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Safety concerns on cable tray fires in urban utility tunnels, which may further trigger huge casualties, ceiling structure damages, power failures and other domino effects, attract increasing attention in recent years. Determining the maximum excess ceiling gas temperature (MECT) induced by cable tray fires in urban utility tunnels is crucial to evaluate the fire risks. A series of one-layer horizontal cable tray fire experiments to explore the MECT were carried out in a large-scale utility tunnel without mechanical ventilations. The number of cables on the tray was varied from 8 to 18 in the experiments. The experimental results showed that the cable tray fire burning could be divided into three distinct stages, including ignition, self-sustaining and decaying stages. In the self-sustaining combustion stage, the cable tray was found to burn relatively steady. The mean MECT was also investigated since it represents one of the main characteristics of the cable tray fire. By redefining two parameters (the heat release rate and the effective ceiling height) in three classical MECT models proposed originally based on pool-fire, these three models could be extended to be able to predict the mean MECT generated from the cable tray fire (solid combustible) within 20% deviations. Consequently, two novel models were respectively proposed to predict the mean MECT at the self-sustaining burning period and the instantaneous MECT of one-layer horizontal cable tray fire in utility tunnel, which would be useful in the field of fire protection engineering.
The CCQM-K148.a comparison was coordinated by the BIPM on behalf of the CCQM Organic Analysis Working Group for NMIs and DIs which provide measurement services in organic analysis under the CIPM MRA. It was undertaken as a "Track A" comparison within the OAWG strategic plan. CCQM-K148.a demonstrates capabilities for assigning the mass fraction content of a solid organic compound having moderate molecular complexity, where the compound has a molar mass in the range (75 - 500) g/mol and is non-polar (pKow < −2), when present as the primary organic component in a neat organic solid and where the mass fraction content of the primary component in the material is in excess of 950 mg/g.
Participants were required to report the mass fraction of Bisphenol A present in one supplied unit of the comparison material. Participants using a mass balance method for the assignment were also required to report their assignments of the impurity components present in the material. Methods used by the seventeen participating NMIs or DIs were predominantly based on either stand-alone mass balance (summation of impurities) or qNMR approaches, or the combination of data obtained using both methods. The results obtained using thermal methods based on freezing-point depression methods were also reported by a limited number of participants. There was excellent agreement between assignments obtained using all three approaches to assign the BPA content.
The assignment of the values for the mass fraction content of BPA consistent with the KCRV was achieved by most of the comparison participants with an associated relative standard uncertainty in the assigned value in the range (0.1 - 0.5)%.
The comparison required the assignment of the mass fraction of folic acid present as the main component in the comparison sample. Performance in the comparison is representative of a laboratory's measurement capability for the purity assignment of organic compounds of medium structural complexity [molecular weight range 300–500] and high polarity (pKOW < −2).
Methods used by the eighteen participating NMIs or DIs were based on a mass balance (summation of impurities) or qNMR approach, or the combination of data obtained using both methods. The qNMR results tended to give slightly lower values for the content of folic acid, albeit with larger associated uncertainties, compared with the results obtained by mass balance procedures. Possible reasons for this divergence are discussed in the report, without reaching a definitive conclusion as to their origin.
The comparison demonstrates that for a structurally complex polar organic compound containing a high water content and presenting a number of additional analytical challenges, the assignment of the mass fraction content property value of the main component can reasonably be achieved with an associated relative standard uncertainty in the assigned value of 0.5%
Our ability to produce and transform engineered materials over the past 150 years is responsible for our high standards of living today, especially in the developed economies. Yet, we must carefully think of the effects our addiction to creating and using materials at this fast rate will have on the future generations. The way we currently make and use materials detrimentally affects the planet Earth, creating many severe environmental problems. It affects the next generations by putting in danger the future of economy, energy, and climate. We are at the point where something must drastically change, and it must change NOW. We must create more sustainable materials alternatives using natural raw materials and inspiration from Nature while making sure not to deplete important resources, i.e. in competition with the food chain supply. We must use less materials, eliminate the use of toxic materials and create a circular materials economy where reuse and recycle are priorities. We must develop sustainable methods for materials recycling and encourage design for disassembly. We must look across the whole materials life cycle from raw resources till end of life and apply thorough life cycle assessments based on reliable and relevant data to quantify sustainability.
KEY COMPARISON
Under the auspices of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a key comparison, CCQM K55.c, was coordinated by the Bureau International des Poids et Mesures (BIPM) in 2012. Twenty National Measurement Institutes or Designated Institutes and the BIPM participated. Participants were required to assign the mass fraction of valine present as the main component in the comparison sample for CCQM-K55.c. The comparison samples were prepared from analytical grade L-valine purchased from a commercial supplier and used as provided without further treatment or purification.
Valine was selected to be representative of the performance of a laboratory's measurement capability for the purity assignment of organic compounds of low structural complexity [molecular weight range 100300] and high polarity (pKOW > –2).
The KCRV for the valine content of the material was 992.0 mg/g with a combined standard uncertainty of 0.3 mg/g. The key comparison reference value (KCRV) was assigned by combination of KCRVs assigned from participant results for each orthogonal impurity class. The relative expanded uncertainties reported by laboratories having results consistent with the KCRV ranged from 1 mg/g to 6 mg/g when using mass balance based approaches alone, 2 mg/g to 7 mg/g using quantitative 1H NMR (qNMR) based approaches and from 1 mg/g to 2.5 mg/g when a result obtained by a mass balance method was combined with a separate qNMR result.
The material provided several analytical challenges. In addition to the need to identify and quantify various related amino acid impurities including leucine, isoleucine, alanine and a-amino butyrate, care was required to select appropriate conditions for performing Karl Fischer titration assay for water content to avoid bias due to in situ formation of water by self-condensation under the assay conditions. It also proved to be a challenging compound for purity assignment by qNMR techniques.
There was overall excellent agreement between participants in the identification and the quantification of the total and individual related structure impurities, water content, residual solvent and total non-volatile content of the sample. Appropriate technical justifications were developed to rationalise observed discrepancies in the limited cases where methodology differences led to inconsistent results.
The comparison demonstrated that to perform a qNMR purity assignment the selection of appropriate parameters and an understanding of their potential influence on the assigned value is critical for reliable implementation of the method, particularly when one or more of the peaks to be quantified consist of complex multiplet signals.
Under the Comité Consultatif pour la Quantité de Matière (CCQM), a key comparison, CCQM-K104, was coordinated by the National Institute of Metrology (NIM). The comparison was designed to demonstrate a laboratory's performance in determining the mass fraction of the main component in a complex high purity organic material. Nine NMIs or DIs participated in the comparison. Eight participants reported their results. An additional impurity was resolved from the avermectin B1a peak and was tentatively identified as an unknown impurity by NMIA (National Measurement Institute (Australia)). It was subsequently identified by NIM as a diastereoisomer of avermectin B1a at the C-26 position. Final reference value (KCRV) = 924.63 mg/g, with uncertainty (k=1) = 3.89 mg/g, and expanded uncertainty = 8.97 mg/g. The degrees of equivalence with the avermectin B1a KCRV for each participant were reported. The measurement results and degrees of equivalence should be indicative of the performance of a laboratory's measurement capability for the purity assignment of organic compounds of high structural complexity (relative molecular mass range of 500 Da -1000 Da and low polarity (-log KOW ≤ -2).
Aiming for a round-robin test, a new method for the direct determination of fluorine in niobium oxide has been developed. It is based on the use of high-resolution molecular absorption spectra of calcium mono-fluoride (CaF) generated in the graphite tube, combined with the slurry sampling technique. The absorption measurement was performed at the 606.44 nm CaF rotational line. By using graphite tubes with zirconium carbide (ZrC) modified platform, the molecular absorption sensitivity of CaF has been improved by a factor of 20, and no additional chemical modifier was necessary. Generally, non-spectral interferences were observed in the presence of HCl, H2SO4, and H3PO4. For HCl, additional spectral interference occurred due to an overlap of the absorption spectra of CaF and CaCl. However, due to the absence of these mentioned substances in the current material, such interferences do not exist for this application. The characteristic mass found for the CaF 606.44 nm line was 0.1 ng; the limit of detection was 5 mg fluorine per kg solid sample (3σ criterion). The results obtained by the method were within the range of certified values. Comparing to the classical method such as the pyrohydrolysis-photometric method, the developed new method showed clear advantages regarding sensitivity and specificity. The time requirement for one sample analysis was strongly shortened from several hours to only some minutes.
Metal-Assisted and Solvent-Mediated Synthesis of Two-Dimensional Triazine Structures on Gram Scale
(2020)
Covalent triazine frameworks are an emerging material class that have shown promising performance for a range of applications. In this work, we report on a metal-assisted and solvent-mediated reaction between calcium carbide and cyanuric chloride, as cheap and commercially available precursors, to synthesize two-dimensional triazine structures (2DTSs). The reaction between the solvent, dimethylformamide, and cyanuric chloride was promoted by calcium carbide and resulted in dimethylamino-s-triazine intermediates, which in turn undergo nucleophilic substitutions. This reaction was directed into two dimensions by calcium ions derived from calcium carbide and induced the formation of 2DTSs. The role of calcium ions to direct the two-dimensionality of the final structure was simulated using DFT and further proven by synthesizing molecular intermediates. The water content of the reaction medium was found to be a crucial factor that affected the structure of the products dramatically. While 2DTSs were obtained under anhydrous conditions, a mixture of graphitic material/2DTSs or only graphitic material (GM) was obtained in aqueous solutions. Due to the straightforward and gram-scale synthesis of 2DTSs, as well as their photothermal and photodynamic properties, they are promising materials for a wide range of future applications, including bacteria and virus incapacitation.
Most studies about the interaction of nanoparticles (NPs) with cells have focused on how the physicochemical properties of NPs will influence their uptake by cells. However, much less is known about their potential excretion from cells. However, to control and manipulate the number of NPs in a cell, both cellular uptake and excretion must be studied quantitatively. Monitoring the intracellular and extracellular amount of NPs over time (after residual noninternalized NPs have been removed) enables one to disentangle the influences of cell proliferation and exocytosis, the major pathways for the reduction of NPs per cell. Proliferation depends on the type of cells, while exocytosis depends in addition on properties of the NPs, such as their size. Examples are given herein on the role of these two different processes for different cells and NPs.
High-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GF-MAS) was employed for determining adsorbable organic chlorine (AOCl) in water. Organic chlorine was indirectly quantified by monitoring the molecular absorption of the transient aluminum monochloride molecule (AlCl) around a wavelength of 261.42 nm in a graphite furnace. An aluminum solution was used as the molecularforming modifier. A zirconium coated graphite furnace, as well as Sr and Ag solutions were applied as modifiers for a maximal enhancement of the absorption signal. The pyrolysis and vaporization temperatures were 600 °C and 2300 °C, respectively. Non-spectral interferences were observed with F, Br, and I at concentrations higher than 6 mg L-1, 50 mg L-1, and 100 mg L-1, respectively. Calibration curves with NaCl, 4-chlorophenol, and trichlorophenol present the same slope and dynamic range, which indicates the chlorine atom specificity of the method. This method was evaluated and validated using synthetic water samples, following the current standard DIN EN ISO 9562:2004 for the determination of the sum parameter adsorbable organic halides (AOX) for water quality. These samples contain 4-chlorophenol as the chlorinated organic standard in an inorganic chloride matrix. Prior to analysis, organic chlorine was extracted from the inorganic matrix via solid-phase extraction with a recovery rate >95%. There were no statistically significant differences observed between measured and known values and for a t-test a confidence level of 95% was achieved. The limits of detection and characteristic mass were found to be 48 and 22 pg, respectively. The calibration curve was linear in the range 0.1–2.5 ng with a correlation coefficient R2 = 0.9986.
Niobium carbide for wear protection - tailoring its properties by processing and stoichiometry
(2016)
Niobium carbide is a hardly explored carbide but its functional profile shows a high potential for wear protection and tribological applications, which are currently dominated by tungsten carbide. Surprisingly little information is available on niobium carbide (NbC). Niobium carbide can be either synthesized by carbothermal conversion of Nb2O5 or be metallurgically grown and leached out. Furthermore, NbC hardmetal grades can be bonded by all known metallic binders and processed and sintered in exactly the same way as WC-based hardmetals. Niobium is today largely available. NbC can be efficiently produced, provides comparably low friction in many relevant tribo-contacts and displays low wear. NbC and Nb2O5 have so far no REACH classification related to human toxicology and are not listed as substances of very high concern contrary to WO3 and Co3O4. This contribution demonstrates the key characteristics of NbC and discusses its sustainability and reliable value chain.
Substitution of tungsten carbide by niobium carbide as cutting materials and for wear protection
(2016)
Several phases, like Nb₄ C₃ , Nb₆C₅ and other short and long range ordered phases occur in the region of homogeneity of NbCₓ (0.75 ≤ x ≤ 1.0) in the binary phase diagram. Properties, like micro-hardness, hot hardness, sliding wear resistance, elastic modulus and toughness can be tailored by the C/Nb ratio, the addition of secondary carbides and the type of binder. Supporting results from different grades with varying C/Nb ratio or binder types were illuminated. Thus, the NbC system offers to producers a wider process window, than WC. The impact of these tailored properties on sliding wear and cutting performance was illuminated by tribological and machining results.
Niobium is today largely available. NbC can be synthesized by carbothermal conversion of Nb₂O₅ or be metallurgically grown and leached out, provides comparably low friction in many relevant tribo-contacts and displays low wear. NbC and Nb₂O₅ have so far no REACH classification related to human toxicology and are not listed as substances of very high concern contrary to WO₃ and Co₃ O₄ .
Development of NbC-based hardmetals: Influence of secondary carbide addition and metal binder
(2015)
Research and development of WC grades is 90 years ahead of niobium carbide-based hard materials, which showed already as light-weight and unexplored material a very high potential for many technical applications, especially for wear protection and machining. NbC evoluted recently from lab scale to pilot scale, especially in areas where established WC-based materials are causing economic, environmental or technical concerns. Benchmark trials of NbC-based hard metals indicated already a favorable performance in machining of steel components.
Full densification of Fe, Co and Ni bonded NbC based cermet’s was achieved by pressure less liquid phase sintering in vacuum for one hour at 1420°C. The hardness and toughness of the NbC matrix cermet’s can be mainly tailored by the binder composition and secondary carbide additions. Ni binder based NbC cermet’s allow the combination of high hardness and improved toughness. The addition of lesser amounts of VC/Cr3C2 in a NbC partially substituted WC-Co cemented carbide increased significantly the hardness in combination with a moderate fracture toughness.
Lanthanide-doped upconversion nanoparticles (UCNPs) are of great interest for biomedical applications. Currently, the applicability of UCNP bionanotechnology is hampered by the generally low luminescence intensity of UCNPs and inefficient energy Transfer from UCNPs to surface-bound chromophores used e.g. for photodynamic therapy or analyte sensing. In this work, we address the low-Efficiency issue by developing versatile core-Shell nanostructures, where high-concentration sensitizers and activators are confined in the core and Shell Region of representative hexagonal NaYF2:Yb,Er UCNPs. After Doping concentration optimization, the sensitizer-rich core is able to harvest/accumulate more excitation energy and generate almost one order of Magnitude higher luminescence intesity than conventional homogeneously doped nanostructures. At the same time, the activator Ions located in the Shell enable a ~6 times more efficient resonant energy Transfer from UCNPs to surface-bound acceptor dye molecules due to the short distance between donor-acceptor pairs. Our work provides new insights into the rational design of UCNPs and will greatly encrease the General applicability of upconversion nanotechnologies.
In the present work it was shown that the addition of VC or a combination of VC + Ti(C0.7N0.3) was efficient in reducing the NbC grain growth during liquid phase sintering, when compared to NbC-Ni equivalents. A finest NbC grain size of 1.48 µm was obtained in the NbC-15 Ti(C0.7N0.3)-10 Ni-7.5 VC cermet, exhibiting a hardness of 1486 +/- 7 kg/mm2 and a fracture toughness of 8.7 +/- 0.1 MPa m 1/2.
The origin of the intrinsic wear resistance of NbC-based materials is investigated through an assessment of the tribological performance of fully dense, crack-free spark plasma sintered Nb2O5 (here as a reduced polymorph: monoclinic Nb12O29 or NbO2.416). The most likely wear mechanism on NbC is the tribo-oxidation to Nb2O5. The unlubricated (dry) friction and wear behavior of alumina (99.7%) mated against rotating disks of crack-free niobium(V)oxide (Nb2O5) under unidirectional sliding (0.03–10m/s; 22°C and 400°C) and oscillation (f=20 Hz, dx=200 mm, 2/50/98% rel. humidity, n=105/106 cycles) will be presented. The microstructure and mechanical properties of the crack-free Nb2O5 are assessed. The tribological data obtained are benchmarked with different NbC grades, ceramics, cermets and thermally sprayed coatings.
A fast and simple method for sulfur quantification in crude oils was developed by using high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS). For this, heavy crude oil samples were prepared as microemulsion (shake) and injected into a graphite furnace (shut). Finally, the concentration of sulfur was determined by monitoring in situ the transient molecular spectrum of GeS at wavelength 295.205nm after adding a germanium solution as molecular forming agent (and go). Zirconium dioxide in the form of nanoparticles (45–55nm) was employed as a permanent modifier of the graphite furnace. Calibration was done with an aqueous solution standard of ammonium sulfate, and a characteristic mass (m0) of 7.5ng was achieved. The effectiveness of the proposed method was evaluated analizing, ten heavy crude oil samples with Sulfur amounts ranging between 0.3 and 4.5% as well as two NIST standard reference materials, 1620c and 1622e. Results were compared with those obtained by routine ICP-OES analysis, and no statistical relevant differences were found.
The sales of niobium carbide (NbC) have grown in the last years, but NbC is still a hidden carbide and mainly used as grain growth inhibitor in hard metals. In the present work it was shown that the progress in the key properties, like HV30, KIC and strength, followed by machining and tribological results of the respective NbC grades.
The current study reports on the influence of the Addition of 5–15 vol% VC or/and Mo2C carbide on the microstructure and mechanical properties of nickel bonded NbC cermets, which are compared to cobalt bonded NbC cermets. The NbC, Ni and secondary carbides powder mixtures were liquid phase sintered for 1 h at 1420 °C in vacuum. The fully densified cermets are composed of a cubic NbC grains matrix and an evenly distributed fcc Ni binder. NbC grain growth was significantly inhibited and a homogeneous NbC grain size distribution was obtained in the cermets with VC/Mo2C additions. The mechanical properties of the NbC-Ni matrix cermets are strongly dependent on the carbide and Ni binder content and are directly compared to their NbC-Co equivalents.
The liquid phase sintered NbC-12 vol% Ni cermet had a modest Vickers hardness (HV30) of 1077 ± 22 kg/mm2 and an indentation toughness of 9.1 ± 0.5 MPa·m1/2. With the addition of 10–15 vol% VC, the hardness increased to 1359 ± 15 kg/mm2, whereas the toughness increased to 11.3 ± 0.1 MPa·m1/2. Addition of 5 and 10 vol% Mo2C into a NbC-12 vol% Ni mixtures generated the same values in HV30 and KIC when compared to VC additions. A maximum flexural strength of 1899 ± 77 MPa was obtained in the cermet with 20 vol% Ni binder and 4 vol% VC+4 vol% Mo2C addition, exhibiting a high fracture toughness of 15.0 ± 0.5 MPa·m1/2, but associated with a loss in hardness due to the high Ni content. The dry sliding wear behaviour was established at room temperature and 400 °C from 0.1 to 10 m/s.
For the purpose of finding suitable molecules applicable to sulfur determination and to compare their analytical sensitivity systematically, high-resolution overview molecular absorption spectra of sulfides of group 14 elements produced in a graphite furnace were investigated. To that end a modular simultaneous echelle spectrograph (MOSES) was used, which allows recording sub-ranges of spectra out of a total wavelength range from 190 nm to 735 nm. The combined overview spectra show a complex structure with many vibrational bands, each of them consisting of a multitude of sharp rotational lines. The absorption of rotational lines of SiS (282.910 nm), GeS (295.209 nm), SnS (271.578 nm), and PbS (335.085 nm) has been analyzed for optimizing the particular experimental conditions regarding to the sulfur determination. Using the commercial CS AAS instrument contrAA 600 under optimized conditions such as the temperature program, the modification of the platform with Zr and the use of chemical modifiers, the achieved characteristic masses for sulfur are 12 ng (CS), 15.7 ng (SiS), 9.4 ng (GeS), 20 ng (SnS), and 220 ng (PbS). The first four sulfides provide an analytical sensitivity with roughly the same level, but the GeS molecule seems to be the best one with respect to analytical sensitivity and flexibility in molecular formation control. The PbS molecule provides the lowest analytical sensitivity, and together with its low bond strength it is not recommended for sulfur determination.
Boron isotope amount ratios n(10B)/n(11B) have been determined by monitoring the absorption spectrum of boron monohydride (BH) in a graphite furnace using high-resolution continuum source molecular absorption spectrometry (HR-CS-MAS). Bands (0→0) and (1→1) for the electronic transition X1Σ+ → A1Π were evaluated around wavelengths 433.1 nm and 437.1 nm respectively. Clean and free of memory effect molecular spectra of BH were recorded. In order to eliminate the memory effect of boron, a combination of 2% (v/v) hydrogen gas in argon and 1% trifluoromethane in argon, an acid solution of calcium chloride and mannitol as chemical modifiers was used. Partial least square regression (PLS) for analysis of samples and reference materials were applied. For this, a spectral library with different isotopes ratios for PLS regression was built. Results obtained around the 433.1 nm and 437.1 nm spectral regions are metrologically compatible with those reported by mass spectrometric methods. Moreover, for the evaluated region of 437 nm, an accuracy of 0.15‰ is obtained as the average deviation from the isotope reference materials. Expanded uncertainties with a coverage factor of k = 2 range between 0.15 and 0.44‰. This accuracy and precision are compatible with those obtained by mass spectrometry for boron isotope ratio measurements.
Niobium is today largely available. The initial NbC grade was substoichiometric, SPS sintered and cobalt bonded (NbC0.88-12Co SPS). The NiMo-bonded stoichiometric NbC1.0 grades enable the subtituion of cobalt by nickel, SPS by conventional sintering and NbC0.88 by NbC1.0 in view of functional properties. Nickel bonded NbC grades have improved toughnesses versus cobalt bonded NbC grades, but lose hardness. NiMo and NiMo2C bonded NbC1.0 grades compensated the loss in hardness while keeping the toughness.
The current study reports on the effect of the sintering temperature and secondary carbide (VC, Mo2C and TiC) additions on the microstructure and concommitant Vickers hardness (HV30) and fracture toughness of Ni-bonded NbC cermets. All cermets were prepared by pressureless sintering in vacuum. Detailed microstructural investigation was performed by electron probe microanalysis (EPMA) and X-ray diffraction (XRD) analysis. Sintering results indicated that both the sintering temperature and secondary carbide additions had a significant effect on the properties of NbC-Ni cermets. Nickel pools and residual pores were observed in the cermets sintered at temperatures ≤ 1340 °C. Increasing of the sintering temperature up to 1420 or 1480 °C resulted in fully densified NbC-Ni based cermets composed of homogeneous contrast cubic NbC grains for the single carbide (VC or Mo2C) modyfied system, whereas core-rim structured NbC grains were observed with the additon of TiC + VC or TiC+Mo2C. The secondary carbide doped cermets with 5–10 vol.% VC/Mo2C and 10 vol.% TiC showed a significantly improved hardness and fracture toughness, as compared to the plain NbC-Ni cermets.
The mechanism of action of zirconium permanent modifiers on graphite surfaces was investigated in order to understand its influence on the analytical signal in atomic and molecular absorption spectrometry (AAS/MAS). For this, the molecule formation of CaF was studied, which is used for the indirect analytical determination of fluorine in high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS). The kinetics of this reaction was established by monitoring its molecular spectrum at different atomisation temperatures. An Arrhenius plot showed a pseudo-first order reaction with respect to fluorine (n = 1). An intermediate state was isolated, and its structure was elucidated by spectroscopic methods: scanning electron microscopy with energy dispersive X-ray spectroscopy (SEMEDX), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XANES and EXAFS), and Raman microspectroscopy. We propose here a mechanism, where ZrO2 acts as a heterogeneous catalyst: after a pyrolytic step, an intermediate state of ZrO(OCaF) is activated, and at higher temperatures, CaF(g) is released from the zirconium-coated graphite surface. No evidence of the formation of zirconium carbide was found. Consequently, as the CaF formation is catalysed by a heterogeneous catalyst, surface modifications with ZrO2 nanoparticles and ZrO xerogels were investigated in order to increase the surface area. Their influence was evaluated in the molecule formation of CaF, CaCl, CaBr, and CaI. Graphite furnace modification with zirconium oxide nanoparticles proves to be the best choice for fluorine analysis with a signal enhancement of more than eleven times with respect a non-coated graphite furnace. However, the influence of zirconium modifications in the analytical signals of Cl, and I is lower than the F signals or even negative in case of the Br. Understanding zirconium modifiers as heterogeneous catalysts offers a new perspective to AAS and MAS, and reveals the potential of surface analytical methods for development of improved permanent modifiers and graphite furnace coatings.
A boron dipyrromethene (BDP) unit and its monostyryl derivative (MSBDP) were introduced at the axial positions of a silicon(IV) phthalocyanine (SiPc) core. The absorption spectrum of this compound virtually covered the entire visible region (300-700 nm) and could be interpreted as a superposition of the spectra of individual components. The intramolecular photoinduced energy and charge transfer processes of this triad were studied using steady-state and time-resolved spectroscopic methods in polar and nonpolar solvents. Upon BDP-part excitation, a fast and highly efficient excitation energy transfer (EET) occurred resulting in strong quenching of its fluorescence and the formation of the first excited singlet state of SiPc or MSBDP. It was found that both EET and charge transfer (CT) processes competed with each other in the depopulation of the first excited singlet state of the MSBDP moiety. The former strongly superseded CT in nonpolar toluene, whereas the latter was dominant in a polar environment. Direct or indirect (via EET) excitation of the SiPc-part of the triad was followed by CT yielding the charge-separated (CS) species BDP-SiPc center dot--MSBDP center dot+. The energy gap between the CS state and the S-1-state of the SiPc moiety was found to be only 0.06 eV in toluene, which facilitated the back CT process and resulted in the appearance of thermally activated delayed fluorescence. With increasing solvent polarity, the energy of the CS state reduced resulting in the disappearance of the delayed fluorescence in CHCl3, tetrahydrofuran or N,N-dimethylformamide. The charge recombination rate, k(CR), was very fast in polar DMF (3.3 x 10(10) s(-1)), whereas this process was two-orders of magnitude slower in nonpolar toluene (k(CR) = 4.0 x 10(8) s(-1)).
NbC has a relatively high hardness (19.6 GPa) and melting temperature (3600 °C) and is usually applied as a grain growth inhibitor in WC–Co hardmetals. The current study reports on the influence of the sintering technology and overall chemical composition on the microstructure and mechanical properties of NbC-based hardmetals, using Co as a binder. The partial replacement of NbC by 5 wt.% WC, Mo2C, VC or TiC allows one to significantly improve the hardness and toughness of the NbC–Co materials. The influence of different binders, i.e., Co, 316L stainless steel and Fe3Al on the microstructure and mechanical properties of NbC-based hardmetals was also investigated. The powder mixtures were sintered in the solid state by PECS and liquid state by conventional vacuum sintering. Detailed microstructural analysis was conducted by EPMA elemental mapping and WDS point analysis. Mechanical properties, including Vickers hardness and indentation toughness were assessed.
Single particle imaging of upconversion nanoparticles (UCNPs) has typically been realized using hexagonal (β) phase lanthanide-doped sodium yttrium fluoride (NaYF4) materials, the upconversion luminescence (UCL) of which saturates at power densities (P) of several hundred W cm−2 under 980 nm nearinfrared (NIR) excitation. Cubic (α) phase UCNPs have been mostly neglected because of their commonly observed lower UCL efficiency at comparable P in ensemble level studies. Here, we describe a set of sub-15 nm ytterbium-enriched α-NaYbF4:Er3+@CaF2 core/shell UCNPs doped with varying Er3+ concentrations (5–25%), studied over a wide P range of ∼8–105 W cm−2, which emit intense UCL even at a low P of 10 W cm−2 and also saturate at relatively low P. The highest upconversion quantum yield (ΦUC) and the highest particle brightness were obtained for an Er3+ dopant concentration of 12%, reaching the highest ΦUC of 0.77% at a saturation power density (Psat) of 110 W cm−2. These 12%Er3+-doped core/shell UCNPs were also the brightest UCNPs among this series under microscopic conditions at high P of ∼102–105 W cm−2 as demonstrated by imaging studies at the single particle level. Our results underline the potential applicability of the described sub-15 nm cubic-phase core/shell UCNPs for ensemble- and single particle-
level bioimaging.
A mono-component intumescent flame retardant named ethylenediamine-modified ammonium polyphosphate (MAPP) is used in polyethylene-octene elastomer (POE). Insight into the flame-retardant mechanisms of the MAPP is provided from a new perspective. The fire performance of POE/MAPP composites is investigated by oxygen index (OI) and vertical burning (UL-94) tests. POE Composite containing 35 wt% MAPP achieves a V-0 rating, and its OI is 29.3 vol%. The thermogravimetric Analysis (TGA) and Fourier transform infrared spectra (FTIR) confirm that the incorporation of ethylenediamine changes the thermal decomposition of APP, mainly resulting in the formation of char layer with a thermally stable structure. Cone calorimeter analysis revealed the flame-retardant modes of action of MAPP in POE under forced-flaming conditions. Quantitative analysis illustrates that both the residue due to charring and the fuel dilution/flame Inhibition resulting from the release of incombustible products/ phosphorus species decrease the total heat release (fire load) by 20e28%. The residue increases linearly with increasing MAPP content, whereas the reduction in effective heat of combustion levels off. Moreover, the flame-retardant effect resulting from the protective properties of the char is discovered to be the dominant mode of action (up to 85% reduction) with respect to the peak heat release rate, leading to the excellent flame retardancy of POE/MAPP.