3. Unity Molecular Formula Approach
3.2 Experimental Procedure
3.2.2 Glaze Characterization
Cone 10 in a Roller-Hearth Kiln (Alfred University, Alfred, NY). Figure 3.2 illustrates the firing schedule subjected to both groups of glazes. The firing cycle was monitored with nine thermocouples and five Cones. Cones 8-12 were sent through the kiln at regular intervals to monitor the firing schedule (also note that refractory brick was continuously sent through the kiln once the kiln was ignited). Nine bulk glaze samples for each matrix were poured into porcelain crucibles and fired to Cone 10 along with the porcelain substrate to allow for easier XRD sample preparation.
Table III-3. Porcelain Substrate Composition Bisque Fired to 1100°C.
36.5% Clay 34% Nepheline Syenite 29.5% Silica 32.4% 6 Tile Clay A-400 Nepheline Syenite SIL-CO-SIL 4.1% Old Mine #4
0 200 400 600 800 1000 1200 1400
0 2 4 6 8
Time (hours)
Temperature (deg. C)
KNaO Group Lithium Group
10
Figure 3.2. Firing schedule for the two main groups of glazes fired to Cone 10 by means of roller-hearth kiln. Despite the different firing schedules both groups of glazes were fired till Cone 10 (soft) was at a 90° angle.
microstructure, and crystalline species. Post heat treatment these three properties were analyzed by glossmeter, microscopy, and XRD.
Gloss (or luster, shine) gives glazes their special characteristic.
Whether high polish, satin finish, deep gloss, or dull finish, the gloss can be seen and felt. People manufacturing products whose surface gloss is a determining quality characteristic should naturally assess the luster objectively with reproducible measurement methods and this is done with the glossmeter. Luster measurements can serve as objective means for the judgement of surfaces in industrial environments and also the long-term durability of a glaze against chemical attack or against weathering, as well as aid in defining the composition limits for matte formation.
Glaze flaws such as devitrification, mineral stones, blisters, bubbles, pinholes, etc.
may be examined with microscopy methods. SEM with analytical accessory Energy- Dispersive X-Ray Spectrometer (EDS) is utilized in this research to produce images of the glaze microstructures and verify crystalline and glass phase composition.
Products of devitrification and mineral stones left as a result of underfiring are identified by XRD. This analysis technique will allow for accurate representation of glaze quality and purity (free of crystalline phases). Note the bulk glaze samples prepared were used in the XRD analysis.
3.2.2.1 Glossmeter Measurements
After heat treatment of the samples, a glossmeter was used to quantitatively analyze the gloss of the glaze. The glossmeter (Photovolt “G-3” Gloss, ASTM 2457, UMM Electronics Inc., Indianapolis, IN) was used to measure gloss. The glossmeter measures the specular reflection of a light source off the surface of the glaze (Figure 3.3).
In order to obtain a clear differentiation over the complete measurement range from high gloss to matte surface, three different geometry’s (20°, 60°, and 85° angle) can be used.
For the purpose of these experiments the 60° angle is the suggested geometry because this angle allows for more accurate quantification of a wider range of surfaces (from matte to gloss). The glossmeter reports numbers in gloss units (GU) where the typical gloss surface ranged from 94 to 70 GU, the semi-gloss surface ranged from 70 to 20 GU,
and the matte surfaces ranged from 20 GU and below.♥ Gloss units are related to the amount of reflected light from a black glass standard with a defined refractive index (1.567), and not to the amount of incident light. The measurement value for this defined standard is equal to 100 GU (calibration). Materials with higher refractive index can have a value above 100 gloss units, but is not the case for this research. Commercial glazes were also measured with the glossmeter to verify the stated ranges (commercial glazes ranged from 94 to 87 GU).
Diffuse
Specular
Incident Light Detector
Figure 3.3. Schematic diagram of the glossmeter and the measurement of specular reflection off the surface of the glaze. The incident light is at an incident angle of 60° for this experiment.
3.2.2.2 X-Ray Diffraction
XRD was used to detect the crystallizing species between the alumina mattes and the silica mattes. Sample preparation consisted of grinding fired bulk glaze samples with a motorized mortar and pestle made of sintered alumina (Retsch Mortar Mill type RM100, Retsch GmbH & Co. KG, Rheinische Str. 36, Haan, Germany). Samples were ground down below 10 µm in 30-minute time intervals. Once sample preparation was complete it was measured using the XRD (Siemens Goniometer, CuKα radiation, Alfred University, Alfred, NY). The parameters used were: 2θ range: 15-60°, Step size: 0.03°,
♥ Ranges defined by UMM Electronics Inc. for the ASTM 2457 (Indianapolis, IN).
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.