- •Preface to the Second Edition
- •Preface to the First Edition
- •ACKNOWLEDGEMENTS
- •Contents
- •1.1 EXERCISES, QUESTIONS, AND PROBLEMS
- •2.1 INTRODUCTION
- •2.2 CORROSION BY LIQUIDS
- •2.2.1 Introduction
- •2.2.2 Crystalline Materials
- •Attack by Molten Glasses
- •Attack by Molten Salts
- •Electrochemical Corrosion
- •Attack by Molten Metals
- •Attack by Aqueous Media
- •2.2.3 Glasses
- •Bulk Glasses
- •Fiber Glass
- •Bioactive Glass
- •2.3 CORROSION BY GAS
- •2.3.1 Crystalline Materials
- •2.3.2 Vacuum
- •2.3.3 Glasses
- •2.4 CORROSION BY SOLID
- •2.5 SURFACE EFFECTS
- •2.5.1 Surface Charge
- •2.5.2 Porosity and Surface Area
- •2.5.3 Surface Energy
- •2.6 ACID/BASE EFFECTS
- •2.7 THERMODYNAMICS
- •2.7.1 Mathematical Representation
- •2.7.2 Graphical Representation
- •2.8 KINETICS
- •2.9 DIFFUSION
- •2.10 SUMMARY OF IMPORTANT CONCEPTS
- •2.11 ADDITIONAL RELATED READING
- •2.12 EXERCISES, QUESTIONS, AND PROBLEMS
- •REFERENCES
- •3.1 INTRODUCTION
- •3.2 LABORATORY TEST VS. FIELD TRIALS
- •3.3 SAMPLE SELECTION AND PREPARATION
- •3.4 SELECTION OF TEST CONDITIONS
- •3.5 CHARACTERIZATION METHODS
- •3.5.1 Microstructure and Phase Analysis
- •Visual Observation
- •Optical Microscopy
- •X-ray Diffractometry
- •Transmission Electron Microscopy
- •3.5.2 Chemical Analysis
- •Bulk Analysis
- •Surface Analysis
- •3.5.3 Physical Property Measurement
- •Gravimetry and Density
- •Porosity-Surface Area
- •Mechanical Property Tests
- •3.6 DATA REDUCTION
- •3.7 ADDITIONAL RELATED READING
- •3.8 EXERCISES, QUESTIONS, AND PROBLEMS
- •REFERENCES
- •4.1 INTRODUCTION
- •4.2 ASTM STANDARDS
- •4.2.16 Permeability of Refractories, C-577
- •4.2.26 Lead and Cadmium Extracted from Glazed Ceramic Surfaces, C-738
- •4.3 NONSTANDARD TESTS
- •4.4 ADDITIONAL RELATED READING
- •4.5 EXERCISES, QUESTIONS, AND PROBLEMS
- •REFERENCES
- •5.1 ATTACK BY LIQUIDS
- •5.1.1 Attack by Glasses
- •Alumina-Containing Materials
- •Zircon
- •Zirconia
- •Carbides and Nitrides
- •5.1.2 Attack by Aqueous Solutions
- •Alumina
- •Silica and Silicates
- •Concrete, Cement, Limestone, Marble, and Clay
- •Zirconia-Containing Materials
- •Superconductors
- •Titanates and Titania
- •Transition Metal Oxides
- •Carbides and Nitrides
- •5.1.3 Attack by Molten Salts
- •Oxides
- •Carbides and Nitrides
- •Superconductors
- •5.1.4 Attack by Molten Metals
- •5.2 ATTACK BY GASES
- •5.2.1 Oxides
- •Alumina
- •Alumino-Silicatcs
- •Magnesia-Containing Materials
- •Zirconia
- •5.2.2 Nitrides and Carbides
- •Silicon Nitride
- •Other Nitrides
- •Silicon Carbide
- •Other Carbides
- •5.2.3 Borides
- •5.2.4 Silicides
- •5.2.5 Superconductors
- •5.3 ATTACK BY SOLIDS
- •5.3.1 Silica
- •5.3.2 Magnesia
- •5.3.3 Superconductors
- •5.3.4 Attack by Metals
- •5.4 ADDITIONAL RELATED READING
- •5.5 EXERCISES, QUESTIONS, AND PROBLEMS
- •REFERENCES
- •6.1 INTRODUCTION
- •6.2 SILICATE GLASSES
- •6.3 BOROSILICATE GLASSES
- •6.4 LEAD-CONTAINING GLASSES
- •6.5 PHOSPHORUS-CONTAINING GLASSES
- •6.6 FLUORIDE GLASSES
- •6.7 CHALCOGENIDE-HALIDE GLASSES
- •6.8 ADDITIONAL RELATED READING
- •6.9 EXERCISES, QUESTIONS, AND PROBLEMS
- •REFERENCES
- •7.1 INTRODUCTION
- •7.2 REINFORCEMENT
- •7.2.1 Fibers
- •7.2.2 Fiber Coatings or Interphases
- •7.2.3 Particulates
- •7.3 CERAMIC MATRIX COMPOSITES
- •7.3.1 Oxide-Matrix Composites
- •Al2O3-Matrix Composites
- •Other Oxide-Matrix Composites
- •7.3.2 Nonoxide-Matrix Composites
- •Si3N4 Matrix Composites
- •SiC-Matrix Composites
- •Carbon-Carbon Composites
- •Other Nonoxide Matrix Composites
- •7.4 METAL MATRIX COMPOSITES
- •7.5 POLYMER MATRIX COMPOSITES
- •7.6 ADDITIONAL RELATED READINGS
- •7.7 EXERCISES, QUESTIONS, AND PROBLEMS
- •REFERENCES
- •8.1 INTRODUCTION
- •8.2 MECHANISMS
- •8.2.1 Crystalline Materials
- •8.2.2 Glassy Materials
- •8.3 DEGRADATION OF SPECIFIC MATERIALS
- •8.3.1 Degradation by Oxidation
- •Carbides and Nitrides
- •Oxynitrides
- •8.3.2 Degradation by Moisture
- •8.3.3 Degradation by Other Atmospheres
- •Carbides and Nitrides
- •Zirconia-Containing Materials
- •8.3.4 Degradation by Molten Salts
- •Carbides and Nitrides
- •Zirconia-Containing Materials
- •8.3.5 Degradation by Molten Metals
- •8.3.6 Degradation by Aqueous Solutions
- •Bioactive Materials
- •Nitrides
- •Glassy Materials
- •8.4 ADDITIONAL RELATED READING
- •8.5 EXERCISES, QUESTIONS, AND PROBLEMS
- •REFERENCES
- •9.1 INTRODUCTION
- •9.2 CRYSTALLINE MATERIALS—OXIDES
- •9.2.1 Property Optimization
- •9.2.2 External Methods of Improvement
- •9.3 CRYSTALLINE MATERIALS—NONOXIDES
- •9.3.1 Property Improvement
- •9.3.2 External Methods of Improvement
- •9.4 GLASSY MATERIALS
- •9.4.1 Property Optimization
- •9.4.2 External Methods of Improvement
- •REFERENCES
- •Glossary
- •Epilog
Methods to Minimize Corrosion |
385 |
9.4 GLASSY MATERIALS
9.4.1 Property Optimization
The development of more resistant glasses has been predominantly through optimization of compositions. Historically, small amounts of alumina have been added to the basic soda-lime-silicate composition to improve durability. In general, lowering the alkali content increases the durability. This, however, has practical limits based upon melting temperatures, viscosities, softening points, and working ranges. Borosilicate glasses are, in general, more resistant than soda-lime silicate glasses. In general, silicate glasses are less resistant to alkali solutions than they are to acid solutions. Table 6.1 of Chap. 6 lists the corrosion resistance of many glasses of varying compositions.
One technique of composition variation to improve durability that has not received much attention is that of incorporation of nitrogen into the glass structure. Frischat and Sebastian [9.13] have shown that soda-lime-silica glasses containing 1.1 wt.% nitrogen exhibited considerable improvement toward leaching by water at 60°C over compositions containing no nitrogen. This improvement was attributed to a denser structure for the nitrogen-containing glass.
Small changes in the chemistry of the glass can cause a significant change in the dissolution mechanism as shown by Lehman and Greenhut [9.14]. They reported that 1 mol% P2O5 addition to a lead silicate glass caused the formation of lead phosphosilicate crystals on the glass surface when exposed to 1% acetic acid at 22°C. They attributed the reduction in dissolution to the reduction of the apparent average interdiffusion coefficient of lead by a factor of 11.3. This is an example of changing the material chemistry to form an interface reaction product that reduces the diffusion rate of the species being leached.
9.4.2 External Methods of Improvement
The development of coating technology has provided a means to improve corrosion resistance, abrasion resistance, and
Copyright © 2004 by Marcel Dekker, Inc.
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Chapter 9 |
strength. Combinations of coatings applied while the glass is hot and after it has cooled have been developed that form a permanent bond to the glass. These coatings are not removed by cooking or washing.
The most commonly used metallic hot-end coatings are tin and titanium. As the piece goes through the annealing lehr, the metal oxidizes, forming a highly protective ceramic coating. Tin is easier to work with since a thicker coating can be applied before problems of iridescence occur. These hot-end metallic coatings give the glass a high glass-to-glass sliding friction and thus a cold-end coating must be applied over these metallic coatings. The cold-end coatings usually have a polyethylene or fatty acid base.
Another type of coating is one that reacts with the surface of the glass to form a surface layer that is more corrosionresistant than the bulk composition. Chemically inert containers are needed to contain various beverages and pharmaceuticals. To provide increased corrosion resistance, these containers are coated internally to tie up the leachable components. Internal treatment with a fluoride gas provides a new surface that is more corrosion-resistant than the original and is more economical than the older sulfur treatment.
Although not a true coating technique, the manufacturers of flat glass have, for many years, treated the surface of their glass with SO2 gas just prior to the glass being annealed to increase the weatherability of their products. This surface treatment allows the sodium in the surface layers to react with the SO2 forming sodium sulfate. The sulfate deposit that forms on the surface due to this reaction is then washed off prior to inspection and packing. The first step in weathering is then diminished due to the low alkali content of the surface.
It has been shown by Harvey and Litke [9.15] that matrix dissolution of an aluminosilicate glass apparently does not occur if the leaching solution is saturated first with solution products of the same glass composition. This technique is an example of how dissolution can be minimized by decreasing the driving force for corrosion by lowering the concentration
Copyright © 2004 by Marcel Dekker, Inc.