S ubsequent operation from 40 c to 20 c c a u s e s w

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: part of the cell from the water which accumulated around the outer base. A p lastic sleeve also was fitted over the dewar and DSC cell in order t o p revent condensation of water v apor f rom the room. A d ry nitrogen purge of the cell and dewar was also used to remove water vapor from inside the plastic sleeve. 4-6 T emperature Calibration The indium samples provided with the calorimeter were used as calibration standards. Indium sample weights of 1 .59, 3 . 5 0 , 7 . 2 6 a nd 1 9 . 8 2 m g. were hermetically sealed in the aluminum sample pans. Each of the indium samples was run in the DSC cell using an empty sample pan + l id as the reference material. K /min. The programmed heating rate was 10 D ifferent sizes of calibration sample were used in order to determine the dependence of the measured transition temperature on the sample size. The transition temperature as determined from the data was within 2 0 . 5 K o f the melting point o f indium ( 4 2 9 . 6 K ) f or all of the indium samples used. There was no indication of dependence of the transition temperature on sample size although the transition peak was slightly broader for the larger samples. P age - 4 2 - T he temperature calibration of the DSC equipment was then checked by u sing a varie.ty o f different powders a n d c rystals in order to evaluate the accuracy of measured melting transition temperatures especially when powders and small crystals were used as the sample. The following substances were used:. F orm red crystals yellow crystals ACETANILID 388 K white crystals P HENACETIN 408 K white crystals B ENZANILID 436 K white powder S ALOPHEN 464 K white powder D ICYANDIAMID 483 K white powder S ACCHARIN 501 K white crystals In all c a s e s , the recorded transition temperature were within 21 K o f the stated transition temperature. The melting points of gallium and mercury were used to check the calibration temperature at lower temperatures. Small samples of gallium and mercury were frozen using liquid nitrogen and hermetically sealed in aluminum sample pans at temperatures below their respective melting points. . The P a g e - 43m ea...
View Full Document

This note was uploaded on 10/08/2009 for the course CME MAT E 630 taught by Professor Dr. during the Fall '09 term at University of Alberta.

Ask a homework question - tutors are online