7/28/2019 10 Microscopy

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Microscopy

Background

Microscopy techniques are used to produce visible images o polymer micro-structures or details that are too small to be seen by the human eye.

Tere are three main types o microscopy: Optical, Electron and Scanning

Probe. ARDL utilizes Optical and Electron microscopy including LightOptical Microscopy (LOM), Scanning Electron Microscopy (SEM) andransmission Electron Microscopy (EM).

Optical and Electron microscopy both work based on the act that diraction,reection or reraction o radiation instigates the development o an image.

Energy Dispersive X-RAY (EDX) detects elements within a sample usingX-RAYs generated by the SEM. Optical Comparator (OC) can be used ormicromeasurements on parts to make sure they are in specifcation.

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Elemental Analysis

& Multi-Element Dot Mapping (EDX)

Determining elemental composition (anything oversodium in the periodic table) o contaminants in samplesis important when other means o analysis such as FIRand GC/MS did not work. FIR and GC/MS are useul todetermine the organic structure o contaminants present, butdo not do as well as SEM/EDX or identifcation o inorganiccontaminants. Positions and concentrations o dierent elements ina composite can be located with either multi-elemental X-RAY dotmapping or line scan analysis.

Failure Analysis (LOM / SEM / EDX / TEM)

Te preerred starting point o ailure analysis is microscopic analysis, because it can save time and money. Te microscopistfrst attempts to discover the root cause o ailure by utilizing low magni fcation analysis to document macro eatures likecrack propagation. I higher levels o magnifcation are needed , SEM and/or EM analysis can be perormed to allow microeatures, like inorganic fller dispersion, to be seen.

Foam Cell Size (LOM)

Open and closed oam cell size can easily be determined using the light microscope by taking reected light images o theoam cross-section, measuring a fxed distance and counting the number o cells in that distance. Using a specifc mathematicalormula, an accurate determination o the three dimensional volume o the cells can be made and the number o cells per unitmeasure can be obtained.

Internal Structure Features (LOM / SEM / TEM)

Internal structures such as crystallinity (lamellar and spherulitic structures) can be determined by using polarized lightmicroscopy, EM, and, in some cases, SEM depending on how the sample is ractured and the type o sample being analyzed.

Metal-to-Rubber Bonding (SEM / EDX)

Te extent o tire cord adhesion and other rubber-to-metal bonds can be looked at in the SEM using image andelemental analysis. echniques such as reeze racturing and polishing o sample cross-sections can be employed to

get a close look at the interaces in question. Multi-elemental X-RAY dot mapping and line scan techniques canthen be used to measure layer thickness and identiy elements present that are specifc to primers and adhesives.

Micro-Dispersion Analysis (SEM / EDX / TEM)

Fine dispersion o inorganic fllers can be evaluated by image analysis in the SEM using backscatteredelectron imaging, which uses atomic number contrast in order to dierentiate between low and highatomic number elements. Inorganic fllers with higher atomic number elements such as calcium and

zinc would be visually lighter in color in the image and lower atomic number elements such ascarbon and magnesium would be darker.

Particle Size & Particle Size Distribution (LOM / SEM / TEM)

In addition to carbon black typing, the light microscope and EM can also determineparticle size distribution and morphology o inorganic fllers and other compound additives

as long as they dont interact too much with the electron beam. Examples o other types oparticles that could be analyzed includ e recycled rubber, PVC particles and latex.

Carbon Black Testing / Carbon Black Typing (TEM)

Carbon black is a major component o many rubber products and is use d or reinorcementand modifcation o physical properties. Identiying the specifc carbon black in a compound

by EM is important so that the proper carbon black can be use d in ormula reconstruction oroptimization o the physical properties o the rubber. Determinations o type o carbon black in a

compound are ound by particle size distribution. Organic fller particle size can also be determined.It is important in ailure analysis to determine that the appropriate carbon black/other fller has been

added to the rubber compound.

Coating & Film Thickness (LOM / OC / SEM / EDX / TEM)

Many modern rubber and plastic products are manuactured withdierent layers (coextrusions, laminating, and surace coatings ortreatments) that perorm specifc unctions. By embedding andmicrotoming cross-sections through these dierent layers andanalyzing them microscopically using the optical comparator or lightoptical microscope, one can determine the number o layers presentand determine the thickness o each. Subsequent analysis o themicrotomed sections by microscope FIR and SEM/EDX can alsodetermine organic and inorganic compositions o the dierent layers.Analyzing sections in the EM can resolve very thin sections.

Dimensional Analysis (LOM / OC)

Part dimensions can be accomplished by using an opticalcomparator or simply by scanning an image using a at bed scanner.Analysis o this type is usually perormed to determine i a part iswithin the specifcations determined by the manuacturer. Tis isimportant in ailure analysis because i a part is out o specifcation,that may be the sole reason or ai lure.

Dispersion Analysis (LOM)

Dispersion o carbon black or inorganic fllers can bedetermined by cutting or microtoming the rubber

and analyzing with reected light, transmittedlight or electron microscopy. In the case o LOM,

carbon black dispersion can be determined usingthe reected light method commonly known

as the Phillips dispersion rating. More precisecarbon black dispersion can be determined

by microtoming thin sections and usingtransmitted light or the analysis. SEManalysis uses atomic number contrast

rom backscattered electron images todetermine the dispersion o inorganic

fllers with the fllers appearinglighter (high atomic number)

than the surrounding rubber (lowatomic number).

Cell Size Determination of Closed Cell Foam Rubber by LOM

665 Micron

Topcoat Thickness Measurement by LOM

15 Micron

Topcoat

Phillips Dispersion by LOM 665 Micron

Carbon Black Agglomerates

Microscopy Techniques

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Microscopy Techniques (con

Tire Cord Analysis by SEM

Polymer Blend Morphology (LOM / TEM)

Rubber and plastics can be cryogenically microtomed to obtain sections thin enoughto be observed in the EM. Larger eatures can be analyzed with the LOM. By stain

with osmium or ruthenium, polymer morphology o blends can be seen. Subsequentpreparation o the microtomed bulk specimen by etching with the appropriate organ

solvent, acid or base will make certain morphologies more apparent using the SEM.

Room Temperature & Cryogenic Microtoming (LOM / TEM)

Tin sections o most rubber and plastic materials can be obtained using our new RMPowertome XL with RXL cryo attachment. Sections under 100 nm can be obtainedviewed with the EM or LOM and microtomed bulk sections can be viewed with thSEM.

Surface Analysis (LOM / SEM)

Surace eatures o samples can be obtained using the LOM or the SEM, allowing

eatures such as surace roughness and crack propagation to be seen. Discolorationproblems can be detected in the LOM and sometimes identifed elementally by usinatomic number contrast in the SEM. Atomic number contrast uses the backscatteredelectron detector, which can determine dierences in relative atomic number with hatomic number elements (or example, iron or lead) being lighter in color and loweratomic number elements being darker (carbon, silicon, etc.) depending on the matrixthe sample. Specifc elements can then be identifed using the IXRF Systems - EDS20energy dispersive X-RAY system (EDX). High-resolution secondary electron SEMimages can also be obtained to urther characterize the sample.

Where Do I Go From Here?

Whether you need failure analysis or just want to obtain

compound properties, ARDL is ready to help you with

all of your microscopy needs. Call, email or go online

now to nd more information or to request a quotation.