350 Wavelength (nm) 200 250 300 Wavelength (nm) 1580 ± 110 K at 3.3 bar 2470 ± 170 K at 4.2 bar 3480 ± 240 K at 5.1 bar Sonofusion Fraud D-D — 3He(0.82MeV) + n(Z45MeV) D -D — T(LOlMeV)-H(3.02MeV) Time SD, (is H I -3 +3 Compression —Ml PNG Neutron-Induced Luminescence Sonoluminescence 27 + t, us Shock Wave from Bubble reaches Wall of Test Section 54 ^t, us Sonofusion Fraud Degassed deuterated acetone (CD3)2CO, 0 °C 4 105 neutrons s1 PNG Microphone Linear Master Wave Amp Form Generator Chamber with test fluid PZT Slave Wave Form Generator Power Measurement in Sonochemistry Calorimetry P = power, W P el = input power to generator P hf = high-freq. power output P th = power input into liquid © I i Power Measurement in Sonochemistry Calorimetry P = power, W T = temperature, K t = time, s cp = heat capacity, J g1 K1 m = mass, g Volume 50 cm3 Argon atmosphere Error 5% heat capacity, J g1 K1 Water Tetraglyme 4.2 2.08 54 49 O' 19 Calorimetric measurement for water 75% amplitude y = 0,2284x + 20,76 20 40 60 80 Time (s) 100 120 140 Power Measurement in Sonochemistry Chemical dosimetry The Weissler reaction CC14 + H20 —Cl2 + CO + 2 HC1 Volume 50 cm3 Kl 0.1 M cc14 0.2 cm3 Time 30 min 2KI + C12 -► I2 + 2KC1 I2 + 2 S2032- —21+ S4062_ i3 ^max = 355 nm s = 26303 dm3 mol1 cm1 Weissler Reaction |cci4 + h2o 2 ki + ci2 i2 + 2 s2o3 Cl2 + CO + 2 HCll i2 + 2 kc1 21+ S4Q6 020! is s CL. "O-IOJ 0 20 —'—r 40 60 Calori metrically determined ultrasonic power (W) eo Power Measurement in Sonochemistry Chemical dosimetry The Fricke reaction ww ^ ™ H20-+OH Volume 50 cm3 (NH4) Fe(S04)2.6H20 F 2+ + qtt._^ p 3+ + OH 0.001 M H2S04 0.4 M NaCl 0.001 M Time 30 min Fe3+ ^max = 304 nm s = 2197 dm3 mol1 cm 1 Fricke Reaction |H20-^ H +OH ^^^^H Fe2+ + OH Fe3+ + OH 1.0x10"*- (a) e.Qxio-5^- % e.OxlO"5!-o £ 4.0x10"5 2.0x1 O^r- 0.0 -1—I I I I 10 _l_I_I_I_I_I_I_l_ _l_I_I_I_I_I_I_l_ 100 Frequency (kHz) 1000 Power Measurement in Sonochemistry Chemical dosimetry Porphyrin decomposition ratio TPPS 3.3 10 6 M Volume 50 cm3 TPPS ^max = 412 nm 6 = 500000 dm3 mol1 cm 1 Porphyrin Decomposition Frequency (kHz) Power Measurement in Sonochemistry ^ 0.6 h ? 0.2 o ■■ -i-1-1-r n-1-1-1-r -A. -O-o-. O-. O-. ^A-._ —!>-- ■ -A... -A.. C ■A 10 20 SO 40 50 Temperature [°C] TO eo Reactor Optimization cavitating bubbles in the optimised cell (water, 20 kHz, Pus = 10 W) and simulated intensity distribution for the same geometry Heterogeneous Sonochemistry Solid surfaces = implosion, microjets, shock waves 200 jLim minimum particle size at 20 kHz for microjets surface erosion removal of unreactive coatings (oxides, nitrides, carbonaceous) fragmentation of brittle materials, increased surface area Heterogeneous Sonochemistry LARGE PARTICLES SMALL PARTICLES surface cavitation due to defects leading to fragmentation collision can lead to surface erosion or fusion Heterogeneous Sonochemistry Solid particles in liquid = shock waves high speed interparticle collisions (500 km/s) surface smoothing, surface coating removal Ni catalytic activity in hydrogenation increased 105 fold by NiO removal localized melting of metal particles at the impact point fragmentation, increased surface area intercalation rates enhanced 200 fold in layered oxides and sulfides (V2Os, Mo03, MoS2, ZrS2, TaS2) Heterogeneous Sonochemistry Before ultrasound 30 min. ultrasound Cavitational Corrosion of the Tip Control of Sonochemical Reactions sound intensity - minimum for cavitation threshold, depends on frequency, optimum intensity for given reaction conditions, at high powers great number of bubbles hinder sound transmission, decoupling of a liquid from the source, breakdown of transducer material, 10 - 100 W cm2 sound frequency - 20 - 100 kHz, the higher the frequency, the higher power needed to actuate cavitation, stronger cavitation effects, rarefaction phase shortens at high frequency sound attenuation - proportional to the frequency, more power needed at high frequencies Effect of Frequency on Cavitation in Water The frequency dependence of the intensity required to produce cavitation for degassed water at room temperature. The intensity required to produce vaporous cavitation above the frequency of 100 kHz rises rapidly. Control of Sonochemical Reactions volatile reactants - primary reaction site inside the bubbles, diameter 200 urn, 5000 °C, easy bubble formation, more reactant vapors inside bubbles, but the cavitation is cushioned Fe(CO)5 Fe(acac)3 FeS04 nonvolatile reactants - reaction in the thin layer (200 nm) surrounding the bubble, 2000 °C, less cushioning, more energetic cavitation (collapse) high boiling solvents - high vapor pressure inside the bubble cushions the implosion, nonvolatile solvents give less cushioning, more energetic cavitation less cavitation in viscous liquids, viscosity resists shear forces low surface tension facilitates cavitation, in water add surfactants Control of Sonochemical Reactions temperature - higher temperature increases vapor pressure of a medium, lowers viscosity and surface tension, many bubbles formed at temperatures close to solvent boiling point, a barrier to sound transmission, reaction rates decrease with increasing temperature, more vapors in bubbles ambient gas energy developed on bubble collapse: monoatomic (Ar) > diatomic (N2) > triatomic (c02) Xe: low thermal conductivity, heat of the collapsing cavity retained He: high thermal conductivity, heat of the collapsing cavity dissipitated, no reaction external pressure - higher pressure suppresses bubble formation but makes cavitation more energetic, optimum pressure for a given frequency Effect of Temperature on Cavitation in Water 10 20 30 40 50 60 70 80 90 100 Temperature {°C} The effect of temperature on cavitation and its associated hysteresis effect for tap water. The increase in intensity as the temperature is increased can be observed before it falls away at the boiling point. When the temperature is allowed to fall an increase in intensity is found in the region of 50-60 °C. This is quite a significant effect and appears to occur in all liquids. Sonochemical Reactions Solid surfaces = implosion, microjets, shock waves 200 jum minimum particle size at 20 kHz for microjets surface erosion removal of unreactive coatings (oxides, nitrides, carbonaceous) fragmentation of brittle materials, increased surface area Li, Mg, Zn, Al, Cu react at room temperature MC15 + Na + CO -> M(CO)5 (M = V, Nb, Ta) Mo + 6 CO -> Mo(CO)6 r. t, 1 bar, normally needs 300 bar, 300 °C R2SiCl2 + Li -> [-SiR2-SiR2-]n + LiCl monomodal MW distribution Homogeneous Sonochemical Reactions Liquids = heating/cooling by cavity implosions H20 -> H + OH H2 + H202 precursor decomposition: metals Fe(CO)5 -> Fe + 5 CO oxides Ga3+ + H20 -> Ga(0)(OH), diaspore nitrides, carbides, sulfides alkane cracking polymer degradation, lower MW, surface modification emulsification of immiscible liquids (oil-water, Hg-organics, polymer-inorganics) M(acac)n as Precursors Me O Me I ,0--M-—O M(acac) • Well studied class of compounds •Many elements form acac complexes • Metal complexes - precursors in CVD, sol-gel, thermolysis routes to oxides • Easily chemically modified • Volatile, organics soluble Nontoxic Chemistry of M(acac)n Precursors Thermal decompositon pathway CH. 200 °C ^ 3114 JVL 300 °C 765 °C -► MCO, -► MxOy CH.COCH CO Ligand Removal by Water Sonochemical Synthesis of Iron Oxide Nanoparticles ))))) / r Fe203 \ Fe(acac)3 -► ( amorphous 1 hexadecane Amorphous product, by heating to 700 °C converted to a-Fe203 20-40 nm Sonochemical Synthesis of Iron Oxide Nanoparticles Fe(acac)3 Amorphous sono-Fe203 ))))) TG Fe203 maghemite Composite particles (20-30 nm) Amorphous Fe203 particles (2 to 3 nm) Embedded in organic matrix (acetate) 340 °C w dynam/isothermal T Fe203 hematite ^Fe(acac)3 —>- Particle size 20 - 30 nm Spherical shape XT * • 1* A. • 1 J' Uniform size distribution IR Spectrum of Sono-Fe203 0.0 ; 4000 30 00 2000 Wa\A3 number (cm-1) 1000 IR Spectrum of Sono-Fe203 Acetate stretching ♦ ♦ ♦ ■ i i i i i i 12h outgassing periods ) 50 100 150 200 250 300 350 400 Temperature, °C The oxide surface area increases as the acetate groups are removed, then the particle size increases because of sintering Composite Particles of Sono-Fe203 TEM (10 nm bar) Iron oxide particle size 2 to 3 nm Embedded in organic matrix XRD of amorphous Fe203 heated dynamically in air up to 250, 300, and 360 °C 24000 16000 8000 4000 — £ 3000 o o Maghemite Y" Fe203 2000 — 6000 4000 2000 ' I ' ^ ^ ^ maghemite 20 40 60 29 [deg] 360 °C 300 °C 250 °C 80 100 TEM of Fe203 Calcined at 600 °C 10000 9000 8000 7000 Ě 6000 < 5000 4000 3000 2000 1000 20.0 HT-XRD of Sono-Fe20, 280 - 390 °C Hematite Pseudo-isothermal * 330 320 310 300 °C -I 290 Calcination to 1000 °C ^th****^^ ^f^M-^w.*^^ (pseudo-isothermal heating) provides 30.0 a different polymorph - Hematite 70.0 2Theta Hematite Particle Size O 1 ,\J 29,0 • D (nm) m * • coherence • • length • • D (nm) 25,0 23,0 21,0 19,0 17,0 -i c n • • • • • • • • • • 330 380 430 480 T,°C Dependence of the coherence length, D ( nm) of a- Fe203 on the crystallization temperature under dynamic-isothermal conditions of the HT-XRD measurement