EBS 325 – Analytical Chemistry Laboratory Introduction To X-Ray Analysis

1. EBS 325 – Analytical Chemistry LaboratoryIntroduction To X-Ray Analysis School of Materials & Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia. By Mr. Samayamutthirian Palaniandy

2. OUTLINE SAMPLING & SAMPLE PREPARATION XRF XRD

3. SAMPLING & SAMPLE PREPARATION FOR X-RAY ANALYSIS

4. SAMPLING & SAMPLE PREPARATION FOR X-RAY ANALYSIS SAMPLE PREPARATION SAMPLING

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6. GARBAGE IN.......GARBAGE OUT

7. PROPER PREPARATION FOR BEST RESULT Glass Plastics Papers

8. X-RAY analytical errors Sampling Sample preparation Instrumental Standards Statistical

9. SAMPLE • A means by which units are taken from a • population in such a way as to represent the • characteristics of interest in that population.

10. FAQ about samples and sampling accurate representative Well-mixed homogeneous. The equipment does what we want. random Our sampling frequency is fine.

11. Reasons for poor procedures, equipment, and practices of SAMPLING. Lack of knowledge of the consequences of poor sampling. Lack of knowledge of the sampling theory. Trying to save money.

12. Questions to be answer before sampling WHAT is being sampled? WHY is the sample being taken? WHO is taking the sample? WHERE is the sample taken? WHEN and with what frequency is the sample taken? HOW is the sample taken? HOW MUCH material is in the sample•?

13. EXAMPLES OF SAMPLING METHODS Coning & quartering Grab sampling Riffle splitter Fractional shoveling Paper cone riffle splitter

14. CONING AND QUATERING

15. RIFFLE SPLLITING

16. PAPER CONE RIFFLE SPLITTER

17. Fractional Shoveling

18. Grab Sampling Consist of taking a sample using scoop or spatula by simply inserting the sampling device into the sample container and removing an aliquot

19. Sample Mixing Flowing Liquids or Gases A correct cross stream sample may be impossible to obtain. A static mixer can reduce the Grouping and Segregation Error.

20. Precision of Sub-sampling Methods Gerlach, Dobb, Raab, and Nocerino, 2002 Journal of Chemometrics “Gy Sampling in experimental studies. 1. Assessing soil splitting protocols” 16, 321-328

21. Your decisions are only as good as your samples. Your samples are only as good as your sampling systems. Your sampling systems are only as good as your audit and assessment. Summary

22. X-RAY analytical errors Sampling Sample preparation Instrumental Standards Statistical

23. Analytical errors – sampling • Sample must be representative of the process • Sampling must be reproducible (i.e. should be able to take identical duplicate samples)

24. Sample preparation methods must Simple Rapid Reproducible Low cost

25. Quality of sample preparation The quality of sample preparation is at least as important as the quality of the subsequent measurements.

26. Quality of sample preparation An ideal sample would be: • Representative of the material • Homogenous • Of infinite thickness • Without surface irregularities • With small enough particles for the wavelengths being measured

27. SAMPLES METAL POWDER LIQUID XRD and XRF XRF only Why???

28. XRD Working Concept When a monochromatic x-ray beam with wavelength  is incident on the lattice planes in a crystal planes in a crystal at an angle , diffraction occurs only when the distance traveled by the rays reflected from successive planes differs by a complete number n of wavelengths. By varying the angle , the Bragg’s Law conditions are satisfied by different d-spacing in polycrystalline materials. Plotting the angular positions and intensities of the resultant diffraction peaks produces a pattern which is characterised of the sample. Where a mixture of different phases is present, the diffractogram is formed by addition of the individual patterns.

29. XRF Working Concept In X-ray fluorescence spectroscopy, the process begins by exposing the sample to a source of x-rays. As these high energy photons strike the sample, they tend to knock electrons out of their orbits around the nuclei of the atoms that make up the sample. When this occurs, an electron from an outer orbit, or “shell”, of the atom will fall into the shell of the missing electron. Since outer shell electrons are more energetic than inner shell electrons, the relocated electron has an excess of energy that is expended as an x-ray fluorescence photon.  This fluorescence is unique to the composition of the sample. The detector collects this spectrum and converts them to electrical impulses that are proportional to the energies of the various x-rays in the sample’s spectrum.

30. METAL CHIPS POLISHING SOLUTION LIQUID REMELT BELT GRINDER/ LATHE CAST INGOT X-RAY ANALYSIS

31. POWDER SOLUTION GRINDING PRESS FUSION LIQUID GLASS BEAD PELLET X-RAY ANALYSIS

32. LIQUID LIQUID HOLDER DROP METHOD SPOT ANALYSIS DDTC METHOD FILTER X-RAY ANALYSIS

33. Sample types Solids Pressed powders Fused beads Liquids

34. Solids • metal alloys, plastics & glass • relatively easy to prepare by cutting, machining, milling % fine polishing • Avoid smearing of soft metals (e.g. Pb) • Polishing may introduce contamination from the polishing material • do not have particle size problems • Surface needs to be flat • Surface needs to be homogeneous • Surface defects are more critical for light elements if good accuracy is required.

35. Pressed powders • Typical samples types that are prepared as pressed powders include rocks, soil, slag, cements, alumina, fly ash, etc. • Particle size of powder needs to be controlled for light element analysis • If necessary, powders are ground to achieve a particle size of < 50 µm • Grinding can be introduce contamination (e.g. Fe from a chrome steel mill) • Binding agents (e.g. wax or cellulose) can be used to increase sample strength to avoid breakage in the spectrometer • Ground powders are pressed into a solid tablet under pressure using a hydraulic press & 40 mm die • Relatively slow method (≈5 minutes per sample) but relatively low cost • Pressed powders suffer from particle size problems for light elements Preparation equipment needed includes: • Grinding mill and vessel (chrome steel, zirconia, tungsten carbide, etc.) • Hydraulic press and die (usually 40 mm) • Binding agents

36. Fused beads • Typical samples that are prepared as fused beads include rocks, cements, iron ores, etc. when higher accuracy is required. • Weighed sample is mixed with flux • Sample and flux are melted at ≈ 1000 oC • Melt is poured into a 40 mm mold • Bead surface needs to be homogenous (constant color without cracks) • Slow (10-15 minutes/sample) • High cost • Important benefit is that particle size problems disappear (fusion process results in a homogeneous glass) • An additional benefit is that the melting flux (usually Na or Li borate) dilutes the sample, reducing matrix variations, resulting in higher accuracy • Disadvantage –reduced sensitivity for trace elements Preparation equipment includes: • Fusion device (manual or automatic) • Pt/Au crucible(s) & mould(s) • Fusion (melting) flux • A non wetting agent (e.g. KI or LiBr) is sometimes used to help produce a better quality bead and to assist with cleaning the Pt/Au crucible & mould between samples

37. Liquids • Typical samples include environmental (waters, mud) & oils • Easiest to prepare • Should have a constant volume that exceeds maximum penetration depth • Sample is poured into a liquid cell fitted with a thin plastic window • Range of window materials to suit different liquids • Fill to a constant height (e.g. 20 mm) to avoid errors from variable depth • Choose the correct thickness and material to suit the chemistry of the sample being measured • Na is lightest element that can be detected in liquids.

38. Influence of sample preparation

39. Factor of errors in Sample Preparation Grain size and surface roughness Uniformity of sample Contamination through the sample preparation

40. Grain size and surface roughness

41. Uniformity of sample Sand molding Metallic Sample Metal molding Casting condition of the sample in the molding. X-ray intensities differ according to the molding method which comes In the measurement of light elements. Quenching casting which makes the metallic composition fine produces good results Sample polishing

42. Uniformity of sample Contamination during polishing As the contamination form the polishing belt to the sample, the re contamination from The material of the polishing belt and from the remaining trace elements of polished Sample. Contamination effect when carbon steel and Ni-Cr alloy polish after polishing stainless steel.

43. Powder Sample Grinding Condition Different grinding condition cause variation in particle size distribution which leads to variation in X-Ray intensity.

44. Powder Sample Contamination Contamination from the grinding mill and media Brequetting Usual forming pressure – 20 tons with 40mm diameter. X-Ray intensities varies with variation of forming pressure (especially when pressure is low).

45. XRD & XRF ANALYSIS

46. Identification If you are given with four bottles of white powder. What will you do to identify them? CaO,CaCO3,CaMg(CO3)2 Ca(OH)2 etc.

47. What is X-ray diffraction? • non-destructive analytical technique for identification and quantitative determination of the various crystalline forms, known as ‘phases’. • Identification is achieved by comparing the X-ray diffraction pattern

48. Diffractograms and ICDD Card

49. What is X-ray diffraction? XRD able to determine : • Which phases are present? • At what concentration levels? • What are the amorphous content of the sample?

50. How does XRD Works??? • Every crystalline substance produce its own XRD pattern, which because it is dependent on the internal structure, is characteristic of that substance. • The XRD pattern is often spoken as the “FINGERPRINT” of a mineral or a crystalline substance, because it differs from pattern of every other mineral or crystalline substances.