Inhalers – Demonstration of the Use of Surface Analysis Techniques to Resolve Problems Associated with Inhalers
Surface Analysis of Blemishes on the Inner Surfaces of Aluminium Metered Dose Inhaler (MDI) Cans
The purpose of this work was to investigate the appearance of blemishes on the inner surface of aluminium MDI cans.
Surface analysis of the blemishes suggests that the stain is a water drying stain.
It was shown that the area of interest was rich in calcium, sodium and chlorine.
Analysis of a Stain on the Outer Surfaces of Aluminium Metered Dose Inhaler (MDI) Cans
The aim of this work was to analyse a stain on the outer surface of an MDI can.
XPS and ToF-SIMS were used to characterise the stain. Analysis showed the stain to be organic in nature, characterised by a series of compounds which were based on fatty acids and found in lubricating oils.
Investigation into the Molecular Weight Distribution of a Fluorocarbon Coating on Barrels of a Metered Dose Inhaler (MDI)
The aim of this work was to analyse fluorocarbon-coated MDI barrels after partial silver metallisation in order to determine the molecular weight distribution.
ToF-SIMS analysis showed:
Depositions of sub-monolayer levels of silver for silver cationisation experiments were successful. For the three-sputter deposition times, 0.5 s, 1 s and 2 s, the fluorocarbon coating was only partially covered. As expected, the silver coverage increased with the deposition time.
The coating is consistent with an oxygenated fluorocarbon material. There is also evidence for the incorporation of nitrogen-containing species on/in the fluorinated surface.
There is clear evidence for interaction between the deposited silver and the oxygenated fluorocarbon coating, there is no evidence for high mass fluorocarbon-based cations giving rise to an oligomer distribution pattern.
Analysis of Metered Dose Inhaler (MDI) Barrels
The aim of this investigation was to analyse, un-used, filled and ex DTU MDI barrels using XPS and ADXPS.
Surface analysis showed:
There was significant silicone contamination of some of the barrel surfaces. The silicone is thought to originate from the lubricant, which is applied to the barrel assembly during construction/filling.
Generally there is a clear decrease in fluorine concentration with increasing analysis depth for all the barrels. However, the size of the decreases relative to the overall concentrations are marginal but do represent a ‘thinning’ of the coating.
In general the angle dependent data shows a gradual, almost linear, transition between fluoro-carbon character and substrate character which would suggest a diffuse structure rather than a discrete layer of fluoro-carbon on the substrate
No significant trend in CF3:CF2 ratio is found for changes in sampling depth or for the different barrel conditions for any particular batch.
Surface Characterisation of Plasma Fluorinated Polymer Metered Dose Inhaler (MDI) Barrels
The aim of this investigation was to characterise the surface of plasma fluorinated polymer MDI barrels.
XPS and Imaging DSIMS analysis has showed:
Layer thicknesses for all samples typically lie in the range 2nm - 4nm.
Although the coating is thin it is notably uniform and complete despite the fact that the barrels are substantially roughened by machinery.
There is no significant correlation of thickness with feed gas or treatment time.
One sample showed distinct areas of relative F- depletion.
An XPS investigation of Discoloration and “Rusting†on Metered Dose Inhaler (MDI) Stem Samples
This study was commissioned to determine if the brown deposit was in fact rust and to investigate the cause of the other discoloration.
The XPS investigation showed:
Significant differences in surface composition and chemistry.
Boron, probably as nitride, was detected after annealing, suggesting boron impurity in the steel.
There was significant evidence that the brown deposit was rust resulting from corrosive attack by saline (sodium/potassium chloride) material.
There was evidence for iron oxidation and growth of a surface chromium oxide film. A large concentration of organic material was also present on the discoloured surfaces.
Analysis of Inhaler Blends
Surface analysis of inhaler blends by DSIMS imaging, to monitor the relative distribution of active drugs and carriers.
DSIMS mass spectral and image data identified:
Particles of carrier A were identified.
Drugs Y & Z were identified on the surface of particles of carriers A & B
Analysis of the Contents of Inhalers using ToFSIMS and XPS
This work was carried out to determine the presence or otherwise of fluorocarbon species within the contents of inhalers.
ToFSIMS and XPS investigations showed:
Oxygenated fluorocarbon material was detected from the residues of one set of samples only. For these samples the metering chamber and can have a fluorocarbon coating.
Silicone is deposited for all samples and has been attributed to a lubricant used during the assembly of the metered dose inhalers.
XPS Analysis of “Brown Blemishes†on an Aluminium Inhaler Cans
The aim of this work was to investigate the occurrence of Brown blemishes believed to be organic residues on an aluminium inhaler can.
An XPS investigation showed:
The discoloration in the blemishes does not appear to be due to superficial organic contamination since there is as much carbonaceous material off the blemished region as there is on the stain and the stain is not affected by ultrasonic cleaning in acetone.
The presence of sodium and chlorine, albeit at low levels, may indicate that a corrosion mechanism is involved in the formation of the blemishes.
An XPS Investigation of Active Loading on Drug Powders for Dry Powder Inhalers (DPIs)
The aim of this work was to investigate the potential of surface analysis using XPS for measuring directly the active loading at the surface of DPI powders, and for investigating chemical interactions between the active drug species and the lactose carrier.
The XPS investigation showed:
The surface compositions of the reference components were in good agreement with their chemical formulae.
The compositions of the drugs were measured and the relative fractions of the three components derived.
It was not possible to distinguish between the two populations of drug from these XPS data alone.
The ratio of sulfur to fluorine was found to be very variable in the drugs.
Investigation into the Leakage of a Metered Dose Inhaler
The aim of this work was to investigate the cause of a leakage of a metered dose inhaler.
ToFSIMS and XPS investigations concluded:
The large spot of white deposit on the valve gasket is considered to be the symptom of the inhaler leakage problem, not the cause. Leakage is attributed to the presence of an aluminium/aluminium-rich flake on the valve gasket prior to sealing of the inhaler unit. This resulted in localised damage of the softer gasket surface, compromising the seal integrity with subsequent leakage of contents.
Diesel Engine Coolant AnalysisDental Materials
Background
Modern dental practice has become very dependent on its materials, such that the dentist’s greatest challenge is choosing the right combinations of them for the benefit of their patients.
Metallic Fillings
Silver Amalgams
For over 150 years, silver amalgam has been used to fill the cavities made by dentists during the removal of dental decay from teeth. When pure silver (melting point 961°C) is mixed with mercury (mp -39°C) it produces a paste of slowly forming intermetallic compounds. When this is packed into the cavity at body temperature (37°C), the intermetallic compounds interlock and the amalgam hardens. However, setting is accompanied by a considerable expansion, and 100 years ago it was discovered that this can be controlled by adding tin to the silver. Unfortunately, this produces corrodible tin-mercury intermetallic phases, and their loss can cause breakdown of the filling.
By adding copper, the tin-mercury phase is eliminated and modern dental amalgams are made by mixing silver-tin-copper alloy powder with mercury. This results in fillings that resist both the mechanical and chemical onslaughts within the mouth for many years.
Although the amount of mercury lost from such fillings is like the contamination of a drink by a drowning midge, those determined to deny the benefits of having usefully restored teeth have over emphasised the risk, and this has generated a search for an alternative, metallic, mercury-free, filling material.
Alternatives to Silver Amalgams
Gallium (mp 30°C) has been combined with indium and tin to produce an alloy that is molten at normal room temperature, and when this is mixed with powdered silver-tin-copper it produces a paste that sets. However, packing this paste has proved to be a challenge, and the best results have been obtained when packing under ethanol. The fillings produced from these alloys are also very prone to dramatic corrosion. The jury is out over the long-term toxicological effects of gallium, which has a clean record so far.
Experimental silver-coated intermetallic particles have been cold welded under pressure to fill well-supported cavities. Unfortunately, these are not the ones in which amalgam is the most useful.
Resin-Based Composite Fillings
These tooth-coloured filling materials have reached a high degree of sophistication since their appearance on the dental scene in the early 1960s. A modern dental composite consists of a paste created by combining a mixture of dimethacrylate monomers and cross-linking agents (known in dentistry as resins) with up to 80% by weight of silane-coated, ceramic particles (the filler), whose sizes range from 0.04-4 microns. This composite paste is packed into a dental cavity and the dentist exposes it for about 30 seconds to intense visible blue light. The light activates a chemical initiator within the composite and the resins undergo free radical addition polymerisation via their vinyl groups, turning the paste into a durable, solid filling.
Disadvantages of Resin-Based Composite Fillings
Composite fillings have similar strengths to amalgam but they tend to wear away more rapidly. They also shrink as they polymerise, and efforts have to be made to prevent gaps forming between the composite and the tooth. Incremental packing and curing helps, but the dentist uses other techniques and other materials to help form a seal.
Enhancing the Bond between Resins and Teeth
If dental enamel is present, its prismatic structure of apatite (calcium phosphate) can be etched with phosphoric acid to produce mini chasms, into which the resin matrix material of a composite will flow. When this sets, it results in strongly retentive mechanical bonds. However, materials scientists have spent many hours seeking to produce a bond to the dentine, which exists below the layer of protective, inorganic enamel.
Dentine is a wet, porous and sensitive combination of organic and inorganic materials, and current approaches to bond formation involve the use of primers containing bifunctional compounds (table 1). These have hydrophilic molecules at one end and hydrophobic ones at the other. The hydrophilic ends infiltrate the wet dentine and the hydrophobic ends form links with the resins in the composite, and so the composite is bonded to the dentine.
Table 1. Bifunctional primers are molecules with characteristic chemical groups at each end. These groups have an affinity for one particular sort of surface. In dentistry, they are used to form bonds between dissimilar groups.
Material
Application
Group 1
Group 2
Silane
Used to link silica-based porcelains and glass-ceramics to dental resins. They have resin-seeking groups connected to ceramic-seeking groups.
Resin
Ceramic
4-META and MDP
Used with resin-based dental cements to attach base-metal bridges to dental enamel. They have resin-seeking groups connected to metal-seeking groups.
Resin
Metal
Dentine bonding agents
These have hydrophobic groups (which bond to water hating resins) connected to hydrophilic groups (which allow them to infiltrate wet dentine). They are used to link dental resins to dentine.
Hydrophobic
Hydrophilic
4-META = 4-metacryloxyethyl trimellitate anhydride, MDP = 10-methacryloxydecyl dihydrogen phosphate.
Ion-Leachable Glass Cements
The first aesthetic, tooth-coloured filling materials appeared in the second decade of the 20th century. These were the silicate cements, which were formed when phosphoric acid displaced metal ions from a glass made from alumina, silica and several other metal oxides and fluorides. They set when aluminium phosphate was precipitated between the glass particles. These cements were used by dentists for half a century to fill cavities in front teeth, for not only did they match the colour and translucency of enamel and dentine, but they also acted as a source of fluoride. It was unusual to see dental decay recurring in any tooth they were used to fill.
Similar cements also form when variations on this type of glass are exposed to polymeric acids which possess carboxylate groups. The acids displace metallic ions from the glasses and these cross-link the polymeric acid chains causing the cement to set. The acids also undergo ion exchange reactions with the apatite (calcium phosphate) crystals, which form part of both dentine and dental enamel. These glass ionomer cements, as they are known, thus form direct chemical bonds to teeth, without the need for the primers described above.
However, the basic cements lack the strength and resistance to wear that the dental composites have, and recent research has come up with resin-modified versions. These possess not only the carboxylate groups needed to form bonds to teeth, but also the light-curable dimethacrylate components present in the composite resins. Their durability is thus considerably enhanced.
Cast Metal Restorations
For ninety years, dentists have been replacing the damaged crowns of molar teeth with gold alloys. These have been cast by the lost-wax process. In this process, a wax crown is invested in a wet silica-gypsum mixture. Once this has hardened, the wax is burned away and molten gold-copper-silver-palladium-platinum-zinc alloy is cast under pressure into the space left behind. Some of the alloys can be heat treated to form super-lattices and increase their strength. This makes them suitable for the construction of dental bridges, which replace a missing tooth (or teeth) either by cantilevering an artificial tooth from an adjacent tooth, or by suspending it (or them) between two such teeth. In either case the supporting teeth will have been cut down to accommodate a close fitting casting, which is cemented into place.
Bonded Restorations
Since the 1960s, alloy-porcelain combinations, known to the dentist as bonded restorations have been available. These porcelain-covered metal castings combine the strength of a metallic superstructure with the aesthetic appearance of dental porcelain, creating the illusion that the restorations are real teeth. Alloys have been developed to which dental porcelains form durable retentive bonds, and many of these are now based on nickel-chromium. These metal frameworks are so rigid that they can be bonded via composites to the backs of acid etched teeth, thus eliminating the need for cutting down sound teeth, figure 1. Just as etching dental enamel creates retentive ‘chasms’, these nickel-chromium alloys can be electrolytically etched to produce features that allow the formation of mechanical bonds with resin-based composite cements.
Figure 1. Internal view of a dental bridge bonded via a resin-based cement to the backs of acid-etched teeth.
The oxides that form on these alloys can also be used to promote chemical links to cements via bifunctional primers, thus eliminating the challenge of producing a uniformly etched surface.
Dental Ceramics
Ceramic materials have the ability to emulate natural teeth, and they are some of the oldest dental materials, going back to 1792, when complete dentures were made from them. In 1996 they are used to create inlays, veneers, and crowns, as facings on metal substrates, and even as bridges, which can be made completely from high-strength ceramics. Restorations in ceramics are generally made by building up the correct aesthetic combinations of prefired, pigmented particles, and then re-firing under vacuum to sinter them together and eliminate voids.
Overcoming the Brittle Nature of Ceramics
The developers of modern dental ceramics, aware of their inherent brittle nature, have discovered many ways of interfering with the propagation of cracks within them. To this end, dispersion strengthening with alumina was the first approach. However, because of the opaque nature of the alumina, it is limited to the inner most structure of a crown, known to the dentist as a core.
The cracks, which lead to catastrophic failure, nucleate at the internal interface between the prepared tooth and the ceramic crown. A high strength core can prevent the growth of these cracks and the strongest cores are currently made from either alumina or zirconia. The toughest all-ceramic core produced so far actually infills any cracks in a high alumina base with molten glass during a firing stage in its production.
Other approaches to crack inhibition have included low temperature ionic crowding, a process in which small atoms (such as sodium) present in the surface of porcelain are exchanged for larger ones (such as potassium) by immersing the solid material in fused potassium nitrate. This produces a compressive stress in the surface, which constrains the opening of any cracks. Cast glass-ceramics have also appeared, and these are given post-casting heat treatments that produce reinforcing mica-like crystals within the glass.
To bond brittle porcelain to a strong and rigid metal substrate, special porcelaind have been developed with thermal expansion characteristics that match those of the metal. This in turn prevents high interfacial stresses being created between the two as they cool.
Glass Ceramics
Glass ceramics are also used in several CAD/CAM applications in dentistry. In one of these a restoration is designed on a video image of a prepared tooth. It is then machined from a pre-fired block of glass ceramic. All of this takes place in front of the patient. As with all types of ceramic restoration, the machined unit is then coated with a silane bonding agent and cemented to the tooth with a resin-based cement. The tooth itself is also coated with an enamel/dentine bonding agent.
Dental Implants
For years people have been under the impression that the dentist was able to ‘screw in’ teeth to replace those which were missing. However, what they had experienced was the use of one type of metal post. Posts can be either cemented or screwed into the canals of teeth that have lost their crowns but still have their roots. Such teeth are ‘root-treated’ to remove their nerves and blood supplies, and onto the posts ceramic or ceramic metal crowns are themselves cemented.
Although many attempts have been made to replace missing roots with all sorts on metallic implants, the satisfactory use of a screwed in implant goes back only to the mid 1980s. In practice the gum is slit, and a hole is cut slowly in the bone and then tapped under a continuous flow of sterile, cold water to prevent it being damaged by over-heating. A cold-worked Grade 4 commercially pure titanium screw is then inserted slowly and covered with gum tissue for 6 months. During this time the bone grows into intimate contact with the passive oxide layer on the titanium and it is said to be osseointegrated. The gum tissue is cut once more and a titanium sleeve is screwed onto the implant. This will ultimately pass through the healed gum. Onto these sleeves a metallic superstructure can be screwed and this can support, for example, a polymeric denture base and artificial teeth, figure 2.
Figure 2. Side view of a superplastically-formed, titanium alloy, cantilevered superstructure, attached to dental plaster analogues in a plaster model of a patients jaw.
For many years these superstructures have been cast in gold alloys and getting them to sit perfectly on the titanium sleeves has been a challenge of the highest order. However, titanium frameworks are currently being investigated, particularly those constructed by alternative routes to casting, and considerable promise is being shown by those made by superplastic forming. This is undertaken in an inert atmosphere at 900°C on reinforced refractory models.
Ceramics have also been tried as dental implants. However, because of their brittleness and the smallness of the structures, their optimal role has been as coatings on metal implants. Titanium implants, for example, have had their surfaces coated with hydroxyapatite to try and help osseointegration, and surface active glasses (‘bioglasses’) have been used for the same purpose. Also, by placing them in the holes left behind after the extraction of teeth, these glasses have shown promise in preventing bone resorption.
Coated Paper Analysis Using Atomic Force Microscopy – Supplier Data By Pacific Nanotechnology
Background
Several types of microscopes are available for studying and analyzing the surfaces of coated papers. The most common microscopes are optical microscopes which can give a 2-dimensional resolution of approximately 1 micron. The primary advantages of the optical microscope are its ease of use and low cost. For higher resolution imaging, less than 1 micron, a scanning electron microscope (SEM) is typically used. The SEM can resolve surface features as small as a few nanometers. However, the SEM does not give high contrast images on flat samples, requires a vacuum, and often requires substantial sample preparation. The most common type of sample preparation is sputter coating a metal on the surface, which can cause the surface topography of the sample that will be imaged to change. Most recently the Atomic Force Microscope (AFM) is being applied for imaging the surfaces of coated papers. Advantages of the AFM are that it directly gives 3- Dimensional magnification, works in ambient air, requires no sample preparation, and the AFM has a resolution at the nanometer scale.
Atomic Force Microscope Sensor
In an AFM a very fine stylus is scanned over a surface in a raster pattern. By monitoring the motion of the stylus, a 3-Dimensional image of the surface can be created. Images may be displayed in 2-Dimensional or 3-Dimensional representations. Further, line profiles can be extracted from the image. The height and width of surface features are measured from line profiles.
AZoM - The A to Z of Materials - Left - 2-Dimensional image of the surface of a commercially available photo quality inkjet paper. The scan size is 30 microns and the scale indicates the height of the features on the paper’s surface. Right: Line profile showing the width of one of the pores in the paper
Figure 1. Left - 2-Dimensional image of the surface of a commercially available photo quality inkjet paper. The scan size is 30 microns and the scale indicates the height of the features on the paper’s surface. Right: Line profile showing the width of one of the pores in the paper.
Central to the AFM is a force sensor that measures the force between the stylus and the surface. Typically, the force sensor design is based on a light lever. In the light lever a laser beam is reflected off the backside of a cantilever into a two-section photo-detector. (Figure 2) On the bottom side of the cantilever is a stylus. Interactions between the stylus and the surface cause the cantilever to bend and the reflected light to move across the photo-detector. In this type of AFM force sensor, the cantilever is typically 40 microns wide, 100 microns long, and less than a micron thick. With such a small cantilever, forces as low as a nano-newton (10-9 Newtons) are measurable with the light lever force sensor. Thus, very small probes, less than 50 nm, can be used in the AFM and not be broken by interactions with a surface.
AZoM - The A to Z of Materials - Illustration of a light lever force sensor used in atomic force microscope. The laser is reflected from the cantilever into a two-section photo-detector.
Figure 2. Illustration of a light lever force sensor used in atomic force microscope. The laser is reflected from the cantilever into a two-section photo-detector.
The horizontal resolution in an AFM depends on the geometry of the probe and the type of sample being analyzed. On very smooth surfaces only the very end of the probe interacts with the surface and the resolution of the image depends only on the probe diameter. If the specimen has large features, more of the probe than the very end interacts with the surface and the image resolution depends on the macroscopic geometry of the probe. (Figure 3)
AZoM - The A to Z of Materials - Left - On a smooth surface only the very end of the probe interacts with the surface. Right - On a rough surface more of the probe interacts with the surface and the resolution depends on more than the probe diameter.
Figure 3. Left - On a smooth surface only the very end of the probe interacts with the surface. Right - On a rough surface more of the probe interacts with the surface and the resolution depends on more than the probe diameter.
Paper Coating Applications
Because the AFM directly shows the micron and submicron structure of paper coatings, the AFM is useful for helping to develop new paper coating processes. It is also possible to understand process failure by comparing the surface structure of paper from a good process and the structure from a failed process.
Gloss
The length scale of AFM measurements is the same length scale that controls the gloss properties of paper coatings. Thus the AFM is useful for helping to understand the relationship between surface topography, gloss and delta gloss.
Engineered Papers
A second application is the use of the AFM for engineered papers. The AFM readily measures the sizes and shape of surface particles and structure with dimensions ranging from a few nanometers to a few microns. By understanding the relationship between surface structure and coating performance, engineered papers can be improved.
The AFM is useful for visualizing surface structure, for making quantitative surface measurements, and for studying the dispersion of particles in the coating.
Surface Structure Visualization
The properties of a paper coating can depend critically on the micron and submicron structure of the paper coating The AFM is ideal for visualizing the sub micron structure of paper coatings. Such images easily show the particle size and shape of the components of the paper coating. Figure 4 illustrates the AFM images of an Opti-Gloss PCC aragonite coating before and after printing. The change in surface texture is readily visualized.
AZoM - The A to Z of Materials - Left - AFM image of the rod-like pigment particles in an Opti-Gloss PCC aragonite coating. Right - AFM image of the same coating after printing with UV ink.
Figure 4. Left - AFM image of the rod-like pigment particles in an Opti-Gloss PCC aragonite coating. Right - AFM image of the same coating after printing with UV ink.
Quantitative AFM Measurements
For many years mechanical and optical surface profilers could be used for analyzing paper surface texture. However, such profilers are limited in their horizontal resolution to approximately one micron. Thus, they can readily measure at a length scale of a few millimeters. Traditional quantitative surface roughness parameters such as Sa, Sq, Sr and Sm can be directly calculated from AFM images.
AZoM - The A to Z of Materials - Equations for surface texture that are readily used with the AFM images.
Figure 5. Equations for surface texture that are readily used with the AFM images.
As an example, it has been shown that the AFM could be used to explain anomalies in paper gloss. In a study, sheet A had a higher TAPPI (Trade Association of Paper and Pulp Institute) gloss at 75 degrees and sheet B had a higher TAPPI gloss at 20 degrees. By directly measuring the surface texture with an AFM, it was established that although the two sheets of paper had similar surface roughness, the skew and kurtosis were very different. Sheet A was significantly non-Gaussian and Sheet B was approximately Gaussian.
Particle Dispersion
In the case of clays and polycarbonates, the dispersion of particles in paper coatings can be readily established from AFM images. Figure 6 is of an Astr-Plus/Carinal 95 coating. In this image the positions of kaolin hexagonal platelets are clearly visible.
Besides measuring surface topography, images of other surface physical properties such as hardness and adhesion are measurable with the AFM. As an example, in the AFM it is possible to vibrate the stylus as it is scanned over a surface. Then by measuring the change in phase between the modulating signal and the signal coming from the photo-detector, images of surface hardness are obtained. In this technique, both the surface topography and surface hardness image are acquired simultaneously.
AZoM - The A to Z of Materials - AFM image of Astr-Plus/Carbinal 95 coating. This “engineered” coating is comprised of kaolin in a narrow particle size distribution and an ultra fine ground calcium carbonate with a latex binder.
Figure 6. AFM image of Astr-Plus/Carbinal 95 coating. This “engineered” coating is comprised of kaolin in a narrow particle size distribution and an ultra fine ground calcium carbonate with a latex binder.
This technique is ideal for visualizing the location of polymer material used in paper coatings. Figure 7 shows the topography image and hardness image of a commercially available paper coating. The dark areas in the image show the locations of the polymer material in the coating.
AZoM - The A to Z of Materials - Left - Topography . Right - Hardness image of a comercially available paper coating. These images are measured simultaneously. The gray scale in the hardness image represents the surface hardness.
Figure 7. Left - Topography . Right - Hardness image of a comercially available paper coating. These images are measured simultaneously. The gray scale in the hardness image represents the surface hardness.
Conclusion
The AFM is emerging as an important tool for characterizing and studying the micron and submicron topography and properties of paper coatings. Specific applications include the direct visualization of paper coatings, quantitative analysis of paper coatings, and the measurement of particle dispersion. Advantages of the AFM over the SEM are:
·        The AFM provides direct three-dimensional images
·        The AFM does not require sample preparation
·        The AFM can work in ambient conditions
Chemical Analysis Techniques – X-Ray Fluorescence, Optical Emission Spectroscopy, Atomic Absorption Spectroscopy, Gas Analysis, Carbon and Sulphur Analysis, Inductively Coupled Plasma and Wet Chemistry – Supplier Data by Incotest
Background
IncoTest combines instrumental and classical methods of chemical analysis. Providing such a wide range of techniques ensures the client that samples are analysed by the most economical method, depending on the type of material, the form of the sample and the level of accuracy required. Normally, one or more of the following methods are used for analysis of steels and nickel, cobalt, aluminium, copper and titanium-based alloys:
X-ray Fluorescence (XRF)
Simultaneous and sequential X-ray spectrometry is used for the determination of main and residual impurity elements. Accuracy is largely determined by the quality and range of Certified Reference Materials (CRMS) used for calibration. IncoTest has access to a common suite of over 1500 samples covering commercially available CRMs and in-house standards.
Optical Emission Spectrometry (OES)
This method is used by Incotest to determine trace and residual impurity elements and is particularly useful for low atomic number elements such as boron, magnesium, aluminium, phosphorous and calcium.
When coupled with a Hollow Cathode Source, OES is used to determine low boiling point elements such as lead, bismuth, silver and tellurium at very low concentrations. These elements, which can seriously impair the performance of high-temperature steels and nickel-based superalloys, are routinely determined at levels below one part per million. IncoTest uses a wide range of commercial CRMs and in-house reference materials for the determination of low boiling point elements at these levels.
Atomic Absorption Spectrometry
Residual and trace elements are analysed using Atomic Absorption and Graphite Furnace Atomisation (GFA). IncoTest’s equipment employs Zeeman Background Correction to minimize interference’s and improve accuracy at trace levels. This method is particularly useful where there are no CRMs available.
Gas Analysis
Incotest use the Carrier Gas Extraction methods to determine oxygen, nitrogen and hydrogen levels. The sample is melted in an inert gas stream in a graphite crucible and the gasses evolved are measured by thermal conductivity or infra-red absorption.
Carbon & Sulphur Analysis
Carbon and sulphur are determined by RF Combustion in oxygen. This results in evolution of carbon dioxide and sulphur dioxide. Their concentrations are then measured by infra-red absorption
Inductively Coupled Plasma (ICP-OES)
Incotest use This technique as an alternative to XRF and conventional OES when sample size is limited or the sample form is unsuitable (eg turnings, fine wire or powder. With ICP-OES, the sample is dissolved and aspirated in an argon plasma where it vaporizes and emits a characteristic spectrum which is analysed by OES. The analysis involves dissolution of the sample, and therefore it is relatively easy to prepare closely matching calibration standards from pure metals and compounds. This is particularly important where appropriate CRMs are not available or where an independent overcheck is needed.
Wet Chemistry
Classical chemical analysis can be used to supplement instrumental methods and is important where overcheck or referee analyses are required.
Ceramic Bone Graft Material Patented by Orthogem
A new ceramic bone graft material has been patented by Dr Wei-Jen Lo, founder of Orthogem limited, that not only results in rapid, high quality bone growth, but also retains the structural integrity of the implant site while the ceramic implant is gradually replaced by natural bone.
Creating synthetic bone material that accurately mimics the complex, multi-layered porous structure of human bone is one of the greatest challenges in the biomaterials field. Previous materials have been met with scepticism by surgeons, who use bone grafts in around two million orthopaedic procedures worldwide each year. Bone grafts require the patient to have a second operation to harvest bone, which is costly, painful, risky and time-consuming.
The Orthogem synthetic bone uses hydroxyapatite, ß-TCP (tricalcium phosphate) or a combination of both ceramics depending on the application. The material and its porosity have been carefully designed to maximise the movement and attachment of bone cells within the implant. Recent trials at University College London’s Centre for Biomedical Engineering showed that Orthogem’s synthetic implants result in rapid new bone growth that is organised, well vascularised and of an extremely high quality. The synthetic bone was replaced with woven bone (scar) and collagen fibres that were randomly oriented. In turn, woven bone was replaced by osteoblasts (bone replacing cells) to create well vascularised lamellar or long bone.
The bone manufacturing procedure itself is a major breakthrough, and details can not be released during the patenting process. Dr Lo said, ‘It’s exciting to see Orthogem develop from a scientific concept to a practical material with real potential to replace the frankly medieval technique of harvesting a patient’s own bone.’
In future, the material could also carry engineered drugs such as bone morphogenic proteins to enhance the healing process.
Cement and Concrete – History and Development
Background
Concrete is a compound material made from sand, gravel and cement. The cement is a mixture of various minerals which when mixed with water, hydrate and rapidly become hard binding the sand and gravel into a solid mass. The oldest known surviving concrete is to be found in the former Yugoslavia and was thought to have been laid in 5,600 BC using red lime as the cement.
The first major concrete users were the Egyptians in around 2,500 BC and the Romans from 300 BC The Romans found that by mixing a pink sand-like material which they obtained from Pozzuoli with their normal lime-based concretes they obtained a far stronger material. The pink sand turned out to be fine volcanic ash and they had inadvertently produced the first ‘pozzolanic’ cement. Pozzolana is any siliceous or siliceous and aluminous material which possesses little or no cementitious value in itself but will, if finely divided and mixed with water, chemically react with calcium hydroxide to form compounds with cementitious properties.
The Romans made many developments in concrete technology including the use of lightweight aggregates as in the roof of the Pantheon, and embedded reinforcement in the form of bronze bars, although the difference in thermal expansion between the two materials produced problems of spalling. It is from the Roman words ‘caementum’ meaning a rough stone or chipping and ‘concretus’ meaning grown together or compounded, that we have obtained the names for these two now common materials.
Portland Cement
Lime and Pozzolana concretes continued to be used intermittently for nearly two millennia before the next major development occurred in 1824 when Joseph Aspdin of Leeds took out a patent for the manufacture of Portland cement, so named because of its close resemblance to Portland stone. Aspdin’s cement, made from a mixture of clay and limestone, which had been crushed and fired in a kiln, was an immediate success. Although many developments have since been made, the basic ingredients and processes of manufacture are the same today.
Reinforcement
In 1830, a publication entitled, “The Encyclopaedia of Cottage, Farm and Village Architecture” suggested that a lattice of iron rods could be embedded in concrete to form a roof. Eighteen years later, a French lawyer created a sensation by building a boat from a frame of iron rods covered by a fine concrete which he exhibited at the Paris Exhibition of 1855. Steel reinforced concrete was now born. The man normally credited with its introduction as a building material is William Wilkinson of Newcastle who applied for a patent in 1854 for “improvement in the construction of fireproof dwellings, warehouses, other buildings and parts of the same”.
It is not only fire resistance that is improved by the inclusion of steel in the concrete matrix. Concrete, although excellent in compression, performs poorly when in tension or flexure. By introducing a network of connected steel bars, the strength under tension is dramatically increased allowing long, unsupported runs of concrete to be produced.
Steel and concrete complement each other in many ways. For example, they have similar coefficients of thermal expansion so preventing the problems the Romans had with bronze. Concrete also protects the steel, both physically and chemically.
Composition of Portland Cement
Portland cement is a complex mix of many compounds, some of which play a major part in the hydration or chemical characteristics of the cement. It is manufactured commercially by heating together a mixture of limestone and clay up to a temperature of 1300 to 1500°C. Although twenty to thirty percent of the mix becomes molten during the process the majority of the reactions which take place are solid-state in nature and therefore liable to be slow. Once cooled, the resulting clinker is ground to a fine powder and a small amount of gypsum (calcium sulphate dihydrate) is added to slow down the rate at which the cement hydrates to a workable level.
The work of early investigators using optical and X-ray techniques, starting in 1882 with Le Chatelier, has shown that most Portland cement clinkers contain four principal compounds. These are tricalcium silicate (3CaO.SiO2), aluminate (3CaO.Al2O3) and a ferrite phase from the (2CaO.Fe2O3 - 6CaO.2Al2O3.Fe2O3) solid solution series that at one time was considered to have the fixed composition (4CaO.Al2O3.Fe2O3). These phases were named alite, belite, celite and felite respectively by Tornebohm in 1897.
Hydration of Portland Cement
When water is mixed with Portland cement a complicated set of reactions is initiated. The main strength giving compounds are the calcium silicates which react with water to produce a calcium silicate hydrate gel (C-S-H gel) which provides the strength, and calcium hydroxide which contributes to the alkalinity of the cement. Tricalcium silicate reacts quickly to provide high, early strengths while the reaction of dicalcium silicate is far slower, continuing, in some cases, for many years. The other cement compound of particular relevance to steel reinforced concrete is tricalcium aluminate. It reacts rapidly with water to produce calcium aluminate hydrates.
The amount of tricalcium aluminate present may well be limited as in the case of sulphate resisting Portland cement, to prevent adverse reactions between the hydrate and sulphates from the environment which can result in swelling and cracking of the cement matrix.
The great advantage of tricalcium aluminate is its ability to combine with chlorides, so removing them from the liquid phase of the cement. Chloride ions, as will be seen, are one of the major causes of corrosion of embedded steel.
Calcium Titanate ( CaTiO3 ) – Supplier Data by Goodfellow
Background
The chemical formula for Calcium Titanate is CaTiO3. Calcium titanate is a dielectric ceramic material.
The mineral perovskite is comprised of calcium titanate. It has a close packed cubic structure which it shares with other ceramic materials such as barium and strontium titanates, calcium and strontium zirconates just to name a few.
Key Properties
Property                                               Value
Density ( g.cm-3 )Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 4.10
Melting Point ( °C )                              1975
Calcium Phosphate Biomaterials – Solubility of Calcium Phosphates
Background
Most calcium phosphates are classified as resorbable biomaterials. This means that under physiological conditions they will dissolve. The benefit of calcium phosphate biomaterials is that the dissolution products can be readily assimilated by the human body.
Calcium Phosphates as Bone Defect Fillers
Due the resorbable nature of calcium phosphate, with the general exception of hydroxyapatite, they have been proposed as potential bone defect fillers. In this application, they would fill the void and gradually dissolve away, being replaced by bone. However, the uncontrollable resorption rate has hindered their uptake in clinical applications.
Calcium Phosphate Compounds
Listed in the table below are some calcium phosphate compounds of biomaterials interest.
Amorphous calcium phosphate is a phase that is often formed during high temperature processing, such as is the case with plasma spraying of hydroxyapatite. It and other phases, may be associated with hydroxyapatite after high temperature processing and the subsequent decomposition when dealing with hydroxyapatite
Solubility of Calcium Phosphate Compounds
While the forming method and exact stoichiometry will have an effect on solubility, the generally accepted order of solubility is:
ACP > DCP > TTCP > α-TCP > β-TCP >> HAp
The relative insolubility of hydroxyapatite compared to the other calcium phosphate phases is not surprising as it is the only stable calcium phosphate compound at pH’s above 4.2. Below this, dicalcium phosphate dihydrate (CaHPO4.2H2O) is the stable compound. It is not uncommon for unstable calcium phosphates to dissolve and repreciptate as the stable compound at a given pH.
Under normal physiological conditions of pH 7.2, hydroxyapatite is the stable calcium phosphate compound. This may drop to as low as pH 5.5 in the region of tissue damage, although this would eventually return to pH 7.2 over a period of time. Even under these conditions hydroxyapatite is still the stable phase.
Calcium Phosphate and Hydroxyapatite Coatings
Calcium Phosphate Coatings
Porous hydroxyapatite has been accepted that due to its unfavourable mechanical properties it cannot be used under load bearing purposes. For this reason hydroxyapatite has been used as thin film coatings on metallic alloys. Of the metallic alloys investigated titanium based alloys have shown to be the material of preference for thin film coatings. Titanium alloys possesses good mechanical strength and fatigue resistance under load bearing conditions. They are lightweight, with high strength to weight ratios.
Calcium Phosphate Coating Deposition Processes
Of the coating techniques utilized, thermal spraying tends to be the most commonly used and analysed. This technique has been faced with challenges of producing a controllable resorption response in clinical situations. Besides the set backs, thermally sprayed coatings are continually being improved by using different compositions and post heat treatments which converts amorphous phases to crystalline calcium phosphates. Other techniques are being investigated. Techniques that are capable of producing thin coatings include pulsed-laser deposition and sputtering which, like thermal spraying involves high - temperature processing. Other techniques such as electrodeposition, and sol-gel utilise lower temperatures and avoid the challenge associated with the structural instability of hydroxyapatite at elevated temperatures.
The Advantages of the Sol-Gel Process
The advantages of sol-gel technique are numerous; it results in a stoichiometric, homogeneous and pure coating due to mixing on the molecular scale; reduced firing temperatures due to small particles sizes with high surface areas; it has the ability to produce uniform fine-grained structures (Figure 1); the use of different chemical routes (alkoxide or aqueous based); and their ease of application to complex shapes with a range of coating techniques those being dip, spin, and spray coating. The lower processing temperature has another advantage; it avoids the phase transition (~1156 K) observed in titanium based alloys used for biomedical devices.
Figure 1. (a) SEM and (b) AFM image of a sol-gel (alkoxide) derived hydroxyapatite coating.Calcium Phosphate Coatings
Porous hydroxyapatite has been accepted that due to its unfavourable mechanical properties it cannot be used under load bearing purposes. For this reason hydroxyapatite has been used as thin film coatings on metallic alloys. Of the metallic alloys investigated titanium based alloys have shown to be the material of preference for thin film coatings. Titanium alloys possesses good mechanical strength and fatigue resistance under load bearing conditions. They are lightweight, with high strength to weight ratios.
Calcium Phosphate Coating Deposition Processes
Of the coating techniques utilized, thermal spraying tends to be the most commonly used and analysed. This technique has been faced with challenges of producing a controllable resorption response in clinical situations. Besides the set backs, thermally sprayed coatings are continually being improved by using different compositions and post heat treatments which converts amorphous phases to crystalline calcium phosphates. Other techniques are being investigated. Techniques that are capable of producing thin coatings include pulsed-laser deposition and sputtering which, like thermal spraying involves high - temperature processing. Other techniques such as electrodeposition, and sol-gel utilise lower temperatures and avoid the challenge associated with the structural instability of hydroxyapatite at elevated temperatures.
The Advantages of the Sol-Gel Process
The advantages of sol-gel technique are numerous; it results in a stoichiometric, homogeneous and pure coating due to mixing on the molecular scale; reduced firing temperatures due to small particles sizes with high surface areas; it has the ability to produce uniform fine-grained structures (Figure 1); the use of different chemical routes (alkoxide or aqueous based); and their ease of application to complex shapes with a range of coating techniques those being dip, spin, and spray coating. The lower processing temperature has another advantage; it avoids the phase transition (~1156 K) observed in titanium based alloys used for biomedical devices.
Figure 1. (a) SEM and (b) AFM image of a sol-gel (alkoxide) derived hydroxyapatite coating.
Calcium Hydride ( CaH2 ) – Supplier Data by Goodfellow
Background
The chemical formula for Calcium Hydride is CaH2.
Key Properties
Property
Value
Density ( g.cm-3 )
1.9