X-Ray Analysis of Ceramics:A Look into How X-Ray Technology is Utilized in the Ceramic IndustryDan Davis and Robert H. Clifford, Ph.DFebruary 2013

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Introduction

Ceramics are found in most aspects of daily life, as society continues to rely on their versatility. Ceramics are sought after for their strength, making them good structural materials, as well as insulators for heat and electricity. Glass-ceramics are also used to make optical equipment and fiber insulation.

Other attributes: Hardness Abrasion resistance Chemical resistance, especially to caustic applications

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Introduction

As the complexity of ceramic materials evolves, techniques and technologies are required to study, identify and measure them.

Non-destructive X-ray spectrometry is a technique that quickly addresses important questions such as:

Elemental composition Arrangements of those elements Quantity of elements and compounds

This information is needed from the mining of raw materials to the finishes applied to them as final products.

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X-Ray Fluorescence vs. X-Ray Diffraction

This presentation describes two aspects of X-ray spectroscopy:

X-ray fluorescence (XRF) X-ray diffraction (XRD)

These technologies are well-established and used in various industries to answer the same questions of elemental composition and how those elements are connected.

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X-Ray Fluorescence vs. X-Ray Diffraction

Example: Diamonds and Graphite

Although they are made from the same element (carbon), they are two very different compounds with different physical properties.

XRF — Identifies that both compounds are 100% carbon

XRD — Reveals how carbons are connected to each other, which gives diamonds and graphite different properties and values

XRF and XRD spectroscopy provide different information but can complement each other.

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How Does This Apply to Ceramics?

All ceramics have one thing in common:

They did not start out as ceramics. Raw materials were processed to make them.

Consider historic ceramics:

They began as clay and were processed into ceramic materials and objects.

These starting materials need to be mined, identifiedand refined.

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XRD Spectroscopy

XRDs are well-suited for identifying types of clay

Each clay has a specific elemental composition and arrangement of those elements. This gives each type of clay a unique diffraction pattern similar to a fingerprint.

XRDs are used in mining industries to quantify the clays contained in the mines.

Samples are taken and processed by different techniques to achieve a powder sample that can be analyzed.

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Bentonite: a clay consisting mostly of montmorillonite and other minerals.

Industrial applications include:

Mud drilling component Cement additive Making green sand for sand casting Protein absorber in wine making

Diffraction Pattern of Bentonite

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Diffraction Pattern of Bentonite

Figure 1: X-Ray Diffraction of Bentonite Clay (top) and spectral reference of the minerals identified, montmorillonite, quartz, calcite, and cristobalite

Figure 1 shows a diffraction pattern of a sample of bentonite.

Depending on the application, certain ratios or particular minerals are more favorable for different applications.

Therefore, it is useful to be able to quantitate the different minerals contained in the bentonite sample.

Quantitation can be achieved by a few different techniques that are applied to the spectra.

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XRD Quantitation

Empirical Calibration

Response for measureable signal is related to a concentration of that particular analyte

Quantitation of particular minerals is performed by identifying peaks for the minerals of interest and measuring the responses for those minerals at different concentrations.

This generates a calibration curve.

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XRD Quantitation

Refinement

This process models the identified minerals onto the spectra collected.

It uses ratios of the intensities of the minerals to calculate relative concentrations of each mineral to give a semi-quantitative determination.

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XRF Spectroscopy

XRFs have been applied as a tool for the formulationsof ceramics and for impurity testing of raw materials used in manufacture of medical implants:

Good sensitivity Wide elemental analysis range Simple sample preparation techniques

Systems can have elemental ranges for elements as light as beryllium and as heavy as uranium with sensitivity to the parts per million (ppm) level.

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XRF Spectroscopy

Analysis time for XRF measurements is based on desired level of sensitivity

Range from tens of seconds to a few hundred seconds for trace-level determinations

For analysis of materials where light elements are of interest at lower concentrations, removal of atmosphere is required. Commonly practiced methods for this are:

Removal by vacuum system Displacement using a light element gas purge

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XRF Analysis of Mixed Oxides

Figure 2: XRF scan of ceramic medical implant material with iron impurity

 

 

Figure 2 shows the spectra from the analysis of a sample of mixed oxides used in the manufacturing of a medical implant composed mostly of zirconia oxide.

Analysis identified the expected oxides of zirconia, yttrium and hafnium.

Iron was identified as the impurity in the material and quantitated to trace levelof 0.16%

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More XRF Characteristics

Variety of sample forms, ranging from bulk items topowder samples

Small samples (e.g., powders) are placed/packed insample cups or pressed into discs or pellets for analysis. See Figure 3.

Packing and pressing help reducescattered X-rays by increasing thedensity of the sample, whichimproves sensitivity.

Figure 3:Powder Sample Prep

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XRF Analysis of Heavy Metals

X-ray spectroscopy can measure the finishes applied to products for performance purposes or safety reasons(e.g., metal leaching), particularly as it relates toheavy metals.

XRF is well-suited for this analysis because finishedproducts can be measured with little to no sample prep.

Some XRF systems can accommodate fairly large samples, which increase their flexibility by enabling awide variety of samples to be analyzed.

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XRF Analysis of Heavy Metals

Figure 4: Spectra of drinking mug where lead contamination is identified; the mug is placed directly in the sample compartment.

 

Figure 4 shows a drinking mug placed in the sample compartment for analysis.

Analysis of the mug identified that the mug contained lead.

The XRF system determined that the lead levels were in 2,352 ppm.

Lead is a metal that can be leached out of materials with water. Elevating the temperature of the water or reducing its pH increases the rate of leachability.

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XRF Analysis of Heavy Metals

Measurements were conducted on finished and non-finished surfaces of the mug.

This technique determined that lead was contained in the glaze of the mug.

That was of additional concern, as the likelihood of exposure is increased as the lead is contained in a contact surface.

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XRF in Manufacturing

XRF can be used in developing finishes and monitoring the manufacturing and application of these finishes, which impart particular attributes to products.

By adding particular components to ceramic finishes, desired functions can be imparted.

Example: Adding materials to glazes that make their surfaces anti-microbial. These materials contain elements that can be measured by XRF. X-ray spectroscopy also can be used to ensure appropriate levels of microbial-inhibiting materials are added to the glazes, and that the application of the glazes to the products achieves the desired effect.

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Conclusion

X-ray spectroscopy is used in the ceramics industry in many ways, from identifying materials that begin in the mining of raw materials to quantifying minerals and contaminants in those materials.

These techniques are rapid and nondestructive, and they give information about elemental composition and the arrangement of those elements.

XRFs and XRDs answer different questions, but they can be used together to get a more complete picture of the materials used in the ceramics industry.