Sodium Citrate Used to Increase the Strength of Calcium Phosphate Cements for Biomedical Applications
A strengthened cement has been devised specifically for facial reconstructive surgery. Materials Scientists at the University of Birmingham’s School of Dentistry have discovered that by adding sodium citrate to the liquid phase, calcium phosphate cement is more than three times stronger.
A new benefit from this discovery is that metal screws can be fitted to the cement, giving a potential for load bearing and fixation devices, for example long bones such as legs and in jaw surgery. It is injectable through small needles so can get to inaccessible parts of the body with minimal invasive surgery.
Calcium phosphate cement has been used since the late 1980s years by surgeons as it sets rapidly and has a neutral pH at body temperature. However once set, it is a brittle, micro-porous ceramic with a strength less than 50 MPa. An ideal compressive strength should be above 100MPa, close to the average strength of human cortical bone.
Dr Jake Barralet, lecturer in biomaterials at the Birmingham School of Dentistry explains the application of his research: “Concrete is commonly used to patch holes in bones caused by trauma or disease. Unfortunately the strength of concrete is generally much lower than that of surrounding bone, making bone grafts difficult. Adding a small amount of sodium citrate which makes the cement particles pack together better, which combined with pressure to help compaction makes a denser cement with fewer pores. This strong cement may replace bone in critical, load-bearing sites and improve the patient’s recovery and quality of life”.
The research was led by the University of Birmingham’s School of Dentistry and the Department for Functional Materials in Medicine and Dentistry, University of Würzburg. It was published and discussed in the highly regarded Nature Materials journal. Tom Troczynski in the Department of Metals and Materials Engineering at the University of British Colombia called the idea “simple and brilliant”.
Sodium Citrate Modified Calcium Phosphate Cement for Bone Repair Applications
Background
Repairing cracks and holes in bones could be made much easier thanks to a finding that reduces the viscosity of bone cement. By using sodium citrate as a liquefier, clinical calcium phosphate can be altered from a toothpaste-like consistency into a creamy liquid that thickens with time. This means that more cement powder can be added, which in turn reduces the water content making a much stronger cement. Another advantage of this cement lies in the ease of its delivery, as the less viscous cement can be delivered through a needle allowing access to previously inaccessible areas.
Cement Liquefiers
Cement liquefiers are common among civil engineering applications, but using sodium citrate as a liquefier for clinical cement is both novel and non-toxic, which addresses the fundamental challenge of biomaterials - getting new properties from a limited pool of acceptable materials and chemicals.
To illustrate the strength of the resulting material, its developers Dr. Jake Barralet and Liam Grover at the University of Birmingham Dental School, UK, along with collaborators Dr Uwe Gbureck and Professor Roger Thull from the University of Wurzburg stood on a cylinder of the concrete measuring only 6mm in diameter. It supported them easily.
The Effect of Sodium Citrate Addition
Injectability
Barralet’s team started work on this development around 12 months ago armed with the knowledge that citric acid was used already in low concentrations as a retardant in apatite cements. ‘It has been claimed by previous researchers that this improves injectability - but these authors were referring to ejection from a 2mm diameter nozzle, not a 800 micron hypodermic needle. This is an important distinction to make because the ejection pressure is related to the fourth power of (1/diameter), so reducing the diameter by 2.5 times, as we did, would increase the pressure required to eject it by around 40 times. In fact it couldn’t be done and the needle kept getting blocked as at that pressure the liquid and solid in the cement separate, so the needle acts as a quick blocking filter,’ says Barralet.
The Effect of Reducing Pore Size
Barralet’s solution relies on an elegantly simple method of decreasing the pore size of calcium phosphate using trisodium citrate or citric acid. The trisodiurn citrate decreases interparticulate forces by means of an electrostatic mutual repulsion, which allows a reduction in the amount of pores in the sample - meaning a denser packing of particles and a stronger material. Results so far show that calcium phosphate modified in this way is up to 400% stronger that cement mixed with water. Results for trisodium citrate and citric acid gave compressive stresses of 153MPa and 116MPa respectively (using a compaction pressure of 50MPa), which shows an ideal replacement for cortical bone that has compressive stresses around the 100MPa mark.
‘Our finding was that sodium citrate was required for apatite cements, and that much higher concentrations of up to 0.5 molar were needed than had been used before. Citric acid and not sodium citrate is needed to get this effect in brushite cements.’
Applications
Vertebroplasty
One area that this modified cement could open up is in vertebroplasty which would need injectable material forming into a high strength composite to withstand the compressive forces of the spinal vertebrae.
Other Applications
Other areas that could benefit from cement with increased strength and lower viscosity include:
·        Craniofacial distraction - the team is working with researchers at Birmingham Children’s Hospital at expanding applications in this field that works to correct disorders such as obstructive sleep apnoea
·        Anchor points - cortical bone screws can be held in the cement so it could be used to create surgical anchor points
·        Fixation - since the cement is strong enough to be drilled through it may be used in conjunction with fixation hardware
·        Minimally invasive procedures - injectable formulations could be used to simplify procedures such as sinus floor augmentation
·        Pre-sets - such as a porous block made without sintering. Drugs could also be incorporated.
Summary
‘Being non-toxic, alpha hydroxy acid and salts may find other applications in stabilising mixtures such as slurries and liquefying pastes ceramics and cement industries,’ says Barralet. The team is now researching other applications and looking for a licensing partner and / or funds to proceed towards clinical trials.
Scintillation Materials – High Purity Crystals for Detectors in Nuclear Medical Imaging – Data by Sigma Aldrich
Background
Scintillation is the process by which a material converts radiation into light.
The use of scintillation in inorganic salts to detect radiation dates back over a century to when it was first used in the discovery and calibration of radioactivity. Today, scintillation detectors are used in a variety of remote sensing and non-invasive applications such as medical imaging, security screening for nuclear materials, astrophysical exploration and geophysical exploration in the pursuit of new energy reserves. At the heart of such detectors is a high purity material that scintillates in response to ionizing radiation. Over the decades, dozens of different scintillator materials have become commercially available and triggered further developments through continued research.
Key Factors for an Ideal Scintillator
Key factors for an ideal scintillator:
·        High light output (brightness)
·        High gamma ray stopping efficiency
·        Fast response
·        Low cost
·        Good proportionality
·        Minimal afterglow
Overcoming Materials Shortcomings
Although many candidate materials possess a good combination of physical properties, no single material provides the desired combination of stopping power, light output and decay time. To overcome some of these shortcomings, advanced signal processing techniques have been used; however, existing materials and signal processing technologies are approaching their physical limits, creating new material challenges.
Demands of Next Generation Scintillation Detectors
The ever more demanding imaging and exploratory applications call for the next generation of scintillation detectors to have very high response rates, be highly sensitive to low amounts of radiation and be tunable to specific radiation types.
General Types of Scintillator Materials
There are three general types of scintillator materials:
·        Organic
·        Inorganic
·        Gas
Organic Scintillator Materials
Properties of organic scintillator materials:
·        Fast response time
·        Low cost
·        Ease of processing
·        Poor light output
·        Non-linear conversion
Inorganic Scintillator Materials
Properties of inorganic scintillator materials:
·        Best light output
·        Most linear conversion
·        Highest sensitivity
·        Slow response times
Gaseous Scintillator Materials
Properties of gaseous scintillator materials:
·        Fast response time
·        Low scintillation efficiency
Producing the Ideal Inorganic Scintillator
Breakthroughs in materials processing, particularly techniques in making ultra-pure materials and in fabricating unique compositions for crystal growth, are enabling the pursuit of the ideal inorganic scintillator.
Sodium Iodide Doped with Thallium
The 1948 discovery by Hofstadter that sodium iodide doped with thallium exhibits extremely high light-yield and conversion efficiency launched the era of modern radiation spectrometry. More than half a century later, inorganic halide salts, particularly when doped, possess some of the best characteristics of all scintillation materials. Thallium doped sodium iodide, in fact, still exhibits the highest conversion efficiency of any known scintillation material (see Table 1). Scrap shards cut from desired crystals can be reprocessed by Sigma-Aldrich® to provide pristine materials, thus increasing the economic efficiency of scintillation crystal growth.
*Scintillation signal relative to NaI(Tl) at room temperature for g-rays when coupled to a photomultiplier tube with a Bi-alkali photocathode (the absolute energy conversion of NaI(Tl) is 0.12).
Doped Lanthanide Halides – A Promising New Class of Scintillator Materials
Doped lanthanide halides are a promising new class of scintillation crystals. Recent papers show that these materials not only possess high light output, but also the proportionality necessary for high-energy resolution. In addition, doped lanthanide halides exhibit fast response times and good gamma ray stopping efficiency. High-purity, anhydrous lanthanide halide source materials are expensive and difficult to obtain in the quantities necessary for bulk crystal growth. Sigma-Aldrich holds a unique position as a supplier of ultra-dry rare-earth salts available in bulk quantities.
Inorganic Halide Crystals Represent Benchmark Scintillator Materials
Inorganic halide crystals represent the benchmark in scintillator materials. They continue to meet material challenges through active research and development. Essential to the growth of these crystals are ultra-high purity, anhydrous source materials. Proprietary Sigma-Aldrich technology is used to produce beaded materials whose reduced surface area minimize moisture absorption and allow increased crucible loading, boosting crystal yield. Precursor materials must also be free of significant amounts of trace radioactive impurities. Research and manufacturing needs for source materials are met by suppliers like Sigma-Aldrich that can provide high quality materials and the technical knowledge and commitment necessary to help advance high technology applications.
Rubbers and Elastomers – An Introduction
Introduction
Elasticity is a property possessed by many solid materials, but the class of materials known as rubbers or elastomers possess a different property called high elasticity.
This differs from conventional Hookean elasticity in that it exhibits much higher values of elongation at break, up to 1000% or more.
This huge value for elongation at break means that many of the other properties measured in the accepted manner for metals show interesting variations.
Tensile strength, for example, although still calculated in the usual way using the initial cross sectional area, will give values much lower than the true stress in the material because the actual cross section at break will be approximately one tenth of the original value. Another important point is that, over the elongation at break range, the slope of the line varies substantially, giving typically an S-shaped curve, so that the normal engineering term of modulus becomes meaningless.
Rather confusingly a description of the relative stiffness of the rubbery materials, frequently used, is also called ‘modulus’. This is simply a measure of the load at a given elongation, e.g. ‘modulus at 300%’ is simply a stress value for the material at an elongation of 300% (i.e. at four times the original length). Although 300% is a commonly used value, a range of extensions is used to give ‘modulus’ values relevant to different applications. In the context of rubbers and elastomers modulus refers to this rubber property.
High Elasticity or Rubbery Elasticity
Elastomers are materials of a very high molecular weight, generally composed of one or more monomers polymerised or co-polymerised together to form a polymer (or copolymer). The polymer consists of a very long chain of monomer molecules chemically bonded together to form a single molecule with a molecular weight of several million. This large molecule, which will consist of several tens of thousands of the small (monomer) units bound together. It has a very large length to diameter ratio (often more than 10,000 to 1) and does not exist as a straight rod-like structure, but in a form known as a random coil. In a raw uncompounded polymer, each random coil will be entangled with many neighbours making flow difficult. The mass behaves like a liquid but with a viscosity some five million times that of water, but will eventually flow under the effects of stress and temperature.
Flow under stress is a severe limitation to the industrial utilisation of plain elastomers. It can be overcome by cross-linking. In this process the random coils are tied or cross-linked to others at intervals randomly along their length. This is achieved by reaction with added chemicals assisted by heating to 150 to 200°C.
The resultant mass still exhibits the characteristic high elongation and modulus behaviour because lengths of random coil between cross-links can still straighten under load. The extent of elasticity will depend upon the length of random coil between cross-links. A heavily cross-linked polymer will exhibit lower extensibility and higher stiffness than a lightly cross-linked example. A simple indentation hardness test is used to characterise blends for industrial applications.
Range of Properties
Rubber materials in use are required to have a wide range of properties, from very soft to very hard. These are generally obtained by the compounder, using a base polymer or polymer blend to give essential properties such as strength, ageing and environmental resistance, then modifying hardness and modulus properties using additives such as fillers to achieve a suitable compound.
Compounds containing only a vulcanising (cross-linking) system are generally known as gum compounds and generally have a density close to 1.0. Their modulus is affected by both the cross-link density and the ambient temperature.
Cross-link density must be kept between limits to ensure that ‘rubbery’ properties are retained.
The modulus shows an almost linear increase as the cross-link density increases but is mainly manipulated for engineering purposes by use of relatively large quantities of solid particulate materials called fillers. These range from cheap, inert materials such as washed clays and Whitings (calcium carbonates) to active, property enhancing materials, by far the most common being Carbon Black. This is why engineering rubber compounds tend to be black in colour.
By using a range of type, volume fractions, and particle sizes of black, perhaps in conjunction with other fillers, the shear modulus (G) of the compound can be varied over the approximate range 0.3 to 2.5 MNm-2.
Hardness
Rubber hardness is measured, like metals, by an indentation method. The normal UK method is to use International Rubber Hardness Degrees (IRHD). Values range from about 30 for a soft gum rubber to about 85 for a highly filled material. There is an almost linear relationship between Youngs Modulus and IRHD.
Physical Properties
The physical properties of a rubber compound have a complex dependence on the cross-link system, cross-link density, and the type and quantity of filler, but in general can be represented as in figure 1.
Figure 1. How an elastomer’s properties vary with filler loading or cross-linking density.
As the article deforms under a steadily increasing tensile stress its behaviour is not linear. The curve obtained is a characteristic S curve, see Figure 2.
Figure 2. Typical tensile behaviour of an elastomer.
However, the material behaves almost linearly in shear or compression deformation, figures 3a and 3b.
Figure 3. (a) Typical shear behaviour of an elastomer and (b) typical compression behaviour of an elastomer..
The early part of the Tensile curve is linear and the gradient of this is taken as a measure of the Youngs Modulus of the material (E). The Shear modulus, which can also be measured independently, can be shown to be one third of this value for a simple gum rubber network. The Shear modulus (G) ranges from about 0.3 MNm-2 upwards. For filled materials G can increase to about 2.5MNm-2, but E values then increase to 4 to SG. The Bulk (compressive) Modulus has the relatively high value of 1000 to 1300 Mm-2 and elastomers can be regarded, like most liquids, as effectively incompressible in a closed system.
1f the sample is relaxed before failure occurs the return stress strain curve follows closely the outward path, i.e. almost all the energy absorbed by the sample is returned on relaxation. This low level of energy loss (low hysteresis) in a cycle of deformation can be particularly useful. Rubber compounds can he used to isolate vibrating bodies (usually engines of all types), and the energy loss per cycle of vibration, although appearing in the rubber as heat, can be controlled by compound selection so that the bearing does not overheat.
One unique property of high quality rubber compounds is that high stresses can be sustained over a wide range of elongation, thus the area underneath the stress strain plot is high, and a considerable amount of energy can be absorbed before the sample fails.
All cross-linked polymers under stress suffer from stress relaxation or creep as the article undergoes small internal changes such as breaking (and possibly reforming) of individual cross-links suffering the highest stress levels. This is inconvenient but is fortunately quite predictable (linear against log time) and properly formulated Natural Rubber compounds can have very low creep rates (of the order of 2% per decade of time).
Glass Transition Temperature (Tg)
Elastomers have limited performance generally if a wide range of temperatures are considered. Low temperatures increase stiffness, and at a characteristic temperature called the Glass Transition temperature (Tg) the material loses all rubbery properties and becomes ‘glassy’, with characteristically brittle properties.
The Tg for NR is about -72°C, lower than most synthetics, but applications involving arctic environments need careful testing. Many elastomers become progressively `leathery’ as they cool towards Tg, their use in this state is not recommended.
Crystallisation
Under certain conditions some elastomers can ‘crystallise’. This is not usually desirable as it interferes with rubbery properties and occurs at temperatures well above Tg.
Crystallisation involves segments of a random coil coming into close proximity to a neighbouring coil allowing areas of high organisation (crystallites) to form within the bulk. It is not possible particularly with cross-linked polymers, for the whole mass to be crystalline and a ‘percentage crystallinity’ figure is used to describe the condition, which varies with polymer structure, level of orientation, and temperature. The stiffening (increased modulus) effect becomes evident as ambient temperature reduces, and can manifest itself over long periods of time. The effect, however, is completely reversible if the temperature increases.
Vulcanised Natural Rubber also suffers from crystallisation at high levels of extension when polymer chains are in sufficiently close alignment to enable associations to form, this is useful in resistance to cutting and tearing. However, normal usage of NR in applications in compression or shear will not produce this type of crystallinity.
Chloroprene rubbers have a higher tendency to crystallise and can show stiffening (modulus increase) with ageing in service. The type of cross-linking system used can have marked effects on long term performance, and even NR compounds can show stiffening on exposure to temperatures below 10°C, which is commonly experienced in many parts of the world.
Higher Temperature Effects
High temperatures generally increase the rate of ageing (degradation of properties with time) due to the environment. Temperatures of the order of 120°C, typical of automotive under bonnet temperatures, are quite severe for many common elastomers and careful selection of compounds is necessary for satisfactory performance.
Refractories – Self Flowing and Pumpable Castable Refractories
Background
Another development related to the low cement line of castables is that of self-flowing or pumpable castables, this affording a new dimension in installation. In the past most castables were installed by gunning or casting, the latter requiring internal or external vibration for the placement of low cement castables to fill in behind forms.
Advantages of Self Flowing Castables
The ability of the new self-flowing castables to move behind forms and around anchors in difficult to reach areas is a great advantage in installation. Typically, internal or external vibration was necessary for the placement of the low cement type castables to fill behind forms. Additionally, these self-flowing or pumpable castables may be transported to high elevations.
Characteristics and Properties of Self Flowing Castables
With such high self-flowing characteristics, it might be anticipated that these products would have higher shrinkage after curing, drying, and firing than the regular low cement castables. However, by maintaining a low water content with proper mix design that avoids segregation, this is not true. In fact, similar procedures may be used for curing, drying, and firing as for regular castables. Sections through properly prepared self flow LCC reveal the high density and uniform texture of the grain structure. These castables will self flow under their own weight and easily fill intricate shapes. While these self-leveling castables utilize sizing and cement content similar to low cement and ultra low cement castables, many separate features have been optimised to generate the self-flowing property. The physical properties of three types of self-flow castables are shown in Table 1.
Applications
This self-flowing property of a castable is indeed an installation advantage and many manufacturers are adopting their castable product line to be self-flowing. These self-flowing castables are now being used, often times replacing brick, plastics, and conventional castables, in installations in ladles, aluminum furnaces in the upper sidewalls and roofs, ceramic kiln car decks and in the steel industry in ladle covers, tundish covers, tundish safety linings, and precast shapes. They are also used in rotary kilns as nose rings, lifters, firing hoods, coolers, preheater maintenance, and in incinerators in charging zones and burners. Other special mixes are used in the aluminum industry at or near metal contact in the lower sidewalls, hearths, ramps, and door skills/jambs.
Refractories – Low Refractories – Refractory Binders
Background
The sole purpose of a refractory binder is to gel materials together in the green state. At elevated temperature binders then either dehydrate, volatise or sinter leaving behind a refractory material.
There are a number of binders which are commonly used for refractory applications, the most common of which is high alumina cement. They are always selected with the environment of the final application in mind.
Types of Bonds Formed in Monolithic Refractories
All refractory materials after their heat up to high temperatures.
Calcium Aluminate Cements
Calcium aluminate cements are the most common types of refractory binders. Following the addition of water they hydrate to form a network of hydrated species which bond the particulate materials together. During heating they dehydrate then undergo sintering, with the aggregate forming a strong ceramic bond.
Activated Aluminas
Activated aluminas or hydratable aluminas are used in ultra-low and cement-free castables. They consist of high surface area r-alumina species which are formed from partially calcined alumina hydrates. On the addition of water these materials will gel together in a cement-like action by forming alumina hydrates. One advantage of this system is that they do not introduce any calcia into the system, so the fired material will be more refractory. Often the hydration of activated aluminas can be slow and uncontrollable and small amounts of cement additions are required to trigger the reaction.
Recycling of Automotive Composites – The Pyrolysis Process and its Advantages
Background
14 million motor vehicles are scrapped in the EU each year, representing an enormous waste problem. Seventy-five percent of a modern car is composed of ferrous and non-ferrous metals, which are readily recycled back into the metals industries. However, the remaining 25% is composed of plastics, rubber and other components, which are currently disposed of in landfill. Compounding this problem is the automotive industry’s desire to use new, lighter materials, particularly plastic composites, to reduce weight and so improve fuel efficiency. Unfortunately composite plastic materials are generally regarded as being unrecyclable owing to the reinforcing fibres.
Recycling of Automotive Composites by Pyrolysis
The expertise of Leeds University in waste pyrolysis is now being applied to the problem of composite plastic waste. A two-year research project between the university and partners from British industry has led to a defined process to recover the glass fibres from composite plastic waste, and to produce an oil/wax product suitable for use as a liquid fuel or as a chemical feedstock to produce new plastics.
How Much of a Modern Car is Consists of Composites
Replacement of traditional metal components by composite plastics in applications such as bumpers, under bonnet components, body panels and exterior trim has significantly reduced the weight of the average car. Typically, 10% of a vehicle’s weight (wt%) is made up of plastics and plastic composites, and for some lightweight vehicles this may be up to 20 wt%. Composites are increasingly used since they have the advantages of strength, durability and corrosion resistance together with low weight.
Materials Used in Automotive Composites
Composites are composed of many different components, including glass fibre reinforcement, filler material and the thermoset or thermoplastic polymer, which is the matrix or continuous phase. The plastic polymer components commonly used include thermoset polyester, phenolic resin, epoxy resin, polypropylene and vinylester resin. It is the mixture of components embedded in the matrix that make composites difficult to recycle and the reason why such a high percentage is sent to landfill. Consequently, there is a need to identify novel process routes to enable the recycling of composite materials, particularly in light of the European Union End of life Vehicle (ELV) Directive (2000), which requires Member States of the EU to reuse and recover 85 wt% of the average vehicle weight by 2006, increasing to 95 wt% by 2015.
What is Pyrolysis and What is Its Advantage?
The research group at Leeds University has researched the application of pyrolysis for waste processing for more than 15 years funded mainly through research grants from the UK Engineering and Physical Sciences Research Council (EPSRC). Pyrolysis is the thermal degradation of the waste polymer component in the absence of oxygen. The polymer breaks down to produce an oil/wax a gas and a char product, leaving a solid friable residue. Pyrolysis has the advantage that potentially all of the products from the process can be used.
What is The Process Designed to Do?
To date the group’s work has involved collaborations with industrial partners investigating the pyrolysis of scrap tyres, plastic wastes and municipal solid wastes. In this latest project, the research concentrated on developing a process to separate and clean the glass fibre in composite components, and to investigate its use in new products.
Product Yields for Pyrolysis of Various Polymer Matrix Composite
The term composites covers a broad range of mixed components, and pyrolysis will consequently produce a range of products. Table 1 shows the product yield for a range of composite materials pyrolysed at 500°C. Pyrolysis depolymerises the polymer chain producing wax, oil and gas (the gas has sufficient energy content to provide the energy requirements of the pyrolysis process plant) derived from the original plastic. The gas composition produced is again dependent on the original plastic used in the composite. For oxygen-containing plastics such as polyester and phenolic resins, the main gases are carbon dioxide and carbon monoxide. For other plastics, higher concentrations of hydrogen and hydrocarbons, such as methane and ethane, are dominant. The wax and oil are given off as gases during pyrolysis but are condensed downstream. The oil and wax have a high calorific value and can be burnt to provide energy. Alternatively, they can be used as a source of valuable chemicals. The solid residue left behind after pyrolysis is a friable solid containing the glass fibre and filler, and a small amount of carbonaceous char derived from the plastic degradation.
Led by Pera Technology, the research partnership, which included industrial partners from the British Plastics Federation, Society of Motor Manufacturers and Traders, Filon Products, Cray Valley, OSS Group, Reichold and Shanks Waste Solutions, decided to concentrate on glass fibre reinforced styrene-polyester co-polymer composite as a typical high usage material.
Properties and Uses for the Oil and Wax Produced by the Pyrolysis Reaction
Pyrolysis converted 40% of the composite plastic waste into oil, which had fuel properties similar to those of a petroleum-derived gas oil. In addition, the oil contained 25 wt% of styrene, which was used in the production of the styrene-polyester copolymer. As well as producing the oil, the plastic was thermally degraded into a wax composed of more than 95 wt% of phthalic anhydride, which was used in the production of the composite material. The use of the oil and wax as a chemical feedstock in the production of new plastic materials has much greater value than the their use as substitute
Low Temperature Benefits of the Pyrolysis Process
One of the major and valuable constituents of composite plastic wastes is glass fibre. The problem for glass fibre recovery is to use process conditions that do not degrade the fibre strength, and the key parameter is the temperature. Above 800°C the fibres become very brittle and quickly lose strength. Pyrolysis has the advantage of low process temperatures of less than 500°C which retains the strength and flexibility of the virgin glass fibre.
Separation of the Glass Fibres
Separation of the glass fibre from the filler was achieved using a drum carder machine, which gently separates the fibres from the friable char and filler matrix. The fibres can then be used as char-coated fibres to produce new composite plastic materials. Alternatively, the blackened glass fibre can be cleaned using low-temperature furnace oxidation to burn off the char to produce cleaned fibre.
Re-Using Recycled Glass Fibre
The recovered glass fibre, both cleaned and char-coated, were made up into test samples of a new composite by the industrial partners. Test samples incorporating 25 wt% of the recovered glass fibre and 75 wt% virgin glass fibre were compared to a controlled sample containing 100 wt% virgin glass fibre. The results showed that up to 25 wt% of recycled fibre could successfully be incorporated into a new composite while still meeting manufacturers specifications.
Summary
Overall the application of pyrolysis as a process route for a difficult waste stream in the form of composite plastic waste appears to show potential. The next step will involve scaling up the process to pilot plant scale, and the partnership is investigating further funding opportunities. Figure 1 shows a schematic diagram of the proposed pyrolysis recycling process. A cost-effective recycling process is an essential step towards sustainable manufacturing. It will be particularly important for the automotive industry as it prepares to meet the requirements of the European End of life Vehicle Directive. Additionally, for plastics manufacturers, the process could have a major impact in overcoming resistance to composites for new applications in an increasing range of advanced, lightweight components.
AZoM - Metals, Ceramics, Polymer and Composites : Recycling of Automotive Composites – The Pyrolysis Process and its Advantages
Figure 1. Schematic diagram of the proposed pyrolysis recycling process for composites.
Raw Material Assessment and Control as a Factor in Manufacturing Quality
Background
Australia is operating in a global market where increased competition is demanding:
·        More diverse product ranges
·        More complex product shapes
·        Higher product qualities
·        Automated production methods
·        Greater flexibility of production
·        Shorter lead times
·        Lower manufacturing losses.
These driving forces for change have certain implications for raw materials and supplier/manufacturer interaction. In particular, the raw materials must possess tighter specifications, be consistent in terms of key properties and be competitively priced.
Constraints Faced by Australian Organisations
Particular constraints faced by Australian companies include:
·        Lower value of dollar making refined imported raw materials very expensive
·        Transport costs both to and within Australia;
·        Poor continuity of supply of indigenous raw materials. Local Australian raw material suppliers are very mixed in their attention to a “standard supply”. It is probably not viable for multi million dollar mining companies to produce 500 tons per month of clay or feldspar
·        Small industry base with little purchasing power.
Ceramic Whiteware Raw Materials
The term raw materials usually refers to all the materials that are physically incorporated into the final product and often comprise auxiliary materials such as binders which affect the products intermediate properties e.g., unfired strength.
In order to appreciate the behaviour of products during manufacture and to develop new products using the most appropriate materials, an understanding of the various raw materials is essential.
Raw materials can either be:
·        Natural raw materials e.g., clays, feldspars, quartz or
·        Materials that have been highly refined or produced synthetically e.g., frits, oxides, opacifiers, pigments.
Natural Raw Materials
Naturally occurring minerals may either be used “as mined” or in a pre-treated form e.g., calcined, ground, blended. Pre-treatment helps to reduce the natural variability of mineral deposits to give consistent supply when using raw materials and is becoming increasingly commonplace, as processes are automated and require more consistent materials.
Synthetic Raw Materials
The highly refined or synthetically produced materials such as the frits and industrial chemicals which are often used are relatively expensive, but are employed for specific properties which they impart e.g., lower firing temperatures, low contamination.
Criteria for the Choice of Materials
Two basic criteria are used for choosing materials:
·        Cost and availability
·        Chemical and physical properties
Cost and Availability
Fortunately for ceramics, raw materials are plentiful and relatively cheap. Silicon is the second most abundant element in the earth’s crust (after oxygen). Feldspars account for 60% of the earth’s crust and clays occur worldwide.
Another element in cost reduction is to look increasingly at the use of indigenous raw materials instead of more expensive, imported raw materials.
Choosing raw materials on cost alone can however, be very dangerous and the following example, emphasises the influence of careful materials choice on the economics of production.
Table 1 compares a raw sanitaryware glaze prepared using different raw materials. Only the cost of he materials, using current United Kingdom (U.K.) tonnage prices, has been considered and any extra processing or production problems which may be associated with lower grade materials has been ignored.
The “accountants” glaze has been prepared using the cheapest raw materials to give overall glaze composition. However, these materials may have high iron and titanium contents which would cause the glaze to be coloured. They may also require more grinding than more expensive materials. This glaze works out three times cheaper than the “technicians” glaze, which uses the cleanest materials and replaces part of the quartz and calcium carbonate with wollastonite. This would give the whitest glaze with the lowest gas evolution.
Clearly the choice of raw materials lies somewhere between the two depending on the quality of fired product required.
From 1993 to 1995, an international project comprising 25 companies (suppliers and manufactures) worldwide led by CERAM, identified key material properties for both raw materials and prepared bodies and recommended a suite of standard, in-house test methods.
The key properties of raw materials are defined as:
·        Chemical composition and loss on ignition
·        Particle size
·        Mineralogical composition
·        Soluble salts
·        Moisture content
Bulk chemistry and particle size are particularly important as without these two characteristics vitrification and densification at acceptable firing temperatures in acceptable times would not be possible. This means that these two properties can only vary between narrow limits otherwise it will lead to major differences in the way in which formulations interact with water and deflocculating chemicals.
It is often not practical to carry out chemical and mineralogical analysis of the materials at the factory site. However, it is feasible to measure moisture content and particle size and simple observations can be made on the state of the incoming raw materials e.g., specks.
Chemical Composition and Loss on Ignition
The materials primary functions are to supply the requisite oxides to produce the right product when fired and thus should be consistent chemically otherwise they can create problems particularly where automated systems are used or colour matching is required. Both organic and inorganic constituents are important.
The material supplier should provide up-to-date information concerning the materials and provide assurance of consistency of supply.
Particle Size
Along with the composition of the incoming materials, the particle size should be well known and controlled if any grinding operation takes place. Under or over ground materials may both have an adverse effect on the quality of the finished article.
Control of particle size in plastic materials such as clays can influence casting rates, deflocculation demand, packing density, viscosity on standing, cast firmness, strength etc.
Control of particle size distribution for non plastics e.g., flux and silica is crucial in ensuring that vitrification takes place at acceptable temperatures. Too fine (90% <10µm) a flux results in bloating in the body, crawling in a glaze or less intense, pale fired colours.
Mineralogical Composition
Identifies the crystalline materials present e.g., the level of flux and filler. Different clay mineral compositions can severely affect processing properties such as drying shrinkage, cracking and slip deflocculation characteristics.
Soluble Salts
Soluble salts e.g., sulphates and chlorides are also important as these can influence deflocculation demand and hence unfired properties such as strength, firmness, and plasticity.
Their presence may also promote glaze crawling.
Moisture Content
A regular moisture content is important and should be measured not only for slip calculations but also to ensure that water is not being purchased in place of the material.
Other Key Properties
Other factors combine to determine the final choice of material such as the shrinkage on drying and firing, suspension and binding properties, dry strength, and plasticity.
Vitrification characteristics, decomposition on firing, presence of colouring oxides, particle size and mineralogy also influence the choice of raw materials.
Often the requirement of one part of the process requires a material with a property that conflicts with that required for another. For example, the demands of a slip casting process are influenced by the plastic (clay) materials whilst the vitrification process relies on the fineness and nature of the non-plastics. Compromise once again needs to be made and accepted.
The Advantages of Material Characterisation
Material characterisation plays a vital role in trouble shooting and ensures manufacturers become pro-active rather than reactive to loss reduction.
Specking faults for example are a constant problem in the Whiteware industry and can account for up to 10% of total faults. They may be caused by contaminants, which can be introduced by raw materials. Identification prior to manufacture can reduce production losses.
Materials Characterisation Case Study
Particle size variations also account for many production losses. For example, during the course of one year the ball clay used by one sanitaryware organisation gradually become coarser. To compensate for the resultant increase in casting rates, greater levels of organic deflocculant were used such that the viscosity on standing continually increased. The casts that formed had a hard face at the mould surface with a soft centre. Cracks developed from the inside and the casts had a tendency to tear. The slip was also difficult to drain. Production losses gradually increased. Once the particle size increase had been identified as the problem, alternative deflocculation practices were recommended to compensate for the change. Production yields increased by 14%.
Compensating for Raw Material Variations
Although suppliers are taking increasing care in the refining of materials it is inevitable that the clays, in particular, will have variable properties. It is therefore important to understand the effect that variations in the properties of the raw materials may have before they are used and to adjust the composition accordingly (± 2-3%).
The advantages of this approach are that problem batches are detected early and manufacturers have a flexible attitude to product reformulation although it does require investment in acceptance test equipment and procedures.
Summary
By appreciating the requirements placed on each raw material and the properties and oxides they impart, an insight into the performance of the production process and subsequent products can be gained.
Close control of raw material properties is important for automated production, loss reduction and higher quality as the products will posses certain features such as good dimensional stability and colour.
For more details on the recommended suite of test methods to measure the most important properties of raw materials contact CERAM Research.
PVD Materials – Materials Available for Physical Vapour Deposition ( PVD ) from Williams Advanced Materials
Background
Williams Advanced Materials provides materials in a variety of shapes and forms including Slugs, Starter charges, Crucibles, Targets - all configurations. Wire, Clips, Rod, Splatter, Random Shot, Tube
Other related services include:
·        State-of-the-art Bonding Centers located worldwide.
·        Refining and recycling of precious metal scrap.
·        Complete metallurgical, chemical and functional test lab. Receiving
PVD Materials
Williams Advanced Materials provide a vast range of materials for the production on thin films via physical vapour deposition (PVD). These materials can be broadly classed into the following categories:
·        Pure Metals
·        Precious Alloys
·        Alloys & Cermets
·        Borides
·        Carbides
·        Fluorides
·        Nitrides
·        Silicides
·        Oxides
·        Others
Pure Metals
Pure metals PVD materials supplied by Williams Advanced Materials include:
·        Aluminum, Al
·        Antimony, Sb
·        Beryllium, Be
·        Bismuth, Bi
·        Boron, B
·        Cadmium, Cd
·        Calcium, Ca
·        Carbon, C
·        Cerium, Ce
·        Chromium, Cr
·        Cobalt, Co
·        Copper, Cu
·        Erbium, Er
·        Gadolinium, Gd
·        Gallium, Ga
·        Germanium, Ge
·        Gold, Au
·        Hafnium, Hf
·        Indium, In
·        Iridium, Ir
·        Iron, Fe
·        Lanthanum, La
·        Lead, Pb
·        Magnesium, Mg
·        Manganese, Mn
·        Molybdenum, Mo
·        Neodymium, Nd
·        Nickel, Ni
·        Niobium, Nb
·        Osmium, Os
·        Palladium, Pd
·        Platinum, Pt
·        Praseodymium, Pr
·        Rhenium, Re
·        Rhodium, Rh
·        Ruthenium, Ru
·        Samarium, Sm
·        Selenium, Se
·        Silicon, Si
·        Silver, Ag
·        Tantalum, Ta
·        Tellurium, Te
·        Terbium, Tb
·        Tin, Sn
·        Titanium, Ti
·        Tungsten, W
·        Vanadium, V
·        Ytterbium, Yb
·        Yttrium, Y
·        Zinc, Zn
·        Zirconium, Zr
Precious Alloys
Precious alloy PVD materials supplied by Williams Advanced Materials include:
·        Gold Antimony, Au/Sb
·        Gold Arsenic, Au/As
·        Gold Boron, Au/B
·        Gold Copper, Au/Cu
·        Gold Germanium, Au/Ge
·        Gold Nickel, Au/Ni
·        Gold Nickel Indium, Au/Ni/In
·        Gold Palladium, Au/Pd
·        Gold Phosphorus, Au/P
·        Gold Silicon, Au/Si
·        Gold Silver Platinum, Au/Ag/Pt
·        Gold Tantalum, Au/Ta
·        Gold Tin, Au/Sn
·        Gold Zinc, Au/Zn
·        Palladium Lithium, Pd/Li
·        Palladium Manganese, Pd/Mn
·        Palladium Nickel, Pd/Ni
·        Platinum Palladium, Pt/Pd
·        Palladium Rhenium, Pd/Re
·        Platinum Rhodium, Pt/Rh
·        Silver Arsenic, Ag/As
·        Silver Copper, Ag/Cu
·        Silver Gallium, Ag/Ga
·        Silver Gold, Ag/Au
·        Silver Palladium, Ag/Pd
·        Silver Titanium, Ag/Ti
Alloys and Cermets
Alloy and cermet PVD materials supplied by Williams Advanced Materials include:
·        Aluminum Copper, Al/Cu
·        Aluminum Silicon, Al/Si
·        Aluminum Silicon Copper, Al/Si/Cu
·        Aluminum Titanium, Al/Ti
·        Chromium Manganese Palladium, Cr/Mn/Pd
·        Chromium Manganese Platinum, Cr/Mn/Pt
·        Chromium Molybdenum, Cr/Mo
·        Chromium Ruthenium, Cr/Ru
·        Chromium Silicon Oxide, Cr/SiO
·        Chromium Vanadium, Cr/V
·        Cobalt Chromium, Co/Cr
·        Cobalt Chromium Nickel, Co/Cr/Ni
·        Cobalt Chromium Platinum, Co/Cr/Pt
·        Cobalt Chromium Tantalum, Co/Cr/Ta
·        Cobalt Chromium Tantalum Platinum, Co/Cr/Ta/Pt
·        Cobalt Iron, Co/Fe
·        Cobalt Iron Boron, Co/Fe/B
·        Cobalt Iron Chromium, Co/Fe/Cr
·        Cobalt Iron Zirconium, Co/Fe/Zr
·        Cobalt Nickel, Co/Ni
·        Cobalt Nickel Chromium, Co/Ni/Cr
·        Cobalt Nickel Iron, Co/Ni/Fe
·        Cobalt Niobium Hafnium, Co/Nb/Hf
·        Cobalt Niobium Iron, Co/Nb/Fe
·        Cobalt Niobium Titanium, Co/Nb/Ti
·        Cobalt Platinum, Co/Pt
·        Cobalt Zirconium Niobium, Co/Zr/Nb (CZN)
·        Cobalt Zirconium Rhodium, Co/Zr/Rh
·        Cobalt Zirconium Tantalum, Co/Zr/Ta (CZT)
·        Copper Nickel, Cu/Ni
·        Iron Aluminum, Fe/Al
·        Iron Cobalt, Fe/Co
·        Iron Rhodium, Fe/Rh
·        Iron Tantalum, Fe/Ta
·        Iron Tantalum Chromium, Fe/Ta/Cr
·        Manganese Iridium, Mn/Ir
·        Manganese Palladium Platinum, Mn/Pd/Pt
·        Manganese Platinum, Mn/Pt
·        Manganese Rhodium, Mn/Rh
·        Manganese Ruthenium, Mn/Ru
·        Nickel Chromium, Ni/Cr
·        Nickel Chromium Silicon, Ni/Cr/Si
·        Nickel Cobalt Iron, Ni/Co/Fe
·        Nickel Iron, Ni/Fe
·        Nickel Iron Chromium, Ni/Fe/Cr
·        Nickel Iron Rhodium, Ni/Fe/Rh
·        Nickel Iron Zirconium, Ni/Fe/Zr
·        Nickel Manganese, Ni/Mn
·        Nickel Vanadium, Ni/V
·        Tungsten Titanium, W/Ti
Borides
Boride PVD materials supplied by Williams Advanced Materials include:
·        Chromium Boride, CrB2
·        Lanthanum Boride, LaB6
·        Molybdenum Boride, Mo2B5
·        Niobium Boride, NbB2
·        Tantalum Boride, TaB2
·        Titanium Boride, TiB2
·        Tungsten Boride, W2B
·        Vanadium Boride, VB2
·        Zirconium Boride, ZrB2
Carbides
Carbide PVD materials supplied by Williams Advanced Materials include:
·        Boron Carbide, B4C
·        Chromium Carbide, Cr3C2
·        Molybdenum Carbide, Mo2C
·        Niobium Carbide, NbC
·        Silicon Carbide, SiC
·        Tantalum Carbide, TaC
·        Titanium Carbide, TiC
·        Tungsten Carbide, WC
·        Vanadium Carbide, VC
·        Zirconium Carbide, ZrC
Fluorides
Fluoride PVD materials supplied by Williams Advanced Materials include:
·        Aluminum Fluoride, AlF3
·        Barium Fluoride, BaF2
·        Calcium Fluoride, CaF2
·        Cerium Fluoride, CeF2
·        Cryolite, Na3AIF6
·        Lithium Fluoride, LiF
·        Magnesium Fluoride, MgF2
·        Potassium Fluoride, KF
·        Rare Earth Fluorides
·        Sodium Fluoride, NaF
Nitrides
Nitride PVD materials supplied by Williams Advanced Materials include:
·        Aluminum Nitride, AlN
·        Boron Nitride, BN
·        Niobium Nitride, NbN
·        Silicon Nitride, Si3N4
·        Tantalum Nitride, TaN
·        Titanium Nitride, TiN
·        Vanadium Nitride, VN
·        Zirconium Nitride, ZrN
·        Si3N4/TiN
Silicides
Silicide PVD materials supplied by Williams Advanced Materials include:
·        Chromium Silicide, CrSi2
·        Molybdenum Silicide, MoSi2
·        Niobium Silicide, NbSi2
·        Platinum Silicide, PtSi
·        Tantalum Silicide, TaSi2
·        Titanium Silicide, TiSi2
·        Tungsten Silicide, WSi2
·        Vanadium Silicide, VSi2
·        Zirconium Silicide, ZrSi2
Oxides
Oxide PVD materials supplied by Williams Advanced Materials include:
·        Aluminum Oxide, Al2O3
·        Antimony Oxide, Sb2O3
·        Barium Oxide, BaO
·        Barium Titanate, BaTiO3
·        Bismuth Oxide, Bi2O3
·        Bismuth Titanate, Bi4Ti3O12
·        Ba Sr Titanate, BST
·        Chromium Oxide, Cr2O3
·        Copper Oxide, CuO
·        Hafnium Oxide, HfO2
·        Indium Oxide, In2O3
·        Indium Tin Oxide, ITO
·        Lanthanum Aluminate, LaAlO3
·        Lanthanum Oxide, La2O3
·        Lead Titanate, PbTiO3
·        Lead Zirconate, PbZrO3
·        Lead Zirconate-Titanate, PZT
·        Lithium Niobate, LiNbO3
·        Magnesium Oxide, MgO
·        Molybdenum Oxide, MoO3
·        Niobium Pentoxide, Nb2O5
·        Rare Earth Oxides, RE2O)
·        Silicon Dioxide, SiO2
·        Silicon Monoxide, SiO
·        Strontium Oxide, SrO
·        Strontium Titanate, SrTiO3
·        Tantalum Pentoxide, Ta2O5
·        Tin Oxide, SnO2
·        Titanium Dioxide, TiO2
·        Tungsten Oxide, WO3
·        Yttrium Oxide, Y2O3
·        Zinc Oxide, ZnO
·        ZnO/Al2O3
·        ZnO/In2O3
·        Zirconium Oxide, ZrO2
Others
Other PVD materials supplied by Williams Advanced Materials include:
·        Bismuth Telluride, Bi2Te3
·        Cadmium Selenide, CdSe
·        Cadmium Sulfide, CdS
·        Cadmium Telluride, CdTe
·        Lead Selenide, PbSe
·        Lead Sulfide, PbS
·        Lead Telluride, PbTe
·        Molybdenum Selenide, MoSe2
·        Molybdenum Sulfide, MoS2
·        Zinc Selenide, ZnSe
·        Zinc Sulfide, ZnS
·        Zinc Telluride, ZnTe
·        ZnS/SiO2
Paint That Soaks Up Noxious NOx Fumes Thanks to Nanotechnology
Millennium Chemicals is about to release Ecopaint, a revolutionary new paint that can soak up nitrogen oxide NOx, gases. NOx gases are produced by car exhaust emissions and manufacturing operations and are a pollution source that leads to smog as well as respiratory problems.
Ecopaint is claimed to be able to effectively soak up NOx gases for 5 years. Trials of a similar coating in Milan lead to NOx levels being reduced by 60 per cent at the street level, making the air noticeably easier to breathe.
The paint contains spherical nanoparticles of titanium dioxide (TiO2) and calcium carbonate (CaCO3) in a silicon-based polysiloxane polymer. The nanoparticles are 30nm in diameter and the resultant paint clear, so pigments can be added to give it colour.
The polysiloxane polymer is porous, and allows the NOx gases to infuse and adhere to the titanium dioxide particles. Exposure to ultraviolet radiation from sunlight converts the NOx to nitric acid (HNO3), which is neutralised by the calcium carbonate. This interaction produces carbon dioxide (CO2), water and calcium nitrate (Ca(NO3)2) which are harmlessly washed away.