Formation Of Crystal Nuclei Research Articles

RESEARCH OF PHASE FORMATION IN TRANSPARENT GLASS-CERAMIC PROTECTIVE COATINGS FOR CERAMOGRANITE

The perspective of the development and introduction of porcelain stoneware by domestic producers using natural raw materials from the subsoil of Ukraine for the needs of the raw material and fuel-energy complex in the conditions of military operations has been established. The need to create new types of ceramic granite was determined, taking into account new approaches, regarding the use of alternative raw materials and modern technological principles of creating nanostructured glass materials. The purpose and tasks of the work are formulated, which determine the need to study the structure and phase composition of porcelain stoneware under the conditions of high-speed heat treatment. A hypothesis has been formulated regarding the production of transparent wear-resistant protective coatings based on high-calcium alkaline aluminosilicate frits, which consists in the possibility of forming a strengthened optically transparent sytalized glass structure with a high-speed heat treatment mode and the flow of surface crystallization to ensure a wear-resistant structure of the 4th degree. The processes of phase formation that take place during the heat treatment of the base frit and the protective coating for porcelain stoneware have been studied and the priority role of the metastable phase separation of glass in the formation of the sytalized structure has been determined. It was established that the formation of crystallization nuclei by means of metastable phase separation allows for the formation of a sytalized structure of the protective coating for ceramic granite with the content of crystalline phases of anorthite with a size smaller than the wavelength in the visible part of the spectrum and α-corundum in the near-surface layers of the glaze, which simultaneously ensures optical transparency and wear resistance of the developed coating. Transparent glass-ceramic coatings with high operational properties, developed and implemented in the production conditions of PrJSC «KhPZ», will significantly increase the competitiveness of domestic ceramic tiles and contribute to the stabilization of the market in the conditions of sustainable development of the state.

Phase and thermal diffusivity variation of saline water diagnosed by visual and temperature method during freezing process

Freezing step is a fundamental physical phenomenon of cooling a liquid formulation for guaranteeing product quality. In this study, freezing process of saline water under various concentrations was monitored through the visual and temperature methods. The formation of the ice crystal nuclei at the supercooling stage, and the increase of ice and ice/water layers were observed. The formation of the ice crystal nuclei and ice layer was affected by the location of vials placed on a shelf and the concentration of saline water. A saline water solution at a higher concentration had a lower ice layer height under the same freezing settings. The location of vial on the shelf affects the stability and efficiency of thermal transmission. Moreover, the concentration of saline water has the relationship with the thermal diffusivity, and ice layer is an indicator of variation of temperature and thermal diffusivity for saline water during freezing process. This study was able to replicate and observe the physical phenomena of the formation of ice crystal nuclei and the ice layer during the freezing process under laboratory conditions; as well as show how the specific concentration of the saline water solution affected the developmental speed of the ice layer.

Removal of internal lipids enhances the effect of proanthocyanidins on maize starch retrogradation

Internal lipids of normal amylose (NMS) and two high amylose (HMS56, HMS72) maize starches were removed to investigate the effect of proanthocyanidins (PA) on starch short-term (1 d) and long-term (21 d) retrogradation. Removal of internal lipids decreased the degree of retrogradation in PA-starch complexes after 1 d and 21 d retrogradation. The relative crystallinity (RC) of PA-NMS, PA-HMS56 and PA-HMS72 without internal lipid complexes after short-term retrogradation decreased by 5.46 %, 6.47 % and 7.52 % when the addition of PA was 10 %, respectively, compared with corresponding samples without PA. Compared with PA-native starch complexes, PA-starch without internal lipids complexes had lower correlation length (ξ) and tended to form smaller polymeric assemblies suggesting that the size of aggregates growing within gels was decreased because more PA molecules impeded the reformation of ordered starch structures. Removal of internal lipids exposed hydrogen bonds and the cavities of amylose, promoting the interaction between PA and amylose and more formation of PA-amylose complexes, which in turn reduced amylose available for crystal nucleus formation delaying retrogradation. Overall, retrogradation could further slow down by PA after internal lipid removal, which provided a new perspective for enhancing the modification effect of PA on starch.

Optimization of polypropylene high-strength injection molding welding and interface structure analysis

Secondary injection molding is an effective method for joining polymer parts, where the weld interface plays a critical role in the overall performance of the part. This study discusses the influence of injection molding parameters on the interface strength of polypropylene and polypropylene (PP-PP) secondary injection molding and analyzes the welding interface structure. The injection molding parameters for PP-PP were optimized using the Taguchi method and the signal-to-noise ratio (S/N). The optimal injection molding parameters were determined to be a mold temperature of 120°C, injection temperature of 350°C, and injection speed of 100 mm/s. The interface tensile strength was measured at 33.42 MPa, corresponding to 98.1% of the tensile strength of the base material. Among these parameters, mold temperature has the greatest influence on the strength of the welding interface. Secondly, polarizing microscopy, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) were employed to observe and analyze the crystal structure and fracture failure modes at the interface. The results indicate that elevated injection molding parameters promote the formation of crystal nuclei and spherulite growth at the secondary melt interface, with the spherulite size at the interface significantly affecting the interface strength. This study offers valuable reference for the welding of other polymers and fiber-reinforced materials.

Room-Temperature Single-Phase Synthesis of Semiconducting Metal-Covalent Organic Frameworks With Microenvironment-Tuned Photocatalytic Efficiency.

In order to improve the solubility of metallated monomers and product crystallinity, metal-covalent organic frameworks (MCOFs) are commonly prepared via high-temperature sol-vothermal synthesis. However, it hampers the direct extraction of crystallization evolution information. Exploring facile room-temperature strategies for both synthesizing MCOFs and exploiting the crystallinity mechanism is extremely desired. Herein, by a novel single-phase synthetic strategy, three MCOFs with different microstructure is rapidly prepared based on the Schiff base reaction between planarity-tunable C3v monomers and metallated monomers at room temperature. Based on detailed time-dependent experiments and theoretical calculations, it is found that there is a planarity-tuned and competitive growth relationship between disordered structures and crystal nucleus for the first time. The high planarity of monomers boosts the formation of crystal nucleus and rapid growth, suppressing the forming of amorphous structures. In addition, the microenvironment effect on selective photocatalytic coupling of benzylamine (BA) is investigated. The strong donor-acceptor (D-A) MCOF exhibits efficient photocatalytic activity with a high conversion rate of 99% and high selectivity of 99% in 5h under the 520nm light irradiation. This work opens a new pathway to scalable and efficient synthesis of highly crystalline MCOFs.

Correlation of microstructure and magnetic softness of Si-microalloying FeNiBCuSi nanocrystalline alloy revealed by nanoindentation

Abstract Compared to the commercial soft-magnetic alloys, the high saturation magnetic flux density (B s) and low coercivity (H c) of post-developed novel nanocrystalline alloys tend to realize the miniaturization and lightweight of electronic products, thus attracting great attention. In this work, we designed a new FeNiBCuSi formulation with a novel atomic ratio, and the microstructure evolution and magnetic softness were investigated. Microstructure analysis revealed that the amount of Si prompted the differential chemical fluctuations of Cu element, favoring the different nucleation and growth processes of α-Fe nanocrystals. Furthermore, microstructural defects associated with chemical heterogeneities were unveiled using the Maxwell–Voigt model with two Kelvin units and one Maxwell unit based on creeping analysis by nanoindentation. The defect, with a long relaxation time in relaxation spectra, was more likely to induce the formation of crystal nuclei that ultimately evolved into the α-Fe nanocrystals. As a result, Fe84Ni2B12.5Cu1Si0.5 alloy with refined uniform nanocrystalline microstructure exhibited excellent magnetic softness, including a high B s of 1.79 T and very low H c of 2.8 A/m. Our finding offers new insight into the influence of activated defects associated with chemical heterogeneities on the microstructures of nanocrystalline alloy with excellent magnetic softness.

Amorphous Solid Dispersions: Implication of Method of Preparation and Physicochemical Properties of API and Excipients.

The present study investigated the effect of different polymers and manufacturing methods (hot melt extrusion, HME, and spray drying, SD) on the solid state, stability and pharmaceutical performance of amorphous solid dispersions. In the present manuscript, a combination of different binary amorphous solid dispersions containing 20% and 30% of drug loadings were prepared using SD and HME. The developed solid-state properties of the dispersions were evaluated using small- and wide-angle X-ray scattering (WAXS) and modulated differential scanning calorimetry (mDSC). The molecular interaction between the active pharmaceutical ingredients (APIs) and polymers were investigated via infrared (IR) and Raman spectroscopy. The in vitro release profile of the solid dispersions was also evaluated to compare the rate and extend of drug dissolution as a function of method of preparation. Thereafter, the effect of accelerated stability conditions on the physicochemical properties of the solid dispersions were also evaluated. The results demonstrated higher stability of Soluplus® (SOL) polymer-based solid dispersions as compared to hydroxypropyl methylcellulose (HPMC)-based solid dispersions. Moreover, the stability of the solid dispersions was found to be higher in the case of API having high glass transition temperature (Tg) and demonstrated higher interaction with the polymeric groups. Interestingly, the stability of the melt-extruded dispersions was found to be slightly higher as compared to the SD formulations. However, the down-processing of melt-extruded strands plays critical role in inducing the API crystal nuclei formation. In summary, the findings strongly indicate that the particulate properties significantly influence the performance of the product.

Formation of a zirconium oxide crystal nucleus in the initial nucleation stage in aluminosilicate glass investigated by X-ray multiscale analysis

Understanding the nucleation mechanism in glass is crucial for the development of new glass-ceramic materials. Herein, we report the structure of a commercially important glass-ceramic ZrO2-doped lithium aluminosilicate system during its initial nucleation stage. We conducted an X-ray multiscale analysis, and this analysis was used to observe the structure from the atomic to the nanometer scale by using diffraction, small-angle scattering, absorption, and anomalous scattering techniques. The inherent phase separation between the Zr-rich and Zr-poor regions in the pristine glass was enhanced by thermal treatment without changing the spatial geometry at the nanoscale. Element-specific pair distribution function analysis using anomalous X-ray scattering data showed the formation of a liquid ZrO2-like local structural motif and edge sharing between the ZrOx polyhedra and (Si/Al)O4 tetrahedra during the initial nucleation stage. Furthermore, the local structure of the Zr4+ ions resembled a cubic or tetragonal ZrO2 crystalline phase and formed after 2 h of annealing the pristine glass. Therefore, the Zr-centric periodic structure formed in the early stage of nucleation was potentially the initial crystal nucleus for the Zr-doped lithium aluminosilicate glass-ceramic.

Cycling performance of Li metal anode in localized high concentration electrolyte and dynamic mechanism analysis

In this work, we investigated the apparent cycling performance of lithium metal at different chemical compositions and series current densities; examined the microscopic morphology and thickness variation of the deposition layer on the surface of lithium metal anode and the concentration-depth distribution of trace elements in the solid electrolyte interphase (SEI) film; and characterized the kinetic behavior and features of the elementary steps (mass transfer, charge transfer, electro-crystallization) at Li-electrolyte interface using microelectrode technology and various electrochemical test methods. The results show that the lithium metal anode has better cycling performance in high concentration and localized high concentration electrolyte. At the same time, the experimental results confirm that the formation of spherical crystal nucleus is favored only under certain chemical conditions and certain reaction rate; under these conditions, the induction period and the self-smoothing process of critical crystal nucleus can be found. It suggests that there are determined causal among the apparent performance of lithium metal anode, the kinetic parameters of the interfacial charge transfer step and the electro-crystallization step, and these correlations can be used as a reference for screening and evaluating electrolyte systems and battery operating conditions, providing a reliable kinetic basis for future work.

Growth regulation mechanism of nano-silica based on new ammonia-based CO2 capture under external fields

Conventional CO2 capture technologies often focus on the simple capture process, while the absorption and high-value utilization of carbon capture products have profound significance, especially when combined with the utilization of biomass energy. Novel ammonia-based CO2 capture coupled with selective silicon dissolution was proposed with process regulation of external fields (i.e. magnetic field, microwave field, ultrasound field) used to prepare nano silica. The results show that the magnetic field plays a dual role of “vibration stirring” and adding energy (11.2 J/mol) on the formation and dispersion of nano silica. The specific surface area of nano-silica is increased from 140.24 m2/g to 280 m2/g by microwave field (250 W), and its “internal heating” promotes the formation of crystal nuclei. The ultrasonic field reduces the primary particle size of nano-silica by 3.17 nm, and inhibits the particle growth through cavitation and mechanical vibration. It would provide parameter support and optimization guidance for the low-cost high-quality nano silica for high-value utilization of ammonia-based CO2 capture products.

Study on the supercooling and crystallization mechanism of saline soil based on thermodynamic framework

Quantifying the supercooling characteristics of saline soil–water systems is essential for engineering and agriculture in cold regions. However, the crystallization mechanism of supercooling remains unclear. We conducted experimental observations to investigate the impact of salinity on the soil supercooling properties. Additionally, a freezing nucleation thermodynamic model for saline soil was established based on the Negentropic Nucleation Framework (NNF). Statistical analysis methods were employed to analyze the sensitivity of the parameters and interpret the supercooling microscopic mechanism. The results indicated that the supercooling degree distribution of saline soil is best described by a normal distribution (hypothesis testing statistic Dn=0.176). The nucleation rate was primarily controlled by water activity and activation energy of water molecules. The concentration of salt solution played a crucial role in promoting the formation and growth of crystal nuclei. However, the promoting effect decreased with increasing solution concentration when the concentration was below 0.3 mol/L. Moreover, the nucleation potential energy barrier increased with salt concentration, with NaCl environment exhibiting a higher nucleation potential energy barrier compared to Na2SO4 environment at the same salt concentration. In summary, this research provides a theoretical reference for revealing the freezing-thawing hysteretic mechanism and improving the accuracy of numerical calculation models in cold regions.

Particle Formation Mechanism of TiCl4 Hydrolysis to Prepare Nano TiO2

This study utilizes Aspen Plus chemical process simulation software (V11), applies uniform nucleation theory and growth kinetics equations, and explores the particle formation mechanism of TiCl4 hydrolysis to prepare nano TiO2. In the water/ethanol system, the effects of the reaction time, reaction temperature, water addition, pH value, and ethanol amount on the crystal nucleation rate and TiO2 particle distribution (PSD) were studied in detail by adding triethanolamine dropwise and using the Aspen Plus chemical process software simulation calculation method. The calculation results indicate that at room temperature, the formation of TiO2 crystal nuclei mainly occurs in the first 300 s and then enters the growth stage. The reaction was carried out under neutral conditions at room temperature for 4 h in 1 mL TiCl4, 6 mL C6H15NO3, 15 mL H2O, and 30 mL C2H5OH. The maximum number of particles reached 195 mesh per cubic micrometer, and the particle size after crystal nucleus growth was smaller, with a D50 of 6.15 nm. The distribution curve shows a normal distribution, which is basically consistent with the experimental results. When studying various factors, it was found that controlling the reaction time within 60 min and maintaining the reaction temperature at room temperature can reduce the particle size D50 to 2.44 nm. Continuing to adjust the amount of water added, it was found that at 1 mL, D50 decreased again to 0.19 nm. Adjusting the pH value found that maintaining the neutrality did not change the particle size. Continuing to adjust ethanol, it was found that adding an appropriate amount of ethanol promoted nucleation and growth. At 4 mL, the maximum number of particles reached 199 mesh per cubic micrometer, but D50 slightly increased to 0.24 nm.

Experimental investigation of the effect of stable magnetic field on droplet freezing

In this study, the effect of magnetic field on droplet freezing was investigated based on a visualization system. Possible influencing factors on droplet freezing, such as magnetic field intensity, cold surface temperature, and droplet volume, were considered in this study. During the two stages of droplet supercooling and freezing process, the changes of the droplet internal temperature, the formation of initial crystal nucleus, and the freezing time were observed. Experimental results show that in comparison with the non-magnetic surface, the supercooling degree of droplets was increased in the range of 150–300 mT magnetic field intensity, thereby prolonging the freezing time of droplets. Particularly, the droplet was best suppressed on a cold surface with 250 mT magnetic field intensity. The freezing time of droplets was prolonged by 132.0 %. However, the droplets were accelerated to freeze on the cold surface with magnetic field intensities of 350 mT and 400 mT. Droplet freezing on cold surfaces was also affected by surface temperature and droplet volume. As the surface temperature of magnetic cooling dropped from −10 °C to −20 °C, the ability of the magnetic field to inhibit droplet freezing would be gradually weakened. With the increase of droplet volume from 20 μL to 50 μL, the initial freezing time of droplets was shortened. These results are related to the influence of magnetic field on the nucleation process and hydrogen bond in the water molecular cluster.

Intermittent Exothermic and Self-Healing Hydrated Salt Gels for Advanced Thermal Management of Underfloor Radiant Heating System.

Phase change materials (PCMs) have great prospects in thermal management applications because they can store and release latent heat. However, they are not suitable for on-demand heating as they can only release heat once. Herein, this work reports the intermittent exothermic of PCMs based on a supersaturated salt solution, exhibiting fully controlled long-term storage of energy, releasing and suspending heat on demand. Due to the high energy barrier, it is difficult for the supersaturated salt solution to nucleate; thus, it can store energy for a long time. Contact with seeds or other foreign objects can destroy the metastable state of the supersaturated salt solution and promote the formation of crystal nuclei, enabling crystallization and heat release on demand. The release of crystallization heat can be interrupted using scissors dip in water. Additionally, self-healing behavior allows it to be recycled and last longer, due to the presence of Fe3+ , inducing strong dynamic reversible non-covalent crosslinking through metal coordination bonds. Furthermore, the hydrated salts gels are applied for thermal management of underfloor radiant heating system, demonstrating four types of intermittent exotherms sequences amazingly. Further, the intermittent exothermic hydrated salts gels provide a more user-friendly thermal management of underfloor radiant heating systems.

Kinetic Study on the Dehydration Behavior of Titanium Dioxide as a Denitration Catalyst Carrier

The dehydration of titanium dioxide, which is the carrier for denitration catalysts, is a crucial control step in the preparation of functional materials and has an impact on the performance of the product. In this study, the kinetics of the dehydration behavior and reaction mechanism of titanium dioxide were investigated under different atmospheres by measuring the thermal analysis curve of titanium dioxide at different heating rates. The results indicate that the dehydration behavior of the catalyst carrier titanium dioxide is closely related to the calcination atmosphere. The dehydration rate differed for oxygen and no-oxygen atmospheres. Dehydration began quickly in an oxygenated atmosphere and then slowed down towards the end of the reaction, completing slowly in an oxygen-free atmosphere. Kinetic calculations were carried out using modeless and mode function methods. The results show that dehydration of titanium dioxide is consistent with the Avrami–Erofeev equation in an oxygen-containing atmosphere and with the power function rule in an oxygen-free atmosphere, with the process of dehydration being influenced by the formation and growth of crystal nuclei.

Enhancing graphene's resistance to oxidative corrosion by positive charge doping: A DFT view

Although graphene has been widely used as a protective coating for many applications, the failure mechanism and the strategy to improve its resistance to the chemical etching is largely unknown. We herein have comparatively studied the generally oxidative corrosion process of neutral and positive-charge-doping (PCD) graphene via DFT (density functional theory) simulations. It is found that the positive-charge-doping (PCD) generally enhances the protecting ability of graphene for substrates from reactive environments. The C-network breakdown of graphene due to oxidative etching goes through three stages: the formation of oxidative corrosion crystal nucleus (OCCN), subsequent formation and expansion of oxidative lined defect (OLD), then the generation and extension of oxidative corrosion crack (OCC). Comparing to the neutral or negative charge doping, PCD decreases the electronic reactivity and thus suppresses the oxygen atoms diffusing on graphene of the rate-limiting step, especially in the stage of OCCN nucleation. Our work indicates a possible strategy to improve the resistance to oxidative corrosion (ROC) of graphene via positive charge doping. This protection enhancement of graphene can be achieved taking advantages of the electron capture of the neighboring substrates, reactive environments or external gate voltage in applications.

Improvement of near-infrared photoelectric conversion efficiency of solution-coated (C8BTBT)(F4TCNQ) films by adding Fe3O4 nanoparticles

To realize transparent photoelectric conversion elements useful for optical wireless power-transmission systems and sensors, we investigated thin films of 2,7-dioctyl[1]benzothieno [3,2-b][1]benzothiophene and fluorinated derivatives of 7,7,8,8,-tetracyanoquinodimethane (C8BTBT)(F4TCNQ) produced by a simple solution-coating method. We found that the addition of Fe3O4 nanoparticles (NPs) to a (C8BTBT)(F4TCNQ) solution promoted crystal formation and increased the optical absorption of the film. This was because the addition of NPs formed a middle layer, and the NPs acted as starting points for the formation of crystal nuclei. Photocurrent measurements confirmed that the quantum efficiency (QE) of the film with NPs was improved by about 14-fold compared with the film without NPs. The promotion of crystal formation increased optical absorption and significantly improved QE.

Molecular simulation of crystal nucleation and growth of structurally restricted polymer nanocomposites

This study reveals important features of crystal nucleation and growth in coarse-grained structurally restricted polymer systems (i.e., one end of the chain is grafted on the surface of one-dimensional filler) based on the Monte Carlo simulation on cubic lattice. The structurally restricted polymer system includes two kinds of polymers: terminally grafted and free chains. The existence of more grafted chains increases the crystal nuclei number in the structurally restricted polymer systems, which shortens the nucleation induction time and accelerates crystallization. Intramolecular nucleation occurs when the chain structure is limited. Then, with the increase of restricted chains, the nucleation mechanism changes to intermolecular nucleation. When the interface interaction is introduced into the system, the change of crystallization rate is the result of the competition between conformation entropy and chain mobility. The chain elongation increases with the enhancement of interface interaction, which leads to the increase of the loss of conformational entropy and is conducive to the formation of crystal nucleus. However, the chain mobility slows down with the enhancement of interface interaction, which will hinder the formation of crystal nucleus. By tailoring the interface interaction, the crystal morphologies of polymer nanocomposites can be adjusted to form the unique nanohybrid shish-kebab structures, that is, the filler is used as shish, the crystal regions generated by free chains are attached to the outside of crystal regions generated by restricted chains to form kebabs. Furthermore, the length of grafted chains has different effect on the crystallization depending on the concentration of grafted chains.

In situ‐induced epiphytic crystallization of MC PA6 by self‐assembled nucleator and reinforcing effect

AbstractMonomer casting nylon‐6 (MC PA6), as a high‐performance engineering plastic, replaces metals to be widely applied, while further improving the mechanical properties of MC PA6 is significant for its withstanding heavy loads and increasing its range of applications. In this work, amide nucleating agent (NUDA) with good compatibility and crystal matching relationship with PA6 was firstly dissolved in ε‐caprolactam monomer, and MC PA6‐NUDA was synthesized in situ. NUDA self‐assembled into special frameworks and induced epiphytic crystallization of PA6 to form an enhanced sheaf‐like crystal on its surface with microfibrillar structure during the parallel polymerization–crystallization process. Incorporation of appropriate content of NUDA improved the melting/crystallization point and crystallinity with decreasing grain size obviously, and advanced the crystallization process of MC PA6 mainly via reducing the nucleation potential energy and inducing the formation of crystal nuclei. As a result, the glass transition temperature increased, the tensile strength exhibited a significant 22% increase and the fracture toughness was nearly three times that of neat MC PA6. Meanwhile, deformation with many yield folds as well as stress‐whitening phenomena were observed on the impact‐fractured surfaces, presenting a ductile fracture feature, indicating reinforcing and toughening effect of NUDA on the PA6 matrix. © 2023 Society of Industrial Chemistry.

Influence of ammonium nitrate on the crystallisation of ammonium sulfate

ABSTRACT This study aims to explore the influence mechanism of ammonium nitrate produced by ozone denitrification on the crystallisation of ammonium sulfate, a by-product of ammonia desulfurisation. The laser method was used to study the influence of ammonium nitrate on the solubility and metastable zone width of ammonium sulfate. An experiment on the influence of ammonium nitrate on the particle size of ammonium sulfate was designed, and the influence mechanism was explored through scanning electron microscopy and X-ray diffraction. The findings showed that the addition of ammonium nitrate increased the size and aspect ratio of ammonium sulfate crystals. The addition of ammonium nitrate inhibited the dissolution of ammonium sulfate and widened its metastable zone. The addition of ammonium nitrate covered the active sites of crystal nucleus growth, which inhibited the formation of crystal nuclei to a certain extent, and crystal growth dominated the crystallisation process. Moreover, the addition of ammonium nitrate induced the preferred orientation of the specific crystal plane of ammonium sulfate, and the addition of a small concentration of ammonium nitrate decreased the crystallinity of ammonium sulfate. The research results can provide a reference for crystallisation optimisation and quality improvement of ammonium sulfate in the ammonia desulfurisation process.