Original Substrate Research Articles

Wear resistance of cold sprayed Al alloys for aeronautical repairs

ABSTRACTAl–Cu alloys, like Al 2024, and Al–Si alloys, like Al F357 and Al C355, are used in aeronautic gearboxes and fuselage parts operating in severe conditions. It is necessary to develop maintenance and overhaul technologies to extend the life of metallic components used in the aeronautical sector. Cold Spray (CS) could be an alternative as it is real solid-state processing technique. However, the repaired component should exhibit similar properties as the original substrate. This paper evaluates the wear performance of Al coatings CS onto the same Al substrates in sliding and oscillating conditions. The results were compared with the corresponding substrates. The wear rate of coatings processed using new conditions, developed to enhance the coatings performance, was similar or smaller than that measured in the substrate bulk alloys. For Al 2024 and Al C355 CS could be used for repairing, from the tribological point of view.

Mechanical and tribological characteristics of a-C:H:SiOx films formed by PACVD on titanium alloy VT1-0

This paper is devoted to the study of the mechanical and tribological properties of a-C:H:SiOx films deposited on a titanium alloy VT1-0 by a plasma chemical deposition method using pulsed bipolar bias voltage. It was shown that after deposition of 2 μm-thick a-C:H:SiOx film on a titanium alloy VT1-0 sample, the root-mean-square surface roughness Rq measured using atomic force microscopy decreased from 74 to 50 nm compared to the original substrate. The surface hardness H measured using nanoindentation increased from 3.3 to 12.4 GPa with an almost unchanged elasticity modulus E. As a result, the plasticity index (H/E) of titanium samples increased from 0.03 to 0.11, and the plastic deformation resistance (H3/E2) increased from 3 to 156 MPa. Deposition of a-C:H:SiOx film on the titanium alloy VT1-0 surface makes possible to reduce the friction coefficient from 0.3-0.6 to 0.1 and the wear rate from 6 · 10−4 to 7·10−6 mm3/Nm.

Fast Strategy to Functional Paper Surfaces.

Paper, with advantages of low-cost, easy fabrication and disposal, flexibility and renewability, is a suitable substrate material for various applications. Functionalization and patterning on paper substrates are commonly required in many applications. Although many methods have been developed to achieve this, they typically suffer from some drawbacks such as time-consuming process, specific device dependence, lack of flexibility, low patterning resolution, and so forth. Herein, we present a general and fast method to functionalize paper sheets and create patterns. The whole modification process can be completed in 10 min and can be applied on various types of paper substrates and other natural materials such as natural fabrics. By our method, many commonly used functional groups can be covalently attached and patterned on paper substrates, while the characteristic features of the original paper substrates, for example, color, transparency, and conductivity, can be perfectly retained after modification to allow these properties to be incorporated into the resultant materials. High-resolution patterns can be created on paper by applying a photomask during the modification or controlling the time of modification to precisely control the functionality at any area on the obtained paper substrates. We also show the potential applications of our method in the fabrication of superhydrophobic coatings and biomaterials.

Lift-Off Mechanism of GaN Thin Films with Buried Nanocavities Investigated by SEM and TEM

A process to slice and separate GaN layers with buried nanocavities was presented via an annealing process of nanoporous GaN (0002) thin films at 1050°C in an NH3 ambient. We were able to separate and lift off GaN layers over a macroscopic area ( $$ \ge $$ cm2). The several growth stages of buried nanocavities were examined by scanning/transmission emission microscopy techniques. During the early stage of annealing, the annealing leads to variations in morphology from nanopores with rough sidewalls to columnar or hexagonal nanopores with smooth sidewalls. At the same time, amorphous gallium oxide and single crystal GaN with high dislocation density, which are formed by electrochemical etching, are converted into GaN with a perfect crystal lattice. Subsequently, the columnar or hexagonal nanopores are sealed, cut, and then spheroidized. Above a sufficiently high porosity (> 50%), the nanocavities will overlap one another and coalesce, allowing a stand-alone GaN thin film to be lifted off the original substrate.

Functional Characterization of the GH10 and GH11 Xylanases from Streptomyces olivaceoviridis E-86 Provide Insights into the Advantage of GH11 Xylanase in Catalyzing Biomass Degradation.

We functionally characterized the GH10 xylanase (SoXyn10A) and the GH11 xylanase (SoXyn11B) derived from the actinomycete Streptomyces olivaceoviridis E-86. Each enzyme exhibited differences in the produced reducing power upon degradation of xylan substrates. SoXyn10A produced higher reducing power than SoXyn11B. Gel filtration of the hydrolysates generated by both enzymes revealed that the original substrate was completely decomposed. Enzyme mixtures of SoXyn10A and SoXyn11B produced the same level of reducing power as SoXyn10A alone. These observations were in good agreement with the composition of the hydrolysis products. The hydrolysis products derived from the incubation of soluble birchwood xylan with a mixture of SoXyn10A and SoXyn11B produced the same products as SoXyn10A alone with similar compositions. Furthermore, the addition of SoXyn10A following SoXyn11B-mediated digestion of xylan produced the same products as SoXyn10A alone with similar compositions. Thus, it was hypothesized that SoXyn10A could degrade xylans to a smaller size than SoXyn11B. In contrast to the soluble xylans as the substrate, the produced reducing power generated by both enzymes was not significantly different when pretreated milled bagasses were used as substrates. Quantification of the pentose content in the milled bagasse residues after the enzyme digestions revealed that SoXyn11B hydrolyzed xylans in pretreated milled bagasses much more efficiently than SoXyn10A. These data suggested that the GH10 xylanases can degrade soluble xylans smaller than the GH11 xylanases. However, the GH11 xylanases may be more efficient at catalyzing xylan degradation in natural environments (e.g. biomass) where xylans interact with celluloses and lignins.

Effect of Substrates on Fracture Mechanism and Process Optimization of Oxidation–Reduction Bonding with Copper Microparticles

Oxidation–reduction bonding (ORB) is a promising method to achieve Cu-Cu bonding with copper microparticles by a pressureless and low-temperature process. In this study, the influences of Cu substrates with and without Ag-plating and Au-plating on ORB were investigated. The shear strengths of the different bondings were evaluated and the fracture surfaces were observed. The results show that, comparing to original Cu substrates, Ag-plating and Au-plating substrates improved the shear strength of bonding under all conditions, due to the different fracture modes and formation of the intermetallic compound (IMC). Both Ag-plating and Au-plating substrates prevented the formation of oxide film on the substrate, which caused separation at the interface, thereby increasing the shear strength. Au-Cu IMC formed in the Au plating layer; therefore, the bonding with Au-plating was better strengthened. Based upon this observation, an optimized pre-oxidation ORB process with Cu substrates was successfully developed to reduce the process time and improve the bonding strength.

Enzymatic Synthesis of D-pipecolic Acid by Engineering the Substrate Specificity of Trypanosoma cruzi Proline Racemase and Its Molecular Docking Study

Pipecolic acid is an unnatural amino acid mostly used for pharmaceutical purposes. Pipecolic acid has two types of enantiomers with different roles in the synthesis of drugs. The development of efficient catalytic methods for the production of enantiopure pipecolic acid is currently a crucial topic of research. Few chemo- or biosynthetic methods have been proposed for the synthesis of pure enantiomers; however, enzymatic conversion of the chirality of pipecolic acid has not been demonstrated because no pipecolic acid racemase has been reported yet. In this work, we attempted to engineer pipecolic acid racemase activity into Trypanosoma cruzi proline racemase (TcPRAC) for the enzymatic synthesis of D-pipecolic acid from L-pipecolic acid. For the binding of pipecolic acid (C6 ring) into the active site of TcPRAC, which was optimized for the original substrate proline (C5 ring), four bulky aromatic residues (Phe102, Phe120, Phe220, and Phe 290) of TcPRAC were mutated to smaller hydrophobic residues. Among the mutants, six single-point mutants (F102A, F102I, F102L, F102V, F290L, and F290V) exhibited significant racemase activity against L-pipecolic acid. The most efficient variant, F102V, showed 74% racemization. Molecular docking simulations revealed that lowering the binding energy of L-pipecolic acid to the active site was important for achieving high racemization activity of TcPRAC mutant proteins.

Antifungal Activity of Compounds Isolated from Bamboo Vermicompost against <i>Rhizoctonia solani</i> AG1-IB

Vermicompost has become a promising alternative to chemical pesticide because of its disease suppression effect during these decades. However, the mechanisms by which vermicompost suppress plant disease are not well-understood. Antifungal compounds, which are released by beneficial organisms in the vermicompost, may play an important role in inhibiting plant pathogens; however, these mechanisms have not been widely examined. In this study, Sterilized Water Extracts of bamboo vermicompost (SWE), using a 0.22-μm cellulose acetate filter, significantly (P Rhizoctonia solani AG1-IB on a Potato Dextrose Agar (PDA) plate. This suggests that antifungal compounds are present in bamboo vermicompost. The ethanol acetate (EtOAc) crude extracts of bamboo vermicompost showing antifungal activity were further separated. Two compounds were isolated from the EtOAc fraction of bamboo vermicompost and characterized as ergosterol peroxide (1) and (22E, 24R)-5α,8α-epidioxyergosta-6,9(11),22-trien-3β-ol (2). Their chemical structures and mass spectra were determined by nuclear magnetic resonance and mass spectrometry analyses. Ergosterol peroxide tested at 150, 300, 600, and 900 μg showed 13%, 22%, 34%, and 53% mycelial growth inhibition against R. solani AG1-IB, respectively. Because EtOAc crude extracts of the initial substrate materials of bamboo vermicompost did not inhibit mycelium growth of R. solani AG1-IB, antifungal compounds in the vermicompost may be released by microbes but not from the original substrates during vermicomposting.

Balancing Specificity and Promiscuity in Enzyme Evolution: Multidimensional Activity Transitions in the Alkaline Phosphatase Superfamily.

Highly proficient, promiscuous enzymes can be springboards for functional evolution, able to avoid loss of function during adaptation by their capacity to promote multiple reactions. We employ a systematic comparative study of structure, sequence, and substrate specificity to track the evolution of specificity and reactivity between promiscuous members of clades of the alkaline phosphatase (AP) superfamily. Construction of a phylogenetic tree of protein sequences maps out the likely transition zone between arylsulfatases (ASs) and phosphonate monoester hydrolases (PMHs). Kinetic analysis shows that all enzymes characterized have four chemically distinct phospho- and sulfoesterase activities, with rate accelerations ranging from 1011- to 1017-fold for their primary and 109- to 1012-fold for their promiscuous reactions, suggesting that catalytic promiscuity is widespread in the AP-superfamily. This functional characterization and crystallography reveal a novel class of ASs that is so similar in sequence to known PMHs that it had not been recognized as having diverged in function. Based on analysis of snapshots of catalytic promiscuity "in transition", we develop possible models that would allow functional evolution and determine scenarios for trade-off between multiple activities. For the new ASs, we observe largely invariant substrate specificity that would facilitate the transition from ASs to PMHs via trade-off-free molecular exaptation, that is, evolution without initial loss of primary activity and specificity toward the original substrate. This ability to bypass low activity generalists provides a molecular solution to avoid adaptive conflict.

Enzymatic Activity in Fractal Networks of Self-Assembling Peptides.

The tissue environment is exceptionally complex, with well-controlled biochemical communication occurring between similar and dissimilar cells as well as between these cells and local extracellular matrices (ECM). To build an artificial ECM that can directly affect regional cell populations, a designer system should allow for controlled degradation, molecular release, and reorganization as related to local cellular function. (RADA)4 self-assembling peptide (SAP) hydrogels are excellent candidates for precisely tuned ECMs, or nanoscaffolds, with several beneficial qualities. They are a class of materials with uncomplicated fabrication and potentially allow for a diverse set of release strategies for many types of bioactive ligands. Enzyme-induced degradation and release of peptide sequences, synthesized within the SAP for on-demand cell signaling, could prove impactful to a plethora of human health applications. However, the degradation products and their release kinetics from these nanoscaffolds may greatly affect the overall system. To address this, enzyme kinetics in self-assembled hydrogels were studied by tethering matrix metalloproteinase 2 (MMP-2) cleavable peptide substrates of differing activities to the C-terminus of (RADA)4. High and low activity sequences, GPQG+IASQ (CP1) and GPQG+PAGQ (CP2), were respectively chosen for tunable release. When incubated with 5 nM MMP-2, over 3 days, both CP1 and CP2 sequences showed product formation values of ∼32% and ∼9% of the original substrate, respectively. On-demand product formation was found to be dependent upon both SAP composition and enzyme concentrations and could be tuned over the course of several days and weeks. Despite the fact that the self-assembling peptides are not directly cleavable by MMP-2, the CP1 and CP2 nanoscaffold morphology was visibly degraded by the protease. This degradation yielded a lower fractal dimensions for the matrix and suggested clearance of these materials may be possible over time.

The role of organo-zeolitic material in supporting phytoremediation of a copper mining waste dump

The effect of applying organo-zeolitic (OZ) amendment in supporting phytoremediation of a copper mine waste dump, using a substrate obtained from Ľubietová, Central Slovakia, was studied. Three plant growth substrates were prepared: (i) the untreated substrate sample from the contaminated site (D–O), (ii) the contaminated sample treated with OZ material, with 82% D–O and 18% OZ (DO + OZ), (iii) the soil from a reference site (R). The largest amount of dry biomass was obtained from the DO + OZ sample. Whole plants grown on the original substrate (D–O) were accumulating a high concentration of Cu (3057 mg kg−1). The plants root grown on DO + OZ sample accumulated highest Cu concentrations (3127 mg kg−1), but in their aerial part, only 83.54 mg kg−1 was accumulated. The translocation factor’s lower than the unit values prove that these plant species do not transfer heavy metals from root to shoot, this is why their heavy metal excluder role is evident. The value of the bioconcentration factor of the DO + OZ root/substrate obtained to be greater than the unit for Cu, Pb, Zn, Cd, Co, Ni, and Mn, suggests the OZ material’s positive contribution in the phytoremediation process that can be applied for these waste dumps.

A new substrate for glutathione reductase: Glutathione coated Ag2S quantum dots

Glutathione (GSH), a key player in various cellular processes including detoxification, anti-oxidant defense system and cell proliferation is also a potentially good coating material for luminescent quantum dots. GSH is oxidized to oxidized glutathione (GSSG) under oxidative stress and then reduced back by glutathione reductase (GR) enzyme to maintain the balance of GSH/GSSG ratio. In this frame, GSH stabilized quantum dots (QDs) have never been evaluated as GR substrate. Here, GSH coated Ag2S QDs, luminescent in the medical window, were prepared and their GR activity were tested. We have shown by spectrophotometric methods that GSH-Ag2S acted as a substrate-analog for GR enzyme that had lower activity compared to the original substrate GSSG. These results provide a new perspective in the evaluation of QDs in medical applications, enzyme activity or level detection as well as possible means to study enzymes.

Effect of Artemia inherent fatty acid metabolism on the bioavailability of essential fatty acids for Octopus vulgaris paralarvae development

The aim of the present study was to determine the effect of Artemia metanauplii endogenous fatty acid (FA) metabolism in the actual availability of dietary essential fatty acids (EFA) for Octopus vulgaris paralarvae development. To this end, both Artemia metanauplii inherent radiolabelled FA metabolism and the Octopus vulgaris paralarvae FA metabolism, after being fed with Artemia metanauplii incubated with radiolabelled FAs, were determined. Metanauplii were incubated in tissue culture plates during 12 h, with 0.3 μM of a [1-14C]FA, including either 18:3n-3, 20:4n-6 (ARA), 20:5n-3 (EPA) or 22:6n-3 (DHA), added individually to separate wells as their potassium salts bound to bovine serum albumin. A total of 3600 one-day-old paralarvae were reared up to 24 h in order to ensure the ingestion of a minimum amount of the labelled Artemia. Paralarvae rearing was performed in 4 L cylinder conical tanks at a density of 25 paralarvae L−1. Labelled Artemia metanauplii were added to each paralarvae rearing tank according to a specific [1-14C]FA treatment. Artemia in vivo metabolism results showed a preferential catabolism of DHA, which was translated into (1) the lower incorporation of this FA into Artemia total lipids (TL); (2) the highest amount of de novo synthesis of shorter chain-length FAs, as a result of the β-oxidation of the original DHA substrate. The registered amounts of radiolabelled substrates incorporated into O. vulgaris paralarvae TL fed with labelled Artemia metanauplii were extremely low. Nonetheless, certain amount of intact [1-14C]ARA and [1-14C]EPA was recovered into octopus paralarvae TL and particularly into polar lipid classes, suggesting the possibility of using Artemia as a vehicle to provide ARA and EPA to octopus paralarvae without interfering their bioavailability for the de novo synthesis of phospholipids. On the other hand, and despite of the high amount of [1-14C]18:3n-3 incorporated into Artemia TL, the FAs with the highest esterification rate into Artemia TAG (18:3n-3 and DHA) were also the lowest incorporated into paralarvae TL. Therefore, the present results suggest that O. vulgaris paralarvae may have a potentially low capacity to metabolise dietary TAG, and so, Artemia may not be the most appropriate vehicle to provide DHA to paralarvae.

Littorina littorea show small-scale persistent tidal height and habitat partitioning that is resilient to dislodgement through specific movement rates

Dislodgment, in particular by breaking waves, is a widely acknowledged source of stress, if not mortality, in rocky shores intertidal gastropods. This raises the question of understanding if snails dislodged from a specific habitat have the ability to navigate back to their original substrate, and how this is achieved. In this context, we investigated the consequences of dislodgement on a population of Littorina littorea inhabiting two proximate habitats (a seawall ranging from the low to the high intertidal zone and the related low intertidal rocky platform) located on an isolated offshore reef over a three-month period. Using tagged undisturbed, disturbed, translocated and transplanted L. littorea, we assessed a potential tidal height preference and found that L. littorea showed a clear tendency to remain on their original tidal height, with recapture rates ranging between 100% and 88%, respectively 1 and 78 days after dislodgment. We subsequently measured the recapture rates of individuals dislodged from three distinct tidal levels on the seawall and from a horizontal platform. Dislodged L. littorea showed a clear tendency to return to their original tidal level, with return rates ranging between 32 and 48% 78 days after dislodgement; snails from the horizontal platform were never found on the proximate seawall. In addition, high frequency observations conducted on individually tagged dislodged L. littorea during the first 8 successive low tides of our survey indicate that individuals originating from the seawall consistently showed higher movement rates and directionality towards the seawall, while individuals originating from the platform showed no directionality and reduced migration rate. These results show that dislodged L. littorea navigate back to their original substrate and tidal height. Putative processes include a combination of geotaxis, chemotaxis and rheotaxis. At relatively short time scales (i.e. days to months), L. littorea show both tidal and habitat partitioning that is distinct from the movement patterns previously reported in littorinids over a range of temporal scales.

Substrate-Independent Micropatterning of Polymer Brushes Based on Photolytic Deactivation of Chemical Vapor Deposition Based Surface-Initiated Atom-Transfer Radical Polymerization Initiator Films.

Precise microscale arrangement of biomolecules and cells is essential for tissue engineering, microarray development, diagnostic sensors, and fundamental research in the biosciences. Biofunctional polymer brushes have attracted broad interest in these applications. However, patterning approaches to creating microstructured biointerfaces based on polymer brushes often involve tedious, expensive, and complicated procedures that are specifically designed for model substrates. We report a substrate-independent, facile, and scalable technique with which to prepare micropatterned biofunctional brushes with the ability to generate binary chemical patterns. Employing chemical vapor deposition (CVD) polymerization, a functionalized polymer coating decorated with 2-bromoisobutyryl groups that act as atom-transfer radical polymerization (ATRP) initiators was prepared and subsequently modified using UV light. The exposure of 2-bromoisobutyryl groups to UV light with wavelengths between 187 and 254 nm resulted in selective debromination, effectively eliminating the initiation of ATRP. In addition, when coatings incorporating both 2-bromoisobutyryl and primary amine groups were irradiated with UV light, the amines retained their functionality after UV treatment and could be conjugated to activated esters, facilitating binary chemical patterns. In contrast, polymer brushes were selectively grown from areas protected from UV treatment, as confirmed by atomic force microscopy, time-of-flight secondary ion mass spectrometry, and imaging ellipsometry. Furthermore, spatial control over biomolecular adhesion was achieved in three ways: (1) patterned nonfouling brushes resulted in nonspecific protein adsorption to areas not covered with polymer brushes; (2) patterned brushes decorated with active binding sides gave rise to specific protein immobilization on areas presenting polymer brushes; (3) and primary amines were co-patterned along with clickable polymer brushes bearing pendant alkyne groups, leading to bifunctional reactivity. Because this novel technique is independent of the original substrate's physicochemical properties, it can be extended to technologically relevant substrates such as polystyrene, polydimethylsiloxane, polyvinyl chloride, and steel. With further work, the photolytic deactivation of CVD-based initiator coatings promises to advance the utility of patterned biofunctional polymer brushes across a spectrum of biomedical applications.

Experiments, Statistical Analysis, and Modeling to Evaluate the Porosity Influence in SPS Coatings

Suspension plasma spray (SPS) is far more complicated than conventional plasma spray and requires a deep knowledge about the influence of process parameters and their correlations. In this study, YSZ coatings were manufactured by SPS with six different process parameters such as plasma power, suspension mass load, original powder size, substrate surface topology, spray distance, and spray step. Afterward, the porosity of as-prepared coatings was investigated by image method and x-ray transmission technique. A multivariate analysis on the collected experimental data was carried out by employing mathematical statistics methods. The results showed that: (1) coating porosity has a negative correlation with plasma power and suspension mass load and a positive correlation with the original powder size, spray distance, spray step, and substrate roughness; (2) spraying distance is the main factor affecting to coating porosity, followed by suspension mass load and substrate surface roughness, respectively. A linear model for porosity prediction was developed and was verified by experiments. The mechanism by which process parameters influence coating porosity is also discussed.

Preparation of graphene quantum dots through liquid phase exfoliation method

Here we report the preparation of low defect blue fluorescent graphene quantum dots (GQDs) through microwave expansion and liquid phase exfoliation (LPE) of graphite flakes with a high preparation yield of 0.63 g of GQDs per 1 g of original graphite substrate. The maximum emission in the prepared GQDs occurs at 467 nm for 370 nm excitation. The photoluminescence quantum yield of the prepared GQDs was measured as 3.4%. Prepared GQDs are composed of carbon, oxygen and nitrogen elements. They have high percentage (86%) of C-C/C=C, indicating few structural defects of the graphitic core, due to lesser number of edge- or surface-located oxygenated functional groups. This preparation technique, unlike others, does not require additional chemical components and is energetically undemanding. Furthermore, the reported method is also suitable for scalable preparation of quantum structures from other two-dimensional layered materials.

Surface morphology of AlGaN/GaN heterostructures grown on bulk GaN by MBE

In this report the influence of the growth conditions on the surface morphology of AlGaN/GaN heterostructures grown on sapphire-based and bulk GaN substrates is nondestructively investigated with focus on the decoration of defects and the surface roughness. Under Ga-rich conditions specific types of dislocations are unintentionally decorated with shallow hillocks. In contrast, under Ga-lean conditions deep pits are inherently formed at these defect sites. The structural data show that the dislocation density of the substrate sets the limit for the density of dislocation-mediated surface structures after MBE overgrowth and no noticeable amount of surface defects is introduced during the MBE procedure. Moreover, the transfer of crystallographic information, e.g. the miscut of the substrate to the overgrown structure, is confirmed. The combination of our MBE overgrowth with the employed surface morphology analysis by atomic force microscopy (AFM) provides a unique possibility for a nondestructive, retrospective analysis of the original substrate defect density prior to device processing.

Phosphate oxygen isotope evidence for methylphosphonate sources of methane and dissolved inorganic phosphate

The ocean is an important source of methane, however, the sources of oceanic methane and mechanisms of its release to the atmosphere have only recently begun to be understood. Recent studies have identified methylphosphonate (MPn) as a previously unknown and likely source of methane in the aerobic ocean (Karl et al., 2008), as well as shown the biosynthesis of methylphosphonic acid to be a widespread trait in marine microbes (Metcalf et al., 2012). The mechanisms and reaction pathways from MPn to free methane, however, have not been well studied. Here we present results of laboratory studies on the photo-degradation of MPn, a likely mechanism of methane release to the atmosphere and phosphate release to the surface oceans. Phosphonoacetic acid was also studied as an additional model compound for comparison. We used the multi-labeled water isotope probing (MLWIP) approach, involving 18O-labeled waters to probe the photolytic mechanism of CP bond cleavage in phosphates through analysis of P released from MPn as PO4. These studies identified distinct reaction pathways involving phosphates compared with other common organophosphorus compounds (e.g., phosphoesters), as well as suggest the involvement of both ambient water and atmospheric oxygen in CP bond cleavage. There is only a small amount of water oxygen incorporated into product PO4 after cleavage of the CP bond in MPn, suggesting atmospheric O2 or radicals formed from O2 under Ultra Violet Radiation (UVR), as the primary source of O that replaces C in the CP bond of MPn. Model calculations suggest that the δ18OP signature of phosphate released via UV-degradation of phosphates is largely (75%) inherited from the original phosphate substrate. This opens up the possibility of tracing and differentiating specific phosphate sources of dissolved phosphate from other organophosphorus (Porg) sources (e.g., phosphoesters) used in primary production, as well as for tracing specific MPn sources of atmospheric methane.

Tribological properties of B4C reinforced aluminum composite coating produced by TIG re-melting of flame sprayed Al-Mg-B4C powder

Producing a high-performance surface composite layer under severe tribological conditions such as wear was main purpose of this investigation. In this regard, B4C submicron-sized particles were chosen as reinforcement to increase tribological properties of Al-Mg alloy. A surface layer with a mixture of Al and B4C powders (5 wt%B4C) was made using thermal spray process on the substrate and then melted using gas tungsten arc welding (GTAW) technique to produce composite coating. Microstructure, formed phases and reinforcement particles in the composite layer were examined, as well. Wear behavior of samples against steel disc with hardness of 62 HRC was evaluated by a pin-on-disk setup of experiment at ambient temperature. The results illustrated significant reduction in the friction coefficient and weight loss; around 35 and 60% in comparison with uncoated substrate, respectively and showed a decline in wear rate up to 48%. Moreover, a substantial increase, up to 4 times, in the hardness of Al/5 wt%B4C composite coating was observed compared to the original substrate.