Glass Filters Research Articles

Errors and recommended practices that should be identified to reduce suspected concentrations of microplastics in soil and groundwater: A review

Over the last decade, many studies on microplastics (MPs) have only focused on the marine environment, and scientist have recently begun to document soil and groundwater MP contamination. However, many of these studies have included errors that should be addressed. Therefore, the aim of this study is to identify multiple errors in internationally reported soil and groundwater MPs studies and to provide recommendations. Over 185 original research papers on soil and groundwater MPs published between 2017 and 2022 from seven database categories in the Web of Science were sorted. These papers were manually sorted to identify errors in (i) sample quantity, (ii) quality assurance and equipment used, (iii) microplastic identification, and (iv) microplastic classification. The majority of studies were found not to use blank samples, classified MPs incorrectly by mixing MP shapes and forms, used filters with either larger pore sizes, or materials that could be potential sources of MP. In some of these studies, the statistical package or law used for statistical analysis was not specified, with some other studies using problematic MP analysis procedures. As a remediation method to address these errors, MP studies should consider using blank soil samples and metallic filters. Statistical software packages should be used, and the statistical prerequisite laws should be verified prior to analysis. Stereo microscopes should be used simultaneously with Raman or Fourier transform infrared (FTIR) spectroscopy to identify MPs in soils and groundwater. • It is essential plastic kits are not used for storing soil and groundwater after sampling. • Accurate microplastic analysis requires at least one trip and a device blank sample each time. • Film and fragment should be classified as the same microplastics shape, not separate shapes. • A glass filter is preferable to a cellulose filter for accurate microplastics analysis. • It is critical to collect soil weight in the range of 200–1000 g for accurate microplastic analysis.

A pressure driven electric energy generator exploiting a micro- to nano-scale glass porous filter with ion flow originating from water

We demonstrated a pressure driven energy harvesting device using water and that features a glass filter with porous channels. We employed powder sintering to fabricate the glass filter (2 cm diameter, 3 mm thickness) by packing a powder of borosilicate glass particles into a carbon mold and then thermally fusing this at 700°C under pressure. In constant flow rate experiment, the optimum average pore radius of the filter for power generation was 12 μm. Using this filter, power of 3.8 mW (27 V, 0.14 mA, 0.021% energy efficiency) was generated at a water flow speed of 50 mm/s. In constant pressure experiment, a power generator was equipped with a foot press unit with a 60 kg weight (830 kPa) and 50 mL of water. The optimum average pore radius for power generation in this experiment was 12 μm and power of 4.8 mW (18 V, 0.26 mA, 0.017% energy efficiency) was generated with 1.7 s duration. This was enough power for direct LED lighting and the capacitors could store enough energy to rotate a fan and operate a wireless communicator. Our pressure driven device is suitable for energy harvesting from slow movements like certain human physiological functions, e.g. walking.

Silicone Nanofilament Coatings as Flexible Catalyst Supports for a Knoevenagel Condensation Reaction in Batch and Flow Systems.

In this work, silicone nanofilament (SNF) coatings were prepared via a droplet-assisted growth and shaping (DAGS) approach, where the preparation of the coatings is allowed under ambient conditions. The application of SNF coatings as catalyst supports for amino moieties from (3-aminopropyl)triethoxysilane (APTES) was investigated. With the optimized coating conditions identified, the Brunauer-Emmett-Teller surface areas of a bare glass filter substrate and bare glass beads after the coating have increased by 5-fold and 16-fold, respectively. The SNF-coated filters were readily functionalized with amino groups via a liquid-phase deposition process, and their catalytic activities for a Knoevenagel reaction were evaluated using a batch reactor and a packed bed reactor. In both reactors, the as-prepared filters demonstrated superior catalytic performance over the functionalized filters without SNF coatings. Notably, the unique flexibility of the SNF coatings allowed the facile preparation of a packed bed reactor and a scalable catalytic system. It is expected that the packed bed system established in this study will support the development and the use of various SNF-supported organocatalysts and catalytic materials.

Surfactant-free air bubble flotation-coagulation for the rapid purification of chloroquine.

A simple and rapid separation method based on surfactant-free air bubble flotation and coagulation was designed for the purification of chloroquine (CQ) from its crude product. An open glass column having a sintered glass filter (for column chromatography) was used as a flotation vessel. The flotation was conducted by pouring the crude CQ into the aqueous solution containing 0.1% (v/v) of 2-propanol followed by feeding air through the glass filter to generate air bubbles. At pH 12, CQ was enriched into the foam temporary generating on the surface of water to form the coagulates within 90s after the start of the air bubble flotation. On the other hand, reactants; 4,7-dichloroquinoline and 4-amino-1-diethylaminopentane, as well as generated impurities remained in the bulk aqueous solution. The result of dynamic surface tension measurement indicated that CQ molecules selectively adsorbed on the air-water interface and the coagulates more strongly adsorbed the interface. Adsorption and coagulation of CQ molecules on the air-water interface were also reproduced in the calculation results of a molecular dynamic simulation. The coagulates were collected from the surface of water by suction and then poured into another flotation vessel for conducting repeated separation. The time required for the respective separation process including air bubble flotation and collection by suction was within 5min. After three-times separation, highly purified (> 99.0%) CQ was obtained with a yield of 72 ± 8%. The amounts of reactants and other impurities reduced into undetectable levels.

Electrolyte Analysis in Blood Serum by Laser-Induced Breakdown Spectroscopy Using a Portable Laser.

The fast and reliable analysis of electrolytes such as K, Na, Ca in human blood serum has become an indispensable tool for diagnosing and preventing diseases. Laser-induced breakdown spectroscopy (LIBS) has been demonstrated as a powerful analytical technique on elements. To apply LIBS to the quantitative analysis of electrolyte elements in real time, a self-developed portable laser was used to measure blood serum samples supported by glass slides and filter paper in this work. The partial least squares regression (PLSR) method was employed for predicting the concentrations of K, Na, Ca from serum LIBS spectra. Great prediction accuracies with excellent linearity were obtained for the serum samples, both on glass slides and filter paper. For blood serum on glass slides, the prediction accuracies for K, Na, Ca were 1.45%, 0.61% and 3.80%. Moreover, for blood serum on filter paper, the corresponding prediction accuracies were 7.47%, 1.56% and 0.52%. The results show that LIBS using a portable laser with the assistance of PLSR can be used for accurate quantitative analysis of elements in blood serum in real time. This work reveals that the handheld LIBS instruments will be an excellent tool for real-time clinical practice.

Acidic hydrolysis of recycled polyethylene terephthalate plastic for the production of its monomer terephthalic acid

Post-consumer polyethylene terephthalate (PET) plastic bottles, after some pre-processing, were chemically depolymerized for the production of terephthalic acid (TPA), an important monomer of PET resin. The optimized condition of PET hydrolysis was 100°C with 80% v/v aqueous sulfuric acid liquor for 30 min reaction time. The terephthalic acids (TPAs) were filtered out from the reaction mixtures with a sintered glass filter. The viscosity of recycled hydrolysis liquor was measured before it was used in a successive batch of PET depolymerization. The viscosity of hydrolysis liquor increased gradually from 5 mm2/s to 87 mm2/s. TPA yields were obtained from 85.03 ± 0.03% to 99.20 ± 0.06% and the color of TPA changed from bright white to off-white in the final batches. The structure of TPA was confirmed by FTIR, mass analysis, and 1H-NMR spectroscopy. The purity of TPA was found to be 95–98% from the HPLC study via external calibration technique. Thermogravimetric analysis (TGA) determined the thermal degradation patterns of TPAs and residual weights. This experiment reveals that repeated use of sulfuric acid hydrolysis liquor would be a good option for PET depolymerization in terms of resource utilization, TPA quality as well as sustainability.

Lighting gel filters as low-cost alternatives for fluorescence imaging and optical system design

Lighting gel filters are widely used in commercial industries, but their adoption in scientific applications is limited, despite their low cost and form factor advantages. Here, we compare the optical performance of lighting gel filters to commonly used dielectric and colored glass filters in terms of absorbance spectra, passband transmission, angle of incidence dependence, autofluorescence, and photostability. Further comparison is performed in both preclinical and clinical imaging applications. The results show that gel filters might be a superior filter choice in several optical systems, including compact designs and fluorescence imaging applications. Compact designs using gel filters could have a significant advantage for applications such as point-of-care diagnostics, smartphone device add-ons, and single-use fluorescent assays.

Visible‐Blind Deep Ultraviolet Photomultiplication Organic Photodetectors with Ultrahigh Gain for UVB and UVC Light Detection

AbstractPhotomultiplication‐type organic photodetectors (PM‐OPDs) have developed rapidly in UVA, visible and near‐infrared ranges, but they face great challenges in the UVB and UVC ranges, mainly due to the difficulty of simultaneously realizing deep UV light‐transmittance electrode and high gain structure. Here, the copper and silver bilayer composite electrodes are developed to overcome the problem of silver island growth, thus ensuring high deep UV light transmittance and good matching with electrical gain mechanism. The fabricated device shows high external quantum efficiency as high as 195,665% at 255 nm in UVC region. Furthermore, the above electrodes are integrated with low‐cost UV filter glass ZWB1 by simple vacuum evaporation. Finally, low‐cost visible‐blind deep UV PM‐OPDs with a rejection ratio of up to 4788 is achieved through an additional strategy of adjusting the absorption spectrum of the active layer. Benefiting from its fast response speed, the device can be directly applied to faint flame monitoring in real‐time.

Fluorescence-polarization immunoassays within glass fiber micro-chambers enable tobramycin quantification in whole blood for therapeutic drug monitoring at the point of care

Many therapeutic drugs require monitoring of their concentration in blood followed by dose adjustments in order to ensure efficacy while minimizing adverse effects. It would be highly desirable to perform such measurements rapidly and with reduced sample volumes to support point-of-care testing. Here, we demonstrate that the concentration of small therapeutics can be determined in whole blood within paper-like membranes using Fluorescence Polarization Immunoassay (FPIA). Different types of paper-like materials such as glass microfibers, cellulose and filter paper were investigated for artefacts such as scattering or autofluorescence. Accurate determination of the fluorescence polarization of red-emitting fluorophores at sub-nanomolar concentrations was feasible within glass fiber membranes. This enabled the development of a competitive immunoassay for the quantification of the antibiotic tobramycin using only 1 μL of plasma in glass fiber micro-chambers. Furthermore, the same membrane was used for transversal separation of blood cells followed by accurate FPIA read-out at the bottom part of the micro-chamber. For quantification of tobramycin, 1 μL of whole blood was incubated with the immunoassay reagents during only 3 min before deposition in the micro-chamber and analysis. Within the therapeutic window, coefficients of variation were around 20% and recoveries between 80 and 105%. Owing to the simplified procedure requiring no centrifugation, the reduced blood sample volume and the rapid analysis time, we envision that this novel method supports the performance of therapeutic drug monitoring directly at the point of care.

Effectiveness of syntonic phototherapy in amblyopia in terms of improved visual acuity and contrast sensitivity

Purpose: To compare visual acuity and contrast sensitivity in different types of amblyopia and to see the effect of syntonic therapy on amblyopia in terms of visual acuity and contrast sensitivity. Study Design: A Quasi Experimental study Place and Duration of Study: A Qusai Experimental study was carried out from August 2021 to November 2021 at Madina Teaching Hospital Faisalabad. Methods: A total of 30 patients of either gender and age from 8 to 18 years were included. There were 15 patients with anisometropic amblyopia and 15 with strabismic amblyopia. The patients were recruited through non-probability purposive sampling technique. All the patients underwent assessment of visual acuity with Log MAR chart and contrast sensitivity with Pelli-Robsonchart. Syntonic phototherapy with red filter glasses was prescribed for 4 weeks. After 4 weeks, patients returned and underwent post-therapy assessment of visual acuity and contrast sensitivity. Paired sample t test and Independent sample t test was used with the help of IBM SPSS-23 to get a statistical result. Results: Syntonic phototherapy showed significant improvement in mean visual acuity of 0.223 (p=0.00) and contrast sensitivity of -0.200 (p=0.00) in amblyopia. Anisometropic amblyopia showed better improvement in visual acuity (p=0.016) and contrast sensitivity (p=0.035) by syntonic phototherapy as compared to patients with strabismic amblyopia. Conclusion: Significant improvement was seen in visual acuity and contrast sensitivity in patients with amblyopia after syntonic phototherapy. Anisometropic amblyopia showed better improvement as compared to strabismic amblyopia, in terms of visual acuity and contrast sensitivity.

Statistical optimization of process conditions for pyrvinium pamoate elimination using UV/zeolite‐based nanostructures/H 2 O 2

Statistical optimization of process conditions for pyrvinium pamoate elimination using UV/zeolite‐based nanostructures/H ₂ O ₂

P‐110: Analysis of Light Leakage in the Dark State with W Pixel in the Liquid Crystal Display (LCD)

In this paper, we analyze the influence factors on light leakage of dark state for RGBW design by using different pixel designs and different backlights (BL) . W pixel is introduced on the basis of RGB pixels, which causes the deterioration of leakage in dark state. To further study the influence factors, we separate LCD panel as array glass and color filter glass (CF) and measure their transmittances under different types of BLs. Additionally, we choose different types of LC and investigate the influence of the scattering index of LC on light leakage of dark state.

A full-scale tracing study of "ghost peaks" encountered in impurity analysis of budesonide based on experimental operation inspection-liquid chromatography/mass spectrometry fingerprint-mechanism based stress studies integrated strategy.

Budesonide is an active pharmaceutical ingredient used in various dosage forms of finished products for the treatment of asthma. During the process of drug development, unbiased analysis of related substances is of utmost significance for both pharmaceutical research and quality control purposes. In this work, the official method documented in the United States Pharmacopoeia was selected to determine the related substances of budesonide considering the pros and cons of critical chromatographic parameters, compared to the European Pharmacopoeia. In doing so, several unpredictable interference peaks, namely "ghost peaks", were observed occasionally during analysis. A strategy that integrated information derived from experimental operation inspection, liquid chromatography/mass spectrometry fingerprint analysis, and mechanism-based stress studies was then proposed for comprehensively and quickly exploring those non-degradable and degradable peaks. Some ghost peaks were found to originate from nylon syringe filter, illumination, and alkali borosilicate glass high-performance liquid chromatography vials. Besides, degradation pathways under alkaline conditions were also unraveled through liquid chromatography-mass spectrometry qualitative analysis. Overall, an optimization of the analytical methodology based on the United States Pharmacopoeia for its application in impurity analysis of budesonide and corresponding formulations was carried out with the design of experiments, by which "ghost peaks" could be suppressed or prevented. The results obtained herein are not only crucial to studies on budesonide's stability or degradation kinetics but also contribute to clarifying the impurity research of other drugs.

Physico-chemical properties of perturbed water: facts and enigmas

Physico-chemical properties of perturbed water: facts and enigmas

Raspberry Pi-based mobile system of the pupil size evaluation

The article considers development of a human pupil measuring system on the Raspberry platform. The system is aimed at evaluating the variations of the human pupil diameter or area in the process of watching test images or video recordings. To reduce the interference from the eye surface the camera uses a band-stop color glass filter PS 13. In order to increase the pupil image contrast, IR LED backlighting of the eye is implemented. To provide the mobility of the system, battery power of the single-board computer was used while the registered image and the measurement results were transmitted via a Wi-Fi channel. The video camera and the single-board computer Raspberry Pi 4 with the battery bay are attached to the head-mounted flexible belt. The article gives the operation duration evaluation of the battery-supplied system. During the first stage of image processing, binarization by the threshold was performed. The threshold is determined by the image brightness histogram. Since the study is focused on relative variations of the pupil size, the pupil diameter or area values in pixels were chosen as informative parameters. The image recording and processing frequency in the system equalled 25 Hz that provides accurate recording of the pupil variations.

Total integrated centrifugal genetic analyzer for point-of-care Covid-19 testing with automatic and high-throughput capability

We propose a prototype portable genetic analyzer, which performs the entire processes including RNA purification, reverse transcription multiplex loop-mediated isothermal amplification (RT-LAMP), and real-time fluorescence detection. Ten units of integrated functional entity were incorporated on a centrifugal disc, so that 10 samples could be analyzed on single device in one run. The 10 aliquoting chambers were connected sidewards by the zigzag aliquoting channel and were linked to the glass filter column outwards via the passive valves for the RNA extraction. The lower sideward capillary pressure of the zigzag aliquoting channel than the outward capillary pressure of the passive values is capable of automatic division of solution into the 10 aliquoting chambers with one injection by a needle. The sequent loading and partitioning of the sample, the washing, and the elution solutions by centrifugal protocols rendered the RT-LAMP cocktails ready for amplification in the three reaction chambers for each sample, in which the RT-LAMP primers targeting orf1ab, N and S genes were dried. After blocking the reaction chambers by wax to prevent evaporation, RT-LAMP reaction proceeded at 63 °C, and all the positive fluorescent signals in the three chambers verifies the existence of Covid-19 in the sample. For point-of-care testing (POCT), we constructed a portable workstation that consists of a solution storage, a solution injection system, a spinning motor, and a fluorescence detector. Using the proposed platform, we could perform the Covid-19 molecular diagnostics for 10 samples per run on single device in an automatic and high-throughput manner in 1.5 h.

In Situ Impedance Spectra Analysis of Lithium-Sulfur Battery Using Sulfolane-Based Super-Concentrated Electrolyte Solution

Lithium-Sulfur (Li-S) battery has attracted attention as a new generation secondary battery. However, the Li-S battery has some problems toward its realization, one of which is the dissolution of discharge products of lithium polysulfides. Recently, Watanabe and Dokko et al. [1,2] reported that a solvate ionic liquid and a sulfolane-based super-concentrated electrolyte solution had low solubility of the polysulfides, and proposed polysulfides insoluble Li-S batteries using these electrolyte solutions. The discharge reaction paths of the Li-S batteries are currently unclear due to the strong dependence on the electrolyte solution In this contribution, in situ electrochemical impedance spectroscopy (EIS) was applied to the Li-S battery using the sulfolane-based super-concentrated electrolyte solution to obtain further insight into the reaction paths during the discharge. A positive electrode slurry was obtained by mixing a sulfur S8, a Ketjen black (KB) and a carboxymethyl cellulose (CMC2200) at a weight ratio of 60 : 30 : 10. The Slurry was spread on an Al foil to obtain a KB-S composite electrode. The typical loading of the sulfur was 2.0 mg cm-1. A negative electrode and a separator were used a lithium metal foil and a glass filter (GA-50, Advantec), respectively. The sulfolane (SL)-based super-concentrated electrolyte solution was prepared by dissolving lithium bis-(trifluoromethanesulfonyl)amide (LiTFSA) into the SL as the molar ratio of 1 : 2. 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE) was added to the SL-based electrolyte solution as a diluent and finally the molar ratio of LiTFSA : SL : HFE was prepared at 1 : 2 : 2. The Li-S battery was assembled using the CR 2032 coin-type cell in an Ar-filled glove box. The galvanostatic charge-discharge measurement was carried out at the C-rate of 1/12 C. The measurement was stopped at the SOC (state of charge) = 50 % in the second charge step. Then, after relaxing to an equilibrium state, the in situ EIS measurements were performed using an electrochemical system (HZ-7000) in the frequency range from 100 mHz to 100 kHz. The in situ EIS measurement was carried out while charging at the C-rate of 1/8 C for 30 minutes. Afterward, the discharge process was measured under the same condition after keeping open circuit potential for 5 minutes. The amplitude of the AC current was determined to make the AC potential response 10 mV. In the charge-discharge curves for the Li-S battery using the SL-based electrolyte solution, the first and the second plateaus appeared in the range of 16 to 90 mAhg-1 and 180 to 700 mAhg-1, respectively. The charging curve during the in situ EIS measurement was almost identical to the charging curves during the 1st and the 2nd cycles. On the other hand, the discharging curve during the in situ EIS measurement was quite different from one in the steady state of discharging. That is, it took time to achieve the steady state of the discharge. Instantaneous impedance spectra [3, 4] were obtained with compensating the time of the measured impedance spectra. Two capacitive semicircles were observed in the instantaneous impedance spectra. The semicircle appeared in the low frequency region was attributable to the charge transfer resistance and constant phase element related to double-layer capacitance. Curve fittings using an equivalent circuit were performed on the instantaneous impedance spectra. Although the charge transfer resistance was almost constant during the charge, it remarkably increased during the discharge. This suggests that resistances for an increase of Li ion concentration at the positive electrode/electrolyte interface and the Li ion insertion to the active material are quite large. These resistances probably cause to take much time to reach the steady state of discharge. References 1) K. Dokko et al., J. Electrochem. Soc., 160, A1304-A1310 (2013).2) A. Nakanishi et al., J. Phys. Chem. C, 123, 14229-14238 (2019).3) Z. B. Stoynov et al., J. Electroanal. Chem., 183, 133-144 (1985).4) M. Itagaki et al., J. Power Sources, 135, 255-261 (2004).

Electrochemical applications of printed circuit boards: Electrocatalysis and internal reference electrodes

As a chemically resistant hard substrate with surface-mounted metal pads, Printed Circuit Boards (PCBs) have the potential to be utilized as substrates for electrochemical applications such as electrochemical microfluidic devices. Compared with regular electrochemical substrates made with glass slides or filter papers, PCB-based substrates have electrode pads with customized size, shape and position, and more wiring layers. Previous works have shown that the PCB-based electrochemical devices can be used as biosensors, electrochemical impedance cytometers, and electrochemical imaging platforms, while their workability as a platform for electrocatalysis has not yet been presented. This work presents a method to develop PCBs into electrochemical substrates for alcohol electrocatalysis and internal reference electrodes. The copper pads were pretreated and electrodeposited with nickel (Ni), silver (Ag), palladium (Pd), and platinum (Pt) for various electrocatalytic purposes. To show the ability of making PCB-based electrochemical devices, two types of PCB-based reference electrodes were made.

Determination of the multiple-scattering correction factor and its cross-sensitivity to scattering and wavelength dependence for different AE33 Aethalometer filter tapes: a multi-instrumental approach

Abstract. Providing reliable observations of aerosol particles' absorption properties at spatial and temporal resolutions suited to climate models is of utter importance to better understand the effects that atmospheric particles have on climate. Nowadays, one of the instruments most widely used in international monitoring networks for in situ surface measurements of light absorption properties of atmospheric aerosol particles is the multi-wavelength dual-spot Aethalometer, AE33. The AE33 derives the absorption coefficients of aerosol particles at seven different wavelengths from the measurements of the optical attenuation of light through a filter where particles are continuously collected. An accurate determination of the absorption coefficients from the AE33 instrument relies on the quantification of the non-linear processes related to the sample collection on the filter. The multiple-scattering correction factor (C), which depends on the filter tape used and on the optical properties of the collected particles, is the parameter with both the greatest uncertainty and the greatest impact on the absorption coefficients derived from the AE33 measurements. Here we present an in-depth analysis of the AE33 multiple-scattering correction factor C and its wavelength dependence for two different and widely used filter tapes, namely the old, and most referenced, TFE-coated glass, or M8020, filter tape and the currently, and most widely used, M8060 filter tape. For performing this analysis, we compared the attenuation measurements from AE33 with the absorption coefficients measured with different filter-based techniques. On-line co-located multi-angle absorption photometer (MAAP) measurements and off-line PP_UniMI polar photometer measurements were employed as reference absorption measurements for this work. To this aim, we used data from three different measurement stations located in the north-east of Spain, namely an urban background station (Barcelona, BCN), a regional background station (Montseny, MSY) and a mountaintop station (Montsec d'Ares, MSA). The median C values (at 637 nm) measured at the three stations ranged between 2.29 (at BCN and MSY, lowest 5th percentile of 1.97 and highest 95th percentile of 2.68) and 2.51 (at MSA, lowest 5th percentile of 2.06 and highest 95th percentile of 3.06). The analysis of the cross-sensitivity to scattering, for the two filter tapes considered here, revealed a large increase in the C factor when the single-scattering albedo (SSA) of the collected particles was above a given threshold, up to a 3-fold increase above the average C values. The SSA threshold appeared to be site dependent and ranged between 0.90 to 0.95 for the stations considered in the study. The results of the cross-sensitivity to scattering displayed a fitted constant multiple-scattering parameter, Cf, of 2.21 and 1.96, and a cross-sensitivity factor, ms, of 1.8 % and 3.4 % for the MSY and MSA stations, respectively, for the TFE-coated glass filter tape. For the M8060 filter tape, Cf values of 2.50, 1.96 and 1.82 and ms values of 1.6 %, 3.0 % and 4.9 % for the BCN, MSY and MSA stations, respectively, were obtained. SSA variations also influenced the spectral dependence of C, which showed an increase with wavelength when SSA was above the site-dependent threshold. Below the SSA threshold, no statistically significant dependence of C on the wavelength was observed. For the measurement stations considered here, the wavelength dependence of C was to some extent driven by the presence of dust particles during Saharan dust outbreaks that had the potential to increase the SSA above the average values. At the mountaintop station, an omission of the wavelength dependence of the C factor led to an underestimation of the absorption Ångström exponent (AAE) by up to 12 %. Differences in the absorption coefficient determined from AE33 measurements at BCN, MSY and MSA of around 35 %–40 % can be expected when using the site-dependent experimentally obtained C value instead of the nominal C value. Due to the fundamental role that the SSA of the particles collected on the filter tape has in the multiple-scattering parameter C, we present a methodology that allows the recognition of the conditions upon which the use of a constant and wavelength-independent C is feasible.

Laser gas oxidizing of titanium surface in a dilute oxygen environment

Titanium has attracted considerable attention for applications in several industries owing to its low density and high tensile strength ; however, its poor surface hardness and wear rate limit these applications. This study aims to improve the mechanical properties of the titanium surface. A new surface modification process for titanium is proposed, wherein Ar is used to dilute O 2 and laser gas oxidizing is performed on the titanium surface in this dilute O 2 environment. The feasibility of this process was verified at different O 2 /Ar gas flow ratios. The evolution of the molten pool generated by laser irradiation was analyzed using a high-speed camera combined with a welding glass filter. The surface and cross-section of the modified layer were observed by scanning electron microscopy and X-ray diffraction to study its forming characteristics. The microhardness was characterized, and friction and wear tests were carried out to study the properties of the modified layer. The experiments proved that diluting O 2 with Ar can reduce the rate of the reaction between O 2 and titanium and enhance the process controllability; therefore, laser gas oxidizing of the titanium surface in a dilute O 2 environment is feasible. The O 2 to Ar gas flow ratio significantly affected the process controllability, as well as the surface roughness , number of cracks, microhardness, and wear resistance of the modified layer. With a moderate O 2 to Ar gas flow ratio, optimal formation and performance of the modified layer can be achieved. The oxygen content and hardness below the modified layer were lower than those of the modified layer; however, they higher than those of commercially-pure titanium. • Diluting O 2 with Ar reduces Ti oxidation rates and enhances process controllability. • Laser gas oxidizing of Ti surfaces in dilute O 2 is practically feasible. • Moderate O 2 to Ar gas flow ratios are best for modified layer performance. • Hardness and O content below modified layer are higher than in commercial titanium.