Are Electric Furnaces the Future of Glass Manufacturing?

 

Are Electric Furnaces the Future of Glass Manufacturing?

Posted Krista Grayson on May 16, 2019

Overview of glass production 

Glass production is typically energy-intensive. Glass furnaces may reach 1300-1550 ºC for the melting and refinement of the raw materials, depending on the formulation required. 

Natural gas and electricity are the main energy sources, however historically, the glass industry has favored gas because it is an established technology, with low price, high purity, ease of control and the fact that there is no requirement for storage facilities. Gas furnaces have long life-times, on average over 12 years and sometimes up to 20 years.

Until recently electric glass melting furnaces have been used for specialty glasses, and particularly glasses with significant volatile constituents such as fluoride opal glasses, borosilicates and lead crystal. Interest is growing in extending its use through the industry.

Electric glass furnace production

The most effective method of electric glass production is to use electrodes immersed in the glass either as electric boosting (providing 5-20 % of total energy input) or all-electric melting. The immersed electrodes are connected to a power supply and transformer, to pass an electric current through the glass. 

In all-electric furnaces, the melting energy comes from the electrodes (joule heat), with a gas burner being used for the initial start-up, or as an emergency heat source. These furnaces mainly operate ‘cold top’, where the raw material is distributed evenly over the melting surface of the glass, forming an insulating ‘batch blanket’. Melting and refining take place in one vertical process, with glass being drawn through a throat at the bottom of a deep melting tank.

Advantages of electric melting

Electric furnaces offer several advantages over gas furnaces. For example, they have very low direct emissions of CO2, thermal NOx or SOx emissions. With pressure to reduce emissions coming from both customers and legislation, this is a significant benefit. While it is possible to improve conventional gas furnaces to reduce emissions, this can result in more complex technology that results in additional maintenance, the use of non-environmentally friendly chemicals, and limitations to equipment lifespan. 

Another benefit is that heat losses from electric furnaces are much lower. The thermal efficiency of gas furnaces peaks at around 45%. This means more energy is lost as heat than is used to convert the raw materials to molten glass. Heat losses occur from the superstructure of the furnace and in the residual waste gases, even if heat recovery systems are used. In contrast, the electrical approach means that the melting energy is transferred directly into the glass. Thermal efficiency can be over 70% even in a small electric furnace and can reach 85% in a large electric furnace.

All-electric furnaces are also more energy efficient than gas-fired furnaces; they use around 35% less energy. The difference in energy efficiency is particularly important for small furnaces. As furnace size decreases, the energy efficiency of electric furnaces remains very high, whereas the efficiency of gas furnaces drops dramatically and can be less than 20%. 

Electric boosting can be a highly effective way to reduce overall energy consumption. It also means that energy release can be highly focused, helping to determine conditions in the glass bath. In some cases, a well-designed boost system can improve glass quality homogeneity, seed and stone losses. In contrast, in gas furnaces, where focused energy release is not possible, imprecise temperature profiles can be created in the glass. 

A key advantage of the cold-top electric furnace is that everything that goes into the batch stays in the glass, aside from the gases released from the melting process, which permeate out through the batch blanket. Losses of batch constituents such as fluorine, boron, lead, various volatile refining agents and other constituents are almost eliminated. 

Disadvantages of all-electric melting

While electric furnaces have lower capital costs, they have shorter life-times (2-7 years compared to 10-20 years for conventional furnaces) and higher energy costs. The economic viability of electric furnaces is closely related to the cost of electricity compared with gas. Higher thermal and energy efficiencies can offset this cost for smaller furnaces, but this might not be the case for larger furnaces. 

The low environmental impact is only maintained if the furnace can receive power from renewable energy sources and requires a power grid that is reliable and stable. 

There are also operational considerations. For example, the maintenance of electrodes to limit higher resistance caused by wear. It is not possible to melt higher temperature glasses (>1500C) and there is concern of corrosion/erosion of electrode material from certain glass compositions. Further, recycled glass may be an issue that requires new handling methods. 

Conclusion

In most places, it is still environmentally cleaner to burn fossil fuels in a furnace than to use them to generate electricity for electric melting. However, as renewables increase their contribution to electricity production, this situation will change. It also appears that improvements in energy efficiency of fossil fuel combustion technologies have leveled off. As emissions legislation kicks in and consumers increasingly demand materials and technologies that are environmentally friendly, there may be well a swing in glass manufacture from gas to electric energy. The other advantages of electric melting, such as better thermal efficiency and energy consumption, will also count in its favor.

References

1. https://www.eurotherm.com/efficient-future-for-the-glass-industry-is-all-electric 
2. https://www.glassmanevents.com/content-images/speakers/Andy-Reynolds-Fives.pdf 
3. http://www.electroglass.co.uk/articles/2010-09%20Electric%20Melting%20&%20Boosting%20for%20Glass%20Quality%20Improvement.pdf
4. http://ietd.iipnetwork.org/content/electric-melting

Metal inclusions

Two difficulties with metal inclusions in glass are common: stress and bubbles.

Stress

Metal inclusions always create stress in the glass. Different metals have different expansions and different strengths.  They also have different melting points - some so low that they liquify during the fusing process.

The trick in using metals as inclusions is to minimise the amount of stress. Small amounts of stress can be contained within the glass. The thicker or more mass inside the glass, the greater risk of stress breaks. The stronger or more rigid the metal is, the more stress will be generated.

Minimising stress is most easily achieved by using small amounts of the metal.  Thinning the metal as much as possible also reduces stress.  Flattening wire also helps reduce the amount of stress as well as keeping it in the place you want it without rolling away from its placement.

Bubbles

Bubbles often form around inclusions, especially of metals.  Metals that do not melt at fusing temperatures are stiffer than the surrounding glass.  You can see from the table noted above those metals which melt at higher temperatures than fusing.  These metals will create bubbles around their perimeter and elsewhere over the metal wherever there are wrinkles or undulations as the metal holds air in those places.

Thin metals

One possibility to reduce the bubbles is to thin the metal by hammering flat or use foil thicknesses of the metal.  Many specialist metal suppliers have very thin metals, often called shims.  They are increasingly available in online shops.

Weight

Another is to use enough glass on top to flatten the metal.  You should flatten the metal in the cold state as much as you can.  Then the weight of the glass presses down on the metal both in the cold and heated states. With a good long bubble squeeze, you can force more air out to the sides than with less covering glass.

Placing

A third possibility is placement. The further the metal inclusion is from the edges the more air is likely to be trapped to form bubbles.  If the air has less distance to travel, more is likely to escape.

Pressing

Supporting the edges or corners allows the centre to drop before the edges are sealed.  The weight of glass helps to press the air out to the sides.  Thicker glass (6mm/0.25") on top of the metal inclusion can help push the air away from the metal. You can also provide - within the design - paths for the air to escape. This can be elements such as powder, stringers and other glass accessories that can hold the glass up during the bubble squeeze process, but become invisible at fusing temperatures.

Fire in stages

A fifth possibility is to fire differently.  You can place the metal on a kiln shelf which is covered with fibre paper and put the glass on top of the metal and fire to a rounded tack fuse at the minimum.  To avoid dog-boning, you should cut the capping piece several centimetres larger than the final piece, so you can cut off the distorted edges. Clean the bottom and dry very well after firing and put the base under the top piece that has the metal attached.  Fire the combined piece slowly with a good bubble squeeze.  This can be applied to included vegetable matter too. 

Further information is available in the ebook Low Temperature Kiln Forming.

Inclusions often produce stress and bubbles.  There are some things that can reduce both when encasing metals or vegetation.

Glass Ionomers in Dental Restorations and Fillings

 

Glass Ionomers in Dental Restorations and Fillings

Posted Krista Grayson on Mar 27, 2019

It is widely known that eating sugary foods leads to a build-up of bacteria which can result in dental caries (tooth decay). The incidence of dental caries has fallen significantly since fluoride, which makes teeth more resilient to decay, was added to toothpaste. Nonetheless, the majority of dentist visits are still for the repair of teeth damaged by tooth decay. Indeed, in the US, 92% of adults and 21% of children have had dental caries in their permanent teeth.1

Tooth decay is caused by the acid produced by bacteria while they consume the sugars found in food and drink. This acid dissolves the protective enamel coating of teeth and then the dentine below. If the resultant cavity is not treated it can become painful, and this potentially leads to infection and even tooth loss.

The most common corrective action for tooth decay is to remove the decayed tooth tissue and fill the cavity with a filling material. There are several types of filling material currently available, including a variety of composite fillings, and the traditional silver amalgam. Composite filling materials are increasingly popular as many people prefer tooth-colored fillings that are less conspicuous. Composite dental materials can also be used for dental restorations to rebuild chipped or broken teeth. Most recently glass ionomer cements, which can be used in much the same way as composite materials, have been introduced as an additional alternative material for dental restoration.

The quality of a filling material is a key factor in determining the effectiveness of a repair. If the filling material is not durable it will be worn away during eating, and if it is prone to shrinkage bacteria will colonize the gap between the tooth and the filling giving rise to secondary caries. 

The Materials used in Tooth Fillings

In the early days of modern dentistry (1800s), teeth were filled with any metal soft enough to mold into the cavity, eg, tin, silver. This advanced to dental amalgams containing a combination of metals including tin, silver, copper, and mercury as technology improved during the nineteenth century. By the end of the first quarter of the twentieth century silicate dental cements had been developed for both dental filling and the bonding of other dental restorations.2

Amalgam is still the most commonly used filling material today. Even after concerns were raised about the toxic effects of mercury, amalgam fillings continued to be used due to the inferior quality of alternatives. However, now that there are effective alternatives, which have the added aesthetic advantage of being tooth-colored, the proportion of amalgam fillings is steadily declining. 

Today, there are several types of dental filling materials available, including silver amalgam, gold, porcelain, composite resins and glass ionomers. Although effective dental filling materials, gold and porcelain are rarely used due to their high costs. The other main options are compared below.

Amalgam

Amalgam is the least expensive of the dental filling materials and can be applied most quickly.2 It has the added benefit of being highly durable, lasting at least 10?15 years. There are, however, several drawbacks to the use of amalgam fillings, the most concerning of which is the potential toxicity from exposure to mercury during placement and removal of the amalgam, and also whilst in situ if an individual routinely grinds their teeth. The use of amalgam fillings also requires removal of some healthy tooth in order to create a space large enough to hold the amalgam. Lastly, the propensity of amalgam to expand and contract with changing temperature makes it more likely to crack or fracture and damage the surrounding tooth as a consequence of drinking hot and cold liquids.

Resin Composites

Dental composites can vary in formulation but all include a synthetic resin making them similar to plastics in composition. Initially, composite materials lacked the strength and durability of amalgam, but advances in their production mean that they can now be both strong and durable. Their main benefit is that they chemically bond to the tooth structure, providing further support and reducing the marginal gap that encourages bacterial colonization and increases the risk of secondary tooth decay. There is however a risk of subsequent shrinkage that can lead to gap development. Composite fillings are also aesthetically more pleasing since, unlike amalgam fillings, they blend in with the natural tooth surface. Unfortunately, composite materials are still considerably more expensive than amalgam (although still less expensive than gold or porcelain) and are more time-consuming to apply.2 Furthermore, the successful application of composite fillings is very technique sensitive and requires the area to be kept dry during placement. 

Glass Ionomer Dental Cements

Glass ionomer cements (GIC) can have a variety of compositions, but the principal constituents are silica, alumina, and calcium. A source of fluoride, such as fluorite, is also commonly added to provide protection against tooth decay. Additional minerals can also be incorporated into the GIC to promote remineralisation and/or prevent acidification. The glass ionomer may be combined with resin for added strength, and to reduce the sensitivity to the presence of moisture on placement.3 GIC represent a very flexible dental restoration solution since the physical properties of GIC can be modified to meet a specific dental application by adjusting the ratios of the constituent chemicals.2

GIC, like resin composites, are tooth-colored and so have cosmetic appeal. The primary benefit of GIC is their chemical adhesion to enamel and dentin, which improves the strength of the restoration and eliminates the need for a bonding agent during placement.2,4 The bond strength of this adhesion is typically increased by addition of polycarboxylic acid. GIC have been reported to exhibit a contact-free area wear that is five times higher than that of amalgam and three times higher than for resin composite materials.2 Furthermore, in contrast to other restoration materials that can suddenly fail due to mechanical fatigue, GIC become stronger over time as water is absorbed and are thus less prone to failure.2

Most recently, GIC has been created using bioactive glass.5 Resin-modified GIC containing bioactive glass has been shown to result in a thick uniform layer of mineralization on the restoration-dentin interface,6 improve the mechanical properties of a filling,7 and reduced the incidence of secondary tooth decay at restoration margins.8

Conclusion

Despite silver amalgam being the mainstay dental filling material for many decades, there has been a desire to reduce its use due to toxicity concerns. Now that the alternative products available can provide comparable efficacy, the proportion of dental caries being corrected with amalgam fillings is declining. Advances in the formulations of composite and glass ionomer dental materials have given them the required strength and durability to make them effective products for tooth restoration. Although fillings with these newer materials are more expensive and take longer to place, they are often the preferred choice due to their improved aesthetics and low risk of toxicity. 

Glass ionomer cements have the added benefits of flexibility in their physical characteristics, strong adhesion to the tooth surface and lower failure rate. The properties of both composite and glass ionomer dental materials can be improved by the inclusion of bioactive glass. 

Mo-Sci produces a range of high quality glass and bioactive glass powders suitable for use as a dental filling materials and for the fixation or coating of dental implants.9 The precise composition of their glass products can be tailored to suit a specific application. Contact us for for more information.

References & Further Reading

1. National Institutes of Health. NIDCR Data & Statistics. Dental Caries (Tooth Decay) in Adults (Age 20 to 64). Available at: https://www.nidcr.nih.gov/DataStatistics/FindDataByTopic/DentalCaries/DentalCariesAdults20to64.htm
2. Lohbauer U. Dental Glass Ionomer Cements as Permanent Filling Materials? — Properties, Limitations Future Trends. Materials 2010, 3(1), 76-96; doi:10.3390/ma3010076
3. Gao W, et al. Demineralization and remineraliza-tion of dentine caries, and the role of glass ionomer cements. Int Dent J. 2000;50(1):51–56.
4. Benelli EM, et al. In situ anticariogenic potential of glass ionomer cement. Caries Res. 1993;27(4):280–284.
5. Matsuya S, et al. Structure of bioactive glass and its application to glass ionomer cement. Dent Mater J. 1999 Jun;18(2):155–166.
6. Prabhakar AR, et al Comparative Evaluation of the Remineralizing Effects and Surface Micro hardness of Glass Ionomer Cements Containing Bioactive Glass (S53P4):An in vitro Study. Int J Clin Pediatr Dent. 2010 May-Aug;3(2):69-77. doi: 10.5005/jp-journals-10005-1057. Available at https://www.ncbi.nlm.nih.gov/pubmed/27507915.
7. 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
8. Khvostenko D, et al. Bioactive glass fillers reduce bacterial penetration into marginal gaps for composite restorations. Dental materials 2016;32(1):73–81. Available at http://www.demajournal.com/article/S0109-5641(15)00437-6/pdf
9. Mo Sci Corporation website. http://www.mo-sci.com/en/products

Reducing Implant-Related Infection with Bioactive Glass

 

Reducing Implant-Related Infection with Bioactive Glass

Posted Krista Grayson on Feb 13, 2019

Disease, trauma or serious infection may result in extensive bone damage or bone loss which exceeds the body’s capacity to repair itself. In such cases, implants are needed to promote satisfactory healing. These may take the form of screws, plates, or rods to immobilize broken bones in the correct alignment, reinforce weak bones or correct skeletal deformities. Similarly, diseased joints can be replaced with prosthetic joints to restore normal, pain-free movement. 

Despite ongoing medical advances and improvements in materials and procedures, there remains a substantial risk of implanted devices becoming infected. In addition to microbes being introduced into the body during surgery, there is the risk of bacteria transported in the blood from other parts of the body colonizing the surface of an implant. It has been estimated that as many as 2.5% of primary hip and knee replacements and to 10% of joint revision surgeries are complicated by infection.1 Infected implanted devices represent a significant clinical challenge. Typically, despite lengthy antibiotic treatments, it is often necessary for the infected implant to be surgically removed. This not only increases patient morbidity and dissatisfaction, but is also associated with substantial cost.2 

Antibiotics continue to be the mainstay strategy for both the prevention and treatment of implant infections. However, the power of antibiotics in the fight against infection is diminishing as many strains of potent bacteria are developing resistance to even the strongest antibiotics. Consequently, the risk of implanted devices becoming infected is on the rise and researchers are investigating novel ways to reduce such infections.

One strategy is based on the discovery that the majority of bacteria live in surface-bound microbial communities, rather than as free-swimming entities. On binding to the surface, bacteria secrete adhesion proteins that provide an irreversible attachment.3 Such bacterial biofilms account for over 80% of clinical microbial infections.2 It was therefore proposed that making the surface of implants unsuitable for bacterial colonization would dramatically lower infection rates. This can be achieved by coating the implant with bioactive glass.

The Antimicrobial Properties of Bioactive Glass

Bioactive glass is a type of glass made from high-purity chemicals, such as silica, calcium, and boron, which induce specific biological activity.4 Bioactive glass, by virtue of its high strength, low weight and biocompatibility, has been widely used in a range of biomedical applications, including tissue engineering, bone grafting, dental reconstruction and wound healing.5 

Such clinical experience has shown that borate bioactive glass possesses antimicrobial properties against a wide range of bacteria, including MRSA and E-coli.6,7 The antimicrobial efficacy is achieved though an increase in pH of the surrounding body fluids (which is stressful for bacteria) and because any bacteria that do approach are unable to adhere to bioactive glass and so cannot create microfilms on its surface.8,9 In vitro studies have confirmed that bioactive glass has strong anti-staphylococcal and anti-streptococcal activity.10,11

Since the antimicrobial action of bioactive glass arises from it creating an environment that is hostile to bacteria rather than requiring direct contact with the invading microbe in order to kill it, it is effective across a wide range of bacteria. Furthermore, the bacteria cannot adapt to such effects, and so no bacteria have been found to develop resistance to the antimicrobial effects of bioactive glass.9 

Coating Implants with Bioactive Glass

Initial technical challenges have been overcome and a range of titanium implants have been successfully coated with bioactive glass.12 Clinical use of implants coated with bioactive glass has given promising results in both orthopedic and dental applications. There was no evidence of the coated implants causing any adverse effects or inflammatory response in the surrounding tissue. Furthermore, the implants coated with bioactive glass were found to accelerate cell attachment and mineralization of the extracellular matrix, promoting more rapid bone growth. In addition, the proportion of bone-to-implant contact was significantly greater for implants coated with bioactive glass compared with traditional implants.13-15

Enhancing the Antimicrobial Efficacy of Bioactive Glass

Bioactive glass has good antimicrobial action, being effective against a broad spectrum of aerobic and anaerobic bacteria.9 However, the antimicrobial effects can be further enhanced to increase the range of antimicrobial activity, by the addition of ions, such as boron, copper, silver, yttrium, and iodine, or organic nanoparticles.16,17 The chosen antimicrobial agent is incorporated into the bioactive glass during its production and released once the bioactive glass is in an aqueous solution, creating an environment inhospitable for microbial life. The bioactive glass can thus be used as a delivery system for antimicrobials.18

The advantage of ions and nanoparticles over antibiotics is that their efficacy depends solely on contact with the bacterial cell wall; they do not need to enter the cell. Consequently, their lethal effect is delivered irrespective of the specific genetics of the target bacteria and is unaffected by the resistance mechanisms used by bacteria to evade antibiotics.

Conclusion

Infection of medical implants is an increasingly serious clinical and socioeconomic burden. Furthermore, the situation is likely to worsen with the increasing prevalence of bacteria with multi-drug resistance. 

Bioactive glass has inherent antimicrobial activity and does not elicit a toxic response to surrounding tissues. Consequently, coating implants with bioactive glass represents an attractive option for reducing the risk of infection. The antimicrobial properties of bioactive glass can be further enhanced by loading it with antimicrobial agents, such as ions or antibacterial nanoparticles. Such a strategy would reduce the need for prophylactic antibiotic use, whereby protecting against the development of further strains of antibiotic-resistant bacteria. 

Since bacteria cannot adapt to the hostile environment created by bioactive glass or its biofilm-resistant surface, they are unlikely to develop resistance to the antimicrobial action of bioactive glass. 

In addition, the coating of implants with bioactive glass has been shown to speed up the fusion of the implant with bone, accelerating a patient’s recovery.

The use of bioactive glass, either alone or doped with antimicrobial agents, as a coating for orthopedic and dental implants is thus likely to improve the success rate and enhance patient outcomes across a range of reparative and restorative surgeries by promoting rapid healing and minimizing the occurrence of infection. 

Mo-Sci produces high quality bioactive glass powders, the precise composition of which can be tailored to meet specific requirements. They produce bioactive glass suitable for coating orthopedic and dental implants.

References & Further Reading

1. Lentino JR. Prosthetic joint infections: Bane of orthopedists, challenge for infectious disease specialists. Clin Infect Dis. 2003;36:1157–61. doi: 10.1086/374554.
2. Hall-Stoodley L, et al. Bacterial biofilms: from the natural environment to infectious diseases. Nature Reviews Microbiology2004;2(2): 95–108.
3. Davey ME and O’Toole GA. Microbial biofilms: from ecology to molecular genetics. Microbiology and Molecular Biology Reviews2000;64(4):847–867.
4. Brauer DS. Bioactive Glasses—Structure and Properties. Angew Chem Int Ed 2015;54: 4160–4181.
5. Rahaman MN, et al. Bioactive glass in tissue engineering. Acta Biomaterialia 2011;7:2355?2373.
6. Ottomeyer M, et al. Broad-Spectrum Antibacterial Characteristics of Four Novel Borate-Based Bioactive Glasses. Advances in Microbiology 2016;6:776?787.
7. Khvostenko D, et al. Bioactive glass fillers reduce bacterial penetration into marginal gaps for composite restorations. Dental materials 2016;32(1):73–81. Available at http://www.demajournal.com/article/S0109-5641(15)00437-6/pdf
8. Zhang D, et al. Factors Controlling Antibacterial Properties of Bioactive Glasses. Key Engineering Materials 2007;330-332:173?176.
9. Drago L, et al. Recent Evidence on Bioactive Glass Antimicrobial and Antibiofilm Activity: A Mini-Review Materials 2018;11:326?337.
10. Misra SK, et al. Poly(3-hydroxybutyrate) multifunctional composite scaffolds for tissue engineering applications. Biomaterials 2010;31:2806–2815.
11. Rivadeneira J, et al. In vitro antistaphylococcal effects of a novel 45S5 bioglass/agar-gelatin biocomposite films. J Appl Microbiol 2013;115,604–612.
12. Lopez-Esteban S, et al. Bioactive glass coatings for orthopedic metallic implants. Journal of the European Ceramic Society 2003;23:2921–2930.
13. Mehdikhani-Nahrkhalaji M, et al. Biodegradable nanocomposite coatings accelerate bone healing: In vivo evaluation. Dent Res J (Isfahan). 2015;12(1):89?99.
14. Chen Q, et al.Cellulose Nanocrystals–Bioactive Glass Hybrid Coating as Bone Substitutes by Electrophoretic Co-deposition: In Situ Control of Mineralization of Bioactive Glass and Enhancement of Osteoblastic Performance. ACS Appl Mater Interfaces. 2015 Nov 11;7(44):24715?25.
15. van Oirschot BA, et al. Comparison of different surface modifications for titanium implants installed into the goat iliac crest. Clin Oral Implants Res. 2016;27(2):e57?67.
16. Kaur G, et al D. Review and the state of the art: Sol–gel and melt quenched bioactive glasses for tissue engineering. J Biomed Mater Res B Appl Biomater 2016;104, 1248–1275.
17. Karwowska E. Antibacterial potential of nanocomposite-based materials – a short review. Nanotechnology Reviews 2016;6(2):243?254.
18. Rivadeneira J and Gorustovich J. Bioactive glasses as delivery systems for antimicrobial agents. Journal of Applied Microbiology 2016;122, 1424–1437.
19. Mo Sci Corporation website. http://www.mo-sci.com/en/products

Accurate cutting

Cutting glass pieces accurately is a matter of practice whether done by hand or by person-guided machines.  Computer guided machines rely on accurate instructions being given to it. This is mainly about human-guided cutting with some information on saws.

Hand Cutting

The right approach to cutting is necessary to accuracy. 

• ·        You need clean flat surfaces with only a little flexibility, with no glass shards, bumps or warps that would make scoring the glass more difficult. 
• ·        You need to work at a comfortable height – usually about 10cm below your elbow. 
• ·        You should be moving your torso and sometimes your whole body to score, following the cutline.
• ·        Your elbow should be at your side and your wrist should be fixed. 
• ·        You need to work at a corner of the workbench to be able to move your body around as you follow a curve.
• ·        Your cutter should be at right angles to the glass (side to side)
• ·        The cutter should be angled back toward you slightly, so you can see down the barrel to the scoring wheel.  Also, so any unevenness in the glass will not cause the cutter to stall.
• ·        The pressure should consistently be about 2.5kg or 7 pounds. Do not listen for the sound, as it varies between opalescent and transparent glasses.  Heavy pressure on any glass causes unwanted break outs. Score to the pressure, not the sound.
• ·        Keep a consistent speed. Variability in speed also translates to uneven pressure. Even when you could go fast in scoring, keep to a steady pace.
• ·        Score and then break each line before going on to the next.  Do not score all around the piece in one go. It does not allow for any adjustment, if the cut is not accurate.

Oil filled cutter in classic hold

These approaches to hand scoring apply to all the ways of assisting accurate cutting.

There are at least three methods to assist accuracy in addition to the basic requirements, which apply to any method you use. 

• ·        My preference is to score the glass directly over the cartoon. This involves no extra pattern making.
• ·        Drawing the lines from the cartoon on top of the glass and then moving the glass to a separate cutting surface is the preference of many.
• ·        Making pattern pieces with the space for the foil and tolerance already cut out is a preference of many copper foilers.

Each of these assistance methods are acceptable, although the more steps involved in translating the cartoon to the glass, the more chance of introducing inaccuracies.  The accuracy of the final piece depends upon the skill with which you can manoeuvre the cutter around the glass.  This requires practice. With practice, accuracy will improve.

Machines

Glass saws of several types are available to assist in getting accurate shapes.  Mostly they are narrow thin diamond coated blades or diamond coated wire.  The wire-based saw can cut tighter and more intricate shapes than the band saw can.  But you should think about the nature of glass before you get too intricate.  The breakage rate of intricate pieces in stained glass is relatively high, even in the early life of a piece.  In fused glass it is not so difficult as they normally are supported by a base piece of glass.

Accuracy in using these saws relates to:

• ·        Manipulation of the glass to follow the line exactly.
• ·        Permanency of the guiding lines drawn onto the glass.
• ·        Accuracy of the drawn lines.
• ·        Accuracy of the pattern pieces.
• ·        Allowing the machine to cut rather than forcing the glass into the blade.
• ·        Maintenance of the machine.
• ·        Maintenance of the blade or wire.

Your accuracy will increase in the use of hand scoring or machine sawing of the glass with experience.  But, the degree of your critical appreciation of your cutting results is directly related to the accuracy of cutting.  The more you say “that is good enough” the less quickly you will improve your accuracy.

Lead Free Solders

 If you have problems with excessive corrosion of the solder bit when using lead-free solder, try a solder with 1% or 2% copper.

picture credit: reddit

 Without lead in the composition of the solder, the copper is gradually robbed from the bit during soldering. The solder gradually erodes the copper from the soldering bit in the absence of lead. In some, way the lead prevents the erosion of copper and so copper in the solder is not needed.

Picture credit\: RS Components

 Once the copper is eroded, the steel corrodes rapidly. The tips are steel with a copper plate. Eventually the steel is exposed. Then the corrosion occurs really rapidly.

 Having a bit of copper in the lead-free solder prevents the robbing of copper from the tip. There are a variety of lead-free solders available. Many have a little copper in their composition to prevent the erosion of the copper on the bit. There is a listing of some of them here.

 

 

Inhibiting Bacterial Growth with Bioactive Glass

 

Inhibiting Bacterial Growth with Bioactive Glass

Posted Krista Grayson on Jan 14, 2019

Despite numerous advances in technologies, bacteria remain a cause for concern in both clinical and industrial settings. They pose an especially challenging problem in medicine where only bactericidal strategies which have a minimal detriment to human health are feasible, and bacterial infection continues to be a leading cause of morbidity and mortality.

Surgical procedures in particular are associated with an increased risk of infection, and infection is the most frequently encountered post-surgical complication. The primary means of prevention and treatment of bacterial infections is the administration of antibiotics. However, the power of antibiotics in the fight against infection is diminishing as strains of potent bacteria are developing multi-drug-resistance.

In contrast to historical beliefs, it is now apparent that the majority of bacteria live in surface-bound microbial communities, rather than as free-swimming entities. On binding to the surface, bacteria secrete adhesion proteins that provide an irreversible attachment. The bacteria proceed to proliferate and create a colony that ultimately results in the formation of a mature biofilm protected by a peptidoglycan envelope.1 Such biofilms account for over 80% of clinical microbial infections, and so are associated with considerable morbidity and expense.2

In addition to the possibility of biofilms containing antibiotic-resistant strains, the bacteria are protected from antibacterial agents and the body’s immune system by the peptidoglycan envelope. Biofilm-associated bacteria are 100 to 1,000 times less susceptible to antibiotics than free-swimming bacteria, and so patients with biofilm infections are rarely cured by treatment with antibiotic agents, which are used nonetheless due to the lack of alternatives. Furthermore, there is the scope for bacteria to leave the biofilm and colonize other areas throughout the body.

Consequently, there has been much research in to the development of new broad-spectrum antibiotics and also novel antimicrobial strategies.

Novel antimicrobial materials

Nanotechnology has opened up the potential for the development of new types of materials with antimicrobial properties. It allows the physicochemical properties of a material to be changed in order to achieve antimicrobial effects.3

Antimicrobial nanomaterials include a wide range of metal, metal oxide, and organic nanoparticles and so have numerous modes of action. Although a range of chemical interactions are involved, the end result is membrane damage that leads to loss of integrity and impaired metabolism and ultimately cell death.

The advantage of nanoparticles over antibiotics is that their efficacy depends solely on contact with the bacterial cell wall; they do not need to enter the cell. Consequently, their lethal effect is exerted irrespective of the specific genetics of the target bacteria and is unaffected by the resistance mechanisms used by bacteria to evade antibiotics. Furthermore, the large surface area to size ratio of nanoparticles means that high activity can be achieved with a small dose, whereby minimizing the risk of toxicity. It is therefore hoped that nanoparticles may provide an effective alternative to antibiotics for the treatment of both free-swimming and surface bound bacteria.

Nanoparticles could be used in antimicrobial treatments and in the manufacture of nanocomposite products suitable for use in medical materials and devices.

Bioactive glass

Bioactive glass is a type of glass made from high-purity chemicals, such as silicon oxide, calcium oxide, and phosphorus oxide, that induces specific biological activity.4 Furthermore, by modifying the composition and structure of the glass, its physical properties can be tailored to meet a specific need.4

Bioactive glass elicits a negatively benign immune response and has been widely used in a range of biomedical applications, including tissue engineering, bone grafting, dental reconstruction and wound healing.5 It is able to bond to either hard or soft tissue and has been shown to facilitate strong new bone growth, promote soft tissue regeneration and enhance vascularization to ensure a healthy blood flow to the newly regenerated tissue.6–8 It has also been mixed with dental filling materials to promote the remineralization of dental caries.9

In addition, borate bioactive glass has been shown to have antimicrobial properties against a wide range of bacteria, including MRSA and E-coli.10 It has been shown that bacteria are unable to adhere to bioactive glass and so microfilms cannot develop on its surface.11 This is supported by clinical observations; no infections have been reported on bioactive glass implants.11 In addition, the inclusion of bioactive glass into dental filling material reduced bacterial penetration by 40%, whereby reducing the rate of decay and increasing the lifetime of the restoration.12

The antimicrobial action of bioactive glass can be further increased, giving the glass a broader spectrum of antimicrobial activity, by the addition of ions such as silver, yttrium, selenium, and iodine.13

The use of bioactive glass fibers to promote wound healing and soft tissue repair and the inclusion of bioactive glass in bone grafting and dental restoration composite materials to promote bone growth thus gives dual benefit — more rapid healing and reduced risk of infection.

Mo-Sci produces implant grade bioactive glass powders of varying sizes and with specific compositions suitable for mixing with composite materials.14

References

1. Davey ME and O’Toole GA. Microbial biofilms: from ecology to molecular genetics. Microbiology and Molecular Biology Reviews 2000;64(4):847–867.
2. Hall-Stoodley L, et al. Bacterial biofilms: from the natural environment to infectious diseases. Nature Reviews Microbiology 2004;2(2): 95–108.
3. Karwowska E. Antibacterial potential of nanocomposite-based materials – a short review. Nanotechnology Reviews 2016;6(2):243?254.
4. Brauer DS. Bioactive Glasses—Structure and Properties. Angew Chem Int Ed 2015;54: 4160–4181.
5. Rahaman MN, et al. Bioactive glass in tissue engineering. Acta Biomaterialia 2011;7:2355?2373.
6. Gerhardt L-C and Boccaccini AR. Bioactive Glass and Glass-Ceramic Scaffolds for Bone Tissue Engineering. Materials 2010;3:3867?3910
7. Pugely AJ, et al. Influence of 45S5 Bioactive Glass in A Standard Calcium Phosphate Collagen Bone Graft Substitute on the Posterolateral Fusion of Rabbit Spine. Iowa Orthop J. 2017; 37: 193–198.
8. Gorustovich A, et al. Effect of bioactive glasses on angiogenesis: In-vitro and in-vivo evidence: A review. Tissue Eng. Part B Rev. 2010;16:199?207.
9. 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
10. Ottomeyer M, et al. Broad-Spectrum Antibacterial Characteristics of Four Novel Borate-Based Bioactive Glasses. Advances in Microbiology 2016;6:776?787.
11. Zhang D, et al. Factors Controlling Antibacterial Properties of Bioactive Glasses. Key Engineering Materials 2007;330-332:173?176.
12. Khvostenko D, et al. Bioactive glass fillers reduce bacterial penetration into marginal gaps for composite restorations. Dental materials 2016;32(1):73–81. Available at http://www.demajournal.com/article/S0109-5641(15)00437-6/pdf
13. Xu Y, et al. Study on the Preparation and Properties of Silver-Doped Borosilicate Antibacterial Glass. Journal of Non-Crystalline Solids 2008;354:1342?1346.
14. Mo Sci Corporation website. http://www.mo-sci.com/en/products.