Effects Of Different Electrolytes Research Articles

Effects of different electrolytes on the structure and yield ofgraphene oxide produced via electrochemical exfoliation

The most suitable electrolyte for graphene oxide synthesis, in terms of both production efficiency and quality, using the electrochemical exfoliation technique has been investigated and reported in this study. Simultaneous anodic and cathodic graphene oxide production using ten (10) different electrolytes, including acids (H2SO4, HCl, HNO3), bases (KOH, Ca(OH)2, Mg(OH)2, NaOH), and salts (NaCl, (NH4)2SO4, K2SO4), was studied under the same experimental conditions of bias voltage, graphite nature, exfoliation time, electrolyte molarity, and post-exfoliation treatments. Assessment of the graphene oxide structures and production rates was supported using Raman spectroscopy, high-resolution scanning electron microscopy (HRSEM), and EDS (energy dispersive x-ray spectroscopy), attached to the scanning electron microscope. Analysis of the results obtained reveals that H2SO4 showed the highest graphene oxide yield (86%) but with comparably low graphene oxide quality in terms of defect concentration, presence of oxygen functional group contamination, and crystallite properties. The aqueous NaCl, Ca(OH)2 and Mg(OH)2 electrolytes did not show any graphene oxide exfoliation effect. However, from the series of electrolytes examined, aqueous (NH4)2SO4 exhibited an excellent combination of efficient graphene oxide yield and high-quality characteristics due to its relatively high yield of 74% and superior quality of the produced graphene oxide with the comparatively lowest defect density, ?D, and highest C/O (carbon-to-oxygen) ratio. The tortuous, agglomerated, and planar layers of the distinct 2D graphene oxide sheets were also clearly revealed by the SEM images. In essence, the roles played by dissociated sulfate (SO42?), nitrate (NO32?), chlorides (Cl?), and hydroxides (OH?) ions in the series of complex electrochemical reactions toward the intercalation, exfoliation, yield, and properties of graphene oxide produced are discussed. From the series of electrolytes tested, aqueous (NH4)2SO4 emerged as the most relatively suitable electrolyte for the synthesis of graphene oxide because it combines both high yield and fine quality.

Electrolytic Characteristics of Microhole Array Manufacturing Using Polyacrylamide Electrolyte in 304 Stainless Steel.

Because of the ease with which oxide films form on its surfaces, stainless steel has strong corrosion resistance and excellent processing performance. Electrochemical machining (ECM) is a flexible process that can create microstructures on stainless steel (SS304); however, with traditional masked ECM, the efficiency and accuracy of microstructure machining are low. Proposed here is the use of a non-Newtonian fluid [polyacrylamide (PAM)] as the electrolyte. To date, there have been few papers on the electrochemical dissolution behavior of stainless-steel micromachining with a non-Newtonian fluid as the electrolyte. The aims of the study reported here were to investigate the electrochemical properties of SS304 with PAM and PAM-NaOH as electrolytes, and to explain their electrochemical corrosion mechanisms. The effects of different electrolytes were compared, and the polarization curves of SS304 in PAM and PAM-NaOH electrolyte solutions with different components were analyzed and compared with that in NaNO3 electrolyte. Then, the effects of the main processing parameters (pulse voltage, frequency, and duty ratio) on the machining performance were investigated in detail. A microhole array was obtained with a good quality comprising an average diameter of 330.11 µm, an average depth of 16.13 µm, and a depth-to-diameter ratio of 0.048. Using PAM to process microstructures on stainless-steel surfaces was shown to be feasible, and experiments indicated that the mixed electrolyte (PAM-NaOH) had not only the physical characteristics of a non-Newtonian fluid but also the advantages of a traditional electrolyte to dissolve processing products, and it effectively improved the processing accuracy of masked ECM for SS304.

Colorless-to-colorful switching of electrochromic MXene by reversible ion insertion

Electrochromic (EC) materials that change color with voltage have been widely studied for use in dynamic windows. However, colorless-to-colorful switching with high contrast ratio is generically unattainable, especially for colorless-to-black electrochromic materials with an ultrahigh contrast ratio over the entire visible region. In this work, we developed Nb1.33C MXene-based dynamic windows with colorless-to-black switching of up to 75% reversible change in transmittance from 300 to 1,500 nm. By exploring the electrochromic effects of different electrolytes through in situ optical changes and electrochemical quartz crystal microbalance (EQCM), it is found that electrochromic behavior is greatly influenced by the extent of reversible Li+ insertion/deinsertion between the two-dimensional Nb1.33C MXene nanosheets. In addition, a colorless-to-black EC device based on Nb1.33C with an overall integrated contrast ratio over 80% was successfully constructed by a solution-processable spin coating method. This work enables a simple route to fabricate MXene-based high-performance electrochromic smart windows, which is important for further expanding the application of MXenes to optoelectronic and photonic applications.

Effects of Different Electrolytes on Stress Corrosion Properties of 2A12 Aluminum Alloy

Effects of Different Electrolytes on Stress Corrosion Properties of 2A12 Aluminum Alloy

Preparation of Hierarchical Porous Activated Carbon from Banana Leaves for High-performance Supercapacitor: Effect of Type of Electrolytes on Performance.

We demonstrate a facile efficient way to fabricate activated carbon nanosheets (ACNSs) consisting of hierarchical porous carbon materials. Simply heating banana leaves with K2 CO3 produce ACNSs having a unique combination of macro-, meso- and micropores with a high specific surface area of ∼1459 m2 g-1 . The effects of different electrolytes on the electrochemical supercapacitor performance and stability of the ACNSs are tested using a two-electrode system. The specific capacitance (Csp ) values are 55, 114, and 190 F g-1 in aqueous 0.5 M sodium sulfate, organic 1 M tetraethylammonium tetrafluoroborate in acetonitrile, and pure ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6 ]) electrolytes, respectively. The ACNSs also shows the largest potential window of 3.0 V, the highest specific energy (59 Wh kg-1 ) and specific power (750 W kg-1 ) in [BMIM][PF6 ]. A mini-prototype device is prepared to demonstrate the practicality of the ACNSs.

Effects of Different Electrolytes on Microstructure and Antibacterial Properties of Microarc Oxidized Coatings of CP-Ti

Effects of Different Electrolytes on Microstructure and Antibacterial Properties of Microarc Oxidized Coatings of CP-Ti

Effects of electrolyte on the removal of fluorine from red mud by electrokinetic remediation

ABSTRACT Red mud contains high levels of fluorine compounds. Once these fluorides were released, which led to adverse effects on human health and environment. The aim of this study was to investigate the possible use-electrokinetic remediation (EKR) for the removal of fluorine from red mud and explore the effects of different electrolytes on the remediation process. Three runs of EKR experiments were chosen using distilled water (run A), 0.1 mol/L HCl (run B) and 0.1 mol/L NaOH (run C), respectively. Related parameters for EKR, such as electric current, electro-osmotic flow (EOF) and energy consumption, were analysed. Characterisations of red mud were studied by SEM, XRD and FTIR. Experimental results showed that EKR could effectively remove fluorine pollutants from red mud. Electrolyte can obviously affect fluorine removal in EKR. The removal efficiency of run A, B and C was 57.69%, 66.75%, 60.04%, respectively, and run B (adding 0.1 mol HCl) had the best removal efficiency and the lowest residual fluorine in treated red mud after EKR, because of the highest electric current and EOF in all runs. Energy consumption per kilogram dry red mud of run A, B and C was 0.370, 0.726, and 0.506 kWh/kg, respectively. Experimental results showed that electro-osmosis and electromigration were both important removal mechanisms in EKR of fluorine from red mud. After EKR, the proportion of RESF (the residual fraction of fluorine) increased significantly, now fluorine of treated red mud had a good chemical inertness and had a smaller influence on environment.

Weak layer exfoliation and an attempt for modification in anodic oxidation of PAN-based carbon fiber

Effects of different electrolytes on the surface structure and interfacial property with epoxy resin of PAN-based carbon fiber are evaluated, which is used to find out the key factor that affects the improvement in the interfacial adhesion. It is found that the carbon fiber treated in H2SO4 electrolyte owns the most abundant oxidative groups but bonds relatively weak with epoxy resin by the maximum interlaminar shear strength of 60 MPa. The carbon fiber oxidized in NaOH electrolyte and then restored in HCl solution owns less oxidative groups but shows a strongest bonding with epoxy resin by the maximum interlaminar shear strength of 69 MPa. We conclude this phenomenon is mainly ascribed to the graphene layers covering on the fiber surface that are formed during carbonization and connect weakly with the substrate of carbon fiber, thus called weak layers. The weak layers can be peeled off effectively in NaOH electrolyte but not in H2SO4 electrolyte. An attempt for modification is tried by removing the weak layers in NaOH electrolyte and adding more oxygen groups in H2SO4 electrolyte. The interlaminar shear strength of the fiber with epoxy resin is not increased as expected; however, it shows oxidation in H2SO4 electrolyte does not generate weak layers on carbon fiber surface.

Hydrothermal synthesis of high specific capacitance electrode material using porous bagasse biomass carbon hosting MnO2 nanospheres

In this article, a high specific capacitance biomass carbon/MnO2 nanocomposites electrode materials were prepared by hydrothermal method. The porous sugarcane bagasse based biomass carbon was used as the host to load MnO2 nanospheres. The final obtained nanocomposites exhibit high specific capacitance. Besides, the effects of different electrolytes on the electrochemical properties of sugarcane bagasse carbon (SBC)/MnO2 nanosphere composites (SBC/MnO2) were also investigated. In comparison with MnO2 nanospheres, the specific capacitances of the SBC/MnO2 composite materials are improved whether in alkaline electrolyte or neutral electrolyte. Especially, in 1 M Na2SO4 electrolyte, the specific capacitance of SBC/MnO2 composite is up to 747 F·g−1 at a current density of 1 A·g−1, which is much higher than the MnO2 nanospheres at the same current density. At the same time, after 1000 cycles of charge–discharge process in a neutral electrolyte, the specific capacitance retention of SBC/MnO2 composite reaches 77%.

Solvents and Supporting Electrolytes in the Electrocatalytic Reduction of CO2

Different electrolytes applied in the aqueous electrocatalytic CO2 reduction reaction (CO2RR) considerably influence the catalyst performance. Their concentration, species, buffer capacity, and pH value influence the local reaction conditions and impact the product distribution of the electrocatalyst. Relevant properties of prospective solvents include their basicity, CO2 solubility, conductivity, and toxicity, which affect the CO2RR and the applicability of the solvents. The complexity of an electrochemical system impedes the direct correlation between a single parameter and cell performance indicators such as the Faradaic efficiency; thus the effects of different electrolytes are often not fully comprehended. For an industrial application, a deeper understanding of the effects described in this review can help with the prediction of performance, as well as the development of scalable electrolyzers. In this review, the application of supporting electrolytes and different solvents in the CO2RR reported in the literature are summarized and discussed.

Insights into the role of CuO in the CO2 photoreduction process

The CO2 photoreduction process to produce light hydrocarbons is known to be influenced by the presence of CuO nanoparticles, but the actual role of this material, whether as a catalyst or a reactant, has not yet been revealed. In this work, we investigate the role of CuO nanoparticles produced by a solvothermal method as a catalyst in CO2-saturated water reaction media under UV light, considering the effects of different electrolytes (Na2C2O4, KBrO3, and NaOH) and temperatures on nanoparticle phase and activity. The electrolyte strongly influenced product selectivity (NaOH led to evolution of CH4, Na2C2O4 to CO, and KBrO3 to O2) and induced CuO phase change. A long-term analysis of these processes indicated that during the initial steps, CuO acted as a reactant, rather than as a catalyst, and was converted to CuCO3.Cu(OH)2, while the as-converted material acted as a catalyst in CO2 photoreduction, with conversion values comparable to those reported in the literature.

Effects of different electrolytes and film thicknesses on structural and thermoelectric properties of electropolymerized poly(3,4-ethylenedioxythiophene) films.

The effects of the type of electrolyte and film thickness on the structural and thermoelectric properties of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films on indium-tin-oxide (ITO) substrates prepared using electropolymerization were investigated. Two electrolytes were prepared using two different solvents: a water/methanol solvent (protic solvent) and acetonitrile (aprotic solvent) with 3,4-ethylenedioxythiophene (EDOT) and LiCF3SO3, typically included in electrolytes as dopants. The electrochemical properties of the two electrolytes were analyzed; it was found that the polymerization process for EDOT on an ITO substrate varied based on the electrolyte used. When the electropolymerization time was increased, the surface morphology of the PEDOT films prepared using the water/methanol solvent appeared to contain grains approximately 100 nm in size whereas the PEDOT films prepared using acetonitrile appeared to contain aggregated grains connected by polymeric networks. Even though there were differences in the surface morphology and chemical bonds determined using Fourier-transform infrared spectroscopy/attenuated total reflectance analysis, the thermoelectric properties were strongly dependent on the film thickness and were only weakly dependent on the type of electrolyte used. The highest power factor was 41.3 μW (m−1 K−2) for a PEDOT film with a thickness of 0.5 μm prepared using the water/methanol solvent electrolyte.

Precise estimation of transfer free energies for ionic species between similar media.

Transfer properties and partition coefficients for individual ions are relevant in a variety of scientific and engineering contexts, such as predicting the effects of different electrolytes on biomacromolecules in a preferential interaction sense or predicting the distribution of heavy metal ions in soils, rivers, etc. Computer simulations allow free energies of transfer to be estimated by considering single ions explicitly. When the two media under consideration are similar to each other regarding ion solvation, the resultant free energies are small in absolute magnitude. In these cases, it is advisable to simulate the transfer process directly. Here, we demonstrate how this can be achieved using two-dimensional umbrella sampling in conjunction with canonical ensemble molecular dynamics simulations where two liquid media are in direct contact. By calculating full two-dimensional potentials of mean force, these simulations allow the estimation of single-ion transfer free energies by integrating this surface accordingly. We report statistical accuracies to highlight that very high precision is achieved and needed to make even just qualitative statements about the transfer process. We close by discussing implications of our results for the specific case considered: the transfer of polypeptide side chain analogs from water to aqueous denaturant solutions.

Investigations into side gap in wire electrochemical micromachining (wire-ECMM)

Electrochemical machining (ECM) process is now in application in various industries like maritime, automobile, and aerospace. Wire-ECM, a variant of ECM, is now under investigation, for its applications in electronics industries for the fabrication of PCB on conductive metals like copper and in medical industries for the fabrication of micro needles with textures on its surface for the painless delivery of drugs. One of the most important parameters in wire-ECM is side gap. This paper aims at obtaining minimum side gap for the given machining conditions. In order to achieve this, three different workpieces of Al, Cu, and stainless steel are examined. Effects of different electrolytes on the side gap are also examined. Later on, different electrolytes at different temperatures are used to study their effect on the side gap. Finally, optimum parameters are determined in order to keep the side gap to a minimum level. In order to keep the findings significant for industrial applications, machining rate is kept as high as 5 μm/s. Other relevant process parameters are so derived that the machining process can attain stability at high feed rate. To realize this, regulated DC power supply is used. Average side gap was finally reduced to 26.8 μm using a commercially available copper wire of diameter 90 μm.

Experimental investigation into electrochemical milling of Ti6Al4V

Electrochemical milling (EC milling) avoids complex electrode design which is often a burden in sinking ECM. In this process material is removed by a simple geometric tool following a predefined path in a layer-by-layer fashion. High strength temperature resistance (HSTR) material like Ti6Al4V is extensively used in different field starting from the defense to bio-medical industry. Study of comparative effects of different electrolytes on various performance characteristics on titanium alloy, is the soul of this paper. Commencement of making simple shape grooves to complex shape i.e ‘L’ shaped feature was machined by means of electrochemical milling process with layer by layer fashion. In each layer, the tool was controlled to move along a predefined path with a multi downward step. ‘L’ shaped features were machined on Ti6Al4V using three different electrolytes by varying feed rates and frequency followed by the corresponding effects on various performance characteristics were studied. It was observed that NaCl(0.5M)+NaNO3(0.5M) mixed electrolyte gave better result compare to the other two electrolyte as far as accuracy and surface finish of the features were concerned. It was also observed that performance characteristics other than depth and surface finish was improved with increasing feed rate and frequency up to a certain limit and after that short circuit was occurred. After analysing all the graphs and figures, it was concluded that to achieve better accuracy and surface finish, type of electrolytes, feed rate and frequency are the major important factors of EC milling.

In-situ synthesis of Ag-Pi oxygen-evolving catalyst in phosphate environment for water splitting

An efficient Ag-Pi oxygen-evolving catalyst was fabricated in situ in a phosphate electrolyte solution (pH 12.4). The catalyst approaches an amorphous structure, unlike the reported Ag-based oxygen-evolving catalysts. The catalytic activity for water oxidation of the Ag-Pi catalyst is 11.1 μmol h−1 cm−2 and it has a modest oxygen-evolution overpotential of 457.0 mV at 1 mA cm−2 in 0.1 M K3PO4 electrolyte. The effects of different electrolytes on the formation of the Ag-Pi catalyst were investigated. The active component of the Ag-Pi oxygen-evolving catalyst as a water-splitting catalyst is the AgO phase as determined by X-ray diffractometry and X-ray photoelectron spectroscopy analysis. A Ag-Pi mechanism that includes the Ag(I) and Ag(III) cycles is proposed to explain the electrocatalytic oxygen evolution.

Effects of different electrolytes for micro-arc oxidation on the bond strength between titanium and porcelain

PurposeThe aim of this study is to investigate the effects of different electrolytes on the titanium–porcelain bond strength after micro-arc oxidation (MAO) treatment. MethodsThree electrolytes at the same concentration were used as MAO reaction solutions: Na2SiO3, KF, and MgSiF6. Blasting treatment was chosen as a control. After MAO treatment in each electrolyte, the titanium–porcelain bond strengths were measured by the three-point bending test, as described in ISO 9693. The morphologies and elemental compositions of the MAO coating on the titanium substrate were evaluated by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The interface between the titanium and porcelain was also observed by SEM and EDS. ResultsThe MAO coatings created in different electrolytes exhibited completely different morphologies and compositions. The bond strengths of the Na2SiO3 and MgSiF6 groups were significantly higher than those of the other groups (p<0.05). Additionally, the titanium–porcelain interfaces were compact in the former two groups, whereas pores and cracks were visible at the interfaces in the other groups. ConclusionsThese results indicate that MAO treatment with an appropriate electrolyte could be an effective method to increase the titanium–porcelain bonding strength. According to ISO 9693, titanium–porcelain restorations subjected to MAO treatment with an appropriate electrolyte could be appropriate for clinical use.

Effects of Electrolytes on Electrochemical Properties of Cathode Material LaNi0.6Fe0.4O3-d based Fuel Cells

Unique electrochemical properties of LaNi0.6Fe0.4O3-δ (LNF) have made it a better choice of cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with high power density. To improve electrochemical properties of LNF and analyze the effects of different electrolytes on the performance of LNF-based IT-SOFC, half-cells are fabricated with Ce0.9Gd0.1O2 (GDC) electrolyte or porous GDC backbone/GDC electrolyte. Ag paste is used as a current collector deposited on the cathode material surface. Additionally, LNF and GDC powders are synthesized by sol-gel method leading to the polarization resistance (Rp) and current density of half-cells with two kinds of electrolytes to be measured by a three-electrode method. Experimental results at 550-750 oC show that the polarization resistance (Rp) of LNF/GDC backbone/GDC is 0.376 Ω·cm2 at 750 oC in air, a reduction by 67.02 % compared with that of pure GDC electrolyte at the same temperature. And LNF/GDC backbone/GDC has a higher current density, 0.377 A·cm-2 at 750 oC in air. Systematic analysis suggests that porous GDC backbone improves electrochemical properties of LNF cathode materials.

Li Insertion and Extraction of Si Electrodes in Three Types of Electrolytes and Structural Aspects of the Interfaces

Silicon (Si) is a promising anode material for lithium ion batteries (LIB) due to its high specific capacity (3579 mAh g-1). However, the large capacity of Si is accompanied by a large volume expansion which causes severe mechanical degradation within the electrode. Ultimately it leads to loss of electrical contact between the active material and current collector, causing capacity fading. Several approaches have been conducted to enhance the electrochemical performance of Si anode, for example, using nano-sized Si particles, limiting the charge and discharge voltage window, and incorporating additives to the electrolytes. Among these approaches, the use of electrolyte additive can be one of the most effective approaches to improve LIBs. In particular, fluoroethylene carbonate (FEC) is known to be a proper electrolyte additive for Si anode because it can form a stable solid electrolyte interface (SEI). Edstrom et al demonstrated that an SEI layer derived from FEC could improve the capacity retention and Coulombic efficiency of lithium/Silicon in half cell (1). This is largely due to the decomposition of FEC, which mainly forms LiF. It plays an important role in enhancing the electrochemical cycling performance. However, Schroder et al. suggest that FEC eventually runs out. After long term cycling, a similar SEI composition as the non-FEC containing electrolyte is formed (2). In addition, the electrolyte used in LIB is generally carbonate type solvent with LiPF6 as a salt. It has been reported that decomposition of the carbonate electrolyte leads to gas evolution in these cells during charge and discharge. Gas evolution is a significant issue because it affects not only the battery performance, but also the reliability as a safe industrial product. To prevent the electrolyte from gas evolution, gas evolution has to be improved for long cycle stability and safety of cells for in practical use. Therefore, one of the important solutions in the development of a long-life and safe LIB is to change the composition of electrolytes for long cycling. Ionic liquids have been investigated for LIB as a promising electrolyte because of its low volatility, negligible vapor pressure, thermal stability, and high ionic conductivity. The electrochemical performance and interfacial phenomenon with ionic liquid and Si composite anode is not well understood. Herein, we focus on bis(fluorosulfonyl) imide (FSI)-based ionic liquid as a promising electrolyte for Si composite anode. Comparisons among ionic liquid electrolyte and conventional carbonate electrolytes are thoroughly investigated. Effects of different electrolytes including (1) ethylene carbonate/diethyl carbonate (EC/DEC), (2) FEC containing EC/DEC, (3) 1-Ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMI-FSI) on cycling performance and the SEI formation mechanism on Si anodes have been investigated using electrochemical performances, scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). Electrochemical cycle performance (C/10) of Si anodes with FEC additive and EMI-FSI were better than that of EC/DEC without the FEC. Moreover, the electrochemical impedance measurement with FEC additive and with EMI-FSI after cycling demonstrated low interfacial and charge-transfer resistances compared to the corresponding resistances observed in the EC/DEC cycled electrode. Although EMI-FSI has a relatively high viscosity, it showed not only the stable cycling performance, but also the lower impedance for a Si anode. The difference of the SEI formation mechanism among each electrolyte has not yet been clearly understood yet, which is characterized through further studies. 1. Chao Xu, Fredrik Lindgren, Bertrand Philippe, Mihaela Gorgoi, Fredrik Björefors, Kristina Edström, and Torbjörn Gustafsso “Improved Performance of the Silicon Anode for Li-Ion Batteries: Understanding the Surface Modification Mechanism of Fluoroethylene Carbonate as an Effective Electrolyte Additive”, Chem. Mater., 2015, 27 (7), 2591 2. K. Schroder, J. Alvarado, T. A. Yersak, J. Li, N. Dudney, L. J. Webb, Y. S. Meng, and K. J. Stevenson. “The Effect of Fluoroethylene Carbonate as an Additive on the Solid Electrolyte Interphase on Silicon Lithium-Ion Electrolytes”, Chem. Mater., 2015, 27 (16), 5531

Solution plasma synthesis of Si nanoparticles

Silicon nanoparticles (Si-NPs) were directly synthesized from a Si bar electrode via a solution plasma. In order to produce smaller Si-NPs, the effects of different electrolytes and applied voltages on the product were investigated in the experiments detailed in this paper. The results demonstrated that the use of an acidic solution of 0.1 M HCl or HNO3 produced Si-NPs without SiO2 formation. According to the transmission electron microscopy and electron energy-loss spectroscopy, the obtained Si-NPs contained both amorphous and polycrystalline Si particles, among which the smaller Si-NPs tended to be amorphous. When an alkaline solution of K2CO3 was used instead, amorphous SiO2 particles were synthesized owing to the corrosion of Si in the high-temperature environment. The pH values of KCl and KNO3 increased during electrolysis, and the products were partially oxidized in the alkaline solutions. The particle size increased with an increasing applied voltage because the excitation temperature of the plasma increased.