Phase equilibria in the ternary system MgO-Na2O-P2O5. The partial system MgO-Mg3(PO4)2-Mg4Na (PO4)3-Na4P2O7

Article abstract of DOI:10.1016/S0040-6031(01)00715-8

The MgO-Mg₃(PO₄)₂-Mg₄Na (PO₄)₃-Na₄P₂O₇ subsystem of the ternary system MgO-Na₂O-P₂O₅ was investigated using thermal analysis (heating and cooling), X-ray diffraction techniques and microscopy in reflected light. Three intermediate compounds: Mg₄Na(PO₄)₃, MgNaPO₄, and MgNa₄(PO₄)₂ occur in the partial system. Mg₄Na(PO₄)₃ melts incongruently at 1155 °C, MgNa₄(PO₄)₂ melts congruently at 1655 °C, whereas MgNaPO₄ exists only in the solid phase and decomposes at 950-960 °C. A phase diagram for the partial system is proposed. It has been established that the MgNa₄(PO₄)₂ phosphate forms a binary system with Na₄P₂O₇. A phase diagram of this system has been constructed. It has been found that a ternary peritectic (t_P = 1145 ± 3.0 °C) and two ternary eutectics (t_E1 = 984 ± 3.0°C, t_E2 = 732 ± 1.5 °C) occur in the MgO- Mg₃(PO₄)₂-Mg₄Na (PO₄)₃-Na₄P₂O₇ system.

Full text of DOI:10.1016/S0040-6031(01)00715-8

Thermochimica Acta 385 ꢀ2002) 163±169
Phase equilibria in the ternary system MgO±Na O±P O .
2
2 5
The partial system MgO±Mg ꢀPO ) ±Mg NaꢀPO ) ±Na P O
4 2 7
3
4 2
4
4 3
*
Teresa Podhajska-Ka z mierczak
Faculty of Engineering and Economics, Department of Inorganic Chemistry, Wrocøaw University of Economics,
Komandorska 118/120, 53-345 Wrocøaw, Poland
Received16 May 2001; receivedin revisedform 8 August 2001; accepted18 August 2001
Abstract
The MgO±Mg
thermal analysis ꢀheating andcooling), X-ray di ffraction techniques andmicroscopy in re¯ectedlight. Three interme di ate
compounds: Mg NaꢀPO , MgNaPO andMgNa ꢀPO occur in the partial system. Mg NaꢀPO melts incongruently at
ꢀPO melts congruently at 1655 8C, whereas MgNaPO exists only in the solidphase and de composes at
50±960 8C. A phase diagram for the partial system is proposed. It has been established that the MgNa ꢀPO ) phosphate
3 4 2 4 4 3 4 2 7 2 2 5
ꢀPO ) ±Mg NaꢀPO ) ±Na P O subsystem of the ternary system MgO±Na O±P O was investigatedusing
4
4
)
3
4
4
4
)
2
4
4 3
)
1
155 8C, MgNa
4
4
)
2
4
9
4
4 2
forms a binary system with Na
ꢁ
4
P
2
O
7
. A phase diagram of this system has been constructed. It has been found that a ternary
ꢁ
ꢁ
peritectic ꢀtP ˆ 1145 Æ 3:0 C† andtwo ternary eutectics ꢀt E ˆ 984 Æ 3:0 C, tE ˆ 732 Æ 1:5 C) occur in the MgO±
1
2
Mg ꢀPO ) ±Mg NaꢀPO ) ±Na P O system. # 2002 Elsevier Science B.V. All rights reserved.
3
4 2
4
4 3
4 2 7
Keywords: Partial systems; Binary phosphates; Ternary systems
1
. Introduction
magnesium±sodium double phosphates which occur
in the investigatedcomposition range can also be
found: Mg NaꢀPO ) [10±12,17±19], MgNaPO4
In the present paper, the results of a study on the
ternary system MgO±Na O±P O are reported. The
4
4 3
[10,11,20±25] andMgNa ꢀPO ) [11,18,26,27]. The
4 4 2
2
2
5
goal of the research was to construct a phase diagram
of the MgO±Mg ꢀPO ) ±Mg NaꢀPO ) ±Na P O sub-
system.
three phosphates occur as intermediate compounds
formedin the Mg ꢀPO ) ±Na PO system. The phase
3
4 2
4
4 3
4
2
7
3
4 2
3
4
diagrams of the ®rst three of the four side systems
mentionedabove are known.
The MgO±Mg ꢀPO ) system is a simple eutectic
The subsystem is bounded by four side systems:
1) MgO±Mg ꢀPO ) , ꢀ2) Mg ꢀPO ) ±Mg NaꢀPO ) ,
3) Mg NaꢀPO ) ±Na P O andꢀ4) MgO±Na P O .
ꢀ
ꢀ
3
4 2
3
4 2
4
4 3
3
4 2
system. Its phase diagram is given in [4]. The com-
position andtemperature of the eutectic are
4
4 3
4
2
7
4 2 7
The different substances are described in detail in
the literature. Relevant information can be found, for
instance, about MgO in [1±3], Mg ꢀPO ) [4±12] and
ꢁ
48 Æ 1:0 wt:% MgO, and1325 Æ 3:0 C, respectively.
The other two side systems have been worked out
by the present author [11,12,28]. In the fourth side
system, i.e. MgO±Na P O , an intermediate com-
3
4 2
Na P O [13±16]. Characteristic properties of the
4 2 7
4
2 7
*
poundÐMgNa ꢀPO ) occurs. This phosphate melts
4 4 2
Tel.: ‡48-1033-71-367-2853; fax: ‡48-1033-71-368-0292.
E-mail address: tesapk@credit.ae.wroc.pl
T. Podhajska-Ka z mierczak).
congruently at 1655 8C andoccurs in three poly-
ꢀ
morphic modi®cations. MgNa ꢀPO ) divides the
4
4 2
0040-6031/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ꢀ 0 1 ) 0 0 7 1 5 - 8

164
T. Podhajska-Ka z mierczak / Thermochimica Acta 385 ꢀ2002) 163±169
MgO±Na P O system into two partial systems: ꢀ1)
4
substances, namely: ꢀ1) Mg ꢀPO ) andNa PO mixed
3 4 2 3 4
2
7
MgO±MgNa ꢀPO ) andꢀ2) MgNa ꢀPO ) ±Na P O .
4
in a 1:4 molar ratio, ꢀ2) MgO andNa P O mixedin
4 2 7
4 2
4
4 2
4
2
7
The former partial system has been workedout within
a composition range 60±100 wt.% MgNa ꢀPO ) up to
a 1:1 molar ratio, ꢀ3) MgꢀPO ) andNa CO mixedin a
3 2 2 3
1:2 molar ratio. MgNaPO was synthesizedvia a con-
4
4
4 2
a temperature of 1800 8C [27]. The remaining part of
the system was not examinedbecause of the high
melting point of the samples. The system is a simple
eutectic system. The eutectic's composition is app-
roximately 4 Æ 1:0 wt:% MgO and96 Æ 1:0 wt:%
ventional solidstate reaction ꢀ600±900 8C, 72±96 h)
from different initial materials such as Mg ꢀPO ) and
Na PO , MgO andNaPO , andMg P O andNa CO .
3
4 2
3
4
3
2
2
7
2
3
The samples were investigatedusing di fferential
thermal analysis ꢀDTA) for heating andcooling, X-ray
diffraction analysis, and microscopy in re¯ected light.
DTA for heating was performedby means of a type-C
derivatograph ꢀMOM, Hungary); the heating rate
was 5 8C/min in a temperature range 20±1350 8C.
The standard substance was Al O . Platinum crucibles
ꢁ
MgNa ꢀPO ) andits temperature is 1630 Æ 30:0 C.
4
4 2
The MgNa ꢀPO ) ±Na P O system was unknown.
4
4 2
2 2 7
It has been workedout by the present author andits
phase diagram is presented in this paper.
TheMgO±Mg NaꢀPO ) sectionoccursintheMgO±
4
4 3
2 3
Mg ꢀPO ) ±Mg NaꢀPO ) ±Na P O subsystem. The
4 3
in an air atmosphere were used. Samples weighing
0.2±0.9 g were usedfor ed rivatography. DTA for
cooling was carriedout using a resistance furnace
ꢀan in-house design) with a PtRh30 winding. The tem-
perature was measuredby a Pt/PtRh10 thermocouple
standardized for the melting points of the following
substances: NaCl ꢀ801 8C), K SO ꢀ1070 8C) and
3
4 2
4
4 2 7
section's phase diagram can be found in [29]. The
section has been workedout in a composition range
6
0±100 wt.% Mg NaꢀPO ) up to a temperature of
4 4 3
1
a result at high temperatures MgO±Mg NaꢀPO )
800 8C. Mg NaꢀPO ) melts incongruently andas
4
4 3
4
4 3
is multiphase, consisting of four phases: a liquid,
Mg ꢀPO ) , Mg NaꢀPO ) andMgO. Below a tempera-
2
4
Ca P O ꢀ1353 8C) andfor the K SO polymorphic
3
4 2
4
4 3
2
2
7
2
4
ture of 1145 8C only two phases coexist, i.e. MgO and
transition temperature ꢀ583 8C). Three gram samples
crystallizedwith grafting were use d. Above 1350 8C,
the thermal investigations were conducted in an atmo-
sphere of argon in a horizontal resistance furnace with
a molybdenum winding. The samples were pressed
into 1±2 g pellets andplacedinto small boats made
of PtRh30 melt. The temperature was readout by an
optical pyrometer calibratedagainst the melting points
of Na PO ꢀ1583 8C) andCa ꢀPO ) ꢀ1810 8C). In the
thermal analysis, the temperature read-out accuracy
was Æ1.5 8C in a temperature range up to 800 8C,
Æ3 8C above 800 8C, and Æ30 8C when the tempera-
ture was readout by the optical pyrometer. The
composition of the samples was determined with an
accuracy of Æ1.0 wt.% for the binary system and
Æ3.0 wt.% for the ternary system.
Mg NaꢀPO ) . In the subsolidus region, the section is
a real binary system.
4
4 3
2
. Experimental
The samples were prepared from ready-made
reagents andin-house synthesizedcompoun ds . The
ready-made reagents included the following analytical
3
4
3
4 2
grade materials: magnesium oxide MgO, MgHPO Á
4
3
H O, Na HPO Á2H O, Na PO Á12H O andNa CO .
2 3
2
2
4
2
3
4
2
2
3
MgO was annealedat 1000 8C for 1 h. Na CO was
annealedat 200 8C for 3 h. Magnesium diphosphate
Mg P O was obtained by completely dehydrating
MgHPO Á3H O at 900 8C for 1 h. Orthophosphate
2
2 7
4
2
Mg ꢀPO ) was synthesizedfrom Mg P O andMgO
4 2
The samples for phase investigations in both the
binary systems andthe whole partial system were
preparedin a similar way. The initial substances were
weighedout in ®xedamounts, then thoroughly mixed
andgroundin an agate mortar to attain their homo-
geneity. To improve the contact area between the
substances, the weighedportions were pressedinto
pellets. Then the samples were presynthesizedby
sintering ꢀin the solidphase). The sintering tempera-
ture andthe presynthesis time in relation to the initial
3
2 2 7
by annealing the initial components at 1200 8C for
0 min. Na P O was synthesizedby heating Na H-
2
4
2
7
2
PO Á2H O at 200 8C for 1 h. Orthophosphate Na PO
4
2
3
4
was obtainedby slowly dehydrating Na 3PO Á12H O at
4
2
a 200 8C andsubsequently at 300 and600
8C.
Mg NaꢀPO ) was obtainedby heating the Mg ꢀPO ) ±
4 2
4
4 3
3
Na PO mixture ꢀwitha molar ratioof 4:1) at 900 8C for
3
4
7
2 h. MgNa ꢀPO ) was synthesizedvia a solidstate
4 4 2
reaction ꢀat 900 8C for 72 h) from different parent

T. Podhajska-Ka z mierczak / Thermochimica Acta 385 ꢀ2002) 163±169
165
composition of the samples were determined experi-
mentally. Some of the samples showeda ten de ncy to
glaze. To promote the crystallization ꢀat least partial)
of the samples, slow cooling ꢀ2 8C/min) with frequent
grafting was employed. Microsections of the melts
were preparedandexaminedby microscopy in
re¯ectedlight. Also visual observation of the samples
during heating was conducted. The observation con-
sistedin the recording of the temperature at which the
®
rst traces of liquidappearedandthe temperature at
which the sample became transparent. On the basis of
the microscopic examinations, the purity of the sub-
stances andthe phase constitution of the melts were
estimated. The phases in the partial system were
identi®ed and the phase purity of the substances
was determined by X-ray powder diffraction using
Siemens diffractometers D 5000 and HZG 4 with Cu
Ka radiation and a Ni-®lter.
3
. Results
The MgNa ꢀPO ) ±Na P O binary system in
4 2 7
4
4 2
the MgO±Mg ꢀPO ) ±Mg NaꢀPO ) ±Na P O sys-
3
4 2
4
4 3
4 2 7
tem was investigatedandthe phase ida gram was
constructedfor the whole range of composition
andtemperature. Samples of the MgNa ꢀPO ) ±
Fig. 1. Phase diagram of MgNa ꢀPO
4
4
)
2
4
±Na P
2
O
7
system; ꢀL)
liquid, ꢀ*) DTA of cooling, ꢀ~) optical.
4
4 2
Na P O system were presynthesizedat 600 8C for
thermal effect in the heating DTA curves. Whereas the
cooling DTA curves show two successive thermal
effects. The thermal effects corresponding to high-
temperature transitions b/g-Na P O and g/d-Na P O
4
2 7
7
2 h andthen melte .d The phase ida gram of the
MgNa ꢀPO ) ±Na P O binary system is shown in
4
4 2
4 2 7
Fig. 1. The components form a simple eutectic sys-
tem. The eutectic point composition andtemperature
are 58:0 Æ 1:0 wt:% MgNa ꢀPO ) , 42:0 Æ 1:0 wt:%
4
2
7
4 2 7
occur in a composition range 20±100 wt.% Na P O .
The b/g-MgNa ꢀPO ) transition ꢀat 821 8C) hardly
4
2 7
4
4 2
4
4 2
ꢁ
Na P O and900 Æ 3:0 C. Since the samples rich in
proceeds in the system and leads to visible thermal
effects in the DTA curves only in the MgNa ꢀPO ) -
4
2 7
MgNa ꢀPO ) meltedat high temperatures, an optical
4
4 2
4
4 2
pyrometer ꢀwith an accuracy of Æ30 8C) was used
to readthe temperatures. The approximate liqui du s
curve in this region is markedby a da shedline in the
phase diagram.
rich composition range. One can infer that a high
Na P O content inhibits the b/g-MgNa ꢀPO ) poly-
morphic transition.
4
2
7
4
4 2
Sodium diphosphate ꢀNa P O ) shows three poly-
4
2
7
4. Discussion
morphic transitions. In the pure compound, the transi-
tion occurs at: 390 8C for a/b-Na P O , 512 8C for
The phase diagram of the MgO±Mg ꢀPO ) ±
3 4 2
4
2
7
b/g-Na P O and550 8C for g/d-Na P O . Magnesium
Mg NaꢀPO ) ±Na P O system, withsolidi®cationiso-
4 4 3 4 2 7
4
2
7
4
2
7
sodium phosphate ꢀMgNa ꢀPO ) ) shows two poly-
morphic transitions which occur at: 396 8C for
a/b-MgNa ꢀPO ) and821 8C for b/g-MgNa ꢀPO ) .
therms, is shown in Fig. 2. The composition range can
be divided into three partial ternary systems: ꢀ1) MgO±
Mg ꢀPO ) ±Mg NaꢀPO ) , ꢀ2) MgO±Mg NaꢀPO ) ±
4
4 2
4
4 2
4
4 2
3
4 2
4
4 3
4
4 3
The low-temperature, polymorphic a/b transitions
of both phosphates produce a clearly visible, joint
MgNa ꢀPO ) andꢀ3) Mg NaꢀPO ) ±MgNa ꢀPO ) ±
4 4 2 4 4 3 4 4 2
Na P O . Since there are ®ve phosphates, ®ve ®elds
4 2 7

166
T. Podhajska-Ka z mierczak / Thermochimica Acta 385 ꢀ2002) 163±169
Fig. 2. Phase diagram of MgO±Mg
3
4
ꢀPO )
2
±Mg
4
NaꢀPO
4
)
3 4
±Na P
2
O
7
system including solidi®cation isotherms.
ꢁ
of primary crystallization exist, see Fig. 3. The three
ternary invariants, corresponding to one ternary peri-
tectic andtwo ternary eutectics are as follows:
2. Ternary eutectic E at 984 Æ 3:0 C corresponds to
1
the equilibrium:
MgO ‡ Mg NaꢀPO4† ‡ MgNa ꢀPO4† $ liq: E1
4
3
4
2
ꢁ
1
. Ternary peritectic P at 1145 Æ 3:0 C corresponds
The composition of E : 17:5 Æ 3:0 wt:% MgO,
1
to the reaction:
3
1:9 Æ 3:0 wt:% Na O, 50:6 Æ 3:0 wt:% P O .
2
2 5
ꢁ
3
. Ternary eutectic E at 732 Æ 1:5 C corresponds to
2
liq: P ‡ Mg ꢀPO4† $ Mg NaꢀPO4† ‡ MgO
3
2
4
3
the equilibrium:
The composition of P: 39:0 Æ 3:0 wt:% MgO,
1
0:6 Æ 3:0 wt:% Na O, 50:4 Æ 3:0 wt:% P O .
Mg NaꢀPO † ‡Na P O ‡MgNa ꢀPO † $liq: E
2
2
5
4
4
4
2
7
4
4
2
3
2

T. Podhajska-Ka z mierczak / Thermochimica Acta 385 ꢀ2002) 163±169
167
3 4 2 4 4 3 4 2 7
Fig. 3. Isothermal section of MgO±Mg ꢀPO ) ±Mg NaꢀPO ) ±Na P O system at room temperature.
The composition of E : 33:0 Æ 3:0 wt:% MgO,
As a result of the peritectic reaction, excess of liquid
L remains in the molten mixtures representing the
Mg NaꢀPO ) ±P±MgO area.
2
1
7:5 Æ 3:0 wt:% Na O, 49:5 Æ 3:0 wt:% P O .
2
2 5
4
4 3
The peritectic reaction occurs during the solidi®ca-
tion of the molten mixtures corresponding to points in
the Mg ꢀPO ) ±Mg NaꢀPO ) ±P±MgO area ꢀthe triple
Thus the further solidi®cation of the molten mix-
tures proceeds at a varying ꢀfrom 1145 to 984 8C)
temperature along line PE andconsists in the sepa-
1
3
4 2
4
4 3
peritectic quadrangle). The reaction ends the solidi®-
cation of the mixtures corresponding to points within
the triple peritectic quadrangle.
ration of the binary eutectic ꢀMg NaꢀPO † ‡ MgO†.
4
4 3
The lines originating from binary eutectics e ande
1
2
intersect at the point of ternary eutectic E . When
1

168
T. Podhajska-Ka z mierczak / Thermochimica Acta 385 ꢀ2002) 163±169
3 4 2 4 4 3 4 2 7
Fig. 4. Position of the samples in the MgO±Mg ꢀPO ) ±Mg NaꢀPO ) ±Na P O system.
point E is reached, the reaction of the ternary eutectic
1
the secondreaction of the ternary eutectic starts,
yielding three solid phases: Na P O ±MgNa ꢀPO ) ±
starts andproceeds at a constant temperature of 984 8C
4
2
7
4
4 2
yielding three solid phases: MgO±Mg NaꢀPO ) ±
MgNa ꢀPO ) .
Mg NaꢀPO ) . In the molten mixtures from the
4 4 3
4
4 3
Mg NaꢀPO ) ±P±p±darea, the binary peritectic reac-
4 4 3
4
4 2
In the ternary system Mg NaꢀPO ) ±MgNa ꢀPO ) ±
4
tion: Mg ꢀPO † ‡ L ! Mg NaꢀPO † was found
Ppd
4
4 3
4 2
3
4 2
Ppd
4
4 3
to occur. L denotes liquids whose composition cor-
Na P O , the components make up a pseudo-binary
4
2
7
system of the eutectic type. The lines originating from
binary eutectics e , e ande intersect at point E2
responds to points on the P±p±d line.
An intermediate compound MgNaPO occurs in
1
3
4
4
corresponding to a temperature of 732 8C at which
theMgO±Mg ꢀPO ) ±Mg NaꢀPO ) ±Na P O system.
4 3
3
4 2
4
4 2 7

T. Podhajska-Ka z mierczak / Thermochimica Acta 385 ꢀ2002) 163±169
169
[
[
2] A.A. Ogorodnikova, L.M. Lopato, Izv. Akad. Nauk. SSSR
Ser. Neorg. Mat. 9 ꢀ1973) 1940.
This double phosphate forms in the Mg ꢀPO ) ±
3
4 2
Na PO system at an equimolar ratio of the initial
3
4
3] B.T. Melekh, A.A. Andreev, N.F. Kartenko, I.V. Korkin, V.V.
Smirnov, Yu.N. Filin, Izv. Akad. Nauk. SSSR Ser. Neorg.
Mat. 18 ꢀ1982) 98.
phosphates [11]. It exists in the solidphase only and
decomposes in the temperature range 950±960 8C. The
present study indicates that the compound occurs in
three polymorphic modi®cations. As a result of pre-
synthesis a mixture of the polymorphs is obtainedat
room temperature. High-temperature modi®cations of
[4] J. Berak, Roczn. Chem. 32 ꢀ1958) 17.
[
[
5] J. Ando, J. Bull. Chem. Soc. Jpn. 31 ꢀ1958) 201.
6] J.F. Sarver, F.L. Kantack, F.A. Hummel, J. Electrochem. Soc.
1
05 ꢀ1959) 962.
[
7] A.G. Nord, P. Kierkegaard, Acta Chem. Scand. 22 ꢀ1968)
1466.
MgNaPO cannot be stabilizedat room temperature by
4
freezing with ice. A pure low-temperature modi®cation
of MgNaPO can be obtainedby subjecting the pre-
[8] C. Calvo, Am. Min. 53 ꢀ1968) 742.
9] A. Siddique, Pac. J. Sci. Ind. Res. 25 ꢀ1973) 119.
[
4
[
[
10] J. Majling, Chem. Zvesti 27 ꢀ6) ꢀ1973) 732.
11] T. Podhajska-Ka z mierczak, T. Znamierowska, Polish J. Chem.
synthesizedcompoundwith an a ddi tion of 2±3 wt.%
Na P O to prolongedheating at 500±600 8C. The pre-
4
2 7
7
3 ꢀ1999) 279.
sence of MgNaPO plays an essential role in the forma-
4
[12] T. Podhajska-Ka z mierczak, SolidState Sci. 2 ꢀ4) ꢀ2000)
489.
tion of the phase dependencies in the subsolidus region
of the MgO±Mg ꢀPO ) ±Mg NaꢀPO ) ±Na P O sys-
[
13] P. Patridge, V. Hicks, G.W. Smith, J. Am. Soc. 63 ꢀ1941)
54.
3
4 2
4
4 3
4 2 7
4
tem.Inthisregion,theabovephosphateformstwohypo-
thetical sections: one with magnesium oxide ꢀMgO)
[
[
14] G.W. Morey, E. Ingerson, Am. J. Sci. 242 ꢀ1944) 1.
15] C.T. Turkdogan, W.R. Maddocks, J. Iron Steel Inst. ꢀLondon)
172 ꢀ1952) 6.
andthe other with so di um di phosphate ꢀNa
P O ).
4 2 7
The two sections together with the quasi-binary sys-
tems described above divide the investigated composi-
tion range into ®ve partial ternary systems existing
at room temperature, namely:
[16] J. Berak, T. Znamierowska, Roczn. Chem. 46 ꢀ1972)
967.
1
[
17] V.M. Ustiantsev, M.G. Tretnikova, E.I. Kielarieva, Izv. Akad.
Nauk SSSR Ser. Neorg. Mat. 12 ꢀ8) ꢀ1976) 1438.
[
[
18] J. Majling, F. Hanic, Chem. Zvesti 30 ꢀ2) ꢀ1976) 145.
19] V.M. Ustiantsev, M.G. Tretnikova, Ogneupory 5 ꢀ1976)
1
2
3
4
5
. MgO±Mg ꢀPO ) ±Mg NaꢀPO ) ,
3 4 2 4 4 3
5
3.
. MgO±Mg NaꢀPO ) ±MgNaPO ,
4
4 3
4
[
20] H. Rose, Pogg. Ann. 77 ꢀ1849) 289.
. MgO±MgNaPO ±MgNa ꢀPO ) ,
4 3
4
4
[21] L. Ouvrard, Ann. Chim. Phys. 6 ꢀ16) ꢀ1889) 291.
[22] W. Basset, W.I. Bedwell, J. Chem. Soc. 854 ꢀ1933).
. Mg Na-ꢀPO ) ±Na P O ±MgNaPO and
4
4 3
4
2
7
4
[
23] S.I. Berul, N.K. Voskresenskaya, Izv. Akad. Nauk. SSSR Ser.
Neorg. Mat. 2 ꢀ12) ꢀ1968) 2129.
[24] I. Kapralik, M. Potancok, Chem. Zvesti 25 ꢀ1971) 272.
. MgNaPO ±Na P O ±MgNa ꢀPO ) .
4 2
4
4
2
7
4
The isothermal section of the MgO±Mg ꢀPO ) ±
3
4 2
[
[
[
[
[
25] J. Majling, Thesis, Slovak Akad. of Sciences, Bratislava,
971.
Mg NaꢀPO ) ±Na P O system at room temperature
4
4 3
4 2 7
1
is shown in Fig. 3. Position of the samples in the
MgO±Mg ꢀPO ) ±Mg NaꢀPO ) ±Na P O system is
presentedin Fig. 4.
26] A. Ghorbel, F. d'Ywoire, C. Doremieux-Morin, Bull. Soc.
Chim. Fr. 7-8 ꢀ1974) 1239.
27] T. Podhajska-Ka z mierczak, Prace Naukowe AE, Wrocøaw
3
4 2
4
4 3
4 2 7
7
29 ꢀ1996) 93.
28] T. Podhajska-Ka z mierczak, Prace Naukowe AE, Wrocøaw
92 ꢀ1998) 74.
References
7
29] T. Podhajska-Ka z mierczak, T. Znamierowska, Prace Naukowe
AE, Wrocøaw 677 ꢀ1994) 364.
[1] L.T. Brownmiller, R.H. Boque, Bur. Stand. J. Res. 8 ꢀ1932)
289.