Preparation, Characterization and Electrical Conductivity of Condensed Sodium Phosphates

Abstract

Condensed phosphates are generally prepared from their simple phosphates by heating at high temperature. The formation, structure and the morphology of the resultant condensed phosphates depend on the kind of inorganic cations as well as the conditions of preparation, temperature, heating time, and cooling rate of the melt. Condensed sodium phosphates were prepared by thermal treatment of NaH2PO4, the effect of calcinated temperature, also was studied. The products were characterized by X-ray diffraction, IR spectrum, Transmission electron microscope (TEM).The results indicate that the produced phosphate depends on the heat of calcinations. The electrical conductivity of the product was measured in range from room temperature up to 300 0C. The measurements show that the condensed phosphates tend to be a semiconductor material.

Full text

Adli A.Hanna et al.
© 2010 al-Farabi Kazakh National University Printed in Kazakhstan
Preparation, Characterization and Electrical Conductivity of
Condensed Sodium Phosphates
Adli A.Hanna
1
*, Marwa A. Sherief
1
, Reham M.M. Morsi
2
1
Inorg. Chem. Dept., National research centre, Dokki, Cairo, Egypt
2
Physical Chem. Dept., National National research centre, Dokki, Cairo, Egypt
Abstract
Condensed phosphates are generally prepared from their simple phosphates by heating at high
temperature. The formation, structure and the morphology of the resultant condensed phosphates depend
on the kind of inorganic cations as well as the conditions of preparation, temperature, heating time, and
cooling rate of the melt.
Condensed sodium phosphates were prepared by thermal treatment of NaH
2
PO
4
, the effect of
calcinated temperature, also was studied. The products were characterized by X-ray diffraction, IR
spectrum, Transmission electron microscope (TEM).The results indicate that the produced phosphate
depends on the heat of calcinations. The electrical conductivity of the product was measured in range
from room temperature up to 300
0
C. The measurements show that the condensed phosphates tend to be a
semiconductor material.
Introduction
Phosphates have been used for ceramic
materials, catalyst, metal surface treatments,
fertilizers, food additives, etc [1]. Condensed
phosphates are generally produced from simple
phosphates by dehydration – condensation at
elevated temperature [2]. The formation and the
structure of the resultant condensed phosphates
depend on the kind of the inorganic cations as well
as reaction temperatures, heating time, cooling rate
of the melt, and water vapor pressure through the
dehydration processes. In general there are three
types of the condensed phosphates, poly phosphate,
cyclophosphate and ultra phosphate. Poly
phosphate has a chain structure in which PO
4
unit
shares two oxygen atoms, cyclophosphate has a
cyclic structure and ultra phosphate has a network
structure [3]. Depending on the chemical activity
towards the acid and the base, the three types of the
condensed phosphates can be distinguished.
In previous works, the authors prepared and
characterized different types of simple and metal
phosphates such as: sodium phosphate for detergents
and feed animals [4, 5], iron and aluminium
phosphates [6, 7]
and rare earth phosphates as
sensors [8]. Also, they prepared some tetra valent
(Zr,Ti) phosphates as ion exchangers and
semiconductor materials [9, 10]
by applying the
traditional and the sol-gel methods. As continuation
to our policy, this paper aimed to study the
preparation and characterization of sodium
condensed phosphate and study the effects of
dehydration temperature on the structure and
morphology of the products. The electrical
conductivity of the produced phosphates and the
precursor materials were measured at different
temperature to draw some light on the
semiconducting properties of the condensed
phosphate.
Material and methods
The starting material of this work was sodium
dihydrogen phosphate, NaH
2
PO
4
2H
2
O (mark). The
condensed phosphates were prepared by
dehydration process. In this work the precursors
material (NaH
2
PO
4
.2H
2
O) was denoted as sample (I).
Two samples of the condensed phosphate were
prepared. The first one (sample II) was prepared by
_________________________
*corresponding author. Email: a_hanna2006@yahoo.com
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Preparation, Characterization and Electrical Conductivity of Condensed Sodium Phosphates
Eurasian ChemTech Journal 12 (2010) 227-230
ignited NaH
2
PO
4
at 1000
0
C for ~ 2hrs, the second
sample (sample III) was prepared by firing sample
II at 520
0
C for 12hrs.
The three samples (I, II, III) were characterized
by using X-ray diffraction technique to detect the
formed phases and the crystallinity states of the
materials, IR spectra and the transition electron
microscope (TEM) to detect the morphology of the
materials. Also the electrical conductivity of the
produced and the precursors material was measured
at different temperatures. The conductivity was
measured using AG 4311B RLC-Meter, Japan in
the temperature range from 25 to 200
0
C. The values
of conductivity () was obtained after recording the
resistance (R) and using the following equation.
 (
-1
cm
-1
) =1/ = R.A/d (1)
where  the receptivity, R the measured resistance,
A is the surface area of the sample and d is the
thickness.
Results and discussion
The produced phosphates at different
temperature as well as the start material were
characterized to follow the formation of the
condensed phosphates. Fig 1(a, b, c) represents the
X-ray diffraction of the compounds. Fig 1a shows
that the start material was sodium dihydrogen
phosphate NaH
2
PO
4
.2H
2
O in well crystalline form
according to the card no. (10-0198 o). By heating
sample I up to 1000
0
C the material diffused and
goes to form poly phosphate in amorphous state as
shown in Fig 1b. When the resultant material fired
at 520 C for 12hr, Fig 1c, the amorphous phosphate
converted to crystalline poly phosphate having
chemical formula Na
3
P
3
O
9
according to card no.
(72-1628 c).
Fig. 1. (a,b,c) : X-ray diffraction of sodium phosphate
samples a) sample I b) sample II c) sample III
The IR spectra of the three samples was
recorded in Fig 2(a, b, c). The IR absorption of
NaH
2
PO
4
2H
2
O shows different absorption peaks at
615, 959, 527, 1254, 1045, and 1155 corresponding
to the (P
3
O
9
)
-3
, P-O-P, O-P-O, (PO
3
)
-2
respectively.
There peaks characterized the formation of the
phosphate compounds [11]. In addition a peak at
3742 was appeared characterizes the O-H groups.
By heating sample I at 1000
0
C for 2hrs, the IR
spectrum shows the same phosphate groups, but the
deepness of the peaks at 1045,1245,1155 (PO
3
)
-2
were increased indicating to the formation of poly
phosphate. From other hand the depth of the peak
of the hydroxyl group was decreased indicating to
the dehydration of the phosphate. The IR spectrum
of the sample (III) shows that:
1. The specific peaks of the phosphate
compounds still appeared;
2. Two peaks at 1045, 1245, 1155 characterized
to (PO
3
)
-2
were identified;
3. The peaks characterized to the presence of the
water content tend to disappear.
Fig. 2. (a,b,c) : IR spectrum bands of sodium phosphate
samples a) sample I b) sample II c) sample III
The results of the transmission electron
microscope (TEM) for the three samples were
represented in Fig 3(a ,b, c). For sample I, Fig 3a,
the TEM shows that this material have a well
arranged crystalline and having nearly the same
particle size in the range of 16 nm to 82 nm. Also
the boundary of the grains well defined.
By heating the sample I to obtain sample II the
general TEM shape shows that sample I is
converted to amorphous with some clusters
formations without considerable change in the size.
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28

Adli A.Hanna et al.
Eurasian ChemTech Journal 12 (2010) 227-230
Fig. 3. (a, b, c): TEM of sodium phosphate samples
a) sample I b) sample II c) sample III
For sample III the TEM graph 3c shows that:
1. A nanotubes shape was appeared.
2. The appearance of a circle shape with specific
one needle that may be corresponding to the
condensed phosphate formation.
To study the behavior of electrical conductivity
of the starting material as well as the resultant
condensed phosphate, the electrical conductivity
was measured in the temperature range from 25 to
200
0
C at 1KHz. Fig 4 (a, b, c) represents the
variation of log conductivity ( 
-1
cm
-1
) with
reciprocal of absolute temperature (k
-1
). It is
noteworthy that the three samples behave as
semiconducting material with some variation
according to their structure. Fig 4a for NaH
2
PO
4
,
three region on the curve of log  – 1/T can be
specified. The first region between 25 to ~ 70
0
C
where the values of electrical conductivity increase
with temperature which is the typical behavior of
the semi conducting materials. This behavior may
be due to the protonic conductivity which increase
the mobility of charge carriers. So hopping model is
the most suitable one to be applied, where the
charge carriers jump from one localized state to an
other until they reach the conduction band. The
second region between 70 to ~ 150
0
C, where the
electrical conductivity is nearly independent on the
temperature. This region may be corresponding the
melting of NaH
2
PO
4
where the thermal energy
consumed in the fusion of the start material. The
third part, inspire of the values of the electrical
conductivity lies in the range of the semiconducting
material, it tends to loss this property due to a
change in the phases under consideration as
illustrated for X-ray. The formation of non-
conducting layer at the inter-granular spacing
similar to that formed on the ceramic materials
when heated [12].
For the other two samples II and III (Fig 4 b, c)
the values of the electrical conductivity is affected
slightly by the temperature. On other hand, this
behavior may due to the losses of the hydration
water and reducing the movement of the rotated
groups by condensation. In comparison, it is
observed that the values of the electrical
conductivity for the three samples behave as the
following sequence.
NaH
2
PO
4
 crystalline condensed phosphate 
amorphous condensed phosphate
Fig.4. The variation of AC-electrical conductivity with
temperature for sodium phosphate samples a) sample I
b) sample II c) sample III
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Preparation, Characterization and Electrical Conductivity of Condensed Sodium Phosphates
Eurasian ChemTech Journal 12 (2010) 227-230
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Received 15 April 2010
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