final nano whiskers
DESCRIPTION
nanoferraamentasTRANSCRIPT
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NANO
WHISKERS
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General Definition WHISKERS- One of the long stiff tactile
bristles or hairs that grow near the mouth and elsewhere on the head of most mammals
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METALLURGY
Metal whiskering is a crystalline metallurgical phenomenon involving the spontaneous growth of tiny, filiform hairs from a metallic surface.
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Types of metal whiskers
Zinc Whiskers
Silver Whiskers
Gold Whiskers
Cadmium Whiskers
Aluminum Whiskers
Lead (Pb) Whiskers
Indium Whiskers
Tin whiskers
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Pictures of Metal whiskers
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Properties of whiskers
Shapes: Whiskers may be straight, kinked, hooked or forked
Growth Rate: Growth rates from 0.03 to 9 mm/yr
Whisker Diameter: 10 um and rarely less than 100 nm
Temperature: room temperatures (22C to 25C) ; whiskers grow faster
Moisture: high humidity (85% RH)
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Whiskers vs. Dendrites
Whiskers
Hair like shape
Grow perpendicular to the surface (90o)
Doesnt require dissolution of metal/ presence of electromagnetic field
Dendrites
Fern shaped
Grow across the surface
Growth requires dissolution of metals in electromagnetic field
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Mechanism of Growth
A Single accepted explanation of the mechanism has not been established.
Theories suggest that metal whiskers may grow in response to a mechanism of stress relief (especially "compressive" stress) .
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Video Demonstration of Tin whiskers Growth
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Commonly Accepted Factors
Residual stresses within the metal plating
Intermetallic Formation
Externally Applied Compressive Stresses
Bending or Stretching
Scratches or nicks
Coefficient of Thermal Expansion Mismatches
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Recent Attention to Metal Whiskers?
To reduce the use of potentially hazardous materials such as lead (Pb), so the alternatives to the widely used tin-lead alloys used for plating.
Restriction of certain Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE)
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Failures by Whiskers
Galaxy IV satellite in 1998- Tin whiskers
F-15 Radar- Tin whiskers
Heart Pacemaker Recall- Tin whiskers
computer server rooms Zinc whiskers
Paper mills- Silver whiskers
Satmexs Solidaridad HS 601 - Zinc whisker
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Nano Whiskers
The single crystalline metallic hair-like structure in the nanometer scale
Also called as nanowires or nanorods.
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Fullerene, C60 Nano WhiskersHistory
C60 Nanowhiskers were discovered in 2001 in Japan by Kunichi Miyazawa during the preparation of a lead zirconate titanate sol gel.
Thin fibrous structures that grow in the solution were named C60 Nanowhiskers.
The C60 Nanowhiskers are prepared by the liquid-liquid interfacial precipitation method.
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Preparation of C 60 Nanowhiskers: Add 5ml of organic solvent to 20ml glass vial Measure out enough C60 to form saturated solution in organic solvent (using C60
solubility table) Sonicate solution of solvent and C60 until thoroughly dissolved Layer with 5ml of polar solvent Place in 2C refrigerator for several days until whisker formation is observed, black
dusty material on the bottom of the vial Pipette small sample of solution and whiskers onto glass slide and allow solvent to
dry
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Properties of C60 Nano whiskers
The Nanowhiskers were found to be C60 fullerene molecules arranged into a hollow tube by face-centered cubic packing.
Nanowhiskers measure from a couple hundred nanometers to one micrometer in diameter and several millimeters in length
Various experiments have been carried out testing different solvent solutions and the effects of environment on Nanowhiskers growth.
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Solvent Solutions Tested
Organic layer Polar layer
Toluene Iso propyl alcohol
Carbon disulfide Iso propyl alcohol
Cholro benzene Iso propyl alcohol
Pyridine Iso propyl alcohol
Toluene Acetone
Toluene Water
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Carbon: C60Organic: Toluene
Polar: WaterStored in: SolutionMagnification: 60x
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Transmission Electron Microscope 8000x
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Silicon Nanowhiskers
Molecular Beam Epitaxy
Silicon wafers were used as substrates
Desorption of the oxide layer by a thermal annealing at 850 C.
Afterward, a thin Au film was deposited at a substrate temperature of 525 C with thicknesses between 1.5 nm and 2 nm.
The size of the thereby generated droplets could be chosen between 70 and 200 nm.
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SEM cross section images of Silicon whiskers grown on a Silicon substrate for a) 60 min b) 120 min growth time at TS 525 C.
TEM cross section image of a Silicon whisker with a length of about 300nm and a diameter of 95 nm on a Silicon substrate.
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Crossed Nanowhiskers
Bi-2212 superconducting single crystal Nano whiskers have been fabricated by annealing a melt quenched glass Bi3Sr2Ca2Cu3Ox precursor.
A couple of Nano Whiskers obtained were placed crosswise on a YSZ single crystal substrate and then heat treated at 830o C for 25 minute to form Nano-scale junction
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Glass-ceramic method were used for preparation of the whiskers
Bi2O3; SrCO3; CaCO3 and CuO were mixed to give a composition of Bi3Sr2Ca3Cu3O10+x.
The mixture was melted in an alumina crucible at 11000C for 2 h.
The melt was then rapidly quenched between two cold copper plates
After the heat treatment cycle, whiskers were grown on the surface of the glass sheets
Then a couple of whiskers were placed crosswise on a Yittria stabilized Zirconia, (YSZ:(ZrO2)1-m(Y2O3)m)) substrate and heat treated at 8300C for 25 min. to form Nano-scale junction.
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Cellulose Nanowhiskers
Properties Cellulose Nanowhiskers
Physical structure Needle- whiskers
Chemical structure cellulose
Interactions Hydrogen bond
Tensile modulus ~130 GPa
Tensile strength 10 GPa
Electrical resistivity 1010 - 1016 ohms cm
Thermal conductivity Insulator
Density 1.2 g/cm3
Coef. Thermal expan 8 -16X 10-6
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Preparation of Cellulose Nanowhiskers
Cellulose Nanowhiskersregenerated from aqueous sodium hydroxide urea solvent system on the basis of their temperature-dependent solubility.
AFM topography image of cellulose Nanowhiskers after drying on a mica surface
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Nanowhiskers in use
Water Repellant
In Nature, many small tubes or whiskers keep water and solid at minimal contact for super hydrophobia (extreme water repellency)
water droplet
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Stain Resistance
Billions of Nanowhiskers(10 nm long) create a thin cushion of air above the cotton fabric, smoothing out wrinkles and allowing liquids to bead up and roll off without a trace.
Water droplets form spherical globules Rough nanoscale surface picks up dirt Water and dirt roll off Biomimicry
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Bioceramics
The calcium phosphate Nanowhiskers produced by microwave assisted method can be used as Bioceramicsto human bone
Gas sensor
SnO2 Nanowhiskers showed a high sensitivity of 2350 ppm ethanol gas at 300C, which is much higher than that of regular SnO2 films.
FE-SEM image of SnO2Nanowhiskers synthesized by thermal evaporation
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Electronics
Nio2 Nanowhiskers having long life-cycle, High specific capacitance, high power, high stability, and low cost of the electrode materials are favorable factors for commercial applications
Anisotropic Etching of SiC Whiskers were used as building blocks in the fabrication of sensors, cellular probes, electronic, optoelectronic, electromechanical, and other devices.
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Betray the Worst.