Plot the change in absorbance of the 3500-3600 cm-1 band against the reduction time and the length of the sample for various concentrations. Plot the change in absorbance of the 3500 cm-1 band against the reduction time and the length of the sample for SLS glasses containing 0.9 Ni.
INTRODUCTION
LITERATURE REVIEW
- Introduction
- Hydrogen Diffusion
- Hydrogen Reaction
- Nucleation and Growth Theory
- Redox Equilibria in Glasses
- Instrumentation Background
- Spectroscopy
- Optical Spectroscopy
- IR Spectroscopy
- GIXRD
They attribute these differences to the fact that these measurements are related to the sizes of the clusters formed. The free energy of the system increases when small nuclei are introduced due to the surface energy term dominating.
EXPERIMENTAL PROCEDURE
- Melting/Annealing
- Cutting/Polishing
- Hydrogen Reduction
- Spectroscopy
- X-Ray Diffraction
The sample was placed in a smaller silica tube to maintain the integrity of the outer silica ampoule. A roughing pump was used to evacuate the system, and the tube furnace was centered over the sample in the silica ampoule.
SODIUM INDIUM SILICATES
Introduction
Experimental
Results
- Microscopy
- Spectroscopy
Clusters again appear to be larger at greater distances from the sample surface. The depleted zone is very similar to the sample treated at 670°C; however, this sample exhibits widening of the depletion zone. The darkest contrast points are much larger for the sample treated at 720°C than for any of the other treatment temperatures.
Representative EDS spectra of the relative indium concentration for the surfaces of the samples treated at different temperatures. The metallic clusters appear to exist only on the actual surface of the sample treated at 770C. The clusters found on the surface of the sample treated at 770C are not as spherical as seen for the other samples.
These three bands are typically attributed to hydroxyl (-OH) in the structure of the glass. Some of the spectra show a decrease in intensity near the IR edge around 2500 cm-1. Representative plot of the visible absorbance changes during reduction for the sample containing 10 mol% In2O3 and 15 mol% Na2O.
Representative plot of the visible absorbance changes during reduction for the sample containing 10 mol% In2O3 and 20 mol% Na2O.
Discussion
- Reaction
- Nucleation and Growth
This concept is possibly confirmed by the light and dark phases indicated in the BSE SEM micrographs of the glass surfaces. This scratch can be powerful enough to dislodge any indium particles exposed to the surface of the glass and will explain the pits. Comparison of the spectra of the indium-containing glasses with the alumina-containing glasses shows clear similarities and differences.
The intensity ratios of the bands in the base glass all increased after reduction at 500°C. It should be noted that the difference spectra always appear to mimic those of the base glass. This is believed to be due to the difficulty of background correction and to the reverse reaction of dehydroxylation discussed earlier.
The SEM data shows the existence of larger metal particles deeper beneath the glass surface. It is also clear that the viscosity of the glass has a major influence on the size and shape of the clusters.
THE REDUCTION OF 2+ IONS IN SODA LIME SILICA GLASSES
Introduction
Results
Plot of the change in absorbance of the 3500 cm-1 band against the reduction time and the length of the sample for SLS glasses containing different 2+ metal ions at 550°C for IR spectra. In all glasses, an increase in the change in absorbance of the 3500 cm-1 band with increasing treatment temperature was observed. Plot of the change in absorbance of the 3500 cm-1 band against the reduction time and the length of the sample for SLS glasses containing different 2+ metal ions at 600°C for IR spectra.
There is then an initial increase and a very small increase in the absorption of the 3500 cm-1 band. Plot of the change in absorbance of the 3500 cm-1 band against reduction time and sample length for SLS glasses containing nickel ions for different temperatures. Plot of the change in absorbance of the 3500 cm-1 band against reduction time and sample length for SLS glasses containing cobalt ions for different temperatures.
The leaded glass has no related absorptions in the visible region of the spectrum. The particle size of the lead particles dispersed in the glass matrix also increases with the treatment temperature.
Discussion
- Reaction
- Nucleation/Growth
This means that the reaction rate is so fast that the moving boundary is completely controlled by gas diffusion. It is clear that the slow measured reactions for nickel and cobalt probably contribute to the skewed relationship between the increase in "free" absorbance. The nickel and cobalt data appear to become linear at higher temperatures, indicating that the reaction rates are approaching a sufficiently high rate for the dimming model being used.
This is consistent with literature that as temperature increases, there is at some point a transition to a diffusion-controlled boundary growth instead of the reaction-controlled growth seen at lower temperatures.7 This makes sense since the permeability must be the same for all the samples and the permeability is directly related to the slope of the data in the plots. It is also possible that the reaction rate still slows down the formation of hydroxyl, which can also lower the calculated permeability. The reduction is believed to produce atoms that agglomerate and then grow metal clusters.
It is also the case that the reaction rate is faster for the copper-containing glass. It is reasonable to assume that the particle sizes are less than 30 nm for the first few hours of treatment.
THE FORMATION OF NI-CU ALLOYS IN GLASSES THROUGH
Introduction
Results
The two lines are too close together within the error of the measurement and the apparent scatter for the data points of the sample containing 0.9 Ni/0.1 Cu (mol%) to make any more concrete statements. Plot of the change in absorbance of the 3500 cm-1 band against reduction time and sample length for SLS glasses treated with 0.9 Ni/0.1 Cu (mol%) at different temperatures. Plot of the change in absorbance of the 3500 cm-1 band against reduction time and sample length for SLS glasses treated with 0.5 Ni/0.5 Cu (mol%) at different temperatures.
Plot of change in absorbance of the 3500 cm-1 band versus reduction time and sample length for SLS glasses containing 0.1 Ni/0.9 Cu (mol%) processed at different temperatures. The calculated data do not agree well in the lower wavelength regions of the spectrum. The calculated data agree well even in the lowest wavelength regions of the collected spectra.
The composition of all measured particles appears to increase in nickel content with an increase in the nickel content of the base glass except for the samples containing 0.1 Ni/0.9 Cu (mol%) for all processing temperatures. All the estimated particle sizes increase with increasing treatment temperature except for the sample containing 0.5 Ni/0.5 Cu and treated at 550 and 600°C.
Discussion
The changes in absorbance of pure nickel-containing glass show a curved relationship with the square root of time and this is believed to be due to the slow reaction rate of nickel spreading the diffusion limit. Again this could be due to the discussion from the previous section regarding the Gibb's free energy of oxide formation. These calculations assume that individual nickel and copper particles are present in the matrix and that the sum of their absorptions contributes to the measured spectra.
Optical data were not found for the alloy system, so it could not be modeled in the same way, but due to the inability to accurately reproduce the measured spectra of the other two mixtures, this appears to be a reasonable possibility. . This complicates these findings, but as the data show, the displacement due to each strain is small compared to the measured displacement in the opposite direction. It is possible that initially the particles were formed separately, or even stacked on top of each other, due to the speed aspect of the reduction reaction (Figure 67).
The reaction rate would indicate that nickel reduces after copper, and this would mean that nickel forms separate particles or forms on copper particles, effectively minimizing absorptions due to the copper particles. The copper particles would form first, and at greater depths than the nickel particles due to the.
CONCLUSIONS
This is difficult for the measurements made in this study, as higher temperatures remove reaction rate issues, but higher temperatures also increase the likelihood of water diffusing and reacting out of the glass. The indium silicate glasses also showed the most variable hydroxyl formation data of any of the glasses studied and it is suggested that this is a direct result of the saturation limits that may be exceeded. Indium, being the durable component of the sodium indium silicates, makes a very stable glass system.
The reaction rate of the reduction process is not important as long as the reduced atoms have sufficiently high diffusion coefficients at the processing temperatures that the composition of the alloy particle approaches some sort of equilibrium. This equilibrium may take a long time to reach, since equilibrium is clearly not reached in these data, but the particle compositions should be similar to the base compositions. It is thought that the indium-containing glasses, with a very fluid surface layer of sodium silicate, allowed the formation of much larger particles than would be present in a more viscous material.
This fits well with nucleation and growth theory in terms of the activation energy for viscous flow which is clearly important. This contraction, if the particle is bound, should result in a uniform lattice strain as observed in the collected GIXRD data.
FUTURE WORK
James, "Influence of Water Content on the Rate of Crystal Nucleation and Growth in Lithia-Silica and Soda- Lime-Silica Glasses," J. Rawson, "The Calculation of Transmission Curves of Glass Stained by Copper and Silver Compounds," Phys. Riu, "Infrarød spektroskopisk analyse af vand indarbejdet i strukturen af industrielle soda-kalk-silicaglas," Glastech.
Kluyev, "Properties of phase-separated soda-silica glasses as a means of studying their structure," Disc. This led to the development of an oblique background extraction technique based on the initial linear part of the spectra from 4100-3800 cm-. It became apparent during this procedure that a curvature develops in much of the data.
After subtracting the background, it is clear that there is a difference between the two (Figure 69). As the degree of curvature of the background increases, the difference of the lower wavenumber regions also increases.
