Thermal Conductors

Calorimetry

Temp dependent variable in the experiment

Thermal Analysis

Temp is the independent variable in the experiment

SCRAM

sample preparation mantra

Sample

• Ground into powder?

• Known impurities?

• Sample history?

• Pre-treatment?

Crucible

-sealed or not

size and shape of container. Depths hinders gas flow, wide and shallow gets more gas flow

-pan material recorded (some can act as catalysts)

Rate of Heating

-get different results and different values

-thermal lag minimizes at low rate

Atmosphere

-looking at inert atmosphere

-high flow rate rapidly sweeps product, eliminating reverse reactions

Mass

• may need to be a larger sample to be able to see a feature associated with it

• large samples suffer from greater thermal lag

Gravimetry (Thermograms)

Measure the weight, very accurate, but slow.

DTG

The differential of a thermogram

Area under DTG is proportional to the mass, loses signal/noise ratio

Onset of Transition

On a TGA plot, the start of the peak (best measure for a rxn or transition)

Transition Temperature

-The intersection between the baseline and the transition tangent line to the steepest part. Find the onset point

DTA (Differential Thermal Analysis)

A sample and reference subjected to a temperature program (typical program is a linear ramp).

deltaT= Tr- Ts and plotted vs. Ts where a differential thermogram is given.

Reference Material DTA

-inert solid with very high mp

-Alumina, silicon carbide, glass

What happens when Ts changes?

Smaller: shows thermal lag—an exothermic reaction when delta T is positive.

Bigger: taking in heat from surroundings, endothermic reaction when delta T is negative

Weakness of DTA

sample and reference are too close to each other so thermal equilibrium tries to happen in the process

hurt the sensitivity and ability to do qualitative analysis

DSC (differential scanning calorimetry)

-sample and reference both have circuits (heaters and power) to keep them both at the same temperature

plot delta Power= Pr - Ps

Is calorimetry due to the temp being the dependent variable in the experiment

Pros and Cons

-DSC better for quant analysis

-DTA better for temperature precision

-DSC cannot do temps over 1500 C, not very good above 750 C

Scan Rate

-important to keep scan rate constant while doing quantitative analysis

-better qualitative ability by doing a faster scan rate

-Fewer seconds to scan, watts get’s bigger

Isotropic

Independent of chemical medium angle that you are approaching it from

Measuring Capacity Change

deltaC= delta baseline/( mass* b) (→rate of heating)