Comparing Fusion, Crushing, and Pelletising Techniques in XRF Labs

In X-ray fluorescence (XRF) laboratories, the choice of sample preparation method determines analytical precision and accuracy by governing sampling representivity, physical stability, and matrix effects. Because the XRF spectrometer interrogates only a small volume of material, any heterogeneity introduced or left unresolved during preparation is expressed directly in the reported result. Sample preparation techniques therefore function as analytical controls, each addressing a specific limitation associated with solid samples rather than serving as interchangeable processing steps. Crushing, pelletising, and fusion differ in how much variability they suppress, how much effort they require, and which sources of uncertainty remain present at the point of analysis. Comprehending such differences is central to selecting an XRF sample preparation strategy that supports both the analytical goal and the constraints of routine XRF lab operation.

Crushing in XRF Labs

Crushing is the starting point for almost every solid sample analysed in XRF labs. Its purpose is straightforward but vital: to reduce heterogeneous bulk material into a form that can be reliably subsampled. If representivity is lost at this stage, no downstream technique can recover it.

Crushing techniques

• Jaw crushers

Used as the primary crushing step within XRF labs, jaw crushers process large, hard materials like rocks, ores, slags, and cement products. They offer high throughput and mechanical reliability, producing a coarse but consistent output that supports representative subsampling and further size reduction without introducing significant sampling bias.

• Vibratory disc mills

Following primary crushing, vibratory disc mills reduce material to analytical fineness, typically below 75 microns. At this particle size, segregation effects are minimised and powders behave more predictably during preparation. Disc milling is thus a common requirement for both pelletising and fusion workflows.

Comparing crushing with pelletising and fusion

When compared with pelletising and fusion, crushing provides the lowest level of analytical refinement. Crushing improves the representivity of the analytical sample relative to the bulk material but does not stabilise the analytical surface or remove mineralogical effects. Crushing alone is rarely sufficient for direct XRF analysis. Its value lies in producing, for XRF analysis, a representative intermediate material suitable for pelletising or fusion. Be mindful, however, that poor crushing cannot be corrected by pelletising or fusion, which makes it a critical technique for establishing representativity at the start of the XRF sample preparation workflow despite its limited analytical reach.

Pelletising in XRF Labs

Pelletising converts finely crushed and milled powder into a dense, self-supporting disc through mechanical compaction. The resulting surface improves physical consistency for XRF analysis without altering sample chemistry.

Pelletising techniques

• Manual hydraulic pellet presses

Apply mechanical pressure to compact finely milled powder into a solid disc, often with a binder to improve cohesion. This produces a flat, mechanically stable analytical surface that is easier to measure than loose powder and delivers more consistent XRF results. Since pressure and handling are controlled manually, some variability between pellets can occur.

• Automated pellet presses

Utilise the same compaction principle while controlling pressure, dwell time, and decompression automatically. Controlled automation reduces operator-related variability and yields pellets with more consistent density and surface quality. These systems are well suited to higher sample throughput where reproducibility becomes increasingly important.

Comparing pelletising with crushing and fusion

Pelletising improves XRF performance beyond crushing by increasing sample density and stabilising sample surface during measurement, leading to more consistent X-ray intensities and improved precision. However, such benefits rely on the representivity already established during crushing, as pelletising does not correct bulk sampling bias. Unlike fusion, pelletising preserves the original mineral structure of the XRF sample, maintaining higher sensitivity for trace elements through avoiding dilution with flux. That same mineral structure introduces absorption and particle size effects but requires greater preparation effort compared to crushing alone. Pelletising thus occupies an intermediate role in XRF sample preparation, offering greater control and precision than crushing while stopping short of the full chemical homogenisation achieved with fusion.

Fusion in XRF Labs

Fusion represents the highest level of sample preparation used in XRF labs and differs fundamentally from both crushing and pelletising. Instead of improving physical uniformity, fusion generates chemical homogeneity. Its purpose is to eliminate mineralogical and matrix-related variability by converting the XRF sample into a chemically uniform state.

Fusion techniques

• Borate fusion

The XRF sample is dissolved in a lithium borate flux and cast into a glass bead. This process destroys original mineral phases and eliminates grain-size effects, preferred orientation, and most matrix-related variability. The elimination of mineralogical and matrix-related variability yields a fused glass bead with a uniform analytical surface and predictable X-ray behaviour.

• Gas fusion systems

Designed to maximise throughput, gas fusion systems utilise high thermal energy and rapid heating cycles to process large numbers of samples efficiently using standard fusion recipes.

• Electric fusion systems

Offer precise temperature control through programmable heating profiles, making them a good fit for complex matrices and samples containing volatile components.

Comparing fusion with crushing and pelletising

Crushing and pelletising address different analytical limitations to fusion. Crushing improves bulk representivity by reducing sampling bias, but it does not resolve mineralogical or chemical variability within the material. Pelletising stabilises physical measurement conditions, yet original mineral phases remain intact. Fusion goes beyond both techniques through removing chemical and mineralogical variability entirely, producing a homogeneous material for analysis. This enables higher accuracy for major element determination than pelletising or crushing can achieve, albeit with longer preparation times, higher consumable use, and reduced trace element sensitivity due to dilution.

Integrating Crushing, Pelletising, and Fusion with XRF Scientific

XRF Scientific equips XRF labs with dedicated tools for crushing, pelletising and fusion, including jaw crushers, disc mills, pellet presses, fusion systems, and certified fluxes. By applying the right equipment for the different stages of XRF sample preparation, laboratories can undertake preparation methods that align with their analytical objectives, performance requirements, and material behaviour. Connect with our experts to uncover more information about our XRF sample preparation solutions.