Characterization of Glaze Compositions

3. Unity Molecular Formula Approach

3.3 Results and Discussion

3.3.1 Characterization of Glaze Compositions

Dwell time: 3 sec. Phase Identification was conducted using commercial software routines (Jade+, Version 3.1, Materials Data, Inc., Livermore, CA, 1995).

3.2.2.3 Scanning Electron Microscopy (SEM)

Images were taken of the glaze surface using SEM (Philips Electron Microscope, Alfred University, Alfred, NY). After samples were fired, five samples from each series of glaze were chosen based on difference in appearance. The best gloss, two alumina mattes, and two silica mattes were chosen. Samples were cut using a diamond saw and mounted using carbon paste. Images were taken of the microstructure as well as qualitative analysis by EDS measurements to verify the crystalline phase compositions formed from the devitrification process. Precise qualitative analysis of the crystalline material is not possible due to interaction volume affects and the environment or the inhomogeneous nature of the glaze that analysis is conducted on. EDS is also unable to detect lithium due to lithium’s low energy (0.5 eV), so it used only as reinforcement to the other characterization techniques.

through the aid of SEM/EDS and XRD. The two matte formation regions identified are mattes of devitrification (alumina mattes) and mattes of underfiring (silica mattes). The reason for these labels (alumina and silica mattes) are that alumina mattes (devitrified) are generally found in the low silica compositional ranges (both high and low alumina range) and the silica mattes (underfired) are found in the low alumina ranges (high silica).

For this study the alumina mattes and silica mattes will be defined to separate the two matte regions based on these criteria. The alumina matte and silica matte regions have been given the following general compositional ranges in past experimentation:

Alumina Matte:

}

⁰^.¹⁰ ⁰^.⁶⁰^Al₂^O₃

}

¹^.⁵ ³^.⁰^SiO₂

Flux

Variable − −

Silica Matte:

}

⁰^.¹⁰ ⁰^.³⁰^Al₂^O₃

}

³^.⁰ ⁵^.⁰^SiO₂

Flux

Variable − −

Note that previous work has demonstrated that the silica matte region is devitrified and the alumina matte region is unfused (or underfired).² Also, the limit formulas do not differentiate between the two types of matte formation.¹⁹

This research will demonstrate these general compositional ranges for matte formation are not accurate enough to represent the true trend seen in each glaze system (Series A through Q), meaning some of the data is excluded rather than included. For this reason, a more complete evaluation of these limits or constraints needs to be determined.

The gloss results found in Figures 3.4-3.18, clearly and accurately, demonstrate the change from gloss to matte surface with changing alumina and silica levels. When applying the general compositional ranges for both alumina and silica matte surfaces it can be seen that some of the gloss data collected is not included in the matte ranges. To provide a better representation and to avoid excluding important data, lines are drawn for the boundaries between gloss and alumina matte regions as well as gloss and silica matte regions. This is demonstrated for Series A glaze system seen in Figure 3.19.