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Inert Gas Condensation Method:
The inert gas evaporation–condensation (IGC) technique, in which nanoparticles are formed via the evaporation of a metallic source in an inert gas, has been widely used in the synthesis of ultrafine metal particles since the 1930s.
A similar method has been used in the manufacture of carbon black, an ink pigment, since ancient times. The technique employed now for the formation of nanopowders, in reality, differs from that used to produce carbon and lampblack primarily in the choice of atmospheric composition and pressure and in the use of a chemically reactive source.
Thus, although the technology is old, the application to the production of truly nanoscaled powders is relatively recent.

In its basic form, the method consists of evaporating a metallic source, using resistive heating (although radio frequency heating or use of an electron or laser beam as the heating source are all equally effective methods) inside a chamber which has been previously evacuated to about 10 power -7 torr and backfilled with inert gas to a low pressure.
The metal vapour migrates from the hot source into the cooler inert gas by a combination of convective flow and diffusion and the evaporated atoms collide with the gas atoms within the chamber, thus losing kinetic energy. Ultimately, the particles are collected for subsequent consolidation, usually by deposition on a cold surface.

Most applications of the inert gas condensation technique carry this approach to extremes by cooling the substrate with liquid nitrogen to enhance the deposition efficiency.
Particles collected in this manner are highly concentrated on the deposition substrate. While the particles deposited on the substrate have complex aggregate morphology, the structure tends to be classified in terms of the size of the crystallites that make up these larger structures.
The scraping and compaction processes take place within the clean environment to ensure powder surface cleanliness (i.e., to reduce oxide formation) and to minimise problems associated with trapped gas.
Arc discharge
Arc Discharge Method:
The principle of this technique is to vaporize carbon in the presence of catalysts (iron, nickel, cobalt, yttrium, boron, gadolinium, and so forth) under reduced atmosphere of inert gas (argon or helium). After the triggering of the arc between two electrodes, a plasma is formed consisting of the mixture of carbon vapor, the rare gas (helium or argon), and the vapors of catalysts. The va- porization is the consequence of the energy transfer from the arc to the anode made of graphite doped with cata- lysts. The anode erosion rate is more or less important depending on the power of the arc and also on the other experimental conditions. It is noteworthy that a high an- ode erosion does not necessarily lead to a high carbon nanotube production.
It consists of a cylinder of about 30 cm in diameter and about 1m in height, equipped with diametrically op- posed sapphire windows located so that they face the plasma zone in view of observing the arc. The reactor possesses two valves, one for carrying out the primary evacuation (0.1Pa) of the chamber, the other permit- ting it to fill with a rare gas up to the desired working pressure.

In the arc discharge method, a DC bias of 20–30 V is applied between two carbon electrodes in a helium atmosphere. Carbon atoms are ejected from the anode, and accumulate in the form of nanotubes on the cathode. The electrodes are typically 5–20 mm in diameter. As with laser evaporation, the anode includes small quantities of nickel, cobalt or iron, which are also deposited onto the cathode to act as a catalyst. Arc discharges tend to produce narrower and shorter tubes than those obtained from laser ablation (up to $5nm in diameter and around 1mm long). Like laser ablation, arc discharges tend to produce bundles of nanotubes.
Electric explosions
Exploding Wire Method
From Wikipedia, the free encyclopedia
Exploding Wire Method (also known as EWM) is a high energy density process by which a rising current is applied to a thin electrically conductive wire. The heat vaporizes the wire, and an electric arc over that vapor creates a shockwave and explosion. Exploding Wire Method is best known to be used as a detonator in nuclear munitions, high intensity light source, and production method for metal nanoparticles.
• 1History
• 2Mechanism
• 3Practical Application
o 3.1Detonator
o 3.2Light Source
o 3.3Production of Nanoparticles
• 4References
• 5External links
Exploding Wire Method has a surprisingly long history for a process only recently appropriated. Progress on the comprehension of the mechanism was intermittent, and even at present day there are many aspects that remain not fully understood.
One of the first documented cases of using electricity to melt a metal occurred in the late 1700s [1] and is credited to Martin van Marum who melted 70 feet of metal wire with 64Leyden Jars as a capacitor. Van Marum's generator was built in 1784, and is now located in the Teylers Museum in the Netherlands. Years later, Benjamin Franklin vaporized thin gold leaf to burn images onto paper.[2][3] While neither Marum nor Franklin actually incited the exploding wire phenomenon, they were both important steps towards its discovery.
Edward Nairne was the first to note the existence of the exploding wire method in 1774 with silver and copper wire. Subsequently Michael Faraday used EWM to deposit thin gold films through the solidification of vaporized metal on adjacent surfaces. Then, vapor deposits of metal gas as a result of EWM were studied by August Toepler during the 1800s.Spectrography investigation of the process, led by J.A. Anderson, became widespread in the 1900s. The spectrography experiments enabled a better understanding and subsequently the first glimpses of practical application. The mid 20th century saw experiments with EWM as a light source and for the production of nanoparticles in aluminum, uranium and plutonium wires. Congruently, Luis Álvarez and Lawrence Johnston of the Manhattan Project found use for EWM in the development of nuclear detonators. [3] [4]
Current day research focuses on utilizing EWM to produce nanoparticles as well as better understanding specifics of the mechanism such as the effects of the system environment on the process.
The basic components needed for the exploding wire method are a thin conductive wire and a capacitor. The wire is typically gold, aluminum, iron or platinum, and is usually less than 0.5mm in diameter. The capacitor has an energy consumption of about 25kWh/kg and discharges a pulse of charge density 104 - 106 A/mm2,[5] leading to temperatures up to 100,000K. The phenomena occurs over a time period of only 10−5-10−8 seconds. [6]

The process is as follows:
1. A rising current, supplied by the capacitor, is carried across the wire.
2. The current heats up the wire through ohmic heating until the metal begins to melt. The metal melts to form a broken series of imperfect spheres called unduloids. The current rises so fast that the liquid metal has no time to move out of the way.
3. The unduloids vaporize. The metal vapor creates a lower resistance path, allowing an even faster current increase.
4. An electric arc is formed, which turns the vapor into plasma. A bright flash of light is also produced.
5. The plasma is allowed to expand freely, creating a shock wave.
6. Electromagnetic radiation is released in tandem with the shock wave.
7. The shock wave pushes liquid, gaseous and plasmatic metal outwards, breaking the circuit and ending the process.

Practical Application[edit]
EWM research has suggested possible applications in the excitation of optical masers, high intensity light sources for communications, spacecraft propulsion, joining difficult materials such as quartz, and generation of high power radio-frequency pulses.[3] The most promising applications of EWM are as a detonator, light source, and for the production of nanoparticles.
EWM has found its most use as a detonator, named the exploding-bridgewire detonator, for nuclear bombs. Bridgewire detonators are advantageous over chemical fuses as the explosion is consistent and occurs only a few microseconds after the current is applied, with variation of only a few tens of nanoseconds from detonator to detonator.[7]
Light Source[edit]
EWM is an effective mechanism by which to get a short duration high intensity light source. The peak intensity for copper wire, for example, is 9.6*108 candle power/cm2.[8] J.A. Anderson wrote in his initial spectrography studies that the light was comparable to a black body at 20,000K.[9] The advantage of a flash produced in this way is that it is easily reproducible with little variation in intensity. The linear nature of the wire allows for specifically shaped and angled light flashes and different types of wires can be used to produce different colors of light.[10] The light source can be used in interferometry, flash photolysis, quantitative spectroscopy, and high-speed photography.
Production of Nanoparticles[edit]
Nanoparticles are created by EWM when the ambient gas of the system cools the recently produced vaporous metal.[11] EWM can be used to cheaply and efficiently produce nanoparticles at a rate of 50-300 grams per hour and at a purity of above 99%.[6][5] The process requires a relatively low energy consumption as little energy is lost in an electric to thermal energy conversion. Environmental effects are minimal due to the process taking place in a closed system. The Particles can be as small as 10nm but are most commonly below 100nm in diameter. Physical attributes of the nanopowder can be altered depending on the parameters of the explosion. For example, as the voltage of the capacitor is raised, the particle diameter decreases. Also, the pressure of the gas environment can change the dispersiveness of the nanoparticles.[6] Through such manipulations you can alter the functionality of the nanopowder.
When EWM is performed in a standard atmosphere containing oxygen, metal oxides are formed. Pure metal nanoparticles can also be produced with EWM in an inert environment, usually argon gas or distilled water.[12] Pure metal nanopowders must be kept in their inert environment because they ignite when exposed to oxygen in air.[5] Often, the metal vapor is contained by operating the mechanism within a steel box or similar container.
Nanoparticles are a relatively new material used in medicine, manufacturing, environmental cleanup and circuitry. Metal oxide and pure metal nanoparticles are used in Catalysis, sensors, oxygen antioxident, self repairing metal, ceramics, UV ray protection, odor proofing, improved batteries, printable circuits, optoelectronic materials, and Environmental remediation. [13][14] The demand for metal nanoparticles, and therefore production methods, has increased as interest in nanotechnology continues to rise. Despite its overwhelming simplicity and efficiency, It is difficult to modify the experimental apparatus to be used on an industrial scale. As such, EWM has not seen widespread utilization in material production industry due to issues in manufacturing quantity.

Molecular beam epitaxy takes place in high vacuum or ultra-high vacuum (10−8 Pa). The most important aspect of MBE is the deposition rate (typically less than 3000 nm per hour) that allows the films to grow epitaxially. These deposition rates require proportionally better vacuum to achieve the same impurity levels as other deposition techniques. The absence of carrier gases as well as the ultra high vacuum environment result in the highest achievable purity of the grown films.
In solid-source MBE, elements such as gallium and arsenic, in ultra-pure form, are heated in separate quasi-Knudsen effusion cells until they begin to slowly sublime. The gaseous elements then condense on the wafer, where they may react with each other. In the example of gallium and arsenic, single-crystal gallium arsenide is formed. The term "beam" means that evaporated atoms do not interact with each other or vacuum chamber gases until they reach the wafer, due to the long mean free paths of the atoms.
During operation, reflection high energy electron diffraction (RHEED) is often used for monitoring the growth of the crystal layers. A computer controls shutters in front of eachfurnace, allowing precise control of the thickness of each layer, down to a single layer of atoms. Intricate structures of layers of different materials may be fabricated this way. Such control has allowed the development of structures where the electrons can be confined in space, giving quantum wells or even quantum dots. Such layers are now a critical part of many modern semiconductor devices, including semiconductor lasers and light-emitting diodes.
In systems where the substrate needs to be cooled, the ultra-high vacuum environment within the growth chamber is maintained by a system of cryopumps, and cryopanels, chilled using liquid nitrogen or cold nitrogen gas to a temperature close to 77 Kelvin (−196 degrees Celsius). Cryogenic temperatures act as a sink for impurities in the vacuum, so vacuum levels need to be several orders of magnitude better to deposit films under these conditions. In other systems, the wafers on which the crystals are grown may be mounted on a rotating platter which can be heated to several hundred degrees Celsius during operation.
Molecular beam epitaxy is also used for the deposition of some types of organic semiconductors. In this case, molecules, rather than atoms, are evaporated and deposited onto the wafer. Other variations include gas-source MBE, which resembles chemical vapor deposition.
Lately molecular beam epitaxy has been used to deposit oxide materials for advanced electronic, magnetic and optical applications. For these purposes, MBE systems have to be modified to incorporate oxygen sources.[2]
The Asaro-Tiller-Grinfeld (ATG) instability, also known as the Grinfeld instability, is an elastic instability often encountered during molecular beam epitaxy. If there is a mismatch between the lattice sizes of the growing film and the supporting crystal, elastic energy will be accumulated in the growing film. At some critical height, the free energy of the film can be lowered if the film breaks into isolated islands, where the tension can be relaxed laterally. The critical height depends on the Young's modulus, mismatch size, and surface tension.
Some applications for this instability have been researched, such as the self-assembly of quantum dots. This community uses the name of Stranski–Krastanow growth for ATG.

Physical vapor deposition (PVD) describes a variety of vacuum deposition methods which can be used to produce thin films. PVD uses physical process (such as heating or sputtering) to produce a vapor of material, which is then deposited on the object which requires coating. PVD is used in the manufacture of items which require thin films for mechanical, optical, chemical or electronic functions. Examples include semiconductor devices such as thin film solar panels,[1] aluminized PET film for food packaging and balloons,[2] and coated cutting tools for metalworking.[3] Besides PVD tools for fabrication, special smaller tools (mainly for scientific purposes) have been developed.[4]
Common industrial coatings applied by PVD are titanium nitride, zirconium nitride, chromium nitride, titanium aluminum nitride.[5]
The source material is unavoidably also deposited on most other surfaces interior to the vacuum chamber, including the fixturing used to hold the parts.
• 1Examples
• 2Comparison to other deposition techniques
o 2.1Advantages
o 2.2Disadvantages
• 3Application
• 4See also
• 5Notes
• 6References
• 7External links
• Cathodic Arc Deposition: In which a high-power electric arc discharged at the target (source) material blasts away some into highly ionized vapor to be deposited onto the workpiece.
• Electron beam physical vapor deposition: In which the material to be deposited is heated to a high vapor pressure by electron bombardment in "high" vacuum and is transported by diffusion to be deposited by condensation on the (cooler) workpiece.
• Evaporative deposition: In which the material to be deposited is heated to a high vapor pressure by electrical resistance heating in "high" vacuum.[6][7]
• Pulsed laser deposition: In which a high-power laser ablates material from the target into a vapor.
• Sputter deposition: In which a glow plasma discharge (usually localized around the "target" by a magnet) bombards the material sputtering some away as a vapor for subsequent deposition.
• Sublimation sandwich method
Various thin film characterisation techniques can be used to measure the physical properties of PVD coatings, such as:
• Calo tester: coating thickness test
• Nanoindentation: hardness test for thin-film coatings
• Pin on disc tester: wear and friction coefficient test
• Scratch tester: coating adhesion test
• X-ray micro-analyzer: investigation of structural features and heterogeneity of elemental composition for the growth surfaces [8]
Comparison to other deposition techniques[edit]
• PVD coatings are sometimes harder and more corrosion resistant than coatings applied by the electroplating process. Most coatings have high temperature and good impact strength, excellent abrasion resistance and are so durable that protective topcoats are almost never necessary.
• Ability to utilize virtually any type of inorganic and some organic coating materials on an equally diverse group of substrates and surfaces using a wide variety of finishes.
• More environmentally friendly than traditional coating processes such as electroplating and painting.
• More than one technique can be used to deposit a given film.
• Specific technologies can impose constraints; for example, line-of-sight transfer is typical of most PVD coating techniques, however there are methods that allow full coverage of complex geometries.
• Some PVD technologies typically operate at very high temperatures and vacuums, requiring special attention by operating personnel.
• Requires a cooling water system to dissipate large heat loads.
As mentioned previously, PVD coatings are generally used to improve hardness, wear resistance and oxidation resistance. Thus, such coatings use in a wide range of applications such as:
• Aerospace
• Automotive
• Surgical/Medical [9]
• Dies and moulds for all manner of material processing
• Cutting tools
• Firearms
• Optics
• Watches
• Thin films (window tint, food packaging, etc.)
• Darts barrels
• Metals (Aluminum, Copper, Bronze, etc.)

Thermal evaporation in a resistive heated boat
Evaporation is a common method of thin-film deposition. The source material is evaporated in a vacuum. The vacuum allows vapor particles to travel directly to the target object (substrate), where they condense back to a solid state. Evaporation is used inmicrofabrication, and to make macro-scale products such as metallized plastic film.
• 1Physical principle
• 2Equipment
• 3Optimization
• 4Applications
• 5Comparison to other deposition methods
• 6References
• 7External links
Physical principle[edit]
Evaporation involves two basic processes: a hot source material evaporates and condenses on the substrate. It resembles the familiar process by which liquid water appears on the lid of a boiling pot. However, the gaseous environment and heat source (see "Equipment" below) are different.
Evaporation takes place in a vacuum, i.e. vapors other than the source material are almost entirely removed before the process begins. In high vacuum (with a long mean free path), evaporated particles can travel directly to the deposition target without colliding with the background gas. (By contrast, in the boiling pot example, the water vapor pushes the air out of the pot before it can reach the lid.) At a typical pressure of 10−4 Pa, an 0.4-nm particle has a mean free path of 60 m. Hot objects in the evaporation chamber, such as heating filaments, produce unwanted vapors that limit the quality of the vacuum.
Evaporated atoms that collide with foreign particles may react with them; for instance, if aluminium is deposited in the presence of oxygen, it will form aluminium oxide. They also reduce the amount of vapor that reaches the substrate, which makes the thickness difficult to control.
Evaporated materials deposit nonuniformly if the substrate has a rough surface (as integrated circuits often do). Because the evaporated material attacks the substrate mostly from a single direction, protruding features block the evaporated material from some areas. This phenomenon is called "shadowing" or "step coverage."
When evaporation is performed in poor vacuum or close to atmospheric pressure, the resulting deposition is generally non-uniform and tends not to be a continuous or smooth film. Rather, the deposition will appear fuzzy .
A thermal evaporator with a molybdenum boat fixed between two massive copper feedthroughs cooled by water.
Any evaporation system includes a vacuum pump. It also includes an energy source that evaporates the material to be deposited. Many different energy sources exist:
• In the thermal method, metal material (in the form of wire, pellets, shot) is fed onto heated semimetal (ceramic) evaporators known as "boats" due to their shape. A pool of melted metal forms in the boat cavity and evaporates into a cloud above the source. Alternatively the source material is placed in a crucible, which is radiatively heated by an electric filament, or the source material may be hung from the filament itself (filament evaporation).
• Molecular beam epitaxy is an advanced form of thermal evaporation.
• In the electron-beam method, the source is heated by an electron beam with an energy up to 15 keV.
• In flash evaporation, a fine wire of source material is fed continuously onto a hot ceramic bar, and evaporates on contact.
• Resistive evaporation is accomplished by passing a large current through a resistive wire or foil containing the material to be deposited. The heating element is often referred to as an "evaporation source". Wire type evaporation sources are made from tungsten wire and can be formed into filaments, baskets, heaters or looped shaped point sources. Boat type evaporation sources are made from tungsten, tantalum, molybdenum or ceramic type materials capable of withstanding high temperatures.
Some systems mount the substrate on an out-of-plane planetary mechanism. The mechanism rotates the substrate simultaneously around two axes, to reduce shadowing.
• Purity of the deposited film depends on the quality of the vacuum, and on the purity of the source material.
• At a given vacuum pressure the film purity will be higher at higher deposition rates as this minimises the relative rate of gaseous impurity inclusion.
• The thickness of the film will vary due to the geometry of the evaporation chamber. Collisions with residual gases aggravate nonuniformity of thickness.
• Wire filaments for evaporation cannot deposit thick films, because the size of the filament limits the amount of material that can be deposited. Evaporation boats and crucibles offer higher volumes for thicker coatings. Thermal evaporation offers faster evaporation rates than sputtering. Flash evaporation and other methods that use crucibles can deposit thick films.
• In order to deposit a material, the evaporation system must be able to vaporize it. This makes refractory materials such as tungsten hard to deposit by methods that do not use electron-beam heating.
• Electron-beam evaporation allows tight control of the evaporation rate. Thus, an electron-beam system with multiple beams and multiple sources can deposit a chemical compound or composite material of known composition.
• Step coverage


Evaporation machine used for metallization at LAAS technological facility in Toulouse, France.
An important example of an evaporative process is the production of aluminized PET film packaging film in a roll-to-roll web system. Often, the aluminum layer in this material is not thick enough to be entirely opaque since a thinner layer can be deposited more cheaply than a thick one. The main purpose of the aluminum is to isolate the product from the external environment by creating a barrier to the passage of light,oxygen, or water vapor.
Evaporation is commonly used in microfabrication to deposit metal films
Comparison to other deposition methods[edit]
• Alternatives to evaporation, such as sputtering and chemical vapor deposition, have better step coverage. This may be an advantage or disadvantage, depending on the desired result.
• Sputtering tends to deposit material more slowly than evaporation.
• Sputtering uses a plasma, which produces many high-speed atoms that bombard the substrate and may damage it. Evaporated atoms have a Maxwellian energy distribution, determined by the temperature of the source, which reduces the number of high-speed atoms. However, electron beams tend to produce X-rays (Bremsstrahlung) and stray electrons, each of which can also damage the substrate.
1. astronomical telescope mirror.
2. aluminium PET film.
3. micro fabrication

Lithography (from Ancient Greek λίθος, lithos, meaning "stone", and γράφειν, graphein, meaning "to write") is a method of printingoriginally based on the immiscibility of oil and water.[1] The printing is from a stone (lithographic limestone) or a metal plate with a smooth surface. It was invented in 1796 by German author and actor AloisSenefelder as a cheap method of publishing theatrical works.[2][3]Lithography can be used to print text or artwork onto paper or other suitable material.[4]
Lithography originally used an image drawn with oil, fat, or wax onto the surface of a smooth, level lithographic limestone plate. The stone was treated with a mixture of acid and gum arabic, etching the portions of the stone that were not protected by the grease-based image. When the stone was subsequently moistened, these etched areas retained water; an oil-based ink could then be applied and would be repelled by the water, sticking only to the original drawing. The ink would finally be transferred to a blank paper sheet, producing a printed page. This traditional technique is still used in some fine art printmaking applications.
In modern lithography, the image is made of a polymer coating applied to a flexible aluminum plate. The image can be printed directly from the plate (the orientation of the image is reversed), or it can be offset, by transferring the image onto a flexible sheet (rubber) for printing and publication.
As a printing technology, lithography is different from intaglio printing (gravure), wherein a plate is either engraved, etched, or stippled to score cavities to contain the printing ink; and woodblock printing or letterpress printing, wherein ink is applied to the raised surfaces of letters or images. Today, most types of high-volume books and magazines, especially when illustrated in colour, are printed with offset lithography, which has become the most common form of printing technology since the 1960s. The word lithography also denotes photolithography, amicrofabrication technique used in the microelectronics industry to make integrated circuits and microelectromechanical systems.

The principle of lithography[edit]
Lithography uses simple chemical processes to create an image. For instance, the positive part of an image is a water-repelling ("hydrophobic") substance, while the negative image would be water-retaining ("hydrophilic"). Thus, when the plate is introduced to a compatible printing ink and water mixture, the ink will adhere to the positive image and the water will clean the negative image. This allows a flat print plate to be used, enabling much longer and more detailed print runs than the older physical methods of printing (e.g., intaglio printing, letterpress printing).
Lithography was invented by AloisSenefelder in the Kingdom of Bavaria in 1796. In the early days of lithography, a smooth piece of limestonewas used (hence the name "lithography": "lithos" (λιθος) is the ancient Greek word for stone). After the oil-based image was put on the surface, a solution of gum arabic in water was applied, the gum sticking only to the non-oily surface. During printing, water adhered to the gum arabic surfaces and avoided the oily parts, while the oily ink used for printing did the opposite.

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