Term Alo Zel Lik Ler

8/12/2019 Term Alo Zel Lik Ler

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Fonon (Phonon) Elastik dalga paketi olup malzemeye,dalga boyu veya frekans ile karakterize edilen enerjiyitransfer eder

zgl s (Specific heat) Malzemenin bir gramnnscakln bir derece arttrmak iin gereken enerjimiktardr.

Isl Kapasite ve zgl Is


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Figure 21.1 Heat capacity as a function of temperature formetals and ceramics.


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How much heat must be supplied to 250 g of tungsten to raiseits temperature from 25 oC to 650 oC?

Example 21.1 SOLUTION

Specific Heat of Tungsten

If no losses occur, 5000 cal (or 20,920 J) must be supplied tothe tungsten.


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Lineer termal uzama katsays ( Linear coefficient of thermalexpansion) Scakl bir derece arttrldnda malzemenin

birim boyutunda meydana gelen deiimi ifade eder. Isl gerilmeler ( Thermal stresses) Scaklklarda meydanagelen deiimin, malzeme hacminin farkl noktalarndameydana gelen genleme veya bzlme farklarndan dolaymeydana gelen gerilmelerdir

Isl Genleme


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The relationship between the linear coefficient of thermalexpansion and the melting temperature in metals at 25

C. Highermelting point metals tend to expand to a lesser degree.


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(a)The linear coefficient of thermal expansion of ironchanges abruptly at temperatures where an allotropictransformation occurs.

(b)The expansion of Invar is very low due to the magneticproperties of the material at low temperatures.


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Explain why, in Figure, the linear coefficients of thermal

expansion for silicon and tin do not fall on the curve. Howwould you expect germanium to fit into this figure?

rnek :Bonding and Thermal Expansion

Figure 21.3 Therelationship betweenthe linear coefficientof thermal expansionand the meltingtemperature inmetals at 25

C.Higher melting point

metals tend toexpand to a lesserdegree.


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Example SOLUTION

Silisyum ve Kalay ikisi de Kovalent baldr. Kovalent

balar ok gl olup metalik balardan daha zor uzarlar(genleirler) (a deeper trough in the energy-separationcurve), bu elementler dk katsayldr. Germanyumkovalent bal olup sl genlemesi tahmin edilenden dahada dktr. ekil 21.3.

Figure 21.3 Therelationship betweenthe linear coefficientof thermal expansionand the melting

temperature inmetals at 25

C.Higher melting pointmetals tend toexpand to a lesserdegree.


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Design the dimensions for a pattern that will be used toproduce a rectangular-shaped aluminum casting havingdimensions at 25 oC of 25 cm 25 cm 3 cm.


The linear coefficient of thermal expansion for aluminum is 2510 -6 1/ oC. The temperature change from the freezingtemperature to 25 oC is 660 - 25 = 635 oC. The change in anydimension is given by:

Example: Design of a Pattern for a CastingProcess

For the 25-cm dimensions, l f = 25 cm. We wish to find l 0 :


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A ceramic enamel is to be applied to a 1020 steel plate. The ceramichas a fracture strength of 4000 psi, a modulus of elasticity of 15 10 6 psi, and a coefficient of thermal expansion of 10 10 -6 1/ oC. Designthe maximum temperature change that can be allowed withoutcracking the ceramic.

Example:Design of a Protective Coating


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Example: SOLUTION

If only the enamel heated (and the steel remained at aconstant temperature), the maximum temperature changewould be:

However, the steel also expands. Its coefficient of thermalexpansion (Table 21-2) is 12 10 -6 1/ oC and its modulusof elasticity is 30 10 6 psi. The net coefficient ofexpansion is


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Termal iletkenlik (Thermal conductivity) mikroyapyabaml ve malzeme ierisinde s transfer hznn lsolan bir malzeme zelliidir.

Lorentz sabiti elektrik ve termal zellikleri ilikilendirenbir katsaydr.

ISIL LETM

2003 Brooks/Cole, a division of Thomson Learning, Inc. T homsonLearning is a trademark used herein under license.

Figure: When one endof a bar is heated, a

heat flux Q/A flowstoward the cold ends ata rate determined bythe temperaturegradient produced inthe bar.


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2003 Brooks/Cole, a division of Thomson Learning, Inc. T homson Learning is a trademark used herein under license.

Figure: The effect oftemperature on thethermal conductivityof selectedmaterials. Note thelog scale on the y-axis.


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Design a glass window 4 ft 4 ft square that separates aroom at 25 oC from the outside at 40 oC and allows no morethan 5 10 6 cal of heat to enter the room each day. Assumethermal conductivity of glass is 0.96 W . m -1 K-1 or 0.023cal/cm . s . K.


Example:Design of a Window Glass

where Q / A is the heat transferred per second through thewindow.


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Example: SOLUTION (Continued)


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Termal ok ( Thermal shock) Scaklktaki ani deiimler

sonucu oluan oluan sl gerilmelerin malzemelerdeoluturduu hasardr.

Isl ok

Figure: The effect of quenching temperature difference onthe modulus of rupture of SiAlON. The thermal shockresistance of the ceramic is good up to about 950

C.

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