Volume 7 Issue 4

Volume 7 Issue 4

What’s Happening at Missouri S&T:
(formerly UMR)

Short Course Dates  
 We will be offering "Introduction to Coatings Composition and Specifications" July 18-20, 2011 (Summer 11), course designed for the new coatings person in areas such as sales, marketing or production. The course was initiated by a number of raw material companies and distributors requesting a course with this format. This course is not as heavily technical as is our “Basic Composition of Coatings" and “Introduction to Paint Formulation" courses. The ?Introduction to Coatings Composition and Specifications" course is a two and a half day course which will discuss the types of coatings, the basic composition of coatings and the tests and specifications used by the industry. This course will allow the participant to gain the fundamentals needed to work in this industry and to communicate more clearly.

We will be offering ?Basic Composition of Coatings"  September 19-23, 2011 (Fall 11). The Basic Composition course is intended for new personnel in the coatings profession. It targets the components of coatings (resin, pigments, extenders, solvents and additives), testing and specifications, general formulation and manufacturing methods. Basic Composition is primarily a lecture course with several laboratory demonstrations.

We will be offering ?Introduction to Paint Formulation"  October 10-14, 2011 (Fall 11). This course is intended to give the person a fundamental knowledge of how to approach a starting formulation and troubleshoot it. This course involves both lecture and laboratory work.

For more information see our web site at http://coatings.mst.edu/index.html and to register contact Catherine Hancock at cemv26@mst.edu or coatings@mst.edu or call 573-341-4419. **These courses are held on the Rolla Campus**

Employment Tab

We have started an employment section for our students and companies. We have a full time job section, an intern / co-op section and a graduating and alumni students section . Please explore our section on employment on our web site. Anyone wanting to have job opening listed, please contact us at (573) 341-4419 or e-mail: svgwcc@mst.edu . You can also write to us at Missouri S&T Coatings Institute, BOM #2, 651 W. 13th St., Rolla, MO 65409-1020. Our web site is http://coatings.mst.edu

Technical Insights on Coatings Science

Some unconventional testing methods for coatings

Jigar Mistry, Graduate Research Student, Missouri S&T

 

Testing of an object is usually done to find out a prospective problem with the object or its use and usefulness. Evaluation is the analysis of a problem by means of a testing method1. Modeling is an important tool for the life cycle assessment of an object to detect future defects/problems2. Destructive testing is important to decide what amounts of defect levels are tolerable before something is considered a failure.

The following are some unconventional testing methods for coatings, not commonly used in the industry3 –

Liquid Penetrant Testing - The fundamentals behind this technology is that the liquid should wet the surface to be tested for any deformities and that the defects should intersect the surface. Surface preparation, perception of the inspector, etc. plays an important aspect towards the evaluation of results4. The development of visible or dye penetrant (color contrast) and fluorescent penetrant (brightness contrast) have revolutionized the outlook of liquid penetrant technology.

Radiography - X-rays, discovered by Wilheim Roentgen, in 1895 A.D., is a form of electromagnetic radiation whose energy is 100-100,000 times higher than visible light and can pass through materials, depending upon the elemental composition, density or thickness of the material. With the technological advancements, radiographic methods known as Computer Tomography (CT) has been developed to image all three dimensions of an object, where each voxel are assigned numerical values as liner attenuation coefficients and the final result is a 3D block of data representing the object, which is achieved by acquisition of multiple projection radiographs at different angles. X-ray crystallography is very widely used in the world of Chemistry to know the solid state crystal structure of a compound5.

Ultrasonic Testing - The sound waves above 20,000 Hz are called ultrasonic and are inaudible to humans. Ultrasonic waves can propagate through solids, liquids and air and interact with them accordingly; thereby allowing us to accurately predict the thickness, elasticity, defects, etc. for any particular polymer/film/coating6. An oscilloscope can be used to measure the ultrasound frequency/wavelength. The display is generated in the form of pulse echo on the Amplitude v/s Time axis, where the amplitude varies with defect. Transducer provides the impulse while the receiver provides the signal based on the impulse it receives. Electromagnetic acoustic testing (EMAT) and Laser ultrasonic transducer method (Laser UT) are gaining popularity these days as Nondestructive Testing methods.

Eddy Current Testing - Originally known as Foucault current (German for streams or ripples), Eddy current is induced in conductors, opposing the change in flux that generated them when the conductor is to a changing magnetic field due to relative motion of the field source and conductor; or due to variations of the field with time which causes the flow of electrons or current in the body of the conductor. For a highly conductive material, there are no losses in the EC while for a non-conductive material, we would have losses in EC which can be calculated by the resistivity/resistance values of that material, which can be used to calculate the actual thickness of coatings7.

Acoustic Emission Testing - Stressed materials emits noise (for example creaking timbers and tin cry) which is a signature associated with the final stages of failure, which can be accessed as an effective nondestructive evaluation tool by means of sensors. It can also be used to detect flaw locations due to thermal shocks in ceramics or polymer composites, phase transformations and precipitation in metal deposition (coats), incipient stages of stress corrosion cracking, etc8.

Magnetic Particle Inspection - Magnetic flux lines can be used as an important tool for nondestructive testing and evaluation as the magnetic lines of force are highly distorted across a defect which makes the magnetic particles cluster at that point. Magnetic particle inspection can only be used for detecting defects near the surface or the subsurface; and can be used to detect the onset of corrosion as that process would change the magnetic properties of the substrate which can be inferred to give more information about the actual corrosion on the substrate9.

Thermography - Charged coupled devices (CCDs) in cameras are sensitive to near IR light, which can be used for imaging via temperature difference with the surroundings. Thermography can be used for actual corrosion imaging underneath a coating, flaw location in polymer composites, etc.

Microwaves - Microwaves can measure the dielectric of the material, thereby allowing us to use millimeter waves and microwaves to detect corrosion pitting under coatings. For 1 micron film thickness, there is a phase change of microwaves by 1-1.5 degrees, thereby allowing us to accurately detect the film thickness 2 . Dielectric mixing models can be used to detect porosity, inhomogenity in composites10, delamination in coatings, corrosion pitting, etc.

  References –

  1. Nondestructive Evaluation: Theory, Techniques and Applications; by Peter J. Shull; published by Marcel Dekker, Inc.
  2. Lecture Notes from the course “Nondestructive Testing of Materials” taught by Dr. Reza Zoughi and Dr. Von Richards at the Missouri Univ. of Sci. & Tech.
  3. www.ndt-ed.org
  4. ASTM E1417-05e1, (Standard practice for Liquid Penetrant Testing)
  5. ASTM E94 - 04(2010), Standard Guide for Radiographic Examination
  6. ASTM E1962 - 09, Standard Practice for Ultrasonic Surface Testing Using Electromagnetic Acoustic Transducer (EMAT) Techniques
  7. ASTM E376 - 06, Standard Practice for Measuring Coating Thickness by Magnetic-Field or Eddy-Current (Electromagnetic) Examination Methods
  8. ASTM E1932 - 07, Standard Guide for Acoustic Emission Examination of Small Parts
  9. ASTM E1444 - 05, Standard Practice for Magnetic Particle Testing
  10. ASTM E2533 - 09, Standard Guide for Nondestructive Testing of Polymer Matrix Composites Used in Aerospace Applications