Knowledge
of the thermophysical properties of materials and heat transfer optimization
of final products is becoming more and more important for industrial applications.
Over the past few decades, the flash method has developed into the most
widely used technique for the measurement of the thermal diffusivity and
thermal conductivity of various kinds of solids, powders and liquids.
Using this technique, the front side of a small, usually disk-shaped plane-parallel
sample is heated by a short energy (laser) pulse. The temperature rise
on the rear surface is measured versus time using an infrared detector.
Easy sample preparation, small required sample dimensions, fast measurement
times and high accuracy are only a few of the advantages of this non-contact
and non-destructive measurement technique.
Hardware:
The
NETZSCH LFA 457 MicroFlash™ represents the state-of-the-art
in modern laser flash technology. The table-top unit allows
measurements between –100 and 1100°C. To cover this
temperature range, two user-exchangeable furnaces are available.
The innovative infrared sensor technology employed in the system
allows the measurement of the temperature rise on the back
surface of the sample even at temperatures of –100°C.
The system can be employed for large sample sizes of up to
25.4 mm in diameter or, using the integrated sample changer,
for measurements on several samples at the same time. The vacuum-tight
construction allows tests under well-defined atmospheres. The
vertical arrangement of the sample holder, furnace and detector
facilitates sample change and at the same time enables an optimum
signal-to-noise ratio for the detector signals. The LFA 457
conforms to national and international standards such as ASTM
E-1461, DIN EN 821 or DIN 30905.
Temperature
range:
LT-furnace:
-100 ... 500°C
HT-furnace:
RT
... 1100°C
Measurement range:
Thermal
diffusivity:
0.001 … 10 cm2/s
Thermal
conductivity:
0.1
... 2000 W/(m*K)
Sample geometries:
Square
samples:
8 mm x 8 mm
10 mm x 10 mm
Cylindrical
samples:
10 mm in diameter
12.7 mm in diameter
25.4 mm in diameter
Thickness:
0.05
... 5 mm
Sample
changer:
for
up to 3 samples (except 25.4 mm Æ)
Special sample holders for the measurement of powder, liquids or non-standard sample dimensions are available on request.
The
speed and repeatability of thermal diffusivity measurements have made
this technique the method of choice among researchers worldwide, thereby
replacing traditional steady-state methods that are difficult, costly,
and much slower. By measuring the thermal diffusivity (a) of a material,
its thermal conductivity (λ) can be determined if specific heat (cp) and density (ρ)
are known
The specific heat can be measured in the LFA by a comparative method or by employing differential scanning calorimetry (DSC), the latter of which enables improved flexibility and accuracy and offers further information on phase transition temperatures and
enthalpies.
Software:
The
NETZSCH LFA 457 MicroFlash™ comes with outstanding instrument control
and analysis software unique in the field of commercial laser flash units.
More than 15 different models can be selected to analyze the measured
temperature-versus-time curves of the detector. Therefore, nearly all
possible applications such as metals, ceramics, polymers, semi-transparent
materials or multi-layer systems can be evaluated in the optimum way.
Combined heat loss and finite pulse corrections, crucial for tests with
a high level of accuracy, are available for most models. The models are
based on non-linear regression routines which take the entire measurement
curve (between 500 and 15,000 points) into consideration.
Some analysis models:
Standard
analysis routines (Parker, Azumi,
Clark and Taylor, Cowan, …)
Improved Cape-Lehman model simultaneously taking facial and radial heat losses as well as finite pulse effects into consideration.
Radiation model taking internal radiative heat transfer into consideration.
2- and 3-layer analysis with heat loss and finite pulse correction.
Applications:
The
LFA 457 MicroFlash™ can be employed on a wide range of various solid
and liquid materials from insulating materials to highly conducting metals
or composites
Electrolytic Iron
Water
NETZSCH offers
precision thermal analysis instruments including advanced dilatometers (with
a new basic R&D/QC dilatometer),
classical DSC & TGA (with
a new economical DSC), high temperature DSC
to 1650°C for specific heat, very high temperature STA
(TGA-DSC/DTA) to 2400°C (featuring the new STA
409-PC Luxx®), thermal
/ evolved gas analysis with fully-integrated FTIR & MS, plus
high resolution TMA and DMA.
We also feature leading technology for thermal conductivity and diffusivity measurement
as well as refractories testing including HMOR, CIC, and RUL.
