CALCIUM SULPHATE PHASES IN CALORIMETRY
Saskia Nowak1, Hans-Bertram Fischer2, A. W. Usherov-Marshak3, V. P. Sopov4
1, 2
F. A. Finger-Institute for Building Material Science, Coudraystr. 11, D-99421 Weimar, Germany,
E-mail: [email protected]
2
[email protected]
3, 4
Kharkov State University of building and architecture, Ukraina
E-mail: 3 [email protected]
4
[email protected]
Abstract. In literature, differing informations about the heat of hydration of calcium sulphate hemihydrate can be
found. Our investigations show possible causes for that.
A wide spectrum of low- and medium burned plaster binders were produced by different burning-conditions in the
laboratory experiment. They differ in their specific surface, crystallinity and phase composition in a characteristic
manner. The results of a calorimeter experiment are in contrast to these particular properties. The phase analysis
occurred with very high accuracy by the use of the Rietveld-method.
With regard to the heat of hydration and the kinetics of the heat emission, considerable differences could be
evidenced depending on the burning-regime. Furthermore, the effects of storage conditions of the calcium sulphate
binders were described. Through the interaction with humidity, aged specimen showed generally reduced and slowed
reaction behaviour with the mixing-water.
Keywords: gypsum, calcium sulphate binders, heat of hydration, crystallite size, micro strain, calorimetry, hydration
enthalpy
1. Introduction
Although the hydration enthalpy is known as a
material characteristic, very different information on heat
of hydration of calcium sulphate hemihydrate can be
found in the literature. A reason for that could be inexact
determination of phase content in older publications.
Contemporary methods of analysis, as the Rietveld
Method for the evaluation of X-ray dates (XRD), allow to
determine also smallest phase contents. Therefore it’s
known in the meantime that every calcium sulphate
binder is more or less a multi phase binder. This
circumstance is problematic for the phase-specific
evaluation of hydration heat because phases are
crystallised differently well according to genesis and
influence themselves.
Therefore following questions are important in this
publication:
• How far does the origination (burning and storage
conditions) of beta hemihydrate affect its reactivity
and hydration heat?
• Can significant differences in material properties
(lattice defects, specific surface) be found due to
origination conditions beyond phase composition and
are they cause for changed hydration kinetics and/or
hydration enthalpy?
2. State of knowledge
Study of Literature
It’s sufficiently known, that the alpha and the beta
form of calcium sulphate hemihydrate differ in their
reactivity because of different origination conditional.
In the literature beta hemihydrate is often
distinguished from alpha hemihydrate by means of the
major specific hydration heat. However, information
between 111 and 134 J/g are found. [2, 3, 4, 5, 6, 8, 9, 10,
13, 16, 21, 22, 24].
Values of hydration heat of alpha hemihydrate
between 100 and 118 J/g [24] are indicated.
The varieties don’t distinguish significant in their
structure, that means in their lattice constants,. That was
already confirmed repeatedly [5, 8, 12, 24]. Therefore
their characteristic differences are found in their specific
surface, crystallite size [4, 12] and crystallinity (alpha
hemihydrate crystals are well developed, beta
hemihydrate is cryptocrystalline) as a cause for the
difference in their hydration enthalpy.
But these differences also exist within a variety
according to raw material as well as origination and
storage conditions. Causes for that were not discussed up
to now.
Own investigations
Via BET-, REM- or ESEM- and Adsorption
measurements (moisture uptake) own investigations
showed that also within the beta variety clear differences
concerning the surface characteristic of the particles do
exist. In addition, there are differences in the crystallinity
that were found by use of the Rietveld-analysis of X-ray
data due to production. The results show different
crystallite sizes and lattice defects (micro strain).
In the dry burning process within the dehydration of
gypsum raw material to beta hemihydrate high thermal
stress is caused. Dependently on that the BET-surface
(inner + outer surface) enlarges itself up to ten times.
[19]. Sudden exhaust of crystallisation water leads
increasingly to a destruction of particle. This expresses
through cracks in the nano and micro range up to the
partial particle disaggregation. This phenomenon is
exemplary shown in illustration 1.
a)
destruction of particle
500/24/98/3 (0,5k)
b)
Fig. 1 typical surface characteristic (REM photo) of a a)
beta-hemihydrate-rich binder of FGD gypsum burned at
120 °C and b) at 500 °C of highly burned anhydrite binder
with noticeable destruction of particle
Furthermore the crystallinity changes due to
recrystallisation of dihydrate in hemihydrate and crystal
growth. First of all, the hemihydrate phase is not formed
"ideally" at the beginning of recrystallisation of
dihydrate. The crystallites are still very small. If the
(gentle) heat admission is sufficient, the phase with
increasing dihydrate dehydration stabilizes. With
increasing admission of heat and thus increasing
hemihydrate and decreasing dihydrate content, the
crystallite size of the hemihydrates increases.
But also the transformation of hemihydrate in
anhydrite III leads to modifications of lattice because it’s
always combined with recrystallization in anhydrite II.
The micro strain of hemihydrate inside of multi phase
binders that are rich in anhydrite II is raised noticeably.
The average lattice deformation rests in part at 0,4 % to
compared to 0,2 % of hemihydrate-rich specimens. [19].
The crystal lattice and surface defects and the grain
instability caused by (particle disaggregation [1]) lead
detectably to a raised reaction potential [5, 17, 18, 19, ].
While these defects are just marginal relevant at the alpha
hemihydrate, they are very important due to the high
thermal stress for beta hemihydrate. This expresses both
in an acceleration and/or intensification of hydration
(hydration kinetics) as well as in an increase of the
hydration heat (hydration enthalpy).
In addition, the ageing (interaction with humidity) of
calcium sulphates that occurs during the storage
increasingly has a considerable influence on the reactivity
of binders. From preceded publications [7, 19, 20] it’s
known that the hemihydrate phase stabilizes due to the
ageing. Lattice defects are reduced and the medial
crystallite size increases. These effects of ageing increase
(with same temperature) with increasing moisture and
with increasing ageing duration.
3. Experiments
In laboratory test different beta hemihydrates on base
of a mineral coal FGD-gypsum (power plant Chemnitz/
Germany) were produced and analysed. The thermal
stress was varied by use of different burning temperatures
and burning durations in drying oven. The artifical ageing
occurred at 20 °C and different humidity and storage
duration in exsiccators.
The visualised findings were gained from
comprehensive calorimetric investigations of 3 years.
They were enforce by means of an own isoperibole
differential calorimeter and own solution calorimeter as
well as a further isoperibole differential calorimeter and a
differential scanning calorimeter (with the cooperation of
the "Calorimetry Centre for Material Science" at the
Kharkov State University of building and architecture,
Ukraina). The shown diagrams are determined
representatively for all results and by means of the own
isoperibole differential calorimeter.
The phase composition of the produced gypsum
binders was determined both, wet-chemical as well as by
means of Rietveld-refinement (XRD). Particularly, the
wet-chemical analysis is essential for the determination of
the Anhydrit III content. The hemihydrate content which
was wet-chemically determined within a hydration
duration of 60 minutes could be confirmed by Rietveldmethod (XRD). Dihydrate content was determined via
Rietveld-method, too. Because impurities and the
anhydrite II content within the framework of this
publication do not have any relevancy, the anhydrite II
content was determined under disregard for impurities to
100 % (approx. 5 % insoluble CaCO3) as a difference of
the analysed calcium sulphate phases.
4. Results and discussion
4.1. Influence of the genesis of the hemihydrates
Influence of the thermal stress during the burningprocess (at the same ageing conditions)
First of all, it is supposed to be shown by the
following figures that the kind of the origination of the
binder affects the hydration kinetics.
Figure 2 b shows three gypsum binders that are
comparable concerning to the hemihydrate content. They
were produced at a defined ageing for 14 days at 98 %
relative humidity from different AIII-containing multi
phase binders. Figure 2a shows the DCA graph of these
basic materials.
400
RateWärmerate
of hydration
heat
[J/gh]
350
300
0 % DH
0 % HH
85 % AIII
15 % AII
250
4 % DH
52 % HH
41 % AIII
3 % AII
200
150
48h/110°C
2h/250°C
3 % DH
77 % HH
18 % AIII
2 % AII
3h/250°C
The amounts of heat Q(tmax) tents to this result, too.
With reference to the hemihydrate content the hydration
heat of the strongly stressed specimen (QHH = of 95 J/g) in
comparison with the two gentle dehydrated specimen
(QHH ~ of 110 J/g) is approx. 15 % lower.
The crystallite size affects the energy content of the
hemihydrate phase. Demonstrable nascent, very small
hemihydrate crystallites show a raised hydration heat.
Tab. 1 illustrates this connection. Binders dehydrated
more or less incompletely in the low temperature range
(110 °C) by variation of burning time that contain
dihydrate (DH) and hemihydrate (HH) in different
contents were produce. The binder that was burned with a
hemihydrate content of only 12 % (DH = 88 %), shows
the highest hydration heat (related to this content). With
increasing hemihydrate content and with that crystallite
size increasing the hydration enthalpy decreases because
the more stable crystallites show a smaller inner energy.
100
Tab 1: hemihydrate binders of FGD-gypsum burned at
110 °C
50
0
0:00
0:10
0:20
0:30
0:40
0:50
1:00
1:10
1:20
1:30
Hydratationsdauer
[h]
Hydration time [h:mm]
m]
Fig 2a. Hydration kinetics of different multi phase binders
of FGD-gypsum produced in laboratory
Rate ofWärmerate
hydration[J/gh]
heat
reaction rate. Accordingly, the hemihydrate formed at
ageing of anhydrite III is more low-reactivity opposite the
aged hemihydrate.
300 Q
(6,6h)=93 J/g
12 % DH
250 85 % HH
0 % AIII
200 3 % AII
150
48h/110°C_14d/98%
Q(6,3h)=89 J/g
17 % DH
80 % HH
0 % AIII
3 % AII
3h/250°C_14d/98%
Q(6,2h)=79 J/g
2 % DH
83 % HH
0 % AIII
15 % AII
50
0
0:00
0:10
0:20
0:30
0:40
0:50
1:00
1:10
1:20
QHH*
[J/g]
HH-content crystallite
size
[%]
[nm]
BETsurface
[m²/g]
4
132
12
136
1,07
10
129
38
187
2,84
24
128
77
171
7,31
* heat quantity (Q) based on hemihydrate (HH) content of
phase composition
2h/250°C_14d/98%
100
burning
duration
[h]
1:30
[h:mm]
Hydratationsdauer
[h]
Hydration time [h:mm]
Fig 2b. Hydration kinetics of the multi phase binders after
defined ageing (14 d/ 98 % rel. .humidity)
From fig. 2 b it is recognizable, that the formerly
AIII-richest binder reacts most slowly (at the same
ageing) although the thermal stress was the highest. On
the other hand, the gentle dehydrated, aged hemihydraterich binder reacts fastest.
Based on current state of knowledge an increase of
the hydration enthalpy results from a raised inner energy.
That can result from lattice defects. An extremely strong
thermal stress and the sudden complete dehydration to the
anhydrite III and II going along with that leads to an
increasing deformation of the crystal lattice of
hemihydrate [19]. The example shows, that in
comparison the chemical composition (more exactly the
AIII content) has the dominating influence on the
Because interfaces also are parts of raised energy, the
decrease of energy content with increasing crystallite size
is also explainable due to the decreasing of interface
areas.
Table 1 exemplify a illustration of a tendency
observed in many experiments. The represented decrease
of hydration heat of arising hemihydrate is extremely
small. But the relatively strong increase of the wetting
heat represents an effect in the opposite direction.
Increase of the wetting heat demonstrable results due to
the drastically increasing BET-surface that is also
performed in table 1. It increases with progressive
application of heat.
The grain disaggregation also increases and leads to a
further heat emission. Both values of energy are part of
the value of the total hydration heat measured in heat flow
calorimeter into the. Nevertheless, these heat effects do
not superpose the decreasing hydration enthalpy of
hemihydrate due to the improved crystallinity. Lattice
defects and crystallite size represent accordingly the
primary influence of a changeable hydration enthalpy.
Influence of the ageing conditions
In order to represent the context between crystallinity
and hydration enthalpy, hydration heat graphs are shown
of different aged hemihydrate binders in figure 3b. Fig.
3a shows the non aged basic material (a multi phase
binder produced lab-moderately of FGD-gypsum).
Fig. 3b shows a three days (lowest hygric stress) and
a 14 days (highest hygric stress) aged binder at 66 %
relative humidity as well as a three days aged binder at
98 % relative humidity. The figure illustrates that both,
rate and intensity of reaction decreases with increasing
ageing [7, 17, 18, 19].
The shown specimen were aged exclusive in the
manner, that AIII completely converts into hemihydrate
and does not form any dihydrate. Thus all aged specimen
show the same phase composition. Due to that, it is
possible to show graphically that the hydration heat Qmax
decrease with increasing ageing. In addition to that a
decreasing hydration enthalpy of hemihydrate can
suggested. The AII-content is identical and very small at
all specimen and has only a negligible influence on the
ageing.
400
350
300
0 % DH
55 % HH
40 % AIII
3 % AII
Qmax=108 J/g
120
100
80
250
60
200
150
BKr
100
40
20
50
Wärmemenge
Heat
quantityQ(t)
[J/g][J/g]
Rate of
hydrationdQ/dt
heat [J/gh]
[J/gh]
Wärmerate
450
0
0
0:00 0:10 0:20 0:30 0:40 0:50 1:00 1:10 1:20 1:30
Hydration
[h:mm]
Zeittime
[h:min]
Fig 3a. AIII rich lab-moderately produced binder (BKr) of
REA-gypsum (12 h burned at 120 °C in drying oven without
circulating air)
0 % DH
300 95 % HH
0 % AIII
250 3 % AII
200
150
100
50
120
0 % DH
95 % HH
0 % AIII
3 % AII
0 % DH
95 % HH
0 % AIII
3 % AII
Qmax= 96 J/g
Qmax= 92 J/g
Qmax= 88 J/g
100
80
60
BKr 72h/66%
BKr 72h/98%
40
BKr 14d/66%
20
Wärmemenge
Q(t) [J/g]
Heat
quantity [J/g]
Rate of
hydrationdQ/dt
heat [J/gh]
Wärmerate
[J/gh]
350
0
0
0:00 0:10 0:20 0:30 0:40 0:50 1:00 1:10 1:20 1:30
Zeit [h:min]
Hydration
time [h:mm]
Fig 3b. lab-moderately produced binder (BKr) aged at
different conditions (72 h and 14 d at 66 % and/or 98 % rel.
humidity)
The decreasing wetting heat due to the reduced BETsurface has to be considered, too. The range of this
decrease (of 14 d at 98 % aged specimen) is maximum
3 J/g [11]. According to this, the shown decrease of the
hydration enthalpy is absolutely relevant.
In addition, the solution enthalpy of aged calcium
sulphate binders is raised fractionally. According to
following equation of solution heat (within indirect
determination of the hydration enthalpy) this also leads to
lower values because solution heat of dihydrates arisen
from that remains all about the same. Accordingly, more
energy is required in order to overcome the lattice energy
of the phases stabilized by ageing in the case of the
process of dissolution.
∆HH = ∆HS(HH)
–
∆HS(DH)
∆HH – hydration
∆HS(HH) – solution of hemihydrate
∆HS(DH) – solution of dihydrate
5. Summary
It is known that the amount of hydration heat of
alpha and beta hemihydrate differ in characteristic
manner. As a cause for that differences in crystal
formation and specific surface are argued because the two
varieties do not differ, neither chemically nor structurally.
These
material
characteristics
distinguish
production-conditional obviously also within the beta
variety. Within the framework of this publication it was
shown that not only the hydration kinetics is changeable,
but also the hydration enthalpy of the hemihydrate phase.
This is caused by material properties.
The production-conditional changes are result of
particular to thermal stress during the burning-process,
but also the influence of humidity (ageing) during the
storage of calcium sulphate binders at air. Both influences
the specific surface and the crystallinity (crystallite size
and micro strain) next to phase composition and leads in
case of increasing thermal stress to an increase and at
increasing ageing to a decrease of reactivity.
The condition of the particle, in particular thermally
conditional high specific surface and particle instability,
expresses in a accelerated and intensified reaction
kinetics. At the measurement in heat flow calorimeter the
higher wetting and grain disaggregation heat influence
into the total heat amount of gypsum binder, but they are
detectable only at comparable crystallinity.
Finally the change of hydration enthalpy results from
the crystals condition. Small crystallites and major lattice
defects that occur in particular in case of high thermal
stress express in a raised reaction enthalpy. Ageing results
in the growth of hemihydrate crystallites and in the
healing of lattice defects. In that case both, reactivity and
hydration enthalpy, decrease.
References
1.
2.
3.
Abdussaljamov, B. A.: Untersuchungen zur hygromechanischen Stabilität von kristallinem CalciumsulfatHalbhydrat, Dissertation, FIB BUW, Weimar 2003
Babuškin, V. I.; Matveev, G.M., Mčedlov-Petrosjan, O. P.:
Thermodynamik der Silikate, VEB Verlag für Bauwesen,
Berlin (1965)
Babuškin, V. I.; Matveev, G.M., Mčedlov-Petrosjan, O. P.:
Termodinamika silikatov, Moskva, Strojizdat (1986)
4.
5.
6.
Eipeltauer, E.: Aufbereitung und Überführung des Rohgipssteines in seine verschiedenen Halbhydratplasterformen, ZKG 11 (1958), S. 264-272; S. 304-316
Eipeltauer, E.: Die Bedeutung kalometrischer Messungen
für die Gipserzeugung und Gipsprüfung, ZKG (1956), S.
501-505
Ферронской, А.В.: Гипсовые материалы и изделия
(производство и применение), Под общей редакцией
профессора, доктора технических наук. Издательство
Ассоциации строительных вузов, Справочник,
2004
Fischer H.-B.; Nowak, S.; Müller, M.: `Alterung` von
Calciumsulfaten, ibausil Tagungsband 1, Weimar 2006, S.
1-0717 – 1-0731
Fietsch,
G.;
Ramdohr,
H.:
Anwendung
der
differentialkalorimetrischen
Analyse
(DCA)
zur
Charakterisierung von Gipsbindemitteln, Silikattechnik
(1991) 42, S. 328-333
Henning, O.; Oelschläger, A.: Bindebaustofftaschenbuch,
Band 1, Verlag für Bauwesen, Berlin 1984
Kelley, K. K.; Southard, J. C.; Anderson, C.T.:
Thermodynamic Properties of Gypsum and its Dehydration
Products, Technical Paper Nr. 625, Bureau of Mines,
Berkeley, Calif., Washington 1941
Kugler, L.: Spezielle Untersuchungen oberflächenenergetischer Aspekte an Calciumsulfaten, Diplomarbeit, FIB
BUW, Weimar (2006)
Lehmann, H.; Metha, S.K.: Einfluß der Kristallitgröße auf
die physikalisch-chemischen Eigenschaften verschiedener
Calciumsulfat-Hydrate, TIZ 91(1973) 8, S. 217-222
Matsuda, O.: Heat of Hydratation of Gypsum
Hemihydrate, Gypsum & Lime No. 177 (1982), S. 74-80
Mschedlov-Petrossian O. P.; Usherov-Marshak, A. V.:
Thermokinetic estimation of quality of gypsum,
Silikattechnik (1974) 5
Mschedlov-Petrossian O. P.; Usherov-Marshak, A. V., Sen
A. A.: Zur Untersuchung der Hydratation von Bindemitteln
nach der Methode der Differential-Mikrokalorimetrie,
Silikattechnik (1969) 7, S. 229-231
-Петросян, О.П.; Ушеров, А.В.,
Урженко, А. .: Тепловыделение при твердении
вяжущих веществ и бетонов,
осква, Стройиздат
(1984)
Nowak, S.: Charakterisierung des Alterungsverhaltens
spezieller Mehrphasengipsbinder, Diplomarbeit, FIB
BUW, Weimar 2004
Nowak, S.: Kalorimetrische Charakterisierung von
Calciumsulfatbindern, Studienarbeit, FIB BUW, Weimar
2003
Nowak, S.; Fischer, H.-B.: To the aging behavior of
Calcium Sulphate Binders, Cheminė Technologija Nr. 3
(33), Kaunas Technologija 2004, pp. 58-65
Ostradecký, I.; Nowak, S.; Fischer, H.-B.: Změny
vlastností alfa a beta sádry při uložení ve vlhkém prostrédí
(Eigenschaftsänderungen von Alpha- und Beta-Halbhydrat
durch Alterung in feuchter Umgebung), Sádra 2005,
Sbornik příspěků semináře, Brno, pp. 12-19
Рябин, В.А.; Остроумов,
.Ф.; Свит, Т.Ф.:
Термодинамические свойства веществ,Справочник,
Издательство «Химия», Ленинградское отделение
(1977)
Seidel, G.; Huckauf, H.; Stark, J.: Technologie der
Bindebaustoffe, Verlag für Bauwesen, Berlin 1976
Usherov-Marshak, A.: Calorimetry of cement and
concrete,, Selected works, Kharkov „Fakt“ (2002)
Wirsching, F.: Die Phasen des Systems CaSO4CaSO4*2H2O, ZKG 19 (1966) 10, S. 487-492
Москва
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
Мчедлов
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М
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