CONCEPT CHECK QUESTIONS AND ANSWERS
Chapter 2
Atomic Structure and Interatomic Bonding
Concept Check 2.1
Question Why are are the atomic weights of the the elements generally generally not integers? Cite two reasons. Ans!er T"e atomic !eig"ts !eig"ts o# t"e e$ements e$ements ordinari$% are not integers &ecause &ecause '() t"e atomic masses o# t"e atoms norma$$% are not integers 'e*ce+t #or (,C)- and ',) t"e atomic !eig"t is ta.en as t"e !eig"ted a/erage o# t"e atomic masses o# an atom0s natura$$% occurring isoto+es1
Concept Check 2.2
Question Give electron configurations configurations for the Fe 3+and S2- ions. Ans!er T"e 2e 34 ion is an iron atom t"at "as $ost t"ree e$ectrons1 Since t"e e$ectron con#iguration o# t"e 2e atom is ( s,,s,, 53s,3 53d56s, 'Ta&$e ,1,)- t"e con#iguration #or 2e 34 is (s,,s,, 53s,3 53d71 T"e S,8 ion a su$#ur atom t"at "as gained t!o e$ectrons1 e$ectrons1 Since t"e e$ectron con#iguration con#iguration o# t"e S atom is (s ( s,,s,, 53s,3 6 'Ta&$e ,1,)- t"e con#iguration #or S ,8 is (s (s,,s,, 53s,3 51
Concept Check 2.3
Question Question !"lain why covalently #onded materials are generally less dense than ionically or metallically #onded ones. Ans!er Co/a$ent$% &onded materia$s materia$s are $ess dense t"an meta$$ic meta$$ic or ionica$$% &onded &onded ones &ecause co/a$ent &onds are directiona$ in nature !"ereas meta$$ic and ionic are not9 !"en &onds are directiona$- t"e atoms cannot +ac. toget"er in as dense a manner- %ie$ding %ie$ding a $o!er mass densit%1
Chapter 3
2undamenta$s o# Cr%sta$$ogra+"%
Concept Check 3.1
Question What is the difference difference #etween crystal structure and crystal system? Ans! Ans!er er
A cr%st cr%sta$ a$ stru struct ctur uree is desc descri ri&e &ed d &% &ot" &ot" t"e t"e geom geomet etr% r% o#o#- and and atom atomic ic
arrangements !it"in- t"e unit ce$$- !"ereas a cr%sta$ s%stem is descri&ed on$% in terms o# t"e unit ce$$ geometr%1 geometr%1 2or e*am+$e- #ace8centered cu&ic cu&ic and &od%8centered cu&ic are cr%sta$ structures structures t"at &e$ong to t"e cu&ic cr%sta$ s%stem1
Concept Check 3.2
Question Question
$o noncrystalline noncrystalline materials dislay the henomenon of allotroy allotroy %or
olymorhism&? olymorhism&? Why or why not? Ans!er Noncr%sta$$ine Noncr%sta$$ine materia$s do not dis+$a% dis+$a% t"e +"enomenon o# a$$otro+%9 since a noncr%sta$$ine materia$ does not "a/e a de#ined cr%sta$ structure- it cannot "a/e more t"an one cr%sta$ structure- !"ic" is t"e de#inition o# a$$otro+%1 a$$otro+%1
Chapter 4
T"e Structure o# Cr%sta$$ine So$ids
Concept Check 4.1
Questions %a& What is the coordination coordination num#er for the simle-cu#ic crystal structure? structure? %# ) Calculate the atomic ac'ing factor for simle cu#ic.
Ans!ers 'a) 2or t"e sim+$e cu&ic cr%sta$ structure t"e coordination num&er 't"e num&er o# nearest neig"&or atoms) is si*1 T"is is demonstrated demonstra ted in t"e #igure &e$o!1 &e$o!1
Consider t"e atom $a&e$ed A- !"ic" is $ocated at t"e corner o# t"e reduced8s+"ere sim+$e cu&ic unit ce$$1 It "as t"ree nearest neig"&ors neig"&ors $ocated in t"is unit ce$$:$a&e$ed ce$$:$a&e$ed (- 3- and 71 In additiont"e t"ree s"aded atoms- $a&e$ed ,- 6- and 5- are a$so nearest neig"&ors t"at &e$ong to ad;acent unit ce$$s1 '&) T"e atomic atomic +ac.ing #actor is t"e tota$ s+"ere s+"ere /o$ume8ce$$ /o$ume8ce$$ /o$ume /o$ume ratio 'E
N f
2
+
Nc
8
0
8
2
8
= 0+ +
> ( atom?+er unit ce$$ T"ere#ore- t"e tota$ s+"ere /o$ume in terms o# t"e atomic radius ( is e
4 3 4 3 π R ÷ = π R 3 3
= (1 atom/unit cell) V S
Because t"e unit ce$$ is cu&ic- its /o$ume is e
3
And &ecause a > , ( V = (2 R) C
3
= 8 R3
2ina$$%- using E
APF =
V S V C
=
3
π R3
8 R3
> @17, Concept Check 4.2
Question )a#le *.* gives the ionic radii for + and ,2- as .3/ and .* nm0 resectively. %a& What would #e the coordination num#er for each ,2- ion? %#& 1riefly descri#e the resulting crystal structure for 2,. %c& !"lain why this is called the antifluorite structure. Ans!er 'a) 2irst- $et us #ind t"e coordination num&er o# eac" O ,8 ion #or K ,O1 Ta.ing t"e cation8anion radii ratio
r + K
r 2O
=
0.138 nm 0.140 nm
= 0.986
2rom Ta&$e 613- t"e coordination num&er #or o*%gen is eig"t1 '&) According to Ta&$e 617- #or a coordination num&er o# eig"t #or &ot" cations and anions- t"e cr%sta$ structure s"ou$d &e cesium c"$oride1 Ho!e/er- t"ere are t!ice as man% K 4 as
O,8 ions1 T"ere#ore- t"e centers o# t"e K4 ions are +ositioned at t"e corners o# cu&ic unit ce$$s!"i$e "a$# o# t"e cu&e centers are occu+ied &% O ,8 ions1 'c) T"is structure is ca$$ed t"e anti#$uorite cr%sta$ structure &ecause anions and cations are interc"anged !it" one anot"er #rom t"e #$uorite structure '2igure 61)1
Concept Check 4.3
Question %a& Comare the crystalline state in metals and olymers. %#& Comare the noncrystalline state as it alies to olymers and ceramic glasses. Ans!ers 'a) 2or cr%sta$$ine meta$s- t"e indi/idua$ atoms are +ositioned in a +eriodic or ordered arrangement o/er re$ati/e$% $arge atomic distances1 T"e $ong8range order in +o$%mer cr%sta$s resu$ts #rom t"e +ac.ing o# ad;acent +o$%mer c"ains1 '&) 2or noncr%sta$$ine ceramic g$asses- t"e atomic randomness e*ists outside t"e
SiO
4 4
−
unit1 T"e disorder in +o$%mers resu$ts #rom c"ain misa$ignment1
Concept Check 4.4
Question For cu#ic crystals0 as values of the lanar indices h0 '0 and l increase0 does the distance #etween adacent and arallel lanes %i.e.0 the interlanar sacing& increase or decrease? Why? Ans!er T"e inter+$anar s+acing &et!een ad;acent and +ara$$e$ +$anes decreases as t"e /a$ues o# h- ' - and l increase1 As /a$ues o# t"e +$anar indices increase- t"e magnitude o# t"e denominator in E
Chapter 5
Structures o# Po$%mers
Concept Check 5.1
Question $ifferentiate #etween olymorhism %see Chater *& and isomerism. Ans!er olymorhism is !"en t!o or more cr%sta$ structures are +ossi&$e #or a materia$ o# gi/en com+osition1 4somerism is !"en t!o or more +o$%mer mo$ecu$es or re+eat units "a/e t"e same com+osition- &ut di##erent atomic arrangements1
Concept Check 5.2
Question ,n the #asis of the structures resented in the revious section0 s'etch the reeat unit structure for oly%vinyl fluoride&. Ans!er Inasmuc" as +o$%'/in%$ chloride) "as t"e re+eat unit structure s"o!n in 2igure 71,'&)- re+$acing t"e side8&onded c"$orine atom !it" a #$uorine atom !i$$ %ie$d a +o$%'/in%$ fluoride) re+eat unit- as s"o!n &e$o!1
Concept Check 5.3
Question What is the difference #etween con#iguration and con#ormation in relation to olymer chains? Ans!er
Re$ati/e to +o$%mer c"ains- t"e di##erence &et!een configuration and
conformation is t"at con#ormation is used in re#erence to t"e out$ine or s"a+e o# t"e c"ain mo$ecu$e- !"ereas- con#iguration re#ers to t"e arrangement o# atom +ositions a$ong t"e c"ain t"at are not a$tera&$e e*ce+t &% t"e &rea.ing and re#orming o# +rimar% &onds1
Concept Check 5.4
Question
Some olymers %such as the olyesters& may #e either thermolastic or
thermosetting. Suggest one reason for this. Ans!er T"ermosetting +o$%esters !i$$ &e cross$in.ed- !"i$e t"ermo+$astic ones !i$$ "a/e $inear structures !it"out an% a++recia&$e cross$in.ing1
Chapter 6
Im+er#ections o# So$ids
Concept Check 6.1
Question Can Schott'y defects e"ist in 2,? 4f so0 #riefly #riefly descri#e this this tye of defect. defect. 4f they cannot e"ist0 then e"lain why. why. Ans!er T"is
Concept Check 6.2
Question 4s it ossi#le for three three or more element to form solid solid a solution? !"lain your answer. Ans!er es- it is +ossi&$e +ossi&$e #or t"ree or or more e$ements to #orm a so$id so$ution1 so$ution1 2or t"ree or more e$ements- t"e same criteria a++$% as #or t!o e$ements- as sti+u$ated &% t"e Hume8Rot"er% ru$es1
Concept Check 6.3
Question Question !"lain why comlete solid solu#ility may occur for su#stitutional su#stitutional solid solutions #ut not for interstitial solid solutions. Ans!er Ans!er One re
interstitia$ sites1 Conse
Question What oint defects are ossi#le for 5g, as an imurity in 6l 2, 3? 7ow many 5g,4 ions must #e added to form each of these defects? Ans!er 2or e/er% g,4 ion t"at su&stitutes #or A$ 34 in A$ ,O3- a sing$e +ositi/e c"arge is remo/ed1 T"us- in order to maintain c"arge c"arge neutra$it%neutra$it%- eit"er a +ositi/e c"arge must &e added or a negati/e c"arge must &e r emo/ed1 Positi/e c"arges are added &% #orming A$ 34 interstitia$s- and one A$ 34 interstitia$ !ou$d &e #ormed #or e/er% t"ree g ,4 ions added1 Negati/e c"arges ma% &e remo/ed &% #orming O ,8 /acancies- and one o*%gen /acanc% !ou$d &e #ormed #or e/er% t!o g ,4 ions added1
Concept Check 6.5
Question Question
)he surfac surfacee ener energy of a singl singlee crysta crystall deend deendss on crysta crystallo llogra grah hic ic
orientation. $oes this surface energy energy increase or decrease decrease with an increase increase in lanar density? Why? Ans!er T"e sur#ace energ% o# a sing$e cr%sta$ de+ends on t"e +$anar densit% densit% 'i1e1- degree o# atomic +ac.ing) o# t"e e*+osed sur#ace sur#ace +$ane &ecause o# t"e num&er num&er o# unsatis#ied &onds1 As t"e +$anar densit% increases- t"e num&er o# nearest atoms in t"e +$ane increases- !"ic" resu$ts in an increase in t"e num&er o# satis#ied atomic &onds in t"e +$ane- and a decrease in t"e num&er o# unsatis#ied &onds1 &onds1 Since t"e num&er o# unsatis#ied unsatis#ied &onds diminis"esdiminis"es- so a$so does t"e t"e sur#ace energ% decrease1 'T"at is- sur#ace energ% decreases !it" an increase in +$anar +$anar densit%1) densit%1)
Concept Check 6.6
Question $oes the grain-si8e num#er %G of !9uation :.2& increase increase or decrease decrease with decreasing decreasing grain si8e? Why? Ans!er Ta.ing Ta.ing $ogarit"ms o# E
lo! n lo! 2
T"us- G increases !it" increasing n1 But as n 't"e a/erage num&er o# grains +er s
Chapter 7
Di##usion
Concept Check 7.1
Question (an' the magnitudes of the diffusion coefficients from greatest to least for the following systems; < in Fe at =° C Cr in Fe at = ° C < in Fe at >° C Cr in Fe at > ° C
N in 2e at @@°C9 $N'@@) N in 2e at @@°C9 $N'@@) Cr in 2e at @@ °C9 $Cr'@@) Cr in 2e at @@ °C9 $Cr'@@)
Nitrogen is an interstitia$ im+urit% in 2e 'on t"e &asis o# its atomic radius)- !"ereas Cr is a su&stitutiona$ im+urit%1
Since interstitia$ di##usion occurs more ra+id$% t"an su&stitutiona$
im+urit% di##usion- $N F $Cr1 A$so- inasmuc" as t"e magnitude o# t"e di##usion coe##icient increases !it" increasing tem+erature- $'@@) F $'@@)1
Concept Check 7.2
Question
Consider the self-diffusion of two hyothetical metals 6 and 1.
,n a
schematic grah of ln $ versus A)0 lot %and la#el& lines for #oth metals given that $ @'A) B $@'B) and also that d'A) B d'B)1 Ans!er T"e sc"ematic $n $ /ersus (?) +$ot !it" $ines #or meta$s A and B is s"o!n &e$o!1
As e*+$ained in t"e +re/ious section- t"e interce+t !it" t"e /ertica$ a*is is e
Chapter 8
ec"anica$ Pro+erties o# eta$s
Concept Check 8.1
Question
Cite the rimary differences #etween elastic0 anelastic0 and lastic
deformation #ehaviors. Ans!er
E$astic de#ormation is time8inde+endent and non+ermanent- ane$astic
de#ormation is time8de+endent and non+ermanent- !"i$e +$astic de#ormation is +ermanent1
Concept Check 8.2
Questions ,f those metals listed in )a#le /.30 %a& Which will e"erience the greatest ercent reduction in area? Why? %#& Which is the strongest? Why? %c& Which is the stiffest? Why?
Ta&$e J13 is gi/en &e$o!
ateria$
ie$d Strengt" 'Pa)
Tensi$e Strengt" 'Pa)
Strain at 2racture
2racture Strengt" 'Pa)
E$astic odu$us 'Pa)
A
3(@
36@
@1,3
,57
,(@
B
(@@
(,@
@16@
(@7
(7@
C
6(7
77@
@1(7
7@@
3(@
D
@@
J7@
@1(6
,@
,(@
57@
37@
E
2ractures &e#ore %ie$ding
Ans!ers 'a) ateria$ B !i$$ e*+erience t"e greatest +ercent area reduction since it "as t"e "ig"est strain at #racture- and- t"ere#ore is most ducti$e1 '&) ateria$ D is t"e strongest &ecause it "as t"e "ig"est %ie$d and tensi$e strengt"s1 'c) ateria$ E is t"e sti##est &ecause it "as t"e "ig"est e$astic modu$us1
Concept Check 8.3
Question 5a'e a schematic lot showing the tensile engineering stressDstrain #ehavior for a tyical metal alloy to the oint of fracture.
T"e initia$ $inear 'e$astic) +ortions o# &ot" cur/es !i$$ &e t"e same1 Ot"er!ise- t"ere are t"ree di##erences &et!een t"e t!o cur/es !"ic" are as #o$$o!s '() Be%ond t"e e$astic region- t"e tension cur/e $ies &e$o! t"e com+ression one1 T"e reason #or t"is is t"at- during com+ression- t"e cross8sectiona$ area o# t"e s+ecimen is increasing :t"at is- #or t!o s+ecimens t"at "a/e t"e same initia$ cross8sectiona$ area ' 6@)- at some s+eci#ic strain /a$ue t"e instantaneous cross8sectiona$ area in com+ression !i$$ &e greater t"an in tension1 Conse
σ
F A0
t"e a++$ied #orce is greater #or com+ression- so a$so !i$$ t"e stress &e greater 'since 6@ is t"e same #or &ot" cases)1
',) T"e com+ression cur/e !i$$ not dis+$a% a ma*imum inasmuc" as t"e s+ecimen tested in com+ression !i$$ not e*+erience nec.ing:t"e cross8sectiona$ area o/er !"ic" de#ormation is occurring is continua$$% increasing #or com+ression1 '3) T"e strain at !"ic" #ai$ure occurs !i$$ &e greater #or com+ression1 Again- t"is &e"a/ior is e*+$ained &% t"e $ac. o# nec.ing #or t"e s+ecimen tested in com+ression1
Concept Check 8.4
Question ,f those metals listed in )a#le /.30 which is the hardest? Why? Ans!er ateria$ D is t"e "ardest &ecause it "as t"e "ig"est tensi$e strengt"1
Chapter 9
Dis$ocations and Strengt"ening ec"anisms o# eta$s
Concept Check 9.1
Question
Which of the following is the sli system for the simle cu#ic crystal
structure? Why? L(@@M〈((@〉 L((@M〈((@〉 L(@@M〈@(@〉 L((@M〈(((〉 '
Concept Check 9.2
Question !"lain the difference #etween resolved shear stress and critical resolved shear stress1 Ans!er (esolved shear stress is t"e s"ear com+onent o# an a++$ied tensi$e 'or com+ressi/e) stress reso$/ed a$ong a s$i+ +$ane t"at is ot"er t"an +er+endicu$ar or +ara$$e$ to t"e stress a*is1 T"e critical resolved shear stress is t"e /a$ue o# reso$/ed s"ear stress at !"ic" %ie$ding &egins9 it is a +ro+ert% o# t"e materia$1
Concept Check 9.3
Question When ma'ing hardness measurements0 what will #e the effect of ma'ing an indentation very close to a ree"isting indentation? Why? Ans!er T"e "ardness measured #rom an indentation t"at is +ositioned /er% c$ose to a +ree*isting indentation !i$$ &e too $arge1 T"e materia$ in t"is /icinit% !as co$d8!or.ed !"en t"e #irst indentation !as made1
Concept Check 9.4
Question Would you e"ect a crystalline ceramic material to strain harden at room temerature? Why or why not? Ans!er No- it !ou$d not &e e*+ected1 In order #or a materia$ to strain "arden it must &e +$astica$$% de#ormed9 &ecause ceramic materia$s are &ritt$e at room tem+erature- t"e% !i$$ #racture &e#ore an% +$astic de#ormation ta.es +$ace1
Concept Check 9.5
Question 1riefly e"lain why some metals %i.e.0 lead0 tin& do not strain harden when deformed at room temerature. Ans!er eta$s suc" as $ead and tin do not strain "arden at room tem+erature &ecause t"eir recr%sta$$i=ation tem+eratures $ie &e$o! room tem+erature 'Ta&$e 1,)1
Concept Check 9.6
Question
Would you e"ect it to #e ossi#le for ceramic materials to e"erience
recrystalli8ation? Why or why not? Ans!er
No- recr%sta$$i=ation is not e*+ected in ceramic materia$s1
In order to
e*+erience recr%sta$$i=ation- a materia$ must #irst &e +$astica$$% de#ormed- and ceramic materia$s are too &ritt$e to +$astica$$% de#orm1
Chapter 10
2ai$ure
Concept Check 10.1
Question Cite two situations in which the ossi#ility of failure is art of the design of a comonent or roduct. Ans!er Se/era$ situations in !"ic" t"e +ossi&i$it% o# #ai$ure is +art o# t"e design o# a com+onent or +roduct are as #o$$o!s '() t"e +u$$ ta& on t"e to+ o# a$uminum &e/erage cans9 ',) a$uminum uti$it%?$ig"t +o$es t"at reside a$ong #ree!a%s:a minimum o# damage occurs to a /e"ic$e !"en it co$$ides !it" t"e +o$e9 and '3) in some mac"iner% com+onents- a s"ear +in is used to connect a gear or +u$$e% to a s"a#t:t"e +in is designed s"ear o## &e#ore damage is done to eit"er t"e s"a#t or gear in an o/er$oad situation1
Concept Check 10.2
Question 5a'e a schematic s'etch of a stress-versus-time lot for the situation when the stress ratio ( has a value of +. Ans!er 2or a stress ratio ' () o# 4(- t"en- #rom E
>
ma*
min
T"is is to sa% t"at t"e stress remains constant 'or does not #$uctuate) !it" time- or t"e stress8 /ersus8time +$ot !ou$d a++ear as
Concept Check 10.3
Question Esing !9uations .: and .=0 demonstrate that increasing the value of the stress ratio ( roduces a decrease in stress amlitude a1 Ans!er 2rom E
σ
min
Rσ
ma"
2urt"ermore- E
σ
σ − σ ma" min a 2
Su&stitution o# min #rom t"e #ormer e*+ression into t"e $atter gi/es
σ
σ ma" a
Rσ
−
2
ma"
σ ma" (1 − R) 2
T"ere#ore- as t"e magnitude o# ( increases 'or &ecomes more +ositi/e) t"e magnitude o# a decreases1
Concept Check 10.4
Question Surfaces for some steel secimens that have failed #y fatigue have a #right crystalline or grainy aearance. aymen may e"lain the failure #y saying that the metal crystalli8ed while in service. ,ffer a criticism for this e"lanation. Ans!er To cr%sta$$i=e means to &ecome cr%sta$$ine1 T"us- t"e statement T"e meta$ #ractured &ecause it cr%sta$$i=ed is erroneous inasmuc" as t"e meta$ !as cr%sta$$ine +rior to &eing stressed '/irtua$$% a$$ meta$s are cr%sta$$ine)1
Concept Check 10.5
Question Suerimose on the same strain-versus-time lot schematic cree curves for #oth constant tensile stress and constant tensile load0 and e"lain the differences in #ehavior. Ans!er Sc"ematic cree+ cur/es at &ot" constant stress and constant $oad are s"o!n &e$o!1
Wit" increasing time- t"e constant $oad cur/e &ecomes +rogressi/e$% "ig"er t"an t"e constant stress cur/e1 Since t"ese tests are tensi$e ones- t"e cross8sectiona$ area diminis"es as de#ormation +rogresses1 T"us- in order to maintain a constant stress- t"e a++$ied $oad must corres+onding$% &e diminis"ed since stress > $oad?area1
Chapter 11
P"ase Diagrams
Concept Check 11.1
Question
What is the difference #etween the states of hase e9uili#rium and
metasta#ility? Ans!er 2or t"e condition o# +"ase e
Concept Check 11.2
Question )he hase diagram for the co#alt-nic'el system is an isomorhous one. ,n the #asis of melting temeratures for these two metals0 descri#e andAor draw a schematic s'etch of the hase diagram for the Co-
Concept Check 11.3
Question 6 coer-nic'el alloy of comosition = wt
Concept Check 11.4
Question 4s it ossi#le to have a coer-nic'el alloy that0 at e9uili#rium0 consists of an
hase of comosition 3= wt
Concept Check 11.5
Question 6t =HC %2>HF&0 what is the ma"imum solu#ility %a& of Cu in 6g? %#& ,f 6g in Cu? Ans!er 'a) 2rom t"e co++er8si$/er +"ase diagram- 2igure 1- t"e ma*imum so$u&i$it% o# Cu in Ag at @@HC corres+onds to t"e +osition o# t"e −' 4 ) +"ase &oundar% at t"is tem+erature- or to a&out 5 !t Cu1 '&) 2rom t"is same #igure- t"e ma*imum so$u&i$it% o# Ag in Cu corres+onds to t"e +osition o# t"e −' 4 ) +"ase &oundar% at t"is tem+erature- or a&out 7 !t Ag1
Concept Check 11.6
Question )he following is a ortion of the 7 2,-
%a& Esing this diagram0 #riefly e"lain how sreading salt on ice that is at a temerature #elow HC %32HF& can cause the ice to melt. %#& 6t what temerature is salt no longer useful in causing ice to melt?
So$ution 'a) S+reading sa$t on ice !i$$ $o!er t"e me$ting tem+erature- since t"e $i
Concept Check 11.7
Question )he following figure is the hafnium-vanadium hase diagram0 for which only single-hase regions are la#eled. Secify temerature-comosition oints at which all eutectics0 eutectoids0 eritectics0 and congruent hase transformations occur. 6lso0 for each0 write the reaction uon cooling1
Ans!er T"ere are t!o eutectics on t"is +"ase diagram1 One e*ists at (J !t 8J, !t H# and (677HC1 T"e reaction u+on coo$ing is L
→
β #$ + #$%2
T"e ot"er eutectic e*ists at 3 !t 85( !t H# and (7,@ HC1 T"is reaction u+on coo$ing is L
→
#$%2 + %(&oli' &olution)
T"ere is one eutectoid at 5 !t 86 !t H# and ((@ HC1 Its reaction u+on coo$ing is
β #$
→
α #$ + #$%2
T"ere is one congruent me$ting +oint at 35 !t 856 !t H# and (77@ HC1 T"e reaction u+on coo$ing is L
No +eritectics are +resent1
→
#$%2
Concept Check 11.8
Question For a ternary system0 three comonents are resentI temerature is also a varia#le. What is the ma"imum num#er of hases that may #e resent for a ternary system0 assuming that ressure is held constant? Ans!er 2or a ternar% s%stem 'C > 3) at constant +ressure ' < > ()- i&&s +"ase ru$eE C 4 < > 3 4 ( > 6 Or > 6 F
T"us- !"en F > @- !i$$ "a/e its ma*imum /a$ue o# 6- !"ic" means t"at t"e ma*imum num&er o# +"ases +resent #or t"is situation is 61
Concept Check 11.9
Question 1riefly e"lain why a roeutectoid hase %ferrite or cementite& forms along austenite grain #oundaries. 7int; Consult Section :./. Ans!er Associated !it" grain &oundaries is an inter#acia$ energ% 'i1e1- grain &oundar% energ%:Section 51J)1 A $o!er net inter#acia$ energ% increase resu$ts !"en a +roeutectoid +"ase #orms a$ong e*isting austenite grain &oundaries t"an !"en t"e +roeutectoid +"ase #orms !it"in t"e interior o# t"e grains1
Chapter 12
P"ase Trans#ormations
Concept Check 12.1
Question Which is more sta#le0 the earlitic or the sheroiditic microstructure? Why? Ans!er S+"eroiditic microstructures are more sta&$e t"an +ear$itic ones1 Since +ear$ite trans#orms to s+"eroidite- t"e $atter is more sta&$e1
Concept Check 12.2
Question Cite two maor differences #etween martensitic and earlitic transformations. Ans!er T!o ma;or di##erences are () atomic di##usion is necessar% #or t"e +ear$itic trans#ormation- !"ereas t"e martensitic trans#ormation is di##usion$ess9 and ,) re$ati/e to trans#ormation rate- t"e martensitic trans#ormation is /irtua$$% instantaneous- !"i$e t"e +ear$itic trans#ormation is time8de+endent1
Concept Check 12.3
Question 5a'e a coy of the isothermal transformation diagram for an iron-car#on alloy of eutectoid comosition %Figure 2.22& and then s'etch and la#el on this diagram a timetemerature ath that will roduce fine earlite. Ans!er Be$o! is s"o!n an isot"erma$ trans#ormation diagram #or a eutectoid iron8 car&on a$$o% on !"ic" is inc$uded a time8tem+erature +at" t"at !i$$ +roduce (@@ #ine +ear$ite1
Concept Check 12.4
Question 1riefly descri#e the simlest continuous cooling heat treatment rocedure that would #e used to convert a *3* steel from %martensite + #ainite& into %ferrite + earlite&. So$ution In order to con/ert #rom 'martensite 4 &ainite) into '#errite 4 +ear$ite) it is necessar% to "eat a&o/e a&out ,@C- a$$o! com+$ete austeniti=ation- t"en coo$ to room tem+erature at a rate e
Concept Check 12.5
Question (an' the following iron-car#on alloys and associated microstructures from the highest to the lowest tensile strength; .2 wtC with sheroidite .2 wtC with coarse earlite .: wtC with fine earlite .: wtC with coarse earlite. Justify this ran'ing. Ans!er T"is ran.ing ca$$ed #or is as #o$$o!s '() @15 !tC !it" #ine +ear$ite ',) @15 !tC !it" coarse +ear$ite '3) @1,7 !tC !it" coarse +ear$ite '6) @1,7 !tC !it" s+"eroidite
T"e @1,7 !t C- coarse +ear$ite is stronger t"an t"e @1,7 !t C- s+"eroidite &ecause coarse +ear$ite is stronger t"an s+"eroidite9 t"e com+osition o# t"e a$$o%s is t"e same1 T"e @15 !t C- coarse +ear$ite is stronger t"an t"e @1,7 !t C- coarse +ear$ite- &ecause increasing t"e car&on content increases t"e strengt" '!"i$e maintained t"e same coarse +ear$ite microstructure)1 2ina$$%- t"e @15 !t C- #ine +ear$ite is stronger t"an t"e @15 !t C- coarse +ear$ite inasmuc" as t"e strengt" o# #ine +ear$ite is greater t"an coarse +ear$ite &ecause o# t"e man% more #errite8 cementite +"ase &oundaries in #ine +ear$ite1
Concept Check 12.6
Question For a eutectoid steel0 descri#e an isothermal heat treatment that would #e re9uired to roduce a secimen having a hardness of >3 7(1. Ans!er 2rom 2igure (,13@'a)- in order #or a @15 !t C a$$o% to "a/e a Roc.!e$$ "ardness o# 3 HRB- t"e microstructure must &e coarse +ear$ite1 T"us- uti$i=ing t"e isot"erma$ trans#ormation diagram #or t"is a$$o%- 2igure (,1,,- a#ter austeniti=ing at a&out 5@ C- ra+id$% coo$ to a tem+erature at !"ic" coarse +ear$ite #orms 'i1e1- to a&out 57 C)- and a$$o! t"e s+ecimen to isot"erma$$% and com+$ete$% trans#orm to coarse +ear$ite1 At t"is tem+erature an isot"erma$ "eat treatment #or at $east ,@@ s is re
Concept Check 12.7
Question 6 steel alloy is 9uenched from a temerature within the austenite hase region into water at room temerature so as to form martensiteI the alloy is su#se9uently temered at an elevated temerature which is held constant. %a& 5a'e a schematic lot showing how room-temerature ductility varies with the logarithm of temering time at the elevated temerature. %1e sure to la#el your a"es.& %#& Suerimose and la#el on this same lot the room-temerature #ehavior resulting from temering at a higher temering temerature and #riefly e"lain the difference in #ehavior #etween these two temeratures. Ans!er 'a) S"o!n &e$o! is t"e +$ot t"at !as re
'&) T"e $ine #or t"e "ig"er tem+erature '$a&e$ed ) ) !i$$ $ie a&o/e t"e one at t"e $o!er 7 tem+erature '$a&e$ed ) ) &ecause t"e 2e3C +artic$es in tem+ered martensite !i$$ gro! #aster at t"e "ig"er tem+erature9 t"us- at some gi/en tem+ering time t"e% !i$$ &e $arger at t"e "ig"er tem+erature1 T"e a$$o% tem+ered at t"e "ig"er tem+erature !i$$ &e more ducti$e &ecause t"ere !i$$ &e #e!er 82e3C +"ase &oundaries 'due to t"e $arger 2e 3C +artic$es) t"at ma% im+ede dis$ocation motion1
Chapter 13
Pro+erties and A++$ications o# eta$s
Concept Check 13.1
Question
1riefly e"lain why ferritic and austenitic stainless steels are not heat
treata#le. 7int; you may want to consult the first ortion of Section 3.2. Ans!er
2erritic and austenitic stain$ess stee$s are not "eat treata&$e since "eat
treata&$e is ta.en to mean t"at martensite ma% &e made to #orm !it" re$ati/e ease u+on
Concept Check 13.2
Question 4t is ossi#le to roduce cast irons that consist of a martensite matri" in which grahite is em#edded in either fla'e0 nodule0 or rosette form. 1riefly descri#e the treatment necessary to roduce each of these three microstructures. Ans!er
2or gra+"ite #$a.es- gra% cast iron is #ormed- !"ic" is t"en "eated to a
tem+erature at !"ic" t"e #errite trans#orms to austenite9 t"e austenite is t"en ra+id$%
Concept Check 13.3
Question What is the main difference #etween #rass and #ron8e? Ans!er Bot" &rasses and &ron=es are co++er8&ased a$$o%s1 2or &rasses- t"e +rinci+a$ a$$o%ing e$ement is =inc- !"ereas t"e &ron=es are a$$o%ed !it" ot"er e$ements suc" as tina$uminum- si$icon- or nic.e$1
Concept Check 13.4
Question !"lain why0 under some circumstances0 it is not advisa#le to weld a structure that is fa#ricated with a 33 aluminum alloy. 7int; @ou may want to consult Section >.2. Ans!er Strengt"ening o# a 3@@3 a$uminum a$$o% is accom+$is"ed &% co$d !or.ing1 We$ding a structure o# a co$d8!or.ed 3@@3 a$$o% !i$$ cause it to e*+erience recr%sta$$i=ation- and a resu$tant $oss o# strengt"1
Concept Check 13.5
Question ,n the #asis of melting temerature0 o"idation resistance0 yield strength0 and degree of #rittleness0 discuss whether it would #e advisa#le to hot wor' or to cold wor' %a& aluminum alloys0 and %#& magnesium alloys. 7int; @ou may want to consult Sections >. and >.2. Ans!er ost a$uminum a$$o%s ma% &e co$d8!or.ed since t"e% are ducti$e and "a/e re$ati/e$% $o! %ie$d strengt"s1 agnesium a$$o%s are norma$$% "ot8!or.ed inasmuc" as t"e% are
Chapter 14
Pro+erties and A++$ications o# Ceramics
Concept Check 14.1
Question %a& For the Si,2-6l2, 3 system0 what is the ma"imum temerature that is ossi#le without the formation of a li9uid hase? %#& 6t what comosition or over what range of comositions will this ma"imum temerature #e achieved? Ans!er 'a) According to 2igure (616 t"is ma*imum tem+erature is (J@ (@C- '&) !"ic" is +ossi&$e #or com+ositions &et!een a&out !t A$ ,O3 and /irtua$$% (@@ !t A$,O31
Concept Check 14.2
Question 1riefly e"lain why glass-ceramics are generally not transarent. 7int; @ou may want to consult Chater 22. Ans!er $ass8ceramics ma% not &e trans+arent &ecause t"e% are +o$%cr%sta$$ine1 ig"t !i$$ &e scattered at grain &oundaries in +o$%cr%sta$$ine materia$s i# t"e inde* o# re#raction is anisotro+ic- and !"en t"ose grains ad;acent to t"e &oundar% "a/e di##erent cr%sta$$ogra+"ic orientations1 T"is +"enomenon is discussed in Section ,,1(@1 A$so- as noted in Section ,,1(@g$ass8ceramics ma% &e trans+arent in t"e si=e o# t"e cr%sta$s are sma$$er t"an t"e !a/e$engt" o# /isi&$e $ig"t1
Concept Check 14.3
Question Eon consideration of the Si, 2-6l2, 3 hase diagram %Figure *.*& for the following air of comositions0 which would you udge to #e the more desira#le refractory? Justify your choice. 2 wt 6l2, 3-/ wt Si,2 2 wt 6l2, 3-= wt Si,2
Ans!er T"e ,7 !t A$,O387 !t SiO, !i$$ &e more desira&$e &ecause t"e $i
Concept Check 14.4
Question !"lain why it is imortant to grind cement into a fine owder. Ans!er It is im+ortant to grind cement into a #ine +o!der in order to increase t"e sur#ace area o# t"e +artic$es o# cement1 T"e "%dration reactions &et!een !ater and t"e cement occur at t"e sur#ace o# t"e cement +artic$es1 T"ere#ore- increasing t"e a/ai$a&$e sur#ace area a$$o!s #or more e*tensi/e &onding1
Chapter 15
C"aracteristics and A++$ications o# Po$%mers
Concept Check 15.1
Question When citing the ductility as ercent elongation for semicrystalline olymers0 it is not necessary to secify the secimen gauge length0 as is the case with metals. Why is this so? Ans!er T"e reason t"at it is not necessar% to s+eci#% s+ecimen gauge $engt" !"en citing +ercent e$ongation #or semicr%sta$$ine +o$%mers is &ecause- #or semicr%sta$$ine +o$%mers t"at e*+erience nec.ing- t"e nec. norma$$% +ro+agates a$ong t"e entire gauge $engt" +rior to #racture9 t"us- t"ere is no $oca$i=ed nec.ing as !it" meta$s and t"e magnitude o# t"e +ercent e$ongation is inde+endent o# gauge $engt"1
Concept Check 15.2
Question 6n amorhous olystyrene that is deformed at 2HC will e"hi#it which of the #ehaviors shown in Figure .? Ans!er Amor+"ous +o$%st%rene at (,@ HC &e"a/es as a ru&&er% materia$ '2igure (71Jcur/e C )9 t"ere#ore- t"e strain8time &e"a/ior !ou$d &e as 2igure (717c1
Concept Check 15.3
Question For the following air of olymers0 do the following; %& state whether it is ossi#le to decide if one olymer has a higher tensile modulus than the otherI %2& if this is ossi#le0 note which has the higher tensile modulus and then cite the reason%s& for your choiceI and %3& if it is not ossi#le to decide0 then state why not. Syndiotactic olystyrene having a num#er-average molecular weight of *0 gAmol 4sotactic olystyrene having a num#er-average molecular weight of :0 gAmol. Ans!er
No- it is not ossi#le1
Bot" s%ndiotactic and isotactic +o$%st%rene "a/e a
tendenc% to cr%sta$$i=e- and- t"ere#ore- !e assume t"at t"e% "a/e a++ro*imate$% t"e same cr%sta$$init%1 2urt"ermore- since tensi$e modu$us is /irtua$$% inde+endent o# mo$ecu$ar !eig"t- !e !ou$d e*+ect &ot" materia$s to "a/e a++ro*imate$% t"e same modu$us1
Concept Check 15.4
Question For the following air of olymers0 do the following; %& state whether it is ossi#le to decide if one olymer has a higher tensile strength than the otherI %2& if this is ossi#le0 note which has the higher tensile strength and then cite the reason%s& for your choiceI and %3& if it is not ossi#le to decide0 then state why not. Syndiotactic olystyrene having a num#er-average molecular weight of :0 gAmol 4sotactic olystyrene having a num#er-average molecular weight of 0 gAmol. Ans!er es- it is ossi#le1 T"e s%ndiotactic +o$%st%rene "as t"e "ig"er tensi$e strengt"1 Bot" s%ndiotactic and isotactic +o$%mers tend to cr%sta$$i=e- and- t"ere#ore- !e assume t"at &ot" materia$s "a/e a++ro*imate$% t"e same cr%sta$$init%1 Ho!e/er- tensi$e modu$us increases !it" increasing mo$ecu$ar !eig"t- and t"e s%ndiotactic PS "as t"e "ig"er mo$ecu$ar !eig"t '5@@-@@@ g?mo$ /ersus 7@@-@@@ g?mo$ #or t"e isotactic materia$)1
Concept Check 15.5
Question For the following air of olymers0 lot and la#el schematic stress-strain curves on the same grah. oly%styrene-#utadiene& random coolymer having a num#er-average molecular weight of 0 gAmol and of the availa#le sites crosslin'ed and tested at 2HC. oly%styrene-#utadiene& random coolymer having a num#er-average molecular weight of 20 gAmol and of the availa#le sites crosslin'ed and tested at D/HC. 7int; oly%styrene-#utadiene& coolymers may e"hi#it elastomeric #ehavior. Ans!er S"o!n &e$o! are t"e stress8strain cur/es #or t"e t!o +o$%'st%rene8&utadiene) random co+o$%mers1
T"e co+o$%mer tested at ,@C !i$$ dis+$a% e$astomeric &e"a/ior 'cur/e C o# 2igure (71() inasmuc" as it is a random co+o$%mer t"at is $ig"t$% cross$in.ed9 #urt"ermore- t"e tem+erature o# testing is a&o/e its g$ass transition tem+erature1 On t"e ot"er "and- since −J7HC is &e$o! t"e g$ass transition tem+erature o# t"e ot"er +o$%'st%rene8&utadiene) co+o$%mer- t"e stress8strain &e"a/ior under t"ese conditions is as cur/e 6 o# 2igure (71(1
Concept Check 15.6
Question 4n terms of molecular structure0 e"lain why henol-formaldehyde %1a'elite& will not #e an elastomer. %)he molecular structure for henol-formaldehyde is resented in )a#le .3.& Ans!er T"e mo$ecu$es in e$astomers must &e t!o8dimensiona$ c"ains t"at are $ig"t$% cross$in.ed and ca+a&$e o# &eing t!isted and .in.ed in t"e unstressed state1
P"eno$8
#orma$de"%de "as a rigid t"ree8dimensiona$ structure consisting o# tri#unctiona$ re+eat units!"ic" does not meet t"ese criteria #or c"ain con#ormation and #$e*i&i$it%1
Concept Check 15.7
Question For each of the following two olymers0 lot and la#el a schematic secific volume-versus-temerature curve %include #oth curves on the same grah&; Sherulitic olyroylene0 of 2 crystallinity0 and having a weight-average molecular weight of =0 gAmol Sherulitic olystyrene0 of 2 crystallinity0 and having a weight-average molecular weight of 0 gAmol Ans!er
S"o!n &e$o! are t"e s+eci#ic /o$ume8/ersus8tem+erature cur/es #or t"e
+o$%+ro+%$ene and +o$%st%rene materia$s1
Since &ot" +o$%mers are ,7 cr%sta$$ine- t"e% !i$$ e*"i&it &e"a/ior simi$ar to cur/e 1 in 2igure (71(J1 Ho!e/er- +o$%st%rene !i$$ "a/e "ig"er me$ting and g$ass transition tem+eratures due to t"e &u$.ier side grou+ in its re+eat unit structure- and since it "as a "ig"er !eig"t8a/erage mo$ecu$ar !eig"t1
Concept Check 15.8
Question For the following two olymers0 %& state whether is ossi#le to determine whether one olymer has a higher melting temerature than the otherI %2& if it is ossi#le0 note which has the higher melting temerature and then cite reason%s& for your choiceI and %3& if it is not ossi#le to decide0 then state why not. 4sotactic olystyrene that has a density of .2 gAcm 3 and a weight-average molecular weight of 0 gAmol Syndiotactic olystyrene that has a density of . gAcm 3 and a weight-average molecular weight of 20 gAmol. Ans!er es- it is ossi#le to determine !"ic" o# t"e t!o +o$%st%renes "as t"e "ig"er ) m1 T"e isotactic +o$%st%rene !i$$ "a/e t"e "ig"er me$ting tem+erature &ecause it "as a "ig"er densit% 'i1e1- $ess &ranc"ing) and a$so t"e greater !eig"t8a/erage mo$ecu$ar !eig"t1
Concept Check 15.9
Question $uring the winter months0 the temerature in some arts of 6las'a may go as low as DHC %D:HF&. ,f the elastomers natural isorene0 styrene-#utadiene0 acrylonitrile#utadiene0 chlororene0 and olysilo"ane0 which would #e suita#le for automo#ile tires under these conditions? Why? Ans!er
2rom Ta&$e (716- on$% natura$ +o$%iso+rene- +o$%'st%rene8&utadiene)- and
+o$%si$o*ane "a/e use#u$ tem+erature ranges t"at e*tend to &e$o! 77 HC1 At tem+eratures &e$o! t"e $o!er use#u$ tem+erature range $imit- t"e ot"er e$astomers $isted in t"is ta&$e &ecome &ritt$eand- t"ere#ore- are not suita&$e #or automo&i$e tires1
Concept Check 15.10
Question Silicone olymers may #e reared to e"ist as li9uids at room temerature. Cite differences in molecular structure #etween them and the silicone elastomers. 7int; @ou may want to consult Sections . and .>. Ans!er
T"e $i
cross$in.ing- !"ereas t"e mo$ecu$ar !eig"ts #or t"e e$astomers !i$$ &e muc" "ig"er9 t"e e$astomers !i$$ a$so "a/e some cross$in.ing1
Chapter 16
Com+osite ateria$s Concept Check 16.1
Question Cite the general difference in strengthening mechanism #etween large-article and disersion-strengthened article-reinforced comosites. Ans!er T"e ma;or di##erence in strengt"ening mec"anism &et!een $arge8+artic$e and dis+ersion8strengt"ened +artic$e8rein#orced com+osites is t"at #or $arge8+artic$e t"e +artic$e8 matri* interactions are not treated on t"e mo$ecu$ar $e/e$- !"ereas- #or dis+ersion8strengt"ening t"ese interactions are treated on t"e mo$ecu$ar $e/e$1
Concept Check 16.2
Question )he following ta#le lists four hyothetical aligned fi#er-reinforced comosites %la#eled 6 through $&0 along with their characteristics. ,n the #asis of these data0 ran' the four comosites from highest to lowest strength in the longitudinal direction0 and then ustify your ran'ing.
Com+osite
2i&er T%+e
o$1 2raction 2i&ers
2i&er Strengt" 'Pa)
A/e1 2i&er engt" 'mm)
Critica$ engt" 'mm)
A
g$ass
@1,@
317 × (@
J
@1@
B
g$ass
@137
317 × (@
3
(,
@17
C
car&on
@16@
717 × (@
3
J
@16@
D
car&on
@13@
717 × (@
J
@17@
3
3
Ans!er T"e ran.ing #rom "ig"est to $o!est strengt" in t"e $ongitudina$ direction is as #o$$o!s
C- D- B- and A1 Com+osite C is t"e strongest inasmuc" as t"e car&on #i&ers are
continuous and are stronger t"an g$ass- and it "as t"e "ig"est #i&er /o$ume #raction1 Com+osite D is o# $o!er strengt" t"an C &ecause it "as a $o!er K f 9 ot"er!ise t"e car&on #i&ers are a$so continuous1 ateria$ B is ne*t &ecause t"e g$ass #i&ers are !ea.er t"an car&on9 t"ese #i&ers are
a$so continuous1 Com+osite A is t"e !ea.est since it is com+osed o# t"e !ea.er g$ass #i&ers- t"e #i&ers are discontinuous- and K f is t"e $o!est o# a$$ #our materia$s1 Concept Check 16.3
Question Cite one desira#le characteristic and one less desira#le characteristic for each of %& discontinuous- and oriented-fi#er-reinforced comosites and %2& discontinuous- and randomly oriented-fi#er-reinforced comosites. Ans!er
2or discontinuous8 and oriented8#i&er8rein#orced com+osites one desira&$e
c"aracteristic is t"at t"e com+osite is re$ati/e$% strong and sti## in one direction9 a $ess desira&$e c"aracteristic is t"at t"e mec"anica$ +ro+erties are anisotro+ic1 2or discontinuous8 and random$% oriented8#i&er8rein#orced com+osites- one desira&$e c"aracteristic is t"at t"e +ro+erties are isotro+ic9 a $ess desira&$e c"aracteristic is t"ere is no sing$e "ig"8strengt" direction1
Chapter 17
2a&rication and Processing o# Engineering ateria$s
Concept Check 17.1
Question %a& Cite two advantages of owder metallurgy over casting. %#& Cite two disadvantages. Ans!er 'a) Ad/antages o# +o!der meta$$urg% o/er casting are as #o$$o!s () It is used #or a$$o%s "a/ing "ig" me$ting tem+eratures1 ,) Better dimensiona$ to$erances resu$t1 3) Porosit% ma% &e introduced- t"e degree o# !"ic" ma% &e contro$$ed '!"ic" is desira&$e in some a++$ications suc" as se$#8$u&ricating &earings)1 '&) T"e disad/antages o# +o!der meta$$urg% o/er casting are as #o$$o!s () Production o# t"e +o!der is e*+ensi/e1 ,) Heat treatment a#ter com+action is necessar%1
Concept Check 17.2
Question What are the rincial differences #etween welding0 #ra8ing0 and soldering? @ou may need to consult other references. Ans!er 2or !e$ding- t"ere is me$ting o# t"e +ieces to &e ;oined in t"e /icinit% o# t"e &ond9 a #i$$er materia$ ma% or ma% not &e used1 2or &ra=ing- a #i$$er materia$ is used !"ic" "as a me$ting tem+erature in e*cess o# a&out 6,7C 'J@@2)9 t"e #i$$er materia$ is me$ted- !"ereas t"e +ieces to &e ;oined are not me$ted1 2or so$dering- a #i$$er materia$ is used !"ic" "as a me$ting tem+erature $ess t"an a&out 6,7C 'J@@2)9 t"e #i$$er materia$ is me$ted- !"ereas t"e +ieces to &e ;oined are not1
Concept Check 17.3
Question
Concept Check 17.4
Question 7ow does the thic'ness of a glassware affect the magnitude of the thermal stresses that may #e introduced? Why? Ans!er T"e t"inner t"e t"ic.ness o# a g$ass !are t"e $o!er t"e t"erma$ stresses t"at are introduced !"en it is eit"er "eated or coo$ed1 T"e reason #or t"is is t"at t"e di##erence in tem+erature across t"e cross8section o# t"e !are- and- t"ere#ore- t"e di##erence in t"e degree o# e*+ansion or contraction !i$$ decrease !it" a decrease in t"ic.ness1
Concept Check 17.5
Question )hic' ceramic wares are more li'ely to crac' uon drying than thin wares. Why is this so? Ans!er T"ic. ceramic !ares are more $i.e$% to crac. u+on dr%ing t"an t"in !ares &ecause o# t"e di##erentia$ in s"rin.age #rom t"e sur#ace to t"e interior o# a cross8section !i$$ &e greater #or a t"ic. !are1 T"e reason #or t"is is t"at t"e !ater &eing e$iminated during dr%ing "as a $onger distance to tra/e$ #rom t"e interior to t"e sur#ace #or t"e t"ic.er !are1
Concept Check 17.6
Question !"lain why a clay0 once it has #een fired at an elevated temerature0 loses its hydrolasticity. Ans!er T"e +"enomenon o# "%dro+$asticit% resu$ts !"en !ater mo$ecu$es #orm a t"in #i$m around t"e sma$$ c$a% +artic$es1
During #iring- t"ese indi/idua$ +artic$es &ecome #used
toget"er &% t"e /iscous $i
Concept Check 17.7
Question
State whether the molecular weight of a olymer that is synthesi8ed #y
addition olymeri8ation is relatively high0 medium0 or relatively low for the following situations; %a& (aid initiation0 slow roagation0 and raid termination %#& Slow initiation0 raid roagation0 and slow termination %c& (aid initiation0 raid roagation0 and slow termination %d& Slow initiation0 slow roagation0 and raid termination. Ans!er 'a) 2or ra+id initiation- s$o! +ro+agation- and ra+id termination t"e mo$ecu$ar !eig"t !i$$ &e re$ati/e$% $o!1 '&) 2or s$o! initiation- ra+id +ro+agation- and s$o! termination t"e mo$ecu$ar !eig"t !i$$ &e re$ati/e$% "ig"1 'c) 2or ra+id initiation- ra+id +ro+agation- and s$o! termination a medium mo$ecu$ar !eig"t !i$$ &e ac"ie/ed1 'd) 2or s$o! initiation- s$o! +ro+agation- and ra+id termination t"e mo$ecu$ar !eig"t !i$$ &e $o! or medium1
Concept Check 17.8
Question
Ans!er T"e #o$$o!ing re+resents t"e reaction &et!een "e*amet"%$ene diamine and adi+ic acid to +roduce n%$on 5-5 !it" !ater as a &%+roduct
Concept Check 17.9
Question %a& Why must the vaor ressure of a lastici8er #e relatively low? %#& 7ow will the crystallinity of a olymer #e affected #y the addition of a lastici8er? Why? %c& 7ow does the addition of a lastici8er influence the tensile strength of a olymer? Why? Ans!ers 'a)
I# t"e /a+or +ressure o# a +$astici=er is not re$ati/e$% $o!- t"e +$astici=er ma%
/a+ori=e- !"ic" !i$$ resu$t in an em&ritt$ement o# t"e +o$%mer1 '&)
T"e cr%sta$$init% o# a +o$%mer to !"ic" "as &een added a +$astici=er !i$$ &e
diminis"ed- inasmuc" as t"e +$astici=er mo$ecu$es #it in &et!een t"e +o$%mer mo$ecu$es- !"ic" !i$$ cause more misa$ignment o# t"e $atter1 'c) T"e tensi$e strengt" o# a +o$%mer !i$$ &e diminis"ed !"en a +$astici=er is added1 As t"e +$astici=er mo$ecu$es #orce t"e +o$%mer c"ain mo$ecu$es a+art- t"e magnitudes o# t"e secondar% interc"ain &onds are $essened- !"ic" !ea.ens t"e materia$ since strengt" is a #unction o# t"e magnitude o# t"ese &onds1
Concept Check 17.10
Question For a ru##er comonent that is to #e vulcani8ed in its final form0 should vulcani8ation #e carried out #efore or after the forming oeration? Why? 7int; @ou may want to consult Section .>. Ans!er u$cani=ation o# a ru&&er com+onent s"ou$d &e carried out +rior to t"e #orming o+eration since- once it "as &een /u$cani=ed- +$astic de#ormation 'and t"us #orming) is not +ossi&$e since c"ain cross$in.s "a/e &een introduced1
Chapter 17
Corrosion and Degradation o# ateria$s
Concept Check 18.1
Question Would you e"ect iron to corrode in water of high urity? Why or why not? Ans!er Iron !ou$d not corrode in !ater o# "ig" +urit% &ecause a$$ o# t"e reduction reactions- E
Concept Check 18.2
Question 5odify !9uation /.> for the case in which metals 5 and 5 2 are alloys. Ans!er 2or t"is case- it is necessar% to ta.e into account t"e com+ositions o# meta$s ( and ,1 I# G( and G, re+resent concentrations o# meta$s ( and , in t"eir res+ecti/e a$$o%s- t"e e
∆V ( V 2 − 0
V 1
0
)
−
RT nF
ln
1n+ * 2 * 2n+ * 1 *
Concept Check 18.3
Question
1riefly e"lain why concentration olari8ation is not normally rate
controlling for o"idation reactions. Ans!er
Concentration +o$ari=ation is not norma$$% rate contro$$ing #or o*idation
reactions &ecause an un$imited su++$% o# meta$ atoms at t"e corroding e$ectrode inter#ace !i$$ a$!a%s &e +resent1
Concept Check 18.4
Question %a& From the galvanic series %)a#le /.2&0 cite three metals or alloys that may #e used to galvanically rotect nic'el in the active state. %#& Sometimes galvanic corrosion is revented #y ma'ing an electrical contact #etween #oth metals in the coule and a third metal that is anodic to these other two. Esing the galvanic series0 name one metal that could #e used to rotect a coer-aluminum galvanic coule. So$ution 'a) T"e #o$$o!ing meta$s and a$$o%s ma% &e used to ga$/anica$$% +rotect nic.e$ in t"e acti/e state 'i1e1- $ie &e$o! Ni in t"e ga$/anic series) tin- $ead- 3(5 and 3@6 stain$ess stee$scast iron- iron- stee$- a$uminum a$$o%s- cadmium- commercia$$% +ure a$uminum- =inc- magnesiumand magnesium a$$o%s1 '&) inc- magnesium- and magnesium a$$o%s ma% &e used to +rotect a co++er8a$uminum ga$/anic cou+$e1
Concept Check 18.5
Question Cite two e"amles of the #eneficial use of galvanic corrosion. 7int; ,ne e"amle is cited later in this chater. Ans!er T!o &ene#icia$ uses o# ga$/anic corrosion are corrosion +re/ention &% means o# cat"odic +rotection- and t"e dr%8ce$$ &atter%1
Concept Check 18.6
Question 4s !9uation /.23 e9ually valid for uniform corrosion and itting? Why or why not? Ans!er E
Concept Check 18.7
Question )in cans are made of a steel0 the inside of which is coated with a thin layer of tin. )he tin rotects the steel from corrosion #y food roducts in the same manner as 8inc rotects steel from atmosheric corrosion. 1riefly e"lain how this cathodic rotection of tin cans is ossi#le since tin is electrochemically less active than steel in the galvanic series %)a#le /.2&1 Ans!er Tin o##ers ga$/anic +rotection to t"e stee$ in tin cans e/en t"oug" it 'tin) is e$ectroc"emica$$% $ess acti/e t"an stee$ #rom t"e ga$/anic series1 T"e reason #or t"is is t"at t"e ga$/anic series re+resents t"e reacti/ities o# meta$s and a$$o%s in sea!ater9 "o!e/er- #or t"e #ood so$utions t"at are contained !it"in t"e cans- tin is t"e more acti/e meta$1
Concept Check 18.8
Question From a molecular ersective0 e"lain why increasing crosslin'ing and crystallinity of a olymeric material will enhance its resistance to swelling and dissolution. Would you e"ect crosslin'ing or crystallinity to have the greater influence? Justify your choice. 7int; @ou may want to consult Sections *.3 and .=. Ans!er During s!e$$ing and disso$ution o# +o$%meric materia$s- t"e so$ute mo$ecu$es di##use to and occu+% +ositions among t"e +o$%mer macromo$ecu$es- and t"ere&% #orce t"e $atter a+art1 Increasing &ot" t"e degrees o# cross$in.ing and cr%sta$$init% !i$$ en"ance a +o$%mer0s resistance to t"ese t%+es o# degradation since t"ere !i$$ &e a greater degree o# intermo$ecu$ar &onding &et!een ad;acent c"ains9 t"is restricts t"e num&er o# so$ute mo$ecu$es t"at can #it into t"ese $ocations1 Cross$in.ing !i$$ &e more e##ecti/e1 2or $inear +o$%mers t"at are "ig"$% cr%sta$$ine- t"e intermo$ecu$ar &onds are secondar% ones '/an der Waa$s and?or "%drogen)- and re$ati/e$% !ea. in com+arison to t"e strong co/a$ent &onds associated !it" t"e cross$in.s1
Concept Check 18.9
Question ist three differences #etween the corrosion of metals and each of the following; %a& the corrosion of ceramics %#& the degradation of olymers Ans!er 'a) T"ree di##erences &et!een t"e corrosion o# meta$s and t"e corrosion o# ceramics are () Ceramic materia$s are more corrosion resistant t"an meta$s in most en/ironments1 ,) Corrosion o# ceramic materia$s is norma$$% ;ust a c"emica$ disso$ution +rocess!"ereas #or meta$s it is usua$$% e$ectroc"emica$1 3) Ceramics are more corrosion resistant at e$e/ated tem+eratures1 '&) T"ree di##erences &et!een t"e corrosion o# meta$s and t"e degradation o# +o$%mers are ()
Degradation o# +o$%mers is ordinari$% +"%sioc"emica$- !"ereas #or meta$scorrosion is e$ectroc"emica$1
,)
Degradation mec"anisms #or +o$%mers are more com+$e* t"an t"e corrosion mec"anisms #or meta$s1
3) ore t%+es o# degradation are +ossi&$e #or +o$%mers:e1g1- disso$ution- s!e$$ingand &ond ru+ture '&% means o# r adiation- "eat- and c"emica$ reactions)1
Chapter 19
E$ectrica$ Pro+erties
Concept Check 19.1
Question 4f a metallic material is cooled through its melting temerature at an e"tremely raid rate0 it forms a noncrystalline solid %i.e.0 a metallic glass&. Will the electrical conductivity of the noncrystalline metal #e greater or less than its crystalline counterart? Why? Ans!er
T"e e$ectrica$ conducti/it% #or a meta$$ic g$ass !i$$ &e $ess t"an #or its
cr%sta$$ine counter+art1 T"e g$ass !i$$ "a/e /irtua$$% no +eriodic atomic structure- and- as a resu$t- e$ectrons t"at are in/o$/ed in t"e conduction +rocess !i$$ e*+erience #re
Concept Check 19.2
Question )he room-temerature electrical resistivities of ure lead and ure tin are 2.:
× -= and . × -= OPm0 resectively. %a&
5a'e a schematic grah of the room-temerature electrical resistivity versus
comosition for all comositions #etween ure lead and ure tin. %#& ,n this same grah0 schematically lot electrical resistivity versus comosition at HC. %c& !"lain the shaes of these two curves0 as well as any differences #etween them. 7int; @ou may want to consult the lead-tin hase diagram0 Figure .= Ans!ers 'a) and '&) Be$o! is s"o!n t"e e$ectrica$ resisti/it% /ersus com+osition #or $ead8tin a$$o%s at &ot" room tem+erature and (7@ HC1
'c) U+on consu$tation o# t"e P&8Sn +"ase diagram '2igure ((1) !e note u+on e*tra+o$ation o# t"e t!o so$/us $ines to at room tem+erature 'e1g1- ,@ C)- t"at t"e sing$e +"ase
+"ase so$id so$ution e*ists &et!een +ure $ead and a com+osition o# a&out , !t o# Sn8J !t P&1
In addition- t"e com+osition range o/er !"ic" t"e +"ase is sta&$e is &et!een
a++ro*imate$% !t Sn8( !t P& and +ure tin1 Wit"in &ot" o# t"ese com+osition regions t"e resisti/it% increases in accordance !it" E
In addition- #rom 2igure ((1- at (7@HC t"e so$u&i$it% o# Sn in P& increases to
a++ro*imate$% (@ !t Sn:i1e1- t"e +"ase #ie$d is !ider and t"e increase o# resisti/it% due to t"e so$id so$ution e##ect e*tends o/er a greater com+osition range- !"ic" is a$so noted in t"e a&o/e #igure1
T"e resisti/it%8tem+erature &e"a/ior is simi$ar on t"e tin8ric" side- !"ere- at
(7@HC- t"e +"ase #ie$d e*tends to a++ro*imate$% , !t P& 'J !t Sn)1 And- as !it" t"e room8tem+erature case- #or com+ositions !it"in t"e 4 t!o8+"ase region- t"e +$ot is a++ro*imate$% $inear- e*tending &et!een resisti/it% /a$ues #ound at t"e ma*imum so$u&i$ities o# t"e t!o +"ases1
Concept Check 19.3
Question Which of QnS and CdSe will have the larger #and ga energy ! g? Cite reason%s& for your choice. Ans!er inc su$#ide !i$$ "a/e a $arger &and ga+ energ% t"an cadmium se$enide1 Bot" are II8I com+ounds- and n and S are &ot" "ig"er /ertica$$% in t"e +eriodic ta&$e '2igure ,1) t"an Cd and Se1 In mo/ing #rom &ottom to to+ u+ t"e +eriodic ta&$e- !g increases1
Concept Check 19.4
Question
6t relatively high temeratures0 #oth donor- and accetor-doed
semiconducting materials will e"hi#it intrinsic #ehavior %Section >.2&.
,n the #asis of
discussions of Section >. and the revious section0 ma'e a schematic lot of Fermi energy versus temerature for an n-tye semiconductor u to a temerature at which it #ecomes intrinsic. 6lso note on this lot energy ositions corresonding to the to of the valence #and and the #ottom of the conduction #and. Ans!er Be$o! is s"o!n t"e sc"ematic +$ot o# 2ermi tem+erature /ersus tem+erature1
As noted in t"e +re/ious section- at $o! tem+eratures- t"e materia$ is e*trinsic and t"e 2ermi energ% is $ocated near t"e to+ o# t"e &and ga+- in t"e /icinit% o# t"e donor $e/e$ #or an n8 t%+e semiconductor1 Wit" increasing tem+erature- t"e materia$ e/entua$$% &ecomes intrinsic- and t"e 2ermi energ% resides near t"e center o# t"e &and ga+ 'Section (17)1
Concept Check 19.5
Question Will Qn act as a donor or as an accetor when added to the comound semiconductor Ga6s? Why? %6ssume that Qn is a su#stitutional imurity&. Ans!er inc !i$$ act as an acce+tor in aAs1 Since n is #rom grou+ IIB o# t"e +eriodic ta&$e- it !i$$ su&stitute #or a9 #urt"ermore- a n atom "as one $ess /a$ence e$ectron t"an a a atom1
Concept Check 19.6
Question ,n the #asis of Figure >.=0 as doant level is increased0 would you e"ect the temerature at which a semiconductor #ecomes intrinsic to increase0 to remain essentially the same0 or to decrease? Why? Ans!er According to 2igure (1(- as do+ant $e/e$ is increased- t"e +osition o# t"e "ori=onta$ E*trinsic Region $ine mo/es u+!ard1 T"us- t"e +oint at !"ic" t"e intrinsic region &ecomes dominant mo/es "ori=onta$$% to "ig"er tem+eratures1
Concept Check 19.7
Question ,n the #asis of the electron-concentration-versus-temerature curve for ntye silicon shown in Figure >.= and the deendence of logarithm of electron mo#ility on temerature %Figure >.>a&0 ma'e a schematic lot of logarithm electrical conductivity versus temerature for silicon that has #een doed with 2 m-3 of a donor imurity.
(ecall that !9uation >.: e"resses the deendence of
conductivity on electron concentration and electron mo#ility 1 Ans!er T"e sc"ematic +$ot o# $ogarit"m e$ectrica$ conducti/it% /ersus tem+erature is s"o!n &e$o!1
According to E
σ µ n µ e
2rom 2igure (1(a- t"ere is no cur/e #or n > (@,( m839 "o!e/er- i# one !ere +$otted it !ou$d reside &et!een and "a/e t"e same genera$ s"a+e as t"e V (@ ,@ m83 and (@,, m83 cur/es:t"at is- t"e $ogarit"m o# t"e e$ectron mo&i$it% decreases !it" increasing tem+erature1 et us no! consider indi/idua$$% t"e t"ree regions on t"e $og e$ectron concentration /ersus tem+erature +$ot o# 2igure (1(1 2or t"e #ree=e8out region o# t"e cur/e 'i1e1- at $o! tem+eratures)- t"e $ogarit"m o# t"e e$ectron concentration increases signi#icant$% !it" increasing tem+erature1 T"e +roduct o# t"is +ortion o# t"e cur/e and t"e region o# t"e cur/e in 2igure (J1( a o/er t"e com+ara&$e tem+erature range resu$ts in a net increase in $og conducti/it% !it" increasing tem+erature '+er t"e a&o/e +$ot):t"e diminis"ment o# $og e !it" tem+erature is more gradua$ t"an t"e increase o# $og n1 O/er t"e e*trinsic region o# 2igure (1(- $og n remains constant !it" increasing tem+erature- !"ereas $og e continues to decrease '+er 2igure (1(a)1 T"e net resu$t o# ta.ing t"e +roduct o# t"ese t!o cur/es is t"at conducti/it% !i$$ decrease !it" increasing tem+erature1 It #o$$o!s t"at t"e $og /ersus tem+erature cur/e !i$$ necessari$% "a/e to +ass t"roug" a ma*imum at some tem+erature ;ust &e$o! t"e onset o# t"e e*trinsic region1 2ina$$%- #or t"e intrinsic region o# 2igure (1(- $og n increases dramatica$$% !it" tem+erature- and !"i$e $og e continues to decrease 'a$&eit not as dramatica$$%- 2igure (1( a) t"e net resu$t o# ta.ing t"e +roduct o# t"ese t!o cur/es is an increase o# e$ectrica$ conducti/it% !it" increasing tem+erature- +er t"e a&o/e +$ot1 2urt"ermore- t"e $og 8tem+erature cur/e a$so +asses t"roug" a minimum at some tem+erature near t"e &eginning o# t"e intrinsic region o# 2igure (1(1
Concept Check 19.8
Question Would you e"ect increasing temerature to influence the oeration of -n unction rectifiers and transistors? !"lain. Ans!er I# t"e tem+erature o# a -n ;unction recti#ier or a ;unction transistor is raised "ig" enoug"- t"e semiconducting materia$s !i$$ &ecome intrinsic and t"e de/ice !i$$ &ecome ino+erati/e1 2urt"ermore- di##usion o# do+ant s+ecies #rom a to an n region and /ice /ersa ma% occur- !"ic" !ou$d a$so $ead to +er#ormance +ro&$ems1
Concept Check 19.9
Question For solid lead titanate %#)i, 3 & what 'ind%s& of olari8ation is %are& ossi#le? Why? .3&. Ans!er !lectronic- ionic- and orientation +o$ari=ations !ou$d &e o&ser/ed in $ead titanate1 E$ectronic +o$ari=ation occurs in a$$ die$ectric materia$s1 T"e $ead- titanium- and o*%gen !ou$d undou&ted$% &e $arge$% ionic in c"aracter1 2urt"ermore- orientation +o$ari=ation is a$so +ossi&$e inasmuc" as +ermanent di+o$e moments ma% &e induced in t"e same manner as #or BaTiO3 as s"o!n in 2igure (1371
Chapter 20
T"erma$ Pro+erties
Concept Check 20.1
Question %a& !"lain why a #rass lid ring on a glass canning ar will loosen when heated. %#& Suose the ring is made of tungsten instead of #rass. What will #e the effect of heating the lid and ar? Why? Ans!er 'a) A &rass $id on a g$ass canning ;ar !i$$ $oosen !"en "eated &ecause &rass "as t"e greater coe##icient o# t"erma$ e*+ansion G,@ × (@ 85 'C)8( /ersus a++ro*imate$% × (@ 85 'C)8( #or g$ass- Ta&$e ,@1(1 '&) I# t"e ring is made o# tungsten instead o# &rass- t"e ring !i$$ tig"ten u+on "eating inasmuc" as t"e g$ass !i$$ e*+and more t"an tungsten1 T"e /a$ues o# l #or g$ass and tungsten are × (@85 'C)8( and 617 × (@85 'C)8(- res+ecti/e$%1
Concept Check 20.2
Question )he thermal conductivity of a lain car#on steel is greater than for a stainless steel. Why is this so? 7int; you may want to consult Section 3.2. Ans!er T"e t"erma$ conducti/it% o# a +$ain car&on stee$ is greater t"an #or a stain$ess stee$ &ecause t"e stain$ess stee$ "as muc" "ig"er concentrations o# a$$o%ing e$ements1 Atoms o# t"ese a$$o%ing e$ements ser/e as scattering centers #or t"e #ree e$ectrons t"at are in/o$/ed in t"e t"erma$ trans+ort +rocess1
Concept Check 20.3
Question )he thermal conductivity of a single-crystal ceramic secimen is slightly greater than a olycrystalline one of the same material. Why is this so? Ans!er T"e t"erma$ conducti/it% o# a sing$e cr%sta$ is greater t"an a +o$%cr%sta$$ine s+ecimen o# t"e same materia$ &ecause &ot" +"onons and #ree e$ectrons are scattered at grain &oundaries- t"us decreasing t"e e##icienc% o# t"erma$ trans+ort1
Concept Check 20.4
Question Which of a linear olyethylene % M n R *0 gAmol& and a lightly #ranched olyethylene % M n R :0 gAmol& has the higher thermal conductivity? Why? 7int; @ou may want to consult Section *.3. Ans!er T"e $inear +o$%et"%$ene !i$$ "a/e a $arger conducti/it% t"an t"e $ig"t$% &ranc"ed +o$%et"%$ene &ecause t"e #ormer !i$$ "a/e a "ig"er degree o# cr%sta$$init% &% /irtue o# its $inear mo$ecu$ar structure1 Since "eat trans#er is accom+$is"ed &% mo$ecu$ar c"ain /i&rations- and t"e coordination o# t"ese /i&rations increases !it" +ercent cr%sta$$init%- t"e "ig"er t"e cr%sta$$init%t"e greater t"e t"erma$ conducti/it%1 Concept Check 20.5
Question !"lain why0 on a cold day0 the metal door handle of an automo#ile feels colder to the touch than a lastic steering wheel0 even though #oth are at the same temerature. Ans!er On a co$d da%- t"e meta$ door "and$e #ee$s co$der t"an t"e +$astic steering !"ee$ &ecause meta$ "as t"e "ig"er t"erma$ conducti/it%- and- t"ere#ore- conducts "eat a!a% #rom one0s s.in more ra+id$%1
Chapter 21
agnetic Pro+erties
Concept Check 21.1
Question
Cite the maor similarities and differences #etween ferromagnetic and
ferrimagnetic materials. Ans!er T"e simi$arities &et!een #erromagnetic and #errimagnetic materia$s ar e as #o$$o!s '() T"ere is a cou+$ing interaction &et!een magnetic moments o# ad;acent atoms?cations #or &ot" materia$ t%+es1 ',) Bot" #erromagnets and #errimagnets #orm domains1 '3) H%steresis 1-7 &e"a/ior is dis+$a%ed #or &ot"- and- t"us- +ermanent magneti=ations are +ossi&$e1 T"e di##erences &et!een #erromagnetic and #errimagnetic materia$s are as #o$$o!s '() agnetic moment cou+$ing is +ara$$e$ #or #erromagnetic materia$s- and anti+ara$$e$ #or #errimagnetic1 ',) 2erromagnetics- &eing meta$$ic materia$s- are re$ati/e$% good e$ectrica$ conductors9 inasmuc" as #errimagnetic materia$s are ceramics- t"e% are e$ectrica$$% insu$ati/e1 '3) Saturation magneti=ations are "ig"er #or #erromagnetic materia$s1
Concept Check 21.2
Question
What is the difference #etween the sinel and inverse sinel crystal
structures? 7int; @ou may want to consult Sections *.> and *.=. Ans!er Bot" s+ine$ and in/erse s+ine$ cr%sta$ structures consist o# 2CC c$ose8+ac.ed stac.ings o# anions 'O , + ions)1 T!o t%+es o# sites- tetra"edra$ and octa"edra$- e*ist among t"e anions !"ic" ma% &e occu+ied &% t"e cations1
T"e di/a$ent cations 'e1g1- 2e ,4) occu+%
tetra"edra$ +ositions #or &ot" structures1 T"e di##erence $ies in t"e occu+anc% #or t"e tri/a$ent cations 'e1g1- 2e34)1 2or s+ine$- a$$ tri/a$ent ions reside in octa"edra$ sites9 !"ereas- #or t"e in/erse s+ine$- "a$# are +ositioned in tetra"edra$ sites- t"e ot"er "a$# are $ocated in octa"edra$ sites1
Concept Check 21.3
Question !"lain why reeatedly droing a ermanent magnet on the floor causes it to #ecome demagneti8ed. Ans!er Re+eated$% dro++ing a +ermanent magnet on t"e #$oor causes it to &ecome demagneti=ed &ecause t"e ;arring causes $arge num&ers o# magnetic di+o$es to &ecome misa$igned &% di+o$e rotation1
Concept Check 21.4
Question
Schematically s'etch on a single lot the 1-versus-7 #ehavior for a
ferromagnetic material %a& at 0 %#& at a temerature ust #elow its Curie temerature0 and %c& at a temerature ust a#ove its Curie temerature. 1riefly e"lain why these curves have different shaes. Ans!er T"ese 18/ersus8 7 &e"a/iors are s.etc"ed sc"ematica$$% &e$o!1
At @ K- t"e saturation magneti=ation !i$$ &e a ma*imum- and t"e "%steresis $oo+ !i$$ "a/e t"e $argest area1
At a "ig"er tem+erature '%et &e$o! t"e Curie tem+erature) t"e saturation
magneti=ation !i$$ decrease and t"e si=e o# t"e "%steresis $oo+ !i$$ diminis"1 2ina$$%- a&o/e t"e Curie tem+erature- #erromagnetic &e"a/ior ceases- and t"e materia$ &ecomes +aramagnetic- !it" $inear 18/ersus8 7 &e"a/ior9 t"e s$o+e o# t"is $ine segment is /er% sma$$1
Concept Check 21.5
Question
Schematically s'etch the hysteresis #ehavior for a ferromagnet that is
gradually demagneti8ed #y cycling in an 7 field that alternates direction and decreases in magnitude. Ans!er A sc"ematic s.etc" s"o!ing t"e "%steresis &e"a/ior #or a #erromagnet t"at is gradua$$% demagneti=ed &% c%c$ing an 7 #ie$d t"at a$ternates direction and decreases in magnitude is s"o!n &e$o!1
Concept Check 21.6
Question 4t is ossi#le0 #y various means %e.g.0 alteration of microstructure and imurity additions&0 to control the ease with which domain walls move as the magnetic field is changed for ferromagnetic and ferrimagnetic materials.
S'etch a schematic 1-versus-7
hysteresis loo for a ferromagnetic material0 and suerimose on this lot the loo alterations that would occur if domain #oundary movement were hindered. Ans!er
Hindering domain &oundar% mo/ement !i$$ en"ance t"e coerci/it% o# t"e
magnetic materia$- !it"out +roducing a signi#icant a$teration o# t"e saturation #$u* densit%1 T"ussc"ematic 1-7 &e"a/iors !it" and !it"out domain &oundar% o&struction are s"o!n &e$o!1
Chapter 22
O+tica$ Pro+erties
Concept Check 22.1
Question 1riefly discuss the similarities and differences #etween hotons and honons. 7int; @ou may want to consult Section 2.2. Ans!er Simi$arities &et!een +"otons and +"onons are () Bot" ma% &e descri&ed as &eing !a/e8$i.e in nature1 ,) T"e energ% #or &ot" is
P"onons are e$astic !a/es t"at e*ist !it"in so$id materia$s1
P"otons are
e$ectromagnetic energ% +ac.ets t"at ma% e*ist in so$id materia$s- as !e$$ as in ot"er media1 ,) T"ere is a considera&$e dis+arit% &et!een t"e /e$ocities o# +"otons and +"onons1 T"e /e$ocit% o# a +"oton is t"e same as t"e /e$ocit% o# $ig"t in t"e +articu$ar medium9 #or a +"onon- its /e$ocit% is t"at o# sound1
Concept Check 22.2
Question !lectromagnetic radiation may #e treated from the classical or the 9uantummechanical ersectives. 1riefly comare these two viewoints. Ans!er
2rom t"e c$assica$ +ers+ecti/e- e$ectromagnetic radiation is !a/e8$i.e in
c"aracter- and t"e +ossi&$e energies o# t"e radiation are continuous1
2rom t"e
mec"anica$ +ers+ecti/e- e$ectromagnetic radiation is dua$8$i.e in c"aracter '&eing &ot" !a/e8$i.e and +artic$e8$i.e)- and not a$$ energies are +ossi&$e 'i1e1- energ% is
Concept Check 22.3
Question Why are metals transarent to high-fre9uency "-ray and -ray radiation? Ans!er Energies o# t"ese "ig"8#re
Concept Check 22.4
Question Which of the following o"ide materials when added to fused silica %Si, 2 &0 increases its inde" of refraction; 6l 2, 30 )i,20
Concept Check 22.5
Question 6re the elemental semiconductors silicon and germanium transarent to visi#le light? Why or why not? 7int; @ou may want to consult )a#le >.3. Ans!er We !ant to decide !"et"er or not Si and e are trans+arent to /isi&$e $ig"t on t"e &asis o# t"eir &and ga+ energies1 Ta&$e (13 cites (1(( and @15 e- res+ecti/e$%- as t"e !g0s #or t"ese t!o semiconductors1 According to E
