A Comparative Investigation of Lead Sulfate and Lead Oxide Sulfate Study of Morphology and Thermal Decomposition

The compound lead oxide sulfate PbSO4.PbO was prepared in our laboratory. The Thermal behavior of PbSO4 was studied using techniques of Thermogravimetry under air atmosphere from 25 to 1200 ̊C. The identity of both compounds was confirmed by XRD technique. Results obtained using both techniques support same decomposition stages for this compound. The electron microscopic investigations are made by SEM and TEM. The compound is characterized by XRD and the purity was determined by analytical Methods. Also a series of thermogravimetric analysis is made and the ideal condition is determined to convert this compound to pure lead oxide.


Introduction
Lead compounds are used in different industries worldwide due to their chemical and physical characteristics [1][2][3][4][5][6].One of the most important characteristics of the lead is its reactions with acids and bases as well as with air, which are well-known as oxidation.In consequence of these kinds of reactions compounds like "lead (II) oxide, lead (IV) oxide, sulfate, lead carbonate, lead nitrate as well as alkaline lead acetate" have been produced.Some are the end product of a desired process but most of them are undesired byproducts and are known as disturb compounds [8,9].
Lead (IV) oxide is one of the most important compounds used in lead-acid batteries, which are produced daily all over the world [5,7].
The goal of this work was to investigate the morphology and crystal size of PbSO 4 .PbO and study of thermal properties of lead sulfate in different temperature conditions.Pure lead (II) oxide has been reported to be the final product of thermal decomposition process of number of different lead compounds [10][11][12].The Morphology of these compounds was also reported [13][14][15].

Materials and Equipment
Lead oxide sulfate was prepared in this laboratory as described in this paper.Alkaline lead (II) acetate purchased from Fluka (Art.No.: 15317).H 2 NSO 3 H amido sulfonic acid purchased from Merck (Art.No.: 10010 30250).

PbO
The lead oxide sulfate sample was prepared for X-ray using Bedacryl and exposed with CuKα1 radiation for two hours.Figure 1 shows the XRD diagram of the compound PbSO 4 .PbO.

PbO
The morphologic investigations of lead oxide sulfate and lead sulfate that is the goal of this work, were accomplished by an electron microscope SEM(REM-JEOL-JSM-840).The preparation of the samples consisted of coating of the surface with gold steam during 2 to 4 minutes (Figures 3 and 4).
The second series of electron microscopic investigation with TEM equipment were accomplished (EM-Hitachi, H-600).The sample was prepared as follows.The white powdery sample was coated first with a thin coal film.This film was then treated with HF acid from the surface and investigated in the TEM equipment.The applied enlargement was 20000× (Figure 5).

TGA Analysis of Lead Sulfate PbSO 4
8.197 mg of PbSO 4 were weighted in a standard container from corundum.This sample was heated (5˚C/min) from 25 to 1200˚C under air atmosphere (15 ml/min) (Figure 6).

PbO
As indicated from Figure 3, crystals are round and hexagonal with a diameter of 1 to 10 µm, the reasonable enlargement in SEM photographs was 3000 times.They are arranged well next to each other and form large round crystals.Figure 4 shows the SEM photographs of PbSO 4 .PbO.As we can see large crystals was formed in the form of long and laminar texture.These crystals have a length of ca.300 µm and a diameter of about 20 µm.The reasonable enlargement in SEM photographs was 200 times.In addition to the large crystals can be seen even small crystals, which have a diameter of about 5 µm.
Figure 5 shows TEM photographs of PbSO 4 .PbO.The crystals are somewhat larger, they form also small   crystals.Individual particles look angular and hexagonal and can be observed in small and larg of dimensions.
Apart from brocken crystals they are mainly arranged crystals.The reasonable enlargement in TEM photographs was 20,000 times.

Thermal Investigations of Lead Sulfate PbSO 4
TGA-results: TGA curve of thermal d composition of PbSO 4 is e  shown in Figure 6.The curve shows the weight loss (vertical axis) versus increase in temperature (horizontal axis).
The results indicate thermal decomposition consists of two subsequent stages in the temperature range of 880˚C -1200˚C and summarized in Table 1.
The first stage takes place between 886˚C -1142˚C.The regarding calculations of weight loss are reported.
The computed stoichiometry of decomposition products are in good agreement with experimental results (quantitative and percent decrease in weight).
1) First & second points o TGA curve (25˚C -886˚C) A heating rate of 5˚C/min was chosen to determine the real value of adsorbed quantity of water as well as finding out more information on what is taking place in this temperature range.The experiment was accomplished in the air atmosphere with a constant gas flow of 15 ml/min.In these two temperatures range i.e., points 1 & 2 we consider no significant weight decrease.In other words it takes place no reaction.
2) Third & fourth points of TGA curve (886˚C -1200˚C) In the temperature range of 886˚C -1142˚C we consider weight loss equal to about 89.19% starting material and occur in the temperature range of 886 -1142˚C.The X-ray analysis of the product confirms presence of α-& β-PbO.This was checked by spectrometric analysis and the calculated brutto formula of PbO is reached.We want to point out again that the pyrolysis of PbSO 4 within the range 886˚C -1142˚C in the air atmosphere led to PbO, i.e. the reaction PbSO 4 → PbO ran off completely with approximately 1100˚C.From the above TG diagram it is evident that the pyrolysis reaction of PbSO 4 in the range 886˚C -1142˚C consists of two stages.The final decomposition product is PbO.
Therefore, study of thermal Behavior of PbSO 4 , by Thermogravimetry suggests four different stages as discussed above.At first the compound losses SO 3 followed

Conclusions
It was clearly stated that the final product consists only of α-and β-PbO, which was a good result.The chemical analysis showed no impurities.The thermal investigations of PbSO 4 by TG method showed that under air atmosphere the compound decomposes to α-and β-PbO.Since PbO does not contain impurities, one can reuse in the industry.Lead sulfate can be converted to PbO in industry which is an economical procedure.

Table 1 . Results from the thermal investigations of α-PbO 2 in temperature range 25˚C -1200˚C in air atmosphere.
PbO in the approximately temperature range of 1100˚C to 1200˚C.We are not able to consider these two phenomenons separately because these two reactions overlap each other.