Electrocatalytic Oxidation of Formic Acid at Pt Modified Electrodes: Substrate Effect of Unsintered Au Nano‐Structure

A Pt‐modified Au catalyst featured with novel layered structures and ultra‐low Pt loading has been designed and electrochemically fabricated on a glassy carbon (GC) electrode. SEM characterization suggests that as‐formed Pt/Au/GC electrode grows in a Stranski–Krastanov mode, resulting in a nearly ideal layered structure with Au at the inner layer and Pt at the outer layer. The electrocatalytic activity of the synthesized Pt/Au/GC electrode towards formic acid electrooxidation was studied, and comparative experiments with other modified electrodes (i.e., Pt/GC, Pt/Au, and Pt/Pt) were also conducted. As a result, the electrocatalytic activity of the outer‐layered Pt depends significantly on the intrinsic properties of the substrates. The prepared Pt/Au/GC electrode with Au nanoparticles modified GC as the substrate shows remarkable catalytic activity for the formic acid oxidation, much higher than that of its counterparts, Pt/GC, Pt/Au, and Pt/Pt electrodes. Additionally, the measured electrochemical impedance spectra indicate that the charge‐transfer resistance for formic acid electrooxidation on Pt/Au/GC electrode is smaller than that on other Pt modified electrodes.     

Electropreparation of (±)‐10‐camphorsulfonate‐doped poly(o‐phenylenediamine) in acetonitrile and its use in determination of glucose

Poly(o‐phenylenediamine) (PoPD) film has been electrochemically prepared on Pt electrode in an acetonitrile–water medium containing o‐phenylenediamine (oPD) monomer and (±)‐10‐camphorsulfonic acid (HCSA) by using the cyclic voltammetry (CV). The PoPD film (PoPD–CSA) has been characterized by FTIR, CV, EIS, FESEM, and conductivity measurement. The glucose biosensor (Pt/PoPD–CSA/GOx) has been prepared from the PoPD coated electrode by immobilizing glucose oxidase (GOx) enzyme using glutaraldehyde. The biosensor shows a low detection limit and wide linear working range, a good reusability, long‐term stability, and anti‐interference ability. The Pt/PoPD–CSA/GOx has possesses higher sensitivity (2.05 μA/mmol L^?1) and affinity to glucose due to the use of CSA ion as dopant. The linear concentration ranges of Pt/PoPD–CSA/GOx have been found to be 9.6 × 10^?3 to 8.2 mmol L^?1 from calibration curve and 4.6 × 10^?2 to 100 mmol L^?1 from the relationship between the (1/glucose concentration) and (1/current difference). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39864.     

Synthesis of Novel Submicrometer‐Scale Flat Carbon Fibers and Application in the Electrooxidation of Methanol

Novel submicrometer‐scale flat carbon fibers (SFCF) have been synthesized by catalytic chemical vapor deposition of acetylene over an Ni‐Al layered double hydroxide (NiAl‐LDH) compound, and the electrochemical activity of Pt supported on as‐synthesized SFCF for methanol oxidation has been investigated. The materials were characterized by power X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra, and cyclic voltammetry tests. The results reveal that the active crystal facets of the NiAl₂O₄ spinel phase derived from NiAl‐LDH can deposit carbon atoms to grow SFCF, and that the co‐growing Ni nanoparticles are not catalytically active for the formation of SFCF. Furthermore, after support with Pt, the resultant Pt/SFCF electrocatalyst shows much higher activity for methanol oxidation than the Pt/C one in both acid and alkaline media, which is attributed to the combined beneficial effects of the microstructure of the SFCF support, improved electrical conductivity originating from the NiAl₂O₄ spinel catalyst embedded in SFCF, and improved dispersion of Pt particles through exposed Ni nanoparticles adhering intimately to the SFCF.     

Anthranilic acid assisted preparation of Fe3O4–poly(aniline‐co‐o‐anthranilic acid) nanoparticles

Magnetic Fe₃O₄–poly(aniline‐co‐o‐anthranilic acid) nanoparticles were prepared by a novel and simple method: anthranilic acid assisted polymerization. The synthetic strategy involved two steps. First, Fe₃O₄ nanoparticles capped by anthranilic acid were obtained by a chemical precipitation method, and then the aniline and oxidant were added to the modified Fe₃O₄ nanoparticles to prepare well‐dispersed Fe₃O₄–poly(aniline‐co‐o‐anthranilic acid) nanoparticles. Fe₃O₄–poly(aniline‐co‐o‐anthranilic acid) nanoparticles exhibited a superparamagnetic behavior (i.e., no hysteresis loop) and high‐saturated magnetization (M_s = 21.5 emu/g). The structure of the composite was characterized by Fourier‐transform infrared spectra, X‐ray powder diffraction patterns, and transmission electron microscopy, which proved that the Fe₃O₄–poly(aniline‐co‐o‐anthranilic acid) nanoparticles were about 20 nm. Moreover, the thermal properties of the composite were evaluated by thermogravimetric analysis, and it showed excellent thermal stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1666–1671, 2006     

Electrochemical effect of gold nanoparticles on Pt/α-Fe2O3/C for use in methanol oxidation in alkaline solution

A catalyst containing gold nanoparticles with Pt/α-Fe₂O₃/C was prepared by a co-precipitation method and its catalytic activity for the oxidation of methanol, formaldehyde, and formic acid in alkaline solutions was evaluated by an electrochemical method and high-performance liquid chromatography (HPLC). The addition of gold nanoparticles improved catalytic activity only for the oxidation of methanol and formaldehyde, and not for the oxidation of formic acid. HPLC analysis was performed for methanol oxidation to detect the oxidative products. In HPLC analysis, only formate anion could be detected in the electrolyte solution and the ratio of formate anion obtained to the total passed charge in Pt/nano-Au/α-Fe₂O₃/C was less than that in Pt/C, indicating that formic acid is not the final product of methanol oxidation. These results show that gold nanoparticles promoted methanol oxidation up to CO₂.     

Influence of Pyridine‐Polybenzimidazole Film Thickness of Carbon Nanotube Supported Platinum on Fuel Cell Applications

Pyridine‐polybenzimidazole (PyPBI) films of different thickness (∼1.0–2.4 nm) are wrapped on the surfaces of multi‐walled carbon nanotubes (CNTs). To prepare Pt on PyPBI/CNT (Pt‐PyPBI/CNT) catalysts, Pt⁴⁺ ions are immobilized on these PyPBI wrapped CNTs (PyPBI/CNTs) via Lewis acid‐base coordination between Pt⁴⁺ and :N‐ of imidazole groups, followed by reducing Pt⁴⁺ to Pt nanoparticles. The influence of PyPBI film thickness on the Pt particle size, loading and electrochemical surface area, respectively, of Pt‐PyPBI/CNTs is investigated. Fuel cell performances of the PBI/H₃PO₄ based membrane electrode assemblies (MEAs) prepared from these Pt‐PyPBI/CNT catalysts are also evaluated at 160 °C with unhumidified H₂/O₂ gases. Among the catalysts, the Pt‐PyPBI/CNT catalyst with a PyPBI film thickness of ∼1.6 nm (which is around half of the Pt particle size), a Pt loading of ∼44 wt.%, and a Pt particle size of ∼3.3 nm exhibits the best fuel cell performance.     

Improvements of electrocatalytic activity of PtRu nanoparticles on multi-walled carbon nanotubes by a H2 plasma treatment in methanol and formic acid oxidation

A H₂ plasma has been used to treat the PtRu nanoparticles supported on the plasma functionalized multi-walled carbon nanotubes (PtRu/PS-MWCNTs). The plasma treatment does not change the size and crystalline structure of PtRu nanoparticles, but reduces the fraction of the oxidized species at the outermost perimeter of particles. The electrochemical results show that these plasma treated PtRu/PS-MWCNTs exhibit increased electrochemically active surface area, improved electrocatalytic activity and long term stability toward methanol and formic acid oxidation, and enhanced tolerance to carbonaceous species relative to the sample untreated with the H₂ plasma. The electrocatalytic activities of the plasma treated PtRu/PS-MWCNTs are found to be dependent upon the Pt:Ru atomic ratios of PtRu nanoparticles. The catalysts with a Pt:Ru atomic ratio close to 1:1 show superior properties in the electrooxidation of methanol and formic acid at room temperature and better tolerance to carbonaceous species.     

Preparation and fluorescence properties of poly(o‐methyl‐acrylamideyl‐benzoic acid)‐ZnS composites

Poly(o‐methyl‐acrylamideyl‐benzoic acid)‐ZnS (P(o‐MAABA)‐ZnS) nanocomposites have been prepared and characterized. The resultant P(o‐MAABA)‐ZnS nanocomposites in solution show two emissions in the purple‐light area (370 nm) and in the blue‐light area (425 nm), which are assigned to the polymer and ZnS nanoparticles, respectively. The coordination between the polymer and Zn²⁺ and the surface chemical composition has been studied by Infrared spectroscopy and X‐ray photoelectron spectroscopy (XPS). The particle size of ZnS nanoparticles was homogeneous and the average size was 3.8 nm, which were characterized by UV absorption spectrum and X‐ray Diffraction. The P(o‐MAABA)‐ZnS composites displays good film formability and the films also show two emissions in 370 and 425 nm. After doped with Tb³⁺, there was effective energy transfer from ZnS nanoparticles to Tb³⁺. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Improving the Performance of Platinum Nanocrystal Catalysts by Square‐wave Potential Electrochemical Pretreatment

Cube‐shaped Pt nanocrystals (with the size of about 160 nm) are prepared by a square‐wave potential electrochemical pretreatment at the expense of Pt nanospheres. A cyclic voltammogram of Pt nanospheres in sulphuric acid shows two pairs of hydrogen adsorption/desorption peaks, which corresponds to the characteristics of a Pt polyoriented surface. However, a cyclic voltammogram of cubic Pt nanocrystals in sulphuric acid shows another pair of hydrogen adsorption/desorption peak at 0.22 V (vs. NHE), which corresponds to the characteristics of Pt (100) surface orientation. Cubic Pt nanocrystals show enhanced electrocatalytic activity over Pt nanospheres for methanol oxidation. The peak current density of cubic Pt nanocrystals is 1.39 mA cm^–2_Pt, which is 1.48 times that of Pt nanospheres. The poison resistant and oxygen reduction reaction (ORR) activity of cubic Pt nanocrystals are also enhanced compared with those of Pt nanospheres.     

Electrochemical preparation of poly(o‐toluidine) film and its application as a permselective membrane

Poly(o‐toluidine) films were electrochemically synthesized on Pt electrodes at a constant potential (0.75 V versus Ag/AgCl) from a deoxygenated aqueous solution of 0.1M toluidine dissolved in 0.1M KCl. To form permselective polymeric film electrodes, poly(o‐toluidine) films at different thicknesses were prepared by varying the amount of charge consumed during electrochemical polymerization. Then, experimental parameters (e.g., concentrations of monomer and electrolyte and pH of the phosphate buffer salt solution) affecting the polymeric film thickness were optimized. Permeation of the various electroactive and nonelectroactive species such as ascorbic acid, oxalic acid, hydrogen peroxide, lactose, sucrose, and urea through the optimized poly(o‐toluidine)‐coated electrodes was investigated using a chronoamperometric technique. From experimental results, it was found that a poly(o‐toluidine)‐coated electrode permitted the oxidation of hydrogen peroxide and prevented the permeation of the mentioned electroactive and nonelectroactive species. In other words, it was seen that this polymeric electrode responded to only hydrogen peroxide selectively. Thus, it has been claimed that a poly(o‐toluidine)‐coated Pt electrode can be used as a permselective polymeric membrane to overcome interference problems occurring in the hydrogen peroxide‐based biosensor applications. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2141–2146, 1999     

Influence of formic acid on electrochemical properties of high‐porosity Pt/TiN nanoparticle aggregates

Platinum‐deposited titanium nitride (Pt/TiN) nanoparticle aggregates with high porosities were successfully prepared via a self‐assembly‐assisted spray pyrolysis method. The addition of formic acid (HCOOH) had a significant influence on the process, promoting the simultaneous formation of metallic Pt and reduction on the surface of the TiN support material. Complete reduction of the Pt/TiN nanoparticle aggregates improved the catalytic activity. The electrochemical surface area (ECSA) of Pt/TiN with HCOOH (Pt/TiN_w/HCOOH) was 87.15 m²/g‐Pt, which was higher than that of Pt/TiN without HCOOH (Pt/TiN_w/o‐HCOOH). The catalytic durability of Pt/TiN_w/HCOOH was twice that of Pt/TiN_w/o‐HCOOH. An effective strategy for obtaining carbon‐free catalysts with high activities and durabilities was identified. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2753–2760, 2013     

Sonochemical synthesis of Pt-doped Pd nanoparticles with enhanced electrocatalytic activity for formic acid oxidation reaction

Pt-doped Pd nanoparticle catalysts (Pd _n Pt, n is 12, 15 and 19) supported on carbon were synthesized by an ultrasound assisted polyol method. The catalysts were characterized by X-ray diffraction, transmission electron microscopy, and energy dispersive X-ray spectroscopy. The electrochemical activity of the electrocatalysts was investigated in terms of formic acid oxidation reaction (FAOR) at low concentration of formic acid in 0.1 M perchloric acid at room temperature. Formic acid oxidation on the Pd _n Pt/C commences at lower potential than a commercial Pt/C. Pd₁₉Pt/C catalyst showed the highest catalytic activity in FAOR compared to that of other catalysts. The obtained electrochemical results from voltammograms indicate that Pt-doped Pd catalysts can be a promising candidate for the anode material in direct formic acid fuel cells. The synthesis procedure is not only a very facile route but also a mass producible method for preparing carbon supported alloy nanoparticles.     

Enhanced Electrocatalysis for Methanol Oxidation on Ordered {[PdPW11O39]5–/Pt/PAMAM}n Multilayer Composites

The {[PdPW₁₁O₃₉]^5–/Pt/PAMAM}_n multilayer composites constructed from G4.0 Amino‐terminated poly (amidoamine) dendrimer (PAMAM), Pt and Keggin‐type palladium(II)‐substituted polyoxometalates anion ([PdPW₁₁O₃₉]^5–) were prepared via layer by layer electro‐depositing technique. The X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), and field emission scanning electron microscope (FE‐SEM) characterization indicate that the Pt nanoparticles have been anchored on the as‐prepared nanocomposites. And the morphologies of Pt nanoparticles are influenced by deposition potential, the number of layers of {[PdPW₁₁O₃₉]^5–/Pt/PAMAM}_n multilayer nanocomposites, and the existence of PAMAM. The electrocatalytic properties and stability of {[PdPW₁₁O₃₉]^5–/Pt/PAMAM}_n multilayer nanocomposites were investigated by cyclic voltammetry. Experimental investigation results reveal that PAMAM is a good support for Pt nanoparticle growth due to its interior cavity structure and high stability. [PdPW₁₁O₃₉]^5– play an important role to prevent intermediate product (mainly as CO) in the methanol oxidation from poisoning the as‐prepared catalyst. The {[PdPW₁₁O₃₉]^5–/Pt/PAMAM}₃/GC shows better electrocatalytic properties, stability, and CO tolerance ability than Pt/GC and {Pt/PAMAM}₃/GC fabricated by similar electrodeposition processes.     

ZrC–C and ZrO2–C as Novel Supports of Pd Catalysts for Formic Acid Electrooxidation

The Pd/ZrC–C and Pd/ZrO₂–C catalysts with zirconium compounds ZrC or ZrO₂ and carbon hybrids as novel supports for direct formic acid fuel cell (DFAFC) have been synthesized by microwave‐assisted polyol process. The Pd/ZrC–C and Pd/ZrO₂–C catalysts have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), energy dispersive analysis of X‐ray (EDAX), transmission electron microscopy (TEM), and electrochemical measurements. The physical characteristics present that the zirconium compounds ZrC and ZrO₂ may promote the dispersion of Pd nanoparticles. The results of electrochemical tests show that the activity and stability of Pd/ZrC–C and Pd/ZrO₂–C catalysts show higher than that of Pd/C catalyst for formic acid electrooxidation due to anti‐corrosion property of zirconium compounds ZrC, ZrO₂, and metal–support interaction between Pd nanoparticles and ZrC, ZrO₂. The Pd/ZrC–C catalyst displays the best performance among the three catalysts. The peak current density of formic acid electrooxidation on Pd/ZrC–C electrode is nearly 1.63 times of that on Pd/C. The optimal mass ratio of ZrC to XC‐72 carbon is 1:1 in Pd/ZrC–C catalyst with narrower particle size distribution and better dispersion on surface of the mixture support, which exhibits the best activity and stability for formic acid electrooxidation among all the samples.     

Thermal degradation of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) as studied by TG,TG–FTIR,and Py–GC/MS

The thermal degradation kinetics of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [poly(HB–HV)] under nitrogen was studied by thermogravimetry (TG). The results show that the thermal degradation temperatures (T_o, T_p, and T_f) increased with an increasing heating rate (B). Poly(HB–HV) was thermally more stable than PHB because its thermal degradation temperatures, T_o(0), T_p(0), and T_f(0)—determined by extrapolation to B = 0°C/min—increased by 13°C–15°C over those of PHB. The thermal degradation mechanism of PHB and poly(HB–HV) under nitrogen were investigated with TG–FTIR and Py–GC/MS. The results show that the degradation products of PHB are mainly propene, 2‐butenoic acid, propenyl‐2‐butenoate and butyric‐2‐butenoate; whereas, those of poly(HB–HV) are mainly propene, 2‐butenoic acid, 2‐pentenoic acid, propenyl‐2‐butenoate, propenyl‐2‐pentenoate, butyric‐2‐butenoate, pentanoic‐2‐pentenoate, and CO₂. The degradation is probably initiated from the chain scission of the ester linkage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1530–1536, 2003     

Improving the Stability and Ethanol Electro‐Oxidation Activity of Pt Catalysts by Selectively Anchoring Pt Particles on Carbon‐Nanotubes‐Supported‐SnO2

To improve the stability and activity of Pt catalysts for ethanol electro‐oxidation, Pt nanoparticles were selectively deposited on carbon‐nanotubes (CNTs)‐supported‐SnO₂ to prepare Pt/SnO₂/CNTs and Pt/CNTs was prepared by impregnation method for reference study. X‐ray diffraction (XRD) was used to confirm the crystalline structures of Pt/SnO₂/CNTs and Pt/CNTs. The stabilities of Pt/SnO₂/CNTs and Pt/CNTs were compared by analyzing the Pt size increase amplitude using transmission electron microscopy (TEM) images recorded before and after cyclic voltammetry (CV) sweeping. The results showed that the Pt size increase amplitude is evidently smaller for Pt/SnO₂/CNTs, indicating the higher stability of Pt/SnO₂/CNTs. Although both catalysts exhibit degradation of electrochemical active surface area (EAS) after CV sweeping, the EAS degradation for the former is lower, further confirming the higher stability of Pt/SnO₂/CNTs. CV and potentiostatic current–time curves were recorded for ethanol electro‐oxidation on both catalysts before and after CV sweeping and the results showed that the mass specific activity of Pt/CNTs increases more than that of Pt/SnO₂/CNTs, indicating that Pt/CNTs experiences more severe evolution and is less stable. The calculated area specific activity of Pt/SnO₂/CNTs is larger than that of Pt/CNTs, indicating SnO₂ can co‐catalyze Pt due to plenty of interfaces between SnO₂ and Pt.     

Carbon‐Supported CoSe2 Nanoparticles for Oxygen Reduction Reaction in Acid Medium

Carbon‐supported CoSe₂ nanoparticles, as non‐precious metal cathodic catalyst, were prepared via the in situ surfactant‐free method with the conventional heating. Structural and electrochemical properties of the obtained 20 wt.‐% CoSe₂/C nanoparticles were investigated by means of powder X‐ray diffraction (PXRD), differential thermal gravimetric analysis (DTA‐DTG) and rotating disc electrode (RDE) techniques. CoSe₂ nanoparticles have two kinds of crystal structure after heat treatment under nitrogen at different temperature: orthorhombic at 250 and 300 °C; cubic at 400 and 430 °C. The latter structure has higher oxygen reduction activity than the former in 0.5 M H₂SO₄. CoSe₂/C nanoparticles after heat treatment from 250 to 430 °C, have an onset potential from 0.78 to 0.81 V versus the reference hydrogen electrode (RHE) in O₂‐saturated 0.5 M H₂SO₄ at 25 °C. 20 wt.‐% CoSe₂/C nanoparticles, after heat treatment at 300 °C, promote ca. 3.5 electrons, per oxygen molecule, transferred during the oxygen reduction process. They have an oxidation wave centred at 0.96 V versus RHE and display higher methanol tolerance as compared to 20 wt.‐% Pt/C (E‐TEK).     

Fabrication of Pt–Cu/RGO hybrids and their electrochemical performance for the oxidation of methanol and formic acid in acid media

Pt–Cu/reduced graphene oxide (Pt–Cu/RGO) hybrids with different Pt/Cu ratios were prepared by the reduction of H₂PtCl₆ and CuSO₄ by NaBH₄ in the presence of graphene oxide (GO). The Pt–Cu nanoparticles were characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The reduction of GO was verified by ultraviolet–visible absorption spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Compared to Pt/RGO, the Pt–Cu/RGO hybrids have superior electrocatalytic activity and stability for the oxidation of methanol and formic acid. Thus they should have potential applications in direct methanol and formic acid fuel cells.     

Towards enhanced electrochemical capacitance with self‐assembled synthesis of poly(pyrrole‐co‐o‐toluidine) nanoparticles

Poly(pyrrole‐co‐o‐toluidine) (PPOT) nanoparticles for electrochemical capacitors are easily and productively synthesized by a chemical oxidative polymerization of pyrrole (PY) and o‐toluidine (OT) in 0.5M HCl without any external additive. The polymerization yield, electrical conductivity, and size of the copolymer nanoparticles can significantly be optimized by the oxidant/monomer molar ratio and polymerization temperature. The chemical structure of the obtained copolymer is characterized by UV–vis and FTIR. The copolymer nanoparticles synthesized at 10°C are found to generally have irregular granular morphology with a diameter of 60–100 nm and a small polydispersity index of 1.06 by laser particle‐size analyzer, FE‐SEM, and TEM, and good dispersibility in water. The formation mechanism of the nanoparticles is proposed based on the powerful amphipathicity from comonomer aggregate formed by PY and OT in the monomer solution. The PPOT nanoparticles possess a specific capacitance of 310 F g^?1 at 25 mV s^?1 as well as retain 81% of the initial specific capacitance value after 1000 cycles, while its energy density and power density are found to be 40.2 and 1196 W Kg^?1 at 2 A g^?1. The enhanced electrochemical properties can be attributed to the nanostructural advantage of the PPOT. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42995.     

C18‐unsaturated branched‐chain fatty acid isomers: Characterization and physical properties

Iso‐oleic acid is a mixture of C₁₈‐unsaturated branched‐chain fatty acid isomers with a methyl group on various positions of the alkyl chain, which is the product of the skeletal isomerization reaction of oleic acid and is the intermediate used to make isostearic acid (C₁₈‐saturated branched‐chain fatty acid isomers). Methyl iso‐oleate, a mixture of C₁₈‐unsaturated branched‐chain fatty acid methyl ester isomers, is obtained via acid catalyzed esterification of iso‐oleic acid with methanol. The branched‐chain materials are liquid at room temperature and their “oiliness” property makes them an attractive candidate for the lubricant industry. In this paper, we report characterization of these branched‐chain materials using comprehensive two‐dimensional GC with time‐of‐flight mass spectrometry (GC × GC/TOF‐MS) and their physical and lubricity properties using tribology measurements.