Sputtering, i.e., the removal of surface atoms due to energetic particle bombardment,
is caused by collisions between the incoming particles and the atoms in
the selvage, i.e., the near surface layers of a solid. First discovered more than
125 years ago, it took about 50 years until the physical process involved in
sputtering was recognised and 100 years until a quantitative description began
to be developed. Sputtering is measured by the sputtering yield Y giving the
mean number of atoms removed per incident particle. For describing the
energy and angular distribution as well as the state of the emitted particles,
differential yields are defined. Most sputtering investigations have been performed
up to now on monoatomic targets like metals bombarded with noble gas
ions. Sputtering measurements on alloys and compounds as welt as sputtering by
ions which may react chemically with the atoms of the solid have only recently
begun. For crystalline targets, the sputtering yields are influenced by the lattice
structure especially for particle incidence and atom emergence in close packed
crystal directions.
Today sputtering is no longer just an unwanted effect which destroys
cathodes and contaminates a plasma. Sputtering is widely applied to surface
cleaning and etching, for thin film deposition, for surface and surface layer
analysis and for sputter ion sources.
(Sputtering by Particle Bombardment I,Physical Sputtering of Single-Element Solids,Edited by R. Behrisch
With Contributions by H. H. Andersen H.L. Bay R. Behrisch M. T. Robinson H.E. Roosendaal R Sigmund,
p.2)
Sputtering (old)
When a solid surface is bombarded with energetic particles such as accelerated ions, surface atoms of the solid are scattered backward due to collisions between the surface atoms and the energetic particles. This phenımenon is called back-sputtering, or simply sputtering.
(Kiyota Wasa, Thin Film Materials Technology: Sputterşng Of Compound Materials, P.39)
**My definition is comprehensive and better.Because old definition is only about kinds of sputtering.**
**My definition is comprehensive and better.Because old definition is only about kinds of sputtering.**
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PYROMETER (new better)
A pyrometer is a temperature measuring device with two interchangeable
temperature tips. The one for melt temperature is needlelike; the other is for
fl at surfaces. It can be an analog or digital type, but analog responds much
faster. The digital pyrometer can, however, be forced to respond faster by
preheating the temperature probe to the anticipated temperature to be measured.
This will save time by not allowing the melt to cool off while rising to
the temperature reading. Molders prefer analog style as it records temperature
changes faster, but it is not nearly as precise for recording the temperature.
The analog needle swings to a point on a scale, whereas the digital has a
numerical output.
(Total Quality Process Control for Injection Molding Yazar: M. Joseph Gordon, Jr., p.312)
Pyrometer 07-04-11 10:18 (old)
A pyrometer is an instrument for measuring high tenperatures. As mercury boils at about 660°, we can estimate the temperature of fused metlas, and the like, only by the expansion of solids. The only instrument of this sort which we need mention, as it is the only one susceptible ıf accuracy, is Daniell's Register Pyrometer. It consists of a hollow case of black lead, or plumbago, into which is dropped a bar of platinum, secured to its place by a strap of platinum and a wedge of porcelain. The whole is then heated, as, for instance, by placing it in a pot of molten silver, whose temperature we wish to ascertain. The metal bar expands much more than the case of black lead, and being confined from moving in any but an upward direction, drives forward the arm of a lever over a graduated arc, on which we read the degrees of Fahrenheit's scale: this instrument gives very acurate results; by it the melting point of cast iron has been found to be 2786°F, and of silver 1860°F.
(Benjamin Siliman, First Principles of Chemistry, p.78)
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Dry Pressing (Ceramics) (new)
Dry pressing refers to forming methods that require up to 15 wt% water in which plastic
deformation of the clay–water mixture is minimal. At the lower end of the water
contents, water is present as a partially adsorbed layer. At the higher end, the particle
surfaces will be completely covered by the adsorbed layer and some water will condense
in fine pores. The amount of water needed for a pressing operation varies depending
on the pressing characteristics desired, the state of hydration of the clay, how the clay
interacts with water, and the particle size of the clay . In dry pressing, water acts
mainly as a binder that promotes green strength in a compacted body.
Dry pressing is defined as the simultaneous shaping and compaction of a powder in
either a rigid die or a flexible container . Common variations on the technique include
uniaxial pressing and isostatic pressing . The water content must be sufficient to promote
binding of the clay particles without forming a continuous water film that would
allow for excessive plastic deformation under an applied load. Dry pressing is the most
common forming technique used in the ceramics industry and it is used to form a variety
of clay-based ceramics including floor and wall tile, bricks, and electrical insulators.
Shapes with a low aspect ratio (height to diameter) are commonly formed by pressing
operations . A schematic representation of a die used for uniaxial dry pressing, along
with the resulting forces on the powder compact, is shown in Fig. 8. Compaction pressures
range from 20 to 400 MPa (3–60 ksi) with an upper pressure limit of around
100 MPa for uniaxial pressing. Fabrication of parts with high aspect ratios or the use of
pressing pressures above 100 MPa can lead to the development of pressure gradients
and other defects that affect the quality of parts after pressing and after firing.
(Ceramic and Glass Materials: Structure, Properties and Processing Yazar: James F. Shackelford,Robert H. Doremus p.125)
Dry Pressing (old)
The moisture content of the starting clay in dry pressing is typically below 5%. Binders are usually added to the dry powder mix to provide sufficient strength in the pressed part for subsequent handling. Lubricants are also added to prevent die sticking during pressing and ejection. Because dry clay has no plasticity and is very abrasive, there are differences in die design and operating procedures, compared to semi-dry pressing. The dies must be made of hardened tool steel or cemented tungsten carbide to reduce wear. Since dry clay will not flow during pressing, the geometry of the part must be relatively simple, and the amount and distribution of starting powder in the die cavity must be right. No flash is formed in dry pressing, and no drying shrinkage occurs, so drying time is eliminated and good accuracy can be achieved in the dimensions of the final product. The process sequence in dry pressing is similar to semi-dry pressing. Typical products include bathroom tile, electrical insulators, and refractory brick.
(Groover M. P., Fundamentals of modern manufacturing: Materials, processes and systems 3rd edition, p. 368)
Mechanical Alloying (new)
Mechanical alloying, the subject matter of this book, is a powder processing technique
that was developed in the mid-1960s by John Benjamin to produce nickel-based
oxide dispersion strengthened (ODS) superalloys for gas turbine applications .
Subsequently, it was realized that mechanical alloying can also be used to synthesize a
variety of both equilibrium and nonequilibrium materials at room temperature and
starting from blended elemental powders. This technique has attracted the attention of
a large number of researchers during the past 15–20 years or so. The processing
involves repeated cold welding, fracturing, and rewelding of powder particles in a
high-energy ball mill resulting in the formation of alloy phases. This technique is also
capable of synthesizing a variety of equilibrium and nonequilibrium alloy phases
starting from prealloyed powders. In fact, all the nonequilibrium effects achieved by
RSP of metallic melts have also been observed in mechanically alloyed powders.
Consequently, interest in this technique has been constantly growing .Mechanical
alloying is presently one of the most popular nonequilibrium processing techniques.
(Cury Suryanarayana, Mechanical Alloying and Milling 2004,p.7-8)
Mechanical Alloying (old)
Mechanical alloying is a high energy dry ball milling process used to make composite metallic powders with a controlled fine microstructure. Powders of the desired composition are blended and then placed in a high energy ball mill. The intensive milling process repeatedly fractures and then rewelds the powder particles. During each collision with the grinding balls, the particles are plastically deformed to the extent that the surface oxides are broken, exposing clean metal surfaces.
On subsequent impacts, the clean surfaces are welded together. This cold welding process increases the size of the particles, while at the same time additional impacts are fracturing particles and reducing their size. As the process continues, the microstructure of the particles is continually being refined. Milling is continued until every powder particle contains the same composition as the starting mix.
(Campbell F.C., Manufacturing Technology for Aerospace Structural Materials, pg.232, Kayra Ermutlu)
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Feedback control (new,better)
Feedback control is about regulating the characteristics of a system.
The measured output, which is the characteristic to be regulated to a desired value; the control input, which is what influences themeasured output; and a disturbance, which affects the way in which the input affects the output.For example ;
A cruise control system achieves the desired speed by adjusting the
accelerator pedal based on a velocity measurement from the speedometer. Here,the accelerator pedal adjustments are the control input that provides a means to
regulate speed, the measured output. The desired speed is maintained even when
the car goes up or down hills or encounters head or tail winds, all of which are
examples of disturbances that affect the relationship between the control input
and the measured output. A thermostat achieves the desired temperature (output)
by adjusting the furnace cycle and fan (input). The desired temperature is maintained
even when the outside temperature increases or decreases (disturbance).
The sensorimotor system achieves the desired hand position (output) to pick up
an object by adjusting the muscle tensions (inputs) based on the current position
sensed by the eyes and touch.
(Joseph L. Hellerstein, Yixin Diao, Sujay Parekh, Dawn M. Tilbury Feedback Control of Computing Systems 2004, p3-4)
Feedback Control 02.04.2011 21:26 (old)
A feedback control system is a control system that tends to maintain a prescribed relationship of one system variable to anohter by comparing functions of these variables and usig the difference as a means of control.With an accurate sensor, the measured output is a good approximation of the actual output of the system.
A feedback control system often uses a function of a prescribed relationship between the output ans reference input to control the process.
(Richard C.dorf and robert H.Bishop,Modern Control Systems, 11th edition page 3)
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