1、,热重分析(TGA),Theory&Applications,2,TGA:The Technique,Thermogravimetric Analysis(TGA)measures the amount and rate of change in the weight of a material as a function of temperature or time in a controlled atmosphere.,热重分析的结果用热重曲线或微分热重曲线表示。,样品在热环境中发生化学变化、分解、成分改变时可能伴随着重量的变化。热重分析就是在不同的热条件（以恒定速度升温或等温条件下延长时
2、 间）下对样品的质量变化加以测量的动态技术。,3,What TGA Can Tell You,Thermal Stability of MaterialsOxidative Stability of MaterialsComposition of Multi-component SystemsEstimated Lifetime of a ProductDecomposition Kinetics of MaterialsThe Effect of Reactive or Corrosive Atmospheres on MaterialsMoisture and Volatiles Cont
3、ent of Materials,热稳定性,氧化稳定性,组成,产品寿命,分解动力学,反应或腐蚀气氛对材料的影响,材料水分和挥发份含量,4,Mechanisms of Weight Change in TGA,Weight Loss:Decomposition:The breaking apart of chemical bonds.Evaporation:The loss of volatiles with elevated temperature.Reduction:Interaction of sample to a reducing atmosphere(hydrogen,ammonia
4、,etc).Desorption.Weight Gain:Oxidation:Interaction of the sample with an oxidizing atmosphere.Absorption.All of these are kinetic processes(i.e.there is a rate at which they occur).,5,DTG曲线微分型曲线,TG曲线积分型曲线,6,初始热分解温度(B、G),反应终了温度(C、H),最大失重速率温度,7,影响热重测定的因素:Purge Gas,TGA:Always purge through balance hous
5、ing with dry inert gasTGA:Only introduce reactive/corrosive gases through sample area/furnace housing Nitrogen most common.Helium often provides best baseline but will make furnace work hard at high temperature.Air can sometimes improve resolution because of differences in the oxidative stability(ve
6、rsus thermal stability)of components.,气氛不同反应机理的不同。,8,TGA:Purge Gas Flow,60ml/min,90ml/min,10ml/min,40ml/min,Standard Furnace,EGA Furnace,9,Test for Oxygen Contamination of N2 Purge Gas,320.79C,10 minute N2 pre-purge,+,Copper Oxalate,10,Effect of Oxygen on Copper Oxalate Decomposition,11,TGA:Baseline
7、 Considerations,Good way to quantify how the TGA/SDT is working.Especially important for measuring small weight losses associated with volatilization or small amounts of residue.Run clean,empty,tared pan,over temperature range of interest,at desired heating rate.Plot weight in g vs.temperature.,12,T
8、GA:Accurate Residuals,13,TGA:Sample Preparation(cont.),Use brass tweezers to eliminate static effectsTare a clean sample pan before every runDistribute sample evenly over bottom of panLiquid samples-use hermetic pan with a pin-hole lid,14,Platinum(useful for most materials)Easy to CleanNonporousAllo
9、ys with most metalsAlumina(Ceramic)Corrosives/InorganicsLarge samplesAluminum(TGA)(designed for one-time use)Lower costLower temperature limit(=600C),TGA:Sample Pan Selection,15,TGA:Sample Pans-Types/Sizes,16,Effect of Sample Size,17,Effect of Heating Rate,18,Mass Effect Semi-crystalline PE,19,Pan S
10、hape Effect Amorphous PMMA,20,Sample Morphology Effects PET,2.9 mg;amorphous PET2.8 mg;semi-crystalline PET,21,Shift in Onset with Ramp Rate,22,Time to Complete Degradation,23,Q5000 IR High-Heating Rate TGA Analysis,24,Typical Applications,Thermal StabilityCompositional AnalysisOxidative Stability,2
11、5,Thermal Stability of Polymers,26,Block versus Random Copolymers,27,Effect of Epoxy Cure Temperature,260,280,300,320,340,360,380,400,420,440,0,20,40,60,80,100,Temperature(C),Weight(%),100C,125C,150C,175C,200C,Prog:10C/min,28,Curie Point（居里温度）Determination,29,Thermal Stability of an Explosive Materi
12、al,30,Thermal Stability of an Explosive Material,31,TGA of an Adhesive,25.18mg of an adhesive 10C/min,32,Inset View Shows Strange Result,Is this real?,33,Use time based derivative of temperature to plot the heating rate,34,Aberration in Heating Rate,Usually means that the sample touched the thermoco
13、uple,35,TGA of Drug A,Sample:Drug A Size:22.5850mg Heating Rate:10C/min,36,TGA of Drug A Monohydrate,Sample:Drug A Monohydrate Size:15.1740mg Heating Rate:10C/min,Water weight loss,Decomposition,37,TGA of Drug A Microspheres,Sample:Drug A Microspheres Size:14.2940mg Heating Rate:10C/min,38,TGA Analy
14、sis of Cold/Allergy Tablet,Sample:Cold/Allergy Tablet Size:18.4890mg Heating Rate:10C/min,Volatiles,Decomposition,39,DSC-TGA Sodium Tungstate,Small Sample Size(3mg)and 10C/min Heating Rate,Dehydration,Solid state and melting transitions,40,Dehydration Sensitivity,41,TGA-DSC Soda Ash,Dehydration,Heat
15、 flow Integrations automatically normalized using weight at start of transition,Polymorphic phase transitions,Melting transition,42,Compositional AnalysisCalcium Oxalate,Sample:CaOx Size:6.9610mg Heating Rate:10C/min,43,EVA Copolymer,%Vinyl Acetate=%Acetic Acid*Molecular Weight(VA)/Molecular Weight(
16、AA),VA%=16.85(86.1/60.1)=24.2%,Sample:EVA(25%)Size:19.2030mg Heating Rate:10C/min,44,PET w/Carbon Black Filler,How much Carbon Black was in this sample?,45,PET,46,Comparison of Filled&Un-Filled PET,47,Styrene-Butadiene Rubber Analysis,48,Filled Polymer Analysis,Inert filler,Inert filler,Inert filler
17、,49,Oxidative StabilityEpoxy,50,Resolution Enhancement by Changing Purge,PET,N2AirN2 w/switch to air,gas switch,51,传统TGA 与高分辨TGA之比较聚氨酯,52,传统TGA 与高分辨TGA之比较,Characterization of a PTFE/PEEK/Carbon Fiber Blend,53,Decomposition Kinetics Background,Includes isothermal and constant heating rate methods.Con
18、stant heating rate method is the fastest and will be discussed here.Based on method of Flynn and Wall Polymer Letters,19,323,(1966).Requires collection of multiple curves at multiple heating rates.Ultimate benefit obtained in Life-Time plots.,Requires at least 3 TGA runs at different heating rates o
19、r 1 Modulated TGA runCalculates Activation energy&conversion curvesUltimate benefit is predictive curves“Lifetime Plots”,54,Kinetic Analysis,The rate at which a kinetic process proceeds depends not only on the temperature the specimen is at,but also the time it has spent at that temperature.Typicall
20、y kinetic analysis is concerned with obtaining parameters such as activation energy(Ea),reaction order(k),etc.and/or with generating predictive curves.,55,Kinetic Analysis,cont.,Activation energy(Ea)can be defined as the minimum amount of energy needed to initiate a chemical process.,State 1,State 2
21、,Ea,With Modulated TGA,Ea can be measured directly.,56,TGA Kinetics Example,57,TGA Kinetics-Heating Rate vs.Temperature,Activation Energy(Ea)Slope,58,TGA Kinetics-Estimated Lifetime,59,Why Use Evolved Gas Analysis?,TGA measures weight changes(quantitative)Difficult to separate,identify,and quantify
22、individual degradation products(off-gases)Direct coupling to identification techniques(Mass Spec,FTIR)reduces this problem,Evolved Gas Analysis,60,Mass-Spectrometry Benefits,Additional information for the interpretation of the reactions in the TGA resultsSensitive method for the analysis of gaseous
23、reaction productsExact control of the furnace atmosphere before starting and during the experimentLocation of air leaks around the furnace,61,TGA-Mass Spectroscopy,Advantages:Higher sensitivity and wider dynamic range than FTIR(1ppm vs.10ppm).Measures non-IR absorbing gases.More rapid response.Disad
24、vantage:Cannot distinguish between isomers.(e.g.N2 and CO),62,TGA-FTIR,FTIR Advantages:On-line measurement Hydrocarbons are easy to identifyDisadvantages:No detection of inert gases(no dipole moment)Detection of inorganic gases limited,63,TGA-MS:System Schematic,64,TGA of Calcium Oxalate,65,TGA-MS Calcium Oxalate,66,TGA-MS,67,TGA-MS,During weight loss,a reaction occurs between H2 in purge and sample in which H2O and HO are produced.,68,TGA-MS,Benzene is a component of smoke.Much reduced in the flame retardant sample.,69,Compositional Analysis by TGA-MS,
