Wednesday, 13 April 2022
Craft Fair Checklist
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Sunday, 10 April 2022
Glass 101: Glass Processing Temperatures
Glass 101: Glass Processing Temperatures
Posted Rebecca Molt on Aug 14, 2019
Glass is an amorphous solid with no long-range order. This lack of order is what differentiates a glass from a crystalline solid. For example, when silicon dioxide is cooled slowly through the crystallization temperature, it is allowed to form crystals, giving the solid a geometric structure throughout the material. When silicon dioxide is heated and then rapidly cooled, it’s ordered crystalline structure is unable to reform and it becomes an amorphous solid (glass). [1]
Glass goes through different transitions during melting. The glass transition temperature, softening point, and crystallization temperature are all part of the glass forming process. Careful maneuvering through these steps is critical to the formation of a stress-free glass product.
Glass Transition Temperature
The glass transition temperature (Tg) characterizes a range of temperatures where an amorphous material transitions from a hard brittle state to a viscous state relative to increasing temperature.[2] The solid begins to exhibit viscoelastic properties above Tg. When disordered molecules are below Tg, they have less energy, and the molecules aren’t able to move into new positions when stress is applied. When above Tg, the molecules have more kinetic energy, allowing them to move in order to alleviate applied stresses.[3] The annealing temperature is selected based on the glass transition temperature, allowing any stress to be released before completely cooling the glass.
Littleton Softening Point
The Littleton softening point (Ts) of glass is the temperature at which the glass moves under its own weight. As a glass is heated, the glass flows more easily. The resistance to flow is known as viscosity. At the softening point, the glass has a viscosity of 107.6 poise.[4] This point is often used to define the working range of the glass. Once the glass has reached the softening point, it is malleable without melting.
Crystallization Temperature
The crystallization temperature (Tx) characterizes the onset of crystallization. Crystallization is the process of forming a solid. The molecules become highly organized into a geometric structure known as a crystal. This occurs in two steps. The first step is the nucleation or “seed” formation. Nucleation can be influenced by the initiation of a secondary phase formation within the matrix or the introduction of an outside substance, such as particles from the crucible. The second step is crystal growth, which is the growth around the original nucleation sites in layers.[5] Crystallizing brings the melt down to a lower energy state. If a melt crystallizes it will not become a glass since glass is a disordered solid. Crystallization is avoided by rapidly quenching through the glass transition region.
Coefficient of Thermal Expansion
The coefficient of thermal expansion (CTE) describes a material’s change in shape, area, and volume in response to temperature change.[6] Heat is a type of kinetic energy. When a material is heated, its kinetic energy increases which causes the molecules to vibrate at a higher frequency. The molecules then take up more space than usual. The reverse is true when cooling a material. When cooled, the molecules have less kinetic energy, and they contract, taking up less space....
Mo-Sci Corporation’s extensive glass knowledge and research experience make it a perfect candidate for custom development needs. Mo-Sci has partnered with companies across a wide variety of industries, creating custom glass solutions for unique applications. Contact us for more information on how we can help with your next glass product.[8]
References
- NDT Resource Center, http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Structure/solidstate.htm, Center for NDE, Iowa State University.
- ISO 11357-2: Plastics – Differential scanning calorimetry – Part 2: Determination of glass transition temperature (1999).
- The Glass Transition. https://pslc.ws/macrog/tg.htm. Accessed: 21 June 2019.
- Technical Glasses: Physical and Technical Properties | SCHOTT Technical Brochure. https://www.us.schott.com/d/tubing/ffed51fb-ea4f-47d3-972e-5a2c20f123f5/1.0/schott-brochure-technical-glasses_us.pdf. Accessed: 21 June 2019.
- Crystallization |Reciprocal Net http://www.reciprocalnet.org/edumodules/crystallization/. Accessed: 24 June 2019.
- Tipler, Paul A.; Mosca, Gene (2008). Physics for Scientists and Engineers – Volume 1 Mechanics/Oscillations and Waves/Thermodynamics. New York, NY: Worth Publishers. pp. 666–670. ISBN 978-1-4292-0132-2.
- Novel Sealants to Significantly Improve the Lifetime and Performance of Solid Oxide Fuel Cells | Mo-Sci Blog https://mo-sci.com/novel-sealants-Improve-solid-oxide-fuel-cells. Accessed: 25 June 2019
- Mo-Sci Corporation Website https://mo-sci.com/en/custom-development. Accessed: 24 June 2019.
Wednesday, 6 April 2022
Calibrating your new kiln
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Idle Creativity |
Sunday, 3 April 2022
Glass 101: An Introduction to Glass
Glass 101: An Introduction to Glass
Posted Krista Grayson on Jul 17, 2019
Everyone knows what glass is…or do they? We are all surrounded by glass in a myriad of forms and serving a diverse array of functions, from jars and glasses to windows and TV screens, but do we really know much about it? Glass has become so ubiquitous that it is widely accepted as an everyday commodity. Consequently, most of us take it for granted without considering what it is or how it shows such amazing properties and versatility.
Through the ages, glass has provided answers to many technological challenges and enabled unbelievable advances across most areas of our lives.1,2 However, despite being at the center of an ongoing success story, glass receives little attention from the majority.
What is glass?
Glass is commonly categorized as a type of ceramic, but it is not like any other ceramics. Ceramics generally have a crystalline structure and are opaque, whereas glass has a non-crystalline atomic structure and is transparent. Furthermore, glass exhibits a range of remarkable properties that set it apart from other ceramics. In a perfect state, glass is mechanically very strong, even when subjected to extreme changes in temperature, and has a hard surface that is resistant to abrasion and corrosion. Paradoxically, it is also elastic, being able to give under stress (up to a breaking point) and then rebound to its original shape. Glass also has extensive optical properties, is heat-absorbent and an electrical insulator.3
Glass is so unique that it cannot be simply defined. It is neither a crystalline solid nor a liquid; it is a disordered, amorphous solid. It is this amorphous structure that gives glass its unique properties. Neither can the composition of glass be described since there are infinite varieties of glass. A current database lists over 350,000 types of known glass and new workable glass compositions are being developed every day.
The production of glass
Glass is formed when the constituent parts are combined by intense heating and then rapid cooling. The rapid cooling immobilizes the atoms of the glass before they have a chance to assume a regular crystalline structure. This can occur naturally, as in the case of fulgurite that is formed by lightning striking sand, and obsidian that arises from the rapid cooling of volcanic lava.
Man-made glasses are produced from varying mixtures of oxides. Although the precise chemical composition varies widely between different types of glass, it typically includes three components: a former, a flux and a stabilizer. Glass formers, such as silicon dioxide (silica), make up the largest proportion of the mixture and provide the transparency. Fluxes, such as sodium carbonate (soda) lower the temperature at which the formers will melt. Stabilizers, such as calcium carbonate (lime) provide the strength and make the glass water resistant. Without the inclusion of a stabilizer, water and humidity will attack and dissolve the glass.4
Immediately after glasses are batched and melted, they are slowly and evenly cooled. This process is known as annealing. This is an important step that enhances the strength of the glass by reducing internal stresses. It ensures that sections of varying thickness cool at the same rate. This avoids the development of steep temperature gradients that could cause the glass to crack.
Types of glass
The precise chemical composition of the mixture melted to produce glass determines the mechanical, electrical, chemical, optical, and thermal properties of the final product. Glass can thus be manufactured with broad-ranging characteristics. Through careful selection of the basic initial mixture and additives used in production, glass is produced with properties and structures to meet the requirements of specific applications.3
Although there are many thousands of different glass compositions, glass can be categorized as belonging to one of the six basic types, based on the chemical composition that endows it with specific properties.5
Soda-lime glass
Soda-lime glass is the most common, and least expensive, type of glass, accounting for 90% of all glass made. It usually contains 60–75% silica, 12–18% soda, and 5–12% lime. This is the type of glass used to make bottles and windows. It is mechanically strong but does not have good resistance to high temperatures, sudden changes in temperature, and corrosive chemicals.
Lead Glass
Lead glass (more commonly known as crystal) contains at least 20% lead oxide, which makes the glass brilliant, resonant, and heavy. Although lead glass, like soda-lime glass, will not withstand high temperatures or sudden changes in temperature, it exhibits excellent electrical insulating properties. Consequently, it is commonly used for electrical applications. It is also used for thermometer tubing and art glass.
Borosilicate glass
The addition of at least 5% of boric oxide to a silicate glass gives it high resistance to temperature change and chemical corrosion. Borosilicate glass is not as convenient to produce as either lime or lead glass, but is useful for pipelines, light bulbs, photochromic glasses, sealed-beam headlights, and vessels for laboratory or kitchen use.
Silica glass
Removal of almost all the non-silicate elements from borosilicate glass after normal melting and forming produces 96% silica glass. The resulting pores are sealed by reheating the glass to 1200° resulting in glass that is resistant to heat shock up to 900°C. 96% silica glass is used for the outer panes of the forward windshields of space shuttles to enable them to withstand the high temperatures reached during atmospheric re-entry.6
Aluminosilicate glass
Similar to borosilicate glass is aluminosilicate glass that includes aluminum oxide in its composition. Aluminosilicates are more difficult to manufacture than borosilicate glass, but have even greater chemical durability and can withstand higher operating temperatures. Aluminosilicate glass can also be used as a resistor in electronic circuits.3
Fused silica glass
Fused silica glass is the most difficult type of glass to produce, and so it is the most expensive of all glasses. Fused silica glass is pure silicon dioxide in the non-crystalline state and can withstand temperatures up to 1200°C for short periods. Fused silica is used to create astronomical telescopes, optical waveguides, and crucibles for growing crystals.6
Glass additives
Additives can be used to change the characteristics of glass. This may be done be for aesthetic purposes, for example, heavy metals, such as lead or manganese may be added to give the glass color. It may also be altered for functional purposes, for example, the addition of selenium makes the glass a light-sensitive conductor of electricity; a feature that forms the basis of photocopying.
Versatility of glass
Glass has an extensive range of potential forms and shapes. Its desirable properties can be manipulated during manufacturing, such as mechanical strength and chemical stability. This has led to the development of novel glass formats for use across an entirely new scope of applications.
Controlled-pore glass, which is porous glass with a sharply defined and adjustable pore size, can be used as a support for solid-phase oligonucleotide synthesis7 and as a stationary phase for a variety of chromatography techniques.8,9 Hollow glass biospheres have unique optical properties that have enabled the development of new research techniques, which hold huge potential for analytical devices of the future.10
Glass is also increasingly being adopted for a range of applications in medicine and dentistry. Bioactive glass is biocompatible and demonstrates antimicrobial activity. Furthermore, it can bond with both soft tissue and bone to promote healing. Bioactive glass has thus become an invaluable tool in tissue engineering and bone implants11 as well as in dental reconstruction procedures.12 It is also used in toothpaste and dental fillings to strengthen enamel and reduce bacterial colonisation.13
The future of glass
Glass has become the material of choice for solving a range of technological challenges. It is lightweight yet has the potential for strength, durability and optical clarity and its precise properties can be fine-tuned to meet a specific need. It can also be produced in a range of very different formats, including flat sheets, fine tubes, beads, and powder.
The versatility of glass has enabled incredible achievements, but the journey has by no means reached its end. With new production techniques and types of glass being continually developed, potential applications of glass products continue to expand and facilitate further remarkable advances. We are already benefitting from great interactive user experiences through the glass screens of mobile phones and tablets, but prototypes are now in development for touch-activated glass surfaces through which a range of digital devices can be accessed. Similarly, glass screens have been developed that provide a medium for virtual and augmented reality experiences.
Scientists continue to take advantage of the unique characteristics of glass, redefining what is possible. The latest projects include cleaning up nuclear waste by vitrification and using glass to develop safer batteries.
With a long and successful history, glass is still an active field of discovery and innovation with a future of exciting and ever-expanding capabilities.
Mo-Sci is a world leader in high-quality precision glass technology and produces a wide range of specialist glass products, the precise composition of which can be tailored to meet specific requirements.14
References
- Rasmussen SC. Origins of Glass: Myth and Known History. In How Glass Changed the World. Springer 2012. Briefs in History of Chemistry, DOI: 10.1007/978-3-642-28183-9_2
- Main D. Humankind’s Most Important Material. Object Lessons 2018. Available at https://www.theatlantic.com/technology/archive/2018/04/humankinds-most-important-material/557315/
- What is Glass | Corning Museum of Glass. All about Glass. https://www.cmog.org/article/what-is-glass
- Chemisty of Glass | Corning Museum of Glass. All about Glass. https://www.cmog.org/article/chemistry-glass
- Types of Glass | Corning Museum of Glass. All about Glass.
https://www.cmog.org/article/types-glass - Glass and The Space Orbiter | Corning Museum of Glass. All about Glass.
https://www.cmog.org/article/glass-and-space-orbiter - Grajkowski A, et al. A High-Throughput Process for the Solid-Phase Purification of Synthetic DNA Sequences. Curr Protoc Nucleic Acid Chem. 2017 Jun 19;69:10.17.1-10.
- Zucca P and Sanjust E. Inorganic Materials as Supports for Covalent Enzyme Immobilization: Methods and Mechanisms. Molecules 2014, 19, 14139—14194.
- Igata Y, et al. A ‘catch and release’ strategy towards HPLC-free purification of synthetic oligonucleotides by a combination of the strain-promoted alkyne-azide cycloaddition and the photocleavage. Bioorg Med Chem. 2017 Nov 1;25(21):5962—5967.
- Ward JM, Dhasmana N, Chormaic N. Hollow core, whispering gallery resonator sensors. The European Physical Journal Special Topics 2014;223(10):1917–1935.
- Rahaman MN, et al. Bioactive glass in tissue engineering. Acta Biomaterialia 2011;7:2355—2373.
- Sohrabi K, et al. An evaluation of bioactive glass in the treatment of periodontal defects: a meta-analysis of randomized controlled clinical trials. J Periodontol 2012; 83: 453—464.
- Chatzistavrou X, et al. Fabrication and characterization of bioactive and antibacterial composites for dental applications. Acta Biomater. 2014;10:3723–3732. Available at https://www.ncbi.nlm.nih.gov/pubmed/24050766
- Mo Sci Corporation website. http://www.mo-sci.com/en/products
Wednesday, 30 March 2022
Attending Craft Fairs is Important
Credit: Artefact Contemporary Craft Fair at Vessel Gallery |
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Sunday, 27 March 2022
Vitrification: The Workhorse of Nuclear Waste Management
Vitrification: The Workhorse of Nuclear Waste Management
Posted Krista Grayson on Jun 18, 2019
Nuclear power has been used to produce electricity for over 60 years, and is responsible for around 16% of the electrical energy produced worldwide. This percentage is likely to increase, as countries move away from fossil fuels and require a source of energy to make up the shortfall this will cause.
With more reactors coming online, more fuel will be used, and this presents a problem: there is no conclusive method to handle the spent fuel. Vitrification (the transformation into glass) of nuclear waste is one established solution, but there is still plenty of room for improvement in this method.
The issue of nuclear waste
A key problem with nuclear power is what to do with the waste products generated when the fuel is completely spent. Although it is no longer useful in power generation, this waste is still very dangerous if not stored correctly.
The most problematic waste, called ‘high level’ nuclear waste (HLW), is highly radioactive, has an extremely long half-life and requires cooling and containment due to the elemental decay, which gives off heat and radiation.
Additionally, some radioactive isotopes such as Tc-99, Se-79, and I-129 are mobile in water, which requires further measures in order to reduce their ability to move into the groundwater. Secondary waste streams can also present issues as this waste can contain large amounts of molybdenum and noble metals.
Safely storing nuclear waste through vitrification
One method of long term storage and disposal involves the processing and transformation of the spent fuel into a glass, a technique known as vitrification. It has been used for HLW immobilization for over 40 years in most countries that have a nuclear power program, including France, Germany, Belgium, Russia, UK, Japan, and the USA.
Glass is desirable as a long-term storage form as it is a relatively insoluble, compact and solid. In this form it is easier to store and handle, saving space and reducing cost. Glass also possesses high chemical durability, allowing it to remain in a corrosive environment for thousands or even millions of years without failing. While glass is often thought of as a fragile material, a properly treated block of borosilicate glass is incredibly resilient.
How vitrification works
The process of vitrification is quite simple but can be difficult to execute. First, the waste is dried, then heated to convert the nitrates to oxides. Glass-forming additives are added to the waste material and heated again to around 1000 °C. The molten liquid is poured into a suitable containment vessel to cool and form the glass. Once solidified, the final vitreous product has incorporated the waste contaminants in its macro- and micro-structure, and the hazardous waste constituents are immobilized.
The two main types of glass currently used to immobilize nuclear waste are borosilicate and aluminophosphate glasses. Both of these materials allow high waste loadings and can immobilize large amounts of actinides. Borosilicate glasses can accommodate up to 7.2 mass pct of PuO2 for example.
Advantages and limitations of nuclear waste vitrification
Although vitrification is often the preferred method of waste storage, there are some drawbacks to the current techniques, both with the necessary setup and materials used. Vitrification has a high initial investment cost, high operational cost and complex technology requiring qualified personnel.
This makes it most economically viable in locations where relatively large volumes of radioactive waste with stable composition are available, such as HLW from nuclear power plants.
Unfortunately, the current generation of glasses cannot handle large amounts of MoO3 and noble metals that are produced from secondary waste streams. These compounds are poorly soluble in borosilicate glasses and this limits the amount of waste that can be loaded into the material, increasing process time and material costs.
New materials to process molybdenum-rich nuclear waste
It is clear that vitrification is of vital importance for the long term success of nuclear power. Mo-Sci has been working on new types of glass that can immobilize a higher percentage of waste, as well as methods within the processing that can speed up the vitrification.
This includes an iron phosphate waste form able to contain 40 wt% of the simulated molybdenum-rich nuclear waste. This vitrified nuclear waste is prepared by melting the mixture of simulated waste components and iron phosphate glass additives in a commercial-scale cold crucible induction melter (CCIM). When the chemical durability of the waste form was measured, it was found to be as good as or better than that of borosilicate glass.
The CCIM melting technology can also process waste forms faster, safer and at a lower cost than other melting technologies as it removes the metal electrodes that directly contact the molten glass and refractory used to contain the melt. This novel CCIM-processed iron phosphate waste form could drive large savings in time and money in the industry’s need to remediate nuclear waste, and make nuclear power an even more attractive option for the future.
See our article on iron phosphate waste forms for more information on these new developments.
References
- Thompson, L. (2010) Vitrification of Nuclear Waste http://large.stanford.edu/courses/2010/ph240/thompson2/
- Criscenti, L. et al. (2013). An international initiative on long-term behavior of high-level nuclear waste glass. Materials Today, 16 https://doi.org/10.1016/j.mattod.2013.06.008
- Ojovan, M. I., & Lee, W. E. (2011). Glassy Wasteforms for Nuclear Waste Immobilization, 42 https://doi.org/10.1007/s11661-010-0525-7
- Ojovan, M. I. (2007). Glasses for Nuclear Waste Immobilization, WM’07 Conference. https://www.researchgate.net/publication/267700284_Glasses_for_Nuclear_Waste_Immobilization/download
- Cheol-Woon, K. (2018) Iron Phosphate Waste Forms for Nuclear Waste Disposal https://mo-sci.com/iron-phosphate-nuclear-waste-disposal
Tuesday, 22 March 2022
Selling online
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