Lecture - fh-muenster.de · Lecture: Overview of nanomaterials ceramics Methods of producing...

Lecture

Nanoceramics

Prof. Dr. Julian Plewa

FH Münster

Applied Material Sciences

FB Chemical Engineering

Properties of nanoceramics:

Transparent ceramics and

coatings

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FH Münster

Lecture:

Overview of nanomaterials

ceramics

Methods of producing nanopowders

Phenomena in disperse systems

Consolidation of nanopowders

Properties of nanoceramicsTransparent ceramics and coatings

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FH Münster

opaque ceramic translucent ceramic

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FH Münster

Transparent ceramics and coatings

TRANSPARENT CERAMICS

nanooptics nanoelectronics other

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FH Münster

MULTIFUNCTIONAL CERAMICS

PZT - PbZrO3,

PLZT - (Pb,La)(Zr,Ti)O3

transparent and

piezoelectric

for sensor applications

YSZ - ZrO2 with stabilizer

transparent and ion conductive

for fuel cells, fiber optics, EUV-

litography

YAG - Y3Al5O12 with

activator

transparent and durable

for Laser Technology and

Turbine Blade Construction

Corundum - Al2O3

transparent and chemically

and mechanically resistant

for optical and armour

protection inserts

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FH Münster

The microstructural units (grains, pores, interfaces) of

the ceramic are smaller than about 100 nm, because

light is scattered with about 1/4 of the shortest

wavelength.

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FH Münster

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FH Münster

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FH Münster

Part of the incident light is reflected by all transparent materials. The

reflection is based on the abrupt change of the refractive index at the

interface of two media. Submicrostructured surfaces can

significantly reduce reflection. The surface structures, which are

smaller than the light wavelength, cannot be perceived visually - the

structures cause a continuous transition of the refractive index at the

surface and thus reduce the reflection.

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transmission

the intensity I of a light wave after passing

through a possibly selectively weakening

medium of thickness d in relation to the

intensity I0 of the original light wave

is a constant, the absorption coefficient is

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FH Münster

transmission

The transmission in a disc after a

simplification of drilling and Huffmann

The real-in-line transmission to Peelen and

Metselaar

(1-RS) multiple reflections at boundary surfaces according to an

mathematical series development according to G. Kortüm.

scattering factor, = scattering at grain boundaries and pores

Transmission without

scattering

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FH Münster

At normal incidence, the reflection R1 on one surface is related to the material

refractive index n, given by

and the total reflection loss, including multiple

reflection, is

Therefore, the maximum transmission is as follows:

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FH Münster

the actual inline transmission (RIT) of a fully dense transparent ceramic:

where n/n is the ratio of the refractive index difference between the polarization

perpendicular and parallel to the c-axis to the average index n, 2r is the grain size of

the ceramic, the wavelength of the incident light, and d is the thickness of the

sample. This equation implies that the RIT is closely related to n/n and r at a given

thickness. The smaller the values of n/n and r, the higher the RIT. If n/n is an

intrinsic property of materials, r is an extrinsic parameter that can be controlled by

material processing. Therefore, the grain size of the ceramic for given materials

should be small enough to achieve a high RIT. For example, the grain size of a high

density sintered Al2O3 must be about 0.5 mm for a RIT of 60 to 65% at = 640 nm

and d = 1 mm [Wang].

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FH Münster

transmission

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FH Münster

The most important requirement that nanoparticles have to meet is a small size.

Typically, particle diameters smaller than 50 nm are necessary to obtain optically

transparent materials. The reason for this is the strongly increasing scattered light

intensity with increasing particle size. This connection is described by the law of

Rayleigh:

I is the intensity of the transmitted beam, I0 the intensity of the input beam, r the

radius of spherical particles, np the refractive index of the particles and nm the

refractive index of the matrix. λ is the wavelength of the light, Φp the volume

fraction of the particles and x the optical path length. A high scattering intensity is

associated with a cloudy appearance of the nanocomposite material and thus with

a loss of quality of the material for optical applications.

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FH Münster

Distortion introduced into the incident laser beam as it propagates through the PLM. The dark lines shown

inside the PLM body are representative of local refractive index inhomogeneities and discontinuities

observed by the incident laser beam. The incident laser beam has a uniform circular shape and a

Gaussian intensity distribution. After passing the PLM sample, the transmitted beam has a distorted shape

due to mass scattering. [Sharma]

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FH Münster

Transparent Al2O3 ceramics

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FH Münster

YAG Arctube Ceramic Metal Halide, Toto

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FH Münster

YAG:Nd for laser applications

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FH Münster

YAG:Nd

for laser applications

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FH Münster

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FH Münster

YAG:Nd

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FH Münster

YAG:Nd

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FH Münster

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YAG:Nd

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FH Münster

YAG:Nd

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FH Münster

YAG:Nd

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FH Münster

YAG:Nd

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FH Münster

Since 1999, Yanagitani and Yagi Group in Konoshima Chemical, Co., in cooperation

with the Ueda Group at the University of Konoshima, started the development of highly

transparent neodymium-doped YAG ceramics in vacuum sintering process, where the

starting materials were produced by nanocrystalline technology.

Compared to YAG single crystal, transparent ceramic laser materials have the following

advantages, namely:

(1) Ease of production;

(2) less expensive;

(3) Production of large and high concentrations;

(4) multilayer and multifunctional ceramic structure;

(5) Mass production etc.

The optical properties of Nd: YAG ceramics, such as absorption, emission and

fluorescence lifetime as well as thermal conductivity, are similar to those of Nd: YAG

single crystal.

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FH Münster

The SSHCL (Solid-State Heat Capacity Laser)

requires slabs that are 2 centimeters thick

The SSHCL uses the world's

largest laser-quality

transparent ceramic amplifier

plates, measuring 10 x 10 x 2

centimeters [Konoshima

Chemical Co.].

Konoshima is the leader in polycrystalline YAG production

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FH Münster

Transparent ceramics are produced by forming a nanopowder with a desired

shape and then sintering the sample in a vacuum to form an aggregate of

microcrystals [Konoshima ].

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FH Münster

Production method used by Konoshima (1)

Transparent ceramics are produced by shaping a nanopowder of constituents

into the desired shape, then sintered in vacuum (heated below the melting point)

to form an aggregate of microcrystals with optical and thermal properties almost

identical to those of a monocrystal.

The precipitate of a solution of yttrium, neodymium and aluminium salts with the

addition of a solution of ammonium bicarbonate is then filtered, washed and

dried.

The co-precipitated amorphous carbonate is agglomerated to particles of about

10 nanometers.

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FH Münster

In a process known as slip casting, a suspension of the fine powder is poured

into a plaster mould and allowed to settle.

The green compact (preform) still contains many pores and is only 40 to 45

percent dense. The preform structure is then sintered in a vacuum at high

temperature for many hours. This sintering process involves the diffusion of

surface atoms, which causes the particles to fuse together and reduce the total

surface energy.

Some of the pores are squeezed out, and the structure shrinks, but retains its

overall shape. In addition, many physical and thermal properties are dramatically

improved during sintering.

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FH Münster

The precursor is heated to about 1100ºC to decompose the carbonates and form

particles of neodymium-doped yttrium aluminium garnet (Nd: YAG) about 100

nanometres in size. Highly agglomerated, the particles are treated with

ultrasound and then the large particles are removed to obtain a uniform small

15-millimeter-diameter

samples of transparent

ceramic yttrium–

aluminum–garnet

[Livermore Res.].

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FH Münster

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FH Münster

Transparent ceramics

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FH Münster

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FH Münster

Considering the experimental arguments, there are three conditions to obtain

optically transparent ceramics:

The material must be > 99.985% of theoretical density

no second phases must not be present in the microstructure

The material system must be optically isotropic or the average grain size must be

<200 nm.

Why nanopowders?

Sintering favoured by huge surface energy

the specific surface area increases with decreasing particle size

the surface energy increases with decreasing particle size (Kelvin Eqn.)

the sintering force increases with decreasing particle size

Step 1: Preparation high purity powder

Step 2: High-temperature powder pre-pressing

Step 3: High Temperature Isostatic Presses (HIP) (to clear transparency)

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Segregation on the grain boundaries

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applications

defense

scintillator

smart gear

engineered materials

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FH Münster

scintillators

Absorption coefficient of X-rays

effabs Z density, Zeff effective atomic

number of the material

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FH Münster

The scintillator can be considered as a phosphor material for radiation that converts high-energy

particles, such as X-rays, X-rays and X-rays, into visible or UV light. The application of scintillator

has a great variety. It is usually combined with photodetectors and uses medical devices such as

X-ray CT, PET / SPECT, high energy physics, and a well-known example is baggage screening

in airports.

scintillators

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FH Münster

scintillators

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scintillators

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FH Münster

scintillators

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FH Münster

scintillators

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FH Münster

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FH Münster

Nano layer Thin layer Thick layer

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FH Münster

Nano layer Thin layer Thick layer

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FH Münster

Functions of thin layers

• tribological protection against wear / scratches

• reduction of friction / dry lubrication

• sterile and protection against corrosion / chemicals

• Color and glossyness

• anti-reflection

• electrical conductivity / insulation / electro-magnetic shielding

• bio compatibility / protection against microbes

• matrix for catalysts

• thermal conductivity / protection against heat and cold

• 3D surface structures / micro reactors / nano technology

• 2D surface structures

• protection against diffusion

• wettability / bonding agent / protection against dirt

• sensors / actuators

• photo voltaic

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FH Münster

Functions of nanolayers (ultrathin films)

Easy-to-clean surfaces

dirt resistant surface

protection against abrasion

scratch resistancy

antibacterial surfaces

corrosion protection

moisture protection

Acid / base resistant

high permanence

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FH Münster

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FH Münster

UV protection

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FH Münster

Light is reflected at both interfaces of an anti-reflective layer. The two reflected

waves of a certain wavelength can cancel each other out completely by

interference, if both the phase and amplitude conditions are fulfilled.

Clean layer

anti-reflection

Hardness

Colors

Substrate

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FH Münster

Light is reflected at both interfaces of an anti-reflective layer. The two reflected

wave trains of a certain wavelength can cancel each other out completely by

interference, if both the phase and amplitude conditions are fulfilled.

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FH Münster

The anti-reflection layer reduces the reflection.

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FH Münster

The anti-reflection layer reduces the reflection.

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