APTAC - Automatic Pressure Tracking Adiabatic Calorimeter Hazards Laboratory Michigan Tech University Room 207 Chemical Sciences

The entire APTAC unit. The upper center contains the test cell. The right-hand cabinet contains the computer and data acquisition and control equipment. The left cabinet is the materials unit to handle reactants and products.

Purpose

The APTAC is used to characterize the reactive nature of a substance. The substance is place in the test cell (100 ml) shown below and then installed in the apparatus (also shown below). The APTAC has two heating modes: (1) heat and search, and (2) heat.

In the heat and search mode, the substance is heated by fixed temperature increments, say 5 deg. C., and then the ARC waits at the specified temperature until an exotherm is detected. If an exotherm is detected, the ARC goes into adiabatic mode and follows the exotherm. If an exotherm is not detected, then the ARC moves to the next highest temperature.

In the heat mode, the temperature is increased continuously until an exotherm is detected, at which point the ARC goes into adiabatic mode and follows the exotherm.

The unique feature of the APTAC is its ability to follow the pressure inside the test cell. This pressure is matched (or nearly matched) on the outside of the test cell - preventing the cell from rupturing due to high pressures.

Data

The data from the APTAC test includes the temperature and pressure as a function of time. These data can be used to calculate the following parameters used to characterize reactive chemicals:

• maximum self heat rate
• maximum pressure rate
• onset temperature
• reaction order and Arrhenius parameters
• others as required

Sensitivity

The APTAC is capable of detecting self heat rates as low as 0.04 deg. C per minute and as high as 400 deg. C per minute. One of the advantages of the APTAC is the low thermal inertia of the reactor vessel. The APTAC will operate from vacuum to 2,000 psig and is capable of tracking pressure rates up to about 10,000 psi/min.

This is a typical APTAC bomb. This one is made out of titanium - other materials are available.The thin-walled vessels are prevented from bursting during the reaction by pressurizing the containment vessel at a rate sufficient to keep a constant pressure differential across the wall of the bomb.

This is a close-up of the containment vessel. The bomb is attached to the assembly at the top (note the thermocouple and pressure leads) and is lowered into the chamber at the bottom.

This is the complete APTAC unit with all of the cabinet doors open. The left-hand cabinet contains the reactant and product processing equipment. The central cabinet contains the valves and transducers to operate the unit. The right-hand cabinet contains the data acquisition and control equipment.