API PUBL 935-1999

$20.15

Thermal Conductivity Measurement Study of Refractory Castables

Published By	Publication Date	Number of Pages
API	1999	33

Guaranteed Safe Checkout

Category: API

If you have any questions, feel free to reach out to our online customer service team by clicking on the bottom right corner. We’re here to assist you 24/7.
Email:[email protected]

Description

Thermal conductivity is defined as the amount of heat transferred through a unit area of a material in a unit time, through a unit thickness, with a unit of temperature difference between the surfaces of the two opposite sides.

Thermal conductivity of refractory castables is difficult to measure accurately due to the presence of moisture (chemically combined water) in the matrix. When heated the first time, cementitious castables expel water (dehydration) from the hydrated cement. The moisture is responsible for affecting the identification of heat flowing through the refractory mass.

Manufacturers of refractory products use various measurement techniques to develop thermal conductivity of refractory castables. The following list identifies commonly used procedures.

a. Water Calorimeter—ASTM C-201 apparatus; C-417 procedure.

b. Calorimeter—Pilkington Method.

c. Hot Wire Method—ASTM C-1113.

d. Comparative Thermal Conductivity Method—Dynatech.

e. Panel Test.

Each procedure addresses unique concerns about measuring thermal conductivity of unfired castable refractories. This study was initiated to compare differences in the five test methods at six laboratories. The scope of the study was limited to one set of data for each of six products. Therefore, numeric relationships and direct evaluations between the various methods were not desired nor achieved.

The study concentrated on products with high to moderate cement contents. These products have distinct thermal conductivity curves during initial heating (ascending) and cooling (descending). Low and No Cement products were not evaluated and may or may not follow the same trends developed for the cementitious products.

Cement bonded castables develop physical properties through proper hydration of the cement. Upon heating, the hydrated cement dehydrates as the chemically bonded water dissociates from the calcium aluminate cement. Use of Thermo-Gravimetric Analyses (TGA) provides a good understanding of the dehydration process. Figure A-1 shows a TGA curve for a cement bonded castable refractory. Dehydration begins at approximately 425°F and continues through 1250°F. However, approximately 70% of the water loss due to dehydration occurs between 500°F and 850°F.

Additional information