**2.2. Thermogravimetric (TG) analysis**

272 Heat Treatment – Conventional and Novel Applications

other thermally based synthetic method.

**2.1. Preparation of starting material** 

of 65 A/m2 according to the reactions:

What we will describe here in this chapter is a method for identifying the optimum thermal synthesis conditions, and then explore their effects on the resultant material properties. The system we will use to demonstrate the approach is the heat treatment process used to remove water from the structure of γ-MnO2 prior to its use in non-aqueous Li-MnO2 cells. While this will be used as a representative example, the general method is applicable to any

The sample of γ-MnO2 used in this work was prepared by anodic electrodeposition, and hence given the designation electrolytic manganese dioxide, or EMD. The cell used for electrolysis was based on a temperature controlled 2 L glass beaker in which two 144 cm2 (72 cm2 on either side) titanium sheets were used as the anode substrate, and three similarly sized copper sheets were used as the cathode substrate. The electrodes were arranged alternately so that each anode was surrounded on both sides by a cathode. The electrolyte was an aqueous mixture of 1.0 M MnSO4 and 0.25 M H2SO4 maintained at 97°C. Electrodeposition of the manganese dioxide was conducted with an anodic current density

( ) <sup>2</sup> Anode Ti : Mn 2H O MnO 4H 2e 2 2

( ) Cathode Cu : 2H 2e H2

<sup>2</sup> Overall : Mn 2H O MnO 2H H 2 22

The overall process was carried out for three days, during which time the electrolyte Mn2+ concentration was of course depleted, while the H+ concentration increased. To counteract this, and hence maintain a constant electrolyte concentration over the duration of the deposition, a concentrated (1.5 M) MnSO4 solution was added continually at a suitable rate to replenish Mn2+ and dilute any excess H2SO4 produced. Under these conditions control of

After deposition was complete, the solid EMD deposit was mechanically removed from the anode and broken into chunks ~0.5 cm in diameter, and then immersed in 500 mL DI water to assist in the removal of entrained plating electrolyte. The pH of this chunk suspension was adjusted to pH 7 with the addition of 0.1 M NaOH. After ~24 h at a pH of 7 the suspension was filtered and the chunks then dried at 110°C. After drying the chunks were then milled to a -105 μm powder (mean particle size ~45 μm) using an orbital zirconia mill.

the solution conditions was typically maintained to within ±2%.

<sup>+</sup> + − + ⎯⎯→ ++ (1)

+ + + ⎯⎯→ ++ (3)

+ − + ⎯⎯→ (2)

**1.6. This work** 

**2. Methods** 

TG analysis was conducted using a Perkin Elmer Diamond TG/DTG controlled by Pyris software. Approximately 10 mg of γ-MnO2 sample was added to an aluminium sample pan and placed into the analyser. The same mass of α-Al2O3 in a similar aluminium pan was used as the reference material for DTA measurements. With the sample and reference materials loaded, and the furnace closed, dry nitrogen gas was passed over the sample at 20 mL/min for 30 minutes prior and during the heating profile. The heating profile applied to the sample was essentially a linear ramp at rates ranging from 0.25°-10°C/min.
