Hygroscopic compounds are substances that absorb moisture from their surrounding environment, which is a critical property of many inorganic compounds, particularly those found in atmospheric aerosols, construction materials, pharmaceuticals, and engineered composites [1] [2] . In inorganic chemistry and materials science, understanding hygroscopic behavior is essential for predicting stability, performance, and environmental interactions of substances under varying humidity conditions [3] - [5] .

Solid accumulation in upstream oilfield facilities is a common issue that can lead to equipment blockage, reduced flow efficiency, and operational downtime [1] [6] . These solids originate from a variety of sources, including:

Understanding the composition of these solids is essential for developing mitigation strategies. However, some of these materials are hygroscopic, meaning they absorb atmospheric moisture [3] [4] . This moisture absorbance can lead to changes in crystallinity, peak broadening, or even full structural transformation factors that severely affect the accuracy of X-ray diffraction (XRD) analysis [7] .

XRD remains a fundamental tool for identifying crystalline phases in solid samples [7] [9] . However, the reliability of the technique relies heavily on proper sample handling and preparation [2] [10] . This study aims to investigate how humidity affects the diffraction patterns of representative hygroscopic compounds and to recommend best practices for dealing with such materials in analytical laboratories [2] .

A recent study by Randhawa (2022) leverages water contact angle measurements and surface energy analyses to systematically investigate how these additives influence the hygroscopic response of PA6 composites. Results indicate that boron reinforcements, particularly h-BN, effectively impede water absorption: as water conditioning time increases, composite surface energies decrease while contact angles increase, signaling restricted moisture uptake [11] .

Critically, delaying water penetration using boron-based fillers helps maintain integrity in mechanical performance and tribological behavior over time. The study also quantifies how these composites evolve under prolonged water exposure, detailing changes in strength, hardness, and friction properties across conditioning intervals [11] .

The aim of this study is to characterize selected hygroscopic compounds under dry and moisture-absorbed conditions, and to evaluate how environmental exposure affects their diffraction patterns. Specifically, we seek to:

-Analyze peak position and width (FWHM) changes in dry vs. wet states. Scherrer crystallite size calculations were performed only for samples with well-defined, isolated peaks and minimal phase interference (e.g., calcium carbonate), as other samples exhibited peak overlap, amorphous signals, or significant chemical instability under moisture, making them unsuitable for accurate calculation.

-Apply the Scherrer equation to estimate crystallite size.

-Identify trends in structural stability across sample types.

-Recommend best practices for handling moisture-sensitive solids during XRD analysis.

Six compounds were selected for this study: Ammonium Persulfate, Calcium Carbonate, Lithium Meta-borate, Calcium Aluminate Cement, Gypsum, and Sodium Chloride. All compounds were obtained and prepared by the manufacturer. Prior to analysis, they were stored under controlled conditions to prevent contamination or degradation. Each material was analyzed using XRD in both dry and moisture-affected (wet) states.

X-ray diffraction was conducted using a Bruker D8 Advance diffractometer equipped with Cu Kα radiation (λ = 1.5406 Å). The samples were scanned from 5˚ to 70˚ 2θ at a step size of 0.02˚ with sufficient dwell time to resolve sharp peaks.

Dry samples were prepared at normal room temperature, while wet samples were exposed to a high-humidity environment by placing them uncovered in a laboratory room with elevated ambient humidity for a period ranging from two days to one week prior to wet-state XRD analysis. Moisture uptake was assessed qualitatively through visual inspection of surface changes, without performing weight measurement.

FWHM and peak positions were compared between dry and wet conditions to assess crystallinity and structural change.

The selected compounds represent a range of hygroscopic behaviors, from highly moisture-sensitive to completely stable. This diversity enables a comprehensive evaluation of how moisture affects XRD patterns across different material classes:

-Ammonium Persulfate ((NH₄)₂S₂O₈) is a highly hygroscopic oxidizer known for rapid decomposition in humid environments. It was chosen to demonstrate extreme degradation in crystallinity.

-Calcium Carbonate (CaCO₃) is affected by moisture and is commonly found in oilfield scales. Its strong (104) peak makes it suitable for quantitative FWHM analysis.

-Lithium Meta-borate (LiBO₂) is used as a flux in XRF sample preparation. It transforms easily between semi-crystalline and amorphous states upon humidity exposure.

-Calcium Aluminate Cement (CAC) undergoes significant hydration reactions, forming new crystalline phases such as C₃AH₆ and C₂AH₈. It illustrates real-world chemical phase transitions.

-Gypsum (CaSO₄∙2H₂O) is a naturally hydrated mineral with stable crystalline water. It is included to show mild peak distortion in response to added moisture.

-Sodium Chloride (NaCl) is non-hygroscopic and structurally stable under all tested conditions. It serves as a control reference for comparison and calibration.

This selection allows the study to span the spectrum from unstable to inert materials, enhancing the relevance of the conclusions to both analytical laboratories and field applications.

Table 1 compares key diffraction parameters before and after moisture exposure for each sample:

To evaluate the impact of moisture on crystallite size, the Scherrer equation was applied using the main peak of dry calcium carbonate at 2θ = 29.4˚, with an FWHM of 0.14˚:

$\text{D}=\left(\text{K}\times \lambda \right)/\left(\beta \times \cos \theta \right)$

where:

•D = Crystallite size

•K = 0.9 (shape factor)

• λ = 1.5406 Å (Cu Kα radiation)

• β = 0.00244 rad (converted from 0.14˚)

• θ = 14.7˚ ≈ 0.2567 rad

This yields a crystallite size of approximately 58 nm for the dry state.

After moisture exposure, the FWHM increased to 0.20˚, corresponding to a reduced crystallite size of approximately 41 nm.

This broadening of peaks suggests enhanced structural disorder or lattice strain due to water absorption, confirming the material’s sensitivity to humidity.

Note: Only calcium carbonate was selected for crystallite size analysis because it exhibited a single, well-defined primary peak with minimal phase interference. Other materials showed overlapping peaks, amorphous background signals, or significant structural instability under moisture, making them unsuitable for accurate Scherrer-based size calculation.

This study demonstrates the significant structural impact that moisture absorption can have on hygroscopic materials when analyzed by X-ray diffraction (XRD).

The comparison between dry and wet states revealed that compounds such as ammonium persulfate, calcium carbonate, and lithium meta-borate are particularly prone to peak broadening, intensity loss, and phase transformations. These effects were clearly observable in their XRD patterns, indicating a degradation of crystallinity.

In contrast, sodium chloride remained structurally stable, showing no significant changes after moisture exposure, validating its use as a reliable reference material in mineralogical analysis.

However, this study is limited by the use of a relatively small number of samples and the focus on selected hygroscopic compounds. Future work should include a wider range of materials and controlled humidity conditions to improve the generalization of the results.