Advanced Surface Characterization Research Articles

Electrochemical Hydrogen Charging on Corrosion Behavior of Ti-6Al-4V Alloy in Artificial Seawater

This study employs advanced electrochemical and surface characterization techniques to investigate the impact of electrochemical hydrogen charging on the corrosion behavior and surface film of the Ti-6Al-4V alloy. The findings revealed the formation of γ-TiH and δ-TiH2 hydrides in the alloy after hydrogen charging. Prolonging hydrogen charging resulted in more significant degradation of the alloy microstructure, leading to deteriorated protectiveness of the surface film. This trend was further confirmed by the electrochemical measurements, which showed that the corrosion resistance of the alloy progressively worsened as the hydrogen charging time was increased. Consequently, this work provides valuable insights into the mechanisms underlying the corrosion of Ti-6Al-4V alloy under hydrogen charging conditions.

Tuning Dopant Distribution for Stabilizing the Surface of High‐Nickel Layered Oxide Cathodes for Lithium‐Ion Batteries

AbstractLayered oxide cathodes with a high‐nickel (Ni ≥ 0.9) content exhibit great potential for enabling high‐energy‐density lithium‐ion batteries. However, their practical feasibility and cycle life are hampered by severe surface reactivity with the electrolyte. A LiNi0.90Co0.05Al0.05O2 cathode is presented enriched with Al on the surface (S‐NCA) and benchmark it against a LiNi0.90Co0.05Al0.05O2 cathode obtained by a conventional co‐precipitation method that has a uniform Al distribution throughout the bulk (B‐NCA). The S‐NCA cathode greatly outperform with an impressive capacity retention of 84% after 1000 cycles in pouch full cells with graphite anode compared to 62% retention for B‐NCA. Advanced surface characterization methodologies, including time‐of‐flight secondary‐ion mass spectrometry, reveal that the Al‐enriched surface morphology facilitates the formation of a robust, thin electrode‐electrolyte interphase (EEI), effectively suppressing the oxidative decomposition of the electrolyte, gas generation, and metallic dead lithium formation on graphite anode. The results illustrate that surface reactivity with the electrolyte is the primary factor limiting the cycle of cells with high‐Ni cathodes. The work provides valuable insights toward the practical viability of ultrahigh‐Ni cathodes in lithium‐ion batteries.

Ordered derivatives on Ti surface enhance the OER activity and stability of Ru-based film electrode

The RuO2 catalytic film electrode with long-term durability is becoming increasingly urgent and challenging for catalysis oxygen evolution reaction (OER). Herein, the Ti-oxides (HxTi2+2xOδ/Ti, HTi/Ti) with ordered porous morphology is derived directly from metallic Ti by using a combination method of hydrothermal and ion exchange, and served as a substrate to support RuO2 catalytic film. The porous HTi plays a wedge-like effect, which significantly improve the adhesion of RuO2 catalytic layer and reducing surface cracks. Moreover, the advanced surface characterization techniques evidence a strong catalyst-support interaction between HTi and RuO2, furtherly enhances the binding strength and modifies the orbital structure of Ru-sites. Electrochemical measurements revealed that the prepared RuO2/HTi/Ti possess a low overpotential of 220 mV and 265 mV to afford the current density of 10 mA cm−2 and 50 mA cm−2, respectively, and exhibits a high mass activity of 1760 ± 60 mA gRu−1 at overpotential of 290 mV. Accelerated life test confirmed the robust durability of RuO2/HTi/Ti, which can run stably for up to 11 h at 500 mA cm−2 current density with a low mass loading of 0.1 mg cm−2. The remarkable OER performance is closely associated with the ordered porous HTi and interfacial interactions, which demonstrate the surface engineering to create ordered derivative layers directly from the substrate is important to improve the activity and stability of catalytic film electrode.

A comprehensive investigation of surface morphology during grinding of Inconel 625 using conventional grinding wheels

Grinding difficult-to-grind (DTG) materials such as superalloys have shown an upward trend for manufacturing high-precision and durable components. Superalloys, such as Inconel, have superior thermo-mechanical properties that allow them to withstand caustic working conditions and simultaneously make their grindability difficult. In this context, the present work investigates the grinding performance of Inconel 625 (IN 625) using conventional grinding wheels in dry condition. The current investigation uses the alumina wheel and the silicon carbide wheel to keep the cost factor minimum. The outcome of the experiments has been evaluated in terms of grinding forces and surface roughness. Advanced surface characterization techniques such as Scanning electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy have been employed to analyze the surface morphology of the ground surfaces produced by both wheels. It has been observed that the alumina wheel has performed much better than the silicon carbide wheel for a higher depth of cut. These observations have also been supported by wheel loading, in which loading for the silicon carbide wheel was approximately four times that of the alumina wheel. Moreover, long and flow types of chips produced by the alumina wheel indicate the better suitability of the alumina wheel while grinding IN 625. The findings of the present work are expected to provide an economical way of grinding IN 625, preferably using an alumina grinding wheel.

Vol4 num2-16 CFRP advanced surface characterization prior to adhesive bonding. Peel ply treatment vs UV laser

Surface treatment is one of the most important issues for obtaining high quality adhesive bonding. The main objective of this treatment is the removal of surface contaminants, the modification of surface roughness and the increase of surface free energy, without damaging the surface of the composite material. Nowadays, the treatments which are approved by the aeronautical sector for the surface preparation of CFRP prior to adhesive bonding are manual and some of them depend on the skills of the operator. Because of this, different automatable alternatives are being studied in order to substitute these traditional methods. One of these alternatives is the use of UV laser radiation. In this work the advanced surface characterization of CFRP surfaces treated with peel ply and processed with UV laser have been performed. Advanced techniques have been used in order to evaluate the changes that occur in the surface and which can be related to adhesiveness. Thus, techniques such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), surface free energy determination and 3D optical confocal profilometry have been used to evaluate chemical and physical properties of treated surfaces. Obtained results show that UV laser radiation leads to surface changes which would improve the adhesiveness of the surfaces, although these changes suggest that the mechanism by which adhesion happens is different from the one which is related to peel ply. &nbsp

UV laser surace activation in co-bonding of CFRP elements. Comparison with other certified methods

There is an increasing trend towards the substitution of mechanical joining by adhesive bonding in carbon fibre elements (CFRP) in aeronautical sector. However, it is mandatory to perform a previous step of surface preparation in order to obtain the best adhesive properties to the surface. There are some certified superficial preparation methods by the aeronautical sector, being shot peening, grinding and peel-ply the most used ones. All of them have the disadvantage of not being automatable. Hence, new potentially automatable methods for surface activation are being studied. In this work it has been studied the use of UV laser radiation as a surface activation method previous to adhesive bonding, and its behaviour has been compared to peel-ply activated samples. To this end, an advanced surface characterization has been performed, by means of surface free energy determination, surface chemical composition determination by XPS measurement, surface roughness and morphology observation with SEM. Mode I fracture toughness test have been performed for all surface activation methods. The obtained results show that adhesive bonding of UV laser treated samples have mode I fracture toughness comparable values to those obtained for peel-ply and peel-ply plus grinding samples. Furthermore, all the failure modes observed are accepted by the sector normative. This makes that UV laser surface preparation could be considered as an alternative for certified surface method of CFRPs.

Novel CNT Supported Molybdenum Catalyst for Detection of L-Cysteine in Its Natural Environment

In this study, novel carbon nanotube-supported Mo (Mo/CNT) catalysts were prepared with the sodium borohydride reduction method for the detection of L-cysteine (L-Cys, L-C). Mo/CNT catalysts were characterized with scanning electron microscopy with elemental dispersion X-ray (EDX-SEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectrometry (UV-vis), temperature-programmed reduction (TPR), temperature programmed oxidation (TPO), and temperature-programmed desorption (TPD) techniques. The results of these advanced surface characterization techniques revealed that the catalysts were prepared successfully. Electrochemical measurements were employed to construct a voltammetric L-C sensor based on Mo/CNT catalyst by voltammetric techniques such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Further measurements were carried out with electrochemical impedance spectroscopy (EIS). Mo/CNT/GCE exhibited excellent performance for L-C detection with a linear response in the range of 0–150 µM, with a current sensitivity of 200 mA/μM cm2 (0.0142 μA/μM), the lowest detection limit of 0.25 μM, and signal-to-noise ratio (S/N = 3). Interference studies showed that the Mo/CNT/GCE electrode was not affected by D-glucose, uric acid, L-tyrosine, and L-trytophane, commonly interfering organic structures. Natural sample analysis was also accomplished with acetyl L-C. Mo/CNT catalyst is a promising material as a sensor for L-C detection.

Surface morphology effects on clathrate hydrate wettability

HypothesisClathrate hydrates preferentially form at interfaces; hence, wetting properties play an important role in their formation, growth, and agglomeration. Experimental evidence suggests that the hydrate preparation process can strongly affect contact angle measurements, leading to the different results reported in the literature. These differences hamper technological progress. We hypothesize that changes in hydrate surface morphologies are responsible for the wide variation of contact angles reported in the literature. ExperimentsExperimental testing of our hypothesis is problematic due to the preparation history of hydrates on their surface properties, and the difficulties in advanced surface characterization. Thus, we employ molecular dynamics simulations, which allow us to systematically change the interfacial features and the system composition. Implementing advanced algorithms, we quantify fundamental thermodynamic properties to validate our observations. FindingsWe achieve excellent agreement with experimental observations for both atomically smooth and rough hydrate surfaces. Our results suggest that contact line pinning forces, enhanced by surface heterogeneity, are accountable for altering water contact angles, thus explaining the differences among reported experimental data. Our analysis and molecular level insights help interpret adhesion force measurements and yield a better understanding of the agglomeration between hydrate particles, providing a microscopic tool for advancing flow assurance applications.

Nanoscaled Morphology and Mechanical Properties of a Biomimetic Polymer Surface on a Silicone Hydrogel Contact Lens.

Materials taking advantage of the characteristics of biological tissues are strongly sought after in medical science and bioscience. On the natural corneal tissue surface, the highly soft and lubricated surface is maintained by composite structures composed of hydrophilic biomolecules and substrates. To mimic this structure, the surface of a silicone hydrogel contact lens was modified with a biomimetic phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), and the nanoscaled morphology and mechanical properties of the surface were confirmed with advanced surface characterization and imaging techniques under an aqueous medium. Concavities and convexities on the nanometer order were recognized on the surface. The surface was completely covered with a PMPC layer and remained intact even after 30 days of clinical use in a human ocular environment. The mechanical properties of the natural corneal tissue and the PMPC-modified surface were similar in the living environment, that is, low modulus and frictional properties comparable to natural tissues. These results show the validity of material preparation by biomimetic methods. The methodologies developed in this study may contribute to future development of human-friendly medical devices.

Hydrogen Production at a NiO Photocathode Based on a Ruthenium Dye–Cobalt Diimine Dioxime Catalyst Assembly: Insights from Advanced Spectroscopy and Post-operando Characterization

The production of hydrogen by efficient, low-cost, and integrated photoelectrochemical water splitting processes represents an important target for the ecological transition. This challenge can be addressed thanks to bioinspired chemistry and artificial photosynthesis approaches by designing dye-sensitized photocathodes for hydrogen production, incorporating bioinspired first-row transition metal-based catalysts. The present work describes the preparation and photoelectrochemical characterization of a NiO photocathode sensitized with a phosphonate-derivatized ruthenium tris-diimine photosensitizer covalently linked to a cobalt diimine dioxime hydrogen-evolving catalyst. Under simulated AM 1.5G irradiation, hydrogen is produced with photocurrent densities reaching 84 ± 7 μA·cm-2, which is among the highest values reported so far for dye-sensitized photocathodes with surface-immobilized catalysts. Thanks to the unique combination of advanced spectroscopy and surface characterization techniques, the fast desorption of the dyad from the NiO electrode and the low yield of electron transfer to the catalyst, resulting in the Co demetallation from the diimine dioxime framework, were identified as the main barriers limiting the performances and the stability of the system. This work therefore paves the way for a more rational design of molecular photocathodes for solar fuel production and represents a further step toward the development of sustainable processes for the production of hydrogen from sunlight and water.

Clinically Relevant Bacterial Outer Membrane Models for Antibiotic Screening Applications.

Antibiotic resistance is a growing global health concern that has been increasing in prevalence over the past few decades. In Gram-negative bacteria, the outer membrane is an additional barrier through which antibiotics must traverse to kill the bacterium. In addition, outer membrane features and properties, like membrane surface charge, lipopolysaccharide (LPS) length, and membrane porins, can be altered in response to antibiotics and therefore, further mediate resistance. Model membranes have been used to mimic bacterial membranes to study antibiotic-induced membrane changes but often lack the compositional complexity of the actual outer membrane. Here, we developed a surface-supported membrane platform using outer membrane vesicles (OMVs) from clinically relevant Gram-negative bacteria and use it to characterize membrane biophysical properties and investigate its interaction with antibacterial compounds. We demonstrate that this platform maintains critical features of outer membranes, like fluidity, while retaining complex membrane components, like OMPs and LPS, which are central to membrane-mediated antibiotic resistance. This platform offers a non-pathogenic, cell-free surface to study such phenomena that is compatible with advanced microscopy and surface characterization tools like quartz crystal microbalance. We confirm these OMV bilayers recapitulate membrane interactions (or lack thereof) with the antibiotic compounds polymyxin B, bacitracin, and vancomycin, validating their use as representative models for the bacterial surface. By forming OMV bilayers from different strains, we envision that this platform could be used to investigate underlying biophysical differences in outer membranes leading to resistance, to screen and identify membrane-active antibiotics, or for the development of phage technologies targeting a particular membrane surface component.

Advanced Nanoscale Surface Characterization of CuO Nanoflowers for Significant Enhancement of Catalytic Properties

In this work, advanced nanoscale surface characterization of CuO Nanoflowers synthesized by controlled hydrothermal approach for significant enhancement of catalytic properties has been investigated. The CuO nanoflower samples were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), selected-area electron diffraction (SAED), high-angular annular dark field scanning transmission electron microscopy (HAADF-STEM) with elemental mapping, energy dispersive spectroscopy (STEM-EDS) and UV–Vis spectroscopy techniques. The nanoscale analysis of the surface study of monodispersed individual CuO nanoflower confirmed the fine crystalline shaped morphology composed of ultrathin leaves, monoclinic structure and purified phase. The result of HR-TEM shows that the length of one ultrathin leaf of copper oxide nanoflower is about ~650–700 nm, base is about ~300.77 ± 30 nm and the average thickness of the tip of individual ultrathin leaf of copper oxide nanoflower is about ~10 ± 2 nm. Enhanced absorption of visible light ~850 nm and larger value of band gap energy (1.68 eV) have further supported that the as-grown material (CuO nanoflowers) is an active and well-designed surface morphology at the nanoscale level. Furthermore, significant enhancement of catalytic properties of copper oxide nanoflowers in the presence of for the degradation of methylene blue (MB) with efficiency ~96.7% after 170 min was obtained. The results showed that the superb catalytic performance of well-fabricated CuO nanoflowers can open a new way for substantial applications of dye removal from wastewater and environment fields.

A novel experimental and density functional theory study on palladium and nitrogen doped few layer graphene surface towards glucose adsorption and electrooxidation

At present, few layer graphene (G) and nitrogen doped few layer graphene (N doped-G) are firstly coated on Cu foil via chemical vapor deposition (CVD) method and G and N doped-G coated Cu foil is transferred to the indium tin oxide (ITO) substrate surface to obtain electrodes. Pd metal is electrodeposited onto the N doped-G/ITO electrode (Pd-N doped-G/ITO). Pd-N doped-G/ITO electrode are characterized with advanced surface characterization methods such as Raman spectroscopy and SEM-EDX. Characterization results reveal that G and N structures are succesfully obtained and the presence of Pd on Pd-N doped-G/ITO is confirmed with SEM-EDX mapping. The cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) are employed to examine glucose electrooxidation of G/ITO, N-doped G/ITO, and Pd-N-doped G/ITO electrodes. P–N-dopedG/ITO electrode exhibits the best glucose electrooxidation activity with 2 mA/cm2 specific activity. Density functional theory (DFT) calculations are also carried out to better understand the interaction of the molecules on Pd modified G (Pd-G) and Pd modified N-doped G (Pd-3NG) surfaces.

In silico analysis of argon adsorption and porous properties of Fe-soc-MOF pre-adsorbed with nonpolar and polar fluids

Abstract In this molecular simulation work, we provide a profound insight into the textural and adsorptive properties of a microporous metal-organic framework with soc topology (soc-MOF) using combined argon physisorption and pre-adsorption with fluids having different polarities (CCl4, NH3, and H2O) at 87 K. With different amounts of pre-adsorbed molecules added to the framework, the adsorption isotherms, snapshots, and isosteric heats of argon at 87 K are investigated using the grand canonical Monte Carlo simulation (GCMC), whereas the porous properties are obtained by using the Monte Carlo integration technique (MCI). It is found that insertion of pre-adsorbed molecules has a substantial effect on argon adsorption uptake in the regions of Henry's law and saturation capacity since the accessible pore space becomes smaller in volume and size. By observing the pre-adsorption mechanisms of non-polar (CCl4) and mildly polar (NH3) fluids, it is clear that the pre-adsorbed molecules mainly prefer to locate at the cages due to stronger interaction between Fe sites and pre-adsorbed molecules, followed by pre-adsorption in the channels when the cages are utterly or nearly fulfilled. Therefore, post-adsorption of argon initially occurs in the cages because of the enhancement of interactions between pre-adsorbed molecules existing in the framework, as confirmed by isosteric heat at low loading. Conversely, for highly polar fluids like H2O, pre-adsorption is proceeded by non-selective pore filling. From the analysis at the molecular level, it can be concluded that pre-adsorption could be used as another tool for advanced surface characterization to provide a better understanding of the structural and adsorptive properties of other soc-MOFs and MOFs that have different topological framework types.

Pitting Corrosion Resistance Influencing Corrosion Fatigue Behavior of an Austenitic Stainless Steel in Chloride-Containing Environments

Strain-hardened austenitic stainless steels are commonly used as structural materials in drilling equipment because they meet the demanding requirements in terms of mechanical, magnetic, and chemical properties necessary for drilling technologies in subterranean energy resources exploration. Drilling operational conditions might become a challenge for the integrity of these materials due to the cyclic loading the drillstring is subjected to, in combination with the downhole temperature, and the corrosivity of the drilling fluid. In this research work, the relationship among the pitting corrosion resistance of one Mn-stabilized austenitic stainless steel and its corrosion fatigue behavior has been determined by means of electrochemical methods, advanced surface characterization, and corrosion fatigue testing in brines of near-neutral pH with different chloride contents at room temperature (RT) and 150°C. It has been determined that the corrosion fatigue behavior of the investigated CrMn stainless steel is strongly affected by its susceptibility to pitting corrosion. The synergistic effect between the corrosive environment and the mechanical load depends upon the applied stress amplitude and the pitting resistance of the material. The corrosion fatigue behavior of the austenitic stainless steel at RT was synergistically affected by the environmental and loading conditions at low stress amplitudes. In contrast, the large susceptibility to pitting of the material at 150°C has a significant detrimental effect on its corrosion fatigue behavior when subjected to high stress amplitudes. The observed damage mechanism at 150°C can be described as pitting-induced corrosion fatigue because pit propagation controlled the corrosion fatigue behavior of the CrMn stainless steel. The obtained experimental results have shown that the pitting resistance, assessed for instance by multiple electrochemical methods, could in cases where pitting susceptibility has a large influence on the environmentally sustained cracking mechanism, be used as an indicator of the expected corrosion fatigue behavior of the material. As demonstrated in this study, however, results from accelerated electrochemical testing solely might have a limited prediction capability of long-term corrosion behavior.

On Friction Reduction by Surface Modifications in the TEHL Cam/Tappet-Contact-Experimental and Numerical Studies

The overall energy efficiency of machine elements and engine components could be improved by using new technologies such as surface modifications. In the literature, surface engineering approaches like micro-texturing and the application of diamond-like carbon (DLC) coatings were frequently studied separately, with focus on a specific model contact and lubrication conditions. The contribution of the current study is to elucidate and compare the underlying friction reduction mechanisms of the aforementioned surface modifications in an application-orientated manner. The study applied the operating conditions of the thermo-elastohydrodynamically lubricated (TEHL) cam/tappet-contact of the valve train. Therefore, tribological cam/bucket tappet component Stribeck tests were used to determine the friction behavior of ultrashort pulse laser fabricated microtextures and PVD/PECVD deposited silicon-doped amorphous carbon coatings. Moreover, advanced surface characterization methods, as well as numerical TEHL tribo-simulations, were utilized to explore the mechanisms responsible for the observed tribological effects. The results showed that the DLC-coating could reduce the solid and fluid friction force in a wide range of lubrication regimes. Conversely, micro-texturing may reduce solid friction while increasing the fraction of fluid friction.

In Vitro Degradation of Absorbable Zinc Alloys in Artificial Urine.

Absorbable metals have potential for making in-demand rigid temporary stents for the treatment of urinary tract obstruction, where polymers have reached their limits. In this work, in vitro degradation behavior of absorbable zinc alloys in artificial urine was studied using electrochemical methods and advanced surface characterization techniques with a comparison to a magnesium alloy. The results showed that pure zinc and its alloys (Zn–0.5Mg, Zn–1Mg, Zn–0.5Al) exhibited slower corrosion than pure magnesium and an Mg–2Zn–1Mn alloy. The corrosion layer was composed mostly of hydroxide, carbonate, and phosphate, without calcium content for the zinc group. Among all tested metals, the Zn–0.5Al alloy exhibited a uniform corrosion layer with low affinity with the ions in artificial urine.

(Invited) Bulk and Surface Chemistry of High-Nickel Layered Oxide Cathodes

Lithium-ion batteries have become the choice of power source for portable electronics and electric vehicles as they offer higher energy density than other rechargeable systems. They are also being intensively pursued for grid storage of electricity produced from renewable sources like solar and wind. Cost, safety, cycle life, energy, power, and environmental impact are the major factors in adopting them for a specific application. Among the various practically viable insertion-compound cathode chemistries available, the layered LiMO2 (M = Mn, Ni, Co, and their solid solutions) oxides offer the highest energy density. Accordingly, there is immense interest in both academia and industry in increasing the charge-storage capacities of the layered oxide cathodes beyond the current levels. In this regard, layered oxide cathode compositions with higher nickel contents (> 50 %) are drawing much attention in recent years since Ni offers higher capacity than Co as Ni3+ can be oxidized fully to Ni4+ without releasing oxygen from the lattice unlike Co3+, which can be oxidized only to ~ 3.5+ to avoid oxygen release from the lattice. Unfortunately, compositions with high Ni contents suffer from (i) multiple phase transitions, resulting in volume change and internal stress and (ii) high surface reactivity with the organic liquid electrolyte, resulting in a growth of cell impedance and fast capacity fade during cycling. They also suffer from high surface reactivity with ambient air to form lithium hydroxide and lithium carbonate on the particle surface, which not only degrades the electrochemical performance but also severely hampers the electrode fabrication process. Innovative approaches to overcome the above challenges are needed to employ high-nickel layered oxide cathodes in practical lithium-ion cells. This presentation will focus first on developing a fundamental understanding of the factors that control the capacity fade and air-reactivity of high-nickel layered oxide cathodes, employing samples with secondary particle sizes of ~ 10 microns and advanced bulk and surface characterization methodologies. In-depth understanding obtained with high-nickel layered oxide cathodes with Ni contents of as high as 94% and graphite anodes retrieved from full cells before and after 1,000 – 3,000 cycles based on a combination of characterization techniques, viz., X-ray photoelectron spectroscopy (XPS), time-of-flight – secondary ion mass spectroscopy (TOF-SIMS), and high-resolution transmission electron microscopy (TEM), will be presented. Utilizing the understanding gained, the presentation will then focus on the design and development of layered oxide compositions with controlled bulk and surface structures as well as new electrolytes that offer a robust interface with both the graphite anode and high-nickel layered oxide cathodes will be presented. Viability to realize lithium-ion cells with cathode capacities of as high as ~ 220 mAh/g, high power capability, and high volumetric energy density will be discussed.

Qualitative and Quantitative Characterization of Composition Heterogeneity on the Surface of Spray Dried Amorphous Solid Dispersion Particles by an Advanced Surface Analysis Platform with High Surface Sensitivity and Superior Spatial Resolution

Surface composition critically impacts stability (e.g., crystallization) and performance (e.g., dissolution) of spray dried amorphous solid dispersion (ASD) formulations; however, traditional characterization techniques such as Raman and infrared spectroscopies may not provide useful information on surface composition on the spray dried ASD particles due to low spatial resolution, high probing depth, and lack of quantitative information. This study presents an advanced surface characterization platform consisting of two complementary techniques: X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Such a platform enables qualitative and quantitative measurements of surface composition for the fine spray dried ASD particles with ultrasurface-sensitivity (less than 10 nm from the surface) and superior spatial resolution (approximately 250 nm for ToF-SIMS). Both XPS and ToF-SIMS demonstrated that the polymer (PVPVA) was dominantly enriched on the surface of our spray dried naproxen-PVPVA ASD particles. Of a particular note was that XPS could differentiate two batches of spray dried ASD particles with a subtle difference in surface composition produced by varying feed solution solvents. This advanced surface characterization platform will provide essential surface information to understand the mechanisms underlying the impact of surface composition on stability (e.g., crystallization) and functionality (e.g., dissolution) in future studies.

Lubricant-surface interactions of polymer-coated engine journal bearings

This work provides the methodology for the improved understanding of tribocontacts with tribolayers formed from the interactions of an engine oil and the surface of a journal bearing under boundary lubricating conditions. In particular, advanced surface characterisation combining X-ray photoelectron spectroscopy (XPS) and high resolution mass spectroscopy (MS) contributed to integrated knowledge on tribochemical and tribomechanical processes in the tribocontact studied. An engine connecting rod bearing lubricated with commercial 0W-20 GF5 engine oil was evaluated as part of the tribosystem. Bearing material was a recently developed polymer-based overlay which increased in popularity in the automotive market owing to the durability and superior tribological properties. After engine bench tests and fatigue experiments, conventional oil analyses showed only minor changes regarding oil chemistry whereas MS revealed significant additive degradation, e.g., formation of organic phosphates from ZDDP and depletion of tris(2,4-di-tert-butylphenyl)phosphite additive. Regarding the fatigue experiments, surface analysis by XPS showed the formation of tribofilms with a thickness only in the range of a few nanometers and composed of P, S and Zn, i.e., mainly elements in ZDDP. This publication reports for the first time on surface characterisation by laser desorption ionisation MS applied to engine journal bearings: the presence of an organic phosphorus compound the origin of which is assumed from ZDDP could be revealed by this approach.