EN 821-3-2005 pdf download.Advanced technical ceramics – Monolithic ceramics. Thermophysical properties – Part 3: Determination of specific heat capacity.
4.4 Temperature measurement and calibration
4.4.1 For furnace temperatures below 1650 ‘C. the initial temperature of the test piece in the furnace shall be measured by a PUPt 13 % Rh (Type R) or PtIPt 10 % Rh (Type S) thermocouple with a tolerance conforming to EN 60584-2. allowing use of the reference tables in EN 60584-1. or alternatively calibrated in a manner traceable to the International Temperature Scale.
For furnace temperatures above 1650 ‘C. an alternative thermocouple type shall be required.
A thermocouple shall be sited with its junction on the inside of the furnace tube in order to record furnace wall temperature. A similar thermocouple shall be placed inside a platinum capsule or a dummy test piece. The furnace wall temperature shall be allowed to equilibnate for at least 15 mm. The capsule or dummy test piece shall then be raised or lowered through the thermal centre of the furnace in steps of not more than 10 mm in order to plot the temperature distribution. This procedure Is used to establish the optimum position of the capsule or test piece in the furnace and to calibrate the difference between capsule or test piece and the furnace wall. This calibration is performed at a series of temperatures at intervals not exceeding 100 ‘C up to the maximum furnace temperature, and is used as an indirect measure of initial test piece temperature.
4.4.2 The procedure for a massive copper block calorimeter or similar device in which a temperature rise is recorded is as follows. The calorimeter temperature is measured using a platinum resistance thermometer (PRT) connected into an a.c. bridge circuit, on the opposite arm of which is a matching standard resistor kept at a known stabilized temperature ± 0,1 C, which may conveniendy be the temperature of the controlled environment. In order to calibrate the calorimeter, a known electrical power is dissipated in the heating resistor for a known time period, At, determined either using a stopwatch or other calibrated timing device, The output of the a.c. bridge is monitored continuously and the data are recorded at intervals of not less than 30 s. The electrical Input power is measured by recording the voltage, V, across the heating resistor, and across a series standard resistor to measure the current. I (Figure 3). A typical bridge output trace is shown in Figure 4. To determine the calorimeter calibration, the following procedure is used. The output curve is extrapolated at X and Y as shown in Figure 4 using line-fitting routines A time t,,.., is chosen such that the areas A and B are equal. The output r!iV, is taken as the distance between lines X and V at time t,. The calibration factor for the calonmeter, C. is given by:
A cell comprising a test piece in an enclosing platinum or other suitable test piece holder incorporating a lid shall be heated at a defined temperature rise rate, dTldt, from an initial temperature. 7;, to a final temperature, T. The differential output between a temperature sensor, such as a PRT or thermocouple contained within the test piece cell and that from a similar device in a similarly heated but empty reference cell shall be recorded. This output is directly related to the heat capacity of the test-piece. In order to calibrate this output, the test piece shall be replaced by a cahbrant of known specific heat. The baseline behaviour is determined by a test with an empty test piece cell. The calibrant is normally a-alumina for which calibration data are given in [1J,
Adherence to the procedure described below should give results accurate to better than 5 %.
5.3 Apparatus
5.2.5.3.1 Generally. specialised commercially available apparatus is employed for specific heat measurement using this principle. Operating practices vary according to the manufacturer’s design, and the output signal S may be obtained either from the differential power required to maintain the set heating rate (powercompensation DSC) or from differential heat fluxes determined by the use of thermopiles. PRTs or thermocouples between the test piece holders and their cells.
5.3.2 A balance is required, which is capable of weighing the ce’l and its contents to ± 0,1 mg or 0,1 % of the test piece mass, whichever is the smaller.
5.4 Test piece
A test piece may be a powder, granules or solid material of size and mass appropriate to the size of the test
piece holder, but is typically 10 mg – 100 mg. Before any test, the test piece shall be dried at 110 C ± 5 °C to
constant mass. Solid materials machined to fit the capsule shall first be cleaned with a suitable solvent to
remove grease or other contaminants. The dry mass of the test piece shall be determined to an accuracy of ±
0.1 mg or ± 0,1 % whichever is the smaller.EN 821-3-2005 pdf download.