46
Life Science / Addictive Junk Food
« on: February 21, 2013, 11:31:27 PM »
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47
Applied Science / How battery improvements will revolutionize the design of the electric car
« on: February 20, 2013, 11:05:03 AM »
Tesla could have never created the Model S — it’s second-generation electric car that won Motor Trend’s car of the year award for 2012 — with battery technology from a few decades ago, said Tesla’s CTO and co-founder J.B. Straubel at the Cleantech Investor Summit last week. He explained, “The type of vehicle we can create is fundamentally different every time that tech [batteries] moves a little forward.â€
While battery innovation appears gradual, the incremental leaps add up over time. Battery innovation is improving around 5 to 8 percent per year, which can deliver a doubling in core performance metrics every ten years, which is ultimately really “revolutionary†said Straubel. Because of the large size and heavy physical weight of batteries involved with electric cars, the impact of battery innovation on the design of the car can be even more significant than Moore’s Law has on some computing products, added Straubel.
For car design, “It’s almost as if the properties of steel were improving at a rate of 5 to 8 percent per year,†said Straubel.
The new design and engineering of the Model S has been Tesla’s differentiator, and it is what the company is hoping will help it move into profitability and success as a more mainstream auto maker down the road. The car is one of the first electric cars in the world that was designed from the ground up as electric. In contrast most auto makers that have built electric cars have taken an existing traditional gas-powered car and put batteries in it.
The Model S, in comparison, has placed the battery along the bottom of the car, so that it doesn’t take up seating and storage space, and also so that the car has a low center of gravity and is more aerodynamic. The Tesla Roadster (it’s first car) and the Nissan LEAF are based on the bodies of gas-powered cars.
Shai Agassi, the founder and former CEO of Better Place, also touted the importance of the rate of battery innovation during his talk at the Cleantech Investor Summit. He said the energy density of batteries goes up 15 percent every 18 months; the cost per kilowatt hour goes down 15 percent every 18 months; the life cycles of the batteries (how many times it can charge and recharge) goes up 15 percent every 18 months; and the cost per lifecycle-mile does down 50 percent every 18 months. “If you don’t like the margins in this [electric car] business just wait 12 months,†said Agassi.
The crucial factor for both Tesla and Better Place will be surviving in an early market place as these improvements emerge. As with all startups, timing and execution will be key.
While battery innovation appears gradual, the incremental leaps add up over time. Battery innovation is improving around 5 to 8 percent per year, which can deliver a doubling in core performance metrics every ten years, which is ultimately really “revolutionary†said Straubel. Because of the large size and heavy physical weight of batteries involved with electric cars, the impact of battery innovation on the design of the car can be even more significant than Moore’s Law has on some computing products, added Straubel.
For car design, “It’s almost as if the properties of steel were improving at a rate of 5 to 8 percent per year,†said Straubel.
The new design and engineering of the Model S has been Tesla’s differentiator, and it is what the company is hoping will help it move into profitability and success as a more mainstream auto maker down the road. The car is one of the first electric cars in the world that was designed from the ground up as electric. In contrast most auto makers that have built electric cars have taken an existing traditional gas-powered car and put batteries in it.
The Model S, in comparison, has placed the battery along the bottom of the car, so that it doesn’t take up seating and storage space, and also so that the car has a low center of gravity and is more aerodynamic. The Tesla Roadster (it’s first car) and the Nissan LEAF are based on the bodies of gas-powered cars.
Shai Agassi, the founder and former CEO of Better Place, also touted the importance of the rate of battery innovation during his talk at the Cleantech Investor Summit. He said the energy density of batteries goes up 15 percent every 18 months; the cost per kilowatt hour goes down 15 percent every 18 months; the life cycles of the batteries (how many times it can charge and recharge) goes up 15 percent every 18 months; and the cost per lifecycle-mile does down 50 percent every 18 months. “If you don’t like the margins in this [electric car] business just wait 12 months,†said Agassi.
The crucial factor for both Tesla and Better Place will be surviving in an early market place as these improvements emerge. As with all startups, timing and execution will be key.
48
Astronomy / Jupiter's Europa moon is 'more likely to support life than the deserts of Mars
« on: February 20, 2013, 10:55:30 AM »
NASA scientists believe that one of Jupiter's moons is the most likely place in the universe beyond the Earth that could harbour life.Europa, the sixth closest moon to the planet, is far more likely to be habitable than desert-covered Mars which has been the focus of recent US exploration, they say.It's ocean, thin shelf of ice and the presence of oxidants on Europa make it far more likely to be home to a life form than the red planet.Now NASA says it has revised plans to explore Europa, coming up with a cheaper way of completing its mission.Robert Pappalardo, a planetary scientist at NASA's jet propulsion Laboratory (JPL) in Pasadena, California, told France 24: 'Europa is the most promising in terms of habitability.'It is the place we should be exploring now that we have a concept mission we think is the right one to get there for an affordable cost.'
Speaking at the American Association for the Advancement of Science (AAAS) annual conference, Mr Pappalardo said that a new $2 billion exploration project called Clipper would see NASA team up with physicists from the John Hopkins University in Maryland if it gets the go ahead.The mission follows the success of Cassini, a probe that closely explored Titan - a moon of Saturn.
NASA will send a spacecraft into Jupiter's orbit and conduct a number of close flybys of Europa.Mr Papparlardo says that exploring Europa using the flyby method will allow scientists to explore the moon in its entirety.Clipper could be launched by 2021 and would take a further three to six years to reach Europa.But NASA announced late last year that there are currently no funds for the mission.Instead, it will send a new robot to Mars in 2020, similar to Curiosity, the craft which has been exploring the surface of the planet since last August, at a cost of around $2.5 billion.The probe Juno is to arrive in the orbit of Jupiter in 2016, but after it is crashed a year later, the US will have no probe's in the outlying reachers of the solar system.
It could however, team up with the European Space Agency which plans to launch a mission to Jupiter in 2030.Europa was first examined by the Voyager mission in 1979 and by Galileo in the 1990s.As well as Europa, scientists believe that Encelade, a moon belonging to Saturn, could also be habitable.
Speaking at the American Association for the Advancement of Science (AAAS) annual conference, Mr Pappalardo said that a new $2 billion exploration project called Clipper would see NASA team up with physicists from the John Hopkins University in Maryland if it gets the go ahead.The mission follows the success of Cassini, a probe that closely explored Titan - a moon of Saturn.
NASA will send a spacecraft into Jupiter's orbit and conduct a number of close flybys of Europa.Mr Papparlardo says that exploring Europa using the flyby method will allow scientists to explore the moon in its entirety.Clipper could be launched by 2021 and would take a further three to six years to reach Europa.But NASA announced late last year that there are currently no funds for the mission.Instead, it will send a new robot to Mars in 2020, similar to Curiosity, the craft which has been exploring the surface of the planet since last August, at a cost of around $2.5 billion.The probe Juno is to arrive in the orbit of Jupiter in 2016, but after it is crashed a year later, the US will have no probe's in the outlying reachers of the solar system.
It could however, team up with the European Space Agency which plans to launch a mission to Jupiter in 2030.Europa was first examined by the Voyager mission in 1979 and by Galileo in the 1990s.As well as Europa, scientists believe that Encelade, a moon belonging to Saturn, could also be habitable.
49
Astronomy / Ancient impact of a gargantuan asteroid changed southern Australia
« on: February 20, 2013, 10:48:44 AM »
A gargantuan asteroid which struck Australia more than 300million years ago changed the face of the Earth forever, a new study claims.The six-mile diameter asteroid left an impact zone more than 120 miles wide - the third largest such site on the planet - and likely led to mass extinctions worldwide.
'The dust and greenhouse gases released from the crater, the seismic shock and the initial fireball would have incinerated large parts of the Earth,' said Andrew Glikson, visiting fellow at the Australian National University.Evidence of the ancient catastrophe was only discovered after another researcher alerted Dr Glikson to unusual mineral deposits in the East Warburton Basin in South Australia.As the ages have passed, the mammoth impact zone has been buried beneath nearly 2.5 miles of earth.o identify it Dr Glikson and his colleagues analysed quartz grains drawn from the site and studied underground seismic and magnetic anomalies.
The strike may have been part of an asteroid impact cluster which caused an era of mass extinction, wiping out primitive coral reefs and other species, added Dr Glikson.However, he added, the impact happened well before the time of the dinosaurs.'It’s significant because it's so large. It's the third largest impact terrain anywhere on Earth found to date,' he told Australian science news site The Conversation.'It’s likely to be part of a particular cluster that was linked with a mass extinction event at that time.'
He said there was a chance that the incoming asteroid actually split in two as it made its fiery descent through the Earth's atmosphere.'We are studying another anomaly in West Warburton that could well be its twin but we don’t know yet,' he said.
Dr Simon O'Toole, research astronomer at the Australian Astronomical Observatory, told The Conversation that the find offered fresh evidence of the links between asteroid impacts and mass extinctions.'Australia is a fantastic place for impact crater hunters because we have huge open space with nothing in it,' said Dr O'Toole, who was not involved in the research.
'It's huge,' he added. 'Most asteroid impacts are about 100m in diameter.'
'The dust and greenhouse gases released from the crater, the seismic shock and the initial fireball would have incinerated large parts of the Earth,' said Andrew Glikson, visiting fellow at the Australian National University.Evidence of the ancient catastrophe was only discovered after another researcher alerted Dr Glikson to unusual mineral deposits in the East Warburton Basin in South Australia.As the ages have passed, the mammoth impact zone has been buried beneath nearly 2.5 miles of earth.o identify it Dr Glikson and his colleagues analysed quartz grains drawn from the site and studied underground seismic and magnetic anomalies.
The strike may have been part of an asteroid impact cluster which caused an era of mass extinction, wiping out primitive coral reefs and other species, added Dr Glikson.However, he added, the impact happened well before the time of the dinosaurs.'It’s significant because it's so large. It's the third largest impact terrain anywhere on Earth found to date,' he told Australian science news site The Conversation.'It’s likely to be part of a particular cluster that was linked with a mass extinction event at that time.'
He said there was a chance that the incoming asteroid actually split in two as it made its fiery descent through the Earth's atmosphere.'We are studying another anomaly in West Warburton that could well be its twin but we don’t know yet,' he said.
Dr Simon O'Toole, research astronomer at the Australian Astronomical Observatory, told The Conversation that the find offered fresh evidence of the links between asteroid impacts and mass extinctions.'Australia is a fantastic place for impact crater hunters because we have huge open space with nothing in it,' said Dr O'Toole, who was not involved in the research.
'It's huge,' he added. 'Most asteroid impacts are about 100m in diameter.'
50
Natural Science / The record setting car powered by coffee
« on: February 20, 2013, 10:09:58 AM »
The driver of a coffee-powered car set a speed record today. With a Guinness World Records adjudicator looking on, conservationist Martin Bacon, 42, got his specially modified Ford P100 pick-up truck to go more than 65mph.
Watched by his wife Jill, father-of-two Mr Bacon, from Teesdale, north-east England, completed his run at Woodford Airfield in Stockport, Greater Manchester.
The speed is the fastest ever for this type of vehicle.The vehicle uses coffee chaff pellets - the waste product from coffee production - which are heated in a charcoal fire where they break down into carbon monoxide and hydrogen.The gas is cooled and filtered before hydrogen is combusted to drive the engine.The car was commissioned by The Co-Operative to mark the 10th anniversary of it converting all its coffee to Fairtrade. Mr Bacon said: 'We’re thrilled to have taken the speed record for the fastest car of this kind. 'This Coffee Car has been years in the making, although any car can run on gasification.
'In fact, during the Second World War, there were over 100,000 vehicles in the UK that ran on gasification, including cars, buses and delivery vehicles.
'At the beginning of the 20th century, there were over 900,000 vehicles running on gasifiers across the world.'
The Co-operative Food Chief Executive, Steve Murrells, said: 'The Bean Machine’s record and UK tour are a great way to get people talking about Fairtrade and how buying Fairtrade products can make a real difference to the lives of producers, their families and local communities in developing countries.
Watched by his wife Jill, father-of-two Mr Bacon, from Teesdale, north-east England, completed his run at Woodford Airfield in Stockport, Greater Manchester.
The speed is the fastest ever for this type of vehicle.The vehicle uses coffee chaff pellets - the waste product from coffee production - which are heated in a charcoal fire where they break down into carbon monoxide and hydrogen.The gas is cooled and filtered before hydrogen is combusted to drive the engine.The car was commissioned by The Co-Operative to mark the 10th anniversary of it converting all its coffee to Fairtrade. Mr Bacon said: 'We’re thrilled to have taken the speed record for the fastest car of this kind. 'This Coffee Car has been years in the making, although any car can run on gasification.
'In fact, during the Second World War, there were over 100,000 vehicles in the UK that ran on gasification, including cars, buses and delivery vehicles.
'At the beginning of the 20th century, there were over 900,000 vehicles running on gasifiers across the world.'
The Co-operative Food Chief Executive, Steve Murrells, said: 'The Bean Machine’s record and UK tour are a great way to get people talking about Fairtrade and how buying Fairtrade products can make a real difference to the lives of producers, their families and local communities in developing countries.
51
Nutrition and Food Engineering / Eating chips more than once a week raises the risk of prostate cancer
« on: February 20, 2013, 09:55:05 AM »
Men who eat fried foods more than once a week may increase their risk of prostate cancer by a third.New research suggests that junk food staples such as chips, fried chicken, battered fish and doughnuts may play a significant role in the formation of aggressive and life-threatening forms of the disease.
Although previous studies have suggested poor diet can affect a man's chances of getting prostate cancer, this is the first to indicate that deep-fried convenience foods in particular pose such a big danger.
Results published in the journal The Prostate found snacking on deep fried foods at least once a week appeared to increase the risk of cancer by between 30 and 37 per cent compared to men who claimed to eat them less than once a month.Nearly 40,000 cases of prostate cancer are diagnosed every year in the UK and 10,000 men die from it - the equivalent of more than one an hour. The risks increase with age, with men over 50 more likely to develop a tumour, and there is a strong genetic element to it.
Although previous studies have suggested poor diet can affect a man's chances of getting prostate cancer, this is the first to indicate that deep-fried convenience foods in particular pose such a big danger.
Results published in the journal The Prostate found snacking on deep fried foods at least once a week appeared to increase the risk of cancer by between 30 and 37 per cent compared to men who claimed to eat them less than once a month.Nearly 40,000 cases of prostate cancer are diagnosed every year in the UK and 10,000 men die from it - the equivalent of more than one an hour. The risks increase with age, with men over 50 more likely to develop a tumour, and there is a strong genetic element to it.
52
Latest Technology / Tensile Testing
« on: February 20, 2013, 09:25:05 AM »
Tensile testing, also known as tension testing, is a fundamental materials science test in which a sample is subjected to a controlled tension until failure. The results from the test are commonly used to select a material for an application, for quality control, and to predict how a material will react under other types of forces. Properties that are directly measured via a tensile test are ultimate tensile strength, maximum elongation and reduction in area. From these measurements the following properties can also be determined: Young's modulus, Poisson's ratio, yield strength, and strain-hardening characteristics. Uniaxial tensile testing is the most commonly used for obtaining the mechanical characteristics of isotropic materials. For anisotropic materials, such as composite materials and textiles, biaxial tensile testing is required.
53
Latest Technology / MICROHARDNESS TEST
« on: February 20, 2013, 09:08:21 AM »
Hardness is the property of a material that enables it to resist plastic deformation, usually by penetration. However, the term hardness may also refer to resistance to bending, scratching, abrasion or cutting. Hardness is not an intrinsic material property dictated by precise definitions in terms of fundamental units of mass, length and time. A hardness property value is the result of a defined measurement procedure.
The term microhardness test usually refers to static indentations made with loads not exceeding 1 kgf. The indenter is either the Vickers diamond pyramid or the Knoop elongated diamond pyramid. The procedure for testing is very similar to that of the standard Vickers hardness test, except that it is done on a microscopic scale with higher precision instruments. The surface being tested generally requires a metallographic finish; the smaller the load used, the higher the surface finish required. Precision microscopes are used to measure the indentations; these usually have a magnification of around X500 and measure to an accuracy of +0.5 micrometres. Also with the same observer differences of +0.2 micrometres can usually be resolved. It should, however, be added that considerable care and experience are necessary to obtain this accuracy.
The term microhardness test usually refers to static indentations made with loads not exceeding 1 kgf. The indenter is either the Vickers diamond pyramid or the Knoop elongated diamond pyramid. The procedure for testing is very similar to that of the standard Vickers hardness test, except that it is done on a microscopic scale with higher precision instruments. The surface being tested generally requires a metallographic finish; the smaller the load used, the higher the surface finish required. Precision microscopes are used to measure the indentations; these usually have a magnification of around X500 and measure to an accuracy of +0.5 micrometres. Also with the same observer differences of +0.2 micrometres can usually be resolved. It should, however, be added that considerable care and experience are necessary to obtain this accuracy.
54
Latest Technology / Electron Probe Micro-Analysis
« on: February 19, 2013, 05:44:26 PM »
EPMA works by bombarding a micro-volume of a sample with a focused electron beam (typical energy = 5-30 keV) and collecting the X-ray photons thereby emitted by the various elemental species. Because the wavelengths of these X-rays are characteristic of the emitting species, the sample composition can be easily identified by recording WDS spectra (Wavelength Dispersive Spectroscopy). WDS spectrometers are based on the Bragg's law and use various moveable, shaped monocrystals as monochromators.
• EPMA is a fully qualitative and quantitative method of non-destructive elemental analysis of micron-sized volumes at the surface of materials, with sensitivity at the level of ppm. Routine quantification to 1% reproducibility is obtained over several days. It is the most precise and accurate micro-analysis technique available and all elements from B to U and above can be analyzed.
• EPMA is fully compatible with routine analysis sessions, with easy and direct interpretation of the results.
• EPMA instruments are equipped with a complete kit of built-in microscopy tools that allow simultaneous X-ray (WDS and EDS), SEM and BSE imaging, plus sophisticated visible light optics; they provide very flexible sample inspection with image magnification ranging from 40 to 400,000.
• Determination of thickness and elemental composition from nm to mm thick layers in stratified materials is possible.
Major applications are found in geochemistry, mineralogy, geochronology, physical metallurgy, nuclear metallurgy, materials science including glass, ceramics, superconductors, cements, microelectronics,biochemistry,etc.
EPMA provides much better results than standard SEM/EDS systems. Because of the internal properties of WDS, the general sensitivity, analysis of light elements and risks of erroneous interpretation of qualitative spectra are all superior with EPMA. Spectral resolution and detector dead time are much better than EDS (Energy Dispersive Spectroscopy).
The excitation beam regulation system and sophisticated sample stage capabilities guarantee that this technique provides outstanding stability and measurement repeatability.
• EPMA is a fully qualitative and quantitative method of non-destructive elemental analysis of micron-sized volumes at the surface of materials, with sensitivity at the level of ppm. Routine quantification to 1% reproducibility is obtained over several days. It is the most precise and accurate micro-analysis technique available and all elements from B to U and above can be analyzed.
• EPMA is fully compatible with routine analysis sessions, with easy and direct interpretation of the results.
• EPMA instruments are equipped with a complete kit of built-in microscopy tools that allow simultaneous X-ray (WDS and EDS), SEM and BSE imaging, plus sophisticated visible light optics; they provide very flexible sample inspection with image magnification ranging from 40 to 400,000.
• Determination of thickness and elemental composition from nm to mm thick layers in stratified materials is possible.
Major applications are found in geochemistry, mineralogy, geochronology, physical metallurgy, nuclear metallurgy, materials science including glass, ceramics, superconductors, cements, microelectronics,biochemistry,etc.
EPMA provides much better results than standard SEM/EDS systems. Because of the internal properties of WDS, the general sensitivity, analysis of light elements and risks of erroneous interpretation of qualitative spectra are all superior with EPMA. Spectral resolution and detector dead time are much better than EDS (Energy Dispersive Spectroscopy).
The excitation beam regulation system and sophisticated sample stage capabilities guarantee that this technique provides outstanding stability and measurement repeatability.
55
Science Discussion Forum / To reduce the particle size by high energy ball mill
« on: February 19, 2013, 02:21:32 PM »
A ball mill, a type of grinder, is a cylindrical device used in grinding (or mixing) materials like ores, chemicals, ceramic raw materials and paints. Ball mills rotate around a horizontal axis, partially filled with the material to be ground plus the grinding medium. Different materials are used as media, including ceramic balls, flint pebbles and stainless steel balls. An internal cascading effect reduces the material to a fine powder. Industrial ball mills can operate continuously, fed at one end and discharged at the other end. Large to medium-sized ball mills are mechanically rotated on their axis, but small ones normally consist of a cylindrical capped container that sits on two drive shafts (pulleys and belts are used to transmit rotary motion). A rock tumbler functions on the same principle. Ball mills are also used in pyrotechnics and the manufacture of black powder, but cannot be used in the preparation of some pyrotechnic mixtures such as flash powder because of their sensitivity to impact. High-quality ball mills are potentially expensive and can grind mixture particles to as small as 5 nm, enormously increasing surface area and reaction rates. The grinding works on the principle of critical speed. The critical speed can be understood as that speed after which the steel balls (which are responsible for the grinding of particles) start rotating along the direction of the cylindrical device; thus causing no further grinding.
Ball mills are used extensively in the Mechanical alloying process in which they are not only used for grinding but for cold welding as well, with the purpose of producing alloys from powders.
Ball mills are used extensively in the Mechanical alloying process in which they are not only used for grinding but for cold welding as well, with the purpose of producing alloys from powders.
56
Latest Technology / Transmission Electron Microscope (TEM)
« on: June 25, 2012, 04:08:50 PM »
A Transmission Electron Microscope (TEM) utilizes energetic electrons to provide morphologic, compositional and crystallographic information on samples. Transmission electron microscopy (TEM) is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through. An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging device, such as a fluorescent screen, on a layer of photographic film, or to be detected by a sensor such as a CCD camera.
The Transmission Electron Microscope (TEM) uses electron translucent specimens with images directly projected on a screen or camera. Resolution better than 0.1 nm are now achievable, delivering atomic scale resolution.
TEMs are capable of imaging at a significantly higher resolution than light microscopes, owing to the small de Broglie wavelength of electrons. This enables the instrument's user to examine fine detail—even as small as a single column of atoms, which is tens of thousands times smaller than the smallest resolvable object in a light microscope. TEM forms a major analysis method in a range of scientific fields, in both physical and biological sciences. TEMs find application in cancer research, virology, materials science as well as pollution, nanotechnology, and semiconductor research.
At smaller magnifications TEM image contrast is due to absorption of electrons in the material, due to the thickness and composition of the material. At higher magnifications complex wave interactions modulate the intensity of the image, requiring expert analysis of observed images. Alternate modes of use allow for the TEM to observe modulations in chemical identity, crystal orientation, electronic structure and sample induced electron phase shift as well as the regular absorption based imaging.[/font][/size][/size][/font]
The Transmission Electron Microscope (TEM) uses electron translucent specimens with images directly projected on a screen or camera. Resolution better than 0.1 nm are now achievable, delivering atomic scale resolution.
TEMs are capable of imaging at a significantly higher resolution than light microscopes, owing to the small de Broglie wavelength of electrons. This enables the instrument's user to examine fine detail—even as small as a single column of atoms, which is tens of thousands times smaller than the smallest resolvable object in a light microscope. TEM forms a major analysis method in a range of scientific fields, in both physical and biological sciences. TEMs find application in cancer research, virology, materials science as well as pollution, nanotechnology, and semiconductor research.
At smaller magnifications TEM image contrast is due to absorption of electrons in the material, due to the thickness and composition of the material. At higher magnifications complex wave interactions modulate the intensity of the image, requiring expert analysis of observed images. Alternate modes of use allow for the TEM to observe modulations in chemical identity, crystal orientation, electronic structure and sample induced electron phase shift as well as the regular absorption based imaging.[/font][/size][/size][/font]
57
Science Discussion Forum / Introductory information about Scanning Electron Microscopy (SEM)
« on: April 26, 2012, 11:08:31 AM »
Scanning Electron Microscopy (SEM)
What is Scanning Electron Microscopy (SEM)?
A typical SEM instrument, showing the electron column, sample chamber, EDS detector, electronics console, and visual display monitors.
The scanning electron microscope (SEM) uses a focused beam of high-energy electrons to generate a variety of signals at the surface of solid specimens. The signals that derive from electron-sample interactions reveal information about the sample including external morphology (texture), chemical composition, and crystalline structure and orientation of materials making up the sample. In most applications, data are collected over a selected area of the surface of the sample, and a 2-dimensional image is generated that displays spatial variations in these properties. Areas ranging from approximately 1 cm to 5 microns in width can be imaged in a scanning mode using conventional SEM techniques (magnification ranging from 20X to approximately 30,000X, spatial resolution of 50 to 100 nm). The SEM is also capable of performing analyses of selected point locations on the sample; this approach is especially useful in qualitatively or semi-quantitatively determining chemical compositions (using EDS), crystalline structure, and crystal orientations (using EBSD). The design and function of the SEM is very similar to the EPMA and considerable overlap in capabilities exists between the two instruments.
Applications
The SEM is routinely used to generate high-resolution images of shapes of objects (SEI) and to show spatial variations in chemical compositions: 1) acquiring elemental maps or spot chemical analyses using EDS, 2)discrimination of phases based on mean atomic number (commonly related to relative density) using BSE, and 3) compositional maps based on differences in trace element "activitors" (typically transition metal and Rare Earth elements) using CL. The SEM is also widely used to identify phases based on qualitative chemical analysis and/or crystalline structure. Precise measurement of very small features and objects down to 50 nm in size is also accomplished using the SEM. Backescattered electron images (BSE) can be used for rapid discrimination of phases in multiphase samples. SEMs equipped with diffracted backscattered electron detectors (EBSD) can be used to examine microfabric and crystallographic orientation in many materials.
What is Scanning Electron Microscopy (SEM)?
The scanning electron microscope (SEM) uses a focused beam of high-energy electrons to generate a variety of signals at the surface of solid specimens. The signals that derive from electron-sample interactions reveal information about the sample including external morphology (texture), chemical composition, and crystalline structure and orientation of materials making up the sample. In most applications, data are collected over a selected area of the surface of the sample, and a 2-dimensional image is generated that displays spatial variations in these properties. Areas ranging from approximately 1 cm to 5 microns in width can be imaged in a scanning mode using conventional SEM techniques (magnification ranging from 20X to approximately 30,000X, spatial resolution of 50 to 100 nm). The SEM is also capable of performing analyses of selected point locations on the sample; this approach is especially useful in qualitatively or semi-quantitatively determining chemical compositions (using EDS), crystalline structure, and crystal orientations (using EBSD). The design and function of the SEM is very similar to the EPMA and considerable overlap in capabilities exists between the two instruments.
Applications
The SEM is routinely used to generate high-resolution images of shapes of objects (SEI) and to show spatial variations in chemical compositions: 1) acquiring elemental maps or spot chemical analyses using EDS, 2)discrimination of phases based on mean atomic number (commonly related to relative density) using BSE, and 3) compositional maps based on differences in trace element "activitors" (typically transition metal and Rare Earth elements) using CL. The SEM is also widely used to identify phases based on qualitative chemical analysis and/or crystalline structure. Precise measurement of very small features and objects down to 50 nm in size is also accomplished using the SEM. Backescattered electron images (BSE) can be used for rapid discrimination of phases in multiphase samples. SEMs equipped with diffracted backscattered electron detectors (EBSD) can be used to examine microfabric and crystallographic orientation in many materials.