7 ta routine maintenance guide EN

Thermal Analysis GuideTips and Hints for Routine Analysis Taking Samples Sample Insertion Unattended Operation... Good thermal analysis measurements depend also on the correct choice of

Thermal Analysis Guide

Tips and Hints for Routine Analysis

Taking Samples Sample Insertion Unattended Operation

Dear Reader

Since the first experiments by Henry Louis Le Chatelier in 1887 thermal analysis has developed to a group of measuring techniques undispensable for material characterization of polymers, metals and inorganics, oils and fats, pharmaceuticals as well as food

A major breakthrough was the invention of heat flow DSC in 1955 by S L Boersma The heat flow principle is still applied by present day instruments and reached its top with the recent introduction of the Flash DSC by METTLER TOLEDO The model Flash DSC 1 allows ultra high heating rates of up to 2 400 000 K/min in the temperature range of -95°C up to maximum 500 °C

The availability of powerful computer hardware and software influenced thermoanalytical methods enormously It simplified method setup and instrument operation and turned curve evaluation and result calculation into common and easily understandable tasks However, thourough thermal analysis knowledge and diligent instrument operational skills remain essential to achieve meaningful and precise results

This guide presents some solutions to perform thermal analysis tests safely and easily in the daily routine

METTLER TOLEDO

Disclaimer

The information contained in this guide is based on the current knowledge and experience of the authors The guide represents selected, possible application examples The experiments were conducted and the resulting data evaluated in our lab with the utmost care using the instruments specified in the description of each application The experiments were conducted and the resulting data evaluated based on our current state of knowledge However, this guide does not absolve you from personally testing its suitability for your intended methods, instruments and purposes As the use and transfer of an application example are beyond our control, we cannot accept responsibility therefore.

When chemicals, solvents and gases are used, the general safety rules and the instructions given by the manufacturer

or supplier must be observed.

® ™ All names of commercial products can be registered trademarks, even if they are not denoted as such.

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When it comes to analyze many samples in limited time, analytical instruments have to be well "calibrated" and need to perform at their best These requests are typical for the quality control of received goods, intermediate specimen taken from a production line, produced parts and failure analysis and material research Furthermore, operation of the instruments should be as simple and safe as possible

Basic maintenance tasks executed periodically assure good working conditions of the instruments A seamless workflow takes care that an analysis can be done without any interrupting delays Automation accessories help avoiding error-prone manual steps

The METTLER TOLEDO Thermal Analysis Excellence systems offer new possibilities to achieve exactly such targets Test methods include several work steps and can be set to high automation levels if desired Few basic skills and a minimum of training are necessary to conduct a complete thermal analysis Routine tests can be executed with one click from the instrument's touch screen terminal without the need to have access to the controlling PC

Efficient and reliable 7 day 24 hours operation is supported by a sample changer robot Thanks to its clever design, the robot offers flexible crucible handling and reliable single axis movement It is factory endurance tested

On the following pages we will show selected routine maintenance tasks as easy and convenient tools to achieve good thermal analysis results

Figure 1: Selection of crucibles for thermal analysis

2 Taking Samples

A sample has to be representative, clean and original Thus, good laboratory and good manufacturing practice guidelines (GLP, GMP) point out sampling rules to assure that final results are meaningful and characteristic For thermal analysis, sample size and shape are two additional important aspects

100 g or 100 mL, small sized samples can undergo thermal analysis only Hence, the selection of the right part of the sample is crucial for the analysis

Shape Flat surface to allow for good thermal contact

e.g Dilatometry of polymers: 5 x 5 x 3 millimeters (LxWxT)

For 3 point bending of thermosets: 50 x 2 x 1 millimeters (LxWxT)

Table 1: Typical sample size for thermal analysis

For TGA measurements in addition, the sample's

minimum weight has to be considered The minimum

weight depends on the type of the built-in balance

and the uncertainty requirements for a certain weight

step or the weight of the residue Also the upper

sample size limit is defined based on available crucible

volume, desirable heating rate and analysis time

Both values can be entered into the method in form

of sample limits This means that an operator having

prepared too small or too large a sample is not

allowed to start the measurement

Good thermal analysis measurements depend also

on the correct choice of crucibles and lids Typical

crucible materials are aluminum, alumina, platinum,

steel, gold plated steel, copper, etc They are selected

according to the maximum temperature and to avoid

or minimize reactions with the sample

Lids seal the crucible hermetically to avoid evaporation of the sample and to avoid interferences with the surrounding atmosphere Lids with a small hole e.g a pre-punched 50 µm hole, allow for a self-generated atmosphere in the crucible due to restricted exchange with the ambient On the other hand, open crucibles without a lid or with a lid with a big hole allow the ambient atmosphere to come into contact with the sample

Figure 2: Weighing samples for DSC tests on a microbalance

Table 2: Selection of TA crucibles and recommended use

How different types of samples are

filled into crucibles can be watched in

the DSC sample preparation video

www.mt.com/ta-videos

More details, tips and hints see

Thermal Analysis in Practice,

Application Handbook, chapters 7.3,

9.3, 10.3 and 11.3

To assure safe and easy starting of analyses, the thermal analysis instruments and methods are prepared ac-cordingly

performance before analyses are due

Select suitable evaluation range and procedure, Store method to be available for One Click™

Methods started with One Click™ provide increased safety and efficiency:

• No confusion about methods to apply

• No operating errors

• No time consuming method entry

• Minimized error-prone manual data entry

The unique One Click functionality introduced by

METTLER TOLEDO to a variety of instruments allows

easy and safe starting of predefined measuring

meth-ods After one click on the instruments’ color

touch-screen display the method is started automatically or

a next screen asks for further data displaying entry

fields for sample name, sample weight and position if

a sample robot is used

To avoid transcription errors and simplify the task

at the utmost we recommend a barcode reader for

sample identification entry

Sample insertion to DSC and TGA instruments can be done in two ways:

1 Manual insertion

DSC and TGA systems standout by their intelligent ergonomic design This means in particular that a tray with the prepared crucibles can be placed very near to the sensor area where the measurement takes place Hand rests with ergonomically shaped and soft touch coated surfaces support the operator Thus, operators can easily and safely insert the samples into the measurement cell

2 Automatic insertion using the sample robot

The main advantages of a sample robot are unattended operation for increased efficiency, extended working period to overcome regular shifts and improved repeatability thanks to reduced operator influence The METTLER TOLEDO sample robot can process up to 34 samples even if every sample requires a different method and a different crucible The

robot can remove the protective crucible lid from the crucible or pierces the lid of hermetically sealed aluminum crucibles immediately before measurement This unique feature prevents the sample taking up or losing moisture between weighing-in and measurement It also protects oxygen-sensitive samples from oxidation

Thanks to a clever design, the piercing pin does not contact the sample and refrains from contamination of the next sample

Please see the sample changer robot in action at

www.mt.com/ta-automation

For DMA measurements, the sample needs to be fixed by clamps and then inserted Several insertion modes are applied in TMA measurement

Figure 4: DSC oven ready for manual sample entry

Figure 5: Sample robot handling several types of crucibles

Sample insertion modes for TMA

Penetration or expansion

measurement

Figure 6a: Sample placed on sample

support and topped by sensor probe

Figure 6b: Sample fixed by clamps and hanging in sample support

Figure 6c: Sample in crucible topped by sensor probe

Unattended measurements are a perfect set for error free, safe and reliable experiments All experimental

parameters have been entered beforehand to the method and stored for repetitive use Thus, any recall of

the method assures correct execution of the test Once the measurement is started, the method is worked off automatically

Many features of METTLER TOLEDO's Thermal Analysis Excellence instruments contribute nicely to safe and unattended measurements Here is some selection:

• FlexCal®, a functionality of the STARe software, takes care that always the correct calibration data are applied

to calculate results It automatically considers variations of gases, crucibles, heating rate etc from one measurement to the next This results in accurate and precise measurements

• The gas flow is programmed within the method

Thus, no manual flow adjustments are necessary and FlexCal is able to take it into account

• Set the TGA instrument for automatic buoyancy

compensation This is an easy and effective measure to achieve accurate TGA results Buoyancy compensation reduces the experimental time needed

to produce accurate results by more than 50%:

• It eliminates the need to run and subtract blank curves

• It makes waiting for cooling time between blank and sample measurement obsolete

• After the measurement itself is finished and the

resulting curve is recorded, a preprogrammed macro evaluates the effect(s) of interest and performs a conformity check against given limits

A result text can be displayed, e.g "The sample has passed"

The evaluated curve including results can be printed

and/or transferred to a LIMS system automatically

Even a good/bad distinction can be executed

automatically

• When a measurement has ended, the method can

be set to inform the user by email This is especially helpful, when operating an instrument manually and one is waiting to insert the next sample

Another aspect of unattended measurement is the application of a sample changer robot It extends the period

of unattended operation considerably, even out of regular lab working hours METTLER TOLEDO's sample robot for DSC and TGA stores up to 34 samples Its universal gripper handles various crucible types It even applies lid piercing when specified in the method

Figure 7: Excellent agreement between the time saving buoy-ancy compensated and a conventional TGA measurement.

Figure 8: Preconfigured gas supply which does not need any user interaction

A calibration, also called a "check", determines the difference of a measured value from a reference value The calibration provides information about the current state of the instrument Calibration data must be within the acceptable error limits The adjustment changes the instrument parameters in a way that the measured value agrees with the reference value Adjustments are only made, if the deviation evidenced by the calibration is unacceptable

The measured signal (ordinate) and the physical properties in conjunction with the abscissa of a diagram need to

be calibrated Typically, one should calibrate temperature and heat flow for DSC and weight for TGA

Ordinate • DSC: Heat flow in Watt, normalized heat flow in Joule per gram

• TGA: Mass in g (automatically performed in the electronic microbalance, optional manually)

• TMA and DMA: Length (displacement) in mm and force in N

• Time (e.g for isothermal measurements) in second or minutes Since time is derived from the quartz clock of a microprocessor, it is extremely accurate and calibration may be omitted

Table 3: Ordinates and abscissae

The acceptable deviations of the measured from the reference values depend on the deviation which is later allowed for the measurements of samples, i.e the acceptable measurement uncertainty Also the temperature range of the calibration depends on the range later applied to the sample testing For instance it is not necessary

to calibrate a DSC system up to 660 °C (aluminum point) if the sample measurements always end at 200 °C

As a check interval, we suggest a period of once a month If the results are repeatedly within acceptable error limits, this interval can be doubled If several measurements with unacceptable results are obtained, the interval should be reduced to half However, the frequency of checks (calibrations) depends on several factors e.g

internal regulations, legal requirements, the frequency of use of the instruments, the applications, etc For some users it may be enough to calibrate once per half year, others may require daily calibration In any way, it is recommended to document calibrations to record the calibration history

After an adjustment, one should always perform a calibration to verify that correct values are obtained

Any combination of a measuring module, type of crucible and atmosphere can be used to perform calibrations and adjustments With the STARe software of METTLER TOLEDO the calibration parameters are stored in the database Example methods are available in the database for the most important standard combination of

measurement parameters (e.g DSC, 40 µL Al crucible, air)

Figure 9 The results of this DSC calibration are within the permissible error limits

An adjustment is not necessary.

More details see Thermal Analysis in Practice, Application Handbook, chapter 6.5

^exo

20

mW

Integral -181.13 mJ normalized -28.84 Jg^-1 Onset 156.57 °C

The DSC module is within specifications (27.85…29.05 J/g, 156.3…156.9 °C)

Indium Check

Sample: Indium, 6.2800 mg

Sampling and sample preparation

Start experiment with One Click™

Sample identification with barcode

Measurement of sample

Correct experimental data including

- Automatic load of most current calibration data

- Automatic gas delivery and control

- Automatic buoyancy compensation (in case of TGA)

Printout of the result and/or Transfer to a LIMS system

Automatic evaluation of the resulting curve Automatic results calculation

e.g for Pass/fail decision, material conformity

check, curing rate

7 Conclusions

Instrument maintenance, test method setup and sample preparation are important pillars of good measurements They have to be carried out carefully and contribute equally to accurate and reliable results

They also are prerequisite to lab efficiency and enable seamless workflows

Table 4: A seamless thermal analysis workflow

Thermal Analysis Excellence instruments support users in many ways from crucible selection to instrument check and measurement accuracy They help to safely achieve the ultimate target of accurate and reliable test results