Overview

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Overview

This section brings together a number of applications of powder diffraction around a wide theme of forensic powder diffraction. By this stage you should have a thorough grounding in the background theory and techniques of powder diffraction and this section will bring these together in an overview of important commercial applications. This section comprises four topics, namely patents, polymorphism, and forensic and impurity analyses:

Patents

Patents and intellectual property are responsible for a major part of the gross domestic product of countries where the provision and use of powder diffraction is most widespread. Patents are an agreement whereby inventions, including novel chemical phases, can be given protection by the state. We start with an outline on patents and what they are, and then proceed with an overview of the use of powder diffraction in patents. In particular, we consider the impact of modern drugs and the multi-billion US$ litigations to protect the most valuable patents.

Polymorphism

Polymorphism is the phenomena of a chemical substance exhibiting more than one crystallographic structure. A common example is ice, which has many structural phases, especially at non-ambient pressures. Polymorphism should be distinguished from isomerism, in which the same chemical elements are bonded together in different ways: familiar examples of which are the various forms of carbon such as diamond, graphite, and the various fullerenes. Crystallography is the essential tool for studies of polymorphism since unlike other techniques that may only be sensitive to the chemical entity, crystallography is sensitive to the shape and size of the unit cell, as well as to its contents. One factor in determining whether certain polymorphs form is seeding, and the effect of this will be discussed.

Forensic Analysis (Qualitative)

The forensic applications of powder diffraction are rarely more tested than in archaeological studies where sample preparation, purification, amount, etc. are not a matter of choice or instruction. Metallurgical, mineralogical, pigment, and corrosion analyses can be used to attempt to determine the provenance, history of manufacture and use, authenticity, and indirectly the date of various artefacts and finds. This section describes some analytical uses of powder diffraction of samples of archaeological interest. As has been discussed earlier, powder diffraction was used extensively to test the provenance of the world's most important hoard of late Roman silver.

Impurity Analysis (Quantitative)

The essence of all the examples above often lies not in the simple identification of the major phase in a sample, but more often hinges on the impurities. This section explores the vital questions of impurities and quantitative analysis, starting with a discussion of concentration limits, and finishing with a detailed legal case study to illustrate some of the scientific, forensic, and statistical questions that arise in such cases. This part in particular illustrates such matters with full use of diffraction patterns, which for reasons of confidentiality are not available in many of the other cases above.

We finally conclude with some advice for those who want to get involved in this type of work. It is always worth remembering that powder diffraction work may start of as apparently routine, but end up being quoted and tested in a court of law. This reason alone should be sufficient reason for always obtaining the best, but appropriate, data in powder diffraction experiments.

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