PHYSICS and CHEMISTRY of NANOMATERIALS, lecture 6 Alexander A. Gromov gromov@tpu.ru Chair of Silicates and Nanomaterials, Faculty of Chemical Technology, Tomsk Polytechnic University, RUSSIA Technological Aspects of Metal Nanopowders
Tomsk Polytechnic University, Department of Chemical Technology
METAL NANOPARTICLES
RECENT APPLICATION FOR METAL NANOPOWDERS 1. ~10 % of estimated market Lubricant compositions for internal combustion engines, fuels, machine oils (Cu, Ni, Fe, Cu-Ni alloys) : - micro-cracks recovery, - wear and tear decreasing, - fuel burning catalysts. 2. ~10 % Catalysts for hydrocarbon conversion (Ag, Pt, Cu, alloys): - higher conversion degree, - low metal consumption, - stability to catalysis poisons. 3. ~20 % Coatings of different origin (Ti, W, Mo, intermetallides, alloys) : - information holders, - electronic devices.
RECENT APPLICATION FOR METAL NANOPOWDERS 4. ~40 % Energetic Systems (Al, Ti, Zr, Mg, Fe, Cu-Ni alloys): - burning characteristics regulations, - C-H-N conversion catalysts, - hydrogen sources. 5. ~10 % Ceramics additions (Al, Ti, Zr, Mg): - sintering process activation, - low-shrinkage ceramics, - solid-phase synthesis activation. 6. ~10 % Others
PROBLEMS OF METAL-BASED NANOTECHNOLOGY 1. Almost all method for nanopowders production have: - low productivity (few grams/1 machine), - high cost of powders (~ 1000 Euro (USD)/kg), - low yield of nano-fraction (a few percents in a total mass of powder). 2. New level of technological requirements for industrial production - a lot of absolutely hermetic apparatuses, - toxicity of powder (Ni!!!), - sterile conditions (like for biotechnological plants) 3. Problems of particles agglomeration during production and stabilization - particles condensed through liquid phase, - reactivity in air is extremely high, - metal content is low 4. New nano-scale raw materials requires new technologies.
History of the Wires Electrical Explosion Method 1. Discovery - 18th Century (M. Faraday exploding wires ) 2. First development, 1950-60 USSR (Efforts of Al-H Obtaining) USA (Initiation of Nuclear Explosion) 3. Fast development, 1980s ( cold war ) USSR, Tomsk (Industrial-Scale Production of Aluminum Nanopowders for Energetic Systems) 4. Current situation, 2000-2005 ALEX and Analogues are Commercially Available Product As Well As Machines for Nanopowders Production
Investigations dwell on such properties of Al-based nanopowders as a size and morphology, phase composition, thermal properties, and activity in reactions with air and water, in combustion with gelled water Exploding wire method allows producing Al based nanopowders with the specific surface S BET > 20 m 2 /gram. Compared to conventional Alex the specific surface is three times higher An ultrafine aluminum oxyhydroxide with the specific surface S BET = 370 m 2 /gram has been produced Combustion rate sufficiently grows when a high dispersed powder is used
Experimental Methods Experimental methods include the installation for powder production, characterization of the powder produced, investigation of powder activity in oxidation reactions and in combustion
Experimental Methods C - capacitor L - inductance R - resistor S - switch EW - wire The effectiveness of electrical energy consumption is more than 0,75 The productivity is of 50 1000 g/hour depending on powder constitution
Wires Electrical Explosion Technology Voltage Current t 1 t 2 t 3 Parameters : t ~ 50 μ sec W = 10 8-10 13 (J/sec) P = 10 9 (Pa) Cooling velocity of particles : 10 8 (K/sec) Stage : 1. Formation of primary EEW products (T 10 4 K) 2. Particle formation (T 10 4 K)
Major Factors to Control the Process 1. The introduced energy 2. The density and chemical reactivity of surroundings 3. The wire diameter 4. The current density, or heating rate 5. The microstructure of exploded metal
Periodic Table of Investigated Metals Li Be B C Na Mg Al Si K Ca Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge Rb Sr Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb The advantage of the Exploding Wire method is the possibility to produce powders of different metals, which are market in the Table
Characterization of Powders SPECIFIC SURFACE 5-points BET MORPHOLOGY TEM, SEM PHASE AND CHEMICAL COMPOSITION TEM, XRD, mass spectrometry, Content of bonded gases, Determination of Active Al, % ACTIVITY DTA, TG, Reactions with hot water, Burning in manometric bombs
Al nanopowder: Sample N 2 /air б 40 N i 20 0 20 40 60 80 100 D,нм BET: S=17,5 м 2 /г, d S =127 нм TEM: D=40,2 нм, σ =16,4 нм
Al samples N 2 /CO 2 and CO 2 / CO 2 N 2 /CO 2 CO 2 /CO 2 BET: S=21,0 м 2 /г, d S =106 нм TEM: D=40,4 нм, σ =6,1 нм BET: S=38,0 м 2 /г, d S =72 нм TEM: D=30,8 нм, σ =5,9 нм
SUPERTHIN NANOLAYERS FORMATION ON METAL NANOPARTICLES а BEFORE PASSIVATION Al Me Ar Me Al Ar Me Al Ar б AFTER PASSIVATION Me Al Me Al Al Me H2O OH- H2O Воздух AIR OH- H2O OH- O2- O2 O2- O2 O2- O2 Оксидная OXIDE LAYER пленка Kwon Y.S., Gromov A.A. et al. // Appl. Surf. Sci. Vol. 211. 2003.
SIZE AND MORPHOLOGY OF METAL NANOPOWDERS Cu SEM & TEM Shape : sphe. 100nm BET BET : 8.67 77nm
SIZE AND MORPHOLOGY OF METAL NANOPOWDERS Ni SEM & TEM Shape : sphe. 100nm BET BET : 9.54 71nm
Sample The Size of Particles and Crystallites BET TEM XRD S, m 2 /g d S, nm D, nm, nm D RCS, nm N 2 /air 17.5 127 40.3 16.4 29 N 2 /CO 2 21.0 106 40.4 6.1 30 N 2 +CO 2 /N 2 34.3 65 32.4 4.7 32.5 N 2 /air designation corresponds to the powder produced in nitrogen and passivated by air etc. d S = 6/ S, where is the density Particles of N 2 +CO 2 /N 2 sample are monocrystal, and comparison between values d S and D shows that the particles of this sample are slightly agglomerated
Constitution of Powder Samples S, Al, Water Sum of gases, XRD, volume % Sample m 2 /g % mass % mass % Al Al 2 O 3 AlN Al N 5 O 14 N 2 /N 2 18.2 75.4 6.4 1.7 96 4 N 2 /CO 2 21.0 70.7 0.4 2.9 90 5 5 N 2 + CO 2 /N 2 34.3 60.7 1.5 5.2 91 9 Sample Al, Water, Sum of gases, Gases, volume % % mass % mass % H 2 O N 2 O 2 CO 2 Ar N 2 /N 2 75.4 6.4 1.7 11.4 78.5 8.6 1.5 Steps N 2 /CO 2 70.7 0.4 2.9 8.0 14.1 3.9 74 No CO 2 /CO 2 16.4 0.4 4.0 1.6 2.3 0.6 95.5 No Ar/air 79.8 6.5 3.9 18.9 52.0 14.2 6.3 0.7
I, relative units Relative Intensity Releasing of Gases Under Heating in Vacuum 1 0,9 0,8 0,7 1 1,0 0,8 0,6 0,5 0,4 2 3 0 100 200 300 400 T, o C A variation of relative intensity of a gas release in vacuum at various heating temperatures. Samples: 1 Ar/air, 2 N 2 /air, 3 N 2 /CO 2 0,6 0,4 0,2 T, 0 0 100 200 300 400 500 Kinetics of gas evolution shows two steps: the first step is caused by loosely-bounded gases, and the second by chemically bounded gases
Oxidation of Powders in Reactions with Air Sample Al, S BET, D, % m 2 /g nm T onset, 0 C N 2 /N 2 75.4 18.2 44.2 375 N 2 /air 74.0 17.5 40.3 400 N 2 /CO 2 70.7 21.0 40.4 425 N 2 +CO 2 / N 2 60.8 34.3 32.4 397 CO 2 /CO 2 16.4 38.0 30.8 400 Ar/air 79.8 16.7 54.6 420
One example of nanopowders life Metal nanopowders combustion in air results in interaction with nitrogen, but not with oxygen!!!
Degree of Oxidation, % Temperature of teaction onset, 0 C Oxidation in reaction with water 60 100 80 60 40 20 35 14 16 18 20 22 24 26 28 30 32 34 36 38 40 S, m 2 /g 1 2 55 50 45 40 The specific surface dependence of Al oxidation degree with water (1) at 60 C and the dependence of the reaction onset temperature (2) The more active is the powder, the lower is the temperature of reaction onset with water and the higher is the oxidation degree
Thank you so much for your attention! Vielen Dank! Большое спасибо за внимание!