It seems a mysterious and even a magical force.
History[ edit ] Electron-beam welding was developed by the German physicist Karl-Heinz Steigerwald in who was at the time working on various electron-beam applications. Steigerwald conceived and developed the first practical electron-beam welding machine, which began operation in Russell has also been credited with designing and building the first electron-beam welder.
They exist either bound to an atomic nucleusas conduction electrons in the atomic lattice of metalsor as free electrons in vacuum. Free electrons in vacuum can be accelerated, with their paths controlled by electric and magnetic fields.
In this way narrow beams of electrons carrying high kinetic energy can be formed, which upon collision with atoms in solids transform their kinetic energy into heat.
Electron-beam welding provides excellent welding conditions because it involves: Strong electric fields, which can accelerate electrons to a very high speed. Thus, the electron beam can carry high power, equal to the product of beam current and accelerating voltage. By increasing the beam current and the accelerating voltage, the beam power can be increased to practically any desired value.
Using magnetic lensesby which the beam can be shaped into a narrow cone and focused to a very small diameter. This allows for a very high surface power density on the surface to be welded.
Shallow penetration depths in the order of hundredths of a millimeter. The effectiveness of the electron beam depends on many factors. The most important are the physical properties of the materials to be welded, especially the ease with which they can be melted or vaporize under low-pressure conditions.
Electron-beam welding can be so intense that loss of material due to evaporation or boiling during the process must be taken into account when welding.
At higher power density, the material affected by the beam can totally evaporate in a very short time; this is no longer electron-beam welding; it is electron-beam machining. Cathode - the source of free electrons Tungsten cathodes: They cannot leave the metal unless their kinetic energy in eV is higher than the potential barrier at the metal surface.
The number of electrons fulfilling this condition increases exponentially with increasing temperature of the metal, following Richardson's rule. As a source of electrons for electron-beam welders, the material must fulfill certain requirements: The emitter must be mechanically stable, not chemically sensitive to gases present in the vacuum atmosphere like oxygen and water vapoureasily available, etc.
These and other conditions limit the choice of material for the emitter to metals with high melting points, practically to only two:Solar Power.
From an environmental perspective, solar power is the best thing going. A kilowatt PV system will keep more than , pounds of carbon dioxide, the chief greenhouse gas, out of the atmosphere over the next 25 years. Cooling curve of stearic acid – Teacher Notes 1 Driving Question: – Electrical heater or Bunsen heater, tripod and gauze for heating water bath.
Procedure of water; this will ensure that a good range of cooling may be observed during the liquid state. Constructing Heating/Cooling Curve Words | 10 Pages | Chemistry Lab Report | Constructing Heating/Cooling Curve | | Salman Ishaq E | 1/27/ | | BACKGROUND As energy flows from a liquid, its temperature drops.
The entropy, or random ordering of its particles, also decreases until a specific ordering of the particles . Electron-beam welding (EBW) is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined.
The workpieces melt and flow together as the kinetic energy of the electrons is transformed into heat upon impact. EBW is often performed under vacuum conditions to prevent dissipation of the electron beam.
View Notes - PreLab - Constructing Heating and Cooling Curves from CHEMISTRY Laboratory at High Technology High Sch. Ethan Sackett Lab Partner: _ Constructing a Heating. Remark: By constructing the composite curve we loose information on the vertical arrangement of heat transfer between streams Cooling Heating TH1,in TC,out TC,in TH1,out Q2 TH2,out TH2,in Q1 QH QC Smallest ∆T Notice that for this simple example the smallest ∆T takes place in the end of the.