Benchtop X-ray diffraction (XRD) instrument

Powder X-ray diffractometers can readily measure bulk samples if techniques are devised for sample preparation, and measurement conditions are properly set. When measuring samples which have curved surfaces, such as pharmaceutical tablets and ball bearings, various effects are seen due to the curvature, such as shifting of the diffraction angle and widening of the full width at half maximum.

What do you think about when you hear the word chocolate? Yummy! Dark or milk? If you look at the back of your unsweetened/baking cocoa or chocolate you may expect to see cocoa or chocolate. Yes, but what else do you see? You may see "contains X% protein" or "Y% fat and fiber", perhaps more. Dietitians beware; this can significantly alter your caloric intake. Many people use the terms chocolate and cocoa interchangeably.

Barite is primarily used in the oil drilling industry for lubrication of their drill bits during the drilling and cutting process. It is also used in a variety of other applications including pigments, inks, plastics and X-rays. The density and color of this natural mineral make this a valuable product. However, in each application the purity and composition of the contaminants should be closely monitored as it may alter the properties and function of the barite material. Shown in the provided diffractogram is a sample of barite collected on the MiniFlex.

With the MiniFlex300/600, it is possible to select a fine focus tube (focal point size 0.4 x 8 mm²) in addition to a normal focus tube (focal point size 1 x 10 mm²) of the type generally used with powder X-ray diffractometers. Fig. 1 shows an overlay of diffraction peaks obtained by measuring with a normal focus tube and fine focus tube. Table 1 shows a comparison of intensity, and full width at half maximum (FWHM), which varies proportionally with resolution.

Pictured below is a diffractogram comparing the adhesive side of duct tape from different manufacturers. It is used as part of the material identification in forensic labs as every manufacturer uses a slightly different adhesive and a slightly different upper refractory surface with a different web support structure. An XRD scan of the upper surface, using Rigaku's MiniFlex benchtop diffractometer, combined with a scan of the adhesive side is sufficient to identify the duct tape to a specific manufacturer.

Fig. 1 shows the appearance of the MiniFlex300 main unit. The main unit dimensions are 560(W) x 530(D) x 700(H) mm. The water cooling system is integrated into the rear of the unit, so the diffractometer can be setup and used virtually anywhere, as shown in Fig. 2.

Forensic analysis on drugs and pharmaceuticals using XRD identifies compound purity and composition. The analysis is non-destructive and sensitive to the presence of both polymorphs and contaminants. Polymorphs are substances which are chemically identical but have different chemical activity in certain environments, like dextrose and levulose (two forms of C₆H₁₂O₆). Only dextrose is useful to most life forms. A number of instruments can determine the difference between them, but XRD can do it in their solid (crystalline) forms.

General X-ray diffraction phase/composition identification will distinguish the major, minor, and trace compounds present in a sample. The data usually includes mineral (common) name of the substance, chemical formula, crystalline system, and reference pattern number from the ICDD International database. A summary table of analysis results and diffraction plot with reference pattern markers for visual comparison is shown below:

Dr. Joel Sparks, Laboratory Manager, Department of Earth Sciences at Boston University reports:

The MiniFlex300/600 can be equipped with the D/teX Ultra high-speed 1-dimensional detector to obtain greater intensity. By using this detector, it is possible to obtain intensity a few tens to roughly 100 times greater than a scintillation counter. Using this feature, it is possible to greatly reduce measurement time, detect trace components, and measure micro-samples with high sensitivity. Fig. 1 shows the diffraction profiles obtained with a scintillation counter and the D/teX Ultra high-speed 1-dimensional detector.

The MiniFlex300/600 can be equipped with the D/teX Ultra high-speed 1-dimensional detector to obtain greater intensity. This detector energy resolution, so fluorescent X-rays can be removed from the diffraction pattern without using a diffracted beam monochromator. Fig. 1 shows the X-ray diffraction patterns from measuring hematite in the standard energy range (standard mode) and the energy range enabling removal of fluorescent X-rays due to iron (fluorescent X-ray reduction mode).

For industrial samples, quality control or failure analysis is vital to future product improvements. This polypropylene coated metal sample failed quality control tests due to poor coating adhesions. A section of the coating was removed and the entire sample was inserted in the MiniFlex for testing.

Phase identification using X-ray diffraction (XRD) works much like fingerprint analysis. XRD patterns are collected on unknown samples and compared to patterns obtained from known materials. The primary database for these XRD patterns is compiled and maintained by the International Center for Diffraction Data (ICDD). In some industrial cases the preferred XRD patterns for optimal analysis of a specific process may not be present in the ICDD database.

The oil drilling industry can encounter a wide variety of samples, including rocks, scales, cements, cuttings, and muds throughout the drilling process. X-ray diffraction (XRD) is an essential tool for phase identification analysis of these commonly identified solids in the oil field. Three phases are identified in the figure below; the major is a barite phase and the two minor phases consist of calcite and quartz. The primary goal of this application is to quickly identify the phases contained within the sample material.

A common marketing approach in the cosmetics industry today is the branding of natural products. These natural cosmetics claim to use natural ingredients for effects such shine, whitening, and sun protection. X-ray diffraction (XRD ) is an excellent technique to identify the composition of materials in the cosmetics industry. As an example four brands of so called "natural" cosmetic foundations were analyzed for composition using the MiniFlex benchtop diffractometer. The scans and phase identification results can be seen in figures 1 through 4.

Ensuring quality control can be a daunting task in industrial processes. The key to a quality product is to maintain that quality throughout the entire process and having the appropriate materials is essential to this accomplishment. The wrong materials could alter the properties of the desired product. It could even change the product and everyone would certainly want the finished product to be able to function with its desired task. Observe the white powder in Figure 1.

Zeolites are commonly used in a vast variety of industrial applications, including environmental clean-up, petroleum cracking, filtering/separations and cation exchange. These materials can be mined from natural sources or can be commercially synthesized. A basic structure of five silicon and aluminum tetrahedra result in a cage-like structure with large open spaces or "pores". These pores have charged regions which attract or exchange cations. For effective activity and specific cation incorporation, the zeolites need to be very specific and pure.

Crystalline silica is a very common, naturally occurring mineral consisting of silicon and oxygen. Differences in temperatures and pressures can cause the atomic structure to change creating polymorphs of silica. These are commonly known as alpha quartz, beta quartz, cristobalite and tridymite. Damage to lungs and respiratory systems, known as silicosis, can be traced to exposure to very small particles of crystalline silica and acidic reactions within the human body.

TiO₂ is widely used in white pigments, electronics materials, optical catalysts and UV absorbents. It exists in three polymorphs: rutile, anatase and brookite. The efficiencies of rutile and anatase as optical catalysts are different, so a method to determine the rutile:anatase ratio is needed. The quickest way to do quantitative XRD analysis is to determine the RIR (Relative Intensity Ratio). Data from the MiniFlex, profiled below, is of a prepared mixture of rutile and anatase in a 3:1 ratio.

Shale and slate are both metamorphic materials and the two terms are sometimes use interchangeably, but the materials are not the same. Many of the items sold today for landscaping (flagstones, retaining walls) and construction (chalkboards, roofing tiles, pool tables, etc.) uses as "slate " is actually the much more inferior form—shale. Shale is metamorphic clay-like sediments, lightly compacted into thin, crumbly layers. It may contain high concentrations of quartz, feldspars, pyrites amorphous silica, and clay minerals: illite, kaolinite, chlorite and smectite (montmorillionite).

With the MiniFlex300/600, it is possible to select Soller slits with small widths in order to obtain high resolution. In particular, the 0.5° receiving Soller slit and the 5 mm or 2 mm incident high limiting (DHL) slits can suppress the axial divergence, or umbrella effect which is prominent on the low-angle side. Fig. 1 shows a comparison of the X-ray diffraction profiles of zeolite-A when the receiving Soller slit and DHL are changed (the incident Soller slit is 2.5°). Intensity is normalized, and the actual intensity ratios are as shown in Table 1.

XRD can be used to validate minting ages of coins. A 2005 US penny has a zinc metal core and a combination Cu/Nickel alloy coating. Before 1986, the US pennies were comprised entirely of a copper and zinc alloy. When looking at the diffraction patterns from a MiniFlex in the figures it can be seen that no zinc core was discovered in the 1985 penny.

What do greenhouse gases, pearls, antacids, lasers, cement and sea shells have in common? They are all related to calcium carbonate phases. Calcium carbonate is one of the most commonly occurring natural minerals. It can be observed in three different forms, calcite, aragonite and vaterite. Figure 1 shows the calcite and aragonite forms. These forms share the exact same chemical formula, but have a slightly different crystal structure and are known as polymorphs. Polymorphs have different energies of activation, dissolution rates and degrees of reactivity.

Figure 1 shows a diffraction pattern of Painaway, an over-the-counter headache product containing caffeine, aspirin (acetylsalicyclic acid), and acetaminophen. This combination of compounds with caffeine makes the product much more effective. Using the MiniFlex benchtop XRD system, the individual components can easily be determined. The peak positions for caffeine are identified by the purple lines, aspirin positions are marked by the blue lines and the acetaminophen positions are marked by the red lines.