Elisa B. 2002

TABLE OF CONTENTS Abstract Purpose Hypothesis Experiment Design Materials Procedures Research Report Results Graphs and Data Tables Conclusion Bibliography Acknowledgments     Left: This was the 1st Place winner at the  Mid-Columbia Regional Science Fair!

 I hypothesized that the most effective additive to lower the required vitrification temperature would be lead carbonate. The resulting glass would corrode (leak the least simulated contaminant) the least.

 In this experiment, additives were introduced into a waste-glass simulant. There were five variable additive glasses and one control glass.

The responding variable was the amount of sodium that was leached out of the glass into surrounding deionized water, determined using the Atomic Absorption method.

The constants were the number of trials per additive, preparation, storing and testing environments and procedures.

To increase validity, the experiment included 3 trials per sample glass, and 6 additive glasses. Using six additives would hopefully create a varied spectrum of effects in the glass. These six additives included:

 Because of the results of this experiment, I decided to reject my hypothesis on the grounds that the additive lead carbonate was not actually most effective at lowering the vitrification temperature or reducing corrosion.  Feldspar was actually the additive which best prevented glass corrosion. These findings are however useful. Now researchers will know which additives to investigate further and which not to try at all.
 

I became interested in solving this problem because of the current crisis at the Hanford Nuclear Reservation. The goal of the Hanford Vitrification Project is to clear up wastes from decades of plutonium production for national defense. Hanford's 177 underground tanks contain approximately 53 million gallons of radioactive and chemical wastes, and are beginning to leak, and in turn, to contaminate the environment. The waste will be retrieved from the aging tanks and incorporated into a stable glass form in large melters in the vitrification plant.

The information gained from the results of this experiment could aid scientists working on this vitrification project in several places throughout the world. It could possibly provide new information to help future generations control radioactive waste contamination.

I base this hypothesis on my previous experiment, which showed that lead carbonate was an effective ceramic flux (reduced final maturing temperature). Also, lead carbonate greatly reduced porosity in a clay body, which would seem to lead to less contamination of the environment.
 

1. Custer Feldspar
2. Gerstley Borate
3. Magnesium Carbonate
4. Zinc Oxide
5. Lead Carbonate

To test the tendency of the glass to corrode, each sample was crushed.  Three portions of each sample were then placed in de-ionized water to track corrosion or leaching of contaminants into the water.

One responding variable in this experiment was the amount of contamination of the deionized water in which the simulated waste-glass particles were immersed. This figure was determined by using the atomic absorption method to measure the amount of residual sodium (the simulant radioactive/hazardous material in the deionized water formed by corrosion of glass) after soaking for 24 hours, three, seven, and 21 days, at a temperature of 99°Celsius.

A secondary responding variable was the resulting pH of each deionized water sample after being exposed to each particle sample.

Preparation and testing conditions that were controlled for each group included:

• All glasses were derived from the same basic batch
• Percentages of additive oxides
• Melting procedures
• Number of trials (samples)
• Soaking periods for both tests
• Temperature at which test samples were maintained throughout the 21 days
• Ratio of Water volume to total particle surface area per sample at 7.5 cm-1
• Method of removing samples of water exposed to glasses.
• Atomic Absorption and pH testing methods

---

Materials

SECTION A) CREATING BASE BATCH MIXTURE
  (Will also be the control glass)

1. Gather all materials.
2. Calculate percentages and weights of all simulated waste materials and additives required in glass composition
3. Put on all protective gear (lab coat, glasses, gloves)
4. Set up scale, measuring instruments, and containers.
5. Prepare measuring station by covering all surfaces with paper towels, protecting against harmful substances.
6. Set one plastic measuring boat on scale and tare (scale will read 0.000)
7. Add the following ingredients to create the base batch:

8. Remove mix from scale and pour into beaker, transport to chemical hood.
9. Pour dry batch into agate mill, which will further mix the glass making oxides into a homogeneous mixture.
10. With ethanol, clean agate mill, all devices and measuring utensils.

SECTION B) MIXING THE FLUXING ADDITIVES INTO SIMULATED WASTE BATCH:

1. Calculate total weights of additives required to mix with 90 grams of base batch.
2. Put on protective gear (eyewear, gloves) and prepare measuring station by covering all surfaces with paper towels, shielding against harmful substances.
3. Label six large plastic containers with additive names.
4. Divide base mixture into six 90gram groups, each into separate, labeled containers.
5. Use the table to determine the amount of additive to use:

6. Remove “boat” containing desired additive from scale and pour into container, which already contains 90 grams of the base mixture.
7. Seal container.
8. Clean measuring utensils every time and follow procedures 5, 6, and 7; repeating with subsequent additives (using appropriate mass shown in table) and new containers.
9. Leave one container of only the control (base batch) mixture, which will contain no extra flux additive.
10. Grind singular mixtures in the agate mill 2 minutes to create a more homogeneous mix.

SECTION C) MELTING AND POURING THE SIMULATED WASTE-GLASSES
1. Under a fume hood, scoop half of milled homogeneous mix into a fused silica crucible (use only half at first to avoid bubbling and foaming of mixture as it begins to melt).
Stop: Ask a trained advisor to handle the furnace because of extreme heat conditions. Do not touch the crucible at any time with your hands until WELL after the molten glass has been poured, and cooled sufficiently.
2. Place crucible in furnace and raise door.
3. Set furnace at 1200°C to initiate heating process.
4. After 10 minutes, open door, check crucible and add other half of mixture.
5. If melting process has not adequately begun, raise temperature.
6. Allow mixture to melt for approximately 45 minutes.
7. Using tongs, remove crucible from furnace and set on a block of alumina. Alumina quickly absorbs a portion of the original heat to avoid melting any surrounding objects. Avoid looking directly at objects immediately after coming out of furnace, to prevent eye injury from ultraviolet rays
8. Pick up the crucible with the tongs and pour molten glass onto a sheet of steel. Steel will disperse the heat away from the molten glass, so it can cool efficiently.
9. After glass has had sufficient cooling time (no more red “spots” are observed), use flat metal spatula, to create stress points that will cause glass to crack safely.

SECTION D) CRUSHING THE GLASS
Repeat the following procedures, separately for each of the additive glasses.
1. Using the Tungsten Carbide mill for 5 seconds, crush glass into particles.
2. Stack 20 mesh on top of 40 mesh sieve pour glass particles onto 20 mesh screen and cover.
3. Shake sieves approximately 6 minutes to ensure all particles have filtered.
4. Separate sieves and collect particles resting on 40-mesh into a plastic container.
5. Ascertain that mass of particles alone is above twelve grams.
6. Clean mill using ethanol.
7. Using coarse-wire brush, clear meshes of any particles.

SECTION E) CLEANING AND PREPARATION FOR TESTING GLASS
1. Pour particle groups (separated by additive) into beakers. Cleaning will remove ‘fines’ allowing a more accurate measurement of particle surface area.
2. Into each beaker, spray deionized water in a swift, circular motion, applying agitating pressure, to approximately twice the volume of the particles.
3. Place all beakers in the sonic cleaner for a two-minute cycle.
4. After cleaning cycle ends, wait five seconds to allow particles to settle.
5. Decant to remove fines suspended at surface.
6. Once more, follow steps 2 through 5 with deionized water.
7. Repeat procedures 2 through 5 substituting ethanol for deionized water.
8. After cleaning is complete, cover beakers with watch glasses.
9. Place beakers in a drying oven for 1 hour at approximately 90° C.
10. Separate general additive groups into 4-gram sub-groups.
11. Place each new sub-group into a labeled, Teflon® containers.
12. Suggested Labeling: test day, additive, replicate number. (example- D1, Control 2)
13. Based on density of particles, add appropriate amount of deionized water to form a ratio of particle surface area vs volume of water equaling 7.5 cm-1.
14. Place in an oven at approximately 99°Celsius to accelerate corrosion rates in glass.

SECTION F) TESTING THE GLASS
After 24 hours, three days, seven days, and 21 days, remove samples from 99°C oven and test in the following manner:

 -atomic absorption testing-
1. Prepare a lanthanum chloride solution: add 2.7g LaCl + 1 mL of Citric acid per liter.
2. Pipet 5 mL sample water from each glass sample and put into labeled collection vial (to be tested).
3. Return 5 mL deionized water to glass particle sample.
4. Immediately return all Teflon® containers (holding glass samples) to oven, to maintain a temperature of 99°C.
5. From each test vial, pipet one-tenth milliliter of sample water and add to 9.9 milliliters of Lanthanum Chloride solution, per sample (into test tubes) for a 1/100 dilution, etc.
6. Create a 10 ppm Na standard consisting of 1mL sodium solution (at 1000 µg per mL)+ 99 mL Lanthanum Chloride.
7. Swirl each of the 19 test tubes.
8. Check parameters and calibrate Atomic Absorption apparatus to test for sodium content.
9. Run tests by placing aspirator tube of apparatus into each test tube in successive order.
10. Allow system to take reading before continuing with the next tube.
11. If readings error or are above maximum absorbance (1.2), re-dilute sample to a 1/1000 dilution.

-pH testing-
1. Calibrate pH meter using pH 4 and pH 7 buffers.
2. Test pH of each sample on pH meter.
3. Record measurement readings.
 
 

The base batch used in this experiment was designed to reflect the contents of a typical C-104 tank at the Hanford site.

Twenty-eight of the underground tanks are newer double-shell tanks that can hold over one million gallons of waste, and the remaining 149 are older single-shell tanks ranging in size from 500,000 to one- million gallons in storage capacity. The waste will be retrieved from the aging tanks and incorporated into a stable glass form in large melters in the vitrification plant. Construction of the vitrification plant on Hanford's Central Plateau is scheduled to begin in 2002, and operations will take place in 2007.
 

GLASS
Glass is an amorphous substance made primarily of silica fused at high temperatures with borates or phosphates. Glass is also found in nature, as the volcanic material obsidian and as the enigmatic objects known as tektites (see Tektite). It is neither a solid nor a liquid but exists in a vitreous, or glassy, state in which molecular units have disordered arrangement but sufficient cohesion to produce mechanical rigidity. Glass is cooled to a rigid state without the occurrence of crystallization; heat can reconvert glass to a liquid form. Usually transparent, glass can also be translucent or opaque. Color varies with the ingredients of the batch.

Process of Glassmaking
The processes of glassmaking have remained essentially the same since ancient times. After careful preparation and measurement, raw materials are mixed and undergo initial fusion before being subjected to the full heat needed for vitrification. The materials are fused at high temperatures in seasoned fireclay containers, boiled down, skimmed, and cooled several hundred degrees; and cooled.

In the past, melting was done in clay pots heated in wood- or coal- burning furnaces. Pots of fireclay, holding from 0.5 to 1.5 metric tons of glass, are still used when relatively small amounts of glass are needed for handworking. In modern glass plants, most glass is melted in large tank furnaces, first introduced in 1872, that can hold more than 1000 metric tons of glass and are heated by gas, oil, or electricity. The glass batch is fed continuously into an opening (doghouse) at one end of the tank, and the melted, refined, and conditioned glass is drawn out the other end. In long holding chambers, the molten glass is brought to the correct working temperature, and the vitreous mass is then delivered to the forming machines.

Molten glass is plastic and can be shaped by means of several techniques. When cold, glass can be carved. At low temperatures glass is brittle and breaks with a shell-like fracture on the broken face. Such natural materials as obsidian and tektites (from meteors) have compositions and properties similar to those of synthetic glass.

History of Glass
Glass was first made before 2000 B.C. and has since served humans in many ways. It has been used to make useful vessels as well as decorative and ornamental objects, including jewelry. Glass also has architectural and industrial applications.

 Composition and Properties
The basic ingredient of glass compositions is silica, derived from sand, flint, or quartz. As glass is composed mainly of fused silica, it is generally impermeable. Because silicate glass has a high melting point and does not shrink or expand greatly with changing temperatures, it is suitable for laboratory apparatus and for such objects subject to heat shock as telescope mirrors. Glass is a poor conductor of both heat and electricity and therefore useful for electrical and thermal insulation.

Physical Properties of Glass
Depending on the composition, some glass will melt at temperatures as low as 500° C (900° F); others melt only at 1650° C (3180° F). Tensile strength, normally between 280 and 560 kg per sq cm (4000 and 8000 lb per sq in), can exceed 7000 kg per sq cm (100,000 lb per sq in) if the glass is specially treated. Specific gravity ranges from 2 to 8, or from less than that of aluminum to more than that of steel. Similarly wide variations occur in optical and electrical properties.

Glass Ceramics
Glass containing certain metals will form a localized crystallization when exposed to ultraviolet radiation. If heated to high temperatures, the glass will convert to crystalline ceramics with mechanical strength and electrical insulating properties greater than that of ordinary glass. Such ceramics are now made for such uses as cookware, rocket nosecones, and space-shuttle tiles. Other metallic glasses—including alloys of pure metals—can be magnetized, are strong and flexible, and prove very useful in high-efficiency electrical transformers.

A Quartz Inversion is the phenomenon that occurs as a ceramic glaze or glass body is melted. The crystalline structure of silica (quartz) changes during the firing of a ceramic body. At 573°C, quartz crystals evolve from Alpha to Beta, and silica bonds with oxygen, causing expansion.  By 1010°C, tough crystals composed of silica and alumina interlock, giving the body its strength.

ADDITIVES
For most glass, silica is combined with other raw materials in various proportions. The following substances were used because of their known ceramic uses and flux properties.

Zinc Oxide, chemical compound, ZnO, is nearly insoluble in water but soluble in acids or alkalis. It occurs as white hexagonal crystals or a white powder commonly known as zinc white. Crystalline zinc oxide exhibits the piezoelectric effect, is luminescent, and is light sensitive. Zinc oxide occurs in nature as the mineral zincite.

Magnesium oxide (MgO), or magnesia, is prepared by burning magnesium in oxygen or by heating magnesium carbonate and often used as a heat-refractory and insulating material. In the form of limestone or dolomite, magnesium carbonate will act as a stabilizer for the batch.
The fine-quality table glass known as crystal is made from potassium-silicate formulas that include lead oxide. Lead glass is heavy and has an enhanced capacity to refract light, which makes it suitable for lenses and prisms, as well as for imitation jewels. Because lead absorbs high-energy radiation, lead glasses are used in shields to protect personnel in nuclear installations.

Borosilicate glass contains borax as a major ingredient, along with silica and alkali. Noted for its durability and resistance to chemical attack and high temperatures, borosilicate glass is widely employed for cooking utensils, laboratory glassware, and chemical process equipment. Borax (used in the form of Gerstley Borate for this study) is often introduced to a glass batch for thermal and electrical resistance.
 

Feldspar is a large group of minerals composed of aluminosilicates of potassium, sodium, calcium, or occasionally barium. They occur as single crystals or as masses of crystals and form an important constituent of many igneous and metamorphic rocks. Feldspars are the most abundant of all minerals and account for nearly half of the volume of the earth's crust. Used extensively in the pottery industry, Feldspars are a useful ceramic flux and coloring agent. Although the feldspar minerals may belong to either the monoclinic or triclinic systems, they nevertheless resemble each other in crystal habit, methods of twining, and especially by having cleavage surfaces inclined to each other at an angle of nearly 90°. All the feldspars weather readily to form a type of clay known as kaolin. Orthoclase, monoclinic feldspar with the formula KAlSi3O8, is one of the most common of all minerals. It is often white, gray, or flesh-red in color and sometimes occurs as colorless crystals. Orthoclase is used extensively in the manufacture of porcelain and glass.

 ATOMIC ABSORPTION SPECTROPHOTOMETRY
Flame converts metal ions into atoms. For example, when a sodium chloride solution is placed in a flame, the solvent evaporates, leaving behind solid crystalline sodium chloride. This evaporation is then followed by the dissociation for the sodium chloride crystals into individual ground state atoms. This process is termed atomization.

In the atomic absorption apparatus, a flame is produced to give a reasonably long pathlength for detecting small concentrations of sodium atoms in the flame. Most of the atoms at this point are left in the ground (stable) state, and few are excited. If a light beam is produced, it will take advantage of the stable concentrations and the atoms in the flame will reach a more excited state. A hollow cathode tube serves as a light source, emitting the exact wavelength required for analysis. The light is directed at the flame containing the sample, which is continuously fed into the flame aspirated through a SMALL TUBE.  Then, the light beam enters the monochromator that is tuned to a wavelength that is absorbed by the sample. A detector measures the light intensity, which is then output to the readout.
 

ATOMIC ABSORPTION TESTS
 Atomic Absorption was used to test sodium content in the glass soak water. Samples of the soak water were tested from days zero, one, three, seven and 21. The only additive that truly slowed corrosion of the glass was Feldspar. Especially after 21 days the feldspar glass was leaching much less sodium into the soak water than was the control glass. The control glass itself had low sodium release values. Lead Carbonate, when added to the simulated waste glass provided more of an opportunity for sodium, the waste simulant, to leak out than did the Control glass. When Zinc Oxide was the employed additive, the results were similar to lead carbonate, but to slightly greater effect after 21 days. Worst additives utilized were Gerstley Borate, a popular pottery flux ingredient, and Magnesium Carbonate. By day 21, sodium levels in the water samples from Gerstley Borate and Magnesium Carbonate were 179.973µ per mL and 466.653µ per mL respectively. In contrast, sodium levels in the control were 68.963 µ per mL after 21 days, making sodium concentration levels of water samples of magnesium carbonate nearly 7 times as strong.

 PH TESTS
 pH tests gave results that showed each soak water sample increasing in pH and becoming more basic over the span of 21 days.  After 21 days of soaking, the magnesium carbonate water was most basic, at a pH over 11. Also, on day 21, the least basic soak water was feldspar with a pH near 9.5.

Originally, I hypothesized that the most effective additive to lower the required vitrification temperature would be lead carbonate. The resulting glass would leak the least simulated contaminant, sodium.

Because of the results of this experiment, I have decided to reject my hypothesis on the grounds that the additive lead carbonate was not actually most effective.  It turned out that the lead glass and the control glass had very similar sodium leakage values throughout the tests. In this case, it would not be beneficial to add lead carbonate.

After seeing the results of the experiment, I wonder why lead carbonate did not affect the glass the way I predicted.  Is there truly a relationship between ceramic vitrification temperature and a contamination barrier? Does porosity include absorption and leakage? In my previous experiment with clay, the lead carbonate lowered the maturing temperature and hastened the vitrification process, causing it to absorb less water. In contrast, the lead GLASS leached slightly more sodium than the control glass. Why then, did lead carbonate not have similar effects in the glass, as it did in clay, making the lead additive glass leach less sodium?

Lead and Magnesium values were originally switched accidentally when testing on the Atomic Absorption apparatus. I re- tested them, but for some reason, although water samples were isolated on day 21 from the glass, the sodium levels in the water samples went up even higher than the first time. This may be due to some variation in the dilution technique or the function of the atomic absorption instrument, or calibration error.
 
 
 

Athanasopoulos, Nick. Flame Methods Manual for Atomic Absorption. Victoria, Australia: GBC Scientific Equipment,n.d.

Choho, Anne-Marie. "Nuclear Waste Vitrifcation." Vitrification Waste Product Qualification. WSU-Tri Cities, Washington.
29   Nov. 1999.

Choho, Anne-Marie. "Nuclear Waste Vitrifcation." Principles of Nuclear Waste Glass Manufacturing. WSU-Tri Cities, Washington. 15 Nov. 1999.

"Glass." Microsoft Encarta Encyclopedia Deluxe 2000. CD-ROM. Microsoft Corporation, 2000.

Hanford Press Releases. Office of River Protection. 13 Dec. 2001 <http://www.hanford.gov>.

Information Please Reference. Learning Network. 8 Jan. 2002 <http://infoplease.com>.

RAKON. Rakon, Ltd. 2 Feb. 2002 <http://www.rakon.com>.

"Research in Glass Technology." U.S.A.: Battelle, 2001.
 

Mike Schweiger, John Vienna, and Kevin Minister, the scientists at PNNL. Thank you for the patience and time you all took to give me instruction, encouragement, and help when I needed it.

Anne-Marie Choho, thank you for the provided information and references, getting me + in touch with Pacific Northwest National Laboratory.  I would never have gotten to experience the "real world" of glass making without your helpful assistance- I was able to learn a lot from working at the lab.

My science teacher Mr. McMillen, who has given me instruction, encouragement, and support .

All my family, but especially my  mom, who has given up time and energy to support and encourage me. Thanks for the genes!  Thanks for all the driving!