Microbac Laboratories Inc. has extensive expertise and analytical capabilities to identify unknown materials and substances.
In general, these investigations start with a client discovering some problem with a product or process, whereby they are not obtaining the appropriate performance or behavior. As they investigate within their systems what is not in specification or typical, they find a material or substance that appears to be causative of the problem, but they do not know what it is. They then come to Microbac for assistance in identification.
The following examples will be discussed in greater detail:
- Electronic Device Manufacturer: A manufacturer of electronic devices experiences a field failure within a product, and the product is returned for inspection.
- Food Processor: A food processor discovers a contaminant within their product during routine Quality Assurance testing.
- Pharmaceutical Manufacturer: A pharmaceutical manufacturer replaces a filter on a prescribed maintenance schedule, and upon removal of the old filter, finds black particles.
Microbac approaches these problems in approximately the same way: the unknown material is visually inspected, sometimes using optical stereo microscopy to better understand morphology and homogeneity.
During this stage of analysis, scientists will perform one of two testing techniques, one that is best for organic materials, and one that is best for inorganic materials. These two techniques, Fourier Transform Infrared (FTIR) Spectroscopy and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS), are discussed in greater detail below.
Fourier Transform Infrared (FTIR) Spectroscopy
Fourier Transform Infrared Spectroscopy (FTIR) works by exciting chemical bonds with infrared light and is best for identification of organic materials. The different chemical bonds in this excited state absorb the light energy at frequencies unique to the various bonds. This activity is represented as a spectrum (See Figure 1).
The spectrum can be expressed as % transmittance (%T) or % absorbance (%A) versus wavenumber. The wavenumber of the peak tells what types of bonds are present and the
%T tells the signal strength. Low signal strength directly affects the resolution of the peaks making sample size and preparation key for acquiring a quality spectrum.
The spectrum is essentially a “fingerprint” of the compound that can be used to search against reference spectra from libraries for the purpose of identification. A ratio of specific peak heights can sometimes be used to quantify proportions in simple mixtures, degree of oxidation or decomposition, purity, etc.
The method can be performed as either a macro- or micro-analytical technique, and thus extremely small samples can be analyzed. If a test specimen can be seen and interacted with using up to approximately 10X magnification, micro-FTIR can be performed.
Additionally, liquids, dried residues, viscous materials, films, and other sample matrices can be accommodated. The testing is generally performed in accordance with ASTM E334.
The FTIR aids in identifying chemical bonds, and thus chemical composition of materials. FTIR works best when the sample matrix is either homogeneous or composed of only a few materials. Mixtures of multiple materials tend to “confuse” the library search function due to complexity of overlapping spectral fingerprints.
Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS) The scanning electron microscope is essentially a large vacuum tube with the sample placed inside. The electrons in the vacuum tube are generated from a heated filament and driven by a high voltage to the sample, which is conductive or which has been made conductive by coating with a conductive material. The SEM generates an image of the sample from this electron beam.
This process allows much higher magnification of the sample area of interest than is possible with optical microscopes, and much greater depth of field, so very small features on irregular topographies can be imaged clearly.
In conjunction with generating images, the electrons generate x-rays from the surface of the materials in the sample. The x-rays emitted from the sample can be interpreted using energy dispersive spectroscopy (EDS) to determine of which elements (atoms) the surface of the sample is composed, and the elemental composition of the features on the sample. SEM/EDS can thus be used to determine the surface elemental composition, but only for elements heavier than boron, not including nitrogen.
The typical sample size that can be accommodated within the chamber of the SEM is a maximum of a few cubic centimeters. This small sample size necessitates the sectioning of larger samples. For imaging purposes, the sample must be conductive or made conductive by coating with a thin layer of gold. The EDS testing is generally performed in accordance with ASTM E1508.
In addition to having the capability to identify the surface elemental composition of materials, particles, and contaminants, the SEM is ideal for imaging and analyzing the surfaces of fractures and corrosion sites. The features revealed can be used to determine the mode of failure and clues to the cause of failure (i.e. in support of a failure analysis). SEM/EDS can be considered a non-destructive testing technique, if sectioning and gold coating is not required.
Case Study #1: Electronic Component Manufacturer. A manufacturer of electronic devices experienced a field failure within a product, and the product is returned for inspection. During inspection, an area on a circuit board within the device is found to have white crystalline contamination. A test specimen is obtained from the contaminated area, which is then analyzed by SEM/EDS.
SEM/EDS results indicate that the contaminant is principally composed of carbon and oxygen, but also contains elevated levels of tin, lead, aluminum, and copper. This elemental mixture is consistent with typical tin lead solder flux residues from electronic device manufacturing. Based on experience, the contaminant was visually identified by color and morphology as solder flux residue, which was subsequently confirmed by SEM/EDS test results. The leftover solder flux residue contamination allowed unwanted currents to flow across the surface of the circuit board, causing premature failure of the device.
Case Study #2: Food Processor. A food processor discovered a foreign object within their product during routine Quality Assurance testing. The foreign object appeared to be polymeric based upon results of visual inspection, and a test specimen was obtained for analysis by FTIR. FTIR testing identified the material as PolyVinyl Chloride (PVC), a polymer typically used in food contact equipment and hand tools. At the client’s request, a similar test specimen was obtained from a hand tool (a large spatula) used in the manufacturing process. FTIR testing of this known sample gave an identical spectral fingerprint, indicating this as the most likely source of the foreign object.
Case Study #3: Pharmaceutical Manufacturer. A pharmaceutical manufacturer is required to replace filters on a prescribed maintenance schedule, and upon removal of the old filter found black particles. The black particles were observed to have a low hardness, and appeared to be elastomeric (rubber). Due to the black color, which is almost always due to carbon black filler in elastomers, a test specimen could not be directly obtained from a particle (carbon black is an IR absorber, and FTIR cannot resolve the polymer from the filler). However, this is easily solved by solvent extracting a portion of the sample, and obtaining a test specimen from the re-cast material. This re- cast material was then analyzed by FTIR, with results indicating an ethylene-propylene- diene (elastomer) material. However, to make sure of the material identification, a particle was also tested by SEM/EDS, where carbon and oxygen were found with elevated levels of silicon. Based on the silicon content determined from SEM/EDS, and the elastomer identification, the material was fully identified as a silicone modified carbon-based synthetic elastomer, such as siliconized EPDM.
Additional tools available within Microbac that assist in the identification of unknown materials include ThermoGravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Gas Chromatography/Mass Spectrometry (with numerous preparation techniques such as Heated Headspace, Direct Injection, and Thermal Desorption), Gel Permeation Chromatography (GPC), High Performance Liquid Chromatography (HPLC, including LC/MS/MS), and numerous other items of chemical and mechanical test equipment.
