Analytical Instrumentation Laborotory Observation

8/12/2019 Analytical Instrumentation Laborotory Observation

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Por-tion (]i- t,l'l* (trLrrvc alr re-prt:sr:rlts ar r}}ixtr-rr-crepresents n rcsitlrre of the rr rixtrrre of l\{S()t:(l r-e1>rilsilrlt l.ueight rz1 atrcl ,rr], respectieela'.

of decomposition of materials using Thermo gravimetricThermal Analysis anrl Differential Scanning Calorimetry.

Aim:To determine the decomposition kinetics of materials and to determine the amount of

elements present in a mixture rtf calcium and magnesium carbonates using TGA analysis.Procedure:

A rypic:rl lfCi cr-rr-v* trl-ir nrixtrrrr: r;l'cirlcitrrrr rtrrrl rrr:r.lrrcsittr.tr t'lrrlrrrrtrrles is sl:rrrtrtin [iig- 16, \"r:r"r cart rt


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.o-o\t

^ lrr tttr.llr.'r r,[ ('lr( ) Iirt'ltrt=tl-\r..-} th*,rrln,trrtt ot' {';to Intrst\{hr:re. Mr{(-'ufi} is th* rt-lative

,o-,\ .- - t'-./1,r\', \\'Frt:,n: tltr: ;rht-rv* *r.lttirtiott I trlole of CaCos gives I mt-rle of CO: andIrttt - trt s )('rr( ). 'l-lrtrs. rr(,lL'\ t,l ('( ). irr the si'err exirillples :;i,a=[1 -rd

l mole t:tthis is *qual

Ittl' -ttt.llre. lirr : Ji:____ x Il.{ , t CaO t4-[rnolar rnass t:f CaO.intr-tttt)rttt: _r17: x -.,o9

rnt: l.17ltrtr - ,rz:, S\ 'r: krrou, tlri: rltlrss l:l'l'tsirltte leti. i-e-. fltt, the mass of h'{g{} {rrt+} can Lrecitlt:t-tlatqlrl.llil.1 = 171' -- 711,-Here m: is l[tt-: ntirss r-r['CaO t-orrned. rvtric:h is equal to 1.27 {rrr1-frr2}. Thus

rrl: - rlrl - l.:7 (tt'y- ntll[.1ass +l'tl-r*: ('lr {ru1.,r) in the origin:rl sa::tplrr'cult also be rt:latedto rnl andrrltrytt':e- l'olIort itig l'nrt:-trtll

rrtrr= t).r)I {rl: - ttt:lThis call hc- itbtiritrecf :rs follo*-s:Yru krlnu. iultot"tr:r r:f Cir in CaCO,i and CirLJ w=ill be c-quirl in moles- therefc'rrt:rur)ount ..,['Clr itt ,/r'Arr Ca r AxCa )illcir: rrii*=]i* : l'2J (li' -rtt'lx.

-'^ iLl,(CtOl77 I ' M'{CaO)

'' tr)AS\ and relative nlL)lal',vhi:rr. Ar({-';r} unJ I\1r i(ludi'are ttre relative :rtortticlr);rsc o1'(-'it trncl ['ir(). respec-tivell'. Thtts.= I .3? (ntt - rnr) x +ty-56 : O.9l imr- rn=-)

Siltti lirrlv. nlilss Lll- ma:rnesitltr in the original sartrple r-an be related to rrrr atrtlrtrl:,t f{ r^.^crli'Thrrr. tire rrrrrs< r''l' NIS irt rrriginul sunrple (rrt\r8)

^^ ^ A.(fuIg)= { Iliils\,ok-itlue - l,tllss of ClrO,*ftO;v'i- 24.3: (nr.-m, lx-40--3

Result:The amount of calcium and magnesium present in the given sample is . . . . . . .. .

A- rN,Is I/rl\ o = ltll - - rrt.1 iX -r---l14. tlv-tg{) 1fll1,1, = {},{rL} {rn:- /.I-r-}

.,''-.\ -

,aJ\': '''af,.\\ -.}r'- I


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/'.-> )( -..Aim:To determine Tg, T. and Tn-. using DSC curve of a Polymer sample (PEEK).Principle:

Differential scanning r:alorimetry or DSC is a thermoanalytical technique in which thedifference in the amount of heat required to increase the temperature of a sample and reference ismeasured as a function of tenrperature. Both the sample and reference are maintained at nearlythe same temperature througho",,,l: :iryii*f *The basic principle underly+ng this technique is that when the sample undergoes aph1-sical transformation such as phase transitions. more or less heat will need to flow to it thanthe reference to maintain both at the same temp-rerature. Whether less or more heat must flow tothe sample depends on whether the process is exothermic or endothermic. For example, as asolid sample melts to a liquid it will require more heat flowing to the sample to increase itstemperature at the same rate as the reference. This is due to the absorption of heat by the sampleas it undergoes the endothernric phase transiticn from solid to liquid. Likewise, as the sampleundergoes exothermic processes (such as cgstitllization) less heat is required to raise the sampletemperature. By observing the difference in heat flow between the sample and reference,differential scanning calorim:ters are able to rneasure the amount of heat absorbed or releasedduring such transitions. DSC rnay also be used to observe more subtle physical changes, such asglass transitions.-Itiswidely +rsed in industrial settings as a qu-dlitytontrol instrument dtrs to itsappiieability-in evaluating sanple purity and for studying polymer curinpInstrumentation:

The main assembly o1'a typical heat-flur DSC cell is enclosed in a heating block (forexample Ag), which dissipates heat to the specimens (S and R) via a constantan disc attached tothe Ag block. The constantan disc has tu'o platforms on which the S (specimen) and R(reference) pans are placed. A chromel disc and connecting wire are attached to the underside ofeach platform: the resulting chromel-constantan thermocouples are used to determine thedifferential temperatures of interest. Alumel u'ires are also attached to the chromel discs toprovide chromel-alumel junctions which measure the sample and reference temperaturesseparately. Another thermocouple is embedded in the Ag block and serves as temperaturecontroller for the programmed heating/cooling c1cle.


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HeatingC0l Fst,.rrcrdaHEiE=iacocooeoLrert-Cas +(Vccuuu) I :AT

lhenl,rcouplesIn heat-flux DSC instruments, the difference in energy required to maintain both S and R at thesame temperature is a measure of the energy changes in the test specimen S (relative to the inertreference R). Tne thermocouples are usually not embedded in neither S or R materials. Thetemperature difference DT that develops between S and R is proportional to the heat-flirwbetween the two. In order to detect such small temperature differences, it is essential to ensurethat both S and R are exposed to the same temperature programme. The measurements areusually performed under vacuum or inert-gas flow: the flow rate (typically around 40 ml/min.) ismaintained oonstant throughout the experiment.

=L.-Eaa

J

itLI...t,/ QnET?r ****

.F*

- Diflarential Scanning C*odmeter (OSG) Potyethercth*etcne {PEECI

Fi**e=s I TransithnSclid-sdid EansitionCrystallizatiwrMellingVaporizationSublimationAdsorptionDesorptionDryin g (sotvent rernovd)DecompositionSolid-state readioaSolid-liquid rcactiurSolid4as redionFolymerizatimCatalytic readhrs

Exotlxlrtnl**End*iilerm*i*

****+****

rC\:rtA* z irr 1',

H=r$Ct

HH'"-.r E@lM .{_'i :/-- -,Jlr

)crydrLrGil er' * er , lr.lllrsI..ildr r.nr1d ilI]liP..r i 16 $

t--/

r*'",**_*;*d ldr@+t'S

T*Tr'raa=lt


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Inference:Differential scanning calorimetry can be used to measure a number of characteristicE") ' a-\propertiesofasaryple.Elsitgffinique-+ri@fusion,#crysta|1ization?,e:*en+s.as--rirc$-as-glass transition temperatures fs. DSC can also be used to study oxidation, as

well as other chemical reactions- Glass transitions may occur as the temperature of an amorphoussolid is increased. These transitions appear as a step in the baseline of the recorded DSC signal.This is due to the sample undergoing a change in heat capacity; no formal phase change occurs,As the temperature increases, an amorphous solid will become less viscous. At some point themolecules may obtain enough freedom of motion to spontaneously affange themselves into acrystalline form. This is known as the crystallization temperature (2.). This transition fromamorphous solid to crystalline solid is an exothermic process, and results in a peak in the DSCsignal. As the temperature increases the sample eventually reaches its melting temperature (7,,).I, depends on the molecular weight of the poly'mer and thermal history, so lower grades mayhave lower melting points than expected. The rnelting process results in an endothermic peak inthe DSC curve. The percent crystalline content of a polymer can be estimated from thecrystalhzation/melting peaks of the DSC graph. The ability to determine transition temperaturesand enthalpies makes DSC a valuable tool in producing phase diagrams for varicus chemicalsystems.

Result: u , :The given sample has T*, T. and T, value to be ..lA:).":. , (6:% , 3j I


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/,,Aim: ,, ^ "1' '1., ,i ,- ,To&tetndasPrinciple:

u, ''l '

using DTA analysis.

The principle of the DTA technique resumes to heating (or cooling) a test sample (S) andan inefi reference (R) under identical conditions while measuring the temperature difference DTbetween S and R. In this technique it is the lreatflc.w to the sample and reference that remains thesame rather than the temperature. When the sample and reference are heated identically, phasechanges and other thermal processes cause a difference in temperature between the sample andreference. Both DSC and DTA provide similar information. DSC measures the energy requiredto keep both the reference and tire sample at the same temperature r,vhereas DTA measues thedifference in temperature bet\\'een the sample and the reference when they are both prrt under thesame heat.

The differential temperature DT is then plotted against time or against temperature.Chemical, physical, structural and microstructural changes in the sample S lead to the absorption(endothermal event) or evolution of heat (exotherrnal event) relative to R. If the response of twoinert samples submirted to an applied heat-treatinent programme is not identical, differentialtemperatures DT arise as well. Therefore. DTA can also be used to study thermal properties andphase changes which do not necessarill lead to a. change in enthalpy. The baseline of the DTAcurve exhibits discontinuities at transition temperatures and the slope of the cun'e at any pointwill depend on the microstructural constitution althat temperature. The area under a DTA peakcan be related to the enthalpy change and is not affected b1-the heat capacitl'of the sample.Instrumentation :

The samples are placed in P1rex. silica, Ni or Pt crucibles (according to the temperatureprogramme and purpose of the experiment). Thermocouples should not be placed in directcontact with the sample to avoid contamination and degradation, even though sensitivity may becompromised. 'fhe sample assemblJ' is isolated against electrical interference with the wiring ofthe oven with an earthed metallic or Pt-coated ceramic sheath. For heating experiments up toabout 500oC, an uniform transfer of heat away fiom the sample may be difficult. Disc-shapedthermocouples must then be used to ensure optimum thermal contact with the bottom-side of thesample container (Al or Pt foil). The fumace should provide a stable, large enough hot-area and a


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fast response to the temperature-controller commands. Data acquisition and/or the real-timedispla,v is handled by a computer system or an analog device (plotter).

Experimental details: potential sources of error.Experimental parameters such as specimen environment, chemical composition. size.

surface-to-volume ratio must carefully be selccted, since they might modif,v fr:r example thethermal decomposition of pou der materials even though their solid-state phase transitions are notaffected. The packing state of pou'der samplc's is important in these thermal decompositionreactions and may lead to significant differences in thermal behaviour between otherwiseidentical samples. Moreover, DTA measurements on powder materials do not always correctlyillustrate the thermal behaviour of bulk specimens, for which most phase transitions will alsoexhibit the influence of built-in strain energy.

The heat flow rate ma;r sometimes satulate the response capability of the DTA system. Itis then advisable to dilute the specimen with a thermally-inert material. For the detection ofphase transition temperatures, one must also check that the peak temperature T, does not varywith sample size. The shape of DTA peaks depends on sample weight and on the heating rateemployed. Low heating rates or small sample rveights lead to better resolved (sharper) DTApeaks, but the signal-to-noise ratio might hou'eler be compromised. Reducing the specimen sizeor the heating rate is also important in kinetic analysis (isothermal) experiments, where thermalgradients should be minimized.Data Analvsis:

The heat capacity and thermal conductir itv of the test specimen (S) and reference sample(R) are usually not identical. fhis gives rise to a certain displacement between their response in


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the linear regions of the DTA trace. The DTA peaks correspond to evolution or absorption ofheat following physical or chemicai changes in the specimen (S) under analysis. The detection ofphase transition temperatures using DTA is not verl- accurate. The onset of the DTA peakindicates the start of the phase transition, but temperature shifts from the true values are likely tooccur depending on the location of the thermocouples riith respect to the specimen, reference orto the heating block. Therefore. the temperatur:e calibration of the DTA instrument usingstandard materials with known melting points is necessan"

The area (A) enclosed betseen the DTA peak and the baseline is related to the enthalpychange (e) of the specimen during the phase transition. \\-hen the thermocouples are in thermal(but not in physical) contact riith the specimen and reference materials, it can be shown that thepeak alea A is given bY

r?? 'tls.fiWhere m: sample mass (ueighl: Q: enthalpy change of the specimen; q: enthalpy changeper unit rnass; g : (ureasuredl geometrical shape iactor; K : thetmal conductivitl' of sample )

Errors in estimating the correct DTA peak areas are likel1'to occur for porvder materialsand compacted'samples which rerain some degree of porosity'. The gas filling the pores or whicheventually evolves frorn the specimen itself. aiters the thermal conductivitl' of the DTA cellenvironrnent (compared to calibration e\periments), leading to rather large errors in the DTApeak areas.Enthalpv calibration:The energy scale of the DTA instrument must also be calibrated to absolute enthalpy values bymeasuring peak areas on standard samples over specified temperature ra11ges. The enthalpycalibration implies measuring at least 2 different samples for which both heating and coolingexperiments must be perfo.tmed. lt is then possible to measure the constant pressure heat capacity(CP) using the DTA method :

T. -T,-7- : IL - - lt'-r nt. If


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where H is the heating rate emploved,, k 2frKeenthalpy calibration constant and)t'iaT2 are thedifferential temperatures generate d Wgan initial 'empty' run (witho ,y&*land during the

x:: i&* t.1ttr ,=rC rC,|s . :-0 r:rl

t: S * B*at+-gf, HffiEilJH.E.L4ist[CrFiro. j femperalure ('C)t-r Cv{*7 a ,. {} t.-zrcz

llsi?c *' E 'tr.t0;:.ls ;lrt S;:.1 *,r* tr,E \Et1,,4 *,t-.2 .S:0+1**'.@-#-----T-- ---*"*{73 6tt Er3 lqir+ 1f;?BTf i{

Result:

:@s&t?7f;

*i3ss*:,.. :=e75=qte{:i,q' ESjt "i*9_SE= r.

xrF

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Analytical Instrumentation Laborotory Observation