Photonic crystals of tungsten emit visible light but without the same wasteful emission of infrared, say researchers aiming to reinvent the light bulb.
 
Photonic crystals are nanoscopic structures designed to channel light of specific wavelengths while blocking other wavelengths.
 
This ability to control and filter light with great efficiency makes them hugely useful for applications such as increasing the efficiency of photovoltaic cells by absorbing light at certain optimal wavelengths.
 
Today, Sergei Belousov and buddies at the Kintech Lab in Moscow and a number of friends at the GE Global Research Center in New York state,  say they have another application for photonics crystals. They’ve worked out how photonic crystals can dramatically improve the light emitting efficiency of tungsten in the hope of reinventing the light bulb.
 
Tungsten bulbs have had a bad press, to say the least. Tungsten has a high melting point (3695 K) and so can be heated until it glows without melting. The problem is that only 5 per cent of the light it emits is visible, the rest being infrared, which simply goes to waste.   With an efficiency of only 5 per cent, tungsten bulbs have rapidly fallen out of favour.
 
The question Belousov and co set out to answer is whether they can engineer the nanostructure of tungsten to create a photonic crystal that emits visible light while suppressing the emission of infrared light.

They theoretically studied the properties of several structures, such as nanoscopic tungsten log piles and spheres embedded in another medium. While tungsten log piles make little difference, tungsten spheres just a fraction of a micrometre in radius do just the job, emitting light mainly in the visible region of the spectrum.

Belousov and co then tested their idea by making a tungsten photonic crystal of the required design and measuring the amount of light it emits at different frequencies. They say the new structure emits far less infrared light and has an efficiency of 15 per cent, significantly higher than the bulk material.
 
That’s a significant improvement and improvements on this will surely be possible. But whether it will be enough to trigger a tungsten revolution in light bulbs is open to question. The current generation of compact fluorescent bulbs can match the light output of a 100 Watt tungsten bulb using less than 30 Watts and LED lights can do it using less than 20 Watts.
 
If Belousov and co want to put tungsten back into light bulbs, they’ll have to beat some stiff opposition first.

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Introduction
Super alloys are metallic alloys that function at high temperature environment where high surface stability and deformation resistance are mainly required. Three major classifications of super alloys include iron-base, nickel-base and cobalt-base alloys. Based on its application and composition, nickel-base and cobalt-base super alloys may be cast or wrought. The iron-base super alloys are generally wrought alloys having stainless steel technology. Super alloys are commonly forged, rolled to sheet or produced in various shapes. However, highly alloyed compositions are produced as castings. These alloys contain different elements in various combinations in order to achieve the desired result.
 
The following section provides detailed description of super alloy IN-102™, which is a nickel super alloy with high strength and ductility.
 
Chemical Composition
The following table shows the chemical composition of super alloy IN-102™.
Element                Content (%)
Chromium, Cr           15
Iron, Fe                     7
Molybdenum, Mo       3
Niobium, Nb              3
Tungsten, W             3
Titanium, Ti             0.5
Aluminum, Al          0.5
Carbon, C               0.06
Nickel, Ni             Balance
 
Physical Properties
 
The physical properties of super alloy IN-102™ are given in the following table.
Properties          Metric           Imperial
Density             8.5 g/cm³       0.309 lb/in³
Melting point     1371°C           2500°F

Fabrication and Heat Treatment
 
Machinability
Super alloy IN-102™ can be machined using conventional techniques employed for iron based alloys. High speed operations like milling, grinding or turning can be performed using water-base coolants. Heavy lubricants are recommended for operations such as boring, broaching, tapping or drilling.
 
Forming
Super alloy IN-102™ can be formed by conventional means. For cold forming this alloy, heavy-duty lubricants can be used.
 
Welding
Welding of super alloy IN-102™ is performed through commonly used welding techniques such as gas tungsten arc welding, shielded metal-arc welding, metal-arc welding and submerged-arc welding. However, an alloy filler metal that suits this alloy need to be used.
 
Cold Working
Super alloy IN-102™ can be cold worked using standard tooling methods. As plain carbon steels has an ability to produce galling, they are not preferred for forming this alloy. Galling can be minimized with the help of soft die materials.
 
Annealing
Super alloy IN-102™ can be annealed at 982°C (1800°F) followed by rapid cooling of air.
 
Hardening
Super alloy IN-102™ can be hardened by cold working.
 
Applications
The following are the major applications of super alloy IN-102™:
 
    Industrial furnaces
    Gas turbine hot section components

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Extensive training for onsite facility personnel is one of the key strategies for limiting ignition sources at oil and gas sites. A Houston-based company is trying to build on this approach by making the tools site personnel use safer.

"These tools could have prevented most events where a grinder or torch was the source of ignition for an explosion," said Hector Maggi, vice president of marketing and sales with TFT-Pneumatic, LLC, which sells "sparkless" power tools to customers in the oil and gas and other industries.

Maggi said the tools use grinding disks, cutting disks and rotating files made from a proprietary alloy containing 95 percent tungsten carbide. Although  tungsten carbide typically produces sparks when it grinds, cuts or files another metal, TFT-Pneumatic maintains that its blend of tungsten carbide and other components does not.

"This alloy is as unique as can be and holds one of the biggest secrets of our technology," Maggi said. "As of today, no other company in the world has been able to come up with something similar."

Maggi is keeping the non- tungsten carbide composition of the alloy a secret, but he did divulge that his company's products differ from more traditional tools in terms of speed and shape. On the first count, he explained that TFT's grinders and cutting tools rotate at speeds of 800 to 3,000 revolutions per minute (rpm) rather than the more conventional 7,000 to 30,000 rpm.

"The principle is very simple," Maggi said. "Our tools simulate the work of a milling machine rather than a grinder."

In addition to rotating more slowly, the Houston-based company's tools apply cutting disks, grinding disks and rotating files that are shaped in a manner to generate less heat metal-on-metal.

"By minimizing friction we are able to minimize heat and thus sparks, therefore eliminating completely the risk of explosion," said Maggi. He noted that sparkless tools are well-suited for applications throughout the oil and gas value chain, particularly in areas classified as Hazardous/Explosive (Class 1 Divisions 1 and 2).

"The applications are so vast that a very large percentage of grinding and/or cutting can be achieved by our tools," Maggi said.

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Introduction

Super alloys or high performance alloys are available in a variety of shapes and contain elements in different combinations to obtain a specific result. These alloys are of three types that include iron-based, cobalt-based and nickel-based alloys.

Super alloys have good oxidation and creep resistance and can be strengthened by precipitation hardening, solid-solution hardening and work hardening methods. They can also function under high mechanical stress and high temperatures and also in places that require high surface stability.

The following datasheet provides an overview of Udimet 720™.

Chemical Composition

The chemical composition of Udimet 720™ is outlined in the following table.

Element                       Content (%)
Nickel, Ni                     55.16-59.705
Chromium, Cr               15.5-16.5
Cobalt, Co                   14.0-15.5
Titanium, Ti                  4.75-5.25
Molybdenum, Mo         2.75-3.25
Aluminum, Al               2.25-2.75
Tungsten, W               1.00-1.50
Zirconium, Zr            0.0250-0.0500
Boron, B                  0.0100-0.0200
Carbon, C                0.0100-0.0200

Physical Properties

The following table shows the physical properties of Udimet 720™.

Properties                Metric                    Imperial
Density                    8.08 g/cm³             0.292 lb/in³
Melting point            1371°C                  2500°F

Thermal Properties
The thermal properties of Udimet 720™ are given in the following table.

Properties                                                              Metric                   Imperial
Thermal expansion co-efficient (@93°C/199°F)        12.24 µm/m°C       6.800 µin/in°F

Fabrication and Heat Treatment

Annealing
Udimet 720™ is annealed at 1121°C (2050°F) and then cooled in air in a rapid manner.

Cold Working
Standard tooling methods are used for cold working Udimet 720™. Usage of plain carbon steels is not recommended as they may produce galling. Galling can be reduced by the usage of soft die materials and heavy duty lubricants. Tooling is recommended in the cold working process to allow liberal radii and clearances.

Welding
Welding processes recommended for Udimet 720™ include gas-tungsten arc welding, gas metal-arc welding and shielded metal-arc welding. Submerged-arc welding is not recommended as cracks may develop due to the high heat input. This alloy can be welded by the commonly used welding procedures and the welding surfaces should be free from paint, crayon markings or oil.

Forging
Udimet 720™ is capable of being forged as it is ductile.

Forming
Conventional methods are used to readily form Udimet 720™ that has good ductility. To obtain good forming results a powerful equipment is used along with heavy-duty lubricants. Usage of heavy-duty lubricants is recommended during the cold forming process of this alloy. After the forming process all traces of the lubricant should be cleaned to prevent embrittlement of this alloy at high temperatures.

Machinability
Udimet 720™ can be machined by conventional machining methods and contains higher strength, gumminess and work-hardening qualities. Work-hardening of the alloy before the cutting process and chatter can be minimized by tooling and a heavy duty machining equipment. Usage of water-base coolants is preferred for milling, turning or grinding. Usage of heavy lubricants is preferred for boring, drilling, broaching or tapping operations.

Aging
Udimet 720™ is treated under four different temperatures to be air-hardened.

    Heat for 2 h at 1113°C (2035°F) and cool in air.
    Heat for 4 h at 1079°C (1975F) and oil quench.
    Heat for 24 h at 649°C (1200°F) and cool in air.
    Heat for 8 h at 760°C (1400°F) and cool in air.

Heat Treatment
Udimet 720™ can be age-hardened in the heat-treatment process.

Applications
Udimet 720™ is used for gas turbine hot section components.

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