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Experimental results on the correlation between the areas of DTG and DTA peaks and the sample weight
Note
Experimental results on the correlation peaks and the sampfe weight
DTA
G. SlFtACUSA
l AhD
V_
between
areas of DTG and
the
CUCIN~A
ktirvro di Ckimim Genera&. i.hirmit& di G~ankz, Viuk A. BMa, 8,95125 Gzmmkx(itaky)
(Rccdvcd 21 Mach
1977)
‘Ihe determination of the enthalpy change of a process by DTA involves in any case the measurement of the area of the peak corresponding to the considerexi process. Also for the evaluation of kinetic data under non-isothermal conditions, owing to the earlier development of DTA with respect to TG, and particularly for processes occurring without weight change of the sample, several methods involve the measurement of the DTA peak areat-‘. While in kinetic s:udies an ideal bchaviour of the system is generally assumed, in thermodynamic studies the influence of the actual experimental conditions is more carefu!ly considered. Thus, the calibration procedure is practically used only for the TABLE t AXECS(C&)
OF
DTA A?cD D-l-G PEAKS
FOR
*Pk
w&h
Rtczffion (I) -.-.-
ifwl
DTA
23.2 34.7 45.7
61.3 71.2 100.5 147.0 2m.3
260.0 3023
330.5 353.4 375.4
--
RlXCTIO.SS
(I)
_.-.-
-. On;
113
JE
280
152 200 237
142 z
ApiL)
(2)
AND
bCUA-IWE
fLruniwl(2) _ - .- .-
DTG 95 145
80 Jr) 150 185
180 2.45 280 410 575
290 41s
375
ZE
602
42s 440
825 951
755
-
(Rl&
-. -. .___.__._
-65
342
1tHb JlJS 1198
WEKZTI-S
DTA
310 330
451 475 490
SALaPlS
St?5 1015 1145
E
1275 KM5 ,I420
875 885
. i .
186 determination of enthalpy changes ‘_ However, in all me&hods, general equations need to be de&cd, bezause it is impossible to take into eccount all the experimental factors, many of which depend on the particular appa‘ratus used. In this note, we report data concerning the correlation between the area of DTG and DTA peaks and the amount of material analyzed. The data flable i) were found for the following reactions of CaC,O, - Hz0 in nitrogen atmoqhere:
caczO4 - Hz0 (s) + CaC204 CZCOJ (s) --,
cao (s)
-:-
co,
(s) f
Hz0
(g)
(1)
(2)
(g)
AI1 experiments were performed with a Mettler thermoanalyzr T-TD2 sample holder, A1,0, as reference material, q5 : . 15’C recorder’s chart speed is 12 in_ h- ‘_
.
. 0 I
.
0
.
0 0 300,
0 -I
Q
-,
o* -
-0
r.
3.
l
0 .
0
0
O
using a Mettler min”, and the
-
.
.
:
187
Figure I shows the results of our measurements_ While for the DTG peaks, the linearity between the peak areas and the sample amounts is verified in the entire investigated range, for the DTA peaks we observe a discontinuity. Two straight lines with different slopes can be traced as graphic representation of the correlation between our experimental data. The exact sampk weighs which is different for the two &&ions & be identifi&_ Thii allows separation of two tangu’of linearity, corresponding to different values of the proportionality constant between the DTA peak areas and the sample weight. The first suggestion of these results is thal, when possible, as for kinetic measurements of processes with a weight change &associated, it is preferable to use the DTG cucyes9= lo_ For a &r&t enthalpy change determination, it ap_pears advisable, besides the usual calibration with a process whose An is known, to do danadditional calibration of our kind on an adequately wide range of sample weights. The relationship we have obtained is surprising in some aspects, as it denotes the presence of a point of discontinuity_ In our opinion, the sampk weight which separates the two ranges of linearity is connazted with a’particular apparatus and with the considered reaction. Thus, no theoretical “a priori” derivation can be made of this value. Presumably, the characteristics of thermal conductibility inside the sample and bctwecn the sample and the thermocoupIe joint, in relation with the geometrical experimental arnngement determine the diseontinuity-
I 2 3 4 5
H. J. Ikncbadt aFd F_ J. Danie& J. Am. Ckm_ SIC.. 79 (1957) 41. H. J. Borchadt, 1. Itwtyg_ ffucl. Ckm., 12 (1960) 257. P_ Baum&artnaand P. Duhaut,Bufl.Sec. C&m. Fr_, (1960) 1187. L. Rtkh.
1. Znorg. Nucl. Cliorr.28
(I!h%) 1329.
D. Fam, J. lkrm_ And_. 1 (1969)285. ; $ r W$dIzu&. 1. C&m. *... 3%(l%l) 571. -r znd J. KmFisher. J_ Zrrorg.Ntd C&m.. 24 (VW) If%_ 8 J. &c& V. Satava and W. W_ Wax&a&t. Xkmw&im_ Ada, 7 (1973) Js?_ 9 S_ Gurrih, V. -ua apd C. G&lr. Boll.Ace. G&&z, 11(?973)123. 10 S. Gurricri.G. siracinati R. CU. 1. 7km1. Ad., 6 (3974) 293.
Experimental results on the correlation peaks and the sampfe weight
DTA
G. SlFtACUSA
l AhD
V_
between
areas of DTG and
the
CUCIN~A
ktirvro di Ckimim Genera&. i.hirmit& di G~ankz, Viuk A. BMa, 8,95125 Gzmmkx(itaky)
(Rccdvcd 21 Mach
1977)
‘Ihe determination of the enthalpy change of a process by DTA involves in any case the measurement of the area of the peak corresponding to the considerexi process. Also for the evaluation of kinetic data under non-isothermal conditions, owing to the earlier development of DTA with respect to TG, and particularly for processes occurring without weight change of the sample, several methods involve the measurement of the DTA peak areat-‘. While in kinetic s:udies an ideal bchaviour of the system is generally assumed, in thermodynamic studies the influence of the actual experimental conditions is more carefu!ly considered. Thus, the calibration procedure is practically used only for the TABLE t AXECS(C&)
OF
DTA A?cD D-l-G PEAKS
FOR
*Pk
w&h
Rtczffion (I) -.-.-
ifwl
DTA
23.2 34.7 45.7
61.3 71.2 100.5 147.0 2m.3
260.0 3023
330.5 353.4 375.4
--
RlXCTIO.SS
(I)
_.-.-
-. On;
113
JE
280
152 200 237
142 z
ApiL)
(2)
AND
bCUA-IWE
fLruniwl(2) _ - .- .-
DTG 95 145
80 Jr) 150 185
180 2.45 280 410 575
290 41s
375
ZE
602
42s 440
825 951
755
-
(Rl&
-. -. .___.__._
-65
342
1tHb JlJS 1198
WEKZTI-S
DTA
310 330
451 475 490
SALaPlS
St?5 1015 1145
E
1275 KM5 ,I420
875 885
. i .
186 determination of enthalpy changes ‘_ However, in all me&hods, general equations need to be de&cd, bezause it is impossible to take into eccount all the experimental factors, many of which depend on the particular appa‘ratus used. In this note, we report data concerning the correlation between the area of DTG and DTA peaks and the amount of material analyzed. The data flable i) were found for the following reactions of CaC,O, - Hz0 in nitrogen atmoqhere:
caczO4 - Hz0 (s) + CaC204 CZCOJ (s) --,
cao (s)
-:-
co,
(s) f
Hz0
(g)
(1)
(2)
(g)
AI1 experiments were performed with a Mettler thermoanalyzr T-TD2 sample holder, A1,0, as reference material, q5 : . 15’C recorder’s chart speed is 12 in_ h- ‘_
.
. 0 I
.
0
.
0 0 300,
0 -I
Q
-,
o* -
-0
r.
3.
l
0 .
0
0
O
using a Mettler min”, and the
-
.
.
:
187
Figure I shows the results of our measurements_ While for the DTG peaks, the linearity between the peak areas and the sample amounts is verified in the entire investigated range, for the DTA peaks we observe a discontinuity. Two straight lines with different slopes can be traced as graphic representation of the correlation between our experimental data. The exact sampk weighs which is different for the two &&ions & be identifi&_ Thii allows separation of two tangu’of linearity, corresponding to different values of the proportionality constant between the DTA peak areas and the sample weight. The first suggestion of these results is thal, when possible, as for kinetic measurements of processes with a weight change &associated, it is preferable to use the DTG cucyes9= lo_ For a &r&t enthalpy change determination, it ap_pears advisable, besides the usual calibration with a process whose An is known, to do danadditional calibration of our kind on an adequately wide range of sample weights. The relationship we have obtained is surprising in some aspects, as it denotes the presence of a point of discontinuity_ In our opinion, the sampk weight which separates the two ranges of linearity is connazted with a’particular apparatus and with the considered reaction. Thus, no theoretical “a priori” derivation can be made of this value. Presumably, the characteristics of thermal conductibility inside the sample and bctwecn the sample and the thermocoupIe joint, in relation with the geometrical experimental arnngement determine the diseontinuity-
I 2 3 4 5
H. J. Ikncbadt aFd F_ J. Danie& J. Am. Ckm_ SIC.. 79 (1957) 41. H. J. Borchadt, 1. Itwtyg_ ffucl. Ckm., 12 (1960) 257. P_ Baum&artnaand P. Duhaut,Bufl.Sec. C&m. Fr_, (1960) 1187. L. Rtkh.
1. Znorg. Nucl. Cliorr.28
(I!h%) 1329.
D. Fam, J. lkrm_ And_. 1 (1969)285. ; $ r W$dIzu&. 1. C&m. *... 3%(l%l) 571. -r znd J. KmFisher. J_ Zrrorg.Ntd C&m.. 24 (VW) If%_ 8 J. &c& V. Satava and W. W_ Wax&a&t. Xkmw&im_ Ada, 7 (1973) Js?_ 9 S_ Gurrih, V. -ua apd C. G&lr. Boll.Ace. G&&z, 11(?973)123. 10 S. Gurricri.G. siracinati R. CU. 1. 7km1. Ad., 6 (3974) 293.