Field of invention
The present invention generally relates to material/ specimen shrinkage/ expansion test of fuel ash using a thermo mechanical analyzer (TMA). The present invention relates to a method of protecting crucibles,probes/pushrod and sample holder/assembly used in athermo-mechanical analyzer from contamination/ damage due to melting of the fuel ash during the thermo mechanical analysis.
Background of the Invention
Thermo mechanical analyzers (TMA) are used to measure a variety of material properties, including coefficients of thermal expansion (CTE), glass transition temperatures, heat deflection, and elevated temperature creep or stress relaxation behavior. Thermo mechanical analysis easily and rapidly measures sample displacement (growth, shrinkage, movement, etc.) as a function of temperature, time and applied force. Traditionally TMA is used to characterize linear expansion, glass transitions, and softening points of materials by applying a constant force to a specimen while varying temperature.
TMA consists of an analytical train that allows precise measurements of dimensional changes of a sample. A temperature control system of a furnace(4), and a heat sink and temperature measuring device (thermocouple) (3) are coupled to the sample. Fixtures (sample holder and probes) to hold the sample during the run are normally made out of quartz or ceramics. Different type of fixtures (sample holder and probes) are commercially available for expansion, flexure, and penetration tests for TMA.

In the typical operation of a TMA, a small sample with parallel and flat top and bottom surface is placed between a pushrod/ probe and the sample holder assembly near a thermocouple (3). Every dimensional changes of the sample is transmitted via the pushrod/ probe to a highly precise inductive transducer (LVDT) (2)
Since the TMA is capable of heating a sample to 1600 C, it is very possible that a fuel ash samples will melt. A melted ash sample can easily stick to the sample holder and probe upon solidification. This is likely to break or make the instrument to show inaccurate results. For each TMA run for fuel ash samples having melting temperature in the range of 800- 1500 C, the probe and sample holder may damage due to melting of the ash. To avoid the contact between the ash and probe sample holder, the ash pellet (5) samples are sandwiched between high purity alumina crucible (10) and alumina plates.
For each TMA run, instead of damaging the sample holder and probe, the alumina crucible (10) and cover plate are generally damaged due to ash melting. The cost of one set of high purity alumina crucible (10) and alumina plate is at least USD 75.00.
G.W.Bryant et al describes in a non-patent literature, the influence of the material for the sample assembly for Thermo mechanical analysis of fuel ash. Ref: Energy & Fuel 2000, 14,326-335.
Another non-patent literature by A.A. Tortosa Masia et al described the use of TMA to predict deposit behaviour of biomass ash using molybdenum crucible . Ref: FUEL 86 (2007) 2446-2456.
Yinghui Liu et al reported the Thermo mechanical analysis of laboratory ash, combustion ash and deposit from coal combustion using molybdenum crucible . Ref: Fuel Processing Technology, 88 (2007) 1099-1107.

The operating instructions of Thermo mechanical analysis manufactured by M/S TA instruments, describes that since the TMA is capable of heating sample to 1000˚ C, it is very possible that the sample will melt. A melted sample can easily stick to sample stage, probe or furnace (4) upon solidification. This will likely to break or damage the instrument. Thus do not heat an unencapsulated sample to any higher than 75% 0f its melting temperature. To avoid reactions between sample and probe / sample stage, the ash pellet (5) should be sandwiched between two plates of Aluminum oxide. But in this case, the two Aluminum plates will get damaged due to melting of ash.
The above prior art data pertain to use of TMA for studying the ash, using different crucibles and encapsulating / sandwiching the sample pellet between plates/ crucible.
Accordingly, the prior art fail to provide a method of protecting a crucible including a lid, a probe and a sample holder / assembly during testing of fuel ash which are likely to melt in the testing temperature range, using TMA.
The present invention relates to a method of protecting alumina crucible , probe and sample holder assembly from contamination due to melting of ash during TMA runs.
Objects of the Invention
It is therefore an object of the present invention to propose a method for protecting a crucible,a cover plate, and a probe-sample holder assembly from damage during testing of solid fuel ashes in thermo-mechanical analyzers.
Another object of the present invention is to propose a method for protecting a crucible, a cover plate, and a probe-sample holder assembly from damage during testing of solid fuel ashes in thermo-mechanical analyzers, in which metal oxides capable of withstanding without any deformation at high temperature, are selected so as to protect the sample assembly during the testing.

Summary of the Invention
Accordingly, there is provided a method for protecting a crucible, a cover plate, and a probe-sample holder assembly from damage during testing of solid fuel ashes in thermo-mechanical analyzers.
The method is enabled to measure shrinkage and expansion measurements in the temperature range of 700 – 1500oC.
According to the present invention, a suitable metal oxide powder is identified which is spread over the ash sample pellet in such a way that the ash pellet is not exposed to direct contact with the crucibles / plate / probe/ sample holder assembly. Even if the ash pellet melts, the melt will not be in direct contact with the above said components, thereby protecting the above said components from damage during testing of solid fuel ashes in the temperature range of 700 to 1500oC in TMA.
Detailed Description of the Invention
Thermo mechanical analyzers (TMA) are used to measure a variety material properties, including coefficients of thermal expansion (CTE), glass transition temperatures, heat deflection, and elevated temperature creep or stress relaxation behavior.
Thermo mechanical analysis easily and rapidly measures sample displacement (growth, shrinkage, movement, etc.) as a function of temperature, time and applied force. Traditionally TMA is used to characterize linear expansion, glass transitions, and softening points of materials by applying a constant force to a specimen while varying temperature.

TMA allows the calculation of thermal expansion coefficient of thermal expansion and (CTE) from the TMA data. Since many materials are used in contact with a dissimilar material in the final product, knowing the rate and amount of thermal expansion helps design around mismatches that can cause failure of the final product.
If the material is heterogeneous or anisotropic nature, it will have different melting behaviour and hence different shrinkage pattern.
In TMA measurement, the real time finger print of continuous recording of the dimensional changes (shrinkage / expansion) of the ash is made. Hence the start of liquid formation or start of melting will result in shrinkage of ash even in micron level is recorded. Hence the complete finger print of shrinkage or sintering of ash pellet (5) is observed in TMA.
In the typical operation of a TMA, a small sample with parallel and flat top and bottom surface is placed on a sample holder assembly near a thermocouple(3). A probe is lowered against the specimen with a constant applied force, the sample stage assembly is placed in the furnace(4). As the sample is heated or cooled, and changes in dimension are measured by monitoring the motion of the quartz/ceramic probe. The schematic figure below shows the typical setup for thermal expansion measurements.
For expansion measurements, a probe rests on a sample on a stage with minimal downward pressure. Every dimensional changes of the sample is transmitted via the pushrod/ probe to the highly precise inductive transducer (LVDT) (2).
Since the TMA is capable of heating sample to 1600˚ C, it is very possible that fuel ash samples will melt. A melted ash sample can easily stick to the sample holder and probe upon solidification. This will likely break or damage the instrument. For each TMA run for fuel ash samples heaving melting temperature in the range of 700- 1500 C, the probe and sample holder may damage due to melting of the ash. To avoid the contact

between the ash and probe sample holder the ash pellet (5) samples are sandwiched between high purity alumina crucible (10) and alumina plates.
For each TMA run, the alumina crucible (10) and cover plate and sometimes the sample holder and the probes are damaged due to melting of ash. Once the melted ash is in contact with any components of the sample assembly like crucible (10), cover plate, probe and sample holder assembly, the components got damaged and are to be replaced. The cost of one set of high purity alumina crucible (10) and alumina plate in USD 75.00. The present invention provides a method of protecting alumina crucible (10), cover plate, probe and sample holder assembly from contamination due to melting of solid ash fuel during TMA runs.
According to the present invention, an aluminum oxide powder (9) or any ceramic powder of – 75 micron size without any impurities is selected and spread inside the alumina or graphite crucible (10) as a layer. The thickness of the oxide layer can vary from approximately 10 to 30 micron depending on the size of the ash pellet (5). The ash pellet (5) is kept in the crucible (10) over the oxide layer, in such a way that the ash pellet (5) is not in direct contact with the crucible (10). The oxide powder is also spread over the top surface of the ash pellet (5) for approximately 10-15 micron thickness. Then the cover plate / lid (8) is placed on the top of the ash pellet (5) as shown, in such a way that the cover plate/ lid (8) is not in direct contact with the sample.
Now the crucible (10) and the cover plate assembly having the ash pellet (5) is placed between the sample holder assembly and the push rod / probe (6) of the TMA. During heating, even if the sample i.e, ash pellet (5) melts, it will not damage the crucible (10) or cover plate, since the sample is not in direct contact with the above.

The size of the crucible (10) and cover plate/lid (8) are selected in such a way that, in case, there is expansion / or high viscous liquid formation of the ash pellet (5), the damage is not spread to the probe (6) or the sample holder assembly and the melt
is contained within the alumina or ceramic oxide powder itself. The effect of introducing this protective oxide layer can be corrected by running the TMA blank with sample and without sample.

We claim:
1. A method of protecting crucibles (10), cover plate / lid (8), probes (6) /pushrod and sample holder / assembly from contamination / damage due to melting of a solid fuel ash during thermo mechanical analysis (TMA),comprising the steps of :
- selecting and applying a finely ground metal oxide powder or any ceramic powder (9) of size less than 75 micron which is unmeltable at a desired temperature range of the test requirement, say 700 – 1500˚C in the case of solid fuel ash;
- preparing an ash pellet (5) for the TMA;
- spreading a metal oxide or ceramic powder (9) in the TMA crucible (10) to form a protective layer of thickness about 10 to 30 micron and placing the ash sample pellet (5) in the crucible (10);
-spreading the metal oxide or ceramic powder (9) on the top surface of the ash
pellet to form a layer of thickness of about 10 to 15 micron, and placing the
crucible (10) and lid (8) over the top of the ash pellet (5) covered with said
protective oxide powder (9); and
- placing the sample pellet (5) sandwiched between the crucible (10) including
the crucible / lid (8) with the protective oxide in the TMA sample holder
assembly.
2) The method as claimed in claim 1, wherein the crucibles (10) and the cover plate / lid (8) are formed of platinum, alumina, graphite, molybdenum, Zirconium oxide.

3) The method as claimed in claim 1, wherein the probe (6) / pushrod and sample holder/ assembly of the TMA analyser comprise of quartz, or alumina.
4) The method as claimed in claim 1, wherein the solid fuel ash comprises biomass ash, coal ash, lignite ash, pet coke ash or any material which exhibits melting during the temperature range of a known TMA run.
5)The method as claimed in claim 1 , wherein the metal oxide powder (9) or ceramic powder (9) is selected from a group consisting of aluminum oxide, graphite,
molybdenum, Zirconium oxide or any powder (9) exhibiting with refractory nature and which is not meltable in the temperature range of a known TMA run.